bit error rate analysis of cactus technologies sd card products（cactus sd卡产品的比特误码速率分析—外文翻译_学位论文.doc

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1、BitErrorRateAnalysisofCactusTechnologiesSDCardProducts1.IntroductionCactusTechnologiesproductsarebuiltusingonlythehighestqualitySLC(SingleLevelCell)NANDflashdevices.However,similartoharddiskmedia,NANDflashmediaisnotperfectandsofterrorswillinevitablyoccurduringusage.

2、VariouspublishedpapershaveshownthattherawBER(BitErrorRate)ofSLCNANDisintherangeof1E9to1E11.WhilethisisquitegoodandsignificantlybetterthanthatofMLC(MultiLevelCell)NAND,manypplicationsrequireBERsthatareonparwith,orbetterthanthoseprovidedbytraditionalharddiskdrives,whi

3、chtypicallyhasBERsintherangeof1E15.Fortunately,thesofterrormechanismsinSLCNANDarewellunderstoodandcanbeeasilycompensatedforwiththeuseofarobustECC.Inthispaper,wewillprovideabriefanalysisoftheBERofCactusSDCardproductsandshowhowthestrongbuiltinECCinthecontrollerisablet

4、oprovidetypicalapplicationBERsthatcanmatchorevensurpassthatoftypicalharddiskdrives.2.TheProblemBit'disturb'phenomenaisinherenttotheNANDCactusTechnologiesLimitedasharchitecture.Therearethreebasiccausesofsuchbit'disturbs':●Programdisturb●Readdisturb●ChargeleakageProgr

5、amdisturboccurswhenunselectedcellsareexposedtohighvoltageswhenneighboringcellsarebeingprogrammed.Theresultofthisinadvertentexposuretohighvoltagesisthattheaffectedcellappearsslightlyprogrammed.Readdisturboccurswhenunselectedcellsareexposedtonormaloperatingvoltageswhe

6、nneighboringcellsarebeingread.Theresultofthisistheaffectedcellappearsslightlyprogrammed.Duetothemuchlowervoltagesusedduringreadoperations,readdisturbeffectsaremuchweakerthanthoseofprogramdisturb.Chargeleakageoccursbecausethestoredchargeonthefloatinggateoftheflashcel

7、lwillslowlyleakawayovertime,thuscausingaprogrammedcelltograduallybecomeunprogrammed.Fortunately,allthreetypesofdisturbmechanismdescribedabovearenotpermanentandtheaffectedcellsare'restored'oncetheblockiserased.Therefore,toovercomethesofterrorsthatarecausedbythesebit'

8、disturbs',allthatisrequiredisasufficientlypowerfulECCthatisdesignedfortheerrorcharacteristicsoftheflashmedia.3.BERAnalysisCactusTechnologi