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Help with non-overlapping clock generator

Discussion in 'Homework Help' started by andrea22, Oct 12, 2010.

  1. andrea22

    andrea22 New Member

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    Hi everyone!
    Does anyone know to help me with non overlapping clock generator?
    I need to draw how non-overelapping clcks are made?
    I tried that but I can't get non-overlapping clocks.
    I need to draw signals at the output of each logic gate in this circuit
    Actually I need timing diagrams for Vin,V1,V2,V3,V4,V5,V6,V7?
    Logic gates are realised in CMOS technology and all logic gates have some delay.
     

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    Last edited: Oct 12, 2010
  2. Roff

    Roff Well-Known Member

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  3. andrea22

    andrea22 New Member

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    Thank you but I need to draw this circuit on the paper,actaully
    I need to explain how non-overlapping clocks are made,so I must
    draw that without LTSpice,Pspice...?
    What I ment I don't know how much is delay for each logic gate.
     
    Last edited: Oct 12, 2010
  4. dave

    Dave New Member

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  5. andrea22

    andrea22 New Member

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    Thank you but I need to draw this circuit on the paper,actaully
    I need to explain how non-overlapping clocks are made,so I must
    draw that without LTSpice,Pspice...?
    What I ment I don't know how much is delay for each logic gate.
     
  6. Roff

    Roff Well-Known Member

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    Gate delay is a function of the logic family, or if you are designing an IC, the process. For commercially available gates, look up gate delays in datasheets.
     
    Last edited: Oct 12, 2010
  7. andrea22

    andrea22 New Member

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    I think that you don't understand me.I need an explanation why
    these clocks are non-overlapped? I don't know what device are used (by type number),
    I only know that all logic gates are realised in CMOS technology.
    So I don't know how to draw signal at the output of first NAND gate,actually why on the diagram
    you were posted rise time and fall time (tphl i tplh are diffrent) of signal V1 are diffrent,but
    rise time and fall time at the output of the inverter are the same?
     

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    Last edited: Oct 12, 2010
  8. Roff

    Roff Well-Known Member

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    NAND gate rise and fall times in this simulation differ by less than a nanosecond. Exact transition times are not very important when analyzing this circuit. Propagation delays are the relevant numbers. The ones shown in the simulation are from models, and may not accurately reflect the datasheet values.
    If you were not given part numbers, I would think you could assign arbitrary propagation delay specs, and then analyze the circuit based on these specs. Alternately, pick a logic family, like CD4000, or 74HC, or whatever, and use those specs to analyze the circuit.
    My schematic has part numbers. The datasheets of these parts have propagation delay and transition time specs. What else do you need in order to analyze the circuit? Do you know how to analyze the circuit?
     
    Last edited: Oct 12, 2010
  9. andrea22

    andrea22 New Member

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    Well,now I am confused.
    Can you help me to analyze the circuit?
    I only need to draw that diagrams without using LTSpice,Pspice?
     
  10. Roff

    Roff Well-Known Member

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    What did I do to confuse you?
    Start the analysis when the clock goes low. Why? Because this will force node 1 low, independent of the other input to U1 (node 7).
    Plot nodes 2, 3, and 4.
    Calculate node 5.
    Plot nodes 5, 6, and 7.
    Calculate node 1.
    Repeat the process.
     
    Last edited: Oct 12, 2010
  11. andrea22

    andrea22 New Member

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    How can I draw node 2,3,4 without node 1,I don't understand that?
    In your simulations pulse width logic 1 of signal V2 is less then pulse width logic 1 of input clock V(clk)?
    Can you give me an example?
     
    Last edited: Oct 12, 2010
  12. Roff

    Roff Well-Known Member

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    First, let's agree that Tpd is the value of the propagation delay.
    When the clock goes low, node 1 will go high Tpd later. Node 2 will go low Tpd later. Node 3 will go high Tpd later, etc. Just proceed through node 7, which goes back to Q1. You will find that node 7 goes low. This means that node 1 will not change immediately when clk goes high. Q6 WILL be immediately affected when clk goes high. Trace that transition through nodes 5, 6, 7, etc.
     

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  13. andrea22

    andrea22 New Member

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    Ok,thank you.I wiill try that tomorrow and I tell you if I get results.
     
    Last edited: Oct 13, 2010
  14. andrea22

    andrea22 New Member

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    My questions is:How can you draw V4 on this way?
    In last diagrams which you posted nand gate and inverters have same propagation delay?
     
  15. Roff

    Roff Well-Known Member

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    V4 is clk, inverted and delayed by Tpd.
    Yes, I used the same Tpd for NAND and inverters, but that was for simplicity. You need to use the Tpd values specified for the devices in your circuit.
     
  16. andrea22

    andrea22 New Member

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    On that way in your diagrams will be that V4 and V1 are the same signals?
    That's not possible.
    There I 'm confused.How to draw V4 and V1 on way you posted?
     
  17. Roff

    Roff Well-Known Member

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    If Tpd for the NAND and the inverter are identical, V4 and V1 will look the same on the falling edge of clock, but not on the rising edge. You have to follow the process I outlined in post #11, and plot all signals through an entire cycle of clk. Do not try to plot both edges at the same time!
     
  18. andrea22

    andrea22 New Member

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    Does it mean that I must plot both of edges at the same time only for signal V4,but
    for signal V1,V2,V3,V5,V6,V7 must not.
     
  19. Roff

    Roff Well-Known Member

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    You can plot clk and V4 first, over a couple of cycles if you want, because clk is independent, and V4 is only dependent on clk.
     
  20. andrea22

    andrea22 New Member

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    Thank you.I wiill try that now.
     
  21. andrea22

    andrea22 New Member

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    I tried everything you said,but I always get overlapped clocks.
    I don't where is my mistake.I am desperate.
    I can't get non-overlapping clocks.
    Can you help me with that,I need that for tomorrow?
     
    Last edited: Oct 13, 2010

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