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Sample and Hold Circuts

Discussion in 'Electronic Design' started by Sunil, Feb 16, 2008.

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  1. Sunil

    Sunil Guest

    hi, i was reading about sample and hold circuits and i dint quite
    understand a few sentences......it said that s and h ckts are not
    required for low speed signals while they are of the utmost necessity
    for high speed circuits. can someone explain y?
    thanx
    sunil
     
  2. D from BC

    D from BC Guest

    A slow moving turtle is easy to capture. It doesn't move much and one
    can just run up to it and grab it.
    But if you try that with rabbits..You'll miss and miss and miss..
    So you set out a trap (sample).
    Once trapped, the rabbit is 'holding' and that gives you time to do
    whatever.


    D from BC
    British Columbia
    Canada.
     
  3. Tim Wescott

    Tim Wescott Guest

    Because whatever follows the sample and hold needs time to do it's job on
    the measurement. Most commonly, the thing following will be an ADC, and
    you want to (a) sample at a well-controlled point in time and (b) give
    the ADC time to do a conversion. A successive-approximation converter
    goes through several steps that need to happen when the input voltage is
    constant, if the input signal moves significantly during this conversion
    period then the measurement will be confused.

    Note that life is more complicated than this: Few ADCs require sample-
    and-hold circuits these days. Unless you're doing something special with
    a special ADC chances are that the ADC has a built-in sample & hold
    circuit, or is a switched-capacitance type that incorporates the sample &
    hold function into the fabric of the A to D conversion.

    --
    Tim Wescott
    Control systems and communications consulting
    http://www.wescottdesign.com

    Need to learn how to apply control theory in your embedded system?
    "Applied Control Theory for Embedded Systems" by Tim Wescott
    Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html
     
  4. donald

    donald Guest

    Tims very good response cut.

    I am going to save questions like these for the next project I get, that
    says they want to take their project off-shore.

    If guys like this can not figure out these functions in the classroom,
    what good will they be on a real project/product.

    My $.02

    donald
     
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