AND gate transistor sizing

Discussion in 'Homework Help' started by vead, May 16, 2014.

  1. vead

    Thread Starter Active Member

    Nov 24, 2011
    621
    8
    AND gate with cmos transistor
    we can create cmos AND gate with 3 nmos and 3 pmos transistor

    Equation X=AB

    AND gate cmos circuit= <-NAND--Inverter->

    I want to size the transistor so that the output resistance is same as that of inverter with nmos W/L=3/2 and pmos W/L=6/2

    inverter with nmos W/L=3/2 and pmos W/L=6/2

    parallel pmos (L will double with same W)

    pmos 1 W/L=6/4 and pmos 2 W/L = 6/4

    nmos series ( W will double with same L)

    nmos 1 W/L= 3/4 and nmos 2 W/L=3/4
    transistor size for AND gate cmos

    nmos 1 W/L=6/4
    nmos 2 W/L=6/4
    nmos 3 W/L=3/2


    pmos 1 W/L=3/4
    pmos 2 W/L=3/4
    pmos 3 W/L=3/2

    IS this correct sizing for AND gate
     
    Last edited: May 16, 2014
  2. WBahn

    Moderator

    Mar 31, 2012
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    Isn't the output resistance of an AND gate due entirely to the inverter that follows the NAND gate?
     
  3. vead

    Thread Starter Active Member

    Nov 24, 2011
    621
    8
    look at this Image

    given, Q5 nmos W/L=3/2
    Q6 pmos 3 W/L=3/1

    I want to determine size Q1,Q2,Q3 ,Q4a

    I made following
    Q1 nmos W/L=6/4
    Q2 nmos W/L=6/4
    Q3 pmos 1 W/L=3/4
    Q4 pmos 2 W/L=3/4
     
  4. WBahn

    Moderator

    Mar 31, 2012
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    What is "Q6 pmos 3"? Or Q4a? Or "Q3 pmos 1"?

    What is your question?
     
  5. vead

    Thread Starter Active Member

    Nov 24, 2011
    621
    8
    how to size transistors for AND gate

    look at Image that I have uploaded

    AND gate create with NAND gate INVERTER
    there are six transistor used to create AND gate
    two nmos connected in series before the Inverter
    two pmos connected in parallel in NAND gate (before inverter)

    sizing ratio for nmos W/L=3/2 and pmos W/L =6/2 in inverter circuit

    how to size for all transistor ?
     
  6. vead

    Thread Starter Active Member

    Nov 24, 2011
    621
    8
    look at this sizing
    Nmos W/L=3/2 and Pmos W/L=6/4( transistor in inverter circuit)

    caseI - when to mosfet in series this is similar to one transistor with double length and same width
    Example two series nmos with W=1 and L=1
    resultant W/L=1/2

    case II when to mosfet in parallel W will be double with same L
    Example- two pmos in parallel with w=1 and L=1
    resultant W/L=2/1

    So I made following sizing for AND gate circuit
    nmos W/L=3/2 and pmos W/L=6/4 (inverter circuit)
    nmos W/L=3/1 and pmos W/L=3/4 (for nand gate circuit)
     
  7. WBahn

    Moderator

    Mar 31, 2012
    17,715
    4,788
    You stated in the original post: "I want to size the transistor so that the output resistance is same as that of inverter with nmos W/L=3/2 and pmos W/L=6/2"

    Will: "nmos W/L=3/2 and pmos W/L=6/4 (inverter circuit)" accomplish that?
     
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