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Title: Developing low distortion linear and nonlinear circuits with GaAs FETs using the Parker Skellern model
Author: Webster, Danny Richard
Awarding Body: University of London
Current Institution: University College London (University of London)
Date of Award: 1996
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This Thesis begins by reviewing GaAs MMIC technology, MESFET models used in popular simulators, circuit design techniques for low and high frequencies, distortion specification, analysis and reduction. The section on modelling describes in detail an emerging state of the art MESFET model, proposed by Parker and Skellern, which is used extensively in this work. The main body of the thesis covers four interrelated subject areas. It begins by studying a common unwanted distortion mechanism in FET circuits and showing how this leads to frequency dependant distortion in common gate, cascode and multi-FET circuits. This mechanism is an interaction of the device nonlinearity with the linear components that surround it. Next, a square law nonlinear circuit synthesis for MESFETs, proposed by Haigh & Toumazou, is analysed with an improved analytical model. Then the distortion behaviour of a single device under different bias and loading is studied for a selection of simulator models and compared with measured behaviour. Finally a powerful novel synthesis technique, based on the real nonlinear behaviour of MESFETs, is presented. The technique relies on the superposition of the transconductance derivatives to define a customised linear or nonlinear transfer characteristic. This synthesis technique is shown to be useful for amplifier linearisation, reducing distortion in active mixers as well as leading to novel frequency doublers, triplers and limiters. A two device demonstrator relying on derivative superposition to minimise large signal distortion is measured confirming this principle.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Circuit design; MESFET