CMOS Inverter

CMOS Inverter diagram
DC voltage transfer char
Regions of operation of NMOS and PMOS transistors, (mark in transfer char and table )
When both transistors are in saturation region, they have high g_m and high output resistance(r_o). Therefore high gain, leading to sharp transition in the transfer characteristic.

t_{pLH} defines delay for output going from LOW to HIGH
t_{pHL} defines delay for output going from HIGH to LOW
In general t_{pLH} and t_{pHL} are not same.
Therefore propagation delay, t_p, is defined as

(1)   \begin{equation*} t_p = {t_{pLH} +  t_{pHL} \over 2}  \end{equation*}

Rise time(t_r) and fall time(t_f) is defined as the time required for the signal to change from 10% to 90% of it’s steady state value.