I am using the ADS1299 to read EEG signals and during a recording session of 4 or more hours a second phase shifted signal is introduced into the recorded sampled data.
This can be seen below. It looks like a square wave superimposed onto the original signal. This happens for a few minutes and then does not show up again for a while.
I am wondering if this could be introduced from clock jitter or SPI data read timing offsets.
Does anyone have any input on how I can solve this?