Oversampling ADC

Discussion in 'The Projects Forum' started by rakeshm55, Jun 24, 2011.

  1. rakeshm55

    Thread Starter Member

    Oct 19, 2010
    My ADC has a samploing rate of 15kbps. its a 10 bit ADC.

    ADC non - linear error is .5LSB

    I am using switching regualators for AVCC (Analog AVCC for ADC). But the reference signal (AVREF) is external and is clean(From battery source).

    My sensor output is a clean signal too with no noise.

    Now if i try over sampling and then decimation will i be able to improve the resolution of ADC??? say from 10 to 12 bit.

    My signal bandwidth is minimal. A slow rising signal much less than 1Hz.

    Can i try oversampling for improving ADC resolution. I believe that a noisy AVCC will add in adequate noise to ADC count reads.
    Will the oversampling work??
  2. MrChips


    Oct 2, 2009
    The answer is yes. You already appear to understand what you are doing.
  3. kkazem

    Active Member

    Jul 23, 2009
    In principle, you are on the right track, but oversampling followed by decimation per se will not really help you. Here is what I can add to the discussion:
    1) In order to improve accuracy, we must make some assumptions about the ckt first. We must assume that the noise is roughly Gaussian in nature, in other words, that it's symmetrical. We must also assume that your ADC converter error is roughly Gaussian as well, over the range of the converter you'll be using. And I recommend that you make the design such that you use as much of the dynamic range of the converter as possible, perhaps by amplifying the sensor signal or similar.
    2) In decimation, you basically throw-out samples (the literal meaning is keep the 1st, throw out the next nine, keep the 10th, but that will be our 2nd output sample, etc.). OF course, it need not be 10:1, but that illustrates the meaning. This will not help you. What you want to do is make use of the information in the '9' samples you would otherwise throw out by simply averaging the first '10' samples into the 1st output sample, avg the next 10 into the 2nd output sample, etc. Again, 10:1 need not be the ratio, but I'm trying to illustrate here. Since we assume gaussian noise, averaging will tend to average out the noise.
    3) Make sure you have a proper analog anti-aliasing filter in front of the ADC input to prevent artifact. Remember, even though your sensor may be very band-limited, from your post, there is noise present, likely with frequencies beyond 7.5 kHz (Nyquist Freq. in your case).

    I hope that helps and good luck.
    Kamran Kazem
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