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1、SelecttheamplifierfrequentlyFirst,operationprincipleandonepairoffrequenciescharacteristicofTelectricbridgeSelectamplifierfrequently,itamongmanykindsofinputsignaloffrequency,onefrequencysignalneededtochooseamplifyanddownandpursueshownblock-diagramcancommitandselectandamplifycircuitfrequently,amongth
2、emsquareframeKenlargesthecircuitbasically,squareframeFselectsthenegativefeedbacknetworkfrequently,soselectamplifierwhetheronehaveandselectactonfrequentlydefeatbythefeedbackcircuitinfactfrequently.ClosingringbenefitofcircuitisKF=K/(1+FK)Inthetype:K=UO/UIholdstheringtogainF=UF/UOfeedbackscoefficientG
3、enerallyselectsthenetworkfrequentlyandrealizesselectingonewithRC,pursue(b)toshowsandfeedbackscoefficientFtovarywithfrequencyfoneinthecurve(frequencycharacteristic),actasf=Fohour,thenF=0.Thereasonwhy,forfrequencyfoofresonance,donothavenegativefeedbacktoenlargethecircuit,soKF=K,theoutputoftheamplifie
4、risthelargestinvoltageatthismoment.Asfrequencyisfarawayfromfo,Fincreasesrapidly,correspondingKFdecaystozeroquicklytoo,seethattherefore,theoutputwhichdeviatesfromotheruselessfrequencythatfoclicksisverysmallandverysmallinvoltagetohaveFig.C,asforthespeedofdecayofKF,theonesthatmainlydependonfeedbacking
5、thenetworkselectthecharacteristicfrequently,takepairsofTelectricRCofbridgeselectnetworkfrequently,itinnotusingactually,amostfrequentlyusedonehavetwokindsusually:Waitforonepursueandshowasabove,supposepowerhinderRSasymmetrypairsofTelectricbridge=0,loadRL=00,calculateformulaeasfollows:Anglefrequencyωo
6、fresonanceO=1/RC-------------------------AtypeFiguresofmeritQ=[1/2(1+a)]=[△fooffo/2.7]---------2typesThemodelwhotransmitscoefficient(feedbackscoefficient),ananglearerespectively:3typesφ=arctg1/QYInthetype:Y=σ-(1/σ)morebroadthandetuningforcoefficientσ=F/foistherelativedetuningcoefficient------------
7、-----------4types2△fo.7mainfactsarehalfthebandwidththattheworkisclickedCanbeseenby2types:Toregularresonancefrequencyfo,thebiggerQis,thenarrowertheopenfrequencybandis;ThesmallerQisonthecontrary,thewidertheop
