F.E.T. high-frequency analysis

The equations describing the small-signal sinusoidal operation of the ‘intrinsic’ field-effect transistor are derived from a consideration of the basic physical principles of the operation of the device. Expressions for the small-signal short-circuit parameters in series form are obtained. Truncated forms of these series are used to compute the elements of a convenient equivalent circuit. The dependence of the computed equivalent-circuit elements on bias voltages is presented. An indication of the frequency at which the equivalent circuit derived from the truncated series for the admittance parameters becomes inaccurate is obtained by considering higher-order terms. Finally, consideration is given to ‘extrinsic’ equivalent-circuit elements, and a convenient form of the complete equivalent circuit is presented.