Circuits and passive components for radio-frequency power conversion

Abstract

This thesis focuses on developing technology for high efficiency power converters operating at very high frequencies. The work in the thesis involves two aspects of such converters: rf (radio-frequency) power circuit design techniques and magnetic material characterization and application. In the aspect of circuit design techniques, the thesis investigates a new class of matching networks that overcomes a major limitation of rf converter circuits - their high sensitivity to loading condition. These networks, which are termed resistance compression networks, serve to substantially decrease the variation in effective resistance seen by a tuned rf inverter as loading conditions change. The thesis explores the operation, performance characteristics, and design of these networks, and present experimental results demonstrating their performance. The thesis also presents analysis and design considerations for lumped (inductor and capacitor) matching networks operating at high efficiency (> 95%). Formulas for calculating matching network efficiency are given and used to evaluate the optimum number of matching stages as a function of conversion ratio. Both simulation and experimental results are presented that validate the analytical formulation. In the aspect of magnetic materials and applications, the thesis investigates the loss characteristics of several commercial rf magnetic materials for power conversion applications in the 10 MHz to 100 MHz range.

(cont.) A measurement method is proposed to identify loss characteristics of different commercial rf magnetic core materials. The loss characteristics of these materials, which have not previously been available, are illustrated and compared in tables and figures. Based on results in characterization of magnetic materials, the thesis describes a procedure for magnetic components design with low permeability magnetic materials that is for very high frequency power conversion applications. This procedure provides a method to compare and evaluate different magnetic materials for given specifications of a magnetic-core inductor. Some important information, e.g. quality factor and size of the inductor can be predicted before the final design. The thesis also investigates some problems such as optimization of a magnetic-core inductor.