Module III : Basics of Analog and
Digital Electronics
Semiconductor, PN junction diode, Zener diode, rectifier- Half
wave, full wave and Bridge rectifier, Introduction to Number
system, basic Boolean laws, reduction of Boolean expressions
and implementation with logic gates.
1
Introduction
• All the matters are composed of three fundamental
particles.
Fundamenta
l particle
Nature of
charge
Mass in kg
Neutron
Proton
no charge
positive
charge
negative
charge
1.675 x 10-27
1.675 x 10-27
Electron
9.107 x 10-31
2
Cont.,
 Every atom consists of a nucleus carrying a positive
charge around which electrons move in orbits/shells at a
certain distance from the nucleus.
 The maximum number of electrons in any orbit is 2(n)2.
 Atom structure of copper is,
3
Cont.,
 Electrons that are in shells close to nucleus are tightly
bound to the atom and have low energy.
 Electrons that are in shells away from the nucleus are
lightly bound to the atom and have high energy.
 Electrons with highest energy level exists in the
outermost orbit.
 The outer most orbit is called as valence shell and the
electrons are known as valence electron.
4
Energy Band
 The high energy outermost shell electrons can be easily
extracted and take part in chemical reactions.
 In solids, atoms are close together.
 The outermost electrons are shared by other atoms. It
forms a bond known as ‘covalent band’. As they are
shared by adjacent atoms, they are not free under normal
condition.
 Due to the coupling between the valence electrons, the
energy levels associated with the valence electrons
merge into each other. The merging forms an ‘energy
band’.
5
Cont.,
 Similarly, the energy levels of various electrons in
various orbit levels merge to form various energy bands.
 Out of all the energy bands, the most important are,
1. Valence band
2. Conduction band
3. Forbidden band
6
Cont.,
1. Valence band :
 The energy band formed due to merging of energy levels
associated with valence electrons.
 The electrons in this bond are not free under normal
condition.
 When certain energy is imparted, the electrons become
free.
7
Cont.,
2. Conduction band :
 The energy band formed due to merging of energy levels
associated with the free electrons.
 Under normal condition, conduction band does not have any
electrons.
 When certain energy is imparted, the electrons jump from
valence band to conduction band and become free.
 While jumping from valence band to conduction band, the
electrons have to cross an energy gap.
8
Cont.,
3. Forbidden band :
 The energy gap which is separating the conduction band and
valence band.
 The electrons cannot exist in the forbidden gap.
9