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AFE44I30: Calibration for the Automatic LED DC Cancellation

Jonathan Fisher
Prodigy 30 points
Part Number: AFE44I30

Hello,

I am working to implement the "8.3.5.3.2 Calibration for the Automatic LED DC Cancellation" from section 8.3.5.3.2 in the datasheet. However, I believe I am doing something incorrectly, as the code words I get back appear to be wrong, at times.

For instance, the values I read from the FIFO are: 16529817, 16529698. This leads to a calculation of:

CALIB_AACM_LOOP: 0x000fff
CHANNEL_OFFSET_AACM: 0x001e1c

However, at other times, I get more "correct" sounding numbers, in the low thousands. For example, I've also seen 4743, 4721 from the FIFO, which leads to:

CALIB_AACM_LOOP: 0x000fff
CHANNEL_OFFSET_AACM: 0x000009

Is there a way to check that I've followed the steps properly for this calibration? For instance, I'm not certain that I'm correctly setting IOFFDAC_PH and USE_AMB_DAC_FOR_LED.

Thank you,

Jonathan

  • 0
    TI__Expert 4614 points

    Hello Jonathan, 

    Welcome to the E2E design forum! 

    Is this on the AFE44I30EVM or your own board? Additionally, could you share the output waveform when testing PPG?

    I would like to highlight section 9.2.2 Detailed Design Procedure in the AFE44I30 datasheet, as it has useful guidelines to ensure you can get the best results possible. 

    Kind regards,
    Nick Z

  • 0 in reply to Nick Zahabizadeh
    Prodigy 30 points

    Hello,

    This is on the AFE44I30EVM. When you say the output waveform, I assume you mean running with the normal phase definition, not the calibration one?

    Here's the output waveform with the calibration applied:

    <Image removed>

    And a waveform without the calibration applied:

    <Image removed>

    I've attached the output of the spreadsheet tool for generating the settings.

    Thank you,

    Jonathan

    EDIT: Settings removed

  • 0 in reply to Jonathan Fisher
    TI__Expert 4614 points

    Hi Jonathan, 

    It seems like your PPG waveform is inversed from what a typical PPG waveform should be. This is why the dicrotic notch is showing up on other side of the peak. 

    One common cause for odd PPG waveforms is ADC saturation, so reducing gain and/or offset should help. This would throw the AACM calibration loop off as well, so let's see what we can do about the raw PPG signal itself before the cancellation loops. 

    Alternatively, you could invert this digitally by subtracting the raw data from the some fixed threshold level and see what the output is like.

    Kind regards,
    Nick Z

  • 0 in reply to Nick Zahabizadeh
    Prodigy 30 points

    Hello,

    Regarding the inversed waveform - I've attached the PPG settings I'm using for this post, and a screenshot of the Eval Kit document (Fig 3-7 in slau828.pdf), which to me looks relatively the same?

    PPG Readings (TIA1-3 - units are in mV)

    <Edit: Image removed>

    Screenshot of the eval kit user guide:

    <Edit: Image removed>

    Settings: <EDIT: Settings removed>

    Thank you,

    Jonathan

  • 0 in reply to Jonathan Fisher
    TI__Expert 4614 points

    Hi Jonathan,

    Since this is a restricted device, as we're getting deeper in the weeds I'll need us to move this conversation offline. 

    I just sent you an email. 

    Kind regards,
    Nick Z