[volt-nuts] Best reference after LTZ1000
Charles P. Steinmetz
charles_steinmetz at lavabit.com
Sun Aug 22 21:03:16 UTC 2010
>At least empirically, Geller's reference has been around since 2004,
>he now has longevity statistics on his side that his board is a
>capable of at least a 1 month transfer of 10. 000 00 Vdc reference
>from his lab to you, if so inclined.
>Its interesting this has come up for his services several times, the
>issue of sales. But I think differently.
Geller has a patent covering a method of improving the temperature
coefficient of an AD58x or similar monolithic reference using an
LM399 or other ovenized reference
(http://www.pat2pdf.org/patents/pat7382179.pdf). A friend has a
little reference box he bought from Geller that claimed to use a
circuit based on the patent. However, according to the patent,
Geller didn't use opposite tempcos to offset each other, he
essentially just swamped the internal reference and used the AD58x as
an output scaling amplifier for the ovenized reference. So why use
an AD58x in the first place? You could do significantly better with
a precision op amp and the ovenized reference, with a little
attention to details. So, the patent appears to be what we used to
call a puff patent.
I notice that his current offering is just a PCB with an AD587 and a
(http://gellerlabs.com/SVR%20schematic.pdf). Apparently, he
concluded that his patented circuit didn't improve things over the
current AD parts enough to be worthwhile.
This is not to say that his references aren't any good, or don't do
what he says, or aren't good value. They are certainly reasonably
priced, and he is very clear about what they are and are not
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