[sdiy] What is a quadrature oscillator good for?

[jhaible at debitel.net]

> I've performed similar tests, but not that one exactly.  I'll set it
> up and try it soon, and maybe get a scope photo.

Similar tests is close enough. (I just picked a random example.)


> I don't expect to find any problems though.  This circuit really
> doesn't mind going through zero Hz, bouncing off zero Hz, or sitting
> at zero Hz.  Although sitting close to zero Hz does require trimming
> the OTA offset voltages accurately.

But doesn't the offset voltage change slightly with the amplifier
bias current? You're avoiding the split into sign and magnitude,
but you "pay" for this with the need of precise 2-quadrant
multiplication, where "ordinary" triangle cores just need the
OTA for switching.

(I'm still convinced your design is far superior to others
for audio rate thru zero FM; maybe even the first one that
really does the trick! My dogged questions are just to
check if this could also be a better choice for a frequency 
shifter VCO.)

JH.

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