The design of band-gap reference circuits - trials &  tribulations.
Bob Pease.

Aimed more at IC designers BUT of value to people wanting to use references
and understand them a little.

        http://manuales.elo.utfsm.cl/datasheet/national/htm/nsc03420.htm


        http://www.national.com/rap/Application/0,1570,24,00.html


Both the same paper but the first has more references attached.

MAY even be of value to someone wanting to implement their own on the cheap
:-)
Reference ICs are dear! You can but a bottom end microcontroller for less
than a reference circuit good enough to give you 10 to 12 bits accuracy. .

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