Electronic filter
Electronic filters remove unwanted frequency components from the applied signal, enhance wanted ones, or both.Multipole LC filters provide greater control of response form, bandwidth and transition bands.A major step forward was taken by Wilhelm Cauer who founded the field of network synthesis around the time of World War II.These types are collectively known as passive filters, because they do not depend upon an external power supply and they do not contain active components such as transistors.Resistors on their own have no frequency-selective properties, but are added to inductors and capacitors to determine the time-constants of the circuit, and therefore the frequencies to which it responds.In this context, an LC tuned circuit being used in a band-pass or band-stop filter is considered a single element even though it consists of two components.Three-element filters can have a 'T' or 'π' topology and in either geometries, a low-pass, high-pass, band-pass, or band-stop characteristic is possible.Some common circuit topologies are: Historically, linear analog filter design has evolved through three major approaches.This reflected the radio receiver application of filtering as Q was a measure of the frequency selectivity of a tuning circuit.From the 1920s filters began to be designed from the image point of view, mostly being driven by the requirements of telecommunications.The higher mathematics used originally required extensive tables of polynomial coefficient values to be published but modern computer resources have made that unnecessary.It has the disadvantage that accuracy of predicted responses relies on filter terminations in the image impedance, which is usually not the case.[4] The network synthesis approach starts with a required transfer function and then expresses that as a polynomial equation of the input impedance of the filter.
Distributed-element filtersignal processing filterlumpeddistributed-element filtersintegrated circuitpassiveactiveanalogdigitalhigh-passlow-passband-passband-stopall-passdiscrete-timecontinuous-timelinearnon-linearinfinite impulse responsefinite impulse responselinear filtersAnalogue filterresistorscapacitorsinductorstransition bandsconstant k filterGeorge Campbelltransmission lineOtto Zobelimage parameter filtersWilhelm Cauernetwork synthesisWorld War IItransistorsinductorattenuationlow-pass filterhigh-pass filterreactiveLC tuned circuitmegahertzRC circuithybrid LC filterm-derived filterladder networkActive filtersOperational amplifiersQ factorresonanceFilter (signal processing)digital filterscrystal filtersmechanical filterssurface acoustic wavethin-film bulk acoustic resonatorgarnet filtersatomic clockstransfer functiondistributedrational functionpassive filteractive filterelectronic filter topologyCauer topologySallen–Key topologyMultiple feedback topologyState variable topologyBiquadratic topologyNetwork synthesis filtersButterworth filterChebyshev filterElliptic (Cauer) filterBessel filterGaussian filterOptimum "L" (Legendre) filterLinkwitz–Riley filterImage impedance filtersGeneral image filtersZobel networkLattice filterBridged T delay equaliserComposite image filtermm'-type filterRC filterRL filterLC filterRLC filterKirchhoff's lawsComposite image filtersAnalog filterAudio crossoverAudio filterCascaded integrator-comb filterComb filterDSL filterElectronic low-pass filterNyquist filterRF and microwave filterSwitched-capacitor filterTone control circuitsVoltage-controlled filterapplication noteSignal-processing filtersLow-pass filter (LPF)High-pass filter (HPF)All-pass filterBand-pass filterBand-stop filter