Measurement and computer-aided-design techniques for predicting distortion in u.h.f. field effect transistor amplifiers

Barnett, Richard John (1977) Measurement and computer-aided-design techniques for predicting distortion in u.h.f. field effect transistor amplifiers. University of Southampton, Doctoral Thesis.

Abstract

The use of Computer-Aided-Design (C.A.D.) techniques in the design of electronic circuits necessitates accurate representations of the circuit elements. The nonlinear modelling of three different types of FieldEffect Transistor (F.E.T.) at u.h.f. frequencies for this purpose is investigated. Devices used are Double-Diffused Metal-Oxide-Semiconductor (D.M.O.S.) and Junction (J.) F.E.T.s, including a Ga As J.F.E.T. Device theory and experimental measurements are used in the derivation of these models, which are then capable of predicting distortion, especially third order intermodulation. The extension of the modelling techniques to higher frequency F.E.T.s is achieved by high frequency measurement of the device nonlinearities. An interactive nonlinear circuit analysis computer program is developed to analyse the models directly in the frequency domain using Volterra aeries techniques. Analyses up to fifth order are performed. The accuracy of the models is checked by experimental measurements. Distortion as a function of device sample, input signal level, frequency and bias voltage is investigated. The dominant nonlinearities of the F.E.T. are shown to be a function of the circuit environment. The application of the nonlinear models to low distortion amplifier design is evaluated, using techniques of out-of band impedance matching, alternative device configuration and predistortion. The alternative representation of the nonlinear characteristics of a device in terms of nonlinear scattering parameters is presented, and a technique for the measurement of these parameters is developed.

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