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AND Gate vs NAND Gate Propagation Time

Discussion in 'Electronic Design' started by Tam/WB2TT, Oct 29, 2007.

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  1. Tam/WB2TT

    Tam/WB2TT Guest

    Usually the NAND.
  2. Ecnerwal

    Ecnerwal Guest

    IIRC it's typically the NAND.
  3. D from BC

    D from BC Guest

    What generally has less propagation time. ?
    A 2 input AND or
    a 2 input NAND gate for a given series?

    I might have to dig up the datasheets for this...
    If anybody knows offhand, let me know..

    D from BC
  4. That used to be easy to answer. Gates were made of inverting elements
    (common emitter/drain transistor), and were unbuffered, so the inverting
    functions were faster (7400 vs. 7408, CD4011 vs. CD4081). However, it
    soon became common to buffer the inputs and/or outputs, sometimes even
    with 2 stages. There's no longer any general answer. A 74LVC08 is faster
    than a 74LVC00.
    Anybody who tells you that he knows offhand, should not be trusted :)
  5. Jim Stewart

    Jim Stewart Guest

    LOL and almost a coffee spew..
  6. Jim Thompson

    Jim Thompson Guest

    Yep. Pre- and Post-Buffering are now commonly used to "standardize"
    propagation times.

    ...Jim Thompson
  7. D from BC

    D from BC Guest

    Wow...I didn't know about the internal buffering spoiling the trend
    for NAND to have a shorter tp.
    I was rooting for NAND to be faster due to fewer transistors due to
    the already intrinsic inverting circuits to make the NAND topology.

    Things change... I suppose it's always best to not skip out on
    checking the datasheets.

    Thanks for responses everybody.
    D from BC
  8. Rich Grise

    Rich Grise Guest

    FWIW, that's pretty much what I was going to say. :)

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