charlie@oakhill.UUCP (Charlie Thompson) (07/07/90)
I would like to use an IIR filter in a particular application. I also need linear phase response. Does anyone have any good references to papers/books/chapters concerning digital phase correction for IIR filters. I can't use an FIR in place of the IIR because it is a switched capacitor design and must be kept simple. I CAN however use a small FIR or an IIR to digitally correct the phase...additionally, the phase ripple can be as high as +-10 degrees and still be considered acceptable correction. Any help would be apprieciated. -Charlie Thompson
rk76073@naakka.tut.fi (Risto Kotalampi) (07/10/90)
In article <3504@radio.oakhill.UUCP> you write: > >I would like to use an IIR filter in a particular application. I >also need linear phase response. Does anyone have any good references >to papers/books/chapters concerning digital phase correction for >IIR filters. I can't use an FIR in place of the IIR because it is >a switched capacitor design and must be kept simple. I CAN however >use a small FIR or an IIR to digitally correct the phase...additionally, >the phase ripple can be as high as +-10 degrees and still be considered >acceptable correction. Any help would be apprieciated. > > -Charlie Thompson A solution to your problem could be Allpass Filters. With Allpass' you can design approximately linear phase filters. Some good references : S.K.Mitra,K. Hirano : Digital All-Pass Networks, IEEE Trans. on Circuits and Systems, Vol. Cas-21, pp. 688-700, No.5, September 1974. M.Renfors, T.Saram{ki : A Class of Approximately Linear Phase Digital Filters Composed of Allpass Subfilters. Was presented at IEEE Int. Symp. Circuits Syst. (San Jose, CA), May 1986. # Risto Kotalampi rk76073@tut.fi # Phones : # # Tampere University of Technology # Work (room SL 212) : (931) 162 921 # # Signal Processing Laboratory # Home : (931) 615 025 # # P.O.Box 527, 33101 TAMPERE # Radioclub (SH 101) : (931) 162 010 #
james@phred.UUCP (JAMES Taylor) (07/13/90)
In article <1990Jul10.122121.28209@funet.fi> rk76073@naakka.tut.fi (Risto Kotalampi) writes: >In article <3504@radio.oakhill.UUCP> you write: >> >>I would like to use an IIR filter in a particular application. I ... >>the phase ripple can be as high as +-10 degrees and still be considered >>acceptable correction. Any help would be apprieciated. ... >> -Charlie Thompson > >A solution to your problem could be Allpass Filters. With Allpass' you ... ># Risto Kotalampi rk76073@tut.fi # Phones : # If you have the luxury of redesigning your IIR filter, I have had very good results designing filters using Yule-Walker type techniques, certainly producing +- 10 degrees in the passband, even for fairly funny filters (ie. low pass things with integral 50Hz notches, notch just outside the pasband). Reference: Roberts and Mullis, Digital Signal Processing, Addison-Wesley, 1987 Although I used the functions delivered with Pro-Matlab from The Math Works to do the design. Also interesting (and of no personal design experience) is an article: Clements, "On Causal Linear Phase IIR Digital Filters", IEEE Trans. ASSP, Vol 37, No. 4, Apr 1989 Good stuff - James Taylor
fede@ethz.UUCP (F. Bonzanigo) (07/17/90)
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) CH-8092 Zurich, Switzerland E-mail: bonzanigo@nimbus.ethz.ch EARN/BITNET: BONZANIGO@CZHETH5A.bitnet EUNET/UUCP: fede@ethz.UUCP Phone: +41 (1) 256-5134 (+ = whatever you have to dial Fax: +41 (1) 251-2172 to call outside your country) Telex: 817115 vaw ch