why we don't consider about group delay in analog design?

[gunner_fan]

In RF design, there is a group delay specification. If delay is different in different frequency component, a serious wave distortion named as Phase Distortion comes out.
In analog design, such distortion exists as well. But it is neglected as i know. At least, it is not considered in Gray,Allen and Razavie's books.

why? why we don't consider about such distortion in analog design?
i hope somebody give me some advice.

Thanks very much!

 

[renwl]

Re: why we don't consider about group delay in analog design

this depend on the application.
I think it's important for the communication circuit.

 

[venkateshr]

Re: why we don't consider about group delay in analog design

well the speed is the reason. we should go for maximally flat response to get delay(transient)-bandwidth(ac) balance. if there is peaking u may have better bw but the delay will be more than the circuit without the peaking.
in normal analog design the delay does'nt come into picture and in RF we should look into group delay as RF design is in Ghz range.so you will see some distortion(wrong signal).I am not 100% confident .Correct me if I am wrong.

 

[gunner_fan]

Re: why we don't consider about group delay in analog design

thanks for you giving me advice.

venkateshr wrote:

in normal analog design the delay does'nt come into picture and in RF we should look into group delay as RF design is in Ghz range.so you will see some distortion(wrong signal).

i think the distortion comes from different delay in different frequency component, it has noting to do with large delay if the delay is same in any frequency component.
if bw of the input signal is small, the Phase Distortion can be neglected, even if the delay is large. i'm not very clear about your words. can you give me a more detailed explanation.

Thank you very very much!

 

[Borber]

Re: why we don't consider about group delay in analog design

Specifying a group delay for a device is nothing but giving a measure of linearity of phase characteristic of it. At RF where frequency band is mostly limited by relativelly narrow bandpass filter the linearity of phase is particular problem. So the group delay is specified. It is easier to compensate phase characteristic over a group delay than sloping straight line.
And what do you mean by analog design. RF is analog too.

 

[venkateshr]

Re: why we don't consider about group delay in analog design

so the phase remains constant over the narrow Radio frequency band of interest instead of linear decrement as in ordinary case. can the 3-db frequency be lesser than this band and I introduce a zero in the band where my RF lies.

can the graph be like the one that I have attached