propagation delay in logic gates

Discussion in 'General Electronics Chat' started by shiva kumar, Feb 3, 2012.

  1. shiva kumar

    Thread Starter Member

    Jun 27, 2008
    11
    0
    Hi,,I have a query regarding the propagation delay in a gate,propagation delay is generally measured between 50 percent points on the input and output waveforms, why cannot we measure it between 20% or 80% points on the waveforms ? Is there any specific reason for opting 50% points ??

    Regards,
    Shiva.
     
  2. MrChips

    Moderator

    Oct 2, 2009
    12,453
    3,371
    In theory, if the rise times and fall times are the same then it does not matter where you choose. You have to pick a common point somewhere and the 50% point is the best because the slope is at the maximum.
     
    shiva kumar likes this.
  3. holnis

    Member

    Nov 25, 2011
    50
    4
    It is possible to characterize various output transition times (e.g. 10%, 50%, and 90%) as a function of the input transition time, If it is needed.

    On the other hand and by definition: Propagation Delay, Is the time between a change in an input and a low to high (or high to low) change on the output. Measured from 50% point on input signal to 50% point on the output signal.
     
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