[sdiy] Temperature Compensated VCO attempt - help?

[Don Tillman]

   > Date: Wed, 29 Jan 2003 13:39:54 -0800
   > From: Scott Bernardi <sbernardi at attbi.com>
   >
   > I've made an attempt at an electronically temperature compensated
   > exponential generator and VCO. I built it into a thru-zero FM VCO based
   > on an Electronotes design. 

I'm really curious how the thru-zero VCO works?  (Perhaps I may have
to break down and finally buy a copy of Electronotes.)

   > The VCO works, but the exponential generator suffers from
   > linearity problems. 
   > http://home.attbi.com/~sbernardi/elec/og2/tempcomp_vco_theory.htm

(Wow, that's a complicated exp amp!)

I would think that the linearity of the OTA would be a major issue.
OTA's aren't especially linear... in the sense that they make great
triangle to sine converters.

It should be easy to see if the OTA is at fault; tap off the output of
U13, maybe crank up it's gain, and check the linearity from the input
to that point.

   -- Don

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