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How to make DDS AD9854 output Phase-Coherent ?

Discussion in 'Electronic Design' started by [email protected], Apr 12, 2007.

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  1. Guest

    Dear all,

    I am new to DDS AD9854 and was wondering if you can help me with a
    specific problem not
    directly solvable.

    My main aim is to generate a simple chirp signal which should be Phase-
    Coherent. The standard output is Phase-Continuous. Does anyone have
    any suggestions how to do it ?

    Many Thanks.
     
  2. Phase coherent with what?
     
  3. Guest

    Dear John,

    In a chrip signal, the output goes from F1 to F2 and then back to F1
    at each I/O UD pulse. I want the phase to remain the same (or zero) at
    every transition from F2 to F1. This is what I mean by phase-
    coherent.

    Many Thanks.
     
  4. So, the phase behavior should be the same on successive chirps? It
    sounds as if you would have to synchronize the pulse that starts the
    transition from F1 to F2 with the state of the device, or reset the
    device, and it would have to behave stably enough during the chirp to
    keep the phase from deviating at F2. If you also mean that the return
    from F2 to F1 must begin at zero absolute phase, then the length and
    rate of change of the chirp would have to be controlled as well. I'm
    not familiar with the device you mention, but logic would seem to
    require synchronization.
     
  5. Guest

    Thanks John for your help. Yes I think synchronization would be the
    answer.

    But instead of reseting the device everytime wouldn't clearing the
    Phase Accumulator be a better option?

    regards,
    Farrukh
     
  6. As I mentioned, I'm not familiar with it. Would resetting the phase
    accumulator make an instantaneous discontinuity? Does it have to run
    all the time, even when it's not chirping? Maybe detecting a certain
    state of the device and synchronizing the external request to that
    would be better than resetting or changing it. Good luck.
     
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