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Hello folks,

I would really appreciate your insight in terms of how to design 
digital filters to match both magnitude and phase of a narrow band 
complex Analog gain(simple 1st order or 2nd or 3nd order gain). This 
is for impedance matching in voice band. I understand Matlab can be 
used to design FIR and IIR filters with arbitary magnitude reponse, 
which is easy. However, there is no mention anywhere on how to match 
phase response other than the group delay equalization. I really 
think in order to approximately match a given low order complex gain, 
both magnitude and phase should be matched. When I use bilinear 
transform to tranfer the analog gain into digital domain, the phase 
is no longer preserved.

Now I have seen some system using a FIR+ a low order IIR combination 
to do this but I have could be find the theory beind it and how the 
phase can be tuned.

Thanks a lot if you have any idea,

Gordon
	

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