The appropriate design of the reconstruction filter and its influence on the output power and efficiency of class-S and quasi class-S power amplifiers

Abstract

The aim of this workshop is a more or less complete analysis of reconstruction filters for current mode class-S and partial of quasi class-S power amplifier systems. The workshop attempts to show and to discuss the requirements for reconstruction filters suitable for class-S (delta-sigma or pulse-length modulation) and quasi class-S (band-pass pulse-length modulation) power amplifier systems. Regarding the final stage architecture representing the main interface to the reconstruction filter all deliberations are focused on the current-mode power amplifier system because at given maximum ratings of the transistors this architecture generates the highest output power. Very crucial to the maintenance of the rectangular shape of the drain current and thus to high efficiency are not only the choice of the pass-band and stop-band of the reconstruction filter, but also the specification of input impedance for different modes of excitation over a wide frequency range. The main focus of the workshop is on the design of the reconstruction filter. It will be shown that the electrical and geometrical constraints for the design of a reconstruction filter are well satisfied by balanced input comb-line filters. Especially doubly and singly terminated filters are subjected to theoretical consideration, simulation, testing and measurement. Several filter architectures are demonstrated, and critically analysed in terms of differential and common mode impedances. Finally the simulation and measurement results of current mode class-S power amplifier systems and a single ended quasi class-S power amplifier system including appropriate designed reconstruction filters are shown.