chapter6-singlestageICamplifier

1Chapter6SingleStageICAmplifiers2Outline•Introduction•BiasingmechanismforICs•Highfrequencyresponse•TheCSandCEamplifierwithactiveloads•HighfrequencyresponseoftheCSandCEamplifier•TheCGandCBamplifierwithactiveloads•TheCascodeamplifier•TheCSandCEamplifierwithsource(emitter)degeneration3Introduction•Designphilosophyofintegratedcircuits•ComparisonoftheMOSFETandtheBJT(Self-Study)4DesignPhilosophyofIntegratedCircuits•StrivetorealizeasmanyofthefunctionsrequiredaspossibleusingMOStransistorsonly.LargeevenmoderatevalueresistorsaretobeavoidedConstant-currentsourcesarereadilyavailable.Couplingandbypasscapacitorsarenotavailabletobeused,exceptforexternaluse.5DesignPhilosophyofIntegratedCircuits•Low-voltageoperationcanhelptoreducepowerdissipationbutposesahostofchallengestothecircuitdesign.•Bipolarintegratedcircuitsstilloffermanyexcitingopportunitiestotheanalogdesignengineer.6BiasingmechanismforICs•MOSFETCircuitsThebasicMOSFETcurrentsourceMOScurrent-steeringcircuits•BJTCircuitsThebasicBJTcurrentsourceBJTCurrent-steeringcircuits7BiasingmechanismforICs(cont’d)•Current-mirrorcircuitswithimprovedperformanceCascodeMOSmirrorsAbipolarmirrorwithbase-currentcompensationThewilsoncurrentmirrorThewilsonMOSmirrorThewidlarcurrentsource8TheBasicMOSFETCurrentSource12))LWLWIIREFo（（22'2121'12121tnGSnDoGSDDREFDtnGSnDVVLWKIIRVVIIVVLWKI9TheBasicMOSFETCurrentMirror)1())212AGSoREFoVVVILWLWI（（10OutputCharacteristicoAooIVrR22oAooIVrR2211MOSCurrent-SteeringCircuits4545133122)()()()()()(LWLWIILWLWIILWLWIIREFREF12TheBasicBJTCurrentMirror2112REFoIIEREFEoIIII12113ASimpleBJTCurrentSource.CQAoonBECCREFREFoIVrRRVVIII02)(14CurrentSteeringREFREFREFREFBEEBEECCREFIIIIIIIIRVVVVI3243212115Current-MirrorCircuitswithImprovedPerformanceTwoperformanceparametersneedtobeimproved:a.Theaccuracyofthecurrenttransferratioofthemirror.b.Theoutputresistanceofthecurrentsource.16CascodeMOSCurrentMirror23323333)(1oomoombmoorrgrrggrR17CurrentMirrorwithBase-CurrentCompensation2211REFoII18TheWilsonBipolarCurrentMirror2211REFoII2oorREoEREFIIII1121219TheWilsonMOSCurrentMirror233oomorrgR20TheWidlarCurrentSourceoEmooREFETorrRgRIIRVI)//(1)ln(EoBEBEoREFTBEBESoTBESREFTBERIVVIIVVVIIVVIIVV212121lnlnln21TheadvantagesofWidlarCurrentSource•Example6.2p518•Widlarcircuitallowsthegenerationofasmallconstantcurrentusingrelativelysmallresistors(savinginchiparea).•Anotherimportantcharacteristicofthewidlarcurrentsourceisthatitsoutputresistanceishigh.oEmoEmEorRgrRgRR)1()1('''22HighFrequencyResponse•Thehigh-frequencygainfunction•Determiningthe3-dBfrequencyBydefinitionDominant-poleOpen-circuittimeconstants23IntroductionofFrequencyResponse•Whyshallwestudythefrequencyresponse?Actualtransistorsexhibitchargestoragephenomenathatlimitthespeedandfrequencyoftheiroperation.24AmplifierTransferFunction(a)acapacitivelycoupledamplifier(b)adirect-coupledamplifierHMMLHABWAGBBW:productbandwidth-Gain:Bandwidth25TheGainFunction•Gainfunction•Midband:Nocapacitorsineffect•Low-frequencyband:couplingandbypasscapacitorsineffect•High-frequencyband:transistorinternalcapacitorsineffect)()(sFAsAHM)()()(sFsFAsAHLM)()(sFAsALMMAsA)(26TheHigh-FrequencyGainFunctionDirectlycoupledLowpassfiltergaindoesnotfalloffatlowfrequenciesMidbandgainAMextendsdowntozerofrequency27TheHigh-FrequencyGainFunction•Gainfunction•ωP1,ωP2,….ωPnarepositivenumbersrepresentingthefrequenciesofthenrealpoles.•ωZ1,ωZ2,….ωZnarepositive,negative,orinfinitenumbersrepresentingthefrequenciesofthenrealtransmissionzeros.)1().....1()1()1.....()1)(1()()()(2121PnPPZnZZHHMsssssssFsFAsA28Determiningthe3-dBFrequency•Definitionor•AssumeωP1ωP2….ωPnandωZ1ωZ2….ωZn2)(MHAAdBAAMH3)(....)11(2....)11(122212221ZZPPH29Determiningthe3-dBFrequency•DominantpoleIfthelowest-frequencypoleisatleasttwooctaves(afactorof4)awayfromthenearestpoleorzero,itiscalleddominantpole.Thusthe3-dBfrequencyisdeterminedbythedominantpole.•Singlepolesystem11/1)(PHPMsAsA30Determiningthe3-dBFrequency•Open-circuittimeconstants•ToobtainthecontributionofcapacitanceCiReduceallothercapacitancestozeroReducetheinputsignalsourcetozeroDeterminetheresistanceRioseenbyCi•Thisprocessisrepeatedforallothercapacitanceinthecircuit.iioiHRC131ExampleforTimeConstantAnalysisHigh-frequencyequivalentcircuitofaMOSFETamplifier.Theconfigurationiscommon-source.32ExampleforTimeConstantAnalysisCircuitfordeterminingtheresistanceseenbyCgsandCgd33TheCSAmplifierwithActiveLoada.Currentsourceactsasanactiveload.b.Sourceleadissignalgrounded.c.Activeloadreplacesthepassiveload.34TheCSAmplifierwithActiveLoadSmall-signalanalysisoftheamplifierperformedbothdirectlyonthecircuitdiagramandusingthesmall-signalmodelexplicitly.TheintrinsicgainomvorgA35TheCSAmplifierwithActiveLoad)//()(21112211oomoooomoLLvovrrgrrrrgRRRAAREFAoIVr2236TheCEAmplifierwithActiveLoad(a)Active-loadedcommon-emitteramplifier.(b)Small-signalanalysisoftheamplifierperform