Tektronix P7380A Service
Technical Reference
P7380A
8 GHz Z-Activet
Differential Probe
071-1715-03
www.tektronix.com
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Contacting Tektronix
Tektronix, Inc.
14200 SW Karl Braun Drive
P.O. Box 500
Beaverton, OR 97077
USA
For product information, sales, service, and technical support:
H In North America, call 1-800-833-9200.
H Worldwide, visit www.tektronix.com to find contacts in your area.
Table of Contents
General Safety Summary v...................................
Introduction 1..............................................
Theory of Operation 3.......................................
Input Voltage Limits 3..............................................
Maximum Input Voltage 3.......................................
Operating Voltage Window 4.....................................
Differential-Mode Signal Range 4.................................
Common-Mode Rejection 4.........................................
Probing Techniques to Maximize Signal Fidelity 5.......................
Input Impedance and Probe Loading 6.................................
Electrical Effects of Accessories 8....................................
Reference 9.................................................
Single-Ended Measurements 9.......................................
Differential Measurements 10.........................................
Common-Mode Rejection Ratio 10.................................
Assessing CMRR Error 11........................................
Input Impedance Effects on CMRR 11..............................
Serial Bus Standards 12..............................................
Specifications 13.............................................
Warranted Characteristics 13..........................................
Typical Characteristics 14............................................
Nominal Characteristics 17...........................................
Tip-Clip Assembly Specifications 20...................................
Performance Verification 29...................................
Equipment Required 29..............................................
Special Adapters Required 31.........................................
Equipment Setup 33................................................
Output Offset Voltage 34.............................................
DC Gain Accuracy 35...............................................
Gain Check at 5X Attenuation 35..................................
Gain Check at 25X Attenuation 36.................................
Rise Time 37......................................................
Rise Time Measurements Using the Probe Calibration Fixture 38.........
Rise Time Check at 25X Attenuation 39.............................
Test Record 43.....................................................
User Service 45..............................................
Probe/Adapter/Oscilloscope Compatibility 45............................
Error Condition 45..................................................
Replacement Parts 45...............................................
Preparation for Shipment 46..........................................
P7380A Z-Active Differential Probe\
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Table of Contents
List of Figures
Figure 1: Dynamic range 4....................................
Figure 2: Use the Short Flex, Small Resistor Tip-Clip assembly 5...
Figure 3: Typical probe input model 6..........................
Figure 4: Symmetric coupled line 7............................
Figure 5: Transmission line equivalent 7........................
Figure 6: Lumped element equivalent 7.........................
Figure 7: Simplified model of a differential amplifier 10............
Figure 8: Typical Common-Mode Rejection Ratio (5X attenuation) 15
Figure 9: Typical differential input impedance verses frequency 15...
Figure 10: Probe and Tip-Clip dimensions 16.....................
Figure 11: Z-Active probe dynamic range verses frequency
5X gain setting 17.........................................
Figure 12: Z-Active probe dynamic range verses frequency
25X gain setting 18.......................................
Figure 13: P7380A, P7360A, and P7340A dynamic range
5X gain setting 18.........................................
Figure 14: P7380A, P7360A, and P7340A dynamic range
25X gain setting 19........................................
Figure 15: TekConnect-to-SMA adapter 31.......................
Figure 16: Probe Calibration fixture 31..........................
Figure 17: Adapter fixture 32..................................
Figure 18: Preliminary test setup 33.............................
Figure 19: Setup for the output offset zero test 34..................
Figure 20: DC Gain Accuracy setup 35..........................
Figure 21: Reverse the power supply polarity on the probe inputs 36.
Figure 22: Handheld adapter and calibration fixture 38............
Figure 23: PPM203B Articulated Arm with the Handheld adapter 38.
Figure 24: Test system rise time setup 39.........................
Figure 25: Setting the TDR parameters 40.......................
Figure 26: Test probe rise time setup 41..........................
ii
P7380A Z-Active Differential Probe\
List of Tables
Table of Contents
T able 1: Offset ranges 9......................................
T able 3: Warranted electrical characteristics 13.................
T able 4: Typical electrical characteristics 14......................
Table 5: Typical mechanical characteristics 16....................
T able 6: Nominal electrical characteristics 17.....................
Table 7: Test equipment 29....................................
Table 8: Differential probe compatibility issues 45................
P7380A Z-Active Differential Probe\
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Table of Contents
iv
P7380A Z-Active Differential Probe\
General Safety Summary
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 the system. Read
the General Safety Summary in other system manuals for warnings and cautions
related to operating the system.
ToAvoidFireor
Personal Injury
Connect and Disconnect Properly. Connect the probe output to the measurement
instrument before connecting the probe to the circuit under test. Disconnect the
probe input 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 manual for further ratings
information before making connections to the product.
Do not apply a potential to any terminal, including the common terminal, that
exceeds the maximum rating of that terminal.
Do Not Operate Without Covers. Do not operate this product with covers or panels
removed.
Avoid Exposed Circuitry. Do not touch exposed connections and components
when power is present.
Do Not Operate With Suspected Failures. If you suspect there is damage to this
product, have it inspected by qualified service personnel.
Do Not Operate in Wet/Damp Conditions.
Do Not Operate in an Explosive Atmosphere.
Keep Product Surfaces Clean and Dry.
P7380A Z-Active Differential Probe\
v
General Safety Summary
Symbols and Terms
Terms in this Manual. These terms may appear in this manual:
WARNING. Warning statements identify conditions or practices that could result
in injury or loss of life.
CAUTION. Caution statements identify conditions or practices that could result in
damage to this product or other property.
Symbol on the Product. The following symbol may appear on the product:
CAUTION
Refer to Manual
vi
P7380A Z-Active Differential Probe\
Introduction
This manual discusses topics not covered or otherwise mentioned briefly in the
P7313 12.5 GHz, P7380A 8 GHz, P7360A 6 GHz, and P7340A 4 GHz Z-Active
Differential Probe Family User Manual.
The following is a list of brief explanations:
H Theory of Operation — Contains probe details not mentioned in the user
manual.
H Reference — Contains information about differential measurements and how
to increase measurement accuracy.
H Specifications — Contains warranted, typical, and nominal characteristics
for the probe and probe Tip-Clip assemblies.
H Performance Verification — Describes the procedures for verifying the
warranted specifications.
H User Service — Describes troubleshooting and probe maintenance.
P7380A Z-Active Differential Probe\
1
Introduction
2
P7380A Z-Active Differential Probe\
Theory of Operation
This section discusses operating considerations and probing techniques. For
more detailed information about differential measurements and common-mode
rejection ratio (CMRR), see the Reference sectiononpage9.
The P7380A Probe is optimized for high bandwidth; it is not a general purpose
probe. The probe head and tips are miniaturized for electrical characteristics and
access to dense circuitry, and must be handled carefully.
CAUTION. To prevent damage to the probe, use care when handling the probe.
Rough or careless use can damage the probe.
Input Voltage Limits
The P7380A Differential Probe is designed to probe low-voltage circuits. B efore
probing a voltage, take into account the limits for maximum input voltage, the
common-mode signal range, and the differential-mode signal range. For specific
limits, refer to page 14.
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 P7380A Differential Probe, do
not apply more than ±15 V (DC + peak AC) between each input or between
either probe input and ground.
P7380A Z-Active Differential Probe\
3
Theory of Operation
Operating Voltage Window
Differential-Mode Signal
Range
The operating voltage window defines the maximum voltage that you can apply to
each input, with respect to earth ground, without saturating the probe input circuitry.
See Figure 1. A common-mode voltage that exceeds the operating voltage window
may produce an erroneous output waveform even when the differe ntial- mode
specification is met. For specifications, refer to page 14.
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 in a clipped or otherwise
inaccurate measurement. For specifications, refer to page 14.
1.3 V
+4.0 V
5X
25X
Figure 1: Dynamic range
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 gain to the common-mode gain. The higher the ratio, the greater the
ability to reject common-mode signals. CMRR varies with frequency, usually
decreasing at higher frequencies. For additional information about CMRR, see
page 15.
5.0 V
-- 3 . 0 V
4
P7380A Z-Active Differential Probe\
Probing Techniques to Maximize Signal Fidelity
Signal fidelity is an indication of how accurately a probe represents the signal
being measured. The signal fidelity of the probe is best when the probe is applied
directly to the circuit with the Short Flex, Small Resistor, Tip-Clip assembly
shown in Figure 2. This Tip-Clip assembly achieves high signal fidelity by
minimizing the distance between the probe head and the signal source. This
reduces probe interconnect parasitics that tend to degrade signal fidelity.
However, some probing tasks are made easier using other accessories included
with the probe.
The Tip-Clip specifications starting on page 20 show pulse response illustrations
that give some indication of signal fidelity with different Tip-Clip assemblies.
Signal fidelity is affected by both the probe interconnect and the speed of the
signal. It is recommended that the longer Tip-Clip assembly be used with
somewhat slower speed signals for better signal fidelity.
Theory of Operation
Figure 2: Use the Short Flex, Small Resistor Tip-Clip assembly
P7380A Z-Active Differential Probe\
5
Theory of Operation
Input Impedance and Probe Loading
When you connect the probe inputs to a circuit, you are introducing a new
resistance, capacitance, and inductance into the circuit. Each input of the
differential probe has a characteristic input impedance of 50 kΩ to ground.
60 fF
3.12 pF
3.12 pF
60 fF
Input
+
Input
--
1
See the following figures for an explanation of cpl.
2
Short Tip-Clip (blue) length
38 Ω
38 Ω
37 Ω
20 fF
20 fF
37 Ω
1
Cpl
Zodd=95
Zeven=190
L=3.7 mm
Kodd ~ Keven ~ 1
2
140 Ω
50 kΩ
310 Ω
310 Ω
50 kΩ
140 Ω
Figure 3: Typical probe input model
For signals with low source impedance and frequency, the 50 kΩ input impedance on each input is large enough to prevent the inputs from loading the signal
sources. As the signal source impedance on an input increases, the more the
probe loads the source and reduces the signal amplitude. The greater the source
impedances and the higher the signal frequencies, the more you must take these
factors into account. See Figure 3.
The frequency of the signal also affects signal measurement. As the frequency of
the signal increases, the input impedance of the probe decreases. The lower the
impedance of the probe relative to that of the source, the more the probe loads
the circuit under test and reduces the signal amplitude. For a graph of input
impedance versus frequency, refer to Figure 9 on page 15.
6
P7380A Z-Active Differential Probe\
Cpl
ZOO= 100 Ω
ZOE= 190 Ω
L=3.7mm(air)
Figure 4: Symmetric coupled line
Z0 = ZOE= 190 Ω,
Td = 12.1 ps
Z0 = 2(ZOOZOE)/(ZOE-- ZOO) =211 Ω,
Td = 12.1 ps
Theory of Operation
Z0 = ZOE= 190 Ω,
Td = 12.1 ps
TD = 12.1 ps
(3.7 mm in air)
Figure 5: Transmission line equivalent
Cg = (C11+C12)/2
= 31.9 ff
Cg = --0.5C
= 14.4ff
12
Lp = Ls = L11=1.76nH
= 0.545 nH
M=L
12
11+C12
)/2
Cg = (C
= 31.9ff
Cg = --0.5C
= 14.4 ff
12
Figure 6: Lumped element equivalent
P7380A Z-Active Differential Probe\
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Theory of Operation
Electrical Effects of Accessories
The Tip-Clip accessories included with your probe help connect to different
types of components. The Tip-Clip accessories are designed to provide optimum
performance as a system. Each Tip-Clip accessory has distinct characteristics.
While these accessories make connections easier, be aware that the Tip-Clip
accessory you choose affects the signal you are measuring, depending on a
variety of factors, including signal frequency, source impedance, and lead length.
Refer to Specifications on page 13 for more Tip-Clip information.
8
P7380A Z-Active Differential Probe\
Reference
This section contains important reference information about differential
measurements and how to increase measurement accuracy.
Single-Ended Measurements
A differential probe, for example the P7380A Differential Probe, can be used for
single-ended measurements within the limits of its dynamic and offset voltage
ranges. Single-ended probes such as the P7240 typically have a wider offset
range than corresponding differential probes (see Table 1).
Table 1: Offset ranges
Probe examples DC Offset, 5X Dynamic
Range, 5X
P7240 +/-- 5 V
P7380A Differential Probe
+4 V, --3 V 2V
-- -- --
PP
DC Offset, 25X Dynamic
Range, 25X
-- --
+4 V, --3 V 5V
-- -- --
PP
Differential probes are ideal for a class of single-ended measurements where the
reference voltage is not ground:
H SSTL_1,2: V
H PECL: V
TT,VREF=VDD
REF=VCC
/2
--1.3
To measure single-ended signals in this class, connect the negative input of the
P7380A Differential Probe to V
REF
.
A differential probe in these applications displays the true signal despite any AC
or DC variation in V
displays the signal plus the variation in V
from its nominal value. While a single-ended probe
REF
.
REF
Differential probes can also be used to make ground referenced single-ended
measurements on either single-ended signals or differential signals like PCI Express or Serial ATA. To measure ground referenced single-ended signals, connect
the negative input of the P7380 to ground.
Single-ended measurements on differential signals are used to measure common
mode voltage and check for differential signal symmetry.
P7380A Z-Active Differential Probe\
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