Types of transistors

Types of transistors

1. Different Types of
Transistors and Their
Functions
By Unsa Shakir

2. Introduction:
Different Types of Transistors and
Their Functions
Transistorisanactivecomponentandthatisestablishingin
alloverelectroniccircuits.Theyareusedasamplifiersand
switchingapparatus.Therearelow,mediumandhigh
powertransistors,forfunctioningwithhighandlow
frequencies,forfunctioningwithveryhighcurrentandor
highvoltages.

4. Bipolar Junction Transistor
(BJT)
BJTtransistorsarebuiltupof3regions,thebase,thecollector,
andtheemitter.
BipolarJunctiontransistorsarebi-polarcurrent-controlled
devices.
Bipolarjunctiontransistorscomeintwomajortypes,NPNand
PNP.
ANPNtransistorisoneinwhichthemajoritycurrentcarrier
areelectrons.
APNPtransistorisoneinwhichthemajoritycurrentcarrierare
holes.

5. Bipolar Junction Transistor
(BJT)

6. Transistor
Symbol

7. Field Effect
Transistor
FieldEffectTransistorsaremadeupof3regions,agate,asource,
andadrain.
FETsareuni-polarvoltage-controlleddevices.
TheFETconsistsofasemiconductorchannelwithelectrodesat
eitherendreferredtoasthedrainandthesource.
Acontrolelectrodecalledthegateisplacedinverycloseproximity
tothechannelsothatitselectricchargeisabletoaffectthe
channel.
Inthisway,thegateoftheFETcontrolstheflowofcarriers
(electronsorholes)flowingfromthesourcetodrain.

8. Field Effect
Transistor
FieldEffectTransistorscomein2maintypes:JFETsand
MOSFETs.

9. Junction FET
Transistor
TheJunctionFieldEffectTransistorhastwoPN-junctions.
Ithasanarrowpartofhighresistivitysemiconductormaterial
forminga“Channel”ofeitherN-typeorP-typesilicon.
Themajoritycarrierstoflowthroughwithtwoohmicelectrical
connectionsateitherendnormallycalledtheDrainandthe
Source.
Thereareatwobasicconfigurationsofjunctionfieldeffect
transistor.
•TheN-channelJFETandtheP-channelJFET.

10. Junction FET Transistor

11. Metal Oxide Semiconductor Field Effect Transistor
•MOSFETisaunipolartransistor,whichactsasavoltage-
controlledcurrentdeviceandinwhichcurrentatdrainandsource
iscontrolledbytheactionofanelectricfieldatgate,havingin-
betweensemiconductorandmetalveryathinmetaloxidelayer.
•TheMOSFETisacoreofintegratedcircuitanditcanbedesigned
andfabricatedinasinglechipbecauseoftheseverysmallsizes.
•TheMOSFETisafourterminaldevicewithsource(S),gate(G),
drain(D)andbody(B)terminals.

12. •TheMOSFETworksbyelectronicallyvaryingthewidthofachannel
alongwhichchargecarriersflow(electronsorholes).
•Thechargecarriersenterthechannelatsourceandexitviathe
drain.
•Thewidthofthechanneliscontrolledbythevoltageonan
electrodeiscalledgatewhichislocatedbetweensourceanddrain.
•Itisinsulatedfromthechannelnearanextremelythinlayerof
metaloxide.TheMOScapacitypresentinthedeviceisthemain
part

13. The MOSFET can function in two ways
Inmetaloxidefieldeffecttransistortherearetwomajortransistor
modeofoperation,correspondingtowhetherthetransistorisin
anONstateoranOFFstateatzerogate-sourcevoltage
•Depletion Mode
•Enhancement Mode

14. Depletion Mode
•Whenthereisnovoltageonthegate,thechannelshowsits
maximumconductance.
•Inadepletion-modeMOSFET,thedeviceisnormallyONatzero
gate–sourcevoltage
•Keypoints:Indepletionmode(normallyONatVGS=0,OFFona
VoltagebetweenGateandSource)

15. Enhancement mode
•Whenthereisnovoltageonthegatethedevicedoesnotconduct.
Moreisthevoltageonthegate,thebetterthedevicecanconduct.
•Enhancement-modeMOSFETsarethecommonswitchingelementsin
mostMOS.Thesedevicesareoffatzerogate–sourcevoltage
•Keypoint:Inenhancementmode(normallyOFFatVGS=0,ONata
ThresholdVoltageVDS)

16. TheMOSFETcanbecategorizedintothreeseparatemodeswhenin
operation.
•Thefirstisthesub-thresholdorcut-offmode:VGS<Vt,whereVtis
thethresholdvoltage.InthismodethedeviceisessentiallyOFF,andin
theidealcasethereisnocurrentflowingthroughthedevice.
•ThesecondmodeofoperationisthelinearregionwhenVGS>Vt.
Essentially,theMOSFEToperatessimilartoaresistorinthismodewith
alinearrelationbetweenvoltageandcurrent.
•ThethirdmodeofoperationissaturationmodewhenVGS>Vt.Inthis
modetheswitchisonandconducting,howeversincedrainvoltageis
higherthanthegatevoltage,partofthechannelisturnedoff.This
modecorrespondstotheregiontotherightofthedottedline,whichis
calledthepinch-offvoltage.
MOSFET Operation

17. •Pinch-offoccurswhentheMOSFETstopsoperatinginthelinear
regionandsaturationoccurs.
•IndigitalcircuitsMOSFETSareonlyoperatedinthelinearmode,
whilethesaturationregionisreservedforanaloguecircuits.

18. Types of MOSFETS
n-channel
Enhancement Mode
(nMOSFET)
p-channel
Enhancement Mode
(pMOSFET)
n-channel
Depletion Mode
(nMOSFET)
p-channel
Depletion Mode
(pMOSFET)

19. P-Channel MOSFET
•TheMOSFEThavingP-channelregionbetweensourceanddrainis
calledasP-channelMOSFET.
•HerethesourceanddrainterminalsareheavilydopedwithP-type
materialandthesubstrateisdopedwithN-typematerial.
•Thecurrentflowbetweensourceanddrainisbecauseofholes
concentration.
•Theappliedvoltageatgatewillcontrolstheflowofcurrentthrough
channelregion.

21. N-Channel MOSFET
•TheMOSFEThavingN-channelregionbetweensourceanddrainis
calledN-channelMOSFET.
•Herethesourceandgateterminalsareheavilydopedwithn-type
materialsandsubstrateisdopedwithp-typesemiconductormaterial.
•Herethecurrentflowbetweensourceanddrainisbecauseofelectrons.
•Thegatevoltagecontrolsthecurrentflowinthecircuit.
•N-channelMOSFETismostpreferablethanP-channelMOSFET
becausethemobilityofelectronsishighthanmobilityofholes.