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repeated data conversions

Discussion in 'Electronic Basics' started by Jon Slaughter, Jul 6, 2007.

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  1. I was wondering just how bad data is corrupted through repeated conversions.
    I have this idea to test it and was wondering how hard it would be to set

    Essentially you have a ADC, DAC, buffer, and control system.

    you initially setup the buffer with the required digital data.

    Then the buffer sends the data into the DAC and the DAC feeds the ADC which
    then goes back into the buffer. The control system handles all the necessary
    stuff and counts each time a full conversion of the buffer has happened.


    DAC -------> ADC
    ^ /
    \ /
    \ /
    \ /
    \ /
    \ V

    After the nth conversion(of the buffer) you can then compare the buffer with
    the original data and see just how different it really is.

    I'm wondering if such a system could be designed to handle virtually and DAC
    and ADC for testing purposes?

    Any ideas?

  2. "Information theory" says that every conversion gives you error of the
    least significant unit of measurement.
    No arguments on this! How many repeats of it will give you recognisable
    error from original depends on your setup.
    One way is to define the ending error and let the system repeat those
    cycles, counting them, till it gets there.

    Have fun

  3. Well, I don't know if thats information theory but the error is obviously in
    the least significant bits because that is how the devices work. The issue
    is how the error propagates. Also there is a difference between the
    mathematical representation of the error and what actually happens. i.e.,
    just cause you assume it is guassian distributed doesn't mean it actually is
    and I'm interested in what really happens rather than what happens
    mathematically(not that it can't be described mathematically but its much
    more complex that I care to deal with).

    Well, I want to actually see what happens... ideally I would take a snapshot
    after each step and I could then have a time series of how the error

    The reason I'm interested in this is because I have some things I'd like to
    do but they require going in and out of the digital domain many times and
    I'm not sure the signal will ultimately be affected to due the conversion
    process. For example, if the signal is dithered then how will that affect
    the outcome? with errors from the conversion process creep into significant

  4. Your guess is as good as mine, the converter cannot close one eye and/or
    tilt its head to "better" read the displayed value. It will simple guess
    depending of the size of the known to it smallest digit. For this
    accuracy the converter IS built, you want better accuracy use more
    smaller units in conversion or use statistics. Nothing is absolute.
    "Significant" means what percentage of the whole? On how many digital
    digits on what accuracy of the analog conversion against what reference.
    When looking for creeping errors it is good to have _very_ reliably
    performing setup.

    Good luck

  5. If you wanted to model the basic parameters (# bits, AWGN or other
    noise) of the system, you could probably model it in Simulink pretty
    easily. If you actually want to test physical parts, you could still
    use Matlab/Simulink to provide the original data, and to recirculate
    the data in digital form using the data acquisition toolbox, putting
    the current digital state into successive dimensions of a variable.
    Then you could plot the whole thing pretty easily. You'd just need to
    attach a supported digital I/O to the computer. Try a new ADC/DAC
    pair? Just hook them up and press run again.
  6. Rich Grise

    Rich Grise Guest

    When I was a kid, we used to do this with a tape loop. We'd say something,
    and it would echo, and echo, and echo, getting noisier, and noisier, and
    noisier until it was like listening to ocean waves.

    As far as your scheme, the only errors will be in the analog part.

    Have Fun!
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