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Latches, Flip flops and Timers

Discussion in 'Electronics Homework Help' started by vick5821, Apr 28, 2012.

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  1. vick5821


    Jan 22, 2012
    Hey guys, what is the difference between set up time and the propagation delay (tPLH and tPHL) from clock to output ? Anyone can help me to make me clear about it ? Thank you
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    Setup time is the time the data inputs (e.g. D, T, J, K etc.) have to be stable befor the active clock edge. If the data inpit changes in a sjorter tiem (meaning nearer to the active clock edge) there is no guarantee that the flipflop will recognize the state as intended. In the extrem case a so called "metastable" state can be reached ( where is can take arbitraily long for the flipflop to settle into a defined state.

    Propagation delay, as the name says, is the time it takes for the input to propagate to the output. Or expressed in a different way: the time for the output of a flipflop to react (e.g. latch data, toggle state etc.) to the active clock edge.

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