Re: Sinewave oscillator without gain control.

On 30/01/2025 2:31 am, Edward Rawde wrote:

"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vnck1i$295d5$1@dont-email.me...

On 24/01/2025 5:02 pm, Edward Rawde wrote:

"Bill Sloman" <bill.sloman@ieee.org> wrote in message news:vmv6ac$22ufe$1@dont-email.me...

On 24/01/2025 11:14 am, Edward Rawde wrote:

Before you can make a 1kHz sinewave oscillator with constant output level and better than 120dB harmonic distortion you'll need
an
oscillator which does better than that when it passes through the required output level.

>
This is obviously true. Why do you think you need to tell us about it?
>

>
You do make me laugh sometimes Bill.
Your circuit doesn't come anywhere close to 120dB but it does depend on which simulator you ask.

>
I never said it did.

 I never said you said it did.
Facts are still facts whether anyone says them or not.

But your line does imply that I did, and that is a fact.

I was looking for comments on the way the current mirrors might screw up the waveform. I didn't get any.
>

Adding a FET gain stabilizer to the circuit I posted seems to have negligible effect on the distortion.

>
Then you haven't looked at the current waveform going through the the FET.

 But I have looked at the distortion level both with and without the FET stabilizer and I have not found any difference worth having
in an LTSpice simulation.

Then you haven't looked hard enough. Get LTSpice to plot the current through the FET minus the sine function current that ought to be running through it.
In any case the current going through the FET also goes through the parallel resistor which, as you pointed out some time ago,

should be as small as possible.

That's not what I said, which you have clearly misunderstood.

Perhaps JL would like to elaborate on what he means by two FETs in anti-parallel. How would you drive the gate of the other FET?

The same way as you drive the gate of a single FET, from the error signal coming out of the rectifier-filter-integrator stage, but with opposite polarity and with a DC offset reflecting differences in the FET gate on-voltages (which have a fairly large production tolerance).
It call for a fairly elaborate setting up procedure and microcontroller and a  DAC or two to make it work = loads of components.

So I'd concentrate on the oscillator distortion level rather than the gain controller contribution if I wanted to attempt better
than 120dB.

>
And you'd probably better dump LTSpice 24.1 - it has been claimed that it has a serious bug.

 Could you please provide a reference to this claim.

My informant said it had come up on the LTSpice user's group, wherever that is.

Who has claimed that it has a serious bug and is there an online discussion anywhere?

Obviously there is, but I don't know where it is.

Exactly what is this serious bug other than the fact that your circuit gets completely different results?

I'm not claiming that this is the result of the bug - whatever it is - just raising it as a possibility.

That might explain why your simulations of my circuit run a thousand times slower for you than they do for me and a couple of
other people.

 There is obviously a big difference but I have not so far seen any evidence to confirm that it is a serious bug.

No surprise there.
--
Bill Sloman, Sydney