the last revolution happened ~ 60 years ago, when vacuum tubes were replaced by semiconductor...
TRANSCRIPT
The last revolution happened ~ 60 years ago, when vacuum tubes were replaced by semiconductor devices
1918
1960s
Vacuum tubes show high performance but are too big
Vacuum tubes can survive a nearby nuclear explosion
What is a vacuum tube?
What vacuum tubes are for
_
+
gate
Diode: a valve for electrons
Triode: a switch or an amplifier
First digital computers
ENIAC (1946) weighed 30 tons, occupied 1800 square feet and had 17,468 vacuum tubes.It could make 5000 additions per second
First computer bug was a real bug Harvard Mark II computer, 1947
1954-1963: SAGE Air Defense Project
• 2 32-bit computers • Each contains 55,000 vacuum tubes, weighs 250 tons, and consumes 3 Megawatt• Tracks 300 flights• Total cost: $60 billion (double the price of Manhattan Project!)• Performance equivalent to $8 calculator built on transistors!
Dangers of forecasting
ENIAC (1946) weighed 30 tons, occupied 1800 square feet and had 17,468 vacuum tubes.It could make 5000 additions per second
Computers in the future may weigh no more than 1.5 tons. (Popular Mechanics, 1949)
1940's - IBM Chairman Thomas Watson predicts that "there is a world market for maybe five computers".
1950's - There are 10 computers in the U.S. in 1951. The first commercial magnetic hard-disk drive and the first microchip are introduced. Transistors are first used in radios.
1960's-70's - K. Olson, president, chairman and founder of DEC, maintains that "there is no reason why anyone would want a computer in their home." The first microprocessor, 'floppy' disks, and personal computers are all introduced. Integrated circuits are used in watches.
Semiconductor Revolution“One should not work on semiconductors, that is a filthy mess; who knows whether they really exist.”
Wofgang Pauli 1931
Transistor invention: 1947John Bardeen, Walter Brattain, and William Shockley AT&T Bell Labs
Nobel Prize in Physics 1956
energy
Conduction band
Valence band
Band gap
Semiconductor or dielectric
metal
The coolest thing about semiconductors: they can be doped
Even tiny fraction of impurities (0.00001) dramatically increases the ability to conduct current (conductivity)
Energy diagram of doped semiconductors
Free electrons are supplied to the empty conduction band Holes are left in the full valence band
Both electrons and holes can now conduct current!
Reverse bias
+_
P-type N-type
P-n junction
neutral neutral_ +Forward bias
+ _
Field-effect transistor
+_ +
Commons.wikimedia.org
_
Voltage on gate controls the current of electrons from source to drain.
FET can be made very small using nanotechnology!
Current, Ohm’s Law, Etc.
dt
dQi
)(;:' VoftindependenConstRi
VRLawsOhm
A
lR
Ej
jE
The Continuity Equation for Steady State Currents
0Sdj
Currents and current densities are constant in time – steady state. The flux of out of any closed surface must be zero.
j
Drift velocity
nq
jv
For steady state situation
1.Kirchhoff’s junction rule: The algebraic sum of the currents into any junction is zero.
2.Kirchhoff’s loop rule: The algebraic sum of the potential differences in any loop must be zero.
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0 rdE
Resistors in parallel:
Resistors in series:
21 RRR
21
111
RRR
Circuit with capacitors
Joule’s Law
R
VRiViP
22
Why does a light bulb burn out when you switch the light on and never when you turn it off?
The amount of current drawn by a given device is determined by its power inputi
V
PiiVP
The current in a 100-W light bulb is
AV
W
V
Pi 83.0
120
100
14483.0
120
A
V
i
VR
A kitchen circuit
An 1800-W toaster, a 1.3-kW electric frying pan, and a 100-W lamp are plugged into the same 20-A, 120-V circuit.
a) What current is drawn by each device, and what is the resistance of each device?
b) Will this combination blow the fuse?
To prevent the fuse from blowing, you replace the fuse with one rated at 40 A.Is this a reasonable thing to do?
RiP 2
Wheatstone bridge
British scientist and inventor1802-1875
Charles Wheatstone
Samuel Hunter Christie, British scientist and mathematician
Wheatstone English concertina
Electromotive force
The Magnetic Field
The force on a charge q moving with a velocity F
v
)( BvEqF
The magnitude of the force
sinqvBF
sec)//(][ meterCoulombNewtonsB
gausssmCNewtonmwteslaT 42 10//1/1)(1
TGaussBEarth4101
left-hand ruleright-hand rule