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Wednesday, March 11, 2009

Characterization of FET Dynamics and Nonlinearity

Characterization of FET Dynamics and Nonlinearity

Abstract

Field Effect Transistors exhibit a variety of complicated dynamic and nonlinear
interactions that this session will attempt to demystify. The dynamics include self
heating, bias dependent change in trapped charge, and variations due to impact
ionization. These are feedback mechanisms that contribute to intermodulation as a
memory effect does. A similar contribution to distortion arising from external
impedances is intimately linked to the nonlinearity of the FET. Identifying and
characterizing FET dynamics and linearity is a key step in the design process, but a
variety of measurement issues arise. These include extraction of intrinsic
characteristics, exploration of nonlinearities across the whole spectrum, and
determination of rate dependencies from small-signal and pulse data. A FET is better
viewed as a nonlinear system with feedback, bias dependent rates, and high-order
nonlinear conductance and charge storage with specific terminal to terminal
interaction.

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