电气专业中英文对照翻译毕业设计.docx
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电气专业中英文对照翻译毕业设计.docx
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电气专业中英文对照翻译毕业设计
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Chapter3DigitalElectronics
3.1Introduction
Acircuitthatemploysanumericalsignalinitsoperationisclassifiedasadigitalcircuitputers,pocketcalculators,digitalinstruments,andnumericalcontrol(NC)equipmentarecommonapplicationsofdigitalcircuits.Practicallyunlimitedquantitiesofdigitalinformationcanbeprocessedinshortperiodsoftimeelectronically.Withoperationalspeedofprimeimportanceinelectronicstoday,digitalcircuitsareusedmorefrequently.
Inthischapter,digitalcircuitapplicationsarediscussed.Therearemanytypesofdigitalcircuitsthatelectronics,includinglogiccircuits,flip-flopcircuits,countingcircuits,andmanyothers.Thefirstsectionsofthisunitdiscussthenumbersystemsthatarebasictodigitalcircuitunderstanding.TheremainderofthechapterintroducessomeofthetypesofdigitalcircuitsandexplainsBooleanalgebraasitisappliedtologiccircuits.
3.2DigitalNumberSystems
Themostcommonnumbersystemusedtodayisthedecimalsystem,inwhich10digitsareusedforcounting.Thenumberofdigitsinthesystemiscalleditsbase(orradix).Thedecimalsystem,therefore,thecountingprocess.Thelargestdigitthatcanbeusedinaspecificplaceorlocationisdeterminedbythebaseofthesystem.Inthedecimalsystemthefirstpositiontotheleftofthedecimalpointiscalledtheunitsplace.Anydigitfrom0to9canbeusedinthisplace.Whennumbervaluesgreaterthan9areused,theymustbeexpressedwithtwoormoreplaces.Thenextpositiontotheleftoftheunitsplaceinadecimalsystemisthetensplace.Thenumber99isthelargestdigitalvaluethatcanbeexpressedbytwoplacesinthedecimalsystem.Eachplaceaddedtotheleftextendsthenumbersystembyapowerof10.
Anynumbercanbeexpressedasasumofweightedplacevalues.Thedecimalnumber2583,forexample,isexpressedas(2×1000)+(5×100)+(8×10)+(3×1).
Thedecimalnumbersystemiscommonlyusedinourdailylives.Electronically,thebinarysystem.Electronically,thevalueof0canbeassociatedwithalow-voltagevalueornovoltage.Thenumber1canthenbeassociatedwithavoltagevaluelargerthan0.Binarysystemsthatusethesevoltagevaluesaresaidto,thischapter.
Thetwooperationalstatesofabinarysystem,1and0,arenaturalcircuitconditions.Whenacircuitisturnedoffortheoff,or0,state.Anelectricalcircuitthattheon,or1,state.ByusingtransistororICs,itiselectronicallypossibletochangestatesinlessthanamicrosecond.Electronicdevicesmakeitpossibletomanipulatemillionsof0sandisinasecondandthustoprocessinformationquickly.
Thebasicprinciplesofnumberingusedindecimalnumbersapplyingeneraltobinarynumbers.Thebaseofthebinarysystemis2,meaningthatonlythedigits0and1areusedtoexpressplacevalue.Thefirstplacetotheleftofthebinarypoint,orstartingpoint,representstheunits,oris,location.Placestotheleftofthebinarypointarethepowersof2.Someoftheplacevaluesinbase2are2º=1,2¹=2,2²=4,2³=8,2⁴=16,25=32,and26=64.
Whenbasesotherthan10areused,thenumbersshouldexample.
Thenumber100₂(read“one,zero,zero,base2”)isequivalentto4inbase10,or410.Startingwiththefirstdigittotheleftofthebinarypoint,thisnumberthismethodofconversionabinarynumbertoanequivalentdecimalnumber,writedownthebinarynumberfirst.Startingatthebinarypoint,indicatethedecimalequivalentforeachbinaryplacelocationwherea1isindicated.Foreach0inthebinarynumberleaveablankspaceorindicatea0'Addtheplacevaluesandthenrecordthedecimalequivalent.
Theconversionofadecimalnumbertoabinaryequivalentisachievedbyrepetitivestepsofdivisionbythenumber2.Whenthequotientisevenwithnoremainder,a0isrecorded.Whenthequotientprocesscontinuesuntilthequotientis0.Thebinaryequivalentconsistsoftheremaindervaluesintheorderlasttofirst.
3.2.2Binary-codedDecimal(BCD)NumberSystem
Whenlargenumbersareindicatedbybinarynumbers,theyaredifficulttouse.Forthisreason,theBinary-CodedDecimal(BCD)methodofcountingwasdevised.Inthissystemfourbinarydigitsareusedtorepresenteachdecimaldigit.Toillustratethisprocedure,thenumber105,isconvertedtoaBCDnumber.Inbinarynumbers,ToapplytheBCDconversionprocess,thebase10numberisfirstdividedintodigitsaccordingtoplacevalues.Thenumber10510givesthedigits1-0-5.Convertingeachdisplayedbythisprocesswithonly12binarynumbers.ThebetweeneachgroupofdigitsisimportantwhendisplayingBCDnumbers.
ThelargestdigittobedisplayedbyanygroupofBCDnumbersis9.Sixdigitsofanumber-codinggrouparenotusedatallinthissystem.Becauseofthis,theoctal(base8)andthebinaryformbutusuallydisplaytheminBCD,octal,orabase8systemis7.Theplacevaluesstartingattheleftoftheoctalpointarethepowersofeight:
80=1,81=8,82=64,83=512,84=4096,andsoon.
Theprocessofconvertinganoctalnumbertoadecimalnumberisthesameasthatusedinthebinary-to-decimalconversionprocess.Inthismethod,equivalentdecimalis25810.
ConvertinganoctalnumbertoanequivalentbinarynumberissimilartotheBCDconversionprocess.Theoctalnumberisfirstdividedintodigitsaccordingtoplacevalue.Eachoctaldigitisthenconvertedintoanequivalentbinarynumberusingonlythreedigits.
Convertingadecimalnumbertoanoctalnumberisaprocessofrepetitivedivisionbythenumber8.Afterthequotientdetermined,theremainderisbroughtdownastheplacevalue.Whenthequotientisevenwithnoremainder,a0istransferredtotheplaceposition.Thenumberforconverting409810tobase8is100028.
Convertingabinarynumbertoanoctalnumberisanimportantconversionprocessofdigitalcircuits.Binarynumbersarefirstprocessedataveryoutputcircuitthenacceptsthissignalandconvertsittoanoctalsignaldisplayedonareadoutdevice.
mustfirstbedividedintogroupsofthree,startingattheoctalpoint.Eachbinarygroupisthenconvertedintoanequivalentoctalnumber.Thesenumbersarethencombined,whileremainingintheirsamerespectiveplaces,torepresenttheequivalentoctalnumber.
3.2.4HexadecimalNumberSystem
Thedigitalsystemstoprocesslargenumbervalues.Thebaseofthissystemis16,whichmeansthatthelargestnumberusedinaplaceis15.Digitsusedbythissystemarethenumbers0-9andthelettersA-F.ThelettersA-Pareusedtodenotethedigits10-15,respectively.Theplacevaluestotheleftofthe.
Theprocessofchangingaproperdigitalorder.Theplacevalues,orpowersofthebase,arethenpositionedundertherespectivedigitsinstep2.Instep3,thevalueofeachdigitisrecorded.Thevaluesinsteps2and3arethenmultipliedtogetherandadded.Thesumgivesthedecimalequivalentvalueofa.Initially,theconvertedtoabinarynumberusingfourdigitspergroup.Thebinarygroupiscombinedtoformtheequivalentbinarynumber.
Theconversionofadecimalnumbertoa,aswithothernumbersystems.Inthisprocedurethedivisionisby16andremainderscanbeaslargeas15.
Convertingabinarynumbertoagroupsoffourdigits,startingattheconvertedtoadigitalcircuit-designapplicationsbinarysignalsarefarsuperiortothoseoftheoctal,decimal,orbeprocessedveryeasilythroughelectroniccircuitry,sincetheycanberepresentedbytwostablestatesofoperation.Thesestatescanbeeasilydefinedasonoroff,1or0,upordown,voltageornovoltage,rightorleft,oranyothertwo-conditionstates.Theremustbenoin-betweenstate.
Thesymbolsusedtodefinetheoperationalstateofabinarysystemareveryimportant.Inpositivebinarylogic,thestateofvoltage,on,true,oraletterdesignation(suchasA)isusedtodenotetheoperationalstate1.Novoltage,off,false,andtheletterAarecommonlyusedtodenotethe0condition.Acircuitcanbesettoeitherstateandwillremaininthatstateuntilitiscausedtochangeconditions.
Anyelectronicdevicethatcanbesetinoneoftwooperationalstatesorconditionsbyanoutsidesignalissaidtobebistable.Relays,lamps,switches,transistors,diodesandICsmaybeusedforthispurpose.Abistabledevice.Byusingmanyofthesedevices,itispossibletobuildanelectroniccircuitthatwillmakedecisionsbasedupontheappliedinputsignals.Theoutputofthiscircuitisadecisionbasedupontheoperationalconditionsoftheinput.Sincetheapplicationofbistabledevicesindigitalcircuitsmakeslogicaldecisions,theyarecommonlycalledbinarylogiccircuits.
Ifweweretodrawacircuitdiagramforsuchasystem,includingalltheresistors,diodes,transistorsandinterconnections,wewouldfaceanoverwhelmingtask,andanunnecessaryone.Anyonewhoreadthecircuitdiagramwouldintheirmindgroupthecomponentsintostandardcircuitsandthinkintermsofthe"system"functionsoftheindividualgates.Forthisreason,wedesignanddrawdigitalcircuitwithstandardlogicsymbols.Threebasiccircuitsofthistypeareusedtomakesimplelogicdecisions.ThesearetheANDcircuit,ORcircuit,andtheNOTcircuit.Electroniccircuitsdesignedtoperformlogicfunctionsarecalledgates.Thistermreferstothecapabilityofacircuittopassorblockspecificdigitalsignals.Thelogic-gatesymbolsareshowninFig.3-1.ThesmallcircleattheoutputofNOTgateindicatestheinversionofthesignal.Mathematically,thisactionisdescribedasA=.Thuswithoutthesmallcircle,therectanglewouldrepresentanamplifier(orbuffer)withagainofunity.AnANDgatethe1statesimultaneously,thentherewillbea1attheoutput.TheANDgateinFig.3-1producesonlya1out-putwhenAandBareboth
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