第二模块：集成运放基本电路

第十二讲理想运算放大器1理想运放的概念理想运放的技术参数应满足下列条件开环差模电压增益Aod=∞差模输入电阻Rid=∞输出电阻Rod=0共模抑制比KCMR=∞输入偏置电流IIB=0开环带宽KCMR=∞Introduction-Basics•BasicConfigurationofOpamps–Threeterminals(2inputsand1output)–Bipolarpowersupply–Referencegroundisthe“powersupplyground”BasicConfigurationofOpampsCharacteristicsofOpamps•Outputvoltageisproportionaltothedifferencebetweenthetwoinputs.•Theopen-loopgainAisveryverylarge,andcanbeconsideredasinfiniteCharacteristicsofOpamps•Thetwoinputterminalsare“virtuallyopen”.•Thatis,theinputimpedanceoftheterminalsareveryverybig(infinite).•Theoutputimpedanceisveryverysmallandcanbeconsideredaszero.CharacteristicsofOpamps•Wewouldlikeopampsto–amplifytheamplitudeofinputsignalbyafactorofanyarbitraryvalue;•However,theopen-loopgainisfixedandtoolarge,thereforesomeexternalcircuitsshouldbeusedtomakethesystemclose-loop;•Therearetwoconfigurationsintermsofusingtheexternalcircuits:–Non-invertingand–Inverting.•Avirtualshortcircuitmeansthatwhatevervoltageisat2willautomaticallyappearat1becauseoftheinfinitegainA.Butterminal2happenstobeconnectedtoground;thusv1=0andv2=0.WespeakofterminalIasbeingavirtualground—thatis,havingzerovoltagebutnotphysicallyconnectedtoground.(3)理想运算放大器的等效模型理想运算放大器的开环电压增益Aod=∞uuouiuodoidAuu∞0uuuiduu虚短差模输入电阻Rid=∞idididRui∞iidi+i-iiiid00ii虚断Ⅰ：理想运放输出为有限值uo0IIuuII：理想运放输出电阻Rod=0i-运放电路简化分析的要点输出端相当于理想电压源0ii虚断uu虚短idoduAuuouiduR’运放构成的两种基本负反馈电路1反相放大器(D01fanxiang.ms7)uoRfuuiii+ifi-ui平衡电阻R’=Rf//R1何种反馈？电压并联深度负反馈②电路性能分析：①电路结构：由虚断：由虚短：0iiffiiiiifoiRuuRuu10ii0uuu0u00ifouRRu1R1“虚地”0uu“虚地”是反相放大器的特点ifouRRu1反相比例运算放大器完成比例运算Rif输入电阻iiifiuR11RiRiii1RRuuAfiouf电压增益R1ui2同相放大器(D02tongxiang.ms7)①电路结构：uoRfuui1i+ifi-R’平衡电阻R’=Rf//R1何种反馈？电压串联深度负反馈②电路性能分析：由虚断：0ii由虚短：iuuufii1foRuuRu1iffouRRuRRu1111电压增益11RRuuAfiouf输入电阻iiifiuR0iu输出电阻0ofR电压串联深度负反馈uRRufo11R1uiuoRfuuR’ififouRRuRRRu1111iouu电压跟随器一、电压比较器基本概念电压比较器是集成运放的另一类基本应用电路，作用是对两个输入电压进行比较，比较的结果及输出只有两种状态，既高电平和低电平当uiuREFuouiuREFuo=uoH→“1”当uiuREFuo=uoL→“0”模拟与数字电路的接口电路一位模数转换电路电压比较器D03(dianyanbijiaoqi).ms72集成运算放大器的非线性应用1理想运放工作在非线性区的特点1)开关特性非线性区的理想运放内某些三极管饱和或截止，使运放工作在开关状态uouiuREFuu输出电压的值只有两种可能：或等于正向饱和值；或等于负向饱和值。OHOUu;uuOLOUu;uuuu时，发生状态的转换。此时的输入电压称为“阀值电压”或“门限电压”，用UTH表示。UOLUOH非线性区非线性区uOu+-u-0一般运放输出端不接限幅的情况下，输出电压的高、低电平在数值上分别与运放的正负电源电压值接近uouiuREFuuVCC－VCC理想特性线性区uo=Aoduid=Aod(u+-u-)理想运放工作在非线性区时的特点2)理想运放的输入电流等于零——“虚断”理想运放rid=，0iiuouiuREFVCC－VCCi+i-3)理想运放工作在非线性区时不引入负反馈，一般工作在开环状态只在判断临界状态时才适用“虚断”、“虚短”UOLUOH非线性区非线性区uOu+-u-0线性区鉴别不灵敏区iu0uREFUOHUOLUU4)鉴别灵敏度uouiuREFVCC－VCCAud=∞由于实际的运放Aud≠∞ui在UREF附近的一个很小范围内存在一个鉴别不灵敏区，在该范围内输出状态即非UOH又非UOL，故无法实现对输入电平大小进行判别。一般Aud↑→△U↓→鉴别灵敏度↑2电压比较器1)反向电压比较器uiURuouu基准参考电压uu时，发生状态的转换。此时的输入电压ui称为“阀值电压”或“门限电压”，用UTH表示。UTH＝UR0uiuOUoLUoHUR输入电压00uiuO2)过零比较器（零电平检测器）-+uiuORR'根据虚断：0ii;0u;uui:0uiuuOLOUu:0uiuuOHOUuUOLUOHROZUZU阀值电压：0UTHuituot-+uiuORR'RO过零比较器的输入、输出波形003集成运算放大器的线性应用加法运算电路反相加法运算电路同相加法运算电路差动加法运算电路uuou1反相加法运算电路R’uoii1i+ifi-ui1R1RfR2ui2R3ui3平衡电阻R’=Rf//R1//R2//R3由虚断：0iiii2ii3fiiiiiii32111Ruui22Ruui33RuuifoRuu由虚短：uu0由虚地：0000332211ifififouRRuRRuRRu若R1＝R2＝R3＝R321iiifouuuRRu反相加法运算电路优点（1）改变R1R2R3可调相加比例参数（2）由于叠加点为虚地，输入信号之间满足线性叠加定理，互不影响。2同相加法运算电路电路平衡Rf//R=R’//R1//R2//R3由虚断：0iiii3R2ui2R3ui3ii2R1ui1uoRfuui+ifi-Rii1R’fiifoRuuRu1iR’'321Riiiiiii11Ruui22Ruui33RuuiRu由虚短：uu消除u+和u-得uo和ui关系式3322111ipipipfouRRuRRuRRRRuRRRRRp//////321若R1＝R2＝R332111iiifpouuuRRRRuifouRRu11Rui1uoRfuui1i+ifi-R1同相加法运算电路缺点输入信号之间相互影响321////RRRRpiuRRufo11R1uiuoRfuui1i+ifi-R’ifouRRu11uRRufo11由虚断：0ii'321Riiiiiii11Ruui22Ruui33RuuiRu332211ipipipuRRuRRuRRuii3R2ui2R3ui3ii2R1ui1uoRfuui+ifi-Rii1R’iiR’3322111ipipipfouRRuRRuRRRRuii3R2ui2R3ui3ii2R1ui1uoRfuui+ifi-Rii1R’iR’i3322111ipipipfouRRuRRuRRRRuRRRRRRp//////321RRRRf//332211iiifouRRuRRuRRRRRufRfRR1332211ifififouRRuRRuRRu7.4.2差动放大器ui2R2R1ui1uoRfuui+ifi-ii1R’ii2平衡电阻R’//R2=Rf//R1由虚断：0iiffiiiiifoiRuuRuu1RRRuui22由虚短：uu111212iffiouRRRRRRRRuu一般要求：R’=RfR2=R1Rf121iifouuRRu差模电压增益121RRuuuAfiiouf112RRuuuAfiioufui2R2R1ui1uoRfuui+ifi-ii1R’ii2uRRufo1111RRufo22iuRRR11ifuRR111212iffiouRRRRRRRRuuR3R1u1uoR’R/2R’R/2u2R2R4例1求输出电压表达式uo2uo1同相放大器输出1121uRRuo同相放大器输出2221uRRuo差动放大器输出1121434212ooouRRRRRRRRuu11221434212121uRRRRuRRRRRRRRuo例2求输出电压表达式R’uoR2uui1i+i2i-uiR1R4R3i4i3由虚断：0ii221iiii21RuuRuuMiＭ432iii4320RuuRuRuuOMMM由“虚地”0u1342142RuRRRRuRRuiiouoR4ui2R1R1ui1uui+i-R2R2R3R5例3求输出电压表达式i3ii1ii2由虚断：0ii331iiiiuo12111RuuRuuoi2122RRRuui由虚短：uu由反相放大器：oouRRu431213142iiouuRRRRu例4求输出电压表达式ui4R’uoii1i+ii4i-ui1R1R2ui2R3ui3ii2ii3KuXuYYXuo1R4由虚断：0ii4321iiiiiiii由“虚地”0u41332211RuuRuuRuuRuuoiii