Comparison of the load-pull power characteristics of common-emitter and common-base heterojunction bipolar transistors

The power characteristics of common-emitter and common-base AlGaAs-GaAs based HBTs are compared using on-wafer load/pull measurements. Gain compression is more pronounced for common-base HBTs. The sensitivity of the device gain on the load termination conditions is smaller for common-emitter than common-base HBTs. Device self-bias is strongly dependent on load termination at high power levels for CE but not for CB HBTs. As a result, a unique load termination exists resulting in both maximum gain and power added efficiency in the case of CB HBTs. In the case of CE HBTs optimum load terminations can be selected through tradeoffs between the output power and efficiency load-pull contours.