97 Digital Electronics Lecture1 Fundmental Electronics(BJT CMOS)

8/12/2019 97 Digital Electronics Lecture1 Fundmental Electronics(BJT CMOS)

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Fundamental

ElectronicsBJT,CMOS

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

1Electronics Fundamentals:

Circuits, Devices, andApplications

Thomas L.Floyd

PearsonEducation

Inc.

2

Electronic circuit analysis and

Design

Donald A ,

Neaman

Irwin

3

Microelectronics:DIGITAL ANDANALOG CIRCUITS ANDSYSTEMS

JacobMillman,Arvin Grabel

McGraw-Hill

4Microelectronic Circuits Sedra & Smith Oxford

University Press


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Objectives

The History of VLSI

Describe the basic structure and operation ofbipolar junction transistors (BJT)

Describe the basic structure and operation ofMOSFETs

Describe the basic structure and operation of

CMOS


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The History of VLSI

IC(Integrated Circuits) History Evolution vacuum tube,

single transistor,

IC (Integrated Circuits) SSI, MSI, LSI, VLSI, SoC


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The History of VLSI

1926Lilienfeld proposed FET

1947Brattin, Bardin, Schockley

proposed BJT from Bell Lab. 1957TI Kilby proposed the first IC

1960Hoerni invent the planar process

70sIC composed mainly by pMOSand BJT


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The History of VLSI

80sIC composed mainly by nMOSand BJT

90sIC composed mainly by CMOSand BiCMOS

1995NEC, AT&T, Phillips proposed

SOC


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The evolution of IC technique

Transistor

Singlecomponent

SSI MSI LSI VLSI ULSI GSI

LogicGate

count

---- ---- 10 100~

1000

1000~

20000

20000~

500,000

>500,000

>10,000,000

Produ-

ction ----

8bit

ROMRAM

16/32bits

SOC

1947 1950 1961 1966 1971 1980 1985 1990


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Moores Law plot

The transistor count in an IC would double every 18momths


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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


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Architecture of BJTs

The bipolar junction transistor (BJT) isconstructed with three dopedsemiconductor regions separated by two

pnjunctions

Regions are called emitter, baseandcollector


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Architecture of BJTs There are two types of BJTs, the npnandpnp

The two junctions are termed the base-emitterjunction and the base-collectorjunction

The term bipolar refers to the use of both holesand electrons as charge carriers in thetransistor structure

In order for the transistor to operate properly,the two junctions must have the correct dc biasvoltages

the base-emitter (BE) junction is forwardbiased(>=0.7V for Si, >=0.3V for Ge)

the base-collector (BC) junction is reversebiased


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FIGURE Transistor symbols.

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

Copyright 2004 by Pearson Education, Inc.Upper Saddle River, New Jersey 07458

All rights reserved.


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Basic circuits of BJT


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Operation of BJTs

BJT will operates in one of followingfour region Cutoff region (for digital circuit)

Saturation region (for digital circuit) Linear (active) region (to be an amplifier)

Breakdown region (always be a disaster)


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Operation of BJTs


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DC Analysis of BJTs

Transistor Currents:IE= IC+ IB

alpha(DC)

IC= DCIE beta(DC)

IC= DCIB DCtypically has a value between 20 and

200


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DC Analysis of BJTs

DC voltages for the biasedtransistor:

Collector voltageVC= VCC- ICRC

Base voltage

VB= VE+ VBE

for silicon transistors, VBE= 0.7 V

for germanium transistors, VBE= 0.3 V


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Q-point

The base current, IB, isestablished by thebase bias

The point at which thebase current curveintersects the dc load

line is the quiescent orQ-point for the circuit


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Q-point


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DC Analysis of BJTs

The voltage dividerbiasing is widelyused

Input resistance is:RINDCRE

The base voltage is

approximately:VBVCCR2/(R1+R2)


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BJT as an amplifier

Class A Amplifiers

Class B Amplifiers


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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 lineis drawn on the collector curvesbetween saturation and cutoff


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BJT Class A Amplifiers


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BJT Class A Amplifiers Three biasing mode for class A

amplifiers

common-emitter(CE) amplifier common-collector(CC) amplifier

common-base(CB) amplifier


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

capacitors are used for coupling ac withoutdisturbing dc levels


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

voltage gain is approximately 1, but currentgain is greater than 1


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BJT Class A Amplifiers The third configuration is thecommon-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


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BJT Class B Amplifiers When an amplifier is biased such that it operatesin the linear region for 180of the input cycle andis in cutoff for 180, it is a class B amplifier

A class B amplifier is more efficient than aclass A In order to get a linear reproduction of the input

waveform, the class B amplifier is configured in apush-pull arrangement

The transistors in a class B amplifier must bebiased above cutoff to eliminate crossoverdistortion


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BJT Class B Amplifiers


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

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

junction is not forward-biased. VCEisapproximately equal to VCC

When the base-emitter junction is forward-

biased and there is enough base current toproduce a maximum collector current, thetransistor is saturated


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The BJT as a Switch


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An example -- NOR


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Architecture of MOS Field-

Effect Transistors (FETs) The metal-oxide semiconductor field-effect transistor (MOSFET): the gate isinsulated from the channel by a silicon

dioxide (SiO2) layer


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Effect Transistors (FETs) Two types of MOSFETs

depletion type (D-MOSFETs) have aphysicalchannelbetween Drain and Source, with novoltage applied to the Gate

enhancement type (E-MOSFETs) have nophysical Drain-Source channel


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Effect Transistors (FETs) D-MOSFET

Channel may beenhanced or

restricted by gatevoltage

E-MOSFET Channel is created

by gate voltage


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Simplified

symbol


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Biasing Circuits


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FET Amplifiers Voltage gain of a FET is determined by the

transconductance (gm) with units ofSiemens (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 inputresistance

P i i l f MOSFET


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Principle of MOSFETfor E-MOS (n-channel)

(+)


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Principle of MOSFETfor E-MOS (n-channel)

TNV The threshold voltage


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Principle of MOSFET

for E-MOS (n-channel)

P i i l f MO FET


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Principle of MOSFETfor D-MOS (n-channel)


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Principle of MOSFET

for D-MOS (n-channel)


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Voltage-current relations


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p-cnannel MOS

(pMOS)

P+ P+

n-substrate

S G D

B

body

All the characteristics are similar to NMOS.

+ - -

+++++++


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An inverter

Voltage transfer


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Voltage transfer-- see the time delay

Complementary MOS


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Complementary MOS(CMOS)

P PP NN N

p-well

n-substrate

Vss input output Vdd

pMOS

nMOS

in out

Vss

Vdd

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97 Digital Electronics Lecture1 Fundmental Electronics(BJT CMOS)