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ADS8862: Noise on ANIP

Hao Wang14
Expert 4415 points
Part Number: ADS8862


Hi Team,

We have designed a circuit for ADS8862(it should be ADS8862 in the schematic) as shown in the picture below:

We found that there is noise on Vainp, which has the same frequency with sampling frequency(100kHz).

However, when R2 is removed and connect Vopa_out to Vainp directly, there is no noise.

Could you help analysis why this happens? How can the noise be filtered or where can we improve? Thanks

Best Regards,

Hao

  • 0
    TI__Mastermind 47650 points
    Hello Hao,

    If I understand your question correctly, I would expect to see charge kickback on the AINP pin for each acquisition/sample. The charge bucket filter made up of R2, R3, and C6 is intended to supply 1/2 of the charge to the internal ADC sampling capacitor, and will droop for each sample. The amplifier will then replenish the total charge, but at a slower rate. I expect to see this behavior, but not such a large droop. I also do not expect to see the noise 'go away' when you short R2.

    Are you taking multiple samples every 4-5mS? If you are taking multiple samples, what is the sampling rate during this period of time, 100ksps? Can you measure/confirm the value of R2 and R3? I would expect to see this behavior with 10kohm resistors, not 10ohm.

    Regards,
    Keith N.
    Precision ADC Applications