method to size the PMOS and NMOS transistor (when Load andpropagation delay is given)

[imperza]

Hi all,
I need explaination of method to size the PMOS and NMOS transistor (when Load and propagation delay is given).
Thanks.

 

[BradtheRad]

The ampere load is one factor but what also matters is how the device will be used to control current. Will it provide resistive drop (linear mode)? Or will it serve as a switch?

The first case requires that it must dissipate more heat. In the second case it dissipates less heat.

Propagation delay enters into the equation when we consider how fast we want to switch the device. Suppose it opens and closes slowly in comparison to the speed of gate pulses. The result is that the device is in a state of transition for a greater percentage of time per cycle. It will dissipate more heat.