[volt-nuts] 3458A patents

[Frank Stellmach]

>  The "basic" HP patent is 4357600:
>  <http://www.google.com/patents?id=vCUxAAAAEBAJ>
>  I think this is the HP3458A.

>  There is a later HP one 4951053 which refines it with a greatly improved
>  switching technique<http://www.google.com/patents?id=INImAAAAEBAJ>. But
>  the 3458A does not use it AFAIK.

Well, only the 2nd HP patent is for the 3458A, as the author Wayne Goeke 
definitely was one of the engineers designing its A/D.
(See HP Journal 4/1989).

But there should be several others, concerning cancellation of charge 
injection effect, as described in the journal, and realized by the ASIC 
they have designed.

It's quite interesting, that no other instrument, wether DVM, or 
calibrator (i.e. Fluke 5720A) comes near the linearity of the 3458A 
(0.02..0.05ppm of input),
after all those years.
And as far as I overview the situation, the 3458A and the 5720A are 
today the only instruments having complete auto calibration from 2 or 3 
references only.

Btw: There's now the full Fluke 5700/5720A service manual including 
schematics hosted on ko4bb.com, saved just before Fluke has violently 
cut off the most interesting part of this manual.
It's an interesting read about the 13V reference hybrid and the D/A.

Frank