>Trivia time. I seem to remember that the best reference zener diodes
>(either 6.2 volt or 8.2 volt, I think) are actually a zener diode in
>series with a signal diode. This is done so that the temperature
>coefficients of the 2 diodes cancel out. Does anyone else remember the
>same thing?

Nearly correct. The 6V point is the nominally 0 temp coefficient, but it is not
done by putting a diode in series with it. It has more to do with the zener
mechanism inside the diode. Below 6V there is a different process in the way the
majority carriers move in the silicon to the way they move above 6V. I guess it
is related to the processing to achieve the zener action.

Anyway the important thing is that one process has a positive temp coeff, and
the other has a neg coeff. You will find all zeners below 6V will have one temp
coeff and above 6V they have the opposite, but by happy circumstance the
manufacturing process uses both processes to achieve the 6V breakdown and hence
the temp coeff cancel.

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