Thesis (Ph.D.)--Tufts University, 2002. / Adviser: Mohammed Afsar. Submitted to the Dept. of Electrical Engineering. Includes bibliographical references (leaves 121-128). Access restricted to members of the Tufts University community. Also available via the World Wide Web;

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1995. / Vita. Abstract. Includes bibliographical references (leaves 202-207). Also available via the Internet.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 60-61). Also available via the Internet.

by Shankar Sastry. / "September 1982." / Bibliography: p. 37-38. / Air Force Office of Scientific Research grant AFOSR-82-0258

Numerical frequency-domain techniques are widely used for the a.c. steady-state analysis of nonlinear electric circuits. Such techniques require that one compute the Fourier series for the response of each nonlinear circuit element, given a known excitation. Current approaches to this computation encounter difficulty when the response is almost periodic (that is, when the frequencies in its Fourier series are not all harmonically related), especially when the nonlinear characteristic is abrupt and the Fourier series for the response contains many significant terms. This dissertation develops an alternative approach that is theoretically sound and computationally efficient, for the important special case of a memoryless nonlinearity described by a continuous, bounded function. To begin the development, basic properties of almost periodic functions are presented. It is proven that the response of a memoryless nonlinearity is almost periodic whenever the excitation is. Next, the concept of a basis for a set of frequencies is introduced. The frequency content of the response is investigated, and it is proven that the frequencies in the response have the same basis as those in the excitation. The Fourier series for an almost periodic function is discussed, and its coefficients are expressed as mean values taken over an infinite interval. Results are given for the summability of the series. Starting with a theorem from Diophantine Approximation, it is proven that the normalized (Hertzian) phases corresponding to a set of M basis frequencies have their fractional parts uniformly distributed in an M-dimensional unit cube. This property of uniform phase distribution is then used to convert the single-dimensional integral for the Fourier series coefficients into a multiple integral over the unit cube, with the dimension of the integral equal to the number of basis frequencies in the Fourier series. A multi-dimensional extension of the Discrete Fourier Transform is used to evaluate the multiple integral, and expressions for aliasing are derived. It is shown that the multiple integral formulation compares favorably with existing approaches, and several numerical examples are presented to illustrate this formulation's capabilities. / Ph. D.

This thesis describes the design of a baseband digital predistortion architecture for radio frequency (RF) amplifier linearization. Existing amplifier linearization techniques are first examined. The nonlinearity of an amplifier can be characterized as amplitude-to-amplitude distortion and amplitude-to-phase distortion. The distortion can be corrected by providing a predistorted driver signal (both in amplitude and phase) to the amplifier. This counteracts the nonlinearity of the amplifier so that the overall system is more linear. A pipelined predistortion architecture is designed to allow fast processing speed, and is capable of providing linearization for a bandwidth of 25 Mhz. The simulation results show significant improvement in amplifier's performance using predistortion technique. The system bandwidth versus cost is examined by using commercially available components. / Graduation date: 1996

Thesis (Ph. D.)--Carleton University, 2004. / Includes bibliographical references (p. 156-176). Also available in electronic format on the Internet.

The combined effect of group velocity dispersion (GVD) and nonlinearity limits the transmission distance of fiber optic communication systems. By designing a circuit that can model this effect and simulating it using the Block Oriented Systems Simulator (BOSS), we can study the pulse distortion and broadening that may occur. The nonlinearity considered here is self-phase modulation (SPM). A loop system is designed where each pass of the system corresponds to 200 km of fiber. The system mainly consists of a Butterworth bandpass filter which models the dispersion in the fiber and a VCO that imposes a phase modulation on the input signal thus modeling the intensity dependent phase shift due to SPM. By changing various parameters of the circuit, the dispersion limited distance, the nonlinearity limited distance and other related factors can be altered. With D=-0.04 ps/km.nm, the effect of changing the nonlinear limited distance and thus the nonlinear effect is studied and simulated. The results are compared with a simple theoretical model for pulse broadening that has appeared in the literature. Although the simulation results exhibit the same qualitative behavior as the theory, there are significant quantitative differences. The reason for these differences are discussed. / Master of Science

A generalized, discrete-time modeling and simulation program, applicable to any PWM, resonant or quasi-resonant converter, has been developed. From a circuit description, this program automatically generates state-space equations corresponding to each switching interval and performs time-domain simulations by using state-transition equations with a fast-convergence algorithm for topological changes. / M.S.

Thesis (Ph. D.)--Carleton University, 2004. / Includes bibliographical references (p. 217-223). Also available in electronic format on the Internet.