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MIT中的一种基于全相位的IQ正交相位解调算法.docx

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MIT中的一种基于全相位的IQ正交相位解调算法 Introduction Incommunicationsystems,In-phase(I)andQuadrature(Q)channelsignalsarewidelyusedformodulationanddemodulationpurposes.TheprocessofseparatingthesetwosignalsisreferredtoasIQdemodulation.OneofthepopulartechniquesforIQdemodulationistheall-phasescheme,whichgeneratesafullquadraturedemodulatedsignal.Inthispaper,wewilldiscussapopularIQdemodulationtechniquecalledtheAll-Phasemethod,whichhasbeenwidelyusedinvariouscommunicationsystems. OverviewoftheAll-PhaseMethod TheAll-PhaseMethodisanIQdemodulationtechniquethatusesanall-passfiltertoachieveperfectquadrature.Theall-passfilterisacircuitthatpassesallthefrequencieswithoutanyattenuationbutmodifiesthephaseofthesignal.Byusinganall-passfilter,thephaseoftheincomingsignalcanbemodified,resultinginaperfectquadraturesignalduringdemodulation. Theall-passfilterisusedtogeneratetwooutputs,onewithaphaseshiftof0degreesandtheotherwithaphaseshiftof90degrees.Thisway,theIandQsignalscanbegenerated,whichareorthogonaltoeachother.Theall-passfiltercanbeimplementedusingdifferentcircuitssuchasRCcircuitsorcoupledresonators. TheAll-PhaseMethodinPractice Inpractice,theAll-PhaseMethodcanbeimplementedusingdifferentcircuittopologiessuchasdelay-linecircuits,quadraturedelay-linecircuits,andall-passfiltercircuits.However,themostcommoncircuittopologyusedisthequadraturephaseshifter. Thequadraturephaseshifterconsistsofacombinationofcapacitorsandresistorsconnectedinaspecificconfigurationtoproduceaphaseshiftof90degrees.Theinputsignalisdividedintotwosignalpaths,andonepathispassedthroughthequadraturephaseshiftertogeneratetheQsignal.TheotherpathispassedthroughaninvertertogeneratetheIsignal. ToimplementtheAll-PhaseMethod,theincomingsignalisfirstpassedthroughabandpassfiltertoremoveanyunwantednoiseorsignals.Thefilteredsignalisthenpassedthroughalownoiseamplifiertoincreaseitsamplitude.TheamplifiedsignalisthenpassedthroughaquadraturephaseshiftertogeneratetheQsignal.Thequadraturephaseshiftergeneratestwosignals,onewithaphaseshiftof0degreesandtheoth