模拟电子及技术基础-5b-放大器的频率响应

5b-15.2.3共射放大器的频率响应RB1RCC1C2RB2CERERLiURssU+-oUrb'eRCoUbIcIebmUgRBC1RssU+-iURLC2CECb'eCb'cRErbb'RB=RB1//RB25b-2rb'eRCoUbIcIebmUgRBC1RssU+-iURLC2CECb'eCb'cRErbb'rb'eRCoUbIcIebmUgRBRssU+-iURLC2CECb'eCb'cRErbb'rb'eRCoUbIcIebmUgRBRssU+-iURLCECb'eCb'cRErbb'rb'eRCoUbIcIebmUgRBRssU+-iURLCb'eCb'cRErbb'一、中频区C1、C2、CE视为短路，Cb'e、Cb'c视为开路iRiebbbebebUrrrU)//(ebbbBrrRoULCLRRRLebmRUg//rb'eRCoUbIcIebmUgRBRssU+-iURLCb'eCb'crbb'rb'eRCoUbIcIebmUgRBRssU+-iURLCb'crbb'rb'eRCoUbIcIebmUgRBRssU+-iURLrbb'5b-30ebmrgoUiebbbebLmUrrrRgiouIUUAebbbebLmrrrRguIsiiuIsARRRAebbbBrrRebbbirrRebbbebLmsebbbebbbrrrRgRrrrrsebbbLebmRrrRrgsbeL0RrR5b-4二、高频区C1、C2、CE视为短路，Cb'e、Cb'c保留rb'eRCoUbIcIebmUgRBC1RssU+-iURLC2CECb'eCb'cRErbb'rb'eRCoUbIcIebmUgRBRssU+-iURLC2CECb'eCb'cRErbb'rb'eRCoUbIcIebmUgRBRssU+-iURLCECb'eCb'cRErbb'rb'eRCoUbIcIebmUgRBRssU+-iURLCb'eCb'crbb'rb'eRCoUbIcIebmUgRBRssU+-iURLCb'eCb'crbb'ebU5b-5密勒定理Z1I2U1U12UUK2IZ11I2U1U12UUK2IZ2ZK11Z1Z1KKZ2rb'eRCoUbIcIebmUgRBRssU+-iURLCb'eCb'crbb'ebUcbCj1Z5b-612UUKeboUUebLebmURUgLmRgZK11Z1cbLmCj1Rg11cbLmCRg1j1)(1MCj1cbLm1MCRg1C)(1K2Z1KKZcbCj1ZZcbCj1cb2MCC5b-7rb'eRCoUbIcIebmUgRBRssU+-iURLCb'erbb'ebUCM1CM21MebiCCCCM2很小，可以忽略R'L=RL//RCrb'eoUbIcIebmUgRBRssU+-rbb'ebUCiiURCRLrb'eoUbIcIebmUgRBRssU+-rbb'ebUCiiUR'LRBRSrb'eoUbIcIebmUgRssU+-rbb'ebUCiR'L5b-8oUebmUgR'ssU+-ebUCiR'LR's=rb'e//(rb'b+Rs)sebbbsebsUrrRrUsisiebUCjRCjU11sisUCRj11sebbbsebisUrrRrCRj115b-9ebLmoURgUsisebbbsLebmUCRj11rrRRrgsisuIsUCRjA11sousUUjA)(isuIsCRjA1HuIsjA1isCR1H令isHCRf212HHuIsffj1A5b-10|A(jω)|dBff0fH-90o-45o-20dB/十倍频程-45o/十倍频程10fH0.1fH)(juIsA20lg21)(HuIsusffAjA)arctan()(Hffj5b-11oUR'ssU+-ebUCiCL-+负载电容和分布电容的影响oUebmUgR'ssU+-ebUCiR'LCLLebmRUgR'L5b-12oULebmRUgR'ssU+-ebUCiR'LCL-+sebbbsebisUrrRrCRj11ebUoULLLebLmCj1RCj1URgsLLLebbbsebLmisUCj1RCj1rrRrRgCRj115b-13sLLisuIsUCRj1CRj1A))((oUisCR1H1令LLCR1H2sousUUjA)())((LLisuIsCRj1CRj1A2H1HuIsusj1j1AjA)(5b-14-20dB/十倍频程-45o/十倍频程|A(jω)|dBωωH1ωH2uIsA20lg0.1ωH1-40dB/十倍频程ω0-90o-45o)(jωH1ωH20.1ωH1-180o-90o/十倍频程22H21HuIsus11AjA)()arctan()arctan()(2H1Hj5b-15在二阶低通系统中，如果一个极点远离另一个极点，那么频率低的极点对整体的频率响应起决定作用，称之为主极点。例如，若ωH2ωH1，则电路的上限频率近似等于主极点频率fH122H21HH111