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Why Nand is more preferred than NOR

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phutanesv

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why nand gates are faster than nor

Dear friends,

why do NAND gates are more preferred than NOR gates

One reason is NAND has series NMOS and Parallel.

But what is the reason behind this. If Nmos in series what is benifit

Excat explanation i need.

Pls do
 

the sum of internal capacitance of Nmos in series is less than that of in parallel, so VDD have a more faster charge rate for Nand.

we can instead of Nor by four nands.in my opinion, nand is more fundation than nor.
 

As far as I know in case of

1. PMOS device has less mobility. In case of NAND PMOS are in parallel and they try to compensate the mobility factor during charging. where as NMOS has more mobility and series resistance compensate for discharging time. In other words charging and discharging are balance in this case.

2. In case of NOR this is not the case and discharging of output cap is very good ( More e mobility + parallel NMOS) but charging is slow so we have bad rise time.

I hope I am clear enough :|
 

It is basically related to the gate sizing.Lets say you have a library with basic inverter size would be 2:1(Wp/Wn).To make this condition true for NAND gate you have to use two Wp pmos in pull up device and two Wn nmos in NMOS device.

In NOR gate you have to use two PMOS devices of width 4Wp as pullup device with two Wn NMOS. So you have more utilization in NOR gate.
 

In the design and implementation of a logic circuit, its becomes easier if the parameters are in SOP(sum of products form) other than POS(product of sum form).
NAND gate implementation of the SOP is straightforward, but POS implementation using NOR gate is abit involving, and offcourse many designers will go for the NAND gate to implememt thre circuits since its easier hence superior!

kind regards
manenef
 

In FF based design mostly data is sampled at the rising edge of the clock. so 0->1 transition should be faster. since in nand pmos xtrs are in parallel, 0->1 transition will be faster due to lower effective resistance.
 

imagine connecting pmos in series.......becos of its allmost double width than nmos ....and less mobility .........it will take much time for output to change to 1,

also PMOS is better in sending logic 1 than logic 0, whereas NMOS better in sending logic 0........
 

fantastic discussion here...
NAND is faster than NOR.. as explained by Sinde
shiv
 

For read operation, NOR is faster than NAND, a bit.
For write operation, NAND is faster than NOR, many.

If do erasure, NAND is about 4ms, while NOR is about 5s.
 

excellent discussion
The ultimate result is nand is faster than nor
 

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