Negative group delay and envelope advance

1. What is negative group delay?
2. Can phase delay be negative?
3. What does group delay tell you?
4. What does the group delay mean in the small signal ac analysis?

What is negative group delay?

If we insist on the idea that the group delay is a measure of, well, delay, then negative group delay would imply that a signal can exit an electronic circuit before it enters it.

Can phase delay be negative?

If you check the phase delay its negative, so is the group delay. Phase response is positive.

What does group delay tell you?

The so-called “group delay” is simply the time lag between the envelope of input burst and the envelope of the amplitude of the output burst. So, group delay means a propagation delay through a filter, measured on the envelope of the signal.

What does the group delay mean in the small signal ac analysis?

The group delay is a convenient measure of the linearity of the phase with respect to frequency in a modulation system.