Chapter 6 Differential and+日Multistage Amplifiers1896Introduction6.1 The BJT differntial pair6.2Small-signal operationof theBJTdifferential amplifie6.3Othernonidealcharacteristicsofthedifferentialamplifier6.4MOS diffenrential amplifiers6.5Biasing in intergrated circuits6.6TheBJT differential amplifierwithactiveload6.9MultistageamplifiersMicroelectronicCircuits
Microelectronic Circuits Chapter 6 Differential and Multistage Amplifiers Introduction 6.1 The BJT differntial pair 6.2 Small-signal operation of the BJT differential amplifier 6.3 Other nonideal characteristics of the differential amplifier 6.4 MOS diffenrential amplifiers 6.5 Biasing in intergrated circuits 6.6 The BJT differential amplifier with active load 6.9 Multistage amplifiers
Introduction> The differential amplifier(pair) configuration is themost widely usedbuilding block in analogIC design.VClUC?BJT differential amplifieris the basis of a very-OOhigh-speedlogic circuitfamily, called emitter-UBUB2Ecoupled logic (ECL),Why?Microelectronic Circuits
Microelectronic Circuits Introduction ➢ The differential amplifier (pair) configuration is the most widely used building block in analog IC design. ➢ BJT differential amplifier is the basis of a veryhigh-speed logic circuit family, called emittercoupled logic (ECL). Why?
Reasons:uo++直接耦合u,=0uo放大电路.-(b)(a)Direct coupling between signal source and amplifierwill easily cause temperature Drift (zero drift)What shall we do?MicroelectronicCircuits
Microelectronic Circuits Reasons: Direct coupling between signal source and amplifier will easily cause temperature Drift (zero drift). What shall we do?
CCCCRR+uoC4ORoR.TuoR.VBBBBo(a)(b)VcCRpRT2RellRe.VBBVBB(c)CCCCRc2Rb2R.RbKK3T2TT1412iBliBIig2iE2VBBRRO-VBE(d)(e)
Microelectronic Circuits
Advantages There are 2 reasons for using differentialin preference to single-ended amplifiers(1) Differential circuits are much less sensitive to noiseand interference than single-ended circuits.(2) It enables us to bias the amplifier and to coupleamplifier stage without the need of bypass andcoupling capacitors which are impossible tofabricate economically by IC technologyMicroelectronicCircuits
Microelectronic Circuits Advantages ➢ There are 2 reasons for using differential in preference to single-ended amplifiers. (1) Differential circuits are much less sensitive to noise and interference than single-ended circuits. (2) It enables us to bias the amplifier and to couple amplifier stage without the need of bypass and coupling capacitors which are impossible to fabricate economically by IC technology
6.1 The BJTDifferential PairBasic Operation-l:Common-mode inputVco>The differential pair with a common-mode input signal VcM.RR>Two transistors are matched.>Current source with infinite outputresistanceO>CurrentIdivide equallybetweentwo+UCMtransistors.>The difference in voltagebetweenthe0.7UCAtwo collectoris zero.>Thedifferentialpairrejectsthecommon-mode input signal as long astwo transistors remain in active region-VEE(a)Microelectronic Circuits
Microelectronic Circuits 6.1 The BJT Differential Pair Basic Operation-1:Common-mode input ➢The differential pair with a commonmode input signal vCM. ➢Two transistors are matched. ➢Current source with infinite output resistance. ➢Current I divide equally between two transistors. ➢The difference in voltage between the two collector is zero. ➢The differential pair rejects the common-mode input signal as long as two transistors remain in active region
Basic Operation-2>The differential pair with aQIRCVCC“large" differential input signal.+IVoQ>Qi is on and Q2 is off.OftOn0.>Current I entirely flows in Qi+0.3VEE(b)Microelectronic Circuits
Microelectronic Circuits Basic Operation-2 ➢The differential pair with a “large” differential input signal. ➢Q1 is on and Q2 is off. ➢Current I entirely flows in Q1
Basic Operation-3Vcc>The differential pair with aVcaIRlarge differential input signal ofpolarity opposite to that in (b)QQ21VoOff>Q2 is on and Q, is off.OT10>Current I entirely flows in Q20VEE(c)Microelectronic Circuits
Microelectronic Circuits Basic Operation-3 ➢The differential pair with a large differential input signal of polarity opposite to that in (b). ➢Q2 is on and Q1 is off. ➢Current I entirely flows in Q2
Basic Operation-4:Difference-mode orDifference signalsIcC>The differential pair with asmall differential input signal V;RRlVeeRaAIRd>Small signal operation orRaVce=20AIRlinear amplifier.+AIRJAQ(small)>Assuming the bias currentsource I to be ideal and thus Iremains constant with thechange in VcM.>Increment in Q andVEEdecrement in Q2(d)Microelectronic Circuits
Microelectronic Circuits Basic Operation-4:Difference-mode or Difference signals ➢The differential pair with a small differential input signal vi . ➢Small signal operation or linear amplifier. ➢Assuming the bias current source I to be ideal and thus I remains constant with the change in vCM. ➢Increment in Q1 and decrement in Q2
Large-Signal Operation(VBI-V15e2E1α(VB2-VELinear regionIVTe~E2α1.01iElic2iclC11(VB2-VB1)+iE210.8/VTE11+e1iE20.6(VB1-VB2)ien+ie2/VT1+e0.4=I+ig2iEl0.21VEYH(VB2-VB1)/0VT-2028-8-6-44101+e106Vid1Normalized differential input voltage,E2(VB1-VB2)//VT1+eMicroelectronic Circuits
Microelectronic Circuits Large-Signal Operation ( ) ( ) ( ) ( ) ( ) ( ) T B B T B B T B B T B B T B E T B E V E v v V E v v E E V v v E E E V v v E E E V v v S E V v v S E e I i e I i i i I e i i i e i i i e I i e I i 1 2 2 1 1 2 2 1 2 1 1 1 1 1 1 1 2 1 1 2 1 2 2 1 2 1 2 1 − − − − − − + = + = + = + = + + = +