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一种基于开关电容的基准电压源.docx

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一种基于开关电容的基准电压源 Introduction Voltagereferencesareanimportantelementinelectroniccircuits,providingastablevoltagethatcanbeusedasareferenceforothercircuits.Therearemanymethodstoobtainastablevoltagereference,butoneofthemostpopularandwell-knownisbasedontheuseofswitchedcapacitor(SC)circuits.Thesecircuitsusetheideaofchargetransferbetweencapacitorsinordertogenerateastablevoltage.Inthisessay,wewilldiscussavoltagereferencecircuitbasedonswitchedcapacitors,specificallytheswitched-capacitorvoltagereference(SCVR). Background Ingeneral,voltagereferencesaredesignedtoprovideastablevoltageoutputregardlessoftheinputvoltageorload.Avoltagereferencecanbeusedinmanyapplicationssuchasinbiasingcircuits,analog-to-digitalconverters(ADC),digital-to-analogconverters(DAC),andprecisionvoltageregulators.Therearemanydifferenttypesofvoltagereferences,includingzenerdiodes,bandgapreferences,andswitched-capacitorvoltagereferences. TheSCVRisatypeofvoltagereferencethathastheadvantageofbeingsimple,lowcost,andeasytoimplementonanintegratedcircuit(IC).ThebasicideaofanSCVRistouseswitched-capacitorcircuitstogenerateavoltagereferencethatisproportionaltothesupplyvoltage.Thevoltagereferenceisgeneratedbycharginganddischargingacapacitorthroughswitchesatadefinedrate.Bycontrollingthecharginganddischargingratesofthecapacitor,astablevoltagecanbegeneratedthatisproportionaltothesupplyvoltage. OperationofSCVR TheSCVRconsistsoftwoparts:aswitched-capacitorladderandafeedbackloop.Theswitched-capacitorladderisaseriesofcapacitorsthatareswitchedusingswitches,generatingavoltageladder.Thefeedbackloopcomparesthevoltageladderwithareferencevoltageandadjuststheswitchingfrequencytoachieveadesiredoutputvoltage.Thefeedbackloopalsoprovidesameansofcompensatingforvariationsinthesupplyvoltageandtemperature. ThebasicoperationoftheSCVRisasfollows.Initially,allthecapacitorsintheladderaredischarged.Atthebeginningofeachcycle,aswitchisclosedandthecapacitorischargedwithaninputvoltageV_in.Thentheswitchisopenedandthechargedcapacitorisconnectedinseriesw