SAMPLED-DATA SIMULATION OF CIRCUITS WITH INTERNALLY CONTROLLED SWITCHES - Computer Methods for Analysis of Mixed-Mode Switching Circuits - page 178

1.3 Static CMOS Inverters
The switching variable of the complementary static CMOS inverter
shown in Fig.8.3 is defined as
where is the threshold voltage of the inverter. For most applications,
and is achieved by the appropriate sizing of the NMOS and
PMOS transistors. The output of the inverter is solely controlled by its
input in accordance with