Introduction
Semiconductorswitchingelementscontrolledbyelectricalsignalsthatcanperformlogicoperations,alsoknownasgatecircuits.Itisanewtypeofautomationcomponentdevelopedonthebasisofinverters,flip-flops,oscillatorsandvariousRC,RLandotherbasicsemiconductorcircuits.Theuseofelectroniclogicelementsintheautomaticcontrolsystemcanrealizethelogiccombination,conversion,delay,storage,countingandotherfunctionsofthecontrolsignal.Theadvantagesofelectroniclogiccomponentsareshortswitchingtime,smallsize,lightweight,flexiblecombination,longlifeandnomovingparts.Itisanindispensablebasiccomponentinautomationtechnology.Thegatecircuithasatleasttwoinputterminalsandoneormoreoutputterminals.Fromthepointofviewoflogicfunction,themostbasicgatecircuithasthreekindsof"ORgate","ANDgate"and"NOTgate".Throughthecombinationofthesethreebasiclogiccircuits,differentgatecircuitssuchas"NOR","NAND","ANDNOR",monostable,bistable,flip-flop,etc.canbeobtained.Thetwokindsoflogiccircuitsarethemostconvenientandwidelyused.
Detailedexplanation
ORgatealsoknownaslogicandcircuit.Whenatleastoneofitsinputterminalshasaninputpulse,itsoutputterminalhasapulseoutputwiththesamesign(Figure1).InFigure1a,whenalltheinputterminalsarezero,allthediodesareinaconductingstate,andthepowersupplyvoltageisalladdedtotheresistanceRtomaketheoutputzero.Aslongasthereisanegativepulseinputatoneinputterminal,thediodeatthisendisstillconducting,andtheotherdiodesbecomedisconnected,sothattheoutputterminalchangesfromzerotonegative,andanegativepulseisoutput.Figure1bisanORgatecircuitsuitableforpositivepulseinput,andtheprincipleisanalogous.
Andgatealsoknownaslogicalmultiplicationcircuit,onlywhenseveralinputterminalsinputpulsesignalsatthesametime,theoutputterminalwillhavethesamesignofpulseoutput(Figure2).InFigure2a,aslongasoneoftheinputendsiszero,thediodeatthatendisturnedon,sothatthepowersupplyvoltageisalladdedtotheresistanceR,andtheoutputiszero.Therefore,onlywhenthreediodesinputnegativepulsesatthesametime,theoutputterminalwillchangefromzerotonegative,andanegativepulsewillbeoutput.Figure2bisanANDgatecircuitsuitableforpositivepulseinput,andtheprincipleisanalogous.NOTgateisalsocalledaninvertercircuit.Whenitsinputishighorlow,theoutputisloworhighrespectively(Figure3).InFigure3,whentheinputiszero(ie,highpotential),thetransistoriscutoff,sothatthevoltagedroponR0iszero,andtheoutputisnegative(lowpotential).Whentheinputterminalisanegativepulse(lowpotential),thetransistoristurnedon,sothatthepowersupplyvoltageisalladdedtoR0,andtheoutputterminaliszero(highpotential).