[sdiy] Quadrature Trapezoid VCO (What?!?!)

[Don Tillman]

   > Date: Sat, 19 Jul 2003 20:44:36 -0600
   > From: Ian Fritz <ijfritz at earthlink.net>
     > 
   > At 07:46 PM 7/19/2003, Don Tillman wrote:
   > >   http://www.till.com/articles/QuadTrapVCO
   > >
     > >(Also, I *believe* this is original.  Has anybody seen anything
   > >remotely like it before?)
     > 
   > Not exactly the same, but it seems related to Henry's through-zero 
   > quatrature VCO:
   > 
   > http://homepage.ntlworld.com/henry01/frequency_shifter/frequency_shifter.htm
  
(Wow, that is the most difficult to read schematic I've ever seen in
my life!)

I hadn't seen that one before!  That's really strange -- it's two
oscillating biquad filters wired back to back and cross fading
between them.  That's wild.

I would guess that amplitude stability gets to be an issue near 
zero Hz, or that it drifts toward one particular phase.  Whatever it
does, I'll bet it's interesting!

  -- Don

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