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

[Ian Fritz]

At 07:46 PM 7/19/2003, Don Tillman wrote:
>Hi folks!
>
>I have a new VCO design that I've been working on for a long time;
>tweaking it, building it, testing it, debugging, and writing it up.
>
>   http://www.till.com/articles/QuadTrapVCO
>
>This is the one that gives you graceful thru-zero FM.  And nice
>quadrature outputs.  And a few other features.
>
>Enjoy!
>
>(Also, I *believe* this is original.  Has anybody seen anything
>remotely like it before?)
>
>   -- Don

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

   Ian