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ADS1299 Spikes in data - double wave

Other Parts Discussed in Thread: ADS1299

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?

  • Hi Mike,

    Thanks for posting your question. More probable than not, your SPI timing may be drifting with respect to /DRDY. Over time, this drift might violate a critical timing spec that is causing your data to be corrupted.

    Is it possible to capture your SPI signals with a scope at different moments during your data recording? We should verify that all timing specs are satisfied and are not drastically changing over time. We would need to look at /DRDY, /CS, SCLK, and DOUT.

    Best Regards,

  • Hey Ryan,

    Thank you for the reply.

    The data is collected via an interrupt routine which is triggered by the /DRDY signal. It should be pretty constant with the rate at which /DRDY is toggled.

    I will see if I can sample /DRDY, /CS, SCLK, and DOUT for 5 - 8 hour duration with a logic analyzer.