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ADPD6000 PPG Signal Polarity Flipping During Runtime (Not Constant Inversion)

Category: Hardware
Product Number: ADPD6000

Hi,

I am currently working with the ADPD6000 Kit for PPG signal acquisition (Green, Red, IR).

Observed Behaviour:

  • The PPG waveform polarity is not constant

  • The signal:

    • Sometimes appears as expected (systolic peak upwards)

    • Sometimes appears inverted (systolic peak downwards)

  • More importantly:

    • The inversion can change during runtime

    • It is also different across subjects and even between hands of the same subject

Example:

  • Red LED appears consistently inverted for some subjects

  • Green LED may be inverted on one hand but not the other

This behaviour makes it difficult to rely on simple post-processing inversion.

Questions:

  1. What could cause dynamic polarity inversion in PPG signals on ADPD6000?

  2. Are there recommended register settings or debugging methods to ensure stable polarity?

Could you please suggest:

  • Possible root causes

  • Debugging steps (register-level if possible)

  • Recommended signal conditioning approach

Thanks in advance!

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