Electronic Filter Topology

Electronic filter topology defines electronic filter circuits without taking note of the values of the components used but only the manner in which those components are connected.

Filter design characterises filter circuits primarily by their transfer function rather than their topology. Transfer functions may be linear or nonlinear. Common types of linear filter transfer function are; high-pass, low-pass, bandpass, band-reject or notch and all-pass. Once the transfer function for a filter is chosen, the particular topology to implement such a prototype filter can be selected so that, for example, one might choose to design a Butterworth filter using the Sallen–Key topology.

Filter topologies may be divided into passive and active types. Passive topologies do not contain a generator of energy, either in reality or, due to non-linearity, in their equivalent circuit, but only capacitors, inductors and also, in some topologies, resistors: particularly, variable resistors are often included in order to control the depth of filtering. Active topologies include components that require power. Further, topologies may be implemented either in unbalanced form or else in balanced form when employed in balanced circuits. Implementations such as electronic mixers and stereo sound may require arrays of identical circuits.