Importance of matching in expo convertors?!

[Rene Schmitz]

>From the Ebers Moll equation follows: (With no matching assumed)
(with Ic >> Is) dVbe= kT/q * ln(Is1/Is2 * Ic2/Ic1) where Is are the reverse
leakage currents. Is depends on material, doping, geometry and temperature
(something else?). I don't know the exact dependancy, but I *think* that
for any given pair of transistors Is1/Is2 is a constant, if both
transistors are on the same temperature. One gets the usual form of this
equation when both transistors are matched, then Is1=Is2. Now, wouldn't
this mean that we needn't use matched pairs in expo convertors?!

Any opinions? of experts in semiconductor physics?

Bye
 René





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