[sdiy] quadrature sine wave oscillator question

[Czech Martin]

has anybody dealt whith those?

This looks like a state var filter, but the Q
regulation is set up so that a sine wave can build
up.

To prevent heavy saturation and distortion a amplitude
regulation is needed, like in all low distortion designs
be it Wien bridge or else.

Unfortunately the gain/phase characteristics change
a lot if the frequency is changed a lot, so
the regulator must work fast.

Usually this is done via saturation devices (zeners etc.).
This will cause some distortion.
Or by some peak detector and very slow lowpass filter.

If the quadrature outputs are squared und summed up,
this term will be DC (ideal) and can be taken for
instanteneous amplitude regulation:

SQR(sin(x)) + SQR(cos(x)) = 1

I know there was a single chip or hybride package for
this. Has anybody tried to build an audio range quadrature
VCO using this method?

Cheers
Martin Czech

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