AFE4404: SPO2 measurement

Bruce li

Part Number: AFE4404

Dear TI Expert,

One of my customer has finished prototype based on AFE4404 for SPO2 measurement , they have encountered below two questions,

1) When measuring on same person's different wrist's position, they found that the radio of DC value of Red Vs. IR were changing. This will influence the stability of measurement. How can they adjust some parameter to eliminate this influence?

2) some times, AC signal is very weak, and when amplifying the AC signal by increasing TIA_GAIN, once approached 100K gain, the DC value of IR will be saturated(closed to 2^21). How can they accomplish higher gain than 100K without saturation of IR's DC value?

Thanks a lot.

over 7 years ago

0 Praveen Aroul over 7 years ago

TI__Mastermind 49946 points

Hello Bruce,

We have received your inquiry about the AFE4404 and hope to have some answers shortly.

0 Prabin Yadav over 7 years ago in reply to Praveen Aroul

TI__Genius 12575 points

Hi Bruce,

Usually the DC of the heart rate signal can drift due to some biological phenomenon and it is called DC wandering.
This kind of drift can be removed in the MCU by implementing a digital DC removal filter ( i.e. HPF ).

The DC of IR signal ( or any other signal) can be removed by using AFE4404's offset cancellation DAC. Typically an algorithm is needed in the MCU that tracks the DC of all the phases and applies the correction to cancel out the DC as much as possible. With the DC cancelled the TIA's gain can be increased to amplify the AC signal.

Regards,
Prabin

0 Bruce li over 7 years ago in reply to Prabin Yadav

Genius 5580 points

Dear Prabin,

Thanks a lot for your support.

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AFE4404: SPO2 measurement