Higher-Order Filters
F. William Stephenson, W.B. Kuhn · 2020
There are two broad approaches to the design of higher-order active filters. Cascade design entails the interconnection of first- and second-order sections to yield the desired characteristic. This chapter reviews the major features of cascade, direct replacement, and multiloop synthesis of high-order active filters. When designing a cascade structure, both the pole-zero pairing and the order of sections in the cascade are important. Direct inductor replacement methods or multi-loop/active analogs yield less-sensitive realizations than the cascade of biquads. However, tuning is necessarily more difficult because of the strong interdependence of components within the structure. A variety of higher-order filter design methods have been derived from the generalized flowgraph of a state variable system. The chapter discusses for situations where off-the-shelf solutions are not appropriate, custom filters may be designed using the techniques.