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ADC keeps outputting negative numbers, how?

Discussion in 'Embedded' started by Frank, Nov 28, 2005.

  1. Frank

    Frank Guest

    I have some digital waveforms, during the idle interval, it's zero, while in
    active
    mode, some patterns are output. This waveform is send through DAC (TI
    DAC290x-EVM) and ADC (Analog AD9218). I am expecting a clean
    zeros during the idle interval, however the ADC output are not. How can I
    correct this problem?

    Thanks in advance.
     
    Frank, Nov 28, 2005
    #1
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  2. Frank

    Thad Smith Guest

    How does it compare with the analog signal? What is the magnitude of
    your error? IF there an AC component to your reading during idle? If
    the error is small, it is probably system noise.
     
    Thad Smith, Nov 28, 2005
    #2
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  3. Frank

    Frank Guest

    Thank you Thad. I have a 4 channel oscilloscope and can see three ADC
    pins only. My digital signal is 20MS/s, 10us idle and 30us active. I channel
    of DAC is fed into oscilloscope and Q channel to ADC. From what I saw,
    during idle interval, bits 4,5,6 (0~9) have level changes during the idle
    and
    active interval.

    I am setting DFS/GAIN pin to low for ADC board, and the DAC's I channel
    waveform lies between -20mV~20mV (idle) ~ 0.8V(active) on oscilloscope.
     
    Frank, Nov 29, 2005
    #3
  4. Frank

    Frank Guest

    Thank you Thad. I have a 4 channel oscilloscope and can see three ADC
    pins only. My digital signal is 20MS/s, 10us idle and 30us active. I channel
    of DAC is fed into oscilloscope and Q channel to ADC. From what I saw,
    during idle interval, bits 4,5,6 (0~9) have level changes during the idle
    and
    active interval.

    I am setting DFS/GAIN pin to low for ADC board, and the DAC's I channel
    waveform lies between -20mV~20mV (idle) ~ 0.8V(active) on oscilloscope.
     
    Frank, Nov 29, 2005
    #4
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