Balancing Emitter Follower
Original Publication Date: 1985-Nov-01
Included in the Prior Art Database: 2005-Feb-19
In order to obtain a better noise margin on emitter follower output devices used to drive diode inputs, the base-emitter voltage (Vbe) of the emitter follower output device must match that of the receiver input device. This article describes a circuit solution to this requirement whereby the heavy 'up level' current is shunted away from the output device in order to maintain its base-emitter voltage at a value very close to that of the receiver input device. Emitter follower devices normally drive a higher current load when at 'up level' than when at 'down level'. With reference to the Fig. 1 circuit of a normal emitter follower, this is seen to occur because the voltage across the resistor 2 is larger at 'up level'.