Accurate Analysis of Emitter Ballasting in HBT Power Transistors

An accurate analysis of emitter ballasting, taking into account the current gain dependence on the temperature and the collector current is presented in this paper. Numerical computations of current-voltage characteristics have been performed using the emitter ballasting resistance as a parameter. Power HBTs for mobile communications have been fabricated. Load-pull measurements at the L band have shown 30 dBm maximum output power and 45% power added efficiency with 8.5dB associated gain.