[sdiy] Temperature Compensated VCO attempt - help?

[Scott Bernardi]

Cool, let me know the results.
I did some computer simulations of the circuit, and it seemed to work well.
Then I ran some temperature variations, and it didn't stay constant at all. But
then I realized the simplified LM13700 model I downloaded from National ignored
temperature effects!
I'm going to retrofit my thru-zero FM VCO. It will look weird, but that's DIY.

patchell wrote:

>     Scott, tomorrow morning I should be ready to test a slightly modified
> version of your circuit (basically your temp sensor in what I already had).
> Got it all wired up and working, but, I don't see so good in artificial
> light anymore...so first thing in the morning.  Also have my blue ice
> freezing in the freezer...gonna give this thing a wide range of temps.
>
> 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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> * Visit:http://www.silcom.com/~patchell/
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> *I'm sure glad Merry Christmas comes just once a year
> * -Yogi Yorgensen
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