REINVESTIGATION AND EXTENSION OF THE STEADY-STATE NYQUIST THEOREM FORMULTITERMINAL SEMICONDUCTOR-DEVICES AND ITS APPLICATION TO MINIMUM NOISE-FIGURE IN MICROWAVE FIELD-EFFECT TRANSISTORS

The steady-state Nyquist theorem for multi-terminal semiconductor devi ces, which describes the short-circuit thermal noise currents in arbit rarily shaped multi-terminal semiconductor devices, is reinvestigated. The concept of the equipotential surfaces for small ac signals is fou nd to be wrong, which forces us to introduce a new approach to find th e equipotential surfaces for noise voltages, Using this new approach, we rederive the steady-state Nyquist theorem with the same results as in the previous derivation, and extend it to the hot carrier regime. U sing the extended theorem, we express the minimum noise figure for mic rowave field effect transistors as a function of the measurable device parameters with no fitting constant. The derived minimum noise figure is shown to reduce to a simple form, which can also be used as an emp irical relation with one fitting constant. This simple form can explai n the experimental results very well in wide frequency ranges, and giv es through a clear mathematical relation the empirically known require ments for the low noise design of microwave field effect transistors. (C) 1996 American Institute of Physics.