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1、SECTION1SINGLE-SUPPLYAMPLIFIERSRail-to-RailInputStagesRail-to-RailOutputStagesSingle-SupplyInstrumentationAmplifiers1SECTION1SINGLE-SUPPLYAMPLIFIERSAdolfoGarciaOverthelastseveralyears,single-supplyoperationhasbecomeanincreasinglyimportantrequirementassystemsg
2、etsmaller,cheaper,andmoreportable.Portablesystemsrelyonbatteries,andtotalcircuitpowerconsumptionisanimportantandoftendominantdesignissue,andinsomeinstances,moreimportantthancost.Thismakeslow-voltage/lowsupplycurrentoperationcritical;atthesametime,however,accu
3、racyandprecisionrequirementshaveforcedICmanufacturerstomeetthechallengeof“doingmorewithless”intheiramplifierdesigns.SINGLE-SUPPLYAMPLIFIERSSingleSupplyOffers:LowerPowerBatteryOperatedPortableEquipmentSimplifiesPowerSupplyRequirementsButWatchOutfor:Signal-swin
4、gslimited,thereforemoresensitivetoerrorscausedbyoffsetvoltage,biascurrent,finiteopen-loopgain,noise,etc.MorelikelytohavenoisypowersupplybecauseofsharingwithdigitalcircuitsDCcoupled,multi-stagesingle-supplycircuitscangetverytricky!Rail-to-railopampsneededtomax
5、imizesignalswingsInasingle-supplyapplication,themostimmediateeffectontheperformanceofanamplifieristhereducedinputandoutputsignalrange.Asaresultoftheselowerinputandoutputsignalexcursions,amplifiercircuitsbecomemoresensitivetointernalandexternalerrorsources.Pre
6、cisionamplifieroffsetvoltagesontheorderof0.1mVarelessthana0.04LSBerrorsourceina12-bit,10Vfull-scalesystem.Inasingle-supplysystem,however,a"rail-to-rail"precisionamplifierwithanoffsetvoltageof1mVrepresentsa0.8LSBerrorina5VFSsystem,and1.6LSBerrorina2.5VFSsystem
7、.Furthermore,amplifierbiascurrents,nowflowinginlargersourceresistancestokeepcurrentdrainfromthebatterylow,cangenerateoffseterrorsequaltoorgreaterthantheamplifier’sownoffsetvoltage.Gainaccuracyinsomelowvoltagesingle-supplydevicesisalsoreduced,sodeviceselection
8、needscarefulconsideration.Manyamplifiershavingopen-loopgainsinthemillionstypicallyoperateondualsupplies:forexample,theOP07familytypes.However,manysingle-supply/rail-to-railamplifiersforpr
