Freq. Independent Phase Shifter
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From: MooseFET on 13 May 2010 09:24 On May 12, 8:51 pm, George Herold <gher...(a)teachspin.com> wrote: > 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. These are the numbers for the 0..90 degree case For the 0..100, case, I will let you do the figuring The 120 degree case requires quite a low Rneg I suggest avoiding that case if you can. > > I've never built an AGC circuit Jan, there must be some amplitude > error as the input changes. The phase changes with the input amplitude in a way that varies with the frequency so an AGC is not a good thing to put into a frequency independent phase shifter > 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. If you don't mind doing a little coding, you can do it with one of those Analog Devices ADUC70xx devices on the development PCB. I have also done in it on the Silabs micros. If you make the DAC update rate 42949.67296 Hz, the math comes out easy to get frequencies as nice round numbers. Unfortunately it means that the phase values are a little ugly but not too bad. 119.3046471111111111 looks bad until you multiply it by 2^24
From: Jan Panteltje on 13 May 2010 10:07 On a sunny day (Wed, 12 May 2010 18:41:57 -0700 (PDT)) it happened MooseFET <kensmith(a)rahul.net> wrote in <27a317af-fd39-424c-8364-149ab8918af4(a)s4g2000prh.googlegroups.com>: >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 MooseF= >ET >> <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. Have not use spreadsheet for at least a month..... >The amplitude error on the 90 degree version is about 0.36% >with a max phase error of 0.03 degrees assuming ideal parts That is acutally very good. >Rpot=1000 >RtoWiper=1805 >Rneg=-667 Better remember that :-) Thank you for the correction, I will think about this until I figure it out.. hehe
From: Jan Panteltje on 13 May 2010 10:11 On a sunny day (Wed, 12 May 2010 20:51:37 -0700 (PDT)) it happened George Herold <gherold(a)teachspin.com> wrote in <5f7f25e0-5ec8-4f2f-b4e6-cceaa647866a(a)l31g2000yqm.googlegroups.com>: >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 Moos= >eFET >> > <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. Nice for such small ranges, you can stil have constant amplidtude with AGC over a factir 100 and more signal level change. Take any old AM radio. >OK that's not quite true, I've made a rectifier, integrator, minus >reference level driving FET as varible feed back resistor... So have I, for audio. >MooseFET's circuit is much easier. Tue, but Istill have to write down the math one day. >George H. > >PS >Seems like DDS beats it all. I have seen J.L. posting about programming DDS here, I like just a simple pot to change frequency, and indeed maybe phase, programming a DDS seems much more complicated, and then how do you control it?
From: John Fields on 13 May 2010 10:48 On Wed, 12 May 2010 20:51:37 -0700 (PDT), George Herold <gherold(a)teachspin.com> wrote: >PS >Seems like DDS beats it all. --- What does direct digital synthesis have to do with generating two sine waves 120 degrees apart over a range of frequencies?
From: George Herold on 13 May 2010 15:26
On May 13, 10:48 am, John Fields <jfie...(a)austininstruments.com> wrote: > On Wed, 12 May 2010 20:51:37 -0700 (PDT), George Herold > > <gher...(a)teachspin.com> wrote: > >PS > >Seems like DDS beats it all. > > --- > What does direct digital synthesis have to do with generating two sine > waves 120 degrees apart over a range of frequencies? Hmm, Can't you just have a simple offset from two look up tables. Run them off the same clock and change the clock rate to change frequency. Some one already posted that I thought? George H. |