Low frequency analog VCO with sinewave output?

Never heard of HP?

John

First problem: it'll take two adjustable elements, and they have to change at the same time, in matched fashion. That's how a Wein bridge works. Matched jFET pairs are unobtainium.

Second problem: the voltage range for a jFET as variable resistance is under a volt, and the usual bias assumes one of the terminals of the FET is grounded. The Wein bridge oscillator doesn't support that.

A possible workaround (if you can find 'em) is to use photoresistors, in a matched-pair illuminated by a common light source.

It was kind of an off the cuff suggestion. You could make a state-space oscillator, i.e. two op-amp integrators one after the other, each with a JFET-based attenuator. That'd give you the same effect as a Wien bridge, and the only thing that mismatch would do would be to make the amplitudes of the two stages mismatched.

I don't think you'd get close to the OP's desired 50:1 frequency ratio with JFETs, though, and any wholly analog solution would be challenging.

True. I'm not sure how important an exact match is -- a Wien bridge will probably still oscillate just fine with mismatched resistors, just with the states imbalanced somewhat. How would they be imbalanced -- I dunno. That's an exercise for the reader.

At one point you could get 74HC4040 parts -- dunno if they're still out there.

I was thinking of that part because of the built-in oscillator -- what programmable logic part has that?

Curiosity (well, sloth): does it have an on-board ADC?

This is basically what I suggested (except I suggested a PIC). The OP wants analog only, for whatever reason.

You'd need more than "a JFET" to make the frequency adjustable over any singificant range. Most Wien bridges use a JFET as an adjustable resistor to control the amplitude, so it wasn't exactly obvious that your single JFET was intended to adjust the frequency.

Quite a part from the fact that it would be hard to make it work well for other reasons.

-- Bill Sloman, Nijmegen

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Sorry about that. But the OP was asking for a voltage-controlled oscillator. I admit that if you stuck a DC motor on the front of an HP200 you could make it act as a voltage-controller oscillator, but this is a long way from the single-chip soluution that the OP was asking for

From the pictures it looks as if the fine control of frequency depended on a pair of rotating segment variable capacitors, which isn't an approach that anybody seems to have duplicated inside a single chip.

-- Bill Sloman, Nijmegen

Some of the biggish CMOS counters RCA made at that time had built-in oscillator drivers, but the 4040 wasn't one of them.

-- Bill Sloman, Nijmegen

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I'm waiting for someone to suggest using two ceramic Z5U caps as the frequency tuning elements in a Wien bridge. I'm not they would do the 50:1 frequency range. Of course you'd have to keep the AC amplitude relatively low.

George H.

Then -- as I stated in my original reply -- it's either the 4020 or the

National's AN-31 describes a "Wein Bridge Sine Wave Oscillator" on page 8, right side, using an incandescent bulb (Eldema 1869, with about 100k hr lifetime.)

Jon

Sorry, forgot to add that page 11 shows amplitude stabilization using 2 BJTs and a JFET.

Jon

It was the 4060

as if anybody cared. The original poster clearly isn't interested in going down that route, and if he were he'd be more likely to go for a programmable logic device which could provide all the logic he wanted

- including providing the gates to activate a simple oscillator - in a single chip.

Sadly, he doesn't want to think about digitally-based solutions.

-- Bill Sloman, Nijmegen

For the love of Jobs will you PLEASE learn how to snip. PLEASE.

Jim

For the love of Jobs will you PLEASE learn how to snip. PLEASE.

Jim

For the love of Jobs will you PLEASE learn how to snip. PLEASE.

Jim

For the love of Jobs will you PLEASE learn how to snip. PLEASE.

Jim

For the love of Jobs will you PLEASE learn how to snip. PLEASE.

Jim

His entire post was only 25 lines!

John