Quiescent operating point shift in bipolar transistors with AC excitation

Describes the rectification response of a bipolar transistor to a small AC signal applied at the base. An RC transmission line model based upon device material and geometrical properties is used to calculate the AC voltage distribution across the emitter. Small changes in the DC operating point at each location across the emitter are then calculated and summed to obtain the terminal characteristic. It is found that the effects of AC crowding and nonlinearity combine to cause DC crowding where the new rectification induced DC current distribution favors the perimeter of the emitter. A model based upon the hybrid pi format is found to be consistent with RF distribution and resultant crowding equations. Also, it is shown how a high frequency rectification response measurement, which, because of severe AC crowding, is edge sensitive, may be used to study recombination near the edge of the emitter.