santuvlsi said:Hai every body,
Nand Gates are more preferred than Nor gates,
becos in Nand gates NMOS connected in series.
What is the logic behind this?
pichuang said:NAND gates is more preferred than NOR gates because of sizing.
NAND is NMOS in series and PMOS in parallel, while NOR is the other way around.
As people have already mentioned, the mobility of hole is less than that of the electron. Therefore, to achieve the same delay (current capability), PMOS needs to be approximately 3 times bigger than NMOS (0.18um technology).
I am not sure if you have taken any digital IC course before, but in essence when you do the transistor sizing any transistor in series need to be sized up more (depending on the number of transistors in series). Therefore, we want to avoid PMOS transistors in series (because they take up more space than NMOS in series at same delay).
That is why NAND is a better choice than NOR.
why Digital Circuits mostly use the 0->1 transition not the 1-> transition?sekapr said:Digital circuits mostly use the the low-high transition for sampling data which faster in NAND compared with Nor