# nor gate cmos circuit

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

473
14
Nov 27, 2011
hello
I made Nor gate with coms transistor
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 KappModeratorModerator

10,836
2,443
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.

473
14
Nov 27, 2011
If pmos =6/1 then nmos will be 3/1

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

circuit is here

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4. ### Harald KappModeratorModerator

10,836
2,443
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.

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 KappModeratorModerator

10,836
2,443
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.

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 KappModeratorModerator

10,836
2,443
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.