Forums

Quadrature Oscillator

Started by George Herold May 13, 2014
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
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 10n
How 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.
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.
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. -- Tim Wescott Wescott Design Services http://www.wescottdesign.com
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.JPG
It is perhaps a special case of the ring oscilator: http://panteltje.com/pub/rgb.jpg That has as many phase [stages] as you want.
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
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
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
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.
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