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ADC reading flutuation

pooja trivedi
Intellectual 455 points

Other Parts Discussed in Thread: ADS1247

Hi,

I am using ADS1247 ADC for one of our project. When i use ADC at 20SPS it works OK. But when i use it at 80SPS or more than that with gain 1 reading is OK but spikes come in reading means ADC gives random count in between.

 Is these problem is related to noise? How can i remove this problem?

  • 0
    TI__Guru** 113765 points

    Hi Pooja,

    When you increase the data rate you also increase the bandwidth of the conversion.  Another thing to consider is the digital filter for the ADS1247 is FIR and the response changes with data rate.  Look at the filter responses starting on page 27 of the datasheet.  One thing that is often overlooked is aliasing.  High frequency content can fold back into the pass band.  This requires some sort of anti-aliasing filter on the input to the ADC.  Usually all that is needed is a single pole RC filter.  Do you have any filtering on the inputs of the ADS1247?

    Best regards,

    Bob B

     

  • 0 in reply to Bob Benjamin
    Intellectual 455 points

    Hi Bob,

    Thank you for your reply. Yes i have placed RC filter at ADC input of 159Hz. Reading of ADC is OK. But random value comes in between which creates spikes in output.

  • 0 in reply to pooja trivedi
    TI__Guru** 113765 points

    Hi Pooja,

    Again. take a look at the filter plots.  At about 159Hz, there is a pretty fast roll off of the digital filter at 20sps (~-60dB), but is well within the passband at 80sps.  At 80Hz data rate rate you can set the roll off much closer to 40Hz.  This should improve the noise performance considerably.

    Best regards,

    Bob B