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Quadrature Oscillator

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

formatting link

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

Reply to
George Herold
Loading thread data ...

[snip... complete file at Message-ID: ]

How about this...

...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 to
Jim Thompson

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.

Reply to
George Herold

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
Reply to
Tim Wescott

On a sunny day (Tue, 13 May 2014 07:36:36 -0700 (PDT)) it happened George Herold wrote in :

It is perhaps a special case of the ring oscilator:

formatting link

That has as many phase [stages] as you want.

Reply to
Jan Panteltje

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.

Reply to
George Herold

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.

Reply to
George Herold

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 to
Phil Hobbs

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.

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 to
Jim Thompson

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
Reply to
Tim Wescott

Why yes, I have done a DDS design. In 1989. It worked great, but I suspect the parts are completely unobtainable by now.

--

Tim Wescott 
Wescott Design Services 
http://www.wescottdesign.com
Reply to
Tim Wescott

What? You mean I should think about it? :^)

OK.. From my limited oscillator experience it will depend on how good the cap is. (good, as in low dissipation.)

George H.

Reply to
George Herold

[snip]

If you run the numbers you'll find that dissipation factor (in active filters) is only a problem at low frequencies.

See...

for how I cured (in the early '70's) the dissipation factor problem in telephone-signaling low-frequency filters. ...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 to
Jim Thompson

Hmm OK, I always figured it just needed the right bit of gain somewhere. I've never had that much problem getting oscillators to start...They always seem to get going and bump into the rail right away. (I love the way LTspice goes up to several tera volts, before it pukes.... Can you even make a tera volt without ripping apart the fabric of space-time?)

George H.

Reply to
George Herold

[snip]

Here's a link to the BP filter math...

...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 to
Jim Thompson

[snip]

I don't have that problem... I devised parts that know to stop at some bounds, like the rails...

Also makes for faster convergence. ...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 to
Jim Thompson

This is getting way too complicated. Analog circuits drift and can never guarantee quadrature. A simple 74HC74 will. See

formatting link

Reply to
John Silverman

It's field strength, not voltage, that would potentially (pun not intended) rip apart the fabric of space-time.

Assuming that you could achieve a high enough field strength without ripping electrons off of your negative electrode, you would eventually generate real positron/electron pairs from the quantum foam. I think -- I'm not a quantum mechanic.

--

Tim Wescott 
Wescott Design Services 
http://www.wescottdesign.com
Reply to
Tim Wescott

There's ways to make an analog signal lock-in to a digital quadrature clock, of course.

There's also a switched-capacitor solution, see figure 15

And, if one wishes to go old-school, an LC oscillator puts out sin(wt) voltage on the capacitor, and cos(wt) current through the inductor; you can make a sense coil lightly coupled to the inductor to pick off the second phase. If Q is high, it needs no correction; if Q is low, you can make a weighted sum of the two signals that is tunable to get closer to 90.00 degrees phase, and a simple multiplicative mixer makes a DC signal of the error, to guide the tuning.

Reply to
whit3rd

If George can deal with square waves, yes, that's going to work way better than an analog solution.

If he needs sine waves, by the time he's gotten the harmonics beaten out of that he'll be back to depending on analog components for his precision.

--

Tim Wescott 
Wescott Design Services 
http://www.wescottdesign.com
Reply to
Tim Wescott

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