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AFE4404: Question about AFE4404

Part Number: AFE4404

Hello TI experts,

My customer considers AFE4404 for their new product, wearable smart wrist band.

and they want to know the answers about 2 questions below.

1. they will use photo sensor which is same as AFE4404 EVM. (NJL5513R - NJR)

is it okay that photo diode locates any position of wrist? (front of the wrist or back of the wrist)

2. How about the layout length of photo sensor? if the photo sensor is positioned back of the wrist, we have to use additional cable to connect photo sensor and AFE4404.

Does it affect to the quality of signal? (for example. lots of noise if the length is too long or something)

Please check these 2 issues. Thanks.

Best regards,


  • Hi Chase, 

    1. Skin directly on top of bone generally performs worse than skin muscle or veins underneath it. Therefore, the bottom of the wrist has more capillaries for effective PPG signal acquisition. Please note that the photodiode placement needs to avoid crosstalk with the transmitter LEDs, so some optical placement testing is highly recommended. 

    2. A cable can couple to environmental noise, so it's recommended to reduce the length of the analog inputs to the AFE as much as possible. 

    Kind regards,
    Nick Z