October 14, 2005

ME 435

Basi

c E

lectr

on

ics:

B

asi

c E

lectr

on

ics:

Dio

des

an

d T

ran

sist

ors

Dio

des

an

d T

ran

sist

ors

EEşş ref E

ref Eşş kinat

kinat

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ctr

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icit

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Electric circuits are connections of conductive wires

Electric circuits are connections of conductive wires

and other devices whereby the uniform

flow of

and other devices whereby the uniform

flow of

electrons occurs.

electrons occurs.

Electronic circuits add a new

dim

ension to electric

Electronic circuits add a new

dim

ension to electric

circuits in that some means of

circuits in that some means of

cont

rol

cont

rolis exerted over the

is exerted over the

flow of electrons by another electrical signal, either a

flow of electrons by another electrical signal, either a

voltage or a current.

voltage or a current.

Electronics technology exp

erienced a revolution in

Electronics technology exp

erienced a revolution in

1948

with the invention of the

1948

with the invention of the

tran

sistor

tran

sistor

. . Transistors

Transistors

control the flow of electrons through

solid

control the flow of electrons through

solid

sem

icon

ductor

sem

icon

ductor

substances

substances . T. Transistor

ransistortechnology is often referred to as

technology is often referred to as

solid

solid

-- sta

testat

eelectronics.

electronics.

Acti

ve v

ers

us

pass

ive d

evic

es

Acti

ve v

ers

us

pass

ive d

evic

es

An

An a

ctiv

eac

tivedevice is any type of circuit component with

device is any type of circuit component with

the ability to electrically control electron flow

the ability to electrically control electron flow

(electricity controlling electricity).

(electricity controlling electricity).

In order for a circuit to be properly called

In order for a circuit to be properly called e

lectro

nic

elec

tron

ic, it

, it

must contain at least one active device. Components

must contain at least one active device. Components

incapable of controlling current by means of another

incapable of controlling current by means of another

electrical signal are called

electrical signal are called p

assive

pass

ivedevices.

devices.

Resistors, capacitors, inductors, transform

ers, and even

Resistors, capacitors, inductors, transform

ers, and even

diodes are all passive devices.

diodes are all passive devices.

Active devices in

clude, vacuum tubes, transistors,

Active devices in

clude, vacuum tubes, transistors,

silicon

silicon-- controlled rectifiers (

controlled rectifiers ( SCRs

SCRs ), and TRIA

C), and TRIA

C’’ s s

Am

pli

fiers

Am

pli

fiers

The practical benefit of active

The practical benefit of active

devices is their

devices is their

ampl

ifyin

gam

plify

ingability

ability..

AAn active device allows a

n active device allows a

smal

lsm

all

amount of electricity to control a

amount of electricity to control a

larg

ela

rgeam

ount of electricity.

amount of electricity.

Devices utilizing a vo

ltage as the

Devices utilizing a vo

ltage as the

controlling sign

al are

controlling sign

al are

called

called v

olta

gevo

ltage

--co

ntro

lled

cont

rolle

ddevices. D

evices working

devices. D

evices working

on the principle of one current

on the principle of one current

controlling another current are

controlling another current are

known as

known as

curr

ent

curr

ent --

cont

rolle

dco

ntro

lleddevices.

devices.

Sem

icon

du

cto

rsSem

icon

du

cto

rs

Semiconductors have had a

Semiconductors have had a

monumental impact. You find

monumental impact. You find

semiconductors at the heart of

semiconductors at the heart of

microprocessor chips as well as

microprocessor chips as well as

transistors. A

nything that's

transistors. A

nything that's

computerized or uses radio waves

computerized or uses radio waves

depends on sem

iconductors.

depends on sem

iconductors.

Today, m

ost sem

iconductor chips

Today, m

ost sem

iconductor chips

and transistors are created with

and transistors are created with

sili

co

nsi

lico

n. Y

ou m

ay have heard

. You m

ay have heard

expressions like "Silicon Valley"

expressions like "Silicon Valley"

and the "silicon economy," and

and the "silicon economy," and

that's why

that's why ----silicon is the heart of

silicon is the heart of

any electronic device.

any electronic device.

Clo

ck

wis

e f

rom

top

: A

ch

ip, an

LE

D a

nd

a

tran

sist

or

are

all m

ad

e f

rom

sem

icon

du

cto

r m

ate

rial.

Un

ders

tan

din

g S

ilic

on

U

nd

ers

tan

din

g S

ilic

on

Silicon is a very common element

Silicon is a very common element . I. It is the main

t is the main

elem

ent in sand.

elem

ent in sand. ““SSilicon

ilicon" in the periodic table,

" in the periodic table, isis

next to

next to AA

luminum

luminum, b

elow carbon and above

, below carbon and above

germ

anium.

germ

anium.

Carbon, silicon and germanium have a unique

Carbon, silicon and germanium have a unique

property in their electron structure

property in their electron structure ----each has

each has

fou

r ele

ctr

on

s in

its

ou

ter

orb

ital

fou

r ele

ctr

on

s in

its

ou

ter

orb

ital . This allo

ws

. This allo

ws

them

to form

nice crystals. The four electrons

them

to form

nice crystals. The four electrons

form

perfect covalent bonds with four

form

perfect covalent bonds with four

neigh

boring atoms, creating a

neigh

boring atoms, creating a

latt

ice

latt

ice. In carbon,

. In carbon,

we kn

ow the crystalline form

as diamond. In

we kn

ow the crystalline form

as diamond. In

silicon, the crystalline form

is a silvery, m

etallic

silicon, the crystalline form

is a silvery, m

etallic--

looking substance.

looking substance.

Metals tend to be go

od conductors of electricity

Metals tend to be go

od conductors of electricity

because they usually have "free electrons" that

because they usually have "free electrons" that

can m

ove easily between atoms, and electricity

can m

ove easily between atoms, and electricity

invo

lves the flow of electrons. All of the outer

invo

lves the flow of electrons. All of the outer

electrons in a silicon crystal are invo

lved in

electrons in a silicon crystal are invo

lved in

perf

ect

covale

nt

bon

ds

perf

ect

covale

nt

bon

ds , so they can't move

, so they can't move

around. A

pure silicon crystal is nearly an

around. A

pure silicon crystal is nearly an

insu

lato

rin

sula

tor

Do

pin

g S

ilic

on

D

op

ing

Sil

icon

You can change the behavior of silicon and turn it into a

You can change the behavior of silicon and turn it into a

conductor by

conductor by

dop

ing

dop

ingit. In doping, you m

ix a small am

ount of

it. In doping, you m

ix a small am

ount of

an

an i

mp

uri

tyim

pu

rity

into the silicon crystal.

into the silicon crystal.

NN

-- typ

ety

pe--In N

In N

-- type doping,

type doping, phosphorus

phosphorusor

or arsenic

arsenicis added to

is added to

the silicon in small quantities. P

hosphorus and arsenic each

the silicon in small quantities. P

hosphorus and arsenic each

have five outer electrons

have five outer electrons . . The fifth electron has nothing to

The fifth electron has nothing to

bond to, so it's free to m

ove around. N

bond to, so it's free to m

ove around. N

-- type silicon is a good

type silicon is a good

conductor. Electrons have a

conductor. Electrons have a nnegative charge, h

ence the nam

e egative charge, h

ence the nam

e NN-- type.

type.

PP

-- typ

ety

pe--In P

In P-- type doping,

type doping, boron

boronor

or gallium

gallium

is the

is the dopant

dopant . .

Boron and galliu

m each have only three outer electrons. W

hen

Boron and galliu

m each have only three outer electrons. W

hen

mixed into the silicon lattice, they form

"holes" in

the lattice

mixed into the silicon lattice, they form

"holes" in

the lattice

where a silicon electron has nothing to bond to. T

he absence

where a silicon electron has nothing to bond to. T

he absence

of an electron creates the effect of a

of an electron creates the effect of a ppositive charge, hence the

ositive charge, hence the

nam

e P

nam

e P-- type. H

oles can conduct current. A hole

type. H

oles can conduct current. A hole accepts an

accepts an

electron from a neigh

bor, m

oving the hole over a space. P

electron from a neigh

bor, m

oving the hole over a space. P-- type

type

silicon is a go

od conductor.

silicon is a go

od conductor.

NN-- type and P

type and P-- type silicon are not that amazing by them

selves;

type silicon are not that amazing by them

selves;

but when you put them

together, you get some very in

teresting

but when you put them

together, you get some very in

teresting

behavior at the junction.

behavior at the junction.

PP-- N

Ju

ncti

on

N J

un

cti

on

The free electrons in the N-type silicon are repelled

by the negative term

inal of the battery. The holes in

the

P-type

silicon are

repelled by

the

positive

term

inal. At the

jun

cti

onbetween the N-type and P-

type

silicon, holes

and free electrons

meet. The

electrons

fill

the

holes. Those holes

and free

electrons cease to exist, and new

holes and electrons

spring

up to take their place. The

effect is that

cu

rren

t fl

ow

sthrough

the junction.

The negative electrons in the N-type

silicon get attracted to the positive

term

inal of the battery. T

he positive

holes in the P-type silicon get attracted

to the negative term

inal of the battery.

No current flows across the junction

because the holes and the electrons are

each m

oving in the wrong direction.

Jun

cti

on

Dio

des

Jun

cti

on

Dio

des

A PN junction passes current only in one direction.

A d

iode

is an electrical d

evice allowing current to m

ove through

it in

one direction

with far greater ease than in

the other.

Dio

de O

pera

tion

Dio

de O

pera

tion

When the diode is forw

ard

When the diode is forw

ard--

biased and conducting

biased and conducting

current, there is a small

current, there is a small

voltage dropped across it,

voltage dropped across it,

leaving most of the battery

leaving most of the battery

voltage dropped across the

voltage dropped across the

lamp. W

hen the battery's

lamp. W

hen the battery's

polarity is reversed and the

polarity is reversed and the

diode becomes reverse

diode becomes reverse--

biased, it drops

biased, it drops

all

allof the

of the

battery's voltage and leaves

battery's voltage and leaves

none for the lamp.

none for the lamp.

Dio

de C

hara

cte

rist

ic C

urv

eD

iod

e C

hara

cte

rist

ic C

urv

e

A real diode requires about 0.7 V to enable significant current flow.

Revie

wR

evie

w

A

A d

iode

diod

eis an electrical component acting as a one

is an electrical component acting as a one --way valve for

way valve for

current.

current.

When voltage is applied across a diode in such a way that the

When voltage is applied across a diode in such a way that the

diode allows current, the diode is said to be

diode allows current, the diode is said to be

forw

ard

forw

ard --

bias

edbi

ased. .

When voltage is applied across a diode in such a way that the

When voltage is applied across a diode in such a way that the

diode prohibits current, the diode is said to be

diode prohibits current, the diode is said to be

reve

rse

reve

rse --

bias

edbi

ased. .

The vo

ltage dropped across a conducting, forw

ard

The vo

ltage dropped across a conducting, forw

ard-- biased diode

biased diode

is called the

is called the

forw

ard

volta

gefo

rwar

d vo

ltage. F

orw

ard voltage for a diode varies

. Forw

ard voltage for a diode varies

only slightly for changes in forw

ard current and tem

perature, an

only slightly for changes in forw

ard current and tem

perature, and

d

is fixed principally by the chem

ical composition of the P

is fixed principally by the chem

ical composition of the P-- N

N

junction.

junction.

Silicon diodes have a forw

ard voltage of approximately 0.7 vo

lts

Silicon diodes have a forw

ard voltage of approximately 0.7 vo

lts

Half

Wave R

ecti

fier

Cir

cu

itH

alf

Wave R

ecti

fier

Cir

cu

it

•When V

iis positive, d

iode is reverse biased and

is equivalent to open circuit.

Therefore V

0=V

i.

•When Vi is negative, diode is forw

ard biased and is

equivalent to short circuit.

Therefore V

0=0 V.

Application : Light dim

ming

Fu

ll W

ave R

ecti

fier

Fu

ll W

ave R

ecti

fier

If we need to rectify AC

If we need to rectify AC

power so as to obtain the

power so as to obtain the

full use of

full use of

both

both

half

half --cycles

cycles

of the sine wave, a

of the sine wave, a

different rectifier circuit

different rectifier circuit

configuration m

ust be

configuration m

ust be

used. S

uch a circuit is

used. S

uch a circuit is

called a

called a ful

lfu

ll-- w

ave

wav

erectifier.

rectifier.

Fu

ll r

ecti

fier

Fu

ll r

ecti

fier

Ind

ucti

ve K

ick

Ind

ucti

ve K

ick

The sw

itch attem

pts to change the current instantaneously.

Inductors generate vo

ltage to oppose current changes.

The diode allows the vo

ltage to dissipate through

the resistor.

Fly

back

dio

de

Fly

back

dio

de

without

with

Peak

Dete

cto

r P

eak

Dete

cto

r

When a tim

e varying sign

al V

inis applied at the input,

the output V

outretains the maxim

um positive value of the input

sign

al. In the actual circuit there is some

decrease of Vout in tim

e because of the capacitor leakage.

Zen

er

Dio

des

Zen

er

Dio

des

When a diode is reverse biased with large voltage, it allo

ws a

When a diode is reverse biased with large voltage, it allo

ws a

large reverse current to flow : Breakdown.

large reverse current to flow : Breakdown.

Special diodes with well defined breakdown voltages m

aintain

Special diodes with well defined breakdown voltages m

aintain

constant vo

ltage over a wide range of currents. T

hey are Zener

constant vo

ltage over a wide range of currents. T

hey are Zener

diodes and used as vo

ltage regu

lators.

diodes and used as vo

ltage regu

lators.

Zener diode should be reverse biased with a voltage in excess of

Zener diode should be reverse biased with a voltage in excess of

its zener voltage V

its zener voltage V

z.

z. Typically : V

Typically : V

zz= 3.3

= 3.3 ––

75 V.

75 V.

Zen

er

Dio

de a

s V

olt

ag

e r

eg

ula

tor

Zen

er

Dio

de a

s V

olt

ag

e r

eg

ula

tor

In the above circuit, o

utput vo

ltage of the source, V

In the above circuit, o

utput vo

ltage of the source, V

z z , is kept

, is kept

relatively constant, because of the breakdown characteristic of

relatively constant, because of the breakdown characteristic of

the Zener diode.

the Zener diode.

Zener diodes are often rated by their power dissipation, w

hich

Zener diodes are often rated by their power dissipation, w

hichis:

is:

PPZZmax

max=

= ii ZZmax

max

VVZZ

Op

toele

ctr

on

ic d

iod

es

Op

toele

ctr

on

ic d

iod

es

Light em

itting diode : L

ED

Photodiode light detector circuit.

LE

D (

Lig

ht

Em

itti

ng

Dio

des)

LE

D (

Lig

ht

Em

itti

ng

Dio

des)

While all diodes release light, m

ost

While all diodes release light, m

ost

don't do it very effectively. In an

don't do it very effectively. In an

ordinary diode, the semiconductor

ordinary diode, the semiconductor

material itself ends up absorbing a lot

material itself ends up absorbing a lot

of the light energy.

of the light energy. LEDs

LEDsare specially

are specially

constructed to release a large number

constructed to release a large number

of photons outw

ard.

of photons outw

ard.

LED

LED’’ ssform

the numbers on

form

the numbers on digital

digital

clocks

clocks , transm

it inform

ation from

, transm

it inform

ation from

remote controls

remote controls, light up watches and

, light up watches and

tell you when your appliances are

tell you when your appliances are

turned on. C

ollected together, they can

turned on. C

ollected together, they can

form

images on a

form

images on a jumbo television

jumbo television

screen

screen

or

or illuminate a traffic light

illuminate a traffic light . .

Dio

de V

ideo

Dio

de V

ideo

Tra

nsi

stors

an

d C

hip

s T

ran

sist

ors

an

d C

hip

s

A

A t

ran

sist

or

tran

sist

oris created by using

is created by using

thre

e layers

thre

e layers

rather than the tw

o

rather than the tw

o

layers used in a diode. You can create either an N

PN or a PNP

layers used in a diode. You can create either an N

PN or a PNP

sandwich.

sandwich. A transistor can act as a sw

itch or an amplifier

A transistor can act as a sw

itch or an amplifier . . WWhen

hen

you apply a small current to the

you apply a small current to the

cen

ter

layer

cen

ter

layerof the sandwich, a

of the sandwich, a

much larger current can flow through

the sandwich as a whole.

much larger current can flow through

the sandwich as a whole.

This gives a transistor its

This gives a transistor its

swit

ch

ing

swit

ch

ingbehavior. A small current

behavior. A small current

can turn a larger current on and off.

can turn a larger current on and off.

A

A s

ilic

on

ch

ipsi

lico

n c

hip

is a piece of silicon that can hold thousands of

is a piece of silicon that can hold thousands of

transistors. W

ith transistors acting as switches, you can create

transistors. W

ith transistors acting as switches, you can create

Boolean gates

Boolean gates, and with Boolean gates you can create

, and with Boolean gates you can create

microprocessor chips

microprocessor chips . .

The natural progression from silicon to doped silicon to

The natural progression from silicon to doped silicon to

transistors to chips is what has m

ade microprocessors and other

transistors to chips is what has m

ade microprocessors and other

electronic devices so inexpensive. T

he fundam

ental principles ar

electronic devices so inexpensive. T

he fundam

ental principles are e

surprisingly simple.

surprisingly simple. TToday

oday, tens of millions of transistors can be

, tens of millions of transistors can be

inexpensively form

ed onto a single chip.

inexpensively form

ed onto a single chip.

October 14, 2005

ME 435

Tra

nsi

sto

rsT

ran

sist

ors

Transistors consist of multiple layers of

Transistors consist of multiple layers of

nn --and

and pp

--silicon,

silicon,

exam

ple

exam

plessare

are

npn

npnconfiguration or a

configuration or a

pnp

pnpconfiguration

configuration

in the bipolar junction transistor (BJT

).

in the bipolar junction transistor (BJT

).

A small am

ount of current introduced at the base (center) of the

A small am

ount of current introduced at the base (center) of thetransistor

transistor

will cause the overall device to be forw

ard biased and allo

w cur

will cause the overall device to be forw

ard biased and allo

w cur rent to flow

rent to flow

from collector to emitter

from collector to emitter

BJT

Tra

nsi

stor

(NP

N)

BJT

Tra

nsi

stor

(NP

N)

I E=I C+I B

V

BE= V

B-V

E V

CE = V

C-V

E V

C> V

B> V

E

I C= β

I B Typically β

≈10

0.

Tra

nsi

stor

Vid

eo

Tra

nsi

stor

Vid

eo

Sim

ple

Tra

nsi

stor

Ap

pli

cati

on

Sim

ple

Tra

nsi

stor

Ap

pli

cati

on

1K

10V 0.1A

Lamp

+10V

Mechanical

Switch

Exam

ple

Ap

pli

cati

on

sE

xam

ple

Ap

pli

cati

on

s

Ch

ara

cte

rist

ics

of

a c

om

mo

n e

mit

ter

Ch

ara

cte

rist

ics

of

a c

om

mo

n e

mit

ter

NP

N B

JTN

PN

BJT

Cutoff : V

BE< 0.7 V , i B=0

→i C≈0, V

CE > 0.

Active : V

BE= 0.7 V

→i C=βi B, V

CE> 0.7 V

Saturation : i B>i C/β

and V

BE= 0.7 V

→V

CE= V

SAT = 0.2 V.

Pow

er

dis

sip

ati

on

in

Tra

nsi

stors

Pow

er

dis

sip

ati

on

in

Tra

nsi

stors

VCE

RC

I B

I C

+

-

+ -

•• The transistor is forw

ard biased when the base

The transistor is forw

ard biased when the base --toto-- emitter vo

ltage is 0

emitter vo

ltage is 0.. 7 V.

7 V.

•• When designing a transistor sw

itch,

When designing a transistor sw

itch, the transistor must be in saturation

the transistor must be in saturation

when it is on

when it is on(otherwise it will heat up and m

ight fail)

(otherwise it will heat up and m

ight fail)

••FFor

or BJT

BJT

’’ ss, the

, the

VVC

EC

Eat saturation is about

at saturation is about 00.2V

.2V.

VBE

The common emitter transistor circuit

The common emitter transistor circuit for a

for a npn

npn

transistor.

transistor.

Gu

ara

nte

ein

g t

hat

the t

ran

sist

or

is i

n s

atu

rati

on

Gu

ara

nte

ein

g t

hat

the t

ran

sist

or

is i

n s

atu

rati

on

Given a typical signal transistor, 2N3904

specifications :

Max. collector current, I

C(m

ax)= 200mA, V

CE

at saturation = 0.2V, β

= 100

Findthe necessary in

put vo

ltage to ensure

saturation:

Since V

CEis 0.2 V, I

C=10-0.2/10kΩ

= 9.8 m

A.

Thus, the base current must be at least 9.8/βor

0.098 mA

and I B=(V

in-.7)/10kΏ

: Vin=

0.98+0.7 = 1.68 V.

Rem

ember these gu

idelines for a transistor

switch:

The base-to-emitter vo

ltage must be 0.7 V to be

on.

Maxim

um values of

I C, I

Band V

CEmust be

observed and m

aintained.

There must be sufficient base current to ensure

saturation (

I B >

IC/β

, and V

CE

= 0.2 V))

Collector current is in

dependent of base current

at saturation.

This is a very poor am

plifier. Clip

s the negative

This is a very poor am

plifier. Clip

s the negative

values of I

values of I BB

We shall not study am

plifiers in this course.

We shall not study am

plifiers in this course.

Darl

ing

ton

Pair

Darl

ing

ton

Pair

An

d G

ate

An

d G

ate

OR

gate

OR

gate

FIE

LD

EF

FE

CT

TR

AN

SIS

TO

RS

FIE

LD

EF

FE

CT

TR

AN

SIS

TO

RS

•Three term

inals : G

ate, D

rain, S

ource.

•BJT

is current controlled amplifier, FET is vo

ltage (V

D) controlled. i

D ~

VG

•FET’s have very high input im

pedance, therefore : I G

= 0. T

his sim

plifies circuit design

•FET’s require less operating power compared to BJT

.

•Have better high frequency characteristics than BJT

: up to 200

kHz.

•However, they are sensitice to static electricity. Therefore, elctrical insulation is very

important for FET’s.

n

JFE

TJF

ET

’’ ss

With no voltage applied between gate

With no voltage applied between gate

and source, the channel is a

and source, the channel is an

n open path

open path

for electrons to flow

for electrons to flow

II f a voltage is applied between gate and

f a vo

ltage is applied between gate and

source of such polarity that it reverse

source of such polarity that it reverse--

biases the PN ju

nction, the flow

biases the PN ju

nction, the flow

between source and drain connections

between source and drain connections

becomes limited

becomes limited

. . This behavior is due

This behavior is due

to the depletion region of the PN

to the depletion region of the PN

junction.

junction.

This action m

ay be likened to reducing

This action m

ay be likened to reducing

the flow of a liq

uid through

a flexible

the flow of a liq

uid through

a flexible

hose by squeezing it: w

ith enough

force,

hose by squeezing it: w

ith enough

force,

the hose will be constricted enough

to

the hose will be constricted enough

to

completely block the flow.

completely block the flow.

Beh

avi

or

of

FE

TB

eh

avi

or

of

FE

T’’ ss

Cutoff : V

GS< V

T, i

G=0

→i C≈0, V

DS ≈

VDD.

VT = 1-2 V.

Active (Ohmic Region) :

VGS> V

T

→i D

~(V

GS-V

T)2,

VDS> V

GS-V

T

Saturation : V

GS >> V

T

→i D

= V

DD /RD: ≈

constant V

DS ≈

i DR

ON

VGS

Saturation

MO

SF

ET

Ch

ara

cte

rist

ics

MO

SF

ET

Ch

ara

cte

rist

ics

Vos

4V

I o

VGS = 5V

3V

2V

30V

10mA

5mA

150 µA

I o

0.1

0.2

0.3

100 µA

50 µA

Vos(V)

VGS = 5V

4V

3V

2VRos= 1/gm

Ap

pli

cati

on

s of

MO

SF

ET

Ap

pli

cati

on

s of

MO

SF

ET

’’ ss

When V

When V

GG-- VV

TT≈≈VV

DD

DD, ,

the mosfet enters in

to

the mosfet enters in

to

saturation, resulting

saturation, resulting

nearly full vo

ltage V

nearly full vo

ltage V

DD

DD

across the load (R

across the load (R

on

onis

is

small) .

small) .

If the load is in

ductive, a

If the load is in

ductive, a

flyback diode is

flyback diode is

necessary to prevent

necessary to prevent

dam

age to the mosfet,

dam

age to the mosfet,

when switched off.

when switched off.

Mosfet power switch circuit.

Mosfet power switch circuit.