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UBC Theses and Dissertations

Representation of multivariable-controlled MOSFET nonlinearities in transient analysis programs Ma, Hong


This thesis deals with the modelling and circuit simulation problems of nonlinear electronic devices. Emphasis has been aimed at MOSFET devices. A Piecewise Linear (PWL) modelling scheme has been proposed for a general four-terminal nonlinear charge device. The charge functions are all nonlinear and are approximated by PWL functions. If analytical expressions for the nonlinear functions are not available, PWL function approximations can be built from a data table in which discrete data points are recorded. In the time domain, the critical-damping-adjustment (CDA ) scheme is used as the integration rule in the discretization of dynamic charge devices. Piecewise linear modelling combined with the CDA integration scheme gives a fast yet adequately accurate simulation algorithm. The algorithm is based on linear analysis because the entire circuit becomes linear with PWL modelling of nonlinear elements. In order to avoid an iterative solution, PWL region extrapolation is permitted when the circuit solution switches PWL regions. The extrapolation approximation will generate an overshoot error in the solution vector. However, with caution in the selection of the integration step size, the error can be limited to an acceptable range. Two types of MOSFETs have been modelled and simulated with the algorithm introduced in this thesis, and satisfactory results have been obtained as compared to Newton's iteration solutions.

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