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AFE4404: PPG signal reversal

Part Number: AFE4404


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.