Backplane ConnectorsWord格式文档下载.docx
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Backplane ConnectorsWord格式文档下载.docx
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6.Marketdrivers
Whylearnaboutbackplanes?
Drivenbymarketdemandforfaster,morecomplexsystems,backplanetechnologyhasevolvedrapidly.Backplaneshavepenetratedmanymarketsbeyondthetelecomindustryforwhichtheyweredeveloped.Backplaneconnectorsrepresentamajorpotentialinthismarket.
Takeaguessatthepercentagedollarvaluethatbackplaneconnectorsrepresentinatypicalbackplaneapplication.
Whatisabackplane?
AbackplaneisaspecialtypeofPCBthatisspecificallydesignedtointerconnectotherPCBs.Itissaidtobea"
passive"
devicebecauseithasnoactivecomponents,suchasprocessors.
Abackplanefunctionsasasystembackbonebyprovidingmechanicalstabilityandservingasacontactplaneforintegratingsystemcomponentsandsignalandpowerlines.
Backplane,motherboard,anddaughterboard
Backplanesaresometimesmistakenlycalledmotherboards.
Thisisincorrectbecauseamotherboardhasactivecomponents,suchasmicroprocessors.AgoodexampleisthemotherboardinaPC,whichcontainstheCPUandmemory.AbackplanesimplyinterconnectsotherPCBs,called
daughtercards
or
daughterboards.
Onceabackplaneispopulatedwithdaughtercards,thecombinedunitissometimescalleda
backpanel.
However,inthiscourse,we'
llusetheterms
backplane
andbackpanel
synonymously.
Thebookshelfanalog
Backplanesaresometimesdescribedusingabookshelfanalogy.Abookshelfallowsawidevarietyofbookstobefreelyinsertedandremoved.
Similarly,onabackplane,daughtercardsthatperformdifferentfunctionscanbeinsertedandremovedtomeettherequirementsoftheapplication.
Forexample,oneapplicationmaystressI/Ofunctionality,whileanotheremphasizesprocessing.Thebackplaneineachcanbeconfiguredforthespecificneedusingthedesiredcombinationofdaughtercards.Andcardscanbeadded,removed,orreplacedatanytime.
Advantageofbackplanes
Applicationdesignerslikebackplanesbecausetheyallowthemodularityandflexibilitythatisessentialtohigh-endproductslikeroutersandservers.Complex,customsystemscanbebuiltusingthedesiredcollectionofdaughtercardbuildingblocks.
ManufacturerscouldsoldermostorallsystemcomponentsontoasinglePCBatsignificantlylowercost.Buttheapplicationconfigurationwouldthenhavemajorlimitations.
Modularityofbackplanes
Takeamomentandthinkaboutthisconceptofmodularityinelectronicsystems.
Imagineaserver,forexample.Canyouthinkoffouradvantagesthatmodularityofferstosystemdesignersandcustomers?
Answerthequestionontheright.
Wherearebackplanesused?
Backplanesmaybeusedanywherehighperformanceandmodularityaresystemrequirements.
Thefollowinglistshowssomeofthekeyapplications.
▪Computers
▪Datastorage
▪Internetworking
▪Telecominfrastructure
▪Testsystems
▪Medicalequipment
Howbackplanescommunicate
Backplanesinterconnectsystemcomponentsviadaughtercards.Thisallowsthevariouscomponentsto"
talk"
toeachother.
Thiscommunicationamongcomponentstakesplacethroughelectricalchannelscalled
traces
onandinsidethecircuitboard.TracesleadtoPCBholes,intowhichconnectors(andcards)areinserted.
Thetracesonabackplaneareconfiguredineitheroftwotopologies:
bussed
(sometimescalledmulti-point)and
point-to-point.
Eachtypeoftraceisexplainedonthefollowingpages.
Whatisabus?
Abusisatracetopologythathasthefollowingcharacteristics:
▪Signalsaretransmittedalongacontinuousmediumtoallboardsinthesystem
▪Allboardsreceivethesameinformation,butonlyaddressedboardsusetheinformation
▪Aboardpluggedanywhereonthebackplanereceivestheinformationitneeds
Intheimageshownhere,thepairsofholesontheleftholddifferentdaughtercards.Bothcardsreceivethesameinformation,butonlytheaddressedboardusesthatinformation.
Ifthisbusconceptsoundsfamiliar,itshould.Bustechnologyisthebasisofthecomputeryouareusingrightnow.
PCI,forexample,isacommonhighspeedI/ObusforPCsliketheoneyou'
reusingnow.PCIconnectsperipheralslikevideocards,diskstorage,andnetworkinterfaces,tothecomputer'
smemory,chipset,andprocessoronthemotherboard.
Astrictpinstandardisemployedtopermitthedrop-incapabilitythatgivesPCIsystemstheirmodularity.
Point-to-pointwiring
Thesecondtracepatternispoint-to-pointwiring.Systemcomponentscommunicatethroughdedicatedtracesbetweenpairsofboards.
Thisdesigneliminateselectricaldisruptioncommontobuswiring,inwhichmanymorepinsandholesareneeded.
Point-to-pointwiringiscommoninhigher-performanceapplications,suchastelecomswitches.Itispreferredforhighdatarateexchangesbecausededicatedsignalpathsassuregreatersignalintegrity.
Designersrefertotheeaseandflexibilitywithwhichtracescanberoutedasroutability.
Partofgoodbackplaneconnectordesignistheabilitytoaccommodateefficienttracerouting.
Busorpoint-to-point?
Devicesthatoperateatdataspeedsofupto200Mbpscommonlyusebuswiring.
Forhighdatarates,suchas2.5Gbpsandabove,signalintegrityissuescallforthededicatedconductivepathwaysofpoint-to-pointtracerouting.
Backplaneconfigurations
Daughtercardsconnecttobackplanesmainlyinthetwoconfigurationsshownhere.
Standard
Inastandardconfiguration,daughtercardsconnecttothebackplanefromthefront.
Midplane
Inamidplaneconfiguration,pinspassthroughthebackplaneandconnecttoaheaderontheotherside.
Daughtercardsoneachsidemayperformdifferentfunctions.Oneboardmightperformswitchfunctions,whiletheotherperformsI/Ofunctions.Eitherboardcanbechangedwithoutaffectingtheother.
Marketdrivers–convergence
Aswemoveintothefuture,expertsagreethatthesinglebiggestbackplaneconnectormarketdriverwillbetheconvergenceofnetworkingandtelecom,ordataandvoice.Thiswillfurtherboosttheneedforgreaterdensityandbandwidth.
Thetermconvergence
describestheefforttomeetthesevarioustransmissionneedsonasinglelocaland/orwideareanetwork.Asthechartontherightshows,thisintegrationrequiresabalancebetweendensityandspeed,performanceandcost.
1.FirstMateLastBreak
2.Longwipelength
3.Highdensity
4.Shielding
5.Modularity
6.Ruggedness
7.Compliantpins
8.Guidepins
9.Codekeys
10.Boardorientations
BackplaneConnectorFeatures
Backplaneconnectorsperformthesamefunctionasotherboard-to-boardconnectors.
However,becausetheyfocusonmaximizingdensityand/orspeed,theyhaveafewdistinctiveorimportantcharacteristics.Backplaneapplicationsalsomakesomespecificdemandsonmechanicalperformance.
Thislessonintroducesthecommonfeaturesofbackplaneconnectors.
FirstMateLastBreak
FirstMateLastBreak(FMLB)isamatingtechniquethatpreventsdamagetoelectricalcircuitrybymatingpinsofdifferentlengthsinaspecificsequence.Generally,groundpinsmatefirst,thenpowerpins,andfinallythesignalpins.
FMLBisthefeaturethatallowsbackplaneconnectorstobehot-plugged.
Toviewasimplifiedmatingsequence,clicktheStart
button.
1.
Apowerreturnpinmakescontactfirst.Thisprovidesgroundingbeforethesignalpinsmate.
2.
Secondtomatearepre-chargecapacitorpins.
3.Finally,signalpinsmate.
Longwipelength
Wipingistheactionthatoccurswhencontactsarematedwithaslidingaction.Wipingremovescontaminantsfromthecontactsurfaceforbetterelectricalcontact.
Thewipeonbackplaneconnectorsisoftenextended,likethetoponeshownhere.Longerwipelengthsoffergreaterassuranceofcontaminantremoval.
Here'
saquestionaboutwipingandbackplaneinterconnects.
Highdensity
Today'
shigh-endapplicationsuseallthepindensitydesignerscanprovide.Injustafewyears,densityhasgrownfrom20circuitsper25mmontheoriginaledgecardbackplaneconnectorto80differentialpairsperinch
inMolex'
sImpact™system.Movingcircuitsclosertogether,inparticularathighertransmissionspeeds,raisesahostofsignalintegrityissuesthatbackplanesystemdesignersmustdealwith.
Shielding
Asignaltransmissiongeneratesanelectromagneticfieldarounditself.Highersignalspeedsamplifythefield.Unlesscontrolled,thefieldcaninterferewithsignalsonnearbyconductors.Backplaneconnectorsemployshieldingtoelectricallyisolatesignalsfromthisinterference.
Forexample,Molex'
sVHDM6-rowconnector(rightandbelow)addsinternalmetalshieldsbetweenpincolumns.
Modularity
Backplaneconnectorsoftenofferbuildingblockcomponentsthatcanbeassembledinmanyconfigurationstoaccommodatethecomplexityandscalabilityofbackplaneapplications.
Theconnectorontherightrepresentsthismodularapproach.Customerscancombinesignal,power,andguidancemodules.Ametalstiffenerintegratesthemonoblock.
Ruggedness
Manybackplaneconnectorsareexceptionallyruggedbecausebackplanesarecommonlyusedinapplicationsthataresubjecttostressandotherenvironmentalfactors.Backplaneconnectorsmustthereforehaveaboveaveragemechanicalandelectricalintegrity.
Inadd
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