🚀 go-pugleaf

In article <3187@phred.UUCP> james@phred.UUCP (JAMES Taylor) writes:
>
>Also interesting (and of no personal design experience) is an article:
>Clements (and Pease), "On Causal Linear Phase IIR Digital Filters",
>	IEEE Trans. ASSP, Vol 37, No. 4, Apr 1989

From the Summary (on p. 483) of the above paper:

"The main focus of this paper has been of a theoretical nature.
(Although) the nonrationality of the system described render them
unrealizable,..."

Before someone tries again to invent the perpetuum mobile, it has been
shown long ago that a causal and stable IIR filter with a rational (and
therefore realizable) transfer function cannot have a (exactly) linear
phase. A linear phase IIR filter should have its poles in reciprocal
pairs and therefore cannot be stable. The original proof can be found
in: A.G. Deczky, "General Expression for the Group Delay of Digital
Filters", Electronics Letters, Vol.5, No. 25, Dec. 11, 1969.


Federico Bonzanigo
  Electrical Engineering Dept.
  Swiss Federal Institute of Technology (ETH)
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