Re: Special XOR for half-adder and full-adder

Posted by jonk on Mar 03, 2016; 9:00pm
URL: http://nand2tetris-questions-and-answers-forum.52.s1.nabble.com/Special-XOR-for-half-adder-and-full-adder-tp4029600p4029619.html

By the way, I think I recall that in CMOS the NAND is preferred to the NOR, as the propagation delay is significantly shorter for the NAND structure (two N-channel devices in series to ground for NAND vs two slower P-channel devices in series to the Vcc rail for NOR.) But the 4-NAND XOR would require some 16 transistors.

Faster XOR circuits don't depend on NAND. They just use A as a MUX selector for transmission gates passing along B and /B to the output.