[sdiy] Matched transistors and EFM circuits?

[Paul Schreiber]

> The transistors in an expo converter need to be matched so as to cancel the Is 
> prefactor.
>
> Late night?

True, but if they are not on the same die, they really don't "cancel" over 
temperature.

And then there is base-spreading resistance :)

I suppose the general answer: if you want tracking "good enough" for VCOs,
use a matched monolithic pair. A SSM2210/2220 are <$4.50, you can get
tempcos for ~ $5, so why even *worry* about it?

For a VCF, even something like a 3086/3046 is fine. As if $10 blows your whole 
budget :)

Paul S.
life is too short to worry over $10