supplykosspp
kosspp 时间:2021-01-13 阅读:()
AN-1429APPLICATIONNOTEOneTechnologyWayP.
O.
Box9106Norwood,MA02062-9106,U.
S.
A.
Tel:781.
329.
4700Fax:781.
461.
3113www.
analog.
comDesignConsiderationsandSolutionsforHeadphoneDriversinMobilePhonesByDavidGuoRev.
0|Page1of8INTRODUCTIONHighfidelitydescribesthequalityofaudioequipment.
Highfidelityaudioequipmenthasidealtotalharmonicdistortionplusnoise(THD+N)performanceandaccuratefrequencyresponse,resultinginexcellentsubjectivetestresults.
Portablehighfidelityaudioequipmentbringscustomersahigherqualitymusiclisteningexperience.
Comparedtomobilephones,however,portablehighfidelityaudioequipmentisinconvenientlylarge.
Thoughgivenincreasedmarketdemandandtechnicaladvances,itisnowpossibletointegratethehighfidelityfunctionintothinnermobilephones.
Typically,audiodigital-to-analogconverters(DACs)cannotdrivelowimpedanceheadphoneswell.
However,toreachqualityperformance,operationalamplifiersareusedwithaudioDACsforsignalconditioning,includingcurrenttovoltage(ItoV)conversion,filter,attenuation,anddifferentialtosingle-endedconversion.
Theoperationalamplifiersmusthavelownoise,lowdistortion,andstrongdrivecapability.
Theoperationalamplifiermustalsoperformwellinsubjectivetestingwithcustomers.
ManyAnalogDevices,Inc.
,operationalamplifiersarereputablewithmusicfans,liketheAD797,OP275,AD8620,andADA4627-1.
Inportablemobilephoneapplications,thequiescentcurrentandpackageofadeviceisimportant.
TheADA4841-2,ADA4896-2,ADA4075-2,ADA4807-2,andAD8397haveidealnoiseanddistortionperformances.
Thisapplicationnotefocusesonthecircuitdiscussionandoperationalamplifierrecommend-dationsforthishighfidelityheadphonedriverapplication.
SIGNALCHAINInthistypeofapplication,usehighperformanceandlowpoweraudioDACstodeliveradynamicrange(DNR)ofupto127dBandTHD+Nof120dB.
SomehighperformanceaudioDACscanbeconfiguredasavoltageoutputorcurrentoutput.
ConfigurecurrentoutputforbetterDNRandTHD+N.
Foravoltageoutputconfiguration,theconditioningcircuitisadifferentamplifiercircuit,whichconvertsthedifferentialsignalfromtheRchannelorLchanneltoasingle-endedsignal(seeFigure1).
Figure1.
VoltageOutputConfigurationForacurrentoutputconfiguration,implementanItoVcircuittoconvertthedifferentialcurrentsignalfromtheRchannelandtheLchanneltothedifferentialvoltagesignal,followedbyadifferenceamplifiercircuit(seeFigure2).
Inmobilephoneapplications,thepowerconsumptionofdevicesiskey.
Inthisapplicationnote,a±5Vpowerischosenastheexampleforanalysisconvenience.
Figure2.
CurrentOutputConfigurationRDACV+V–DIFFERENTIALTOSINGLE-ENDVOLTAGEOUTPUTLV+V–15032-001RDACI+I–DIFFERENTIALTOSINGLE-ENDITOVCURRENTOUTPUTLI+I–15032-002AN-1429ApplicationNoteRev.
0|Page2of8TABLEOFCONTENTSIntroduction1SignalChain1RevisionHistory2ItoVStage.
3OperationalAmplifierRecommendationsforItoVStageinMobilePhones3THD+Nvs.
VOUTMeasurement4THD+Nvs.
VOUTResult.
4HeadphoneBasics4OutputStage(First-OrderLow-PassFilter)6OutputStage(Second-OrderLow-PassFilter)6OperationalAmplifierRecommendationsforOutputStage.
.
6THD+Nvs.
VOUT/IOUTMeasurement.
7THD+Nvs.
VOUT/IOUTResult.
7Summary8REVISIONHISTORY10/2016—Revision0:InitialVersionApplicationNoteAN-1429Rev.
0|Page3of8ITOVSTAGEAnidealItoVconverterforacurrentoutputDACisaresistortoground.
However,mostDACsdonotoperatelinearlywithvoltageattheoutput.
ItisstandardpracticetooperateanoperationalamplifierasanItoVconverter,creatingavirtualgroundattheinvertinginput.
Normally,theoperationalamplifieroutputstageabsorbsclockenergyandcurrentsteps.
However,Figure3showstheCFcapacitorshuntshighfrequencyenergytogroundwhilecorrectlyreproducingthedesiredoutputwithextremelylowTHDandintermodulationdistortion(IMD).
Figure3.
ItoVStageTherearefourcomponentsinthecircuit:RFisthefeedbackresistor.
Forlowestnoise,maximizegaininthefirststage(ItoV).
However,distortionisrelatedtotheopen-loopgain(AOL)oftheoperationalamplifier.
ThehigherAOL,thebetterthedistortionperformance.
Normally,AOLisspecifiedwithincertainoutputvoltages(seeFigure3).
TheADA4896-2AOLmustbe100dBminimumwhentheoutputis4Vto4Vat±5Vpowersupply,orwhendistortionincreasesbeyond4Vto4V.
AssumingthemaximumoutputcurrentofaDACis1mA,then,kΩ4mA1V4===OUTOUTFIVRCFisthefeedbackcapacitorinparallelwithRF.
CFandRFformapoleinthetransferfunction,thereforethecutofffrequency(fC)ofthelow-passfilterisFFCCRfπ=21AssumingfCis100kHz,then,pF390kΩ100kΩ42121≈**π=π=CFFfRCRSistheresistorinserieswithCF.
Typically,RS=100forbetterstabilityandTHD+Nperformance.
VBIASisthevoltagebias.
Typically,audioDACsgenerateadcoffsetcurrent.
Formaximizingtheeffectiveoutputsignal,addaVBIASatthenoninvertinginputterminaltocancelthedcvoltagebytheDACdcoffsetcurrent.
OPERATIONALAMPLIFIERRECOMMENDATIONSFORITOVSTAGEINMOBILEPHONESThekeyspecificationsofoperationalamplifiersastheItoVstageinheadphonedriversincludepowersupply,IQ,voltageandcurrentnoise,THD+N,package,common-moderejectionratio(CMRR),powersupplyrejectionratio(PSRR),AOL,andslewrate.
TheADA4841-2,ADA4896-2,ADA4075-2,andADA4807-2arerecommendedforItoVconversion.
Keypointsaboutthesedevicesincludethefollowing:Alldevicesarelownoise,lowpower,andhaveasmallpackage.
ADA4807-2usesthelowestIQtoachievelownoiseandrail-to-railinput/output(RRIO)anditintegratesthedisablefunction,whichcanfurtherdecreasethepowerconsumption.
TheADA4075-2specifiedpowersupplyis9Vminimum,isnotarail-to-railoutput(RRO),andhasthesmallestpackage.
THD+Nisthekeyspecification.
SeeFigure4andFigure5forthetestcircuitandtestresultofTHD+N,respectively.
Figure4.
THD+NTestWithoutLoadI+ITOVVBIASRfRSCf15032-0031kΩ1kΩSYS-27121kHzBNC-UNBALANCEBNC-UNBALANCE+5V–5V15032-004AN-1429ApplicationNoteRev.
0|Page4of8THD+NVS.
VOUTMEASUREMENTTodeterminethemaximumoutputwithoutTHD+Ndegrading,measureTHD+Nvs.
VOUT.
Typically,anaudioDACcurrentoutputactsasaresistorinserieswithavoltagesource.
Thatis,theItoVcircuitcanbeconsideredaninvertingamplifiercircuit.
Forsimplicity,gain=1todeterminetheTHD+Nperformanceofoperationalamplifiers(seeFigure5).
ThefollowingdetailstheproceduretomeasureTHD+Nvs.
VOUTusingtheSYS-2712fromAudioPrecision:Thepowersupplyis±5V.
TheSYS-2712analoganalyzergeneratesa1kHzsinewaveastheinputoftheamplifiercircuit.
TheoutputoftheamplifiercircuitfeedsintotheSYS-2712toobtainTHD+Ndata.
ThebandwidthoftheSYS-2712analyzerisconfiguredas22kHz.
TofindTHD+NattheoutputrangeintheSYS-2712evaluatingsoftware,theinputoftheanaloganalyzerisconfiguredasautorange,thatis,theinputstagegainoftheanalyzerincreasesautomaticallybythedifferentinputsignals,including40mV,160mV,300mV,600mV,1.
2V,2.
5V,and5V.
Typically,thelargerthegain,theworsethenoiseleveloftheanalyzerandTHD+N.
THD+NVS.
VOUTRESULTFigure5showsTHD+Nvs.
VOUTresultsfortherecommendedoperationalamplifiers.
WhenVOUTislessthan1.
2Vrms,THD+Nperformanceofthefouroperationalamplifiersissimilar.
WhenVOUTislargerthan1.
2Vrms,theanaloganalyzeroftheSYS-2712isswitchedto2.
5Vscale,increasingthegainofinternalprogrammablegainamplifier(PGA).
ThenoiseworsensandTHD+Ndegradesslightly.
TheSYS-2712causesthisdeg-radation.
ThisisnotthetrueperformanceoftheoperationalamplifierbecausetheSYS-2712hasworsenoisewithalargerPGAgain.
AsVOUTcontinuestoincrease,THD+Ndegradesdramaticallyatthemaximumoutputvoltageoftheamplifier.
FortheADA4841-2,ADA4896-2,andADA4807-2,thevoltageisabout3.
5Vrms(4.
9Vpeak).
ThismatchestheRROfeatureofthesedevices.
FortheADA4075-2,thevoltageisabout2.
13Vrms(3.
0Vpeak).
Thismatchesthe2VoutputvoltagetotherailintheADA4075-2datasheet.
Figure5.
THD+NResultofRecommendedOperationalAmplifiersHEADPHONEBASICSThecharacteristicsofload(headphones)determinestheoutputstage.
Theheadphoneshavetwokeyspecifications:impedanceandsensitivity.
Impedanceistypicallymeasuredat1kHz.
Lowimpedanceheadphonesareintherangeof8Ωto32Ω.
Highimpedanceheadphonesareintherangeofabout100Ωto600Ω.
Astheimpedanceincreases,morevoltage(atagivencurrent)isrequiredtodriveit.
Asaresult,theloudnessoftheheadphonesforagivenvoltagedecreases.
Inrecentyears,impedanceofnewerheadphoneshasgenerallydecreasedtoaccommodatelowervoltagesavailableonbattery-poweredportableelectronics,likemobilephones.
Lowerimpedancemeansheavierloadtotheoperationalamplifier,whichrequiresoperationalamplifierstohavelargercurrentdrivecapabilitieswithoutdistortion.
Sensitivitymeasureshowloudtheheadphonesareforagivenelectricaldrivelevel.
Itcanbemeasuredindecibelsofsoundpressurelevel(SPL)permilliwatt(dB/mW)ordecibelsofSPLpervolt(dB/V).
Byanalyzingthewavefileofaliverecording,themaximumSPLcanreach120dB.
TheaverageSPLislessthan100dB.
Findtherequiredpeakpowerusingthefollowingformula:=1010ySensitivitSPLRequiredP–120–100–80–60–40–2000.
114THD+N(%)OUTPUTVOLTAGE(V)15032-005ADA4841-2ADA4896-2ADA4075-2ADA4807-2ApplicationNoteAN-1429Rev.
0|Page5of8Table1detailsthekeyspecificationsofsomeheadphones.
Theimpedancerangesfrom8Ωto600Ω.
Therequiredpeakpower,peakvoltage,andpeakcurrentarelisted.
Therequiredaveragepowerislessthan2mW.
Toreproducetheeffectofliverecording,theheadphonedrivermustoutputmorepower.
SeeTable1.
Forlowimpedanceheadphones,therequiredpeakcurrentcanreach80mAmaximum,andTHD+Nofthecurrentcannotdegrade.
Forhighimpedanceheadphones,theoutputvoltagemustbehigh.
Forexample,usingtheDT880fromBeyerDynamic(600Ω)requiresanoperationalamplifieroutputof12V,whichisimpossibleina±5Vsystem.
Iftheproducttargetsdrivinghighimpedanceheadphones,increasethepowersupplyoftheamplifiercircuit.
Table1.
Sensitivity,Impedance,PeakVoltage,andPeakCurrentofHeadphonesManufacturerModelSensitivity(dB/mW)Impedance(Ω)Frequency(Hz)AveragePower(mW)PeakPower(mW)PeakVoltage(V)PeakCurrent(mA)SONYXBA-410883to280000.
15815.
8490.
35644.
510Audio-TechnicaATH-CHX71001615to220001.
000100.
0001.
26579.
057ShureSE2151072022to175000.
20019.
9530.
63231.
585AppleEarpod109235to210000.
12612.
5890.
53823.
396GradoAliceM11003220to220001.
000100.
0001.
78955.
902CreativeAURVANAAir1023220to200000.
63163.
0961.
42144.
404KOSSPP1016010to250000.
79479.
4332.
18336.
385SennheiserHD6509830010to395001.
585158.
4896.
89522.
985BeyerDynamicDT880966005to350002.
512251.
18912.
27720.
461AN-1429ApplicationNoteRev.
0|Page6of8OUTPUTSTAGE(FIRST-ORDERLOW-PASSFILTER)Theoutputstageconvertsthedifferentialvoltagesignaltothesingle-endedvoltagesignal.
Figure6depictsacommondifferenceamplifiercircuit,alsoknownasasubtractorcircuit.
Figure6.
DifferentialSingle-EndedCircuitRGandRFdeterminethegainofthecircuit,whichisnormallygain<1.
Theresistanceofresistorsmustbesmall,typically1k,toavoidinducingmorenoise.
RFandCFformsapoleinthetransferfunction.
Therefore,fCofthelow-passfilterisFFCCRfπ=21RSdeterminestheoutputimpedanceorthedampingfactoroftheheadphonedriver.
Thehighdampingfactor(RL/RS)improvesthecontrolthesource(headphonedriver)hasovertheload(headphone).
Theimpedanceoftheheadphonedoesnothavepureresistanceandvariesbyfrequency.
AhigherRScaninducemoredistortion(especiallylowfrequencydistortion)becauseofthefrequencyvariedimpedance.
Fromaperformanceperspective,makeRSlow.
Generally,thedampingfactorremainsaboveone.
Fromasafetyperspective,higherRScanattenuatepowertoprotecttheheadphonefromdamaging,whilealsoprotectingtheamplifierincasetheoutputshortstoground.
Thiscanhappenwhenhotpluggingtheheadphones.
Figure7showstheADA4807-2(LFCSP)maximumpowerdissipationvs.
ambienttemperaturefora4-layerevaluationboard.
Figure7.
ADA4807-2MaximumPowerDissipationvs.
AmbientTemperaturefora4-LayerEvaluationBoardPowerdissipation(PD)canbe1.
274Wat85°Cambienttemperature.
Assuming±5Visthepowersupply,themaximumoutputvoltageis2Vrms.
RS=10,andRSisshortedtoground.
PDperchanneloftheADA4807-2is()LOUTLOUTSSSDRVRVVIVP2*+*=2PD=610mWConsideringtheADA4807-2isadual-channeldevice,thetotalPDis1.
22W.
Theoutputcurrentinthisexampleis200mA.
TheADA4807-2short-circuitcurrentis80mA,soRScanbesmallertoincreasethedampingfactor.
Foroperationalamplifierswithashort-circuitcurrentlargerthan200mA,RSmustbe10minimumtoavoidoperationalamplifierdamageinoutputshorttogroundstatus.
OUTPUTSTAGE(SECOND-ORDERLOW-PASSFILTER)Comparedtothefirst-orderlow-passfilter,thesecond-orderlow-passfilterhasasteeperroll-offresponse,removingmorenoiseoutofthespecifiedband.
Thetwo-polelow-passfilterwithdifferentialinputiseasilydesignedusingthedesignequationsforthesingle-endedinputmultiple-feedbacklow-passfilter.
ShowninFigure8,duplicatingthecomponentresultsinanequivalentfrequencyresponse.
Normally,thefiltergivesaBesselresponse,whichhasalinearphase.
Figure8.
Second-OrderMultipleFeedback(MFB)FilterOPERATIONALAMPLIFIERRECOMMENDATIONSFOROUTPUTSTAGEThekeyspecificationsfortheoutputstageoperationalamplifierissimilartotheItoVstage.
Theoutputstageoperationalamplifiermusttypicallyhave<100dBTHD+Nat32Ωload.
TheADA4841-2,ADA4807-2,andAD8397operationalamplifiersarerecommendedfortheoutputstageofheadphonedriversinmobilephones.
Therearefourpointstoconsider:Alloftheoperationalamplifiersarelownoise,lowpower,andsmallpackagedevices.
ADA4807-2achieveslownoiseandRRIObylowestIQ.
Italsointegratesadisablefunction,whichcanfurtherdecreasepowerconsumption.
RGRSRLRFCF15032-00600.
51.
01.
52.
02.
53.
03.
54.
0–40–25–105203550658095110125MAXIMUMPOWERDISSIPATION(W)AMBIENTTEMPERATURE(°C)15032-007C5SINGLE-ENDEDINPUTSINGLE-ENDEDOUTPUTDIFFERENTIALINPUTSINGLE-ENDEDOUTPUTR3R1R4C2C5R3R1R3R1R4C5C2R4C215032-008ApplicationNoteAN-1429Rev.
0|Page7of8AD8397typicallyhas<100dBTHD+Nat32Ωload.
Italsotestssubjectivelywell.
ThedisadvantageistheAD8397IQishigher,atabout12mA.
<100dBTHD+Nat32Ωloadisakeyspecification.
SeeFigure9andFigure10forthetestcircuitandtestresult,respectively.
SeetheADA4841-2,ADA4807-2,andAD8397datasheetsforrelevantspecifications.
THD+NVS.
VOUT/IOUTMEASUREMENTFigure9showsthecircuitusedtofindTHD+Nataheavyload.
ThefollowingdetailstheTHD+Nvs.
VOUT/IOUTmeasurement:Thepowersupplyis±3.
3V.
Thegainofthesubtractorisabout0.
243.
TheSYS-2712generatesa1kHzsinewaveastheinputoftheamplifiercircuit.
FeedtheoutputoftheamplifiercircuitintotheSYS-2712analoganalyzertodetermineTHD+N.
ConfigurethebandwidthoftheSYS-2712analyzerto22kHz.
TomeasureTHD+Nvs.
VOUT/IOUT,SYS-2712isconfiguredtooutputa100mVrmsto4Vrmssignal.
Figure9.
THD+NTestwith16ΩLoadTHD+NVS.
VOUT/IOUTRESULTFigure10andFigure11depictsTHD+Nvs.
VOUT/IOUToftherecommendedoperationalamplifiers.
Figure10.
THD+Nvs.
VOUToftheADA4841-2,ADA4807-2,andAD8397Figure11.
THD+Nvs.
IOUToftheADA4841-2,ADA4807-2,andAD8397Table2detailsthemaximumcurrentandmaximumoutputpowerwithparameterssetat<100dBTHD+Nat16load.
Figure11showsthefollowingresults:THD+NdegradesdramaticallywhenIOUTreachesacertaincurrentthreshold.
TheAD8397hashighcurrentdrivecapabilitiesat16load.
TheADA4807-2maximumoutputcurrentis42mAwithonly1.
2mAIQ,whichisrecommendedwhenprioritizingthepowerconsumptionbudget.
Inmostcases,2mWoutputpowerisenoughtodrivetheheadphones.
THD+N,inthiscase,isimportant;asdetailedinTable2,THD+Nat2mWofallrecommendedoperationalamplifiersis<100dB.
Table2.
MaximumCurrentandOutputPowerat16LoadParameterADA4841-2ADA4807-2AD8397MaximumCurrentat<100dBTHD+N29.
1mA42.
1mA125mAOutputPowerat<10dBTHD+N13.
6mW28.
4mW250mWTHD+Nat2mWOutputPower102.
7dB102.
7dB101.
4dBDESIGNGUIDELINESResistancemeasuredat1kΩinduces4nV/√Hznoise,whichismorethanthevoltagenoiseofmostoperationalamplifiers.
Inthecircuit,theresistanceoftheresistorsmustbechosencarefullyandmustnotexceed1k.
Shieldingisveryimportantinmobilephones.
Toreach<100dBTHD+Nspecifications,thetiniestofinterferencescandegradeTHD+Nperformance,particularlywhenlisteningtomusicandbrowsingtheinternetsimultaneously.
Metalshieldingcanhelppreventperformancedegradation.
+3.
3V–3.
3V16Ω200Ω200Ω820Ω820ΩSYS-2712BALANCEBNC-UNBALANCE1kHz/1.
0Vrms15032-009–120–100–80–60–40–2000.
020.
2THD+N(dB)OUTPUTVOLTAGE(Vrms)ADA4807-2=16ΩADA4841-2=16ΩAD8397=16Ω15032-010–120–100–80–60–40–200110100THD+N(dB)OUTPUTCURRENT(mA)ADA4807-2=16ΩADA4841-2=16ΩAD8397=16Ω15032-011AN-1429ApplicationNoteRev.
0|Page8of8Forbetterheatdissipation,soldertheexposedpadoftheLFCSPpackagetotheboardpadandconnectittoabigsolidcopperplaneattheoppositesideoftheboardbyvias.
Thecopperplanecanbethegroundorpowerplaneoftheboard,butconsulttheADA4841-2,ADA4807-2,andAD8397datasheetstospecifywhichplanetouse.
Usealowdropoutregulator(LDO)asthepowersupplyofoperationalamplifiers.
Placethedecouplingcapacitors(0.
1μFand4.
7μF)neartheoperationalamplifierpowerpins.
ThecapacitorsintheaudiopathmustbeanNP0ceramictype,astheyofferbetterdistortionperformance.
UsethinfilmresistorsforoptimumTHDperformance.
Metalfilmresistorsarealsosuitable,buttypicallycostmore.
SUMMARYTable3liststhedifferentsolutionsanddifferentconsiderationsforvoltageoutputDACorcurrentoutputDAC.
Therearemanythingstoconsiderwhencreatinganexcellentproduct.
Inrealapplications,accordingtodifferentconditions(forexample,powersupply,targetedloadresistance,powerconsumptionbudget,andexpectedperformance),customerscanchoosetherightsolutionanddesignthecircuittoachievepersonalexpectations.
Table3.
RecommendedDifferentSolutionsDACCurrentOutputParameterDACVoltageOutputItoVStageOutputStageLowCostADA4841-2ADA4841-2ADA4841-2HighPerformanceAD8397ADA4807-2,ADA4896-2,ADA4075-2AD8397QualityPerformancebyLowPowerConsumptionADA4807-2ADA4807-2,ADA4896-2,ADA4075-2ADA4807-22016AnalogDevices,Inc.
Allrightsreserved.
Trademarksandregisteredtrademarksarethepropertyoftheirrespectiveowners.
AN15032-0-10/16(0)
O.
Box9106Norwood,MA02062-9106,U.
S.
A.
Tel:781.
329.
4700Fax:781.
461.
3113www.
analog.
comDesignConsiderationsandSolutionsforHeadphoneDriversinMobilePhonesByDavidGuoRev.
0|Page1of8INTRODUCTIONHighfidelitydescribesthequalityofaudioequipment.
Highfidelityaudioequipmenthasidealtotalharmonicdistortionplusnoise(THD+N)performanceandaccuratefrequencyresponse,resultinginexcellentsubjectivetestresults.
Portablehighfidelityaudioequipmentbringscustomersahigherqualitymusiclisteningexperience.
Comparedtomobilephones,however,portablehighfidelityaudioequipmentisinconvenientlylarge.
Thoughgivenincreasedmarketdemandandtechnicaladvances,itisnowpossibletointegratethehighfidelityfunctionintothinnermobilephones.
Typically,audiodigital-to-analogconverters(DACs)cannotdrivelowimpedanceheadphoneswell.
However,toreachqualityperformance,operationalamplifiersareusedwithaudioDACsforsignalconditioning,includingcurrenttovoltage(ItoV)conversion,filter,attenuation,anddifferentialtosingle-endedconversion.
Theoperationalamplifiersmusthavelownoise,lowdistortion,andstrongdrivecapability.
Theoperationalamplifiermustalsoperformwellinsubjectivetestingwithcustomers.
ManyAnalogDevices,Inc.
,operationalamplifiersarereputablewithmusicfans,liketheAD797,OP275,AD8620,andADA4627-1.
Inportablemobilephoneapplications,thequiescentcurrentandpackageofadeviceisimportant.
TheADA4841-2,ADA4896-2,ADA4075-2,ADA4807-2,andAD8397haveidealnoiseanddistortionperformances.
Thisapplicationnotefocusesonthecircuitdiscussionandoperationalamplifierrecommend-dationsforthishighfidelityheadphonedriverapplication.
SIGNALCHAINInthistypeofapplication,usehighperformanceandlowpoweraudioDACstodeliveradynamicrange(DNR)ofupto127dBandTHD+Nof120dB.
SomehighperformanceaudioDACscanbeconfiguredasavoltageoutputorcurrentoutput.
ConfigurecurrentoutputforbetterDNRandTHD+N.
Foravoltageoutputconfiguration,theconditioningcircuitisadifferentamplifiercircuit,whichconvertsthedifferentialsignalfromtheRchannelorLchanneltoasingle-endedsignal(seeFigure1).
Figure1.
VoltageOutputConfigurationForacurrentoutputconfiguration,implementanItoVcircuittoconvertthedifferentialcurrentsignalfromtheRchannelandtheLchanneltothedifferentialvoltagesignal,followedbyadifferenceamplifiercircuit(seeFigure2).
Inmobilephoneapplications,thepowerconsumptionofdevicesiskey.
Inthisapplicationnote,a±5Vpowerischosenastheexampleforanalysisconvenience.
Figure2.
CurrentOutputConfigurationRDACV+V–DIFFERENTIALTOSINGLE-ENDVOLTAGEOUTPUTLV+V–15032-001RDACI+I–DIFFERENTIALTOSINGLE-ENDITOVCURRENTOUTPUTLI+I–15032-002AN-1429ApplicationNoteRev.
0|Page2of8TABLEOFCONTENTSIntroduction1SignalChain1RevisionHistory2ItoVStage.
3OperationalAmplifierRecommendationsforItoVStageinMobilePhones3THD+Nvs.
VOUTMeasurement4THD+Nvs.
VOUTResult.
4HeadphoneBasics4OutputStage(First-OrderLow-PassFilter)6OutputStage(Second-OrderLow-PassFilter)6OperationalAmplifierRecommendationsforOutputStage.
.
6THD+Nvs.
VOUT/IOUTMeasurement.
7THD+Nvs.
VOUT/IOUTResult.
7Summary8REVISIONHISTORY10/2016—Revision0:InitialVersionApplicationNoteAN-1429Rev.
0|Page3of8ITOVSTAGEAnidealItoVconverterforacurrentoutputDACisaresistortoground.
However,mostDACsdonotoperatelinearlywithvoltageattheoutput.
ItisstandardpracticetooperateanoperationalamplifierasanItoVconverter,creatingavirtualgroundattheinvertinginput.
Normally,theoperationalamplifieroutputstageabsorbsclockenergyandcurrentsteps.
However,Figure3showstheCFcapacitorshuntshighfrequencyenergytogroundwhilecorrectlyreproducingthedesiredoutputwithextremelylowTHDandintermodulationdistortion(IMD).
Figure3.
ItoVStageTherearefourcomponentsinthecircuit:RFisthefeedbackresistor.
Forlowestnoise,maximizegaininthefirststage(ItoV).
However,distortionisrelatedtotheopen-loopgain(AOL)oftheoperationalamplifier.
ThehigherAOL,thebetterthedistortionperformance.
Normally,AOLisspecifiedwithincertainoutputvoltages(seeFigure3).
TheADA4896-2AOLmustbe100dBminimumwhentheoutputis4Vto4Vat±5Vpowersupply,orwhendistortionincreasesbeyond4Vto4V.
AssumingthemaximumoutputcurrentofaDACis1mA,then,kΩ4mA1V4===OUTOUTFIVRCFisthefeedbackcapacitorinparallelwithRF.
CFandRFformapoleinthetransferfunction,thereforethecutofffrequency(fC)ofthelow-passfilterisFFCCRfπ=21AssumingfCis100kHz,then,pF390kΩ100kΩ42121≈**π=π=CFFfRCRSistheresistorinserieswithCF.
Typically,RS=100forbetterstabilityandTHD+Nperformance.
VBIASisthevoltagebias.
Typically,audioDACsgenerateadcoffsetcurrent.
Formaximizingtheeffectiveoutputsignal,addaVBIASatthenoninvertinginputterminaltocancelthedcvoltagebytheDACdcoffsetcurrent.
OPERATIONALAMPLIFIERRECOMMENDATIONSFORITOVSTAGEINMOBILEPHONESThekeyspecificationsofoperationalamplifiersastheItoVstageinheadphonedriversincludepowersupply,IQ,voltageandcurrentnoise,THD+N,package,common-moderejectionratio(CMRR),powersupplyrejectionratio(PSRR),AOL,andslewrate.
TheADA4841-2,ADA4896-2,ADA4075-2,andADA4807-2arerecommendedforItoVconversion.
Keypointsaboutthesedevicesincludethefollowing:Alldevicesarelownoise,lowpower,andhaveasmallpackage.
ADA4807-2usesthelowestIQtoachievelownoiseandrail-to-railinput/output(RRIO)anditintegratesthedisablefunction,whichcanfurtherdecreasethepowerconsumption.
TheADA4075-2specifiedpowersupplyis9Vminimum,isnotarail-to-railoutput(RRO),andhasthesmallestpackage.
THD+Nisthekeyspecification.
SeeFigure4andFigure5forthetestcircuitandtestresultofTHD+N,respectively.
Figure4.
THD+NTestWithoutLoadI+ITOVVBIASRfRSCf15032-0031kΩ1kΩSYS-27121kHzBNC-UNBALANCEBNC-UNBALANCE+5V–5V15032-004AN-1429ApplicationNoteRev.
0|Page4of8THD+NVS.
VOUTMEASUREMENTTodeterminethemaximumoutputwithoutTHD+Ndegrading,measureTHD+Nvs.
VOUT.
Typically,anaudioDACcurrentoutputactsasaresistorinserieswithavoltagesource.
Thatis,theItoVcircuitcanbeconsideredaninvertingamplifiercircuit.
Forsimplicity,gain=1todeterminetheTHD+Nperformanceofoperationalamplifiers(seeFigure5).
ThefollowingdetailstheproceduretomeasureTHD+Nvs.
VOUTusingtheSYS-2712fromAudioPrecision:Thepowersupplyis±5V.
TheSYS-2712analoganalyzergeneratesa1kHzsinewaveastheinputoftheamplifiercircuit.
TheoutputoftheamplifiercircuitfeedsintotheSYS-2712toobtainTHD+Ndata.
ThebandwidthoftheSYS-2712analyzerisconfiguredas22kHz.
TofindTHD+NattheoutputrangeintheSYS-2712evaluatingsoftware,theinputoftheanaloganalyzerisconfiguredasautorange,thatis,theinputstagegainoftheanalyzerincreasesautomaticallybythedifferentinputsignals,including40mV,160mV,300mV,600mV,1.
2V,2.
5V,and5V.
Typically,thelargerthegain,theworsethenoiseleveloftheanalyzerandTHD+N.
THD+NVS.
VOUTRESULTFigure5showsTHD+Nvs.
VOUTresultsfortherecommendedoperationalamplifiers.
WhenVOUTislessthan1.
2Vrms,THD+Nperformanceofthefouroperationalamplifiersissimilar.
WhenVOUTislargerthan1.
2Vrms,theanaloganalyzeroftheSYS-2712isswitchedto2.
5Vscale,increasingthegainofinternalprogrammablegainamplifier(PGA).
ThenoiseworsensandTHD+Ndegradesslightly.
TheSYS-2712causesthisdeg-radation.
ThisisnotthetrueperformanceoftheoperationalamplifierbecausetheSYS-2712hasworsenoisewithalargerPGAgain.
AsVOUTcontinuestoincrease,THD+Ndegradesdramaticallyatthemaximumoutputvoltageoftheamplifier.
FortheADA4841-2,ADA4896-2,andADA4807-2,thevoltageisabout3.
5Vrms(4.
9Vpeak).
ThismatchestheRROfeatureofthesedevices.
FortheADA4075-2,thevoltageisabout2.
13Vrms(3.
0Vpeak).
Thismatchesthe2VoutputvoltagetotherailintheADA4075-2datasheet.
Figure5.
THD+NResultofRecommendedOperationalAmplifiersHEADPHONEBASICSThecharacteristicsofload(headphones)determinestheoutputstage.
Theheadphoneshavetwokeyspecifications:impedanceandsensitivity.
Impedanceistypicallymeasuredat1kHz.
Lowimpedanceheadphonesareintherangeof8Ωto32Ω.
Highimpedanceheadphonesareintherangeofabout100Ωto600Ω.
Astheimpedanceincreases,morevoltage(atagivencurrent)isrequiredtodriveit.
Asaresult,theloudnessoftheheadphonesforagivenvoltagedecreases.
Inrecentyears,impedanceofnewerheadphoneshasgenerallydecreasedtoaccommodatelowervoltagesavailableonbattery-poweredportableelectronics,likemobilephones.
Lowerimpedancemeansheavierloadtotheoperationalamplifier,whichrequiresoperationalamplifierstohavelargercurrentdrivecapabilitieswithoutdistortion.
Sensitivitymeasureshowloudtheheadphonesareforagivenelectricaldrivelevel.
Itcanbemeasuredindecibelsofsoundpressurelevel(SPL)permilliwatt(dB/mW)ordecibelsofSPLpervolt(dB/V).
Byanalyzingthewavefileofaliverecording,themaximumSPLcanreach120dB.
TheaverageSPLislessthan100dB.
Findtherequiredpeakpowerusingthefollowingformula:=1010ySensitivitSPLRequiredP–120–100–80–60–40–2000.
114THD+N(%)OUTPUTVOLTAGE(V)15032-005ADA4841-2ADA4896-2ADA4075-2ADA4807-2ApplicationNoteAN-1429Rev.
0|Page5of8Table1detailsthekeyspecificationsofsomeheadphones.
Theimpedancerangesfrom8Ωto600Ω.
Therequiredpeakpower,peakvoltage,andpeakcurrentarelisted.
Therequiredaveragepowerislessthan2mW.
Toreproducetheeffectofliverecording,theheadphonedrivermustoutputmorepower.
SeeTable1.
Forlowimpedanceheadphones,therequiredpeakcurrentcanreach80mAmaximum,andTHD+Nofthecurrentcannotdegrade.
Forhighimpedanceheadphones,theoutputvoltagemustbehigh.
Forexample,usingtheDT880fromBeyerDynamic(600Ω)requiresanoperationalamplifieroutputof12V,whichisimpossibleina±5Vsystem.
Iftheproducttargetsdrivinghighimpedanceheadphones,increasethepowersupplyoftheamplifiercircuit.
Table1.
Sensitivity,Impedance,PeakVoltage,andPeakCurrentofHeadphonesManufacturerModelSensitivity(dB/mW)Impedance(Ω)Frequency(Hz)AveragePower(mW)PeakPower(mW)PeakVoltage(V)PeakCurrent(mA)SONYXBA-410883to280000.
15815.
8490.
35644.
510Audio-TechnicaATH-CHX71001615to220001.
000100.
0001.
26579.
057ShureSE2151072022to175000.
20019.
9530.
63231.
585AppleEarpod109235to210000.
12612.
5890.
53823.
396GradoAliceM11003220to220001.
000100.
0001.
78955.
902CreativeAURVANAAir1023220to200000.
63163.
0961.
42144.
404KOSSPP1016010to250000.
79479.
4332.
18336.
385SennheiserHD6509830010to395001.
585158.
4896.
89522.
985BeyerDynamicDT880966005to350002.
512251.
18912.
27720.
461AN-1429ApplicationNoteRev.
0|Page6of8OUTPUTSTAGE(FIRST-ORDERLOW-PASSFILTER)Theoutputstageconvertsthedifferentialvoltagesignaltothesingle-endedvoltagesignal.
Figure6depictsacommondifferenceamplifiercircuit,alsoknownasasubtractorcircuit.
Figure6.
DifferentialSingle-EndedCircuitRGandRFdeterminethegainofthecircuit,whichisnormallygain<1.
Theresistanceofresistorsmustbesmall,typically1k,toavoidinducingmorenoise.
RFandCFformsapoleinthetransferfunction.
Therefore,fCofthelow-passfilterisFFCCRfπ=21RSdeterminestheoutputimpedanceorthedampingfactoroftheheadphonedriver.
Thehighdampingfactor(RL/RS)improvesthecontrolthesource(headphonedriver)hasovertheload(headphone).
Theimpedanceoftheheadphonedoesnothavepureresistanceandvariesbyfrequency.
AhigherRScaninducemoredistortion(especiallylowfrequencydistortion)becauseofthefrequencyvariedimpedance.
Fromaperformanceperspective,makeRSlow.
Generally,thedampingfactorremainsaboveone.
Fromasafetyperspective,higherRScanattenuatepowertoprotecttheheadphonefromdamaging,whilealsoprotectingtheamplifierincasetheoutputshortstoground.
Thiscanhappenwhenhotpluggingtheheadphones.
Figure7showstheADA4807-2(LFCSP)maximumpowerdissipationvs.
ambienttemperaturefora4-layerevaluationboard.
Figure7.
ADA4807-2MaximumPowerDissipationvs.
AmbientTemperaturefora4-LayerEvaluationBoardPowerdissipation(PD)canbe1.
274Wat85°Cambienttemperature.
Assuming±5Visthepowersupply,themaximumoutputvoltageis2Vrms.
RS=10,andRSisshortedtoground.
PDperchanneloftheADA4807-2is()LOUTLOUTSSSDRVRVVIVP2*+*=2PD=610mWConsideringtheADA4807-2isadual-channeldevice,thetotalPDis1.
22W.
Theoutputcurrentinthisexampleis200mA.
TheADA4807-2short-circuitcurrentis80mA,soRScanbesmallertoincreasethedampingfactor.
Foroperationalamplifierswithashort-circuitcurrentlargerthan200mA,RSmustbe10minimumtoavoidoperationalamplifierdamageinoutputshorttogroundstatus.
OUTPUTSTAGE(SECOND-ORDERLOW-PASSFILTER)Comparedtothefirst-orderlow-passfilter,thesecond-orderlow-passfilterhasasteeperroll-offresponse,removingmorenoiseoutofthespecifiedband.
Thetwo-polelow-passfilterwithdifferentialinputiseasilydesignedusingthedesignequationsforthesingle-endedinputmultiple-feedbacklow-passfilter.
ShowninFigure8,duplicatingthecomponentresultsinanequivalentfrequencyresponse.
Normally,thefiltergivesaBesselresponse,whichhasalinearphase.
Figure8.
Second-OrderMultipleFeedback(MFB)FilterOPERATIONALAMPLIFIERRECOMMENDATIONSFOROUTPUTSTAGEThekeyspecificationsfortheoutputstageoperationalamplifierissimilartotheItoVstage.
Theoutputstageoperationalamplifiermusttypicallyhave<100dBTHD+Nat32Ωload.
TheADA4841-2,ADA4807-2,andAD8397operationalamplifiersarerecommendedfortheoutputstageofheadphonedriversinmobilephones.
Therearefourpointstoconsider:Alloftheoperationalamplifiersarelownoise,lowpower,andsmallpackagedevices.
ADA4807-2achieveslownoiseandRRIObylowestIQ.
Italsointegratesadisablefunction,whichcanfurtherdecreasepowerconsumption.
RGRSRLRFCF15032-00600.
51.
01.
52.
02.
53.
03.
54.
0–40–25–105203550658095110125MAXIMUMPOWERDISSIPATION(W)AMBIENTTEMPERATURE(°C)15032-007C5SINGLE-ENDEDINPUTSINGLE-ENDEDOUTPUTDIFFERENTIALINPUTSINGLE-ENDEDOUTPUTR3R1R4C2C5R3R1R3R1R4C5C2R4C215032-008ApplicationNoteAN-1429Rev.
0|Page7of8AD8397typicallyhas<100dBTHD+Nat32Ωload.
Italsotestssubjectivelywell.
ThedisadvantageistheAD8397IQishigher,atabout12mA.
<100dBTHD+Nat32Ωloadisakeyspecification.
SeeFigure9andFigure10forthetestcircuitandtestresult,respectively.
SeetheADA4841-2,ADA4807-2,andAD8397datasheetsforrelevantspecifications.
THD+NVS.
VOUT/IOUTMEASUREMENTFigure9showsthecircuitusedtofindTHD+Nataheavyload.
ThefollowingdetailstheTHD+Nvs.
VOUT/IOUTmeasurement:Thepowersupplyis±3.
3V.
Thegainofthesubtractorisabout0.
243.
TheSYS-2712generatesa1kHzsinewaveastheinputoftheamplifiercircuit.
FeedtheoutputoftheamplifiercircuitintotheSYS-2712analoganalyzertodetermineTHD+N.
ConfigurethebandwidthoftheSYS-2712analyzerto22kHz.
TomeasureTHD+Nvs.
VOUT/IOUT,SYS-2712isconfiguredtooutputa100mVrmsto4Vrmssignal.
Figure9.
THD+NTestwith16ΩLoadTHD+NVS.
VOUT/IOUTRESULTFigure10andFigure11depictsTHD+Nvs.
VOUT/IOUToftherecommendedoperationalamplifiers.
Figure10.
THD+Nvs.
VOUToftheADA4841-2,ADA4807-2,andAD8397Figure11.
THD+Nvs.
IOUToftheADA4841-2,ADA4807-2,andAD8397Table2detailsthemaximumcurrentandmaximumoutputpowerwithparameterssetat<100dBTHD+Nat16load.
Figure11showsthefollowingresults:THD+NdegradesdramaticallywhenIOUTreachesacertaincurrentthreshold.
TheAD8397hashighcurrentdrivecapabilitiesat16load.
TheADA4807-2maximumoutputcurrentis42mAwithonly1.
2mAIQ,whichisrecommendedwhenprioritizingthepowerconsumptionbudget.
Inmostcases,2mWoutputpowerisenoughtodrivetheheadphones.
THD+N,inthiscase,isimportant;asdetailedinTable2,THD+Nat2mWofallrecommendedoperationalamplifiersis<100dB.
Table2.
MaximumCurrentandOutputPowerat16LoadParameterADA4841-2ADA4807-2AD8397MaximumCurrentat<100dBTHD+N29.
1mA42.
1mA125mAOutputPowerat<10dBTHD+N13.
6mW28.
4mW250mWTHD+Nat2mWOutputPower102.
7dB102.
7dB101.
4dBDESIGNGUIDELINESResistancemeasuredat1kΩinduces4nV/√Hznoise,whichismorethanthevoltagenoiseofmostoperationalamplifiers.
Inthecircuit,theresistanceoftheresistorsmustbechosencarefullyandmustnotexceed1k.
Shieldingisveryimportantinmobilephones.
Toreach<100dBTHD+Nspecifications,thetiniestofinterferencescandegradeTHD+Nperformance,particularlywhenlisteningtomusicandbrowsingtheinternetsimultaneously.
Metalshieldingcanhelppreventperformancedegradation.
+3.
3V–3.
3V16Ω200Ω200Ω820Ω820ΩSYS-2712BALANCEBNC-UNBALANCE1kHz/1.
0Vrms15032-009–120–100–80–60–40–2000.
020.
2THD+N(dB)OUTPUTVOLTAGE(Vrms)ADA4807-2=16ΩADA4841-2=16ΩAD8397=16Ω15032-010–120–100–80–60–40–200110100THD+N(dB)OUTPUTCURRENT(mA)ADA4807-2=16ΩADA4841-2=16ΩAD8397=16Ω15032-011AN-1429ApplicationNoteRev.
0|Page8of8Forbetterheatdissipation,soldertheexposedpadoftheLFCSPpackagetotheboardpadandconnectittoabigsolidcopperplaneattheoppositesideoftheboardbyvias.
Thecopperplanecanbethegroundorpowerplaneoftheboard,butconsulttheADA4841-2,ADA4807-2,andAD8397datasheetstospecifywhichplanetouse.
Usealowdropoutregulator(LDO)asthepowersupplyofoperationalamplifiers.
Placethedecouplingcapacitors(0.
1μFand4.
7μF)neartheoperationalamplifierpowerpins.
ThecapacitorsintheaudiopathmustbeanNP0ceramictype,astheyofferbetterdistortionperformance.
UsethinfilmresistorsforoptimumTHDperformance.
Metalfilmresistorsarealsosuitable,buttypicallycostmore.
SUMMARYTable3liststhedifferentsolutionsanddifferentconsiderationsforvoltageoutputDACorcurrentoutputDAC.
Therearemanythingstoconsiderwhencreatinganexcellentproduct.
Inrealapplications,accordingtodifferentconditions(forexample,powersupply,targetedloadresistance,powerconsumptionbudget,andexpectedperformance),customerscanchoosetherightsolutionanddesignthecircuittoachievepersonalexpectations.
Table3.
RecommendedDifferentSolutionsDACCurrentOutputParameterDACVoltageOutputItoVStageOutputStageLowCostADA4841-2ADA4841-2ADA4841-2HighPerformanceAD8397ADA4807-2,ADA4896-2,ADA4075-2AD8397QualityPerformancebyLowPowerConsumptionADA4807-2ADA4807-2,ADA4896-2,ADA4075-2ADA4807-22016AnalogDevices,Inc.
Allrightsreserved.
Trademarksandregisteredtrademarksarethepropertyoftheirrespectiveowners.
AN15032-0-10/16(0)
- supplykosspp相关文档
- 运算放大器kosspp
- kossppKoss pp 还是 AKG K420。。。犹豫中
- kosspp高分！KOSS PP急求解，耳机发烧友入！
- kossppkoss pp 的低音强到什么程度,大家说说听感
- kossppkoss pp 这款耳机怎么样
- kosspp问下KOSS PP有必要买吗。。。
ATCLOUD-KVM架构的VPS产品$4.5,杜绝DDoS攻击
ATCLOUD.NET怎么样？ATCLOUD.NET主要提供KVM架构的VPS产品、LXC容器化产品、权威DNS智能解析、域名注册、SSL证书等海外网站建设服务。 其大部分数据中心是由OVH机房提供，其节点包括美国(俄勒冈、弗吉尼亚)、加拿大、英国、法国、德国以及新加坡。 提供超过480Gbps的DDoS高防保护，杜绝DDoS攻击骚扰，比较适合海外建站等业务。官方网站：点击访问ATCLOUD官网活...
创梦网络-江苏宿迁BGP云服务器100G高防资源,全程ceph集群存储,安全可靠,数据有保证,防护真实,现在购买7折促销,续费同价！
官方网站：点击访问创梦网络宿迁BGP高防活动方案：机房CPU内存硬盘带宽IP防护流量原价活动价开通方式宿迁BGP4vCPU4G40G+50G20Mbps1个100G不限流量299元/月 209.3元/月点击自助购买成都电信优化线路8vCPU8G40G+50G20Mbps1个100G不限流量399元/月 279.3元/月点击自助购买成都电信优化线路8vCPU16G40G+50G2...
BGP.TO日本和新加坡服务器进行促销，日本服务器6.5折
BGP.TO目前针对日本和新加坡服务器进行促销，其中日本东京服务器6.5折，而新加坡服务器7.5折起。这是一家专门的独立服务器租售网站，提供包括中国香港、日本、新加坡和洛杉矶的服务器租用业务，基本上都是自有硬件、IP资源等，国内优化直连线路，机器自动化部署上架，并提供产品的基本管理功能(自助开关机重启重装等)。新加坡服务器 $93.75/月CPU：E3-1230v3内存：16GB硬盘：480GB ...
kosspp为你推荐
-
php虚拟主机免费的国内的php虚拟主机有吗linux虚拟主机如何配置linux虚拟主机vps国内VPS哪个好免费网站空间如何免费做网站 免费域名+免费空间+免费网站100m虚拟主机虚拟主机 100M 和200M 的区别？那个速度快？为什么？1g虚拟主机想买个1G虚拟主机，不限流量的，但不知道哪个建站网站靠谱，求推荐！北京虚拟主机租用北京云主机租用哪家资质正规，价格便宜，服务好？要真云主机不要那种vps的假云主机，机房要在北京的！北京虚拟主机北京的虚拟主机提供商哪个经济实惠？深圳虚拟主机深圳市虚拟主机深圳双线虚拟主机深圳主机合租深圳合租主机空推荐有哪?广西虚拟主机南宁有实力的网络公司推荐下？