Enhanced high-current VBIC model

The widely used vertical bipolar inter-company (VBIC) model for bipolar junction transistor-heterojunction bipolar transistors (HBTs) was modified to incorporate high-current effects. The modified VBIC model keeps all features of the original model and adds new features such as mobile carrier modulation of the base-collector capacitance, high-current Kirk effects, high-current reverse emitter-base injection, and current dependence of the reverse transit time in HBTs. The new model accurately fits the dc I-V characteristics, the bias-dependent transit-time, and S-parameters at active and quasi-saturation region biases. It is shown that the new formulation accurately models the strong current dependence of f_t and G_max over a wide range of biases. It also predicts very well the power performance in class-AB operation and at the loading for maximum power-added efficiency and maximum output power. The model also shows good fitting of two-tone linearity characteristics when simulated with the same fundamental and harmonic load conditions as in the measurements.