低功耗高增益宽带放大器外文翻译

中北大学2010届毕业设计说明书第1页共15页ABroadbandAmplifierwithHugeGain-bandwidthProductandLowPowerConsumptionGainThegainofanamplifieristheratioofoutputtoinputpoweroramplitude,andisusuallymeasuredindecibels.(Whenmeasuredindecibelsitislogarithmicallyrelatedtothepowerratio:G(dB)=10log(Pout/(Pin)).RFamplifiersareoftenspecifiedintermsofthemaximumpowergainobtainable,whilethevoltagegainofaudioamplifiersandinstrumentationamplifierswillbemoreoftenspecified(sincetheamplifier'sinputimpedancewilloftenbemuchhigherthanthesourceimpedance,andtheloadimpedancehigherthantheamplifier'soutputimpedance).Example:anaudioamplifierwithagaingivenas20dBwillhaveavoltagegainoften(butapowergainof100wouldonlyoccurintheunlikelyeventtheinputandoutputimpedanceswereidentical).BandwidthThebandwidthofanamplifieristherangeoffrequenciesforwhichtheamplifiergivessatisfactoryperformance.Thedefinitionofsatisfactoryperformancemaybedifferentfordifferentapplications.However,acommonandwell-acceptedmetricisthehalfpowerpoints(i.e.frequencywherethepowergoesdownbyhalfitspeakvalue)ontheoutputvs.frequencycurve.Thereforebandwidthcanbedefinedasthedifferencebetweenthelowerandupperhalfpowerpoints.Thisisthereforealsoknownasthe−3dBbandwidth.Bandwidths(otherwisecalledfrequencyresponses)forotherresponsetolerancesaresometimesquoted(−1dB,−6dBetc.)orplusorminus1dB(roughlythesoundleveldifferencepeopleusuallycandetect).Thegainofagoodqualityfull-rangeaudioamplifierwillbeessentiallyflatbetween20Hztoabout20kHz(therangeofnormalhumanhearing).Inultrahighfidelityamplifierdesign,theamp'sfrequencyresponseshouldextendconsiderablybeyondthis(oneormoreoctaveseitherside)andmighthave−3dBpoints10and65kHz.Professionaltouringamplifiersoftenhaveinputand/oroutputfilteringtosharplylimitfrequencyresponsebeyond20Hz-20kHz;toomuchoftheamplifier'spotentialoutputpowerwouldotherwisebewasted中北大学2010届毕业设计说明书第2页共15页oninfrasonicandultrasonicfrequencies,andthedangerofAMradiointerferencewouldincrease.Modernswitchingamplifiersneedsteeplowpassfilteringattheoutputtogetridofhighfrequencyswitchingnoiseandharmonics.EfficiencyEfficiencyisameasureofhowmuchofthepowersourceisusefullyappliedtotheamplifier'soutput.ClassAamplifiersareveryinefficient,intherangeof10–20%withamaxefficiencyof25%fordirectcouplingoftheoutput.Inductivecouplingoftheoutputcanraisetheirefficiencytoamaximumof50%.ClassBamplifiershaveaveryhighefficiencybutareimpracticalforaudioworkbecauseofhighlevelsofdistortion(See:Crossoverdistortion).Inpracticaldesign,theresultofatradeoffistheclassABdesign.ModernClassABamplifiersarecommonlybetween35–55%efficientwithatheoreticalmaximumof78.5%.CommerciallyavailableClassDswitchingamplifiershavereportedefficienciesashighas90%.AmplifiersofClassC-Fareusuallyknowntobeveryhighefficiencyamplifiers.Moreefficientamplifiersruncooler,andoftendonotneedanycoolingfanseveninmulti-kilowattdesigns.Thereasonforthisisthatthelossofefficiencyproducesheatasaby-productoftheenergylostduringtheconversionofpower.Inmoreefficientamplifiersthereislesslossofenergysointurnlessheat.InRFPowerAmplifiers,suchascellularbasestationsandbroadcasttransmitters,specialistdesigntechniquesareusedtoimproveefficiency.Dohertydesigns,whichuseasecondtransistor,canliftefficiencyfromthetypical15%upto30-35%inanarrowbandwidth.EnvelopeTrackingdesignsareabletoachieveefficienciesofupto60%,bymodulatingthesupplyvoltagetotheamplifierinlinewiththeenvelopeofthesignal.LinearityAnidealamplifierwouldbeatotallylineardevice,butrealamplifiersareonlylinearwithinlimits.Whenthesignaldrivetotheamplifierisincreased,theoutputalsoincreasesuntilapointisreachedwheresomepartoftheamplifierbecomessaturatedandcannotproduceanymoreoutput;thisiscalledclipping,andresultsindistortion.中北大学2010届毕业设计说明书第3页共15页Inmostamplifiersareductioningaintakesplacebeforehardclippingoccurs;theresultisacompressioneffect,which(iftheamplifierisanaudioamplifier)soundsmuchlessunpleasanttotheear.Fortheseamplifiers,the1dBcompressionpointisdefinedastheinputpower(oroutputpower)wherethegainis1dBlessthanthesmallsignalgain.Sometimesthisnonlinearityisdeliberatelydesignedintoreducetheaudibleunpleasantnessofhardclippingunderoverload.Theproblemofnonlinearityismostoftensolvedwithnegativefeedback.Linearizationisanemergentfield,andtherearemanytechniques,suchasfeedforward,predistortion,postdistortion,EER,LINC,CALLUM,cartesianfeedback,etc.,inordertoavoidtheundesiredeffectsofthenon-linearities.NoiseThisisameasureofhowmuchnoiseisintroducedintheamplificationprocess.Noiseisanundesirablebutinevitableproductoftheelectronicdevicesandcomponents,alsomuchnoiseresultsfromintentionaleconomiesofmanufactureanddesigntime.Themetricfornoiseperformanceofacircuitisnoisefigureornoisefactor.Noisefigureisacomparisonbetweentheoutputsignaltonoiseratioandthethermalnoiseoftheinputsignal.OutputdynamicrangeOutputdynamicrangeistherange,usuallygivenindB,betweenthesmallestandlargestusefuloutputlevels.Thelowestusefullevelislimitedbyoutputnoise,whilethelargestislimitedmostoftenbydistortion.Theratioofthesetwoisquotedastheamplifierdynamicrange.Moreprecisely,ifS=maximalallowedsignalpow