SV: Re: SV: [sdiy] QVCO schemo up

[JH.]

> infact this cirquit is nothing more then a variation of the SVF!

Sure - what else should it be?
It's a 2nd order differential equation in the most direct realisation.
If it's dampded, it's a filter. If it's not, it's an oscillator. The art
lies
in keeping it _just_ so undamped, that it oscillates without increasing
amplitude.


> But i have doubth that the source of the triangle syndrome are caused by
the
> diode biasing because you can repalce the zener folder into a single diode
> folder stage and the triangle dissapers, only sine are possible no matter
> whether you bias the stages or not.
> So i wonder how can you shape an sine into a triangle with one OTA?

If you make the circuit withtwo slightly different integrator capacitors,
you'll
see that as a result either sin or cos output will be of larger amplitude
than the other.
Now make them dramatically different (by removing the diode bias in one
integrator), and make one of the integrator inputs prone to overdrive at low
levels (also a side effect of removing diode bias), and a tri / sin
combination
isn't surprising.

A sine wave with large amplitude and severe slew limiting (because the
integrator is overdriven) is ...
... a triangle wave.

JH.