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    Audio sigma delta ADC help on spurious interference.

    Hi, I'm working on a project about audio sigma . There are some spurious components in audio band(20Hz~20KHz) when the ADC is stimulated with no signal or small amplitude signal such as 10mVpeak-to-peak 1kHz audio signal while no other analog or digital modules can generates that low frequency (such as 2.3kHz, 10kHz) components on the same chip.
    I wonder what can cause these spurious components in audio band. Could anybody encounter such problems and give me some hints on it?

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    Re: Audio sigma delta ADC help on spurious interference.

    One of these references may help.
    Zapper
    Curmudgeon Elektroniker


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    Re: Audio sigma delta ADC help on spurious interference.

    THX, the link that you provided cannot be openned in my country for I'm in China whose goverment blocks Google for political reasons.
    But I've got your idea that you might think that the reason for the spurious components in audio band is due to limit cycle. However for high order SDM such as MASH 2-1 structure, would limit cycle be so problematic?
    When I stimulate the ADC with large signal such as -1dBFS or -3dBFS, the annoying compoents still exist. As a result, I don't think limit cycles give rise to my problem.



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    Re: Audio sigma delta ADC help on spurious interference.

    Limit cycles and and some spurios compnents are generated by design and can be reproduced in a simulation with ideal circuit elements, other interferences are caused by non-ideal hardware properties. You should be able to sort out which kind of interferences shows in your case.


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