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1、UNIT2A:TheOperationalAmplifierOneproblemwithelectronicdevicescorrespondingtothegeneralizedamplifiersisthatthegains,AuorA~,dependuponinternalpropertiesofthetwo-portsystem(p,fl,R~,Ro,etc.)?~Thismakesdesigndifficultsincetheseparametersusuallyvaryfromdevicetodevice,aswellaswithtempera
2、ture.Theoperationalamplifier,orOp-Amp,isdesignedtominimizethisdependenceandtomaximizetheeaseofdesign.AnOp-Ampisanintegratedcircuitthathasmanycomponentpartsuchasresistorsandtransistorsbuiltintothedevice.Atthispointwewillmakenoattempttodescribetheseinnerworkings.Atotallygeneralanaly
3、sisoftheOp-Ampisbeyondthescopeofsometexts.Wewillinsteadstudyoneexampleindetail,thenpresentthetwoOp-Amplawsandshowhowtheycanbeusedforanalysisinmanypracticalcircuitapplications.Thesetwoprinciplesallowonetodesignmanycircuitswithoutadetailedunderstandingofthedevicephysics.Hence,Op-Amp
4、sarequiteusefulforresearchersinavarietyoftechnicalfieldswhoneedtobuildsimpleamplifiersbutdonotwanttodesignatthetransistorlevel.InthetextsofelectricalcircuitsandelectronicstheywillalsoshowhowtobuildsimplefiltercircuitsusingOp-Amps.Thetransistoramplifiers,whicharethebuildingblocksfr
5、omwhichOp-Ampintegratedcircuitsareconstructed,willbediscussed.ThesymbolusedforanidealOp-AmpisshowninFig.1-2A-1.Onlythreeconnectionsareshown:thepositiveandnegativeinputs,andtheoutput.NotshownareotherconnectionsnecessarytoruntheOp-Ampsuchasitsattachmentstopowersuppliesandtogroundpot
6、ential.ThelatterconnectionsarenecessarytousetheOp-Ampinapracticalcircuitbutarenotnecessarywhenconsideringtheideal0p-Ampapplicationswestudyinthischapter.ThevoltagesatthetwoinputsandtheoutputwillberepresentedbythesymbolsU+,U-,andUo.Eachismeasuredwithrespectt~groundpotential.Operatio
7、nalamplifiersaredifferentialdevices.BythiswemeanthattheoutputvoltagewithrespecttogroundisgivenbytheexpressionUo=A(U+-U-)(1-2A-l)whereAisthegainoftheOp-AmpandU+andU-thevoltagesatinputs.Inotherwords,theoutputvoltageisAtimesthedifferenceinpotentialbetweenthetwoinputs.Integratedcircui
8、ttechnologyallowsconstructionofma
