AFE4404: PPG signal interference

kim minseo

Intellectual 400 points

Part Number: AFE4404

Hi, I am developing nRF52832 and AFE4404.

I am measuring PPG for three colors, IR, Green, and Red at the same time.

Green and IR come out clean, but Red always has noise and PPG waveforms are hard to see.

The picture below is measured and checked by Python plot

If we measure three PPG at the same time, will there be a problem of interfering with each other?

Or is my setting wrong?

Below is my setting (I only checked the register value by setting it to AFE4404, but I didn't use AFE4404 EVM)

Help me.

Thank you.

over 2 years ago

0 Nick Zahabizadeh over 2 years ago

TI__Expert 4184 points

Hello Kim,

I have a couple preliminary questions:
What is the y-axis on the graph with the waveforms?
If the y-axis is the output of the ADC, is there a why each waveform is fixed at 0, 1, and 2V?

In your configuration, which DAC offset row corresponds to which LED?

Kind regards,
Nick Z

0 kim minseo over 2 years ago in reply to Nick Zahabizadeh

Intellectual 400 points

Hi.

Thank you very much for your reply.

What is the y-axis on the graph with the waveforms?
If the y-axis is the output of the ADC, is there a why each waveform is fixed at 0, 1, and 2V?

It's an HPF that I can easily see and then sort it out. The value of y-axis is meaningless

The picture below is just regular raw PPG

In your configuration, which DAC offset row corresponds to which LED?

LED1 - RED, LED2 - IR, LED3 - GREEN

Thank you.

0 Nick Zahabizadeh over 2 years ago in reply to kim minseo

TI__Expert 4184 points

Hi Kim,

This will take a few hours to look over. I'll have a response within a day.
However, at a quick glance, looking at the DAC offset, you may be oversaturating the ADC. Could you check what the RED and IR would look like with a DAC offset closer to 0?

Kind regards,
Nick Z

0 Nick Zahabizadeh over 2 years ago in reply to Nick Zahabizadeh

TI__Expert 4184 points

Hi Kim,

Follow up questions as I'm looking at these waveforms. Is the y-axis the raw output code from the ADC? Is the x-axis milliseconds?

Kind regards,
Nick Z

0 kim minseo over 2 years ago in reply to Nick Zahabizadeh

Intellectual 400 points

Hi,

I set the DAC offset close to 0, but there was no significant change.

And y-axis is raw output code from the ADC, and x-axis is the number of data.

I measured 120 Hz & 30 seconds, so the x-axis is up to 3600.

Thank you.

0 Nick Zahabizadeh over 2 years ago in reply to kim minseo

TI__Expert 4184 points

Hi Kim,

What are you using for test data for the PPG waveform?
Could I see a schematic and layout for how you set up the AFE4404?

Kind regards,
Nick Z

0 kim minseo over 2 years ago in reply to Nick Zahabizadeh

Intellectual 400 points

Hi.

Thank you for replying.

I received the data from nRF52832 to I2C and sent the data to BLE to check.

Could you tell me your email address?

I will send you the schematic by mail.

Thank you.

0 Nick Zahabizadeh over 2 years ago in reply to kim minseo

TI__Expert 4184 points

Hi Kim,

Just sent you an email on the email associated with your myTI account.

Kind regards,
Nick Z

0 kim minseo over 2 years ago in reply to Nick Zahabizadeh

Intellectual 400 points

Hi.

I sent you a schematic by email.

Thank you.

0 Nick Zahabizadeh over 2 years ago in reply to kim minseo

TI__Expert 4184 points

Hi Kim,

Great, thank you, I'll need a couple days to look and will message you Monday via email.

Kind regards,
Nick Z

0 Nick Zahabizadeh over 2 years ago in reply to Nick Zahabizadeh

TI__Expert 4184 points

Hi Kim,

I've sent answers for your original post over email. Since the problem has been solved, I'll be closing this thread.

If you need any additional support, please follow up with me on that email thread.

Kind regards,
Nick Z

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AFE4404: PPG signal interference