Drop In Measured Voltage on a PXIe-4309 When the Signal Frequency Is Above 100 KHz

Updated Apr 27, 2023

Reported In

Hardware

  • PXIe-4309

Issue Details

I am trying to acquire a 1 Vp-p signal varying from 1 KHz to 200 KHz on a PXIe-4309. I can observe from my measurements that there is a gradual voltage drop over the 100 KHz frequency. I am sure that my signal source is generating the correct 1 Vp-p signal throughout. We are running the measurement at 2 MS/s sampling rate. What could be the possible reason for this measured voltage drop?

Solution

PXIe-4309 has an anti aliasing input low pass filter on each channel which prevents the high frequency undesired components to be sampled by the ADC. This filter has a gradual roll-off starting from 100 KHz to 1 MHz as depicted by the below Magnitude Response plot in PXIe-4309 specifications.

image.png

Hence, the drop in measured voltage beyond 100 KHz is the result of decrease in gain of the anti aliasing input filter. Also, the cutoff frequency of this filter is not user configurable and does not change with sample rate.

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