How to reduce Over-shoot and Under-shoot Problems?

Discussion in 'General Electronics Chat' started by muthukumar_ece2004, May 26, 2011.

  1. muthukumar_ece2004

    Thread Starter New Member

    May 20, 2011
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    Hi,

    Over-shoot and Under-shoot effect mostly occur in digital gates, sometimes it may affect the noise margin of the gate and even damage the internal FET of the gate IC. My question is How to reduce or avoid this Over and Under shoots effects in Digital Gate ICs?
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    You can slow the rise and fall times of the signals by adding some resistance and capacitance at the gate inputs. This will limit your bandwidth too, of course.
     
  3. t06afre

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    May 11, 2009
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  4. Ron H

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    Apr 14, 2005
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    No, not for reducing overshoot on digital signal lines.
     
  5. creakndale

    Active Member

    Mar 13, 2009
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    1) Use a ground plane so there's a return current path directly above or below the signal.
    2) Is the undershoot/overshoot real? Measuring fast transition signals requires an exceptionally good scope probe ground lead. Use the shortest ground lead possible. Make sure the scope probe ground wire is making perfect contact with the clip (soldered to it) and the connection to the probe body is clean.
    3) Try grounding the probe to a different ground point to see if it makes any difference.
    4) Add a small series resistor as others have suggested.

    They make electrical ground leads that connect right next to the probe tip so to minimize scope probe induced ringing, under and/or overshoot. Here's an example.
    http://www.testpath.com/Items/Ground-Lead-117-256.htm

    creakndale
     
  6. Ron H

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    Apr 14, 2005
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    Long traces are transmission lines. In addition to the suggestions above, if the round trip delay of the line is more than the risetime of the signal, matching the source impedance to the transmission line impedance will reduce the ringing substantially.
    If the line fans to multiple destinations, this may not work well.
     
  7. muthukumar_ece2004

    Thread Starter New Member

    May 20, 2011
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    ok, if we are using oscilloscope to measure something means we ca use a valuable probe to avoid overshoot. But if it is not properly matched, then it may cause seriousness to the IC (either it may damage the IC).
     
  8. Ron H

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    Overshoot and ringing due to a long oscilloscope ground wire will not damage an IC, since it is strictly a measurement error. Overshoot due to a poorly terminated transmission line can damage an IC, or at least cause it to malfunction.
     
  9. nigelwright7557

    Senior Member

    May 10, 2008
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    Decoupling hasnt been mentioned yet.
    This is vital.
     
  10. Ron H

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    Apr 14, 2005
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    Very good point!
     
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