Quadrature VCO Module finished

Haible_Juergen#Tel2743 HJ2743 at denbgm3xm.scnn1.msmgate.m30x.nbg.scn.de
Mon Sep 11 22:35:00 CEST 1995

>I'm not sure if it would work, but I thought of a two-OTA state
>variable filter with enough resonance to self-oscillate. Then the
>band-pass output would be 90 deg out of phase with the low-pass
>output. But I guess it's good for sine waves only, if it works
>at all, that is. Just a thought.

Well, sines were what I actually wanted ...
It *is* possible to build a state variable quadrature VCO. As in all
sine wave oscillators, You will need an amplitude regulation,
however. This will either cause a tradeoff between distortion and
reaction time (think of an LFO with 10 seconds period, Your
amplitude regulation would have time constants in the *minutes*
region!), or would need such efforts as true-rms-measurement.
(If You are squaring sine and cosine, and make the sum of it,
You'll have the amplitude information without ripple!).
All in all, going for triangles and converting them to sines seemed
much easier to me, granted that I can use the two OTA's used
for sine-shaping as VCA's as well.


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