Introduction to Transistors

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2 Νοε 2013 (πριν από 3 χρόνια και 10 μήνες)

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Transistors

Camille Cruz

Chase Thompson

Tyler Nelson


September 26, 2013

Outline


Introduction


Transistors Types


Bipolar Junction Transistors


Field Effect Transistors


Power Transistors


Example

Transistors

Different types and sizes

BJT (PNP) Electrical
Diagram

First Transistor

Modern Electronics

FET and BJT Transistor


Purpose


To amplify and switch electronic signals on or off
(high or low)



Modern Electronics



Microprocessor

Cell Phones

Motor Controllers

Vacuum tubes


Purpose


Used as signal amplifiers and switches


Advantages


High power and frequency operation


Operation at higher voltages


Less vulnerable to electromagnetic pulses



Disadvantages


Very large and fragile


Energy inefficient


Expensive


Invention


Evolution of electronics


In need of a device that was small, robust, reliable,
energy efficient and cheap to manufacture


1947


John Bardeen, Walter Brattain and William
Schockly

invented transistor


Transistor Effect


“when electrical contacts


were applied to a crystal


of germanium, the output


power was larger than

the input.”

General Applications

Doping


Process of introducing impure elements
(
dopants
) into semiconductor wafers to form
regions of differing electrical conductivity


Negatively charged Semiconductor

Positively charged semiconductor

Doping Effects


P
-
type semiconductors


Created positive charges, where electrons have
been removed, in lattice structure



N
-
type semiconductors


Added unbound electrons create negative charge
in lattice structure



Resulting material


P
-
N junction


P
-
N junction

Forward Biasing

Reverse Biasing


P
-
N junction


Controls current flow via external voltage


Two P
-
N junctions (bipolar junction transistor,
BJT)


Controls current flow and amplifies the current
flow

Transistor Categories


Semiconductor material


Structure


Polarity


Maximum power rating


Maximum operating frequency


Application


Physical packaging


Amplification factor

Types of Transistors


Bipolar Junction Transistor (BJT)




Field Effect Transistors (FET)





Power Transistors



BJT Introduction


Bipolar Junction Transistors (BJT)
consists of three “sandwiched”
semiconductor layers


The three layers are connected to collector
(C), emitter (E), and base (B) pins


Current supplied to the base controls the
amount of current that flows through the
collector and emitter

BJT Schematic


NPN


BE forward bias


BC reverse bias



PNP


BE reverse bias


BC forward bias



NPN

PNP

BJT Characteristic Curves

Transfer Characteristic


Characteristic curves can be drawn to show other useful parameters
of the
transistor


The slope
of I
CE

/ I
BE


is
called the Transfer Characteristic
(
β
)


BJT Characteristic Curves

Input Characteristic


The

Input

Characteristic

is

the

base

emitter

current

I
BE

against

base

emitter

voltage

V
BE



I
BE
/V
BE

shows

the

input

Conductance

of

the

transistor
.


The

increase

in

slope

of

when

the

V
BE

is

above

1

volt

shows

that

the

input

conductance

is

rising


T
here

is

a

large

increase

in

current

for

a

very

small

increase

in

V
BE
.

BJT Characteristic Curves

Output Characteristic


collector

current

(
I
C
)

is

nearly

independent

of

the

collector
-
emitter

voltage

(
V
CE
),

and

instead

depends

on

the

base

current

(
I
B
)

I
B1

I
B2

I
B3

I
B4

BJT Operating Regions

Operating
Region

Parameters

Mode

Cut Off

V
BE

<
V
cut
-
in


V
CE
>
V
supply

I
B

=
I
C

= 0

Switch OFF

Linear

V
BE

=
V
cut
-
in

V
sat

<
V
CE
<
V
supply

I
C

=
β
*
I
B

Amplification

Saturated

V
BE

=
V
cut
-
in
,

V
CE

<
V
sat

I
B

>
I
C,max
,
I
C,max

> 0

Switch ON

BJT Applications

BJT Switch


Offer
lower cost and substantial reliability over conventional
mechanical relays.



T
ransistor operates purely in
a
saturated or cutoff state (on/off)


This can prove very useful for digital applications (small current
controls a larger current)

BJT Applications

BJT Amplifier


BJT Applications

BJT Amplifier


Field Effect Transistors (FET)

Chase Thompson

FET Basics


Electric Field



Voltage Controlled



FET includes three distinct pieces


Drain


Source


Gate




FET versus BJT?

Same:


Applications: amplifier,
switch, etc.


Relies on PNP or NPN
junctions to allow current
flow

Difference:


Voltage
vs

Current Input


Unipolar
vs

Bipolar


Noise


Higher input impedance


Fragile and low gain bandwidth

Types of Field
-
Effect
Transistors

Type

Function


J
unction
F
ield
-
E
ffect
T
ransistor

(
JFET)

Uses reversed biased p
-
n junction to separate gate from body


M
etal
-
O
xide
-
S
emiconductor
FET



(MOSFET
)

Uses insulator (usu. SiO
2
) between gate and body


I
nsulated
G
ate
B
ipolar
T
ransistor

(
IGBT)

Similar to MOSFET, but different main channel


O
rganic
F
ield
-
E
ffect
T
ransistor



(
OFET)

Uses organic semiconductor in its channel


N
anoparticle

O
rganic
M
emory
FET

(NOMFET
)

Combines the organic transistor and gold
nanoparticles

JFET


Reverse Biased PN
-
junction


Depletion mode devices


Creates a potential
gradient to restrict
current flow. (Increases
overall resistance)

http://www
-
g.eng.cam.ac.uk/mmg/teaching/linearcircuits/jfet.html

JFET



N
-
channel JFET










P
-
channel JFET uses same principles but


Channel current is positive due to holes instead of
electron donors


Polarity of biasing voltage must be reversed


N
-
Type Characteristics

Characteristics and Applications of FETs

JFETs


Simplest type of FET


easy to make


High input impedance and resistance


Low Capacitance


Slower speed in switching


Uses?


Displacement sensor


High input impedance amplifier


Low
-
noise amplifier


Analog switch


Voltage controlled resistor

MOSFET


Similar to JFET


A single channel of single doped SC
material with terminals at end


Gate surrounds channel with doping that
is opposite of the channel, making the
PNP or NPN type


BUT, the MOSFET uses an insulator to
separate gate from body, while JFET uses
a reverse
-
bias p
-
n junction

p
-
channel

n
-
channel

MOSFET

enhanced mode

MOSFET

depleted mode

How does a MOSFET work?

Simplified Notation

No current flow

“Short” allows current flow

No Voltage to Gate

Voltage to Gate

Source

Source

Drain

Drain

n

n

MOSFET

Triode Mode/Linear Region



V
GS

>
V
th

and
V
DS

< ( V
GS

-

V
th

)

V
GS

: Voltage at the gate

V
th

: Threshold voltage

V
DS

: Voltage from drain to source

μ
n
: charge
-
carrier effective mobility

W
: gate width

L
: gate length

C
ox

: gate oxide capacitance per unit area

λ : channel
-
length modulation parameter

Saturation/Active Mode



V
GS

>
V
th

and
V
DS

> ( V
GS

-

V
th

)

Characteristics and Applications of FETs

MOSFETs


Oxide layer prevents DC current from
flowing through gate


Reduces power consumption


High input impedance


Rapid switching


More noise than JFET


Uses?


Again, switches and amplifiers in
general


The MOSFET is used in digital
CMOS logic, which uses p
-

and n
-
channel MOSFETs as building
blocks


To aid in negating effects that cause
discharge of batteries

Use of MOSFET in battery

protection circuit

Power Transistors


Concerned with delivering high power


Used in high voltage and high current application

In general

Fabrication process different in order to:


Dissipate more heat


Avoid breakdown


Different types: Power BJTs, power MOSFETS, etc.

Comparison

Property

BJT

MOSFET

JFET

Gm

Best

Worst

Medium

Speed

High

Medium

Low

Noise

Moderate

Worst

Best

Good
Switch

No

Yes

Yes

High
-
Z Gate

No

Yes

Yes

ESD
Sensitivity

Less

More

Less

References
(32)

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-
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Questions
?