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From: john larkin <jl@glen--canyon.com>
Newsgroups: sci.electronics.design
Subject: Re: Random thoughts on sinewave oscillators
Date: Fri, 18 Oct 2024 10:15:25 -0700
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On Fri, 18 Oct 2024 17:04:15 -0000 (UTC), Cursitor Doom
<cd999666@notformail.com> wrote:

>On Fri, 18 Oct 2024 08:36:15 -0700, john larkin wrote:
>
>> On Fri, 18 Oct 2024 09:48:17 +0100, liz@poppyrecords.invalid.invalid
>> (Liz Tuddenham) wrote:
>> 
>>>Edward Rawde <invalid@invalid.invalid> wrote:
>>>
>>>> Is the reason why this doesn't produce a better looking sinewave
>>>> because the amplifier slew rate is faster going down than it is going
>>>> up or some other reason?
>>>> 
>>>> Ignore the wild decoupling, it took me long enough to get the concept
>>>> to work at all.
>>>> 
>>>> I'm aware that a single package containing two op amps could probably
>>>> do a much better job.
>>>
>>>if noise is more important than waveform, I found amplitude control by
>>>clipping gave the lowest noise.  The oscillators in this...
>>>
>>><http://www.poppyrecords.co.uk/other/DistortionMeter/intermodmeter.htm>
>>>
>>>...are amplitude stabilised by clipping.
>> 
>> If the gain of an oscillator loop is close to 1.00, say 0.98 to 1.02, 
>> one can add in a small tweak, a crude multiplier or even a clipper, to
>> make up the difference.
>> 
>> Of course, with many-bit DACs being cheap nowadays, it's easier to do a
>> DDS sine wave generator, and get super-precise frequency and amplitude.
>> A 70 cent uP can do that, and even use PWM to eliminate the DAC.
>> 
>> All sorts of elegant analog circuits are blown away by cheap digital
>> junk. Sigh.
>
>Put the output you get from that through a spectrum analyzer and it won't 
>look quite so super-duper.

Of course a DDS needs a post-DAC lowpass filter, but a 16 or 20 bit
DAC can make extremely good sine waves.

Just don't push the Nyquist rate.