AgilentImprovingThroughputwithFastRFSignalGeneratorSwitchingIntroduction odaysmanufacturersofwirelesscomponents,devices,andsystemsfacesigni?cantpressuretoincreasethroughputandlowerthecostoftest.Improvingthespeedofautomatedtestequipment(TE)canbeanimportantfactorinreducingoveralltesttimes.ThisnotedescribestechniquesforoptimizingRFsignalgeneratorswithinTEstoreducetesttimesandimprovethroughput.Althoughtheseconceptscanbeappliedtoanysignalgenerato,theexamplesshowninthisnoteapplytotheAgilentN5181AMXGanalogandN5182AMXGvectorsignalgenerators(250kHzto6GHz).Whenequippedwiththefastswitchingcapability(OptionUNZ),thesesignalgeneratorscanswitchfrequenc,amplitude,orwaveforminlessthan1millisecondinmostcases.MotivationforfastertestsMoreandmorefunctionalityisintegratedintowirelesssystems,requiringmoretestswithmoresetupsundermoreconditions.ConnectivitymethodsareexpandingtoincludenotjustvoiceanddatathroughGSMandCDMA,butavarietyofdataconnectionssuchasRFID,Bluetooth?,iMAX,andUWB.Newbroadcastfunctionsarealsobeingsupported,suchasFMradio,MobileT,andAssistedGPS.Thesemodesrequiretestingandveri?cation,overmultiplechannels,anddifferentpowerlevels,andwithrealisticwaveforms.Thiscanmaketheeffortstoreducetesttimeandtestcostevenmorechallenging.UnderstandingtheRoleoftheSignalGeneratorooptimizeasignalgenerato,itisimportanttounderstanditsroleintheTEsystemandhowitisprogrammedinrelationtootherelementsinthesystem.ThroughputversusswitchingspeedItrepresentsatypicalTEsystemandthestepsneededtomakeatypicalmeasurement.Overallthroughputisnormallystatedpermeasurementorperdevice,andisdeterminedbymanyfactorsbesidesthesignalgeneratorsettlingshowninstep5.Howeve,inhighlyrepetitivetestsequences,thesignalgeneratormaybesteppedtohundredsorthousandsofpointsbecomingasigni?cantfactorinoveralltesttime.Inthesecases,itiscriticalnotonlytochooseasourcewithfastswitchingcapabilities,butalsotoimplementtestprogramsthattakeadvantageofthisspeed.Somequickcaculationscanhelpdeterminetheimpactofsourceswitchingtimeonsystemthroughput.Foragivenmeasurement,thetotalsourceswitchingtimecanbeestimatedbymultiplyingthepointswitchingtimebythenumberofsourcesettings.Manymeasurementsmayrequirechangesinfrequenc,amplitude,andwaveformsettings,andeachtypeofchangemayhaveadifferentswitchingtimespeci?cation.Switchingspeedspeci?cationsThereareavarietyoftechniquesformeasuringandspecifyingswitchingspeed.Importantconsiderationsaretypicallystepsizeconstraints;limitationsonthesizeofthestep,andthesettlingwindow;thatishowclosetothedesiredvaluethesourceisbeforeitisconsiderednishedswitching.Itisimportanttoconsiderthetimesforfrequenc,amplitude,andwaveformswitching,dependingontheapplication.AgilentMXGfrequencyandamplitudesettlingtimesforLISTsweepandSCPImodesareshowninable1.OptimizingnestedloopsAtestsequencemayrequirethattheDUTbetestedwithdifferentfrequenc,amplitude,andwaveformconditions.Forexample,aGSM/GPRS/EGPRSdevicecalibrationmayrequire10channelsin4bands(40frequencies),8powerlevels,and2waveforms,foratotalof640stimulusconditions.Applicationslikethisrequirenestedloopsintheprogram,asrepresentedinFigure2.Planninghowtonesttheloopsmayhaveanimportantimpactonthroughput.Theswitchingintervaloftheinnerloop,loop3inthediagram,isexercisedmostfrequentl,sincethenumberismultipliedbythenumberofrepetitionsinloop2andthenmultipliedagainbythenumberofrepetitionsinloop1.Foroptimaltime,thefastestswitchingcharacteristicshouldbeplacedinloop3,andtheslowestinloop1.NotethatLISTsweepmode,discussedlate,allowsupto1601pointswitharbitraryfrequenc,amplitude,andwaveformsettings,andfastswitchinglessthan1msperpoint.MultipleloopscanbeembeddedinasingleLISraditionallyforsignalgenerators,waveformswitchinghasbeentheslowest,andhasthereforebeeninloop1.Whenswitchingbetweenwaveformsintheinternalbasebandgenerato,theAgilentN5182Avectorsignalgeneratorwave-formswitchingtimesareveryclosetotheplitudeandfrequencyswitchingtimes.Thismayenabletheprogrammertoswitchwaveformstoloop2orloop3,whilemaintainingorimprovingthroughput,dependingontheapplicationDownloadingwaveformsWhenusingtheN5182Avectorsignalgenerato,waveformscanbestoredwithintheinternal64Megasample(MS)basebandgeneratoror100MSofnonvolatilememor.Downloadingthewaveformsfromthecomputerorfromthenonvolatilememorycantakesecondsorevenminutes;atypicaltransferrateoverLANintothebasebandgeneratoris270kilosamplespersecond.Thiscanthereforebecomeasignicantpartofthroughputforsomeapplications.aveformloadingshouldthereforebedoneasinfrequentlyaspossible.Thismaybedif?cultwhenusingverylargewaveformssuchasvideowaveformsusedinSatelliteDigitalMultimediaBroadcast(S-DMB).SourceswitchingspeedbackgroundRFsignalgeneratorshaveadvancedtoincludemanymoderndigitalfeatures.ButswitchingcharacteristicsandlimitationsareofteninherentintheRFarchitecture.AtypicalsignalgeneratorblockdiagramisshowninFigure3.Wheneverthesignalgeneratorissettoanewfrequenc,thefrequencysynthesisloopisusedtophaselockthevoltagecontrolledoscillator(VCO).Wheneveranewpowerlevelisset,theautomaticlevelcontrol(ALC)loopisusedtosetthepowerversusaprecisereference.Theswitchingbehaviordependsonstepsizeandissubjecttoinherentbandwidthlimitationsandsettlingtimes.FordigitalwaveformstheI/Qdatamustalsobecomputedanddownloadedintotheplaybackmemor.Thesamplerateanddigital-to-analogconverter(DAC)valuesmustbecomputedandstoredwiththeleforaccurateplayback.TheN5182Avectorsignalgeneratorhas64Megasamplesofplaybackmemor.ComputerI/OconsiderationsThechoiceofcomputerI/OcanalsoimpactthroughputwhenusingSCPIprogramming.GPIB(IEEE-488-2)hastheshortestlatency;commandsaretransferredveryquickl,upto500KBytes/secfora1-metercable.USBandLANhavelongertransferperiods,andatypicalcommandmaytakeupto1.5mstotransfe.Howeve,USBandLANprovidefasterdatathroughputandofferbetterperformanceforlargerdatatransferssuchaswhendownloadingwaveformsorLISTsweepparameters.GPIBoffersbetterspeedperformancewhenprogram-mingeverypointviaSCPI,andfastertriggeringforsweepmodeusinggroupexecutetrigger(GET).Seethesection,“ChoosingtheBestriggeringMethod”formoreinformationontriggeringtheAgilentMXGsignalanalyzersoverthebus.aveformsequencingThesignalgeneratorson-boardplaybackmemorycanbeloadedwithmultiplewaveformtypes.Individualplaybacksegmentscanberepeatedandsequencedinprede?nedpatternsandtheusercansendSCPIcommandstoswitchtodifferentlocationsintheplaybackmemor.AnexamplesequenceisshowninFigure7.aveformsequencingoffersadvantagesofveryfastwaveformswitchingandcontinuoustransitionsfromonewaveformtoanothe.Howeve,waveformsequencingrequiresthatthefrequenc,amplitude,andsampleratebeidenticalinallsegments.TEapplicationsoftenrequireswitchingsignalswithdifferentsampleratesaswellasfrequencyandamplitudesettings.Inthiscase,sweepmodeintheAgilentMXGmaybepreferred.Sweepmodeenablesthesourcetojumptoanypre-con?guredfrequenc,amplitudeandwaveformstate,includingdifferentsamplerates.AbriefdescriptionoftheAgilentMXGsweepmodesisprovidedinthesection,“ChoosingtheSignalGeneratorControlMethod”.使用Agilent對(duì)快速射頻信號(hào)發(fā)生轉(zhuǎn)換器的生產(chǎn)改良介紹今天的無線元件、裝置和系統(tǒng)的制造商正在面對(duì)具體的來自增加生產(chǎn)而又要降低測(cè)試的費(fèi)用的壓力。在全面減少測(cè)試的時(shí)代,改良自動(dòng)化的測(cè)試設(shè)備(ATE)的速度可能是一個(gè)重要的因素。這個(gè)注解描述啦,為了優(yōu)化射頻信號(hào),而使用自動(dòng)化的測(cè)試設(shè)備去減少測(cè)試時(shí)間而改善生產(chǎn)的技術(shù)。雖然這些觀念能被適用于任何的信號(hào)產(chǎn)生器,但是,在這次的注解中被顯示的例子適用于AgilentN5181AMXG模擬器和N5182AMXG矢量信號(hào)產(chǎn)生器(250仟赫至6個(gè)十億赫茲)。當(dāng)使用快速轉(zhuǎn)變能力的設(shè)備時(shí),這些信號(hào)發(fā)生器在大部份的情形下能在少于1毫秒中轉(zhuǎn)變頻率,幅度或波形。對(duì)于使用快速測(cè)試的目的越來越多的功能被整合在無線系統(tǒng)內(nèi),而這樣就使在更多的條件下,要求更多的設(shè)備并且需要更多的測(cè)試。通過GSM和CDMA,這種連接方法正在擴(kuò)展到不只包括是聲音和數(shù)據(jù),還有多種數(shù)據(jù)連接,像是RFID,Bluetooth,WiMAX和UWB。新的廣播功能也正在被支持,像是FM收音機(jī),移動(dòng)電視,還有協(xié)助全球定位的測(cè)量站。在多個(gè)通道和不同的能量級(jí)上,這些模式都需要測(cè)試和和現(xiàn)實(shí)的波形進(jìn)行確認(rèn)。這能盡力減少測(cè)試時(shí)間,而且測(cè)試花費(fèi)更低廉。了解信號(hào)發(fā)生器的角色為了要將一個(gè)信號(hào)發(fā)生器最優(yōu)化,了解它在自動(dòng)化的測(cè)試設(shè)備系統(tǒng)的角色和它是如何與系統(tǒng)其他部分聯(lián)系很重要。對(duì)變換速度的生產(chǎn)能力表現(xiàn)一典型的自動(dòng)化的測(cè)試設(shè)備(ATE)系統(tǒng)和需要制造一個(gè)典型的測(cè)量步驟。整個(gè)的生產(chǎn)通常是通過每一測(cè)量或者每一裝置表現(xiàn)的,而且除了包括在第5步驟顯示的信號(hào)發(fā)生器以外還有很多的因素決定。然而，在高度地重復(fù)的測(cè)試序列中，信號(hào)發(fā)生器可能被應(yīng)用成百上千次,這就使得信號(hào)發(fā)生器在整個(gè)的測(cè)試時(shí)間內(nèi)變成一個(gè)具體的因素。在這些條件下,它是非常重要的,不只是因?yàn)橛修D(zhuǎn)變能力的來源,而且也是利用這種速度實(shí)現(xiàn)測(cè)試任務(wù)的工具。一些快速的計(jì)算能決定在系統(tǒng)生產(chǎn)中轉(zhuǎn)變時(shí)間來源的影響。對(duì)于一個(gè)給定的量，轉(zhuǎn)變時(shí)間的總計(jì)來源能通過轉(zhuǎn)變來源的種類來估計(jì)測(cè)量的時(shí)間。許多測(cè)量可能在頻率、幅度和波形方面需要改變?cè)O(shè)定,而且每種類型的變化可能有不同的轉(zhuǎn)變時(shí)間敘述。變換速度的敘述有多種測(cè)量和敘述轉(zhuǎn)變速度的技術(shù)。重要參考量典型地是步驟類型的限制;在步驟的大小方面的限制,和解決方案;在思考完成變換之前,最要考慮的是源的類型。在轉(zhuǎn)變的頻率、幅度和波形種考慮時(shí)間很重要,要看使用的范圍。為目錄清除和SCPI模態(tài)設(shè)定時(shí)間,AgilentMXG頻率和幅度展示在表1中。佳化套入的環(huán)測(cè)試序列可能需要DUT與不同的頻率、幅度和波形一起測(cè)試。舉例說,GSM/GPRS/EGPRS裝置校準(zhǔn)可能需要4條基帶(40頻率),8個(gè)能量級(jí)和2個(gè)波形中需要10個(gè)通道,即總數(shù)為640種的刺激條件。像這樣需要在程序中嵌入的步驟所適用的范圍將在如圖2中展現(xiàn)。如何在程序中嵌入步驟可能對(duì)生產(chǎn)產(chǎn)生重要的影響。內(nèi)部環(huán)的轉(zhuǎn)變間隔,在圖表中的環(huán)3,時(shí)常被應(yīng)用,因?yàn)閿?shù)字是在環(huán)2中以重復(fù)的數(shù)字相乘然后與環(huán)1的數(shù)字再乘。最佳的時(shí)間,最快速的轉(zhuǎn)變特性應(yīng)該被放在內(nèi)環(huán)3中和最慢的應(yīng)該被放在環(huán)1中。注意：目錄清除模態(tài),稍后討論,允許直到1601點(diǎn)為止以任意的頻率幅度和波形設(shè)定,而且快速地轉(zhuǎn)變得每點(diǎn)比1ms少。多個(gè)環(huán)能在一個(gè)信號(hào)中應(yīng)用。傳統(tǒng)來說對(duì)于信號(hào)發(fā)生器,波形的轉(zhuǎn)變已經(jīng)是最慢的,而因此應(yīng)該被放在環(huán)1中。當(dāng)內(nèi)部的基帶發(fā)生器在波形之間轉(zhuǎn)變的時(shí)候,AgilentN5182A矢量信號(hào)發(fā)生波轉(zhuǎn)變時(shí)間與需求的幅度和頻率非常接