Untitled Lesson

Course Contents

• COURSE OBJECTIVES: To teach the

fundamentals of semiconductor devices and
its applications, principles of digital
electronics

• UNIT I SEMICONDUCTOR DEVICES

• Introduction - Evolution of electronics –

Vacuum tubes to nano electronics -
Characteristics of PN Junction Diode —
Zener Effect — Zener Diode and its
Characteristics. Bipolar Junction Transistor
—CB, CE.

UNIT II BASIC ELECTRONIC CIRCUITS AND INSTRUMENTTAION

Rectifiers and power supplies: Block diagram description of a dc power
supply, working of a full wave

bridge rectifier, capacitor filter (no analysis), working of simple zener voltage
regulator.

Amplifiers: Circuit diagram and working of common emitter (RC coupled)
amplifier with its frequency

response. Electronic Instrumentation: Block diagram of an electronic
instrumentation system.

UNIT III DIGITAL ELECTRONICS

Overview of Number Systems, Logic gates including Universal Gates, BCD
codes. Boolean Algebra,

Basic Theorems and properties of Boolean Algebra, Truth Tables and
Functionality of Logic Gates –

NOT, OR, AND, NOR, NAND,and XOR.

Simple combinational circuits–Half and Full Adders. Introduction to
sequential circuits, Flip flops.

Textbooks:

1. R. L. Boylestad& Louis Nashlesky, Electronic
Devices & Circuit Theory, Pearson Education, 2021.

2. R. P. Jain, Modern Digital Electronics, 4th Edition,
Tata Mc Graw Hill, 2009

Reference Books:

1. R. S. Sedha, A Textbook of Electronic Devices and
Circuits, S. Chand & Co, 2010.

2. SantiramKal, Basic Electronics- Devices, Circuits
and IT Fundamentals, Prentice Hall, India, 2002.

3. R. T. Paynter, Introductory Electronic Devices &
Circuits – Conventional Flow Version,

Pearson Education,2009.

EVOLUTION OF ELECTRONICS –

VACUUM TUBES TO NANO

ELECTRONICS

WHAT IS
ELECTRONICS……?

• Electronics means study of flow of
electrons in electrical circuits.

• Electronics is the branch of science
that deals with the study of flow and
control of electrons (electricity) and the
study of their behavior and effects in
vacuums, gases, and semiconductors

ELECTRICAL V/S ELECTRONICS ENGG

Deals with the current flow in

semiconductors. Most

electronic components are very
small, and require small direct
current (DC) voltages (3 – 12V

DC).

Deals with the current flow in

conductors. Electrical

components tend to be larger,
and use alternating current (AC)

voltages (230V AC).

EVOLUTION OF
ELCTRONICS

• Evolution of electronics is mainly
through 3 key components

• The vacuum tube
• The transistor
• The integrated circuits

VACUUM TUBES

(1904)

9

INTRODUCTION

• Vacuum tubes (or electron valves)
were invented in 1904 by John Ambrose
Fleming and served as a basic
component for electronics throughout
the first half of the 20th century

• Applications included radio,
television, radar, sound recording,
large telephone networks, industrial
process control and first-generation
computers

10

DISADVANTAGES

•Following the invention of semiconductor devices in the 1940s, the use of
vacuum tubes was gradually replaced by transistors

•When compared to transistors, vacuum tubes have several disadvantages:

1. Large size

2. Higher operating voltages

3. Less efficient

4. Glass tubes are fragile

5. Higher cost

6. Needs regular replacement

A few applications remained, such as the Cathode-ray tube (CRT) in video
monitors, but those too were eventually superseded in the 21st century

In 1883, Thomas Alwa

Edison discovered that

electrons will flow from

one metal conductor to

another through vacuum

– Edison effect

In 1904 John Fleming applied Edison

effect in inventing two element electron

tube called vacuum diode.

• In 1906, following this Lee De Forest developed a
three element tube called vacuum triode. This was the
real begining of electronics.

In 1927, Marconi invented radio

which was the primary form of

education and entertainment.

In

1947,

the

transistor

was

invented by John Bardeen, Walter

brattain and William Shockley in

Bell Laboratories.

This invention revolutionized electronics industry due to its features such as
light weight, low cost, less power, reliability etc. Which reduced the size of
electronic devices.

Another breakthrough happened in 1956 when Bell Laboratories invented
Thyristor also called Silicon Controlled Rectifier (SCR).

▪In 1958 Jack Kilby an engineer of Texas
instruments demonstrated the first IC.

▪Large no of electronic components could be
fabricated together on a single chip.

▪Beginning of microelectronics revolution.

▪In the year 2000 Jack Kilby won the Nobel
Prize in Physics for miniaturized electronic
circuits.

As the technology advanced, no of components fabricated on a single

chip also increased. This advancement in chip fabrication is accordingly

called as SSI, MSI, LSI, VLSI, ULSI etc. This resulted the new era of

computers, mobile phones, microprocessors etc. 4 bit microprocessor

was developed by Intel in 1971.

1900

• Vacuum tube (1st generation)

1947

• Transistor (2nd generation)

1958

• IC (3rd generation)

1960

• SSI (Small Scale Integration)

1966

• MSI (Medium Scale Integration)

1969

• LSI (Large Scale Integration)

1975

• VLSI (Very Large Scale Integration) – 4th gen.

1995

• ULSI (Ultra Large Scale Integration) – 5th gen.

IMPACT OF ELECTRONICS IN MODERN WORLD

21st century rely on electronics. Electronic technology is employed

in the field of Industry, Communication, Military, Entertainments,

Education, Automobiles, etc. In fact it is difficult to find an area

where electronic technology is not applied.

ELECTRONICS IN COMMUNICATION & ENTERTAINMENT

• Telegraphy

• Telephony

• Fax

• Radio Communication

• Television

• Cable T V

• Mobile communication

• Internet/social media

• Teleconferencing

• Video conferencing

• Bluetooth

• Wifi

• Music players

• Public address system

• Television programs

• Social media

•Video games

ELECTRONICS IN MEDICAL FIELD

• Electronic equipments such as ECG, EEG, Artificial pacemaker,

Electronic spigmomanometer, Heart-Lung machine, Laser based

surgical equipments.

• Scanning equipments such as X-ray, Computer tomography, MRI,

Ultrasound, Nuclear imaging, etc

• Telemedicine

ELECTRONICS IN INSTRUMENTATION

• CRO

• Function generators

• DSO

• Finger print security systems

• Drones in air traffic control

• Multimeter

• Strain gauges

• CCTV

•Microwave oven

• Air conditioner

• Induction heater

ELECTRONICS IN DEFENCE

• RADAR

• Missiles

• Rocket launching

• SONAR

Characteristics of PN

Junction Diode

Insulators, Conductors, Semiconductors
from energy band structures

Classification of
semiconductors

The semiconductors may be classified based on its

constructure into:-

1.

Intrinsic semiconductors

2.

Extrinsic semiconductors

Semiconductor Materials

• Materials commonly used in the development of
• semiconductor devices:
• • Silicon (Si)
• • Germanium (Ge)
• • Gallium Arsenide (GaAs

Extrinsic

Semiconductor:

When an impurity is added to an
intrinsic semiconductor its
conductivity changes.

This process of adding impurity to
a semiconductor is called Doping
and the impure semiconductor is
called extrinsic semiconductor.

N-type

semiconductor

When a small current of Pentavalent impurity is added to
a pure semiconductor it is called as n-type
semiconductor.

Addition of Pentavalent impurity provides a large number
of free electrons in a semiconductor crystal.

Typical example for pentavalent impurities are Arsenic,
Antimony and Phosphorus etc. Such impurities which
produce n-type semiconductors are known as Donor
impurities because they donate or provide free electrons
to the semiconductor crystal

P-type

semiconductor:

When a small amount of trivalent impurity is added to a
pure semiconductor it is called p-type semiconductor.

The addition of trivalent impurity provides large number of
holes in the semiconductor crystals.

Example: Gallium, Indium or Boron etc. Such impurities
which produce p-type semiconductors are known as
acceptor impurities because the holes created can accept
the electrons in the semi conductor crystal

Semiconductor

Diode

i. In a piece of semiconductor, one half
is doped by P-type impurity and the
other half is doped by N-type impurity.
Thus PN junction is formed.

ii. This formation of PN junction is
called diode as it has two electrodes
one for P region called as Anode and
the other for N region called as
Cathode

Semiconductor

Diode

Diffusion :

The tendency of the free electrons to diffuse
from the n-side to p-side and holes from p-
region to n-region is called diffusion.

Diffusion is the process by which charge
carrier moves from high concentration
region to low concentration region.

Depletion Region

The free electrons diffuse from 'n' side to 'p' side
region and recombine with the holes in P region.
Thus, negative charged immobile ions are
formed near the junction.

Also, the holes diffuse from P-region to n-region
and recombine with the electrons in n-region
and leaves positively charged immobile ions
near the junction of n-side.

Semiconductor

Diode

Semiconductor

Diode

This process continues over certain time duration. After
certain extent, the net negative charge on P-side prevents
further diffusion of electrons into P-side. Similarly, the net
positive charge on N-side repels holes crossing from P-side to
N- side. These immobile positive and negative ions form a
region called as depletion region.

Depletion region is defined as the region over which all the
free charge carriers are depleted. This region is also known as
space charge region since there are no free charge carriers
available for conduction. In equilibrium condition, the
depletion region gets widened upto a point where no further
electrons or holes can cross the junction. The physical
distance from one side to other side of the depletion region is
called width of the depletion region.

Semiconductor Diode

Barrier Potential:
The electric filed is developed across the depletion region due
to the potential difference between P and N regions. This
potential acts as barrier for further conduction between the
junction. This potential is called as barrier potential or
diffusion potential or contact potential or cut in voltage.

The value of contact potential is 0.3 V for Germanium and
0.72V for Silicon at 25° C.

Operation of PN Junction Diode

Biasing
Applying any external voltage to electronic device is called biasing. Biasing
refers to provide minimum external voltage and current to activate the
device.
There are two types of biasing for PN junction.
Forward Bias
The positive terminal of the battery is connected to P-type semiconductor
and negative terminal is connected to n-type semiconductor material.
Reverse Bias
The positive terminal of the battery is connected to n - type semiconductor
and the negative terminal is connected to P-type semiconductor material.

FORWARD BIASED PN JUNCTION

In unbiased PN junction, there is no flow of current, when forward bias is
applied to the PN junction, the applied forward voltage creates an electric
field opposite to the potential barrier.

i. Thus the potential barrier is reduced at the junction. As the potential
barrier is very small (0.7 V for Si and 0.3 V for Ge), a small forward voltage
is sufficient to eliminate the barrier potential.

ii. The applied positive potential repels the holes in P-type region towards
the junction. The electrons in the n-type region are also repelled towards
the junction due to the negative voltage applied in n-region.

FORWARD BIASED PN JUNCTION

FORWARD BIASED PN JUNCTION

When the applied potential is more than the internal barrier potential, the
depletion region completely disappears and the junction resistance
becomes zero.

junction provides a low resistance path and thus current flows in the circuit.
This current is called forward current.

When the forward voltage is increased, the large number of majority charge
carriers can cross the junction. These large number of majority charge
carriers constitute the forward current.

REVERSE BIASED P-N JUNCTION

• The P-region is connected to negative terminal of the battery and n -region is connected to positive

terminal of the battery.

• When p-n junction is reverse biased, the negative terminal attracts the holes in p - region and the

positive terminal attracts the free electrons in n - region away from the junction.

• The electrons and holes move away from the junction and the width of depletion region increases.

• The charge carriers are unable to cross the junction.

• Thus there are more positive ions in the n- region and more negative ions in the p- region.

• When the depletion region widens, the barrier potential across the junction also increases.

REVERSE BIASED P-N JUNCTION

REVERSE BIASED P-N JUNCTION

• The applied reverse voltage creates an electric field which is in same direction of potential

barrier and thus the barrier width is increased.

• This increased potential barrier prevents the flow of charge carriers across the junction.

• When PN junction is reverse biased, it has high resistance path and no current flows in the

circuit.

• After certain extent, the junction breakdown occurs. Then a small amount of current flows

through it due to minority charge carriers i.e., the electrons on p-side and holes on n- -side
constitute current in reverse biased condition. So, the reverse current is always very small.
The reverse current remains constant even if the reverse voltage is increased upto a certain
limit. Hence, it is called Reverse saturation current. The magnitude of reverse saturation
current depends on junction temperature