Book excerpt: Interest in filter theory and design has been growing with the telecommunications industry since the late nineteenth century. Now that telecommunications has become so critical to industry, filter research has assumed even greater importance at companies and academic institutions around the world. The CRC Handbook of Electrical Filters fills in the gaps for engineers and scientists who need a basic introduction to the subject. Unlike the currently available textbooks, which are filled with detailed, highly technical analysis geared to the specialist, this practical guide provides useful information for the non-specialist about the various types of filters, their design, and applications. The handbook covers approximation theory and methods and introduces CAD packages that perform approximation and synthesis for both analog and digital filters. Also included are design methods for LCR, active-RC, digital, mechanical, and switched capacitor (SC) filters. A thorough survey of current design trends rounds out this complete assessment of a key field of study.