# CSC258H1 Lecture Notes - Voltage Source, Computer Hardware, Current Source

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Published on 20 Apr 2013
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TRANSISTORS
Transistors Introduction
o Transistors form the basic building blocks of all computer hardware
Allowed logical devices modern computer
o Used for applications such as amplification, switching and digital logic
design.
Where do transistors fit
o LOGIC GATE (made from) Transistors (based on) pn-
pn-junctions = a junction made from 2 materials a “p” and a “n”
Eletricity Introduction
o Electricity is caused by the flow of charged particles, usually electrons
Some materials allow flow better than others
ex. Metals vs. Rubber/Plastic (disallow eletrons to flow)
o Particle flow from of high electrical potential regions to low
electrical potential
Similar to gravitational potential
o This potential is referred to as voltage
How much electrical potential is in a source
Group = 0 V, charge energy are compared vs. the ground
Charges above 0 V (high voltage) wants a path to the ground
(low voltage)
o The rate of this flow is called the current
Eample Circuit Design
o Circuit diagrams are composed of:
Sources
Voltage source & Current source
Components (resistors, capacitors, inductors)
Notes on Current and Ground
o Even though electrical current is the flow of eletrons through a
medium, its direction is typically expressed as the movement of the
positive charges
o Current always from towards the zero valtage point of a circuit
Commonly referred to as the ground
Resistance = higher resistance of a material, slow eletrons moves through
it from high V to low V
o Water Analogy to picture the concept of voltage and current
Charged particles are the drops of water
Voltage is the elevation of the water above the ground
Current is the flow of water form high to low potential
Water from a resovior, large pipe = low resistance, small pipe =
high resistance
o Resistance measured in ohms (Ω) and indicates how well a material
conducts electricity
High resistance (aka insulators) don’t conduct eletrciity at all, or
only under special circumstances ex. Rubber
Low resistance (aka conductors) conduct electricity well, and are
generally used for wires ex. Metal
These are largely determined by the position on the element on
the periodic table
o Anything will conduct electricity if enough voltage is put through it
Ex. Air lightning/sparks
The relationship between voltage (V) and current (I) and resisance (R)
o V = IR
Conductivity of materials
o Eletricity can flow freely through a solid if there are free valence
electrons in outter layer after the solid is formed
o Elements conductivity depending on # eletrons in the it’s valence
shell and orbit of the valence shell
Eletroncs entering a material on one side traverse through the
elements through the valence shell
By exchanging positions with valence electrons of
elements exit electron != initial electron
Elements w/ full valence shell = not conductors
Higher outter orbit better flow b/c less attraction force from
protons in neucleus
Carbon bonds closer b/c lower outter orbit
Silicon bonds further b/c higher outter orbits
Both have 4 eletroncs in the valence shell, shares w/ 4
other of the element to complete orbit, but silicon
materials are better conductors
o Semiconductor materials (silicon, germanium) straddle the boundary
between conductors and insulators
behaving like one or the other, depending on factors like
temperature and impurities in the material
o Semiconductor conductivity
Semiconducotrs are solid and stable at room temp.
But energy can loosen the valence shell electrons
A weak current will still flow through the matieral at room temp.
Less than that of a conductor
Impurity
o Semiconductor don’t conduct electricity naturally
b/c the valence eletroncs of each atom at joined to their
neighbors
o to encourage the semiconducor’s conductivity, impurities can be
introduced in the fabrication process, to increase the number of free
charge carriers
n type: (from group 15) have 5 electrons in valence shell
the carriers are eletrons that are not bound to the solid,
and can flow more freely through the material
elements w/ extra electrons better conductivity
ex. Phosphrous
p type: (group 13) have 3 electrons in valence shell
the carriers are called holes, to represent the electron
gap as a partical as well
elements w/ less electrons = absorbs electrons flowing
through matieral less conductivity
process is referred to as doping the semiconductor
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## Document Summary

Conductivity of materials: eletricity can flow freely through a solid if there are free valence, transistors form the basic building blocks of all computer hardware electrons in outter layer after the solid is formed. Allowed logical devices modern computer: elements" conductivity depending on # eletrons in the it"s valence, used for applications such as amplification, switching and digital logic shell and orbit of the valence shell design. Where do transistors fit: logic gate (made from) transistors (based on) pn- junctions (made from) semiconductors. Pn-junctions = a junction made from 2 materials a p and a n . Eletroncs entering a material on one side traverse through the elements through the valence shell. By exchanging positions with valence electrons of elements exit electron != initial electron. Elements w/ full valence shell = not conductors. Higher outter orbit better flow b/c less attraction force from: electricity is caused by the flow of charged particles, usually electrons protons in neucleus.