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1 MOS Field-Effect Transistors (MOSFETs)

1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

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Page 1: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

1

MOS Field-EffectTransistors (MOSFETs)

Page 2: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

MOSFET ( Voltage Controlled Current Device)• MOS Metal Oxide Semiconductor

Physical Structure

• FET Field Effect TransistorThe current controlled mechanism is based on an electric field established by the

voltage applied to the control terminal – GATE

• Uni-polar Current is conducted by only one carrier

• IGFET Insulated Gate FET

• CMOSFET Complementary MOSFET

• 1930 was Known, 1960s Commercialized

1970s Most commonly used VLSI

• NMOSFET/PMOSFET n/p-channel enhancement mode MOSFET

Page 3: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

MOSFET• Small Size

• Manufacturing process is simple

• Requires comparatively low power

• Implement digital & analog functions with a fewer resistors very large scale Integrated (VLSI) circuit

• Study Includes– Physical structure– Operation– Terminal characteristics– Circuit Models– Basic Circuit application

Page 4: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Figure 4.1 Physical structure of the enhancement-type NMOS transistor:

Page 5: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Device Structure• Types “n” channel enhancement MOSFET

“p” channel enhancement MOSFET

• “n” Channel MOSFET– Fabricated on a p-type substance that provides physical support for the

device.

– Two heavily doped n-type region are created • n+ Source (‘S’) n+ for lightly doped ‘n’ type silicon• n+ Drain (‘D’) n+ for heavily doped ‘n’ type

silicon

– Area between source & Drain• Thin Layer of Silicon dioxide (SiO2) is grown with thicker of tox = 2-

50 nanometers An excellent electrical insulator

• Metal is deposited on top of the oxide layer to form the Gate electrode. Metal contact is made to Source & Drain and the substrate (Body)

Page 6: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Figure 4.1 Physical structure of the enhancement-type NMOS transistor

Cross-section. Typically L = 0.1 to 3 m, W = 0.2 to 100 m, and

the thickness of the oxide layer (tox) is in the range of 2 to 50 nm.

Page 7: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

• Four terminals– Source (S)– Gate (G)– Drain (D)– Body (B)

• L Length of channel region

W Width of the substrate

tox Thickener of An oxide Layer

Device Structure

Page 8: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

• Metal oxide semiconductor - name is derived from its physical structure

• Insulted – Gate FET (IGFET) – gate is electrically insulated from the device body– Current in gate terminal is small (10-15 A)

• Substrate forms pn junctions with the source & drain region & is kept reversed biased all the time

• Drain will be at a positive voltage relative to the source, two junctions are at cutoff mode if substrate is connected to the source. Thus Body will have no effect on operation of the device.

Device Structure

Page 9: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Principle of operation

• Voltage applied to the Gate controls current flow between Source & Drain with direction from Drain to Source in channel region

• It is a symmetrical device thus Drain & Source can be interchanged with no change in devices characteristics

• • With no bias gate voltage, two back-to-back diodes exist

in series between drain and source.

• No current flows even if vDS is applied. In fact the path between Source & Drain (1012Ω) has very high resistance

Page 10: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Figure 4.2 The enhancement-type NMOS transistor with a positive voltage applied to the gate. An n channel is induced at the top of the substrate beneath the gate.

Page 11: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Creating a Channel for Current Flow

• Source & Drain are grounded and a positive voltage (vGS) is applied to the gate.

• Holes are repelled-leaving behind a carrier depletion-region.

• Depletion region is populated with the bounded negative charges associated with the acceptor atoms and are uncovered because the neutralizing holes have been push downward into the substrate.

Page 12: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

• Positive gate attracts electrons from the n+ source & drain region into the channel region.

• Due to electrons accumulated under the gate, an ‘n’ region is created & connects source & drain region.

• Thus if voltage is applied between source & drain, current flows due to mobile electrons between drain & source.

• ‘n’ region forms a channel – ‘n’ channel MOSET (NMOSFET)

Channel for Current Flow

Page 13: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

• An ‘n’ channel MOSFET is formed in a ‘p’ type substrate. Known as “Inversion Layer”.

• The value of vGS that causes sufficient number of mobile electrons to be accumulate in the channel region to form conducting channel is called threshold Voltage “Vt”.

• Vt for ‘n’ channel is positive & value is 0.5 to 1V

Channel for Current Flow

Page 14: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Channel for Current Flow

• Gate & channel region form a parallel plate capacitor, with oxide layer as the capacitor dielectric.

• Positive charge is accumulated on gate electrode & negative charge on channel electrode.

• An electric field thus develops in the vertical direction.

• Capacitor charge controls the current flow through the channel when a voltage vDS is applied.

• Gate Channel

Page 15: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Figure 4.3 An NMOS transistor with vGS > Vt and with a small vDS applied.

The device acts as a resistance whose value is determined by vGS.

Specifically, the channel conductance is proportional to vGS – Vt’

and thus iD is proportional to (vGS – Vt) vDS.

Page 16: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Applying a Small vDS• vDS is applied (vDS = 50mV) causes iD to flow through induced ‘n’ channel.

– Direction is opposite to that of the flow of negative charges. – Magnitude of iD depends upon density of electrons and in term on vGS .

• vGS ≤ Vt – Negligible current iD as the channel has been just induced.

• vGS > Vt – iD current increases, increases conductance of the channel & is proportional

to Excess gate voltage (vGS - Vt )

– vGS - Vt is known as Excess gate Voltage , Effective Voltage Overdrive Voltage (VOV

)

– MOSFET operatrates as a linear resistance whose value is controlled by vGS.

– vGS above Vt enhances the channel – named Enhanced Mode operation & enhanced type MOSFET

iD = iS, iG = 0

Page 17: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Figure 4.4 The iD–vDS characteristics of the MOSFET

When the voltage applied between drain and source, vDS, is kept small.

The device operates as a linear resistor whose value is controlled by vGS.

Page 18: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Figure 4.5 Operation of the enhancement NMOS transistor as vDS is increased. The induced channel

acquires a tapered shape, and its resistance increases as vDS is increased. Here, vGS is kept constant at a value >

Vt.

Page 19: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

The drain current iD versus the drain-to-source voltage

vDS for an enhancement-type NMOS transistor operated

with vGS > Vt.

Page 20: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Increasing vDS causes the channel to acquire a tapered shape. Eventually,

as vDS reaches vGS – Vt’ the channel is pinched off at the drain end.

Increasing vDS above vGS – Vt has little effect (theoretically, no effect)

on the channel’s shape.

Page 21: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Derivation of the iD–vDS characteristic of the NMOS transistor.

Page 22: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Drain Current iD• Directly Proportional to:

– Mobility of Electrons in the channel μn (μm2/V)

– Gate Capacitance per unit gate area Cox (μF/ μm)

– Width of the substrate (μm)

– Gate-Source Voltage vGS (Volts)

– Drain-Source Voltage v DS (Volts)

• Indirectly Proportional to:– Length of the channel (μm)

Page 23: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

iD – vDS relationshipTroide Mode

Saturation Mode

Page 24: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

The p Channel MOSFET

• Fabricated on an n-type substrate with p+ regions for Drain & Source

• Holes are the current carriers.

• vGS & vDS are negative

• Threshold voltage Vt is negative.

• Both NMOS & PMOS are utilized in Complementary MOS or CMOS circuits

Page 25: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Cross-section of a CMOS integrated circuit. Note that the PMOS transistor is formed in

a separate n-type region, known as an n well. Another arrangement is also possible in

which an n-type body is used and the n device is formed in a p well. Not shown are the

connections made to the p-type body and to the n well; the latter functions as the body

terminal for the p-channel device.

Complementary MOS or CMOS

Page 26: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

• Modes of operation

– Cutoff

– Triode (Saturation in BJT)

– Saturation ( Active in BJT)

iD – vDS Charateristics

Page 27: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

The iD–vDS characteristics for a device with k’n (W/L) = 1.0 mA/V2

.

Page 28: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

The iD–vGS characteristic for an enhancement-type NMOS transistor in saturation (Vt =

1 V, k’n W/L = 1.0 mA/V2

).

Page 29: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Large-signal equivalent-circuit model of an n-channel MOSFET

operating in the saturation region.

Page 30: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Increasing vDS beyond vDSsat causes the channel pinch-off

point to move slightly away from the drain, thus reducing the

effective channel length (by DL).

Finite Output Resistance in Saturation

Page 31: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Effect of vDS on iD in the saturation region. The MOSFET parameter VA depends on the

process technology and, for a given process, is proportional to the channel length L.

Finite Output Resistance in Saturation

Page 32: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Large-signal equivalent circuit model of the n-channel MOSFET in saturation,

incorporating the output resistance ro. The output resistance models the linear

dependence of iD on vDS

Finite Output Resistance in Saturation

Page 33: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Circuit symbol for the p-channel enhancement-type MOSFET.

Page 34: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Characteristics of PMOSFETTriode Mode of Operation

Page 35: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Characteristics of PMOSFETSatuaration Mode of Operation

Page 36: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

The Roll of Substrate :Body Effect

• Substrate for many Transistors

• Body is connected to the most negative power supply to maintain cutoff conditions for all the substrates to channel junctions

• Another gate

Page 37: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Temperature Effects• Vt and K’n are effected by the temperature

• Vt increases by 2mV per 10C rise in temperature

• K’n decreases with rise in temperature thus drain current increases. The effect is dominant. Thus ID decreases with increase in temperature

MOSFET in Power circuits

Page 38: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect
Page 39: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect
Page 40: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect
Page 41: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect
Page 42: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Graphical construction to determine the transfer characteristic of the

amplifier in (a).

Page 43: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Circuit for Example 4.9.

Page 44: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect
Page 45: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Biasing the MOSFET using a large drain-to-gate feedback resistance, RG.

Page 46: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Biasing the MOSFET using a constant-current source

Page 47: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Conceptual circuit utilized to study the operation of the MOSFET

as a small-signal amplifier.

Page 48: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Recap : Transfer Function

Page 49: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Transfer characteristic showing operation as an amplifier biased at point

Q.

Page 50: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Conceptual circuit utilized to study the operation of the MOSFET as a small-signal amplifier.

The DC BIAS POINT

To Ensure Saturation-region Operation

Page 51: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Signal Current in Drain Terminal

Page 52: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Total instantaneous voltages vGS and vD

Page 53: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Small-signal ‘π’ models for the MOSFET

Page 54: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Common Source amplifier circuit

Example 4-10

Page 55: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Small Signal ‘T’ Model : NMOSFET

Page 56: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Small Signal Models

‘T’ Model

Page 57: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Single Stage MOS Amplifier

Page 58: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Amplifiers Configurations

Page 59: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Common Source Amplifier (CS) :Configuration

Page 60: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Common Source Amplifier (CS)• Most widely used

• Signal ground or an ac earth is at the source through a bypass capacitor

• Not to disturb dc bias current & voltages coupling capacitors are used to pass the signal voltages to the input terminal of the amplifier or to the Load Resistance

• CS circuit is unilateral – – Rin does not depend on RL and vice versa

Page 61: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Small Signal Hybrid “π” Model (CS)

Page 62: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Small Signal Hybrid “π” Model : (CS)

Gin RR sig

sigG

Ggs v

RR

Rv

LDogsmo RRrvgv ||||

sigG

GLDom

gs

ov RR

RRRrg

v

vG ||||

Doo Rr ||R

sig

gs

gs

o

sig

ov v

v

v

v

v

vG

Page 63: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Small-signal analysis performed directly on the amplifier circuit with the MOSFET model implicitly

utilized.

Gin RR

sigG

GLDom

gs

o

RR

RRRrg

v

v||||

Doo Rr ||R

Page 64: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

BJT / MOSFET

LCosigB

Bm

sig

o

Coout

Bin

RRrRrR

rRg

v

v

RrR

rRR

||||||

||

||

||

LDosigG

Gm

sig

o

Doout

Gin

RRrRR

Rg

v

v

RrR

RR

||||

||

1,

Page 65: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

• Input Resistance is infinite (Ri=∞)

• Output Resistance = RD

• Voltage Gain is substantial

Common Source Amplifier (CS) Summary

Gin RR

sigG

GLDom

gs

o

RR

RRRrg

v

v||||

Doo Rr ||R

Page 66: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Common-source amplifier

with a resistance RS in the source lead

Page 67: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

The Common Source Amplifier with a Source Resistance

• The ‘T’ Model is preferred, whenever a resistance is connected to the source terminal.

• ro (output resistance due to Early Effect) is not included, as it would make the amplifier non unilateral & effect of using ro in model would be studied in Chapter ‘6’

Page 68: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Small-signal equivalent circuit with ro neglected.

Sm

g

Rg

vi

1

Page 69: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Do

Gin

RR

RR

Small-signal Analysis.

Page 70: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

sig

i

i

gs

gs

o

sig

ov v

v

v

v

v

v

v

vG

Sm

LDm

sigG

Gv

sig

o

sigsigG

Gi

Sm

ii

Sm

mgs

LDgsmo

Rg

RRg

RR

RG

v

v

vRR

Rv

Rg

vv

Rg

gv

RRvgv

1

||

11

1

||

Voltage Gain : CS with RS

Page 71: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Common Source Configuration with Rs

• Rs causes a negative feedback thus improving the stability of drain current of the circuit but at the cost of voltage gain

• Rs reduces id by the factor

– (1+gmRs) = Amount of feedback

• Rs is called Source degeneration resistance as it reduces the gain

Page 72: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Small-signal equivalent circuit directly on Circuit

Page 73: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

A common-gate amplifier based on the circuit

Page 74: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Common Gate (CG) Amplifier• The input signal is applied to the source

• Output is taken from the drain

• The gate is formed as a common input & output port.

• ‘T’ Model is more Convenient

• ro is neglected

Page 75: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

A small-signal equivalent circuit

Page 76: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

A small-signal Analusis : CG

mim

i

i

iin gvg

v

i

vR

1

Dout RR

Page 77: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

A small-signal Analusis : CG

sigm

LDm

sig

ov

sigm

sigsig

sigm

msig

sigin

ini

LDimo

sig

i

i

o

sig

ov

Rg

RRg

v

vG

Rg

vv

Rg

gv

RR

Rv

RRvgv

v

v

v

v

v

vG

1

||

11

1

||

Page 78: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Small signal analysis directly on circuit

Page 79: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

The common-gate amplifier fed with a current-signal input.

Page 80: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Summary : CG

4. CG has much higher output Resistance

5. CG is unity current Gain amplifier or a Current Buffer

6. CG has superior High Frequency Response.

Page 81: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

A common-drain or source-follower amplifier.

Page 82: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Small-signal equivalent-circuit model

Page 83: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Small-signal Analysis : CD

Page 84: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

(a) A common-drain or source-follower amplifier :output resistance Rout of the source

follower.

mmoout gg

rR11

||

Page 85: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

(a) A common-drain or source-follower amplifier. : Small-signal analysis performed directly on the

circuit.

Page 86: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Common Source Circuit (CS)

Page 87: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Common Source Circuit (CS) With RS

Page 88: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Common Gate Circuit (CG)

Current Follower

Page 89: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Common Drain Circuit (CD)

Source Follower

Page 90: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Summary & Comparison

Page 91: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Quiz No 4• Draw/Write the Following:

27-03-07

BJT MOSFET

Types npn pnp nMOS pMOS

Symbols

‘π’ Model

T Model

gm

Re/rs

rπ/rg

Page 92: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Problem 5-44

Page 93: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

SOLUTION : DC Analysis

Page 94: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

SOLUTION : DC Analysis

IE

mAI

II

II

E

EE

BE

1

101100

3.3

7.05

0100)1(

7.03.35

01007.03.35

250.1

25

E

te I

Vr

IB

gm = 40mA/V

Page 95: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Solution Small Signal Analysis

Page 96: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Solution Small Signal Analysis

Page 97: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Solution Small Signal Analysis : Input Resistance

Rin

ib

LCee

b

b

bin RRr

i

v

i

vR ||)1(

)1(

+

vb

-

Page 98: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Solution Small Signal Analysis : Output ResistanceItest

IE

IE/(1+ß)

IRC

Rout

test

testout I

VR

)1(||

)1(

)1(

)1(

sigeC

sigeC

sigeC

sige

test

C

test

testout

RrR

RrR

RrR

Rr

VR

VV

R

ERtest IIIC

)1(

sig

e

testE R

r

VI

C

testR R

VI

C

Page 99: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Solution Small Signal Analysis : Voltage Gain

+

-

LCmeb

o RRgv

v||+

-

vi

+

-

veb

sig

i

i

eb

eb

o

sig

o

v

v

v

v

v

v

v

v

Vo

Page 100: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Solution Small Signal Analysis : Voltage gain

sig

i

i

eb

eb

o

sig

o

v

v

v

v

v

v

v

v

LCmeb

o RRgv

v||+

-

vi

+

-

veb

LCe

e

i

eb

RRr

r

v

v

||

Page 101: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Solution Small Signal Analysis : Voltage Gain

sig

i

i

eb

eb

o

sig

o

v

v

v

v

v

v

v

v

LCmeb

o RRgv

v||

+

-

vi LCe

e

i

eb

RRr

r

v

v

||

LCein RRrR ||)1(

sigLCe

LCe

sigin

in

sig

i

RRRr

RRr

RR

R

v

v

||)1(

||)1(

Page 102: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Solution Small Signal Analysis : Voltage Gain

sig

i

i

eb

eb

o

sig

o

v

v

v

v

v

v

v

v LCm

eb

o RRgv

v||

LCe

e

i

eb

RRr

r

v

v

||

sigin

in

LCe

eLCm

sig

o

RR

R

)R(Rr

r)||R(Rg

v

v

||

sigin

in

sig

i

RR

R

v

v

sigin

in

LCe

LC

sig

o

RR

R

)R(Rr

)||R(R

v

v

||

sigin

in

LCe

LCem

sig

o

RR

R

)R(Rr

)||R(Rrg

v

v

||

Page 103: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Solution Small Signal Analysis : Voltage Gain

+

-

LCe

LC

i

o

RRr

RR

v

v

||

||

+

-

vi

sig

i

i

o

sig

o

v

v

v

v

v

v

sigin

in

sig

i

RR

R

v

v

sigin

in

LCe

LC

sig

o

RR

R

)R(Rr

)||R(R

v

v

||

Vo

Page 104: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Problem

Page 105: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Small Signal Model MOSFET : CD

Page 106: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Solution Small Signal Analysis

1/gm

gmvsg

D

Page 107: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

1/gm

gmvsg

D

Solution Small Signal Analysis : Input Resistance

Rin

Ig=0

inR

Page 108: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

1/gm

gmvsg

D

Solution Small Signal Analysis : Output ResistanceItest

ID

IG=0

IRD

Rout

test

testout I

VR

mD

m

test

D

test

testout g

R

gV

RV

VR

1||

/1

DRtest IIIC

m

testD

g

VI

1

D

testR R

VI

D

Vtest

0 V

Page 109: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

1/gm

gmvsg

D

Solution Small Signal Analysis : Voltage Gain

+

-

LDmsg

o RRgv

v||+

-

vi

+

-

vsg

sig

i

i

sg

sg

o

sig

o

v

v

v

v

v

v

v

v

vo

Page 110: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

1/gm

gmvsg

D

Solution Small Signal Analysis : Voltage gain

+

-

vi

+

-

vsg

LDm

m

i

sg

RRg

g

v

v

||1

1

Page 111: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

1/gm

gmvsg

D

Solution Small Signal Analysis : Voltage Gain

+

-

vi

inRsigi vv

Page 112: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Solution Small Signal Analysis : Voltage Gain

)R(Rg

g)||R(Rg

v

v

LDm

mLDm

sig

o

||1

1

sigi vv LDmsg

o RRgv

v||

sig

i

i

sg

sg

o

sig

o

v

v

v

v

v

v

v

v

LDm

m

i

sg

RRg

g

v

v

||1

1

)R(Rg

)||R(R

v

v

LDm

LD

sig

o

||1

Page 113: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

1/gm

gmvsg

D

Solution Small Signal Analysis : Voltage Gain

+

- LD

m

LD

i

o

RRg

RR

v

v

||1||

+

-

vi

sig

i

i

o

sig

o

v

v

v

v

v

v

sigi vv

LD

m

LD

sig

o

RRg

RR

v

v

||1||

Page 114: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Solution Small Signal Analysis

LCein RRrR ||)1(

)1(

||

sigeCout

RrRR

sigin

in

LCe

LC

sig

o

RR

R

)R(Rr

)||R(R

v

v

||

1

inR

mDout g

RR1

||

LD

m

LD

sig

o

RRg

RR

v

v

||1||

Page 115: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Problem 6-127(e)

Page 116: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

DC Analysis 6-127(e)

mAI

AI

mAI

C

B

E

5.0

05101/5.0

5.0

100

1

1

1

mAI

AI

mAI

C

B

E

5.0

05101/5.0

5.0

100

2

2

2

eActiveinQ

VVVVV

VV

BC

C

mod

6.44.054.0

5105.010

2

22

2

eActiveinQ

VVVV

VV

BC

C

mod

4.04.0)10(5104.0

3.47.05

1

311

1

Page 117: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Small Signal Model

Page 118: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Small Signal Model

Page 119: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Small Signal Model

Rin

1rRin

Page 120: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Small Signal Model

Rout

0 sigCout VRR

+

vbe1

-

01 bev

+

vbe2

-

02 bev

Page 121: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Small Signal Model

sigsig

be

Rr

r

v

v

1

11

sig

be

be

eb

eb

o

sig

o

v

v

v

v

v

v

v

v 1

1

2

2

211

2em

be

eb rgv

vCm

eb

o Rgv

v2

2

11211212

rR

R

rR

rrgRg

v

v

sig

C

sig

emCm

sig

o

Page 122: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Problem6-127(f)Replacing BJT with MOSFET

Page 123: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Small Signal Model

Page 124: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Small Signal Model

Page 125: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Small Signal Model

Rin

inR Rout

0 sigDout VRR

sigsg vv 1sig

gs

gs

sg

sg

o

sig

o

v

v

v

v

v

v

v

v 1

1

2

2

2

1

1

2

m

m

gs

sg

g

g

v

vDm

sg

o Rgv

v2

2

Dmm

mDm

sig

o Rgg

gRg

v

v1

2

12

Page 126: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

1rRin

Cout RR

121

rR

R

v

v

sig

C

sig

o

1

inR

Dout RR

Dmsig

o Rgv

v1

11

2

1

m

sig

C

sig

o

g

RR

v

v

Page 127: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Problem 6-127(f)

Page 128: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Solution P6-127(f)

+

+

-

-

vbe2

veb1

Page 129: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

+

+

-

-

vbe2

veb1

+

vi

-

Solution P6-127(f)))(1( 211

1

1ee

b

bin rr

i

vR

Lout RR

sig

i

i

be

be

O

sig

O

v

v

v

v

v

v

v

v 2

2

21

22

ee

e

i

be

rr

r

v

v

sigee

ee

sigin

in

sig

i

Rrr

rr

RR

R

v

v

))(1(

))(1(

211

211

Page 130: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Problem 6-127(f) with MOSFET

Page 131: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

-

-

vgs2

vsg1

+

+

Solution P6-127(f)

Page 132: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

-

-

vgs2

vsg1

+

+

Solution P6-127(f)

+vi

-

1g

iin i

vR

sig

i

i

gs

gs

O

sig

O

v

v

v

v

v

v

v

v 2

2

21

1

21

22

11

1

mm

m

mm

m

i

gs

gg

g

gg

g

v

v

sigi vv

ig1=0

Page 133: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Comparison BJT/MOSFET Cct

inR))(1( 211 eein rrR

Lout RR

sige

L

sig

o

Rr

R

v

v

)2)(1(

)1(

1

21

1

Page 134: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Figure P6.123

Problem 6-123

VBE=0.7 V

β =200

K’n(W/L)=2mA/V2

Vt=1V

Page 135: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Figure P6.123

DC Analysis

Page 136: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

DC AnalysisVBE=0.7 V

β =200

K’n(W/L)=2mA/V2

Vt1=1V

Vt2=25mV

0.7V

I=0.7/6.8=0.1mA

0 ,1. 211 BSD ImAoII

VVV GSGS 316.112211.0 2

21 '2

1tGSnD VV

L

WKI

IG=0

2V

VVVV BEGSC 22

1mA

mAII C 13

252

VmAV

Ig

VOV

Dm /63.0

2 11

kg

rVmAV

Ig

mt

Cm 5,/40

22

22

Page 137: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Small Signal Model

Page 138: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Small Signal Model

Page 139: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Small Signal Model : Voltage Gain

ig=0

+

vi

-

+

vbe2

-

1

2

2 gs

i

i

be

be

o

sig

o

v

v

v

v

v

v

v

v

MRofeffectgNegelectin

RRgv

v

G

C Lmbe

o

10

-30V/V )||(22

VVrR

g

rR

v

v

Sm

S

i

be /64.0)||(

1)||(

211

212

VVRR

R

v

v

sigin

in

sig

i /83.0

VVgRR

R

rRg

rRRRg

v

v

siin

ni

Sm

SCLm

sig

/16)||(

1)||(

)||(

211

212

0

Page 140: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Small Signal Model : Input Resistance

Rin

+

vi

-

ii

VVrR

g

rRRRg

v

v

Sm

SCLm

i

/2.19)||(

1)||(

)||(

211

212

0

ig=0

Page 141: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

ig=0

+

vi

-

Rout

Vtest = vo

Itest

test

testout I

VR

IRG

Small Signal Model : Output Resistance

Page 142: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

The Miller Theorem.

Page 143: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

The Miller equivalent circuit.

Page 144: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

K

Z

I

VZ

Z

KVV

Z

KVI

Z

VI

K

ZZ

I

V

Z

KV

Z

KVVI

Z

VI

K

ZZ

K

ZZ

11

00

1

1

11

1

2

22

11

2

1

2

22

11

1

1

11

1

1

21

1

Miller Theorem

Page 145: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Miller theorem

• Miller theorem states that impedance Z can be replaced by two impedances: Z1 connected between node 1 and ground and Z2 connected between node 2 and ground where

circuitequivalenttheobtainto

functiongainV

Vkwhere

K

ZZ

K

ZZ

11

& 1

1

2

21

Page 146: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

• Miller equivalent circuit is valid only as long as the rest of the circuit remains unchanged

• Miller equivalent circuit cannot be used directly to determine the output resistance of an amplifier. It is due to the fact for output impedance test source is required and thus circuit has a major change.

Miller theorem

Page 147: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Circuit for Example 6.7.

Page 148: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Example

VVRZ

Z

V

V

V

V

V

V

M

K

ZZ

kk

K

ZZ

MZ

sig

sig

O

sig

O

/ 497100

99.01

1

9.91001

100

1

1

1

1

1

1

2

1

1

K=-100 V/V, Z = 1 M Ω

Page 149: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

OBSERVATIONS

• The Miller replacement for a negative feedback results in a smaller resistance [by a factor of (1-K)] at the input.

• The multiplication of a feedback impedance by a factor (1-k) is referred as Miller Multiplication or Miller Effect

Page 150: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Small Signal ModelCE with RE includng r0

Page 151: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

A CE amplifier with emitter degeneration : Input Resistance

1

23

4

5

6

7

Page 152: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

A CE amplifier with emitter degeneration : Input Resistance

Page 153: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Figure 6.49

A CE amplifier with emitter degeneration to determine Avo.

Open Circuit Voltage Gain

Page 154: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

A CE amplifier with emitter degeneration

to determine Output Resistance

1

2

3

4

5

6

7

Page 155: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Figure 6.33

Active-loaded common-base amplifier

Page 156: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Figure 6.33

Active-loaded common-base amplifier

to determine Input Resistance

1

2

3

4 5

6

7

Page 157: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Figure 6.33

Active-loaded common-base amplifier

With output open-circuit

1

28

3

4

5

6

7

Page 158: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

A CB amplifier to determine Output Resistance

1

2

3

4

5

6

7

Page 159: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Quiz No 8

DE 28 EE

Page 160: 1 MOS Field-Effect Transistors (MOSFETs). MOSFET ( Voltage Controlled Current Device) MOS Metal Oxide Semiconductor Physical Structure FETField Effect

Quiz No 8

DE 28 EE