[sdiy] Temperature Compensated Exponential Converter Using SSM2164

[Ian Fritz]

At 11:32 AM 8/30/2009, David G. Dixon wrote:
>Missing the next octave by 1 Hz is no big deal
>if your target is 1760 Hz, but it is a very big deal if your next octave is
>55 Hz.  Capiche?

Ummm ... no.   :-)

What is most objectionable about mistuning is the beating it creates.  In 
your example there would be a 1 Hz beat rate (against a perfect 
reference)  for either case.  Not bad at all.

This why I set my VCOs up so that deltaVbe at the converter pair 
corresponds to something around 2 kHz.  (deltaVbe = 0 
--->  exp(a*deltaVbe/kT) = 1, so there is no T dependence at this 
point)  Drift above this point isn't too important, because you rarely use 
fundamental frequencies much above 3 kHz.  Drift below this point becomes 
less and less critical as you go down, because a 1 Hz beat represents 
smaller and smaller fractional error.

Just my personal philosophy, I guess.  :-)

Ian