Active RC Filters Using Opamps

This chapter deals with the realization of active filters using resistors, capacitors and active devices such as opamp. Simple circuits such as amplifiers, integrators, differentiators, and first-order low-pass, high-pass, and all-pass filters are considered. The effect of finite opamp frequency-dependent gain is considered. Various configurations for realizing second-order filters using single opamp such as Sallen–Key filter, Friend’s biquad, multiple-feedback type, and recently derived circuits using differential output opamp are considered. The design equations, practical considerations such as spread in components, sensitivity to non-ideal opamp, and tolerances of components are derived in detail. Second-order filters which use two opamps, such as GIC-based biquads, and which use three opamps, such as Tow-Thomas biquad, KHN biquad, and Tarmy–Ghausi biquad, are described. Techniques for compensating the finite bandwidth of the opamp in order to extend the performance are described. Second-order filters which use only one capacitor and opamp finite pole (bandwidth) are considered, and two opamp-based active R filters which do not use any capacitors are also studied in detail. The design of active RC filters derived from passive RLC ladder filters based on operational simulation and component simulation and other techniques such as Yoshihoro’s technique have been considered. Design procedures of low-pass, high-pass, and band-pass types are described. The use of FDNR for realizing low-pass filters is also described. The various multiloop feedback techniques are briefly introduced. Techniques for noise analysis and distortion analysis of active RC filters are described. Several SPICE simulation examples are presented to illustrate modeling of various nonidealities of opamps and analysis of total noise. These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.