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ID:17627283
大小:5.93 MB
页数:71页
时间:2018-09-04
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1、WebEnhancedWThisWebaddendumtoCMOSVLSIDesigncontainssectionsthathavebeenmovedoutoftheprintedbooktoreducethelength.9.4MoreCircuitFamiliesStaticCMOSissatisfactoryforthegreatmajorityoflogicgatesinmodernintegratedcir-cuitsandanassortmentofdomino,pass-transistorcircuits,andpseudo-nMOSac
2、countsfornearlyalloftheremaininggates.Alargenumberofothercircuitfamilieshavebeenproposedintheliterature.Thissectiondescribessomeofthesecircuitfamiliesandtheirstrengthsandlimitations.9.4.1DifferentialCircuitsSeveraldifferentialcircuitfamiliesusingnMOSpulldownnetworksarederivedfromt
3、hebasicCVSLform,asshowninFigureW9.1.DSLCNTLYYYYV=refV/2+VXXXXDDtInputsInputsffffFIGUREW9.1Differentialcircuitfamilies9.4.1.1DifferentialSplit-Level(DSL)DifferentialSplit-Level(DSL)[Pfennings85]placesnMOStransistorsinserieswiththebasicCVSLpulldownnetworks.Byapplyingareferencevoltag
4、eofVDD/2+Vttothesetransistors,theswingontheinternalnodes(XandX)arelimitedto0–VDD/2.Thisreducestheparasiticdelayofthepulldownstacks.Thelowerinternalvoltagesalsoleadtolowerelectricfieldsacrossthepulldowntransis-tors.Theinventorstookadvantageofthislowervoltagetoreducethechannellengths
5、ofthetransistorswithoutcompromisinghot-electronreliability.TheyclaimedatenfoldspeedupoverastaticCMOSfulladder;thiswasattributedtoafactorof2fortheCVSL12ChapterWWebEnhancedstructure,anotherfactorof2fromthelow-swingsignals,andafactorof2.5forusingshortertransistors.Inananometerprocess
6、,transistorsaregenerallyasshortascanbereliablymanufac-tured,soDSLcannotuseevenshortertransistors.Theauthorshavebeenunabletorepro-duceanyadvantageoverstaticCMOSinasubmicronprocess.Theresistanceoftheextraseriestransistordoesnothelp.AnotherdisadvantageofDSListhatthevoltagesonthepMOSg
7、atesonlyswingbetween0andVDD/2.Therefore,thepullupthatshouldbeOFFisactuallypartiallyON,resultinginstaticpowerdissipation.Finally,generatinganddis-tributingthereferencevoltagerequiressomeeffortandthereferencemaybesensitivetopowersupplynoiseandthresholdvoltagevariations.9.4.1.2Cascod
8、eNonthresholdLogic(CNTL)CascodeNo
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