The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Design >> Analog Design >> Group Delay
https://designers-guide.org/forum/YaBB.pl?num=1320753290

Message started by summi on Nov 8^th, 2011, 3:54am

Title: Group Delay
Post by summi on Nov 8^th, 2011, 3:54am

Dear forum,
Can any one please explain what is group delay clearly. Up to my knoeledge it represent delay of the signal and if i have constant group delay then there is no phase distortion

Br,
Summi.

Title: Re: Group Delay
Post by loose-electron on Nov 8^th, 2011, 4:05am

http://en.wikipedia.org/wiki/Group_delay_and_phase_delay

Title: Re: Group Delay
Post by buddypoor on Nov 8^th, 2011, 4:18am

Loose-electron gave you a link, which contains good information on group delay.
I like to emphasize the fact that group delay is NOT simply "the delay of a signal". It is rather the delay of a group of sinusoidal signals, which are relativ close to another in frequency (bandwidth small against the average frequency). Think of a signal that is amplitude modulated. In this case, the ENVELOPE is delayed by a time value that is identical to the group delay.
Remark: It is surprising but the group delay also can be negative!
(Example: Notch filter).

Title: Re: Group Delay
Post by raja.cedt on Nov 8^th, 2011, 5:58am

hello buddypoor,
what is the meaning of -ve group delay?

Thanks,
raj.

Title: Re: Group Delay
Post by buddypoor on Nov 8^th, 2011, 6:51am

raja.cedt wrote on Nov 8^th, 2011, 5:58am:

hello buddypoor,
what is the meaning of -ve group delay?
Thanks,
raj.

Hi Raj,

as you know - group delay is defined as the negative slope of the phase-vs-frequency response.
That means: If you have a system with a positive slope of this kind the resulting group delay is negative (and also the group velocity).
What does it mean? According to its definition the information (e.g. envelope of an AM signal) is available at the output before it appears at the input. Sounds surprising - but it is the truth and has been prooved by several experiments.