oscillator with constant amplitude

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.

If you can run at a constant amplitude, use a switching regulator.

What frequency range are you looking at?

Here's a simple-minded one...

...Jim Thompson

A square wave could be made extremely stable; generate it from CMOS logic powered by a voltage regulator. The supply current would be almost entirely the load current, so the regulator really doesn't waste power.

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

What do D5 and D6 do? Are they supposed to be back to back? I can see if they were zeners but 4148s?

Miniscule amount of capacitance... in other words... a hack quickly thrown together.

In practice I'd probably use a diff-pair with controlled tail current derived from measuring the amplitude... something simple like...

What about the 1648 ECL VCO, that had built in AGC?

Michael

ICL8038 or similar triangle wave generator with built in triangle to sine converter ?

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.

Low KHz.

On 06/08/15 17:03, Tom Del Rosso wrote:

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

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"

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.

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.

If you can find a suitable grain-o-wheat bulb it's fun to make a thermally stabilized oscillator.

The bulbs aren't easy to find these days, though -- LEDs just don't work the same.

J-fet

I've done that. Distortion becomes more of an issue.

Apparently there are (or at least were) some studio-quality mixers that were implemented by shining variable amounts of light onto CdS cells for low-noise, low-distortion variable resistance controlled by a DC voltage.

Sure thing. I built circuits vaguely like that as a kid (audio companders for tape).

Jim Williams went on a long digression about HP200A oscillators and JFETs and such, and came up with something pretty good, if a bit involved.

Cheers

Phil Hobbs

Has many ways to do it, including CDS cells or jfet (.002%)

uses a cap to block DC across the jfet for an improvement in THD they only claim .01% though. With a jfet with interchangeable D-S it does better