SMALL-SIGNAL NON-QUASI-STATIC MODEL FOR SINGLE AND DOUBLE-HETEROJUNCTION BIPOLAR-TRANSISTORS

A non-quasi-static small-signal model for single and double heterojunction bipolar transistors (HBTs) is presented. The model takes into consideration the non-quasi-static effect (NQS) by introducing a current source between the base and collector to account for the change in the base charge, due to the change of the input applied voltages. The admittance of the current source is found to have a capacitance-like behavior, which is termed ''transcapacitance'', since the value of the current source depends on the base-emitter voltage rather than on the terminal voltage, i.e. the base-collector voltage. The magnitude of this transcapacitance depends on the concentration of the minority carriers injected into the base region. The present model is used to study the frequency response of HBT's for frequencies up to 100 GHz. The results show that this model is in good agreement with the results obtained from the numerical calculations. This model can, therefore, be used to obtain a more accurate simulation for HBT integrated circuits.