Electronics Review. EETS8320 SMU Session 4, Fall 2005 (print slides only, no notes pages). Electric and Magnetic Fields. When electric charges or currents (moving electric charges) interact at a distance, there are forces acting on the charges and currents.
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Session 4, Fall 2005
(print slides only, no notes pages)
Notes: A newton is the International metric unit of force, approximately equal to 0.2248 pounds of force.
A coulomb is the amount of electric charge produced by one ampere flowing for one second.
A volt is the ratio of one joule (one watt•second) of energy divided by one coulomb of electric charge
Note: a volt•second is also called a weber.
The product of a volt of voltage, with an ampere of current, is an amount of power called a watt. Power is the time rate at which energy flows or “moves.”
The unit of energy is the result of one watt of power “flowing” for one second. This is called a watt•second or a joule (rhymes with “foul.”)
Force on charge is parallel
to electric field.
Force on current element
is perependicular to both
current element and
Note 1: The “resistance” of thermal insulation for use in walls or ceilings of buildings is also denoted “R,” but in that case it is the ratio of heat flow (analogous to current flow) to temperature difference (analogous to voltage). In North America, English units are used: BTU/min/sq.ft and degrees Fahrenheit.
Nucleus consists of
protons (positive charge)
and neutrons (electrically
Point object electrons whirling
around the nucleus in specific
circular or elliptical orbits.
This frequently shown
Picture (symbolic of
Lithium) is known to be
wrong in several ways.
Niels Bohr, Danish physicist, invented this theoretical model ca. 1913.
*also written Schroedinger
Ê = h•f (the Greek letter (pronounced nu) is used rather than f in some documents)
Ionizing radiation frequency range
TV and FM
(VHF and UHF)
Band (car radio)
Band (1.9 GHz)
On this logarithmic scale each mark represents a value 10 times the value to its left.
Diffraction grating, a front
surface mirror with tiny
Some lenses used to focus
the image are not shown
Greatly enlarged view of
with slit. Width
of slit is actually
Light source such as
hydrogen gas in a sealed
glass tube with electric
Images of the slit are formed on photographic film.
Non-radiating high energy ÊH orbit
Non-radiating low energy EL orbit
Radiated light frequency f,
where h•f= ÊH- ÊL
ÊH - ÊL = h •f
Note: Planck’s constant h is both a unit of energy·time product (joule•sec) or alternatively a unit of angular momentum (kg•m2/s)
Electron cloud areas
are the places where the
other molecules will form
molecular bonds, due to the
mutual attraction of the negative
charge electron cloud(s) and the
positive charge nuclei of the
atom shown here and the other
atoms which will attach.
wave speed = wavelength/cycle time
wave speed = wavelength • frequency
wave direction b
wave direction a
1. Diamond has a highly symmetrical crystal structure, with each atom having four equidistant nearest atoms
2. Graphite (used for writing pencil “lead” and as a dry lubricant), with each atom having two close neighbors and two more distant neighbors
1. Those with an electron energy gap
2. Those with no energy gap
* Resistivity is measured in ohm•meters, and is the resistance measured between two opposite faces of a 1 meter cube sample. For practical purposes, the ohm•centimeter unit is often used also.
Resistivity in ohm•meter
Theoretical semiconductor with no wave scattering
due to thermal vibration of atom nuclei in the solid.
Typical electric conductor (metal)
*“Doping” is alloying using very small amounts of minor materials
Yellow-highlighted names are elements used in practical room-temperature semiconductor devices.
So-called “depletion layers”
Region of extra electrons,
represented by green color.
Region of missing or
represented by red color.
Graph shows net electric charge
density vs. distance right or left
*Called depletion layers, although only one of them is actually “depleted” below the normal number of electrons.
Adjustable or variable voltage source,
can produce both positive and negative
Ideal voltmeter measures diode’s voltage, but no current flows through the voltmeter. Real voltmeters allow very small current flow. Anode (top) of diode symbol is the conventional positive voltage terminal.
1 mA=0.001 A.
B is approx. boundary
and linear parts.
Note: a section of negative
voltage axis is not shown.
Origin of graph,
* Blame Benjamin Franklin for using negative numbers for one kind of static electricity. If he knew then that electric current is mainly from electrons, he would have made the opposite choice, I’m sure! Before Franklin’s suggestion “positive” electricity was classified as vitreous (from rubbing glass) and “negative” electricity was classified as resinous (from rubbing amber). Franklin realized that they were two polarities of the same qualitative type, instead of two qualitatively different things.
Forward region is described
as a resistance Rf.
case is Rf=0 ohms.
1 mA= 0.001 A
Reverse current is described
as zero. No description of
breakdown voltage region
in this example.
Origin of graph,
Vertical axis is
net electric charge
Negative voltage on
Zero volts on
on diode (red)
distance right or left
n(Ê) = e ((Ê-Êf)/kT) +1Electron Energy
Very low temperature (blue)
Medium temperature (green)
Very high temperature (red)
Shaded area on graph indicates
energy levels with electrons at medium
temperature. Gap surrounding Êf is due
to the band gap in a semiconductor.
Êb, a typical “barrier” energy
Êf (the Fermi energy level)
Note 1: The name “transistor” is a contraction of the two terms trans-resistor. Name due to John R. Pierce, Bell Laboratories scientist.
In the usual amplifying configuration,
the base is more positive than the emitter,
and the collector is at an even more positive
voltage. The E-B junction is thus ON and the
C-B junction is OFF (reverse biased). The thick
arrow represents the magnitude of electron flow.
Most of the electrons that pass from the Emitter
to the Base are collected by the Collector.
NPN unit is shown.
PNP units also
are made, and use
polarities from NPN.
The graphic symbol
for a PNP transistor
has the opposite arrow
iB (A current-controlled current source.)
iE= iB (1+)
The words “source”
and “drain” are based
on the concept of
positive charge flow.
P-gate, N-channel unit
Notice the “blob” in the
N-side depletion layer due
to electric field interaction
with Drain electrode.
The arrow indicates
direction of electron
of arrow suggests
effect from negative
gate voltage, which
neutral N channel.
1. Variable resistor between Source and Drain
2. Current source between Source and Drain, controlled by gate voltage
The parameter g is the so-
called trans-conductance of
the FET. It is the ratio of a change in
iS-D to the causative change in vG.
Note that there is no current path
in this model between the gate and
other parts of the FET. This is due
to assuming that the reverse current
of the gate-body junction is zero. In
fact it is typically a few microamperes.
+ vG -
Also called insulated gate FET
(IGFET). A layer of SiO2 (equi-
valent to beach sand, shown in
blue on the drawing) electric
insulation here is actually much
thinner than the illustration. No
P-type layer! This still produces
a positive (red) depletion layer
in the N-type part and channel
width is controlled by the gate
voltage. No steady (dc) gate
current flows for either positive
or negative gate voltage.
Multiple gate electrodes are
used to implement digital
logic functions (to be discussed
more in a later lecture). This
form with side-by-side gates
allows some source-drain current
to flow when either gate 1 OR
gate 2 has a positive voltage. This
implements the inclusive OR
logical function with a minimum
number of components, particularly
when implemented in an integrated
Current from source to drain
flows only when both gate 1
AND gate 2 are positive. Note
that there are two places where
negative gate voltage could
pinch off the channel. This
implements the digital logic
All of these configurations can
be implemented in integrated
circuits, although these pictures
show source and drain electrodes
on the edges.
RL , “load” resistor (or
(source or collector)
Fixed voltage power
supply, shown here
as a battery symbol.
Often the power supply
device and the wire from
power source to ground is omitted from drawings.
This box is replaced
by a particular transis-
tor in a real amplifier.
(drain or emitter)
Generic “ground” or “earth”
graphic symbol. Actually represents
the frame or cabinet in most modern
i = Io (e (qv/kT) -1), is itself temperature dependent