Chapter 9 output stages andpower amplifiersIntroduction9.1 Classification of output stages9.2 Class A output stage9.3 Class B output stage9.4 Class AB output stage9.5 Biasing the class AB circuitMicroelectronicCircuits
Microelectronic Circuits Chapter 9 output stages and power amplifiers Introduction 9.1 Classification of output stages 9.2 Class A output stage 9.3 Class B output stage 9.4 Class AB output stage 9.5 Biasing the class AB circuit
PowerAmplifier Small-signal approximation and modelseither are not applicable or must be usedwith care. THD (total harmonic distortion)Deliver the power to the load in efficientmanner. Ex. To provide the amplifier with alow output resistance so that it can deliverthe output signal to the load without loss ofgain. Power dissipation is as low as possibleMicroelectronic Circuits
Microelectronic Circuits Power Amplifier ⚫ Small-signal approximation and models either are not applicable or must be used with care. THD (total harmonic distortion) ⚫ Deliver the power to the load in efficient manner. Ex. To provide the amplifier with a low output resistance so that it can deliver the output signal to the load without loss of gain. ⚫ Power dissipation is as low as possible
Classificationof PowerAmplifier Power amplifiers are classified accordingto the collector current waveform thatresults when an input signal is applied Conducting angleMicroelectronicCircuits
Microelectronic Circuits Classification of Power Amplifier ⚫ Power amplifiers are classified according to the collector current waveform that results when an input signal is applied. ⚫ Conducting angle
Classification of Power Amplifier-0-3元2元2T7T3元wtTwt(b)(a)conduction angle = 180°conduction angle = 360°Collector current waveforms for transistorsoperating in (a) class A, (b) class BMicroelectronicCircuits
Microelectronic Circuits Classification of Power Amplifier C c I I ˆ o conduction angle = 360 Collector current waveforms for transistors operating in (a) class A, (b) class B o conduction angle =180
Classification of Power Amplifieric02元3元2元3元Twtwt(c)(d)conduction angle <180°180°< conduction angle < 360°class ABclass CMicroelectronic Circuits
Microelectronic Circuits Classification of Power Amplifier o o 180 conduction angle 360 class AB class C o conduction angle 180
CEamplifier is notproper for usingas apoweramplifieric直流负载线交流负载线BOuy0OUcEQUcEo+IcoR' Vcc ucE(b)aDCsupplypower:IcQVcc,theareaofABCOco(Rc // R,)/ /2Rcpower:IcQURc,theareaofQBCDCollectordissipationpower:lcUcEQ,theareaofAQDOPomLoad power:MicroelectronicCircuits
Microelectronic Circuits CE amplifier is not proper for using as a power amplifier ( ) 2 1 2 ( // )/ 2 ' ' 2 ' L CQ CQ L CQ om CQ C L R I I R I P I R R = = DC supply power: ICQVcc , the area of ABCO Rc power: ICQURc， the area of QBCD Collector dissipation power: ICQUCEQ， the area of AQDO Load power:
Class A Output Stage+Vcc。= V -VBEIQU1o+Vomax = Vcc -VcE1satUBEItElOO= -IR,VominRRorOQ文Vomin =-Vcc +VVCE2satVccMicroelectronic Circuits
Microelectronic Circuits Class A Output Stage o CC CE sat o L o CC CE sat o I BE v V V v IR v V V v v v min 2 min max 1 1 or = − + = − = − = −
UoA(Vce-VcEIsat)0UVBEI-IRL(-Vcc+VcE2sat)Figure14.3 Transfer characteristic of the emitter follower.This linearcharacteristic is obtained by neglecting the change in VBEi with iz. ThemaximumpositiveoutputisdeterminedbythesaturationofOi.Inthenegative direction, the limit of the linear region is determined either by Qturning off or by Q2 saturating, depending on the values of I and Rz.MicroelectronicCircuits
Microelectronic Circuits Figure 14.3 Transfer characteristic of the emitter follower. This linear characteristic is obtained by neglecting the change in vBE1 with iL . The maximum positive output is determined by the saturation of Q1 . In the negative direction, the limit of the linear region is determined either by Q1 turning off or by Q2 saturating, depending on the values of I and RL
Vo4UCEIA2VccVccC00V(a)(b)PDTici21Vccl10(c)(d)Figure 14.4 Maximum signal waveforms in the class A output stage of Fig. 14.2underthe condition I =Vcc/R,or, equivalently,R, = Vcc/I.MicroelectronicCircuits
Microelectronic Circuits Figure 14.4 Maximum signal waveforms in the class A output stage of Fig. 14.2 under the condition I = VCC /RL or, equivalently, RL = VCC /I
Class AOutput Stagepower dissipatio n : Pp1 = Vce1 :icpower conversion efficiency :load power(PL)n =supply power(Ps)1 VPLPs = 2Vccl2 RLV2Iowhen V。 = Vcc = IR,,n = 25%n4.IR,VccMicroelectronic Circuits
Microelectronic Circuits Class A Output Stage when ˆ , 25% ˆ 4 1 2 ˆ 2 1 supply power(P ) load power(P ) power conversion efficiency : power dissipatio n : 2 2 S L 1 1 1 = = = = = = = = o CC L L CC o S CC L o L D CE C V V IR IR V V P V I R V P p v i