低功耗高增益宽带放大器外文翻译.docx

低功耗高增益宽带放大器外文翻译.docx

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低功耗高增益宽带放大器外文翻译

ABroadbandAmplifierwithHugeGain-bandwidthProductandLowPowerConsumption

Gain

Thegainofanamplifieristheratioofoutputtoinputpoweroramplitude,andisusuallymeasuredindecibels.（Whenmeasuredindecibelsitislogarithmicallyrelatedtothepowerratio:

G（dB）=10log（Pout/（Pin））.RFamplifiersareoftenspecifiedintermsofthemaximumpowergainobtainable,whilethevoltagegainofaudioamplifiersandinstrumentationamplifierswillbemoreoftenspecified（sincetheamplifier'sinputimpedancewilloftenbemuchhigherthanthesourceimpedance,andtheloadimpedancehigherthantheamplifier'soutputimpedance）.

Example:

anaudioamplifierwithagaingivenas20 dBwillhaveavoltagegainoften（butapowergainof100wouldonlyoccurintheunlikelyeventtheinputandoutputimpedanceswereidentical）.

Bandwidth

Thebandwidthofanamplifieristherangeoffrequenciesforwhichtheamplifiergives"satisfactoryperformance".Thedefinitionof"satisfactoryperformance"maybedifferentfordifferentapplications.However,acommonandwell-acceptedmetricisthehalfpowerpoints（i.e.frequencywherethepowergoesdownbyhalfitspeakvalue）ontheoutputvs.frequencycurve.Thereforebandwidthcanbedefinedasthedifferencebetweenthelowerandupperhalfpowerpoints.Thisisthereforealsoknownasthe−3dBbandwidth.Bandwidths（otherwisecalled"frequencyresponses"）forotherresponsetolerancesaresometimesquoted（−1dB,−6dBetc.）or"plusorminus1dB"（roughlythesoundleveldifferencepeopleusuallycandetect）.

Thegainofagoodqualityfull-rangeaudioamplifierwillbeessentiallyflatbetween20 Hztoabout20 kHz（therangeofnormalhumanhearing）.Inultrahighfidelityamplifierdesign,theamp'sfrequencyresponseshouldextendconsiderablybeyondthis（oneormoreoctaveseitherside）andmighthave−3dBpoints<10and>65 kHz.Professionaltouringamplifiersoftenhaveinputand/oroutputfilteringtosharplylimitfrequencyresponsebeyond20 Hz-20 kHz;toomuchoftheamplifier'spotentialoutputpowerwouldotherwisebewastedoninfrasonicandultrasonicfrequencies,andthedangerofAMradiointerferencewouldincrease.Modernswitchingamplifiersneedsteeplowpassfilteringattheoutputtogetridofhighfrequencyswitchingnoiseandharmonics.

Efficiency

Efficiencyisameasureofhowmuchofthepowersourceisusefullyappliedtotheamplifier'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.

Linearity

Anidealamplifierwouldbeatotallylineardevice,butrealamplifiersareonlylinearwithinlimits.

Whenthesignaldrivetotheamplifierisincreased,theoutputalsoincreasesuntilapointisreachedwheresomepartoftheamplifierbecomessaturatedandcannotproduceanymoreoutput;thisiscalledclipping,andresultsindistortion.

Inmostamplifiersareductioningaintakesplacebeforehardclippingoccurs;theresultisacompressioneffect,which（iftheamplifierisanaudioamplifier）soundsmuchlessunpleasanttotheear.Fortheseamplifiers,the1dBcompressionpointisdefinedastheinputpower（oroutputpower）wherethegainis1dBlessthanthesmallsignalgain.Sometimesthisnonlinearityisdeliberatelydesignedintoreducetheaudibleunpleasantnessofhardclippingunderoverload.

Theproblemofnonlinearityismostoftensolvedwithnegativefeedback.

Linearizationisanemergentfield,andtherearemanytechniques,suchasfeedforward,predistortion,postdistortion,EER,LINC,CALLUM,cartesianfeedback,etc.,inordertoavoidtheundesiredeffectsofthenon-linearities.

Noise

Thisisameasureofhowmuchnoiseisintroducedintheamplificationprocess.Noiseisanundesirablebutinevitableproductoftheelectronicdevicesandcomponents,alsomuchnoiseresultsfromintentionaleconomiesofmanufactureanddesigntime.Themetricfornoiseperformanceofacircuitisnoisefigureornoisefactor.Noisefigureisacomparisonbetweentheoutputsignaltonoiseratioandthethermalnoiseoftheinputsignal.

Outputdynamicrange

Outputdynamicrangeistherange,usuallygivenindB,betweenthesmallestandlargestusefuloutputlevels.Thelowestusefullevelislimitedbyoutputnoise,whilethelargestislimitedmostoftenbydistortion.Theratioofthesetwoisquotedastheamplifierdynamicrange.Moreprecisely,ifS=maximalallowedsignalpowerandN=noisepower,thedynamicrangeDRisDR=（S+N）/N.[1]

Inmanyswitchedmodeamplifiers,dynamicrangeislimitedbytheminimumoutputstepsize.

Slewrate

Slewrateisthemaximumrateofchangeoftheoutput,usuallyquotedinvoltspersecond（ormicrosecond）.Manyamplifiersareultimatelyslewratelimited（typicallybytheimpedanceofadrivecurrenthavingtoovercomecapacitiveeffectsatsomepointinthecircuit）,whichsometimeslimitsthefullpowerbandwidthtofrequencieswellbelowtheamplifier'ssmall-signalfrequencyresponse.

Risetime

Therisetime,tr,ofanamplifieristhetimetakenfortheoutputtochangefrom10%to90%ofitsfinallevelwhendrivenbyastepinput.ForaGaussianresponsesystem（orasimpleRCrolloff）,therisetimeisapproximatedby:

tr*BW=0.35,wheretrisrisetimeinsecondsandBWisbandwidthinHz.

Settlingtimeandringing

Thetimetakenfortheoutputtosettletowithinacertainpercentageofthefinalvalue（forinstance0.1%）iscalledthesettlingtime,andisusuallyspecifiedforoscilloscopeverticalamplifiersandhighaccuracymeasurementsystems.Ringingreferstoanoutputvariationthatcyclesaboveandbelowanamplifier'sfinalvalueandleadstoadelayinreachingastableoutput.Ringingistheresultofovershootcausedbyanunderdampedcircuit.

Overshoot

Inresponsetoastepinput,theovershootistheamounttheoutputexceedsitsfinal,steady-statevalue.

Stability

Stabilityisanissueinallamplifierswithfeedback,whetherthatfeedbackisaddedintentionallyorresultsunintentionally.Itisespeciallyanissuewhenappliedovermultipleamplifyingstages.

StabilityisamajorconcerninRFandmicrowaveamplifiers.Thedegreeofanamplifier'sstabilitycanbequantifiedbyaso-calledstabilityfactor.Thereareseveraldifferentstabilityfactors,suchastheSternstabilityfactorandtheLinvilstabilityfactor,whichspecifyaconditionthatmustbemetfortheabsolutestabilityofanamplifierintermsofitstwo-portparameters.

Electronicamplifiers

Mainarticle:

Electronicamplifier

Therearemanytypesofelectronicamplifiers,commonlyusedinradioandtelevisiontransmittersandreceivers,high-fidelity（"hi-fi"）stereoequipment,microcomputersandotherelectronicdigitalequipment,andguitarandotherinstrumentamplifiers.Criticalcomponentsincludeactivedevices,suchasvacuumtubesortransistors.Abriefintroductiontothemanytypesofelectronicamplifierfollows.

Poweramplifier

Theterm"poweramplifier"isarelativetermwithrespecttotheamountofpowerdeliveredtotheloadand/orsourcedbythesupplycircuit.Ingeneralapoweramplifierisdesignatedasthelastamplifierinatransmissionchain（theoutputstage）andistheamplifierstagethattypicallyrequiresmostattentiontopowerefficiency.Efficiencyconsiderationsleadtovariousclassesofpoweramplifier:

seepoweramplifierclasses.

Vacuumtube（valve）amplifiers

Mainarticle:

Valveamplifier

Theglowfromfour"ElectroHarmonixKT88"brandpowertubeslightsuptheinsideofaTraynorYBA-200guitaramplifier

AccordingtoSymons,whilesemiconductoramplifiershavelargelydisplacedvalveamplifiersforlowpowerapplications,valveamplifiersaremuchmorecosteffectiveinhighpowerapplicationssuchas"radar,countermeasuresequipment,orcommunicationsequipment"（p. 56）.Manymicrowaveamplifiersarespeciallydesignedvalves,suchastheklystron,gyrotron,travelingwavetube,andcrossed-fieldamplifier,andthesemicrowavevalvesprovidemuchgreatersingle-devicepoweroutputatmicrowavefrequenciesthansolid-statedevices（p. 59）.[2]

Valves/tubeamplifiersalsohavenicheusesinotherareas,suchas

inrussianmilitaryaircraft,fortheirEMPtolerance

nicheaudiofortheirsoundqualities

Transistoramplifiers

Mainarticles:

Transistor,Bipolarjunctiontransistor,Audioamplifier,andMOSFET

Theessentialroleofthisactiveelementisto