IntegratedCircuitsplayaveryimportantpartinelectronics.Mostarespeciallymadeforaspecifictaskandcontainuptothousandsoftransistors,diodesandresistors.SpecialpurposesIC''ssuchasaudio-
amplifiers,FMradios,logicblocks,regulatorsandevenawholemicrocomputersintheformofamicrocontrollercanbefittedinsideatinypackage.SomeofthesimpleIntegratedCircuitsareshowninfigure
7.1.
Fig.7.1:Integratedcircuits
Dependingonthewaytheyaremanufactured,integratedcircuitscanbedividedintotwogroups:hybridandmonolithic.Hybridcircuitshavebeenaroundlonger.Ifatransistorisopened,thecrystalinsideisvery
small.Thismeansatransistordoesn''ttakeupverymuchspaceandmanyofthemcanbefittedintoasingleIntegratedCircuit.
Thepin-outforsomeofthecommonpackagesisshowninFigure7.2:
Fig.7.2:Pin-outandsymbolsforsomecommonintegratedcircuits
MostintegratedCircuitsareinaDILpackage-DualInLine,meaningtherearetworowsofpins.(DIL16andDIL8areshownin7.2band7.2c).Thedeviceisviewedfromthetopandthepinsarenumberedinan
anti-clockwisedirection.Highpowerintegratedcircuitscangeneratealotofheatandtheyhaveametaltagthatcanbeconnected
toaheatsinktodissipatetheheat.ExamplesoftheseIC''sareshownin7.2dand7.2e,and7.2f.
Symbolsusedtorepresentintegratedcircuitsareshownin7.2gand7.2i.Symbol7.2giscommonlyusedtorepresentamplifiers.
Figure7.2ishowsanoperationalamplifier.Signs+and-representinvertingandnon-invertinginputs.Thesignaltobeamplifiedisappliedbetweenoneoftheinputsandground(groundandsupplyaren''t
represented,butarenecessaryforthecircuittooperate).Integratedcircuitscanbedividedintotwofurthergroups:analog(linear)anddigital.Theoutput
voltageofalinearcircuitsiscontinuous,andfollowschangesintheinput.TypicalrepresentativeofalinearICisanintegratedaudioamplifier.Whenasignalfromamicrophoneisconnectedtotheinputtheoutput
willvaryinthesamewayasthevoltagefromthemicrophone.Ifwatchedonanoscilloscope,thesignalontheoutputwillbethesameshapeasthemic''ssignal,onlythevoltagewillbehigherdependingonthe
amplificationoftheintegratedcircuit.ItisadifferentsituationwithdigitalIC''s.Theiroutputvoltageisnotcontinuous.ItiseitherLOWorHIGH
anditchangesfromonestatetotheotherveryquickly.
7.1Analogintegratedcircuits
Whileonthetopicofanalogcircuits,wewilllookattheLM386IC.Ithasallthecomponentsforacompleteaudio-amplifier.Figure7.3ashowsanexampleofanamplifiermadewiththisintegratedcircuit,whichcanbe
usedasacompleteamplifierforawalkman,interphone,cassetteplayerorsomeotheraudiodevice.Itcanalsobeusedasatestcircuitfortroubleshooting.
Fig.7.3:a-AlowfrequencyamplifierusingtheLM386
Thesignalisbroughttothenon-invertinginput(betweenpin3andground).Invertinginput(pin2)isconnectedtoground.If10μFisplacedbetweenpins1and8avoltageamplificationof200iscreated.If
thiscapacitorisremovedtheamplificationis20.Itispossibletoachievein-betweenamplificationbyaddingaresistorandconnectingitinserieswiththecapacitor.
Oneoftheessentialcomponentsinthiscircuitisthe100nFcapacitorwhichisplacedbetweenpin6(whichisconnectedtothepositiveofthesupply)andground.Thecapacitorshouldbeceramicandshouldbe
mountedasclosetotheintegratedcircuitaspossible.Thisiscommonpracticewhenworkingwithintegratedcircuits,evenwhenitisn''tshowninthediagramasacapacitorconnectedbetweenthepositive
andnegativestabilizesthevoltageandprotectsthecircuitfromspikesandaphenomenoncalledinstability.ThisisduetoinductanceinthepowersupplytracksallowinghighcurrentstakenbytheICto
upsetitsoperation.
7.2Digitalintegratedcircuits
TheCD4011willbeour"show-and-tell"ICtocoverthemaincharacteristicsofdigitalcircuits.Itisa14pinDILpackage.Thepin-outisshowninfigure7.4a.Notethesmallhalf-roundslitononeendoftheIC.It
identifiespin1.Pins7and14connecttoasupply(batteryorDCpowersupply).Negativeisconnectedtopin7.Positiveisconnectedtopin14.
TherearefourlogicNANDgatesinaCD4011IC.Eachhastwoinputsandoneoutput.ForgateN1theinputsarepins1and2,andoutputispin3.ThesymbolforaNANDgateisdisplayedinfigure7.4b.The
inputsaremarkedAandBandoutputisF.Thesupplyvoltagecanbeupto16vandaslowas5V.Theoutputwilldeliverupto10mAat12vbutthisisreducedasthesupplyvoltageisreduced.
Figure7.4bshowsthetruthtableforaNANDgate.Itshowstheoutputvoltage(voltagebetweenFandground)withdifferentinputstates.Becausethereareonlytwovoltagesforeverypin,wecallthemstates,
withlogiczerowhenthevoltageiszero,andlogiconewhenthevoltageonthepinisthesameasthesupplyvoltage.
Fromthiswecanreadthesecondrowofthetruthtable:iflogiczeroisonbothinputpins,outputislogicone,thirdrowissimilar:ifthefirstinputisone,andthesecondoneiszero,outputislogicone,fourth
row:ifthefirstinputiszero,andthesecondoneisone,outputislogicone.Fifthrowisdifferent,sincebothofitsinputsareone,thedefinitionofNANDgatestatesthattheoutputiszero.
Fig.7.4:a-4011pinplacements,b-symbolandthetruthtableforNANDgates,
Logiccircuitshavemanyapplications,buttheirmainuseisincomputercircuits.Thefollowingcircuitisasimpleexampletoshowhowthegatescanbeconnectedtoproduceaprojectthat
turnsonaglobewhenafingerisplacedona"touchpad."Theglobeturnsoffafteraperiodoftime,determinedbythevalueofthe470uand2M2resistor.
TheoperationofaNANDgate
Letslookatthefunctionalitiesofthefollowingcircuit.BothinputsofNI1areconnectedtoeachother,sowheninputPisHIGH,outputiszero.ThislogiczeroispassedontoNI2,sonomatterwhatisontheinput
6,output4islogicone.Thismeansthat,betweenthegroundandpin4,thevoltageisequalto12V.
Fig.7.5:Sensorswitchusinga4011
CurrentflowsthroughcapacitorCandresistorR,socapacitorbeginstocharge.Everyunchargedcapacitorbehaveslikeashortcircuit.Becauseofthat,when12Vappearsonpin4,itisalsopresentonresistorR
andalsoonpins8and9.Pin10showslogiczerobecauseofthiswhichisconnectedtopin6.Fromnowon,logiczeroonpin5isnolongerneededbecauseonlyoneinputneedstobezerofortheoutputtobe
logicone.SoinputPisnolongerneeded.GatesNI2andNI3maintainlogiczeroonpin4.Howlongwillthislast?Itdependsonthevalueofthecapacitorandresistor.Asthecapacitorcharges,thevoltageonthe
resistordropsandwhenitfallsto1/2ofthesupplyvoltage(6Vinourcase),NI3detectsalowonitsinputssologiconeappearsonpin10.Sincelogiconeisnowoninput5(nologiconepresentonP),and
oninput6,output4iszero,capacitordumpsitschargeviadiodesontheinputsonpins8and9andthecircuitstartsoperatingagain.
Aswesaw,foracertainperiodoftime,whichisequaltoT=0.7RCoutputofpin10waslogiczero.DuringthattimeoutputE(pin11)islogicone.Forexample,ifR=2M2andC=47μF,fortimeT=
2.210^64710^-6=94secfromthemomentimpulseoninputPsubsided,voltageonoutputEis12V.Theendresultofourexperimentisondiagram7.5a.ShortpositivepulsesappearingonPinthetimet1
causedalongervariableulseonoutputE.Schematic7.5bdisplaysthiscircuitwhichallowsustolightabulbusingfourNANDgatesinterconnectedin
thewayshownonpicture7.5a.Thesensoristwocopper(orsomeotherconductingmaterial)platesgluedtosomenon-conducting
material(plastics,wood,etc.)incloseproximitytoeachother.So,whenwetouchthesensorwiththetipofourfinger,weclosethecircuit.12VappearsoninputP,whichinturnconductsthevoltagetotheoutput
E,resistorR=22kconductsbasecurrentandthebulblights.Whenweremoveourfinger,outputEwilllastfor94seconds,afterwhichitgoestologiczeroandthelightgoesout.
TransistorTisselectedsothatitsmaximumallowedcollectorcurrentishigherthanthecurrentoftheglobe.
(Theglobescurrentflowvalueisfoundbydividingitspowerbyitsvoltage.Forexample,ifitspowerisP=6WandvoltageisU=12V,currentthroughtheglobeisI=P/U=6W/12V=0.5Aorhigher.Onething
youmustrememberwithaglobeisthestartingor"turn-on"current.Itisaboutsixtimestheoperatingcurrentandthetransistormustbeabletopassthiscurrentfortheglobetoilluminate.
7.3Practicalexamples
Diagram7.6showsacircuitforastereoaudio-ampusingaTDA4935IC.Itisamodernintegratedcircuit
withtwoseparatepre-ampsandstereooutputs.LeftandrightinputsignalsaremarkedULandUD,whicharebroughttotwoinputsoftheamplifier.The
chipalsohasbuilt-inheatandoverloadprotection.Maximumoutputforeachamplifieris15W,sotheycanbeusedinstereomodeof2x15Wamplifiers.
Fig.7.6:Stereoaudio-amplifierusingtheTDA4935
AnotherexampleisanaudioamplifierusinganLM386circuit,withapreampusingaBC107transistor.Theseriesconnectedcapacitorandresistorbetweenpins1and5produceslowfrequencyamplification(around
100Hz)improvingthecharacteristicsofthecircuit.Thisamplifiercouldbeusedwithanylowfrequencysource(gramophone,microphone,etc.).
Fig.7.7:completeaudio-amplifierusingtheLM386
Thethirdexampleisasimplealarm,showninfigure7.8.ItusesaCD4011IC.GatesNI3andNI4forma600Hzaudiooscillator.ThissignalisamplifiedusinganNPNtransistorandpassedtoan8Rspeaker.To
hearthe600Hztone,removetheconnectiontopin8andconnectpin8topin9.Thisproducesaconstanttone.GatesNI1andNI2forma4Hzoscillator,whoseoutputisconnectedtopin8.Thisturnsthe600Hz
toneonandoffat4Hz.Tousethisalarminyourhome,ondoorsforexample,connectedpin1to7viaaswitch.
Fig.7.8:AlarmusingaCD4011IC
ThelastcircuitinthischapterisanexampleofamonoFMreceiverusingaTDA7088TIC,whichcanbe,alongwiththeSMDcomponents,housedinamatch-boxalongwithtwominiaturewatchbatteries.Youcan
purchaseaready-builtscanningradioina"junkshop"foraslittleas$5.00withstereohead-phonesAlwayslookinthetoysectionsoflargestoresforthelatesttechnologyatthecheapestprice.
Fig.7.9:MonoFMradioreceiverwithanelectronicpreset
TuningtoalowfrequencystationisdoneautomaticallybypressingtheRUNbutton.Thisturnsonthepartoftheintegratedcircuitwhichisdesignatedforscanningoveragivenrange.Whenitfindsastationitlocks
onuntiltheRUNbuttonispressedagain.Whenitreaches108MHzitwaitsfortheRESETsignalwhichreturnsthescanto88MHz.
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