Microwave Transitor Modeling for Time Domain Simulation

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  • Author: Firas Mohammed Ali
High frequency models of transis-tors are of inter-est because they have applications to computer-aided design of high fre-quency circuits. When these models are derived, a problem encountered is that measured tran-sistorS-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 opti-mization 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 pro-grams to predict the transistor behavior.