Drift of Signal Generated by PXIe-5451 in Certain Frequencies

Updated Jul 21, 2023

Reported In

Hardware

  • PXIe-5451

Issue Details

I am generating a signal with a PXIe-5451 (400 MS/s), but a drift around 3 ns appears after measuring with an oscilloscope, that has 40 GS/s. This drift is appearing only for certain signal frequencies that are not a multiple of the clock (13 MHz for example). When it is a multiple (10 MHz for example), no drift is happening.
See example of the drift for 13 MHz square waves here:
Square_1Vpp_13M.png

Solution

The problem is the number of samples generated each second.
Indeed, for 12 MHz for example, the number of samples is not a round number (33.33 samples) so the samples will be for 1 period of 33 or 34, creating a 2.5 ns drift. This drift is easier to see with square waves as it is a less continuous shape than a sine wave, but the drift exists for every shape, and so there is loss of information in this case. The solution is to have lower frequencies for less drift or to have a round number of samples.

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