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oscillator with constant amplitude

Started by Tom Del Rosso August 5, 2015
George Herold wrote:


> Audio frequencies? > I've done Wein bridges with amplitude control from diodes and > resistor ratio's.. not great temperature coef.
** The peak level drops about 0.4% for each degree C, using silicon diodes. Zeners can do better, if the voltage is carefully picked. ... Phil
On Wed, 5 Aug 2015 12:39:09 -0400, "Tom Del Rosso"
<fizzbintuesday@that-google-mail-domain.com> wrote:

>I don't want anybody to design it for me, but in general how would you >make an oscillator with a sine output of constant amplitude over a range >of supply voltage (let's say the operating range of the op-amp). What I >have in mind is a battery supply, but with no power wasted in a >regulator. Sure the oscillator would also waste power but not as much. >Would a square output be simpler?
ICL8038 or similar triangle wave generator with built in triangle to sine converter ?
On Thursday, 6 August 2015 15:28:34 UTC+10, upsid...@downunder.com  wrote:
> On Wed, 5 Aug 2015 12:39:09 -0400, "Tom Del Rosso" > <fizzbintuesday@that-google-mail-domain.com> wrote: > > >I don't want anybody to design it for me, but in general how would you > >make an oscillator with a sine output of constant amplitude over a range > >of supply voltage (let's say the operating range of the op-amp). What I > >have in mind is a battery supply, but with no power wasted in a > >regulator. Sure the oscillator would also waste power but not as much. > >Would a square output be simpler? > > ICL8038 or similar triangle wave generator with built in triangle to > sine converter ?
Distortion performance is unremarkable. If you aren't pathologically nervous about winding a centre-tapped transformer (or getting it wound) - and a lot of our regular posters are - you can do a lot better with less power dissipation. -- Bill Sloman, Sydney
More responses than I expected.  I appreciate it but can't respond to 
all right now.

Tim Wescott wrote:
> > I would use AGC. > > If wasting power is an issue then you're going about it more or less > backwards -- at best, a linear oscillator on an unregulated rail with > a constant output is going to use just as much power as an oscillator > being powered through a linear regulator -- and it'll probably be > worse.
I understand what you mean. The idea came that it must be possible, but I've never seen it done specifically, so I got curious about how complex such an oscillator would be. More complex than a regulator it turns out.
> If you can run at a constant amplitude, use a switching regulator. > > What frequency range are you looking at?
Low KHz. --
On 06/08/15 17:03, Tom Del Rosso wrote:
> More responses than I expected. I appreciate it but can't respond to > all right now. > Tim Wescott wrote: >> I would use AGC. >> If wasting power is an issue then you're going about it more or less >> backwards -- at best, a linear oscillator on an unregulated rail with >> a constant output is going to use just as much power as an oscillator >> being powered through a linear regulator -- and it'll probably be >> worse. > I understand what you mean. The idea came that it must be possible, but > I've never seen it done specifically, so I got curious about how complex > such an oscillator would be. More complex than a regulator it turns > out.
Here's an example of an oscillator (for 3.6MHz) that uses AGC. It's not very complicated, though it's unsuitable for "Low KHz" because of the size of the inductor you need. If you want to run it, you'll need to supply a transistor model, as I didn't include my library part (and you might need to change some resistor values for the AGC to work). But I suspect you'll be able to see how it works without doing that (use LTSpice to view!) Clifford Heath. Version 4 SHEET 1 1952 708 WIRE 304 -336 192 -336 WIRE 752 -336 304 -336 WIRE 192 -288 192 -336 WIRE 192 -176 192 -208 WIRE 192 -176 -64 -176 WIRE 432 -176 192 -176 WIRE 528 -176 432 -176 WIRE 192 -144 192 -176 WIRE 304 -96 304 -336 WIRE 752 -96 752 -336 WIRE -48 -48 -64 -48 WIRE 32 -48 -48 -48 WIRE 96 -48 32 -48 WIRE 192 -48 192 -64 WIRE 192 -48 160 -48 WIRE 240 -48 192 -48 WIRE 432 -48 432 -176 WIRE 32 112 32 -48 WIRE 96 112 32 112 WIRE 640 112 160 112 WIRE 32 208 32 112 WIRE 528 208 528 -176 WIRE 432 304 432 32 WIRE -48 320 -48 -48 WIRE 32 352 32 272 WIRE 304 352 304 0 WIRE 304 352 32 352 WIRE 368 352 304 352 WIRE 192 400 192 -48 WIRE 304 400 304 352 WIRE 32 416 32 352 WIRE -48 528 -48 400 WIRE 32 528 32 480 WIRE 32 528 -48 528 WIRE 192 528 192 480 WIRE 192 528 32 528 WIRE 304 528 304 480 WIRE 304 528 192 528 WIRE 432 528 432 400 WIRE 432 528 304 528 WIRE 528 528 528 272 WIRE 528 528 432 528 WIRE 752 528 752 -16 WIRE 752 528 528 528 WIRE 752 544 752 528 FLAG 752 544 0 FLAG -64 -48 Vosc IOPIN -64 -48 Out FLAG -64 -176 Vbias IOPIN -64 -176 Out FLAG 640 112 Vout IOPIN 640 112 Out SYMBOL voltage 752 -112 R0 WINDOW 123 24 126 Left 2 WINDOW 39 24 111 Left 2 SYMATTR InstName V1 SYMATTR Value 3.2v SYMBOL cap 16 208 R0 SYMATTR InstName C1 SYMATTR Value 150pf SYMBOL cap 16 416 R0 SYMATTR InstName C2 SYMATTR Value 2.2nF SYMBOL ind -64 304 R0 SYMATTR InstName L3 SYMATTR Value 15&#2013266101;H SYMBOL npn 240 -96 R0 SYMATTR InstName Q1 SYMATTR Value CA3046 SYMBOL res 176 -160 R0 SYMATTR InstName R4 SYMATTR Value 100k SYMBOL npn 368 304 R0 SYMATTR InstName Q2 SYMATTR Value CA3046 SYMBOL res 176 -304 R0 SYMATTR InstName R2 SYMATTR Value 47k SYMBOL cap 512 208 R0 SYMATTR InstName C4 SYMATTR Value 2.2n SYMBOL res 288 384 R0 SYMATTR InstName R6 SYMATTR Value 2.2k SYMBOL cap 160 -64 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C3 SYMATTR Value 10pF SYMBOL res 176 384 R0 SYMATTR InstName R3 SYMATTR Value 100k SYMBOL res 416 -64 R0 SYMATTR InstName R8 SYMATTR Value 10k SYMBOL cap 160 96 R90 WINDOW 0 0 32 VBottom 2 WINDOW 3 32 32 VTop 2 SYMATTR InstName C6 SYMATTR Value 3.3pF TEXT 320 576 Left 2 !.tran 0 200uS 0 1nS TEXT -160 576 Left 2 !.inc "..\\Lib\\Transistors\\ca3000.lib"
On Wednesday, August 5, 2015 at 11:06:29 PM UTC-4, Phil Allison wrote:
> George Herold wrote: > > > > Audio frequencies? > > I've done Wein bridges with amplitude control from diodes and > > resistor ratio's.. not great temperature coef. > > ** The peak level drops about 0.4% for each degree C, using silicon diodes. > > Zeners can do better, if the voltage is carefully picked. > > > ... Phil
Yeah I think that's about right. (2mV out of 500 mV) But I use the diodes to trim off the top of the sine wave so it might be worse than that...(or better?) I'd have to do the math. https://www.dropbox.com/s/lmso5zx69g2l1lc/DSCF0047.JPG?dl=0 I was thinking you might be able to use Spehro's "ideal diode" trick with an opamp (or two). (Of course it would then need some other voltage reference.) George H.
On Thu, 06 Aug 2015 03:03:48 -0400, Tom Del Rosso wrote:

> More responses than I expected. I appreciate it but can't respond to > all right now. > > Tim Wescott wrote: >> >> I would use AGC. >> >> If wasting power is an issue then you're going about it more or less >> backwards -- at best, a linear oscillator on an unregulated rail with a >> constant output is going to use just as much power as an oscillator >> being powered through a linear regulator -- and it'll probably be >> worse. > > I understand what you mean. The idea came that it must be possible, but > I've never seen it done specifically, so I got curious about how complex > such an oscillator would be. More complex than a regulator it turns > out. > > >> If you can run at a constant amplitude, use a switching regulator. >> >> What frequency range are you looking at? > > Low KHz.
If you want dead-constant amplitude and lowest harmonic generation, then with or without a regulated rail you need some sort of AGC. Moreover, your AGC itself needs to be well-behaved enough that it, itself, does not cause harmonic distortion. If you don't just throw your hands in the air and use a DDS, your best bet is probably a Wein bridge oscillator. If you want to go old school with the ADC, use a light bulb. -- www.wescottdesign.com
On Wed, 05 Aug 2015 12:39:09 -0400, Tom Del Rosso wrote:

> I don't want anybody to design it for me, but in general how would you > make an oscillator with a sine output of constant amplitude over a range > of supply voltage (let's say the operating range of the op-amp). What I > have in mind is a battery supply, but with no power wasted in a > regulator. Sure the oscillator would also waste power but not as much. > Would a square output be simpler?
Can you get by with a squarer wave? If yes, then your easiest and most fuel-efficient way to do this would be to regulate with a switcher and then generate a square wave by any of the many acceptable ways. Just plain easiest, and not too bad on current consumption if you don't need any appreciable power on the output, would be a linear regulator powering your oscillator. Maybe tell us what this is for so we can ground our opinions in fact instead of spinning off into our own versions of theory-land? -- www.wescottdesign.com
On Wed, 5 Aug 2015 10:01:04 -0700 (PDT), George Herold
<gherold@teachspin.com> wrote:

>On Wednesday, August 5, 2015 at 12:39:19 PM UTC-4, Tom Del Rosso wrote: >> I don't want anybody to design it for me, but in general how would you >> make an oscillator with a sine output of constant amplitude over a range >> of supply voltage (let's say the operating range of the op-amp). What I >> have in mind is a battery supply, but with no power wasted in a >> regulator. Sure the oscillator would also waste power but not as much. >> Would a square output be simpler? >> >> -- > >Audio frequencies? >I've done Wein bridges with amplitude control from diodes and >resistor ratio's.. not great temperature coef. >
I've done quadrature oscillators (two opamp integrators) with diodes (or zeners) to limit the voltage. If you put the diodes on one integrator only, the waveform from the other has very little distortion (<.1% is fairly easy to do, IIRC). Both sine and cosine are available, if needed.
Tim Wescott wrote:
> On Wed, 05 Aug 2015 12:39:09 -0400, Tom Del Rosso wrote: > >> I don't want anybody to design it for me, but in general how would >> you make an oscillator with a sine output of constant amplitude over >> a range of supply voltage (let's say the operating range of the >> op-amp). What I have in mind is a battery supply, but with no power >> wasted in a regulator. Sure the oscillator would also waste power >> but not as much. Would a square output be simpler? > > Can you get by with a squarer wave? If yes, then your easiest and > most fuel-efficient way to do this would be to regulate with a > switcher and then generate a square wave by any of the many > acceptable ways. > > Just plain easiest, and not too bad on current consumption if you > don't need any appreciable power on the output, would be a linear > regulator powering your oscillator. > > Maybe tell us what this is for so we can ground our opinions in fact > instead of spinning off into our own versions of theory-land?
It's mainly for general knowledge, since my test signal doesn't have to be that constant. I just got the idea that it must be possible, so, if it was easy then I'd do it, or else just use a regulator. The Wein Bridge is easy enough to be worth a try so I'll breadboard a few and try it with a variable supply to see what happens. Thanks very much to all. --