# Fundamentals of Electronic Circuit Design

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Republic of Iraq
Ministry of Higher Education and Scientific Research
University of Technology
Department of Computer Engineering and information Technology

First Class   Year 2010-2011

Fundamentals of Electronic Circuit Design

Contents
1- Structure of an Atom
1.1 Material Photo effective
2- Material types (Conductor, and Semiconductor, Insulator)
3- Intrinsic semiconductor
3.1 Extrinsic semiconductor (P-type and N-type)
4- P-N Junction (Diode)
4.1 Diode Equivalent cct.
4.2 Diode DC analysis
5- Diode AC applications
5.1 Rectifier
5.2 Clipper circuits
5.3 Clamper circuits
6- Zener Diode
7- Bipolar junction transistor (BJT)
8- Field Effect Transistor FET
8.1 Junction Field Effect Transistor ( JFET)
8.2 Metal Oxide Semiconductor field Effect Transistor (MOSFET)

Reference
1-Thomas L .Floyd “Electronsic Devices” 2005.
2-U.A Bakshi “ Electronics Engineering “ First Edition ,2008
3-Jacob Millman”Microelectronics “ second Edition 1987

Dr.Ekbal Hussian Ali
1.Structure of an Atom

1.1 The nature of the Atom

The atom consists of a central nucleus surrounded by orbiting
electrons ,as shown in the Fig.1 The nucleus consists of positively
charged particles called protons and uncharged particles called neutron.
The basic particles of negative charege are called electrons
In a normal atom the number of protons is equal to the number
electrons .The number of protons in an atom is called as its atomic
number .While the atomic weight is approximately equal to the total
number of protons and neutrons in the nucleus of an atom.

Electron

+            Nucleus

Fig.1 Atom structure               Orbital

The charge of proton ( inside the nucleus) equal to the electrons
charge. The fource of the the attraction between electron and proton
follows by Columb's Law.

Dr.Ekbal Hussian Ali
1-2 The Number of Electron in Each orbit(or shell)

The electrons which are revolving round the nucleus ,do not move
in same orbit .The electrons are arranged in the different orbits at an orbit
can contain maximum number of electrons (Ne)can be calculated by the
formula
Ne= 2n 2 ,n is the number of orbil.The first orbit can occupy
electrons ( 2  12 =2)
The maximum number of electrons that can exist in the second shell is
Ne=2 (2) 2 =8
The maximum number of electrons that can exist in the third shell
Ne=2 (3) 2 =8
All shells in a given atom must be completely filled with electrons except
the outer (Valence )shell
1-3 Bohr Atom
The hydrogen contain one electron in his orbital call (Bohr Atom). There
are two attractive Forces
FP : Potential Force
FK : Kinetic Force.
q2
FP                         (1)                -
40 r 2                 FK
FP
m v2                                            r
FK                    (2)
r                                       +
where
q: electron Charge = 1.602 *10-19 C
-31
Fig. (2) Bohr Atom (H+)
m : electron mass = 9.11*10                Kg
 0 : permittivity of air = 8.859 *10
-12
F/m
v : velocity of electron (m/sec)

Dr.Ekbal Hussian Ali
r : radius of the orbit (m)
The condition for equilibrium the two force is equal, that lead to

q2          m v2

40 r 2                   r
(3)
q2
v 2

40 m r

The stationary state is determined by the condition, the angular
momentum of electron in this state be integral multiple of h /(2 ) as

nh
mvr                           (4)
2
where
h : Plank'c constant = 6.626 * 10-34 J.sec
n : orbital number

nh
v                             (5)
2 m r

by using Eq. (3) by Eq. (5) the result is

h 2
r                 0
n2    (6)
 m q          2

by using Eq.(3) with Eq.(6) the r by

q2   1
v                                   (7)
2 h 0 n
Dr.Ekbal Hussian Ali
1-4Atomic Energy
There are two types of energy at the atom.
i- Potential Energy EP of electron at distance from the nucleus

 q2
EP                         (8
40 r

ii. Kinetic Energy EK for the electron moving around the nucleus

m v2
EK                         (9)
2

therefore the total Energy are

ET = Ek+Ep
m v2     q2
ET  Ek  Ep       
2     40 r
 q4          m q4 1
ET                                  (Joule )    (10)
80 r        8h 2  0 n
2  2

Putting    values     of       m    ,q,  o , h 2 in   equation    (10)   for    electron
inhydrogenatom ,we have
 13.6
ET           (ev)
n2
ev : the electron volt unit.

Dr.Ekbal Hussian Ali
Example
Determine the first three allowed electron energies in the hydrogen
atom and draw the energy level diagram

 13.6
ET               (ev)
n2
For the First energy level n=1
 13.6
ET              (ev)  13.6ev
12
For the second energy level n=2
 13.6
ET              (ev)  3.39ev
22
For the third energy level n=3
 13.6
ET              (ev)  1.51ev
32
n =  (Ionization Level)
ET = 0 ev

n =4
ET = -0.87 ev

n =3
ET = -1.56 ev

n=2
ET = -3.41 ev
n=1 (G.S)
ET= -13.6 ev                 (Ground Level)
Nucl.

Fig. The Energy levels of Bohr atom (H+)

Dr.Ekbal Hussian Ali
1-5 Atomic Energy Levels
The energy level of shell one is lowermost while the energy level
of valence shell is highest .More energy level indicates that the
electrons of that shell are loosely bound to the nucleus as having
highest energy level .The concept of energy level is shown in the
Fig.(3)
Energy level increases from first
shell to valence shell as the distance
from the nucleus the increases

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Lowest energy level
Valence shell highest energy level
4
Fig.(3) Concept of energy level
The Ionization level is the level of number n  .
The atom by ionize is absorbed energy equal to the level energy.
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An electron which is not subjected to the force of attraction of the the
nucleus is called a free electron .More the number of free electrons
,better is the conductivity of the metal
4
4
1.6Photo Affective
The electron in ground state (G.S) absorbed an light (Photon) then
transfer to upper state this case call photon absorbsion, if the photon
transfer from upper state to lower state radiate photons this case call
photon emission. The photon Energy EPh calculated by

Dr.Ekbal Hussian Ali
hC
EPh  h f            (11)

where
f : Photon frequency (Hz)
 : Photon wavelength (m)
C=3*108 (m/sec)

Hint: Angistrom (A0) = 10-10 m

a- Absorbsion
The electron absorb energy when it excite from lower energy
level to higher energy level . Fig.(4). The energy of final orbital can
calculate his energy by

E 1  E 2  hf      (12)

E2

EPh

E1
Fig.(4) Absorbsion

If photon Energy greater or equal to the Energy level then the electron
transfer to level n= Inf., the atom in this case call Ionize and this
phenomena call Photo ionization see Fig. (5).

n= 

EPh >=E1

Fig.(5) Photo Ionization                                 E1
Dr.Ekbal Hussian Ali
b- Emission
In this case the electron loss the amount of energy as photon
(Light), this phenomena called (Emission).It jump from higher energy
level to lower energy . The Photon energy calculated by

E 2  E1  hf              ….(13)
E2
EPh

E1
Fig.(6) Emission
2 Material Types
There are three type of material :
i. Insulator is very poor conducting material the energy gap between
valance band and conduction band very high.
ii. Conductor is excellent conducting material the energy gap
between valance band and conduction band very small.
iii. Semiconductor is subtended material between conductor and
Insolate material, the energy gap between valance band and
conduction band small, for that the semiconductor is transfer
case between conducted and insolated material.(two types
intrinsic and Extrinsic semiconductor)
Energy Band, its know as group of orbital have the same
performance. There are two type of Bands, Valance Band (V.B) and
Conduction Band (C.B). The electron in C.B call free electrons, this
electrons cause conducing in material. As shown Fig.().
Energy Gap (E.G), it’s the region separates between valence band
and conduction band. The energy gap is

Eg =EC - EV        …. (14)
Dr.Ekbal Hussian Ali
2.1 Metals, Semiconductors and insulators (on the basic of
band diagram)

The different electrical behavior of materials can be explained
qualitatively in terms of their energy band diagrams because
each solid has its own characteristics energy band structure as
shown in Fig(7).

E(ev)
Conduction band

Valence band

Metals Conductors              x

E                                          Ec
ev           Conduction band

Eg                            Forbidden gap
Ev
Valence band

Semicoducors             x

E
ev           Conduction band
Ec

Eg >=3ev                       Forbidden gap

Ev
Valence band

Insulators        x
Fig.(7) Band diagram for conductor, semiconductor and insulator
Dr.Ekbal Hussian Ali

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