[sdiy] VCO - sine output - why bother?

[mskala at ansuz.sooke.bc.ca]

On Fri, 26 Aug 2016, Quincas wrote:
> Is there not a way to make a sine core oscillator and derive the other waves
> from it? Like a filter with fixed high resonance for the sine, a comparator
> for the square etc...
> Why doesn't anybody do that?

I think the sawtooth is tricky to do by waveshaping, and the triangle
isn't trivial either.  But just today I was thinking about a hybrid
design:  have the exponential converter generate two duplicate currents,
one drives a sine core, integrate the other for a sawtooth, but don't use
a comparator on the sawtooth for resetting the integrator.  Instead, use
the zero crossings of the *sine* core to decide when to reset the sawtooth
core's integrator.  That way reset time doesn't affect the accuracy of the
sawtooth's tracking.  The triangle shape would most naturally come from
rectifying the sawtooth (with the usual glitch of doing that).

This would not necessarily be better overall than a more conventional
design, but it seems like it would at least have *different* issues, and
would be fun to try.

-- 
Matthew Skala
mskala at ansuz.sooke.bc.ca                 People before principles.
http://ansuz.sooke.bc.ca/