RF Power Supply Design and Layout Guide | Blog - Altium ...

The main role of an RF power supply is to provide power to an RF system at the frequency of interest, which includes standard components used to ... Skiptomaincontent Mobilemenu PCBDesign AltiumDesigner World’sMostPopularPCBDesignSoftware AltiumNEXUS TheLastMileofDigitalTransformation CircuitStudio EntryLevel,ProfessionalPCBDesignTool CircuitMaker FreePCBdesignformakers,opensourceandnon-profits Parts&Data AltiumConcordPro CompleteSolutionforLibraryManagement Octopart Extensive,Easy-to-UseSearchEngineforElectronicParts Subscriptions Altium365 Resources&Support ExploreProducts FreeTrials Downloads Extensions FreeAltium365Tools OnlinePCBViewer Resources&Support AllResources SupportCenter Documentation TrainingandEvents Webinars AltiumCommunity Forum BugCrunch Ideas Store SearchOpen Search SearchClose SignIn Home RFDesign RFPowerSupplyDesignandLayoutGuide RFPowerSupplyDesignandLayoutGuide ZachariahPeterson |&nbspCreated:August27,2021 Onethingiscertain:powersupplydesignscangetmuchmorecomplexthansimplyroutingDCpowerlinestoyourcomponents.RFpowersupplydesignsrequirespecialcaretoensuretheywillfunctionwithouttransferringexcessivenoisebetweenportionsofthesystem,somethingthatismademoredifficultduetothehighpowerlevelsinvolved.Inadditiontocarefullayout,circuitryneedstobedesignedsuchthatthesystemprovideshighlyefficientpowerconversionanddeliverytoeachsubsectionofthesystem. Veryhighpowersystemsarestillbeingdesignedwithdiscretecomponentsthatmaybeconnectedinalargehousingorcabinet,butsmallerpowersystemscanbeplacedonaPCBwithsomenewercomponentsandpowerregulationstrategies.Challengesinthesesystemsfallintotwomajorareas: HeatgenerationinFETsandamplifiers,whichmotivatestheuseofadvancedsemiconductorslikeGaNonSiCforRFamplification Parasiticsthatcouldallowhighpowertoleakintonearbycircuitsalongthepowerfeedline,whichrequirescarefulplacementandrouting Thefirstpointhappensonthefrontendwhencomponentsareselectedforpowercircuitsandplacedintoyourschematicsheets.The2ndpointaboveiswherelayoutandroutingbecomemoreimportant.We’llcoverabitofbothareasinthisarticlesothatnewerRFdesignerscangettheirstackupandplacementcompletedbeforerouting. StartingYourRFPowerSupplyDesign Fromtheperspectiveofcircuitdesign,RFpowersuppliesrequiresomeofthesameregulationandfiltrationstagesasanyotherpowersupplyintendedforaDCsystem.ThemainroleofanRFpowersupplyistoprovidepowertoanRFsystematthefrequencyofinterest,whichincludesstandardcomponentsusedtogenerateandconditionanRFsignal(oscillators,activefilters,amplifiers,etc.).Thepowersupplyalsoneedstobeabletorespondtomodulation.Inadditiontoaccommodatingmodulation,anRFpowersupplydesignshouldsharesomeofthesamerequirementsasatypicalRFcircuitboard,namelylowlossathighfrequencies,aswellassufficientlyhightemperatureratingsandthermalproperties. TheblockdiagrambelowshowsatahighlevelhowtogenerateRFpowerathighfrequencies. RFpowersupplytopologywithanRFamplifier.RFpowersuppliesalsooperateintheinverse,wheretheyreceiveanRFsignalandrectifyitdowntoaDCvoltage.ThisrequiresbuildinganRFrectifiercircuit,whichwewon’tlookatsomuchinthisarticleasitcanberatherinvolved.Instead,we’llfocusontheRFsourcingaspect. RegulatorsandFiltration RFpowersuppliesthatneedtosourceathighfrequencies,meaninghighMHzorGHz,aretypicallybuiltfromdiscretecomponents.However,youcanputalloftheabovesectionsonthesameboard.Thefirststepisregulatorselectionandfilterdesign.Intheaboveblockdiagram,thehigherorderfilterandswitchingregulatorneedtobebuilttofollowtheenvelopeofanymodulatedsignal(forAMoutput),ortomodulateitsoutputatthebasebandfrequency(forFMoutput).Thismightrequireamultiphase,multileveltopologyforyourdesign;readthisarticletolearnmoreabouttheregulatorandfilterportionofthedesign. Inselectinganydownstreamregulators(thesecouldbeswitchingorLDOs),becarefultowatchoutfortheefficiency.Ifyou’reusinganLDO,thevoltagedifferentialshouldnotbetoohighasthiswilldropalotofpowerovertheLDO,andthehighthermalresistanceofthecomponentcancauseittoquicklyheatupaboveitstemperaturerating.Inarecentprototypemycompanybuilt,weoptedforLDOswithconductioncoolingviatheenclosure.Ifyouneedtodropdownthevoltagebyalargeamount,youshoulduseaswitchingregulatorandapplyanotherhigherorderfiltertoensurelownoiseisgiventotheVDDport,VGGport,andoscillator. HowtoHandleGround Justlikeanyothermixedsignaldesign,don’ttryandgalvanicallyisolateyourswitchingregulatoroutput(ifyou’reusingone)fromtheRFsectionbyroutingoversplitgrounds.You’llcreatethesametypeofEMIproblemyouwouldseewhenasingle-endeddigitalsignalisroutedoveragapinagroundplane.Thisisacommonmistakeinmixedsignalsystems,andit’seasytomakethesamemistakeinanRFsystembyassumingthattheoutputfromtheswitchingregulatorispurelyDC.Evenwithenvelopetracking,you’restilldrawingyourtime-averagedpoweratthebasebandfrequency,whichcouldbeontheorderoftensorhundredsofMHz. Anexampleofbadgroundingbetweenaregulatoroutputandanamplifier/oscillatorsection.RoutingathighfrequenciesoverthisgroundplanegapcreatesradiatedEMI.Keepuniformgroundandpracticegoodplacementwhilemaintainingimpedancecontroloncoplanarlines,ratherthantryingtotaketheeasyrouteandsplittingupyourgroundlayer.IfyoucanplacetheRFcomponentsintheirownsections,andplacetheDC/regulationcomponentsintheirownsections,youcanpreventinterferencebetweenthemaslongasyoucanproperlytrackreturnpaths. StackupDesignandMaterialSelection Whendesigningyourstackup,you’llneedtoconsidertheoperatingfrequencyforyourregulatorandthelengthofyourRFlinesontheboard.ForlongerRFlines,you’llneedtousealowlosslaminate,possiblyaPTFElaminate.RFpowersuppliesthataren’troutinglonglines,orifyou’rejustnotworriedaboutlosses,youcanusuallygetawaywithFR4laminatesasstackupmaterials.Onewaytocompromiselowlossandlowcostistouseahybridstackupwithalow-lossdielectricsupportingyourRFlines. Theaboveexamplewithpowerrailroutingovergroundcanbedoneona4-layerboardaslongasyoualsorouteRFlinesonasurfacelayer.Youcouldalsouseauniformgroundandapowerplanetoprovidepowerfromtheregulatorsectiontothecomponents,androutetheRFlinesonthesurfacelayertomaintaina4-layerboard.Thisisagoodwaytouseahybridstackupwithlow-lossPTFEonthesurfacelayer.However,theonlyisolationyoucanreliablyachieveinthisboardcomesfromcoplanarityinyourrouting,i.e.,fromtheviafenceyouplacearoundRFlinesandaroundcomponentstopreventnoisecouplingbetweenboardsections. These4-layerstackupscouldbeusedforlowormoderatepowerlevels.Thegoalistoprovideisolationaspowerlevelsincreaseaswellasaccommodatethehighvoltage/currentthatmightbeneededathigherpowerlevels.Youcouldalsousea6-layeror8-layerstackupforthistypeofdesignwhenyouneedtoworkwithhigherpowerswhilealsoprovidinghighisolation.Forexample,youcouldmakeL3asignallayerforcoplanarRFlinesbetweentwoGNDplanes(onL2/L4),thenplacepoweronL5,andpossiblyrouteanyothersignalsyoumightneedonthesurfacelayersorL6(seebelow).Thisisbetterforahighpowerdesignthatrequiresalotofisolationasthegroundplanewillprovideshieldingbetweenlayers. This8-layerstackupprovidesapowerplaneandhighisolationfortheRFsignalsonaninnerlayer.Thiscouldalsobeusedasa6-layerboardbyremovingthetwobottomlayers.Byprovidingisolationbetweendifferentsectionsofthedesign,youcanhelppreventthetypeofparasiticcouplingthatallowsnoisetopropagateintotheoutput.Theoutputfromthesupplyshouldhavesufficientlylownoiseanddistortiontoprovidecleanpowertoothercomponents.Therearetwomainsourcesofnoiseinthistypeofdesign: NoisefromtheswitchingregulatororanoisyDCinput.  Noisecouplingbacktotheamplifierinputfromtheoutput Bothpointsaresolvedwiththestackupdesigntipsmentionedhere,aswellaswithsmartplacementofthenoisysectionsawayfromtheRFoutputsection.Thesecondpointismorechallengingathigherfrequencies,anditispossibletoseetheRFoutputexperiencepositivefeedbackbycouplingbackintotheinputoftheamplifierstage.Routingandfiltrationarealsoquiteimportantasthesecanhelpprovideadditionalisolationandnoiseelimination. PlacementandRouting ThesetwoaspectsofthedesignarecriticalasyouneedtosuppressthenoiseproblemsImentionintheabovetwopoints.RoutetheRFtracesfromtheoscillator,throughtheamplifier,andtotheoutputasgroundedcoplanarwaveguides(eitheronthesurfaceoroninternallayers)toensurethereissomeisolation.Don’tuseguardtracestoprovideanyshieldingastheywillcreatemorenoisecoupling;onlyusetheviafencestylethatyoucalculateforyourcoplanarlines.Also,makesurethatifyoudorouteonaninternallayer,todeterminewhetheryouneedbackdrillingbyanalyzingyourviastubs. Anyotherconditioningthatmightberequiredontheoutputdependsonthefunctionofthesupply.Willitroutedirectlytoanantenna,ortoanSMA/u.FLcoaxialline?It’stypicaltoputtheRFoutputthroughafilter(eitheraBAWorSAWfilter),althoughbecarefulwithcomponentselectionaschip-packagedBAWandSAWfilterscan’talwaysacceptthehighRFpowersusedinsomeRFpowersupplies. OneothercomponentyoumightneedontheRFOutnetincludeanisolator/circulatortopreventanyreflectionfromtravelingbacktotheamplifier.TherearesomeSMDisolatorsyoucanuseontheoutput,whichisparticularlyimportantifyou’reimplementingpoweroverRForsendingyourRFoutputdirectlytoanantenna. SMDRFisolatorslikethesearecompatiblewithreflowsolderingprocessesandcanhandlehighpowers(upto20Wormore).IfyoudoneedtorouteanysignalsthroughanexternalRFmodule,youcanplaceSMDu.FLorSMAconnectorstomaketheseconnections.Youcantakethesignalofftheboard,throughthemodule,andbackontotheboardasneededintheeventyourpowerlevelexceedstheallowedvalueforanequivalentSMD/through-holecomponentontheboard. InSummary WhileRFpoweramplifiersandpowersupplydesignshavetypicallybeenbuiltfromdiscretefilterelements,newercomponentsallowyoutobeveryaggressivewithyourformfactorandconsolidatemanyoftheseelementsontoasingleboard.Andofcourse,makesureyouconsultyourfabricatoraboutyourstackuptoensureit’smanufacturableasahybridboard.AlsomakesureyouaccountforcopperroughnessanddielectricdispersioninyourtransmissionlinedesigntoensureyourRFtransmissionlineimpedancehasthetypical50Ohmsvalue. WhenyouneedthebestPCBtoolsforRFpowersupplydesign,looktothecompletesetofPCBdesign,layout,andsimulationfeaturesinAltiumDesigner®.AfteryoucompleteyourphysicalRFpowersupplylayout,youcanusetheEDBExporterextensiontoimportadesignintoAnsysfieldsolversandperformarangeofSI/PI/EMIcalculationsforyourdesign.Whenyou’vefinishedyourdesign,andyouwanttoreleasefilestoyourmanufacturer,theAltium365™platformmakesiteasytocollaborateandshareyourprojects. Wehaveonlyscratchedthesurfaceofwhat’spossiblewithAltiumDesigneronAltium365.StartyourfreetrialofAltiumDesigner+Altium365today. RFPCBDesignOverview WhatisRFCircuitDesign? RFPCBDesignSoftware AboutAuthor AboutAuthor ZachariahPetersonhasanextensivetechnicalbackgroundinacademiaandindustry.Hecurrentlyprovidesresearch,design,andmarketingservicestocompaniesintheelectronicsindustry.PriortoworkinginthePCBindustry,hetaughtatPortlandStateUniversity andconducted researchonrandomlasertheory,materials, andstability.Hisbackgroundinscientificresearchspanstopicsinnanoparticlelasers,electronicandoptoelectronicsemiconductordevices,environmentalsensors,andstochastics.Hisworkhasbeenpublishedinoveradozenpeer-reviewedjournalsandconferenceproceedings,andhehaswritten1000+technicalblogsonPCBdesignforanumberofcompanies.HeisamemberofIEEEPhotonicsSociety,IEEEElectronicsPackagingSociety, andtheAmericanPhysicalSociety,andhecurrentlyservesontheINCITSQuantumComputingTechnicalAdvisoryCommittee. MorecontentbyZachariahPeterson RecentArticles DesigningaHomeAutomationIoTdevice InthisarticleAriMahpourwalksyouthroughhowtocreateyourownIoTconnecteddeviceandcontrolothersmarthomeproducts. ReadArticle OnTrackNewsletter:AltiumandIPCformPartnership,FabNotesandFoodforyourBrain-November2021 November2021VOL.5No.5FullArticle|WatchVideo|BrainFoodIPCjoinsAltiumasNewestNexarEcosystemPartnerRecentlyIPCandAltiumformallyannouncedthatIPCisjoiningthegrowingbodyoftheNexarecosystem.Inthisinterview,wetalktoDavidBergman,VPofstandardsandtechnologyatIPC.Hetalksabouthowhethinksthisnewpartnershipwillbringbi-directionalvaluetobothorganizations.ReadFullArticleWhat'sInPCB ReadArticle HowtoDesigntoaDifferentialImpedanceSpecification Differentialimpedanceissometimesmisunderstoodanditdependsonmultiplefactors.Learnmoreabouttracewidthdesignneededtoreachaspecificdifferentialimpedancetarget. 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