[sdiy] What is a quadrature oscillator good for?

[Don Tillman]

   > Date: Fri, 12 Sep 2003 12:38:56 +0200
   > From: jhaible at debitel.net
   > 
   > > The other is that any offset voltages in the integrators will
   > > cause the triangle outputs to slew at wildly different rates at
   > > frequencies near zero Hz.  Possibly even slewing in different
   > > directions.
   > 
   > I don't think so. There is this 200k feedback resistor from the
   > 2nd integrator to the schmitt trigger that will (hopefully)
   > prevent this.

Sure, but that's a correction that adjusts the trigger points and
therefore only works averaging over multiple cycles, right?  Or am I
confused?

I'm thinking of a specific case where the VCO is sitting at 0 Hz, then
you nudge it to a very slightly positive frequency for a tiny bit, and
then nudge it to very slightly negative frequency for another tiny
bit, then back to 0 Hz, not moving more than a fraction of a cycle
total.

That's a weird and difficult case, certainly, but handling this case
with the quadrature phase relationships precisely intact was a goal of
mine.  I could not find a way to implement a triangle core that kept
the phase relationships intact in this situation, so that led me to
the trapezoid core.

Does this ever come up in real life?  Sure, if you want to accurately
model the position of a freely rotating object.  That's one of my
goals (though it might not be anybody else's goal).

  -- Don

-- 
Don Tillman
Palo Alto, California
don at till.com
http://www.till.com