Crosstalk in NI-6040E?

[Armánd]

Situation:
NI-6040E with connected to it a SCB-68

Problem:
When applying a square wave to one differential channel i see something that seems like cross talk on some but not all of the other differential channels. The the channels that display cross talk, have difference in amplitude.

Except for the one differential channel the others are grounded.

Has someone else got this problem or solved this?

[srm@viewpointusa.com]

by just grounding the other channels, you have not "forced" those values to anything. It may be a kind of reverse "charge injection". (look up charge injection on ni site). Say there is a 5V signal on the amplifier and you switch to a "grounded" channel. Where does the 5V get disipated too? try tying the grouded differential channels to analog ground through a 10k resistor and try again. This should produce a more ideal impedance for the mux. If this works, next point to look to is the quality of your signal generater. It must have low output impedance at high frequency (not just DC) in order to achive highes throughput. With non-ideal signal sources, you end up lengthing the interchannel delay to allow the mux to settle.