Practice question · Multiple choice
A CMOS chip is built almost entirely from NAND and NOR gates, and AND is constructed as NAND followed by an inverter. Why is the 'simpler' gate the more expensive one?
Hints
- Ask what a CMOS transistor pair does to a signal by default.
- Count the transistors: NAND is four. What is AND?
Show the answer
C. Because CMOS transistors naturally produce inverting logic
Why
The physics is inverting, so NAND and NOR are the cheap primitives and the intuitive gates are the composites. AND costs six transistors to NAND's four. It is a clean case of the implementation layer disagreeing with the conceptual one, and the manufacturing follows the physics.
Practise Boolean Variables and Logic Gates
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