Unit - 3 Switching Characteristics of Diodes and Transistors.pdf

The "Electronic Devices & Circuits - Study Material" is a comprehensive and detailed PDF document designed to provide students of the Bachelor of Engineering in Computer Science program at Rajiv Gandhi Proudyogiki Vishwavidyalaya Bhopal with a comprehensive understanding of the fundamental concepts related to electronic devices and circuits. This study material covers the topics taught in Semester 3 of the program, focusing on the subject of Electronic Devices & Circuits.

Content Overview:

Switching Characteristics of Diode and Transistor
Understanding the Turn ON and Turn OFF Time of Diodes and Transistors.
Exploring the importance of Switching Characteristics in digital circuits and switching applications.
Analyzing how Diodes and Transistors transition between different states during switching.

Reverse Recovery Time of Diode
Investigating the phenomenon of Reverse Recovery Time in diodes.
Examining the implications of Reverse Recovery Time in high-frequency rectifiers and switching circuits.
Understanding how charge carriers affect the transition from conducting to non-conducting state in diodes.

Transistor as a Switch
Utilizing transistors as electronic switches in various applications.
Exploring the operation of transistors in the ON (saturation) and OFF (cutoff) states.
Discussing the applications of transistor switches in digital logic circuits, amplifiers, and power control.

Multivibrators
Understanding the operation and applications of Bistable, Monostable, and Astable Multivibrators.
Analyzing how Bistable Multivibrators can be used as memory elements and in sequential logic circuits.
Exploring the application of Monostable Multivibrators in time delay circuits and pulse generation.
Examining the use of Astable Multivibrators as free-running oscillators in clock generation and tone generation.

Clippers and Clampers
Studying the working principles of Clippers, including positive and negative clippers.
Understanding how Clippers are used in waveform shaping and noise elimination.
Analyzing the operation and applications of Clampers in restoring AC-coupled signals to a specific voltage level.

Differential Amplifier and CMRR Calculation
Exploring the significance of Differential Amplifiers in communication and instrumentation applications.
Calculating the Differential Gain and Common Mode Gain using h-parameters.
Understanding the importance of Common Mode Rejection Ratio (CMRR) in noise rejection.

Benefits:

Provides in-depth explanations of critical topics related to Electronic Devices & Circuits.
Equips students with the knowledge required to design and analyze electronic circuits.
Covers essential concepts for digital circuit design and signal processing applications.
Supports students in preparing for examinations and assignments related t

1. RGPV दे Bunkers

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Unit — 3:SwitchingCharacteristicsof
DiodesandTransistors
1.SwitchingCharacteristicsofDiodeandTransistor
1.1SwitchingCharacteristicsofDiodeandTransistorTurnON/OFFTime
Switchingcharacteristicsarevitalforunderstandingthebehaviorofelectronicdeviceslike
diodesandtransistorswhentransitioningbetweendifferentstates.Thesecharacteristicsare
particularlyrelevantindigitalcircuitsandswitchingapplications.
DiodeSwitchingCharacteristics:
●TurnONTime:WhenadiodeisinitiallyintheOFFstate(reverse-biased)andaforward
voltageisappliedacrossit,ittakesacertaintimetoovercomethedepletionregion’s
barrierandallowcurrentflow.ThistimeintervalisknownastheturnONtimeofthe
diode.
●TurnOFFTime:Conversely,whenadiodeisintheONstate(forward-biased)andthe
voltagepolarityacrossitisreversed,ittakesacertaintimeforthediodetocease
conductingcurrent.ThisdurationiscalledtheturnOFFtimeofthediode.
Theswitchingtimesofdiodesareessentialinhigh-frequencyrectifiers,switchingpower
supplies,andsignalprocessingapplications.
TransistorSwitchingCharacteristics:
●TurnONTime:Inthecontextoftransistors,theturnONtimereferstothetimeittakes
forthetransistortoswitchfromitsOFFstatetotheONstate.Thisprocessoccurswhen
thebase-emitterjunctionisforward-biasedsufficientlytoallowcurrenttoflowbetween
thecollectorandtheemitter.
●TurnOFFTime:TheturnOFFtimeofatransistoristhetimetakenforthetransistorto
switchfromtheONstatetotheOFFstate.Thishappenswhenthebase-emitterjunction
isreversedbiased,haltingthecurrentflowthroughthecollector-emitterpath.

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Transistorsarecommonlyusedasswitchesindigitallogiccircuits,amplifiers,andpowercontrol
circuits.
1.2ReverseRecoveryTimeofDiode
Whenadiodeisconductingcurrentintheforward-biasedstate,andtheappliedvoltageacross
thediodeissuddenlyreversedtomakeitreverse-biased,thediodedoesnotinstantaneously
stopconducting.Instead,ittakesashortperiodtotransitionfromtheconductingstatetothe
non-conductingstate.Thistimeintervalisknownasthe“ReverseRecoveryTime”ofthediode.
Duringthistime,theexcesschargecarrierspresentinthediode’ssemiconductorregionsneed
torecombinebeforethediodecancompletelyblockthecurrentinthereversedirection.The
reverserecoverytimeisacriticalparameterinpowerdiodesusedinhigh-frequencyrectifiers
andswitchingcircuits.Itaffectsthediode’sswitchingefficiencyandpowerlossduring
high-speedswitching.
1.3TransistorasaSwitch
Transistors,especiallybipolarjunctiontransistors(BJTs)andfield-effecttransistors(FETs),can
beutilizedaselectronicswitchesinvariousapplications.
BJTasaSwitch:
●WhentheBJTisintheONstate(activeregion),itactsasaclosedswitch,allowing
currenttoflowfreelybetweenthecollectorandemitterterminals.
●WhentheBJTisintheOFFstate(cutoffregion),itactsasanopenswitch,effectively
blockinganycurrentflowbetweenthecollectorandemitterterminals.
BJTsarecommonlyusedasswitchesindigitalcircuits,amplifiers,andsignalprocessing
applications.
FETasaSwitch:
●IntheONstate,theFEToperatesinitssaturationregion,allowingasignificantcurrent
flowbetweenthesourceanddrainterminals.
●IntheOFFstate,theFEToperatesinitscutoffregion,effectivelyblockinganycurrent
flowbetweenthesourceanddrainterminals.
FETsfindapplicationsinpowercontrol,low-powerdigitalcircuits,andswitchingapplications.

4. RGPV दे Bunkers
2.Multi-vibrators
2.1BistableMultivibrator
Abistablemultivibrator,alsoknownasaflip-flop,isadigitalcircuitcapableofmaintainingtwo
stablestatesindefinitelyuntilanexternaltriggerisappliedtochangeitsstate.Thebistable
multivibratorhastwooutputs,commonlydenotedasQandQ̅(complementofQ).
Operation:Thebistablemultivibratorcanbeconstructedusingvariousconfigurations,suchas
cross-coupledtransistors,NANDgates,orNORgates.Whenoneoutput(e.g.,Q)isHIGH(logic
1),theotheroutput(e.g.,Q̅)willbeLOW(logic0),andviceversa.Oncesetinoneofthestable
states,itremainsinthatstateuntilanexternaltriggerisreceived,causingittoswitchtothe
otherstablestate.
Applications:Bistablemultivibratorsarewidelyusedindigitalcircuitsformemoryelements,
suchasDflip-flops,Tflip-flops,JKflip-flops,andSRflip-flops.Theyalsoformthefundamental
buildingblocksofcounters,registers,andstatemachinesindigitalsystems.
2.2MonostableMultivibrator
Amonostablemultivibrator,alsoknownasaone-shotmultivibrator,hasonlyonestablestate
andrequiresanexternaltriggertoswitchtotheunstablestatemomentarily.Afterapredefined
timeduration,itreturnstoitsstablestateautomatically.
Operation:Themonostablemultivibratorcircuitincludesoneenergystorageelement,typically
acapacitor.Whentriggered,thecapacitorchargesordischargestochangethestateofthe
circuit.Theoutputremainsintheunstablestateforafixeddurationdeterminedbythevaluesof
externalresistorsandcapacitorsconnectedtoit.
Applications:Monostablemultivibratorsareusedinapplicationsrequiringaprecisetimedelay
orpulsegeneration.Theyareusedintimers,pulsegenerators,debouncingcircuits,and
time-delayrelays.
2.3AstableMultivibrators
Astablemultivibratorsarefree-runningoscillatorsthatcontinuouslyswitchbetweentwounstable
stateswithoutanyexternaltriggering.

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Operation:Astablemultivibratorsdonothaveanystablestate,unlikebistableandmonostable
multivibrators.Thecircuitcontinuouslyalternatesbetweenitstwounstablestates,generatinga
continuoussquarewaveorpulsetrainatitsoutput.
Applications:Astablemultivibratorsarewidelyusedinapplicationslikeclockgeneration,
frequencydivision,tonegeneration,andpulse-widthmodulation(PWM)formotorcontroland
powerelectronics.
3.ClippersandClampers
3.1Clippers
Clippers,alsoknownaslimiters,areelectroniccircuitsusedtocliporremoveaportionofan
inputsignalthatexceedsaspecifiedvoltagelevel.Positiveandnegativeclipperscanbe
employedtoshapethewaveformaccordingtothedesiredoutput.
PositiveClippers:Apositiveclipperremovesthepositiveportionoftheinputsignalthat
exceedsapredeterminedvoltagelevel.Theoutputwaveformwillonlyshowthenegativepartof
theinputsignalbelowtheclippingvoltage.
NegativeClippers:Anegativeclipperremovesthenegativeportionoftheinputsignalthatfalls
belowaspecifiedvoltagelevel.Theoutputwaveformwillonlydisplaythepositivepartofthe
inputsignalabovetheclippingvoltage.
Applications:Clippersarewidelyusedinaudioandvideosignalprocessing,waveform
shaping,andnoiseeliminationincommunicationsystems.
3.2Clampers
Clampers,alsoknownasDCrestorersorlevelshifters,arecircuitsusedtoaddor“clamp”aDC
leveltoanACwaveform.ThepurposeofclampersistosetareferencevoltagelevelfortheAC
signal.ThisisparticularlyusefulwhentheACsignalistobefurtherprocessed,andanyDC
offsetneedstoberemoved.
PositiveClampers:ApositiveclamperaddsapositiveDCleveltotheinputsignal.Itshiftsthe
entirewaveformupwards,ensuringthatthemostnegativepointofthewaveformalignswiththe
referenceDClevel.

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NegativeClampers:AnegativeclamperaddsanegativeDCleveltotheinputsignal.Itshifts
theentirewaveformdownwards,aligningthemostpositivepointofthewaveformwiththe
referenceDClevel.
Applications:Clampersarecommonlyusedindisplaysystems,whereAC-coupledsignals
needtoberestoredtoaspecificvoltagelevelforpropervisualization.Theyarealsousedin
communicationsystemsandsignalprocessingapplications.
4.DifferentialAmplifierandCMRRCalculation
4.1DifferentialAmplifier
Adifferentialamplifierisatypeofelectronicamplifierthatamplifiesthedifferencebetweentwo
inputsignalswhilerejectinganysignalsthatarecommontobothinputs(common-mode
signals).Differentialamplifiersarecriticalcomponentsinvariouselectronicsystems,especially
incommunicationandinstrumentationapplications.
Operation:Adifferentialamplifierusuallyconsistsoftwotransistors,oftenimplementedwith
BJTsorFETs,andresistorsconnectedinadifferentialconfiguration.Theinputsignalsare
appliedtothebases(forBJTs)orgates(forFETs)ofthetransistors,andtheamplifiedoutputis
takenfromthecollectors(forBJTs)ordrains(forFETs).Thedifferentialamplifieramplifiesthe
voltagedifferencebetweenthetwoinputsignalswhileattenuatinganysignalthatiscommonto
bothinputs.
Applications:Differentialamplifiersareextensivelyusedinbalancedcommunicationsystems,
audiosignalprocessing,instrumentationamplifiersforprecisemeasurements,andinvarious
sensorinterfaces.
4.2CalculationofDifferentialGain,CommonModeGain,andCMRRusingh-parameters
Indifferentialamplifieranalysis,h-parameters(alsoknownashybridparametersortwo-port
parameters)arecommonlyusedtorelatetheinputandoutputvoltagesandcurrentsofthe
amplifier.
DifferentialGain:Thedifferentialgain,oftendenotedbyAd,istheratioofthechangeinthe
outputvoltagetothechangeinthedifferentialinputvoltage.Itquantifieshoweffectivelythe
amplifieramplifiesthedifferencebetweenthetwoinputsignals.
CommonModeGain:Thecommon-modegain,oftendenotedbyAc,istheratioofthechange
intheoutputvoltagetothechangeinthecommon-modeinputvoltage.Itindicateshowmuch

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theamplifieramplifiesanyinputsignalthatappearssimultaneouslyandidenticallyatboth
inputs.
CommonModeRejectionRatio(CMRR):TheCMRRisacrucialparameterthatquantifiesthe
differentialamplifier’sabilitytorejectcommon-modesignals.Itiscalculatedbydividingthe
differentialgain(Ad)bythecommon-modegain(Ac).CMRRistypicallyexpressedindecibels
(dB).
Importance:CMRRisparticularlycrucialinapplicationswherethedifferentialamplifierneedsto
amplifysmalldifferentialsignalswhilerejectingcommon-modenoiseeffectively.HighCMRR
ensuresaccurateandnoise-freemeasurementsinvarioussensorandcommunicationsystems.
Bymasteringthesetopics,studentswillgainacomprehensiveunderstandingofelectronic
devices,theirbehavior,andpracticalapplicationsinmodernengineering.Thesefundamental
conceptsformthebackboneofelectroniccircuitdesignandanalysisandareessentialforany
aspiringcomputerscienceengineer.