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how to achieve desired delay time in cmos inverter

Discussion in 'General Electronics Discussion' started by vead, May 21, 2014.

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  1. vead

    vead

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    Nov 27, 2011
    what should we do to achieve specific delay
    just for example ( 215 ps)

    I think I need following thing but its not all I am missing some
    1.power supply
    2.threshold voltage for nmos
    3.threshold voltage for pmos
    4.load capacitance

    please anyone tell me what should we do to achieve 215 ps delay
     
  2. duke37

    duke37

    5,364
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    Jan 9, 2011
    I had a look at the delay of a 4001 chip, this was given as 60ns. I do not see how CMOS can get down to 215ps.

    The speed of light is 300E6 m/s so you could use a short delay line and subtract one delay from another.
     
  3. BobK

    BobK

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    Jan 5, 2010
    Well, modern microprocessors are all CMOS and run at frequencies as high as 4GHz which is a 250 ps clock cycle, so they must have gate delays of well under 215 ps.

    Bob
     
  4. vead

    vead

    473
    14
    Nov 27, 2011
    can anyone explain little bit how to achieve delay time
     
  5. BobK

    BobK

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    Jan 5, 2010
    Are you talking about in fabricating an IC or using existing CMOS logic ICs?

    Bob
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    1ps = 0.3mm at the speed of light. Let's assume half of that in coax. so 215ps will require a piece of coax 32.25mm in length.
     
  7. vead

    vead

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    Nov 27, 2011
    cmos lo
    CMOS logic ICs?
     
  8. BobK

    BobK

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    Jan 5, 2010
    Bob: Why do you answer a question with a question?
    vead: Why not?

    Bob
     
    Allen Bong likes this.
  9. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    To do this with a CMOS Logic IC, you buy a hex inverter and a piece of wire 60mm in length.

    You then discard the CMOS logic IC and connect the wire between the two points, trimming it to achieve the desired delay.
     
    Allen Bong likes this.
  10. BobK

    BobK

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    Jan 5, 2010
    Except that it wont be inverted.

    I think he is asking not asking about using existing logic chips, but rather about design logic chips that would have that gate delay.

    Bob
     
  11. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    The signal becomes inverted by altering the definition of a logic 1 and 0 at both ends of the wire. The use of inverted logic at one end solves that problem very neatly.
     
  12. vead

    vead

    473
    14
    Nov 27, 2011
    suppose we are designer and our inverter circuit need 215 ps delay time

    If I know following thing then can I achieve desired delay time
    1.power supply
    2.threshold voltage for nmos
    3.threshold voltage for pmos
    4.load capacitance

    how to think and what should we know to achieve 215 ps delay as designer?
     
  13. BobK

    BobK

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    Jan 5, 2010
    This is where I am having a problem.

    Bob
     
  14. JimW

    JimW

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    Oct 22, 2010
    You can never build a chip that will have 215 ps propagation delay (unless it is a coincidence). The prop delay will change over time, output load, temperature, supply voltage, different production runs, and probably a few more variables. As a designer, you could build (design? specify? imagine?) a chip that has a maximum propagation delay of 215ps. And that max delay would have to be specified into a certain capacitive and resistive load. Strict controls on the active high and low thresholds would be key, I would think. That and output drive parameters. Having gates internal to a chip with that short a delay is reasonable. But a packaged inverter with that kind of speed? A whole lot tougher. Consider ECL instead of CMOS.

    Never built a production chip, just used the fast ones, so any specifics are beyond me.

    JimW
     
  15. vead

    vead

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    Nov 27, 2011
    I am not going to design real chip. I just want to learn method, how does chip design
    I have made temporary specification for inverter If you want to see I can post here
     
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