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External clock for Analog to Digital Converter

Discussion in 'Electronic Basics' started by Bilal Amin, Feb 27, 2007.

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  1. Bilal Amin

    Bilal Amin Guest

    Hi Everyone,
    I am working on Jitter in Analog to Digital Converters(ADCs). I am
    trying to setup an experiment to see the effects of jitter in real
    time ADCs. I have an ADC evalutaion board with external clock input
    for sampling (i.e Sampling clock).
    Now I want to produce a self created jittery signal to see the effects
    of jitter in ADC. Can anyone out there have any idea(s) how I can
    produce a real time clock signal with "variable jitter" for the input
    of external clock? Producing a simple clock signal (i.e. without
    jitter) is straight forward with the help of any signal generator but
    a clock signal with "variable jitter" is a problem.

    Thanks for your help.


  2. Bob Masta

    Bob Masta Guest

    This may be a whole lot easier than you think, depending
    on how much jitter you need. If you simply add the good
    clock signal and some other modulating signal through a
    simple resistive mixer into the input of a logic gate, the
    modulating signal will bias the clock to hit the gate threshold
    earlier or later than otherwise. Works best if the clock
    has slow edges, which you might want to encourage
    by a bit of capacitance at the gate input.

    If you want a modulating source with plenty of
    options (uniform white, pink, gaussian, band-limited noise,
    standard waves, arbitrary waveforms, AM, FM, bursts,
    sweeps, etc) you can use the sound card signal generator
    in my Daqarta package. (Daqarta is shareware, but the
    signal generator keeps working after the trial period so
    that part is effectively freeware.)

    Best regards,

    Bob Masta

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    Scope, Spectrum, Spectrogram, Signal Generator
    Science with your sound card!
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