Filtering techniques with switched-capacitor circuits

Abstract

Filters are frequency selective circuits that have wide applications in electronic systems. Among the available passive type filters, the doubly terminated reactance ladder two-parts have many attractive features, the most important being their low-sensitivity to variations of all element values. However, the recent trend in electronics has been toward reducing the size of circuits, a trend which led to the development of integrated circuits. It is relatively simple to reduce greatly the dimensions of resistors and capacitors; unfortunately, it proved impractical to achieve a comparable reduction in the size of inductors mainly because no ferromagnetic effect can be obtained in semiconductors; the building material of integrated circuits. This led to the development of R-C active filters, in which inductors are replaced by active elements. This paper discusses the development of these filters using switched-capacitor circuits.