位AD转换器中英文翻译资料.doc
- 文档编号:16836872
- 上传时间:2023-07-17
- 格式:DOC
- 页数:21
- 大小:281.63KB
位AD转换器中英文翻译资料.doc
《位AD转换器中英文翻译资料.doc》由会员分享,可在线阅读,更多相关《位AD转换器中英文翻译资料.doc(21页珍藏版)》请在冰点文库上搜索。
英文原文
12-BitA/DConverter
CIRCUITOPERATION
TheAD574Aisacomplete12-bitA/Dconverterwhichrequiresnoexternalcomponentstoprovidethecompletesuccessiveapproximationanalog-to-digitalconversionfunction.AblockdiagramoftheAD574AisshowninFigure1.
Figure1.BlockDiagramofAD574A12-BitA-to-DConverter
Whenthecontrolsectioniscommandedtoinitiateaconversion(asdescribedlater),itenablestheclockandresetsthesuccessiveapproximationregister(SAR)toallzeros.Onceaconversioncyclehasbegun,itcannotbestoppedorrestartedanddataisnotavailablefromtheoutputbuffers.TheSAR,timedbytheclock,willsequencethroughtheconversioncycleandreturnanend-of-convertflagtothecontrolsection.Thecontrolsectionwillthendisabletheclock,bringtheoutputstatusflaglow,andenablecontrolfunctionstoallowdatareadfunctionsbyexternalcommand.
Duringtheconversioncycle,theinternal12-bitcurrentoutputDACissequencedbytheSARfromthemostsignificantbit(MSB)toleastsignificantbit(LSB)toprovideanoutputcurrentwhichaccuratelybalancestheinputsignalcurrentthroughthe5kΩ(or10kΩ)inputresistor.Thecomparatordetermineswhethertheadditionofeachsuccessively-weightedbitcurrentcausestheDACcurrentsumtobegreaterorlessthantheinputcurrent;ifthesumisless,thebitislefton;ifmore,thebitisturnedoff.Aftertestingallthebits,theSARcontainsa12-bitbinarycodewhichaccuratelyrepresentstheinputsignaltowithin1/2LSB.
Thetemperature-compensatedburiedZenerreferenceprovidestheprimaryvoltagereferencetotheDACandguaranteesexcellentstabilitywithbothtimeandtemperature.Thereferenceistrimmedto10.00volts±0.2%;itcansupplyupto1.5mAtoanexternalloadinadditiontotherequirementsofthereferenceinputresistor(0.5mA)andbipolaroffsetresistor(1mA)whentheAD574Aispoweredfrom±15Vsupplies.IftheAD574Aisusedwith±12Vsupplies,orifexternalcurrentmustbesuppliedoverthefulltemperaturerange,anexternalbufferamplifierisrecommended.AnyexternalloadontheAD574Areferencemustremainconstantduringconversion.Thethin-filmapplicationresistorsaretrimmedtomatchthefull-scaleoutputcurrentoftheDAC.Therearetwo5kWinputscalingresistorstoalloweithera10voltor20voltspan.The10kWbipolaroffsetresistorisgroundedforunipolaroperationandconnectedtothe10voltreferenceforbipolaroperation.
DRIVINGTHEAD574ANALOGINPUT
Figure2.OpAmp–AD574AInterface
Theoutputimpedanceofanopamphasanopen-loopvaluewhich,inaclosedloop,isdividedbytheloopgainavailableatthefrequencyofinterest.Theamplifiershouldhaveacceptableloopgainat500kHzforusewiththeAD574A.Tocheckwhethertheoutputpropertiesofasignalsourcearesuitable,monitortheAD574’sinputwithanoscilloscopewhileaconversionisinprogress.Eachofthe12disturbancesshouldsubsideinsorless.
Forapplicationsinvolvingtheuseofasample-and-holdamplifier,theAD585isrecommended.TheAD711orAD544opampsarerecommendedfordcapplications.
SAMPLE-AND-HOLDAMPLIFIERS
AlthoughtheconversiontimeoftheAD574Aisamaximumof35ms,toachieveaccurate12-bitconversionsoffrequenciesgreaterthanafewHzrequirestheuseofasample-and-holdamplifier(SHA).IfthevoltageoftheanaloginputsignaldrivingtheAD574Achangesbymorethan1/2LSBoverthetimeintervalneededtomakeaconversion,thentheinputrequiresaSHA.
TheAD585isahighlinearitySHAcapableofdirectlydrivingtheanaloginputoftheAD574A.TheAD585’sfastacquisitiontime,lowapertureandlowaperturejitterareideallysuitedforhigh-speeddataacquisitionsystems.ConsidertheAD574Aconverterwitha35msconversiontimeandaninputsignalof10Vp-p:
themaximumfrequencywhichmaybeappliedtoachieveratedaccuracyis1.5Hz.However,withtheadditionofanAD585,asshowninFigure3,themaximumfrequencyincreasesto26kHz.
TheAD585’slowoutputimpedance,fast-loopresponse,andlowdroopmaintain12-bitsofaccuracyunderthechangingloadconditionsthatoccurduringaconversion,makingitsuitableforuseinhighaccuracyconversionsystems.ManyotherSHAscannotachieve12-bitsofaccuracyandcanthuscompromiseasystem.TheAD585isrecommendedforAD574Aapplicationsrequiringasampleandhold.
Figure3.AD574AwithAD585SampleandHold
SUPPLYDECOUPLINGANDLAYOUT
CONSIDERATIONS
ItiscriticallyimportantthattheAD574Apowersuppliesbefiltered,wellregulated,andfreefromhighfrequencynoise.Useofnoisysupplieswillcauseunstableoutputcodes.Switchingpowersuppliesarenotrecommendedforcircuitsattemptingtoachieve12-bitaccuracyunlessgreatcareisusedinfilteringanyswitchingspikespresentintheoutput.Rememberthatafewmillivoltsofnoiserepresentsseveralcountsoferrorina12-bitADC.
CircuitlayoutshouldattempttolocatetheAD574A,associatedanaloginputcircuitry,andinterconnectionsasfaraspossiblefromlogiccircuitry.Forthisreason,theuseofwire-wrapcircuitconstructionisnotrecommended.Carefulprintedcircuitconstructionispreferred.
UNIPOLARRANGECONNECTIONSFORTHEAD574A
TheAD574Acontainsalltheactivecomponentsrequiredtoperformacomplete12-bitA/Dconversion.Thus,formostsituations,allthatisnecessaryisconnectionofthepowersupplies(+5V,+12V/+15Vand–12V/–15V),theanaloginput,andtheconversioninitiationcommand,asdiscussedonthenextpage.Analoginputconnectionsandcalibrationareeasilyaccomplished;theunipolaroperatingmodeisshowninFigure4.
Figure4.UnipolarInputConnections
Allofthethin-filmapplicationresistorsoftheAD574Aaretrimmedforabsolutecalibration.Therefore,inmanyapplications,nocalibrationtrimmingwillberequired.Theabsoluteaccuracyforeachgradeisgiveninthespecificationtables.Forexample,ifnotrimsareused,theAD574AKguarantees±1LSBmaxzerooffseterrorand±0.25%(10LSB)maxfull-scaleerror.(Typicalfull-scaleerroris±2LSB.)Iftheoffsettrimisnotrequired,Pin12canbeconnecteddirectlytoPin9;thetworesistorsandtrimmerforPin12arethennotneeded.Ifthefull-scaletrimisnotneeded,a50W±1%metalfilmresistorshouldbeconnectedbetweenPin8andPin10.
TheanaloginputisconnectedbetweenPin13andPin9fora0Vto+10Vinputrange,between14andPin9fora0Vto+20Vinputrange.TheAD574Aeasilyaccommodatesaninputsignalbeyondthesupplies.Forthe10voltspaninput,theLSBhasanominalvalueof2.44mV;forthe20voltspan,4.88mV.
Ifa10.24Vrangeisdesired(nominal2.5mV/bit),thegaintrimmer(R2)shouldbereplacedbya50Ωesistor,anda200ΩtrimmerinsertedinserieswiththeanaloginputtoPin13forafull-scalerangeof20.48V(5mV/bit),usea500WtrimmerintoPin14.Thegaintrimdescribedbelowisnowdonewiththesetrimmers.ThenominalinputimpedanceintoPin13is5kΩ,and10kΩintoPin14.
UNIPOLARCALIBRATION
TheAD574Aisintendedtohaveanominal1/2LSBoffsetsothattheexactanaloginputforagivencodewillbeinthemiddleofthatcode(halfwaybetweenthetransitionstothecodesaboveandbelowit).Thus,thefirsttransition(from000000000000to000000000001)willoccurforaninputlevelof+1/2LSB(1.22mVfor10Vrange).
IfPin12isconnectedtoPin9,theunitwillbehaveinthismanner,withinspecifications.Iftheoffsettrim(R1)isused,itshouldbetrimmedasabove,althoughadifferentoffsetcanbesetforaparticularsystemrequirement.Thiscircuitwillgiveapproximately±15mVofoffsettrimrange.
Thefull-scaletrimisdonebyapplyingasignal1/2LSBbelowthenominalfullscale(9.9963fora10Vrange).TrimR2togivethelasttransition(111111111110to111111111111).
BIPOLAROPERATION
TheconnectionsforbipolarrangesareshowninFigure5.Again,asfortheunipolarranges,iftheoffsetandgainspecificationsaresufficient,oneorbothofthetrimmersshowncanbereplacedbya50W±1%fixedresistor.Bipolarcalibrationissimilartounipolarcalibration.
Figure5.BipolarInputConnections
CONTROLLOGIC
TheAD574Acontainson-chiplogictoprovideconversioninitiationanddatareadoperationsfromsignalscommonlyavailableinmicroprocessorsystems.Figure6showstheinternallogiccircuitryoftheAD574A.
ThecontrolsignalsCE,CS,andR/Ccontroltheoperationoftheconverter.ThestateofR/CwhenCEandCSarebothasserteddetermineswhetheradataread(R/C=1)oraconvert(R/C=0)isinprogress.TheregistercontrolinputsAOand12/8controlconversionlengthanddataformat.TheAOlineisusuallytiedtotheleastsignificantbitoftheaddressbus.IfaconversionisstartedwithAOlow,afull12-bitconversioncycleisinitiated.IfAOishighduringaconvertstart,ashorter8-bitconversioncycleresults.Duringdatareadoperations,AOdetermineswhetherthethree-statebufferscontainingthe8MSBsoftheconversionresult(AO=0)orthe4LSBs(AO=1)areenabled.The12/8pindetermineswhethertheoutputdataistobeorganizedastwo8-bitwords(12/8tiedtoDIGITALCOMMON)orasingle12-bitword(12/8tiedtoVLOGIC).The12/8pinisnotTTL-compatibleandmustbehard-wiredtoeitherVLOGICorDIGITALCOMMON.Inthe8-bitmode,thebyteaddressedwhenAOishighcontainsthe4LSBsfromtheconversionfollowedbyfourtrailingzeroes.Thisorganizationallowsthedatalinestobeoverlappedfordirectinterfaceto8-bitbuseswithouttheneedforexternalthree-statebuffers.ItisnotrecommendedthatAOchangestateduringadatareadoperation.Asymmetricalenableanddisableti
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- AD 转换器 中英文 翻译 资料