Fundamentals of Electronic Circuit Design

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Fundamentals of Electronic Circuit Design Powered By Docstoc
					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

  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)

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.


                                +            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
        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.
                           FP                         (1)                -
                                     40 r 2                 FK
                                m v2                                            r
                         FK                    (2)
                                 r                                       +
q: electron Charge = 1.602 *10-19 C
                                                                             Fig. (2) Bohr Atom (H+)
m : electron mass = 9.11*10                Kg
 0 : permittivity of air = 8.859 *10
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
                      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

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

                       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)

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)
ev : the electron volt unit.

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

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

                                                      n =4
                                              ET = -0.87 ev

                                                      n =3
                                              ET = -1.56 ev

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

         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
                                                    Energy level increases from first
                                                    shell to valence shell as the distance
                                                    from the nucleus the increases


                                      Lowest energy level
                                                                Valence shell highest energy level
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.
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
      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
         EPh  h f            (11)
    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)



                                          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)

                                                   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).

                                                Conduction band

                                                      Valence band

                      Metals Conductors              x

E                                          Ec
ev           Conduction band

                      Eg                            Forbidden gap
               Valence band

                       Semicoducors             x

 ev           Conduction band

                     Eg >=3ev                       Forbidden gap

                Valence band

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