cdc@uafhcx.uucp (C. D. Covington) (06/27/90)
In article <267ADD3E.18081@maccs.dcss.mcmaster.ca>, darel@maccs.dcss.mcmaster.ca (Darel Mesher) writes: > > I was wondering if anyone has a reference to an analog implementation > of a Hilbert transformer (ie. 90 degree phase shift). I also need > a digital implementation but that should be fairly easy to find > (Oppenheimer/Schafer). I would say the analog version would be difficult to come by. The digital version benefits from the fact that the signal is lowpass by definition (Nyquist and all that). If memory serves me, the digital version is simply: 1/n n odd h(n) = 0 n even Or even simpler in the frequency domain. C. David Covington (WA5TGF) cdc@uafhcx.uark.edu (501) 575-6583 Asst Prof, Elec Eng Univ of Arkansas Fayetteville, AR 72701
kchen@Apple.COM (Kok Chen) (06/27/90)
cdc@uafhcx.uucp (C. D. Covington) writes: >In article <267ADD3E.18081@maccs.dcss.mcmaster.ca>, darel@maccs.dcss.mcmaster.ca (Darel Mesher) writes: >> >> I was wondering if anyone has a reference to an analog implementation >> of a Hilbert transformer (ie. 90 degree phase shift). I also need >> a digital implementation but that should be fairly easy to find >> (Oppenheimer/Schafer). > I would say the analog version would be difficult to come by. ^^^^^^^^^ Not quite. There is a simple (and, very insensitive to component tolerances) iterative method in the analog world for successively approximating quadrature shifts known as a Phase Sequence Filter. Unfortunately, the only references I have found on it are in Horowitz and Hill's "The Art of Electronics" and the ARRL (yeah, no kidding) "1990 Radio Amateur Handbook." Both of which are a little embarassing to use as citations (sorry, Paul) :-) :-). I, myself, would appreciate Email from anyone who knows a source with a better mathematical description of the Phase Sequence filter. My interest in that is whether an equally simple analogous (no pun intended) animal exists in the digital world. Kok Chen, AA6TY kchen@apple.com Apple Computer, Inc.
cdc@uafhcx.uucp (C. D. Covington) (06/28/90)
> > I would say the analog version would be difficult to come by. > > Not quite. There is a simple (and, very insensitive to component > tolerances) iterative method in the analog world for successively > approximating quadrature shifts known as a Phase Sequence Filter. I really haven't done much with phase shifting in the analog world. The point I was making was that you would have to constrain the bandwidth in some way. I guess that's what you mean by 'iterative', perhaps a ladder of some kind. d. covington
schw@maxwell.tmc.edu (David Schwartz) (06/29/90)
Here are some analog Hilbert Transformer references to get you started. They work by using two all-pass filter sections where the phase difference betweeen the sections is 90 degrees of the frequency band of interest ----------------------------------------------------------------------------- [1] Frederrick Shirley, "Shift Phase Independent of Frequency," Electronic Design 18, Sept, 1970, pp. 62-66. [2] Gerald Roberts, "The Design of Broad-Band Active Delay Line/90 Degree Phase Difference Networks," IEEE Trans. on Circuits and Systems, Vol. CAS-21, No. 5, Sept. 1974, pp. 614-617. [3] S.D. Bedrosian, "Normalized Design of 90 Degree Phase Difference Networks," IRE Trans. on Circuit Theory, vol CT-7, June 1963, pp. 128-136. ------------------------------------------------------------------------------ David Schwartz, Ph.D. schw@maxwell.hrl.hac.com Hughes Research Laboratories RL69 3011 Malibu Canyon rd Malibu, CA 90265
fogelberg@lne.kth.se (Ingemar Fogelberg SM0AJV) (07/06/90)
In article <267ADD3E.18081@maccs.dcss.mcmaster.ca>, darel@maccs.dcss.mcmaster.ca (Darel Mesher) writes: > > Hello; > > I was wondering if anyone has a reference to an analog implementation >of a Hilbert transformer (ie. 90 degree phase shift). I also need >a digital implementation but that should be fairly easy to find >(Oppenheimer/Schafer). > >Thanks in advance for any leads; > > Darel > > >-- >============================================================================= >Darel Mesher >Electrical and Computer Engineering >McMaster University darel@maccs.dcss.mcmaster.ca In "Introduction to Digital Signal Processing" by Manolakis & Proakis chapter 8.1.5 you will find a very good description on how to make DIGITAL Hilbert Transformers. I have used it as reference my self. MATLAB (from Mathworks) have a routine called REMEZ were you easily can design a FIR-filter wich approximate the Hilbert-transformer. In my application I used the filter in a Quadratur-modulator used to perform a exp(-jw) multiplication. Good Luck --------------------------------------------------------------------------- ! Ingemar Fogelberg e-mail: fogelberg@lne.kth.se ! Grev Magnigatan 8 phone : (sweden)-8-662 73 28 ! S-114 55 STOCKHOLM call : SM0AJV ! SWEDEN org : EE-student at Royal Inst. of Tech. --------------------------------------------------------------------------