Tektronix 071-0590-00 User Manual

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User Manual

gigaBERT1400 1400 Mb/s Bit Error Rate Tester

Generator and Analyzer

071-0590-00

This document supports firmware version 2.2 and above.

Copyright © 2000 Tektronix, Inc. All rights reserved. Licensed software products are owned by Tektronix or its suppliers and are protected by United States copyright laws and international treaty provisions.

Use, duplication, or disclosure by the Government is subject to restrictions as set forth in subparagraph (c)(1)(ii) of the Rights in Technical Data and Computer Software clause at DFARS 252.227-7013, or subparagraphs (c)(1) and (2) of the Commercial Computer Software - Restricted Rights clause at FAR 52.227-19, as applicable.

Tektronix products are covered by U.S. and foreign patents, issued and pending. Information in this publication supersedes that in all previously published material. Specifications and price change privileges reserved.

Tektronix, Inc., P.O. Box 1000, Wilsonville, OR 97070-1000 TEKTRONIX and TEK are registered trademarks of Tektronix, Inc.

GB1400 User Manualii

WARRANTY

Tektronix warrants that this product will be free from defects in materials and workmanship for a period of one (1) year from the date of shipment. If any such product proves defective during this warranty period, Tektronix, at its option, either will repair the defective product without charge for parts and labor, or will provide a replacement in exchange for the defective product.

In order to obtain service under this warranty, Customer must notify Tektronix of the defect before the expiration of the warranty period and make suitable arrangements for the performance of service. Customer shall be responsible for packaging and shipping the defective product to the service center designated by Tektronix, with shipping charges prepaid. Tektronix shall pay for the return of the product to Customer if the shipment is to a location within the country in which Tektronix service center is located. Customer shall be responsible for paying all shipping charges, duties, taxes, and any other charges for products returned to any other locations.

This warranty shall not apply to any defect, failure or damage caused by improper use or improper or inadequate maintenance and care. Tektronix shall not be obligated to furnish service under warranty a) to repair damage resulting from attempts by personnel other than Tektronix representatives to install, repair or service the product; b) to repair damage resulting from improper user or connection to incompatible equipment; or c) to service a product that has been modified or integrated with other products when the effect of such modification or integration increases the time or difficulty of servicing the product.

THIS WARRANTY IS GIVEN BY TEKTRONIX WITH RESPECT TO THIS PRODUCT IN LIEU OF ANY OTHER WARRANTIES, EXPRESSED OR IMPLIED. TEKTRONIX AND ITS VENDORS DISCLAIM ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. TEKTRONIX’ RESPONSIBILITY TO REPAIR OR REPLACE DEFECTIVE PRODUCTS IS THE SOLE AND EXCLUSIVE REMEDY PROVIDED TO THE CUSTOMER FOR BREACH OF THIS WARRANTY. TEKTRONIX AND ITS VENDORS WILL NOT BE LIABLE FOR ANY INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES IRRESPECTIVE OF WHETHER TEKTRONIX OR THE VENDOR HAS ADVANCE NOTICE OF THE POSSIBILITY OF SUCH DAMAGES.

GB1400 User Manual iii

How to Reach Customer Service

If you have any questions regarding the operation, maintenance, repair, or application of your Tektronix equipment, contact your local sales and service office. For a complete list of the Worldwide Sales and Service Offices contact (800) 426-2200.

Tektronix provides high quality Technical Support on applications, operation, measurement specifications, hardware, and software by expert application engineers. For Applications Support, call the Customer Support Center listed below.

Mailing Address

Tektronix, Inc. Measurement Business Division P.O. Box 500 Beaverton, Oregon 97077-0001 USA

Customer and Sales Support

800-TEK-WIDE or 800-835-9433 Ext 2400

Center

Direct Fax

503-627-2400 503-627-5695

E-Mail tm_app_supp@tek.com

Web Site http://www.tek.com

Attn. Customer Service

Hours are 6:00 AM to 5:00 PM, Pacific Time.

After hours Voice Mail is available.

GB1400 User Manual

Table of Contents

Safety.................................................................................................. xii

Getting Started

Features............................................................................................... 1-1

Ordering Information ............................................................................ 1-4

gigaBERT comparison chart.................................................................. 1-5

Initial Self-Check Procedure ................................................................. 1-7

Operating Basics

Functional Overview....................................................................................... 2-1

BERT Basics - GB1400 ........................................................................ 2-2

Controls, Indicators, and Connectors...................................................... 2-4

Display Formats ................................................................................... 2-6

Outputs & Inputs.................................................................................. 2-9

Generator OUTPUT ....................................................................... 2-9

Generator CLOCK ......................................................................... 2-10

Generator OUTPUT (Set-up) ........................................................... 2-11

Generator Rear Panel...................................................................... 2-12

Changing the Line Fuse .................................................................. 2-12

Analyzer INPUT............................................................................ 2-13

Analyzer MONITOR ...................................................................... 2-14

Analyzer Rear Panel....................................................................... 2-15

Changing the Line Fuse .................................................................. 2-15

Connectors, Terminations and Levels .............................................. 2-16

Controls & Indicators............................................................................ 2-18

Power Switches .............................................................................. 2-18

Unit Mounting ............................................................................... 2-18

Unit Cooling .................................................................................. 2-18

View Angle and Panel Lock Keys ................................................... 2-18

Reset to Factory Default.................................................................. 2-18

GPIB Controls................................................................................ 2-19

Pattern Controls and Function Keys ................................................. 2-20

Function (Soft) Keys (F1, F2, F3, F4) ............................................... 2-21

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Table of Contents

Generator ERROR INJECT ............................................................ 2-22

Analyzer INPUT............................................................................ 2-23

Analyzer Error History.................................................................... 2-24

Analyzer ERROR DETECTION ..................................................... 2-25

Analyzer SYNC Controls ................................................................ 2-25

Burst Mode Option ............................................................................... 2-26

Burst Mode Usage.......................................................................... 2-27

Specifications for Burst Mode ......................................................... 2-27

PECL Option for GB1400 Tx ................................................................ 2-29

Tutorial........................................................................................................... 2-30

Applications .................................................................................................... 2-38

Method for Very Fast Automatic RX Synchronization

and Eye Width Measurement ......................................................... 2-38

GB700/ GB1400 Optical Component Test........................................ 2-46

Reference

Menu Overview.................................................................................... 3-1

Functions common to TX and RX.......................................................... 3-1

Selecting a Pattern................................................................................ 3-2

Fibre Channel Link Testing Parallel and High-Speed Serial............... 2-47

Testing QPSK Modems, I & Q ........................................................ 2-48

QPSK BER Testing using PRBS Data for 2-Channel I & Q ............... 2-49

AC Power...................................................................................... 3-1

Selecting 115 VAC or 230 VAC operation ....................................... 3-1

Turning Instrument Power ON/OFF................................................. 3-1

LCD Viewing Angle ....................................................................... 3-1

Recalling Default Setup................................................................... 3-2

Locking the Front Panel.................................................................. 3-2

Pattern Definitions.......................................................................... 3-2

PRBS Patterns ............................................................................... 3-2

Word Patterns ................................................................................ 3-3

Selecting an Active Pattern................................................................... 3-3

Selecting PRBS Patterns ................................................................. 3-3

Selecting the Current Word Pattern.................................................. 3-3

Selecting (Recalling) a Saved Word Pattern..................................... 3-4

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Table of Contents

Word Patterns ...................................................................................... 3-5

Basics............................................................................................ 3-5

Creating Word Patterns using front panel controls ............................. 3-5

Creating Word Patterns using menus................................................ 3-7

Creating Word Patterns using remote control.................................... 3-8

Saving Word Patterns ..................................................................... 3-9

Recalling Word Patterns ................................................................. 3-9

Generator Functions ....................................................................................... 3-10

Clock Source and Frequency................................................................. 3-10

External Clock Input............................................................................. 3-10

Clock Source........................................................................................ 3-10

Step Size and Frequency ....................................................................... 3-10

Saving a Frequency.............................................................................. 3-11

Recalling a Frequency........................................................................... 3-11

Data and Clock Outputs ........................................................................ 3-12

Amplitude and Baseline Offset.............................................................. 3-14

Logically Inverting Output Data (D-INV) .............................................. 3-15

Single-Ended or Differential Operation ................................................. 3-16

Pattern SYNC (PYNC) and CLOCK/4 Outputs ...................................... 3-16

Error Injection ...................................................................................... 3-17

Selection an Error Inject Mode .............................................................. 3-17

Error INJECT Input.............................................................................. 3-18

Analyzer Functions ......................................................................................... 3-19

Automatic Setup Functions (SYNC)...................................................... 3-19

AUTO SEARCH with PRBS Patterns.................................................... 3-20

AUTO SEARCH with "Non-PRBS" Patterns ......................................... 3-21

How to DISABLE Automatic Pattern Resynchonization.......................... 3-21

Relationship between AUTO SEARCH and DISABLE........................... 3-21

Synchronization (LOCK) Threshold ....................................................... 3-22

Clock, Data, and Reference Data Inputs................................................. 3-23

Input Data Delay.................................................................................. 3-24

Input Termination................................................................................. 3-25

Input Decision Threshold ...................................................................... 3-26

Logically Inverting Input Data ............................................................... 3-26

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Table of Contents

Single-Ended or Differential Operation .................................................. 3-27

Selecting the Reference Data Mode ....................................................... 3-27

Monitor Outputs................................................................................... 3-28

Error Detection Set-up .......................................................................... 3-29

Display Mode: Totalize, Window or Test ............................................... 3-33

Clearing Results and Starting Tests ........................................................ 3-33

Totalize Process Setup.......................................................................... 3-33

Window Process Setup.......................................................................... 3-34

Test Process Setup................................................................................ 3-35

Viewing Results ................................................................................... 3-36

Printing Results (Reports) ..................................................................... 3-37

Result Definitions ................................................................................. 3-42

Error History Indicators ........................................................................ 3-44

CLEAR Control.................................................................................... 3-45

Audio (Beeper) Function....................................................................... 3-45

Analyzer Error Messages...................................................................... 3-45

Starting & Stopping Measurements........................................................ 3-46

Menus ............................................................................................................. 3-48

Functions Performed using the Menu System......................................... 3-48

Menu and Function "Pages".................................................................. 3-48

General Rules for using the Menu System .............................................. 3-51

Menu Summaries.................................................................................. 3-52

Menu Function Definitions.................................................................... 3-55

Word Edit (EDIT) .......................................................................... 3-56

Word Length (LENGTH) ................................................................ 3-57

Word Fill (FILL) ............................................................................ 3-58

Word Order (ORDER).................................................................... 3-59

Word Synchronization Threshold (SYNC) ....................................... 3-60

Buffer............................................................................................ 3-61

Auto .............................................................................................. 3-62

Test Length (LENGTH) .................................................................. 3-63

Test Mode (MODE) ....................................................................... 3-64

Test Reports (REPORT) ................................................................. 3-65

Test Threshold (THRES)................................................................. 3-66

Test Squelch (SQUEL)................................................................... 3-67

GB1400 User Manualviii

Table of Contents

Test Print (PRINT)......................................................................... 3-68

Test View Previous (VIEW-PRE).................................................... 3-69

Test View Current (VIEW-CUR) .................................................... 3-70

Window Mode (MODE)................................................................. 3-71

Window Interval in Bits (BITS)....................................................... 3-72

Window Interval in Hrs:Min:Sec (SECOND)................................... 3-73

Window Reports (REPORT) ........................................................... 3-74

RS-232 Baud Rate (BAUD)............................................................ 3-75

RS-232 Parity (PARITY) ................................................................ 3-76

RS-232 Data Bits (SIZE) ................................................................ 3-77

RS-232 End-of-Line Char.(EOL)..................................................... 3-78

RS-232 Xon/Xoff (XON/XOFF)...................................................... 3-79

RS-232 Echo (ECHO) .................................................................... 3-80

GPIB............................................................................................. 3-81

Utility Option (OPTION) ................................................................ 3-82

Utility Version (VER) ..................................................................... 3-83

Time Option (DATE)...................................................................... 3-84

Time Option (TIME)....................................................................... 3-85

Appendices

Specifications .................................................................................................. A-1

BERT Primer/ Technical Articles ................................................................... B-1

Remote Commands ......................................................................................... C-1

Using GPIB, RS-232 ....................................................................................... D-1

Customer Acceptance Test ............................................................................. E-1

Default Settings .............................................................................................. F-1

Cleaning Instructions ..................................................................................... G-1

Pattern Editing Software ................................................................................ H-1

Theory of Operation ....................................................................................... I-1

Glossary.......................................................................................................... Glossary-1

Index .............................................................................................................. Index-1

GB1400 User Manual ix

Table of Contents

List of Figures

2-1 Example of BERT Application........................................................ 2-2

2-2 Nominal Generator NRZ Data and Clock Output Waveforms ........... 2-3

2-3 & 2- 4 Generator (TX) Front & Rear Panels ..................................... 2-4

2-5 & 2-6 Analyzer (RX) Front & Rear Panels ....................................... 2-5

2-7 Generator Display .......................................................................... 2-6

2-8 Analyzer Display........................................................................... 2-7

2-9 Transmitter Burst Mode Operation.................................................. 2-28

2-10 Receiver Burst Mode Operation .................................................... 2-28

3-1 Nominal Generator Clock, Data Waveforms showing Amplitude,

Baseline Offset and Vtop................................................................ 3-13

3-2 Generator Clock and Data Output Equivalent Circuits...................... 3-17

3-3 Analyzer Clock and Data Input Equivalent Circuits .......................... 3-22

3-4 TOTALIZE Measurement Process.................................................. 3-30

3-5 WINDOW Measurements Process.................................................. 3-31

3-6 TEST Measurement Process........................................................... 3-32

B-1 Three-stage PRBS generator .......................................................... B-5

B-2 Four-stage PRBS generator............................................................ B-5

B-3 Seven-stage PRBS generator.......................................................... B-6

I-1 Block Diagram - GB1400 TX.......................................................... I-5

I-2 Block Diagram - GB1400 RX.......................................................... I-6

GB1400 User Manualx

List of Tables

2-1 Generator Inputs & Outputs............................................................ 2-16

2-2 Analyzer Inputs & Outputs............................................................. 2-17

3-1 PRBS (2N-1) Test Patterns............................................................. 3-3

3-2 Output Setup Rules vs. Termination Impedance ............................... 3-14

3-3 Data Inhibit Logic .......................................................................... 3-18

3-4 Actions taken by Analyzer when Synchronization is Lost................. 3-20

3-5 Synchronization Threshold ............................................................. 3-22

3-6 How F2, F3 determine Input Set-up ................................................ 3-24

3-7 Input Terminations for CLOCK, DATA, and REF DATA ................ 3-25

3-8 Input Threshold Range as a Function of Termination ........................ 3-26

3-9 How to Tell which Display Mode is Active ...................................... 3-37

3-10 Menu Descriptions ....................................................................... 3-52

Table of Contents

3-11 Analyzer Menu System Overview ................................................. 3-53

3-12 Generator Menu System Overview................................................ 3-54

B-1 PRBS Polynomials and Shift Register feedback taps for PB200........ B-4

B-2 PRBS Polynomials, Shift Register feedback taps, GB700/ GB1400 .. B-4

GB1400 User Manual xi

Safety

Safety Terms Used in This User's Guide

CAUTION!

WARNING! Indicates an operation or practice that could result in

Indicates an operation or practice that could harm the instrument.

personal injury or loss of life.

Safety Labels Found on the Instrument

DANGER

High Voltage

Protective Ground

(Earth) Terminal

ATTENTION

Refer to Manual

AC Power

The instrument is designed to operate from a power source that provides no more than 250 volts RMS between the two supply conductors or between either supply conductor and ground.

Ground the Instrument

The GB1400 is grounded through its AC power cord. Plug this power cord only into a properly grounded, three-conductor outlet. If you operate the instrument without a proper ground then all metal surfaces on the instrument become potential shock hazards.

To avoid potential hazards, use this product only as specified.

Use the Proper Fuse

Operating the instrument with an improper fuse creates a fire hazard. The correct fuses to install in the GB1400 are shown below:

Power Voltage Fuse Type

115 VAC 5A, Slo-Blo 230 VAC 5A, Slo-Blo

Do Not Operate in Explosive Atmospheres

This instrument does not provide protection from static discharges or arcing components and therefore must not be operated in an explosive atmosphere.

xii GB1400 User Manual

Table of Contents

Do Not Remove Instrument Covers

To avoid a shock hazard and to maintain proper air flow, never operate the GB1400 with any of its outside covers removed.

Static Sensitive Device Notice

GB1400 outputs use a GaAs FET design and therefore are susceptible to damage from externally applied over-voltage or electrostatic discharge. Never apply reverse voltage to DATA or CLOCK outputs or voltages that are outside the range specified in Appendix A of this manual. Operate the instrument only in a static-controlled environment.

SMA Connectors

Be careful when attaching test cables to SMA connectors. Always tighten the nut on the SMA connector rather than the cable itself. Never tighten an SMA connector nut using more than 10 lb.-in. of torque.

Behavior of Outputs - Turning Power On or Off

When the GB1400 Generator is powered or de-powered its DATA and CLOCK outputs may saturate to their specified positive or negative rail, that is +2 V or - 2 V, for up to 400 milliseconds. If this condition could be harmful to your equipment, then remove all connections to your GB1400 Generator CLOCK and DATA outputs before powering or de-powering the instrument.

Unit Mounting

The GB1400 is designed to be placed: (1) flat on a level surface, capable of supporting its weight, or (2) angled from the surface with the rotating carrying handle. To change the handle's orientation, press both handle-locking buttons (located at the hubs of the handle), rotate the handle to the desired angle, and release the buttons. The handle will click into a locked position. Assure that the handle is locked before placing the unit on a work surface. A Rack mounting option is available for installation of the unit into a 19" rackmount. The rack height for the GB1400 is 7 inches (four RMU).

Unit Cooling

The rear panel fan openings and top-mounted ventilation slots must be kept clear for proper cooling of the unit. Allow a minimum of two (2) inches of rear panel clearance, and one (1) inch of top clearance, while operating the unit.

GB1400 User Manual xiii

Preface

This manual describes how to use the Tektronix GB1400 Test Set. The product is also known by the name, gigaBERT1400. This manual is your primary source of information on how to use the GB1400 functions.

How This Manual is Organized

This manual is divided into four sections: Getting Started, Operating Basics, Reference, and Appendices.

Getting Started provides an overview of the GB1400 and describes first time

operation. Operating Basics describes the hardware controls, indicators, connectors, and

display elements for Tx, Rx and the cabling required. There is also a tutorial and an application note in this section.

Reference describes the LCD Menus and Screens. The Appendices provide a listing of specifications, a BERT technology primer,

Theory of Operation, Remote Commands, default factory settings, an extensive Customer Acceptance Test and other useful information.

Conventions

This manual uses the following conventions:

• The names of front-panel controls and menus appear in all upper case letters,

for example, TRANSMIT and HELP.

• Names appear in the same case in this manual as they appear on the display

screens of the GB1400.

• Within a procedure, a specific button to be pressed or a parameter to be

selected appears in boldface print.

Some procedures require several iterations of highlighting parameters and selecting choices. Some procedures may require more than one menu button or menu page selection as well.

xiv GB1400 User Manual

Related Manuals

The following document is also complementary to the GB1400:

• The GB700 BER Tester User Manual (Tektronix part number

Preface

070-9393-02) describes how to operate the GB700 test set.

GB1400 User Manual xv

Preface

GB1400 User Manualxvi

Getting Started

GB1400 Pattern Generator and Error Detector

Features

• Test digital data transmission up to 1400 Mb/s

• Set Data Rate with 1 kHz resolution

• Vary Clock and Data timing with 5 pS

resolution

• Phase-Synchronous Clock and Data Edge

Tracking

• 1-Mbit data pattern memory

• Measure Eye-Width at Specific BER

Automatically

• Auto-Synchronization Rx/Tx Lock-up

• Front panel or computer control operation

The GB1400 is a general-purpose 1400 Mb/s bit error rate tester (BERT) built to meet the exacting standards of design engineers who need to verify and characterize high-speed serial data transmission circuits, interfaces and systems. While primarily a lab instrument, the GB1400’s compact design, full computer programmability and relatively light weight also enable it to serve in manufacturing ATE and field test applications.

The quality of a digital link depends on many factors, but everything comes down to the issue of whether the circuit exhibits a satisfactory BER (bit error rate) and has sufficient margin to function under stress conditions.

The GB1400 has all of the features you expect in a general-purpose BERT, and some you expect only in more expensive instruments, such as automated eyewidth measurements at a specified BER, and the ability to accept an external real-time data stream for bit error testing. Also, the GB1400 has options to add advanced features, such as Burst Mode (which also extends external clock range down to 150 kb/s), and a 1-Mbit programmable pattern memory option.

GB1400 User Manual 1-1

Getting Started

Symmetrical, Low-Jitter Output Waveforms

The GB1400 generates low-jitter, symmetrical waveforms over its entire operating frequency range. The clock and data ports provide both true and inverted output signals. The instrument can drive single-ended or differential ECL inputs.

Applications

The GB1400 is focused on the research, design, and manufacturing of telecommunication components, modules, or links operating at data rates to 1400 Mb/s. It is frequently employed in testing and development well under this top speed rating, where sharp clock and data waveforms are especially desired, or where additional frequency range is thought to be needed in the future.

Sample Applications

• Development of Gigabit LAN/Data Comm Devices:

• High-Speed Fibre Channel, Ethernet

• Digital Video (MPEG, SDV, HDDV)

• Wideband Satellite Data Links

• SONET/SDH Network Devices up to OC-12e/STM4e

• High-speed GaAs/ECL/E/O device testing

• Test Clock Recovery Circuits

• Parallel-to-Serial Analysis with Tektronix MB100

• Testing of High Speed Fibre Channel links up to 1,063 Mb/s

• Gigabit Ethernet at 1,250 Mb/s.

• Testing of high-speed Optical Busses (Opto Bus, Opto Bahn) at 800 Mb/s per

channel.

• Satellite system testing and TDMA (Burst Mode) at 400, 800 Mb/s

• GaAs, ECL and optical component testing

PRBS Or User-Defined Test Patterns

The GB1400 can generate pseudo-random bit sequences (PRBS) up to 223−1 bits and others up to 1-Mbit in length, via user-programmable patterns. Patterns can be created locally using setup menus or externally by using a workstation or PC. A PC Windows-based MLPE Pattern Editor software package comes with the 1-Mbit Memory Option. Externally created patterns can be downloaded via the GPIB or RS-232 port. All user patterns are saved in battery-backed RAM.

1-2 GB1400 User Manual

Getting Started

Adjustable Inputs For Maximum Flexibility

The clock and data ports on the GB1400 Error Detector accept both true and inverted inputs. Single-ended or differential signals can be internally terminated. Input data delay is adjustable over a 4 ns range to accommodate different clock and data signal path delays.

Auto Search For Easy Setup

Auto search greatly simplifies the Error Detector setup. The GB1400 Error Detector automatically synchronizes to the incoming signal by 1) Setting the input data decision voltage to its optimum value; 2) Adjusting input data delay for an optimum clock/data phase relationship; 3) Selecting the correct PRBS test pattern; and 4) selecting the correct pattern polarity (normal or inverted).

It synchronizes with any pattern sourced by a gigaBERT Pattern Generator. It can perform a bit-by-bit comparison of an external data stream via the Reference Data input. Thus the GB1400 can perform bit error analysis on any data pattern with a known good reference pattern.

Powerful Analysis And Reporting Functions

The GB1400 performs a full-rate, bit-by-bit analysis of the received signal. Bit error results are then used to calculate three bit error rate (BER) measures. Total BER is calculated from the last power-on or reset. Window BER is calculated over a sliding window specified in terms of time (1 second to 24 hours) or bits (18- to 116-bits). Test BER is calculated from the start of the current test. A hard copy of all test results can be generated locally by connecting a printer to the parallel printer port or GPIB or RS-232 port. Reports may be printed when an error is detected, at the end of test intervals, or both.

Front Panel Or Automated Operation

The GB1400 provides easy operation augmented by set-up store and recall. Clear, concise LCD displays of setup and results make it easy to use. The 1 Megabit memory option for both the Pattern Generator and the Error Detector is sufficient for storing and outputting complex data such as SONET frames, ATM cells, MPEG digital video, etc, allowing designers to simulate “live” traffic. The GB1400 Pattern Generator and Error Detector can be controlled via the GPIB or RS-232 interface ports. The gigaBERT remote command set includes commands for all setup menus and front panel selections. The status of front panel indicators and test results can be remotely accessed.

Burst Mode

BURST mode, allows for operation with non-continuous external clocks. Use of BURST mode requires ECL-level signals with a minimum rate during the burst of 150 kHz. This is an option to the GB1400. See a write-up on Burst Mode at the end of the Functional Overview section of Chapter 2.

GB1400 User Manual 1-3

Getting Started

Ordering Information

gigaBERT GB1400

1400 Mb/s BERT Generator and Detector. Not available in Europe. Includes: Power Cord, Manual. Opt. 02 - 75 Ohm Both Sets. Opt. 05 - BURST Mode Both Sets. Opt. 07 - Positive ECL (Pattern Generator Only). Opt. 08 - 1-Mbit RAM WORD Both Sets & PC Pattern Editor Software. Opt. 2M - Rack Mounts - 2 rackmount kits Opt. A3 - Australian 240 V, 50 Hz.

gB1400T

1400 Mb/s BERT Pattern Generator. Opt. 02 - 75 Ohm Pattern Generator Only. Opt. 05 - BURST Mode Pattern Generator Only. Opt. 07 - Positive ECL Pattern Generator Only Opt. 08 - 1-Mbit RAM WORD, Generator Only, w/ PC Pattern Edit software Opt. 1M - Rack Mount. Opt. A3 - Australian 240 V, 50 Hz.

gB1400R

1400 Mb/s BERT Error Detector. Opt. 02 - 75 Ohm Error Detector Only. Opt. 05 - BURST Mode Error Detector Only. Opt. 08 - 1-Mbit RAM WORD, Detector Only w/ PC Pattern Edit Software Opt. 1M - Rack Mount. Opt. A3 - Australian 240 V, 50 Hz

1-4 GB1400 User Manual

Getting Started

GB Comparison Feature

Transmitter

Frequency range Internal Clock Source External Clock External Clock w/Burst Mode Freq Resolution CR/LF (Internal Clock) Clock /Data Output Amplitude

Clock/Data Output Offset

Clock/Data Threshold Resolution Std. Programmable Memory 16 bits 128 Kbits 16 bits

Optional Memory 128 Kbits none 1 Mbit PRBS Patterns (2n-1) 7,15,17,20,23 7,15,17,20,23 7,15,17,20,23 Burst Mode New Line (External Clk Only)

Receiver

Frequency range w/Burst Mode Burst Mode (Ext Clk Only) Standard Feature Standard Feature Optional Feature

Clock/Data Input levels (max) 500 mV to 6.0 V p-p 500 mV to 6.0 V p-p 500 mV to 2.0 V p-p Clock Input Threshold -3.00 to +4.5 V -3.00 to +4.5 V Fixed threshold levels Data Input Threshold -3.00 to +4.5 V -3.00 to +4.5 V -1.5V to 1.0 V Clock/Data Threshold Resolution Clock/Data Input Terminations GND, AC, -2V, +3V GND, AC, -2V, +3V GND, AC, -2V Single-Ended operation Automatic selection Automatic selection Requires external

Clk/Data Delay Range / Resolution

GB660/CSA907A Tx and Rx

150 kHz to 700 MHz 150 kHz to 700 MHz

150 kHz to 700 MHz 1 kHz 1 kHz 1 kHz (was 10 kHz)

500mV to 2.0 V 500mV to 2.0 V 500mV to 2.0 V

-2.0V to +1.8 V -2.0V to +1.8 V -2.0V to +1.0 V

50 mV steps 50 mV steps 50 mV steps

Standard Feature Standard Feature Optional Feature

150 kHz to 705 MHz 150 kHz to 705 MHz

50 mV steps 50 mV steps 50 mV steps

±4 ns in 100 pS steps

GB700 Tx and Rx

150 kHz to 705 MHz 150 kHz to 705 MHz 150 kHz to 705 MHz

150 kHz to 705 MHz 150 kHz to 705 MHz

±4 ns in 20 pS steps ±4 ns in 5 pS steps

GB1400 Tx and Rx

1 MHz to 1405 MHz 1 MHz to 1405 MHz 150 kHz to 1405 MHz

-2.0V to +1.8 V with PECL opt.

1 MHz to 1405 MHz 150 kHz to 1405 MHz

cable

Note 1 Burst mode operation requires ECL levels and is DC coupled Note 2 Single-ended operation requires ext. cable connection from rear panel DATA THRESHOLD SMA

GB1400 User Manual 1-5

Getting Started

GB1400 Instrument Configurations - Standard and Burst Option

GB1400 instruments are sold with and without the BURST option. To determine if the burst option is installed in a GB1400, press the F1 key several times until you get to the UTIL menu. Then select the OPTION menu. The OPTIONS menu will tell you if the Burst option is installed in the unit. External indications of the BURST option are unique labels for both transmitter and receiver. See a write-up on Burst Mode at the end of the Functional Overview section of Chapter 2.

GB1400 with no Burst Option Standard instrument configuration All standard configuration GB1400 Generators (no burst option) have an AC coupled external clock

input. All standard configuration GB1400 Analyzers (no burst option) have AC coupled paths in the receiver clock input circuitry.

GB1400 with Burst Option

When the BURST option is installed in the GB1400, the AC coupled paths in both transmitter and receiver are eliminated. This will also change several specifications listed in the table below. External clock inputs to the GB1400 transmitter must be ECL levels when the BURST option is installed. Clock inputs into the GB1400 receiver must be ECL levels and are terminated into 50 Ohms to -2V.

GB1400 Clock Signals for Standard and Burst and Instruments

Standard Coupling Burst (Option) Coupling

GB1400 TX

External Clock Input 50 Ohm, AC coupled,

2V max

GB1400 RX

Clock Input 50 Ohm, AC coupled,

2.0V max

50 Ohm to -2V, DC coupled, ECL levels

1-6 GB1400 User Manual

Initial Self-Check Procedure

You may perform the following procedure as an initial self-check of your GB1400 Generator and Analyzer. It is also a useful introduction to the basic features and operation of the GB1400.

The fan openings of the GB1400 needs 2-inches of clearance for proper ventilation.

Procedure

1. Make sure both the Generator and Analyzer are equipped with the proper

fuse.

2. Make sure that the Generator and Analyzer rear-panel power switches

are ON, and that their front-panel power switches are in the STBY position.

3. Plug both instruments into grounded (three-conductor) AC power outlets.

4. Connect a 50-Ohm SMA cable from the Generator CLOCK output to the

Analyzer CLOCK input. If using 75-Ohm option, use &5 OHM SMA/BNC cable.

Getting Started

5. Connect a 50-Ohm SMA cable from the Generator DATA output to the

Analyzer DATA input.

6. Connect a 50-Ohm SMA cable from the Analyzer rear panel DATA

THRESHOLD output to the Analyzer DATA BAR input (required for single-ended data inputs).

7. Power the Generator while pressing and holding its VIEW ANGLE,

MSB 1 and (PATTERN) CLEAR keys simultaneously. Release the key after the message Default Settings appears in the display. Repeat this procedure with the Analyzer. This will force both the Generator and Analyzer to power up using factory default settings.

8. Set up the Generator clock and data outputs using controls in the

OUTPUT box as follows:

Set this parameter… to this value … using this procedure.

DATA amplitude. 2 volts Press the DATA key.

Press AMPLITUDE up/down keys until data amplitude is set to 2.00V.

DATA baseline offset -1 volt Press BASELINE OFFSET up/down keys

until data baseline offset is set to -1.00V.

CLOCK amplitude 2 volts Press CLOCK.

Press AMPLITUDE up/down keys until clock amplitude is set to 2.00V.

CLOCK baseline offset -1 volt Press BASELINE OFFSET up/down keys

until clock baseline OFFSET is set to

-1.00V.

GB1400 User Manual 1-7

Getting Started

9. Set Generator pattern to a 223-1 bit PRBS using controls in the

PATTERN box as follows: a. Press PRBS. b. Press the pattern up/down keys until PATTERN is set to PN 23.

10. Verify that the Generator error injection rate is off. If the LED in the

error inject RATE key is on, then press RATE one or more times until it turns off.

11. Verify that the Analyzer auto-search function is enabled. If the LED in

the AUTO SEARCH key is off, then press AUTO SEARCH one time to turn it on. At this point, verify that the green LOCK LED in the Analyzer SYNC box is on.

12. Zero all Analyzer error counts by pressing CLEAR in the ERROR

DETECTION group.

13. Reset all Analyzer history LEDs by pressing CLEAR in the ERROR

HISTORY group.

14. Verify GB1400 Analyzer can detect errors by pressing the Generator

error inject SINGLE key several times. Verify that the Number of Errors count displayed by the Analyzer increments each time the Generator SINGLE key is pressed.

In effect you are now performing a bit error rate test on the test cables connecting the GB1400 Generator and Analyzer. In an actual BER test, GB1400 Generator clock and data outputs would be connected to inputs on a "device under test" (DUT) while GB1400 Analyzer inputs would be connected to outputs on the DUT.

1-8 GB1400 User Manual

Operating Basics

Functional Overview

This section describes how to use and navigate through the basic functions of the GB1400, including:

• BERT Basics

• Controls, indicators and connectors

• Display Formats

• Outputs and Inputs

Also in this section is:

• Tutorial - "Understand GB1400 instrument setup for BER testing using

PRBS patterns";

• Application Note - Auto Search Synchronization with GB1400; and,

• Application Example - GB700/ GB1400 Optical component test.

GB1400 User Manual 2-1

Functional Overview

BERT Basics - GB1400

The GB1400 Generator and Analyzer together comprise a 1400 Mb/s, serial, bit error rate test system or BERT.

A BERT is an instrument designed to measure the bit error rate (BER)—or more generally, the error performance—of a digital communications device, module, or system.

A typical BERT application, for example, would be to measure the error performance of the electrical-to-optical (E/O) and optical-to-electrical (O/E) output modules of a high-speed fiber optic transmission system (FOTS), as shown in the figure below.

GB1400 Generator GB1400 Analyzer

CLOCK DATA OUT OUT

E/O

O/E

CLOCK DATA IN IN

Figure 2- 1. Example, BERT Application

The GB1400 is described as a serial BERT because it is designed to test one digital path at a time. The term serial also distinguishes the GB1400 from parallel BERTs, such as the Tektronix MB100, which is designed to test multiple digital signal paths simultaneously.

The GB1400 Generator, also known as the transmitter or "Tx", can generate various test patterns, including pseudo-random bit sequences (PRBS) and userdefined word patterns. The Generator output consists of a two level, non-return to zero (NRZ) data signal and its associated clock signal, as illustrated in Figure 2-2. In the NRZ format, the data signal remains at either a logic "1" or logic "0" level for the entire duration of each bit time slot, except for a small transition period between time slots containing different data. The corresponding clock signal is a nominal "square wave" whose frequency defines the bit rate of the test signal.

2-2 GB1400 User Manual

Functional Overview

Falling edge of CLOCK

in middle of DATA "eye"

Rising edge of CLOCK Coincident with DATA transitions

CLOCK

DATA

Figure 2- 2. Nominal Generator NRZ Data and Clock Output Waveforms

The nominal Generator clock/data phase relationship is fixed so that the falling edges of the clock signal occur in the middle of bit time slots of the data signal. The amplitude and baseline offset of the Generator's clock and data outputs are adjustable to insure compatibility with a wide range of input circuit designs and logic families including ECL, positive ECL, and GaAs.

The GB1400 Analyzer, also known as the receiver or "Rx", can terminate and analyze the NRZ output of a digital device, module, or system being tested by the GB1400 Generator or an equivalent signal source. The decision voltage or threshold of the Analyzer DATA and CLOCK inputs can be adjusted to accommodate different logic families. The Analyzer can also add a variable amount of delay to the input data signal to accommodate different clock/data phase relationships at the output of the device under test.

The primary measurements made by the GB1400 Analyzer are bit errors and bit error rate.

GB1400 User Manual 2-3

Functional Overview

Controls, Indicators and Connectors

The first four figures in this section identify the controls, indicators and connectors located on the front and rear panels of the GB1400 Generator (Tx) and GB1400 Analyzer (RX).

VIEW

ANGLE

FREQUENCY (kHz)

MEMORY

PATTERN

gigaBERT1400 GENERATOR

OUTPUT

AMPL

OFFSET

ERROR INJECT

RATE SINGLE

PANEL

LOCK

GPIB

ADDR

LOCAL

REMOTE

POWER

OFF

CLOCK

FREQUENCY

STEP

RECALL SAVE

EXT

INPUT

50 Ohm 2 V Max

PRBS

WORD

RECALL SAVE

PATTERN SYNC CLOCK/4 CLOCK

(2) (1)

50 Ohm SOURCE

PATTERN

WORD

F1 F2 F3 F4

LENGTH

BIT

MSB 1 2 3 4 5 6 7 8

(1) With Option 2, these outputs are 75 Ohm. (2) With Option 5, the input is ECL levels only.

Figure 2- 3. Front Panel, GB1400 Generator (Tx)

PHASE A PHASE B CLOCK/2 ERROR INJECT DATA INHIBIT

CLEAR SET CLOCK DATA

OUTPUT

CLOCK

50 Ohm SOURCE

RS-232C

INVERT DATA (D-INV)

DATA

OUTPUT

AMPLITUDE

GPIB

OFFSET

DATA

WARNING

ELECTRICAL SHOCK HAZARD

THIS INSTRUMENT MUST BE GROUNDED

DO NOT OPEN INSTRUMENT REFER SERVICING TO

QUALIFIED PERSONNEL

DISCONNECT POWER CORD BEFORE REPLACING

FOR CONTINUED FIRE PRODUCTION REPLACE ONLY

INPUT MAX LINE VOLTAGE RANGE POWER FUSE

115 90-132V 175W 5A SLOBLO

230 180-250V 175W 5A SLOBLO

AUTO SELECT FREQUENCY 47-63 Hz

FUSE

WITH SPECIFIED FUSES

AC-LINE

Figure 2- 4. Rear Panel, GB1400 Generator (Tx)

2-4 GB1400 User Manual

VIEW

ANGLE

DELAY/ MEMORY

FREQUENCY (kHz) ERROR RATE TOTALIZE

Functional Overview

gigaBERT 1400 ANALYZER

ERROR HISTORY SYNC LOSS BIT PHASE POWER

CLEAR

PANEL

LOCK

GPIB ADDR

LOCAL

REMOTE

POWER

OFF

INPUT

DELAY

V-TERM V-THRESH

D-INV

DATA DATA

PRBS

WORD

RECALL SAVE

REFERENCE DATA CLOCK

(1) (2)(1)

PATTERN

WORD

LENGTH

MSB 1 2 3 4 5 6 7 8

EXT

(1) With Option 2, this input is 75 Ohm. (2) With Option 5, the input is ECL levels only.

Figure 2- 5. Front Panel, GB1400 Analyzer (RX)

DATA THRESHOLD

ERROR INHIBIT RZ ERROR

OUTPUT

PRINTER

F1 F2 F3 F4

CLK REF

BIT

ERROR DETECTION

SYNC

DISPLAY

CLEAR

AUDIO

VOL

MONITOR

CLOCK

50 Ohm SOURCE 50 Ohm, 1.5V MAX 50 Ohm, 2V MAX

CLEAR SET

CLOCK

PATTERN

RS-232C GPIB

RATE

SYNC

AUTO

LOCK

DISABLE

DATA

WARNING

ELECTRICAL SHOCK HAZARD

THIS INSTRUMENT MUST BE GROUNDED

DO NOT OPEN INSTRUMENT REFER SERVICING TO

QUALIFIED PERSONNEL

DISCONNECT POWER CORD BEFORE REPLACING

FOR CONTINUED FIRE PRODUCTION REPLACE ONLY

INPUT MAX LINE VOLTAGE RANGE POWER FUSE

115 90-132V 175W 5A SLOBLO 230 180-250V 175W 5A SLOBLO

AUTO SELECT FREQUENCY 47-63 Hz

FUSE

WITH SPECIFIED FUSES

AC-LINE

Figure 2- 6. Rear Panel, GB1400 Analyzer (RX)

GB1400 User Manual 2-5

Functional Overview

Display Formats

The normal display format for the Generator and Analyzer are explained below. Note that the "normal" format is simply the format of the display when not in the menu mode.

Generator (Tx) Display

The Generator has a two-line by 24-character high-contrast liquid crystal display (LCD). The Generator display in its normal (non-menu) mode is illustrated in the figure below.

Frequency (kHz) Pattern Output

1405000 PN23 2.00 V FREQ 0 ERR OFF -1.00 V

Memory

Figure 2- 7. Generator Display in Its Normal (Non-menu) Mode

The function of each field in the normal Generator display format—that is the format used when the Generator is not in the menu mode - is described below:

• The top left section of the Generator display is used to show the current

frequency of the internal clock in MHz. For example a display of

622.050 indicates a frequency of 622.050 MHz.

• The top middle section normally shows the current test pattern. For example

PN23 INV indicates that the current pattern is an inverted 2

• The top right section of the display shows the amplitude of the CLOCK or

DATA output, depending on which output control ( CLOCK or DATA) is

selected.

• The bottom left section of the Generator display may show either the

presently selected word memory (WORD 0 ... WORD 7) or the selected frequency memory (FREQ 0 ... FREQ 9).

AMPL

OFFS

-1 PRBS.

• The bottom middle section of the display shows the currently selected

Generator error inject mode.

• The bottom right section of the Generator display will normally show the

baseline offset of the CLOCK or DATA output, depending on which output control (CLOCK or DATA) is selected.

2-6 GB1400 User Manual

Analyzer (RX) Display

Like the Generator, the Analyzer has a two-line by 24-character high-contrast liquid crystal display (LCD).The Analyzer display in its normal (non-menu) mode is illustrated in the figure below.

Frequency (kHz) Error Rate Totalize

1405000 5.0E-06 2410538

1.2 ns PN23 -0.05 V

Delay/ Memory

Figure 2- 8. Analyzer Display in Its Normal (Non-menu) Mode

Like the Generator, the Analyzer has a two-line by 24-character high-contrast liquid crystal display (LCD). The function of each field in the normal Analyzer display format -that is the format used when the Analyzer is not in the menu mode -is described below:

Functional Overview

• The top left section of the Analyzer display is used to show the measured

frequency of the input clock signal in MHz. For example a display of

622.05 indicates a measured frequency of 622.05 MHz. Note that the

Analyzer frequency display contains five significant digits while the Generator frequency display contains six. This is because the frequency shown in the Analyzer display is a measurement result while the frequency shown in the Generator display is an instrument setup which is known with more precision.

• The top middle and top right sections of the display normally show measured

bit error rate and bit errors respectively. BER is expressed in exponential or "E" notation. For example, a display of 1.5E-09 indicates a measured BER

of 1.5 x 10-9. The Analyzer calculates BER and counts bit errors in three modes simultaneously: Window, Test, and Totalize. The symbol in front of the BER field indicates which mode has been selected for display. Window results are preceded by a blank space, that is no symbol. Totalize results will be preceded by an ∞ (infinity) symbol. Test results will be preceded by a T, U, or R depending on the selected test mode: timed, untimed, or repeat. Refer to Chapter 4 for more information on displaying Analyzer results and starting and stopping tests.

GB1400 User Manual 2-7

Functional Overview

• The bottom left section of the Analyzer display can show the following setup

parameters: delay in nanoseconds for the DATA or REF DATA input; the selected input termination (GND, -2V, or AC) for the CLOCK, DATA, or REFERENCE DATA input, or the selected word memory (WORD 0 ... WORD 7), Note that DATA input delay may be set manually by the user, or automatically by the AUTO SEARCH feature.

To control the delay, termination or threshold settings for the DATA input, make sure F2 and F3 LEDs are turned OFF.

Pressing F2 places the unit into CLOCK control (F2 LED illuminated). The V-TERM key is redefined to allow control of the Input CLOCK Termination voltage. The status of each key LED and LCD displayed value now reflects the CLOCK Input signal.

Pressing F3 places the unit into REF Data control mode (F3 LED illuminated). The Delay, V-TERM and V-THRS keys are redefined to allow control of the Input REF DATA Delay, Termination Volga and Threshold. The status of each key LED and LCD displayed value now reflects the REF DATA Input signal.

• The bottom middle section of the display shows the currently selected

Analyzer pattern, for example PN23 indicates a 223-1 PRBS. This section will also indicate when input pattern inversion is enabled by displaying INV after the pattern name.

• The bottom right section of the Analyzer display shows the current value of

the input threshold in volts for the CLOCK, DATA, or REF DATA inputs. Note that the CLOCK and DATA input thresholds may be set manually by the user, or automatically by the AUTO SEARCH feature.

2-8 GB1400 User Manual

Outputs and Inputs

This section introduces all inputs and outputs of the GB1400 Generator and Analyzer. Unless otherwise indicated, all signal inputs and outputs are equipped with SMA female connectors and have a nominal input or output impedance of 50 ohms. However, a 75 Ohm Option is available for both the Generator and Analyzer which changes nominal impedance of key inputs and outputs to 75 ohms.

Note: The same term can be expressed three different ways.

Functional Overview

clock

DATA

= clock bar = NOT clock

= DATA BAR = NOT DATA

The front panel of the GB1400 Tx is divided into nine sections:

LCD Display Error Inject Clock Pattern Output Controls GPIB Power Switch Output Connectors

Generator OUTPUT Connectors Section

The OUTPUT connectors section of the Generator front panel contains the outputs listed below.

PATTERN SYNC CLOCK/4 CLOCK

OUTPUT

CLOCK

DATA

50 Ohm SOURCE

• CLOCK and DATA [outputs]: These two connectors comprise the main

test signal output of the Generator. DATA is the NRZ output of the pattern generator and CLOCK is its corresponding clock signal. The amplitude and baseline offset of CLOCK and DATA are variable. CLOCK and DATA may be used to drive single-ended clock and data inputs, respectively.

• CLOCK-BAR and DATA-BAR [outputs]: These are complimentary

outputs to CLOCK and DATA. That is, CLOCK and CLOCK-BAR together can drive a differential clock input, while DATA and DATA-BAR together can drive a differential data input. These complementary outputs should be terminated with a 50 Ohm load (or a 75 Ohm load if the 75 Ohm Option is

GB1400 User Manual 2-9

Functional Overview

installed) when not in use—that is, when the Generator is driving singleended inputs.

• CLOCK/4 [output]: This is a clock signal at one quarter the frequency of

CLOCK. This output may be useful when observing generator outputs using an oscilloscope that does not have the bandwidth to trigger on the CLOCK output.

• PATTERN SYNC [output]: This is a pulse that occurs once per pattern

frame. This output may be useful as a trigger signal when observing the Generator data output using an oscilloscope. The location of PATTERN SYNC is fixed. A pulse is generated at the start of the pattern frame.

Generator CLOCK Section

Controls in the CLOCK section of the Generator are used to select clock mode (internal or external) and to set up the instrument's internal clock. The CLOCK section also contains the input connector for an external clock source. These controls and input are introduced below.

FREQUENCY

STEP

RECALL

SAVE

EXT

INPUT

50 Ohm 2 V Max

(2)

• FREQUENCY: When this key is selected (LED on), the clock up/down

keys may be used to adjust the frequency of the internal Generator clock up or down. Each press of the frequency up or down key will increment or decrement frequency by the current step size.

• STEP: Select this key to adjust the frequency adjustment step size from

1 kHz to 100 MHz.

• SAVE: Use this key to save the present frequency into one of 10 frequency

memory locations.

• RECALL: Use this key to recall a previously saved frequency.

• EXT: Press this key to toggle between internal clock mode (LED off) and

external clock mode (LED on).

• INPUT: This is an input for an external clock source. A signal must be

provided to this input when clock mode is set to external. However, when clock mode is internal, any signal appearing at this input will be ignored.

2-10 GB1400 User Manual

Functional Overview

Generator OUTPUT Section

The controls shown below are used to set up the Generator's clock and data outputs.

OUTPUT

CLOCK DATA

OFFSET

AMPLITUDE

INVERT DATA (D-INV)

• CLOCK: Use this key to select clock amplitude and offset set up mode.

• DATA: Use this key to select data amplitude and offset set up mode.

• AMPLITUDE (↑↑, ↓↓): Use these up/down keys to adjust clock or data

output amplitude.

• BASELINE OFFSET (↑↑, ↓↓): Use these up/down keys to adjust clock or

data baseline offset.

• INVERT DATA: Use this key to toggle between output data inverted (LED

on) and non-inverted (LED off) mode.

GB1400 User Manual 2-11

Functional Overview

Generator Rear Panel

The rear-panel of the Generator contains the auxiliary signals, remote control, and AC-power inputs shown below. See the appendix for instruction on how to set up the RS-232 and GPIB ports, and general information on using external controllers with the Generator.

PHASE A PHASE B CLOCK/2 ERROR INJECT DATA INHIBIT

• PHASE A: An SMA connector provides signal output for DATA Phase A.

This phase-shifted data pattern provides signals suitable for MUX/DEMUX testing. Phase A/B outputs are half rate data patterns (alternating bits).

• PHASE B: : An SMA connector provides signal outputs for DATA Phase

B. This phase-shifted data pattern provides signals suitable for MUX/DEMUX testing.

• CLOCK/2: : An SMA connector provides signal outputs for CLOCK/2.

• ERROR INJECT: An ECL signal applied to this input may be used to

control error injection when the Generator is in the external (EXT ERR) injection mode. One error will occur for each rising edge of this signal.

• DATA INHIBIT: An ECL signal applied to this input may be used to

asynchronously gate off the data outputs of the Generator.

• RS-232C [input/output]: A two-way serial port that may be connected to

an external controller or serial printer.

• GPIB [input/output]: An IEEE-488 standard I/O port that may be

connected to a GPIB compatible controller. This port is not compatible with stand-alone GPIB printers.

• AC LINE [power input]: This is the AC power input connector for the

Generator.

Changing the Line Fuse

1. Disconnect the AC line cord.

2. Slide the fuse cover upwards and remove the fuse.

3. Install the correct line fuse into the holder.

115 VAC 5A, Slo-Blo 230 VAC 5A, Slo-Blo

4. Close the fuse cover.

5. Plug in the line cord. Allow at least two inches of clearance for the rear panel fan opening and at least

one inch of clearance for the top of the unit. This assures proper cooling of the unit. Do not operate the Generator on its rear side.

2-12 GB1400 User Manual

Functional Overview

Analyzer INPUT Section

The INPUT section of the Analyzer front panel contains the test signal NRZ data and clock inputs shown below.

DATA

REFERENCE DATA CLOCK

CLOCK

• CLOCK and DATA [inputs]: These inputs comprise the main test signal

input to the Analyzer. DATA is the main NRZ data input to the Analyzer pattern detector and CLOCK is its corresponding clock signal. Both inputs have selectable input terminations. In addition, a variable amount of delay may be added to the DATA input to properly phase-align the clock and data signals. CLOCK and DATA may be used to terminate singled-ended clock and data outputs, respectively.

For single-ended applications, the DATA input threshold is programmable. This requires an external cable connection from the rear panel DATA THRESHOLD output to the unused DATA input. Only the unused "DATA-BAR" input needs the threshold signal. The CLOCK input is selfbiasing for single-ended applications.

• CLOCK-BAR and DATA-BAR [inputs]: These are complimentary inputs

to CLOCK and DATA. That is, CLOCK and CLOCK-BAR together comprise a differential clock input, while DATA and DATA-BAR together comprise a differential data input. When the Analyzer is connected to singled-ended clock and data signals, these inputs are not used.

Note: In DIFFERENTIAL applications, the programmed threshold voltage is not used.

• REFERENCE DATA [input]: This is an input for a reference data signal.

When the external reference mode is selected (LED in EXT key is on), the signal appearing at the REF DATA input will be used as the reference signal to perform bit error analysis instead of a (reference) pattern generated by the Analyzer's error detection circuit. Note that REF DATA uses the same clock signal as DATA, however different amounts of delay can be added to the DATA and REF DATA inputs to account for phase differences between the two signals.

GB1400 User Manual 2-13

Functional Overview

Analyzer MONITOR Section

The MONITOR section of the Analyzer front panel contains the auxiliary outputs shown below. These outputs may be used to monitor the test signal as seen by the Analyzer.

PATTERN

SYNC

MONITOR

CLOCK

50 Ohm SOURCE

DATA

• CLOCK [output]: A buffered copy of the clock signal received by the

Analyzer.

• DATA [output]: A regenerated (re-clocked) version of the data signal

received by the Analyzer.

• PATTERN SYNC [output]: A train of pulses that occur once per pattern

frame. This output may be used to trigger an oscilloscope to view the beginning (first bit/byte) of the data pattern.

2-14 GB1400 User Manual

Functional Overview

Analyzer Rear Panel

The rear-panel of the Analyzer contains the auxiliary signal, remote control, printer, and AC-power inputs shown below. See the appendix for instruction on how to set up the RS-232 and GPIB ports, and general information on using printers and external controllers with the Analyzer.

DATA THRESHOLD

ERROR INHIBIT RZ ERROR

OUTPUT

• DATA THRESHOLD OUTPUT: The programmed DATA threshold

voltage is set via the front panel. Connect to DATA BAR input for singleended applications. Requires external cable connection.

• ERROR INHIBIT INPUT: An ECL signal applied to this input may be

used to asynchronously gate on/off the error detection function of the Analyzer. That is, while the signal at this input is low, errors are counted. While it is high, error counting is inhibited.

• RZ ERROR OUTPUT: This is an ECL output signal. One pulse will be

generated at this output for each bit error detected. May be connected to an external recording device, for example, to log the exact times that errors occur.

• PRINTER [output]: A one-way port that may be connected to a "parallel

printer"—that is, any printer compatible with the parallel port (LPT1 etc.) of an IBM-compatible PC.

• RS-232-C [input/output]: A two-way serial port that may be connected to

an external controller (e.g. a PC or workstation) or to a serial printer.

• GPIB [input/output]: A two-way, IEEE-488 compatible I/O port that may

be connected to an external controller via a GPIB cable.

PRINTER

RS-232C GPIB

Changing the Line Fuse

1. Disconnect the AC line cord.

2. Slide the fuse cover upwards and remove the fuse.

3. Install the correct line fuse into the holder.

115 VAC 5A, Slo-Blo 230 VAC 5A, Slo-Blo

4. Close the fuse cover.

5. Plug in the line cord. Allow at least two inches of clearance for the rear panel fan opening and at least

one inch of clearance for the top of the unit. This assures proper cooling of the unit. Do not operate the Analyzer on its rear side.

GB1400 User Manual 2-15

Functional Overview

Connectors, Terminations, and Levels

Tables 2-1 and 2-2 below summarize the physical interface characteristics of all GB1400 Generator and Analyzer inputs and outputs.

Table 2-1. Generator (Tx) Inputs and Outputs

Connector Label Signal Type Location Connector

Type

DATA output OUTPUT section SMA,

female

CLOCK output OUTPUT section SMA,

female

DATA-BAR output OUTPUT section SMA,

female

CLOCK-BAR output OUTPUT section SMA,

female

CLOCK/4 output OUTPUT section SMA,

female

PATTERN SYNC output OUTPUT section SMA,

female

Impedance, amplitude, and offset

50 Ohm, see NOTE 1, variable amplitude and offset

50 Ohm, 200mV into 50Ω

CLOCK INPUT input CLOCK section SMA,

female

DATA INHIBIT input rear panel BNC,

female

ERROR INJECT input rear panel BNC,

female

RS-232 I/O rear panel 25 pin, D

type

GPIB I/O rear panel GPIB IEEE-488 standard levels

50 Ohm, 2V max, see NOTE 2

50 Ohm to -2V, ECL

RS-232C standard levels and impedance

and impedance

Note 1: A 75-Ohm version of the GB1400 is an option. Note2: BURST Mode units require ECL-level inputs and are terminated with 50-Ohms to -2V.

2-16 GB1400 User Manual

Table 2-2. Analyzer (RX) Inputs and Outputs

Functional Overview

Connector Label Signal

Type

DATA/DATA BAR Input INPUT SMA, female 50 Ohm, see NOTE 1, variable

CLOCK/CLOCK BAR

REF DATA Input INPUT SMA, female 50 Ohm, ECL, variable delay,

PATTERN SYNC output MONITOR SMA, female

CLOCK output MONITOR SMA, female

DATA output MONITOR SMA, female

ERROR INHIBIT INPUT

RZ ERROR OUTPUT

Input INPUT SMA, female 50 Ohm, see NOTE 1, fixed

input rear panel BNC, female 50 Ohm, ECL

output rear panel BNC, female

Section Connector

Type

Impedance, threshold, and delay

threshold and delay. Selectable termination: GND, -2 V, AC

threshold. Selectable termination: GND, -2 V, AC

selectable termination GND, -2V, AC

50 Ohm, 200mV into 50Ω

PRINTER output rear panel 25-pin, D male Compatible with PC parallel printers RS-232C I/O rear panel 25-pin, D male RS-232 levels and impedance GPIB I/O rear panel GPIB IEEE-488 standard levels and

impedance

Note 1: A 75-Ohm version of the GB1400 is an option.

GB1400 User Manual 2-17

Functional Overview

Controls and Indicators

All of the controls, indicators, inputs, and outputs found on the Generator or Analyzer front or rear panels are discussed in the following section.

Power Switches

The ON/OFF power switch is located on the left side of the test instrument below the LCD screen. The power switch switches the 120/240 VAC to the system power supply. When off, a Battery backup circuit powers the non-volatile RAM.

Unit Mounting

Unit Cooling

The rear panel fan openings must be kept clear for proper cooling of the unit. Allow a minimum of two (2) inches of rear panel clearance, and one (1) inch of top clearance, while operating the unit.

View Angle and Panel Lock Keys

The PANEL LOCK and VIEW ANGLE keys are located near the top, left side of the front panel.

• VIEW ANGLE: Use this key to select the optimum LCD viewing angle.

• PANEL LOCK: Use this key to "lock" and "unlock" the front panel. While

the front panel is locked, all keys that can cause setup changes are disabled. This feature can help prevent accidental loss of data when performing longterm or critical tests.

RESET to Factory Default

To return the Generator or Analyzer to factory default settings, turn the instrument OFF and then re-power it while pressing and holding the VIEW ANGLE, MSB 1, and (PATTERN) CLEAR keys at the same time. Release these keys after the message Default Setup appears in the display.

2-18 GB1400 User Manual

Functional Overview

GPIB Section Controls

There are two keys in the GPIB section:

• ADDR: Key used to set GPIB address in the range 0 to 30.

• LOCAL: The LED in this key indicates whether the instrument is in the

local mode (LED off) or remote mode (LED on). If the LED is on, you can return the instrument to local mode by pressing the LOCAL key.

Note that these two keys are used only when operating the instrument via its GPIB port. For more information on the GPIB port and remote control in general, see the appendix. For detailed descriptions of all remote commands, see the appendix.

GB1400 User Manual 2-19

Functional Overview

Pattern Controls and Function Keys

The PATTERN section of both the Analyzer and Generator front panels contains two basic types or groups of controls: "pattern" and "function". The four function or "soft" keys —F1, F2, F3, and F4—have different functions depending on the current mode of the instrument. A primary function of these controls is to access and navigate the menu system. Pattern controls, which includes all other controls in the PATTERN section, are used to select edit, save, and recall test patterns.

WORD

PRBS

LENGTH

F1 F2 F3 F4

CLEAR SET

WORD

RECALL

SAVE

MSB 1 2 3 4 5 6 7 8

CLK REF

• PRBS: Press this key, and then the pattern up/down keys to select a PRBS

pattern.

• WORD: Press this key either to select a word or ROM pattern or to edit the

current word pattern.

• SAVE and RECALL : Use these keys to save and recall user-created word

patterns to and from non-volatile memory. The standard GB1400 can store

up to ten 16-bit or short word patterns. When equipped with the 1-Mbit option, the GB1400 Generator and Analyzer can store up to ten (10) 65-kbit patterns, depending upon the buffer size set for word memory.

• WORD LENGTH: Press this key and then the up/down keys, to adjust the

length of the current word pattern.

• (↑↑,↓↓): These are the pattern up/down keys. Their effect depends on which of

the above pattern keys has been selected.

• MSB 1 to 8: Use these keys to edit the displayed byte in the current word

pattern. Each key will toggle one bit in the displayed byte.

• CLEAR: Pressing this key forces all bits in the displayed byte to 0.

• SET: Pressing this key forces all bits in the displayed byte to 1.

2-20 GB1400 User Manual

Functional Overview

Function (Soft) Keys (F1, F2, F3, and F4)

Menu Functions: The primary use of the function keys in the Generator and Analyzer is to access and navigate each instrument's menu system. F1 may be thought of as the main menu key. Pressing F1 will display the instrument's first level menu. Once inside the menu system, you may use the F1, F2, F3, and F4 keys to select different menus, or to make choices within a selected menu. Note that pressing the F1 key enough times will always get you out of the system. See Chapter 3 - Reference for an explanation of each Generator and Analyzer menu.

Analyzer Inputs

These function keys provide signal inputs and control of parameters (Input Termination, Threshold, Logic Polarity and Data/Clock Phase Delay) for DATA, Ref DATA, and CLOCK.

Selecting DELAY, V-TERM or V-THRS permits the INPUT Up/Down keys to vary the Input parameters for DATA, as described below. Holding the Up/Down key repeats the function five times a second.

Function key F2 (CLOCK) permits the V-TERM key to vary only the Input termination parameters for CLOCK.

Function key F3 (Ref DATA) permits the DELAY, V-THRS, and V-TERM keys to vary the Input parameters for Reference DATA.

DELAY - Pressing DELAY selects Input Data Delay adjust mode. The Input Data signal can be delayed over the range 0.0 nS to 3.9 nS in sub-nanosecond steps. The delay is modified with the INPUT Up/Down keys. The current Delay is displayed on the lower left side of the LCD.

An illuminated Delay LED light indicates that the unit's DELAY can be modified by the Up/Down arrow keys.

V-TERM - Pressing V-TERM selects V-termination mode. The input termination voltage for Input Data is selectable between GND, -2.0V, and AC.

-2.0V mode provides active termination for ECL and GaAs signals. AC mode allows RF termination.

An illuminated V-TERM LED light indicates that the input termination can be modified by the Up/Down arrow keys.

V-THRS - Pressing V-THRS selects V-Threshold mode. The Input Data threshold is variable over the range of -1.5V to +1V in 50 mV steps. The currently selected threshold voltage is displayed in the lower right side of the LCD display.

An illuminated V-THRS LED light indicates that the threshold voltage can be modified by the Up/Down arrow keys.

The Data threshold voltage is available at the Analyzer rear panel SMA jack labeled DATA THRESHOLD.

Print Setup Function (Analyzer only): You can print a report showing the current setup of the Analyzer by pressing the F4 key. This function, however, is not active in the menu mode.

GB1400 User Manual 2-21

Functional Overview

Generator ERROR INJECT Section

Controls in the ERROR INJECT section are used to set up the Generator's error injection function.

ERROR INJECT

RATE SINGLE

• RATE: Press this control one or more times to select an internal error inject

rate, or the external error inject mode.

• SINGLE: When the error inject function is set to single (ERR OFF), press

this key to inject single errors. Or, when the error inject function is set to an internal rate, or to external, use this key to turn error injection off. Note that you could then press the RATE key to turn error injection back on at the same rate as before.

• Error Inject (LED): The LED in the ERROR INJECT section will flash

once for each injected error.

2-22 GB1400 User Manual

Functional Overview

Analyzer INPUT Section

The controls shown below are used to set up the Analyzer clock and data inputs.

INPUT

DELAY

V-TERM V-THRESH

D-INV

DATA DATA

50 Ohm, 2V MAX

REFERENCE DATA CLOCK

(1)

EXT

CLOCK

(2)(1)

50 Ohm, 1.5V MAX

• DELAY: Press this key to add delay to the DATA or REF DATA inputs to

adjust the clock/data phase relationship. Note that the Auto_Search function will automatically set data delay to a value which provides the maximum noise immunity, that is so that the active (falling) edge of the clock falls in the middle of data bit time slots.

• V-THRESH: Press this key to set the input decision threshold for the

DATA and REF DATA inputs. Note that threshold does not apply when differential operation is selected. Function keys F2 and F3 are OFF when programming DATA. Function key F3 is ON when programming REF DATA.

• V-TERM: Press this key to select the input terminations for the DATA,

CLOCK, or REF DATA inputs. Available selections are: (GND, -2 V, or AC). See table below.

• D-INV: Press this key to select either the data non-inverted (LED off) or

data inverted (LED on) mode.

• EXT: This is an input for an external data reference signal.

NOTE: Use the F2 and F3 function keys to determine which input will be

affected by the DELAY, V-THRESH, and V-TERM controls as follows:

F2 F3 Affected Input Allowable Control

off off DATA V-TERM, V-THRESH, DELAY on off CLOCK V-TERM only off on REF DATA V-TERM, V-THRESH, DELAY on on not allowed

GB1400 User Manual 2-23

Functional Overview

SYNC LOSS

PHASE

Analyzer Error History Section

BIT

POWER

SYNC LOSS BIT PHASE POWER

CLEAR

The SYNC LOSS LED is lit when the unit is not synchronized, it will remain lit until cleared by the user.

The BIT LED is lit when bit errors occurs, and remains lit until it is cleared by the user.

The PHASE LED is lit when the guaranteed setup or hold time of the GB1400 input decision circuit is violated. This indicates to the user that the errors that are occurring may be due to input clock/data timing or signal level.

The POWER LED is lit when the unit powers up. It remains lit until it is cleared by the user. It is used to indicate that the unit lost power during a long term (overnight) test.

2-24 GB1400 User Manual

Functional Overview

Analyzer ERROR DETECTION Section

The ERROR DETECTION section contains test setup and display controls.

ERROR DETECTION

DISPLAY

CLEAR

AUDIO

VOL

RATE

DISPLAY SELECT: Use this control to select which results are displayed in the Bit Error Rate (BER) fields. The options are Window, Totalize, or Test.

• CLEAR: Press this key to clear previous results and to start/stop timed tests.

• AUDIO VOL (↑↑, ↓↓): Use these keys to increase or decrease the volume of

the Analyzer's error beeper function.

SYNC

AUTO

LOCK

DISABLE

• AUDIO RATE (↑↑, ↓↓): Use these keys to increase or decrease the error rate

threshold of the beeper function. Selections are 1E-x, where x = 2, 3, ... 16.

Analyzer SYNC Controls

The ERROR DETECTION section contains the following SYNC controls which are used to set up the Analyzer's automatic synchronization functions:

• AUTO SEARCH: Press this key to enable (LED on) or disable (LED off)

AUTO SEARCH. With AUTO SEARCH enabled, each time BER goes above

the synchronization threshold (LOCK LED turns off) the Analyzer will automatically attempt to:

1. set the decision level for the DATA inputs,

2. set input DATA delay,

3. determine which PRBS or short word pattern is being received, and

4. determine if the pattern is inverted or not.

• DISABLE: Use this key to enable or disable automatic pattern re-

synchronization. If DISABLE is off, then the Analyzer will automatically try to resynchronize its pattern detector (by looking for a new pattern alignment) when BER goes above the current synchronization threshold. If DISABLE is on, the Analyzer will not attempt to resynchronize regardless of the BER. This allows for very high BER measurements.

This key controls the "clock slip" operation of the BERT. An illuminated DISABLE LED indicates the synchronization (clock slip) circuit is disabled.

• LOCK (indicator): This indicator turns ON when BER is less than the

current synchronization threshold, and OFF when BER is greater than or equal to this threshold.

GB1400 User Manual 2-25

Functional Overview

Burst Mode Option

The standard GB1400 operates over a clock frequency range of 1 Mbit/s to 1400 Mbit/s. The GB1400 Tx has an internal clock source that has a range of 1 MHz to 1400 MHz. It also has a provision for using an external clock source of the same frequency range. When using the external clock source, it must be applied continuously without interruption. The GB1400 RX also requires that, at all times during the test, a clock signal within the 1 Mbit/s to 1400 Mbit/s frequency range be continuously applied. If the external clock signal should be removed , or go below 1 MHz for any reason during the test, the RX will register OUT OF SYNC as soon as the clock signal is reapplied. This condition will initiate a resynchronization of the receiver and restart any tests.

For the Burst Mode option, the GB1400 RX has been modified to work normally or in Burst Mode from 150 kHz to the normal 1400 MHz upper limit. The RX CLOCK and CLOCK BAR inputs have been modified for DC operation. This modification requires the removal of any blocking capacitors in the input path. The removal of the capacitors limits the allowable input signal to ECL levels only. Levels other than ECL may damage the input circuitry. The three standard clock input termination selections of GND, AC, and -2V are still present.

Note: The Clock may be used either differentially or single-ended. To use a single-ended clock input, connect the ECL clock input to the CLOCK input connector. Select the -2V input termination, and connect DC bias voltage of -1.3 VDC to the CLOCK BAR input connector.

These and other changes will now allow the receiver to maintain synchronization whenever CLOCK and DATA are synchronously stopped and started during a test pattern, providing there has not been a bit slip between CLOCK and DATA.

In both the Tx and RX, there can be any length of time that both CLOCK and DATA are off, and the minimum CLOCK/DATA applied can be as low as a single cycle, providing the minimum of 714 pS and maximum of 667 µs clock period restrictions are observed.

Similar Tx circuit changes allow the Tx DATA and CLOCK outputs to follow, cycle by cycle, the input from a bursted External Clock Input. This means that the Tx can be used in a start-stop, or "Burst Mode".

For every clock cycle into the External Clock Input, there will be the same number of clock cycles and data bits output through the clock and data outputs. The time between clock cycle inputs is unrestricted and can be any length of time. The number of clock cycles can be any number from continuous to a single cycle. During the time there is no clock input to the External Clock Input, the internal code generator is idle (not running). Each clock cycle steps the code generator by one bit. Clock cycle period must not be more than 667 µs (150 kHz) nor less than 714 pS (1400 MHz).

2-26 GB1400 User Manual

Functional Overview

Burst Mode Usage

The Burst Mode option of the GB1400 will find usage in applications where traditional BERTs cannot operate. Traditional BERTs require a continuous CLOCK and DATA signal with no interruption. Should interruptions occur, the RX will resynchronize or indicate errors that actually did not occur due to the asynchronous re-start. The BURST MODE allows operation with a noncontinuous clock.

There are communications and telemetry systems that do not necessarily send data continuously. These systems send data in "bursts" with variable times of inactivity between bursts. Traditional BERTs cannot accurately check these systems, especially if the bursts are of short duration. A traditional BERT may require more bits than are available in the burst to (re)synchronize. Even if the bursts are large, many bits in the burst would not be checked during the (re)synchronization procedure.

In Burst Mode, the GB1400 RX will follow the input CLOCK and DATA without regard for inactive time between bursts. The only requirement is that there be no bit slips between the CLOCK and DATA at the Tx or UUT and there be a clock cycle for every DATA bit received.

See figures on the next page for Transmit and Receive Operation with Burst Mode.

Specifications for Burst Mode

• Maximum time between bursts - no restriction

• Minimum time between bursts - one clock period

• RX Clock Input - ECL level only; User-selectable termination 50 Ohms to

-2V should be used. Minimum rate during burst - 150 kbit/s; Maximum rate during burst - 1400 Mbit/s

• RX Auto Search restriction - Below 500 kbit/s, the Auto Search function can

take a very long time due to code word search. Finding both Threshold and Delay is rapid, but Data Pattern search is lengthy. Because of this, the user should use Manual Search Mode to keep synchronization time as low as possible.

• Restriction on other options - None

GB1400 User Manual 2-27

Functional Overview

Undefined Time Undefined Time

Ext Clk In ……………….. ………………..

Clk Out ……………….. ………………..

Data Out ……………….. ………………..

Data Value 1 0 1 1 0 0

Figure 2- 9. Transmitter Burst Mode Option

[ Sync Time ] [ Measurement

DATA

Sync Attained

Undefined Time Sync Attained

DATA

|------| |

[Msmt ] [ Sync ] [Measurement ]

Start Resync

[Msmt ] [Measurement ] [Msmt ]

Figure 2- 10. Receiver Burst Mode Operation

2-28 GB1400 User Manual

PECL Option for GB1400 Tx

The PECL option is available for the GB1400 Tx only. The PECL option for the GB1400 Tx is a modification that allows for an increased OFFSET RANGE for the clock and data outputs, so that the user will be able to generate PECL levels for testing in a PECL environment. PECL is defined as ECL operating +5.0 V above ground.

Example:

ECL Levels PECL Levels

VOH ≈ -.9V VOH ≈ +4.1V VOL ≈ -1.8V VOL ≈ +3.2V VBB ≈ -1.35V VBB ≈ +3.65V VTT ≈ -2.0V VTT ≈ +3.0V

The GB1400 front panel displays, the clock and data amplitude and offset based on a load of 50 Ohms to ground.

Functional Overview

The inverted output circuit is identical to the true output circuit. In the PECL system, Vtt = +3.0V, therefore, the resulting GB1400 Tx signal will

be shifted by +1.5V. To get PECL levels at the GB1400 Tx output, set the unit levels as follows:

Display Setting Resulting PECL Levels

(50 Ohms to +3.0V)

AMP = .90V OFFSET = +1.7V

GB1400 User Manual 2-29

VOH ≈ +4.10V VOL ≈ +3.20V

Tutorial

Basic BERT testing with the GB1400

A critical element in digital transmission systems is how error-free its transmissions are. This measurement is made by a bit-error-rate tester (BERT). The GB1400 Generator (Tx) and Analyzer (Rx) are designed to operate at bit rates up to 1400 Mb/s. These portable instruments provide PRBS or User Defined Patterns (up to 1Mbit deep) for high speed BERT testing.

Objective of Tutorial

Understand GB1400 instrument setup for BER testing using PRBS patterns.

Procedure

This tutorial programs the GB1400 Generator to provide PRBS clock and data signals for the Analyzer. Using AUTO-SEARCH features, the Analyzer will synchronize to the incoming PRBS test pattern. Bit Error Rate (BER) measurements will be performed on both good (error-free) and bad (user injected faults) data streams.

Key Feature of Tutorial

This lab demonstrates the use of AUTO-SEARCH Synchronization.

Equipment Required

Description Qty Part Number Source

GB1400 Generator 1 GB1400 Tx Tek GB1400 Analyzer 1 GB1400 Rx Tek 50Ω Coax SMA cables, 1 meter

length, male to male

3 174-1341-00 Tek

GB1400 User Manual 2-30

DATA

CLOCK

Tutorial

Instrument Connections and Controls

Data Threshold connection (required for single-ended signals)

GB1400 Analyzer (Receiver)

GB1400 Generator (Transmitter)

CLOCK

DATA

1. Setup units with default settings

Note: Resetting the unit to factory defaults is used infrequently. It helps simplify instructions on this beginners lab. A customer would not normally do this as they would lose their stored setups.

To reset the units to their factory default setting, you must hold down three separate keys while turning on the front panel power switch. Power the Generator while pressing and holding its VIEW ANGLE, MSB 1 and (PATTERN) CLEAR keys simultaneously. Release the key after the message Default Settings appears in the display. Repeat this procedure with the Analyzer. This will force both the Generator and Analyzer to power up using factory default settings.

GB1400 User Manual 2-31

Tutorial

2. Connect the Generator to the Analyzer.

Connect the generator and analyzer as shown below. The generator CLOCK output connects to the analyzer CLOCK input. The generator DATA output connects to the analyzer DATA input. The rear panel THRESHOLD output on the Rx connects to the Receiver NOT-DATA input on the front panel. Terminate the generator NOT_CLOCK and NOT_DATA signals with the 50Ω terminators located on the front panel of the generator.

rear panel threshold output

GB1400 TX GB1400 RX

clk clk data data data data clk clk

data

clock

Note: Do not mix up the clock, not_clock, data, and not_data signals or tutorial results will be different.

3. Setup Generator for PRBS-23 Mode.

Locate the controls in the OUTPUT box of the Generator. Setup the Generator clock and data outputs as follows:

Set this parameter …to this value …using this procedure.

DATA amplitude. 1 volts Press the DATA key. The LED within the switch

should be lit.

Press AMPLITUDE up/down keys until data amplitude is set to 2.00V.

DATA baseline offset -0.5 volt Press BASELINE OFFSET up/down keys until

data baseline offset is set to -0.50V.

CLOCK amplitude 1 volts Press CLOCK. (the LED within switch should be

lit).

Press AMPLITUDE up/down keys until clock amplitude is set to 2.00V.

CLOCK baseline offset

-0.5 volt Press BASELINE OFFSET up/down keys until clock baseline OFFSET is set to -0.50V.

2-32 GB1400 User Manual

B. Locate the controls in the PATTERN box of the Generator. Make sure the PRBS button is enabled (the LED inside this switch should be ON). Set the

Generator pattern to a 2

Set this parameter …to this value …using this procedure.

PRBS type PN 23 Press pattern up/down arrow keys until

-1 bit PRBS as follows:

PATTERN is set to PN 23

C. Locate the controls in the ERROR INJECT box of the Generator. Verify that the Generator ERROR RATE GENERATOR is OFF (the LED within the switch should

be OFF). If the LED in the error inject RATE key is ON, then press RATE one or

more times until it turns off.

4. Setup Analyzer for “AUTO-SEARCH” Operation.

A. Locate the controls in the SYNC box of the Analyzer. Verify that the Analyzer AUTO SEARCH function is ENABLED. The LED in the AUTO SEARCH key should be ON. If the LED is OFF, press the AUTO SEARCH function one time until the LED is ON. At this point, verify that the green LOCK LED is ON.

Tutorial

B. Locate the controls in the ERROR DETECTION box of the Analyzer. Zero all Analyzer error counts by pressing the CLEAR key. Confirm that the number of errors and the error rate were reset to 0 (note: error rate will start changing as more and more bits are received. After several minutes of operation, the error rate should reach 0.0E-9 ⇒ 0.0E-10 ⇒ 0.0E-11 and on).

C. Locate the controls in the ERROR HISTORY box of the Analyzer. Reset all Analyzer history LEDs by pressing this CLEAR key. Confirm that all ERROR

HISTORY LED’s are turned OFF.

D. Locate the controls in the ERROR INJECT box of the Generator. Verify the GB1400 Analyzer can detect errors by pressing the Generator ERROR INJECT

SINGLE key several times. Verify that the number of errors count displayed by

the Analyzer increments each time the Generator SINGLE key is pressed. In effect you are now performing a bit error rate test on the test cables connecting

the gigaBERT1400 Generator and Analyzer. In an actual BER test, gigaBERT1400 Generator clock and data outputs would be connected to inputs on a "device under test" (DUT) while gigaBERT1400 Analyzer inputs would be connected to outputs on the DUT.

GB1400 User Manual 2-33

Tutorial

5. Change the PRBS pattern type

These steps demonstrate one of the many benefits of our Full-Featured AutoSearch algorithm - automatic synchronization to the incoming signal by selecting the correct PRBS test pattern.

A. Locate the controls in the PATTERN box of the Generator. Make sure the PRBS button is enabled (the LED inside this switch should be ON). Set the Generator pattern to a 2

Set this parameter …to this value …using this procedure.

PRBS type PN 7 Press pattern up/down arrow keys until

PRBS as follows:

PATTERN is set to PN 7

As the PRBS pattern type is changed, the Analyzer will start searching for a match. You should see the BIT, PHASE, and SYNC LOSS LED’s turn ON in the Error History section of the Analyzer. While the Analyzer is searching for the correct PRBS type, the LOCK LED in the Error Detection Section should turn OFF. When synchronization is achieved, the LOCK LED should turn ON.

B. Locate the controls in the ERROR DETECTION box of the Analyzer. Zero all Analyzer error counts by pressing the CLEAR key.

C. Locate the controls in the ERROR HISTORY box of the Analyzer. Reset all Analyzer history LEDs by pressing this CLEAR key. Confirm that all ERROR

HISTORY LED’s are turned OFF.

D. Locate the controls in the ERROR INJECT box of the Generator. Press the

ERROR INJECT SINGLE key several times. Verify that the error count

displayed by the Analyzer increments each time the Generator SINGLE key is pressed. Verify the BIT LED light located in the Error History Section of the Analyzer turns on.

6. Turn off AUTO - SEARCH and change Generator Outputs

These steps demonstrate one of the many benefits of our Full-Featured AutoSearch algorithm - setting the input data decision voltage to its optimum value. While the Auto-Search feature is disabled, the Generator output voltage will be adjusted to cause loss of sync. Auto-Search will then be enabled to correct this synchronization problem.

A. Locate the controls in the SYNC box of the Analyzer. Disable the AUTO

SEARCH function by pressing the AUTO SEARCH key. The amber LED within this

switch will be OFF when the Analyzer AUTO SEARCH function is DISABLED. If the LED is ON, press the AUTO SEARCH function one time to turn the LED OFF.

2-34 GB1400 User Manual

Tutorial

B. Locate the controls in the OUTPUT box of the Generator. Adjust the Data amplitude and offset as follows:

Caution: Adjust only the DATA signal. Do not change the CLOCK signal.

Set this parameter …to this value …using this procedure.

DATA amplitude. 0.50 volts Press the DATA key. The LED within the switch

should be lit.

Press AMPLITUDE up/down keys until data amplitude is set to 0.50V.

DATA baseline offset -0.25 volts Press BASELINE OFFSET up/down keys until

data baseline offset is set to -0.25V.

If you examined this output data signal (voltage vs. time) on a scope, it would look similar to:

+0.25 ←←

+0.00

↑↑

-0.25

Voltage ↑↑ 

-0.50

time →→

-0.25 V data offset

 ↓↓

best value to use for THIS data threshold is ~0.00 Vdc ++ 0.05 Vdc

You will now be manually adjusting the data input threshold for the GB1400 Analyzer. Locate the controls in the PATTERN box of the Analyzer. Make sure

F2 and F3 are turned OFF. These switches are used when adjusting

CLOCK or REF DATA input parameters.

C. Locate the controls in the INPUT box of the Analyzer. Verify that the Analyzer THRESH LED is turned ON. This allows manual adjustment of the DATA Input threshold. The threshold for the selected signal (clock or data) is shown on the bottom line of the Analyzer’s alpha-numeric status display. Using the INPUT

UP/DOWN keys, adjust this threshold and confirm the following actions:

Note: The BER display on the Analyzer can be set to totalize, window, or test modes. When in the totalize mode, a small ∞∞ (infinity) symbol will be displayed before the BER error rate. Use totalize mode for this tutorial exercise. Press the

ERROR DETECTION DISPLAY key several times to setup the analyzer for totalize

mode..

↑↑

0.5 V

amplitude

Maximum Level

←← Optimum Threshold

←← Minimum Level

GB1400 User Manual 2-35

Tutorial

Set DATA

THRESHOLD

to this value

-0.50 volts

Approximately

-0.30 volts to

-0.25 volts

+0.00 volts

Verify these results on the Analyzer Comments

Press the ERROR DETECTION and ERROR

HISTORY “CLEAR KEYS”, then confirm:

Data signal not detected. Selected threshold is below the minimum level of your data signal.

SYNC LOSS and BIT LED’s are ON

SYNC LOCK LED is OFF ERROR RATE display shows “ NO

DATA” or a 50% Error Rate.

Press the ERROR DETECTION and ERROR

HISTORY “CLEAR KEYS”, then confirm:

You are starting to detect the data signal. Selected threshold is near the minimum level of your data signal. Data threshold

SYNC LOSS should turn OFF

BIT and PHASE LED’s should turn ON

SYNC LOCK LED should turn ON

Press the ERROR DETECTION and ERROR

HISTORY “CLEAR KEYS”, then confirm:

is NOT CORRECT and you should expect BER errors.

Data signal fully detected. Selected threshold is at an optimum value for the input data signal. This is typically =

SYNC LOSS should turn OFF

1/2*[max level - min level].

+1.00 volts

BIT and PHASE LED’s should turn OFF

SYNC LOCK LED should turn ON ERROR RATE display shows NO BER

ERRORS equivalent to a rate of

0.0E-9 or better.

Press the ERROR DETECTION and ERROR

HISTORY “CLEAR KEYS”, then confirm:

SYNC LOSS and BIT LED’s are ON

SYNC LOCK LED is OFF ERROR RATE display shows “ NO

DATA” or a 50% Error Rate

Signal levels detected above this threshold are considered a logical “1” and signal levels below this threshold are considered a logical “0”.

Data signal not detected. Selected threshold is above the maximum level of your data signal.

2-36 GB1400 User Manual

Tutorial

D. Locate the controls in the SYNC box of the Analyzer. Verify that the

AUTO SEARCH function is ENABLED. The LED in the AUTO SEARCH key should be ON.

If the LED is OFF, press the AUTO SEARCH function one time to turn the ON. At this point, verify that the green LOCK LED is ON.

The Analyzer will now search and calculate a new data threshold. What is the

value of the threshold selected by Auto-Search? You should expect to see this

threshold value within a few hundred millivolts of the “data signal mid-point (or optimum threshold).

Note - Common Setup Problems

• Connecting the Generator’s clock output to the Analyzer’s not-clock (clock-

bar) input

• Connecting the Generator’s data output to the Analyzer’s not-data (data-bar)

input

• Changing Generator’s CLOCK amplitude/offset when lab calls for

adjustments to DATA signals

• Failure to connect the external DATA THRESHOLD cable from rear of unit

to NOT_DATA input.

This Concludes the Tutorial.

GB1400 User Manual 2-37

Applications

Application Note

Method For Very Fast Automatic Receiver Synchronization And Eye Width Measurement

Two Auto Search Synchronization Methods

This application note describes two Auto Search synchronization methods used in the GB1400 Bit Error Rate test set - a FAST method and a BER method. The criteria and sequence of events for the two methods are compared and the differences are described.

Auto Search is the feature that the GB1400 uses to describe its method of automatic setup and synchronization. Both methods of Auto Search synchronization perform the following functions, but in different ways and with differing results depending on the type of data and its quality.

• Analysis of the input data signal amplitude to select the correct threshold

voltage.

• Determine the timing skew between the clock and data signals and

automatically optimize it.

• Determine the correct data sequence and whether it is inverted.

• Measure the data eye width.

So that the following explanations are clear, let us first define some terms.

V–THRESHOLD

This is the absolute DC level above which GB1400 Receiver will declare a data bit value of “1” (HIGH). Below this value, it is considered to be a “0” (LOW).

DELAY

This is the timing difference (skew) between ideal timing and actual timing between the incoming clock and data. Ideal timing will place the falling edge of the clock signal in the center of the data bit. Any deviation from the ideal should, when possible, be corrected by delaying either the clock or the data (as in the GB1400 Receiver) in relation to each other.

2-38 GB1400 User Manual

Application Note - Auto Search Synchronization

PHASE

This is a unique and very fast method of determining where the edge of a data bit is in relation with the clock. The determination of phase errors is done by monitoring the logic value of a data bit at the selected threshold voltage and delay at two slightly different times. If the logic value is the same at the two different times, then a phase error has not occurred. This method will work well with any data that is relatively noise, jitter and glitch free.

SYNCHRONIZATION

When we state that “the receiver is synchronized”, we mean that the GB1400 Receiver’s internal reference data pattern generator is bit for bit properly aligned with the incoming data from the device under test. When in synchronization, the receiver can perform a bit for bit check of the incoming data against its internal reference to determine bit errors.

DATA POLARITY

This refers to whether the device under test has inverted the data logic in relation to what was input to it.

DATA EYE

This is a method of showing the data in a visual form. It is displayed on an oscilloscope using the clock as a trigger, and the data into the vertical amplifier. Case 1 of Diagram 1 of this application note is an example of data eye.

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Application Note - Auto Search Synchronization

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Application Note - Auto Search Synchronization

I. Auto Search Algorithm – “Fast” Method

Auto Search will determine the Data V- Threshold, Data Delay, Data Pattern and Polarity automatically. The so called “FAST” method has been given its name because of the speed with which it determines the threshold voltage setting, delay, data pattern and polarity. This is the default method used by the GB1400 Receiver.

The speed is derived mainly from the use of the GB1400’s PHASE edge detection circuitry which enables the receiver to quickly determine the transition points of the eye without regard to the actual pattern, or even if the receiver is properly linked up to the incoming data pattern.

If the data is not clean (glitches, excessive jitter or noise) this method will possibly not work well. For these cases, use the “BER” method described later in this document.

The “FAST” method of determining the proper settings for the V-Threshold, Delay, Pattern and Polarity is as follows:

Auto Search will find the DATA V-THRESHOLD voltage.

1. The receiver examines DATA ACTIVITY at each of the V-THRESHOLD

settings.

2. The receiver then locates and uses the middle of the largest voltage range

which has data activity. If no activity is detected, or if the range of activity is less than 250 mV, then the receiver indicates “NO DATA” has been detected.

Auto Search will find the DATA DELAY.

1. For each delay setting, the receiver keeps track of the PHASE indication.

2. It then locates the largest contiguous block of delay settings without any

PHASE indication. If BOTH ends of the clear block are within the 4 nS, delay range of the

receiver, it then sets the delay to the middle of the block. A measured eye width is available.

If BOTH ends of the clear block are the edges of the receiver delay range (no crossing found), it then sets the delay to the middle of its delay range (1.995 nS). No eye width is available.

If NO clear block is found (no crossing found); it then sets the delay to the middle of its delay range (1.995nS). No eye width is available.

If ONE end of the clear block is on the edge and the width of the clear block is less than half the data period, it then sets the delay to that edge (0 or

3.99nS). No eye width available. If ONE end of the clear block is on the edge and the width of the clear block

is greater than half the data period, it then sets the delay to be away from the found crossing by half the clock period. A calculated eye width is available.

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Application Note - Auto Search Synchronization

Auto Search will find the DATA PATTERN and POLARITY.

1. The receiver then attempts to SYNC on each data pattern and Polarity (10

possibilities). If sync is found, STOP.

2. Attempt the previous step ten times. If the pattern is not found after ten

times, go back to "Find Data V-Threshold".

II. AUTO SEARCH Algorithm – BER Method

Like the “FAST” method of Auto Search, the “BER” method will also determine the V-Threshold, data delay, data pattern and polarity. For this method to work, the receiver is sensitive to the data it is analyzing and must be synchronized with the incoming data.

This method requires the user to set criteria pertaining to Bit Error Rate threshold and sample size that is used to determine the size and center of the data eye. Because of the adjustability of the threshold and sample size, this method can be made less susceptible to noise and glitches. The methods involved in analyzing the data are quite rigorous and can require considerably more time than the “FAST” method.

Since the GB1400 is capable of measuring and displaying "eye width", the SAMPLE and BER THRESHOLD criteria requirements in the BER method, if selected intelligently, tend to yield more accuracy and repeatability and is less subject to glitches, noise, and jitter than the "FAST" method

The Auto Search BER method of determining the proper settings of the VThreshold, Patter, Polarity and Delay is as follows:

Auto Search will find the DATA V–THRESHOLD voltage.

1. The receiver examines DATA ACTIVITY at each of the V – THRESHOLD

settings.

2. The receiver then locates and uses the middle of the largest voltage range

which has data activity. If no activity is detected, or if the range of activity is less than 250 mV, then the receiver indicates “NO DATA” has been detected.

Auto Search will then attempt to find the DATA PATTERN.

This is because the data pattern needed to be able to do the BER measurements.

1. The receiver first sets the data delay to 0pS and attempts to SYNC on each

data pattern and polarity (10 possibilities). If found, go to the section Determine Data Delay below.

2. The receiver then sets the data delay to 1/2 of the clock period and attempts

to sync on patterns (see step 2a above). If it is found, then go to the section Determine Data Delay below. (If the frequency is less than 250 MHz, the receiver will use 4nS instead of the incoming clock period throughout Find Data Pattern)

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Application Note - Auto Search Synchronization

3. If unsuccessful, it will then try the following data delays in the previous step-

1/4 per, 3/4 per, 1/8 per, 5/8 per, 3/8 per, 7/8 per.

4. If sync is still not found, go back to the first section Find Data V-Threshold.

Auto Search will determine the Data Delay.

1. Initially the entire delay range (0nS to 3.99 nS) in steps of 70pS will be

sampled for 20mS each for error rate. The selectable BER Threshold will be used to determine if the delay settings are within the data eye crossings.

2. The largest contiguous block of delay measurements with error rates below

the threshold will be found. Using that data, the transitions from data crossing to data eye can be found. NOTE: This will be with 70 pS granularity.

If two transitions are within the receiver delay range, two points will be reexamined such that the data eye center and width can be determined. (See illustration /diagram #1, Case #1).

If BOTH ends of the clear block are the edges of the receiver delay range (no Crossing found), set the delay to the middle of the receiver delay range. STOP. No eye width is available.

If NO clear block is found (no crossing found), set the delay to the middle of the receiver delay range. STOP. No eye width is available.

If ONE end of the clear block is on the edge and the width of the clear block is less than half the clock period, set the delay to that edge. STOP. No eye width is available.

If ONE end of the clear block is on the edge and the width of the clear block is greater than half the clock period, two transition points, A and B, will be re-examined further (see Diagram 1, Cases 2 and 3).

3. If the transition points are to be evaluated further, an area 70pS wide will be

examined in steps of 5pS for 20ms each. This starts from the first delay setting in the data crossing and goes to the first delay setting in the data eye (see Diagram 2).

4. After the areas have been measured for error rate, the areas will be examined

for the first transition from below the threshold to above the threshold staring with the end closest to the data eye center. These points will be the NEW transition points.

5. Each of these NEW transition points will be re-examined for a length of time

based upon the SAMPLE size. The error rate will be compared with the selectable BER Threshold.

If the error rate is below the Threshold, the next point away from the Data Eye Center will be examined, and so on, until the error rate transitions to above the Threshold. The last point below the Threshold will be the TRUE transition point.

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Application Note - Auto Search Synchronization

If the error rate is above the Threshold, the next point toward the Data Eye Center will be examined, and so on, until the error rate transitions to below the Threshold. The first point below the Threshold will be the TRUE transition point.

6. After the new transition points are re-examined and the TRUE transition

points are found, the delay will be set as follows: For Case 1, the delay will be set to the middle of the two TRU transition

points (point C). For Cases 2 and 3, the delay will be set to be away from the middle of the

TRUE transition points by half the data clock period (point C).

7. Eye Width Measurement

In the previous step above, if the error rate is below the threshold, the measured eye width is the point B delay measurement minus the point A delay measurement in Diagram 1, Case 1. STOP.

In the previous step above, if the error rate is above the threshold, the calculated eye width for Diagram 1 Case 2 is the delay measurement at point A minus the delay measurement at point C, times two. STOP.

In the previous step above, if the error rate is above the threshold, the calculated eye width for Diagram 1, Case 3 is the delay measurement at point C minus the delay measurement at point B, times two. STOP.

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Application Note - Auto Search Synchronization

Consideration In Determining The Eye Data Width

In most circumstances a test signal data eye displayed on an oscilloscope will appear to be larger than that reported by the GB1400 Receiver. This is expected and is due to several factors. One is that low error rates are virtually impossible to see on an oscilloscope. Other factors such as set-up and hold time and signal characteristics will all have an effect on the measurement by decreasing the apparent eye size.

The value of an eye width measurement made on the GB1400 is when it is used in a relative manner. If a device is determined to be working correctly using a known good signal, its eye width can be measured on the GB1400 Receiver. That measurement can be used as stable reference standard against which all other devices can be measured. It is not possible for the GB1400 Receiver to duplicate all characteristics of the actual device that will be connected in its place, but it will usually suffice as a reasonable approximation.

Consideration In Determining The Data Eye Center

In theory, a plot of bit error versus delay setting will show a smooth curve, almost linear, which has no aberrations and transitions from horizontal to almost vertical at the data eye crossing. For a signal with this curve (a clean signal with no aberrations, jitter or wander), the measurement of the data eye center will be consistent using either of the methods.

In typical applications, the method which will assure a repeatable measurement of the data eye center is to measure each and every delay setting for a significant number of data bits. Because of probable aberrations in the data signals, measuring coarsely over the delay (using 70pS steps) MAY lead to inconsistent measurements due to the aberrations being seen during one search and not the next.

Delay Specifications

The GB1400 programmable delay has the following nominal specifications:

Range: 0 – 3.99 Ns Resolution: 5 pS Accuracy: +/- 20 pS

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Application Example

GB700/ GB1400 Optical Component Test

gB-Series Tx

Data

Clock

Fiber Optic

Clock Recovery

and

Retiming

gB-Series Rx

Clock

Data

Fiber Optic Link Test Example

A typical BERT application is measuring the error performance of the electricalto-optical (E/O) and optical-to-electrical (O/E) output modules of a fiber optic transmission system, as shown in the diagram above. Not all fiber optic links are designed for extremely high speed. For example, many data communications LANs use FDDI at 133 Mb/s. Serial digital video links operate at 270 Mb/s.

External Clock input shown on the BERT Tx would be used to provide jittered clock to stress Clock Recovery (CR) circuit.

Longer PRBS patterns, such as 223 might be used to test DC wander susceptibility of the CR subsystem.

Peak-to-peak amplitude and level offset of the BERT Tx output may be varied to determine acceptable operating range for the DUT input circuitry.

Tests may be made using short and long fiber cables to be able to specify maximum allowable length of fiber runs.

Note that in this application, it may be an advantage to be able to separate the BERT Tx and Rx. Using the BERT internal PRBS generator makes it easy to assure that the Tx and Rx have the same data for error comparison.

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Application Example

Fibre Channel Link Testing Parallel and High-speed Serial

gigaBERT

(Serial)

Parallel stimulus

BUS Interface

BUS - Serial

Interface Under Test

gigaBERT

(Serial)

Fiber

O / E

E / O

Serial - BUS

Parallel results

BUS Interface

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Application Example

Testing QPSK Modems, I & Q

GB700/1400 Tx

I-Channel BERT

GB700/1400 Rx

data clock

DATA

CLOCK

GB700/1400 Tx

EXT CLOCK INPUT

DATA

CLOCK

QPSK

Mod /Demod

up to 1400 Mb/s

data rate

Q-Channel BERT

GB700/1400 Rx

data clock

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Application Note

Application Example

QPSK BER Testing using PRBS Data for 2-Channel I & Q

I-Channel BERT

GB700/1400 Rx

data clock

GB700/1400 Tx

DATA

Q-Channel BERT

GB700/1400 Rx

QPSK Mod / Demod

DATA

CLOCK

Delay line or long coax cable

Delay line can simulate a PRBS pattern with an offset of n-clock bits. Both I and Q channels running PRBS data (but offset by n-clocks).

data clock

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Application Example

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Reference

Menu Overview

A wide range of "auxiliary" setup functions is provided in the GB1400 Generator and Analyzer Menu systems. To enter the Generator or Analyzer Menu system, simply press the instrument's F1 key. At this point the format of the display will change to show the first page of the top level Menu. The top level Menu in both the Generator and Analyzer contains other Menus and various setup parameters. Once inside the Menu system, you use the functions keys, F1 ... F4, to navigate to any Menu function, and to make selections within each Menu function.

Functions Common to Generator (TX) and Analyzer (RX)

AC Power

The GB1400 Generator and Analyzer are both AC powered. The power switch of both instruments is located on the front panel.

Selecting 115 VAC or 230 VAC Operation

Both the GB1400 Generator and Analyzer are equipped with an auto-ranging AC power supply. This supply will operate over a voltage range of 90 to 250 VAC, and a frequency range of 47 to 63 Hz. Thus, no setup change is required to operate from 115 VAC at 60 Hz or 230 VAC at 50 Hz.

Turning Instrument Power ON/OFF

The Generator and Analyzer are equipped with AC power switches on the front panel.

LCD Viewing Angle

The optimum viewing angle of the GB1400 Generator or Analyzer LCD display may be adjusted using the VIEW ANGLE control. Each press of the VIEW ANGLE key will raise the optimum view angle until the highest angle is reached. The next press of VIEW ANGLE will return optimum viewing angle to its lowest angle, and so on.

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Reference

Recalling the Default Setup

The default setup of the Generator and Analyzer are shown in the Appendix. To return the Generator or Analyzer to this setup, use the following procedure:

1. Turn instrument power off.

2. While holding down the VIEW ANGLE, MSB 1, and (PATTERN) CLEAR

keys simultaneously, turn instrument power back on.

3. After you see the message Default Settings appear in the display, release the

three keys. In a few seconds the normal display format will appear and the instrument will be in its default setup.

Locking the Front Panel

The instrument's front panel may be "locked" or "unlocked" using the PANEL LOCK control. When the front panel is locked, all keys that can cause a setup change are disabled. It is often useful to lock the front panel during a long or critical test to prevent accidental loss of test results. Note that the LED in the PANEL LOCK control indicates whether the front panel is locked (LED on) or unlocked (LED off).

Simply press the PANEL LOCK control to toggle between the locked (LED on) and unlocked (LED off) state.

Selecting a Pattern

The following section defines the patterns that can be generated and analyzed by the GB1400 and how to set up the Generator and Analyzer to use a particular pattern. Note that the Generator and Analyzer are compatible with the same suite of test patterns and use the same setup procedures.

Pattern Definitions

The GB1400 can generate and analyze Pseudo-random bit sequence (PRBS) and WORD test patterns. Each type has its own set of advantages and uses.

PRBS Patterns

Pseudo-random bit sequence (PRBS) patterns are designed to simulate "live traffic" and have been standardized by the telecommunications and computer industries. As a result they are often used to characterize or qualify new devices or systems. Two key characteristics of a PRBS are its overall length in bits and maximum number of contiguous 0s. The length of a PRBS pattern has the form

2n-1. For example a 223-1 PRBS contains 8,388,607 bits. The maximum number of contiguous 0s in a PRBS pattern is n-1, for example 22 in a 223-1 PRBS.

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Reference

The PRBS patterns generated and analyzed by the GB1400 are listed below.

Table 3-1. PRBS (2n-1) Test Patterns

n Label Used in Generator

and Analyzer Displays

7 PN 7 127 6 15 PN 15 32767 14 17 PN 17 131,071 16 20 PN 20 1048575 19 23 PN 23 8388607 22

Word Patterns

Word patterns are programmable by the user. Word patterns can be designed to cause specific stress characteristics, such as maximum jitter, or to simulate framed patterns like SONET, SDH, or FDDI. The standard GB1400 Generator and Analyzer will allow you to create and save up to ten 16-bit (two-byte) WORD patterns in battery-backed memory. Or, with the 1-Mbit Option installed, you can create and save up to ten 64 kbit WORD patterns (depends on buffer settings) in battery backed memory. Note that the standard and 1-Mbit instruments also store the current WORD pattern in battery-backed memory.

Selecting the Active Pattern

In this User's Guide, the pattern currently being generated by the Generator or analyzed by the Analyzer is called the active pattern. Procedures to make a selected PRBS or WORD the current active pattern are provided below.

Length (2n-1 bits)

Maximum Number of Contiguous 0s

Selecting PRBS Patterns

To select a PRBS pattern: Press the PRBS key. The instrument will now be in the PRBS pattern mode. Press the pattern up/down keys until the name of the desired PRBS pattern is

displayed. Available PRBS patterns are:

PN 7 PN 15 PN 17 PN 20 PN 23

The displayed PRBS pattern becomes the active pattern immediately.

Selecting the Current Word Pattern

To make the current WORD pattern the active pattern, simply press WORD key.

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Reference

Selecting (RECALLing) a Saved Word Pattern

You can recall a WORD pattern using the Generator or Analyzer RECALL function:

8/16 bit WORD patterns are available on all instruments. Long-WORD (>16bits) are available only in units equipped with the 1-Mbit Option.

Use the following procedure to select (recall) a WORD pattern: Press the WORD key to place instrument in WORD mode. Press the RECALL key. Press the pattern up/down keys until the desired WORD or desired mark density

pattern is displayed. Available selections will depend on the programmed WORD buffer size.

When set to ten 64k buffers, available selections are: WORD 0 WORD 1 …… WORD 9

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Word Patterns

Reference

This section explains how to create, edit, save, and recall WORD patterns using front panel controls or the Menu system.

Basics

You may create and save up to ten WORD patterns in battery-backed memory locations WORD 0 through WORD 9. In addition, the current WORD pattern is stored in battery-backed memory. In standard units, each of the saved WORDs and the current WORD can contain up to 16 bits. In Generators and Analyzers equipped with the 1-Mbit Option, which provides additional battery-backed memory, each of the saved WORDs and the current WORD can contain up to 64kbits (with fewer memory buffers, larger WORD patterns can be saved).

There are three ways to create GB1400 WORD patterns: Using front panel controls. This is usually the quickest way to create and edit

short patterns. It also can be a practical way to edit a few bytes in long patterns if these bytes are located near to each other.

Using the Menu system. Because it provides direct byte addressing, this is often the best method for editing a few widely scattered bytes in long WORD patterns. The Menu system also provides the FILL function, used to load a user-specified 8-bit pattern into all bytes, and the ORDER function, used to set the bit-order in each byte to MSB or LSB first. Thus you can use the Menu system to create long WORDs with simple bit patterns using its byte fill, order, and editing capabilities.

Downloading: This is the best way to create long WORDs with complex patterns. Long WORD patterns may be created on an external controller, using a text editor or specialized software, and downloaded via the instrument's GPIB or RS-232 ports. Downloading is the only practical way to create simulations of SONET, SDH, FDDI or other framed signals.

Creating Word Patterns Using Front Panel Controls

Standard Instruments

Use the following procedure to create WORD patterns using front panel controls in standard instruments, that is Analyzers and Generators not equipped with the 1-Mbit Option:

1. If you are using a previously saved pattern as the basis for the new pattern,

recall this pattern from memory. (See Recalling Word Patterns).

2. Press the WORD key. The LED in the WORD key will turn on (indicating

that the instrument is in the WORD editing mode) and the display will show the bit sequence of the current WORD pattern in binary format. The WORD may contain either one or two bytes, that is 8 or 16 bits. Word length (8 or

16) is displayed after the WORD's bit sequence.

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Reference

3. If you need to change WORD length, press the WORD LENGTH key and

then the pattern up or down key to toggle WORD length between 8 and 16 bits. When the desired WORD length is displayed, press the WORD key to return to the WORD editing mode.

4. To select the first or second byte in a 16-bit pattern, press the up or down

key. The selected byte will be indicated in the display by an arrow located between the two bytes. Byte selection is not required for 8-bit patterns because the first byte is always selected.

5. To edit the selected byte, press the 1 (MSB) through 8 (LSB) bit keys to

toggle individual bits between 0 (LED off) and 1 (LED on).

6. If you need to edit the other byte in a 16-bit pattern, repeat steps 4. and 5.

Instruments Equipped with 1-Mbit Option

Use the following procedure to create WORD patterns using front panel controls in instruments that are equipped with the 1-Mbit Option:

1. If you are using a previously saved pattern as the basis for the new pattern,

recall this pattern from memory. (See Recalling Word Patterns).

2. Press the WORD key. The LED in the WORD key will turn on to indicate

that the instrument is in the WORD editing mode. The selected byte in the current pattern will be displayed in the form AAAAA HH, where AAAAA is the byte's location or "address" within the current WORD in decimal, and HH is the value of the selected byte in hexadecimal. Byte address will be in the range 0, 1, ..., 8192 when BUFFER size is set to 64k or 0, 1, ..., 16384 when BUFFER size is set to 128k.

3. If you need to change WORD length, press the WORD LENGTH key and

then the pattern up/down keys. Pattern lengths of 2048 bytes or less will be displayed in terms of M bytes plus N bits. Pattern lengths above 2048 bytes will be displayed in terms of bytes only. When the desired WORD length is displayed, press the WORD key to return to the WORD editing mode.

4. To select a byte within the current pattern, use the pattern up/down keys to

increment or decrement the displayed byte address.

5. To edit the selected byte, press the 1 (MSB) through 8 (LSB) bit keys to

toggle individual bits. Note that the LED in each bit key indicates whether the associated bit equals 0 (LED off) or 1 (LED on).

6. Repeat steps 4. and 5. until the WORD has been edited as required. You have now created a new WORD pattern and may use it to perform tests. The

current pattern is automatically stored in battery-backed memory. However if the new pattern is important, be sure to save it before creating or RECALLing another pattern.

See an additional list of remote commands in the Appendix that support the 1Mbit Programmable Word option.

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Reference

Creating Word Patterns Using Menus

The Menu functions used to create or edit WORD patterns are:

LENGTH FILL EDIT and ORDER.

These functions are located in the WORD Menu. Note that ORDER is a standard function while the LENGTH, FILL, and EDIT functions are added to the WORD Menu as part of the 1-Mbit Option. Therefore in standard units, all WORD editing procedures, except for bit order, are performed using front panel controls. However in instruments equipped with the 1-Mbit Option, WORD editing may be performed using either front panel controls or the Menu system, depending on which approach is more convenient in a given situation.

Note that the WORD Menu also includes the Pattern Sync and SYNC functions. If you are trying to observe the Data output of the Generator, or the Monitor Data output of the Analyzer, you may want to use the Pattern Sync Menu to select the byte location of the pattern synchronization pulse generated by the rear-panel Pattern Sync output. The SYNC Menu, which appears on the same page of the Analyzer Menu system, is not directly involved in creating or editing WORD patterns. Rather, it is used to set the Analyzer pattern synchronization threshold in terms of BER.

A detailed explanation for each function in the WORD Menu may be found later in this chapter.

In addition, the general procedure for creating WORD patterns in a Generator or Analyzer equipped with the 1-Mbit Option is given below:

1. Use the current pattern or recall a previously saved pattern as the basis for

the new pattern. (See Recalling Word Patterns).

2. Press the F1 key to enter the Menu system.

3. Press the F4 key to access the WORD options.

4. If you need to change current WORD length, select the LENGTH Menu by

pressing F3. Enter a new value for length using the F2, F3, and pattern up/down keys. Then exit the LENGTH Menu by pressing either F4 to set this new length or F1 to "escape" without making any setup changes.

5. If you want to fill a pattern, select the FILL Menu by pressing F4. Edit the

fill byte using the individual bit keys, 1 (MSB) through 7 (LSB). When done, exit the FILL Menu by pressing either F4 to automatically load this eight bit pattern into every byte of the current WORD or F1 to "escape" without making any setup changes.

6. To edit the current WORD, press F2 to enter the EDIT Menu. Use the F2, F3,

and pattern up/down keys to select a byte within the current WORD. Next, use the bit keys to edit the displayed byte. Repeat for each byte to be edited.

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Reference

When done, exit the EDIT Menu by pressing either F4 to lock in these changes or F1 to "escape" without making any setup changes.

7. You now may want to access the ORDER and Pattern Sync Menus by

pressing F1 (MORE). The ORDER Menu determines the bit transmission/analysis order of each byte in the pattern, that is MSB or LSB first. The Pattern Sync Menu determines the byte location of the pattern sync pulse in long WORD patterns. When done with these Menus, press the F1 key until the normal display format appears.

You have now created a new WORD pattern and may use it to perform tests. As noted earlier, the current pattern is automatically stored in battery-backed memory. However if the new pattern is important, be sure to save it before creating or recalling another pattern.

Creating Word Patterns Under Remote Control

The third way to create WORD patterns is by remote control. There are two sets of WORD editing commands: "WORD" and "byte". Word

commands, also known as "short WORD" commands, are part of the standard command set and are used to perform 8 and 16 bit editing functions.

Byte or "long-WORD" commands, which are added to the GB1400 Generator or Analyzer command as part of the 1-Mbit Option, are used to perform editing functions on WORDs of any allowed length up to 16384 bytes. Note that most WORD commands will function normally in instruments equipped with the 1Mbit Option.

This allows instruments equipped with the 1-Mbit Option to operate in automated test applications designed around the 8/16-bit WORD command set. However only byte commands may be used to edit long WORD patterns—that is WORDs that are more than 16 bits long. Therefore a GB1400 Generator or Analyzer must be equipped with the 1-Mbit Option to function in automated test applications designed around the byte command set.

A general discussion of GB1400 remote control functions and an explanation of each remote command may be found in the Appendix. In addition, the general procedure for using byte commands to create and edit WORD patterns is given below:

1. All long-WORD editing procedures must start with an EDIT_BEGIN

command, which may have an argument from -1 to +9. An argument of -1 tells the instrument to copy the current WORD pattern into "scratchpad" memory, while arguments of 0 through 9 tell the instrument to copy the indicated saved WORD pattern into scratchpad memory.

2. The core of a long-WORD editing procedure is constructed from byte

commands such as BYTE_BLOCK, BYTE_FILL, BYTE_INSERT, BYTE_EDIT, and BYTE_DELETE. These commands may be used to download a new pattern into scratchpad memory, or to modify a pattern previously copied or downloaded into scratchpad memory.

3. All long-WORD (byte) editing procedures must end with an EDIT_END

command. This command may have an argument from -2 to +9. An

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Reference

argument of -2 tells the instrument to discard the pattern in scratchpad memory and not to update the front panel. An argument of -1 tells the instrument to copy the pattern in scratchpad memory to the current WORD memory location and to update the front panel. Arguments 0 to +9 tell the instrument to copy the pattern in scratchpad memory to the indicated (save) memory location without updating the front panel.

Note that a WORD or byte editing session in a GB1400 Generator or Analyzer can be started locally from the front panel or remotely via the instrument's RS-232 or GPIB remote ports. However the instrument will allow only one editing session to be in-progress at any given time.

Saving Word Patterns (1-Mbit Memory Option)

You can save the current WORD pattern to one of ten WORD memory locations (WORD 0 to WORD 9), using the following procedure:

1. Press the SAVE key. The LED in the SAVE key should flash to indicate that

you are in the save mode.

2. Press the pattern up/down keys to select a WORD memory location. Note

that the WORD previously stored in this location will be overwritten.

3. Press the SAVE key again to save the current WORD into the selected

location. At this point the SAVE LED will turn off.

Recalling Word Patterns (1-Mbit Memory Option)

To recall a previously saved WORD pattern, use the following procedure:

1. Press RECALL to enter the recall mode. Note that the LED in the RECALL

key turns on. NOTE: If the current WORD is important and has not been previously

saved, you must save it before pressing RECALL. The recalled pattern will overwrite the current pattern.

2. Select a WORD pattern memory location by pressing the pattern up/down

keys. The ten possible WORD memory selections are WORD 0 through WORD 9. The selected WORD becomes the current WORD immediately. In other WORDs, the current WORD is over-written each time you press the up or down key.

You can now use the recalled WORD to perform tests. Note that if you want to edit the recalled WORD, you must press the WORD key again.

Note: The maximum number of WORD patterns is set by the buffer size. Memory can be partitioned into ten segments of 64kbits; six segments of 128kbits; three segments of 256kbits; one segment of 512kbits; and, zero (0) segments of 1-Mbit.

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Generator (TX) Functions

This section defines key functions of the GB1400 Generator and how to set up these functions using front panel controls.

Clock Source and Frequency

The Generator can operate using its internal clock, or an external clock source. The CLOCK section of the Generator front panel is used to select clock mode (internal or external), set internal clock frequency, and store or recall userdefined frequencies. In addition, the CLOCK section contains an input for an external clock source. When using the internal clock, you may set frequency directly, or recall one of 10 previously saved frequencies from memory. The frequency save/recall feature is especially useful if you often switch back and forth between a limited number of different frequencies.

External Clock Input

When the Generator is in external clock mode, a clock source must be connected to the connector labeled INPUT in the CLOCK section of the Generator's front panel. The operating bit rate of the Generator will then be determined by the frequency of this source. However, when the Generator is set to internal clock mode, any signal applied to this input will be ignored.

The EXTERNAL CLOCK input is AC-coupled into 50 Ohms (unless BURST OPTION is installed).

Clock Source

Generator clock source may be set to internal or external using the EXT key in the CLOCK section. When the LED in the EXT key is off, then clock source is internal. If the LED is on, the clock source is external and an external source must be connected to the external clock input (INPUT).

Press the EXT key to toggle clock source between internal and external.

Step Size and Frequency

The frequency of the Generator internal clock may be set using the

FREQUENCY, STEP , and CLOCK section up/down keys. First select a step size.

Then adjust current frequency using this step size. The complete setup procedure follows:

1. Select a step size. Do this by pressing the STEP key one or more times until

the underscore in the frequency field is under the desired digit. Note that the underscore moves right one digit for each key press. The selected digit indicates step size. For example if the current frequency is 622.950 MHz, and the underscore is under the "5" , then current step size is 10 kHz. Or, if the underscore is under the "9" then the current step size is 100 kHz, etc.

2. Press the FREQUENCY key. Verify that the FREQUENCY key LED turns

on.

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3. Press the clock section up/down keys to increment or decrement the current

frequency using the previously selected step size. Note that the underscore position indicates a step size, not which digit will be edited. For example if displayed frequency is 622. 950, and the cursor is under the "9", then step size

is 100 kHz and pressing the up ( ↑) key one time will change frequency to

623.050 MHz.

Saving a Frequency

You may save the current Generator frequency into one of 10 frequency memory locations as follows:

1. Press the clock SAVE key. Verify that the SAVE LED is flashing.

2. Press the clock section up/down keys to select the desired memory location .

Note that frequency memory location is displayed in the bottom left field of the display as FREQ x, where x = 0, 1, ..., 9.

3. Then press SAVE a second time to save the current frequency into this

location. Verify that the clock SAVE key LED turns off.

Recalling a Frequency

You can recall a previously saved frequency as follows:

1. Press the clock RECALL key and verify that the RECALL LED turns on.

2. Press the clock up/down keys until the display shows the desired frequency

(top left) and frequency memory location (bottom left).

NOTE: The displayed frequency becomes the current frequency immediately. That is, you do not have to hit RECALL again.

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Data and Clock Outputs

This section explains how to set up the Generator's clock and data outputs as well as related pattern sync. and clock/4 outputs.

Overview

The OUTPUT section of the Generator front panel contains the instrument's main NRZ (clock + data) outputs:

DATA DATA-BAR CLOCK CLOCK-BAR

Note: The same term can be expressed three different ways.

CLOCK

DATA

= CLOCK BAR = NOT CLOCK = DATA BAR = NOT DATA

DATA and CLOCK are the non-inverted test pattern outputs of the GB1400 Generator. DATA is a non-return to zero (NRZ) data signal and CLOCK is its corresponding clock signal. DATA-BAR and CLOCK-BAR are complementary outputs to DATA and CLOCK respectively. Thus the GB1400 can drive singleended or differential inputs.

The amplitude and baseline offset of the CLOCK and DATA outputs are adjustable. This insures compatibility with a wide range of input circuit designs. The selected clock amplitude applies to both CLOCK and CLOCK-BAR and the selected data amplitude applies to both DATA and DATA-BAR.

Similarly the selected clock baseline offsets becomes the bottom (negative peak voltage) of both the CLOCK and CLOCK-BAR outputs and the selected data baseline offset becomes the bottom voltage of the DATA and DATA-BAR outputs.

The nominal waveform and phase relationship of the four output signals is shown in the figure below. An equivalent circuit model for these four outputs is shown in the second figure.

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CLO CK

top (clock )

CLOCK

Bas eline

Offse t

Reference

CLOCK Amplitude (pk -pk)

CLOCK

DATA

Sa me offset

as CLOCK

top (da ta)

DATA

Bas eline

Offse t

Same offset

as DATA

top

S ame amplitude a s CLOCK

DATA Amplitude (pk-pk)

Sa me amplitude a s DATA

Figure 3-1. Nominal Generator Clock and Data Waveforms Showing

Amplitude, Baseline Offset, and V

Voch = Out high voltage into an open circuit

top

50 ΩΩ 50 ΩΩ

Vh (logic high) DATA or CLOCK Output

Vhl(logic low) DATA or CLOCK Output

l = Vocamp/50

Negative Supply

Figure 3-2. Generator Clock and Data Output Equivalent Circuits

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Amplitude and Baseline Offset

The rules governing the setup of clock and data amplitude and baseline offset are as follows:

RULE 1: When terminated by 50 Ohms to ground, the amplitude adjustment range of clock and data outputs is 0 to 2 V peak-to-peak. However, the absolute voltage of the pulse top cannot exceed +2.0 VDC, that is:

amplitude p-p

+ V

offset

≤ 2.0 VDC

RULE 2: When left unterminated (termination impedance > 2 kΩ) the amplitude adjustment range of clock and data outputs is 0 to 4 V peak-to-peak with a pulse top limit of +4.0 VDC, that is:

amplitude p-p

+ V

offset

≤ 4.0 VDC

RULE 3: Displayed amplitude and baseline offset are calibrated for a termination of 50 Ohms to ground. Any variation of termination impedance or voltage will cause actual amplitude and offset to differ from the values shown in the Generator display.

These rules are summarized in the table below.

Table 3-2. Output Setup Rules vs. Termination Impedance

Termination Amplitude Limit

(V p-p) 50 Ω to ground 50 Ω to -2 VDC AC (50 Ω to AC) Open Circuit 0 - 4 +4.0 2 x displayed as displayed

0 - 2 +2.0 as displayed as displayed 0 - 2 +2.0 as displayed displayed value - 1.0 V 0 - 2 +2.0 as displayed unspecified

Pulse Top

Limit (VDC)

Actual

Amplitude

Actual Baseline Offset

(VDC)

Note: With PECL option installed, the pulse top limits are increased to 2.8 (50Ω) and +5.6 (open circuit).

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The following controls are used to set clock and data output amplitude and baseline offset:

CLOCK: DATA:

AMPLITUDE ( ↑↑, ↓↓ ): BASELINE OFFSET ( ↑↑ , ↓↓):

Note that when the CLOCK key is pressed, its LED turns on and the display shows clock output amplitude and offset. Similarly, when the DATA key is pressed, its LED will turn on and the display shows data output amplitude and offset. The general procedure for setting data and clock output amplitude and baseline offset is shown below.

1. Press DATA. The display will show data output amplitude and offset.

2. Press the BASELINE OFFSET up/down keys to set the desired data signal

baseline offset.

3. Then press the AMPLITUDE up/down keys to set the desired data signal

amplitude.

4. Press CLOCK. The display will now show clock output amplitude and offset.

5. Press the BASELINE OFFSET up/down keys to set the desired clock signal

baseline offset.

6. Then press the AMPLITUDE up/down keys to set the desired clock signal

amplitude.

Logically Inverting Output Data (D-INV)

The INVERT DATA key may be used to logically invert the output data pattern, that is change all 1s to 0s and 0s to 1s. If the INVERT DATA LED is off, then the output data pattern is not inverted. However if the INVERT DATA LED is on, the output data pattern is logically inverted. You can toggle the INVERT DATA function on and off by pressing the INVERT DATA key. Note that logically inverting the output pattern is the same as swapping the connections to the DATA and DATA-BAR outputs.

To toggle output data inversion on or off, press the INVERT DATA key.

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Reference

Single-ended or Differential Operation

DATA-BAR and CLOCK-BAR are complimentary outputs to DATA and CLOCK respectively. Therefore, to drive a single-ended clock or data input simply connect appropriate true output (CLOCK or DATA) while terminating its compliment (CLOCK-BAR or DATA-BAR) with 50 Ohms to ground. Or, to drive a differential clock or data input, connect the appropriate true output (CLOCK or DATA) to the non-inverting input and the complimentary output (CLOCK-BAR or DATA-BAR) to the inverting input. No other setup is required to configure the Generator for singled-ended or differential operation.

Procedure for Single-ended Operation (TX only)

1. For singled-ended operation, connect Generator CLOCK and DATA outputs

to singled-ended inputs on the DUT.

2. Terminate the CLOCK-BAR and DATA-BAR outputs with 50 Ohms to

ground.

Procedure for Differential Operation (TX only)

1. Connect CLOCK and CLOCK-BAR outputs of the Generator to the true and

complimentary clock inputs on the DUT.

2. Connect DATA and DATA-BAR outputs of the Generator to the true and

complimentary data inputs on the DUT.

Pattern Sync and CLOCK/4 Outputs

The OUTPUT section of the Generator front panel contains two additional outputs that may be useful when observing the Generator output with an oscilloscope. The first is the Pattern Sync or output which generates one pulse per pattern frame. This signal may be used to trigger an oscilloscope at the beginning of the output data pattern. The second is the CLOCK/4 output, which is a clock signal at one quarter the frequency of CLOCK. This signal is particularly useful when viewing the output of the Generator using an oscilloscope that doesn't have sufficient bandwidth to trigger on the CLOCK signal.

Both the Pattern Sync and CLOCK/4 outputs have a fixed amplitude of 200 mV pk-pk, centered around ground, when terminated by 50 Ohms to ground. The phase relationship of CLOCK/4 and CLOCK is also fixed, with the nominal location of CLOCK/4 transitions occurring on the falling edge of CLOCK.

The width and location of the Pattern Sync pulse depends on which pattern type is currently active. For PRBS patterns, the Pattern Sync pulse has a width equal to one bit time slot, at a fixed position not adjustable by the user. For shortWORD patterns (1-Mbit Option not installed) the Pattern Sync waveform is a nominal square wave that is high during the first byte of a 16-bit WORD, and low for the second. For long-WORD patterns (1-Mbit Option installed), the Pattern Sync pulse is one byte wide that occurs at the beginning of the frame.

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Error Injection

The GB1400 Generator can inject bit errors, also known as logic errors, into the output data pattern. One use of error generation is to self-test the GB1400 Generator/Analyzer system. Or, when generating WORD patterns containing simulated framed signals, for example a SONET signal, error generation can be used to determine the ability of the terminal under test to detect errors or to stay in-frame in the presence of high error rates.

The available internal error injection rates are 10-n, where n = 7, 6, 5, 4, or 3. In other WORDs, injected BER can be set to integer powers of 10 from 10-7 to 10-3. Using the external error inject mode, errors can be injected at any rate up to 10-3. There is no lower limit on external error injection BER.

Selecting an Error Inject Mode

The controls that determine the error injection mode of the Generator are:

RATE (key) SINGLE (key)

When the LED on the RATE key is off, the Generator is in the single error inject mode. In this mode, no errors are generated except when the SINGLE error key is pressed. That is, each press of the SINGLE key will cause a single, isolated bit error to be injected. However, when the RATE key is on, the instrument is either generating an error rate internally, or under external error generation control. You can determine which by observing the bottom, middle field of the display.

If an error rate is displayed (e.g. ERR 1E-09) then the Generator is in the internal error inject mode. If the message EXT ERR is displayed, then the external error inject mode has been selected indicating that the signal appearing at the rearpanel EXTERNAL ERROR INJECT input will control error injection rate. One error will be generated for each negative-to-positive transition in this signal. In all other error inject modes, the signal appearing at this input will be ignored.

NOTE: In all error injection modes, the ERROR LED will flash each time an error is injected.

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Procedure to Control Error Injection Mode

1. Press the RATE key one or more times to select the desired error injection

mode. Note that the LED in the RATE key will turn on except when mode is set to ERR OFF. Available selections are:

ERR OFF: Single error injection. ERR 1E-7: Generate errors at rate of 10-7. ERR 1E-6: Generate errors at rate of 10-6. ERR 1E-5: Generate errors at rate of 10-5. ERR 1E-4: Generate errors at rate of 10-4. ERR 1E-3: Generate errors at rate of 10-3.

ERR EXT: External error inject mode.

2. Once you have selected an internal error rate, or the external mode, you can

turn this error rate off and on by alternately pressing the SINGLE key and RATE key. Do not press the RATE key two or more times in a row unless you want to change the current error injection mode. However, while the current error rate is off, you can press the SINGLE key as many times as you wish to inject single errors.

3. To return to the single injection mode, press RATE one or more times until

ERR OFF is selected.

ERROR INJECT Input

The ERROR INJECT input is an SMA (female) connector located on the rearpanel of the Generator. When the error injection mode is set to ERR EXT, one bit error will be generated for each rising edge in the signal applied to this input.

Setup - The ERROR INJECT is a 50 Ohm, ECL input. No hardware setup is required.

Data Inhibit - The DATA INHIBIT input is located on the rear-panel of the Analyzer. A signal applied to this input may be used to gate off and on the Generator DATA output signal. The logic of the DATA INHIBIT function is shown in the following table. The DATA INHIBIT function is not bit or frame synchronized with the DATA output signal. Therefore, the gating action caused by the DATA INHIBIT input may occur anywhere within a DATA output bit time slot and anywhere within a pattern frame. DATA INHIBIT is a standard 50 Ohm ECL input and does not require any threshold or delay setup.

Table 3-3. Data Inhibit Logic

Logic Level Applied to

DATA INHIBIT INPUT

OPEN or LOW DATA output operates normally.

HIGH DATA output is disabled, that is forced LOW.

Action

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Analyzer (RX) Functions

This section explains how to enable or disable Analyzer automatic synchronization functions. It further shows how to manually set Analyzer input parameters and error detection functions, and how to start tests, view results, and print results. The section also defines all results calculated by the Analyzer.

Automatic Setup Functions (SYNC )

This section explains how to use the following "SYNC" controls and indicator in the ERROR DETECTION section:

AUTO SEARCH key. DISABLE key. LOCK indicator.

AUTO SEARCH Key

The AUTO SEARCH key is used to enable or disable the auto-search feature. When auto-search is enabled, the Analyzer will automatically attempt to set the following parameters each time pattern synchronization is lost:

Reference

1. clock and data input threshold,

2. data input delay,

3. PRBS pattern,

4. pattern polarity, and

5. pattern alignment. In addition, auto-search will clear (turn off) the BIT and PHASE history

indicators once pattern sync. is regained. Thus, AUTO SEARCH can greatly simplify Analyzer setup and operation, especially when the input clock and data phase relationship and amplitudes are not known.

DISABLE Key

The DISABLE key is used to disable automatic pattern realignment. When automatic pattern realignment is enabled (DISABLE off) the Analyzer will attempt to resynchronize its pattern detector each time BER goes above the pattern synchronization threshold by looking for a new pattern alignment . A change of pattern alignment will occur, for example, if a buffer over flows or under flows in the DUT. A change of pattern alignment will also normally occur if the CLOCK input to the Analyzer is momentarily disconnected.

On the other hand, with pattern realignment disabled (DISABLE on), the Analyzer will not attempt to find a new pattern alignment—even if BER goes above the synchronization threshold—until the start of a new test interval. This allows the analyzer to measure BER and count errors on signals with very high error rates.

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LOCK Indicator and Actions Taken by the Analyzer if Synchronization (Lock) is Lost

The LOCK LED indicates whether or not BER is above or below the current synchronization threshold. The LOCK indicator will turn on while BER is below the current synchronization threshold, and off while BER is above this threshold. The setup actions taken by the Analyzer when BER crosses the synchronization threshold will depend on the state of the AUTO SEARCH and DISABLE keys, as shown in the table below.

Table 3-4. Actions Taken by Analyzer when Synchronization is Lost

AUTO SEARCH DISABLE Action when synchronization is lost (LOCK LED turns off)

on off Analyzer will attempt to find new pattern alignment, input level, input

delay, PRBS pattern and pattern polarity off off Analyzer will attempt to find new pattern alignment. off on

on on (this combination not allowed)

No setup change—Analyzer will continue to measure BER and count

errors.

AUTO SEARCH With PRBS Patterns

When using a PRBS pattern you can enable the AUTO SEARCH feature as follows:

1. Set up the Generator to transmit a PRBS pattern.

2. Set up the Analyzer as follows:

EXT (ref. data input control), off SYNC DISABLE, off AUTO SEARCH, on

After you perform this procedure, the auto-search feature will be enabled and the instrument will immediately attempt to re-synchronize with the received test signal. Once lock is achieved—that is once BER goes below the synchronization threshold—the BIT and PHASE history indicators will be cleared (turned off) and all current error counts will be reset to zero. The SYNC LOSS indicator will remain on, however, until cleared by the user.

NOTE: The AUTO SEARCH feature will work over a wide range of conditions. Therefore if you have set up the Generator to generate a standard PRBS, enabled the AUTO SEARCH feature on the Analyzer, but the Analyzer LOCK LED still fails to turn on, then it is likely that a problem exists in the device under test or your patch cord connections.

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AUTO SEARCH with "Non-PRBS" Patterns

In cases where you need to use a WORD or other type pattern for testing, you can still use AUTO SEARCH to set DATA and CLOCK threshold, and DATA input delay and threshold as follows:

1. Set up the Generator to transmit a PRBS pattern.

2. Enable Analyzer AUTO SEARCH as follows:

EXT (ref. data input control), off SYNC DISABLE, off AUTO SEARCH, on

3. After the Analyzer LOCK LED turns on, disable AUTO SEARCH by

pressing the AUTO SEARCH key. Verify that the LED in the AUTO SEARCH key turns off.

4. Change the pattern setup of the Generator and Analyzer as desired. For

example, to perform a test using a WORD pattern stored in memory: press the Analyzer pattern RECALL key and up/down keys to select the WORD pattern. Repeat these steps on the Generator to select the same WORD pattern. At this point the SYNC LOCK LED should turn on again indicating that the Analyzer has regained synchronization. You may now start a new test interval by clearing previous results (PRESS ERROR DETECTION CLEAR key) and history indicators (PRESS HISTORY CLEAR key).

How to DISABLE Automatic Pattern Resynchronization

The pattern resynchronization disable feature is turned on or off as follows: Press the DISABLE key to toggle automatic pattern resynchronization on or off.

When the DISABLE LED is on, pattern resynchronization is disabled. When the DISABLE LED is off, pattern resynchronization is enabled.

Relationship between AUTO SEARCH and DISABLE

Turning AUTO SEARCH on automatically turns DISABLE off. Similarly, turning DISABLE on automatically turns AUTO SEARCH off. That is, AUTO SEARCH and DISABLE cannot be on at the same time. However you may turn both functions off. There are, therefore, three possible levels of Analyzer synchronization:

1. AUTO SEARCH on: This is the most automated mode.

2. AUTO SEARCH off and DISABLE off: This is a partially automated mode

with AUTO SEARCH functions disabled but auto-pattern resynchronization still enabled.

3. DISABLE on: This is the "fully manual" mode in which all AUTO SEARCH

functions and the auto-pattern resynchronization function, are disabled.

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Synchronization (LOCK) Threshold

The current synchronization threshold depends on pattern, and the setup of the SYNC Menu, as summarized in the table below:

Table 3-5. Synchronization Threshold

Pattern Type Threshold How to Set

PRBS 1,024 errors in 4,096 bits

(BER = 2.5 E-01)

All WORD patterns (up to 16 bits) when 1-Mbit Option not installed. All WORD, mark density, or other ROM patterns with 1-Mbit Option installed.

128 errors in 4,096 bits

(BER = 3.1 E-02)

Based on 256 errors in a rolling

window of x bits. Nine BER levels

available:

1: 3.1 E-02

2: 7.8 E-03

3: 1.9 E-04

4: 9.7E-04

5: 4.8 E-04

6: 2.4 E-04

7: 1.2 E-04

8: 6.1 E-05

9: 3.0 E-05

Fixed Fixed

Use SYNC Menu to select a synchronization level from 1 to 9.

You can change the synchronization threshold for (long) WORD, mark density, and ROM patterns using the SYNC Menu as follows:

Procedure to Set SYNC Threshold

1. Press the F1 key to enter the Menu system.

2. Press F4 key to enter the WORD submenu.

3. Press the F1 key (MORE) until the SYNC option appears.

4. Press F2 (SYNC).

5. Use the pattern up/down keys to select a synchronization threshold level

from 1 to 9.

6. When done, press F4 to enter your choice.

7. Press F1 multiple times until you have exited the Menu system. NOTE: See later in this chapter for a further explanation of the SYNC Menu.

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Clock, Data, and Reference Data Inputs

This section explains how to set up Analyzer clock, data, and reference data inputs using front panel controls and Menus.

Overview

The Analyzer CLOCK, DATA, and REF DATA inputs are designed to accommodate a wide range of output logic levels and circuit designs. An equivalent circuit diagram of the Analyzer input section is shown in the following figure.

Input Comp

ΩΩ

-2Vdc

GND

Figure 3-3. Analyzer Clock and Data Input Circuits

Input Parameters

The following input parameters may be set manually by the user or automatically by the AUTO SEARCH function:

Decision threshold (DATA, and REF DATA) Delay (DATA and REF DATA) Inverted or non-inverted data (DATA).

In addition, there are termination parameters that can be selected only by the user:

Termination (CLOCK, DATA, and REF DATA)

Note that user or manual control functions may be executed locally, via front panel controls or Menus, or remotely via the instrument's RS-232 or GPIB ports.

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Tektronix 071-0590-00 User Manual

Specifications and Main Features

Frequently Asked Questions

User Manual