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Comparator hysteresis using high resolution input signals

Discussion in 'Electronic Basics' started by MRW, Jul 19, 2007.

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  1. MRW

    MRW Guest

    Hi all! :)

    I really don't know how to word this question properly. From reading
    various comparator articles, it seems like any talk about hysteresis
    mentions a signal being affected by noise in the low millivolt range
    (1 mV or so). If I have a 100mV input signal and the trigger point is
    at 100 mV, then noise may get the input signal to bounce between 99mV
    and 101mV allowing the comparator to trigger on and off.

    If an input signal has a resolution of 1mV or 500uV, would adding a
    hysteresis to a comparator still make sense if the resistors in the
    hysteresis network contribute noise anyway?

  2. Andrew Holme

    Andrew Holme Guest

    Hysteresis means there are *two* trigger points: one for rising inputs and
    one for falling inputs. After the input rises above the higher trigger
    point, it has to fall all the way down to below the lower trigger point
    before the output will change again. Hysteresis is the margin between the
    two trigger points. As long as the hysteresis window is wider than the
    peak-to-peak noise amplitude, the output will not chatter.
  3. MRW

    MRW Guest

    Thanks, Andrew! I guess I'm still confusing the term.

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