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max operation frequency of a gate

Discussion in 'Electronic Design' started by [email protected], Feb 27, 2005.

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  1. Guest

    hi all ,

    if the prop delay of a gate is say 4 ns , then what is the max
    frequency that can be applied to the input it 1/Tpd...or is

  2. Andrew Holme

    Andrew Holme Guest

    You should also consider the impact of rise and fall times on waveform
  3. Andrew Holme wrote...
    Well, 1 / 2*Tpd would be closer.
    I agree, and this depends dramatically on the circuitry within
    the gate. But in general, even for unloaded outputs, I'd say the
    maximum frequency is below that predicted from the formulas above.
  4. mann!

    mann! Guest

    Im not so much concerned about the shape of the waveform ...what im
    trying to figure out is whether the input sampling window for a gate is
    the same as the rise/fall time ..or is it lesser?
  5. Fred Bloggs

    Fred Bloggs Guest

    You can apply any frequency you want to the input- just be sure you do
    not exceed the min/max voltage levels.
  6. mann! wrote...
    Gates don't sample, but flip flops do. They have a very small
    sample time indeed, compared to the propagation delay.
  7. Harold Ryan

    Harold Ryan Guest

    The positive delay can be different than the negative delay. Therefore, the
    max freq is 1/(Tpdp +Tpdn). This also assumes that the input is a square
    wave and not a ramp which it probably is.

  8. Rich Grise

    Rich Grise Guest

    The smart-aleck answer, of course, is that there is no limit to
    the frequency that can be applied at the input. The operative
    parameter, I'd think, would be the maximum frequency where it
    reliably functions.

    And actually, prop. delay doesn't say how fast the chip can
    switch from high to low (or l->h) - only how long it takes for
    that transistion to get from input to output.

    Isn't it in the data sheet?

  9. I read in that Rich Grise <>
    Yes, even I refrained from pointing out that you could shine a blue
    laser on the input pin. I decided that the OP didn't even know what
    question to ask, so I left it to others to enlighten, if possible.
  10. Pooh Bear

    Pooh Bear Guest

    The data sheet generally gives the answer ( for reliable operation ).
    Clock gates too fast continually and you're likely to overheat them (
    like overclocking cpus ).

  11. Jim Thompson

    Jim Thompson Guest

    You are probably going to have "complex" structures such as flip-flops
    in your system that will limit your fastest speed.

    In ASIC designs I evaluate the performance of a new process by setting
    up a long ring oscillator in PSpice, with worst-case devices, supply
    voltages, and temperature.

    Then I usually back off by a fudge factor of (typically) 4X as
    insurance ;-)

    ...Jim Thompson
  12. Paul Burke

    Paul Burke Guest

    Not quite true- a FF will read the state of the gate which conforms to
    its setup and hold times. It's worth noting that one or both of these
    can be negative- i.e. the time the state is actually 'read' could be
    slightly before or after the clock edge.

    It's also worth noting that inputs that DON'T conform can produce odd
    effects, like a transient pulse at the output- I remember falling over
    this in one of my first designs, had to change to a 74S74 instead of LS!

    Similarly, with logic gates, if it's not Schmitty, you can't say what
    the output will be if the Tr, Tf and state time are less than the
    propogation delay.
  13. But electronics relies on the movement of discrete (countable) charge
    units (electrons), AKA digital ;-))
  14. Jim Thompson

    Jim Thompson Guest

    Sure. At the noise floor level :)

    ...Jim Thompson
  15. John Fields

    John Fields Guest

  16. keith

    keith Guest

    At some point isn't *everything*?
  17. Is time granular?

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    existence changes dramatically, however, when only one additional
    dimension is opened in the first attention.

    "Right now on Earth the movement of the second dimension of time, what
    would be the fifth dimension, has been suspended 'temporarily' while the
    Mother and Father of Manifestation do the work of finding and rejoining
    with all of the trapped and lost Will in Creation. As Body, it is our job
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  19. John Larkin

    John Larkin Guest

    1e-44 seconds, roughly.

  20. keith

    keith Guest

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