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ADS1299EEGFE-PDK: Data on GUI have gain error

Wei Wang
Prodigy 20 points
Part Number: ADS1299EEGFE-PDK
Other Parts Discussed in Thread: ADS1299

Tool/software:

I'm outputting sine waves of various amplitudes into the ADS1299 development kit and I'm seeing a discrepancy between the output and the measured waveform amplitudes.

Specifically:

  • The measured waveform amplitude is consistently ~1.8× larger than the expected amplitude across multiple tests (e.g., 1 mV and 10 mV sine waves at both 5 Hz and 20 Hz).
  • However, when outputting a ~300 µV amplitude sine wave, the discrepancy increases, and the measured amplitude becomes ~2.4× larger.
  • Changing the PGA gain settings (1 to 24) appears to have no effect on the measured amplitude.

The jumper configuration follows the factory default and the setup described in Section 4.6.2: Single-Ended Inputs of the datasheet.

I've attached a file of my register settings for reference. 

Any idea what might be causing this consistent gain offset or lack of PGA response? Thanks in advance.5315.Device_0_Analysis.xls

5315.Device_0_Analysis.xls

  • +1
    TI__Guru 66466 points

    Hello Wei,

    Thank you for your post.

    It may be that the common-mode voltage is out of range. The expected input common-mode is equal to mid-supply. If you are using the default jumper settings, this means that AVDD = 5V and AVSS = GND. Therefore, the sine wave input signal should be centered around 2.5V. Additionally, the negative channel input should also be connected to the same 2.5V offset, such that the differential measurement is centered around 0V. Ensure that ground of the EVM is shared with your function generator and DC offset supply source.

    Regards,

    Ryan

  • 0 in reply to Ryan Andrews
    Prodigy 20 points

    Hello Ryan and thanks for your response,

    I followed those instructions but the PGA setting on the GUI is still non-responsive. 

  • +1 in reply to Wei Wang
    TI__Guru 66466 points

    Hi Wei,

    You mentioned that sweeping the gain from 1 to 24 has no effect - are you by chance viewing the data in the GUI plot windows with "Analysis Data is Input-Referred" selected?

    Would you be able to export the captured raw data for two different gains along with the settings used by the ADS1299?

    Regards,

    Ryan