Quadrature oscialltor. Hi all, As part of the CV measurements (from a previous post) I'm thinking about a 1 MHz lockin. (Maybe a different thread to talk about how to do the switching.) I was wondering if I could make a quadrature oscillator from opamps. (I've got some AD825's I thought I'd try.) Anyway spice seems to think it's possbile. Comments or ideas welcome. (Oh I had to add the sine wave input to get the thing to start.) You can play with C1 R7 C2 R8 to change the frequency. Here's a circuit scribble if you don't like the spice file https://www.dropbox.com/s/sb5azyl69fy142t/DSCF0012.JPG George H. Version 4 SHEET 1 5945676 13421556 WIRE 2176 -512 1280 -512 WIRE 1616 -416 1584 -416 WIRE 1696 -416 1680 -416 WIRE 2080 -416 2048 -416 WIRE 2096 -416 2080 -416 WIRE 2176 -416 2176 -512 WIRE 2176 -416 2144 -416 WIRE 1120 -352 1024 -352 WIRE 1280 -352 1200 -352 WIRE 1280 -352 1280 -512 WIRE 1584 -320 1584 -416 WIRE 1616 -320 1584 -320 WIRE 1696 -320 1696 -416 WIRE 1696 -320 1680 -320 WIRE 2048 -304 2048 -416 WIRE 2080 -304 2048 -304 WIRE 2176 -304 2176 -416 WIRE 2176 -304 2144 -304 WIRE 1024 -240 1024 -352 WIRE 1280 -208 1280 -352 WIRE 1312 -208 1280 -208 WIRE 1440 -208 1392 -208 WIRE 1488 -208 1440 -208 WIRE 1584 -208 1584 -320 WIRE 1584 -208 1568 -208 WIRE 1600 -208 1584 -208 WIRE 1696 -208 1696 -320 WIRE 1696 -208 1680 -208 WIRE 1888 -208 1856 -208 WIRE 1936 -208 1888 -208 WIRE 2048 -208 2048 -304 WIRE 2048 -208 2016 -208 WIRE 2080 -208 2048 -208 WIRE 2176 -208 2176 -304 WIRE 2176 -208 2160 -208 WIRE 1024 -112 1024 -160 WIRE 1440 -64 1440 -208 WIRE 1488 -64 1440 -64 WIRE 1888 -64 1888 -208 WIRE 1920 -64 1888 -64 WIRE 1696 -48 1696 -208 WIRE 1696 -48 1552 -48 WIRE 1776 -48 1776 -208 WIRE 1776 -48 1696 -48 WIRE 2176 -48 2176 -208 WIRE 2176 -48 1984 -48 WIRE 1280 -32 1280 -208 WIRE 1312 -32 1280 -32 WIRE 1440 -32 1392 -32 WIRE 1488 -32 1440 -32 WIRE 1776 -32 1776 -48 WIRE 1888 -32 1840 -32 WIRE 1920 -32 1888 -32 WIRE 1440 0 1440 -32 WIRE 1888 16 1888 -32 WIRE 1440 128 1440 64 WIRE 1888 160 1888 96 WIRE 0 0 0 0 FLAG 1024 -112 0 FLAG 1440 128 0 FLAG 1888 160 0 SYMBOL voltage 1024 -256 R0 WINDOW 123 24 124 Left 2 WINDOW 39 0 0 Left 2 SYMATTR InstName V1 SYMATTR Value SINE(0 1 1k 0 0 0 1) SYMATTR Value2 AC 1. SYMBOL res 1408 -224 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R1 SYMATTR Value 1k SYMBOL res 1584 -224 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R2 SYMATTR Value 850 SYMBOL res 1872 -224 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R4 SYMATTR Value 1k SYMBOL cap 1456 64 R180 WINDOW 0 24 56 Left 2 WINDOW 3 24 8 Left 2 SYMATTR InstName C1 SYMATTR Value 100p SYMBOL OPAMPS\\OPAMP 1520 -112 R0 SYMATTR InstName U1 SYMATTR SpiceLine2 GBW=50Meg SYMBOL OPAMPS\\OPAMP 1952 -112 R0 WINDOW 39 7 114 Left 2 WINDOW 40 0 146 Left 2 SYMATTR InstName U2 SYMATTR SpiceLine2 GBW=50Meg SYMBOL res 1696 -224 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R3 SYMATTR Value 300 SYMBOL cap 1840 -48 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C2 SYMATTR Value 100p SYMBOL res 2032 -224 R90 WINDOW 0 21 51 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R5 SYMATTR Value 850 SYMBOL res 2176 -224 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R6 SYMATTR Value 300 SYMBOL res 1408 -48 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R7 SYMATTR Value 200 SYMBOL res 1904 112 R180 WINDOW 0 36 76 Left 2 WINDOW 3 36 40 Left 2 SYMATTR InstName R8 SYMATTR Value 200 SYMBOL diode 1680 -336 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D1 SYMBOL diode 1616 -432 M90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D2 SYMBOL diode 2144 -320 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D3 SYMBOL diode 2080 -432 M90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName D4 SYMBOL res 1216 -368 R90 WINDOW 0 0 56 VBottom 2 WINDOW 3 32 56 VTop 2 SYMATTR InstName R9 SYMATTR Value 100meg TEXT 1888 296 Left 2 !.include opamp.sub TEXT 1006 4 Left 2 !.tran 0 1m 0 10n
Quadrature Oscillator
Started by ●May 13, 2014
Reply by ●May 13, 20142014-05-13
On Tue, 13 May 2014 07:36:36 -0700 (PDT), George Herold <gherold@teachspin.com> wrote:>Quadrature oscialltor. > >Hi all, As part of the CV measurements (from a previous post) >I'm thinking about a 1 MHz lockin. >(Maybe a different thread to talk about how to do the switching.) >I was wondering if I could make a quadrature oscillator from opamps. >(I've got some AD825's I thought I'd try.) >Anyway spice seems to think it's possbile. >Comments or ideas welcome. >(Oh I had to add the sine wave input to get the thing to start.) >You can play with C1 R7 C2 R8 to change the frequency. > >Here's a circuit scribble if you don't like the spice file >https://www.dropbox.com/s/sb5azyl69fy142t/DSCF0012.JPG > >George H. > > >Version 4 >SHEET 1 5945676 13421556 >WIRE 2176 -512 1280 -512[snip... complete file at Message-ID: <61c042f3-9272-4d64-8096-6a48875bd58b@googlegroups.com> ]>SYMATTR InstName R9 >SYMATTR Value 100meg >TEXT 1888 296 Left 2 !.include opamp.sub >TEXT 1006 4 Left 2 !.tran 0 1m 0 10nHow about this... <http://www.analog-innovations.com/SED/GyratorFilter_A1A_Oscillator.pdf> ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●May 13, 20142014-05-13
On Tuesday, May 13, 2014 11:36:10 AM UTC-4, Jim Thompson wrote:> On Tue, 13 May 2014 07:36:36 -0700 (PDT), George Herold > > <gherold@teachspin.com> wrote: > > > > >Quadrature oscialltor.> > > How about this... > > <http://www.analog-innovations.com/SED/GyratorFilter_A1A_Oscillator.pdf> >OK I had to redraw it to make it look like the gyrator in AoE. (fig 5.24 Z1=R9, Z2=R7, Z3=r6, Z4=C3, Z5=R8) I've never used a gyrator... How much gain is there in any one opamp stage? And what's going on with U6.. there's a diode clipped gain control, but how does anything get through D5 and D6? Capacitive coupling? George H.> > ...Jim Thompson > > -- > > | James E.Thompson | mens | > > | Analog Innovations | et | > > | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | > > | San Tan Valley, AZ 85142 Skype: Contacts Only | | > > | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | > > | E-mail Icon at http://www.analog-innovations.com | 1962 | > > > > I love to cook with wine. Sometimes I even put it in the food.
Reply by ●May 13, 20142014-05-13
On Tue, 13 May 2014 07:36:36 -0700, George Herold wrote:> Quadrature oscialltor. > > Hi all, As part of the CV measurements (from a previous post) > I'm thinking about a 1 MHz lockin. > (Maybe a different thread to talk about how to do the switching.) > I was wondering if I could make a quadrature oscillator from opamps. > (I've got some AD825's I thought I'd try.) > Anyway spice seems to think it's possbile. > Comments or ideas welcome. > (Oh I had to add the sine wave input to get the thing to start.) You can > play with C1 R7 C2 R8 to change the frequency. > > Here's a circuit scribble if you don't like the spice file > https://www.dropbox.com/s/sb5azyl69fy142t/DSCF0012.JPGHow close to true quadrature and amplitude matching do you need? You'll be pretty dependent on both capacitor and op-amp characteristics for the match and phase shift between channels. If you really want precision, run a DDS at a high clock rate so the filtering can't add much phase shift or attenuation. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
Reply by ●May 13, 20142014-05-13
On a sunny day (Tue, 13 May 2014 07:36:36 -0700 (PDT)) it happened George Herold <gherold@teachspin.com> wrote in <61c042f3-9272-4d64-8096-6a48875bd58b@googlegroups.com>:>Quadrature oscialltor. > >Hi all, As part of the CV measurements (from a previous post) >I'm thinking about a 1 MHz lockin. >(Maybe a different thread to talk about how to do the switching.) >I was wondering if I could make a quadrature oscillator from opamps. >(I've got some AD825's I thought I'd try.) >Anyway spice seems to think it's possbile. >Comments or ideas welcome. >(Oh I had to add the sine wave input to get the thing to start.) >You can play with C1 R7 C2 R8 to change the frequency. > >Here's a circuit scribble if you don't like the spice file >https://www.dropbox.com/s/sb5azyl69fy142t/DSCF0012.JPGIt is perhaps a special case of the ring oscilator: http://panteltje.com/pub/rgb.jpg That has as many phase [stages] as you want.
Reply by ●May 13, 20142014-05-13
On Tuesday, May 13, 2014 12:03:34 PM UTC-4, Tim Wescott wrote:> On Tue, 13 May 2014 07:36:36 -0700, George Herold wrote: ><snip>> > How close to true quadrature and amplitude matching do you need? You'll > be pretty dependent on both capacitor and op-amp characteristics for the > match and phase shift between channels. > > > > If you really want precision, run a DDS at a high clock rate so the > filtering can't add much phase shift or attenuation. >Yeah thanks Tim. Right, DDS would be the way to go. (But there's that whole dang learning curve and then how to do the user interface.) Have you done a DDS design? I guess I was just doing what I know already. I don't care too much about the amplitudes. and I don't think a bit (few degrees) of phase shift will be that bad. I was thinking if I could get a cheap signal generator that would output I and Q then that would solve my problem too. OK time to read my Rigol DG1022 manual. George h.> -- > > > > Tim Wescott > > Wescott Design Services > > http://www.wescottdesign.com
Reply by ●May 13, 20142014-05-13
On Tuesday, May 13, 2014 12:31:15 PM UTC-4, George Herold wrote:> On Tuesday, May 13, 2014 12:03:34 PM UTC-4, Tim Wescott wrote: > > > On Tue, 13 May 2014 07:36:36 -0700, George Herold wrote: > > > > > <snip>> I was thinking if I could get a cheap signal generator that would > output I and Q then that would solve my problem too. > > OK time to read my Rigol DG1022 manual. >OK the Rigol does the job! Well the phase between the two channels is a bit 'screwy', but there is an AligPha button which I assume means Align Phase. And that works! milli hertz to 20 MHz. I and Q outputs. (I've half laid out the opamp version, I should see how bad it is.) George h.> > George h. > > > -- > > > > > > > > > > > > Tim Wescott > > > > > > Wescott Design Services > > > > > > http://www.wescottdesign.com
Reply by ●May 13, 20142014-05-13
On 05/13/2014 12:03 PM, Tim Wescott wrote:> On Tue, 13 May 2014 07:36:36 -0700, George Herold wrote: > >> Quadrature oscialltor. >> >> Hi all, As part of the CV measurements (from a previous post) >> I'm thinking about a 1 MHz lockin. >> (Maybe a different thread to talk about how to do the switching.) >> I was wondering if I could make a quadrature oscillator from opamps. >> (I've got some AD825's I thought I'd try.) >> Anyway spice seems to think it's possbile. >> Comments or ideas welcome. >> (Oh I had to add the sine wave input to get the thing to start.) You can >> play with C1 R7 C2 R8 to change the frequency. >> >> Here's a circuit scribble if you don't like the spice file >> https://www.dropbox.com/s/sb5azyl69fy142t/DSCF0012.JPG > > How close to true quadrature and amplitude matching do you need? You'll > be pretty dependent on both capacitor and op-amp characteristics for the > match and phase shift between channels. > > If you really want precision, run a DDS at a high clock rate so the > filtering can't add much phase shift or attenuation. >One method is to make one section a true integrator. That'll guarantee quadrature. Then servo the frequency to make the amplitudes equal. You'll need to measure the frequency to compute the capacitance, but that's not so bad. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC Optics, Electro-optics, Photonics, Analog Electronics 160 North State Road #203 Briarcliff Manor NY 10510 hobbs at electrooptical dot net http://electrooptical.net
Reply by ●May 13, 20142014-05-13
On Tue, 13 May 2014 08:58:48 -0700 (PDT), George Herold <gherold@teachspin.com> wrote:>On Tuesday, May 13, 2014 11:36:10 AM UTC-4, Jim Thompson wrote: >> On Tue, 13 May 2014 07:36:36 -0700 (PDT), George Herold >> >> <gherold@teachspin.com> wrote: >> >> >> >> >Quadrature oscialltor. > >> >> >> How about this... >> >> <http://www.analog-innovations.com/SED/GyratorFilter_A1A_Oscillator.pdf> >> >OK I had to redraw it to make it look like the gyrator in AoE. >(fig 5.24 Z1=R9, Z2=R7, Z3=r6, Z4=C3, Z5=R8) > > I've never used a gyrator... How much gain is there in any one opamp stage?Walk thru the stages... first stage is essentially an integrator, second stage has inverting gain of unity. Laplace (Heaviside version) is the easiest way to analyze these structures.>And what's going on with U6.. there's a diode clipped gain control, >but how does anything get through D5 and D6? Capacitive coupling? > >George H. >Yep, the Q is so high it takes a bare twiddle to make it go. I threw this together some 8 years ago to demonstrate the gyrator band-pass effect. IRL I used an AGC loop. (An accurate clipper works also.) You can get really low distortion with good OpAmps. I built one for a Sperry Flight Systems synchronous detect at 400Hz... 0.001% harmonic distortion :-) ...Jim Thompson -- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | San Tan Valley, AZ 85142 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
Reply by ●May 13, 20142014-05-13
On Tue, 13 May 2014 13:03:28 -0400, Phil Hobbs wrote:> On 05/13/2014 12:03 PM, Tim Wescott wrote: >> On Tue, 13 May 2014 07:36:36 -0700, George Herold wrote: >> >>> Quadrature oscialltor. >>> >>> Hi all, As part of the CV measurements (from a previous post) >>> I'm thinking about a 1 MHz lockin. >>> (Maybe a different thread to talk about how to do the switching.) >>> I was wondering if I could make a quadrature oscillator from opamps. >>> (I've got some AD825's I thought I'd try.) >>> Anyway spice seems to think it's possbile. >>> Comments or ideas welcome. >>> (Oh I had to add the sine wave input to get the thing to start.) You >>> can play with C1 R7 C2 R8 to change the frequency. >>> >>> Here's a circuit scribble if you don't like the spice file >>> https://www.dropbox.com/s/sb5azyl69fy142t/DSCF0012.JPG >> >> How close to true quadrature and amplitude matching do you need? >> You'll be pretty dependent on both capacitor and op-amp characteristics >> for the match and phase shift between channels. >> >> If you really want precision, run a DDS at a high clock rate so the >> filtering can't add much phase shift or attenuation. >> >> > One method is to make one section a true integrator. That'll guarantee > quadrature. Then servo the frequency to make the amplitudes equal. > You'll need to measure the frequency to compute the capacitance, but > that's not so bad.That works if a "true" integrator is true enough at 1MHz, but leaves you with the problem of balancing the amplitudes. I'd be tempted to integrate-integrate-invert. It would take three op- amps, but you may have a better chance to get each section working correctly. Of course you'd need the obligatory teeny bit of lag somewhere, to make the oscillation start. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
