increasing amplitude of one affects the other signal

[zebraa]

Hi,

I am using NI PXI 6070E. I was trying to acquire signals from 2 photodetectors using photodiode amplifier but saw one signal affecting the other. So to test what's going on I tried to use 2 function generators instead of the signal from my experiment : 1) triangular wave (+-1Volt)  2) Sinusoidal wave (+-4volts). Sampling rate=50kHz. When I increased the amplitude of the sinusoidal signal triangular got distorted as in the image. But when I decreased the sampling rate to 1kHz there was no such problem. Can someone please explain why increasing the amplitude affects the other signal? Thanks.. 

I did  find an article on ghosting effect but I couldn't get why it would be this hard to acquire two signals of different amplitudes.

[Alexander_Sobolev]

6070E does not have simultaneous sampling. There is a single ADC that switches between channels. This switch has capacitance that does not completely discharge between readings. That is why you do not see ghost image at low rate. Try to read 3 channels: +1 grounded channel between high and low amplitude real channels - this will allow capacitor to discharge after reading high value signal. 

Ch 0 - high amplitude signal

Ch 1 - connected to ground

Ch 2 - low amplitude signal

Then discard acquired data for Ch 1

It will reduce your maximum rate, but significantly reduce ghosts.