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EST 130
Part II – Electronics
Module 4 - Basic electronic circuits and instrumentation
25-03-2024 Prof. Agi Joseph George | AP | ECE | AJCE 1

Introduction:
• Almost every object we touch in our day-to-day life carries electronics in
it - television, an air cooler, a refrigerator, a microwave oven, or an
automobile
• Electron – smallest amount of electric charge having the characteristic
called negative polarity.
• Proton - basic particle with positive polarity.
• the arrangement of electrons and protons determines the electrical
characteristics of all substances.
• For example, the paper you use has electrons and protons in it. But no
evidence of electricity. WHY?

Introduction contd…:
• The word Electronics comes from “electron mechanics”
• means learning the way how an electron behaves under different conditions of
externally applied electric or magnetic field
• Definition by IRE(Institution of Radio Engineers)
• that field of science and engineering, which deals with electron devices and their
utilization
• Capabilities of electron devices:
• Rectification (AC to DC conversion),
• Amplification (strengthening of a weak signal),
• Generation (conversion of DC to AC power of any frequency),
• Control and conversion of light into electricity and vice versa.

EVOLUTION OF ELECTRONICS:
• 1890 - First exp. on generation of electromagnetic waves.
• 1894 - Sir J C Bose discovered the propagation of radio waves
• 1894 - Marconi postulated the theory of radio wave propagation
• 1895 - H A Lorentz postulated the existence of electron
• 1897 - J. J. Thomson verified the existence of electron
• 1897 - Braun invented the first electron tube
• 1904 - Fleming invented the diode called valve which was initially based
on Edison’s discovery in 1883 (Edison’s effect).
• 1907 – Lee De Forest invented a 3-electrode vacuum tube that was
capable of amplifying radio signals – Audion.

EVOLUTION OF ELECTRONICS:
• 1947 - invention of the transistor by John Bardeen, Walter H. Brattain,
and William B. Shockley at Bell laboratories. Semiconductor revolution.
• Late 1950s - research on the purification of silicon succeeded =>
semiconductor devices.
• 1958 - invention of the integrated circuit (IC) independently by Jack
Kilby of Texas Instruments Incorporated.
• 1960 - vacuum tubes were rapidly being supplanted by transistors.
• 1970 - up to 1,000 transistors on a chip of the same size at no increase in
cost.
• Continued advances in IC technology gave rise to very large-scale
integration (VLSI) and nano-electronics.

EVOLUTION OF Transistors:
• 1947:
• Brattain and Bardeen invented point-contact transistor.
• Shockley discovered junction transistor
• 1950:
• First junction transistor was invented
• 1951:
• Transistor produced commercially (first germanium and then silicon)
• 1958:
• Kilby (Texas Instruments, USA) gave the idea of monolithic IC
• 1961:
• Fairchild and T.I. commercially produced integrated circuits.

EVOLUTION OF ICs:

Application of Electronics:
• Entertainment & communication:
• Smart TV
• MODEM
• Set Top Box
• Laptop
• Mobiles
• Printer
• Scanner
• Digital Cameras

• Defence:
• RADAR and electronic warfare,
• autonomous weapons,
• guidance and control systems or
• secure communications.
• Surveillance systems

• Industrial:
• Industrial automation and motion control,
• Machine learning,
• motor drive control,
• Mechatronics and robotics,
• Power converting technologies,
• Photo voltaic systems,
• Renewable energy applications,
• Power electronics,
• Biomechanics
• Smart grid

• Medical:
• Anesthesia
• Respiratory monitoring
• Blood pressure analysis
• Oxygen level measurement in the body
• Imaging in diagnostics like MRI, ultrasound, etc
• Stress measurement

• Instrumentation:
• cathode ray oscilloscope (CROs),
• frequency counters,
• pulse and signal generators,
• digital multimeters,
• power supplies,
• pH meters,
• strain gauges

ELECTRONIC COMPONENTS:
• electronic component - any basic discrete device in an electronic system
used to affect electrons or their associated fields.
• are mostly industrial products, available in a singular form
• have several electrical terminals or leads
• Basic electronic components may be packaged
• discretely,
• as arrays or networks of like components, or
• integrated inside of packages such as semiconductor integrated circuits, hybrid
integrated circuits, or thick film devices

ELECTRONIC COMPONENTS:

Electronic Components - types:
• Active:
• rely on a source of energy
• an inject power into a circuit such as amplification or processing.
• E.g.: transistors, triode vacuum tubes (valves), tunnel diodes, Integrated Circuits
or ICs, Logic Gates
• Passive:
• cannot introduce net energy into the circuit
• rely on a source of power, from the (AC) circuit they are connected to.
• they cannot amplify
• although they may increase a voltage or current
• E.g. : resistors, capacitors, inductors, transformers, diodes

Resistors

Resistors:
• used in a wide variety of applications in all types of electronic circuits.
• main function in any circuit is to
• limit the amount of current
• produce a desired drop in voltage
• manufactured in a variety of shapes and sizes
• No direct correlation between the physical size of a resistor and its
resistance value.
• two main characteristics of a resistor are
• its resistance R in ohms (fraction of an ohm to megaohms) and
• its power rating in watts (W).
• Dissipation means that the power is wasted, since the resultant
heat is not used

Resistors – principle of operation:
• foundation for all circuit analysis in electronics.
• Ohm’s law states that
• the current through a conductor between two points is directly proportional to
the voltage across the two points.
• V=I * R

Resistors – specifications:
• Resistance Value:
• The value of a resistor is its value expressed in ohms.
• Tolerance:
• It is the percentage deviation from the rated value.
• Power Rating:
• Maximum power that the resistor can dissipate safely
• Voltage Rating:
• Maximum voltage that can be applied across a resistor

Resistors – symbol:

Resistors – classifications:

Resistors – Fixed:
• are resistors with a specific value.
• one of the most widely used types of resistor.
• used in electronics circuits to set the correct conditions in a circuit

Carbon composition resistors:
• solid cylindrical resistive element is covered with plastic to protect the
resistor from outside heat.
• made from the mixture of carbon or graphite powder and ceramic (made
of clay).
• carbon powder acts as the good conductor of electric current.
• available with different resistance values ranging from one ohm (1Ω) to
22-Mega ohms (22 MΩ)
• Resistance of the carbon composition resistor is depends on three
factors:
• amount of carbon added,
• length of solid cylindrical rod, and
• cross sectional area of the solid cylindrical rod

Carbon composition resistors :

Carbon composition resistors:
• Advantages:
• Small size
• Wide resistance range is available
• Cheap
• Good RF performance
• Disadvantages:
• No precision and high tolerance
• Gets easily heated and crack down on soldering
• Resistance value vary with aging
• Not useful for applications involving power levels above 5 watts

Carbon Film resistors:
• A thin pure film of carbon is deposited onto a small ceramic rod.
• The resistive coating is spiraled away until the two ends of the rod is as close
as possible to the correct value

Carbon film resistors:
• Advantages:
• Available in all resistor values
• Available in miniature size
• Good high frequency properties
• Accuracy with respect to carbon composition
• Low cost
• Disadvantages:
• Cannot withstand high temperatures
• Vulnerable to mechanical shocks
• Vulnerable to atmospheric moisture and humidity
• Chemically reactive and hence unstable

Metal Film resistors:
• usually made of Nichrome, but also other materials such as tantalum
nitride is used.
• The resistive film is printed on a cylindrical or flat insulating substrate.
• The resistive material is a combination of a Ceramic material and a
Metal, also referred to as Cermet.
• stability, temperature coefficient and tolerance are better than for carbon
film.

Metal Film resistors:

Wire wound resistors:
• A wire with a high resistivity is wrapped around an insulating core to
provide resistance.
• Available in very low ohmic high precision values
• resistive wire is usually a nickel-chromium alloy, and the core is often
ceramic or fiberglass.
• spiral winding has capacitive and inductive effects that makes it not
suitable for applications higher than 50 kHz.
• Wirewound resistors are often produced for high precision or high
power applications.
• They have low noise, are robust, and are temperature stable

Wire wound resistors:

Color coding:
• Bands of color are used to represent the resistance value
• 1st and 2nd band – Numerical value of the resistance
• 3rd band – Power-of-ten multiplier
• 4th and 5th band – Percentage tolerance of the resistor

Color coding:

Variable resistors:
• Value of the resistor can be changed during its usage
• normally works by sliding a contact (wiper) over a resistive element.
• Consists of 3 terminals
• Two terminals are fixed. Third one is connected to a movable cap which
slides along the element
• Potentiometers
• Rheostats

Carbon Composition Potentiometer:
• Two types:
• Coated film
• Moulded
• functions as a resistive divider
• used to generate a voltage signal depending on the position of the
potentiometer
• Applications: amplifier gain control (audio volume), tuning of circuits.

Coated film:
• On a ring of insulating material, a mixture of carbon filler and binder is
coated.
• The surface of the film is processed to avoid abrasion
• For contact, material used is brass or phosphor bronze.

Moulded:
• Carbon composition material is moulded in a cavity in a plastic base
• Carbon brush is used as moving tap
• Sealed to prevent the effects of moisture

Wire wound Potentiometer:
• A flat strip is bent into circular form after winding
• For a flat strip, insulating material is used (synthetic resin bonded sheet)
• Can be used only up to 50kHz

Wire wound Potentiometer:
• To have different resistance range, one has to change
• Diameter of the wire
• Cross section of the core
• Spacing between wires
• Turns on the core
• Length of the core
• Type of wire used

Comparison of potentiometers:

Rheostat:
• Used in applications that require the adjustment of current or the
varying of resistance in an electric circuit

Rheostat:
• On a round or hexagonal former, windings of oxidized Ni-Cu are put up
• Former may be of ceramic or enameled steel
• Sliding contact on a metal bar selects the desired resistance value
• Current range: 0.1A to 20A
• Resistance range: 0.5Ω to 10KΩ

Thermistor:
• Type of resistor whose resistance varies significantly with temperature
• Made of
• metallic oxides,
• pressed into a bead, disk, or cylindrical shape and
• then encapsulated with an impermeable material such as epoxy or glass
• Two types:
• Negative Temperature Coefficient (NTC)
• Positive Temperature Coefficient (PTC)
• NTC: When temp inc, resistance decreases
• PTC: When temp inc, resistance increases
• Used as a fuse

Thermistor:

Thermistor - applications:
• Temperature sensing circuit
• Temperature compensators
• Liquid level detector
• Time delay circuit

Photoresistors:
• Also known as light dependent resistors (LDR)
• Light sensitive devices used to indicate the presence or absence of light,
or to measure light intensity
• In the dark, the resistance is very high (1MΩ)
• When exposed to light, resistance decreases (to a few ohms)

Photoresistors:

Photoresistors:
• Made of high resistance semiconductor
• When incident light exceeds a certain frequency, photons absorbed by
the semiconductor give the bound electrons enough energy to jump into
the conduction band
• The resulting free electrons conduct electricity, thereby lowering
resistance

Varistor:
• Electrical component with an electrical resistivity that varies with the
applied voltage
• Also known as voltage dependent resistor (VDR)
• Has characteristics similar to that of a diode
• At low voltage, it has high resistance which decreases as the voltage is
raised
• Used as spike guard in plugs to protect appliances from high voltage or
lightning

Varistor:

Capacitors

Capacitor:
• a two-terminal passive electronic component.
• can store electrical energy in an electric field.
• was originally known as a condenser or condensator
• The ability of a conducting body to accumulate
charge is known as capacitance.
• capacitance value of a capacitor is:
• C = Q/V
• Charge accumulation depends on the plate area
and spacing

Capacitor vs Battery:
• A capacitor stores potential energy in an electric field, while a battery
stores it in a chemical form.
• Batteries store and distribute energy in a linear fashion, while capacitors
release energy in bursts.
• A battery has a better energy density than a capacitor, which means it can
store more energy per unit volume.
• A capacitor is generally used for filtering applications, while batteries are
used as a power supply.
• A battery is an active device as it can supply energy for a continuous
period, while a capacitor is a passive component.

Capacitor – theory of operation:
• Capacitor consists of two parallel conductors separated by a dielectric
• Examples of dielectric are glass, air, paper, vacuum, ceramic, and even a
semiconductor depletion region, etc.
• When a voltage is applied across the capacitor plates, the electrons
accumulate on the side of the capacitor connected to the negative
terminal of the voltage source.
• This accumulation process of electrons at one end is called charging
• This continues until the potential difference across the capacitor is equal
to the applied voltage

Capacitor – theory of operation:

Capacitor – Specifications:
• Voltage Rating: Maximum voltage that can be applied across a capacitor
without damaging its dielectric
• Tolerance: The accepted deviation from the printed value of capacitor
• Power factor: indicates the minimum loss in the capacitor.
• Frequency Range: the maximum frequency up to which the capacitor can
work safely.
• Dielectric Constant: property of the dielectric that affects the capacitance
value

Capacitor – classification:

Fixed Capacitor:
• Capacitance value cannot be varied mechanically or by any other external
means
• The dielectric is permanently kept in between two fixed plates.
• Depending on the type of dielectric used, the properties of the capacitor
can change
• Can be:
• Polar
• Non-polar

Paper Capacitor:
• Made by:
• two long metal foils which are separated by wax paper strips and
• rolled together to take a cylindrical shape
• Connecting leads are joined to each metal foil and the capacitor is
wrapped with a suitable resin binder

Paper Capacitor:

Paper Capacitor:
• Advantages:
• Very cheap
• Readily available in bulk quantities.
• Can withstand high voltages.
• Disadvantages:
• Bulky.
• Poor high frequency characteristics.

Mica Capacitor:
• The dielectric consists of thin rectangular sheets of mica.
• The electrodes are either:
• thin sheets of metal foil stacked alternately with mica sheets or
• thin deposits of silver applied to one surface of each mica sheets.
• The mica sheets and foils are sandwiched alternately.

Mica Capacitor:

Mica Capacitor:
• Advantages:
• Good mechanical strength.
• Can be operated to temperatures as high as 900ºC.
• Can withstand very high voltages.
• Suitable for very high frequency operation.
• Disadvantages:
• Mica is a natural mineral. It will get depleted as years pass on.

Ceramic Capacitor:
• Dielectric is a ceramic material
• Available in different sizes and shapes
• Ceramic dielectric is a compound of titanium, barium, magnesium and
strontium
• Conductor plates – aluminium, tin or silver
• Construction:
• A disc of ceramic material is taken
• On each surface, a metallized electrode is plated (Silver)
• Leads are attached by soldering
• After this, a coating of suitable resin is applied for protection against moisture

Ceramic Capacitor:

Ceramic Capacitor:
• Advantages:
• Can be formed into desired shape and size
• Capacitance value range from a few pF to a few nF
• Inexpensive
• Light weight
• Can withstand high voltages
• Disadvantages:
• Very high voltage ceramic capacitors are not available
• High capacitance values are not available

Polyester / Film / Plastic Capacitor:
• Uses polystyrene, polycarbonate or teflon as the dielectric
• The construction is similar to paper capacitor but use a plastic film
instead of paper

Polyester / Film / Plastic Capacitor:

Electrolytic Capacitor:
• Uses an electrolyte as one of its plates to achieve a larger capacitance per
unit volume than other types
• Used when very large capacitance values are required
• Polarized type.
• Two types:
• Aluminum electrolytic capacitors
• Tantalum electrolytic capacitors

Aluminium Electrolytic Capacitor:
• Two Al foils separated by insulating papers are rolled.
• One of the foils is the anode plate
• An oxide is coated on this anode, which acts as the dielectric
• This roll is saturated with electrolyte which acts as cathode
• Now the roll is stabilized and then sealed in an aluminium container

Aluminium Electrolytic Capacitor:

Tantalum Electrolytic Capacitor:
• Used in applications where size is of importance
• A film of oxide on tantalum is used
• Polarized
• Do not have high working voltages
• Capacitance range from 47nF to 470 μF
• Solid tantalum or a foil of tantalum is used
• Electrolyte may be wet or dry

• Advantage:
• Lower leakage resistance
• Longer life
• Higher stability in operation
• Higher reliability
• Smaller size

Capacitor Coding - mica:

Capacitor Coding - ceramic:

Capacitor Coding:

Variable Capacitor:
• Capacitance value may be changed by some means
• Can be changed by:
• Varying area of the plates
• Adjusting the spacing between them
• Adjusting the thickness of the dielectric
• Dielectric – air, mica, ceramic or plastic
• Two types
• Ganged Capacitor – fixed air gap
• Trimmer Capacitor – fixed plate area

Gang Capacitor:
• Consists of 2 sets of metal plates
• One set of the plates is fixed and the other can be rotated by a shaft
• As the plates move in and out of the fixed plates, the capacitance value
varies
• Used in radio receivers for tuning different radio stations

Trimmers:
• Used for making fine adjustments on the total capacitance of a device
• Trimmer – 2 small flexible metal plates separated by a dielectric
• Spacing between the plates can be changed by means of a screw
adjustment
• 5pF to 30pF

Padders:
• Padders are similar to trimmers but are larger in size
• Capacitance value – 10pF to 500pF

Inductors

Inductors:
• Two terminal passive electric device stores energy in the form of a
magnetic field.
• Principle:
• When current flows through a current carrying conductor, it generates a
magnetic field.
• This oppose any change in the current flowing through the conductor.
• This reaction of magnetic field is known as inductance.
• The resultant force is called induced emf.
• Unit of Inductance – Henry (H)

Permeability:
• Any material let’s say iron when placed inside the magnetic field
possesses magnetism in itself.
• Iron has an ability to allow magnetic fields with high strength in itself,
and that’s why it has high permeability.
• While the material like Wood, Aluminium are reluctant to permit
magnetism in itself.
• Permeability is an ability of any material to permit the density of
the magnetic flux.
• Absolute permeability is related to the permeability of free space and is a
constant value which is given as μ0 = 4Π × 10-7 H.m-1
• Absolute permeability for other materials can be expressed relative to the
permeability of free space, μ = μ0μr

Factors affect the inductance of a coil:
• Number of turns in the coil.
• Diameter of the coil.
• Coil length.
• The type of material used in the core.
• Number of layers of winding in the coil.

Relation between L,A,N and l :
• 𝑳 =
μ0μr AN2
𝒍
• where,
• L - the inductance
• A - the area of cross-section
• l - the length of core,
• N - the number of turns of the coil,
• μ0 - are the absolute permeability of core material and
• μr - relative permeability of the core material

Relation between L,A,N and l :
• When a current of I amperes flows through an inductor of L Henry is
changed at the rate of 𝑑𝑖/𝑑𝑡, due to which a counter emf ‘e’ volts is set
up, then the counter emf
• e = L
𝑑𝑖
𝑑𝑡
• Emf stands for electromotive force.

1 Henry:
• 1 Henry is:
• the inductance the coil has, when the current changing at the rate of 1 A/sec
passes through the coil and sets up the emf of 1 volt
• Inductive reactance:
• XL=𝟐𝛑 𝐟 𝐋

Symbol:

Classification:

Fixed inductors:
• Air core Inductor
• Iron core Inductor
• Ferrite core Inductor

Air core inductors:
• Former is made up of insulating material like ceramic and air is inside the
former.
• Plastic or cardboard is used to wind the coil on the ceramic.
• It has got least inductance per number of turns and length.

Iron core inductors:
• The space inside the former of the coil is filled with solid iron or
laminated iron core.
• Iron is a ferromagnetic material which provides the easier path for the
magnetic flux produced.
• Iron is laminated to reduce the eddy current loss.
• Iron core Inductor is also known as choke.
• Useful at low frequencies.
• Used as filter chokes and Audio frequency chokes.

Ferrite core inductors:
• When iron oxide is mixed with other metal irons to control the magnetic
properties, ferrite core is formed.
• Coil is wound to the ferrite core.
• Minimum eddy current loss.
• This core can be used from audio to radio frequencies up to 100MHz.
• Application: The built-in antennas for radios

Variable inductors:
• Give variation in value of inductance.
• They usually use ferrite core.
• They use hollow former with screw threads inside, on which the coil is
wound.
• Due to the change in position of the ferrite core in the former, the value
of the inductance change.
• L is max when the core is fully in.

Q factor:
• Factor expressing the quality of a coil.
• Resistance of the inductor is primarily responsible for the Q of the coil.
• Q goes down when R is added in series with the circuit.
• Increase in frequency increases the Q.
• For an ideal inductor, R=0;

Mutually coupled coils:
• When the magnetic flux produced by an inductor links with another
inductor, these inductors are said to be mutually coupled.
• When inductors are coupled there exists a mutual inductance (working
principle of transformer) that relates the current in the primary inductor
to the flux linkage in the secondary inductor.

Mutually coupled coils:
• Thus there are three inductors are present
• L1 – The self inductance of the coil 1
• L2 – The self inductance of the coil 2
• M – The Mutual inductance associated with the inductors.

Voltage and current relation:

Specifications of an inductor:
• Nominal Inductance:
• the value of inductance that the inductor is supposed to offer at a particular
frequency and voltage.
• expressed in Microhenry, Millihenry, or Henry.
• Tolerance:
• can change with the frequency of the signal, temperature, and current.
• tolerance is the maximum variation in the value of inductance under all possible
test conditions.
• can have +/-1%, +/-2%, +/-3%, +/-5%, +/-10%, +/-15%, or +/-20%
tolerance with alphabets, F, G, H, J, K, L and M, respectively

• Maximum DC Current
• maximum level of direct current that can pass through the inductor without any
damage.
• Maximum DC Resistance:
• maximum resistance offered by the coil of the inductor with DC current or the
unwanted resistance of the inductor.
• Quality Factor (Q Factor)
• ratio of inductive reactance to the effective resistance
• higher the quality factor, the more energy-efficient is the inductor.

• Self Resonant Frequency (SFR)
• Due to turns of wire in inductor coil, there is always some distributed capacitance
in inductors.
• At a certain frequency, the capacitance and inductance of an inductor become
equal, and they cancel each other.
• At this frequency, the inductor does not show any effect of inductance
• At SFR, the quality factor of the inductor drops to zero
• Frequency range
• Range of frequency over which the inductor can be used
• Loss factor
• Reciprocal of Q factor

Capacitor vs inductor:
Sl.
No
Capacitor Inductor
1 Blocks Direct current (DC) Blocks Alternating current (AC)
2 Passes Alternating current (AC) Passes Direct current (DC)
3 Voltage in capacitor can’t change
instantly
Current in inductor can’t change
instantly
4 Quick voltage changes produces large
current
Quick current changes produces large
voltage
5 Stores energy in electric field Stores energy in magnetic field
6 Current leads voltage Voltage leads current
7 Energy stored in capacitor is ½ CV2 Energy stored in inductor is ½ LI2

Transformer:
• Static electrical machine
• transforms electrical power from one circuit to another circuit
• without changing the frequency

Transformer – working principle:
• Mutual induction
• Consists of two coils that are electrically separated and magnetically
coupled.
• Primary and secondary coils are wound on the magnetic core.

• An alternating voltage (Vp) applied to the primary creates an alternating
current (Ip) through the primary
• This current produces an alternating magnetic flux in the magnetic core
• This alternating magnetic flux induces a voltage in each turn of the
primary (due to self inductance) and in each turn of the secondary (due
to mutual inductance)

• 𝑉𝑠/𝑉𝑝 = 𝑁𝑠/𝑁𝑝
• 𝑁𝑠/𝑁𝑝 – turns ratio of the transformer
• If 𝑁𝑠/𝑁𝑝 >1, voltage induced in secondary winding is more than
primary winding – step up transformer
• If 𝑁𝑠/𝑁𝑝 <1, voltage induced in the secondary winding is less than
primary winding – step down transformer.
• I𝑠/I𝑝 = 𝑁p/𝑁s

• The total voltage induced into the secondary winding of a transformer is
determined mainly by
• the ratio of the number of turns in the primary to the number of turns in the
secondary, and
• by the amount of voltage applied to the primary
• No electrical connection b/w primary and secondary. It provides a
means of isolating one electrical circuit from another

Classification of Materials

Classification of Materials:
• Based on electrical conductivity:
• Conductors
• Conduction in metals is only due to the electrons
• has overlapping valence and conduction bands.
• valence band is only partially filled and the conduction band partially empty.
• Semiconductors
• has a resistivity value in between that of a conductor and an insulator
• conductivity of a semiconductor material can be varied under an external electric field.
• Band gap is of the order of 1eV.
• Insulators
• having extremely poor electrical conductivity
• forbidden energy gap is large, e.g.: 6eV for diamond.
• The number of free electrons in an insulator is very small, roughly about 107 electrons /m3

Classification of Materials:

Classification of Semiconductors:
• Intrinsic semiconductors:
• semiconductors in their purest form
• An example would be a semiconductor crystal with only silicon atoms.
• even at room temperature, some of the valence electrons may acquire sufficient
energy to enter the conduction band to form free electrons.
• Extrinsic semiconductor:
• semiconductors with other atoms mixed in.
• These other atoms are called impurity atoms.
• The process of adding impurity atoms is called doping.
• Doping alters the characteristics of the semiconductor, mainly its conductivity.

Atomic Structure:
• atomic number of silicon is 14,
• meaning that there are 14 protons in its nucleus, balanced by 14 orbiting
electrons.
• The outermost ring of an atom is called the valence ring,
• the electrons in this ring are called valence electrons.
• All semiconductors have four valence electrons.
• The number of valence electrons possessed by any atom determines its
electrical conductivity.

Forming a Crystal:
• When silicon atoms are grouped together, each silicon atom shares its
four valence electrons with other nearby atoms.
• forming a solid crystalline structure.
• This sharing of valence electrons is called covalent bonding.
• The covalent bonds between each silicon atom produce the solid
crystalline structure.

Forming a Crystal:

Electron – hole pair generation:
• All valence electrons of a silicon crystal at absolute zero (-273oC or 0 K)
remain locked in their respective covalent bonds.
• Above absolute zero, however, some valence electrons may gain enough
energy from heat, radiation, or other sources to escape from their parent
atoms.
• When an electron leaves its covalent bond, it becomes a free electron that
can move freely in the material.
• This free electron also produces a vacancy or hole in the covalent bond
structure that it left.
• Hence due to thermal energy, an electron – hole pair is generated.
• Increase in temperature creates more such pairs.

Electron – hole pair generation:

Doping:
• Due to the poor conduction at room temperature the intrinsic
semiconductor as such, is not useful in the electronic devices.
• Doping is a process that involves adding impurity atoms to an intrinsic
semiconductor.
• doped with impurity atoms to increase their conductivity.
• Forms an extrinsic semiconductor.
• Two types:
• N-type
• P-type

N-type semiconductor:
• A pentavalent atom is one that has five valence electrons.
• examples are antimony (Sb), arsenic (As), and phosphorous (P).
• A silicon crystal doped with a large number of pentavalent impurity
atoms results in many free electrons in the material.
• because there is one electron at the location of each pentavalent atom
that is not used in the covalent bond structure.
• Adding of further pentavalent impurities increase the number of free
electrons.
• Since the electron is the basic particle of negative charge, we call this an
n-type semiconductor material.
• But net charge will remain neutral.

N-type semiconductor:
• As there are more free electrons than holes in an n-type semiconductor
material,
• the electrons are called the majority current carriers
• the holes are called the minority current carriers.

P-type semiconductor:
• A trivalent atom is one that has only three valence electrons.
• examples are aluminum (Al), boron (B), and gallium (Ga).
• A silicon crystal doped with a large number of trivalent impurity atoms
results in many holes.
• Adding of further trivalent impurities increase the number of holes.
• Since a hole exhibits a positive charge, we call this a p-type
semiconductor material.
• The net charge of the p-type material is still neutral

P-type semiconductor:
• As there are more free holes than electrons in a p-type semiconductor
material,
• the holes are called the majority current carriers
• the electrons are called the minority current carriers.

P-N junction diode

Formation of P-N junction:

Formation of P-N junction :
• free electrons on the n side migrate or diffuse across the junction to the
p side.
• Once on the p side, the free electrons are minority current carriers.
• The lifetime of these free electrons is short, however, because they fall
into holes shortly after crossing over to the p side.
• When a free electron leaves the n side and falls into a hole on the p side,
two ions are created: a positive ion on the n side and a negative ion on
the p side.
• As the process of diffusion continues, a barrier potential, VB, is created
• the diffusion of electrons from the n side to the p side stops

Depletion region:
• Electrons diffusing from the n side sense a large negative potential on the
p side that repels them back to the n side.
• Likewise, holes from the p side are repelled back to the p side by the
positive potential on the n side.
• The area where the positive and negative ions are located is called the
depletion zone.
• names commonly used are depletion region and depletion layer.
• The word depletion is used because the area has been depleted of all
charge carriers.
• The positive and negative ions in the depletion zone are fi xed in the
crystalline structure and are therefore unable to move.

Barrier Potential, VB:
• Ions create a potential difference at the p-n junction.
• This potential difference is called the barrier potential and is usually
designated VB.
• For silicon, the barrier potential at the p-n junction is approximately 0.7
V.
• For germanium, VB is about 0.3 V.
• The barrier potential stops the diffusion of current carriers.

PN junction diode:
• A popular semiconductor device called a diode is made by joining p- and
n-type semiconductor materials
• the doped regions meet to form a p-n junction.
• Diodes are unidirectional devices that allow current to flow through
them in only one direction.
• side of the diode is called the anode (A), whereas the n side of the diode
is called the cathode (K).

Forward biasing:
• bias is defined as a control voltage or current.
• Forward-biasing a diode allows current to flow easily through the diode.
• the n material is connected to the negative terminal of the voltage
source, V
• the p material is connected to the positive terminal of the voltage source,
V.
• The voltage source, V, must be large enough to overcome the internal
barrier potential VB.
• if the p-n junction is made from silicon, the external voltage source must
be 0.7 V or more to neutralize the effect of the internal barrier potential,
VB, and in turn produce current flow.

Forward biasing:
• The arrow on the diode symbol points in the direction of conventional
current flow.
• electrons flow to the n side, against the arrow on the diode symbol.

Reverse biasing:
• the negative terminal of the voltage source, V, is connected to the p-type
semiconductor material.
• that the positive terminal of the voltage source, V, is connected to the n-
type semiconductor material.
• The effect is that charge carriers in both sections are pulled away from
the junction.
• Free electrons on the n side are attracted away from the junction because
of the attraction of the positive terminal of the voltage source, V.
• Even a reverse-biased diode conducts a small amount of current, called
leakage current.
• The leakage current is mainly due to the minority current carriers in both
sections of the diode.

Reverse biasing:
• Barrier width further increases.
• Any increase in the temperature of the diode increases the leakage
current in the diode.

V–I characteristics of Si and Ge diode:

Reverse breakdown:
• When the reverse voltage reaches breakdown voltage in a normal PN
junction diode,
• the current through the junction will be high and
• the power dissipated at the junction will be high.
• Such an operation is destructive, and the diode gets damaged.
• Whereas diodes can be designed with adequate power dissipation
capabilities to operate in the breakdown region.
• One such diode is known as the Zener diode.
• The Zener diode is heavily doped than the ordinary diode.

Reverse breakdown:
• operation of the Zener diode is same as that of an ordinary PN diode
under forward-biased condition.
• under reverse-biased condition, breakdown of the junction occurs.
• The breakdown voltage depends upon the amount of doping.
• If the diode is heavily doped,
• the depletion layer will be thin and,
• consequently, breakdown occurs at lower reverse voltage and
• further the breakdown voltage is sharp.
• Whereas a lightly doped diode has a higher breakdown voltage.
• Thus, breakdown voltage can be selected with the amount of doping.

Types of Breakdown:
• Avalanche breakdown
• Zener breakdown

Zener Breakdown:
• When the P- and N-regions are heavily doped,
• direct rupture of covalent bonds takes place
• because of the strong electric fields, at the junction of the PN diode.
• The new electron-hole pairs so created increase the reverse current in a
reverse-biased PN diode.
• The increase in current takes place at a constant value of reverse bias
typically below 6 V for heavily doped diodes.
• As a result of heavy doping of P- and N-regions, the depletion-region
width becomes very small.

Zener Breakdown:
• for an applied voltage of 6 V or less,
• the field across the depletion region becomes very high, of the order of 107
V/m,
• making conditions suitable for Zener breakdown.
• For lightly doped diodes, Zener breakdown voltage becomes high and
breakdown is then predominantly by avalanche multiplication.

Avalanche Breakdown:
• As the applied reverse bias increases, the field across the junction
increases correspondingly.
• Thermally generated carriers, while traversing the junction, acquire a
large amount of kinetic energy from this field.
• As a result, the velocity of these carriers increases.
• These electrons disrupt covalent bond by colliding with immobile ions
and create new electron-hole pairs.
• These new carriers again acquire sufficient energy from the field and
collide with other immobile ions thereby generating further electron-hole
pairs.

Avalanche Breakdown:
• This process is cumulative in nature and results in generation of
avalanche of charge carriers within a short time.
• This mechanism of carrier generation is known as avalanche
multiplication.
• This process results in flow of large amount of current at the same value
of reverse bias.

Zener vs Avalanche Breakdown:

Zener Diode:
• Though zener breakdown occurs for lower breakdown voltage and
avalanche breakdown occurs for higher breakdown voltage, such diodes
are normally called Zener diodes.
• under the reverse-bias condition, the voltage across the diode remains
almost constant although the current through the diode increases
• the voltage across the Zener diode serves as a reference voltage.
• Hence, the diode can be used as a voltage regulator.

Zener Diode:

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