Recent advances in solid-state technology and the well-known advantages of integrated circuits (ICs) have made microminiaturized filters and systems an important field of study. For a particular application, the main object of the designer is to select/design a circuit, which is optimized to maximize performance and minimize cost through economic integration. At present, several methods are available to adapt the design of linear networks. Among these, networks (filters) employing resistance, capacitance, and linear active devices, i.e., active RC filters, have become very popular because of their functional versatility, ease of IC implementation and cost reduction. Now, good quality active RC filters are being produced using integrated operational amplifiers (OAs), mainly because of the commercial availability of high quality OAs at low cost.

It is for this reason that the majority of the, presently, available books on linear active filter design and the curriculum at almost all universities include OA-RC based circuit and systems design either as a full course or part of a course on linear integrated circuit design. However, it is only part of a story, which began with passive electric filter design. Approximation was used to develop filter structures, predominantly in the form of either singly or doubly terminated lossless ladders. Great strides were made in developing ladder structures and related information for different approximations, and related information like their transfer function in terms of ratio of polynomials or in terms of poles and zeros, and required values of elements used in the ladders. Not only are passive filter realizations still used today, but the large literature on it also finds application in active network synthesis. Hence, a discussion on passive filter design and properties of ladder structure finds place in books on network analysis/synthesis.

Development of filter circuits from passive to active did not stop at the OA-RC case. The simultaneous development of digital filters and systems, and the replacement of analog sub-systems with digital sub-systems, motivated further advancements in continuous-time as well as discretetime analog filters. Employing the design procedures used with OA-RC filter synthesis, high speed sampling circuits such as the switched capacitor (SC) provided good alternatives to digital filters in many applications.