模拟放大器 外文翻译.docx

模拟放大器 外文翻译.docx

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模拟放大器外文翻译

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AnalogAmplifiers

Atthemostbasiclevel,asignalamplifierdoesexactlywhatyouexpect–itmakesasignalbigger!

However,thewayinwhichitisdonedoesvarywiththedesignoftheactualamplifier,thetypeofsignal,andthereasonwhywewanttoenlargethesignal.[1].Wecanillustratethisbyconsideringthecommonexampleofa“Hi-Fi”audiosystem.

InatypicalmodernHi-Fi:

system,thesignalswillcomefromaunitlikeaCDplayer,FMtuner,oraTape/Minidiskunit.Thesignalstheyproducehavetypicallevelsoftheorderof100mVorsowhenthemusicismoderatelyloud.Thisisareasonablylargevoltage,easytodetectwithsomethinglikeanoscilloscopeoravoltmeter.However,theactualpowerlevelsofthesesignalsarequitemodest.Typically,thesesourcescanonlyprovidecurrentsofafewmilliamps,whichbyP＝VImeanspowersofjustafewmilliwatts.AtypicalloudspeakerwillrequirebetweenafewWattsandperhapsover100Wattstoproduceloudsound.HencewewillrequiresomeformofPowerAmplifier（PA）to“boost”thesignalpowerlevelfromthesourceandmakeitbigenoughtoplaythemusic.

Fig.1.1showsfourexamplesofsimpleanalogamplifierstagesusingvarioustypesofdevice.Ineachcasethea.c.voltagegainwillusuallybeapproximatedbyprovidedthattheactualdevicehasaninherentgainlargeenoughtobecontrolledbytheresistorvalueschosen.Notethenegativesigninexpression1-1whichindicatesthattheexamplesallinvertthesignalpatternwhenamplifying.[2]Inpractice,gainsoftheorderofuptohundredarepossiblefromsimplecircuitslikethis,althoughitisusuallyagoodideatokeepthevoltagegainbelowthis.Notealsothatvacuumstatedevicestendtobecalled“valves”intheUKand“tubes”intheUSA.

Fig.1.1ExamplesofvoltageamplifiersAv≈－R1/R2（1-1）Manypracticalamplifierschaintogetheraseriesofanalogamplifierstagestoobtainahighoverallvoltagegain.Forexample,aPAsystemmightstartwithvoltagesoftheorderof0.1mVfrommicrophones,andboostthistoperhaps10to100Vtodriveloudspeakers.Thisrequiresanoverallvoltagegainof109,soanumberofvoltagegainstageswillberequired.

Inmanycaseswewishtoamplifythecurrentsignallevelaswellasthevoltage.Theexamplewecanconsiderhereisthesignalrequiredtodrivetheloudspeakersina“Hi-Fi”system.Thesewilltendtohaveatypicalinputimpedanceoftheorderof8Ohms.Sotodrive,say,100Wattsintosuchaloudspeakerloadwehavetosimultaneouslyprovideavoltageof28Vrmsand3.5Arms.Takingtheexampleofamicrophoneasaninitialsourceagainatypicalsourceimpedancewillbearound100Ohms.Hencethemicrophonewillprovidejust1nAwhenproducing0.1mV.Thismeansthattotakethisanddrive100Wintoaloudspeakertheamplifiersystemmustamplifythesignalcurrentbyafactorofover109atthesametimeasboostingthevoltagebyasimilaramount.[3]Thismeansthattheoverallpowergainrequiredis1018–i.e.180dB!

Thishighoverallpowergainisonereasonitiscommontospreadtheamplifyingfunctionintoseparatelyboxedpre-andpower-amplifiers.Thesignallevelsinsidepoweramplifiersaresomuchlargerthantheseweakinputsthateventheslightest‘leakage’fromtheoutputbacktotheinputmaycauseproblems.Byputtingthehigh-power（highcurrent）andlowpowersectionsindifferentboxeswecanhelpprotecttheinputsignalsfromharm.

Inpractice,manydeviceswhichrequirehighcurrentsandpowerstendtoworkonthebasisthatitisthesignalvoltagewhichdeterminesthelevelofresponse,andtheythendrawthecurrenttheyneedinordertowork.[4]Forexample,itistheconventionwithloudspeakersthatthevolumeofthesoundshouldbesetbythevoltageappliedtothespeaker.Despitethis,mostloudspeakershaveanefficiency（theeffectivenesswithwhichelectricalpowerisconvertedintoacousticalpower）whichishighlyfrequencydependent.Toalargeextentthisarisesasanaturalconsequenceofthephysicalpropertiesofloudspeakers.Fig.1.2showsatypicalexample.Inthiscase,theloudspeakerhasanimpedanceofaround12Ohmsat150Hzand5Ohmsat1kHz.Soovertwicethecurrentwillberequiredtoplaythesameoutputlevelat1kHzthanisrequiredat150Hz.Thepoweramplifierhasnowayto“knowinadvance”whatkindofloudspeakeryouwilluse,sosimplyadoptstheconventionofassertingavoltageleveltoindicatetherequiredsignallevelateachfrequencyinthesignalandsupplyingwhatevercurrenttheloudspeakerthenrequires.

Fig1.2Impedancepropertiesofatypical“8Ohms”loudspeaker

Thiskindofbehaviorisquitecommoninelectronicsystems.Itmeansthat,ininformationterms,thesignalpatternisdeterminedbythewaythevoltagevarieswithtime,andideallythecurrentrequiredisthendrawn.Althoughtheaboveisbasedonahigh-powerexample,asimilarsituationcanarisewhenasensorisabletogenerateavoltageinresponsetoaninputstimulusbutcanonlysupplyaverylimitedcurrent.Inthesesituationswerequireeitheracurrentamplifierorabuffer.Thesedevicesarequitesimilar,andineachcaseweareusingsomeformofgaindeviceandcircuittoincreasethesignalcurrentlevel.However,acurrentamplifieralwaystriestomultiplythecurrentbyasetamount.Henceitissimilarinactiontoavoltageamplifierwhichalwaystriestomultiplythesignalcurrentbyasetamount.Thebufferdiffersfromthecurrentamplifierasitsetsouttoprovidewhatevercurrentlevelisdemandedfromitinordertomaintainthesignalvoltagetoldtoassert.

Alongwiththedevelopmentoftheages,thetechniquethatisnowadaysisalsograduallyperfect,thecompetitionplaysmorestrong;theoperationthatlistdependstheartificialhasalreadycan'tsatisfiedwiththecurrentmanufacturingindustryforeground,alsocan'tguaranteetherequestofthehigherquantityandhighnewtheimageofthetechniquebusinessenterprise.

Thepeopleseeinproducepractice,automatebroughtthetremendousconvenienceandtheproductquantitiesforpeopleupofassurance,alsoeasedthepersonnel'slaborstrength,reducetheestablishmentonthepersonnel.Thetargetcontrolofthehardrealizationinmanycomplicatedproductionlines,wholeandexcellentturn,thebestdecisionetc.,well-trainedoperationwork,technicalpersonnelorexpert,governorbutcanjudgeandoperateeasily,canacquirethesatisfiedresult.Theresearchtargetoftheartificialintelligencemakesuseofthecalculatorexactlytocarryout,imitatetheseintelligencesbehavior,moderatingtheworkthroughperson'sbrainandcalculators,withthemodethatperson'smachinecombine,forresolvetheverycomplicatedproblemtolookforthebestpath

Wecomeinsightofthecontrolthatlinksaftertheelectricappliancesinvarioussituation,thatisalreadythethattimegenerationpast,nowofafteruseinthemoldaperhapssimpleequipmentsofgrass-rootscontrolthattheelectricappliancescandoforthelowlevelonly;AndthePLCemergencealsobecametheepoch-makingtopic,addingthevividsoftwarecontrolthroughaveryandstablehardware,makingtheautomationheadforthenewhightide.

ThePLCbiggestcharacteristicsliein:

Theelectricalengineeringteacheralreadynolongerelectrichardwareuptoomanycalculationsofcost,aslongasordertheimportationthatthebuttonswitchortheimportationofthesensorsordertolinkthePLCupcansolveproblem,passtooutputtoordertheconjunctioncontactmachineorcontrolthestartequipmentsofthebigpoweraftertheelectricappliances,buttheexportationequipmentsdirectconjunctionofthesmallpowercan.

PLCinternalcontainmenthavetheCPUoftheCPU,andtaketohaveanI/Oforexpandofexteriortoconnectapeople'saddressandsavingmachinethreebigpiecestoconstitute,CPUcoreisfromanormanyistiredtoaddthemachinetoconstitute,mathematicsthattheyhavethelogicoperationability,andcanreadtheproceduresavethecontentsofthemachinetodrivethehomologoussavingmachineandI/Ostoconnectafterpassthecalculation;TheI/Oaddinnerpartistiredtheinputandoutputsystemofthemachineandexteriorlink,anddeposittherelateddataintotheproceduresavingmachineordatasavingmachine;ThesavingmachinecandepositthedatathattheI/Oinputinthesavingmachine,andinworkadjustingtobecometiredtoaddthemachineandI/Ostoconnect,savingmachineseparatelysavingmachineRAMoftheproceduresavingmachineROManddates,theROMcandodepositofthedatapermanenceinthesavingmachine,butRAMonlyfortheCPUcomputesthetemporarycalculationusageofhourofbufferspace.

ThePLCanti-interferenceisveryandexcellent,ourrootneednotconcernitsservicelifeandtheworksituationbad,theseallproblemshavealreadynolongerbecomethetopicthatwefail,butstaytoourisaconcerntocometointernalresourcesofmakeuseofthePLCtostrengthenthecontrolabilityoftheequipmentsforus,makeourequipmentsmoregentle.

PLClanguageisnotweimagineofeditcollectedmaterialsthelanguageorlanguageofCstocarryonweavingthedistance,butthetrapezoiddiagramthattheadoptionisoriginalaftertheelectricappliancestocontrol,maketheelectricalengineeringteacherwhileweavingtowritetheprocedureveryeasycomprehendedthePLClanguage,andalotofnon-electricityprofessionalalsoveryquicklyknowandgodeepintotothePLC.

IsPLConeoftheadvantageaboveandonly,thisisalsoonepartthatthepeoplecomprehendmoreandeasily,inalotofequipments,thepeoplehavealreadynolongerhopedtoseetoomanycontrolbuttons,the