Tektronix P7313SMA Reference manual

P7313SMA 13 GHz Differential Probe Technical Reference

*P071196800*

071-1968-00

P7313SMA 13 GHz Differential Probe Technical Reference

www.tektronix.com

071-1968-00

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Table of Contents

General Safety Summary ... . .. . .. . .. . ... ... ... . .. . .. . .. . .. . .. . ... ... . .. . .. . .. . .. . .. . ... ... ... ... . .. . .. . .. . .. . .. . ... ... ... . .. . .. . .. . .. iii

Preface................................................................................................................................. v

Operating Basics ...................................................................................................................... 1

Differential Measurements for Serial Data Compliance Testing................................................................ 1

Probe Block Dia

Termination Voltage Control ..................................................................................................... 8

Overdrive Error..................................................................................................................10

Differential a

Extending the Input Connections .. . .. . .. . .. . .. . .. . ... ... ... . .. . .. . .. . .. . ... ... . .. . .. . .. . .. . ... ... ... . .. . .. . .. . .. . ... ... ... . .. . . 17

Checking Cable Skew........................................................................................................... 18

Adjusting Cabl

Deskewing Probes . ... . .. . .. . .. . ... ... . .. . .. . .. . ... ... ... . .. . .. . .. . ... . .. . .. . .. . ... ... ... . .. . .. . .. . ... ... ... . .. . .. . .. . ... . .. . .. . 20

Reference ............................................................................................................................. 23

Serial Bus Stan

InﬁniBand . .. . .. . ... ... ... ... . .. . .. . .. . .. . .. . .. . ... ... . .. . .. . .. . .. . .. . ... ... ... ... . .. . .. . .. . .. . .. . .. . ... ... ... ... . .. . .. . .. . .. . .. . . 24

Speciﬁcations .........................................................................................................................25

Warranted Chara

Typical Characteristics ..........................................................................................................26

Nominal Characteristics......................................................................................................... 30

Mechanical Char

Performance Veriﬁcation ............................................................................................................. 32

Equipment Required . .. . .. . .. . .. . ... ... ... . .. . .. . .. . .. . ... ... . .. . .. . .. . .. . ... ... ... . .. . .. . .. . .. . .. . ... ... ... . .. . .. . .. . .. . ... ... . 32

Special Adapter

Equipment Setup................................................................................................................ 34

Input Resistance . ... . .. . .. . .. . .. . ... ... ... ... . .. . .. . .. . .. . ... ... . .. . .. . .. . .. . ... ... ... ... . .. . .. . .. . .. . ... ... ... ... . .. . .. . .. . .. . . 35

Termination Vol

Output Offset Zero .............................................................................................................. 39

DC GainAccuracy .............................................................................................................. 40

Rise Time........................................................................................................................42

Optional Accessories .. ... ... . .. . .. . .. . .. . .. . .. . .. . ... ... ... ... . .. . .. . .. . .. . .. . .. . .. . ... ... ... . .. . .. . .. . .. . .. . .. . .. . ... ... ... ... . ..... 48

Options................................................................................................................................ 49

Maintenance .......................................................................................................................... 50

Inspection and Cleaning . .. . ... ... . .. . .. . .. . .. . .. . ... ... ... ... . .. . .. . .. . .. . .. . ... ... ... . .. . .. . .. . .. . .. . ... ... . .. . .. . .. . .. . .. . ... 50

Replacement Parts.............................................................................................................. 50

Preparation for S

gram (Simpliﬁed) ............................................................................................... 3

nd Single-Ended Signal Measurement . . .. . ... ... . .. . .. . .. . ... ... ... . .. . .. . .. . .. . ... ... . .. . .. . .. . .. . ... . .. . .. . .. . 11

e Skew........................................................................................................... 19

dards ........................................................................................................... 23

cteristics ...................................................................................................... 25

acteristics ..................................................................................................... 31

s Required .. . .. . .. . .. . .. . .. . ... ... ... . .. . .. . .. . .. . ... ... . .. . .. . .. . .. . .. . ... ... ... . .. . .. . .. . .. . .. . ... ... ... . .. . . 33

tage Accuracy .................................................................................................. 36

hipment ....................................................................................................... 50

Table of Content

P7313SMA Technical Reference i

Table of Content

ii P7313SMA Technical Reference

General Safety S

ummary

General Safet

Review the following safety precautions to avoid injury and prevent damage to this product or any products connected to it.

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

Only qualiﬁed personnel should perform service procedures.

While using this product, you may need to access other parts of a larger system. Read the safety sections of the other component manuals for warnings and cautions related to operating the system.

To Avoid Fire or Personal Injury

Connect and Disconnect Properly. Connect the probe output to the measurement instrument before connecting the

probe to the c input. Disconnect the probe input and the probe reference lead from the circuit under test before disconnecting the probe from the measurement instrument.

Observe All Terminal Ratings. To avoid ﬁre or shock hazard, observe all ratings and markings on the product. Consult

the product m

Do Not Operat

qualiﬁed service personnel.

Avoid Exposed Circuitry. Do not touch exposed connections and components when power is present.

ircuit under test. Connect the probe reference lead to the circuit under test before connecting the probe

anual for further ratings information before making connections to the product.

e Without Covers.

e With Suspected Failures.

y Summary

Do not operate this product with covers or panels removed.

If you suspect that there is damage to this product, have it inspected by

Do Not Operate in Wet/Damp Conditions.

Do Not Operate in an Explosive Atmosphere.

Keep Product Surfaces Clean and Dry.

P7313SMA Technical Reference iii

General Safety S

TermsinthisManual

These terms may appear in this manual:

WARNING. Warning statements identify conditions or practices that could result in injury or loss o f life.

CAUTION. Caution statements identify c onditions or practices that could result in damage to this product or other property.

Symbols and Terms on the Product

These terms may appear on the product:

DANGER indicates an injury hazard immediately accessible as you read the marking.

WARNING indicates an injury hazard not immediately accessible as you r ead the marking.

CAUTION indicates a hazard to property including the product.

The following symbols may appear on the product:

ummary

iv P7313SMA Technical Reference

Preface

This is the technical reference manual for the P7313SMA differential probe. This manual provides operating theory, speciﬁcations, and performance veriﬁcation procedures for the probe.

Preface

P7313SMA Technical Reference v

Preface

vi P7313SMA Technical Reference

Operating Basic

Operating Bas

This section discusses differential measurements using an SMA input probe for Serial Data compliance testing. It also provides information on the probe architecture and operational details to aid in its proper application.

ics

Differential Measurements for Serial Data Compliance Testing

Differential

Gigabit serial data signals are commonly transmitted using differential signaling techniques because of improved signal ﬁdelity and noise immunity. Although the physical layer speciﬁcations differ somewhat between the different gigabit serial data communication standards, they have some common elements. Most gigabit serial data signals are transmitted over 50 Ω transmission lines, which are terminated at both ends of a point-to-point differential interconnect. The signal transmitter provides a 50 Ω source impedance from each of its two differential outputs and the s ignal receiver provides an effective 50 Ω input impedance on each of its two differential inputs.

The two complementary single-ended signals that make up the differential signal are generally offset from ground at a common-mode voltage level, which allows the use of unipolar transmitters and receivers that are powered from a s ingle power supply v oltage. The transmitted signals are usually encoded using a DC-balanced encoding technique that allows the signals to be either AC or DC coupled in the transmission path. If DC coupled, the receiver termination must generally be terminated to the same DC common-mode voltage as the transmitter, to reduce DC loading on the transmitter output. An example of the single-ended signals transmitted by an InﬁniBand standard driver and the resultant differential signal that would be measured by a differential measurement system is shown in Inﬁniband. (See Figure 14 on page 24.)

Signaling

Although the differential response is generally the primary measurement of interest for a differential signal, full characterization of the signal also requires measurement of the single-ended response of the two complementary signals including the DC common-mode voltage.

Pseudo-Differential Measurements

A common differential measurement technique uses two single-ended probes or direct connection to two oscilloscope channels for the differential signal capture. By calculating the difference between the two input signals using waveform math, the effec

This meas limitations when compared to the use of a differential probe like the P7313SMA. In addition to the obvious overhead of two oscilloscope channels for the measurement instead of the single channel needed by a differential probe, there are a number o

Unlike t measurement uses two oscilloscope channels, which are physically separated and generally not matched as well. Although it is possible to deskew the timing differences between two high performance oscilloscope channels to improve the accuracy of a pseu oscilloscope parameter, such as vertical gain, is changed.

The gain match between two different oscilloscope channels is also a potential problem, particularly at higher frequencies where channel gain mismatch can contribute to signiﬁcantly reduced CMRR performance. The CMRR performance of a differ full probe bandwidth.

tive differential signal seen by a differential receiver can be displayed for analysis.

urement technique, which is commonly refered to as pseudo-differential measurement, has a number of

f additional problems.

he differential probe, which has been carefully designed with short, matched-input signal paths, a pseudo-differential

do-differential measurement, deskewing is a relatively involved procedure that may need to be repeated if any

ential probe, on the other hand, is generally much better controlled, with fully characterized speciﬁcations over the

P7313SMA Technical Reference 1

Operating Basic

The requirement of generating a math waveform for d isplay of the differential signal in a pseudo-differential measurement can also introduce may not be fully supported with math waveforms. The use of a differential SMA-input probe like the P7313SMA also provides additional features like adjustable termination voltage that may be very useful in fully characterizing the performance of differential voltage, since the oscilloscope termination resistor is connected directly to signal ground.

Differential Probe Measurements

A differential probe is designed to provide a differential input interface for a single-ended oscilloscope channel. It includes a carefully matched differential signal input path and a differential buffer ampliﬁer.

A conventional differential probe input generally has a high DC input resistance and as small an input loading capacitance as possible. The light input loading of a c onventional differential probe is designed to perturb the circuit being measured as little as possible when the probe is attached.

An SMA-input probe like the P7313SMA has a v ery different input structure. It has a dual, matched 50 Ω input that is designed to terminate the measured signal transmission path with minimum reﬂections. It is designed speciﬁcally for serial compliance testing. Its SMA input connectors provide a reliable, repeatable interconnect for making accurate eye pattern measurements that are used to characterize the quality of a serial data transmission channel.

The P7313SMA probe has also been carefully designed for ﬂat amplitude response and very small pulse response aberrations. This helps to ensure accurate eye pattern measurements over a wide data rate range.

some subtle problems with waveform analysis, since some features such as COMM triggering or mask testing

data transmitters. High performance oscilloscope channels are almost always limited to zero volt termination

The differential ampliﬁer is at the heart of any device or system designed to make differential measurements. (See Figure 1.) Ideally, the differential ampliﬁer rejects any voltage that is common to the inputs and ampliﬁes any difference between the inputs. Voltage that is common to both inputs is often referred to as the Common-Mode Voltage (V voltage as the Differential-Mode Voltage (V

) and difference

The simpliﬁed input signal voltage source model driving the differential ampliﬁer shows a complementary differential signal without source or termination impedance. In a real-world measurement, the signal source and measurement termination impedance must be known and included in the measurement analysis.

The model also shows that the output from the differential ampliﬁer has twice the peak-to-peak amplitude of each complementary input signal.

Figure 1

:Simpliﬁed model of a differential ampliﬁer

2 P7313SMA Technical Reference

Operating Basic

Common-Mode Rejection Ratio

Differential ampliﬁers cannot reject all of the common-mode signal. The ability of a differential ampliﬁer to reject the common-mode signal is expressed as the Common-Mode Rejection Ratio (CMRR). The CMRR is the differential-mode gain (A

) divided by the common-mode gain (ACM). It is expressed either as a ratio or in dB.

CMRR = A

DM÷ACM

CMRR(dB) = 20 log (ADM÷ACM)

CMRR generally is highest (best) at DC and degrades with increasing frequency.

The typical CMRR response of the P7313SMA differential probe over frequency is shown in S peciﬁ cations . (See Figure 15 on page 27.) High CMRR in a differential probe requires c areful matching of the two input paths. Poorly matched signal source impedances can signiﬁcantly degrade the C MRR of a measurement. Mismatches between the two differential signal input paths result in an effective conversion of V

Probe Block Diagram (Simpliﬁed)

The SMA inputs and probe termination network provide a high frequency, 50 Ω signal path to the internal probe ampliﬁer. The use of SMA-female connectors provides a reliable, repeatable attachment method for input signals. The s ymmetry of the input ter

Asimpliﬁed s

mination network is designed to reduce skew and maximize CMRR.

chematic of the P7313SMA input termination network is shown. (See Figure 2.)

to VDM, which reduces the CMRR.

Figure 2:

Input termination network

P7313SMA Technical Reference 3

Operating Basic

Matched-Delay Cables

The standard delay-matched cables for the P7313SMA differential probe have been carefully designed to provide guaranteed probe performance at the SMA connector interface on the end of the cable. The delay between the two matched cables in the standard cable assembly is adjusted to provide an initial skew of less than 1 ps. Cable skew this small can be degraded by cable ﬂexure and through other environmental factors. Care should be taken to minimize physical mishandling of this quality cable assembly to preserve probe performance.

The cable used in the standard cable assembly has also been selected for its low-loss characteristics, and the cable length was selected to match the cable loss compensation designed into the probe differential ampliﬁer. If an alternative cable assembly is used in measurements with the P7313SMA differential probe ampliﬁer, this loss compensation characteristic must be considered. The following approximate equation for cable loss compensation can be used as a guideline in custom cable designs and is valid o ver a frequency range of about 1 GHz to 8 GHz:

Loss = –[0.5 dB + 0.15 dB * (F ⁄1.25)], where F is frequency in GHz.

Custom cable pairs must also be designed with very low skew or the skew must be minimized using a pair of adjustable phase trimmer adapters like those listed in the Optional Accessories. (See page 48, Optional Accessories.)

Input Termination Network

The input termination network in the P7313S MA differential probe includes a pair of attenuation resistor networks laser trimmed to 5 The common-mode termination voltage node, V input common-mode signals. The probe termination voltage can be adjusted using several different modes that will be describ

0 Ω terminations, connected together at a common-mode voltage node, labeled V

, is designed to provide a broadband, low impedance termination for

ed later.

. (See Figure 2 on page 3.)

The termina

tion voltage range is +3.6 V/–2.5 V. For DC-coupled serial data signals, the termination voltage, V generally be set to equal the input signal common-mode voltage, V voltage, V

, should generally be set to 0 V.

; for AC-coupled serial data signals, the termination

, should

The adjustability of the termination voltage also provides measurement ﬂexibility for characterizing or stressing serial data signal dri

vers. Because of the low impedance of the input termination and attenuator network, the signal termination c urrents can become quite large. The following table can be used to calculate the DC common-mode voltages and currents at the probe inputs and termination voltage driver under several common source impedance conditions. (See Table 1.)

Table 1: Common-mode voltage and current formulas

. Source impedance

Common-mode term 0 Ω 50 Ω

When inputs are AC coupled: VI=VT,II=0,IT= 16.67 mA x V

40.00 mA x VT- 40.00 mA x V

40.00 mA x

- 23.33 mA x V

0.5 x (VT+VCM)

20.00 mA x VT- 20.00 mA x V

28.33 mA x

- 11.67 mA x V

4 P7313SMA Technical Reference

Operating Basic

The probe block diagram shows that the input termination network is followed by an attenuator and VCMcompensation circuit. The attenuator

is used to increase the effective input dynamic range of the probe differential ampliﬁer.

The P7313SMA probe has two attenuation settings, 2.5X and 12.5X, that allow dynamic range to be traded off against signal noise. The 12.5X attenuator setting has the largest dynamic range; the 2.5X attenuator setting has the lowest noise.

The V

compensation c ircuit automatically minimizes the DC common-mode voltage at the probe differential ampliﬁer inputs

even with varying termination voltage and input signal DC common-mode voltage. This maximizes the differential mode signal input dynamic range. The V

compensation circuit allows the DC common-mode input voltage range to be the same

for both attenuator settings. (See Figure 4 on page 7.)

Internal Probe Ampliﬁer

The P7313SMA differential probe is designed to measure high frequency, low-voltage circuits. Before connecting the probe to your circuit, take into account the limits for maximum input voltage, the common-mode signal range, and the differential-mode signal range. For speciﬁc limits of these parameters, see the Speciﬁcations section. (See page 25, Speciﬁcations.)

Maximum Input Voltage. The maximum input voltage is the maximum voltage to ground that the inputs can withstand

without damaging the probe input circuitry.

CAUTION. To avoid damaging the inputs of the P7313SMA differential probe, do not apply more than ±5 V (DC + peak AC)

between each input and ground. In addition, to avoid probe damage, the maximum termination resistor power must not be exceeded.

Maximum Termination Resistor Power. The internal termination resistors can safely dissipate 0.2 W of power

continuously, which is the case for normal probe operation without termination driver current overload. However, the probe will be damaged if you apply more than 0.5 W of power through the termination resistors for more than 5 minutes.

If you suspect your measurement application will approach these limits, use the formulas that follow to calculate the power dissipated by the termination resistors.

The power calculation formulas are based on the simpliﬁed model, which represents the signal at the probe inputs. (S ee Figure 3 on page 6.) If a signal source with 50 Ω source impedances is used, the signal levels used should match the zero-ohm source impedance model shown in the ﬁgure.

The signal source model de ﬁned for these equations is as follows:

P7313SMA Technical Reference 5

Operating Basic

This results in the terms to be used in the preceding power equations:

NOTE. With a balanced DC signal, in the preceding equations, VDMis half of the value of a conventional differential signal.

Figure 3: Probe maximum input limits

6 P7313SMA Technical Reference

Operating Basic

Common-Mode Signal Range. The common-mode signal range is the maximum voltage that you can apply to each

input, with res exceeds the common-mode signal range may produce an erroneous output waveform even when the differential-mode speciﬁcation is met.

pect to earth ground, without saturating the input circuitry of the probe. A common-mode voltage that

Differential-Mode Signal Range. The differential-mode signal range is the maximum voltage difference between the

plus and minus inputs that the probe can accept without distorting the signal. The distortion from a voltage that is too large can result i n a clipped or otherwise distorted and inaccurate measurement. The differential mode signal range is dependent on the probe attenuator setting as shown. (See Figure 4.)

For a more detailed description of the differential mode dynamic range, see Differential Measurement Topology.

Figure 4: Differential and Common-Mode operating ranges

Common-Mode Rejection. The common-mode rejection ratio (CMRR) is the ability of a probe to reject signals that are

common to both inputs. More precisely, CMRR is the ratio of the differential-mode gain to the common-mode gain. The higher the ratio, the greater the ability to reject common-mode signals.

Probe Ampliﬁer Outputs. The P7313SMA probe has a differential signal output. The positive polarity output is

ed to the oscilloscope through the TekConnect probe interface. The inverted polarity output is connected to the Aux

connect Output SMA connector on the top of the probe.

The positive polarity main output is automatically scaled b y the intelligent TekConnect probe interface to compensate for probe attenuation and display the differential signal voltage at the probe inputs. The inverted Aux Output is an attenuated

n of the differential signal input, which must be manually accounted for in signal measurements or processing.

versio

P7313SMA Technical Reference 7

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Tektronix P7313SMA Reference manual

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