1. ENGN2218 Electronic Systems and Design1
Reading for LECTURE 02
Revision of Diode
Dr. Salman Durrani
School of Engineering,
The Australian National University.
http://people.cecs.anu.edu.au/asp/academics/bio
3. ENGN2218 Electronic Systems and Design3
• The convention used in this course is
• Commonly used symbols in this course are
Terminology
4. ENGN2218 Electronic Systems and Design4
• An electric circuit consists of circuit elements (such as
voltage sources, resistors, capacitors and inductors)
connected in closed paths by conductors.
• A node in an electrical circuit is a point at which two or
more circuit elements are joined together (an essential
node is where three or more circuit elements join).
• A loop in an electrical circuit is a closed path whose last
node is the same as the starting node.
• A mesh is a special case of a loop. A mesh is a loop that
does not contain any other loops.
Electric Circuit Vocabulary
5. ENGN2218 Electronic Systems and Design5
• Kirchhoff’s Current Law (KCL):
• Kirchhoff’s Voltage Law (KVL):
Kirchhoff’s Laws
6. ENGN2218 Electronic Systems and Design6
• Conventional current flows from +ve terminal of battery
to –ve terminal. Flow of electrons is in opposite direction
to conventional current direction.
• The terminal where conventional current enters an
element is assigned +ve polarity and the terminal
where conventional current leaves an element is
assigned -ve polarity.
• Following conventional current in a circuit, if we move
from +ve polarity towards –ve polarity (voltage drop),
the element absorbs energy that appears as heat or
stored chemical energy. If we move from –ve polarity
towards +ve polarity (voltage rise), the element supplies
energy.
Current and Voltage Conventions
7. ENGN2218 Electronic Systems and Design7
• The extreme value of R =infinity Ω is given special name
of open circuit.
– Using analogy of a switch, it corresponds to the case when
switch is open (i.e. OFF)
• The extreme value of R =0Ω is given special name of
short circuit.
– Using analogy of a switch, it corresponds to the case when
switch is closed (i.e. ON)
Open and Short Circuit Concepts
9. ENGN2218 Electronic Systems and Design9
• A semiconductor is neither a good conductor nor a
good insulator.
Semiconductors
10. ENGN2218 Electronic Systems and Design10
• Electronic devices such as diodes and transistors are
made of a semiconductor material.
• A basic knowledge of semiconductor physics helps us to
understand diode and bipolar junction transistor
behaviour.
• Common semiconductor materials are
– Silicon (Si) [single-element semiconductor]
– Germanium (Ge) [single-element semiconductor]
– Carbon (C) [single-element semiconductor]
– Gallium Arsenide (GaAs) [compound semiconductor]
Basic Semiconductor Concepts
11. ENGN2218 Electronic Systems and Design11
• Silicon is the most widely used material in diodes,
transistors other semiconductor devices.
• Intrinsic (pure) Silicon is a crystalline material with Si
atoms held together by covalent bonds.
Intrinsic Silicon
12. ENGN2218 Electronic Systems and Design12
• Extrinsic (impure) semiconductors are formed by
adding small amounts of suitable impurities to intrinsic
semiconductors in order to improve conductivity.
• The process of adding controlled impurities to intrinsic
(pure) semiconductor materials is called doping.
• Two types of extrinsic semiconductor materials are:
– An n-type semiconductor material consists of Si
atoms and pentavalent impurity atoms.
– A p-type semiconductor material consists of Si atoms
and trivalent impurity atoms.
Extrinsic Semiconductors
13. ENGN2218 Electronic Systems and Design13
• An n-type semiconductor material consists of Si atoms
and pentavalent impurity atoms such as Arsenic (As),
Phosphorus (P), Bismuth (Bi) and Antimony (Sb).
N-Type Semiconductors
14. ENGN2218 Electronic Systems and Design14
• A p-type semiconductor material consists of Si atoms
and trivalent impurity atoms such as Boron (B), Indium
(I) and Gallium (Ga).
P-Type Semiconductors
15. ENGN2218 Electronic Systems and Design15
• A pn junction consists of a single crystal of
semiconductor material that is doped to produce n-type
material on one side and p-type on the other side.
• The pn junction is fundamental to the operation of
devices such as diodes and transistors.
• Barrier Potential is the
amount of voltage required
to move electrons through
the pn junction.
(0.7V for Si and 0.3V for Ge)
PN Junction
16. ENGN2218 Electronic Systems and Design16
• Diode is a device that allows current to flow in one
direction but blocks current in reverse direction.
• An diode is a two terminal device (the anode or “p” and
the cathode or “n”) commonly made from Silicon.
• The arrow in the symbol points in the direction of
conventional current flow.
Diode
17. ENGN2218 Electronic Systems and Design17
• Bias is the use of a dc voltage to establish certain
operating conditions for an electronic device.
• A diode is said to be forward biased if the p-side of the
diode is more +ve with respect to the n-side of the diode.
• A diode is said to be reverse biased if the n-side of the
diode is more +ve with respect to the p-side of the diode.
Basic Definitions
18. ENGN2218 Electronic Systems and Design18
• Diode is a non-linear device.
• Diode is usually operated in the forward bias and reverse
bias regions, without entering the breakdown region.
Volt-ampere Characteristics
19. ENGN2218 Electronic Systems and Design19
• V-I characteristics for a typical Si diode.
Volt-ampere Characteristics (contd.)
20. ENGN2218 Electronic Systems and Design20
• The ideal diode acts as a short circuit for forward
currents and as an open circuit with reverse voltage
applied.
Ideal Diode Model
21. ENGN2218 Electronic Systems and Design21
• The practical diode model adds a 0.7V voltage source in
series with an ideal diode model.
Practical Diode Model
22. ENGN2218 Electronic Systems and Design22
• A mechanical switch in “ON” state allows current to
flow in either direction.
• A diode in “ON” state allows current to flow in one
direction only (uni-directional switch). The arrow in the
symbol points in the direction of conventional current
flow.
• Practically, we assume a 0V drop across a mechanical
switch in “ON” state while we assume a 0.7V drop
across a diode in “ON” state.
Comparison with Mechanical Switch
