Explain the operation of a CMOS inverter.

A CMOS inverter consists of PMOS (connected to VDD) and NMOS (connected to GND) with gates tied together. When input is low (0), PMOS is on, NMOS is off, output is pulled to VDD (1). When input is high (1), NMOS is on, PMOS is off, output is pulled to GND (0). At no time are both transistors fully on, minimizing static power consumption. The switching threshold is ideally at VDD/2 for symmetric transistors. CMOS inverter is the fundamental building block of all digital CMOS circuits.