Unit – 1

Introduction to Electronics

1.1           Evolution of Electronics

• Electronics vegan with invention of vacuum diode by J.A Fleming in 1897 and after that vacuum triode invented by lee  de forest to amplify the signals.
• The Transistor Era began with the junction transistor invention in1948.from 1958 to 1975. integrated circuits (Ic’s) introduced which is a small signal chip such as small  scale & very large scale integration .
• . Integrated circuits  drastically changed the entire electronics natures as  entire electronic circuit of integrated in a signal chip which has low cost ,small size, light in weight& more  reliable.
• . The Use Off  Germanium and silicon semiconductor materials made these transistor gain the popularity  & widely used in deferent electronics circuits & devise.

• Inventions/ Discovery

1) 1720 Stephen Gray  Discover edinsalator& conductor

2) 1745 Ewald Georg Von Kleist & Pieter Van Musschenbroetinvenredleyden jars(First Capacitor)

3) 1826 Georg Ohm Introduced OHM'S law

4) 1831 Reverend Nichols calland invented the inductor coil.

5) 1836 Nicholas Callan Invented Transformer

6) 1876 Alexander Graham Bell Invented Telephone

7) 1888 Heinrich Hertz proved that electromagnetic waves (FM) Travel over same distance.

8) 1897 Karl Ferdinand Braun Invented Cathode ray Oscilloscope (cro)

9)1901 Gaglielmo Marconi made First Transatlantic Radio broadcast

10) 1904 John Ambrose Fleming Invested diode

11) 1906 Leede forest  invented  triodes

12) 1912 Edwin Howard Armstrong develop electronic Oscillator.

13) 1920 Otis Frank Boykin invented resistor.

14) 1928 First Ereperimental  television Broadcast in the us

15) 1929 First public TV  Broadcast in Germany

16)1941 Konradzusc developed the first programmable computer

17)1943 Eisler invested the printed ckt board (BCB)

18)1944 John logic baird developed  the first color picture tube.

19) 1947 First transistor at bell labor atonics by William  Shockley, john Bardeen & welter Britain.

20) 1958 Jack Kirby invested the integrated circuit (IC)

21) 1960 Theodore Harold mailman  invented the laser

22) 1962 Holstein  & Heisman  invented misfit  transistors.

23) 1962 Nick Holon yak jr Invented the LED.

24) 1970 Intel Introduced the first Micro processor.

25) 1973 John F.Mitchell & Dr Martin  cooper of Motorola invented the first mobile phone.

26) 2007 Apple introduced the first I phone.

1.2           Impact of Electronics in industry and in society

Electronics engineering Field Have become an important part of human being. starting with an electronic alarm to get up early in the morning ,watch to update current news , microwave oven is used to cook the food , washing machine is used to clean our clothes 7 for entertainment music system is used. Now a  days electronics devices every where is utilized such as in schools, colleges , homes, shops, health care, defense ,industries ,research, geographic, animation, etc

• The electronics industry is growing very fast & is creating good job opportunity in industries like mobile phone, IT Industries television ,computers ,laptops ,tablets ,& palmtops. 
• In Addition to this there are good carrier options in consumer durables, oil, gas chemical &power  electronics.
• In has many Applications ranging from healthcare satellite communication, mobile communication (2G,3G,& 4G) & Internet technology.
• Engineers with Bachelor of Electronics & Telecommunication can work in research , design & development & manufacturing of electronics applications.
• They also have job openings in sale & marketing of electronic Equipment& maintaining & repairing of electronic devices.
• It has various field such as VLSI Design .Microwave  Engineering Integrated CKT .embedded system Nanotechnology , microelectronics & artificial intelligence  soon.

Applications:-

1) Digital Commerce

ii) Mobile Phone

iii)Computers

iv)medical applications such as CT scan 1MRI

V) led traffic lights

vi) Led displays etc

1.3           Introduction to active and passive components

An Electronic components is any basic discrete device or physical entity to affect electronics system used to affect electronics of their  associated fields.

1.4           P-type Semiconductor, N-type Semiconductor

N  type Semiconductor:-

 To increase the number of conduction band electrons  inintrisic silicon ,  pentavalent imparity atoms are  added. these are atoms with five valence electrons such as

i) arsenic (as)

ii) phosphors (p)

iii) Bismuth (Bi)

iii) Antimony ( sb)

• Pentavalent impurity atom  in a silicon  crystal. an antimony (sb) impurity atom shown above-
• Each pentavalent  atom forms covalent bonds with four adjustment silicon atoms, leaving one  extra electron .
• The pentavalent atom  gives up on electron , it often called a donor atom.

•  Majority and minority carriers:- A type here means negative charge of an electron .electron are called the majority carriers  in n-type material.
• Hole in an  n-type material are  called  minority carriers

P Type  Semiconductor :- 

To  increase  the  number of holes in intrinsic silicon  trivalent impurity  atoms are added  these are atoms  with  there  valence electrons  such as 

i) Baron(B)

 ii) Indium(IN) 

   iii)Gallium(GO)

• Trivalent impurity atom in a silicon  crystal structure . A) boron (B) impurity  atom is  shown in  the  center.
• The number  of holes can be carefully controlled  by the number of  trivalent  impurity atoms  added  to  the silicon .
• A  Hole  created by the doping  process  is not accompanied by a conduction (free)   electron.
• Trivalent   Atom   can take  an electron it is often referred to as on accepted atom

1.5           Current in semiconductors(Diffusion and Drift Current)

Drift current :- When a vtg is applied to a semiconductor, the free electrons try to drift toward the positive terminal of the battery due to this current flow called drift current.

Diffusion current : In semiconductor  it is possible to have a non uniform concentration of charge partials due to non uniform doping

eg. the concentration of e- on one side of the surface is more than the density on the other side , so the e-  will move from the side of greater concentration to the side of lower concentration. this transport of result in to  a flow of current which is called diffused current.

1.6           P-N Junction diode construction and its working in forward and reverse bias condition

• A Forward biased showing the flow of majority carriers and the voltage due to the barrier potential across the depletion region-

• To  bias a diode apply  d,c vtg across it .
• Forward bias is the condition that allows current through the PN  junction.
• Negative side of VBIAS  is connected to the N -region of the diode and the positive side is connected to the P- region.
• A selected requirement is that the bias voltage VBIAS must be greater than the barrier potential.
• Because of like charges repel ,the negative side of the bias voltage source pushes the free electrons , which are the majority carriers in the N-region towards the PN junction .the flow of free is called Electron Current.
• The –Ve side  of the source also provide a continues flow of electrons through the external connection (conductor).
• into the N-region as show in fig-B
• The bias voltage source imparts sufficient energy to the free electrons for them to overcome the barrier potential of the depletion region and move on through into the 'p' region once in the P-region .these conduction electrons have lost enough energy to immediately combine with holes in the valence band.
• Now the e- are in the valance band in the P-region simply because they have lost too much energy overcoming the barrier potential  to remain in the conduction band. since unlike charge attract, the positive side of the bias voltage source attracts the valence electrons toward the left end of the region.
• The hole in the P-region provide the medium or "Pathway" for these valence electrons to move through  the P-region.
• The holes which are the majority carriers in the  P-region , effectively (not actually ) move to the right toward the junction as shown in fig-B.
• The defective flow of holes is called the hole current.
• As from Fig-B hole current as the flow of valence electrons through the P-region with the holes providing the only means for these electrons to flow.
• As the electrons flow out of the P-region through the external connection and to the positive side of the bias in the P-region at the same time these electrons become conduction electrons in the mater conductor .
• To these is a continues availability of holes effectively moving towards the PN junction stream of electrons as they come across the junction in to the P-region.

The effect of forward bias on the depletion region:-

    Depletion Region

• Forward bias narrows the depletion region & produce a vtg drop across pn junction equal to the barrier potential.
• As more electrons flow into the depletion region , the number of positive ions is reduce . as more notes effectively flow into the depletion region on the other side of the pn junction ,the number of -ve ions is reduce this reduction in positive & -ve ions during forward bias causes the depletion region to narrow.

 The Effect of the Barrier Potential during forward bias:-

• The electronic field between the positive and negative ions in the depletion region on either side of the junction creates an energy bill, that prevent free R form diffusing across the junction at equilibrium this is known as the barrier potential

• When forward bias is applied the free electrons are provided with enough energy from the bias voltage source to over come the barrier potential and effectively climb the energy bill and cross the depletion region.

• The energy that the electronics repair in order to pass through the depletion region is equal to the barrier potential.

• Electron gives up an amount of energy equivalent to the barrier potential when they cross the depletion region. 

• This energy loss results in a vtg drop across the pn junction equals to the barrier potential (0.7v)

• An additional small vtg drop across the P & N regions due to the internal  resistance of the material.

• For doped Semiconductor material ,this resistance called the dynamic resistance is very small and can usually be neglected.

REVERSE BIAS:-

 Reverse bias is the condition the essentially prevents current through the diode.

V  BIAS

A Diode connected for Reverse Biased-

• Because  unlike charges attract  the positive side of the bia voltage source pulls the free election , which are the majority carriers in the N-region away from the PN  junction. 
• AS  the election  flow  towards the positive side of the voltage source additional positive ions are created
• This results in a widening of the depletion region and a depletion of majority carriers.

• The diode during the short transition time immediately after reverse bias vtg is applied-
• In the P-region electrons from the negative side of the vtg source enter as valence electron and move from hole to hole toward the depletion region where the creators additional -ve ions.
• This results in a widening of the depletion region and a depletion of majority carriers
• As the depletion region widens the availability of majority carriers decreases
  • As more of the N & P regions become depleted of majority carriers ,the electric field between the positive and -ve  ions increase in strength the depletion  region equals  the bios vtg .this point the transition current essentially ceases except for a small  reverse current that can usually be neglected.

Reverse  Current

• extremely small current that exist in reverse bias after the transition current dies act is caused by the minority carrier in the N& P  region that are produced by the manly generated  e hole pairs.
• The conduction band in the P-region is at a higher  energy level then the conduction band in the N-region . therefore the minority easily pass through the depletion region because they required no additional energy.

The Extremely small reverse current in a reverse biased diode is due to the  minority carriers from thermally generated 

e=hole pairs

1.7           V-I characteristics of P-N junction Diode

The Diode -  Before doping the p-type &  N-type  consisting  silicon  material atom acting as a neutral.

   IF a piece of intrinsic silicon is doped so that part is n-type and the other part is p-type , a junction forms at the bounded between the two regions and a diode  is created.

• At the instant  of  junction  formation  , free electrons  in  the  N-region  near  the p-n junction  being to diffuse  across the junction and fall into holes near the junction in the P-region.

For every  electron that defuse  across the junction and combines with a hole , a positive charge is left in the region and a ve charge is created  in the p-region firming a barriers potential. this action continues until the vtg of the barrier ripples  further  diffusion  .

The Depletion region acts as a barriers to the farther movement of electrons across the junction 

As positive ion & -ve  ion across the junction produces a electric field across the junction -according to coulombs law.

 The potential difference of the electric field across the depletion region is the amount of vtg required to move electronics through the electric field, this potential difference is called the barrier potential & is expressed in volt

 The typical barrier potential is approximately  0.7 v for silicon & 0.3 v for germanium at 25c.

1.8           Diode as a switch

Whenever a specified voltage is exceeded, the diode resistance gets increased, making the diode reverse biased and it acts as an open switch. Whenever the voltage applied is below the reference voltage, the diode resistance gets decreased, making the diode forward biased, and it acts as a closed switch.

The following circuit explains the diode acting as a switch.

A switching diode has a PN junction in which P-region is lightly doped and N-region is heavily doped. The above circuit symbolizes that the diode gets ON when positive voltage forward biases the diode and it gets OFF when negative voltage reverse biases the diode.

As the forward current flows till then, with a sudden reverse voltage, the reverse current flows for an instance rather than getting switched OFF immediately. The higher the leakage current, the greater the loss. The flow of reverse current when diode is reverse biased suddenly, may sometimes create few oscillations, called as RINGING.

This ringing condition is a loss and hence should be minimized. To do this, the switching times of the diode should be understood.

1.9           Half Wave Rectifier

1)Due to the unidirectional current flow through the transformer there is a possibility of core saturation to avoid this transformer size must be increased.

2)Ripple factor is high.

3)Low rectification effecting.

4)Law TUF.

5)Law D.C O/P VTG & current.

6)Large filter component are required.

ADVANTAGES:-

1)Simple Construction.

2) Component  required less.

3)Small  size.

APPLICATION:-

Walkman, law cost power supply.

TRANSFORMER UTILISATION FACTOR(TUF) :-It indicates how well the ilp transformer is being utilized

TUF= DC O/P Power / AC power rating of the transformer

1.10     Full wave and Bridge Rectifier

1)A center tapped rectifier is a type of full wave rectifier that uses two diode connected to the secondary of a center tapped transformer.

Center tapped full wave rectifier operation:-

ADVANTAGES

1) law ripple factor as Compared  to HKR.

2)Better rectification efficiency.

3) Better TUF.

4)Higher value of average load vtg & avg load crt.

5)No possibility of transformer core saturation.

DISADVANTAGES

 PIV of diode is 2vm , more size costly.

APPLICATION

I) Battery charges.

2)power supply at laboratory, high current, electronic ckt.

BRIDGE RECTIFIER

 The bridge rectifier uses  four diode connected, when the i/p cycle is positive diode D1 & D2 are forward biased and conduct current in the direction shown a vtg is developed across RL which looks the positive half of the i/p cycle during this diodes D3 and D4 are reverse biased.

When  the ilp cycle is -ve diode D3& D4  are forward biased & conduct current  in the same direction through R1 as during in the positive half cycle during the -ve half cycle D1& D2  are reverse biased. a full wave rectified O/P VTG appears across RL as a result of this action.

NOTE -  Practically  vp(out)= vp sec-1.4v 1000 diode knee vtg.

Advantages :-

1) It require a small size transformer center tap transformer is not required .this makes the bridge rectifier cost effective.

2) This ckt is most suitable for the high vtg application . this is because the max -ve that appears across each diode is -vm therefore the diode with PIV rating of -vm volts are required to be selected (PIV in fall wave rectifier is 2vm

3) Core saturation does not take place.

4) High TUF, high avg, vtg

Disadvantages :-

1)Number of diode used is four instead two for FWR

2)As two diodes conduct simultaneously , the vtg drop increase and the o/p vtg reduces.

Applications :-

Laboratory , high current, battery , electronic , ckt power supply.

1.11     Zener diode

• Zenor diode is a special type of p-n junction  semiconductor diode in this diode the reverse breakdown voltage is adjusted precisely between 3v to 200v. 
• Its  applications are based on this principle hence zenor diode is called as a breakdown diode.
• The doping level of the imparity added to manufacture the zener diode is controlled in order to adjust  the precise value of breakdown voltage.

PRINCIPLE OF OPERATION:-   A zener diode can be forward biased or reverses biased. its operation in the forward biased mode is same as that of a p-n junction diode but its operation in the reverse biased mode is sustainably deferent.

1.12     Light Emitting Diode (LED) and photo diode along with V-I characteristics and their applications.

An LED emits light when electrical energy is applied to it. for proper operation it is necessary to forward bias the LED.

PRINCIPLE  LED OPERATION

 When the led is forward is forward biased the electrons in the n-region will cross the junction and recombine with the holes in the p- type material.

 These free e- reside in the conduction band & hence at a higher energy level than the holes in the valence band

 When recombination takes place  this e- return peak to the valence band which is at a lower energy level than the conduction band.

while returning back the recombining e-give  away the excess energy in the form of  light . this process is called as electroluminescence. in this way an LED emits light.

Color of the Emitted Light 

Material Use                                        Color of Emitted Light  

 i)Gallium Arsenide (GOAS)                                 In fared (IR)

ii)  GaASP(gallium arsenide                                  Red or Yellow

       phosphide)

iii) Gallium phosphide (GAP)                               Red or Green

Application

Used in 7 Segment Display

Photodiode

The photodiode is a p-n junction semiconductor diode which is always operated in the reverse biased condition.

 The light is always focused through a glass lens on the junction of the photodiode  As the photodiode is reverse biased the depletion region is quite wide, penetrated on both side of the junction.

  The photons incident on the depletion region  will impact their energy to the Ions present in depletion region and generates e hole pairs.

 The photons incident on the depletion region so the number of electron hole pairs will be generated depends on the intensity of light [number of photons] These and holes will be attracted towards the +ve& -ve terminals respectively of the photo current ,

  With increase in the light intensity more number of e hole pairs are generated and the photo current increases thus the photocurrent is proportional to the light intensity.

Reference Books:

1. “Digital Fundamentals” by Thomas. L. Floyd, 11th Edition, Pearson

2.     “Mobile Communication” by J. Schiller, 2nd Edition, Pearson

      3. “Sensors Handbook”, by S. Soloman, 2nd Edition.