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對快速射頻信號發生轉換器的生產改良介紹今天的無線元件、裝置和系統的制造商正在面對具體的來自增加生產而又要降低測試的費用的壓力。在全面減少測試的時代,改良自動化的測試設備(ATE)的速度可能是一個重要的因素。這個注解描述啦,為了優化射頻信號,而使用自動化的測試設備去減少測試時間而改善生產的技術。雖然這些觀念能被適用于任何的信號產生器,但是,在這次的注解中被顯示的例子適用于AgilentN5181AMXG模擬器和N5182AMXG矢量信號產生器(250仟赫至6個十億赫茲)。當使用快速轉變能力的設備時,這些信號發生器在大部份的情形下能在少于1毫秒中轉變頻率,幅度或波形。對于使用快速測試的目的越來越多的功能被整合在無線系統內,而這樣就使在更多的條件下,要求更多的設備并且需要更多的測試。通過GSM和CDMA,這種連接方法正在擴展到不只包括是聲音和數據,還有多種數據連接,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,移動電視,還有協助全球定位的測量站。在多個通道和不同的能量級上,這些模式都需要測試和和現實的波形進行確認。這能盡力減少測試時間,而且測試花費更低廉。了解信號發生器的角色為了要將一個信號發生器最優化,了解它在自動化的測試設備系統的角色和它是如何與系統其他部分聯系很重要。對變換速度的生產能力表現一典型的自動化的測試設備(ATE)系統和需要制造一個典型的測量步驟。整個的生產通常是通過每一測量或者每一裝置表現的,而且除了包括在第5步驟顯示的信號發生器以外還有很多的因素決定。然而，在高度地重復的測試序列中，信號發生器可能被應用成百上千次,這就使得信號發生器在整個的測試時間內變成一個具體的因素。在這些條件下,它是非常重要的,不只是因為有轉變能力的來源,而且也是利用這種速度實現測試任務的工具。一些快速的計算能決定在系統生產中轉變時間來源的影響。對于一個給定的量，轉變時間的總計來源能通過轉變來源的種類來估計測量的時間。許多測量可能在頻率、幅度和波形方面需要改變設定,而且每種類型的變化可能有不同的轉變時間敘述。變換速度的敘述有多種測量和敘述轉變速度的技術。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。在轉變的頻率、幅度和波形種考慮時間很重要,要看使用的范圍。為目錄清除和SCPI模態設定時間,AgilentMXG頻率和幅度展示在表1中。佳化套入的環測試序列可能需要DUT與不同的頻率、幅度和波形一起測試。舉例說,GSM/GPRS/EGPRS裝置校準可能需要4條基帶(40頻率),8個能量級和2個波形中需要10個通道,即總數為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。如何在程序中嵌入步驟可能對生產產生重要的影響。內部環的轉變間隔,在圖表中的環3,時常被應用,因為數字是在環2中以重復的數字相乘然后與環1的數字再乘。最佳的時間,最快速的轉變特性應該被放在內環3中和最慢的應該被放在環1中。注意：目錄清除模態,稍后討論,允許直到1601點為止以任意的頻率幅度和波形設定,而且快速地轉變得每點比1ms少。多個環能在一個信號中應用。傳統來說對于信號發生器,波形的轉變已經是最慢的,而因此應該被放在環1中。當內部的基帶發生器在波形之間轉變的時候,AgilentN5182A矢量信號發生波轉變時間與需求的幅度和頻率非常接