Constant-current source with unusually high internal resistance and good temperature stability

A transistor operating at 1 mA, with 10 k¿ in the emitter lead, gives a collector a.c. output resistance in the region of 10 M¿. A 2-transistor circuit is described, having an output resistance of approximately 50 M¿, with much improved temperature stability. A further modification gives an output resistance of about 1000 M¿, corresponding to an `aiming voltage¿ of 1 MV.