Teledyne LeCroy DA1855A - Manual (Page 29)

Operator’s Manual
922258-00 Rev A 23
compensation procedure can result in a significant decrease in the CMRR capability of any
differential probe pair.
It is a good practice to compensate a probe pair for a given amplifier and then leave the probe pair
and amplifier together as a system. Similarly, it is important that, once compensated for given
amplifier, each probe always be used on the same input (one probe always on the +INPUT and the
other always on the –INPUT).
DXC100A Differential Probe Pair
The DXC100A is a high performance matched passive differential probe pair designed for use with
Teledyne LeCroy DA1855A series differential amplifiers. The probe pair consists of two well matched
individual probes that share a common compensation box to allow the attenuation factor on both
probes to be simultaneously switched between ÷10 and ÷100. When used with the DA1855A
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.
Probe Grounding
The DXC100A Probe Pair is supplied with accessories that allow for three methods of connecting
probe grounds.
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. They should be connected to each other. This minimizes the effects of ground loop currents.
The signal corruption caused by not having the probes connected to the ground of the circuit under
test will be common to both inputs and will be 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 gives the least corruption of the differential signal.
When adjusting the compensation and probe CMRR, the use of probe tip to BNC adapters is
required. They provide the best performance of the three grounding method.
General Operating Information
This section will help you become familiar with the operation of the DA1855A and how it interfaces
with an oscilloscope. To carry out the following exercises, you will need an oscilloscope and a
general purpose function generator.