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ADS1299: RTI Noise in ADS1299

Leonardo Sandler1
Prodigy 50 points
Part Number: ADS1299

Hello,

In our design  test RTI noise, in order to evaluate the floor noise of our electronic board. 
In this test, we short all inputs to GND, and we measure the noise on the digital outputs. 

We see a behavior that we don't completely understand.

As a result of this test, we see at the digital side a low noise P2P signal, but floating over a kind of DC level.
If the test run for enough time, the output can reach saturation. 

Although all input are shorted to GND, we still see this behavior. 

Is there any internal reason for this behavior ?

At our analog inputs, we have the typical input circuit:

Thanks.

  • 0
    TI__Guru 66186 points

    Hi Leo,

    Nice to hear from you!

    It sounds like there is some leakage current building charge on the input capacitors. Is the BIAS electrode also connected to the other input electrodes? Instead of shorting the input electrodes to ground, remove the ground connect and short the electrodes to the BIAS electrode. The BIAS should be able to sink/source any current required to hold the input pins near a mid-supply common-mode.

    Best regards,

  • 0 in reply to Ryan Andrews
    Prodigy 50 points

    Hi Ryan !

    Nice to hear from you as well !

    Thank you for your answer. In the past we tested doing short on all inputs, connecting them to RLD (and not to GND).

    The result was the same. 

    But we need to test removing the capacitor before the input to the ADC. 

    Will check and update you.

    Thanks !