UNIT III ANALOG ELECTRONICS (BASIC ELECTRONICS)

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Dr NSR/AP/ECE/PSNACET/BEEE/R2022/AU

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semiconductor
 semiconductor, any of a class of crystalline solids
intermediate in electrical conductivity between
a conductor and an insulator.
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Semiconductor materials
 silicon.
 germanium

Difference between Conductor,
Semiconductor and Insulator
Parameter Conductor Semiconductor Insulator
Definition A material that
allows electric
current to pass
through it very
easily.
A material that has
conductivity in
between
conductors and
insulators.
Materials that do
not allow the
electric current to
pass through them.
Forbidden Energy
Gap
No energy gap i.e.
the conduction
band overlap the
valance band.
Small energy gap
(approx. 1 eV).
Very large energy
gap (approx. 15
eV).

Conductivity High Conductivity
(of the order of
10
-7
mho/m).
Intermediate
conductivity
(ranging from
10
-7
mho/m to
10
13
mho/m).
Very low
conductivity(of the
order of
10
-13
mho/m).
Conduction Due to free
electrons.
Due to movement
of both electrons
and holes (positive
charge carriers).
No conduction.
Valance Electrons
in Outermost Shell
Less than 4 4 More than 4

Application In the
manufacturing of
conducting wires
and cables.
In the
manufacturing of
solid state
electronic devices
like ICs, diodes,
transistors etc.
Used for providing
insulation
electrical and
electronic devices,
for preventing
electric shock etc.

PN JUNCTION DIODE CHARACTERISTICS
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APPLICATION OF PN JUNCTION DIODE
 Switches
 Rectifiers
 Power supplies
 Clippers and clampers
 Digital systems
 Communication systems
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ZENER DIODE CHARACTERISTICS AND
APPLICATIONS
 A Zener diode is a
silicon semiconductor
device that permits
current to flow in
either a forward or
reverse direction.
 The diode consists of a
special, heavily doped
p-n junction,
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ZENER DIODE CHARACTERISTICS AND
APPLICATIONS
When reverse-
biased voltage is
applied to a Zener
diode, it allows
only a small
amount of leakage
current until the
voltage is less
than Zener
voltage.
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ZENER DIODE APPLICATIONS
 Zener diode as a voltage regulator:
 Zener diode in over-voltage protection:
 Zener diode in clipping circuits:
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Types of rectifiers

BIPOLAR TRANSISTOR - BIASING
What is a Bipolar Junction Transistor (BJT)?
 A bipolar junction transistor is a three-terminal
semiconductor device that consists of two p-n
junctions which are able to amplify or magnify a
signal.
 It is a current controlled device.
 The three terminals of the BJT are the base, the
collector, and the emitter.
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BIPOLAR JUNCTION TRANSISTOR
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CONSTRUCTION OF BIPOLAR JUNCTION
TRANSISTOR
 BJT is a semiconductor device
 BJT constructed with 3 doped semiconductor
Regions i.e. Base, Collector & Emitter separated
by 2 p-n Junctions.
 Bipolar transistors are manufactured in two
types, PNP and NPN
 They have a wide application in electronic devices
like mobile phones, televisions, radio
transmitters, and industrial control.
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BJT TYPES
PNP STRUCTURE AND SYMBOL NPN STRUCTURE AND SYMBOL
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What are the applications of BJT?
 It is used as an amplifier
 It is used as an oscillator
 It is used as a demodulator
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BIASING
 Biasing is the process of providing DC voltage
which helps in the functioning of the circuit.
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BIASING
What happens if the transistor is not biased
properly?
 The work efficiency of the transistor reduces
 There will be a distortion in the output signal
 The operating point may shift
 Transistor parameters will change
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TYPES OF BJT BIASING
 Fixed Base Biasing a Transistor
 Collector Feedback Biasing a Transistor
 Transistor Biasing with Emitter Feedback
 Voltage Divider Transistor Biasing
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Fixed Base Biasing a Transistor
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Collector Feedback Biasing a Transistor
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Transistor Biasing with Emitter Feedback
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Voltage Divider Transistor Biasing
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JFET TYPES IV CHARACTERISTICS AND
APPLICATIONS
 JFET or Junction Field Effect Transistor is a unipolar
voltage-controlled semiconductor device with three
terminals: source, drain, and gate.
 JFETs are commonly used as switches and amplifiers.
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JFET TYPES

JFET CONSTRUCTION
 JFET is one of the simplest types of field-effect
transistor.
 JFETs are voltage-controlled devices.
 JFET, the current flow is due to the majority of
charge carriers.
 BJTs, the current flow is due to both minority and
majority charge carriers.
 JFETs are unidirectional.

JFET Operation
 JFET by comparing it to a garden hose pipe.
 Water flows smoothly through a garden hose pipe if
there is no obstruction, but if we squeeze the pipe
slightly, the water flow slows down.
 This is precisely how a JFET works. Here the hose is
analogous to JFET, and the water flow is equivalent to a
current.

JFET Operation

JFET ADVANTAGES
 JFET has a high impedance
 JFETs are low power consumption devices
 JFET can be fabricated in a smaller size, and as a result,
they occupy less space in circuits due to their smaller
size.

JFET CHARACTERISTICS
 Fast switching.
 For low frequency operation, source and drain can be
interchanged.
 Gate voltage that controls drain current.
 Single majority carrier.
 Small in size.
 High “Z” input.

JFET APPLICATIONS
 Switch
 Chopper
 Buffer
 Oscillatory circuits
 Cascade amplifiers

SCR CHARCTERISTICS AND APPLICATIONS
 The Silicon Controlled Rectifier (SCR) is the most
important and mostly used member of the thyristor
family.
 Like a diode, SCR is a unidirectional device that
allows the current in one direction and opposes in
another direction.

SCR STRUCTURE AND SYMBOL

SCR CONSTRUCTION
The SCR is a four layer and three terminal device. The four layers made
of P and N layers, are arranged alternately such that they form three
junctions J1, J2 and J3.

Working or Modes of Operation of SCR
 Forward blocking Mode
 Forward Conduction Mode and
 Reverse Blocking Mode

CHARACTERISTICS OF SCR

SCR APPLICATIONS
 SCR can be used for different applications like
rectification,
 regulation of power
 inversion,

MOSFET CHARCTERISTICS AND
APPLICATIONS
 What is a MOSFET?
 Metal Oxide Silicon Field Effect Transistors commonly known as
MOSFETs are electronic devices used to switch or amplify
voltages in circuits.
 It is a current controlled device and is constructed by three
terminals.
 The terminals of MOSFET are named as follows:
 Source
 Gate
 Drain
 Body

 The p-type semiconductor forms the base of the MOSFET.
 The two types of the base are highly doped with an n-type
impurity which is marked as n+ in the diagram.
 From the heavily doped regions of the base, the terminals
source and drain originate.
 The layer of the substrate is coated with a layer of silicon
dioxide for insulation.
 A thin insulated metallic plate is kept on top of the silicon
dioxide and it acts as a capacitor.
 The gate terminal is brought out from the thin metallic
plate.

MOSFET applications
 Radiofrequency applications use MOSFET amplifiers
extensively.
 MOSFET behaves as a passive circuit element.
 Power MOSFETs can be used to regulate DC motors.
 MOSFETs are used in the design of the chopper
circuit.

Advantages of MOSFET
 MOSFETs operate at greater efficiency at lower
voltages.
 Absence of gate current results in high input
impedance producing high switching speed.
 Disadvantages of MOSFET
 MOSFETs are vulnerable to damage by electrostatic
charges due to the thin oxide layer.
 Overload voltages make MOSFETs unstable.

UNIT III ANALOG ELECTRONICS (BASIC ELECTRONICS)

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UNIT III ANALOG ELECTRONICS (BASIC ELECTRONICS)