So I have been studying about logic gates designed using the CMOS family and in my professors notes it says "Move NMOSFET-B closer to output node, without changing the functionality , to reduce the parasitic capacitance and thus the fall time delay", I couldnt come to an understanding as to why this happens.
2 Answers
I guess your professor meant that if NMOSFET-B is closer to the output, the routing X will be smaller and hence parasitic capacitance on that net will be small and it will improve falltime.
The question is unclear. The canonical layout of a CMOS NAND gate looks like this:
(from Wikipedia)
The A and B inputs are similar lengths of poly, and the node "X" is simply the common channel between the two lower transistors. Is the professor suggesting that there is a better layout than this, or is that his way of describing this layout?