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输入级集成放大电路的基本组成中间级输出级偏置电路差动放大电路基本放大电路功率放大电路恒流源模拟集成基本单元电路3.2.2模拟IC中的恒流源(1)BJT的基本恒流原理i不变,ro=∞Iro+u-iΔuΔiiCuCEIBQUCEQICEQiC基本不变i=iCro≈rce固定UBE恒流源的电路ECRb+uo-Rb2Rc+UBEQ-ECRIRT1T2EC、R和T1构成镜像恒流源的参考回路IR称为参考电流(2)镜像恒流源的电路结构基本镜像恒流源ro≈rce2≈∞RERUEICBECR1UBE1=UBE2=UBE若β1=β2=βIB1=IB2=IB、IC1=IC2=ICBCRIII21)221(/212RRCIII当β1时,可得REIICRC2输出电流IC2与参考电流IR是镜像关系相对误差222CCRIII+UBEQ-接放大器roIRIC2IB2IB12IBIC1BCII22)21(2CIECRIRT1T2IC2T3IC3T4IC4TnIC(n+1)(n+1)IBIB2IB1IB3IB4IBn相对误差)1(n2.精密镜像恒流源设T1~T3的参数相同β1=β2=β3=β1UBE1=UBE2=UBE31BCRIII132ECII)221()1(2122RRCIIIECRIRT1T2+UBEQ-T3IC1IB3IE31222BCIIIC2IC1=IC2133EBIIIB2IB1232BEII1222CCII22BCII相对误差1222222CCRIII由于电路中接了共集电极管T3,对分流电流IB3的放大作用,从而使误差减小了(1+β)倍,精度提高了(1+β)倍。ro≈rce2≈∞ro)21(2CIBCII22BCRIII21RUUEIBEBECR)221(/212RRCIIIREIICRC2相对误差222CCRIIIECRIRT1T23.高输出阻抗串接镜像恒流源β1=β2=β3=β41UBE1=UBE2=UBE3=UBE4=UBET3T4+UBEQ-+UBEQ-IC1IC2IB2IB1IB2IB12IBIR22CBIIb2e2c2rce4ioRβibrce2rbe2b2c2e2e2ibrbe1rbe3rce4+uo-rooooiur)(2boii)//(24RrrbeceobececebooiRrrriiu)//()(24222ceroiR’)//(31beberrRR)()//(2242RriRrribeobeceboobececebeobeceooobececebooooiiRrrrRriRrriiiRrrriiiur)//())()//(()//()(2422242422)()//(224RrRrrbebece2'22)()1(cebeceooorRrriur4.威尔逊(Wilson)恒流源(高输出阻抗精密恒流源)RERUUEICBEBECR12232ECII设Tl~T3完全匹配IR=IC1+IB2=IC1+IC2/β(UBE1=UBE3=UBE)IC3=IE2-2IB2221CCEIII22121CCRIII222222221222CCCIII22222CCRIII相对误差221ceorrECRIRIC2IC1T1T2IC2IRIB3IC2T2T3+UBEQ-+UBEQ-IC1=IC3IC3IB3IB12IB3IE2=IE2-2IC3/β22模拟集成电路中的偏置电路,也可作为放大电路的有源负载,又可组成基本的电流传输器ECRb+uo-Rc+UBEQ-ECRIRT1T2T3IC2roECRIRT1T2ECRIRT1T2T3T4ECRIRIC2IC1T1T2IC2IC2T2T35.比例恒流源UB1=UB2=UB111RIUEBE221212RUUIRRIBEBERCTBESEUUII11expTBESEUUII22expSCTBEIIUU11lnSCTBEIIUU22ln22212lnCRTRCIIRUIRRI22212201ceberRrRRr其中,R1'=R//(R1+rbe1)ECRIRT1T2接放大器R1R2UBIE1RI222RIUEBEIE2IC2IRIE12CIIE2IC2RCIRRI212R1ECRIRT1T2接放大器R2UBIE1IE2IC26.微恒流源(Widlar恒流源)22212lnCRTRCIIRUIRRIR1=022ln2CRTCIIRUI22212201cebeberRrrRrP100恒流源主要特性对照表RCIRRI212T1+ui-+uo-ECRIRT1T2接放大器IC2ECRIRT3T2IC2IRrce2ECbeLcurRRA//2cecrR电压增益大大提高T1+ui-+uo-ECRIRT3T2有源负载共射放大器有源负载放大器从电流源分析提供大的集电极交流负载提供稳定的直流电流,稳定静态工作点+ui--EERIRT3T2R1R2T1ECRL+uo-ioroIRrce2-EELebeLeuRRrRRA//)1(//)1(beLcerRr//)1(有源负载射极跟随器2ceerR1uAoiuu作业:P1283.1P1293.4(1)它由两个完全对称的共射电路组合而成(2)电路采用正负双电源供电长尾差动放大器1.差动放大电路的特点在零输入的情况下uo1=uo2,uo=uo1-uo2=0,实现了零输入、零输出单端输入当温度T↑时RcRbRcRbRLECRem-EEui1ui2uouo1uo2uo→IE1↑和IE2↑→IEE=(IE1+IE2)↑→UE↑→UBE=(UB-UE)↓→IE1↓、IE2↓Rem能稳定静态工作电流IE双端输出Rbui1Rbui2RbRb双端输入RL+uo-RL+uo-单端输出差动放大器具有四种不同的工作状态UERem↑→稳定越好双端输入,双端输出双端输入,单端输出单端输入,双端输出单端输入,单端输出IE1IE2IEE当ui1与ui2大小相同但极性相反时,即ui1=-ui2时,称为差模信号。记做uid当双端输入时当ui1与ui2大小和极性都相同时,称为共模信号,记做uic,即ui1=ui2=uic。2.差模信号与共模信号RcRcRLECRem-EEui1RbRbui2uouo1uo2UEuicRcRcRLECRem-EEui1RbRbui2uouo1uo2UEui1RbRbui2uididu21idu21Cduuu000121Cduuu000221对输出端来说,如果单端输出的信号分别为uo1和uo2共模信号:2121iiiCuuu差模信号:uid=ui1–ui2iCidiiCidiuuuuuu212121ddddduuuuuuu0200100201021210201021uuuCIC1=IC2=IC,IE1=IE2=IE,IB1=IB2=IBemEemEEEERIRIU12emERI21EEEEEIIII2121RcRcRLECRem-EEui1RbRbui2uouo1uo2UE3.静态工作点的估算ui1=ui2=0电路和元件值的对称性IBRb+UBE+2Rem(1+β)IB=EE在工程中,一般由于Rb较小,IB更小,在忽略Rb上的静态电压时UCE1=UCE2=UC-UEIB1IB2IE1IE2IC1IC2IEEIB1RcECIC1Rb-EE2RememR2IE1发射结回路的方程IBRb+UBE+2RemIE=EEbemBEEBRRUEI)1(2emEBREI2BCIIUCE1emEemERERE22=EC-ICRc-(-0.7V)=EC-ICRc+0.7VUE≈-0.7VUC=EC-ICRc-IC1(Rc+2Rem)非电压偏置电路分析步骤?UCE1=UCE2≈EC–(-EEE)→IC1IC2↓RcRcRLECRem-EEui1RbRbui2uouo1uo2T2T1URem↑→URem↑当温度T↑时→IE1↑和IE2↑恒流源偏置的差动放大器→IEE=(IE1+IE2)↑→UE↑→UBE=(UB-UE)↓→IB1↓、IB2↓→IE1↓、IE2↓能稳定静态工作电流IEIB1IB2IE1IE2IE1IE2IEE但Rem↑Rem↑,零点漂移↓电路性能越好→Au↓IC1IC2Q饱和区截止区iCuBEQ在集成电路中Rem的增加还受限于集成工艺和EE的取值。ro代替RemIro-EE-EERIRT4T3R4R3采用比例电流镜作为射极偏置的恒流源差动放大器恒流源偏置的差动放大器的静态工作电流应该以偏置恒流源入手去求解IRIE44ERIIUCEUBE4RRUEIBEERIC3RCIRRI343IC1IC2RCCQIRRII3432121ro3334433))//(1(cebebeemrRrrRRRR希望:能稳定静态工作点,交流等效电阻很大,直流压降不太大的器件代替Remidu21idu21ECRcRcRLRem-EEuouo1uo2UERbRbuid5.差放的性能指标(1)差模电压增益Aud当输入差模信号uid时,输出电压称为差模输出电压uodidoduduuAAud又可分为双端输出Aud(双)或单端输出Aud(单)icocucuuARLuodRLRid(2)差模输入电阻RididididiuR(3)共模电压增益Auc信号差模输入时,由两输入端之间视入的输入电阻即Rid当输入共模信号uic时,输出电压称为共模输出电压uoc,则共模电压增益为icocucuuA(4)共模输入电阻RiciciciciuRRic其实就是将差放两输入端口并联后视入的输入电阻(5)共模抑制比KCMRucudCMRAAKKCMR越大,差放放大差模信号和抑制共模信号的能力就越强RicRcRcRLRem-EEuicRbRbuouo1uo2UE差动放大器的大信号传输特性IEEuid1/2IEEiC24UT2UTiCiC1RcRcRLECui1RbRbui2uouo1uo2T2T1I-EE1/2IEEro=Rem大信号差模传输特性曲线(1)当静态时,ui1=ui2=0,即uid=0EECCCCIIIii212121IC1IC2IEERbui2ui1RbEECCIii21iC1iC2iE1iE2uo1=-uo2RcRcRLECui1RbRbui2uouo1uo2T2T1IEE-EEro=Rem3.3.3差动放大器的微变等效分析ie11.低频单纯差模特性idu21idu21(1)差模电压增益①双端输入、双端输出差模电压增益2121iiooidoduduuuuuuA1111122uioioAuuuuuo1uo2ie2差模输入发射极对称中心交流接地LR21LR21负载中心交流接地bceRc+ui1-RbLR21uo1Rb+ui1-βibrbebceeibioRcic+uo-LR21LcoRiu111iouduuALcLRRR21//bebbirRiu1LbRibebbrRibebLudrRRALcLRRR21//RcRcRLECui1RbRbui2uouo1uo2T2T1IEE-EEro=RemLR21LR21ReReebebLioudRrRRuuA)1(11bebLioudrRRuuA11eR)1
本文标题:恒流源及差动放大器
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