In this chapter, we will: Microelectronics Circuit ...ece.citadel.edu/barsanti/elec 401/L1_MOSFET...

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Neamen Microelectronics, 4e Chapter 3-1McGraw-Hill

Microelectronics Circuit Analysis and Design

Donald A. Neamen

Chapter 3

The Field Effect Transistor


In this chapter, we will:

� Study and understand the operation and characteristics of the various types of MOSFETs.

� Understand and become familiar with the dc analysis and design techniques of MOSFET circuits.

� Examine three applications of MOSFET circuits.

� Investigate current source biasing of MOSFET circuits, such as those used in integrated circuits.

� Analyze the dc biasing of multistage or multitransistor circuits.


Basic Structure of MOS Capacitor


MOS Capacitor Under Bias:Electric Field and Charge

Parallel plate capacitor

Negative gate bias: Holes attracted to gate

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Schematic of n-Channel Enhancement Mode MOSFET


Basic Transistor Operation

Before electron

inversion layer is

formed

After electron

inversion layer is

formed


Current Versus Voltage Characteristics: Enhancement-Mode nMOSFET


Family of iD Versus vDS Curves:Enhancement-Mode nMOSFET

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p-Channel Enhancement-Mode MOSFET


Symbols for n-Channel Enhancement-Mode MOSFET


Symbols for p-Channel Enhancement-Mode MOSFET


n-Channel Depletion-Mode MOSFET

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Family of iD Versus vDS Curves:Depletion-Mode nMOSFET

Symbols


p-Channel Depletion-Mode MOSFET

Symbols


Summary of I-V Relationships

Region NMOS PMOS

Nonsaturation vDS<vDS(sat) vSD<vSD(sat)

Saturation vDS>vDS(sat) vSD>vSD(sat)

Transition Pt. vDS(sat) = vGS - VTN vSD(sat) = vSG + VTP

Enhancement Mode

VTN > 0V VTP < 0V

Depletion Mode

VTN < 0V VTP > 0V

])(2[ 2

DSDSTNGSnD vvVvKi −−= ])(2[ 2

SDSDTPSGpD vvVvKi −+=

2][ TPSGpD VvKi +=2][ TNGSnD VvKi −=


Conduction Parameters

� NMOSFET

� PMOSFET

where:oxoox

p

oxp

p

noxn

n

tC

L

Wk

L

CWK

L

Wk

L

CWK

ε

µ

µ

=

==

==

22

22

'

'

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MOS Circuits


Problem-Solving Technique:NMOSFET DC Analysis

1. Assume the transistor is in saturation.

a. VGS > VTN, ID > 0, & VDS ≥ VDS(sat)

2. Analyze circuit using saturation I-V relations.

3. Evaluate resulting bias condition of transistor.

a. If VGS < VTN, transistor is likely in cutoff

b. If VDS < VDS(sat), transistor is likely in nonsaturation region

4. If initial assumption is proven incorrect, make new assumption and repeat Steps 2 and 3.


NMOS Common-Source Circuit


PMOS Common-Source Circuit

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Load Line and Modes of Operation:NMOS Common-Source Circuit


MOS Small-Signal Amplifier


Microelectronics Circuit Analysis and Design

Donald A. Neamen

Chapter 4

Basic FET Amplifiers



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NMOS Transistor Small-Signal Parameters

� Values depends on Q-point

112

1

][])([

)(

2)(2

−−

−

∂

∂

∂

∂

≅−=

=

=−=

==

DQTNGSQno

v

i

o

DQnTNGSQnm

gs

d

v

i

m

IVVKr

r

IKVVKg

v

ig

DS

D

GS

D

λλ


Simple NMOS Small-Signal Equivalent Circuit


Channel Length Modulation: Early Voltage



AC Small-signal

)( Domiov RrgVVA −==

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Problem-Solving Technique:MOSFET AC Analysis

1. Analyze circuit with only the dc sources to find quiescent solution. Transistor must be biased in saturation region for linear amplifier.

2. Replace elements with small-signal model.

3. Analyze small-signal equivalent circuit, setting dc sources to zero, to produce the circuit to the time-varying input signals only.


Common-Source Configuration

DC analysis:

Coupling capacitor is assumed

to be open.

AC analysis:

Coupling capacitor is assumed

to be a short. DC voltage

supply is set to zero volts.


Small-Signal Equivalent Circuit

))((Sii

iDomiov

RR

RRrgVVA

+−==


DC Load Line

Q-point near the middle

of the saturation region

for maximum symmetrical

output voltage swing,.

Small AC input signal for

output response to be

linear.

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Common-Source Amplifier with Source Resistor


Small-Signal Equivalent Circuitfor Common-Source with Source Resistor

Sm

Dmv

Rg

RgA

+

−=

1


Common-Source Amplifier with Bypass Capacitor

Small-signal equivalent circuit


NMOS Source-Follower or Common Drain Amplifier

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Small-Signal Equivalent Circuit for Source Follower

)(1

Sii

i

oS

m

oS

vRR

R

rRg

rRA

++

=


Determining Output ImpedanceNMOS Source Follower

oS

m

O rRg

R1

=


Comparison of 3 Basic Amplifiers

Configuration Voltage Gain

Current Gain

Input Resistance

Output Resistance

Common Source Av > 1

__RTH

Moderate to high

Source Follower Av ≈ 1

__RTH Low

Common Gate Av > 1 Ai ≈ 1 Low

Moderate to high

In this chapter, we will: Microelectronics Circuit ...ece.citadel.edu/barsanti/elec 401/L1_MOSFET...

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