电气专业中英文对照翻译毕业设计.docx

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