TABLE OF CONTENTS Examination of the block diagram of any wireless transceiver architecture reveals that filters are an essential building block. To satisfy all transceiver design requirements, many different types of filters operating over a wide range of frequency and bandwidth are required. Over a long period of time, several specialised technologies dedicated solely to filter implementation have evolved, for example, filters based on quartz crystal and ceramic resonators, LC filters using ferrites and other specialised magnetic materials, and at the upper end of the frequency range, transmission line elements fabricated as microstrip. These techniques yield high-performance filters; unfortunately, none of these components are available in designs using current IC technologies, and for a long time this created a barrier to the design of highly integrated RF systems, since many filtering functions had to be performed off-chip.
Developments in semiconductor processing and IC circuit design techniques during the past several years mean that it is now possible to implement continuoustime active filters with useful performance over an extremely wide frequency range. The possibility therefore exists of achieving the highly desirable goal of integrating all the filter functions required in many wireless transceiver applications. Single-chip transceivers with no external filtering components are now becoming commonplace for applications such as the Bluetooth and IEEE 802.11 standards [1, 2]. The current trend is to implement these designs using standard CMOS digital processes due to their low cost and ready availability. From the filter designer's point of view, a notable shortcoming...
