Microwave characterization and modeling of GaAs/AlGaAs heterojunction bipolar transistors

The characterization and modeling of a microwave GaAs/AlGaAs heterojunction Bipolar Transistor (HBT) are discussed. The de-embedded scattering parameters are used to derive a small signal lumped element equivalent circuit model using EEsof's Touchstone software package. Each element in the equivalent circuit model is shown to have its origin within the device. The model shows good agreement between the measured and modeled scattering parameters over a wide range of bias currents. Further, the MAG (maximum available power gain) and the h sub 21 (current gain) calculated from the measured data and those predicted by the model are also in good agreement. Consequently, the model should also be capable of predicting the f sub max and the f sub T of other HBTs.