Springer.Electronic.Circuits.Handbook.for.Design.and.Application.(Springer.U.Tietze)

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1、Chapter27:High-FrequencyAmplifiersToday,inthehigh-andintermediate-frequencyassembliesoftelecommunicationsystems,amplifierscomposedofdiscretetransistorsarestillusedinadditiontomodernintegratedamplifiers.Thisisparticularlythecaseinhigh-frequencypoweramplifiersemployedintransmi

2、tters.Inlow-frequencyassemblies,ontheotherhand,onlyintegratedamplifiersareused.Theuseofdiscretetransistorsisduetothestatusquoofsemiconductortechnol-ogy.Thedevelopmentofnewsemiconductorprocesseswithhighertransitfrequenciesissoonfollowedbytheproductionofdiscretetransistors,

3、buttheproductionofintegratedcircuitsonthebasisofanewprocessdoesnotusuallyoccuruntilsomeyearslater.Fur-thermore,theproductionofdiscretetransistorswithparticularlyhightransitfrequenciesoftenmakesuseofmaterialsorprocesseswhicharenot(ornotyet)suitablefortheproduc-tionofinteg

4、ratedcircuitsinthescopeofproductionengineeringorforeconomicreasons.Thehighgrowthrateinradiocommunicationsystemshas,however,boostedthedevel-opmentofsemiconductorprocessesforhigh-frequencyapplications.Integratedcircuitsonthebasisofcompoundsemiconductorssuchasgallium-arseni

5、de(GaAs)orsilicon-germanium(SiGe)canbeuseduptotheGHzrange.Forapplicationsuptoapproximately3GHzbipolartransistorsaremainlyused,which,inthecaseofGaAsorSiGedesigns,areknownashetero-junctionbipolartransistors(HBT).Above3GHz,gallium-arsenidejunctionFETsormetal-semiconductorfie

6、ldeffecttransistors(MESFETs)areused.1Thetransitfrequenciesrangebetween50...100GHz.27.1IntegratedHigh-FrequencyAmplifiersInprinciple,integratedhigh-frequencyamplifiersusethesamecircuitryaslow-frequencyoroperationalamplifiers.Atypicalamplifierconsistsofadifferentialamplifieruse

7、dasavoltageamplifierandcommon-collectorcircuitsusedascurrentamplifiersorimpedanceconverters(seeFig.27.1a).Thedifferentialamplifierisoftendesignedasacascodedif-ferentialamplifiertoreduceitsreversetransmissionanditsinputcapacitance(noMillereffect).SuchcircuitsaredescribedinCha

8、p.4,Sect.4.1.Sincethetransitfrequencyofhigh-frequencytransistors(fT≈50...100GHz)isapproximately100times