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ADS1282EVM-PDK: ADS1282EVM-PDK

Shane Morris
Prodigy 30 points
Part Number: ADS1282EVM-PDK
Other Parts Discussed in Thread: ADS1282, ADS1283

When testing for min noise out of ads1282 with inputs shorted on evm the residual DC is modulating the very lowest FFT bins , how do I stabilize the DC to be a non factor?

  • 0
    TI__Mastermind 18900 points

    Hello Shane,

    Can you share a picture of the FFT with us? I'm not sure what you mean by modulating the lowest bins. Do you mean the DC content is spreading into the nearby bins in the FFT?

    Best,

    -Cole

  • 0
    TI__Mastermind 18900 points

    Hello Shane,

    I did run this past some of the team and, assuming the test set up is good and there's no misinterpretation of the data, the a likely but unique cause could be idle tones wrapping around back into the low frequency bands. We have some recommendations of adding some resistors to add additional offset within the ADC to get rid of the idle tones. You could check this out however, I think there are some other things to rule out first.

    Any combination of 1/f noise, offset, or FFT windowing could be contributing to this. Here's a few things to try and to see if this improves or eliminates the modulating you could be seeing.

    For the windowing and general FFT, I suggest you increase the number of samples you are taking dramatically before running the FFT analysis (such as >500k samples). 

    For offset and or DC, you could change to FILTR[1:0] = 0b11 so that the HPF block is enabled.

    For 1/f noise, you could enable CHOP = 0b1 so that we drastically reduce that.

    If you systematically go through and check which option does or does not help with what you're seeing, then you should get an answer. Of course, if all of these fail, you could look into the idle tone fix we recommended above. Note, this kind of offset correction for idle tones was incorporated in the ADS1283 as a selectable register.  

    Best,

    -Cole