ECE 340
Lecture 2 : Introduction to
Semiconductor Electronics
Class Outline:
•How does a cell phone work?
Thanks to Kent Choquette, Jim Coleman and
Wikipedia.
Things you should know when you leave…
Key Questions
• Why look a cell phones for
motivation?
• What are the major components
of a cell phone?
• Which parts will we discuss more
during this class?
M. J. Gilbert
ECE 340 – Lecture 2
08/24/1 1
How does a Cell Phone Work?
Let’s talk about length scales for a minute…
Thickness of a cellular membrane
Length Scale
1 meter
10 cm
10-1 m
100 m
1 cm
1 mm
100 µm
10 µm
1 µm
10-2 m
10-3 m
10-4 m
10-5 m
10-6 m
100 nm
10 nm
1 nm
10-7 m
10-8 m
10-9 m
HIV Virus
Carbon Nonotube
Thickness
Frequency Scale
1 Hz
1 kHz
100 Hz
103 Hz
33 Hz
Lowest
note on
piano
1 kHz
Highest
note a
female can
sing
M. J. Gilbert
1 MHz
106 Hz
6 MHz
Bandwidth for
each TV channel
sent down a cable
1 GHz
1 THz
109 m
1012 m
1 GHz
Giga Ethernet
is speed many
local networks
operate
ECE 340 – Lecture 2
1 Thz
Frequency of
data in
telecom fiber
optics
08/24/1 1
How does a Cell Phone Work?
Why do we care about cell phones?
If you take apart cell phone, you find it contains a few
parts:
• circuit board with lots of
components
• liquid crystal display
• keyboard
• microphone
• speaker
• battery
It also contains:
•Optoelectronic devices
•MOS devices
•pn junctions
All of the devices that we will be discussing the remainder of the semester.
M. J. Gilbert
ECE 340 – Lecture 2
08/24/1 1
How does a Cell Phone Work?
Now examine the
block diagram for
the cell phone…
signal processing
Optoelectronics
(camera, display)
Transmitter/Reciever
Power Distribution
(minimize drain on battery)
M. J. Gilbert
ECE 340 – Lecture 2
08/24/1 1
How does a Cell Phone Work?
It contains a
microprocessor unit…
Integrated circuit
containing millions of
transistors
Si wafer containing
thousands of ICs
cross section
single
transistor
M. J. Gilbert
ECE 340 – Lecture 2
08/24/1 1
How does a Cell Phone Work?
The cross-section has many different layers, but why?
metal layers
interlevel
dielectric (ILD)
layers
tungsten vias
transistor devices
single MOS transistor
We will learn more about MOS
and bipolar transistors later
M. J. Gilbert
ECE 340 – Lecture 2
08/24/1 1
How does a Cell Phone Work?
Naturally, a cell phone contains many transistors.
Bardeen and Brattain built the first transistor in 1947.
Bardeen, Brattain, and Shockley win the Nobel Prize in
1956 for invention of the transistor
ECE & Physics faculty member at
University of Illinois (1952-1991)
M. J. Gilbert
ECE 340 – Lecture 2
08/24/1 1
How does a Cell Phone Work?
But the size and performance we need doesn’t come from 1 transistor…
The Nobel Prize in Physics 2000
has by The Royal Swedish Academy of Sciences been awarded
with one half jointly to
ZHORES I. ALFEROV
A.F. Ioffe Physico-Technical Institute, St. Petersburg, Russia and
HERBERT KROEMER
University of California at Santa Barbara, California, USA,
and with the other half to
JACK S. KILBY
Texas Instruments, Dallas, Texas, USA.
The researchers' work has laid the foundations of modern information
technology, IT, particularly through their invention of rapid transistors, laser
diodes, and integrated circuits (chips).
M. J. Gilbert
ECE 340 – Lecture 2
08/24/1 1
How does a Cell Phone Work?
Integrated circuits allow us to miniaturize circuits…
JACK S. KILBY
Texas Instruments, Dallas, Texas
BSEE University of Illinois
M. J. Gilbert
ECE 340 – Lecture 2
08/24/1 1
How does a Cell Phone Work
•We
can
string
multiple
transistors together to trace
out logical functionality.
Now let’s start to make something useful…
•CMOS (Complementary Metal
Oxide Semiconductor) Logic
•Reproducible on large scales
•Leads to circuit design
•Left, we show the simple
connection
method
for
different devices on the same
wafer.
•Below, the connection scheme
for a logical inverter.
P-MOS
N-MOS
M. J. Gilbert
Input (A)
Output (Q)
1 (Vdd)
0 (Vss)
0 (Vss)
1 (Vdd)
ECE 340 – Lecture 2
08/24/1 1
How does a Cell Phone Work?
Gordon Moore (co-founder of Intel) made an emperical observation that
the number of transistors in a integrated circuit doubles every two years…
This trend has been evident
for nearly 40 years!
M. J. Gilbert
ECE 340 – Lecture 2
08/24/1 1
How does a Cell Phone Work?
What else
is there in
the block
diagram?
camera
M. J. Gilbert
ECE 340 – Lecture 2
08/24/1 1
How does a Cell Phone Work?
How does the camera in the cell phone work?
microlens
array
color filter
array
sensor array
M. J. Gilbert
ECE 340 – Lecture 2
08/24/1 1
How does a Cell Phone Work?
But this isn’t the whole story, so let’s look deeper…
control electronics,
memory
1 megapixel = 1,048,576 individual sensors
1,024 x 1,024 array
sensor
Each sensor is a pn photodiode (CCD) or
CMOS sensor element
We will learn about photodiodes and
CMOS later
CMOS image sensor
Sensor yield signals in proportion to the
intensity of the light
Each square of four pixels has one
filtered red, one blue, and two
green
Bayer filter
on a sensor
M. J. Gilbert
The human eye is more sensitive to
green than either red or blue
2009 Nobel Prize in Physics
ECE 340 – Lecture 2
08/24/1 1
How does a Cell Phone Work?
Back again to the diagram…
display
backlight
M. J. Gilbert
ECE 340 – Lecture 2
08/24/1 1
How does a Cell Phone Work?
We display output using a
twisted nematic liquid
crystal…
•Using an LC between two
polarizers controls the
transmission of light.
•Need a 2D matrix of LCs to
create pixels with color.
Vert. Polarize light
Electrodes
for display
Glass
substrate
LCD
Horiz.
Polarize
light
Backlit display
M. J. Gilbert
ECE 340 – Lecture 2
08/24/1 1
How does a Cell Phone Work?
The LCD uses back lighting. How else can we produce light?
Can use LEDs to generate white light very efficiently
We will learn more about pn junctions & LEDs later
There are two major approaches:
•
three different colors of semiconductor p-n
junctions
•
hybrid semiconductor/phosphor devices
M. J. Gilbert
ECE 340 – Lecture 2
08/24/1 1
How does a Cell Phone Work?
Henry Round made first observation of electroluminescence (1907) from SiC
Oleg Lossev made detailed study (1923) of electroluminescence in SiC
Nick Holonyak, Jr. (General Electric) demonstrated the practical GaAsP LED (1962)
Henry Joseph Round
Oleg Vladimirovich
Lossev
M. J. Gilbert
from paper by Lossev, 1924
ECE 340 – Lecture 2
ECE faculty member at
University of Illinois
08/24/1 1
How does a Cell Phone Work?
And now our
diagram once
again…
Transmitter/Receiver
digital radio
M. J. Gilbert
ECE 340 – Lecture 2
08/24/1 1
How does a Cell Phone Work?
How does the radio work in a cell phone?
1) develop and process the baseband data signal (0100111011010)
2) generate an RF sine wave with an oscillator circuit
3) mix with the information (data) in a non-linear modulator circuit
pulse code
modulation
(PCM)
frequency
shift keying
(FSK)
M. J. Gilbert
ECE 340 – Lecture 2
08/24/1 1
How does a Cell Phone Work?
The signal is then bounced off of towers…
Cell phones operate in hexagonal cells
only a few miles apart
They can switch (handoff) cells as
they move
Low power transmitters mean nonadjacent cells can reuse
frequencies
Full duplex operation means pairs of
frequencies are needed
full duplex – transmit and receive on
different frequencies simultaneously
M. J. Gilbert
ECE 340 – Lecture 2
08/24/1 1
How does a Cell Phone Work?
Now a bit about the history…
1946: Bell Labs launches the first commercial
mobile telephone service.
At most, three subscribers per city could
make calls at one time.
Each caller used a set of equipment that
weighed nearly 80 pounds.
M. J. Gilbert
In 1947 Bell Labs was the first to
propose a cellular network.
The primary innovation was a
network of small overlapping cell
sites in order to tracks users as they
moved.
Bell Labs installed the first
commercial cellular network in
Chicago in 1970s.
ECE 340 – Lecture 2
08/24/1 1
How does a Cell Phone Work?
The cell phone is most limited in power because it runs on batteries…
Transmitted power, Pt
Received power, Pr
Antenna gains, Gr, Gt
Wavelength, λ
cell
phone
tower
Free space loss
distance, r
M. J. Gilbert
ECE 340 – Lecture 2
08/24/1 1
How does a Cell Phone Work?
For a reasonable S/N ratio (10), a typical receiver needs 50 mV at the terminals of
a 50 W antenna
Cell phone antenna gain ~ 0 dB so Gt = 1 tower antenna gain ~ 17 dB so Gr = 50
Typical distance to a tower is 10 km and typical frequency, f, is 1990 MHz (f λ = c
so λ = 15 cm)
remember a power ratio in dB is
so
M. J. Gilbert
Pt ~ 700 mW
ECE 340 – Lecture 2
08/24/1 1
How does a Cell Phone Work?
So how long can we talk?
A typical Li-ion cell phone battery is
rated for 3.6 V at 1000 mA-hour
Assume the cell phone has an overall
efficiency for transmitted power of 60%
for Pt ~ 700 mW talk time will be about 3 hours
M. J. Gilbert
ECE 340 – Lecture 2
08/24/1 1
How does a Cell Phone Work?
How does the phone talk to the system?
Mobile Telephone Switching Office
(MTSO), also called “data centers”,
where the “wireless” becomes “wired.”
M. J. Gilbert
ECE 340 – Lecture 2
08/24/1 1