Our first pass at transferring over from the CN0540 example onto our own board for sampling IEPE accelerometers has an issue.
This is the fft of the data sampled at 256kHz.
The data in the low frequencies we know should be there. It looks great.
Strange data with a peak around 1/8 Sample Rate or 32kHz:
Strange data with main peak around 1/8 Sample Rate X 2 or 64kHz:
Strange data with main peak around 1/8 Sample Rate X 3 or 96kHz:
We get the same results regardless of the sample rate. Erroneous data shows up in the signal at 1/8 SR and harmonics, which makes us think that it is likely due to something wrong with our board layout.
We are using multiplexors in order to be able to sample more channels, but we tested these with the CN0540 and they worked great, so we are thinking it is likely our layout.
We also had to replace a few components to get the boards produced at a reasonable price, it could be that, but we are unsure.
Attached are the schematic and layout details.
Thank you in advance for any help you may be able to provide!
