Usage of HBTs beyond BV/sub cec/

Abstract

Heterojunction bipolar transistors (HBTs) are preferred devices for designers to realise power amplifiers due to their good noise and HF performance. The collector emitter breakdown with open base (BV/sub CEO/) is in first order limiting the HBT operation conditions, especially for high output power where it is useful to utilise the complete voltage swing. In real applications with an ohmic connection of the base to a voltage source the breakdown condition can be released. We deliver a new formula for the emitter collector breakdown BV/sub CER/ as a function of the external base resistor, the emitter base voltage and the temperature. A safe operating area (SOA) is defined enabling the reliable usage of HBTs for emitter collector voltages higher than BV/sub CEO/ depending on base emitter voltage range and temperatures.