thru zero VCO questions

[Don Tillman]

   Date: Mon, 13 Sep 1999 14:48:52 +0200
   From: Rene Schmitz <uzs159 at uni-bonn.de>

   At 00:40 13.09.99 -0700, Don Tillman wrote:
   >I'm thinking of having two integrators running through four states:
   >
   >   state 1: integrator 1 rises, integrator 2 holds at -Vref
   >   state 2: integrator 1 holds at +Vref, integrator 2 rises
   >   state 3: integrator 1 falls, integrator 2 holds at +Vref
   >   state 4: integrator 1 holds at -Vref, integrator 2 falls
   >
   >This way you can run the oscillator forward and backward, however
   >gradually, without hitting any funny states.

   Well, this sounds interesting. But I'm not sure I got the idea. By
   quadrature you mean that one integrator crosses zero while the
   other one hits the reference?  And the above states are just for
   the moments where the references are hit?!

I didn't explain that very well...

By quadrature I mean having two integrators generating trapazoidal
waves 90-degrees out of phase; during the time one is slewing from the
negative reference to the postive reference the other is holding
still.  (You can convert them to your favorite waveform later.)  The
four states are four quarters of the full cycle, and each state
transition is simple and can occur in the forward or reverse direction
depending on the input polarity.  

It's sort of like the analog equivalent of counting in binary Gray
Code: 00, 01, 11, 10.  (Gray Code is used for some binary counting
applications; the order of the numbers is mixed up so that only one
bit changes per transistion.)

Like I said, I haven't worked out the details yet.

  -- Don