It doesn't produce a clean sine wave where the frequency can be changed electronically. It produces a clean sine wave where the frequency can be changed leisurely by a slow processor.
(I didn't say it was a _good_ solution, just that it's _a_ solution.)
I'm not sure how you build an oscillator without AGC of some sort; you must be a better man than me.
Ok, but if I need a uC I might as well plop down a DDS chip and let it leisurely program that in a loop. Even a brand-name AD9837 can be had for around two Dollars.
I am certainly not a better man. I grew up with RF and most of my oscillators were of the LC kind. It's been too long ago and I think the last oscillator with AGC I built was at my alma mater. Back in nineteen-sumpthin'. We had to prevent it from railing because the rails were considered "unclean" and they wanted to avoid anything being modulated in.
You can do an audio Wein bridge with a few hundred pF. I would be surprised if some in that range aren't still available. Plus you can always parallel a handful.
?-)
The BB201 is nowadays the highest one that is reasonably available in the marketplace. Realistically you can use it up to around 25pF, maybe
30pF. After that the excitation by the oscillator will cause painful nonlinearities.So yeah, you can parallel. But rather than a handful it'll be a bucket full.
hmm, yeah, with an 8 bit dac you can represent 25600 distict evenly spaced phases of 10kHz square-wave on that setup. I guess the sine-wave potential woukd be similar.
There's this guy did a Cordic DDS (on an MSP430 iirc) that might be a better fit if you do need lots of samples
You can do it even without Cordic, one guy always calculated all this stuff anew, on the fly. Luckily ALU cores do not suffer from perspiration and muscle cramps. But that can easily interfere with other realtime routines that have to run.
Luckily, there's also an analog way :-)
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