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AFE4403EVM PPG baseline keep drifting up

nam huynh
Prodigy 35 points
Other Parts Discussed in Thread: AFE4403EVM, AFE4403

Hello,

I'm working on AFE4403EVM and doing some evaluation with GUI to extract PPG signal. I placed the sensor on the finger. The waveform I acquired is reasonably good I believe. However, the baseline keep going up as in the attached photo. I read on some previous posts and found out drifting is common in PPG and it requires some kinds of filter to reduce it. What I concern is that: should the drifting be periodic? like going up and down and repeat. Because my waveform only going up like forever. So I wonder if my signal is sensible. Thank you very much.

  • 0
    TI__Mastermind 49926 points
    Hello Nam,

    The continuous drifting seems odd. Is this repeatable?
    Could you cover the area around the sensor with black tape to provide electrical isolation and repeat the test?
    Could you also try to extract the PPG signal on another person?
  • 0 in reply to Praveen Aroul
    Prodigy 35 points

    Thank you Praveen. I tried and it gets better with periodic drifting. I guess I might push my finger to the sensor too strong last time.

    I have another question regarding PPG signal waveform. The waveform I got looks like a typical PPG signal except the order of diastolic phase (lower peak) and systolic phase (higher peak) reverse. I saw the lower peak happens first (when it's going up to the higher peak) then followed by higher peak, oppostite to what I expect according to most document. Do you have any idea on this? I guess maybe because PPG waveform is different between transmission vs reflection sensor? Thank you very much for your support.

    PS: I use sensor SFH7050

  • 0 in reply to nam huynh
    TI__Mastermind 49926 points
    Hello Nam,

    Please refer to my post below for an explanation on why you notice the PPG waveform inverted.

    e2e.ti.com/.../966236

    This is applicable to AFE4403 as well.