Electronic filter topology

Common types of linear filter transfer function are; high-pass, low-pass, bandpass, band-reject or notch and all-pass.Implementations such as electronic mixers and stereo sound may require arrays of identical circuits.The chart at the bottom of the page shows these various topologies in terms of general constant k filters.Filters designed using network synthesis usually repeat the simplest form of L-section topology though component values may change in each section.A ladder network consists of cascaded asymmetrical L-sections (unbalanced) or C-sections (balanced).In low pass form the topology would consist of series inductors and shunt capacitors.These topologies, invented by Otto Zobel,[1] have the same passbands as the ladder on which they are based but their transfer functions are modified to improve some parameter such as impedance matching, stopband rejection or passband-to-stopband transition steepness.Usually the design applies some transform to a simple ladder topology: the resulting topology is ladder-like but no longer obeys the rule that shunt admittances are the dual network of series impedances: it invariably becomes more complex with higher component count.It is, however, a rarely used design due to increased component count and complexity as well as its normally requiring basic ladder and m-type sections in the same filter for impedance matching reasons.Topologies usually associated with constant resistance filters are the bridged-T and its variants, all described in the Zobel network article; The bridged-T topology is also used in sections intended to produce a signal delay but in this case no resistive components are used in the design.The elementary feedback topology is based on the simple inverting amplifier configuration.A diagram of the circuit topology for a second order low pass filter is shown in the figure on the right.For example, the basic configuration in Figure 1 can be used as either a low-pass or bandpass filter depending on where the output signal is taken from.The Sallen-Key design is a non-inverting second-order filter with the option of high Q and passband gain.
series m-derived topology
Typical bridged-T Zobel network equaliser used to correct high end roll-off
Lattice topology X-section phase correction filter
An elementary filter topology introduces a capacitor into the feedback path of an op-amp to achieve an unbalanced active implementation of a low-pass transfer function
Multiple feedback topology circuit.
Figure 1. The common Tow-Thomas biquad filter topology.
Figure 2. The Akerberg-Mossberg biquad filter topology.
Figure 1: The generic Sallen–Key filter topology
topologyelectronic filterFilter designtransfer functionlinearnonlinearhigh-passlow-passbandpassband-reject or notchall-passprototype filterButterworth filterSallen–Key topologyactiveunbalancedbalancedbalanced circuitselectronic mixersstereo soundlong in development and usetwo-port networks"cascade""daisy-chain"impedanceconstant k filtersnetwork synthesisImage designed filtersWilhelm Cauerelliptic filterGeorge Campbellconstant k filterlow passdual networksOtto Zobelpassbandsimpedance matchingstopbandm-derived filtermm'-type filterGeneral mn-type filtercomposite filterroll-offZobel networkLattice networkall-pass filtersphase equalisationop-amplinear filtersquality factorDigital biquad filterlinear filterquadratic functionsbiquadraticcomplexRC circuitstate variable filterNatural frequencydamping constantoperational amplifierSallen-Key topologyTopology (electronics)