LT1085-Tkool Electronics

Tkool Electronics

IIntroductionLM567isatonedecodingphase-lockedloopintegratedcircuit.Itiscompactindesign,simpleincircuit,andhasawiderangeofapplications.However,ifusingimproperly,itwillbringtroublesindebugging.ThisblogintroducestheworkingprincipleandtipsabouthowtouseLM567tonedecoderforreadersreference.Figure1.LM567ToneDecoderCatalogIIntroductionIILM567InternalStructurePinFunctionIIILM567WorkingPrincipleApplicationIVTipsofUsingToneDecoderLM567Ordering&QuantityIILM567InternalStructurePinFunctionThenameofLM567isphase-lockedlooptonedecoder,itspackageformuses8-pindualin-line,itsinternalstructureandpinfunctionsareillustratedinFigure2.Itsinternalcircuitstructureiscomposedofquadraturephase,detector,phase-lockedloop,amplifier,etc.TheoperatingvoltagerangeofLM567is4.75-9V,theoperatingfrequencycanreach500KHz,andthestaticoperatingcurrentisonly8mA.Thepin③isthesignalinputterminal,whichrequirestheinputsignaltobegreaterthan25mV.Thepin⑧isthelogicoutputterminal.Itcanbeseenfromthefigurethatitisanopencollectortransistoroutput,whichallowsamaximumsinkcurrentof100mA.Theexternalresistanceandcapacitanceofpins⑤and⑥determinethecenterfrequencyf01/1.1RCofICinternalvoltagecontrolledoscillator.Pins①and②areusuallyconnectedtothegroundseparatelytoformanoutputfilternetworkandalooplow-passfilternetwork.Thecapacitorconnectedtopin②determinesthecapturebandwidth.Thelargerthevalueofthecapacitor,thenarrowertheloopbandwidthis.Figure2.TopViewofLM567IIILM567WorkingPrincipleApplicationWhenthetonedecoderLM567works,itsphase-lockedloopinternalcurrent-controlledoscillatorgeneratesanoscillationsignalofacertainfrequencyandphase.Thissignalissenttothequadraturephasedetectortogetherwiththesignalinputatpin③forcomparison.Whenthefrequencyofthesignalfallswithinagivenpassband,thephase-lockedlooplocksthissignal,andatthesametimetheinternaltransistoroftheLM567iscontrolledtobepoweredup,andtheoutputterminaloftheLM567outputslowlevel.The⑤pinofLM567outputstherectangularsignaloftheinternaloscillator,andthe⑥pinoutputsthesawtoothpulse.Thefrequencyofbothisthesameasthecenterfrequencyoftheinternaloscillator.The②pinistheoutputofthephase-lockedloopphasedetector.ThevoltageonisthesignalafterF/Vconversion.Ifthetonesignalisinputtothe②pin,thenthe⑤pinoutputstheFMsquarewavesignalmodulatedbythe②pininputsignal.FromthebasicfunctionofLM567,LM567canbeusedasanoscillator,modulatorordemodulator.Therefore,itcanbeusedasabasicdeviceinthecircuit.TheapplicationofLM567hasthefunctionofdecodingaspecificfrequencyintheinputsignal,anditiswidelyusedincommunication,remotecontrol,measurement,frequencymonitoring,etc.Figure3.LM567ToneDecoderIVTipsofUsingToneDecoderLM567AlthoughLM567hasaverywiderangeofapplications,ifitisnothandledproperlyduringdesignandapplication,itstillfailstoachievetheexpectedresults,andevenbringstroubletothedebuggingoraffectsthereliabilityoftheproduct.Therefore,itshouldbeconsideredfromthefollowingaspectswhenusingit:1.SetOperatingFrequencyandBandwidthofLM567AccuratelyandAppropriatelyWeknowthattheinternaloscillationfrequencyf0ofLM567canbepre-setwithintherangeof0.1KHzto500KHz,anditscorrespondingbandwidthcanalsobedeterminedasrequiredwithinthefieldrangeof7%f0to14%f0.Therefore,afterthedetectedsignalisdetermined,theinternaloscillationfrequencyf0ofLM567shouldbesettocoincidewiththecenterfrequencyofthemeasuredsignal,andthetimingcomponentsRandCconnectedwiththe5and6feetofLM567shouldbeusedwithhighprecision.Amongthem,thesettingofthecenterfrequencycanbedeterminedbytheresistancevalueofthetunerR.Whenadjusting,itisnecessarytopreventRshortcircuitoropencircuit,otherwisetheoutputlevelof⑧pinwillbelowlevelwhetherthereisinputsignalornot.Theexternalcapacitanceofthe②pinofLM567determinesthecapturebandwidth.Thesmallerthecapacity,thewiderthecapturebandwidth.However,thecapacitancecannotbereducedblindlytoincreasethebandwidth,soasnottoreducetheanti-interferenceabilityoreventriggerfalsely,whichaffectsthereliabilityoftheproduct.2.MaketheCenterFrequencyofthePassbandCoincidewiththeCenterFrequencyoftheOscillationAsMuchAsPossibleItshouldbenotedthatthecenterfrequencyofthepassbanddoesnotalwayscoincidewiththecenterfrequencyoftheoscillator,andsometimesitwilldeviateseverely.Thiswillinevitablycauseadecreaseinreliabilityandsensitivity.Therefore,measuresshouldbetakentomakethetwocenterscoincideasmuchaspossible.ThecircuitshowninFigure4canminimizethefrequencyoffsetofthetwocenters.Figure4.CircuitofLM5673.WorkingVoltageofLM567ShouldBeStableThestabilityoftheoperatingvoltageoftheLM567hasafixedresponsetothestabilityofthecenterfrequencyofthetonedecoder.4.AvoidMisoperationWhentheOutputTerminalisPoweredOnLM567outputsalowlevelatthemomentwhenthepoweristurnedon.Therefore,forsomeremotecontrolcircuits,itisnecessarytoaddaCRintegrationdelaycircuittotheoutputendtoavoiderroneousoperationwhenthepoweristurnedon.Thisisespeciallyimportantintheon-offcontrolcircuit.Afterreadingtheblog,haveyoubetterunderstandLM567?Finally,ifyouhaveanyquestionsaboutLM567,pleasedonothesitatetoleaveamessageinthecommentsectionbelow!