[sdiy] Temperature Compensated VCO attempt - help?

[patchell]

    I got enough data now that I could make a calculation, although, before I will
make any claims, I still need more data, but, right now, I came up with 45ppM/C for
the scale drift.  Now, if past experience is any indicator, this number will jump
around a bit as I collect more data, however, this is an oder of magnitude better
(old reading for this same VCO was 400ppM/C) than any data I have ever collected
for a VCO.  I guess if this ends up working out OK, I'll have to send you some
boards Scott.

Scott Bernardi wrote:

> 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
> > ------------------------------------------------
> > * Visit:http://www.silcom.com/~patchell/
> > *-----------------------------------------------
> > *I'm sure glad Merry Christmas comes just once a year
> > * -Yogi Yorgensen
> > ------------------------------------------------

--
 -Jim
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* Visit:http://www.silcom.com/~patchell/
*-----------------------------------------------
*I'm sure glad Merry Christmas comes just once a year
* -Yogi Yorgensen
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