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nor gate cmos circuit

Discussion in 'Electronics Homework Help' started by vead, Sep 25, 2014.

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  1. vead

    vead

    473
    14
    Nov 27, 2011
    hello
    I made Nor gate with coms transistor
    please check the connection
    If my diagram is correct then I want to decide length and width of transistor ?
    still I have not decide width and length I just want to confirm that my diagram is correct ?
     
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    10,079
    2,153
    Nov 17, 2011
    The source of the PMOS transistors is incorrectly tied to the output. It should go to Vdd.

    If you want a more or less symmectrival output you have to take into account that a PMOS has 1/2 the conductivity of an NMOS for the same W/L ratio. Since for a high output you have 2 PMOS in series, you have 1/4 the conductivity of a single NMOS in the pull-down leg of the output (for equal W/L). For a symmetrical output you therefore have to design W/L(PMOS)=4*W/L(NMOS).
    The absolute value of W and L depends mainly upon the available technology and max. output current.
     
    vead likes this.
  3. vead

    vead

    473
    14
    Nov 27, 2011
    If pmos =6/1 then nmos will be 3/1
    according to your formula W/L(PMOS)=4*W/L(NMOS).

    pmos = 6/1 and nmos = 6/2 *4=12/1

    circuit is here
     

    Attached Files:

  4. Harald Kapp

    Harald Kapp Moderator Moderator

    10,079
    2,153
    Nov 17, 2011
    No.
    W/L(PMOS)=4*W/L(NMOS)
    Therefore if W/L(PMOS)=6/1, then W/L(NMOS)=6/1 *1/4= 6/4=/3/2

    The PMOS needs to be wider than the NMOS for the same conductivity and channel length.
     
    vead likes this.
  5. vead

    vead

    473
    14
    Nov 27, 2011
    ok thank you very much

    some specification for cmos nor gate
    .*dc supply voltage
    * dc input voltage
    *dc output voltage
    *dc input current
    *dc output current
    * power dissipation

    ok If we have two known value then we can determine another value
    example If we know voltage and resistance then we can determine current by ohms law

    can you give me some homework ?
    can you give me some numeric value to determine unknown value like I mention in above spcification actually I want to learn by doing some real work, that circuit is mine i want to play with this circuit I will do some home work so please guide me
     
  6. Harald Kapp

    Harald Kapp Moderator Moderator

    10,079
    2,153
    Nov 17, 2011
    Sorry, I've been out of the IC design business for years. Luckily so far your questions were rather basic and I was able to answer them off the cuff. I do not have any material at hand that might be suitable for homework or for more detailed design of your circuit (besides, you'd neeed the parameters of the underlying manufacturing technology).
    I'm pretty sure that if you search the internet, you will find suitable assignments. It seems that especially US American universities often make their material public.
     
    vead likes this.
  7. vead

    vead

    473
    14
    Nov 27, 2011
    ok thanks lot I have question
    I made that circuit on proteus software
    can I use proteus to simulate that circuit ?
     
  8. Harald Kapp

    Harald Kapp Moderator Moderator

    10,079
    2,153
    Nov 17, 2011
    I don't know, because I don't know proteus. If you have suitable models for the transistors it may work. Just try it.
     
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