Fundamental Fundamental ElectronicsElectronics——BJTBJT

Fundamental Fundamental ElectronicsElectronics——BJTBJT

Reference: Thomas L. Floyd, Electronics Fundamentals: Circuits, Devices, and Applications, Pearson Education Inc

Reference Books

1Electronics Fundamentals:

Circuits, Devices, and Applications

Thomas L. Floyd

Pearson Education

Inc.

2Electronic circuit analysis

and DesignDonald A ,

Neaman Irwin

3Microelectronics:DIGITAL

AND ANALOG CIRCUITS AND SYSTEMS

Jacob Millman, Arvin Grabel

McGraw-Hill

4

Microelectronic Circuits Sedra & Smith Oxford University Press

Objectives

• The History of VLSI

• Describe the basic structure and operation of bipolar junction transistors (BJT)

• Describe the basic structure and operation of MOSFETs

• Describe the basic structure and operation of CMOS

The History of VLSI• IC(Integrated Circuits) History Evolution

– vacuum tube, – single transistor, – IC (Integrated Circuits)

• SSI, MSI, LSI, VLSI, SoC

The History of VLSI• 1926—Lilienfeld proposed FET• 1947—Brattin, Bardin, Schockley

proposed BJT from Bell Lab.• 1957—TI Kilby proposed the first IC• 1960– Hoerni invent the planar

process• 70’s—IC composed mainly by pMOS

and BJT

The History of VLSI

• 80’s—IC composed mainly by nMOS and BJT

• 90’s—IC composed mainly by CMOS and BiCMOS

• 1995—NEC, AT&T, Phillips proposed

SOC

The evolution of IC technique

Transistor

Single component

SSI MSI LSI VLSI ULSI GSI

Logic

Gate count

---- ---- 10100~

1000

1000~

20000

20000~

500,000

>500,0

00

>10,000,000

Produ-ction ----

電晶體二極體

平面元件

邏輯閘暫存器

計數器多工器加法器

8bit 微處理器ROMRAM

16/32bits 微處理器

即時影像處理

器SOC

1947 1950 1961 1966 1971 1980 1985 1990

Moore’s Law plot

The transistor count in an IC would double every 18 momths

Main Families in Digital Logic

1. TTL(implemented by BJT)—big area, high consumption, high speed

2. MOS — small area, low consumption, low speed

3. BiCMOS — speed near TTL, area near MOS, hard manufacture

Architecture of BJTs• The bipolar junction transistor (BJT) is

constructed with three doped semiconductor regions separated by two pn junctions

• Regions are called emitter, base and collector

Architecture of BJTs• There are two types of BJTs, the npn and pnp• The two junctions are termed the base-emitter junction

and the base-collector junction• The term bipolar refers to the use of both holes and

electrons as charge carriers in the transistor structure• In order for the transistor to operate properly, the two

junctions must have the correct dc bias voltages– the base-emitter (BE) junction is forward

biased(>=0.7V for Si, >=0.3V for Ge)– the base-collector (BC) junction is reverse biased

FIGURE Transistor symbols.

Thomas L. FloydElectronics Fundamentals, 6eElectric Circuit Fundamentals, 6e

Copyright ©2004 by Pearson Education, Inc.

Upper Saddle River, New Jersey 07458All rights reserved.

Basic circuits of BJT

Operation of BJTs

• BJT will operates in one of following four region– Cutoff region (for digital circuit)– Saturation region (for digital circuit)– Linear (active) region (to be an

amplifier)– Breakdown region (always be a

disaster)

Operation of BJTs

DC Analysis of BJTs• Transistor Currents:

IE = IC + IB• alpha (DC)

IC = DCIE• beta (DC)

IC = DCIB DC typically has a value between 20 and 200

DC Analysis of BJTs

• DC voltages for the biased transistor:• Collector voltage

VC = VCC - ICRC

• Base voltageVB = VE + VBE

– for silicon transistors, VBE = 0.7 V

– for germanium transistors, VBE = 0.3 V

Q-point

• The base current, IB, is established by the base bias

• The point at which the base current curve intersects the dc load line is the quiescent or Q-point for the circuit

Q-point

DC Analysis of BJTs

• The voltage divider biasing is widely used

• Input resistance is:RIN DCRE

• The base voltage is approximately:VB VCCR2/(R1+R2)

BJT as an amplifier

• Class A Amplifiers

• Class B Amplifiers

BJT Class A Amplifiers• In a class A amplifier, the transistor conducts

for the full cycle of the input signal (360°)– used in low-power applications

• The transistor is operated in the active region, between saturation and cutoff– saturation is when both junctions are forward biased– the transistor is in cutoff when IB = 0

• The load line is drawn on the collector curves between saturation and cutoff

BJT Class A Amplifiers

BJT Class A Amplifiers• Three biasing mode for class A

amplifiers– common-emitter (CE) amplifier– common-collector (CC) amplifier– common-base (CB) amplifier

BJT Class A Amplifiers• A common-emitter (CE) amplifier

– capacitors are used for coupling ac without disturbing dc levels

BJT Class A Amplifiers• A common-collector (CC) amplifier

– voltage gain is approximately 1, but current gain is greater than 1

BJT Class A Amplifiers• The third configuration is the common-

base (CB)– the base is the grounded (common) terminal– the input signal is applied to the emitter– output signal is taken off the collector– output is in-phase with the input– voltage gain is greater than 1– current gain is always less than 1

BJT Class B Amplifiers• When an amplifier is biased such that it operates

in the linear region for 180° of the input cycle and is in cutoff for 180°, it is a class B amplifier– A class B amplifier is more efficient than a class

A• In order to get a linear reproduction of the input

waveform, the class B amplifier is configured in a push-pull arrangement– The transistors in a class B amplifier must be

biased above cutoff to eliminate crossover distortion

BJT Class B Amplifiers

The BJT as a Switch• When used as an electronic switch, a

transistor normally is operated alternately in cutoff and saturation– A transistor is in cutoff when the base-emitter

junction is not forward-biased. VCE is approximately equal to VCC

– When the base-emitter junction is forward-biased and there is enough base current to produce a maximum collector current, the transistor is saturated

The BJT as a Switch

An example -- NOR

Architecture of MOS Field-Effect Transistors (FETs)• The metal-oxide semiconductor

field-effect transistor (MOSFET) : the gate is insulated from the channel by a silicon dioxide (SiO2) layer

Architecture of MOS Field-Effect Transistors (FETs)

• Two types of MOSFETs – depletion type (D-MOSFETs) have a

physical channel between Drain and Source, with no voltage applied to the Gate

– enhancement type (E-MOSFETs) have no physical Drain-Source channel

Architecture of MOS Field-Effect Transistors (FETs)• D-MOSFET

– Channel may be enhanced or restricted by gate voltage

• E-MOSFET– Channel is created

by gate voltage

• Simplified symbol

Biasing Circuits

FET Amplifiers• Voltage gain of a FET is determined by the

transconductance (gm) with units of Siemens (S)

gm = Id / Vg

• The D-MOSFET may also be zero-biased• The E-MOSFET requires a voltage-divider-bias• All FET’s provide extremely high input

resistance

Principle of MOSFETfor E-MOS (n-channel)

(+)

Principle of MOSFET for E-MOS (n-channel)

TNV ： The threshold voltage

Principle of MOSFET for E-MOS (n-channel)

Principle of MOSFET for D-MOS (n-channel)

Principle of MOSFET for D-MOS (n-channel)

Voltage-current relations

p-cnannel MOS(pMOS)

•

P+ P+

n-substrate

S G D

B

body

All the characteristics are similar to NMOS.

+ - -

+++++++

An inverter

Voltage transfer-- see the time delay

Complementary MOS(CMOS)

P PP NN N

p-well

n-substrate

Vss input output Vdd

pMOS

nMOS

in out

Vss

Vdd