[sdiy] Temperature compensating capacitors

[Neil Johnson]

René Schmitz wrote:
> I can't see how a changing capacitance would be able to correct for the
> scale factor temperature dependancy?
> The depencancy for T is inside the argument of an exp() function, but the
> caps tempco would act only on the outside as a factor.

Hmmm... yes maybe.  I only gave it the merest moment of thought,
rather than follow through the error flow from CV input to VCO output.

> I could image these might be useful to compensate some tuning drift, if the
> scale factor was compensated by some other means. But then again a PTAT
> sensor does the same.

These capacitors are intended for RF applications (VCOs, filters,
etc), and in a cost-sensitive product every component counts so you
can do with a fancy capacitor where you would otherwise need an
ordinary capacitor and a ptat sensor.

Neil
--
http://www.njohnson.co.uk