DDR Advanced Topics (1)

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1、DDRAdvancedTopicsSanDiskInternalWorkshop2012BenChiaSignalIntegrityConsultant7/18/2012HighSpeedDesignCenter©Outline•Terminationtheory•Vref•Single-endedvsDifferentialsignaling•SSLTvsPODL•GDDRandMobilmemorysystems•MarginforHighVolumeProduction•LPDDRandMobileRoadMapHighSpeed2Design

2、Center©DDRProtocolHighSpeed3DesignCenter©DDR1/2/3ComparisonHighSpeed4DesignCenter©DDR3vsDDR4HighSpeed5DesignCenter©LowPowerDDRHighSpeed6DesignCenter©DDR1TerminationHighSpeed7DesignCenter©DDR2TerminationHighSpeed8DesignCenter©DDR4TerminationsHighSpeed9DesignCenter©SeriesTerminat

3、ionsHighSpeed10DesignCenter©DifferentParallelTerminationsHighSpeed11DesignCenter©Ref:DesignCon2012IBMpaperDifferentParallelTerminationsHighSpeed12DesignCenter©Ref:DesignCon2012IBMpaperSignalIntegrityTopics:ODT•DQbushason-die-termination•Advantagescomparetooff-chiptermination–Te

4、rminatedclosetothereceiver,nostub–Lowcost,easyPCBdesign–DQtimingmarginisnotsensitivetoODTvariation–Useseparateterminationpowerpintoreducenoisecouplingfromothernoisesource–Terminationvaluesareadjustableforbestpowerconsumption/performancetradeoffHighSpeed13DesignCenter©ODTcompare

5、toseriestermination•DDRODTtermination–Apull-uporpull-downparalleltermination–Aidealterminationmethodtoreducereflection–Consumingpowereveninnon-activemode–Apull-uponlyconsumespoweratlowstate•Seriestermination–Cannotremovereflectionfromanopenfarendload–Onlyattenuatesreflection–Si

6、gnalamplitudeisreducedduetoseriesresistor–Consumingunusedpoweratterminationresistor–NeedstobecarefullyselectedandnottoaffectVinthresholdHighSpeed14DesignCenter©SSTL(DDR)andPODL(GDDR4)•SSTLusespullupandpulldowntermination•PODL(Pseudo-Open-DrainLogic)–Onlyhaspull-upterminationtos

7、avepowerathighstate–Pullupdriverisweakertoincreaserisetime–Fasterrisingedgethanfallingedge–ReferencevoltagesetupneedstoaccountforrisingandfallingedgeresponseHighSpeed15DesignCenter©SSTL_1.5I/ODriver1.5v1.5vHighSpeed16DesignCenter©SSONoiseforSSTLDriver(pulldowncase)HighFrequency

8、noisefromexternalloopstillcanbesignificantHighSpeed17D