propagation delay in logic gates

[shiva20587]

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.

 

[K-J]

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.

Because if you used multiple % points, you would be measuring two things combined: propogation delay and edge rate. If you want to know how long it takes a digital something to propogate through a device, you need to measure from the logic threshold point.

Kevin Jennings