Large signal HBT model with measurement based charge formulations

A new large signal HBT model is proposed and experimentally evaluated, which contains measurement based diffusion charge and analytical depletion capacitance formulations. In order to account for the complicated dependency of diffusion charge on bias, transit times at various bias points are extracted from measured data and contour-integrated. Using spline functions in the interpolation of transit times, modeled RF characteristics are continuous and smooth up to 3rd order derivative with respect to collector current in the wide range of bias. Base-emitter depletion capacitance C_be is implemented considering GaAs emitter capping layer as well as InGaP emitter layer. It is shown that the new formulations of diffusion charge and depletion capacitor improves the accuracy of the large-signal model. Simulation results are verified with comparison to measured S-parameter and gain characteristics in the whole bias range.