2024/7/1可編輯1

Chapter2

CircuitSystemandDesign

第二章電路系統與設計

Outline大綱2.1CircuitandSystem電路與系統2.2AnalogandDigitalCircuitsDesign

模擬與數字電路設計2.3RadioReceiverCircuit無線電接收機電路

2024/7/1可編輯22.1CircuitandSystemOutline大綱Basicconcepts基本概念CircuitandSystem電路與系統

2024/7/1可編輯3Terminology術語chargen.負荷,電荷,費用,主管,充電,充氣,裝料conductivityn.傳導性,傳導率insulatorn.絕緣體,絕熱器gravitationaladj.重力的voltagen.[電工]電壓,伏特數voltsn.直流電壓amperen.安培ohmn.[物]歐姆coulombn.[電]庫侖(電量單位)diametern.直徑inductancen.感應系數,自感應2024/7/1可編輯4dielectricn.電介質,絕緣體adj.非傳導性的faradn.[電]法拉(電容單位)polarityn.極性potentialdifference[電]電位差，電勢差equivalentresistance等效電阻SuperpositionTheorem疊加定理Thevenin'sTheorem戴維南定理Norton'sTheorem諾頓定理2024/7/1可編輯5IntheBohrtheoryoftheatom(namedafterNielsBohr,1885–1962),electrons

orbitanucleuscontainingneutronsandprotons.Electricchargeismeasuredincoulombs.IntroductionTexttour文本瀏覽Basicconcepts

Chargeandconductivity

2024/7/1可編輯6Thisrelativemobilityofelectronswithinamaterialisknownaselectricconductivity.Conductivityisdeterminedbythetypesofatomsinamaterial(thenumberofprotonsineachatom'snucleus,determiningitschemicalidentity)andhowtheatomsarelinkedtogetherwithoneanother.2024/7/1可編輯7Itshouldalsobeunderstoodthatsomematerialsexperiencechangesintheirelectricalpropertiesunderdifferentconditions.Whilethenormalmotionof"free"electronsinaconductorisrandom,withnoparticulardirectionorspeed,electronscanbeinfluencedtomoveinacoordinatedfashionthroughaconductivematerial.Thisuniformmotionofelectronsiswhatwecallelectricity,orelectriccurrent.2024/7/1可編輯8Therecanbeelectriccurrentonlywherethereexistsacontinuouspathofconductivematerialprovidingaconduitforelectronstotravelthrough.Ifthepathisblocked,the"flow"willnotoccur.2024/7/1可編輯9

Electriccircuits,voltageandcurrent

Anelectriccircuitisformedwhenaconductivepathiscreatedtoallowfreeelectronstocontinuouslymove.Thiscontinuousmovementoffreeelectronsthroughtheconductorsofacircuitiscalledacurrent,anditisoftenreferredtointermsof"flow,"justliketheflowofaliquidthroughahollowpipe.Theforcemotivatingelectronsto"flow"inacircuitiscalledvoltage,whichtechnicallyisameasureofpotentialenergyperunitchargeofelectrons.

Themoremasssomethinghasandthehigherweliftit,themorepotentialenergyithas.2024/7/1可編輯10Onevoltisdefinedasthatmagnitudeofelectromotiveforcerequiredcauseacurrentofoneamperetopassthroughaconductorhavingaresistanceofoneohm.CurrentflowisrepresentedbythelettersymbolI.Thebasicunitinwhichcurrentismeasuredistheampere(amp).Oneampereofcurrentisdefinedasthemovementofonecoulombpastanypointofaconductorduringonesecondoftime.2024/7/1可編輯11Freeelectronstendtomovethroughconductorswithsomedegreeoffriction,oroppositiontomotion.Thisoppositiontomotionismoreproperlycalledresistance.TheresistanceofamaterialthatfollowsOhm'slawisconstant,orindependentofvoltageorcurrent,andtherelationshipbetweencurrentandvoltageislinear.Wheneveranelectricvoltageexistsbetweentwoseparatedconductors,anelectricfieldispresentwithinthespacebetweenthoseconductors.Electricalenergycanbestoredinanelectricfield.Thedevicetobecapableofdoingthisiscalledacapacitororacondenser.

Resistance,capacitanceandinductance2024/7/1可編輯12Ifacondenserisconnectedtoabattery,theelectronswillflowoutofthenegativeterminalofthebatteryandaccumulateonthecondenserplateconnectedtothatside.Thusthecondenserissaidtobecharged.Thecapacitanceisdirectlyproportionaltothedielectricconstantofthematerialandtotheareaoftheplatesandinverselytothedistanceoftheplates.Thelargertheplatearea,thesmallerthespacebetweenthem,thegreaterthecapacitance.Wheneverelectronsflowthroughaconductor,amagneticfieldwilldeveloparoundthatconductor.Thiseffectiscalledelectromagnetism.Magneticenergycanbestoredinamagneticfield.Thedevicetobecapableofdoingthisiscalledaninductor.2024/7/1可編輯13Tostoremoreenergyinaninductor,thecurrentthroughitmustbeincreased.Thismeansthatitsmagneticfieldmustincreaseinstrength,andthatchangeinfieldstrengthproducesthecorrespondingvoltageaccordingtotheprincipleofelectromagneticself-induction.Whenthecurrentthroughaninductorisincreased,itdropsavoltageopposingthedirectionofelectronflow,actingasapowerload.Inthisconditiontheinductorissaidtobecharging,becausethereisanincreasingamountofenergybeingstoredinitsmagneticfield.Notethepolarityofthevoltagewithregardtothedirectionofcurrent.2024/7/1可編輯142.CircuitandSystemOhm'sLawThefirst,andperhapsmostimportant,relationshipbetweencurrent,voltage,andresistanceiscalledOhm'sLaw,discoveredbyGeorgSimonOhmin1827.Ohm'sprincipaldiscoverywasthattheamountacircuitisdirectlyproportionaltothevoltageofelectriccurrentthroughametalconductorinimpressedacrossit,foranygiventemperature.Ifweknowthevaluesofanytwoofthethreequantities(voltage,current,andresistance)inacircuit,wecanuseOhm'sLawtodeterminethethird.

2024/7/1可編輯15Kirchoff’sCurrentLawandKirchoff’sVoltageLaw

Kirchoff’sCurrentLawisthetotalchargeflowingintoanodemustbethesameasthetotalchargeflowingoutofthenode.Kirchhoff'sVoltageLaw(orKirchhoff'sLoopRule)isaresultoftheelectrostaticfieldbeingconservative.Itstatesthatthetotalvoltagearoundaclosedloopmustbezero.Ifthiswerenotthecase,thenwhenwetravelaroundaclosedloop,thevoltageswouldbeindefinite.2024/7/1可編輯16IntroductiontonetworktheoremsInelectricnetworkanalysis,thefundamentalrulesareOhm'sLawandKirchhoff'sLaws.Whilethesehumblelawsmaybeappliedtoanalyzejustaboutanycircuitconfiguration(evenifwehavetoresorttocomplexalgebratohandlemultipleunknowns),therearesome“shortcut”methodsofanalysistomakethematheasier.2024/7/1可編輯17SuperpositionTheoremThestrategyusedintheSuperpositionTheoremistoeliminateallbutonesourceofpowerwithinanetworkatatime,usingseries/parallelanalysistodeterminevoltagedrops(and/orcurrents)withinthemodifiednetworkforeachpowersourceseparately.Then,oncevoltagedropsand/orcurrentshavebeendeterminedforeachpowersourceworkingseparately,thevaluesareall“superimposed”ontopofeachother(addedalgebraically)tofindtheactualvoltagedrops}currentswithallsourcesactive.2024/7/1可編輯18Thevenin'sTheoremThevenin'sTheoremstatesthatitispossibletosimplifyanylinearcircuit,nomatterhowcomplex,toanequivalentcircuitwithjustasinglevoltagesourceandseriesresistanceconne