[sdiy] Patchell's Boggling 13700 Expo Converter Thing???

[Ian Fritz]

Cynthia, et al. --

It's a boggler, all right.  I spent a big chunk of time a few weeks ago 
analyzing it in great detail, including working out all the possible 
temperature drift sources that I could think of.  The most amazing part 
about it is the tandem OTA part, which casus the usual OTA input 
nonlinearities to cancel to a *very* high degree of accuracy.  These 
nonlinearities were the biggest drawback of other designs that people here 
have worked on.

   Ian

At 05:24 PM 6/21/2003, Cynthia Webster wrote:
>Hi!
>
>Jim, while we're talking about 13700s...
>could you shed some more light on your mystical
>13700 exponential converter circuit?
>
>It's really boggling!  I look at it
>and just don't *get* it...
>
>Please enlighten us on just what is actually
>going on in there?
>
>Thanks a bunch, I feel that this is of
>*major* usefulness, but here I am trying to apply it
>to a discrete oscillator design and I keep
>scratching my head over it?
>
>(please help?)
>
>LOL!
>
>Hey, it's a Sunday!
>(hope no school busses are trying to mow you down today!)
>
>Best Wishes
>
>oh, did I mention...
>
>< HELP! >
>
>LOL!
>
>Thanks
>
>Cynthia