Teledyne Lecroy DXC100A Manual de usuario

Operator’s

Manual

DXC100A

Differential Probe Pair

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.

922259-00 Rev A

February 2013

DXC100A Differential Probe Pair

2 922259-00 Rev A

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.

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

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.

Operator’s Manual

922259-00 Rev A 3

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.

DXC100A Differential Probe Pair

4 922259-00 Rev A

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).

Operator’s Manual

922259-00 Rev A 5

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.

DXC100A Differential Probe Pair

6 922259-00 Rev A

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.

Operator’s Manual

922259-00 Rev A 7

Full Calibration Procedure

If the probe pair has been repaired or is to be used on a DA1855A other than the

one it was originally calibrated with, the probe pair should be calibrated using

the following Full Calibration Procedure. The last step is to perform the Short

Calibration Procedure as needed for high slew rate signals.

Required Equipment

Equipment

Description

Differential Amplifier

Teledyne LeCroy Model DA1855A

or Equivalent

Oscilloscopes

150 MHz Minimum Bandwidth

Calibration Generator

Tektronix PG506A or Equivalent

DVM

HP 34401A or Equivalent

DC Voltage Generator

HP 6209B or other stable source of

150V and 300V

Probe Tip to BNC Adaptor (2)

Supplied with probes

BNC T Adaptor

Two female and one male BNC connector,

no resistors

COAX Cables (2)

50 Ohm

Termination, 50 Ohm

If oscilloscope has no 50 Ohm input

impedance

Termination, 75 Ohm

50 Ohm may be substituted

Trimmer Tool

Not supplied with probes

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.

DXC100A Differential Probe Pair

8 922259-00 Rev A

1. DA1855A and Oscilloscope Setup

Follow the sequence shown in the previous Short Calibration Procedure topic to

set up the DA1855A amplifier with your oscilloscope.

a. Remove the probe’s bottom cover and attach the probe to the

DA1855A.

b. Turn the entire DA1855A and probe to gain access to the adjustments.

NOTE: Do not attach the probe upside down and then reverse the

probes after they are compensated. Reversing the probes after they

have been compensated results in degradation of CMRR performance.

c. Set the probes to X10 attenuation.

d. Initialize the DA1855A to its power-up reset state by turning its power

off and then back on.

At this point, the DA1855A is in the following state:

Setting

Status

+Input

Off

-Input

Off

BW Limit

Full

Gain

Attenuator

÷1

Input Resistance

Precision Voltage Generator

+000.00

Comparison or Differential

Comparison

Effective Gain

÷100

e. Press the ÷1 Attenuator button on the DA1855A. The ÷1 Attenuator light

is now on.

f. Check that the DA1855A Effective Gain indicators change when the

probe is switched from 10X to 100X.

IMPORTANT NOTES ABOUT THIS STEP:

The DXC100A provides probe attenuation factor information to the

DA1855A through an 11” black wire which should be plugged into the

DA1855A Probe Coding Input jack on the DA1855A rear panel. If the

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