A scalable linear model for FETs

A small-signal model of the intrinsic region of a microwave FET that considers four capacitance terms is examined. Four reactive terms in the model are required to describe four imaginary Y -parameter terms. The addition of a fourth capacitance rather than a channel resistance or delay term enables extraction of dispersion-free parameters, better consistency with a large-signal model and better scaling properties. An important aspect of the model topology is clear separation of resistive and reactive elements so that transconductance and output conductance correspond to real parts of the Y -parameters. It is shown that this has an impact on the scaling of noise models that are formulated in terms of these resistive parameters.