Teledyne DXC100A User Manual

Operator’s

Manual

DXC100A

Differential Probe Pair

© 2013 Teledyne LeCroy, Inc. All rights reserved.

Unauthorized duplication of Teledyne LeCroy documentation materials other than for internal
sales and distribution purposes is strictly prohibited. However, clients are encouraged to distribute
and duplicate Teledyne LeCroy documentation for their own internal educational purposes.

WaveSurfer, WaveRunner, and Teledyne LeCroy are registered trademarks of Teledyne LeCroy,
Inc. Windows is a registered trademark of Microsoft Corporation. Other product or brand names
are trademarks or requested trademarks of their respective holders. Information in this
publication supersedes all earlier versions. Specifications are subject to change without notice.

Warranty

Teledyne LeCroy warrants this oscilloscope accessory for normal use and operation within
specification for a period of one year from the date of shipment. Spare parts, replacement parts
and repairs are warranted for 90 days.

In exercising its warranty, Teledyne LeCroy, at its option, will either repair or replace any assembly
returned within its warranty period to the Customer Service Department or an authorized service
center. However, this will be done only if the product is determined by Teledyne LeCroy’s
examination to be defective due to workmanship or materials, and the defect is not caused by
misuse, neglect, accident, abnormal conditions of operation, or damage resulting from attempted
repair or modifications by a non-authorized service facility.

The customer will be responsible for the transportation and insurance charges for the return of
products to the service facility. Teledyne LeCroy will return all products under warranty with
transportation charges prepaid.

This warranty replaces all other warranties, expressed or implied, including but not limited to any
implied warranty of merchantability, fitness or adequacy for any particular purposes or use.
Teledyne LeCroy shall not be liable for any special, incidental, or consequential damages, whether
in contract or otherwise.

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February 2013

DXC100A Differential Probe Pair

High Voltage, risk of electric shock.

CAUTION of potential for damage to probe or instrument it is
connected to, or WARNING of potential bodily injury. Attend to the
accompanying information to protect against personal injury or
damage. Do not proceed until conditions are fully understood and
met.

ELECTROSTATIC DISCHARGE (ESD) HAZARD. Susceptible to damage if
anti-static measures are not taken.

DOUBLE INSULATION

PROTECTIVE (EARTH) TERMINAL

Safety Instructions

This section contains instructions that must be observed to keep this
oscilloscope accessory operating in a correct and safe condition. You are
required to follow generally accepted safety procedures in addition to the
precautions specified in this section. The overall safety of any system

incorporating this accessory is the responsibility of the assembler of the
system.

Symbols

These symbols may appear on the probe body or in this manual to alert you to
important safety considerations.

Precautions

Connect and disconnect properly. Connect probe to the measurement
instrument before connecting the test leads to a circuit/signal being tested.

Use only within operational environment listed. Do not use in wet or explosive
atmospheres.

Use indoors only.

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Keep product surfaces clean and dry. Do not submerge probe. Clean with a
water- or alcohol-moistened cloth. Do not use harsh or abrasive cleansers.

Be careful with sharp tips. Tips may cause bodily injury if not handled properly.

Do not operate with suspected failures. Do not use if any part is damaged.

Cease operation immediately and sequester the probe from inadvertent use.

Operating Environment

The accessory is intended for indoor use and should be operated in a clean, dry
environment. Before using this product, ensure that its operating environment is
maintained within these parameters:

Temperature: Operating, 0° to 50° C; Non-operating, -40° to 71° C

Humidity: ≤ 80% relative humidity (non-condensing).

Altitude: Up to 2000 m (6560 ft).

Introduction

The DXC100A is a high-performance, matched, passive differential probe pair
designed for use with the Teledyne LeCroy DA1855A Differential Amplifiers. The
probe pair consists of two well-matched individual probes sharing a common
compensation box allowing the attenuation factor on both probes to be
simultaneously switched between 10X and 100X. When used with a Teledyne
LeCroy DA1885A Differential Amplifier, the probe’s attenuation factor is
automatically incorporated into the effective gain display and the decimal
properly located in the Precision Voltage Generator (PVG) display.

Although primarily designed for use with Teledyne LeCroy amplifiers, the
DXC100A can be used with any oscilloscope or plug-in unit with an input
impedance of 1 MΩ/15-26pF and one inch (25.4 mm) spacing between
connectors.

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A Word about Differential Amplifiers and Probes

When using a differential amplifier it is very important to understand the role
probes play in the overall measurement system performance. Probes not only
make attachment to the circuit under test more convenient, 10X and 100X
attenuating probes also extend the common mode range of the differential
amplifier. For example, the DA1855A amplifier has a common mode range of ±

15.5 volts when the internal attenuators are set to ÷1 and 155 volts when set to
÷10. The addition of a probe with an attenuation factor of ten extends the
common mode range to 1550 volts or the rating of the probe, whichever is less.

However there is a trade-off in that the Common Mode Rejection Ration (CMRR)
capability of even highly matched differential probe pairs seldom matches that
of the amplifier. In order to preserve the amplifier’s performance at the probe
tips, it is important to use probes designed for differential performance.
Attempting to use normal 10X or 100X attenuating oscilloscope probes, even
high quality probes, results in very poor CMRR performance. Nominally
matching X1 probes, however, provide excellent common mode rejection and
are recommended.

When making differential measurements, probe compensation is just as
important as it is for single-ended measurements. While probe compensation is
important, how well the probes are matched is essential. Most probes depend

on the accuracy of the oscilloscope’s 1 MΩ input resistor to determine the
accuracy of the probe’s attenuation factor. Two probes with a 1% accuracy

specification can yield a CMRR as low as 50 to 1 at DC while the amplifier CMRR
may be higher than 100,000 to 1. At high frequencies, the CMRR is worse.

A differential probe pair must allow for matching at DC as well as over their
useful frequency range. Changing the compensation of a differentially matched
probe set without following the proper compensation procedure can result in a
significant decrease in the CMRR capability of any differential probe pair.

It is considered good practice to compensate a probe pair for a given amplifier
and then keep the probe pair and amplifier together as a system. Similarly, it is

important that once a probe is compensated for a given amplifier, the respective
probe always is used on the same input (meaning, one probe always used on the
+INPUT and the other always on the –INPUT).

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Probe Grounding

The DXC100A Probe Pair is supplied with accessories allowing for three probe
ground connection methods.

In most cases, when the common mode portion of the signal consists mainly of
low frequencies (1 MHz and below), the probe ground leads should not be
connected to the ground of the circuit under test. Instead, they should be
connected to each other to minimize the effects of ground loop currents. The
signal corruption caused by not having the probes connected to the ground of
the circuit under test is common to both inputs and rejected by the differential
amplifier.

However, when working in an environment with high RF ambient noise, it is best
to connect the probe ground leads to a good RF ground near the point where
the signal is being measured.

The best way to determine which probe grounding technique should be used is
to try both methods and use the one that provides the least corruption of the
differential signal. Probe tip to BNC adapters are required when adjusting the
compensation and probe CMRR as they provide the best performance of the
three grounding methods.

Short Calibration Procedure

There are two situations where the Short Calibration Procedure is appropriate:

 When the probe calibration status is unknown or it has been a long time

since the probe has been calibrated. A small difference between the two
probes can result in a significant CMRR loss, even though the error may

be so small that it’s irrelevant to transient response. This makes it rather

important to occasionally check the CMRR performance of the probes.
This can be done by performing Part 1 and adjusting as needed.

 When critical measurements are required. We recommend checking the

DXC100A CMRR by performing at least Part 1 of the short procedure.
When very high slew rate signals (>1V/ns) are encountered,
performance can be enhanced over that of a full calibration procedure
done with commonly available pulse generators. Notice that the Short
Calibration Procedure is the last step in the Full Calibration Procedure.

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DXC100A Differential Probe Pair

Once you are accustomed to making these adjustments, they become quick and
easy. Part 2 can be attempted when high slew rates (>1V/ns) are encountered,
and/or when high frequency (time constraints less than 20ns and frequencies
greater than 1MHz) CMRR is especially important.

Note: Do not change any of the adjustments associated with the +INPUT. Doing
so requires checking the changed adjustment, and perhaps doing the entire Full
Calibration Procedure.

Refer to Figure 1, The DXC100A Board Layout for the location of adjustments,
and to the schematic diagram in Figure 2, The DXC100A Schematic for guidance.
Both figures can be found at the end of this manual.

Part 1

1. Set the oscilloscope sweep speed to 10μs/div. Connect both probe tips

to the same point in the circuit where a measurement is to be made,
and set the DA1855A GAIN, ATTENUATOR and INPUT COUPLING controls
to the same settings to be used in the measurement. Be sure the signal
used does not exceed the maximum common mode voltage allowed
(e.g., 155 volts with 10X and DA1855A ATTENUATOR set to X1).

2. Set the DXC100A to 10X. Adjust C8 (-X10 LF) so as to minimize the total

deflection.

3. Set the DXC100A to 100X. Adjust C18 (-X100 LF1) so as to minimize the

total deflection.

Part 2

4. Set the oscilloscope sweep speed to 20ns/div. Now, set the DXC100A

ATTENUATION to X10. Adjust R2 (-X10 HF1) and R8 (-X10 HF2) so as to
minimize the total deflection.

5. Set the DX100A ATTENUATION to 100X. Adjust R18 (-X100 HF1) so as to

minimize the total deflection.

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