TRANSISTOR MODELING Microwave Transistor Modeling for Time Domain Simulation

High frequency models of transistors are of interest because they have applications to computeraided design of high frequency circuits. When these models are derived, a problem encountered is that measured transistor S-parameters do not agree with the hybrid-π model. In this article, a simplified method is described to obtain an optimized classical hybrid-π model that predicts the measured S-parameters of the device across the desired frequency band. The modeling capabilities of the CAD program Touchstone (now is incorporated with ADS) were utilized to create such a transistor model. The optimization goal is to minimize the error function between the measured S-parameters and those of the RF transistor equivalent circuit. This technique has been implemented to obtain a high frequency circuit model for the RF transistor BFY 90 across the band from 100 MHz to 500 MHz. Such a model can be used in time-domain circuit analysis programs to predict the transistor behavior.