Transcript Computers and How They Work

Relay
Vacuum Tube and CRT
Thermometer using Thermistor
Old Zenith Radio
Individual Transistor
Integrated Circuit (IC)
Video: Transitorized
From Silicon to Transistor
1.
2.
3.
4.
5.
6.
What is Silicon
Doping Silicon
A P-N Junction
The Diode
The LED (Light Emitting Diode)
How does a Transistor work
The Bipolar Transistor
The Field Effect Transistor
7.
Benefits of using transistors
Able to amplify an alternating signal
Used as a fast switch
Low Power
Solid state and small in size
Inexpensive
8.
First uses of Transitors
Replaced Vacuum tubes in radios and computers
Hearing Aids
Airplanes
9.
4004 – First single chip Microprocessor where transistors are
integrated on a single piece of Silicon
Silicon is a Semiconductor, located in Column IV
A semiconductor is a material that in it pure
form does not conduct electricity well.
Silicon is a common semiconductor. It makes
up 25% of the earth’s crust. Only Oxygen is
more abundant than Si.
A silicon atom shares electrons with four
neighboring Si atoms allowing the outer shell to
be filled completely.
http://www.thenakedscientists.com
A small amount of energy knocks
electrons from bonds
Electron-Hole
Pair is produced
when this
happens.
In Pure Silicon,
# of Electrons = # of Holes
A Semiconductor can be used to
measure Temperature
Conductivity
increases
rapidly as
temperature
rises.
Properties of Silicon can be modified
► Contaminants
can be added (1 part per 10
million)
► These contaminants are called Dopant
► Dopants change the electrical properties of
Silicon
► Both types of charge carriers can be added
to Silicon (positive and negative
► Charge Carriers are Electrons and Holes
► By
substituting some of the Silicon with atoms
that have five (instead of four) outer electrons,
there are electrons left over to roam (1 per
Dopant atom).
► By
substituting some of the Silicon with atoms
that have three outer electrons ‘holes’ are
created (1 per Dopant atom).
Negatively doped Silicon
Positively doped Silicon
P-type Dopant
N-type Dopant
Diode is a p-n junction
► Diode
is a one-way electrical switch that
passes current in one direction only.
► Constructed with a semiconductor
► Our Radio uses a Germanium Diode
Electrons and Holes pushed toward junction
when a positive voltage is applied to the p-side
At the junction, Electrons and Holes recombined
When negative voltage is applied to p-side, Electrons
and Holes are swept away from the junction, so no
current flows in circuit
With an LED, light energy is given off
when an electron and hole recombine.
A roaming electron has more energy than
an electron bound to an atom
Converting sunlight directly into DC electricity
using Photovoltaics (PV):
► Sunlight
hits a
sandwich of doped
silicon. Electrons are
knocked out of their
orbits.
► The electron flow
provides the current,
and the cell's electric
field produces a
voltage.
PV was developed
In the 1950’s for
Powering
Satellites.
How do Photovoltaics (PV) work?
►A
is n-type Si (e.g. Phosphorus)
► B is p-type Si (e.g. Boron)
P-Type
N-Type
dopants
dopants
E-field
Just at the junction the electrons and holes mix,
creating a an electric field (voltage) separating
the two sides. This voltage allows electrons to
flow up but resists electrons flowing down.
The solar cell is a large diode; current flows in
one direction only.
Light frees electrons creating Electrons and Holes
http://www.specmat.com/Solar%20Cell%20Description.jpg
A – glass coating
B – contact grid
C – Antireflective coating
D – N-type Si
E – P-type Si
http://www.specmat.com
PV System with Batteries
http://www.wcubed.com/solar/solar_photovoltaics.htm
What is a Transistor
Made of doped semiconductor materials, the
transistor is used to amplify electrical
signals or used as a switch.
http://fourier.eng.hmc.edu
The Diode Forward Biased – Current flows
The Diode Reverse Biased:
Electrons and holes swept away from the junction, so no
current flows in the circuit.
The Bipolar NPN Transistor
The base-emitter junction is forward biased, the
base-collector junction is reverse biased.
The transistor is bipolar because both charge
carriers (holes and electrons) are present.
►
►
►
By doping (adding impurities to) a semiconductor material
(i.e. Silicon or Germanium), very different electrical
properties are created.
By sandwiching these dissimilar materials, a transistor is
made.
If the base is thin, electrons from the emitter are swept
though the base to the collector. Electrons in the collector
then respond to the positive voltage and flow out of the
collector.
Basic Amplifier Circuit using the
NPN Bipolar Transistor
http://www.tpub.com
Model of first Transistor c. 1947
http://www.porticus.org/bell
Fabricating a transistor on a single
piece of doped silicon
wikipedia
CNN.com
The Field Effect Transistor (FET)
Electricity
flows from
the Source
to the Drain
when an
electric field
is applied to
the Gate.
Field Effect Transistor (FET)
FETs are tiny
switches that can
open and close
very quickly.
A negative voltage
will turn this pchannel transistor
on. ‘On’ means
there is a
connection
between the
Source and Drain.
http://www.answers.com
Before the transistor, there was the
Vacuum Tube
► Also
used to
amplify signals
► Also used as a
switch
http://www.privateline.com
Electrons are “boiled” off the cathode and
attracted to the anode because of the applied voltage.
A grid controls the electron flow.
The signal to be amplified is connected
to the grid. A small signal controls
a much larger voltage.
Cathode Ray Tube (CRT)
Still is use Today
Vacuum Tube, Electron Gun, Fluorescent
Screen, and Coils which accelerate and
deflect the electron beam
Prior to Vacuum tube:
►
►
►
►
No coast-to-coast telephone calls
Wireless Telegraph in use – Morse codes received and
boosted using relays.
Alternating Signals could not be amplified with relays
Signals were sent over wires no farther than NY to Denver
Relay: switch that opens
and closes and is
controlled by current
in another circuit.
Two settings: OPEN
And CLOSED
http://www.porthcurno.org.uk/html/morsecircuit.html
On or Off,
current is either
constant or it
does not flow.
Applying a small varying signal
(voice signal) here would not
produce a varying signal in the top
circuit.
AT&T interested in the Transistor
► Vacuum
Tubes were unreliable for
amplifying signals in transcontinental
telephone calls.
► Vacuum Tubes consumed a lot of power
and got hot.
► Competition from other phone companies
made reliable and fast phone service
important.
► Expensive, bulky, and fragile.
ENIAC in 1946
First electronic
computer
► Designed for the
Army
► $500,000
► >17,000 Vacuum
Tubes
► 150 KW of power
► Filled multiple
rooms (700 sq. ft)
► Soldered and
constructed by
hand by the
University of Penn.
►
Hearing Aids - the first commercial
devices that used transistors
c. 1953
http://blog.modernmechanix.com
Some Hearing Aids do not amplify sound:
Cochlear Implants bypass portion of the ear
that is damaged
Cochlear Nerve sends
auditory information to
the brain.
Wikipedia
Cochlear Implant Components
1.
2.
3.
4.
5.
Electrode
Array
Receiver
Speech
Processor
Transmitting
Coil
Microphone
http://deafblind.com/cochlear.html
http://transistorhistory.50webs.com/maico.html
► Individual
Parts
► Integration of parts required hand wiring
Early Sony Transistor Radio
The birth of the integrated circuit
(IC)
►
►
►
1947- using silicon as a transistor is discovered
1959- Texas Instruments put 10 transistors on one piece of
silicon. First company to use Silicon instead of Germanium
Used in Apollo Program to achieve moon landing –
transistors integrated on pieces of silicon offered lower
power and weight. 1961-69
Intel 4004
The World’s first
Microprocessor, made in
1971
Computer on a chip!
It had 2300 transistors and
ran at 740 KHz.
It could execute 45
instructions.
Could execute 96,000
instructions per second
As powerful as the ENIAC
Where’s the chip?
http://www.computerhistory.org/semiconductor/
Chips can have billions
of transistors built on a
small piece of silicon.
CMOS stands for ‘Complimentary
Metal Oxide Semiconductor’. This
means CMOS chips contain both
pMOS and nMOS transistors.
http://www.britannica.com
Sources
http://www.pbs.org/transistor/