Compensated Exp generators and VCO's

[Don Tillman]

Actually you don't need that opamp/fet precision current source
thingie at all.  The negative input of the exponential converter opamp
is gonna be at ground, so all you need is a resistor to a reference
voltage.  The voltage source at the high end of the VCO cap would
probably work fine.

I'm a firm believer in simplicity.

(And I'm really surprised how well this web page approach works --
it's the high-tech equivalent of scrawling on a napkin!)

And this circuit seems to be asking for a p-channel vfet to discharge
the VCO cap.

One other thing, and this is entirely personal user-interface
aesthetics, I'd recommend averaging the switched outputs instead of
summing them. 

  -- Don