Microwave Interference Effect in Bipolar Transistors

This work discusses the active circuit behavior of typical bipolar transistors as they are injected with low level microwave energy. The observed response is found to be due to square law rectification of the energy at the transistor´s emitter-base junction. A rectification efficiency measurement´is described which gives a quantitative measure of a transistors sensitivity to microwave interference in terms of an equivalent rectified base current interference signal per unit of absorbed microwave power. Measurements show that a typical n-p-n Si planar transistor (FT = 450 MHz) has a rectification factor of approximately 0.05 mA/mW for 2 GHz microwave energy. Typically, this factor decreases at about 6 dB/octave as the interference carrier frequency is increased. A model for the rectification effect is propQsed which suggests that it is due to ac crowding and the decrease in transistor a at the edges of the emitter, in addition to the basic nonlinearity of the emitter-base junction volt-ampere characteristic.