Filtros de separação espectral aplicados ao processamento de áudio utilizando técnicas de capacitores chaveados.

Abstract

The compression and expansion of dynamic range of audio signal amplitude has been widely employed in the A M and FM broadcast systems to improve its noise characteristics. Recently similar techniques have also been employed in the design of modern hearing aids. The performance of the systems involving compressors and expanders is greatly enhanced i f the audio signal is separated in different frequency bands with an independent compressor, expander in each band. In this dissertation, design considerations of a set of analog filters as applied to compression and expansion of dynamic range of the audio signals are presented. These filters enable the separation of the audio signals in 4 distinct frequency bands with 24 dB/oetave roll-off in the stop band and yield a theoretically flat overall amplitude response. Instead of implementing the filters with established discrete circuit configuration, topologies of Switched Capacitor filters are proposed and these in turn yield more precise control of the filter transfer characteristics without the need for fine tuning the filter components. The development of a switched capacitor circuit involves the following steps: theoretical design, simulation, circuit layout, fabrication of the chip and eventual modifications after the test of the prototypes. The emphasis in this dissertation is primarily in the first two steps: the analysis and synthesis of switched capacitor filters for separating the audio signal in to 4 bands and the evaluation of the filter performance by simulation studies of the proposed configuration.