[sdiy] Interesting Through-Zero VCO

[Don Tillman]

   > From: "jhaible" <jhaible at debitel.net>
   > Date: Mon, 29 Dec 2003 12:05:54 +0100
   > 
   > > in EDN design ideas...
   > > http://email.ednmag.com/cgi-bin2/DM/y/efIW0Eil3C0Dar0B5rI0AE
   > 
   > Interesting idea!
   > Starting this at low frequencies might be a problem, though. (As with
   > most / all? VCF-based sine oscillator cores)

Yah; Ian Fritz pointed this one out when I introduced the QuadTrap
VCO.  

While this circuit is a delightfully original approach, I don't
believe it will perform very well at 0 Hz, near 0 Hz or going through
0 Hz.  For instance, if I supply a control voltage that holds one
integrator still at 0 Hz, there's nothing keeping the other one in
place.  And likewise there's nothing to hold the quadrature outputs to
cos^2 + sin^2 = 1, or to hold them 90-degrees apart at low
frequencies.

On the other hand, can anybody come up with a creative use for a
thru-zero VCF?

  -- Don

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