[sdiy] Temperature Compensated VCO attempt - help?

[patchell]

    Very preliminary results...but I would say you have a winner here
Scott.  I haven't reduced what little data I have yet, but the expo
converter looks very stable.

    Scale conformity I am getting is pretty much as before, although, I
haven't checked it over 8 octaves yet.  But over 5 octaves I am getting
about +/- 2 cents (same as before, no big surprise).

    I need to get a few more points before I can calculate the tempco.

Scott Bernardi wrote:

> 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. The VCO works, but the exponential generator
> suffers from linearity problems. I can tune it to a nice 1v/octave
> response using my VCO tuner
> (http://home.attbi.com/~sbernardi/elec/og2/vco_tuner.html) at 0v CV, but
> as soon as I deviate from that either higher or lower in frequency, the
> scaling is off.
> I've got a pretty detailed theory of operation and schematic at
> http://home.attbi.com/~sbernardi/elec/og2/tempcomp_vco_theory.htm.
> Jim (Patchell), I was especially interested in your temp compensated
> VCO, and notice you changed the circuit because the previous one was
> "bogus".  I believe on your previous circuit you were using a delta Vbe
> bandgap reference like mine - was that giving you problems? I also
> notice you are using a different configuration for your multiplier OTA
> that "linearizes" it.  I suspect it might be my OTA multiplier that's
> causing the problems.
> Anybody care to comment?

--
 -Jim
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