# Propogation delay

#### aceminer

Joined Aug 26, 2011
21
Hi guys, i am really unsure of how to tackle this question .

A CMOS inverter, operating from a 5V power supply, drives a second inverter which has a
gate capacitance of 0.1pF. The current in the saturation region is I​
D K (VGSVT)2 = 0.1mA,
the propagation delay is t
P = C ΔV/ID, and the dynamic power is PD = S f C V2.

Calculate the approximate propagation delay.

My working would be (0.1 x 10^-10)(3.5 - 1.5)/(0.1 x 10^-3)

i got 3.5 as the minimum voltage for a CMOS inverter to be on a high state and the 1.5 as the maxmimum voltage for a CMOS inverter to be on a low state. Would this working be correct?

#### Georacer

Joined Nov 25, 2009
5,182
I can't say for sure if you are correct, since I haven't been taught thoroughly on that topic, however, wouldn't there be two delays from the input of the first inverter to the output of the second?

First you have the internal delay of the first inverter, due to the logical effort, and then the load delay, since you have to drive the second inverter.

But then again it all depends on how your teacher wants you to answer.