Freq. Independent Phase Shifter
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From: MooseFET on 12 May 2010 09:28 On May 11, 6:27 pm, George Herold <gher...(a)teachspin.com> wrote: > On May 11, 8:58 pm, MooseFET <kensm...(a)rahul.net> wrote: > > > > > On May 11, 11:04 am, whit3rd <whit...(a)gmail.com> wrote: > > > > On May 11, 10:27 am, whit3rd <whit...(a)gmail.com> wrote: > > > > > On May 11, 6:47 am, George Herold <gher...(a)teachspin.com> wrote: > > > > > > On May 11, 3:21 am, billmur...(a)protech.com (Bill Murphy) wrote: > > > > > > > On Mon, 10 May 2010 18:24:52 -0700 (PDT), MooseFET > > > > > > > <kensm...(a)rahul.net> wrote: > > > > > > >What are the two other channels making? > > > > > > > Same signal, all spearated by 120 degrees. Done in CoolEdit. > > > > > > > >If you have two signals at 90 degrees, you can get any other phase > > > > > > >and the same amplitude. > > > > > > The simple way is to mix them in a pot. > > > > > > Sine----+ > > > > > | > > > > > P > > > > > O<----output > > > > > T > > > > > | > > > > > Cosine--+ > > > > > > But this has an amplitude variation as you move the pot wiper around, > > > > > No, it doesn't! Just buffer that output and it's good to go. > > > > Oops, got that wrong; there IS amplitude variation, up to about 30 > > > percent; > > > See my post for a circuit that makes the amplitude nearly constant.- Hide quoted text - > > I should/could have thought of the loaded pot, that's an easy way to > get rid of some of the variation. (I learned that trick from Phil H's > book.) But I've never seen postive feedback used like that before. I > assume that this gives some gain that changes as the source impedance > changes. > Yes the positive feedback causes the gain to rise as the impedance does. It matches up nicely with the loss so that the amplitude ends up nearly flat. The two resistors for the phase fixing don't quite match up perfectly but it makes the error hit zero at 5 points along the travel of the pot so it is darn good.
From: MooseFET on 12 May 2010 09:28 On May 12, 3:08 am, Jan Panteltje <pNaonStpealm...(a)yahoo.com> wrote: > On a sunny day (Tue, 11 May 2010 18:27:34 -0700 (PDT)) it happened George > Herold <gher...(a)teachspin.com> wrote in > <918314d4-a88a-4bd2-8f4b-de3537d2f...(a)e35g2000yqm.googlegroups.com>: > > > > >On May 11, 8:58 pm, MooseFET <kensm...(a)rahul.net> wrote: > >> On May 11, 11:04 am, whit3rd <whit...(a)gmail.com> wrote: > > >> > On May 11, 10:27 am, whit3rd <whit...(a)gmail.com> wrote: > > >> > > On May 11, 6:47 am, George Herold <gher...(a)teachspin.com> wrote: > > >> > > > On May 11, 3:21 am, billmur...(a)protech.com (Bill Murphy) wrote: > > >> > > > > On Mon, 10 May 2010 18:24:52 -0700 (PDT), MooseFET > > >> > > > > <kensm...(a)rahul.net> wrote: > >> > > > > >What are the two other channels making? > > >> > > > > Same signal, all spearated by 120 degrees. Done in CoolEdit. > > >> > > > > >If you have two signals at 90 degrees, you can get any other pha= > >se > >> > > > > >and the same amplitude. > > >> > > > The simple way is to mix them in a pot. > > >> > > > Sine----+ > >> > > > | > >> > > > P > >> > > > O<----output > >> > > > T > >> > > > | > >> > > > Cosine--+ > > >> > > > But this has an amplitude variation as you move the pot wiper aroun= > >d, > > >> > > No, it doesn't! Just buffer that output and it's good to go. > > >> > Oops, got that wrong; there IS amplitude variation, up to about 30 > >> > percent; > > >> See my post for a circuit that makes the amplitude nearly constant.- Hide= > > quoted text - > > >I should/could have thought of the loaded pot, that's an easy way to > >get rid of some of the variation. (I learned that trick from Phil H's > >book.) But I've never seen postive feedback used like that before. I > >assume that this gives some gain that changes as the source impedance > >changes. > > >Thanks, > > >George H. > > Just use AGC. AGC is way more complex than just adding a single resistor to the design so why go that way?
From: Jan Panteltje on 12 May 2010 09:45 On a sunny day (Wed, 12 May 2010 06:28:53 -0700 (PDT)) it happened MooseFET <kensmith(a)rahul.net> wrote in <6124b51e-0bff-49ca-9abe-d4be56254891(a)g5g2000pre.googlegroups.com>: > >> Just use AGC. > >AGC is way more complex than just adding a single resistor to the >design so why go that way? Yes it is more complex, but it sort of get you a 100% correct amplitude. I do not see a flat curve with resistors, that math eludes me.
From: MooseFET on 12 May 2010 21:41 On May 12, 6:45 am, Jan Panteltje <pNaonStpealm...(a)yahoo.com> wrote: > On a sunny day (Wed, 12 May 2010 06:28:53 -0700 (PDT)) it happened MooseFET > <kensm...(a)rahul.net> wrote in > <6124b51e-0bff-49ca-9abe-d4be56254...(a)g5g2000pre.googlegroups.com>: > > > > >> Just use AGC. > > >AGC is way more complex than just adding a single resistor to the > >design so why go that way? > > Yes it is more complex, but it sort of get you a 100% correct amplitude. > I do not see a flat curve with resistors, that math eludes me. Time to fire up your spreadsheet and give it a try. The amplitude error on the 90 degree version is about 0.36% with a max phase error of 0.03 degrees assuming ideal parts Rpot=1000 RtoWiper=1805 Rneg=-667
From: George Herold on 12 May 2010 23:51
On May 12, 9:41 pm, MooseFET <kensm...(a)rahul.net> wrote: > On May 12, 6:45 am, Jan Panteltje <pNaonStpealm...(a)yahoo.com> wrote: > > > On a sunny day (Wed, 12 May 2010 06:28:53 -0700 (PDT)) it happened MooseFET > > <kensm...(a)rahul.net> wrote in > > <6124b51e-0bff-49ca-9abe-d4be56254...(a)g5g2000pre.googlegroups.com>: > > > >> Just use AGC. > > > >AGC is way more complex than just adding a single resistor to the > > >design so why go that way? > > > Yes it is more complex, but it sort of get you a 100% correct amplitude.. > > I do not see a flat curve with resistors, that math eludes me. > > Time to fire up your spreadsheet and give it a try. > > The amplitude error on the 90 degree version is about 0.36% > with a max phase error of 0.03 degrees assuming ideal parts > > Rpot=1000 > RtoWiper=1805 Ohh neat, I was going to try 2k as a guess. > Rneg=-667 Ahh, you did all the work for us. I've never built an AGC circuit Jan, there must be some amplitude error as the input changes. OK that's not quite true, I've made a rectifier, integrator, minus reference level driving FET as varible feed back resistor... MooseFET's circuit is much easier. George H. PS Seems like DDS beats it all. |