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Analog filters, that is continuous-time filters, or filters that can be implemented with resistors, capacitors, inductors, specialized elements or
devices, etc., have enjoyed a long history of use in electrical engineering
applications. In fact, it can be said without fear of contradiction that the modern technological world, as we know it, would not exist without analog filters. Even though digital filters, and digital signal processing in general, has experienced great growth and development in recent years, analog filters are an important topic. At the university where the author is an associate professor, a course in analog filters, taught at the first-year graduate / senior level, is one course in the graduate program of signal processing. Many of the concepts in analog filter theory help establish a foundation of understanding that assists in more advanced courses on digital filters, modern filters, adaptive filters, spectral estimation, etc. And, of course, analog filter concepts, and the ability to design and analyze them, is important in the additional area of analog circuit design, mixed signal circuit1 design, and in integrated circuit development.
Therefore, this textbook presents analog filter theory from a signal processing
perspective (i.e., stressing the signals and systems concepts), but also including
analog circuit design and analysis as well. Concepts such as the relationships among the time domain, frequency domain, and s domain are stressed. Other things stressed are inherent trade-offs dictated by theory, that have nothing to do with
implementation. For example, attempting to eliminate the time-domain ringing of a
high-order Butterworth bandpass filter is an exercise in futility, as theory clearly reveals. Chebyshev and elliptic filters will ring even more: s domain analysis, and the equivalent time-domain analysis clearly reveal this, whereas frequency domain analysis alone may not suggest it. As an educator, and one who concentrates in the area of signal processing, the author believes these concepts to be of vital importance. Almost any book on analog filters will include signal processing / systems conceptsas well as implementation, and the present book is no exception. Most books on analog filter design briefly present the signal processing / systems concepts, and then concentrate on a variety of filter implementation methods. The present book reverses the emphasis, stressing signal processing concepts. The present book does not ignore implementation, as it does present filter implementation topics in Part II: passive filters, and operational amplifier active filters. However, greater emphasis on signal processing / systems concepts are included in Part I of the book than is typical. As suggested above, this emphasis makes the book more appropriate as part of a signal processing curriculum, but should also be of interest to those in analog circuit design
as well.