Re: The low distortion oscillator problem

On Fri, 7 Feb 2025 12:43:17 -0500, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 2025-02-06 00:44, john larkin wrote:

On Thu, 06 Feb 2025 05:08:16 +0000, JM
<sunaecoNoChoppedPork@gmail.com> wrote:
 

On Thu, 6 Feb 2025 03:58:59 +1100, Bill Sloman <bill.sloman@ieee.org>
wrote:
>

There have been quite a few postings about 1kHz low distortion sine wave
oscillators.
>
The problem is that if you want a get stable output from a sine wave
oscillator you have to add a non-linear element to control the gain
around the oscillating circuit.
>

>
You don't.

 
What limits the amplitude?
 

We had a long discussion of this in one of the myriad other 1-kHz
oscillator threads.  One approach is to use a comparator+integrator to
control the tail current source (suitably cascoded).
>
The key is for the gain-setting mechanism to be outside the oscillator
loop, so that it doesn't get run through its range on each cycle.  The
bias of the active device does change some, of course, but that's harder
to avoid.
>
Cheers
>
Phil Hobbs

But where can I buy those linear diodes?

The idea of using a s/h to pick off the sine amplitude, for level
feedback, is interesting. Properly done, it should result in a
zero-ripple amplitude signal.

Or use an active full-wave rectifier to get the average, and filter
the heck out of that.

I suspect that nobody needs a way-sub-PPM THD sine wave, so it's
pretty much a game.

One might Spice using an ohmic mosfet or two as a low distortion
variable resistor. The i/v curves look awfully straight around zero.