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AFE4404: AFE4404 Automatic Gain Control(AGC) algorithm

kim minseo
Intellectual 400 points
Part Number: AFE4404


Hi.

I am developing nRF52832 and AFE4404.

I'm measuring on wrist, but there's a problem that everyone has so much difference.

Some people come out well, some people don't..

Does AFE4404 have AGC function? Or do you have an algorithm like this?(The algorithm for changing Led current, OFFDAC, Gain values for each person..)

Thank you.

  • 0
    TI__Expert 6015 points

    Hello Kim, 

    We do not provide automatic gain control (AGC) for the AFE4404. However, using the EVM to test and validate different register configurations, following section '9 Application and Implementation' in the datasheet should lead to great performance. 

    You mention that the system works well on some, not so well on others. Could you share an example in our email thread?

    A reminder that wrist-worn applications can be tricky from other factors outside of the sensor + AFE configuration. Some external factors like wrist straps being too loose or too tight can cause poor signal fidelity. 

    Kind regards,
    Nick Z

  • 0 in reply to Nick Zahabizadeh
    Intellectual 400 points

    Hi.

    Thank you for your reply.

    Then, is there a PPG chip that provides AGC?

    Thank you.

  • +1 in reply to kim minseo
    TI__Expert 6015 points

    Hello Kim, 

    By AGC, do you mean Automatic Gain Control? This can be defined as a circuit that uses feedback to modify the output of a variable gain amplifier. 

    While we have programmable gain amplifiers in our AFEs, we do not have variable gain amplifiers that would use a control signal to enable AGC functionality, nor would this be needed or suitable for a PPG AFE. 
    (image courtesy of https://www.qsl.net/va3iul/Files/Automatic_Gain_Control.pdf )

    Or, if you're referring to a software implementation of automatic gain control, we do not provide algorithms. However, the programmable gain amplifier can select from a number of gain settings that are controlled by register, which means you could have some software control of the device. 

    Kind regards,
    Nick Z

  • 0 in reply to Nick Zahabizadeh
    Intellectual 400 points

    Hi.

    Thank you very much for your answer.

    Then what's the difference between AGC and Calibration_AFE4404.c in Firmware Source v1.5?

    Thank you

  • 0 in reply to kim minseo
    TI__Expert 6015 points

    Hi Kim, 

    AGC is a type of circuit relies on an analog, variable signal as a feedback input to dynamically change it's out. The AFE4404 does not have an AGC circuit. The Calibration_AFE4404.c will, through software, set configuration registers within the AFE4404 to change device behavior.  

    Kind regards,
    Nick Z