[sdiy] VCO tuning philosophy re-visited

[David G. Dixon]

> As I explained in a previous post today, the LM331 -- that's three three
> one -- has no reset error like other cores do.  Yes, you still have to
> have
> an expo converter and to compensate and correct it.  But at ultrasonic
> frequencies the reset error of a standard core is quite large.  The
> LM331  tracks to within 0.1% up to 120 kHz or so.

Yes, and that's perfect for a DoubleDeka but won't do for an 8-bit (or,
really, even a 4-bit) wavetable VCO.  I need something faster.  I'm out of
my depth now, however, as I have no idea how to convert an exponential
current into an accurate clock frequency in the MHz range.  Any ideas?