BASIC ELECTRONICS

2. Basic Electronics (EEE-231)
Lecture 1
Instructor: Iqbal Ahmed Khurshid
Email: iqbal.ahmed.1@hotmail.com

3. Course Structure
• Credit Hours: 3
• Lectures: 30
• Quizzes: 4
• Assignments: 4
• Mid Exam: After 15 Lectures (25 marks)
• Final Exam of 50 marks
• Minimum 80% attendance (24 Lecs) required to sit in the final exam
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4. Marks Division
• Quizzes 10%
• Assignments 10%
• Mid-Term Exam 30%
• Final Term Exam 50%
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5. Basic Electronics
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6. Course Outline
• Fundamentals of Semiconductor Physics: Band Theory, Intrinsic and
Extrinsic Semi-conductors
• P.N. Junction Diode, P.N. Junction as Rectifier
• Clipper and Clamper Circuits
• Zener Diode and Voltage Regulator, LED and LCD etc.
• Transistors, BJT Transistors, Biasing Techniques, Q Point Variations,
BJT as switch, BJT amplifiers
• Classes of amplifiers, Power amplifiers
• Metal oxide transistors, nMOS, pMOS, and CMOS Inverter circuits
• Introduction to A/D and D/A circuits
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7. Required Literature
Book 1
Electronics Devices and Circuit Theory by Boylestad,
Eleventh Edition
Book 2
Electronic Devices by Thomas L. Floyd Ninth Edition
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8. Prerequisite: DC Circuit analysis
Circuit analysis is the process of finding the voltages across, and the currents through, every
component in the circuit.
For dc circuits the components are resistive only and analysis is simpler.
Ohm Law,
Series, Parallel circuits,
Kirchhoff’s voltage and current laws,
Current, Voltage divider rules,
Thevenin, Norton’s theorems.
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9. THE ATOM
• All matter is composed of atoms; all atoms consist of electrons,
protons, and neutrons except normal hydrogen, which does not have
a neutron.
• The atom is not a single particle but was made up of a small dense
nucleus around which electrons orbit at great distances from the
nucleus, similar to the way planets orbit the sun.
• The nucleus consists of positively charged particles called protons
and uncharged particles called neutrons. The basic particles of
negative charge are called electrons.
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10. THE ATOM
• The atomic number equals the number of protons in the nucleus,
which is the same as the number of electrons in an electrically
balanced (neutral) atom.
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11. Periodic Table
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12. Electrons and Shells
• Electrons orbit the nucleus of an atom at certain distances from the
nucleus.
• Electrons near the nucleus have less energy than those in more
distant orbits.
• Each discrete distance (orbit) from the nucleus corresponds to a
certain energy level.
• In an atom, the orbits are grouped into energy levels known as shells.
• The shells (energy levels) are designated 1, 2, 3, and so on, with 1
being closest to the nucleus.
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13. Electrons and Shells
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14. Equation 1–1
• The Maximum Number of Electrons in Each Shell The
maximum number of electrons (Ne) that can exist in
each shell of an atom is a fact of nature and can be
calculated by the formula,
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15. MATERIALS USED IN ELECTRONICS
• In terms of their electrical properties, materials can be classified into
three groups:
i. Conductors,
ii. Semiconductors
iii. Insulators
• An atom can be represented by the valence shell and a core that consists of
all the inner shells and the nucleus.
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16. Insulators
• An insulator is a material that does not conduct electrical current
under normal conditions.
• Most good insulators are compounds rather than single-element
materials and have very high resistivities.
• Valence electrons are tightly bound to the atoms; therefore, there are
very few free electrons in an insulator.
• Examples of insulators are rubber, plastics, glass, mica, and quartz.
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17. Conductors
• A conductor is a material that easily conducts electrical current.
• Most metals are good conductors. The best conductors are single-
element materials, such as copper (Cu), silver (Ag), gold (Au), and
aluminum (Al), which are characterized by atoms with only one
valence electron very loosely bound to the atom.
• These loosely bound valence electrons become free electrons.
Therefore, in a conductive material the free electrons are valence
electrons.
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18. Semiconductors
• A semiconductor is a material that is between conductors
and insulators in its ability to conduct electrical current.
• A semiconductor in its pure (intrinsic) state is neither a good
conductor nor a good insulator.
• Single-element semiconductors are antimony (Sb), arsenic
(As), astatine (At), boron (B), polonium (Po), tellurium (Te),
silicon (Si), and germanium (Ge).
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19. Band Gap
• Recall that the valence shell of an atom represents a band of energy levels and
that the valence electrons are confined to that band.
• When an electron acquires enough additional energy, it can leave the valence
shell, become a free electron, and exist in what is known as the conduction
band.
• The difference in energy between the valence band and the conduction band is
called an energy gap or band gap.
• This is the amount of energy that a valence electron must have in order to jump
from the valence band to the conduction band.
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20. Band Gap
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21. Band Gap
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22. Band Gap
• The energy gap also reveals which elements are useful in the
construction of light-emitting devices such as light-emitting diodes
(LEDs), which will be introduced shortly.
• The wider the energy gap, the greater is the possibility of energy
being released in the form of visible or invisible (infrared) light waves.
• The unit of measure is appropriate because W (energy) = QV (as
derived from the defining equation for voltage: V = W / Q ).
• Substituting the charge of one electron and a potential difference of 1
V results in an energy level referred to as one electron volt .
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23. Comparison of a Semiconductor Atom to a Conductor Atom
• Silicon is a semiconductor and copper is a conductor. Bohr diagrams
of the silicon atom and the copper atom are shown in Figure 1–8.
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24. Silicon and Germanium
• The atomic structures of silicon and germanium are compared in
Figure 1–9.
• Silicon is used in diodes, transistors, integrated circuits, and other
semiconductor devices.
• Notice that both silicon and germanium have the characteristic four
valence electrons.
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25. Atomic structure of (a) silicon; (b) germanium; and
(c) gallium and arsenic.
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26. Covalent Bonds
• Figure shows how each silicon atom positions itself with four adjacent
silicon atoms to form a silicon crystal.
• This sharing of valence electrons produces the covalent bonds that
hold the atoms together
• Covalent bonding in an intrinsic silicon crystal is shown in Figure. An
intrinsic crystal is one that has no impurities.
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27. Covalent Bonds
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28. Conduction Electrons and Holes
• An intrinsic (pure) silicon crystal at room temperature has sufficient
heat (thermal) energy for some valence electrons to jump the gap
from the valence band into the conduction band, becoming free
electrons. Free electrons are also called conduction electrons.
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29. Conduction Electrons and Holes
• When an electron jumps to the conduction band, a vacancy is left in
the valence band within the crystal.
• This vacancy is called a hole. For every electron raised to the
conduction band by external energy, there is one hole left in the
valence band, creating what is called an electron-hole pair.
• Recombination occurs when a conduction-band electron loses energy
and falls back into a hole in the valence band.
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30. Conduction Electrons and Holes
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31. Electron Current
• When a voltage is applied across a piece of intrinsic silicon, as shown
in Figure, the thermally generated free electrons in the conduction
band, which are free to move randomly in the crystal structure, are
now easily attracted toward the positive end.
• This movement of free electrons is one type of current in a semi
conductive material and is called electron current.
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32. Hole Current
• Another type of current occurs in the valence band, where the holes
created by the free electrons exist.
• A valence electron can move into a nearby hole with little change in
its energy level, thus leaving another hole where it came from.
• Effectively the hole has moved from one place to another in the
crystal structure, as illustrated in Figure.
• Although current in the valence band is produced by valence
electrons, it is called hole current to distinguish it from electron
current in the conduction band.
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33. Electron and Hole Current
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34. N-TYPE AND P-TYPE SEMICONDUCTORS
• Semi conductive materials do not conduct current well and are of limited
value in their intrinsic state.
• This is because of the limited number of free electrons in the conduction
band and holes in the valence band.
• Intrinsic silicon (or germanium) must be modified by increasing the
number of free electrons or holes to increase its conductivity and make it
useful in electronic devices.
• This is done by adding impurities to the intrinsic material.
• Two types of extrinsic (impure) semi conductive materials, n-type and p-
type, are the key building blocks for most types of electronic devices.
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35. N-Type Semiconductor
• To increase the number of conduction-band electrons in intrinsic silicon,
pentavalent impurity atoms are added. These are atoms with five valence
electrons such as arsenic (As), phosphorus (P), bismuth (Bi), and antimony
(Sb).
• As illustrated in Figure, each pentavalent atom (antimony, in this case)
forms covalent bonds with four adjacent silicon atoms.
• Four of the antimony atom’s valence electrons are used to form the
covalent bonds with silicon atoms, leaving one extra electron.
• This extra electron becomes a conduction electron because it is not
involved in bonding.
• Because the pentavalent atom gives up an electron, it is often called a
donor atom.
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36. N-Type Semiconductor
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37. Majority and Minority Carriers
• Since most of the current carriers are electrons, silicon (or
germanium) doped with pentavalent atoms is an n-type
semiconductor (the n stands for the negative charge on an electron).
• The electrons are called the majority carriers in n-type material.
Although the majority of current carriers in n-type material are
electrons, there are also a few holes that are created when electron-
hole pairs are thermally generated.
• These holes are not produced by the addition of the pentavalent
impurity atoms. Holes in an n-type material are called minority
carriers.
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38. P-Type Semiconductor
• To increase the number of holes in intrinsic silicon, trivalent impurity
atoms are added.
• These are atoms with three valence electrons such as boron (B),
indium (In), and gallium (Ga).
• As illustrated in Figure, each trivalent atom (boron, in this case) forms
covalent bonds with four adjacent silicon atoms.
• All three of the boron atom’s valence electrons are used in the
covalent bonds; and, since four electrons are required, a hole results
when each trivalent atom is added. Because the trivalent atom can
take an electron, it is often referred to as an acceptor atom.
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39. P-Type Semiconductor
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40. Majority and Minority Carriers
• Since most of the current carriers are holes, silicon (or germanium)
doped with trivalent atoms is called a p-type semiconductor. The
holes are the majority carriers in p-type material.
• Although the majority of current carriers in p-type material are holes,
there are also a few conduction-band electrons that are created when
electron-hole pairs are thermally generated.
• These conduction-band electrons are not produced by the addition of
the trivalent impurity atoms.
• Conduction-band electrons in p-type material are the minority
carriers
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41. Intrinsic Semiconductors vs Extrinsic Semiconductors
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42. THE PN JUNCTION
• When you take a block of silicon and dope part of it with a trivalent
impurity and the other part with a pentavalent impurity, a boundary
called the pn junction is formed between the resulting p-type and n-
type portions and a diode is created, as indicated in Figure.
• The pn junction is the basis for diodes, certain transistors, solar cells,
and other devices.
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43. THE PN JUNCTION
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44. Formation of the Depletion Region
• At the instant of the pn junction formation, the free electrons near
the junction in the n region begin to diffuse across the junction into
the p region where they combine with holes near the junction, as
shown in Figure.
• The term depletion refers to the fact that the region near the pn
junction is depleted of charge carriers (electrons and holes) due to
diffusion across the junction. Keep in mind that the depletion region
is formed very quickly and is very thin compared to the n region and
p region.
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45. Barrier Potential
• The potential difference of the electric field across the depletion
region is the amount of voltage required to move electrons through
the electric field. This potential difference is called the barrier
potential and is expressed in volts.
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46. The Diode
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47. The Diode
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48. No Applied Bias ( V = 0 V)
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49. Reverse-Bias Condition ( V D < 0 V)
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50. Reverse-Bias Condition ( V D < 0 V)
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51. Forward-Bias Condition ( V D > 0 V)
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52. Forward-Bias Condition ( V D > 0 V)
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53. Characteristics of a semiconductor diode
• It can be demonstrated through the use of solid-state physics that the
general characteristics of a semiconductor diode can be defined by
the following equation, referred to as Shockley’s equation, for the
forward- and reverse-bias regions:
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55. Silicon semiconductor diode characteristics.
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56. Forward-bias
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