power-amplifiers运算放大器习题讲解

Ana[e-mail]@esat.kuleuven.beKULeuvenESAT-MICASAnalogBuildingblocksforsignalprocessing2TheoryPowerAmplifier:deliverpowerinaload(e.g.resistor)-“Largesignal”amplifier(nosmallsignalequivalentmodels)-Classificationofdifferenttypes:-ClassA-ClassB-ClassAB-ClassC-…Classificationbasedontheintervalofcurrentconductionofthetransistorswhenasinewaveisappliedtotheinput.AnalogBuildingblocksforsignalprocessing3TheoryImportantnumbers:-Efficiency-Signalswingattheoutputislimitedby:-Transistors(operatingregion!)-Maximalcurrentavailable-SupplyvoltageloadsupplyPPη=AnalogBuildingblocksforsignalprocessing4Theory:ClassA-Conductionintervaltransistors=360-largeDCbiascurrentneeded(=peakcurrentinload)-lowmaximumefficiency:(largestatic/constantpowerconsumption)%25max=ηAnalogBuildingblocksforsignalprocessing5Theory:ClassB-Conductionintervaltransistors=180-noDCbiascurrent-maximumefficiency:-Crossoverdistortion!max78.5%atpCCVVη==AnalogBuildingblocksforsignalprocessing6Theory:ClassC-Conductionintervaltransistors180-tunedtoafixedfrequencyusingLC-network-maximumefficiencyincaseofperfecttuning-onlyusefulinnarrowfrequencyband(LCtank!)&signalswithaconstantamplitude!max100%η≈AnalogBuildingblocksforsignalprocessing7Exercise1Considerthefollowingamplifier,with:RL=500Ω,Vcc=15V.1.DeterminethemeanpowerdeliveredtoRLiftheoutputisasinewitha14,4Vamplitude.2.Whatisthecorrespondingpowerefficiency?3.Calculatethetotalmaximumimmediateandmeanpowerdissipationsforeachtransistor.AnalogBuildingblocksforsignalprocessing8SolutionIClassBamplifier1.MeanpowerdeliveredtoRL?(output:sinewithA=14,4V)2.Correspondingpowerefficiency?PowerinRL=207mWPowerfromsupply:mWRVPLmL20722=⋅=supply2with9.1727575,3%mmavgccavgLIVPIVImARmWππη=⋅⋅===⋅=⇒=AnalogBuildingblocksforsignalprocessing9SolutionII3.Maximumimmediateandmeanpowerdissipationforeachtransistor?Transistorpowerdissipation=powerdissipatedinthetransistor,notintheload=shouldbeminimized!-meantransistorpowerdissipation:“Whatisthepowerdissipatedinthetransistor,averagedoveroneperiod?”-immediatetransistorpowerdissipation:“Whatistheinstantaneouspowerdissipatedinthetransistor?“1.Meantransistorpowerdissipation:,10,11()33.82TlosstrdisstrsupplyLPtdtTPPPmW=−=∫AnalogBuildingblocksforsignalprocessing10SolutionIII3.Maximumimmediateandmeanpowerdissipationforeachtransistor?2.Immediatetransistorpowerdissipation“Whatistheinstantaneouspowerdissipatedinthetransistor?“FixedrelationshipbetweenVceandIce:Loadline:-transistorbehavior(Ice=f(Vce,Vbe))-loadresistor(Ice=f(R,VR)),1()()()disstrcecePtVtIt=⋅11()()()cccccccececeLLccLLVVVItVtVtRRVRR=−=−AnalogBuildingblocksforsignalprocessing11SolutionIV3.Totalimmediateandmeanpowerdissipationforeachtransistor?ForwhichVceandIcewillthetransistorimmediatepowerdissipationbemaximal?,1122,111()()(t)with()()11202122112.5224ccccccdisstrcecececeLLccLLccceceLLccceceLLccceccccccceLLLccccccdisstrLLVVVPtItVIVtVtRRVRRVVVRRVPVVRRVVVVVIRRRVVVPmWRR=⋅=−=−=⋅−⋅∂=−⋅⋅=∂⇒=⇒=−=⇒=⋅==AnalogBuildingblocksforsignalprocessing12Exercise2AgivenpoweramplifierwithVcc=15V,R1=20kΩ,VCE,sat=0.2V,VBE,on=0.7andβ=50.Calculate:1.Themaximalpositiveandnegativelimitsfortheoutputvoltage2.ThemaximalmeanpowerdeliveredtoRLwithoutclipping.3.Themeanpowerdissipatedineachoutputtransistor4.ThepowerefficiencyAnalogBuildingblocksforsignalprocessing13SolutionI1.Maximalpositiveandnegativelimitsfortheoutputvoltage?MinimalvalueVout:(Q3insaturation)MaximalvalueVout:(Q3incut-off)14,1VVVVVbesatceccout,min−=++−=2,3,max111with1out,maxCE1out,maxcc11be11B1LoutbeLccbe1out,maxLVI1VVIRVIIββRVRVccVRVVV13.75VRRββ=−⋅−====−⋅−−⇒==+⋅AnalogBuildingblocksforsignalprocessing14SolutionII2.ThemaximalmeanpowerdeliveredtoRLwithoutclipping.noclipping:amplitudeofoutputsignal=min(Vout,max,|Vout,min|)=13.75V3.Meanpowerdissipatedperoutputtransistor?totaldissipatedpower:powerdissipatedpertransistor:mW10kΩ2(13.75V)R2VP2L2outL,max45,9=⋅=⋅=13.13mWRπVV2πIV2IV2PLmaxccmaxccsupplyccsupply=⋅⋅⋅=⋅⋅=⋅⋅=supplyloadtrPPP1.84mW2−==AnalogBuildingblocksforsignalprocessing15SolutionIII4.Powerefficiency:loadsupplyPη72%P==AnalogBuildingblocksforsignalprocessing16Exercise3ConsideraclassBamplifierwithoutdeadzone:1.Calculatetheefficiencyasfunctionoftheamplitudeoftheoutputsignal.2.Whatistherelationbetweenthedissipatedpower(relativetothemaximumdissipatedpower)totheamplitudeoftheoutputsignal3.Whatwillhappenincaseofadeadzone?AnalogBuildingblocksforsignalprocessing17SolutionI1.Calculatetheefficiencyasfunctionoftheamplitudeoftheoutputsignal.–Efficiency:–Psupply:meanpowerfromsupplyduring1signalperiod.Psupply=Vdd*Idcinwhich:*Vdd=supplyvoltage*Idc=meancurrentfromsupplyrail=2*meancurrentpertransistorfromsupplyrail=2*ItrsupplyloadPP=ηAnalogBuildingblocksforsignalprocessing18SolutionIIMeancurrentfromsupplyrail?-Supposesinewave:Iload=Ip*sin(ωt)-Meancurrentin1transistor:-Total,meancurrentfromsupplyrail(bothtransistors!):Meanpowerfromsupplyrails:/20011sin()()TTptrloadpIIIdtItdtTTωπ==⋅=∫∫22pdctrIIIπ=⋅=⋅πddpdcddSupplyVIIVP2=⋅=AnalogBuildingblocksforsignalproce