拉扎维《模拟集成电路设计》第二版ppt课件.ppt

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1、Chapter9:OperationalAmplifiers9.1GeneralConsiderations9.2One-StageOpAmps9.3Two-StageOpAmps9.4GainBoosting9.5Comparison9.6OutputSwing9.7CommonFeedback9.8InputRangeLimitations9.9SlewRate9.10High-Slew-RateOpAmps9.11PowerSupplyRejection9.12NoiseinOpAmpsOpAmpDefinitionWelooselydefineanopampasa“

2、high-gaindifferentialamplifier.”Usuallyemployedinafeedbacksystemwhenprecisionisarequirement.ApplicationsrangingfromDCgeneration,high-speedamplificationorfiltering.2OpAmpDesignChallengeThreedecadesagoGeneral-purposeblocksasan“ideal”opampDesigneffortistosatisfyanidealopamp-infinitegain-infin

3、iteinputimpedance-zerooutputimpedanceTodayDesigneffortistomaketrade-offsforaspecificapplication,oftensacrificingtheunimportantaspectstoimprovethecriticalones.E.g.,gainerrorvsspeed,openloopgainvsVDD3PerformanceParameterGain(Precision),Bandwidth(Speed):3-dB/fuOutputSwing,PowerdissipationNois

4、e,Linearity,SupplyRejection,offsetInputCMRange,Input/OutputImpedanceLarge-Signalbehavior(e.g.slewrate)4Example9.1Thecircuithasanominalgainof10.i.e.,1+R1/R2=10.DeterminetheminimalvalueofA1foragainerror1%:Thus,A1>1000.Open-loopgaindeterminesprecision.Solution:5Example9.2Assumetheopampisasing

5、le-polevoltageamplifier.Forasmallstepinput,calculatethetimerequiredfortheoutputtoreachwithin1%anditsunity-gainbandwidthif1+R1/R2=10anditssettlingtimeislessthan5ns.Speedvs.BandwidthSolution:6Example9.3Explainthecircuitbehaviorifweswaptheinvertingandnon-invertinginputsoftheopamp.Solution:Pos

6、itivefeedbackdestabilizesthecircuit.Outputgrowsexponentiallytonon-linearityrange.7One-StageOpAmpsLow-frequencygain:Bandwidth:usuallyproportionalto1/(CL*Rout)OutputSwing(single-side):VDD-3OverdriveMirrorpoleinsingle-endedcircuitPowerandnoise:good,withfourdevices->inputnoise8Example9.4Calcul

7、atetheinputcommon-modevoltagerangeandtheclosed-loopoutputimpedanceoftheunity-gainbuffer.Solution: