AND, NAND n OR, NOR gates

Discussion in 'General Electronics Chat' started by Triaca, Dec 15, 2012.

  1. Triaca

    Thread Starter New Member

    Dec 15, 2012
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    Among AND and NAND , OR and NOR gates, practically which would be preferable
    ?
     
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  2. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    How about the one that fits the circuit the best?
    You can build any circuit from either xors, nors or nands, or from AND and NOT gates, or from OR and NOT gates.
    Nands are sometimes used as basic building blocks, since they only use 4 transistors in cmos circuit. Nor uses 4 transistors as well.
    Without knowing what you´re building it is hard to tell. You could be talking about ASIC design or building from discrete chips..
     
  3. Triaca

    Thread Starter New Member

    Dec 15, 2012
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    em questioning about the time delays.
     
  4. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    Sorry what? Could you please use this cool new concept called sentence and ask something that makes more sense?
     
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  5. ScottWang

    Moderator

    Aug 23, 2012
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    You should post what you want to do?
    What's the input and what's the output?
    I don't think the members at here are the mind readers.
     
  6. JMW

    Member

    Nov 21, 2011
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    Welcome to the forum. In the olden days "N" type gates were preferred. The reason being is they would "sink" or pull down a voltage. If a short occurred no damage. Or's and And's "sourced" a voltage. If you shorted the output you toasted the IC.
     
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  7. crutschow

    Expert

    Mar 14, 2008
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    That's not true of any modern IC logic gates, of course. ;)
     
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  8. Austin Clark

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    Dec 28, 2011
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    If you just wanted to introduce delay in the signal, a BUFFER would be perfect. An EVEN number of NOT gates in series would work as well.
     
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  9. crutschow

    Expert

    Mar 14, 2008
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    If you want minimum delay then you need to look at the data sheets for a particular logic family. Generally AND and OR gates are slower than NAND and NOR gates because they have a stage added to invert the signal from the basic input NAND or NOR function.
     
  10. WBahn

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    Mar 31, 2012
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    Are you sure about that?

    How do you make an OR from nothing but XORs?
     
  11. WBahn

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    Mar 31, 2012
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    As others have indicated, NAND and NOR gates, as a rule, are faster and require less silicon area because they only use 4 transistors instead of the 6 required for an AND or OR (talking CMOS here). Between a NAND and a NOR, the NAND has an advantage because the NFETs are in series and the PFETs are in parallel. NFETs, for the same size, have better drive strength so you can use, roughly, the same size (i.e., minimum geometry) transistors and get a balanced circuit. With a NOR, you generally need to increase the size of the PFETs considerably to achieve this.
     
  12. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    You're right, XORs are not functionalluy complete like NANDs and NORs are.
     
  13. WBahn

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    Mar 31, 2012
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    Yep. Somewhat counterintuitive that they aren't. But when you flip inputs and outputs on and XOR you either get an XOR or an XNOR back.

    Another gate that is functionally complete is a 2:1 MUX.
     
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