PPG signal processing circuit, please help analyze it

blade1080

PPG signal processing circuit, please help analyze it [Copy link]

This is the original circuit diagram: After redrawing, it looks like this: The SON1303 in front is a heart rate sensor, and its output is a current signal. The first op amp feels like a filter, but its specific function is unclear, especially the structure where the input is connected to the same direction and reverse direction ends. In the second picture, C5 is connected to VCC and I don’t know what it is for. The second-stage op amp feels like a comparator, but I don’t know what the RC structure above is used for. I hope everyone can help me take a look, thank you!

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xiaxingxing

Why is the enable signal HRM_ENV in Picture 1 gone in Picture 2?