chapter chapter 6666:::: fieldfield- ---effect ...webstaff.kmutt.ac.th/~suwat.pat/material/ene212...

Chapter Chapter Chapter Chapter 6666::::FieldFieldFieldField----Effect TransistorsEffect TransistorsEffect TransistorsEffect Transistors

Similarities: Similarities: Similarities: Similarities: Similarities: Similarities: Similarities: Similarities: • • • • AmplifiersAmplifiersAmplifiersAmplifiers

• • • • Switching devices Switching devices Switching devices Switching devices

• • • • Impedance matching circuitsImpedance matching circuitsImpedance matching circuitsImpedance matching circuits

Differences:Differences:Differences:Differences:Differences:Differences:Differences:Differences:• • • • FETs are voltage controlled devices. BJTs are current controlled FETs are voltage controlled devices. BJTs are current controlled FETs are voltage controlled devices. BJTs are current controlled FETs are voltage controlled devices. BJTs are current controlled

FETs vs. BJTsFETs vs. BJTs

Copyright ©2009 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458 • All rights reserved.

Electronic Devices and Circuit Theory, 10/eRobert L. Boylestad and Louis Nashelsky

• • • • FETs are voltage controlled devices. BJTs are current controlled FETs are voltage controlled devices. BJTs are current controlled FETs are voltage controlled devices. BJTs are current controlled FETs are voltage controlled devices. BJTs are current controlled

devices.devices.devices.devices.

• • • • FETs have a higher input impedance. BJTs have higher gains.FETs have a higher input impedance. BJTs have higher gains.FETs have a higher input impedance. BJTs have higher gains.FETs have a higher input impedance. BJTs have higher gains.

• • • • FETs are less sensitive to temperature variations and are more easily FETs are less sensitive to temperature variations and are more easily FETs are less sensitive to temperature variations and are more easily FETs are less sensitive to temperature variations and are more easily

integrated on ICs. integrated on ICs. integrated on ICs. integrated on ICs.

• • • • FETs are generally more static sensitive than BJTs.FETs are generally more static sensitive than BJTs.FETs are generally more static sensitive than BJTs.FETs are generally more static sensitive than BJTs.

22

••JFET: JFET: JFET: JFET: JFET: JFET: JFET: JFET: Junction FETJunction FETJunction FETJunction FET

••MOSFET: MOSFET: MOSFET: MOSFET: MOSFET: MOSFET: MOSFET: MOSFET: MetalMetalMetalMetal––––OxideOxideOxideOxide––––Semiconductor FETSemiconductor FETSemiconductor FETSemiconductor FET

��DDDDDDDD--------MOSFET:MOSFET:MOSFET:MOSFET:MOSFET:MOSFET:MOSFET:MOSFET: Depletion MOSFETDepletion MOSFETDepletion MOSFETDepletion MOSFET

FET TypesFET Types



��DDDDDDDD--------MOSFET:MOSFET:MOSFET:MOSFET:MOSFET:MOSFET:MOSFET:MOSFET: Depletion MOSFETDepletion MOSFETDepletion MOSFETDepletion MOSFET��EEEEEEEE--------MOSFET:MOSFET:MOSFET:MOSFET:MOSFET:MOSFET:MOSFET:MOSFET: Enhancement MOSFETEnhancement MOSFETEnhancement MOSFETEnhancement MOSFET

33

JFET ConstructionJFET ConstructionJFET ConstructionJFET ConstructionJFET ConstructionJFET ConstructionJFET ConstructionJFET Construction

There are two types of JFETsThere are two types of JFETsThere are two types of JFETsThere are two types of JFETs

••nnnnnnnn--------channelchannelchannelchannelchannelchannelchannelchannel

••pppppppp--------channelchannelchannelchannelchannelchannelchannelchannel

The nThe nThe nThe n----channel is more widely used.channel is more widely used.channel is more widely used.channel is more widely used.



There are three terminals:

••Drain Drain (D) and SourceSource(S) are connected to the n-channel••GateGate (G) is connected to the p-type material

44

JFET Operation: The Basic IdeaJFET Operation: The Basic IdeaJFET Operation: The Basic IdeaJFET Operation: The Basic IdeaJFET Operation: The Basic IdeaJFET Operation: The Basic IdeaJFET Operation: The Basic IdeaJFET Operation: The Basic Idea

JFET operation can be compared to a water

spigot.

The sourceThe sourceof water pressure is the accumulation of electrons at the negative pole of the drain-source voltage.

The drainThe drainof water is the electron



The drainThe drainof water is the electron deficiency (or holes) at the positive pole of the applied voltage.

The controlThe control of flow of water is the gate voltage that controls the width of the n-channel and, therefore, the flow of charges from source to drain.

55

JFET Operating CharacteristicsJFET Operating CharacteristicsJFET Operating CharacteristicsJFET Operating CharacteristicsJFET Operating CharacteristicsJFET Operating CharacteristicsJFET Operating CharacteristicsJFET Operating Characteristics

There are three basic operating conditions for a JFET:There are three basic operating conditions for a JFET:There are three basic operating conditions for a JFET:There are three basic operating conditions for a JFET:

• VVVVGSGSGSGS = = = = 0000, V, V, V, VDSDSDSDS increasing to some positive valueincreasing to some positive valueincreasing to some positive valueincreasing to some positive value• VVVVGSGSGSGS < < < < 0000, V, V, V, VDSDSDSDS at some positive valueat some positive valueat some positive valueat some positive value• VoltageVoltageVoltageVoltage----controlled resistorcontrolled resistorcontrolled resistorcontrolled resistor



66

JFET Operating Characteristics: VJFET Operating Characteristics: VGSGS = = 0 0 VV

• The depletion region between p-gate and n-channel increases as electrons from n-channel combine with holes from p-gate.

• Increasing the depletion region,

Three things happen when VGS = 0 and VDS is increased from 0 to a more positive voltage



• Increasing the depletion region, decreases the size of the n-channel which increases the resistance of the n-channel.

• Even though the n-channel resistance is increasing, the current (ID) from source to drain through the n-channel is increasing. This is because VDS is increasing.

77

If VIf VIf VIf VGSGSGSGS = 0 and V= 0 and V= 0 and V= 0 and VDSDSDSDS is further increased to is further increased to is further increased to is further increased to

a more positive voltage, then the a more positive voltage, then the a more positive voltage, then the a more positive voltage, then the

depletion zone gets so large that it depletion zone gets so large that it depletion zone gets so large that it depletion zone gets so large that it

pinches offpinches offpinches offpinches offpinches offpinches offpinches offpinches off the nthe nthe nthe n----channel. channel. channel. channel.

This suggests that the current in the nThis suggests that the current in the nThis suggests that the current in the nThis suggests that the current in the n----

JFET Operating Characteristics: JFET Operating Characteristics: Pinch OffPinch OffPinch OffPinch OffPinch OffPinch OffPinch OffPinch Off



This suggests that the current in the nThis suggests that the current in the nThis suggests that the current in the nThis suggests that the current in the n----

channel (Ichannel (Ichannel (Ichannel (IDDDD) would drop to 0A, but it ) would drop to 0A, but it ) would drop to 0A, but it ) would drop to 0A, but it

does just the oppositedoes just the oppositedoes just the oppositedoes just the opposite––––as Vas Vas Vas VDSDSDSDSincreases, so does Iincreases, so does Iincreases, so does Iincreases, so does IDDDD. . . .

88

At the pinchAt the pinchAt the pinchAt the pinch----off point:off point:off point:off point:

• Any further increase in VAny further increase in VAny further increase in VAny further increase in VGSGSGSGS does does does does

not produce any increase in Inot produce any increase in Inot produce any increase in Inot produce any increase in IDDDD. V. V. V. VGSGSGSGSat pinchat pinchat pinchat pinch----off is denoted asoff is denoted asoff is denoted asoff is denoted as VVVVVVVVpppppppp....

JFET Operating CharacteristicsJFET Operating Characteristics: Saturation: Saturation: Saturation: Saturation: Saturation: Saturation: Saturation: Saturation



• IIIIDDDD is at saturation or maximum. It is is at saturation or maximum. It is is at saturation or maximum. It is is at saturation or maximum. It is

referred to as referred to as referred to as referred to as IIIIIIIIDSSDSSDSSDSSDSSDSSDSSDSS....

• The ohmic value of the channel is The ohmic value of the channel is The ohmic value of the channel is The ohmic value of the channel is

maximum.maximum.maximum.maximum.

99

JFET Operating CharacteristicsJFET Operating Characteristics

As VAs VAs VAs VGSGSGSGS becomes more negative, the becomes more negative, the becomes more negative, the becomes more negative, the

depletion region increases. depletion region increases. depletion region increases. depletion region increases.



1010

As VAs VAs VAs VGSGSGSGS becomes more becomes more becomes more becomes more

negative:negative:negative:negative:

• The JFET experiences The JFET experiences The JFET experiences The JFET experiences

pinchpinchpinchpinch----off at a lower voltage off at a lower voltage off at a lower voltage off at a lower voltage

(V(V(V(VPPPP).).).).

• IIIIDDDD decreases (Idecreases (Idecreases (Idecreases (IDDDD < I< I< I< IDSSDSSDSSDSS) ) ) )

JFET Operating CharacteristicsJFET Operating Characteristics



• IIIIDDDD decreases (Idecreases (Idecreases (Idecreases (IDDDD < I< I< I< IDSSDSSDSSDSS) ) ) )

even though Veven though Veven though Veven though VDSDSDSDS is is is is

increased.increased.increased.increased.

• Eventually IEventually IEventually IEventually IDDDD reaches reaches reaches reaches 0 0 0 0 A. A. A. A.

VVVVGSGSGSGS at this point is called Vat this point is called Vat this point is called Vat this point is called Vppppor Vor Vor Vor VGS(off)GS(off)GS(off)GS(off)........Also note that at high levels of VDSDSDSDS the JFET reaches a breakdown situation. IDDDD

increases uncontrollably if VDSDSDSDS > VDSmaxDSmaxDSmaxDSmax.

1111

The region to the left of the The region to the left of the The region to the left of the The region to the left of the

pinchpinchpinchpinch----off point is called the off point is called the off point is called the off point is called the

ohmic region.ohmic region.ohmic region.ohmic region.ohmic region.ohmic region.ohmic region.ohmic region.

The JFET can be used as a The JFET can be used as a The JFET can be used as a The JFET can be used as a

variable resistor, where Vvariable resistor, where Vvariable resistor, where Vvariable resistor, where VGSGSGSGScontrols the draincontrols the draincontrols the draincontrols the drain----source source source source

JFET Operating Characteristics:JFET Operating Characteristics:VoltageVoltage--Controlled ResistorControlled Resistor



2

P

GS

od

V

V1

rr

−−−−

====

variable resistor, where Vvariable resistor, where Vvariable resistor, where Vvariable resistor, where VGSGSGSGScontrols the draincontrols the draincontrols the draincontrols the drain----source source source source

resistance (rresistance (rresistance (rresistance (rdddd). As V). As V). As V). As VGSGSGSGSbecomes more negative, the becomes more negative, the becomes more negative, the becomes more negative, the

resistance resistance resistance resistance (r dddd) increases.increases.increases.increases.

1212

pppppppp--------Channel JFETSChannel JFETSChannel JFETSChannel JFETSChannel JFETSChannel JFETSChannel JFETSChannel JFETS

The The The The pppp----channel JFET behaves the channel JFET behaves the channel JFET behaves the channel JFET behaves the

same as the same as the same as the same as the nnnn----channel JFET, channel JFET, channel JFET, channel JFET,

except the voltage polarities and except the voltage polarities and except the voltage polarities and except the voltage polarities and

current directions are reversedcurrent directions are reversedcurrent directions are reversedcurrent directions are reversed.



current directions are reversedcurrent directions are reversedcurrent directions are reversedcurrent directions are reversed.

1313

pppppppp--------Channel JFET CharacteristicsChannel JFET CharacteristicsChannel JFET CharacteristicsChannel JFET CharacteristicsChannel JFET CharacteristicsChannel JFET CharacteristicsChannel JFET CharacteristicsChannel JFET Characteristics

As VGS increases more positively

• The depletion zone increases



Also note that at high levels of VAlso note that at high levels of VAlso note that at high levels of VAlso note that at high levels of VDSSSS the JFET reaches a breakdown situation: Ithe JFET reaches a breakdown situation: Ithe JFET reaches a breakdown situation: Ithe JFET reaches a breakdown situation: IDincreases uncontrollably if Vincreases uncontrollably if Vincreases uncontrollably if Vincreases uncontrollably if VDSDSDSDS > V> V> V> VDSmaxDSmaxDSmaxDSmax....

increases• ID decreases (ID < IDSS)• Eventually ID = 0 A

1414

NNNNNNNN--------Channel JFET SymbolChannel JFET SymbolChannel JFET SymbolChannel JFET SymbolChannel JFET SymbolChannel JFET SymbolChannel JFET SymbolChannel JFET Symbol



1515

The transfer characteristic of inputThe transfer characteristic of inputThe transfer characteristic of inputThe transfer characteristic of input----totototo----output is not as straightforward in output is not as straightforward in output is not as straightforward in output is not as straightforward in

a JFET as it is in a BJT. a JFET as it is in a BJT. a JFET as it is in a BJT. a JFET as it is in a BJT.

In a BJT, In a BJT, In a BJT, In a BJT, ββββ indicates the relationship between Iindicates the relationship between Iindicates the relationship between Iindicates the relationship between IBBBB (input) and I(input) and I(input) and I(input) and ICCCC (output).(output).(output).(output).

In a JFET, the relationship of VIn a JFET, the relationship of VIn a JFET, the relationship of VIn a JFET, the relationship of VGSGSGSGS (input) and I(input) and I(input) and I(input) and IDDDD (output) is a little more (output) is a little more (output) is a little more (output) is a little more

JFETJFET Transfer CharacteristicsTransfer Characteristics



2

V

V1DSSD

P

GSII

−−−−====

In a JFET, the relationship of VIn a JFET, the relationship of VIn a JFET, the relationship of VIn a JFET, the relationship of VGSGSGSGS (input) and I(input) and I(input) and I(input) and IDDDD (output) is a little more (output) is a little more (output) is a little more (output) is a little more

complicated:complicated:complicated:complicated:

1616

JFET Transfer CurveJFET Transfer Curve

This graph shows This graph shows This graph shows This graph shows

the value of Ithe value of Ithe value of Ithe value of IDDDD for a for a for a for a

given value of Vgiven value of Vgiven value of Vgiven value of VGSGSGSGS....



given value of Vgiven value of Vgiven value of Vgiven value of VGSGSGSGS....

1717

Using IUsing IUsing IUsing IDSSDSSDSSDSS and Vp (Vand Vp (Vand Vp (Vand Vp (VGS(off)GS(off)GS(off)GS(off)) values found in a specification sheet, the transfer ) values found in a specification sheet, the transfer ) values found in a specification sheet, the transfer ) values found in a specification sheet, the transfer

curve can be plotted according to these three steps:curve can be plotted according to these three steps:curve can be plotted according to these three steps:curve can be plotted according to these three steps:

Solving for VGS = 0V ID = IDSS

2

P

GSDSSD V

V1II

−−−−====

Step Step 11

Plotting the JFET Transfer CurvePlotting the JFET Transfer Curve



Solving for VGS = Vp (VGS(off)) ID = 0A

2

P

GSDSSD V

V1II

−−−−====

Step Step 22

Solving for VGS = 0V to Vp

2

P

GSDSSD V

V1II

−−−−====

Step Step 33

1818

JFET Specifications SheetJFET Specifications Sheet

Electrical CharacteristicsElectrical Characteristics



1919

JFET Specifications SheetJFET Specifications Sheet

Maximum RatingsMaximum Ratings



more…more…

2020

Case and Terminal IdentificationCase and Terminal Identification



2121

•• Curve TracerCurve TracerCurve TracerCurve TracerCurve TracerCurve TracerCurve TracerCurve TracerA curve tracer displays the IA curve tracer displays the IA curve tracer displays the IA curve tracer displays the IDDDD versus Vversus Vversus Vversus VDSDSDSDS graph for graph for graph for graph for various levels of Vvarious levels of Vvarious levels of Vvarious levels of VGSGSGSGS....

•• Specialized FET TestersSpecialized FET TestersSpecialized FET TestersSpecialized FET TestersSpecialized FET TestersSpecialized FET TestersSpecialized FET TestersSpecialized FET TestersThese testers show IThese testers show IThese testers show IThese testers show IDSSDSSDSSDSS for the JFET under test.for the JFET under test.for the JFET under test.for the JFET under test.

Testing JFETsTesting JFETs



These testers show IThese testers show IThese testers show IThese testers show IDSSDSSDSSDSS for the JFET under test.for the JFET under test.for the JFET under test.for the JFET under test.

2222

MOSFETsMOSFETsMOSFETsMOSFETsMOSFETsMOSFETsMOSFETsMOSFETs

There are two types of MOSFETs:There are two types of MOSFETs:There are two types of MOSFETs:There are two types of MOSFETs:

•• DepletionDepletionDepletionDepletionDepletionDepletionDepletionDepletion--------TypeTypeTypeTypeTypeTypeTypeType

•• EnhancementEnhancementEnhancementEnhancementEnhancementEnhancementEnhancementEnhancement--------TypeTypeTypeTypeTypeTypeTypeType

MOSFETs have characteristics similar to JFETs and additional characteristics that make then very useful.



2323

DepletionDepletionDepletionDepletionDepletionDepletionDepletionDepletion--------Type MOSFET ConstructionType MOSFET ConstructionType MOSFET ConstructionType MOSFET ConstructionType MOSFET ConstructionType MOSFET ConstructionType MOSFET ConstructionType MOSFET Construction

The The The The DrainDrainDrainDrainDrainDrainDrainDrain (D) and (D) and (D) and (D) and SourceSourceSourceSourceSourceSourceSourceSource (S) connect (S) connect (S) connect (S) connect

to the to to the to to the to to the to nnnn----doped regions. These doped regions. These doped regions. These doped regions. These nnnn----doped regions are connected via an doped regions are connected via an doped regions are connected via an doped regions are connected via an

nnnn----channel. Thischannel. Thischannel. Thischannel. This nnnn----channel is channel is channel is channel is

connected to the connected to the connected to the connected to the Gate Gate Gate Gate Gate Gate Gate Gate (G) via a thin (G) via a thin (G) via a thin (G) via a thin

insulating layer of SiOinsulating layer of SiOinsulating layer of SiOinsulating layer of SiO . . . .



insulating layer of SiOinsulating layer of SiOinsulating layer of SiOinsulating layer of SiO2222. . . .

The The The The nnnn----doped material lies on a doped material lies on a doped material lies on a doped material lies on a pppp----doped substrate that may have an doped substrate that may have an doped substrate that may have an doped substrate that may have an

additional terminal connection called additional terminal connection called additional terminal connection called additional terminal connection called

SubstrateSubstrateSubstrateSubstrateSubstrateSubstrateSubstrateSubstrate (SS).(SS).(SS).(SS).

2424

Basic MOSFET OperationBasic MOSFET OperationBasic MOSFET OperationBasic MOSFET OperationBasic MOSFET OperationBasic MOSFET OperationBasic MOSFET OperationBasic MOSFET Operation

A depletionA depletionA depletionA depletion----type MOSFET can operate in two modes:type MOSFET can operate in two modes:type MOSFET can operate in two modes:type MOSFET can operate in two modes:

•• Depletion modeDepletion modeDepletion modeDepletion modeDepletion modeDepletion modeDepletion modeDepletion mode

•• Enhancement modeEnhancement modeEnhancement modeEnhancement modeEnhancement modeEnhancement modeEnhancement modeEnhancement mode



2525

DDDDDDDD--------Type MOSFET in Depletion ModeType MOSFET in Depletion ModeType MOSFET in Depletion ModeType MOSFET in Depletion ModeType MOSFET in Depletion ModeType MOSFET in Depletion ModeType MOSFET in Depletion ModeType MOSFET in Depletion Mode

• When VWhen VWhen VWhen VGSGSGSGS = = = = 0 0 0 0 V, IV, IV, IV, IDDDD = I= I= I= IDSSDSSDSSDSS

Depletion ModeDepletion Mode

The characteristics are similar to a JFET.



• When VWhen VWhen VWhen VGSGSGSGS = = = = 0 0 0 0 V, IV, IV, IV, IDDDD = I= I= I= IDSSDSSDSSDSS

• When VWhen VWhen VWhen VGS GS GS GS < < < < 0 0 0 0 V, IV, IV, IV, IDDDD < I< I< I< IDSSDSSDSSDSS

• The formula used to plot the transfer The formula used to plot the transfer The formula used to plot the transfer The formula used to plot the transfer

curve still applies: curve still applies: curve still applies: curve still applies: 2

P

GSDSSD V

V1II

−−−−====

2626

DDDDDDDD--------Type MOSFET in Enhancement ModeType MOSFET in Enhancement ModeType MOSFET in Enhancement ModeType MOSFET in Enhancement ModeType MOSFET in Enhancement ModeType MOSFET in Enhancement ModeType MOSFET in Enhancement ModeType MOSFET in Enhancement Mode

• VVVVGSGSGSGS > > > > 0 0 0 0 VVVV

• IIIIDDDD increases above Iincreases above Iincreases above Iincreases above IDSSDSSDSSDSS

• The formula used to The formula used to The formula used to The formula used to

plot the transfer curve plot the transfer curve plot the transfer curve plot the transfer curve

still applies:still applies:still applies:still applies:2

GSV

Enhancement ModeEnhancement Mode



2

P

GSDSSD V

V1II

−−−−====

Note that VGS is now a positive polarity

2727

pppppppp--------Channel DChannel DChannel DChannel DChannel DChannel DChannel DChannel D--------Type MOSFETType MOSFETType MOSFETType MOSFETType MOSFETType MOSFETType MOSFETType MOSFET



2828

DDDDDDDD--------Type MOSFET SymbolsType MOSFET SymbolsType MOSFET SymbolsType MOSFET SymbolsType MOSFET SymbolsType MOSFET SymbolsType MOSFET SymbolsType MOSFET Symbols



2929


Specification SheetSpecification SheetSpecification SheetSpecification SheetSpecification SheetSpecification SheetSpecification SheetSpecification Sheet



more…more…

3030





3131

EEEEEEEE--------Type MOSFET ConstructionType MOSFET ConstructionType MOSFET ConstructionType MOSFET ConstructionType MOSFET ConstructionType MOSFET ConstructionType MOSFET ConstructionType MOSFET Construction

• The The The The DrainDrainDrainDrainDrainDrainDrainDrain (D) and (D) and (D) and (D) and SourceSourceSourceSourceSourceSourceSourceSource (S) (S) (S) (S)

connect to the to connect to the to connect to the to connect to the to nnnn----doped regions. doped regions. doped regions. doped regions.

These These These These nnnn----doped regions are doped regions are doped regions are doped regions are

connected via an connected via an connected via an connected via an nnnn----channelchannelchannelchannel

• The The The The GateGateGateGateGateGateGateGate (G) connects to the (G) connects to the (G) connects to the (G) connects to the pppp----doped substrate via a thin insulating doped substrate via a thin insulating doped substrate via a thin insulating doped substrate via a thin insulating

layer of SiOlayer of SiOlayer of SiOlayer of SiO2222



layer of SiOlayer of SiOlayer of SiOlayer of SiO2222

• There is no channelThere is no channelThere is no channelThere is no channel

• The The The The nnnn----doped material lies on a doped material lies on a doped material lies on a doped material lies on a pppp----doped substrate that may have an doped substrate that may have an doped substrate that may have an doped substrate that may have an

additional terminal connection called additional terminal connection called additional terminal connection called additional terminal connection called

the the the the SubstrateSubstrateSubstrateSubstrateSubstrateSubstrateSubstrateSubstrate (SS)(SS)(SS)(SS)

3232

Basic Operation of the EBasic Operation of the EBasic Operation of the EBasic Operation of the EBasic Operation of the EBasic Operation of the EBasic Operation of the EBasic Operation of the E--------Type MOSFETType MOSFETType MOSFETType MOSFETType MOSFETType MOSFETType MOSFETType MOSFET

• VVVVGSGSGSGS is always positiveis always positiveis always positiveis always positive

• As VAs VAs VAs VGSGSGSGS increases, Iincreases, Iincreases, Iincreases, IDDDDincreasesincreasesincreasesincreases

The enhancementThe enhancement--type MOSFET operates only in the enhancement mode.type MOSFET operates only in the enhancement mode.



• As VAs VAs VAs VGSGSGSGS is kept constant is kept constant is kept constant is kept constant

and Vand Vand Vand VDSDSDSDS is increased, is increased, is increased, is increased,

then Ithen Ithen Ithen IDDDD saturates (Isaturates (Isaturates (Isaturates (IDSSDSSDSSDSS) ) ) )

and the saturation level, and the saturation level, and the saturation level, and the saturation level,

VVVVDSsatDSsatDSsatDSsat is reachedis reachedis reachedis reached

3333

EEEEEEEE--------Type MOSFET Transfer CurveType MOSFET Transfer CurveType MOSFET Transfer CurveType MOSFET Transfer CurveType MOSFET Transfer CurveType MOSFET Transfer CurveType MOSFET Transfer CurveType MOSFET Transfer Curve

To determine ITo determine ITo determine ITo determine IDDDD given Vgiven Vgiven Vgiven VGSGSGSGS::::

Where: Where: Where: Where:

VVVVTTTT = threshold voltage = threshold voltage = threshold voltage = threshold voltage

or voltage at which the or voltage at which the or voltage at which the or voltage at which the

2TGSD )VV(kI −−−−====



or voltage at which the or voltage at which the or voltage at which the or voltage at which the

MOSFET turns onMOSFET turns onMOSFET turns onMOSFET turns on

k, a constant, can be determined by using values at a specific point and the formula:

2TGS(ON)

D(ON)

)V(V

Ik

−−−−====

VDSsatDSsatDSsatDSsat can be calculated by:

TGSDsat VVV −−−−====

3434

pppp----Channel EChannel EChannel EChannel E----Type MOSFETsType MOSFETsType MOSFETsType MOSFETs



The The The The The The The The pppppppp--------channel enhancementchannel enhancementchannel enhancementchannel enhancementchannel enhancementchannel enhancementchannel enhancementchannel enhancement--------type MOSFET is similar to the type MOSFET is similar to the type MOSFET is similar to the type MOSFET is similar to the type MOSFET is similar to the type MOSFET is similar to the type MOSFET is similar to the type MOSFET is similar to the nnnnnnnn--------channel, except that the voltage polarities and current directions channel, except that the voltage polarities and current directions channel, except that the voltage polarities and current directions channel, except that the voltage polarities and current directions channel, except that the voltage polarities and current directions channel, except that the voltage polarities and current directions channel, except that the voltage polarities and current directions channel, except that the voltage polarities and current directions are reversed.are reversed.are reversed.are reversed.are reversed.are reversed.are reversed.are reversed.

3535

MOSFET SymbolsMOSFET SymbolsMOSFET SymbolsMOSFET SymbolsMOSFET SymbolsMOSFET SymbolsMOSFET SymbolsMOSFET Symbols



3636





more…more…

3737





3838

Handling MOSFETsHandling MOSFETsHandling MOSFETsHandling MOSFETsHandling MOSFETsHandling MOSFETsHandling MOSFETsHandling MOSFETs

MOSFETs are very sensitive to static electricity. Because of the very thin MOSFETs are very sensitive to static electricity. Because of the very thin MOSFETs are very sensitive to static electricity. Because of the very thin MOSFETs are very sensitive to static electricity. Because of the very thin

SiOSiOSiOSiO2222 layer between the external terminals and the layers of the device, layer between the external terminals and the layers of the device, layer between the external terminals and the layers of the device, layer between the external terminals and the layers of the device,

any small electrical discharge can create an unwanted conduction.any small electrical discharge can create an unwanted conduction.any small electrical discharge can create an unwanted conduction.any small electrical discharge can create an unwanted conduction.

ProtectionProtectionProtectionProtectionProtectionProtectionProtectionProtection

• Always transport in a static sensitive bagAlways transport in a static sensitive bagAlways transport in a static sensitive bagAlways transport in a static sensitive bag



• Always wear a static strap when handling MOSFETSAlways wear a static strap when handling MOSFETSAlways wear a static strap when handling MOSFETSAlways wear a static strap when handling MOSFETS

•

• Apply voltage limiting devices between the gate and source, such Apply voltage limiting devices between the gate and source, such Apply voltage limiting devices between the gate and source, such Apply voltage limiting devices between the gate and source, such

as backas backas backas back----totototo----back Zeners to limit any transient voltage.back Zeners to limit any transient voltage.back Zeners to limit any transient voltage.back Zeners to limit any transient voltage.

3939

VMOS DevicesVMOS DevicesVMOS DevicesVMOS DevicesVMOS DevicesVMOS DevicesVMOS DevicesVMOS Devices

VMOS (vertical MOSFET) VMOS (vertical MOSFET) VMOS (vertical MOSFET) VMOS (vertical MOSFET)

increases the surface area increases the surface area increases the surface area increases the surface area

of the device.of the device.of the device.of the device.

AdvantagesAdvantages

• VMOS devices handle



• VMOS devices handle higher currents by providing more surface area to dissipate the heat.

• VMOS devices also have faster switching times.

4040

CMOS DevicesCMOS DevicesCMOS DevicesCMOS DevicesCMOS DevicesCMOS DevicesCMOS DevicesCMOS Devices

CMOS (complementary MOSFET) uses a p-channel and n-channel MOSFET; often on the same substrate as shown here.



AdvantagesAdvantagesAdvantagesAdvantagesAdvantagesAdvantagesAdvantagesAdvantages

• Useful in logic circuit designsUseful in logic circuit designsUseful in logic circuit designsUseful in logic circuit designs

• Higher input impedanceHigher input impedanceHigher input impedanceHigher input impedance

• Faster switching speedsFaster switching speedsFaster switching speedsFaster switching speeds

• Lower operating power levelsLower operating power levelsLower operating power levelsLower operating power levels

4141

Summary TableSummary TableSummary TableSummary TableSummary TableSummary TableSummary TableSummary Table



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chapter chapter 6666:::: fieldfield- ---effect ...webstaff.kmutt.ac.th/~suwat.pat/material/ene212...

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