The design of active RC filters for the Analog Front End of IC communication systems

Abstract

In the first part of this tutorial, the concept of the dasiaAnalog Front Enddasia (AFE), which is the interface to the real world in most IC-system chips, is introduced. The course then focuses on active-RC filters which constitute an essential part of most AFEs. The formulation of filter specifications and the basic ideas associated with classical filter approximation theory are then briefly reviewed. Some key points of classical network theory, as needed for the understanding of inductorless filter design, are then briefly recalled. This is followed by some basic concepts of signal-flow graph theory, which permit the transition from transfer function (resulting from approximation theory) to circuit topology. After the review of these introductory and basic concepts, the stage is set to consider some of the most important and established active-RC filter-design techniques. Examples are given for the conversion of classical LCR filter structures into inductorless active-RC filter circuits that are amenable to IC chip design. The examples are taken from typical modern communication systems. Finally, filters designed using the design techniques covered in the course are compared in terms of practical performance criteria such as thermal output noise, sensitivity to component tolerances, and tunablity. In the second part of the tutorial, we introduce analytical tools, which are useful for the formulation of criteria with which we can decide which inductorless active-RC filters of the kind presented in the first part are most suitable for the front end of mixed-mode integrated-circuit system chips. These tools will enable us to select and characterize optimum filter realizations for the analog front end. With the filters selected according to these criteria, we shall then go through the detailed steps necessary for their design. They represent typical, well-proven circuits for the IC design of active RC filters. We shall then check the performance of these designed filters as obtained by computer simulation (e.g. PSpice). Finally, we shall look at some special situations in communications systems that require (i), novel topologies in filter design and (ii), special attention in integrated-circuit design for higher frequency applications and higher bit-rate communications. At the end of the course, the student should be well prepared to embark on the design and performance evaluation of inductorless filters for the front end of typical and emerging communication systems on a chip.