Nonoverlapping clock generator

Discussion in 'The Projects Forum' started by andrea86, Sep 30, 2010.

  1. andrea86

    Thread Starter New Member

    Sep 30, 2010
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    Can anyone help me with nonoverlapping clock generator?
    Why are these clock nonoverlapped?
    I need an expalination.
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    With non-overlapped clocks you can use all of the edges without violating set-up and hold-time restrictions. If the clocks overlap then the leading edge of the next clock precedes the trailing edge of the previous clock.
     
  3. andrea86

    Thread Starter New Member

    Sep 30, 2010
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    I need an explanation why are clocks non overlapping?
     
    Last edited: Dec 16, 2010
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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    Perhaps you can post up the circuit?
     
  5. Wendy

    Moderator

    Mar 24, 2008
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    Older CPUs used to use them a lot, it was to keep data moving inside the CPU. Basically you make an oscillator, then add a simple phase shifter/Schmitt Trigger. Walla! Two separate clock signals that don't overlap. If you try to make two different oscillators this is almost impossible.
     
  6. beenthere

    Retired Moderator

    Apr 20, 2004
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    I question the 200 msec delay as stated. What is the master clock frequency and what devices are you using (by type number)?
     
  7. andrea86

    Thread Starter New Member

    Sep 30, 2010
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    I need a good explanation.
     
    Last edited: Dec 16, 2010
  8. beenthere

    Retired Moderator

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  9. andrea86

    Thread Starter New Member

    Sep 30, 2010
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    Thank you,bat that's not a question.I only need an explanation
    how does this circuits works,or why this circuit makes non-overlapping clocks?
     
  10. Wendy

    Moderator

    Mar 24, 2008
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    The answer is simple, phase shift. You have two identical frequencies (truly identical) which are shifted by some angular amount (which is why the RC circuit is there on the earlier replies).

    You are making this complex, more so than it needs to be.

    The circuits you are showing are depending on propagation delay of the chips. Over complicated, and there won't be much difference between edges, just enough.
     
  11. Kit_Leong

    New Member

    Dec 4, 2010
    5
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    to andrea86,

    Hello,Im using the same circuit u mentioned above for a 2 phase non overlapping clock signal http://tams-www.informatik.uni-hambu...-clock-gen.htm ,Im using it as a clock signal for my modulator/demodulator as I am doing a chopper stabilized bandgap reference circuit.Did you manage to get a non overlapping signal?I cant seem to be able to get it,I'm using mentor graphics for my simulation,attached is a picture of my waveforms and circuit,do you know why it is not overlapping?i already followed this schematic but still not getting the expected results[​IMG]

    if u cant see the picture i attached,try looking here <snip>
     
    Last edited by a moderator: Dec 4, 2010
  12. Kit_Leong

    New Member

    Dec 4, 2010
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    non overlapping clock.png

    non overlapping clock waveform.png

    The pictures I tried to attach in the previous message are here,thanks.
     
  13. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    It depends on understanding what limitations your simulation software has.

    Here is a simulation done the free LTSpice IV.

    [​IMG]
     
  14. Kit_Leong

    New Member

    Dec 4, 2010
    5
    0
    yea thats the same circuit you are using that i'm using as well,thats odd if a circuit can work on one software and not on another,currently I thought of something else but it seems too simplistic to work,though I did manage to get the expected results,what do you think of it?

    I tried to put a Vpulse signal to 1 output,and for the 2nd output,I added a slight delay to the Vpulse so its shifted just nicely to look like a non overlapping waveform.

    Is it ok to do this instead?but if it were that simple I dont think people will use more complicated circuits to get the job done now would they?Thanks.
     
  15. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
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    Anything that works for you works. :)
     
    Kit_Leong likes this.
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