12位AD转换器中英文翻译资料Word格式文档下载.docx

12位AD转换器中英文翻译资料Word格式文档下载.docx

《12位AD转换器中英文翻译资料Word格式文档下载.docx》由会员分享，可在线阅读，更多相关《12位AD转换器中英文翻译资料Word格式文档下载.docx（17页珍藏版）》请在冰豆网上搜索。

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.Thereferenceistrimmedto10.00volts0.2%;

itcansupplyupto1.5mAtoanexternalloadinadditiontotherequirementsofthereferenceinputresistor（0.5mA）andbipolaroffsetresistor（1mA）whentheAD574Aispoweredfrom15Vsupplies.IftheAD574Aisusedwith12Vsupplies,orifexternalcurrentmustbesuppliedoverthefulltemperaturerange,anexternalbufferamplifierisrecommended.AnyexternalloadontheAD574Areferencemustremainconstantduringconversion.Thethin-filmapplicationresistorsaretrimmedtomatchthefull-scaleoutputcurrentoftheDAC.Therearetwo5kinputscalingresistorstoalloweithera10voltor20voltspan.The10kbipolaroffsetresistorisgroundedforunipolaroperationandconnectedtothe10voltreferenceforbipolaroperation.

DRIVINGTHEAD574ANALOGINPUT

Figure2.OpAmp–AD574AInterface

Theoutputimpedanceofanopamphasanopen-loopvaluewhich,inaclosedloop,isdividedbytheloopgainavailableatthefrequencyofinterest.Theamplifiershouldhaveacceptableloopgainat500kHzforusewiththeAD574A.Tocheckwhethertheoutputpropertiesofasignalsourcearesuitable,monitortheAD574’sinputwithanoscilloscopewhileaconversionisinprogress.Eachofthe12disturbancesshouldsubsideinsorless.

Forapplicationsinvolvingtheuseofasample-and-holdamplifier,theAD585isrecommended.TheAD711orAD544opampsarerecommendedfordcapplications.

SAMPLE-AND-HOLDAMPLIFIERS

AlthoughtheconversiontimeoftheAD574Aisamaximumof35s,toachieveaccurate12-bitconversionsoffrequenciesgreaterthanafewHzrequirestheuseofasample-and-holdamplifier（SHA）.IfthevoltageoftheanaloginputsignaldrivingtheAD574Achangesbymorethan1/2LSBoverthetimeintervalneededtomakeaconversion,thentheinputrequiresaSHA.

TheAD585isahighlinearitySHAcapableofdirectlydrivingtheanaloginputoftheAD574A.TheAD585’sfastacquisitiontime,lowapertureandlowaperturejitterareideallysuitedforhigh-speeddataacquisitionsystems.ConsidertheAD574Aconverterwitha35sconversiontimeandaninputsignalof10Vp-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.R