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超声波明渠流量计的设计-外文翻译.doc

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辽宁科技大学本科生毕业设计第11页外文TheOperationalAmplifierOneproblemwithelectronicdevicescorrespondingtothegeneralizedamplifiersisthatthegains,AuorAi,dependuponinternalpropertiesofthetwoportsystem(μ,β,Ri,Ro,etc).[1]Thismarksdesigndifficultsincetheseparametersusuallyvaryfromdevicetodevice,aswellaswithtemperature。

Theoperationalamplifier,orOPAmp,isanintegratedcircuitthathasmanycomponentpartssuchasresistorsandtransistorsbuiltintothedevice.Atthispointwewillmakenoattempttodescribetheseinnerworkings.AtotallygeneralanalysisoftheOpAmpisbeyondthescopeofsometexts.Wewillinsteadstudyoneexampleindetail,thenpresentthetwoOpAmplawsandshowhowtheycanbeusedforanalysisinmanypracticalcircuitapplications。

Thesetwoprinciplesallowonetodesignmanycircuitwithoutadetailedunderstandingofthedevicephysics.Hence,OpAmparequiteusefulforresearchersinavarietyoftechnicalfieldswhoneedtobuiltsimpleamplifiersbutdonotwanttodesignatthetransistorlevel.InthetextsofelectricalcircuitsandelectronicstheywillalsoshowhowtobuiltsimperfiltercircuitusingOpAmp。

Thetransistoramplifiers,whicharethebuildingblocksfromwhichOpAmpintegratedcircuitsareconstructed,willbediscussed.ThesymbolusedforanidealOpAmp.Onlythreeconnectionsareshown:thepositiveandthenegativeinputs,andtheoutput.NotshownareotherconnectionsnecessarytoruntheOpAmpsuchasitsattachmenttopowersuppliesandtogroundpotential。

ThelatterconnectionsarenecessarytousetheOpAmpinapracticalcircuitbutarenotnecessarywhenconsideringtheidealOpAmpapplicationswestudyinthispaper.ThevoltagesatthetwoinputsandoutputwillberepresentedbythesymbolU+,U,andUo.Eachismeasuredwithrespecttogroundpotential.Operationalamplifiersaredifferentialdevice.

BythiswemeanthattheoutputvoltagewithrespecttogroundisgivenbytheexpressionUo=A(OpAmpU)(32)WhereAisthegainoftheOpAmpandU+andUthevoltagesatinputs.inotherwords,theoutputvoltageisAtimesthedifferenceinpotentialbetweenthetwoinputs.Integratedcircuittechnologyallowsconstructionofmanyamplifiercircuitonasingle“chip”ofsemiconductormaterial。

Onekeytothesuccessofanoperationalamplifieristhe“cascading”ofanumberoftransistoramplifierstocreateaverylargetotalgain.Thatis,thenumberAinEq(31)canbeontheorderof100,000ormore.(Forexample,cascadingoffivetransistoramplifiers,eachwithagainof10,wouldyieldthisvalueforA.)Asecondimportantfactoristhatthesecircuitscanbebuiltinsuchawaythatthecurrentflowingintoeachoftheinputsisverysmall。

Athirdimportantdesignfeatureisthattheoutputresistanceoftheoperationalamplifier(Ro)isverysmall.Thisinturnmeansthattheoutputofthedeviceactslikeanidealvoltagesource.Wenowcananalyzetheparticularamplifiercircuit,usingthesecharacteristics.First,wenotethatthevoltageatthepositiveinput,U+,isequaltothesourcevoltage。

U+=Us.Variouscurrentsaredefinedinpartofthefigure.pplyingKVL,aroundtheouterloopandrememberingthattheoutputvoltage,Uo,ismeasuredwithrespecttoground,wehave(32)SincetheOpAmpisconstructedinsuchawaythatnocurrentflowsintoeitherthepositiveornegativeinput,I=0,KCLatthenegativeinputterminalthenyieldUsingEq。

(32)andsetting,(33)WemayuseOhm’slawstofindthevoltageatthenegativeinput,U,notingtheassumedcurrentdirectionandthefactthatgroundpotentialiszerovolts:(U0)/R1=ISo,U=IR1AndfromEq.(33),U=(R1/(R1+R2))UOSincewenowhaveexpressionforU+andU,Eq(31)maybeusedtocalculatetheoutputvoltage,UO=A(U+U)=A(UOR1Uo/(R1+R2))Gatheringterms。

(34)Andfinally,(35a)Thisisthegainfactorforthecircuit.IfAisalargeenoughthat,thedenominatorofthisfractionisdominatedbytheAR1term.ThefactorA,whichisinboththenumeratoranddenominator,thencancelsoutandthegainisgivenbytheexpression(35b)ThisshowsthatifAisverylarge,thenthegainofthecircuitisindependentoftheexactvalueofAandcanbecontrolledbythechoiceofR1andR2。

ThisisoneofthekeyfeatureofPoAmpdesign-theactionofthecircuitonsignaldependonlyupontheexternalelementswhichcanbeeasilyvariedbythedesignerandwhichdonotdependuponthedetailedcharacteroftheOpAmpitself.NotethatifA=100,000and,thepricewehavepaidforthisadvantageisthatwehaveusedadevicewithavoltagegainof100,000toproduceanamplifierwithagainof10。

Insomesense,byusinganOpAmpwetradeoff“power”for“control”.AsimilarmathematicalanalysiscanbemadeonanyOpAmpcircuit,butthisiscumbersomeandtherearesomeusefulshortcutsthatinvolveapplicationofthetwolawsofOpAmpwhichwenowpresent.1)ThefirstlawstatsthatinnormalOpAmpcircuitwemayassumethatthevoltagedifferencebetweentheinputterminaliszero。

thatisU+=U2)ThesecondlawstatesthatinnormalOpAmpcircuitbothoftheinoutcurrentsmaybeassumedtobezero:I+=I=0ThefirstlawisduetothelargevalueoftheintrinsicgainA.Forexample,iftheoutputofanOpAmpis1VandA=100,000,then(U+U)=105V.Thisissuchasmallnumberthatitiscanoftenbeignored,andwesetU+=U.ThesecondlawcomesfromtheconstructionofthecircuitryinsidetheOpAmpwhichisthatalmostnocurrentflowsintoeitherofthetwoinputs。

UltralowOffsetVoltageOperationalAmplifierOP071)FEATURESLowVOS:75μVmaximumLowVOSdrift:1.3μV/CmaximumUltrastablevs.time:1.5μVpermonthmaximumLownoise:0.6μVppmaximumWideinputvoltagerange:14VtypicalWidesupplyvoltagerange:3Vto18V125Ctemperaturetesteddice2)APPLICATIONSWirelessbasestationcontrolcircuitsOpticalnetworkcontrolcircuitsInstrumentationSensorsandcontrolsThermocouplesResistorthermaldetectors(RTDs)StrainbridgesShuntcurrentmeasurementsPrecisionfilters3)GENERALDESCRIPTIONTheOP07hasverylowinputoffsetvoltage(75μVmaximumforOP07E)thatisobtainedbytrimmingatthewaferstage。

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