Tkool Electronics

I.DescriptionAutomaticgaintechnology(AGC)iswidelyusedinthefieldofindustrialautomationclosed-loopcontrol.Inindustrialcontrol,time-varyinggainamplifiersareoftenneededtomeetproductionneeds,ormadeithasacertainregularitytoensurethestabilityofthecontroloutputamplitude,therebyreducingtheinterferenceoftheinputinterferencenoisesignal.Forthesystemtoadjustquikly,thispaperdesignsanAGCcontrollerbasedonthecombinationofAGCchipAD603andswitchingpowersupplychipMC34063,cleverlyusingMC34063sstablereferencevoltageanddynamicvoltageadjustmentoutputtoaccessAD603gaincontrolterminaltocontroltheamplificationgain,thereforeachievethegoalofconstantsystemoutputamplitude.AD603CatalogI.DescriptionII.WorkingPrincipleoftheSystemIII.AD603IV.MC34063V.SystemHardwareCircuitDiagram5.1InputBufferAttenuationCircuit5.2AD603AutomaticGainAmplifier5.3OutputAmplitudeDetector5.4MC34063FeedbackCircuitVI.SystemOperationResultsVII.ConclusionFAQOrdering&QuantityII.WorkingPrincipleoftheSystemThesystemusesAD603asthecorecontroldevice,supplementedbytheswitchingpowersupplychipMC34063tocollecttheoutputofthecontroller,theoutputvoltageistransferredtothevoltagecontrolterminalofAD603throughMC34063tochangetheamplificationgain.ThesystemworkingprincipleblockdiagramisshownasinFig.1.Figure1SystemBlockdiagramInthisclosed-loopcontrolsystem,theMC34063circuitisusedasitsfeedbacklinktodynamicallycollecttheamplitudeoftheoutputsignalofthesystem,andcontroltheamplificationgainofAD603byadjustingthedutycycleoutputvoltageoftheinternalsignal.Thefeedbacklinkinthefigurecanbereplacedwithamicroprocessor.ThemicroprocessorcollectstheoutputvoltageamplitudethroughA/D,transfersittothemicroprocessorchipforsignalprocessing,andthenfeedsbacktotheinputoftheentiresystemthroughD/Aoutputcontrolvoltage.However,thismethodistoocomplicated,becausetheriseandfallofthedigitalchiptakealongtimetosetup,whichaffectstheresponsespeedoftheentiresystem,andrequiresrelativelyhighsignalprocessingalgorithms.Theswitchingpowersupplychipwidelyusedinpowersupplytechnologyisdynamicallyadjustedtoimproveitsoperatingspeed.Inaddition,itsdevelopmentcostislow,whichisconducivetothepromotionoftheindustrialcontrolfield.III.AD603AD603isachipwithprogrammablegain,lownoise,ithas3workingmodes,correspondingtodifferentgainranges.Inordertomakethecontrolmoreextensive,themaximumbandwidthmodeisselectedas90MHz.Thegainisexpressedindecibels,theamplificationgainiscontrolledbythecontrolvoltagetoalinearrelationshipof25mV/dB,andtheslewrateis275V/s.Thegaincontrolvoltageneedstobeinputduringnormaloperation.Thegainformulais:Intheformula:Gisthegain,dB;G0isthestartingpointofthegain,andthesizeofG0isdeterminedbythepinconnection.Thecircuitdesignedinthispapershort-circuitsVOUTandFDBK,G0=10dBisthewidebandmode(90MHzwideband),thegainrangeGofAD603is-11.09~+31.05dB,andVGisinthelinearrangewhentherangeis-500~500mV.ThegaincontrolvoltageVGiscontrolledbytheMC34063output.AD603inputsignalamplitudeUINP1.4V,theactualindustrialcontrolfieldofteninputplusinterferencesumisgreaterthan1.4V,ifthissignalisdirectlyaddedtothesystem,thedistortionislargeandlong-timeworkwilldamagetheAD603,soyoumustaddaninputbufferandattenuationcircuit.IV.MC34063MC34063isamonolithicbipolarintegratedcircuitusedinthefieldofDC-DCconvertercontrol.Itischeapandwidelyusedinthefieldofswitchingpowersupplies.Itcanuseaminimumofexternalcomponentstoachieveswitchingboostandbuck.Itsoperatingfrequencyis0.1-100kHz.ThetraditionalAGCcontrollerconstitutesaclosed-loopcontrolsystem,whichgenerallyneedstoperformA/Dsamplingontheoutputofthesystem,andthentransferthedatatothesingle-chiporcomputerforalgorithmdataprocessing,andjudgetheexecutionsignalD/Aoutputtomaketheactuatorexecute.Inthisfeedbackprocess,sampling,algorithmprocessingandexecutionobviouslyconsumetoomuchtime,andforsomecomplexcontrolsignals,algorithmdataprocessingrequirementsarehigh,andspecialDSPchipsarerequired,whichiscostly.Therefore,theuseofasingleanalogelectroniccircuittoachieveaclosed-loopcontrolsystemhashigherefficiencyandlowercost.InspiredbytheworkingmodeoftheMC34063step-downcircuit,itisanewdesignideatorealizethechangeoftheAD603gaincontrolvoltagebyusingthecharacteristicsoftheMC34063todynamicallyadjusttheoutputvoltage.Theexperimentalverificationisfeasibleanditissimplerandfasterthantheprogramcontrolmethod.Figure2showstheMC34063step-downcircuit.Figure2MC34063step-downcircuitAsshowninFigure2,theinputis+12V,theoutputis+5V,thereferencevoltageofpin5togroundis+1.25V,theresistanceofpin5togroundisR1=1.2k,andtheoutputandpin5areconnectedtoR2=3.6k,Accordingtotheresistancedividerratio,theoutputisclampedat+5V,thusachievingaregulatedoutput.AppliedinthefieldofAGCcontrol,youcanconnecttheoutputofMC34063tothecontrollergaincontrolterminal,andtheinputtotheoutputterminalofthecontroller.Accordingtoitsworkingprinciple,MC34063collectstheoutputoftheAGCcontrollerandtransmitsittopin5.ItsinternaldynamicallyadjuststhePWMdutycycle,dynamicallychangestheAD603gaincontrolvoltage,andcanavoidtheinterferenceofthesystem,andrealizethefunctionsimilartothePIDalgorithm.Itreplacesthealgorithmicdataprocessingmechanism,whichissimpleandeffective,andhascertainreferencesignificancetothefieldofindustrialautomationcontrol.V.SystemHardwareCircuitDiagramFigure3isthesystemhardwarecircuitdiagram.Thesystemismainlydividedintoinputbufferattenuationcircuit,AD603automaticgainamplifier,outputamplitudedetectorandMC34063feedbackcircuit.Figure3SystemHardwarecircuitdiagram5.1InputBufferAttenuationCircuitBecausetheAD603inputsignalamplitudeVINPislessthanorequalto1.4V,fourdiodeclampsareused.Accordingtotheunidirectionalconductivityofthediodeandtheforwardconductionvoltagedropofsilicon,theinputcharacteristicsarelimitedtomeettherequirementsofAD603.Theinputvoltagerequirements,thefollowerplaystheroleofisolatingthechip.AsshowninFigure3,part①.5.2AD603AutomaticGainAmplifierThe3pinofAD603isthesignalinputterminal,the2and4pinsareconnectedtothegroundwithR4=0,R5=0resistancetomakeitworkmorestable.The5and7pinsareconnectedtotheoutput,whichisthesystemoutputoftheAGCcontroller.Pin1isthegaincontrolvoltageVGterminal,thiscontrolvoltageisconnectedtotheoutputterminalofMC34063,MC34063generatesthecorrespondinggaincontrolvoltageVGaccordingtotheoutputofthesystem.5.3OutputAmplitudeDetectorInthefieldofindustrialcontrol,thesignalisonlyintheformofDC,andtheACsignalalsooccupiesacertainproportion.ForthecontroloftheDCsignal,thesystemoutputcanbedirectlytransmittedtotheMC34063forprocessing,buttheamplitudeoftheACsignalmustbedetected,sothedesignisshowninFigure3inpart③.Commonamplitudedetectors,suchasdioderectifierbridges,areonlysuitableforsituationswheretheinputvoltageisfargreaterthanthediodeconductionvoltagedrop.InAGCcontrol,thesignalinthesystemisoftenlowvoltage,soitcannotbeused,soitisverynecessarytodesignanamplitudedetectorthatcanavoiddiodeconductionvoltagedrop.AfterRCcharging,theDCvoltagevaluewithacertainrelationshipisobtained.InFigure3,thevoltageattheintermediatenodeofR13andR14isUf,andtheexpressionis:Intheformula,UINPistheinputamplitude,V.5.4MC34063FeedbackCircuitTheintermediatenodevoltageUfofR13andR14isproperlycalculatedbyasame-invertingamplifierandanadder,andthenconnectedtopin5ofMC34063.Atthistime,itisclampedat5V,andUf=1Vwhenreversed,thentheAGCcontrollersystemcanbedynamicallymaintainedstabilityofoutputvoltageamplitude.Whenthesysteminputisunstableorthereisnoiseinterference,MC34063dynamicallychangestheoutputvoltagevalueaccordingtotheamplitudedetectionresult,soastoachievethepurposeofchangingthegaincontrolvoltageVG.AsshowninthelowerpartofFigure3,theoutputvoltageofpin2ischargedanddischargedthroughswitchingandspecificSchottkydiodes,andtheattenuatedpartialvoltageistransmittedtopin1ofAD603,whichrealizestheautomaticadjustmentoftheamplificationgainandsuccessfullyrealizestheswitchingpowersupplytechnologyapplicationinthefieldofautomaticcontrolgain.VI.SystemOperationResultsTheexperimentalsettingisthatifthesysteminputsaDCsignal,theoutputwillbeaconstant+1VDC;ifanACsignalisinput,theoutputwillbeanACsignalwithaconstantamplitudeof+1V.Intheexperiment,twoinputmethodsweretestedandverified,andbothmetthedesignrequirements.Table1ispartoftheexperimentaldataoftheinputDCsignal.Intheexperiment,theinputoftheAGCcontrollerisconnectedtothevoltageregulatorsource,andtheinputvoltageiscontinuouslyadjusted.Table2ispartoftheexperimentaldataoftheinputACsignal.Intheexperiment,theAGCcontrollerinputisconnectedtotheUTG9002Csignalgenerator,theamplitudeoftheinputsinewaveiscontinuouslyadjusted,andtheoutputisconnectedtotheoscilloscopetoobservethewaveform.Observationfoundthatnomattertheinputamplitudebecomeslargerorsmaller,theoscilloscopewaveformisbasicallyunchanged.ReadtheoscilloscopewaveformamplitudeandfillinTable2.VII.ConclusionThisarticlesummarizesthedesignoftheAGCcontrollerbasedonAD603andMC34063.ExperimentshaveverifiedthattheAGCcontrolleriseffectiveandmeetsthedesignrequirements.Anewapplicationofswitchingpowersupplychipsinthecontrolfieldisproposed.BecausetheinternalPWMdutycycleisfaster,itcanreplacethetraditionalprogrammableAGCcontroller.Amongthem,MC34063canalsobereplacedbyotherswitchingpowersupplychips.Ithastheadvantagesofuniversalapplicability,simpledesign,lowcost,andithasimportantpracticalvalue.FAQWhatisAD603?AD603isalow-noise,voltage-controlledamplifierforradiofrequency(RF)andintermediatefrequency(IF)automaticgaincontrol(AGC)systems.Itprovidesprecisepin-selectablegain,withagainrangeof-11dBto+31dBat90MHzbandwidth,andagainrangeof+9dBto+51dBat9MHzbandwidth.Anyintermediategainrangecanbeobtainedwithanexternalresistor.Thenoisespectraldensityreferredtotheinputisonly1.3nV/Hz,andthepowerconsumptionis125mWwhenusingtherecommended5Vpowersupply.WhataretheproblemsthatneedtobepaidattentiontowhenusingAD603?Thevoltagecannotbetoohigh.Generally,thevoltageisplusorminus5V,andthemaximumvoltagecannotexceedplusorminus7.5V.Theoutputvoltagecannotexceed2V.Howtosolvetheself-oscillationproblemofAD603?Forhigh-frequencyoperationalamplifiers,thefollowingpointsarethebasicwaystosolveself-excitation.Thepowersupplyisstableandnoripple.Theelectricalconnectionwiresareasshortaspossible.Thead603circuitshouldbefarawayfromthepowercircuit,especiallyawayfromthetransformer.Thepowertransformerandthecircuitboardofad603shouldbeshieldedwithametalboxandgroundedifpossible.Onepointisveryimportant.Foropamps,toolargemagnificationcaneasilycauseself-excitation,soreducethemagnificationasmuchaspossibleandminimizethenumberofmagnificationlevels(generallynotgreaterthan4).Reverseamplificationcansuppressself-excitationinmulti-stageamplification.Ifyouwanttoconnecttothepoweramplifierandthenamplify,itisbesttousetwopowersupplies,andthecircuitshouldbeconnectedtothesameground.WhatisthedifferencebetweenAD603AQandAD603AR?Theirdifferencesareinmodel,Temperature,Package.AD603AQ-40Cto+85C8-LeadCERDIPAD603AR-40Cto+85C8-LeadSOIC_NAfterinputtinganACsignalandbeingamplifiedbyAD603,whydoestheoutputcontainaDCsignal?HowtoeliminatetheDCsignal?WhentheDCblockingcapacitorisnotused,thebiasvoltageoftheinputcircuitneedstobeadjustedforcompensation.IftheDCvoltageoftheACsignalisnotfixed,onlyaDCblockingcapacitorcanbeused,ortheaveragevaluecanbeusedtoeliminateitaftersamplingthenumber.

SOT89

I.DescriptionAutomaticgaintechnology(AGC)iswidelyusedinthefieldofindustrialautomationclosed-loopcontrol.Inindustrialcontrol,time-varyinggainamplifiersareoftenneededtomeetproductionneeds,ormadeithasacertainregularitytoensurethestabilityofthecontroloutputamplitude,therebyreducingtheinterferenceoftheinputinterferencenoisesignal.Forthesystemtoadjustquikly,thispaperdesignsanAGCcontrollerbasedonthecombinationofAGCchipAD603andswitchingpowersupplychipMC34063,cleverlyusingMC34063sstablereferencevoltageanddynamicvoltageadjustmentoutputtoaccessAD603gaincontrolterminaltocontroltheamplificationgain,thereforeachievethegoalofconstantsystemoutputamplitude.AD603CatalogI.DescriptionII.WorkingPrincipleoftheSystemIII.AD603IV.MC34063V.SystemHardwareCircuitDiagram5.1InputBufferAttenuationCircuit5.2AD603AutomaticGainAmplifier5.3OutputAmplitudeDetector5.4MC34063FeedbackCircuitVI.SystemOperationResultsVII.ConclusionFAQOrdering&QuantityII.WorkingPrincipleoftheSystemThesystemusesAD603asthecorecontroldevice,supplementedbytheswitchingpowersupplychipMC34063tocollecttheoutputofthecontroller,theoutputvoltageistransferredtothevoltagecontrolterminalofAD603throughMC34063tochangetheamplificationgain.ThesystemworkingprincipleblockdiagramisshownasinFig.1.Figure1SystemBlockdiagramInthisclosed-loopcontrolsystem,theMC34063circuitisusedasitsfeedbacklinktodynamicallycollecttheamplitudeoftheoutputsignalofthesystem,andcontroltheamplificationgainofAD603byadjustingthedutycycleoutputvoltageoftheinternalsignal.Thefeedbacklinkinthefigurecanbereplacedwithamicroprocessor.ThemicroprocessorcollectstheoutputvoltageamplitudethroughA/D,transfersittothemicroprocessorchipforsignalprocessing,andthenfeedsbacktotheinputoftheentiresystemthroughD/Aoutputcontrolvoltage.However,thismethodistoocomplicated,becausetheriseandfallofthedigitalchiptakealongtimetosetup,whichaffectstheresponsespeedoftheentiresystem,andrequiresrelativelyhighsignalprocessingalgorithms.Theswitchingpowersupplychipwidelyusedinpowersupplytechnologyisdynamicallyadjustedtoimproveitsoperatingspeed.Inaddition,itsdevelopmentcostislow,whichisconducivetothepromotionoftheindustrialcontrolfield.III.AD603AD603isachipwithprogrammablegain,lownoise,ithas3workingmodes,correspondingtodifferentgainranges.Inordertomakethecontrolmoreextensive,themaximumbandwidthmodeisselectedas90MHz.Thegainisexpressedindecibels,theamplificationgainiscontrolledbythecontrolvoltagetoalinearrelationshipof25mV/dB,andtheslewrateis275V/s.Thegaincontrolvoltageneedstobeinputduringnormaloperation.Thegainformulais:Intheformula:Gisthegain,dB;G0isthestartingpointofthegain,andthesizeofG0isdeterminedbythepinconnection.Thecircuitdesignedinthispapershort-circuitsVOUTandFDBK,G0=10dBisthewidebandmode(90MHzwideband),thegainrangeGofAD603is-11.09~+31.05dB,andVGisinthelinearrangewhentherangeis-500~500mV.ThegaincontrolvoltageVGiscontrolledbytheMC34063output.AD603inputsignalamplitudeUINP1.4V,theactualindustrialcontrolfieldofteninputplusinterferencesumisgreaterthan1.4V,ifthissignalisdirectlyaddedtothesystem,thedistortionislargeandlong-timeworkwilldamagetheAD603,soyoumustaddaninputbufferandattenuationcircuit.IV.MC34063MC34063isamonolithicbipolarintegratedcircuitusedinthefieldofDC-DCconvertercontrol.Itischeapandwidelyusedinthefieldofswitchingpowersupplies.Itcanuseaminimumofexternalcomponentstoachieveswitchingboostandbuck.Itsoperatingfrequencyis0.1-100kHz.ThetraditionalAGCcontrollerconstitutesaclosed-loopcontrolsystem,whichgenerallyneedstoperformA/Dsamplingontheoutputofthesystem,andthentransferthedatatothesingle-chiporcomputerforalgorithmdataprocessing,andjudgetheexecutionsignalD/Aoutputtomaketheactuatorexecute.Inthisfeedbackprocess,sampling,algorithmprocessingandexecutionobviouslyconsumetoomuchtime,andforsomecomplexcontrolsignals,algorithmdataprocessingrequirementsarehigh,andspecialDSPchipsarerequired,whichiscostly.Therefore,theuseofasingleanalogelectroniccircuittoachieveaclosed-loopcontrolsystemhashigherefficiencyandlowercost.InspiredbytheworkingmodeoftheMC34063step-downcircuit,itisanewdesignideatorealizethechangeoftheAD603gaincontrolvoltagebyusingthecharacteristicsoftheMC34063todynamicallyadjusttheoutputvoltage.Theexperimentalverificationisfeasibleanditissimplerandfasterthantheprogramcontrolmethod.Figure2showstheMC34063step-downcircuit.Figure2MC34063step-downcircuitAsshowninFigure2,theinputis+12V,theoutputis+5V,thereferencevoltageofpin5togroundis+1.25V,theresistanceofpin5togroundisR1=1.2k,andtheoutputandpin5areconnectedtoR2=3.6k,Accordingtotheresistancedividerratio,theoutputisclampedat+5V,thusachievingaregulatedoutput.AppliedinthefieldofAGCcontrol,youcanconnecttheoutputofMC34063tothecontrollergaincontrolterminal,andtheinputtotheoutputterminalofthecontroller.Accordingtoitsworkingprinciple,MC34063collectstheoutputoftheAGCcontrollerandtransmitsittopin5.ItsinternaldynamicallyadjuststhePWMdutycycle,dynamicallychangestheAD603gaincontrolvoltage,andcanavoidtheinterferenceofthesystem,andrealizethefunctionsimilartothePIDalgorithm.Itreplacesthealgorithmicdataprocessingmechanism,whichissimpleandeffective,andhascertainreferencesignificancetothefieldofindustrialautomationcontrol.V.SystemHardwareCircuitDiagramFigure3isthesystemhardwarecircuitdiagram.Thesystemismainlydividedintoinputbufferattenuationcircuit,AD603automaticgainamplifier,outputamplitudedetectorandMC34063feedbackcircuit.Figure3SystemHardwarecircuitdiagram5.1InputBufferAttenuationCircuitBecausetheAD603inputsignalamplitudeVINPislessthanorequalto1.4V,fourdiodeclampsareused.Accordingtotheunidirectionalconductivityofthediodeandtheforwardconductionvoltagedropofsilicon,theinputcharacteristicsarelimitedtomeettherequirementsofAD603.Theinputvoltagerequirements,thefollowerplaystheroleofisolatingthechip.AsshowninFigure3,part①.5.2AD603AutomaticGainAmplifierThe3pinofAD603isthesignalinputterminal,the2and4pinsareconnectedtothegroundwithR4=0,R5=0resistancetomakeitworkmorestable.The5and7pinsareconnectedtotheoutput,whichisthesystemoutputoftheAGCcontroller.Pin1isthegaincontrolvoltageVGterminal,thiscontrolvoltageisconnectedtotheoutputterminalofMC34063,MC34063generatesthecorrespondinggaincontrolvoltageVGaccordingtotheoutputofthesystem.5.3OutputAmplitudeDetectorInthefieldofindustrialcontrol,thesignalisonlyintheformofDC,andtheACsignalalsooccupiesacertainproportion.ForthecontroloftheDCsignal,thesystemoutputcanbedirectlytransmittedtotheMC34063forprocessing,buttheamplitudeoftheACsignalmustbedetected,sothedesignisshowninFigure3inpart③.Commonamplitudedetectors,suchasdioderectifierbridges,areonlysuitableforsituationswheretheinputvoltageisfargreaterthanthediodeconductionvoltagedrop.InAGCcontrol,thesignalinthesystemisoftenlowvoltage,soitcannotbeused,soitisverynecessarytodesignanamplitudedetectorthatcanavoiddiodeconductionvoltagedrop.AfterRCcharging,theDCvoltagevaluewithacertainrelationshipisobtained.InFigure3,thevoltageattheintermediatenodeofR13andR14isUf,andtheexpressionis:Intheformula,UINPistheinputamplitude,V.5.4MC34063FeedbackCircuitTheintermediatenodevoltageUfofR13andR14isproperlycalculatedbyasame-invertingamplifierandanadder,andthenconnectedtopin5ofMC34063.Atthistime,itisclampedat5V,andUf=1Vwhenreversed,thentheAGCcontrollersystemcanbedynamicallymaintainedstabilityofoutputvoltageamplitude.Whenthesysteminputisunstableorthereisnoiseinterference,MC34063dynamicallychangestheoutputvoltagevalueaccordingtotheamplitudedetectionresult,soastoachievethepurposeofchangingthegaincontrolvoltageVG.AsshowninthelowerpartofFigure3,theoutputvoltageofpin2ischargedanddischargedthroughswitchingandspecificSchottkydiodes,andtheattenuatedpartialvoltageistransmittedtopin1ofAD603,whichrealizestheautomaticadjustmentoftheamplificationgainandsuccessfullyrealizestheswitchingpowersupplytechnologyapplicationinthefieldofautomaticcontrolgain.VI.SystemOperationResultsTheexperimentalsettingisthatifthesysteminputsaDCsignal,theoutputwillbeaconstant+1VDC;ifanACsignalisinput,theoutputwillbeanACsignalwithaconstantamplitudeof+1V.Intheexperiment,twoinputmethodsweretestedandverified,andbothmetthedesignrequirements.Table1ispartoftheexperimentaldataoftheinputDCsignal.Intheexperiment,theinputoftheAGCcontrollerisconnectedtothevoltageregulatorsource,andtheinputvoltageiscontinuouslyadjusted.Table2ispartoftheexperimentaldataoftheinputACsignal.Intheexperiment,theAGCcontrollerinputisconnectedtotheUTG9002Csignalgenerator,theamplitudeoftheinputsinewaveiscontinuouslyadjusted,andtheoutputisconnectedtotheoscilloscopetoobservethewaveform.Observationfoundthatnomattertheinputamplitudebecomeslargerorsmaller,theoscilloscopewaveformisbasicallyunchanged.ReadtheoscilloscopewaveformamplitudeandfillinTable2.VII.ConclusionThisarticlesummarizesthedesignoftheAGCcontrollerbasedonAD603andMC34063.ExperimentshaveverifiedthattheAGCcontrolleriseffectiveandmeetsthedesignrequirements.Anewapplicationofswitchingpowersupplychipsinthecontrolfieldisproposed.BecausetheinternalPWMdutycycleisfaster,itcanreplacethetraditionalprogrammableAGCcontroller.Amongthem,MC34063canalsobereplacedbyotherswitchingpowersupplychips.Ithastheadvantagesofuniversalapplicability,simpledesign,lowcost,andithasimportantpracticalvalue.FAQWhatisAD603?AD603isalow-noise,voltage-controlledamplifierforradiofrequency(RF)andintermediatefrequency(IF)automaticgaincontrol(AGC)systems.Itprovidesprecisepin-selectablegain,withagainrangeof-11dBto+31dBat90MHzbandwidth,andagainrangeof+9dBto+51dBat9MHzbandwidth.Anyintermediategainrangecanbeobtainedwithanexternalresistor.Thenoisespectraldensityreferredtotheinputisonly1.3nV/Hz,andthepowerconsumptionis125mWwhenusingtherecommended5Vpowersupply.WhataretheproblemsthatneedtobepaidattentiontowhenusingAD603?Thevoltagecannotbetoohigh.Generally,thevoltageisplusorminus5V,andthemaximumvoltagecannotexceedplusorminus7.5V.Theoutputvoltagecannotexceed2V.Howtosolvetheself-oscillationproblemofAD603?Forhigh-frequencyoperationalamplifiers,thefollowingpointsarethebasicwaystosolveself-excitation.Thepowersupplyisstableandnoripple.Theelectricalconnectionwiresareasshortaspossible.Thead603circuitshouldbefarawayfromthepowercircuit,especiallyawayfromthetransformer.Thepowertransformerandthecircuitboardofad603shouldbeshieldedwithametalboxandgroundedifpossible.Onepointisveryimportant.Foropamps,toolargemagnificationcaneasilycauseself-excitation,soreducethemagnificationasmuchaspossibleandminimizethenumberofmagnificationlevels(generallynotgreaterthan4).Reverseamplificationcansuppressself-excitationinmulti-stageamplification.Ifyouwanttoconnecttothepoweramplifierandthenamplify,itisbesttousetwopowersupplies,andthecircuitshouldbeconnectedtothesameground.WhatisthedifferencebetweenAD603AQandAD603AR?Theirdifferencesareinmodel,Temperature,Package.AD603AQ-40Cto+85C8-LeadCERDIPAD603AR-40Cto+85C8-LeadSOIC_NAfterinputtinganACsignalandbeingamplifiedbyAD603,whydoestheoutputcontainaDCsignal?HowtoeliminatetheDCsignal?WhentheDCblockingcapacitorisnotused,thebiasvoltageoftheinputcircuitneedstobeadjustedforcompensation.IftheDCvoltageoftheACsignalisnotfixed,onlyaDCblockingcapacitorcanbeused,ortheaveragevaluecanbeusedtoeliminateitaftersamplingthenumber.

Introduction74LS138isa3-lineto8-linedecoder/demultiplexer.Thechipisdesignedtobeusedinhigh-performancememory-decodingordata-routingapplications,requiringveryshortpropagationdelaytimes.Inhighperformancememorysystemsthesedecoderscanbeusedtominimizetheeffectsofsystemdecoding.Thethreeenablepinsofchip(inwhichTwoactive-lowandoneactive-high)reducetheneedforexternalgatesorinverterswhenexpanding.CatalogIntroductionIFullAdderCircuitIIResponderCircuitIIILogicFunctionIVFullSubtractorCircuitVThree-inputMajorityVotingFAQOrdering&QuantityIFullAdderCircuitThefulladderhas3inputterminals:An,Bn,Cn-1;2outputterminals:Sn,Cn.The74LS1383-lineto8-linedecoderhas3datainputterminals:A,B,C;3enableterminalsand8outputterminals.Here,the3datainputterminalsofthe3-lineto8-linedecodercanberegardedasthe3inputterminalsofthefulladder.Thatis,theinputsA,B,andCofthe3-lineto8-linedecodercorrespondtotheinputsAn,Bn,andCn-1ofthefulladderrespectively.Setthe3enableterminalsofthe3-lineto8-linedecodertotheeffectiveleveltomaintainnormaloperation.Thekeypointhereistodealwiththerelationshipbetweenthe8outputterminalsofthe3-lineto8-linedecoderandthe2outputsofthefulladder.UsetheoutputOUT(1,2,4,7)ofthe3-lineto8-linedecoderasa4-inputorgateinput,andthegateoutputasthesumoftheadder.UsetheoutputOUT(3,5,6,7)ofthe3-lineto8-linedecoderasa4-inputorgateinput,thegateoutputisusedasthecarryoutputoftheadder.Whentheinputoftheadderis:a=1,b=0,ci=1,theinputofthecorresponding3-lineto8-linedecoderisA=1,B=0,C=1.Theoutputofthedecoderisout(5)=1andtherestis0.Accordingtotheconnectionrelationshipdesignedabove,S=0,CO=1,whichsatisfiesthefunctionoffulladder.Figure1.FullAdderCircuitIIResponderCircuitFigure2.ResponderCircuitIIILogicFunctionF=ABC+ABC+ABC=111+110+101=Y7+Y6+Y5Accordingtotheruleof74LS138,Aisthelowbit(LSB)andDisthehighbit(MSB).The74LS138decodingoutputislowleveleffective.With74LS10NANDgate,theactuallogicisinputlowleveleffectiveorgate.Figure3.CircuitofLogicFunctionIVFullSubtractorCircuitFigure4.FullSubtractorCircuitVThree-inputMajorityVotingThedeviceconsistsofa3-lineto8-linedecoder(74LS138)andtwo4-inputNANDgates(74LS20).Therearethreebuttonsforuser.Pressthebuttontoagree,nottopressmeanstoreject.Whennoonepressesthebutton,orwhenonlyonepersonpressesthebutton,forexample,S1ispressed,butS2andS0arenotpressed.Theredlightison,thegreenlightisoff,andthebuzzerissilent,indicatingveto.Whentwoormorepeoplepressthebutton,forexample,ifS1andS2arepressed,theredlightwillbeoff,thegreenlightwillbeon,andthebuzzerwillsoundtoindicateapass.Use74LS138decoderandfour-inputNANDgate74LS20torealizethislogicfunction.Figure5.CircuitofThree-inputMajorityVotingFAQWhatisthedifferencebetween74hc138and74LS138?Bothhavethesamefunction.74HC138ismadeofhigh-speedCMOSprocess,withlowpowerconsumption,highoutput,lowlevelandwiderange.74LS138adoptstheearlybipolarprocess,anditsdrivingcapabilityisrelativelylarger.Whatisthefunctionaldifferencebetween74ls138decoderand74ls148?74ls138isa3-8wiredecoder/multiplexer,74ls148isan8-3wireoctalpriorityencoder.Oneisdecodingandtheotherisencoding.OppositeeffectWhatsthedifferencebetween74LS138Dand74LS138N?Thosetwoarethesamechip,DisSOPpackage,NisDIPpackage.Whataretheoutputcharacteristicsof74LS138decoder ?UnderthepremisethattheenableterminalsS1(activehigh),S2(activelow),andS3(activelow)arevalidatthesametime,onlyoneoutputterminalislowatatime(therestarehigh);Iftheenableterminalisinvalid,theoutputisallhighlevel.Whatdothelettersandnumbersin74ls138standfor?74ls138isa3-8-linedecoder.Thenumber74representsthe74seriesofthe54/74series,andthe74serieshasanoperatingtemperatureof0degreesto70degrees.LSisaseries,representingthelow-powerSchottkyseries.138isthevarietycode.Whatstheworkingprincipleof74ls138?74LS138workingprinciple①Whenonestrobeterminal(E1)ishighlevel,andtheothertwostrobeterminals(E2)and(E3)arelowlevel,attheoutputterminalscorrespondingtoY0toY7,thebinarycodeofaddressterminals(A0,A1,A2)canbedecodedatlowlevel.Forexample:whenA2A1A0=110,theY6outputterminaloutputsalow-levelsignal.②UsingE1,E2andE3,itcanbecascadedtoexpandintoa24-linedecoder;ifanexternalinverterisconnected,itcanalsobecascadedtoexpandintoa32-linedecoder.③Ifoneofthestrobeterminalsisusedasadatainputterminal,74LS138canalsobeusedasadatadistributor.④Itcanbeusedin8086decodingcircuittoexpandmemory.Description74LS138isa3-lineto8-linedecoder/demultiplexer.Thechipisdesignedtobeusedinhigh-performancememory-decodingordata-routingapplications,requiringveryshortpropagationdelaytimes.Inhighperformancememorysystemsthesedecoderscanbeusedtominimizetheeffectsofsystemdecoding.Thethreeenablepinsofchip(inwhichTwoactive-lowandoneactive-high)reducetheneedforexternalgatesorinverterswhenexpanding.A24-linedecodercanbeimplementedwithnoexternalinverters,anda32-linedecoderrequiresonlyoneinverter.74LS138isusedinde-multiplexingapplicationsbyusingenablepinasdatainputpin.Alsothechipinputsareclampedwithhigh-performanceSchottkydiodestosuppressline-ringingandsimplifysystemdesign.CatalogDescriptionCatalogCADModelsFeaturesApplicationPinoutLogicDiagramPackageParametersProductComplianceComponentDatasheetProductManufacturerFAQOrdering&QuantityCADModels74LS138Symbol74LS138FootprintFeaturesDesignedSpecificallyforHigh-Speed:MemoryDecodersDataTransmissionSystems3EnableInputstoSimplifyCascadingand/orDataReceptionSchottky-ClampedforHighPerformanceApplicationLinedecodersServersDigitalsystemsLineDe-multiplexingTelecomcircuitsMemorycircuitsPinoutPinFunctionPinNameDescription1A0Addressinputpin2A1Addressinputpin3A2Addressinputpin4E1Enableinput(activeLOW)5E2Enableinput(activeLOW)6E3Enableinput(activeHIGH)7O7Outputpin78GNDGround9O6Outputpin610O5Outputpin511O4Outputpin412O3Outputpin313O2Outputpin214O1Outputpin115O0Outputpin016VCCPowersupplypinLogicDiagramPackageParametersFunctionDecoder,DemultiplexerTechnologyFamilyLSVCC(Min)(V)4.75VCC(Max)(V)5.25Channels(#)1Voltage(Nom)(V)5F@nomvoltage(Max)(MHz)35ICC@nomvoltage(Max)(mA)10tpd@nomVoltage(Max)(ns)41Configuration3:8ProducttypeStandardIOL(Max)(mA)8IOH(Max)(mA)-0.4RatingCatalogOperatingtemperaturerange(C)0to70Bits(#)8Digitalinputleakage(Max)(uA)5ESDCDM(kV)0.75ESDHBM(kV)2ProductComplianceECCNEAR99USHTS8542390001ComponentDatasheetDatasheet74LS138DatasheetProductManufacturerTexasInstrumentsInc.(TI)isanAmericantechnologycompanythatdesignsandmanufacturessemiconductorsandvariousintegratedcircuits,whichitsellstoelectronicsdesignersandmanufacturersglobally.ItsheadquartersareinDallas,Texas,UnitedStates.TIisoneofthetoptensemiconductorcompaniesworldwide,basedonsalesvolume.TexasInstrumentssfocusisondevelopinganalogchipsandembeddedprocessors,whichaccountsformorethan80%oftheirrevenue.TIalsoproducesTIdigitallightprocessing(DLP)technologyandeducationtechnologyproductsincludingcalculators,microcontrollersandmulti-coreprocessors.Todate,TIhasmorethan43,000patentsworldwide.FAQWhatisthedifferencebetween74hc138and74LS138?Bothhavethesamefunction.74HC138ismadeofhigh-speedCMOSprocess,withlowpowerconsumption,highoutput,lowlevelandwiderange.74LS138adoptstheearlybipolarprocess,anditsdrivingcapabilityisrelativelylarger.Whatisthefunctionaldifferencebetween74ls138decoderand74ls148?74ls138isa3-8wiredecoder/multiplexer,74ls148isan8-3wireoctalpriorityencoder.Oneisdecodingandtheotherisencoding.OppositeeffectWhatsthedifferencebetween74LS138Dand74LS138N ?Thosetwoarethesamechip,DisSOPpackage,NisDIPpackage.Whataretheoutputcharacteristicsof74LS138decoder?UnderthepremisethattheenableterminalsS1(activehigh),S2(activelow),andS3(activelow)arevalidatthesametime,onlyoneoutputterminalislowatatime(therestarehigh);Iftheenableterminalisinvalid,theoutputisallhighlevel.Whatdothelettersandnumbersin74ls138standfor?74ls138isa3-8-linedecoder.Thenumber74representsthe74seriesofthe54/74series,andthe74serieshasanoperatingtemperatureof0degreesto70degrees.LSisaseries,representingthelow-powerSchottkyseries.138isthevarietycode.Whatstheworkingprincipleof74ls138?74LS138workingprinciple①Whenonestrobeterminal(E1)ishighlevel,andtheothertwostrobeterminals(E2)and(E3)arelowlevel,attheoutputterminalscorrespondingtoY0toY7,thebinarycodeofaddressterminals(A0,A1,A2)canbedecodedatlowlevel.Forexample:whenA2A1A0=110,theY6outputterminaloutputsalow-levelsignal.②UsingE1,E2andE3,itcanbecascadedtoexpandintoa24-linedecoder;ifanexternalinverterisconnected,itcanalsobecascadedtoexpandintoa32-linedecoder.③Ifoneofthestrobeterminalsisusedasadatainputterminal,74LS138canalsobeusedasadatadistributor.④Itcanbeusedin8086decodingcircuittoexpandmemory.

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I.IntroductionTheheartrateisakeyindicatorvaluereflectingthehealthofthebody.Simplyput,theheartratereferstothefrequencyofcardiovascularbeatswithin1minute.Thetestofheartratecanshowscientificevidenceinworksuchasdiseasediagnosis,patientcare,andathletetraining.Inrecentyears,manymedicalequipmentandfitnessequipmentdevelopedandmanufacturedbycountriesaroundtheworldhaveadoptedheartratetestpowercircuits.Thelowcostofproductdevelopmentandhighperformanceheartratetestpowercircuitshaveimportantapplicationvalues.ThearticleintroducesthiskindofheartbeatratedetectionsystembasedonAD620integratedICindetail.Usingtheexcellentlow-noisecharacteristicsofAD620integratedIC,pluseffectivefilteringandamplifyingcircuits,combinedwithmicroprocessorsolutions,ahigh-precisionheartratemonitoringsystemisobtained.Figure1AD620CatalogI.IntroductionII.AD620ChipIII.CircuitDesign3.1BlockDiagram3.2SignalExtractionCircuitBasedonAD6203.3FilterAmplifierCircuit3.4MicroprocessorCircuit3.5ExperimentalResultsandDiscussionIV.ConclusionFAQOrdering&QuantityII.AD620chipAD620isalow-cost,high-precisioninstrumentationamplifier.Itonlyneedsanexternalresistortosetthegain,andthegainrangeis1to10000.Inaddition,AD620adopts8-pinSOICandDIPpackage,thesizeissmallerthanthediscretecircuitdesign,andthepowerconsumptionislower,soitisverysuitableforbattery-poweredandportableapplications.Itscharacteristicsareasfollows:EASYTOUSEGainSetwithOneExternalResistor(GainRange1to10,000)WidePowerSupplyRange(2.3Vto18V)HigherPerformancethanThreeOpAmpIADesignsAvailablein8-LeadDIPandSOICPackagingLowPower,1.3mAmaxSupplyLOWNOISE9nV/Hz,@1kHz,InputVoltageNoise0.28Vp-pNoise(0.1Hzto10Hz)EXCELLENTDCPERFORMANCE(BGRADE)50Vmax,InputOffsetVoltage0.6V/Cmax,InputOffsetDrift1.0nAmax,InputBiasCurrent100dBminCommon-ModeRejectionRatio(G=10)EXCELLENTACSPECIFICATIONS120kHzBandwidth(G=100)15sSettlingTimeto0.01%III.CircuitDesign3.1BlockDiagramThesurfaceofthehumanskincontainshumanECG,EMG,andpowerfrequencysignals.Generally,thenoiseoftheECGsignalcontainingheartrateinformationismuchsmallerthanthatofthepowerfrequencysignal.InordertoextracttheweakECGsignal,alow-noiseoperationalamplifiermustbeusedandareasonablefilteramplifiercircuitmustbedesigned.Figure2isablockdiagramoftheheartratedetectionsystem.Thewholeheartratedetectionsystemconsistsoffourparts:thesensorheadincontactwiththehumanskinsurface,thesignalextractioncircuit,thefilteramplifiercircuitandthemicroprocessorcircuit.Thesensorheadisgenerallyametalthatiseasytoconductelectricity.Aftercontactingthesurfaceofthehumanskin,ithascomplexelectricalsignalssuchashumanECGsignals,electromyographicsignals,andpowerfrequencysignals.Weusethelow-noiseAD620operationalamplifierasthecorechipoftheheartbeatrateextractioncircuit.Inthefilteringandamplifyingcircuitpart,asimplelow-passfilteringcircuitisused.Theexperimentalresultsshowthatthisfilteringcircuitissufficienttoextracttheheartratesignal.Afterfilteringtheamplifiedsignal,anadjustablecomparatorcombinedwithatransistorcircuitisusedtoforma5voltTTLlevelsignal,andfinallyconnectedtothemicroprocessor,theheartbeatsignalisprocessedbythemicrocomputer,andtheheartbeatrateiscalculatedanddisplayed.Figure2Blockdiagramofheartratedetectionprinciple3.2SignalExtractionCircuitBasedonAD620AD620operationalamplifier,usuallyusedinhigh-precisiontestinstruments,themaximumnonlinearerrorof40ppm,themaximumvoltageoffsetof50uV,themaximumtemperaturedriftof0.6uV/℃,becauseofitslownoise,lowbiascurrent,lowpowerconsumptioncharacteristics,itItiswidelyusedinmedicalfieldssuchaselectrocardiogram(ECG)andbloodpressuremonitoring.Figure3isasignalextractioncircuitbasedonAD620,inwhichtheLEFT_ARM,RIGHT_ARM,LEGthreeleadsareconnectedtothealuminumsheet(iethesensorhead),whicharerespectivelyconnectedtotheleftandrighthandsandrightfeetofthehumanbody.OurexperimentalresearchresultsshowthattheR4gainofLEFT_ARMis1K,thecorrespondingAD620operationalamplifiergainis50.Toomuchgainwillweakenthefinalsignal-to-noiseratio,sotheR4resistancevalueshouldbesetreasonablyintheexperiment.The0.1uFcapacitancebetweentheLEFT_ARMandRIGHT_ARMleadsistoeffectivelyweakenthepowerfrequencynoise.TheLEGleadisconnectedtoAD620throughTL082A,whichprovidesthereferencepotentialofthehumanbodyforthedifferentialsignalofLEFT_ARMandRIGHT_ARM.Figure3SignalextractioncircuitbasedonAD6203.3FilterAmplifierCircuitFigure4isafilteramplifiercircuit.Threeoperationalamplifiersconstituteathree-stageamplification,eachamplifying100times.Duetocircuitloss,especiallythelossoftheisolationcapacitor,theactualsignalamplificationislessthan1milliontimes.TheratiooftheresistancevaluesofR6andR5,R9andR8,R11andR10inthecircuitdeterminesthemagnificationfactor,andtheseresistancevaluesshouldbeadjustedreasonablyinpracticalapplications.Alow-passfiltercircuitshouldbeusedwhileamplifyingthesignaltoachievetheeffectoffilteringpowerfrequencynoise.Sincethefrequencyofthepowerfrequencynoiseis50Hz,thedesignedfiltercircuithasapassbandbandwidthoflessthan50Hz,thatis,theRCtimeconstantofthecapacitorresistormustbeofthesameorderofmagnitudeasthepowerfrequencysignalperiod.R7andC10inthecircuitformalow-passfilter.Weuse1uFcapacitorisolationbetweenlevelsofamplification.Thesecapacitorswillattenuatethesignalatthesametime,andthethreeoperationalamplifiersareselectedforsignalamplification,sothesignal-to-noiseratioisimproved.Itshouldbepointedoutthatiftheisolationcapacitoristoolarge,itiseasytocausetheoutputelectricalsignaltodrift.Figure4FilteramplifiercircuitFigure5istheshapingcircuit.Theheartbeatratesignalandsignal-to-noiseratioofthe2ND_OUTleadarelargeenough(thepulserateoftheheartbeatrateis1~5V),afterthehalf-waveshapingofD1,thentheadjustablecomparator,andfinallythetransistorQ1isconvertedtothemicrocontrollerlevel.Figure5Shapingcircuit3.4MicroprocessorCircuitThefinalsignalisprocessedbyAT89C51,andtheheartrateisdisplayedbyLEDdigitaltube.ThemicroprocessorcircuitwithAT89C51asthecoreisverymature,soitsnoneedtorepeathere.3.5ExperimentalResultsandDiscussionFigure6showstheactualmeasurementresultsofthehumanheartrateusingtheabovesystem.Figure6(a)isthevoltagesignalafterthesignal2ND_OUTisshapedbyD1.ItcanbeseenfromthefigurethatthisisactuallyacompleteECGsignal.Inacycleofsignals,therearetwomoreobviouspulsesignals.Thispulsecharacteristicvariesfrompersontoperson.ItisfoundthatthereisatleastonepulsesignalthroughactualmeasurementoftheECGsignalsofdifferentpeople.Figure6(b)showstheelectricalsignalofHEART_PULSE,whichisobtainedafterthesignalofFigure6(a)passesthroughthecomparatorandthetransistorswitch.Thesignalcanbedirectlyinputtotheportofthemicroprocessor,andthemicroprocessorcalculatesandoutputstheheartrate.Figure6HeartratesignaldiagramWhendevelopingtheabove-mentionedheartratedetectionsystem,thereareseveralkeypointstopayspecialattentionto:(1)ConnectingcapacitorstoLEFT_ARMandRIGHT_ARMcangreatlyimprovethesignal-to-noiseratio;themainenergyoftheheartratesignalonLEFT_ARMandRIGHT_ARMisatafrequencyofabout1Hz,andthecapacitorisalow-passfilterthatcanfilterandsuppressnoise;Choosealargecapacitortoeliminatehigh-frequencynoise.Intheexperiment,a10uFnon-polarcapacitorisused,andtheeffectisverygood;(2)Thelow-passfiltercircuiteffectivelyweakensthepowerfrequencysignalandimprovesthesignal-to-noiseratio;itadoptsacombinationofactivefilteringandpassivefilteringtofilterwhileamplifying,whichhasabettereffectthanfilteringafteramplification;(3)Capacitorisolationattenuationandmulti-stageamplificationarebeneficialtoimprovethesignal-to-noiseratio;themainnoiseis50Hzpowerfrequencysignals.Althoughthemulti-stageamplificationandfilteringincreasethermalnoise,ithasgreatsuppressionofpowerfrequencynoise.Ofcourse,thenumberofamplificationstagescannotbeinfinite,andthebestnumberofstagesistheminimumsumofpowerfrequencynoiseandthermalnoise;(4)SmallcapacitorisolationshouldbeusedtosuppressDCsignaldrift.Thisisshownbytheexperimentalresults,andthereasonneedstobefurtherstudied.IV.ConclusionThisarticlediscussesaschemebasedonAD620chipheartratedetection,andintroducesthecircuitdesignofthesensorhead,signalextraction,filteramplificationandmicroprocessorthatmakeupthesystem.Givesthemethodtoimprovethesystemperformance.ExperimentsshowthatthesystemcanobtainbetterECGsignalsandaccurateheartrate.Theheartbeatratedetectionsysteminthisarticlehasstronganti-interferenceability,simplestructureandlowcost.FAQWhatisAD620?AD620isalow-cost,high-precisioninstrumentationamplifier.Itonlyrequiresanexternalresistortosetthegain.Thegainrangeis1to10,000.CanIchangeAD620toAD623whenmakingMCUproducts?BothAD620andAD623aresingleinstrumentationamplifiers,andthepinarrangementisexactlythesame.Themaindifferenceis:AD620mustusepositiveandnegativepowersupplies,AD623canbeapositiveandnegativepowersupplyorasinglepowersupply.IftheoriginalboardisAD620,youcanreplaceitwith623;iftheoriginalboardisAD623,youmaynotbeabletoreplaceitwith620(itdependsonwhetherthepowersupplyoftheoriginalboardcircuitisdualpowersupplyorsinglepowersupply).AfterreplacingAD620andAD623insingle-chipproducts,theprogramcanworknormallywithoutmodification.WhatisthedifferencebetweenAD620BRandAD620AN?Theirpackagesaredifferent.WhatistheoutputresistanceofAD620?Howtoadjustit?AD620isakindoflowpowerconsumptioninstrumentamplifier,itsoutputresistanceisabout10K,thisistheinherentcharacteristicofthischip,generallyitisdifficulttoadjust.Ifyouhaverequirementsforoutputresistance,youcangenerallyuseanexternalcircuittosolveit.IsAD620apositivephaseamplificationorareversephaseamplification?AD620isaninstrumentamplifier,theoutputvoltageis[(Vin+)-(Vin-)]*gain.Ifthedesiredsignalis(Vin+)-(Vin-),thegainispositive,whichisequivalenttopositiveamplification.Conversely,ifthedesiredsignalis(Vin-)-(Vin+),thegainisequivalenttonegative,whichisequivalenttoreverseamplification.Whatisaninstrumentationamplifier?Instrumentationamplifier,animprovementofthedifferentialamplifier,hasaninputbuffer,doesnotrequireinputimpedancematching,sothattheamplifierissuitableformeasurementandelectronicinstrumentsI.IntroductionTheamplificationofweaksignalshashighrequirementsandhighdifficulty.Thesignalamplificationisrelatedtotherequirementsofstabilityandaccuracyofsignalamplification.Differentialamplificationtechnologyhasthecharacteristicsofsuppressingcommonmodesignalsandonlyamplifyingdifferentialmodesignalswithhighgain,soitisappliedtosmallsignalamplificationtechnology.ThesystemdesignadoptstheAD620chipwithdifferentialamplificationfunctiontoamplifytheweakvoltagesignalofthestrainsensortoachievethehighprecisionrequirementsofthesystem.Thisarticleusesvirtualinstrumenttechnologytocollectandanalyzetheamplifiedsignal,andwritethecorrespondingdisplayinterface.Themeasurementdataisanalyzedbythesecond-orderinterpolationmethodtoverifytheaccuracyofthecircuit.AD620CatalogI.IntroductionII.SystemDesignIII.SystemHardwareCircuitDesign3.1PressureMeasurementCircuit3.2VoltageSignalAmplifierCircuit3.3ReferenceVoltageSourceCircuitandVoltageZeroingCircuit3.4Voltage-currentConversionCircuitIV.TheOverallSoftwareDesignoftheSystemV.QuantitativeTestingandResultAnalysis5.1DataProcessingMethod5.2DataProcessingResults5.3ErrorAnalysisVI.ConclusionFAQOrdering&QuantityII.SystemDesignThesystemisprovidedwithtwovoltagesof12Vand5VfromaDCstabilizedsource.Whensetting12Vpowersupply,thesystemvoltageoutputfullrangeis5V,andthesensorwithstandsstaticpressurefullrangeis19.6N.Whenmeasuringwithinthefull-scalerange,themaximumabsoluteerrorofthestaticpressuresignalis9.810-3N,andtherelativeerroris0.02%.Theoutputsignaloftheloadcellprovidestwooutputmodes:voltageoutputandcurrentoutputaftertheamplifiercircuit.III.SystemHardwareCircuitDesignTheoveralldesignprocessofthesystemisshowninFigure1.ThesystemhardwarecircuitismainlycomposedofLC7012loadcell,AD620instrumentationamplifier,referencevoltagesource,voltagezeroingcircuit,signalfilteringandshapingcircuitandvoltage-currentconversioncircuit.Figure1Systemhardwarecircuitoveralldesignprocess3.1PressureMeasurementCircuitPressuremeasurementadoptsLC7012loadcell,withfullbridgemeasurementcircuit.LC7012loadcellhasthefollowingtwocharacteristicswhensubjectedtopressure:(1)Underthesamepressure,thestrainofthesensorstraingaugeandtheoutputvoltageofthebridgeareconstantandhavenothingtodowiththeprecisepositionofthepressureactingontheloadendofthesensor.(2)Theoutputvoltageandpressureofthefullbridgecircuitcomposedofstraingaugesarebasicallylinear.The4piecesofresistancestraingaugesintheLC7012loadcellareattachedtothestrainzoneofthedouble-holebeam.Whenthereisstaticpressure,thedouble-holebeamproducesquadrilateraldeformationundertheactionofthepressureandthesupportingforceofthesystemchassisonthedouble-holebeam.Thefourstraingaugesareconnectedtoafullbridgecircuitinafullbridgemode.Undertheexcitationofthebridgevoltage,differentweakvoltagesignalsareoutputwithdifferentpressures,andtheamplifiercircuitamplifiestheweakvoltagesignalssentbythebridge.Thefull-bridgeequal-armbridgehassimplestructure,strongsymmetry,highsensitivity,andgoodconsistencyoftheparametersofeacharm.Theeffectsofvariousinterferencescancanceleachother,forexample,itcansuppresstheeffectsoftemperaturechangesandsuppresstheinterferenceoflateralforces.Itiseasiertosolvetheproblemofcompensationoftheloadcell.Thefull-bridgemeasurementcircuitenablestheoutputoftheweakvoltagesignaltoeliminateerrorscausedbythecircuititselfasmuchaspossible,andprovidestheinitialguaranteefortheoverallaccuracyofthesystem.3.2VoltageSignalAmplifierCircuitInordertoimprovetheamplificationaccuracyoftheweakvoltagesignaloutputbythebridge,thesignalamplifyingcircuitselectstheAD620chipproducedbyADIasthecoreelement,anddesignsaspecialadjustablereferencevoltagesourceforittomeetthereferencevoltagerequirementsofdifferentvoltagesources.Andtheneedtoaccuratelyamplifyweaksignals.Figure2AD620PinoutAD620isalow-cost,high-precisioninstrumentationamplifier.Itonlyneedsanexternalresistortosetthegain.Thegainrangeis1to10000dB.AndAD620powerconsumptionislow,themaximumoperatingcurrentis1.3mA.AD620hasthecharacteristicsofhighprecision(maximumlinearity4010-6),lowoffsetvoltage(maximum50V)andlowoffsetdrift(maximum0.6V/℃),makingitanidealchoiceforprecisiondataacquisitionsystemssuchassensorinterfaces.Figure2showsitspinarrangement.AD620monolithicstructureandlasercrystaladjustmentallowcircuitcomponentstobecloselymatchedandtracked,thusensuringtheinherenthighperformanceofthecircuit.AD620isathree-op-ampintegratedinstrumentationamplifierstructure,inordertoprotectthehighprecisionofgaincontrol,theinputtransistorprovidesdifferentialbipolarinput,andusesprocesstoobtainlowerinputbiascurrent,throughthefeedbackoftheinputstageinternalop-amp,Keepthecollectorcurrentoftheinputtransistorconstant,andaddtheinputvoltagetotheexternalgaincontrolresistorRG.AD620internalgainresistanceisadjustedtoanabsolutevalueof24.7k,soanexternalresistancecanbeusedtoachievepreciseprogrammingofthegain.ThegainformulaisThevoltagesignalamplifiedbytheAD620canpassthroughafilteringandshapingcircuitandbedisplayedindigitalformwithadigitaltubethroughtheanalog-to-digitalconvertermodule.Inordertofullyutilizeanddemonstratethefunctionsofvirtualinstruments,thesystemusesLabVIEWtodesignthecorrespondingsignalacquisitionandprocessingprogramanddisplayinterface.3.3ReferenceVoltageSourceCircuitandVoltageZeroingCircuitThereferencevoltagesourcecircuitismainlycomposedofaZenerdiodeLM285,alow-powerdualoperationalamplifierchipLM258,avariableresistorandanumberoffixedresistanceresistors,asshowninthelowerleftpartofFigure3.ThisreferencevoltagesourcecircuitcanprovideAD620with1.25Vor2.5Vaccuratereferencevoltage.Figure3VoltagesignalamplifiercircuitThevoltagestabilizingdiodeLM285providestheprimarystablevoltage,butthetemperaturedriftofthediodeislarge,andthevoltagestabilizationvalueofdifferentdiodesinthesamebatchisnotthesame,sothecorrespondingauxiliaryvoltagestabilizingcircuitmustbedesignedforit.TheoperationalamplifierLM258U1AamplifiesthevoltagefromtheZenerdiodeandfeedsbacktheoutputvoltagethroughthefeedbackresistorR2,makingtheoutputvoltagemorestable.ResistorR5andpotentiometerW1dividetheoutputvoltageoftheZenerdiode.PotentiometerW1hastwofunctions:(1)AdjustingW1canmakethevoltagefollowercomposedofoperationalamplifierLM258U1Bhavedifferentoutputvoltages,andthenprovidedifferentstablereferencevoltagestoAD620.(2)ThepotentiometerW1alsoplaysaroleofzeroadjustmentontheamplifyingcircuitcomposedofAD620.Thevoltagefollowerisusedbecausethevoltagefollowercanincreasetheinputimpedanceandreducetheoutputimpedance,andtherequirementofthepowersupplyisthatthecircuithasasmalleroutputresistance.AD620itselfhasaninternalzeroadjustmentfunction,butaccordingtoactualmeasurement,itisfoundthatwhenthedifferentialinputiszero,theoutputisnotzero,butaboutafewtenthsofmV.Therefore,inordertoimprovetheaccuracyoftheoutput,itisnecessarytoperformtheAD620Externalzeroadjustment,byprovidingdifferentreferencevoltagestotheAD620referencevoltagepins,theoutputvoltageoftheinstrumentationamplifierAD620canbezerowhenthedifferentialinputiszero.ThecircuitjustadjustsW1tomaketheoutputterminalofthevoltagefollowerhavedifferentvoltageoutput,adjuststhereferencevoltageofAD620,thusplaystheroleofzeroadjustmenttoAD620.TheinstabilityofthereferencevoltagewilldirectlyaffectthestabilityoftheamplifiercircuitcomposedofAD620,andleadtoinaccuracyofthefinaloutputresult.Therefore,thesystemdoesnotdirectlyusetherelativelystable-12Vor-5VprovidedbytheDCstabilizedsourceasthereferencevoltage.3.4Voltage-currentConversionCircuitThevoltage-currentconversioncircuitenablesthesystemtooutputintheformofcurrent.TheAD620iscombinedwithanAD705operationalamplifierandtworesistors(asshowninFigure4)toformaquietcurrentsource.AD705providesabufferforthereferencepin.Ensuregoodcommonmoderejection(CMR)performance.TheoutputvoltageofAD620appearsontheresistanceRL,thelatterconvertsitintoelectriccurrentoutput.Figure4Schematicdiagramofvoltage-currentconversioncircuitAD705isalow-power,bipolaroperationalamplifierwithabipolarfieldeffecttransistorinputstage.Therefore,ithasthecharacteristicsofhighinputimpedance,lowinputoffsetvoltage,smallinputbiascurrent,andsmallinputoffsetvoltagedrift.TheinputbiascurrenthasreachedthepAlevel.Itnotonlyhasmanyadvantagesofbipolarfieldeffecttransistorsandbipolaroperationalamplifiers,butalsoovercomesthedefectoflargebiascurrentdriftinthefulltemperaturerange.Inthefulltemperaturerange,thetypicalvalueofthebiascurrentofAD705onlyincreasesby5times,andthebiascurrentofthegeneralbipolarfieldeffecttransistoroperationalamplifierincreasesby1,000times.ComparedwithOP07,thetemperaturedriftvalueis1/2ofOP07,themaximuminputbiascurrentisonly1/5ofOP07,andtheinputoffsetvoltageisonly1/20ofOP07.Becauseitisabipolarfieldeffecttransistorinputpole,thesignalsourceimpedanceismuchhigherthanOP07,whileitsDCaccuracyremainsunchanged.IV.TheOverallSoftwareDesignoftheSystemThesystemsoftwareiswritteninLabVIEW.LabVIEWisagraphicalprogramminglanguage,whichiswidelyusedinvariousfieldsasastandardfordataacquisitionandinstrumentcontrolsoftware.LabVIEWisapowerfulandflexiblesoftware.Useittoeasilybuildyourownvirtualinstrument.Inthecaseofonepieceofhardware,differentfunctionsofdifferentinstrumentscanberealizedbychangingthesoftwareprogramming,whichisconvenientandfast.Combinedwiththenewdevelopmentdirectionofthecurrenttestingfieldinstruments,thefinaloutputanalogvoltagesignaliscollectedbyAdvantechsUSB4716universaldataacquisitionmoduleandtransmittedtothecomputer.UseNIvirtualinstrument(LabVIEW)todesignvoltagesignalacquisitioncontrolprogramandvoltagedatareal-timedisplayinterface.UseLabVIEWsoftwareplatformtoanalyzeandprocessthedigitalvoltagesignalfromUSB4716.ThepartprogramofLabVIEWvoltagesignalacquisitioncontrolanddisplayisshowninFigure5.Figure5VoltagesignalacquisitionprogramV.QuantitativeTestingandResultAnalysis5.1DataProcessingMethodSecond-orderinterpolation(parabolicinterpolation):select(x0,y0),(x1,y1),(x2,y2)correspondinginterpolationequationsfromasetofdata.5.2DataProcessingResultsInordertoobtainanaccuratecorrespondencebetweenpressureandvoltageandfacilitatesubsequentanalysisofabsoluteandrelativeerrors,theexperimentusesstaticmeasurementmethodstomeasureaseriesofstaticpressurevalues,andquantitativelyanalyzetheexperimentalresultstodeterminetheaccuracyofthecircuit.Commonlyusedwaveformtimedomainandfrequencydomainanalysismethods.Table1Brightness/ContrastComparisonPressure/N0...2.94...8.829.8...13.72...19.6219.6Voltage/V0...0.75...2.2472.498...3.498...4.755.001Measure20staticpressurevaluesfromsmalltolargewithinthefullscalerange,andmakethepressureincrement△thesame.Let△=0.98N,andusethesecond-orderinterpolationmethodtoanalyzetherelationshipbetweenvoltageandpressure.SelectthreerepresentativepointsfromTable1:(x0,y0)=(0,0);(x1,y1)=(2.498V,9.8N);(x2,y2):(5.001V,19.6N).Bringinsecond-orderinterpolationTherelationshipcurvebetweenthepressureonthesensorandthesystemoutputvoltageisY=(-1.56810-3)x2+3.927x(3)5.3ErrorAnalysisTheabsoluteerrorreflectsthedeviationofthemeasuredvaluefromthetruevalue,thatis,theabsolutevalueofthedifferencebetweenthemeasuredvalueandthetruevalue.Theabsoluteerrorcanbedefinedas:=|X-L|(4)Intheformula,istheabsoluteerror;Xisthemeasuredvalue;Listhetruevalue.Relativeerroristheratioofabsoluteerrortothemeasuredvalueortheaveragevalueofmultiplemeasurements,andtheresultisusuallyexpressedasapercentage,soitisalsocalledpercentageerror.Absoluteerrorcanindicatethereliabilityofameasurementresult,whilerelativeerrorcancomparethereliabilityofdifferentmeasurementresults.Whenmeasuringwiththesametool,thelargerthemeasuredvalue,thesmallertherelativeerrorofthemeasurementresult.TheabsoluteerrorandrelativeerrorofthestraingaugepressuresensortestsystemareshowninFigure6andFigure7.Thetwofiguresrespectivelyshowtheabsoluteerrorandrelativeerrorcurvesoftwootherdataprocessingmethods:linearinterpolationandaverageselectionmethod.ItcanbeseenfromFigure6andFigure7thatthecalculationaccuracyofthesecond-orderinterpolationmethodishigherthantheothertwomethods,whichalsoprovesthatthechoiceofthedataprocessingmethodiscorrect.Figure6AbsoluteerrorcurveFigure7RelativeerrorcurveVI.ConclusionKnownfromtherelativeerrorandabsoluteerrorgraphthat,themeasurementresulterrorofthecircuitintherangeof0~4.9Nisrelativelylarge,butitstillmeetsthesystemdesignrequirements.Afteranalyzingthesensorandtheexperimentalmeasurementcircuit,itisbelievedthatthereasonforthelargererrorcomesfromtherigidityofthecantileverbeammaterialofthesensorandtheflexibleinfluenceoftheviscousmaterialthatfixesthestraingauge.Becausetheaccuracyoftheweakvoltagesignaloutputbythebridgeisaffected,theerrorisalsoamplifiedafterpassingthroughtheamplifyingcircuit,resultinginalargererrorintheexperimentalresultwhenthemeasuredvalueissmall.Insummary,thepressuresignalamplificationsystemsatisfiesthedesignrequirementsofabsolutefull-scaleerror9.810-3Nandrelativeerror.FAQWhatisAD620?AD620isalow-cost,high-precisioninstrumentationamplifier.Itonlyrequiresanexternalresistortosetthegain.Thegainrangeis1to10,000.CanIchangeAD620toAD623whenmakingMCUproducts?BothAD620andAD623aresingleinstrumentationamplifiers,andthepinarrangementisexactlythesame.Themaindifferenceis:AD620mustusepositiveandnegativepowersupplies,AD623canbeapositiveandnegativepowersupplyorasinglepowersupply.IftheoriginalboardisAD620,youcanreplaceitwith623;iftheoriginalboardisAD623,youmaynotbeabletoreplaceitwith620(itdependsonwhetherthepowersupplyoftheoriginalboardcircuitisdualpowersupplyorsinglepowersupply).AfterreplacingAD620andAD623insingle-chipproducts,theprogramcanworknormallywithoutmodification.WhatisthedifferencebetweenAD620BRandAD620AN?Theirpackagesaredifferent.WhatistheoutputresistanceofAD620?Howtoadjustit?AD620isakindoflowpowerconsumptioninstrumentamplifier,itsoutputresistanceisabout10K,thisistheinherentcharacteristicofthischip,generallyitisdifficulttoadjust.Ifyouhaverequirementsforoutputresistance,youcangenerallyuseanexternalcircuittosolveit.IsAD620apositivephaseamplificationorareversephaseamplification?AD620isaninstrumentamplifier,theoutputvoltageis[(Vin+)-(Vin-)]*gain.Ifthedesiredsignalis(Vin+)-(Vin-),thegainispositive,whichisequivalenttopositiveamplification.Conversely,ifthedesiredsignalis(Vin-)-(Vin+),thegainisequivalenttonegative,whichisequivalenttoreverseamplification.Whatisaninstrumentationamplifier?Instrumentationamplifier,animprovementofthedifferentialamplifier,hasaninputbuffer,doesnotrequireinputimpedancematching,sothattheamplifierissuitableformeasurementandelectronicinstrumentsIDescriptionAD620isalow-power,high-precisioninstrumentationamplifier.BasedontheinformationprovidedbytheADcompany,thisblogintroducesthecharacteristicsandtypicalusageofAD620.Besides,thisblogalsointroducestheapplicationofAD620.Theapplicationsaremainlyaboutphotoelectricdetection,ultrasonictesting,etc.Figure1.AD620IDescriptionIIIntroductionIIIAD620PinoutandWorkingPrincipleIVAD620TypicalUsageVAD620Application5.1ApplicationinPhotoelectricDetection5.2ApplicationinUltrasonicTestingVIConclusionFAQOrdering&QuantityIIIntroductionAD620isalow-power,high-precisioninstrumentationamplifier.Anditcansettheamplificationfactorfrom1to1000withonlyanexternalresistor.Itissmallinsize,inan8-pinSOICorDIPpackage;thepowersupplyrangeis2.3V~18V;themaximumpowersupplycurrentisonly1.3mA.AD620hasgoodDCandACcharacteristics.Itsmaximuminputoffsetvoltageis50V,themaximuminputoffsetvoltagedriftis1V/℃,andthemaximuminputbiascurrentis2.0nA.WhenG=10,itscommon-moderejectionratioisgreaterthan93dB.Theinputvoltagenoiseisat1kHz,thepeak-to-peakvalueoftheinputvoltagenoiseis0.28Vintherangeof0.1Hz~10Hz,andtheinputcurrentnoiseisWhenG=1,itsgainbandwidthis120kHz,andthesettlingtimeis15s.Ingeneral,thecharacteristicsofAD620canbesummarizedasfollows:AD620canensuretheperformanceindicatorsrequiredforhigh-gainprecisionamplification.Forexample,lowoffsetvoltage,lowoffsetvoltagedrift,andlownoise,etc.;Withonlyoneexternalresistor,themagnificationcanbesetfrom1to1000;Smallsize,with8pins;Lowpowerconsumptionanditsmaximumsupplycurrentare1.3mA.IIIAD620PinoutandWorkingPrincipleThepinofAD620isshownasinFig.2,itsstructurediagramisshownasinFig.3.Figure2.AD620PinoutFigure3.AD620StructureDiagramAD620isamonolithicinstrumentamplifier.Itisdevelopedonthebasisoftheimprovementofthetraditionalthree-opamplifiercombination.TheinputtransistorsQ1andQ2providetheonlybipolardifferentialinput.Duetotheinternalsuperprocessing,itsinputoffsetcurrentis10timeslowerthannormal.ThroughthefeedbackoftheQ1-A1-R1loopandtheQ2-A2-R2loop,thecollectorcurrentsofQ1andQ2arekeptconstant.Thus,theinputvoltageisequivalenttothetwoendsoftheexternalresistorRg.AndthedifferentialamplificationfactorfromtheinputtotheA1/A2outputisG=(R1+R2)/Rg+1.TheunitygainsubtractorcomposedofA3eliminatesanycommon-modecomponents.Andthenitproducesasingle-channeloutputrelatedtothepotentialoftheREFpin.ThevalueofRgalsodeterminesthetransconductanceofthepreviousstageopamp.WhenRgdecreases,theamplificationfactorincreases.Andthetransconductancetotheinputtransistorgraduallyincreases.Thishasobviousadvantages:theincreaseintheamplificationfactorincreasestheopen-loopgain.Thus,theerrorrelatedtogainisreduced.Thegain-bandwidthproductdeterminedbyC1,C2andthepre-opamptransconductanceincreases.Thus,thefrequencyresponseisimproved.Theinputvoltagenoiseismainlydeterminedbythecollectorcurrentoftheinputtransistorandthebaseresistance.Andtheinputvoltagenoiseisreducedto.TheinternalgainresistorsR1andR2areaccuratelydeterminedas24.7k.Inthiscase,theoperationalamplifiergainisaccuratelydeterminedbyRg.G=49.4k/Rg+1orRg=49.4k/(G-1)IVAD620TypicalUsage(1)Theinputbiascurrentisthecurrentrequiredtobiastheinputtransistoroftheopamp,anditmusthaveareturnloop.Therefore,whenamplifyinganAC-coupledsignalsourcelikeatransformer,eachinputpointmusthaveaDCpathtoground.AsshowninFigure4-6.Figure4.BiasCurrentLoopwithTransformerCoupledInputFigure5.BiasCurrentLoopforThermocoupleInputFigure6.BiasCurrentLoopWhenACCoupledInput(2)Allinstrumentamplifiersrectifythesignaloutsidethechannel.Ifasmallsignalisamplified,thisrectifiedvoltagebecomesaDCoffsetvoltage.ThestructureofAD620allowsafirst-levelfiltertobeinsertedbetweenthebaseandemitteroftheinputtransistortofilteroutunwantedrectifiedsignals,asshowninFigure5.RC=1/2f,fisgreaterthanorequaltothebandwidthofAD620,C150pF.Figure7.PrimaryFilterPrincipleDiagram(3)TheoutputvoltageofAD620isrelatedtothereferenceterminal.ConnectingtheREFterminaltoanappropriategroundingpointcansolvemanygroundingproblems.Manydataacquisitionsystemsseparatetheanaloggroundfromthedigitalground.Howcome?Justaimingtoisolatethelow-levelanalogsignalfromthenoisydigitalenvironment.Thegroundingprincipleisasfollows:eachindependentgroundloopminimizesthecurrentflowingfromthesensitivepointtotheground.Thesegroundloopsmustbeconnectedtogetheratsomepoint,usuallyontheADC.LetstakealookatFigure7.Thereferenceterminal5oftheAD620,thegroundterminalofthesample-and-holdAD585.Andthegroundterminaloftheanalogpowersupplyarerespectivelyconnectedtotheanaloggroundterminaloftheanalog-to-digitalconverterAD574A.Thegroundterminalofthedigitalpowersupplyisconnectedwiththedigitalgroundoftheanalog-to-digitalconverterAD574A.Finally,theanaloggroundanddigitalgroundareconnectedtotheAD574A.Inmanyapplications,shieldedcablesareoftenusedtoreducenoiseinterferenceattheinput.Properdrivetotheshieldcanreducethedifferentialphaseshiftcausedbycablecapacitanceandstraycapacitance.AndensurethattheACcommon-moderejectionratiodoesnotdrop.Figure8showsthedifferentialshielddriveconnection.Figure9showsthecommon-modeshielddriveconnection.Figure8.DifferentialShieldDriveFigure9.CommonModeShieldDriveVAD620Application5.1ApplicationinPhotoelectricDetectionPhotoelectricdetectioniswidelyusedintheindustry.Theprincipleofdesigningaphotoelectricdetectionsystemistoreducethetotalsystemnoisetoaminimum.Thenoiseofthesystemmainlyincludesdetectornoise,resistancenoise,andoperationalamplifiernoise.Becausetheyareindependentofeachother,thetotalnoisecanbeexpressedasUn(T)=[Un2(D)+Un2(L,F)+Un2(A)]1/2Intheformula:Un2(D)Detectornoisevarieswithdifferentphotodetectors.Theappropriatedetectorshouldbeselectedaccordingtothesystemrequirements;Un2(L,F)Loadresistancenoise;Un2(A)Opampnoise.ThenoiseofAD620isverysmall.Therefore,itisoftenusedasthepre-opamplifierofthephotoelectricdetectioncircuit.Takethephotodiodeasthedetectorasanexampletoillustrate.Here,supposethecurrentofthephotodiodeisID,thenID=ISC+IdarkIntheformula:ISCPhotocurrent.Itisproportionaltothelightintensity,whichistheeffectiveinformationdetected;IdarkDarkcurrent.ItconsistsofthecurrentonthesurfaceofthediodeandtheusualPNjunctioncurrent.Itbelongstoinvalidinformationinthesystem.Weneedtoeliminatetheinfluenceofdarkcurrent.TwodiodesD1andD2withthesameperformanceandtworesistorsR1andR2withtheresistancevalueofRareselectedtoformabridge.AsshowninFigure10.Figure10.PhotoelectricDetectionPreamplifierCircuitWhenD1haslightandD2hasnolight,theinputvoltageatbothendsoftheop-ampis(ISC+Idark)-R1-Idark-R=ISC-R1.Itisonlyrelatedtothephotocurrent,thuseliminatingtheinfluenceofthedarkcurrent.5.2ApplicationinUltrasonicTestingInthefieldofultrasonictesting,especiallywhenultrasonicwavespropagateinanon-uniformandattenuatedmedium,theechoafterencounteringtheinterfaceisveryweak.Ifageneralop-ampisusedforpre-processing,thenoiseisoftenlargeandeffectivesignalscannotbeobtained.ChoosingAD620asthepre-amplifiercircuithasasimpleconnectionandlownoise.AsshowninFigure11.Figure11.UltrasonicDetectionReceivingFrontCircuitVIConclusionAD620isahighprecisioninstrumentationamplifier.Intheapplication,wealsoneedtopayattentiontopreventtheblockageoftheamplifier.IfastrongDCsignalissuperimposedontheweaksignal,wemustsetupaseparationcircuit.Inthisway,theDCsignalcanbeseparated.FAQWhatisAD620?AD620isalow-cost,high-precisioninstrumentationamplifier.Itonlyrequiresanexternalresistortosetthegain.Thegainrangeis1to10,000.CanIchangeAD620toAD623whenmakingMCUproducts?BothAD620andAD623aresingleinstrumentationamplifiers,andthepinarrangementisexactlythesame.Themaindifferenceis:AD620mustusepositiveandnegativepowersupplies,AD623canbeapositiveandnegativepowersupplyorasinglepowersupply.IftheoriginalboardisAD620,youcanreplaceitwith623;iftheoriginalboardisAD623,youmaynotbeabletoreplaceitwith620(itdependsonwhetherthepowersupplyoftheoriginalboardcircuitisdualpowersupplyorsinglepowersupply).AfterreplacingAD620andAD623insingle-chipproducts,theprogramcanworknormallywithoutmodification.WhatisthedifferencebetweenAD620BRandAD620AN?Theirpackagesaredifferent.WhatistheoutputresistanceofAD620?Howtoadjustit?AD620isakindoflowpowerconsumptioninstrumentamplifier,itsoutputresistanceisabout10K,thisistheinherentcharacteristicofthischip,generallyitisdifficulttoadjust.Ifyouhaverequirementsforoutputresistance,youcangenerallyuseanexternalcircuittosolveit.IsAD620apositivephaseamplificationorareversephaseamplification?AD620isaninstrumentamplifier,theoutputvoltageis[(Vin+)-(Vin-)]*gain.Ifthedesiredsignalis(Vin+)-(Vin-),thegainispositive,whichisequivalenttopositiveamplification.Conversely,ifthedesiredsignalis(Vin-)-(Vin+),thegainisequivalenttonegative,whichisequivalenttoreverseamplification.Whatisaninstrumentationamplifier?Instrumentationamplifier,animprovementofthedifferentialamplifier,hasaninputbuffer,doesnotrequireinputimpedancematching,sothattheamplifierissuitableformeasurementandelectronicinstruments

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IIntroductionHere,youcanlearnabouttheAD620instrumentamplifiercircuit.Besides,youcanalsobrowseAD620mainfeatures,workingprinciples,andapplications.Thisbloggenerallydiscussesthefollowing3basicquestions:1.Whatisaninstrumentationamplifier;2.Howdoesitwork;3.Howandwheretouse.Figure1.AD620CatalogIIntroductionIIDescriptionIIIAD620TechnicalIndicatorsIVAD620WorkingPrincipleVAD620ApplicationVIConclusionFAQOrdering&QuantityIIDescriptionOperationalamplifiershaveevolvedoverthedecadesandasaresult,thereisawidevarietyofthem.Theycanbeeasilycategorizedaccordingtotheirapplicationrequirements.Themaincategoriesincludegeneral-purpose,low-voltage,low-power,high-speed,andhigh-precisiontypes.Inrecentyears,applicationssuchasconsumerelectronics,communication,andnetworkinghavebeendevelopingcontinuously.Andtheseconstantlydevelopingindustriesalsoputforwardnewtechnicalrequirementsforop-ampproducts.AD620instrumentamplifieristheproductofADcompany.Duetoitssupertechnology,AD620hasthefollowingcharacteristics:1.3mAMaximumWorkingCurrent5VInputOffsetVoltage1V/℃InputOffsetDriftMaximum93dBCommonModeRejectionRatioAdjustableGainRangeEasytoAdjustandLowNoise.AndwhycanAD620becomeanindustry-standardhigh-performance,low-costinstrumentationamplifier?ThatsbecausethecoreofAD620isathree-stageop-ampcircuit,whichhasahighcommon-moderejectionratio,goodtemperaturestability,wideamplificationband,andlownoise.Andithasthecharacteristicsofhighaccuracy,easyuse,andlownoise.sothisisalsothereasonwhyAD620canbesopopular.IIIAD620TechnicalIndicatorsThemaintechnicalindicatorsofAD620areasfollows:Bandwidth800MHzOutputpower2.4mWPowergain120dBWorkingvoltage15VStaticpowerconsumption0.48mWInoltage60VConversionrate1.2V/SPackageformDIP8Operatingtemperaturerange-55℃~+125℃IVAD620WorkingPrincipleThefunctionalstructureoftheAD620amplifierisshowninFig.2.Figure2.AD620FunctionalBlockDiagramDoyouknowwhatthecharacteristicsofthisamplifierare?Theansweris:differentialinput,asingle-endedoutput.ThevoltagegaincanbedeterminedbyaresistorRG.Thegainsareadjustable,whichsolvestheproblemofconnectingthesubsequentloadtotheground.Besides,A1andA2formadifferentialinputandadifferentialoutputwithin-phasehighinputimpedanceandundertakeallgainamplificationtasks.Becausethecircuitstructureissymmetrical,whichmeanswhenthegainchanges,theinputimpedancedoesnotchange.ThefeedbackresistanceRl=R2=24.7k.Thecommon-modegain,offset,drift,andothererrorsoftheamplifiersA1andA2aremutuallycompensated.ThegainofthelatterstageA3is1,whichhasahighercommon-moderejectionratioandanti-interferenceability.AD620isamonolithicintegratedamplifier.Anditisdevelopedonthebasisoftheimprovementofthetraditionalthree-opamplifiercombination.AsshowninFigure2,theinputtransistorsQ1andQ2providetheonlybipolardifferentialinput.Duetotheinternalultra-processing,itsinputoffsetcurrentis10timeslowerthanthegeneralcase.ThroughthefeedbackoftheQ1-A1-R1loopandtheQ2-A2-R2loop,theintegratedpolecurrentofQ1andQ2iskeptconstant.SotheinputvoltageisequivalenttothetwoendsoftheexternalresistorRG.ThedifferentialamplificationfactorfrominputtoA1/A2outputisG=(R1+R2)/RG+1.TheunitygainsubtractorcomposedofA3eliminatesanycommon-modecomponents.Thereby,itproducesasingle-channeloutputrelatedtothepotentialoftheREFpin.Figure3.AD620SowhataboutRG?ThevalueofRGalsodeterminesthetransconductanceofthepreviousstageop-amp.WhenRGdecreases,themagnificationincreases.WhenRGdecreases,thetransconductancetotheinputtransistorgraduallyincreases.Thishasthefollowingtwoobviousadvantages:First,theincreaseintheamplificationfactorincreasestheopen-loopgain.Therebyreducingthegain-bandwidthproductandincreasingthefrequencyresponse;Second,itismainlydeterminedbytheinputtransistorcollectorcurrentandbaseresistance.ByaccuratelycorrectingthevalueoftheinternalgainresistorsR1andR2to24.7k,wecanmaketheoperationalamplifiergain(derivedbycalculation)accuratelydeterminedbyRG:G=49.4k/RG+1orRG=49.4k/(G-1)Figure4.AD620CircuitStructureDiagramRGistheexternalgainadjustment.Tomeettherequiredamplificationfactor,wecanconnectthishigh-precisionresistancebetweenpin1and8.ByusingtheamplifierAD620,thegainerrorcanbelessthan0.01%,andthenon-linearityislessthan0.002%.Fromtheapplicationpointofview,AD620isparticularlysuitableforapplications.Suchassensorinterface,ECGmonitor,precisionvoltagecurrentconversionandotherapplications.Ifweanalyzethecircuittechnologyperformance,wewilladeeperunderstandingofAD620.Thatis,AD620isactuallyalow-power,high-precisioninstrument,broadbandintegratedoperationalamplifier.VAD620ApplicationInstrumentationamplifiersaresometimesmisunderstoodbypeople.Here,weneedtopointout2ideas:First,notallamplifiersusedforinstrumentationareinstrumentationamplifiers;Second,allinstrumentationamplifiersarebynomeansonlyusedforinstrumentation.Instrumentationamplifiersareusedinmanyfields.Frommotorcontroltodataacquisitionandautomotivesystems.Instrumentationamplifierisaclosed-loopgainunit.Andwithdifferentialinputandsingle-endedoutputrelativetothereferenceend.Inmostcases,theimpedanceofthetwoinputendsoftheinstrumentationamplifierisbalanced.Theresistanceisveryhigh,anditstypicalvalueis109.Theinputbiascurrentisalsoverylow,typically1nAto50nA.Liketheoperationalamplifier,itsoutputimpedanceisverylow,usuallyonlyafewmilliohmsinthelowfrequencyrange.Theclosed-loopgainofanoperationalamplifierisdeterminedbytheexternalresistance.Theexternalresistanceisconnectedbetweenitsinvertinginputandoutput.Therearedifferencesbetweentheinstrumentamplifierandtheamplifier.Theinstrumentamplifierusesaninternalfeedbackresistornetwork,whichisisolatedfromitssignalinput.Toapplyinputsignalstothetwodifferentialinputterminalsoftheinstrumentationamplifier.Thegaincaneitherbepresetinternallyorsetbytheuser.Throughapinconnectedtoaninternalorexternalgainresistor,whichisalsoisolatedfromthesignalinputterminal.Figure5showsablockdiagramofadifferentialamplifier.Figure5.DifferentialAmplifierICThistypeofICisaspecial-purposeinstrumentationamplifier.Anditwhichusuallyconsistsofasubtractoramplifierfollowedbyanoutputbuffer(perhapsone-stagegain).ThefourresistorsusedforthesubtractorareusuallyinsidetheIC,sotheycanbepreciselymatchedtoachieveahigherCMR.Manydifferentialamplifiersaresuitableforapplications.Wherethecommon-modevoltageandsignalvoltagemayeasilyexceedthesupplyvoltage.Thesedifferentialamplifiersusuallyusehigh-valueinputresistorstoattenuatethesignal.Generallyspeaking,instrumentationamplifiersanddifferentialamplifiersareusedinthefollowingranges:DataAcquisitionThemainpurposeoftheinstrumentationamplifieristoamplifytheweaksignaloutputbythesensorinanoisyenvironment.Amplificationofsignalsfrompressuresensorsortemperaturesensorsiscommon.Commonbridgeapplicationsincludestrainforceandweightmeasurement.MedicalInstrumentsInstrumentationamplifiersarewidelyusedinmedicalequipment.Suchaselectrocardiographsandelectroencephalographs,bloodpressuremonitors,anddefibrillators.Thedifferentialamplifierofmonitoringandcontrolelectronicscanbeusedtomonitorthevoltageandcurrentinthesystemandtriggerthealarmsystemwhenthenormalvalueisexceeded.Becausedifferentialamplifiershavetheabilitytosuppresshighcommon-modevoltages,theyareoftenusedinsuchapplications.Figure6.ElectrocardiographSoftwareProgrammableApplicationsToallowsoftwaretocontrolthehardwaresystem,wecanturntoinstrumentationamplifiers.Instrumentationamplifierscanbeusedonchipswithsoftwareprogrammableresistors.AudioApplicationsBecauseinstrumentationamplifiershavehighCMR,theyareusedforaudio(e.g.microphonepreamplifiers)toextractweaksignalsinnoisyenvironments.Also,itcanbeusedtominimizetheoffsetcausedbygroundloopsVoltageandnoise.High-speedSignalConditioningDuetotheincreasedspeedandaccuracyrequirementsoftodaysvideodataacquisitionsystems,thedemandforbroadbandinstrumentationamplifiersisincreasing.EspeciallyinthefieldofCCDimagingequipmentthatrequiresoffsetcorrectionandinputbuffering.Inthisfield,doublecorrectionsamplingtechnologyisusuallyusedtocorrecttheCCDimage.Generallyusetwosample-and-holdamplifierstomonitortheimageandreferencelevel,andsendthesignalvoltagetoaninstrumentationamplifiertoprovideaDCcorrectionoutput.Figure7.CCDCameraVideoApplicationsHigh-speedinstrumentationamplifiersareusedinmanyvideoandcableradiofrequency(RF)systemstoamplifyorprocesshigh-frequencysignals.PowerControlApplicationsInstrumentationamplifierscanalsomonitorthemotor(monitoringandcontrollingthemotorsspeed,torque,etc.)bymeasuringthemotorsvoltage,currentandthephaserelationshipofthethree-phaseACmotor.Thedifferentialamplifierisusedwhentheinputsignalvoltageexceedsthepowersupplyvoltage.VIConcusionGenerallyspeaking,high-speedoperationalamplifiersaremainlyusedincommunicationequipment,videosystems,andtestandmeasurementinstruments.Advancedapplicationsintestandmeasurement,communications,medical,imagingandotherfieldsarethemaindrivingforcestoimproveamplifierperformance;DSLandconsumervideoapplicationsareitslargestmarkets.FAQWhatisAD620?AD620isalow-cost,high-precisioninstrumentationamplifier.Itonlyrequiresanexternalresistortosetthegain.Thegainrangeis1to10,000.CanIchangeAD620toAD623whenmakingMCUproducts?BothAD620andAD623aresingleinstrumentationamplifiers,andthepinarrangementisexactlythesame.Themaindifferenceis:AD620mustusepositiveandnegativepowersupplies,AD623canbeapositiveandnegativepowersupplyorasinglepowersupply.IftheoriginalboardisAD620,youcanreplaceitwith623;iftheoriginalboardisAD623,youmaynotbeabletoreplaceitwith620(itdependsonwhetherthepowersupplyoftheoriginalboardcircuitisdualpowersupplyorsinglepowersupply).AfterreplacingAD620andAD623insingle-chipproducts,theprogramcanworknormallywithoutmodification.WhatisthedifferencebetweenAD620BRandAD620AN?Theirpackagesaredifferent.WhatistheoutputresistanceofAD620?Howtoadjustit?AD620isakindoflowpowerconsumptioninstrumentamplifier,itsoutputresistanceisabout10K,thisistheinherentcharacteristicofthischip,generallyitisdifficulttoadjust.Ifyouhaverequirementsforoutputresistance,youcangenerallyuseanexternalcircuittosolveit.IsAD620apositivephaseamplificationorareversephaseamplification?AD620isaninstrumentamplifier,theoutputvoltageis[(Vin+)-(Vin-)]*gain.Ifthedesiredsignalis(Vin+)-(Vin-),thegainispositive,whichisequivalenttopositiveamplification.Conversely,ifthedesiredsignalis(Vin-)-(Vin+),thegainisequivalenttonegative,whichisequivalenttoreverseamplification.Whatisaninstrumentationamplifier?Instrumentationamplifier,animprovementofthedifferentialamplifier,hasaninputbuffer,doesnotrequireinputimpedancematching,sothattheamplifierissuitableformeasurementandelectronicinstrumentsIntroductionInrecentyears,withthecontinuousdevelopmentofnewtechnologies,storagebatteriesasapowersourcenotonlyplayanimportantroleintransportation(railroad,subway,ship),powergeneration,communications,aerospace,chemical,traditionalautomobilesandotherindustries.Inaddition,batterieshavealsobeguntobeusedinthefieldsofelectricvehicles(EV)andhybridelectricvehicles(HEV)aspowersourcesorpowerauxiliarypowersources.Doyouknowwhatare2featuresofbatteriescomparedwithdisposablerechargeablebatteries?Thatismultiplerecyclingandhighefficiencyandenergysaving.Whenthecarisnotstarted,itmustrelyonthebatterytosupplypowertothestarteruntilitdrivestheenginetorotate.Whenthebatteryvoltageisinsufficientorthebatteryisdamaged,itisdifficulttoprovidesufficientpower,thuscausingtheenginetofailtorun.Therefore,thisblogproposesthedesignofalow-batteryalarmsystemforcarbatteriesbasedonLM741.Ingeneral,whenthebatteryvoltagedropstoacertainlimit,itwillsendoutareminder.Theprincipleofthereminderisthatthecircuitjudgeswhetherthebatteryisworkingnormallybyinstallingasoundandlightsignalalarmsystem.Inthisway,wecanrechargeourcarorreplacethebatteryintime.CatalogIntroductionCatalogIDescriptionofLM741IIDesignoftheSystemIIICircuitDesign3.1SystemHardwareCircuitDesign3.2ReferencePowerSupplyCircuit3.3SamplingCircuit3.4OutputCircuit3.5AlarmPrinciple3.6WiringDiagramoftheSystemIVTestResultsoftheSystemFAQOrdering&QuantityIDescriptionofLM741TheLM741seriesaregeneral-purposeoperationalamplifiers.Itisintendedforawiderangeofanalogueapplications.Thehighgainandwiderangeofoperatingvoltageprovidesuperiorperformanceinintegrator,summingamplifier,andgeneralfeedbackapplications.LM741hasbothinvertinginputsandnon-invertinginputs.Whenthevoltageofthenon-invertinginput(+)ishigherthanthevoltageoftheinvertinginput(-),theoutputofthecomparatorishigh.Ifthevoltageattheinvertinginput(-)ishigherthanthenon-invertingterminal(+),theoutputislow.Theoutputoftheoperationalamplifieristheproductofgainandinputvoltage.IIDesignoftheSystemThelowbatteryalarmsystemismainlycomposedofreferencepowersupplycircuit,samplingcircuit,voltagecomparatorcircuitandoutputcircuit.Thereferencepowersupplycircuitconsistsofavoltageregulatorandacurrentlimitingresistor,whichisaddedtotheinvertinginputofthevoltagecomparatorandprovidesareferencevoltageforit.Thesamplingcircuitiscomposedoftworesistorsinseriestoformaseriesvoltagedivider,whichisusedastheinputsignalofthewholecircuit,andapartofthebatteryvoltageiscomparedwiththereferencevoltage.Thevoltagecomparatorcircuitjudgeswhethertheoutputishighlevelorlowlevelbycomparingthevoltageofthereferencepowersupplycircuitandthevoltageofthesamplingcircuit.Theoutputcircuitjudgeswhetherthelight-emittingdiodeisintheconductingstatebythereceivedoutputvoltagefromvoltagecomparator,therebygivinganalarmsignaltoindicatethebatterypoweristoolow.Figure1.StructureoftheSystemIIICircuitDesign3.1SystemHardwareCircuitDesignThehardwarecircuitoflowbatteryalarmsystemisshowninFigure2.ThesystemmainlyincludesvoltagecomparatorLM741,resistor,voltageregulatorandLED.Figure2.HardwareCircuit3.2ReferencePowerSupplyCircuitThereferencepowersupplycircuitconsistsofcurrentlimitingresistorR2andvoltageregulatorVDZ.ThissystemtakesthestablevoltageoftheregulatorasthereferencevoltageofthecomparatorLM741,andconnectsittotheinvertinginputoftheLM741.R2=100k.Thestablevoltageis5V.3.3SamplingCircuitR1andR3areconnectedinseriestoformasamplingcircuit,whichisconnectedtothein-phaseinputterminalofLM741.TheresistancevaluesofR1andR3areequal,taking100ktoformseriespartialvoltage.Theintermediatepointisthesamplingvoltage,thatis,takingpartofthebatteryvoltageasthedetectionvoltage,i.e.theinputvoltage.3.4OutputCircuitTheoutputcircuitconsistsofR4andLED.R4=1K,whichcanlimitthecurrent.AccordingtothevoltagevalueattheoutputofthevoltagecomparatortodeterminedwhethertheLEDisonoroff.3.5AlarmPrincipleWhenthebatteryvoltageishigherthan10V,thatis,thevoltageofsamplingcircuitexceeds5V,theinputsignalvoltageishigherthanthereferencevoltage,thenLM741outputshighlevel,andtheoutputvoltageisbatteryvoltage(10~12V).ItcanbeseenfromFigure4thatthepotentialofpin6ishigherthanthepotentialofpin7.LEDdonotemitlightbecauseofthereversevoltage.Thisindicatesthatthebatteryvoltageisnormalandthealarmfunctionisnotactivated.Whenthebatteryvoltageislowerthan10Vandtheinputsignalvoltage(5V)islowerthanthereferencevoltage,theLM741outputsalowlevel,thatis,theoutputvoltageiszero.Atthistime,thepotentialofpin7ishigherthanthepotentialofpin6,theLEDisturnedonduetotheforwardvoltage.Andthelightindicatesthatthebatterypoweristoolow.Thealarmfunctionisactivated.3.6WiringDiagramoftheSystemFigure3showsthewiringstructureoflowbatteryalarmsystem.Theautomobilebatteryisconnectedtothevoltagecomparisondevicethroughthecarkeyswitch,andprovidespowerfortheautomobilecircuitload(lightingsystem,instrumentsystem,etc.)Whenthebatteryvoltageisnormal,theloadvoltageisnormal.Andthevehiclecanstartnormally.Theinstrumentsystemcandisplayandworknormally.Whenthebatteryvoltageistoolow,thevoltagecomparisondevicewillsendoutalightalarmsignal.Atthesametime,ifthepowersupplyvoltagecannotreachtherequiredvoltagelevelofthesystem,thecorrespondinglighting,instrumentandothersystemswillnotoperate.Figure3.WiringDiagramoftheSystemIVTestResultsoftheSystemItcanbeseenfromtable1thatwhenthebatteryvoltageislowerthan10V,thealarmindicatorison;whenthebatteryvoltageishigherthan10V,thealarmindicatorisoff.Therefore,thecircuitcangiveanalarmwhenthebatteryvoltageislowerthan10V,andstopwhenthebatteryisrechargedtoabove10Vagain.Thealarmsystemdoesnotworkwhentheoutputvoltageofthebatteryisabove10V.Itfullyshowsthatthedesignschemeofthecircuitiscorrectandfeasible.TestResultsoftheSystemBatteryvoltage(V)BatteryvoltagestatusAlarmindicatorstatus6.8toolowon8.1lowon9.6lowon10.3(Aftercharging)normaloff12.8(Aftercharging)normaloff13.6(Aftercharging)toohightoffFAQWhatislm741opamp?AnLM741operationalamplifierisaDC-coupledhighgainelectronicvoltageamplifier.Ithasonlyoneop-ampinside.AnoperationalamplifierICisusedasacomparatorwhichcomparesthetwosignal,theinvertingandnon-invertingsignal.WhyOpampiscalled741?The741OpAmpICisamonolithicintegratedcircuit,comprisingofageneralpurposeOperationalAmplifier.ItwasfirstmanufacturedbyFairchildsemiconductorsintheyear1963.Thenumber741indicatesthatthisoperationalamplifierIChas7functionalpins,4pinscapableoftakinginputand1outputpin.Howdoesa741opampwork?ThemostcommonOp-Ampisthe741anditisusedinmanycircuits.TheOPAMPisaLinearAmplifierwithanamazingvarietyofuses.Itsmainpurposeistoamplify(increase)aweaksignal-alittlelikeaDarlingtonPair.TheOP-AMPhastwoinputs,INVERTING(-)andNON-INVERTING(+),andoneoutputatpin6.Howdoyoucalculatelm386gain?VoltageGainAnalysis:Withoutanyexternalcomponents,ithasagainofGv=2x15K/(150+1350)=20(26dB).Withacapacitor(orshortcutting)betweenpins1and8,ithasagainofGv=2x15K/150=200(46dB).WhydoestheIC741requiredualpowersupply?Operationalamplifiershavetwopowersupplyrailsbecausetheyusuallyneedtoswingbipolar-outputvoltagesthatgoeitherpositiveornegativeinresponsetothenormalrangeofinputsignals....Withoutthedualsuppliestheoutputsignalwouldclipatthegroundpotential.HowdoIcheckmy741IC?Testinga741ICThecircuitiscommonlycalledasvoltagefollower.Avoltageisappliedtopin3oftheop-ampthroughthevariableresistor(10K).AllweneedtodoistoverifywhetherthevoltagesV1andV2areexactlysameornot.Checkthemusingamulti-meter.WhatisIC741?Anopampisacomplexelectronicdevice,whichconsistsofresistors,capacitors,transistorsanddiodes.Itiscommerciallyavailableinintegratedcircuitform.MostcommonlyavailableandusedopampICisIC741.TheIC741isasmallchip.Itcompriseseightpins.Whatisgainbandwidthproductof741?Gain-BandwidthProduct:ForanOp-Ampthegain,Gisdefinedasthegainwhenasignalisfeddifferentiallyintotheop-ampandnofeedbackloopispresent....ItisgenerallygiveninV/s,andforthe741op-ampissomethingcloseto1v/s.WhatarethefeaturesofIC741?Shortcircuitandoverloadprotectionprovided.Intheory,thedcoutputvoltagewillbezeroifboththeinputsofthe741ICareconnectedtotheground.Lowpowerconsumption.Largecommonmoderejectionratio(CMRR)anddifferentialvoltageranges.Noexternalfrequencycompensationisrequired.Whichop-amp(LM356orLM741)isthebetterchoiceforhigherfrequencyapplications?Um,theLM356isanaudiopoweramplifierwitha300KHzbandwidth.TheLM741isanoperationalamplifierwithatypicalunitygainbandwidthof1MHz.Inotherwords,theyareentirelydifferentsortsofthingsandnotatallinterchangeable.Neitherisverygoodathigherfrequencies.YoumightbethinkingoftheLF356,whichisaJFETinputoperationalamplifierwithaunitygainbandwidtharound5MHz.MuchbetterpartinalmosteverydimensionthantheLM741.CanweuseanLM324insteadofanLM741forconstructinganop-ampintegrator?Yes.Itwilllikelyperformslightlybettertooasithasaslightlybetterspecification(frequency,slewrate,etc),plusyougetfouridenticalopampsinasingle14pinpackage.

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IntroductionTheLM386isapoweramplifierdesignedforuseinlowvoltageconsumerapplications.Thegainisinternallysetto20tokeepexternalpartcountlow,buttheadditionofanexternalresistorandcapacitorbetweenpins1and8willincreasethegaintoanyvaluefrom20to200.Theinputsaregroundreferencedwhiletheoutputautomaticallybiasestoone-halfthesupplyvoltage.Thequiescentpowerdrainisonly24mWwhenoperatingfroma6Vsupply,makingtheLM386idealforbatteryoperation.CatalogIntroductionCatalogIHowdoesLM386InternalCircuitWork?1.1Inputstage1.2VoltageAmplifierstage1.3Outputstage1.4FeedbackNetworkIILM386ApplicationCircuit2.1CircuitofInfraredalarm2.2CircuitofAutomobileVoiceHorn2.3CircuitofMicrocomputerStereoPowerAmplifierFAQOrdering&QuantityIHowdoesLM386InternalCircuitWork?TheprincipleofLM386internalcircuitisshowninthefigure.Theinternalcircuitisbasedonatypicalaudiopoweramplifierconfiguration,oftenreferredtoasLintopology.LM386internalcircuitisdividedintoinputstage,voltageamplifierstage(VAS),outputstage(OPS)andfeedbacknetwork.Figure1.LM386InternalCircuit1.1InputstageThefirstmoduleisthePNPemitterfolloweramplifier(Q1,Q3).ItsetstheinputimpedanceanddefinestheDCoperatingpointtoraisetheinputvoltagefromtheground,sothecircuitwillacceptthenegativeinputsignalto-0.4V.Both50Kinputresistors(R1,R3)haveestablishedpathstothebasecurrentground,andtheinputsneedtobecoupledtoavoidinterferingwiththeinternalbias.Sotheinputimpedanceisdeterminedbytheseresistorsandissetto50K.Analysisofvoltagegain:Thegainoflongtailpair(Q2,Q4)ofdifferentialamplifierisregulatedbytwogainsettingresistors1.35k+150(R5+R5).Externalpins1and8canadjustthegainfrom20(minimum)to200(maximum).Thevoltagegaincanbecalculatedunderstaticconditions(withoutinputsignalapplied)asfollows:Figure2.AnalysisofLM386voltagegainThevoltage(vdiff)atbothendsofR4andR5isonlythedifferentialinputvoltage(VIN),becausethebaseemittervoltagedropofPNPtransistors(Q1,Q2,Q3andQ4)onbothsidesofLTPisthesame.ThecurrentmirrorformedbyQ5andQ6producesequalcurrentonbothsidesoftheLTP.ThecurrentismarkedasI.Duetothecurrentmirror,thecurrentintensitythroughR8isequalto2I,whileignoringthecurrent(i7)throughthetwo15Kresistors(R6,R7).thesetworesistorshavealargerimpedancecomparedtotherestofthecircuit,thereby:Inthefigureabove,itiseasytoseethatifi7=0,then:Theformulacanalsoberewritteninamoregeneralway:Z1-5andZ1-8aretheimpedancebetweenthecorrespondingpins.Withoutanyexternalcomponents,thegainisGV=2x15k/(150+1350)=20(26dB).Useacapacitor(orshortcut)betweenpin1and8,thenitsgainofGV=2x15k/150=200(46db).1.2VoltageAmplifierstageThecommonemitteramplifier(Q7)amplifiesthelowamplitudeinputsignaltotheappropriateleveldirectlycoupledtotheoutputstage.1.3OutputstageItisclassABpoweramplifier,thatis,push-pullconfiguration.Eachtransistoramplifiesitscorrespondinghalfwave.BecausethegaindifferencebetweenQ9andQ10ofPNPtransistorsisinacompoundPNPtransistorconfiguration,TOTAL=Q9XQ10.Dividercompensation:DiodesD1andD2areusedtocompensateforcrossdistortion.Infact,inapush-pulltopology,thetransistordoesnotstartconductinguntiltheinputsignalbeginstoexceeditsforwardvoltage(Vbe).Theforwardvoltage(VBE)isthevoltageatthebaseemitterjunction(usuallyabout0.6V).Inordertooffsettheminimumconductionlimit(Vbe)ofthetransistors,theyneedtobebiasedsothattheiridlingvoltagewillneverbelowerthantheforwardvoltage(Vbe).Acertainamountofcurrent(calledabiascurrent)willcontinuouslyfeedintothebaseofthetransistortoensurethattheymaintainthesacrificialefficiencyofconduction.Itisprovedthatusingdiodesisoneofthebestsolutions.Itprovidesatemperature-dependentpressuredrop.Andbymatchingthethermalcoefficienttothetransistor,thebiascurrentcanbekeptfairlystable.Ifaccurateheattracingisrequired,installthediodesonthesameheatsinkasthepowertransistor.Sinceonediodeisusuallynotenough,amplifiersusuallyusemultiplediodejunctions1.4FeedbackNetworkAnegativefeedbackisappliedfromtheoutputtotheemitterQ4viatheresistorR8.ThefunctionoftheDCfeedbackistostabilizetheoutputDCbiasvoltagetohalfofthesupplyvoltage.ThefunctionsofDCfeedbackareasfollows:IfforsomereasonVOincreases,thecorrespondingcurrentincrementwillflowthroughR8andintotheemitterofQ4.Therefore,theincreaseofcollectorcurrentofQ4leadstothepositiveincreaseofbasevoltageofQ7.ThisleadstoanincreaseinthecollectorcurrentofQ7,whichreducesthebasevoltageofQ7,thusreducingVo.IILM386ApplicationCircuit2.1CircuitofInfraredalarmFigure3.CircuitofInfraredalarmFigure3showsthecircuitofinfraredalarm.ThecircuitiscomposedofanANDgatecircuit,amonostabledelaycircuit,afour-wayinfraredtransmittingandreceivingcircuit,atriggerandatwo-colorlight-emittingcircuit,andanaudioalarmcircuit.FourpairsofwarninglinesfortransmissionandreceptioniscomposedofHF1~HF4(infraredlight-emittingdiodes)andBG1~BG4(infraredreceivingpairingtubes).Ifsomeonecrossesthewarninglineandtheinfraredbeamisblocked,thecorrespondingmatchingtubewillbecutoff.AndtheinputofthecorrespondingNANDgateishighlevel.Itmakesthetriggerterminalpin2ofIC3(555)obtainanegativedifferentialpulse,thatis,theoutputterminaloftheANDgatecomposedofD1~D4.Therefore,the555isset,andthehighlevelisoutputfrompin3whichmakesBG5saturatedandturnedon.ThechipIC4(KD-9562)ispoweredonandanalarmsoundisgiven.ThedelaywidthofIC3monostablecircuittd=1.1Rw1R3determinesthesoundtime.Thedelayalarmtimecorrespondingtotheparametersinthefigureisabout100seconds.Atthesametime,thecorrespondingtimecanbechangedbychangingthevalueofWandCaccordingtothespecificsituation.ThevoltagestabilizingtubeDWadopts2cw7or2cw10,andthevoltagerangeisabout3VtoprotectthemusicintegrationKD-9562,soastopreventitfromburningduetoover-voltage(highvoltage).ThechipKD-9562isaneightanalogsoundintegratedcircuit,whichcanselectthecorrespondingmusicaccordingtotheusesituationandpurpose.LM386isasinglepoweraudiopoweramplifierintegratedcircuit,whichisusedtoexpandtherangeofalarmsound.F1-1~F1-6,F2-1~F2-6usesixinverterCD4069.Two-colorlight-emittingdiodesLED1~LED4adopt2EF303.Undernormalconditions,theyemitgreenlight,andwhensomeonecrossesthewarningline,theysendoutredwarninglight.2.2CircuitofAutomobileVoiceHornFigure4.CircuitofAutomobileVoiceHornTheleftsideofthedottedlineinFigure4istheoriginalcircuitdiagramofthevehicleelectrichorn.SListheelectrichornbuttonswitchonthesteeringwheel.S2isanewlyaddedSPDTSwitch,whichisusedforswitchingbetweenelectrichornandvoicehornoftheoriginalvehicle.WhentheswitchS2issetto2,presstheswitchSl,thecapacitorClischarged,thetransistorsVTl,VT2turnon,therelayJlpullsin.J1-1isclosedandheldfor15secondstosupplypowertothecircuit.IClisadedicatedvoiceintegratedcircuitHL-169A.Sinceitsworkingtimeis2.8seconds,theself-excitedmultivibratoriscomposedoftransistorsVT3andVT4.Every3seconds,ahighlevelisoutputasatriggersignal,sothatICloutputsavoicesignalevery3seconds,andsendsittoIC2foraudiopoweramplification,andthespeakerBLemitsvoice.2.3CircuitofMicrocomputerStereoPowerAmplifierBecausetheaudiosignalamplitudeofthelineoutputofthesoundcardistoolarge,theLM386canbedriventopushthespeaker.Inaddition,duetotheinterferenceofvideosignalwhenplayingVCD,itisnotgoodtoconnecttheVCDaccordingtothetypicalcircuit,soitisnecessarytoaddsomecomponentsanddebugthecomponentvalues.TheschematicdiagramisshowninFigure5.Figure5.CircuitofMicrocomputerStereoPowerAmplifierLM386hastwoinputterminals,3pinin-phaseinputand2pininvertinginput.Theinputsignalcanbeinputfromanyendandtheotherinputterminalcanbegrounded.TheinputendisconnectedwithcapacitorC4inordertofilteroutthevideointerferencewhenplayingVCD.Thevaluecanbeincreasedappropriately,butitcanbeusedwithorwithoutC4whenplayingCD.Thepin1andpin8aregaincontrolterminals,whicharecomposedofC2andW2.Thesmallertheresistance,thehigherthegain.ItismoreappropriatetoadjustthegainofW2toabout150.Ifthegainistoohigh,itwilleasilycauseself-excitation.Pin7isconnectedtoa10capacitor.ThehighfrequencycomponentattenuationcircuitiscomposedofR2andC6toeliminatethecrashsoundfromtheloudspeaker.ThecapacityofC6canbeadjustedaccordingtotheactualeffect.Pin6isconnectedtothegroundwitha0.1capacitor,whichactsasafiltertoeliminatethestatichumoftheamplifier.Pin5isconnectedtothecouplingcapacitorC3.Ifonlyoneconespeakerisconnectedtoonechannel,C3capacityshouldnotexceed470,otherwisetheloudspeakerwillbeblockedwhenplayinglowmusic.Ifhigh-frequencyandlow-frequencycrossovertechnologyisadopted,thecapacityofC3canbeincreasedtomakethebassfullyreflected.W1isusedtoadjusttheoutputvolume,whichisparticularlyconvenientwhenplayinggamesorlisteningtoCDs.FAQHowdoesanLM386work?TheLm386integratedchipisalowpoweraudiofrequencyamplifier,whichuseslowlevelpowersupplylikebatteriesinelectroniccircuits.Itisdesignedas8pinminiDIPpackage.Thisprovidesvoltageamplificationof20.Byusingexternalpartsvoltagegaincanberaisedupto200.Islm386anopamp?TheLM386isatypeofoperationalamplifier(Op-Amp)....Inanamplifiercircuit,theLM386takesanaudioinputsignalandincreasesitspotentialanywherefrom20to200times.Thatamplificationiswhatsknownasthevoltagegain.Whatislm386IC?TheLM386isanintegratedcircuitcontainingalowvoltageaudiopoweramplifier.Itissuitableforbattery-powereddevicessuchasradios,guitaramplifiers,andhobbyelectronicsprojects.Howdoyoucalculatelm386gain?VoltageGainAnalysis:Withoutanyexternalcomponents,ithasagainofGv=2x15K/(150+1350)=20(26dB).Withacapacitor(orshortcutting)betweenpins1and8,ithasagainofGv=2x15K/150=200(46dB).WhichICisusedinaudioamplifier?TheICLM386isalow-poweraudioamplifier,anditutilizeslowpowersupplylikebatteriesinelectricalandelectroniccircuits.ThisICisavailableinthepackageofmini8-pinDIP.WhataresomeprojectsthatusetheLM386audioamplifiercircuit?LM386isanintegratedclassABampandisgoodforbeginnerssmallaudioamplifierapplicationsforexampleinaRFreceiver,smallStereosystem,cheaplowvoltageamplifieretcdrawbacksisthatitcannothandlemuchpowerandhencecreatesdistortionwhenyoucrankupthevolumetoomuch..SootherICsareusedinpractical.HowtomakeanLM386audioamplifiercircuit?

IntroductonLM386isalowvoltageaudiopoweramplifier.LM386adopts8-pindoublein-lineplasticpackagewithworkingvoltageof4V-15V.Whenthepowersupplyvoltageis12V,300mWoutputpowercanbeobtainedonan8load.VariousoscillatorscanbeeasilyproducedwithLM386.CatalogIntroductonCatalogISimplestOscillatorIIBlockingOscillatorIIIElectronicPianoIVSquare-waveOscillatorVSinusoidalOscillatorFAQOrdering&QuantityISimplestOscillatorFigure1.CircuitofSimplestOscillatorInFigure1,theoutputendandin-phaseinputendofLM386areconnectedbypiezoelectricceramicchipHTD.Theamplifierformspositivefeedbackandgeneratesoscillation.HereHTDisbothafeedbackcapacitorandasound-generatingdevice.Componentparametersinthefigure:D1~D4are1N4001,C1=220pF,HTDispiezoelectricceramicsheetwithauxiliaryacousticcavity.IIBlockingOscillatorFigure2.CircuitofBlockingOscillatorAsshowninFigure2,asimpleoscillatorconsisitofLM386,C3,C4andloudspeakers.RPandC2makethisoscillatorproduceblocking-oscillation.Afterconnectingthepowersupply,LM386doesnotworkbecausetheinitialterminalvoltageofC2iszero,andthepowersupplychargesC2throughRP.WhenC2chargingvoltageishigherthanacertainvalue,LM386oscillatorstartstovibrate.Astheamplitudecontinuestoincrease,thecurrentconsumptionoftheoscillatoralsoincreases.ThiscurrentflowsthroughRP,anditsvoltagedroponRPalsoincreases,causingtheLM386powersupplyterminal6pinvoltagetocontinuetodrop.EventuallytheLM386cannotworkandtheoscillatorstops.ThepowersupplyrechargesC2viaRPagain,causingthevoltageatC2torise.WhenthevoltageatC2risestoacertainvalue,theLM386oscillatorstartsagain.Inthisway,theoscillatorwillproduceblocking-oscillation,andthespeakeremitsbeep,beep,beepsound.Componentparametersinthefigure:D1~D4are1N4001,C1=C3=220F,C2=47F.C4=0.01F,RP=4.7K.IIIElectronicPianoFigure3.CircuitofElectronicPianoFigure3isasimpleelectronicpianocircuit.Onthepin3ofLM386,theintegratedcircuithasa10Kresistortoground.Thisbuilt-inresistorandtenscaleresistorsRP1~RP10constitutethetimingresistoroftheoscillator.C2isthetimingcapacitor.ByadjustingthevaluesofRP1~RP10,thespeakerscansequentiallyemitmusicalsoundsfromlowoctavedo,re,mitohighoctavedo,re,mi.KI~K10arekeyswitches.Componentparametersinthefigure:Cl=C3=220F.C2=2200FIVSquare-waveOscillatorFigure4.CircuitofSquare-waveOscillatorFigure4showsasquare-waveoscillatorcomposedofLM386.R1isthetimingresistor.C2isthetimingcapacitor.R2andR3providevoltagebiasforLM386in-phaseinput.BecausethevoltageattheC2terminalcannotchangeabruptly,theinvertinginputterminalpin2oftheLM386islowlevel,andpin5isthemidpointoftheinternalOTLoutputstageoftheamplifier.Itis1/2Vocinstaticstate,anditissuppliedtothethird-phaseinputpin3afterdividingpressureviaR2andR3.Obviouslythepotentialofthispinishigherthanthesecondpin.Therefore,pin5outputshighlevel.ThishighlevelchargesC2viaR1.WhenthevoltageofC2terminalishigherthanthepotentialofpin3,pin5outputslowlevel.C2dischargestopin5viaR1.WhenC2isdischarged,thepotentialofpin2dropsandislowerthanthepotentialofpin3.Pin5outputshighlevelagain.Inthisway,thecircuitformsoscillation,andtheoscillationsignaldrivestheloudspeakertosoundthroughC3.Componentparametersinthefigure:C1=C3=220F,smd resistor codeC2=0.33F.R1=22K,R2=1K.R3=9.4KVSinusoidalOscillatorFigure5.CircuitofSinusoidalOscillatorFigure5isasinusoidaloscillatormadeofLM386.ThecircuitadoptsWienbridgeoscillationmode,andtheoutputsignaldistortioncoefficientofthecircuitisverylow.TheflashlampHandtheresistorR3formanegativefeedbackcircuit,whichkeepstheamplitudeoftheoscillatoroutputsignalstableandhaslowdistortion.WhenthevaluesofcapacitorsC1andC2arethesame,theoscillationfrequencyofthecircuitcanbeobtainedbytheformulaf=1/2C1R1R2.Inactualproduction,Hcanuse3V,15mAflashlamp.FAQHowdoesanLM386work?TheLm386integratedchipisalowpoweraudiofrequencyamplifier,whichuseslowlevelpowersupplylikebatteriesinelectroniccircuits.Itisdesignedas8pinminiDIPpackage.Thisprovidesvoltageamplificationof20.Byusingexternalpartsvoltagegaincanberaisedupto200.Islm386anopamp?TheLM386isatypeofoperationalamplifier(Op-Amp)....Inanamplifiercircuit,theLM386takesanaudioinputsignalandincreasesitspotentialanywherefrom20to200times.Thatamplificationiswhatsknownasthevoltagegain.Whatislm386IC?TheLM386isanintegratedcircuitcontainingalowvoltageaudiopoweramplifier.Itissuitableforbattery-powereddevicessuchasradios,guitaramplifiers,andhobbyelectronicsprojects.Howdoyoucalculatelm386gain?VoltageGainAnalysis:Withoutanyexternalcomponents,ithasagainofGv=2x15K/(150+1350)=20(26dB).Withacapacitor(orshortcutting)betweenpins1and8,ithasagainofGv=2x15K/150=200(46dB).WhichICisusedinaudioamplifier?TheICLM386isalow-poweraudioamplifier,anditutilizeslowpowersupplylikebatteriesinelectricalandelectroniccircuits.ThisICisavailableinthepackageofmini8-pinDIP.WhataresomeprojectsthatusetheLM386audioamplifiercircuit?LM386isanintegratedclassABampandisgoodforbeginnerssmallaudioamplifierapplicationsforexampleinaRFreceiver,smallStereosystem,cheaplowvoltageamplifieretcdrawbacksisthatitcannothandlemuchpowerandhencecreatesdistortionwhenyoucrankupthevolumetoomuch..SootherICsareusedinpractical.HowtomakeanLM386audioamplifiercircuit?I.IntroductionThe74HC595isan8-bitserial-inorparallel-outshiftregisterwithastorageregisterand3-stateoutputs.74HC595withthecharacteristicsofhighspeed,lowpowerconsumptionandsimpleoperation,canbeeasilyusedinMCUinterfacetodriveLEDoperation.ThisarticleintroducesthecircuitdesignofLEDdisplaydrivedby74HC595.CatalogI.IntroductionII.BasicDescription2.1LEDDisplay2.274HC595III.CircuitDesign3.1HardwareCircuit3.2DisplayDriverIV.ConclusionFAQOrdering&QuantityII.BasicDescription2.1LEDDisplayA7SegmentLEDDisplay,alsoknownasLEDdisplay,hasbeenwidelyusedinvariousinstrumentsbecauseofitslowprice,lowpowerconsumptionandreliableperformance.TherearemanytypesofLEDdriversonthemarket,andmostofthemhavemultiplefunctions,butthepriceiscorrespondinglyhigher.Ifusedinasimplesystemwithlowcost,itisnotonlyawasteofresources,butalsoincreasesthecostofproducts.Using74HC595chiptodriveLEDhasvariousdisadvantages.Highspeed,lowpowerconsumption,unlimitednumberofLEDs.ItcancontrolboththecommoncathodeLEDdisplayandthecommonanodeLEDdisplay.Thecircuitdesignedwith74HC595isnotonlysimple,butalsolowinpowerconsumptionandstrongindrivingability.Itisalowcostandflexibledesignscheme.2.274HC595The74HC595isan8-bitserial-in/serialorparallel-outshiftregisterwithastorageregisterand3-stateoutputs.Boththeshiftandstorageregisterhaveseparateclocks.Thedevicefeaturesaserialinput(DS)andaserialoutput(Q7S)toenablecascadingandanasynchronousresetMRinput.ALOWonMRwillresettheshiftregister.DataisshiftedontheLOW-to-HIGHtransitionsoftheSHCPinput.ThedataintheshiftregisteristransferredtothestorageregisteronaLOW-to-HIGHtransitionoftheSTCPinput.Ifbothclocksareconnectedtogether,theshiftregisterwillalwaysbeoneclockpulseaheadofthestorageregister.Datainthestorageregisterappearsattheoutputwhenevertheoutputenableinput(OE)isLOW.AHIGHonOEcausestheoutputstoassumeahigh-impedanceOFF-state.OperationoftheOEinputdoesnotaffectthestateoftheregisters.Inputsincludeclampdiodes.ThisenablestheuseofcurrentlimitingresistorstointerfaceinputstovoltagesinexcessofVCC.Figure1.74HC595FunctionalDiagramFigure2.74HC595LogicSymbolIII.CircuitDesign3.1HardwareCircuitFigure3isadisplaypanelcircuitdesignedwithAT89C2051and74HC595interface.Figure3.CircuitofDisplayPanelTheP115,P116,andP117oftheP1portareusedtocontrolthedisplayoftheLED,andtheyareconnectedtotheSLCK,SCLKandSDApinsrespectively.Threedigitaltubesareusedtodisplaythevoltagevalue.Onthecircuitboard,LED3isonthefarleftandLED1isonthefarright.Whensendingdata,firstsendthedisplaycodeofLED3,andfinallysendthedisplaycodeofLED1.ThebrightnessoftheLEDiscontrolledbytheresistanceofPR1toPR3.2.2DisplayDriverUseDISP1,DISP2,andDISP3tostoredisplaydata.AftertheCPUinitializationiscomplete,calltheLRDISPsubroutinetocleartheregisterof74HC595.ThereisnoneedtocalltheclearsubroutinebeforecallingthedisplaysubroutineDISPLAY.Nowwritethetwosubroutinesasfollows.①CLRDISP:MOVR2,how to read resistor#24CLRBIT :CLRSCLKCLRCMOVSDA ,CSETBSCLKDJNZR2,avalanche diodeCLRBITRET②Display:CLRSLCKMOVR3,#3MOVR0,variable resistor symbol#DISP3DISP1:MOVA,@R0MOVR2,variable resistor symbol#8DISP2:CLRSCLKRLCAMOVSDA,CSETBSCLKDJNZR2 ,how to read resistorsDISP2DECR0DJNZR3,DISP1SETBSLCKRETIV.ConclusionItcanbeseenfromtheaboveexamplesthattherearenocomplicatedtechnicalproblemsinthedesignofhardwareandsoftwarewhen74HC595isusedtodesignLEDdrivercircuit.Inaddition,74HC595canbeusednotonlytodriveLEDdisplays,butalsotodrivelight-emittingdiodes.Each74HC595candrive8LEDssimultaneously.Thissolutionisidealwhenthevolumerequirementsoftheproductarenothighandwanttoreducethecost.FAQWhatis74HC595?74HC595isashiftregisterwhichworksonSerialINParallelOUTprotocol.Itreceivesdataseriallyfromthemicrocontrollerandthensendsoutthisdatathroughparallelpins.Wecanincreaseouroutputpinsby8usingthesinglechip.Whatisa74hc595n?8-bitShiftRegister74HC595NAshiftregisterisachipyoucanusetocontrolmanyoutputs(8here)atthesametimewhileonlyusingafewpins(3here)ofyourArduino.Howdoesashiftregisterwork?Shiftregistersholdthedataintheirmemorywhichismovedorshiftedtotheirrequiredpositionsoneachclockpulse.Eachclockpulseshiftsthecontentsoftheregisteronebitpositiontoeithertheleftortheright.How74HC595ShiftRegiesterworks?The595hastworegisters(whichcanbethoughtofasmemorycontainers),eachwithjust8bitsofdata.ThefirstoneiscalledtheShiftRegister.TheShiftRegisterliesdeepwithintheICcircuits,quietlyacceptinginput.Howdoesan8bitshiftregisterwork?TheSN74HC595Nisasimple8-bitshiftregisterIC.Simplyput,thisshiftregisterisadevicethatallowsadditionalinputsoroutputstobeaddedtoamicrocontrollerbyconvertingdatabetweenparallelandserialformats.YourchosenmicroprocessorisabletocommunicatewiththeTheSN74HC595Nusingserialinformationthengathersoroutputsinformationinaparallel(multi-pin)format.Essentiallyittakes8bitsfromtheserialinputandthenoutputsthemto8pins.

DescriptionLED,asthefirstbasicfunctiontobecompletedinMCUlearning,playsaveryimportantroleinMCUlearners,whichalsocalledmagiclampbyMCUlearners.IbelievethateveryoneseesmostandthesimplestLEDcircuitisthefigureshownbelow.Asshowninthefigure,notonlythecircuitissimple,butalsoitsoperationisverysimple.GiveselectricalleveltoI/OcorrespondingtoeightLEDs,andthecorrespondingLEDcanbeonoroff.Figure1.simpleLEDcircuitCatalogDescription74HC595Drives8BitsLEDSFAQOrdering&Quantity74HC595Drives8BitsLEDSButnotallLEDcircuitsaresosimple.Somecircuitswilluse74HC595chiptodrive8LEDsordrivethe8-bitdigitaltubesegmentcode,asshowninthefigurebelow.Figure2.74HC595drives8LEDsWhyisasimplecircuitsocomplicated?Thereasonisobvious.BeforetheeightLEDneedeightI/O,nowonlythreeI/OcandriveeightLED.Letsbrieflyintroduce74CH595anduseitsuccessfullytodriveeightLEDlights.The74HC595isan8-bitserial-inorparallel-outshiftregisterwithastorageregisterand3-stateoutputs.Boththeshiftandstorageregisterhaveseparateclocks.Thedevicefeaturesaserialinput(DS)andaserialoutput(Q7S)toenablecascadingandanasynchronousresetMRinput.SIisitsserialdatainput.Q0toQ7aredataoutput.SCK,istheclockfortheshiftregister.The595isclock-drivenontherisingedge.Thismeansthatinordertoshiftbitsintotheshiftregister,theclockmustbeHIGH.Andbitsaretransferredinontherisingedgeoftheclock.RCK,isaveryimportantpin.WhendrivenHIGH,thecontentsofShiftRegisterarecopiedintotheStorage/LatchRegister;whichultimatelyshowsupattheoutput.Sothelatchpincanbeseenaslikethefinalstepintheprocesstoseeingourresultsattheoutput.SQHisserialdataoutput.Whatwewanttoachievenowistomovethe8-bitsdataofSIinto74HC595onebyoneundertheactionofSCKandRCKandpresenttheminparallelonQ0-Q7.Figure3.How74HC595ShiftRegisterworksWheneverweapplyaclockpulsetoa595,thebitsintheShiftRegistermoveonesteptotheleft.Belowisitscode.FAQWhatis74HC595?74HC595isashiftregisterwhichworksonSerialINParallelOUTprotocol.Itreceivesdataseriallyfromthemicrocontrollerandthensendsoutthisdatathroughparallelpins.Wecanincreaseouroutputpinsby8usingthesinglechip.Whatisa74hc595n?8-bitShiftRegister74HC595NAshiftregisterisachipyoucanusetocontrolmanyoutputs(8here)atthesametimewhileonlyusingafewpins(3here)ofyourArduino.Howdoesashiftregisterwork?Shiftregistersholdthedataintheirmemorywhichismovedorshiftedtotheirrequiredpositionsoneachclockpulse.Eachclockpulseshiftsthecontentsoftheregisteronebitpositiontoeithertheleftortheright.How74HC595ShiftRegiesterworks?The595hastworegisters(whichcanbethoughtofasmemorycontainers),eachwithjust8bitsofdata.ThefirstoneiscalledtheShiftRegister.TheShiftRegisterliesdeepwithintheICcircuits,quietlyacceptinginput.Howdoesan8bitshiftregisterwork?TheSN74HC595Nisasimple8-bitshiftregisterIC.Simplyput,thisshiftregisterisadevicethatallowsadditionalinputsoroutputstobeaddedtoamicrocontrollerbyconvertingdatabetweenparallelandserialformats.YourchosenmicroprocessorisabletocommunicatewiththeTheSN74HC595Nusingserialinformationthengathersoroutputsinformationinaparallel(multi-pin)format.Essentiallyittakes8bitsfromtheserialinputandthenoutputsthemto8pins.Whatisadigitaltube?Lightemittingdiodeconnectstheanodetogetherandthenconnectedtothepowerofpositiveiscalledcommonanodedigitaltube,lightemittingdiodeconnectedtothecathodeandthenconnectedtothepowerofthecathodeiscalledcommoncathodedigitaltube.Whatisthedifferencebetweenshiftregisterandcounter?Inashiftregister,theinputofelementNistheoutputofelementN-1,andallelementsusethesameclock.Inacounter,theinputofelementNistheinverseofitsoutput,andtheclockofelementN+1istheoutputofelementN.IDescriptionDoyouknowwhattheDigitalTubeDisplayneeds?Thedisplayofthedigitaltuberequiresadigitaltubeandacontrolcircuitofmultipledigitaltubes.Takethesingle-chipmicrocomputercontrolcircuitofan8-bitdigitaltubeasanexample.Thesingle-chipmicrocomputerneedstoprovidean8-bitsegmentcodeandan8-bitcode.Thus,weusuallychoosetwoofthefourparallelI/Oportsinthe51single-chipmicrocomputertoprovidesegmentcodesandbitcodesrespectively.Althoughthiscircuithardwareconnectionandsoftwareprogrammingarerelativelysimple,therearealsoproblems.Thatis:ToomanyI/Oportsareoccupied,whichaffectstheoveralluseofthemicrocontroller,andisnotconducivetotheaccessofotherdevices.Howtosolvethisproblem?Wecanuseatypeofshiftregisterforauxiliarycontrol.Here,thisblogusesthe74HC595chip.Figure1.74HC595CatalogIDescriptionIIIntroductionto74HC595III74HC595DisplayControlofMulti-digitDigitalTube3.1HardwareConnection3.2SoftwareProgramming3.3SimulationDebuggingIVConclusionFAQOrdering&QuantityIIIntroductionto74HC59574HC595isaCMOSshiftregisterwithopen-drainoutput.Theoutputportisacontrollablethree-stateoutput.Itcanalsocontrolthenext-levelcascadedchipserially.Itsstructureisusuallya16-pinDIPpackageorSOpackage.The74HC595pinoutisshowninFigure2,andthecorrespondingpinfunctionsareshowninTable1.Figure2.74HC595PinoutThemainfeaturesof74HC595are:8-bitserialinput/8-bitparallelorserialoutput;Three-stateoutputregister(three-stateoutput:agatecircuitwiththreeoutputstatesofhighlevel,lowlevelandhighimpedance);High-speedlow-powerconsumption,high-speedshiftclockfrequencyFmax25MHz.Table1.74HC595PinFunctionPinNumberPinNamePinFunction15,1~7Q0~Q7Paralleltri-stateoutputpin8GNDPowerground9Q7Serialdataoutputpin10/MRClearendofshiftregister(activelow)11SH_CPSerialdatainputclockline12ST_CPOutputmemorylatchclockline13/OEOutputenable(activelow)14DSSerialdatainputline16VCCPowerendIII74HC595DisplayControlofMulti-digitDigitalTubeHere,thisblogtakesthesingle-chipmicrocomputercontrolmulti-digitdigitaltubeasanexample.Tousethechipcorrectly,youmustfirstcorrectlyunderstandthetimingdiagramortruthtableofthechip.Thetruthtableof74HC595isshowninTable2.InputPinOutputPinDSSHCP/MRSTCP/OEHQ0~Q7outputhighimpedanceLQ0~Q7outputeffectivevalueLClearshiftregisterLRisingEdgeHShiftregisterstorelowlevelHRisingEdgeHShiftregisterstorehighlevelFallingEdgeHShiftregisterstateretentionRisingEdgeStatevalueinoutputshiftregisterFallingEdgeOutputmemorystateretentionItcanbefoundthattheserialdataisconnectedtotheDSpin,butitisonlyinputtotheshiftregisterwhenSH_CPisarisingedge,andentersthestorageregisterwhenST_CPisarisingedge.Ifthetwoclocksareconnectedtogether,theshiftregisterisalwaysonepulseearlierthanthestorageregister.Theshiftregisterhasaserialshiftinput(Ds),aserialoutput(Q7),andanasynchronouslow-levelreset.Thestorageregisterhasaparallel8-bit,three-statebusoutput.WhenOEisenabled(lowlevel),thedataofthestorageregisterisoutputtothebus.3.1HardwareConnectionSincethe8-bitdigitaltubeneedstoprovideatotalof16bitsofsegmentcodeandbitcodeatthesametime,itcannotberealizedbyusingone74HC595.Tosolvethisproblem,weusetwo595chipstocascadeseriallytoprovidean8-bitsegmentcode(providedbyU2)andan8-bitcode(providedbyU3).ThesimulationhardwarecircuitisshowninFigure3.Theinputsignalof595isconnectedtothethreeI/OportsofP2.0~P2.2respectively.Amongthem,P2.0providesserialinputsignals,P2.1andP2.2provideoutputandinputclocksignalsrespectively.Figure3.SimulationHardwareCircuitDiagram3.2SoftwareProgrammingHere,weuse2piecesof74HC595chipsforserialcascading.Therefore,youmustpayattentiontothesequenceofserialdataoutputwhenprogramming.Theusualpracticeisasfollows:First,writethedata(iebitcode)ofthe74HC595chipatthenextlevel;Then,writethedata(iesegmentcode)ofthefirst-level74HC595chip;Finally,releasetheparalleloutputpinstogetheratonce.Thesampleprogramisasfollows(partial):voidOneLed_Out(uchari,ucharLocation){ucharj;OutByte=Location;for(j=1;j=8;j++){DS=Bit_Out;SH_CP=0;SH_CP=1;SH_CP=0;OutByte=OutByte1;}OutByte=~Segment[i];for(j=1;j=8;j++){DS=Bit_Out;SH_CP=0;SH_CP=1;SH_CP=0;OutByte=OutByte1;}ST_CP=0;ST_CP=1;ST_CP=0;}3.3SimulationDebuggingWecandrawthehardwarecircuitdiagramontheProteus7platform,andthenwritethesoftwareprogramontheKeil4.0platformandcompileanddebugit.Then,loadthegeneratedHEXfileintothesimulationchipandrunthesimulation.Ifallgoeswell,theresultswillbedisplayedcorrectly.Accordingtothedisplayrequirements,itcanrealize8-bitdigitaltubeshiftdisplayor8-bitdigitaltubesimultaneousdisplay.ThesimulationresultsareshowninFigures4and5.Figure4.ShiftDisplayof8-bitDigitalTubeFigure5.SimultaneousDisplayof8-bitDigitalTubesIVConclusionThetestresultsofthisblogshowthattherearemanyadvantagestothedisplaycontrolofmulti-digitdigitaltubesthroughthecascadeof74HC595chips.Thesebenefitsaremainlyreflectedinthefollowingaspects:Itcangreatlyreducethedisplaycontrolofthesingle-chipdigitaltube;ItcangreatlyreducetheoccupancyoftheMCUI/Oportline;Thecircuitissimpleandeasytoprogram.Themethodintroducedinthisblog,whetheritistoconductsimulationteachingonacomputer,ortobuildactualhardwarecircuits.Ingeneral,Thecurrent74HC595chipiscost-effective,andthecostofbuildingacircuitislow,makingitverysuitableforgeneraluse.FAQWhatis74HC595?74HC595isashiftregisterwhichworksonSerialINParallelOUTprotocol.Itreceivesdataseriallyfromthemicrocontrollerandthensendsoutthisdatathroughparallelpins.Wecanincreaseouroutputpinsby8usingthesinglechip.Whatisa74hc595n?8-bitShiftRegister74HC595NAshiftregisterisachipyoucanusetocontrolmanyoutputs(8here)atthesametimewhileonlyusingafewpins(3here)ofyourArduino.Howdoesashiftregisterwork?Shiftregistersholdthedataintheirmemorywhichismovedorshiftedtotheirrequiredpositionsoneachclockpulse.Eachclockpulseshiftsthecontentsoftheregisteronebitpositiontoeithertheleftortheright.How74HC595ShiftRegiesterworks?The595hastworegisters(whichcanbethoughtofasmemorycontainers),eachwithjust8bitsofdata.ThefirstoneiscalledtheShiftRegister.TheShiftRegisterliesdeepwithintheICcircuits,quietlyacceptinginput.Howdoesan8bitshiftregisterwork?TheSN74HC595Nisasimple8-bitshiftregisterIC.Simplyput,thisshiftregisterisadevicethatallowsadditionalinputsoroutputstobeaddedtoamicrocontrollerbyconvertingdatabetweenparallelandserialformats.YourchosenmicroprocessorisabletocommunicatewiththeTheSN74HC595Nusingserialinformationthengathersoroutputsinformationinaparallel(multi-pin)format.Essentiallyittakes8bitsfromtheserialinputandthenoutputsthemto8pins.Whatisadigitaltube?Lightemittingdiodeconnectstheanodetogetherandthenconnectedtothepowerofpositiveiscalledcommonanodedigitaltube,lightemittingdiodeconnectedtothecathodeandthenconnectedtothepowerofthecathodeiscalledcommoncathodedigitaltube.Whatisthedifferencebetweenshiftregisterandcounter?Inashiftregister,theinputofelementNistheoutputofelementN-1,andallelementsusethesameclock.Inacounter,theinputofelementNistheinverseofitsoutput,andtheclockofelementN+1istheoutputofelementN.

IDescriptionTheinstrumentationamplifiercircuithasthefollowingfeatures:HighInputImpedance;HighCommon-modeRejectionRatio;LowDrift;...Theabovefeaturesmakeitwidelyusedinfieldsofsmallsignalamplificationofsensoroutput.Thisblogwillintroduce4implementationoptionsofinstrumentationamplifiercircuits.These4optionsaredesignedbasedondifferentelectroniccomponents.Andtheyarealsoonthebasisofexplainingthecircuitstructureandprincipleoftheinstrumentamplifier.Theelectroniccomponentsdiscussedinthisbloginclude:LM741,OP07,LM324,AD620.Wewillsummarizefeaturesofthe4circuitthroughtesting,analysisandcomparison.Ibelievethisblogcanprovideacertainreferenceforcircuitdesignbeginners.WhatAreInstrumentationAmpilfiers?CatalogIDescriptionIIIntroduction2.1InstrumentationAmplifierOverview2.2InstrumentationAmplifierStuctureandPrincipleIIIInstrumentationAmplifierCircuitDesign3.1LM741CircuitOption3.2OP07CircuitOption3.3LM324CircuitOption3.4AD620CircuitOptionIVPerformanceTestandAnalysisFAQOrdering&QuantityIIIntroduction2.1InstrumentationAmplifierOverviewThesignalsinputbysmartmetersthroughsensorsgenerallyhavethecharacteristicsofsmallsignals:Thesignalamplitudeisverysmall(millivoltorevenmicrovoltmagnitude);Oftenaccompaniedbyloudnoise.Forsuchsignals,thefirststepofcircuitprocessingisusuallytoamplifysmallsignalswithaninstrumentationamplifier.Themainpurposeofamplificationisnottogain,buttoimprovethesignal-to-noiseratioofthecircuit.Atthesametime,fortheinstrumentationamplifiercircuit,thesmallertheinputsignalthatcanberesolved,thebetter;thewiderthedynamicrange,thebetter.Therefore,theperformanceoftheinstrumentationamplifiercircuitdirectlyaffectstherangeoftheinputsignalthatthesmartinstrumentcandetect.2.2InstrumentationAmplifierStuctureandPrincipleThetypicalstructureoftheinstrumentamplifiercircuitisshownasinFig.1.Itismainlycomposedoftwo-stagedifferentialamplifiercircuit.Figure1.StructureofInstrumentationAmplifierAmongthem,theoperationalamplifierA1,A2arein-phasedifferentialinputmodes.Non-invertinginputcangreatlyincreasetheinputimpedanceofthecircuit.Atthesametime,itcanalsoreducetheattenuationofweakinputsignalsbythecircuit;Differentialinputcanmakethecircuitonlyamplifythedifferentialmodesignal,andonlyfollowthecommonmodeinputsignal.Inthisway,theratiooftheamplitudeofthedifferentialmodesignaltothecommonmodesignal(ie,thecommonmoderejectionratioCMRR)senttothesubsequentstageisimproved.Inthisway,inthedifferentialamplifiercircuitcomposedofoperationalamplifierA3asthecorecomponent,undertheconditionthattheCMRRrequirementsremainunchanged,theaccuracymatchingrequirementsforresistorsR3andR4,RfandR5canbesignificantlyreduced.Asaresult,theinstrumentationamplifiercircuithasbettercommonmoderejectioncapabilitythanasimpledifferentialamplifiercircuit.UndertheconditionsofR1=R2,R3=R4,Rf=R5,thegainofthecircuitinFigure1is:G=(1+2R1/Rg)(Rf/R3)ItcanbeseenfromtheformulathattheadjustmentofthecircuitgaincanbeachievedbychangingtheRgresistance.IIIInstrumentationAmplifierCircuitDesignAtpresent,theimplementationmethodsofinstrumentationamplifiercircuitsaremainlydividedintotwocategories:Thefirstcategoryiscomposedofdiscretecomponents;Thesecondcategoryisdirectlyimplementedbyasingleintegratedchip.Intheblog,withsingleopampLM741andOP07,integratedfouropampLM324andmonolithicintegratedchipAD620asthemainelectroniccomponents,4kindsofinstrumentationamplifiercircuitoptionsaredesigned.3.1LM741CircuitOptionConsistsofthreegeneral-purposeoperationalamplifiersLM741toformathreeoperationalamplifierinstrumentamplifiercircuitform.Andsupplementedbyrelatedresistorperipheralcircuits.Atthesametime,addthebridgesignalinputcircuitofthenon-invertinginputterminalsofA1andA2,asshowninFigure2.Figure2.SingleOpAmpInstrumentationAmplifierA1~A3inFigure2canbereplacedwithLM741respectively.Theworkingprincipleofthecircuitisexactlythesameasthatofatypicalinstrumentationamplifiercircuit.3.2OP07CircuitOptionComposedof3precisionoperationalamplifiersOP07,thecircuitstructureandprinciplearethesameasinFig.2(3OP07sareusedtoreplaceA1~A3inFig.2respectively).3.3LM324CircuitOptionTakeafouroperationalamplifierintegratedcircuitLM324asthemaincomponent,asshowninFigure3.Itscharacteristicistointegrate4functionallyindependentoperationalamplifiersintothesameintegratedchip.WhataretheadvantagesofusingLM324?Thatis,itispossibletogreatlyreducethedifferenceindeviceperformanceofeachopampduetodifferentmanufacturingprocesses.Inaddition,theuseofaunifiedpowersupplyisconducivetothereductionofpowersupplynoiseandtheimprovementofcircuitperformanceindicators.Andthebasicworkingprincipleofthecircuitremainsunchanged.Figure3.LM324InstrumentationAmplifier3.4AD620CircuitOptionThecircuitconsistsofamonolithicintegratedchipAD620asthemainelectroniccomponents,asshowninFigure4.Itischaracterizedbyasimplecircuitstructure:anAD620,againsettingresistorRg,andaworkingpowersupply.Therefore,thedesignefficiencyisveryhigh.ThecircuitgaincalculationformulainFig.4is:G=49.4K/Rg+1.Figure4.AD620InstrumentationAmplifierIVPerformanceTestandAnalysisThefouroptionsoftheinstrumentationamplifiercircuitalladopttheformofabridgecircuitcomposedof4resistors,whichchangesthedouble-endeddifferentialinputintoasingle-endedsignalsourceinput.Theperformancetestismainlytocarryoutsimulationandactualcircuitperformancetestfromthefollowingaspects:1.ThemaximuminputofthesignalsourceVs;2.VsminimuminputofsignalsourceVs;3.Themaximumgainofthecircuit;4.Commonmoderejectionratio.ThetestdataareshowninTable1andTable2.Amongthem,themaximum(small)inputofVsreferstothemaximum(small)inputofthesignalsourcewhenthecircuitoutputisnotdistortedundergiventestconditions.Themaximumgainreferstothemaximumgainvalueofthecircuitthatcanbeachievedwhentheoutputisnotdistortedunderthegiventestconditions.ThecommonmoderejectionratioiscalculatedbytheformulaKCMRR=20|g|AVd/AVC|(dB).Note:fisthefrequencyofVsinputsignal;Thevoltagemeasurementdatainthetableareallexpressedbypeak-to-peakvalue;Duetothesimulationdevice,thesimulationofoption3withMultisimfailedintheexperiment,and-inTable1indicatesthefailuredata;Options1to4inthetablerespectivelyrepresenttheinstrumentationamplifiercircuitcomposedofLM741,OP07,LM324andAD620respectively.FromthemeasureddatainTable2,wecanseefromit:Foroption2,ithasthebestperformanceintermsofsignalinputrange(thatis,themaximumandminimuminputofVs),circuitgain,andcommon-moderejectionratio.Intermsofcomponentprice,itisalittlehigherthanthecostoftheLM741option1andtheLM324option3,butitismuchcheaperthantheAD620option4.Therefore,amongthefouroptions,option2ofOP07hasthehighestcostperformance.Foroption4,inadditiontoitsrelativelysmallmaximumgain,itsotherperformanceissecondonlytooption2.option4hastheadvantagesofsimplecircuit,superiorperformance,andsavingdesignspace.However,thehighcostisitsbiggestdisadvantage.Foroption1andoption3,thereislittledifferenceintheirperformance.option3isslightlybetterthanoption1,andtheyalsohaveabsolutepriceadvantages,buttheirperformanceisnotasgoodasoption2andoption4.Basedontheaboveanalysis,option2andoption4aresuitableforoccasionswithhigherperformancerequirementsforinstrumentamplifiercircuits.Amongthem:Option2ofOP07isthemostcost-effectiveOption4ofAD620issimpleandefficient,butthecostishigh.Option1ofLM741andOption3ofLM324aresuitableforoccasionswhereperformancerequirementsarenothighandcostsavingsareneeded.Accordingtospecificcircuitdesignrequirements,differentoptionsareselectedtoachieveoptimalresourceutilization.Figure5.InstrumentationAmplifierICInaddition,afterthecircuitdesignplanisdetermined,thefollowingaspectsshouldbepaidattentiontointhespecificcircuitdesignprocess:1.Payattentiontotheselectionofkeycomponents.Forexample,forthecircuitshowninFigure2,thereareafewthingstopayattentionto:MakethecharacteristicsofopampA1andA2asconsistentaspossible;Whenselectingresistors,resistorswithalowtemperaturecoefficientshouldbeusedtoobtainthelowestpossibledrift;TheselectionofR3,R4,R5andR6shouldmatchasmuchaspossible.2.Payattentiontoaddingvariousanti-interferencemeasuresinthecircuit.suchas:Thepowersupplydecouplingcapacitorshouldbeaddedatthelead-inendofthepowersupply;RClow-passfilteringshouldbeaddedtothesignalinputterminalorhigh-frequencynoisecancelingcapacitorsshouldbeaddedtothefeedbackloopoftheoperationalamplifierA1andA2;ThePCBdesignshouldbecarefullylaidoutandroutedreasonably,andgroundwiresshouldbehandledcorrectly.FAQWhatislm324?LM324isaQuadop-ampICintegratedwithfourop-ampspoweredbyacommonpowersupply.Thedifferentialinputvoltagerangecanbeequaltothatofpowersupplyvoltage....Generally,op-ampscanperformmathematicaloperations.Whichisthedifferencebetweenlm324andlm339?TheLM324hasacomplementaryoutputwhiletheLM339isopencollector.Inthecomplementaryoutput,currentcanflowineitherdirectionasrequired(eithersourceorsink)whiletheopencollectoroutputcanonlysinkcurrent.Whatisopampusefor?OperationalamplifiersarelineardevicesthathaveallthepropertiesrequiredfornearlyidealDCamplificationandarethereforeusedextensivelyinsignalconditioning,filteringortoperformmathematicaloperationssuchasadd,subtract,integrationanddifferentiation.Howdoesanopampwork?Whatislm324usedfor?LM324ICApplicationsTheapplicationsofICLM324includethefollowing.ByusingthisIC,theconventionalop-ampapplicationscanbeimplementedverysimply.ThisICcanbeusedasoscillators,rectifiers,amplifiers,comparatorsetc.I.IntroductionAsweallknow,theionnitridingprocessrequiresrelativelyhighcontrolofthepressureinsidethefurnace,sothispaperdesignsagasflowcontrollerbasedontheL298NchipdrivenDCmotorcontrol,whichcanbeusedtocontrolthegasflowofthereactor.Soletsfirstunderstandtheionnitridingtheory.CatalogI.IntroductionII.IonNitridingTheoryIII.SystemFlowandPressureMeasurementandControlBlockDiagramIV.L298NChipIntroductionV.ControllerPrincipleVI.ConclusionFAQOrdering&QuantityII.IonNitridingTheoryNitridingisachemicalheattreatmentmethodtostrengthenthemetalsurface.Itistoplacemetalpartsinanactivenitrogenmedium,andatacertaintemperatureandholdingtime,thenitrogenelementcanpenetrateintothemetalsurface,therebychangingthechemicalcompositionofthemetallayertomakeithavehighwearresistance,fatiguestrength,corrosionresistanceandburnresistance,etc.,soitiswidelyusedinindustry.Ionnitridingiscarriedoutinalow-temperatureplasma.Thelow-pressuregasisionizedundertheactionofanelectricfieldtoproducehigh-energyionsandhigh-energyneutralatoms.Thesehigh-energyparticlescanimprovethestructureoftheinfiltrationlayer,promotethechemicalreactionprocess,andacceleratethenitridinglayerformation.Ionnitridingiscarriedoutinglowdischarge.Intheprocessofionnitriding,thepressurecontrolaccuracyofthefurnaceisrelativelyhigh,andthecontroldeviationreachesseveraltensofPa.AccordingtoPaschensLaw:Amongthem:Pisthegaspressure;Disthedistancebetweenparallelplateelectrodes;Visthecathodesecondaryelectronemissioncoefficient;BisStolevsconstant;Aisaconstant.Takingthederivativeofformula(1),thebreakdownvoltageexpression(2)canbeobtained:Itcanbeseenfromformula(2)thatthebreakdownvoltageVisrelatedtothegaspressureandd,andingeneralexperiments,disfixed,soionnitridingisextremelyimportantforpressurecontrol.III.SystemFlowandPressureMeasurementandControlBlockDiagramTheflowmetercontrolsthegasflowattheinlet.Whentheinletandexhaustflowsarebalanced,thefurnacepressureremainsstable.Duetotheinternalinfluenceoffurnacegasleakageandotherinterferencefactors,theinternalpressureofthefurnacefluctuatesupanddown,andthesystemdeviatesfromtheequilibriumstate,whichaffectstheplasmaprocessinseverecases.WeuseanordinaryDCmotortodrivetheDCmotorthroughtheL298N,andthemotordrivestheconetorotatethroughthereductionlever.Whentheconeisscrewedin,thegaspumpedoutperunittimeisreduced;whenitisscrewedout,thegaspumpedoutincreases,sothatthepressureinsidethefurnaceisstabilizedattherequiredvalue.Thechangeoffurnacepressureismeasuredbythepressuresensorandpassedthroughthetransmitter,whichsendsthegasflowcontrollertothefeedbackvoltage.Theelectricvacuumbutterflyvalveusedforthesuctionportisexpensive,asshowninFigure1.Figure1BlockdiagramofsystemflowandpressuremeasurementandcontrolIV.L298NChipIntroductionL298NcanacceptstandardTTLlogiclevelsignalVSS,andVSScanbeconnectedto4.5~7Vvoltage.4pinVSisconnectedtothepowersupplyvoltage,andtheVSvoltagerangeVIHis+2.5~46V.Theoutputcurrentcanreach2.5A,whichcandriveinductiveloads.Theemittersofpin1andpin15areseparatelyledouttoconnectthecurrentsamplingresistortoformacurrentsensingsignal.L298candrivetwomotors,OUT1,OUT2andOUT3,OUT4canbeconnectedtoeachmotor,thisexperimentaldevicewechoosetodriveonemotor.Pins5,7,10and12areconnectedtotheinputcontrolleveltocontroltheforwardandreverserotationofthemotor.EnAandEnBareconnectedtothecontrolpotentialenergyendtocontrolthestallingofthemotor.Figure2istheL298Nfunctionallogicdiagram,Table1istheL298Ninternalfuntionalmodule.Figure2L298NfunctionallogicdiagramEnAIn1In2OperativeCondition0Stop110Rotatingforward101Inversion111Brake100StopTable1L298NinternalfunctionalmoduleThefunctionalmoduleofIn3andIn4isthesameasTable1.ItcanbeseenfromTable1thatwhenEnAislowlevel,theinputlevelhasaneffectonmotorcontrol.WhenEnAishighlevel,whenEnAishigh,theinputlevelisonehighandonelow,andthemotorrotatesforwardorreverse.Iftheyarebothlowlevel,themotorwillstop,andiftheyarebothhighlevel,themotorwillbrake.V.ControllerPrincipleFigure3istheschematicdiagramofthecontroller,composedof3dashedblockdiagrams:Figure3TheschematicdiagramofthecontrollerThefollowingarethefunctionsofthe3dashedblockdiagrams:(1)Thedashedblockdiagram1controlstheforwardandreverserotationofthemotor,U1AandU2Aarecomparators,andVIcomesfromthevoltageofthefurnacepressuresensor.WhenVIVRBF1,U1Aoutputshighlevel,U2Aoutputhighlevelturnsintolowlevelthroughinverter,andthemotorrotatesforward.Similarly,whenVIVRBF1,themotorreverses.Theforwardandreverserotationofthemotorcancontroltheflowofgasextractedbytheairextractor,therebychangingthepressureinsidethefurnace.(2)Inthedashedblockdiagram2,twocomparatorsU3AandU4Aformadual-limitcomparator.WhenVBVIVA,itoutputslowlevel,andwhenVIVA,VIVB,itoutputshighlevel.VA,VBaretheupperandlowerlimitsofthevoltageconvertedbythefurnacepressuretransducer,thatis,thecontrolrangeofthereactionfurnacepressure.Accordingtoprocessrequirements,wecanspecifythevaluesofVAandVBbyourselves,aslongasthefurnacepressureiswithintherangedeterminedbyVAandVB,themotorstops(notethatVB<VRBF1<VA,ifitisnotinthisrange,thesystemisunstable).(3)Thedashedblockdiagram3isalongdelaycircuit.U5Aisacomparator,Rs1isthesamplingresistor,VRBF2isthemotorovercurrentvoltage.ThevoltageonRs1isgreaterthanVREF2,themotorisovercurrent,andU5Aoutputslowlevel.Itcanbeseenfromtheabovethatblock1controlstheforwardandreverserotationofthemotor,andblock2controlsthesizeoftherippleofthefurnacepressure.Whenthefurnacepressureistoosmallortoolarge,themotorturnstoafixedpositionatbothendstostop,accordingtothesteady-stateoperatingequationoftheDCmotor:Amongthem:Фisthemagneticfluxofeachpoleofthemotor;Ceistheelectromotiveforceconstant;Nisthenumberofmotorrevolutions;Iaisthearmaturecurrent;Raisthearmatureloopresistance.WhenthenumberofrevolutionsofthemotorNis0,thecurrentofthemotorincreasessharply,andthemotorwillburnoutifthetimeistoolong.Butwhenthemotorstarts,thecurrentinthecoilinthemotoralsoincreasessharply,sowemustseparatethesetwostates.Thelongdelaycircuitcandistinguishthesetwostates.Theworkingprincipleofthelong-delaycircuit:WhentheRs1overcurrentU5Ageneratesanegativepulseandisdifferentiated,thepulsetriggerspin2of555,thecircuitisset,andpin3outputshighlevel.Becausethedischargeterminal7pinisopen,C1,R5andU6Aformedasanintegration,thenstartworking,thechargingvoltageonthecapacitorC1riseslinearly,andtheintegrationconstantofthedelayoperationalamplifieris100R5C1.WhenthechargingvoltageonC1,thatis,thevoltageonpin6exceeds2/3VCC,the555circuitresetsandoutputsalowlevel.Themotorgenerallystart-upinlessthan0.8s,andtheC1chargingtimeisgenerally0.8~1s.TheoutputlevelofU5AisORedwiththeoutputlevelofpin3of555viaU7.IftheoutputlowlevelofU5AislongerthanthechargingtimeofC1,U7outputslowlevelafterC1ischarged.TheANDgateU8inputstothe6pinENAterminalofL298N.Themotorstops.IftheoutputlevelofU5AislessthanthechargingtimeofC1,pin6willnotactandthemotorwillstartnormally.Thelongdelaycircuitabsorbsthemotorstart-upovercurrentvoltagewaveform,sothatthemotorstartsnormally.VI.ConclusionThisarticlesummarizesthedesignschemeforthepressurecontrolofionnitridingbasedontheL298Nchip.Ithasbeenprovedthattheuseofthiscontrollertocontrolthegasflowcanreduceproductioncosts,increasethesystemcostperformance,andimprovethecontroldynamicperformanceandstabilityoftheentiresystemcontrol.FAQWhatisl298n?ThisL298NMotorDriverModuleisahighpowermotordrivermodulefordrivingDCandStepperMotors.ThismoduleconsistsofanL298motordriverICanda78M055Vregulator.L298NModulecancontrolupto4DCmotors,or2DCmotorswithdirectionalandspeedcontrol.Whatistheuseofl298n?TheL298NisadualH-BridgemotordriverwhichallowsspeedanddirectioncontroloftwoDCmotorsatthesametime.ThemodulecandriveDCmotorsthathavevoltagesbetween5and35V,withapeakcurrentupto2A.Howdoesl298ncontrolDCmotorspeed?1.IfyousendaHIGHsignaltotheenable1pin,motorAisreadytobecontrolledandatthemaximumspeed;2.IfyousendaLOWsignaltotheenable1pin,motorAturnsoff;3.IfyousendaPWMsignal,youcancontrolthespeedofthemotor.Themotorspeedisproportionaltothedutycycle.Whatisl298nmotordrivermodule?ThisL298NMotorDriverModuleisahighpowermotordrivermodulefordrivingDCandStepperMotors.ThismoduleconsistsofanL298motordriverICanda78M055Vregulator.L298NModulecancontrolupto4DCmotors,or2DCmotorswithdirectionalandspeedcontrol.Howdoesl298nmotordriverwork?TheL298NisadualH-BridgemotordriverwhichallowsspeedanddirectioncontroloftwoDCmotorsatthesametime.ThemodulecandriveDCmotorsthathavevoltagesbetween5and35V,withapeakcurrentupto2A.Howdoiuseal298motordriverwithArduino?Startbyconnectingpowersupplytothemotors.InourexperimentweareusingDCGearboxMotors(alsoknownasTTmotors)thatareusuallyfoundintwo-wheel-driverobots.Theyareratedfor3to12V.So,wewillconnectexternal12VpowersupplytotheVCCterminal.WhatisthefunctionofHbridge?AnH-bridgeisanelectroniccircuitthatswitchesthepolarityofavoltageappliedtoaload.ThesecircuitsareoftenusedinroboticsandotherapplicationstoallowDCmotorstorunforwardsorbackwards.Whatisthedifferencebetweenl293dandl298n?L293isquadruplehalf-HdriverwhileL298isdualfull-Hdriver,i.e,inL293allfourinput-outputlinesareindependentwhileinL298,ahalfHdrivercannotbeusedindependently,onlyfullHdriverhastobeused....Hence,heatsinkisprovidedinL298.

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