propagation delay in logic gates

Discussion in 'General Electronics Chat' started by shiva kumar, Feb 3, 2012.

1. shiva kumar Thread Starter Member

Jun 27, 2008
11
0
Hi,,I have a query regarding the propagation delay in a gate,propagation delay is generally measured between 50 percent points on the input and output waveforms, why cannot we measure it between 20% or 80% points on the waveforms ? Is there any specific reason for opting 50% points ??

Regards,
Shiva.

2. MrChips Moderator

Oct 2, 2009
12,636
3,455
In theory, if the rise times and fall times are the same then it does not matter where you choose. You have to pick a common point somewhere and the 50% point is the best because the slope is at the maximum.

shiva kumar likes this.
3. holnis Member

Nov 25, 2011
50
4
It is possible to characterize various output transition times (e.g. 10%, 50%, and 90%) as a function of the input transition time, If it is needed.

On the other hand and by definition: Propagation Delay, Is the time between a change in an input and a low to high (or high to low) change on the output. Measured from 50% point on input signal to 50% point on the output signal.