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ADS1292R: Abnormal frequency response test

Chu Allen
Intellectual 830 points
Part Number: ADS1292R

Tool/software:

Dear teams,

When conducting frequency response testing on ADS1292R, one of the inputs is a 2mV, 0.5Hz sine wave and a 2mV, 10Hz sine wave.

Based on 10Hz, the waveform amplitude at 0.5Hz should be within the range of -10% -5% of the 10Hz waveform amplitude.

As shown in the attachment, our test results are not satisfactory, but we have tested the 0.67Hz waveform and it is satisfactory.

May I ask what methods can be used to make this test pass?

  • 0
    TI__Guru 66466 points

    Hi Chu,

    Thank you for your post.

    Are you testing the two input signals on the same channel (one at a time), or are they tested on separate channels simultaneously?

    In the schematic, Channel 1 has a 10x larger capacitor on the PGA output. This will reduce the differential cutoff frequency (-3dB) to 840Hz. It is possible that the filter response begins attenuating signals at low frequencies just enough to affect the test results. Can you test both input signals on Channel 2 only (one at a time) and compare the results?

    Can you please explain what is the significance of this test?

    Regards,

    Ryan