Tektronix TDS Family Instructions User manual

Instructions

TDS Family
Option 2F Advanced DSP Math

070-8582-01

www.tektronix.com

*P070858201*

070858201

Copyright © T ektronix, Inc. All rights reserved.
T ektronix products are covered by U.S. and foreign patents, issued and pending. Information in this publication supercedes

that in all previously published material. Specifications and price change privileges reserved.
Printed in the U.S.A.
T ektronix, Inc., P.O. Box 1000, Wilsonville, OR 97070–1000
TEKTRONIX, TEK, and TEKPROBE are registered trademarks of T ektronix, Inc.
SureFoot is a trademark of T ektronix, Inc.

WARRANTY

Tektronix warrants that this product will be free from defects in materials and workmanship for a period of three (3) years 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 the 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 this 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 use 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, EXPRESS 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.

Welcome

This instruction manual describes Option 2F, the Advanced DSP Math opĆ
tion. Included in this manual are the following subsections:

H Product Description (follows this introduction)

H Fast Fourier Transforms

H Waveform Differentiation

H Waveform Integration

Related Manuals

Conventions

This manual only documents Option 2F. The following documents cover all
other aspects related to the use or service of the oscilloscope. If ordering
any of these manuals, order by the manual title and the model of your
oscilloscope.

H The TDS User Manual guides the user in operation of this oscilloscope

and describes its features. It also contains a tutorial, a specification, and
other useful information related to your oscilloscope.

H The TDS Series Programmer Manual describes how to use a computer

to control the oscilloscope through the GPIB interface.

H The TDS Reference gives you a quick overview of how to operate your

oscilloscope.

H The TDS Performance Verification tells how to verify the performance of

the oscilloscope.

H The TDS Service Manual provides information for maintaining and servicĆ

ing your oscilloscope.

In this manual, you will find various procedures that contain steps of instrucĆ
tions for you to perform. To keep those instructions clear and consistent, this
manual uses the following conventions:

TDS Series Option 2F Instructions

H Names of front panel controls and menu labels appear in boldface print.

H Names also appear in the same case (initial capitals, all uppercase, etc.)

in the manual as is used on the oscilloscope front panel and menus.
Front panel names are all upper case letters, for example, VERTICAL
MENU, CH 1, etc.

H Instruction steps are numbered. The number is omitted if there is only

one step.

v

Welcome

H When steps require that you make a sequence of selections using front

panel controls and menu buttons, an arrow ( ➞
between a front panel button and a menu, or between menus. Also,
whether a name is a main menu or side menu item is clearly indicated:

Press VERTICAL MENU
tion (main)

Using the convention just described results in instructions that are
graphically intuitive and simplifies procedures. For example, the instrucĆ
tion just given replaces these five steps:

1. Press the front panel button VERTICAL MENU.

2. Press the main menu button Offset.

3. Press the sideĆmenu button Set to 0 V.

4. Press the main menu button Position

5. Press the side menu button Set to 0 divs

H Sometimes you may have to make a selection from a popup menu:

Press SHIFT UTILITY
edly press the main menu button SYSTEM until I/O (for example) is
highlighted in the popĆup menu.

➞ Set to 0 divs (side).

➞ Offset (main) ➞ Set to 0 V (side) ➞ PosiĆ

➞ SYSTEM (popup). In this example, you repeatĆ

) marks each transition

vi

Welcome

Fast Fourier Transforms

Contents

Contents vii. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Safety ix. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Product Description xi. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Description 1Ć1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Operation 1Ć2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Displaying an FFT 1Ć2. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Cursor Measurements of an FFT 1Ć5. . . . . . . . . . . . . . . . . . . . . . . .

Automated Measurements of an FFT 1Ć7. . . . . . . . . . . . . . . . . . . .

Considerations for Using FFTs 1Ć7. . . . . . . . . . . . . . . . . . . . . . . . . . . .

The FFT Frequency Domain Record 1Ć7. . . . . . . . . . . . . . . . . . . . .

Offset, Position, and Scale 1Ć9. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Record Length 1Ć10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Acquisition Mode 1Ć10. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Zoom and Interpolation 1Ć11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Undersampling (Aliasing) 1Ć11. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Considerations for Phase Displays 1Ć12. . . . . . . . . . . . . . . . . . . . . .

FFT Windows 1Ć14. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Waveform Differentiation

Waveform Integration

TDS Series Option 2F Instructions

Description 2Ć1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Operation 2Ć1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Displaying a Differentiated Waveform 2Ć1. . . . . . . . . . . . . . . . . . . .

Automated Measurements of a Derivative Waveform 2Ć2. . . . . . .

Cursor Measurement of a Derivative Waveform 2Ć3. . . . . . . . . . . .

Usage Considerations 2Ć3. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Offset, Position, and Scale 2Ć4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Zoom 2Ć4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Description 3Ć1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Operation 3Ć1. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Displaying an Integral Waveform 3Ć1. . . . . . . . . . . . . . . . . . . . . . . .

Cursor Measurements of an Integral Waveform 3Ć2. . . . . . . . . . .

Automated Measurements of a Integral Waveform 3Ć4. . . . . . . . .

vii

Contents

Index

Usage Considerations 3Ć4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Offset, Position, and Scale 3Ć4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

DC Offset 3Ć4. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Zoom 3Ć5. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

viii

Contents

Safety

Please take a moment to review these safety precautions. They are provided
for your protection and to prevent damage to the digitizing oscilloscope.
This safety information applies to all operators and service personnel.

Symbols and Terms

These two terms appear in manuals:

H

statements identify conditions or practices that could result in

damage to the equipment or other property.

H

statements identify conditions or practices that could result in

personal injury or loss of life.

These two terms appear on equipment:

H CAUTION indicates a personal injury hazard not immediately accessible

as one reads the marking, or a hazard to property including the equipĆ
ment itself.

H DANGER indicates a personal injury hazard immediately accessible as

one reads the marking.

This symbol appears in manuals:

TDS Series Option 2F Instructions

StaticĆSensitive Devices

These symbols appear on equipment:

DANGER

High Voltage

Protective

ground (earth)

terminal

ATTENTION

Refer to

manual

ix

Safety

Specific Precautions

Observe all of these precautions to ensure your personal safety and to
prevent damage to either the digitizing oscilloscope or equipment conĆ
nected to it.

Power Source

The digitizing oscilloscope is intended to operate from a power source that
will not apply more than 250 V
tween either supply conductor and ground. A protective ground connection,
through the grounding conductor in the power cord, is essential for safe
system operation.

between the supply conductors or beĆ

RMS

Grounding the Digitizing Oscilloscope

The digitizing oscilloscope is grounded through the power cord. To avoid
electric shock, plug the power cord into a properly wired receptacle where
earth ground has been verified by a qualified service person. Do this before
making connections to the input or output terminals of the digitizing oscilloĆ
scope.

Without the protective ground connection, all parts of the digitizing oscilloĆ
scope are potential shock hazards. This includes knobs and controls that
may appear to be insulators.

Use the Proper Power Cord

Use only the power cord and connector specified for your product. Use only
a power cord that is in good condition.

Use the Proper Fuse

To avoid fire hazard, use only the fuse specified in the parts list for your
product, matched by type, voltage rating, and current rating.

Do Not Remove Covers or Panels

To avoid personal injury, do not operate the digitizing oscilloscope without
the panels or covers.

Electric Overload

Never apply to a connector on the digitizing oscilloscope a voltage that is
outside the range specified for that connector.

Do Not Operate in Explosive Atmospheres

The digitizing oscilloscope provides no explosion protection from static
discharges or arcing components. Do not operate the digitizing oscilloscope
in an atmosphere of explosive gases.

x

Safety

Product Description

Option 2F, Advanced DSP Math, is an option to the TDS Family Digitizing
Oscilloscopes. It can be ordered only at the time the oscilloscope is purĆ
chased.

TDS oscilloscopes use a proprietary Digital Signal Processor (DSP) to
convert normally acquired waveforms into simple math waveforms (inverts a
waveform, adds, subtracts, multiplies two waveforms). Option 2F adds three
new complex math waveforms to the oscilloscope:

FFT (Fast Fourier Transform) MathĊtransforms a displayed waveform from
the time domain to the frequency domain by applying the Fast Fourier
Transform. FFT Math features the following capabilities:

H Displays the magnitude of the various frequencies the source waveform

contains or, optionally, the phase angle of those frequencies

H Measures magnitude in linear V

sures phase in degrees or radians

H Provides phase suppression to reduce the phase angle to zero for

frequencies with magnitudes below a userĆspecified threshold

H Transforms source waveforms with record lengths of 500, 1,000, 5,000,

15,000, 30,000, 50,000, and 60,000 points. (Your model oscilloscope will
not have all of these these record lengths; consult your User manual to
determine which are available with your TDS model.)

H Operates on source waveforms displayed in any channel or reference

memory (the source cannot be another math waveform)

H Provides the following FFT windows to optimize frequency resolution

and magnitude measurement accuracy: rectangular, Hamming, HanĆ
ning, and BlackmanĆHarris

H Executes an FFT in as little as 64.2 milliseconds (1,000 point FFT)

H Updates the display up to ten times per second (1,000 point FFT)

H Corrects FFT DC error automatically

H Allows cursor and automatic measurements of FFT math waveforms

Derivative MathĊdifferentiates, with respect to time, a waveform displayed
from a channel or from a reference memory. Derivative math waveforms

measure the instantaneous rate of change of a waveform.

or dB with respect to 1 V

RMS

RMS

; meaĆ

TDS Series Option 2F Instructions

Integral MathĊintegrates over time a waveform displayed from a channel or
from a reference memory. Integral math waveforms display the total area
under a waveform with respect to ground.

xi

Product Description

xii

Product Description

Fast Fourier Transforms

Fast Fourier Transforms

Using the Fast Fourier Transform (FFT), you can transform a waveform from
a display of its amplitude against time to one that plots the amplitudes of the
various discrete frequencies the waveform contains. Further, you can also
display the phase shifts of those frequencies. Use FFT math waveforms in
the following applications:

H Testing impulse response of filters and systems

H Measuring harmonic content and distortion in systems

H Characterizing the frequency content of DC power supplies

H Analyzing vibration

H Analyzing harmonics in 50 and 60 cycle lines

H Identifying noise sources in digital logic circuits

Description

The FFT computes and displays the frequency content of a waveform you
acquire as an FFT math waveform. This frequency domain waveform is
based on the following equation:

N

* 1

2

X(k) +

Where: x(n) is a point in the time domain record data array

The resulting waveform is a display of the magnitude or phase angle of the
various frequencies the waveform contains with respect to those frequenĆ
cies. For example, Figure 1Ć1 shows the nonĆtransformed impulse response
of a system in channel 2 at the top of the screen. The FFTĆtransformed magĆ
nitude and phase appear in the two math waveforms below the impulse. The
horizontal scale for FFT math waveforms is always expressed in frequenĆ
cy/division with the beginning (leftĆmost point) of the waveform representing
zero frequency (DC).

1

N

Ă SĂ

n +

X(k) is a point in the frequency domain record data array

n is the index to the time domain data array

k is the index to the frequency domain data array

N is the FFT length

j is the square root of −1

x(n)e

* N

2

*

j2pnk

N

Ă

ĂĂĂĂĂ

Ă

for : k + 0Ă toĂ N * 1

TDS Series Option 2F Instructions

1Ć1

Fast Fourier Transforms

Normal Waveform of an

Impulse Response

FFT Waveform of the

Magnitude Response

The FFT waveform is based on digital signal processing (DSP) of data,
which allows more versatility in measuring the frequency content of waveĆ
forms. For example, DSP allows the oscilloscope to compute FFTs of source
waveforms that must be acquired based on a single trigger, making it useful
for measuring the frequency content of single events. (The TDS 800 model
oscilloscopes must have repetitive triggers; therefore, they cannot compute
FFTs of single events.) DSP also allows the phase as well as the magnitude
to be displayed.

Operation

FFT Waveform of the

Phase Response

Figure 1Ć1:ăSystem Response to an Impulse

To obtain an FFT of your waveform, do these basic tasks:

H Acquire and display it normally (that is, in the time domain) in your

choice of input channels.

H Transform it to the frequency domain using the math waveform menu.

H Use cursors or automated measurements to measure its parameters.

Use the following procedure to perform these tasks.

1Ć2

Displaying an FFT

1. Connect the waveform to the desired channel input and select that
channel.

Fast Fourier Transforms