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AFE4404: PPG signal reversal

kim minseo
Intellectual 400 points
Part Number: AFE4404

Hi.

I am developing PPG measurement with AFE4404 and nRF52832.

I'm getting PPG data from my wrist, and I have a question.

The picture below is my data, and from the top, it's Green, IR, and Red PPG

But most PPG look like the picture below (Google search)

Can you tell me why PPG data is reversed?

Thank you.

  • 0
    TI__Expert 4614 points

    Hi Kim, 

    You could invert this digitally by subtracting the raw data from the some fixed threshold level and see what the output is like. One common cause for odd PPG waveforms is ADC saturation, so reducing gain and offset may help as well. 

    Kind regards,
    Nick Z