High-frequency model

The metal-oxide-semiconductor field effect transistor (MOSFET), a threeterminal nonlinear element used in many electronics applications, is often specified in terms of its y parameters. The ac parameters are strongly dependent on the measurement conditions, and commonly named yis, yrs, yf s, and yos, as in where Ig is the transistor gate current, Id is the transistor drain current, and the third terminal (the source) is common to the input and output during the measurement. Thus, Vgs is the voltage between the gate and the source, and Vds is the voltage between the drain and the source. The typical high-frequency model used to approximate the behavior of a MOSFET is shown in Fig. 17.48.