Transcript 23-1 Semiconductor Devices

Chapter 23
Electronics and Computers
23-1 Semiconductor Devices
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Semiconductors are elements that conduct
electricity under certain conditions.
These are metalloids; elements located on the
periodic table between metals and nonmetals.
They are less conductive than metals but more
conductive than nonmetal insulators.
23-1 Semiconductor Devices
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Semiconductors are used in calculators, cell
phones, remote control cars, computers and
many other electronic devices. Common
semiconductors include silicon and germanium.
Ever heard of Silicon Valley? Silicon Valley is
the original home to the semiconductor chip
making industry that uses silicon as a basic raw
material, prompting a newspaper writer one day
to call it Silicon Valley.
23-1 Semiconductor Devices
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The conductivity of semiconductor crystals can be
increased by adding “impurities” in a process called
doping. Doped silicon is a commonly used
semiconductor. Silicon is often doped with arsenic
or gallium.
Arsenic doped silicon has more electrons than
pure silicon so it is called an n-type (negative type)
semiconductor; whereas gallium atoms have fewer
than 4 electrons so it is called a p-type (positive
type) semiconductor.
By controlling the type and amount of doping,
semiconductors with a variety of conducting
properties can be created.
23-1 Semiconductor Devices
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Cellphones run off battery power which is direct
current (DC) are charged by plugging it into the wall
which provides alternating current (AC). Chargers
contains transformers which reduces the voltage and
rectifiers which change AC to DC.
Household appliances are built to operate on DC. For
simple devices such as smoke detectors and clocks
batteries are used but for TVs and computers
transformers and rectifiers have to be wired into the
circuits.
A diode is a type of rectifier made by doping the ends of
a crystal to create one end with a p-type semiconductor
and the other end with an n-type semiconductor.
Electrons flow easily from the n-type end to the p-type
end. This is called a pn-diode.
23-1 Semiconductor Devices
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A transistor is a semiconductor that amplifies an
electrical signal. Amplifiers use transistors to
amplify sound.
Microphones, guitars, keyboards and electronic
drums use the transistors to send out electronic
sound.
The signal travels many miles from a broadcast
station to your stereo or TV receivers and is too
weak to produce the picture or sound we need.
The small input signal supplied to the transistor
results in a large output current that can vibrate the
speaker.
23-1 Semiconductor Devices
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Before transistors were invented, devices called
vacuum tubes were used to amplify electric
signals. Today's TVs and radios are much smaller.
Today many tiny transistors work within a computer
to calculate and transmit binary codes ( 1’s, 0’s )
to other transistors. The transistors work as a
group called an integrated circuit.
An integrated circuit can contain thousands of
resistors, diodes and transistors on a thin slice of
silicon.
Integrated circuits allow computers to rapidly
process information which increases their speed.
23-2 Radio and Television
We've studied electromagnetic waves and electricity. Let's
put the concepts together to explain radio and television.
1. At the radio station, a microphone changes
compressional sound waves into electrical signals.
2. These signals are then amplified and passed through a
modulator. (two types amplitude modulated or AM
waves or frequency modulated or FM waves)
3. The electric currents are amplified and sent to an
antenna, where they are transformed into radio waves.
4. Your radio has an antenna that “collects” the radio
waves and transforms them into electrical current.
5. The radio's loudspeaker vibrates to cause sound
waves for you to hear.
23-2 Television
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Televisions work the same as radios but they
also use the electrical signals to create a visual
image.
Audio or sound signals are sent as FM signals
and the video images are sent by AM carrier
waves. A TV station simultaneously transmits the
audio and video signals from its antenna.
The most popular flat screen TVs are either LCD
(liquid crystal display) or plasma. Flatscreen
televisions are making the old CRT (cathode ray
tube) TVs obsolete.
Cathode-ray tubes use electrons and fluorescent
materials to produce images on a screen.
23-3 Computers
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The first computers operated on complex circuits
composed of thousands of vacuum tubes. They used
a lot of energy and were large enough to fill entire
rooms.
In the 1970's, the microprocessor was developed. It is
an integrated circuit on the main circuit board. It
functions as the brain of the computer telling other parts
how to respond. Microprocessors reduced the size
and cost of computers while increasing speed and
reliability.
In the 1980's, computers became available as
household items and became as common as TVs and
telephones in the home.
Today, computers are fully programmable and portable
and found in forms like smart phones and iPads.
23-3 Computer Memory
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Information is collected and stored in the memory of
computers using a binary code. Each 1 (on) or 0 (off)
represents one binary digit and is called a bit.
Numbers, letters and symbols are grouped in
arrangements of 8 bits called bytes. Often computer
memory is expressed in terms of larger units such as
megabytes - “million” or gigabytes - “billion”.
Computers have several kinds of memory. Temporary
memory is called “random access memory” or RAM
and permanently stored memory is called “read only
memory” or ROM. To be able to store needed
information external storage devices such as thumb
drives, portable hard drives, CDs and DVDs can be
used.
23-4 Computer Crimes
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Computer crime is any crime committed with the help
of a computer. Cyber crime in all its forms affects
millions of people every year. Identity theft, hacking,
fraud and illegal music downloads are just a few of
the ways people are hurt by the internet.
Cyber crimes are a major problem in the US and in
Mississippi. Laws are continually being passed to
protect individuals from computer crimes. As of 2011,
Mississippi's cyber-bullying law reads as follows:
Posting malicious messages on the internet
(Facebook, MySpace, blogs, message boards, chat
sites, etc.) is a FELONY in Mississippi, punishable by
imprisonment for not more than five (5) years or a
fine of not more than Ten Thousand Dollars
($10,000.00), or both. Miss. Code Ann. § 97-45-17.