Freq. Independent Phase Shifter
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From: Paul Keinanen on 10 May 2010 00:03 On Sun, 9 May 2010 19:57:42 -0700 (PDT), "miso(a)sushi.com" <miso(a)sushi.com> wrote: >On May 9, 2:33�pm, billmur...(a)protech.com (Bill Murphy) wrote: >> I am using a commercial stereo amp to output continuous wave test >> signals in the low audio range, up to about 2KHz. However, I need a >> third channel with a 120 degree phase shift. Is there a circuit that >> will do this evenly across this entire frequency range? >> >> Is it possible to do same using an off-the-shelf transformer and >> current subtraction? >> >> Any advice would be appreciated. >> >> Bill Murphy > >I'd suggest reading up on Hilbert transformers. Once you have an 90 >degree phase shift, you have a sine and cosine, hence an orthogonal >pair. Then you can make any phase you need from those signals. > >In many cases you just need the two signals to be orthogonal, but of >no particular phase to the reference sine wave. You can get two >filters that will be 90 degrees out of phase from old single sideband >radio designs. If you only need the 90 degree phase shift without fast frequency swings, the PLL can be used, since the phase detector produces zero output (after averaging), when the VCO is 90 degree out of phase relative to the reference.
From: George Herold on 10 May 2010 10:56 On May 9, 6:14 pm, Bill Sloman <bill.slo...(a)ieee.org> wrote: > On May 9, 11:33 pm, billmur...(a)protech.com (Bill Murphy) wrote: > > > I am using a commercial stereo amp to output continuous wave test > > signals in the low audio range, up to about 2KHz. However, I need a > > third channel with a 120 degree phase shift. Is there a circuit that > > will do this evenly across this entire frequency range? > > > Is it possible to do same using an off-the-shelf transformer and > > current subtraction? > > > Any advice would be appreciated. > > Check out Horowitz and Hill's "The art of Electronics". Section 5.16 > talks about phase-sequence filters, which give a constant 90 degree > shift over a range of frequencies. They consist of strings of equal > value resistors with cross-connected capacitors whose values decrease > in constant proportion per stage, halving in the example given, which > isn't all that practical to set up. The bottom line is that it isn't > trivial, and if you need to ask, you probably don't know enough to put > together a circuit that will work. > > -- > Bill Sloman, Nijmegen Yeah, I've used this circuit. It gives you nice quadrature output sine/cosine waves that can be used to make any particular phase shift. But phase shift relative to the input signal changes with frequency... The phase tends to keep wrapping around. Mixing the two signals with a potentiometer also causes amplitude variations if that would be a problem. That said I used a 10 section filter that has less than 1 degree of pahse ripple from 3 Hz to 3kHz. Caps are standard 1, 2.2, 4.7, 10... values. The ratio between sections is not as important as keeping the same value in each section. You can also change the order of the sections with no change at the output. If the OP wants only a few known frequincies then he could make a few dedicated RC sections... or some dedicated All-pass opamp filters. and switch each in when testing at that frequency. George H.
From: Joerg on 10 May 2010 12:19 Bill Murphy wrote: > I am using a commercial stereo amp to output continuous wave test > signals in the low audio range, up to about 2KHz. However, I need a > third channel with a 120 degree phase shift. Is there a circuit that > will do this evenly across this entire frequency range? > > Is it possible to do same using an off-the-shelf transformer and > current subtraction? > > Any advice would be appreciated. > Paul's suggestion with multi-channel sound cards is a good one. But keep in mind that phase shifts in the very low range (tens of Hertzes) can be iffy on some cards, output cap tolerances and all that. Unless you want to go in there with a solder iron. A Hilbert shifter works well, depends on the precision and how many octaves you want. Also, you'd need to get hold of 0.5% or better film capacitors which is not easy anymore these days. That was different in the 80's. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: Jan Panteltje on 10 May 2010 15:26 On a sunny day (Mon, 10 May 2010 09:19:56 -0700) it happened Joerg <invalid(a)invalid.invalid> wrote in <84qq1hFobmU1(a)mid.individual.net>: >Bill Murphy wrote: >> I am using a commercial stereo amp to output continuous wave test >> signals in the low audio range, up to about 2KHz. However, I need a >> third channel with a 120 degree phase shift. Is there a circuit that >> will do this evenly across this entire frequency range? >> >> Is it possible to do same using an off-the-shelf transformer and >> current subtraction? >> >> Any advice would be appreciated. >> > >Paul's suggestion with multi-channel sound cards is a good one. But keep >in mind that phase shifts in the very low range (tens of Hertzes) can be >iffy on some cards, output cap tolerances and all that. Unless you want >to go in there with a solder iron. It is too much, all you need is 3 EPROMS, a 4040 counter, and a 4046 PLL as VCO, add a pot to set the frequency. Add 3 R2R networks, or 3 cheap DACS. I have made one variable sine wave generator like that in the long ago past. Milliwats, and in a small box. Mine had auto sweep too, so I could test filters. Just an integrator and a FF, and 2 comparators added. 256 point 8 bits sinewaves. After al this is s.e.d. not 'alt.pc.sales' or whatever. >A Hilbert shifter works well, depends on the precision and how many >octaves you want. Also, you'd need to get hold of 0.5% or better film >capacitors which is not easy anymore these days. That was different in >the 80's. > >-- >Regards, Joerg > >http://www.analogconsultants.com/ > >"gmail" domain blocked because of excessive spam. >Use another domain or send PM. >
From: Joerg on 10 May 2010 15:32
Jan Panteltje wrote: > On a sunny day (Mon, 10 May 2010 09:19:56 -0700) it happened Joerg > <invalid(a)invalid.invalid> wrote in <84qq1hFobmU1(a)mid.individual.net>: > >> Bill Murphy wrote: >>> I am using a commercial stereo amp to output continuous wave test >>> signals in the low audio range, up to about 2KHz. However, I need a >>> third channel with a 120 degree phase shift. Is there a circuit that >>> will do this evenly across this entire frequency range? >>> >>> Is it possible to do same using an off-the-shelf transformer and >>> current subtraction? >>> >>> Any advice would be appreciated. >>> >> Paul's suggestion with multi-channel sound cards is a good one. But keep >> in mind that phase shifts in the very low range (tens of Hertzes) can be >> iffy on some cards, output cap tolerances and all that. Unless you want >> to go in there with a solder iron. > > It is too much, all you need is 3 EPROMS, a 4040 counter, and a 4046 PLL as VCO, > add a pot to set the frequency. > Add 3 R2R networks, or 3 cheap DACS. > I have made one variable sine wave generator like that in the long ago past. > Milliwats, and in a small box. > Mine had auto sweep too, so I could test filters. > Just an integrator and a FF, and 2 comparators added. > 256 point 8 bits sinewaves. > After al this is s.e.d. not 'alt.pc.sales' or whatever. > It all depends. When you do this for a living you need to weigh the time it takes to whip this up against the cost and installation time of a multi-channel sound card. When you are retired, different thing. But many of us aren't there yet. [...] -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM. |