Filters, especially analog filters, are employed in many different systems that electrical engineers embark upon to design. Even many signal processing systems that are apparently digital, often contain one or more analog continuous-time filters either internally or as interface with the real-time world, which is analog in nature. This book on analog filters is intended as an intermediate-level text for a senior undergraduate and/or an entry-level graduate class in an electrical/electronic engineering curriculum. The book principally covers the subject of analog active filters with brief introductions to passive filters and integrated circuit filters. In theclass of active filters, both continuous-time and sampled-data filters are covered. Further, both voltage-mode and current-mode filters are considered. The book is targeted at students and engineers engaged in signal processing, communications, electronics, controls, and so on.
The book is not intended to be an extensive treatise on the subject of analog filters. The subject of (analog) electrical filters is very vast and numerous authors have written excellent books on this subject in the past. Therefore, the question that naturally arises pertains to the need for yet another book on analog filters.
The subject of analog filters is so fascinating that there is always room to introduce the subject with slightly different orientation, especially one that is directed toward certain class of practitioners in the field of electrical engineering. This book exploits the existing wealth of knowledge to illustrate practical ways to implement an analog filter, both for voltage and current signals. Use of currents for signal processing has been a popular subject during the last two decades, and in this respect the book touches on a modern viewpoint of signal processing, relevant to analog filters. In particular, the concept of transposition and its usefulness in obtaining in a very simple manner a current-mode filter from a voltage-mode filter, or vice versa, is presented for the first time in this book. Even though this concept was developed in 1971 itself, its practical use came only after the advent of IC technology, and hence this concept did not receive much attention in earlier books.