Solid state Electronics

1. Lecture by ASIT MEHER
MECHATRONICS
Unit 2

2. Syllabus to be covered….
 Solid state electronic devices
 PN junction diode
 Bipolar Junction Transistors (BJT)
 Field Effect Transistors (FET)
 Diode AC switch (DIAC) and Triode AC switch
(TRIAC)
 Light emitting Diode(LED)
 Analog signal conditioning and Operational amplifiers
 noise reduction and filtering
12/24/20192

3. What is a DAC?
A digital to analog converter (DAC) is a device that
converts digital numbers (binary) into an analog voltage
or current output.
 Either multiplying or non-multiplying
 Non-multiplying contains its own reference
 Multiplying takes external reference.
12/24/20193

4.  Audio/Video
 MP3 players
 Cell phones
 Television
 (well, old ones)
 Signal Generators
 Sine wave generation
 Square wave generation
 Triangle wave generation
 Random noise generation
 Motor, valve, actuator
 Rarely; usually PWM.
Applications.
Kevin Johnson
12/24/20194

5. Solid-State Electronics
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 Modern electronics devices are constructed from a
special class of materials called as semiconductors.
 Semiconductor devices are the most commonly used
active components in mechatronics system buildings
because of their excellent characteristics.
 There are many semiconductor based solid state
switches such as diodes, thyristors, transistors and
integrated-circuit.
 Semiconductors are not good conductor of electrical
current or not an insulator.
 Silicon and germanium is mainly available
semiconductor material.

6. Semiconductor Crystalline
Structure
 Silicon atoms have 4
electrons in outer shell
 inner electrons are very
closely bound to atom
 These electrons are shared
with neighbor atoms on both
sides to “fill” the shell
 resulting structure is very
stable
 electrons are fairly tightly
bound
 no “loose” electrons
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7. Conduction in Crystal Lattices
 Semiconductors (Si and Ge) have 4 electrons in
their outer shell
 2 in the s subshell
 2 in the p subshell
 As the distance between atoms decreases the
discrete subshells spread out into bands
 As the distance decreases further, the bands
overlap and then separate
 the subshell model doesn’t hold anymore, and the
electrons can be thought of as being part of the
crystal, not part of the atom
 4 possible electrons in the lower band (valence
band)
 4 possible electrons in the upper band (conduction
band)
12/24/20197

8. Insulators, Semiconductors, and
Metals
 This separation of the valence and conduction
bands determines the electrical properties of the
material
 Insulators have a large energy gap
 electrons can’t jump from valence to conduction
bands
 no current flows
 Conductors (metals) have a very small (or
nonexistent) energy gap
 electrons easily jump to conduction bands due to
thermal excitation
 current flows easily
 Semiconductors have a moderate energy gap
 only a few electrons can jump to the conduction
band leaving “holes”
 only a little current can flow
12/24/20198

9. Insulators, Semiconductors, and
Metals (continued)
Conduction
Band
Valence
Band
Conductor Semiconductor Insulator
12/24/20199

10. Hole - Electron Pairs
 Sometimes thermal energy is enough to cause an
electron to jump from the valence band to the
conduction band
 produces a hole - electron pair
 Electrons also “fall” back out of the conduction band
into the valence band, combining with a hole
pair elimination
hole electron
pair creation
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11. Improving Conduction by Doping
 To make semiconductors better conductors, add
impurities (dopants) to contribute extra electrons or
extra holes
 elements with 5 outer electrons contribute an extra
electron to the lattice (donor dopant)
 elements with 3 outer electrons accept an electron
from the silicon (acceptor dopant)
12/24/201911 Donor Acceptor

12. What are P-type and N-type ?
 Semiconductors are classified in to P-type and N-type semiconductor
 P-type: A P-type material is one in which holes are majority carriers
i.e. they are positively charged materials (++++)
 N-type: A N-type material is one in which electrons are majority
charge carriers i.e. they are negatively charged materials (-----)
12/24/201912
N- type P- type

13. A bit of history
 Diodes were known as rectifiers until
1919, when a physicist by the name of
William Eccles coined the term diode,
which from its Greek roots means
“through-path.”
 In 1873 Fredrick Guthrie discovered
thermionic diodes (vacuum tube diodes)
. Heating the cathode in forward bias
permitted electrons to be transmitted
into the vacuum, but in reverse bias the
electrons were not easily release from
the unheated anode.
13 12/24/2019

14. Diodes
Electronic devices created by bringing together a
p-type and n-type region within the same
semiconductor lattice. Used for rectifiers, LED
etc
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15. Diodes
It is represented by the following symbol, where
the arrow indicates the direction of positive
current flow.
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16. Forward Bias and Reverse Bias
 Forward Bias : Connect positive of the Diode to
positive of supply…negative of Diode to negative
of supply
 Reverse Bias: Connect positive of the Diode to
negative of supply…negative of diode to positive
of supply.
12/24/201916

17. Characteristics of Diode
 Diode always conducts in one direction.
 Diodes always conduct current when “Forward
Biased” ( Zero resistance)
 Diodes do not conduct current when Reverse
Biased
(Infinite resistance)
12/24/201917

18. P-N Junction Diode
 A P-N junction diode consists of a p-
type semiconductor (silicon) joined
with an n-type semiconductor.
 P-type – A semiconductor doped with
impurities to create positive charge
carriers (holes).
 N-type – A semiconductor doped with
impurities to create negative charged
carriers.
 A depletion region is created when
negative charge carriers from the N-
type region diffuse into the P-type
region, and vice versa.18
np
Depletion Region
Majority carriers
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19. np
Reverse Biased
Depletion Region
ir
V
P-N Junction Diode
 Under reverse bias the depletion
region is greatly increased in size
and requires significantly more
energy from the majority carriers in
order to cross.
 Most majority carriers won’t be
able to cross the depletion region
and thus are unable to induce a
current.
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20. Transistor
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21. 12/24/201921
 The term transistor stands for transfer resistor.
 Transistors are used primarily as amplifying
devices that can transfer current from a low-
resistance circuit to high-resistance circuit.
BI-POLAR JUNCTION TRANSISTOR(BJT)
• One major type of transistor is the bipolar
transistor, a three-terminal component that consists
of two PN diodes connected together with one
common section.
• Three terminals are called the emitter, the collector
and the base.
• The emitter and the collector are made up of same
semiconductor material, while the base is made up
of another semiconductor material.

22. Transistors Configurations:
NPN
Transistor
PNP
Transistor
Sandwiching a
P-type layer
between two n-
type layers.
Sandwiching a
N-type layer
between two p-
type layers.
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23. 23
Bipolar Junction Transistors (BJT)
NPN PNP 12/24/2019
There are two junctions in the BJT. One is the interface at
which the emitter and the base are joined and is called as
base-emitter junction. The other one is the interface where
base and collector meet, known as collector-base junction.

24. How a “NPN” Transistor works?
Forwardbackward
The base-emitter diode
(forward) acts as a switch.
when v1>0.7 it lets the
electrons flow toward
collector. so we can control
our output current (Ic) with
the input current (Ib) by
using transistors.
C B E
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25. Transistor as a Switch
• Transistors can either
conduct or not conduct current.
• i.e., transistors can either be on or off.
Transistor Switch
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26. Common BJT Configuration
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 Common base configuration scheme (CB)- in this
emitter is input terminal, collector is the output and
base is common terminal.
 Common emitter configuration (CE)- here base is the
input terminal, collector is output terminal and emitter
is the common terminal.
 Common collector configuration (CC)- here base is
the input terminal, emitter is output terminal and the
collector is common terminal.

27. Applications of BJT
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 The BJT is used as an oscillator.
 It is used as an amplifier.
 It is used as a multivibrator.
 For wave shaping it is used in clipping circuits.
 Used as a detector or demodulator.
 It is also used as modulator.
 Used in timer and time delay circuits.
 It is used in electronics switch.
 It is used in switching circuits

28. Field Effect Transistor(FET)
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 An FET is a three terminal device such as BJT, but
operates by a different principles.
 Field-effect transistors are so named because a weak
electrical signal coming in through one electrode creates
an electrical field through the rest of the transistor.
 FETs are voltage controlled devices and are unipolar
because conduction in the FET is the result of only one
dominant charge carrier.
 The term (unipolar) refers to the fact that current is
transported by carriers of one polarity (majority),
whereas in the conventional bipolar transistor carriers of
both polarities (majority and minority) are involved.
 The three terminals are called the source, the drain and
the gate.
 The voltage applied to the gate is controls the current
flowing in the source-drain channel.

29. 12/24/201929
 There are two types of FET:
a) Junction field-effect transistor(JFET)
b) Metal oxide semiconductor field-effect
transistor(MOSFET)
JFE
T
MOSFET

30. When the gate is negative ,it repels
the electron in the N-channel. So
there is no way for electrons to flow
from source to drain.
When the negative voltage is
removed from Gate ,the electrons
can flow freely from source to
drain .so the transistor is on.
How a JFET transistor works?
12/24/201930

31. 12/24/201931
JFET:-
• There are two types of JFETs based on semiconductor used, N-
channel and P-channel.
• In the JFET, the gate-channel contact is a reversed-biased PN
junction. The gate-channel junction of the JFET must always be
reversed-biased otherwise it may behave as a diode.
N-Channel P-Channel
• The difference is the arrow head on the gate lead. The arrow head
points inward on the N-channel and points outward on the P-
channel. The operation of both is identical with the exception that
polarities of the voltages are reversed.
• N-channel JFET is normally used with positive voltage supply, while
P-channel JFET is used with negative voltage supply.

32. Junction FETs
 JFET is a high-input resistance device, while the BJT
is comparatively low.
 If the channel is doped with a donor impurity, n-type
material is formed and the channel current will consist
of electrons.
 If the channel is doped with an acceptor impurity, p-
type material will be formed and the channel current
will consist of holes.
 N-channel devices have greater conductivity than p-
channel types, since electrons have higher mobility
than do holes; thus n-channel JFETs are
approximately twice as efficient conductors compared
to their p-channel counterparts.
12/24/201932

33. N-channel JFET
 This transistor is made by
forming a channel of N-type
material in a P-type
substrate.
 Three wires are then
connected to the device.
 One at each end of the
channel.
 One connected to the
substrate.
 In a sense, the device is a
bit like a PN-junction diode,
except that there are two
wires connected to the N-
type side.
12/24/2019 33

34. 12/24/201934
JFET has the following features in a relation to tripolar
transistor. The specific features are:
 Very high input impedance
 Less operational variation with respect to
temperature.
 Noise problem in communication is minimal.
 Operating frequency bandwidth is small.

35. When the Gate is positive voltage ,it allows electrons to
flow from drain to source .In this case transistor is on.
In MOSFET, the Gate is insulated from p-channel or n-
channel. This prevents gate current from flowing, reducing
power usage.
How a MOSFET Transistor works?
12/24/201935
The insulator is typically made of an oxide ( silicon
dioxide, SiO2). The substrate is often connected to the
source internally.

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TERMS BJT JFET MOSFET
Device type
Current
controlled
Voltage
controlled
Voltage
Controlled
Current flow Bipolar Unipolar Unipolar
Terminals
Not
interchangeable Interchangeable Interchangeable
Operational
modes
No modes Depletion mode
only
Both
Enhancement
and Depletion
modes
Input impedance Low High Very high
Output
resistance
Moderate Moderate Low
Operational
speed
Low Moderate High
Noise High Low Low
Thermal stability Low Better High
Comparison between BJT,JFET and MOSFET
Now that we have discussed all the above three, let us try to compare some of their
properties.

37. THYRISTORS
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What are Thyristors?
• The Thyristor is a unidirectional device, that is it
will only conduct current in one direction only, but
unlike a diode, the thyristor can be made to
operate as either an open-circuit switch or as a
rectifying diode depending upon how
the thyristors gate is triggered.
• Wide range of devices, SCR (silicon controlled
rectifier), SCS (silicon controlled switch), Diacs,
Triacs, and Shockley diodes
• Used in high power switching applications
i.e. hundreds of amps / thousands of watts

38. 12/24/201938
 For switching very large current and voltages, a
power electronic device known as thyristor or silicon
controlled rectifier(SCR).
 When a small current flows into the gate(G), a
larger current is allowed to flow from the anode(A)
to the cathode (C).
 Even when the current into the gate stops, the
thyristor continues to allow current to flow from
anode to cathode.

39. Diode AC Switch(DIAC)
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39
 A DIAC is a four layered device whose top and bottom layer contain
both N- and P- type materials.
 The DIAC is a combination of two diodes. Diodes being unidirectional
devices, conduct current only in one direction.
 The construction and symbol of DIAC is shown in figure:

40. 12/24/201940
Main terminal(MT), can serve as either anode or cathode, according
to the polarity of the applied voltage.
Note that MT1 is positive w.r.t. MT2 during positive half cycle,
whereas in the negative half-cycle, MT2 is positive w.r.t. MT1.

41. Physical Operation and
Characteristics:
 The main characteristics are of the DIAC are as
follows:
(i) Break over voltage
(ii) Voltage symmetry
(iii) Break-back voltage
(iv) Break over current
(v) Lower power dissipation
 Although most DIACs have symmetric switching
voltages, asymmetric DIACs are also available. Typical
DIACs have a power dissipations ranging from 1/2 to 1
watt. 12/24/201941

42. Applications of DIAC
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 It can be used mainly in the TRIAC triggering circuit.
The DIAC is connected in the gate terminal of the
TRIAC. When the voltage across the gate decreases
below a predetermined value, the gate voltage will
be zero and hence the TRIAC will be turned off. The
main applications are-
 It can be used in the lamp dimmer circuit.
 It is used in the heat control circuit.
 It is used in the speed control of a universal motor.
 It is used with TRIAC in series combination for
triggering. The gate of TRIAC is connected with a
terminal of the DIAC. When applied voltage across
DIAC increases above the avalanche breakdown,
then only it can conduct. However, when the voltage
across DIAC decreases below its avalanche
breakdown voltage it will be turned off and hence the
TRIAC will also remain in the off state.

43. Triode AC Switch(TRIAC)
12/24/201943
 TRIAC is a bidirectional device that can used to give a controlled
AC output and is essentially a two-way SCR with one gate.
 If two SCRs are joined in back-to-back parallel fashion, we have a
new device known as the TRIAC.
 The TRIAC construction and symbol are shown in figure below:-

44. What are TRIAC
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 A TRIAC (TRIode for Alternating Current) is a 3-terminal AC
semiconductor switch.
 Composed of 2 thyristors facing opposite directions such that it
can conduct current in either direction.
 MT1 and MT2 are current carrying terminals while the Gate
terminal is used for triggering by applying a small voltage signal.
 Once triggered, it continues to conduct current until the current
falls below a threshold value.

45. 12/24/201945

46. TRIAC Operation
•5 layer device
•Region between MT1 and MT2 are parallel switches (PNPN and
NPNP)
•Allows for positive or negative gate triggering
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47. TRIAC Applications
TRIACs usually used in simple, low-power
applications like household dimmer switches.
High Power TRIACS
• Switching for AC circuits, allowing the control of very large power
flows with miliampere-scale control currents
• Can eliminate mechanical wear in a relay.
Low Power TRIACS
• Light bulb dimmers (done by applying power later in the AC cycle
aka PWM of AC wave)
• Motor speed controls for electric fans and other AC motors, and
heaters
• Modern computerized control circuits in household appliances47 12/24/2019

48. Advantages of the TRIAC:
 The TRIAC has the following advantages:
(i) They can be triggered with positive- or negative-
polarity voltage.
(ii) They need a single heat sink of slightly larger
size.
(iii) They need a single fuse for protection, which
simplifies their construction.
(iv) In some dc applications, the SCR has to be
connected with a parallel diode for protection against
reverse voltage, whereas a TRIAC may work without
a diode, as safe breakdown in either direction is
possible. 12/24/201948

49.  The TRIAC has the following disadvantages:
(i) TRIACs have low dv/dt ratings compared to
SCRs.
(ii) Since TRIACs can be triggered in either
direction, the trigger circuits with TRIACs needs
careful consideration.
(iii) Reliability of TRIACs is less than that of SCRs.
Disadvantages of the TRIAC:
12/24/201949

50. Light Bulbs Vs LEDs
Light Bulbs
Filament
 Sudden Failure-
Breaks/Burns down
Recent bulbs last up to
two years at ~20
lumens/watt
Fluorescent tubes last
about 7500 hrs at ~80
lumens/watt
LED’s
No filament
 Gradual Failure-Intensity
decrease over time
Last from 50,000 to
100,000 hrs (5-10 yrs)
Recent LED’s
(orange,red) have
efficiency of ~100
lumens/watt
 Generate little heat
 Reduced A/C costs 12/24/201950

51. Light Emitting Diodes (LEDs)
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• When current flows through a forward-biased PN
junction, free electron cross the N-side and recombine
with holes on the P-side.
• If the free electron in the conduction band recombines
with a hole in valence band, then it releases energy as it
falls into that lower energy state.
• The energy is released in the form of heat and light.

52. 12/24/201952
 The phenomenon of conversion of electrical energy
to light energy is called electroluminescence.
 A PN junction device which emits light when
forward-biased is called LED and is an example of
the phenomenon electroluminescence.

53. How to Connect a LED:
 Requires 1.5~2.5V and 10 mA
 To prevent overloading, use resistor 470 Ω
12/24/201953

54. The Advantage of LED Lighting
Long life – lifetimes can exceed 100,000 hours as compared to
1,000 hrs for tungsten bulbs.
Robustness – no moving parts, no glass, no filaments.
Size – typical package is only 5 mm in diameter.
Energy efficiency – 50- 90% less energy used
translates into smaller power supply.
Non-toxicity – no mercury.
Versatility – available in a variety of colors; can be pulsed.
Cool – less heat radiation than HID or incandescent
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55. Applications
 It is used in optical switching application.
 It is used in burglar alarm system.
 It is used for indicating power ON/OFF conditions, power
level indicators or stereo amplifiers.
 It is used in image sensing circuits in videophones.
 It is used in optical communication system.
 It is used for checking the linearity, speed etc. of opto-
electronic detection circuits.
 It is used in motorcycle and bicycle lights.
 It is used in traffic lights and signals.
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A signal conditioner performs operations on signals to
convert them to a form suitable for the use of another
component.

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 The operations performed by a signal conditioner:-
a) Isolation and Impedance conversion:
The purpose of isolation and impedance conversion is to avoid or
minimize the destruction of the signal measured and to protect
the measuring instruments.
b) Noise reduction and Filtering
c) Amplification:
The small voltage produced by sensors needs to be amplified and
converted into an electrical signal suitable for use by application
devices.
d) Linearization and signal conversion:
Many primary elements produce nonlinear outputs and the signal
must be linearized to produce a nearly ideal calibration. The most
common approach is to provide the nonlinear signal input to a
computer to perform the linearization using a computer algorithm.
Sometimes it is necessary to convert the signal from a voltage to a
current or vice versa. Simple operational amplifier converter
circuits can be used for this purpose.

60. Amplifiers
• Differential Amplifier
– Amplifies difference
between inputs
Single-ended Amplifier
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61. Operational Amplifier (Op-amp)
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 An op-amp is an electronic device that behaves like a
voltage-controlled source.
 It is a high gain differential amplifier ( range of 10^5 to
10^6)
 Op-amps are among the most widely used electronic
components today, and are used in a vast array of
consumer, industrial and scientific devices.
A circuit model of an operational
amplifier.

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Operational Amplifier Notation and Parameter
There are two inputs, the non inverting input(+) and the
inverting input(-).
 Output voltage Vo = A(V+ - V-)
 An ideal op-amp has infinite gain (A=∞), infinite input resistance (
Rin=∞) and zero output resistance.
The circuit symbol for an op-amp is shown,
where:
V+ : non-inverting input
V- : inverting input
Vout : output
Vs+ : positive power supply
Vs- : negative power supply
Gain, A = Vout/Vin where Vin = V+ - V-
Gain (dB), AdB = 20 log (Vout/Vin)

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64. Linear Op-amp Circuits
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1. Inverting Amplifier
The equation for output signal is derived as follows:
Considering the arbitrary current directions and applying Kirchhoff's
current law(KCL), we have
and

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66
2. Non-Inverting Amplifier
The non-inverting amplifier circuit can increase the size of the signal
and in some cases, leave it unchanged.
In this case, the input voltage Vi is applied directly at the non-inverting
input terminal.
Applying Ohm’s law, we have i1+i2 = 0, such that
A non-inverting amplifier is designed to provide a positive volt

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3. Summing Amplifier
A summing amplifier adds two or more input signals forming an output
that is inverse of the sum.
Applying KCL we have,
i= i1 + i2 +i3+……..+in
The equation for the output of the summing amplifier can be derived
as

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 4. Difference Amplifier
A difference amplifier precisely amplifies the difference of
two input signals. The circuit uses two pairs of matched
resistors R1and R2 , Rf and R3.
By taking Vx=Vy and applying voltage divider rule for Vy to
resistor R2 and R3,

69. 12/24/201969
 5. Differentiator
The differentiator generates an output signal proportional
to the rate of change of the input voltage.

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6. Integrator

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72. Noise Reduction & Filters
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 Special circuits called filters are used to reduce
noise in the signals.
 In typical applications the filters are used to remove
a certain band of frequencies from the signal and
allow other signals to transmit.
 The range of frequencies allowed to transmit is
known as pass band.
Active filters use active components such as
transistors and an op-amp including passive
elements.

73. 12/24/201973
Active filters are widely used due to their following
advantages:
 The loading effect is negligible.
 Low signal level can be amplified along with
filtering.
 They are available in a low cost and compact IC
form.
 They are free from electromagnetic interference.
However, passive filters can be used at very high
frequencies, do not require power supply and are
less expensive.

74. Types of Filters
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 Low pass filter
 High pass filter
 Band pass filter
 Band reject (notch) filter

75. 1.Low pass filter
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 A low pass filter allows all signals below certain
frequency to pass through. This frequency is
called cut-off or break-point frequency as shown
in figure.

76. 12/24/201976

77. 2. High Pass Filters
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 A high pass filter is just the opposite of the low pass
filter and allows all signal components above the
cut-off frequency to pass through, and prevents all
signals below the frequency.
 High pass filters do not make much sense in signal
condition due to noise interference.

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79. 3. Band Pass Filters
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 A band pass filter has two frequency values that are
separated by a frequency range called band width.
 All components of the signal that are outside the two
frequency values(ω1 and ω2) are reduced in amplitude.
 The radio turner is an adjustable band pass filter.

80. 12/24/201980

81. 4. Band Reject Filter(Notch
Filter)
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81
 A band reject filter is just the opposite of the band pass filter and used
to filter out narrow bands of noise components from the signal.
 It does not affect the components of signal on either side of frequency
values as shown in figure-
 A passive band reject filter is formed when the output RLC series
resonant circuit is taken off LC series combination and an active
circuit that could serve as a notch filter and its frequency response
are shown in figure:

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