[sdiy] SVF & phase

[Tom May]

Magnus Danielson <cfmd at swipnet.se> writes:

>    There is exactly one solution to placement of equalently many poles and
>    zeros which produces no phase shift - such that the position of one pole is
>    matched by the position of a zero, and that all poles and zeros is matched
>    accordingly. Now, this effectively makes z1 = p1, z2 = p2 etc. and those
>    makes perfert cancelation. There is no way for any amplitude response to
>    change (which is BTW the absolute response of H(s) when s = jomega), since
>    H(s) is now exactly 1!

Is it not also the case that there will be zero phase shift if all the
poles and zeros are symmetric about the jw axis?  In practice this
implies right half-plane or jw axis poles which will be unstable.

But if you don't have the number of poles == number of zeros
constraint, you can get rid of the poles altogether and have a filter
with zeros only (which can be implemented as a FIR filter).

Tom.