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
EEle
ctr
icle
ctr
icit
yit
yto
to
EEle
ctr
on
icle
ctr
on
icss
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.