Influence of the clock's quality on setup's times

Discussion in 'General Electronics Chat' started by HyperText, Dec 4, 2014.

  1. HyperText

    Thread Starter New Member

    Dec 4, 2014
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    Hi,

    I'm searching for some material (papers, slides, books' chapters, etc.) that talks about the influence that the clock's quality has on setup's times and other timing charateristics.
    I've tried to search online, but I've not found much.

    I'd be very grateful if you could give me some direction :)

    Thanks in advance,
    Pierpaolo
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    What do you mean by "quality"? Does it meet the definitions (amplitude, Vil, Vih) on the data sheet of the logic part in question or not?
     
  3. HyperText

    Thread Starter New Member

    Dec 4, 2014
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    Yes, and I would consider also its "shape". As you can see in this figure:
    [​IMG]
    This signal clock has indeed a clock shape, but has some imperfections too (on the rising and falling edges, plus some additional noise). I've heard that these imperfections could lead to different output's timings for some logic (flip-flop, shift-register, etc.). I'm looking for confirmation by reading some papers, books, or anything.
     
  4. Papabravo

    Expert

    Feb 24, 2006
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    I've not heard or seen any material on clock shape having an effect on setup and hold times. Timing relationships between the inputs and the clocks produce what is known as metastability. A flip-flop enters a metastable state when the output cannot decide where it wants to go. The nasty thing about metastable states is that they persist for a non-determistic amount of time.

    http://en.wikipedia.org/wiki/Metastability_in_electronics
     
  5. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    That is a better clock than most of the ones I have worked with...

    The rising and falling edges go through the critical transition between LOW and HIGH (or vice versa) with no ringing. The little steps shown on the oscillograph are pixelation artifacts... The overshoot doesn't effect anything. What the trace does above Vih and below Vil matters not at all.
     
  6. crutschow

    Expert

    Mar 14, 2008
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    Some of that overshoot could be due to the probe not being properly compensated. Have you adjusted the probe compensation for a square waveform using the test square-wave signal?
     
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