ME 6405 Student Lecture
Transistor
Sung-bum Kang
Keun Jae Kim
Hongchul Sohn
Wenwei Xu
October 1, 2009
Georgia Institute of Technology
Contents
1
Introduction to Transistor
2
Bipolar Junction Transistor
3
Field Effect Transistor
4
Power Transistor
5
Applications of Transistor
(Speaker: Sung-bum Kang)
(Speaker: Keun Jae Kim)
(Speaker: Hongchul Sohn)
(Speaker: Wenwei Xu)
(Speaker: Wenwei Xu)
“Transistor” Part 1
1
Introduction to Transistor
2
Bipolar Junction Transistor
3
Field Effect Transistor
4
Power Transistor
5
Applications of Transistor
(Speaker: Sung-bum Kang)
(Speaker: Keun Jae Kim)
(Speaker: Hongchul Sohn)
(Speaker: Wenwei Xu)
(Speaker: Wenwei Xu)
Introduction
 Question #1: How can we transfer original
signal in long distance without loss?
 Question #2: How can we control the TV with
remote-controller?
 Question #3: How can a computer recognize
0(off) and 1(on) for computing?
Amplifier and Electronic Switch are needed.


Amplifier: any device that changes, usually increases, the amplitude of a signal.
Electronic Switch: switch that the physical opening and closing is achieved by
applying appropriate electrical control signals.
Introduction
 Early 20th century, vacuum tube was used for the amplifier and switch.
Vacuum Tube Radio
ENIAC, the first general-purpose electronic
computer, contains 17,468 vacuum tubes.
 However, Vacuum Tube is too big, fragile, and energy-consuming.
Transistor solved this problem.
Introduction – Invention of Transistor
 Invention



In 1947, John Bardeen, Walter Brattain,
and William Schockly, researchers at
Bell Lab, invented Transistor.
They found Transistor Effect: “when
electrical contacts were applied to a
crystal of germanium, the output power
was larger than the input.”
John Bardeen, Walter Brattain,
and William Schockly
In 1956, they were awarded the Nobel
Prize in physics.
 Transistor

is a semiconductor device commonly
used to amplify or switch electronic
signals.
First model of Transistor, 1947
Introduction – Progress of Transistor
1941, Vacuum Tube
Edison effect
1948, the first (Germanium) TR
John Bardeen, Walter Brattain, and William Schockly
1954, Silicon TR
At TI Lab, Ease of processing, lower cost, greater power handling,
more stable temperature characteristics
1958, Integrated Circuit
Now?
Individual electronic
components were soldered
on to printed circuit boards.
Sep 2009, 22nm silicon wafer
Intel CEO Paul Otellini, Sep 23 2009
more than 2.9 billion transistors is
packed into an area of fingernail
IC placed all
components in one chip.
Introduction – Underlying Science
 Semiconductor




is a basic building material of most integrated circuits.
is a material that has an electrical resistivity between that of a
conductor and an insulator.
has a few charge carriers(holes or free electrons) and may hence be
classified as almost insulator.
However, the conductivity increases by adding impurities(doping).
Silicon is used in most
commercial
semiconductors
Introduction – Underlying Science
 Doping


P(positive)-type doping is adding a certain type of atoms to the
semiconductor in order to increase holes.
 P-type semiconductor, acceptor
N(negative)-type doping is adding some amount of an element with
more electrons in order to increase free electrons.
 N-type semiconductor, donor
Add Group V (Phosphorous)
Add Group III(Boron)
Introduction – Underlying Science
 PN Junction

is a junction formed by P-type and
N-type semiconductors together in
very close contact.
What happens at the junction?

Electrons(+) from n(-)
region diffuse to occupy
holes(-) in p(+) region.

Thin depletion region
forms near junction.
Introduction – Underlying Science
 Forward bias




-V pumps electrons into the N-region.
+V pumps more holes into the P-region.
Excess of charge in P and N region will
apply pressure on the depletion region
and will make it shrink.
→ current flows
External Energy
 Backward bias




-V sucked out electrons from N-region.
+V sucked out holes from P-region.
The depletion layer widens and it
occupies the entire diode(p-n).
→ current doesn’t flow
Introduction – Types of Transistor
 Transistor are categorized by
Semiconductor material: germanium, silicon, gallium arsenide, etc.
Structure: BJT, FET, IGFET (MOSFET), IGBT
Polarity: NPN, PNP (BJTs); N-channel, P-channel (FETs)
Maximum power rating: low, medium, high
Maximum operating frequency: low, medium, high
Application: switch, audio, high voltage, etc.
Physical packaging: through hole, surface mount, ball grid array, etc.
Various Types of Transistor:
Amplification factor








http://en.wikipedia.org/wiki/Category:Transistor_types
 General Purpose Transistors



Bipolar Junction Transistor (BJT)
Field Effect Transistors (FET)
Power Transistors
“Transistor” Part 2
1
Introduction to Transistor
2
Bipolar Junction Transistor
3
Field Effect Transistor
4
Power Transistor
5
Applications of Transistor
(Speaker: Sung-bum Kang)
(Speaker: Keun Jae Kim)
(Speaker: Hongchul Sohn)
(Speaker: Wenwei Xu)
(Speaker: Wenwei Xu)
BJT Introduction
NPN

3 Terminals




Base (B)
Collector (C)
Emitter (E)
2 Types: NPN, PNP



Currents flow in opposite
direction
NPN:
 BE forward biased
 BC reverse biased
PNP:
 BE reverse biased
 BC forward biased
PNP
BJT Characteristics
 IC is controlled by IB (Current Control)
 β (beta) is amplification factor for
transistor
 Typical value of is β 20 ~ 200
iE = i C + i B
iC = βiB
VBE = VB – VE
VCE = VC - VE
Georgia Institute of Technology
15
BJT Operating Regions
Operating Regions
BJT Operating Regions
Operating Regions
Operating Region
Parameters
Cut Off
VBE < Vcut-in
VCE > Vsupply
IB = IC = 0
Linear
Saturated
VBE = Vcut-in
Vsat < VCE < Vsupply
IC = β*IB
VBE = Vcut-in,
VCE < Vsat
IB > IC,max, IC,max > 0
Mode
Switch OFF
Amplification
Switch ON
BJT Operating Regions
1) Cutoff Region:

VBE < Vcut-in, iB = 0
iC = 0, VCE > Vsupply
2) Active / Linear Region:

VBE = Vcut-in, iB > 0
iC = βiB, Vsat < VCE < Vsupply
3) Saturation Region:

VBE = Vcut-in, iB > iC,max
iC,max, VCE < Vsat
Vsupply
Vin
Georgia Institute of Technology
18
BJT as Amplifier
 Question: What is the minimum Vin that can use the transistor as an
amplifier?
Vsupply – iC *RC – VCE=0
Given:
• RB = 10 kΩ
• RC = 1 kΩ
• β = 100
• VSupply = 10 V
• Vcut-in = 0.7 V
• Vsat = 0.2 V
iC = (Vsupply – VCE) / RC
Set VCE = Vsat = 0.2V
iC = (10 – 0.2) / 1000 = 9.8mA
iC = βiB
iB = iC / β = 0.0098/100 = 0.098mA
RC
Vin
Vin - iB*RB – VBE = 0
VSupply
Vin = iB*RB + VBE
Set VBE = Vcut-in = 0.7V
RB
Vin = 0.098*(10-3)*10000 + 0.7V
Vin = 1.68V or greater.
BJT as Switch
From
3rd Exercise
Turns
on/off coils
digitally
“Transistor” Part 3
1
Introduction to Transistor
(Speaker: Sung-bum Kang)
2
Bipolar Junction Transistor
3
Field Effect Transistor
4
Power Transistor
5
Applications of Transistor
(Speaker: Keun Jae Kim)
(Speaker: Hongchul Sohn)
(Speaker: Wenwei Xu)
(Speaker: Wenwei Xu)
Field-Effect Transistors
 Basics

Conduction of a “channel” is controlled by electric field effect

Three terminals: gate, source, drain
Voltage-controlled current device

Very little current flows through input (gate) terminals
control terminal
control
voltage
of charge carriers
current channel
for charge carriers
Field-Effect Transistors
 BJT vs. FET

What was BJT then?
A current-controlled current device

Comparison
BJT
FET
Input current controls
output current
Input voltage controls
output current
Base
Gate
Collector
Drain
Emitter
Source
Field-Effect Transistors
 Types

JFET (Junction FET)

MOSFET (Metal-oxide-semiconductor FET)

MESFET (Metal-semiconductor FET)

HFET (Hetero-structure FET)

MODFET (Modulation doped FET)

IGBT (Insulated-gate bipolar transistor)

Power MOSFETs

FREDFET (Fast reverse or fast recovery epitaxial diode FET)

ISFET (Ion-sensitive FET)

DNAFET
JFETs
 JFETs

n-channel

p-channel
 General Properties

Advantages: Much higher input resistance, lower noise, easier
fabrication, ability to handle higher currents and powers

Disadvantages: Slower speeds in switching circuits, smaller
bandwidth for a given gain in an amplifier
n-channel JFET
 Characteristics
n-channel JFET
 Characteristics

Idealized Static
iD  I DSS (1 
vGS 2
)
VP
n-channel JFET
 Characteristics

Practical Static
iD  I DSS (1 
vGS 2
v
) (1  DS )
VP
VA

Transfer
MOSFETs
 MOSFETs or Insulated-gate FET (IGFET)

n-channel Enhancement

n-channel Depletion
 General Properties

Input resistance even higher

Used primarily in digital electronic circuits

Provide controlled-source characteristics in amplifier circuits
n-channel Enhancement MOSFET
 Characteristics
n-channel Enhancement MOSFET
 Characteristics

Practical
iD  K [2(vGS  VT )vDS  vDS ]
2
iD  K (vGS  VT ) 2 (1 
vDS
)
VA
n-channel Depletion MOSFET
 Characteristics

Practical
iD  I DSS [2(1 
vGS vDS
v
)( )  ( DS ) 2 ]
VP VP
VP
iD  I DSS (1 
vGS 2
v
) (1  DS )
VP
VA
Applications
 Amplifiers, Switches

Task: Design a n-channel common-source JFET Amplifier
You CAN do it!!
Psst! You can read it!!
http://www.electronics-tutorials.ws/amplifier/amp_3.html
“Transistor” Part 4
1
Introduction to Transistor
(Speaker: Sung-bum Kang)
2
Bipolar Junction Transistor
3
Field Effect Transistor
4
Power Transistor
5
Applications of Transistor
(Speaker: Keun Jae Kim)
(Speaker: Hongchul Sohn)
(Speaker: Wenwei Xu)
(Speaker: Wenwei Xu)
Power Transistor
 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
Lower gain than signal level transistor
Power BJT
 Same structure to the signal level BJT
 The active area is distinctively higher-high current
capacity
 Thick and low-doped collector region
 Large heat dissipation--- larger dimensions
Power MOSFET
 Same working principles to
MOSFET
 Designed to handle large
power
 Low internal voltage drop
and high current capacity
 High commutation speed
and good efficiency at low
voltages—high speed switch
Applications of Transistor
building blocks for modern electronics








Digital logic circuits
Microprocessors, microcontrollers, chips (TTL)
Photo-transistors
Replaces normal switches, mechanical relays.
A/D converter
Encoders
Multiplexers
Power supplies
microprocessor
wireless
communication
more…
motor
headphone,
microphone
Applications(cont.)
Transistor
applications
Switch
Amplifier
 – Switch for a digital signal: BJT or MOSFET
 – Switch for a analog signal: JFET
 – Switch for a power signal: Power MOSFET or BJT
 – Current controlled-current amplifier: BJT
 – Voltage controlled-current amplifier: JFET or MOSFET
BJT as switches
Small input voltage and large output current
operated in the cut-off region(open) and saturation region(close)
Example:
2N3904 NPN
Assuming LED requires 20-40 mA to provide a bright display
and has 2 voltage drop when forwarded biased
Output=0V—off
Output=5V---on, the transistor is in saturation, with base current
I B  (5V  0.7V ) /10 K   0.43 mA
Collector current (LED current) is limited
by collector resistor
I C  (5V  2V  0.2V ) / 100  28mA
BJT as amplifiers
Low input impedance and high voltage gain
Audio amplifiers, radio frequency amplifiers,
regulated power supplies
Example
Speaker amplifier
BJT series produce higher gain
Applications of FET
Advantages of FET over BJT
 They are devices controlled by voltage with a very high input
impedance (107 to 1012 ohms)
 FETs generate a lower noise level than the Bipolar Junction
Transistor (BJT)
 FETs are more stable than BJT with temperature
 FETs are easier to manufacture than the BJT, because they require
fewer steps to be built and they allow more integrated devices in the
same IC
 FETs behave like resistors controlled by voltage for small drainsource voltage values
 The high input impedance of FET allows them to withhold loads
long enough to allow its usage as storage elements
 Power FETs can dissipate higher power and can switch very large
currents.
Applications of FET
Amplifiers
•Small Signal
•Low Distortion
•High Gain
•Low Noise amplifier
•Selectivity
•High-Frequency
Current Limiters
Resistors
Mixers
Oscillators
Switches
• Chopper-Type
• Analog Gate
• Communicator
Protection Diodes
• Low-leakage
FET as analog switch-example
When VGS = 0, FET becomes saturated and it behaves like a
small resistance(<100 ohm) and, therefore,
VOUT = {RDS/ (RD + RDS (ON))}* Vin
RD>>RDS, VOUT → 0
When a negative voltage equal to VGS (OFF)
is applied to the gate, the FET operates in
the cut-off region and it acts like a very high
resistance usually of some mega ohms.
Hence output voltage becomes nearly
equal to input voltage.
Contact information
(in order of presenting)
 Sung-bum Kang
 Keun Jae Kim
 Hongchul Sohn
 Wenwei Xu
sb.kang@gatech.edu
kkim345@gatech.edu
hsohn7@gatech.edu
xuw3@gatech.edu
References


www.wikipedia.org
www.google.com














“Introduction to Electrical Engineering”, Mulukata S. Sarma, Oxford University Press, 2001, Chap. 7.4~8.4.
Fall 2008 Transistors Slides
http://www-g.eng.cam.ac.uk/mmg/teaching/linearcircuits/index.html
http://en.wikipedia.org/wiki/FET
http://en.wikipedia.org/wiki/JFET
http://en.wikipedia.org/wiki/MOSFET
http://www.slideshare.net/guest3b5d8a/fets
“Introduction to Electrical Engineering”, Mulukata S. Sarma, Oxford University Press, 2001, Chap. 7.4~8.4.
Fall 2008 Transistors Slides
http://www-g.eng.cam.ac.uk/mmg/teaching/linearcircuits/index.html
http://en.wikipedia.org/wiki/FET
http://en.wikipedia.org/wiki/JFET
http://en.wikipedia.org/wiki/MOSFET
http://www.slideshare.net/guest3b5d8a/fets











http://www.electronics.dit.ie/staff/ypanarin/Lecture%20Notes/K235-1/2%20Transistor-Thyristor.pdf
http://ecee.colorado.edu/~bart/book/book/chapter5/ch5_9.htm
http://www.ece.mtu.edu/labs/EElabs/EE3305/Bipolar_Junction_Transistors.pdf
http://www.partminer.com/glossaryhtml/bjt.htm
http://www.lycos.com/info/bipolar-junction-transistor--applications.html
http://jimwarholic.com/uploaded_images/power-supply-768753.jpg
http://abbydamico.files.wordpress.com/2008/09/microprocessor-athlon-64.jpg
http://www.billfrymire.com/blog/wp-content/uploads/2008/05/wireless-communication-connection-1000.jpg
http://www.cybermediatech.com/images/WirelessHeadphone-big.jpg
http://www.colorado.edu/physics/phys3330/phys3330_fa09/pdfdocs/AN101FETintro.pdf
http://www.circuitstoday.com/fet-applications
Thank you!