18cs33_module_1.pptx

ANALOG AND DIGITAL
ELECTRONICS
18CS33
PROF. SURESH P
DEPARTMENT OF CSE, SVCE,
BENGALURU
1

Introduction
 Pre-requisite
 Basic Electrical Engineering (18ELE13/23)
 C programming For Problem Solving
(18CSP13/23)
 Basic Electronics (18ELN14/24)
2

Introduction
 Introduction to digital 1s and 0s
3

Introduction
 Outcome Assessment Questions
 What are the two numeric digits used to represent
states in a digital system?
 What are the two terms used to represent the two
logic levels?
 What is the abbreviation for binary digit?
4

Introduction
 Digital Signals
 The transition between the two states is called an
edge.
 At dawn, when the signal proceeds from HIGH to
LOW, it is considered a falling edge, or negative
edge.
5

Introduction
 Need for Timing Digital
 To show the relationship between changes at the
input and changes at the output in order to
demonstrate the operation of the system.
 This means the logic states must be observed
over time.
 Timing diagrams show the relationship, over time,
between many digital “signals.”
6

Introduction
 Analog and Digital Representations
 Analog representation a quantity is represented by a
continuously variable, proportional indicator.
 E.g.
 Speedometer
 Thermometers
 Digital representation the quantities are represented not
by continuously variable indicators but by symbols called
digits.
 E.g.
 Digital Speedometer
 Digital indoor/outdoor thermometer
 The major difference between analog and digital quantities,
then, can be simply stated as follows:
 Analog ≡ continuous
 Digital ≡ discrete (step by step)
7

Introduction
 Outcome Assessment Questions:
 Which of the following involve analog quantities and
which involve digital quantities?
 (a) Elevation using a ladder
 (b) Elevation using a ramp
 (c) Current flowing from an electrical outlet through a motor
 (d) Height of a child measured by a yard stick ruler
 (e) Height of a child measured by putting a mark on the wall
 (f) Amount of rocks in a bucket
 (g) Amount of sand in a bucket
 (h) Time of day using a sundial
 (j) Time of day using your cell phone
8

Introduction
 Digital and Analog systems
 A digital system is a combination of devices designed to
manipulate logical information or physical quantities that
are represented in digital form; that is, the quantities can
take on only discrete values.
 These devices are most often electronic, but they can
also be mechanical, magnetic, or pneumatic.
 An analog system contains devices that manipulate
physical quantities that are represented in analog form.
 In an analog system, the quantities can vary over a
continuous range of values.
 For example, the amplitude of the output signal to the
speaker in a radio receiver can have any value between
zero and its maximum limit.
9

Introduction
 Advantages of Digital Techniques
 Digital systems are generally easier to design
 Information storage is easy
 Accuracy and precision are easier to maintain throughout the
system
 Operations can be programmed
 Digital circuits are less affected by noise
 More digital circuitry can be fabricated on IC chips
10

Introduction
 Limitations of Digital Techniques
 The real world is analog and digitizing always introduces
some error. Processing digitized signals takes time.
 To take advantage of digital techniques when dealing with analog
inputs and outputs, four steps must be followed:
 1. Convert the physical variable to an electrical signal (analog).
 2. Convert the electrical (analog) signal into digital form.
 3. Process (operate on) the digital information.
 4. Convert the digital outputs back to real-world analog form.
11

Introduction
12
Diagram of a precision digital temperature control
system.

Introduction
13
 Digital Number Systems
 Decimal System
 The decimal system is composed of 10 numerals or
symbols. These 10 symbols are 0, 1, 2, 3, 4, 5, 6, 7, 8,
9. The decimal system, also called the base-10.
 Decimal position values as powers of 10.

Introduction
14
 Decimal Counting

Introduction
15
 Binary System
 Unfortunately, the decimal number system does not
lend itself to convenient implementation in digital
systems.
 For example, it is very difficult to design electronic
equipment so that it can work with 10 different voltage
levels (each one representing one decimal character, 0
through 9).
 On the other hand, it is very easy to design simple,
accurate electronic circuits that operate with only two
voltage levels.
 For this reason, almost every digital system uses the
binary (base-2) number system as the basic number
system of its operations

Introduction
16
 Binary System
 Binary position values as powers of 2.

Introduction
17
 Binary Counting

Introduction
18
 Parallel and Serial Transmission

Introduction
19
 Parallel and Serial Transmission
 Parallel transmission uses one connecting line
per bit, and all bits are transmitted
simultaneously;
 Serial transmission uses only one signal line,
and the individual bits are transmitted serially
(one at a time).

Introduction
20
 Memory
 Difference between non-memory and memory
circuits

Introduction
21
 Memory
 When an input signal is applied to most devices or
circuits, the output somehow changes in response to
the input, and when the input signal is removed, the
output returns to its original state. These circuits do
not exhibit the property of memory because their
outputs revert back to normal.
 Certain types of devices and circuits do have memory.
When an input is applied to such a circuit, the output
will change its state, but it will remain in the new state
even after the input is removed. This property of
retaining its response to a momentary input is called
memory.

Introduction
22
 Digital Computers

Introduction
23
 Digital Computers
 Major Parts of a Computer
 Input unit
 Output unit
 Memory unit
 Arithmetic/logic unit
 Control unit

SEMICONDUCTOR
DIODES, BJT BIASING,
OPERATIONAL
AMPLIFIER APPLICATION
CIRCUITS,
VOLTAGE REGULATOR,
D TO A AND A TO D
CONVERTER
Module-1
24

Referred Books/Sources
 Charles H Roth and Larry L Kinney, Analog
and Digital Electronics, Cengage Learning,
2019
 Robert L. Boylestad Louis Nashelsky :
Electronic Devices and Circuit Theory,
Eleventh Edition, 2013.
 Albert Malvino, David J. Bates : Electronic
principles, Eighth edition, 2016.
 Thomas L. Floyd: Electronic Devices, Ninth
Edition, Prentice Hall, 2012
25

Objectives
 OP-Amp
 Peak Detector Circuit, Active Filters, Non-Linear
Amplifier, Relaxation Oscillator Current-To-
Voltage Converter, Voltage-To-Current Converter.
 Multivibrator circuits configuration around
digital integrated circuits,
 Multivibrator circuits configured around timer IC
555.
26

Semiconductor diodes
28
 Photodiode
 Light Emitting Diode (LED)
 Phtocoupler

Photodiode
29
 The photodiode is a semiconductor p – n
junction device whose region of operation is
limited to the reverse-bias region.
 The reverse saturation current is normally limited
to a few microamperes.
 It is due solely to the thermally generated minority
carriers in the n - and p -type materials.
 The application of light to the junction will result in
a transfer of energy from the incident traveling
light waves (in the form of photons) to the atomic
structure, resulting in an increased number of
minority carriers and an increased level of reverse
current.

Photodiode
30
 Construction

Photodiode
31
 Construction
 The surface of a layer of N type is bombarded with P type silicon
ions to produce a P type layer about 1 µm (micrometre) thick.
 During the formation of the diode, electrons from the N type layer
are attracted into the P type material and holes from the P type are
attracted into the N type layer, resulting in the removal of free
charge carriers close to the PN junction, so creating a depletion
layer.
 The (light facing) top of the diode is protected by a layer of Silicon
Dioxide (SiO2) in which there is a window for light to shine on the
semiconductor.
 This window allow maximum absorption of light and an anode
connection of aluminium (Al) is provided to the P type layer.
 Beneath the N type layer is a more heavily doped N+ layer to
provide a low resistance connection to the cathode.

Photodiode
32
 Working Principle
Photodiode: basic biasing arrangement and construction, symbol and
Photodiode characteristics

Photodiode
33
 Recall that when reverse-biased, a rectifier diode has a very small
reverse leakage current.
 The same is true for a photodiode.
 The reverse-biased current is produced by thermally generated
electron-hole pairs in the depletion region, which are swept across
the pn-junction by the electric field created by the reverse voltage.
 In a rectifier diode, the reverse leakage current increases with
temperature due to an increase in the number of electron-hole
pairs.
 A photodiode differs from a rectifier diode in that when its pn
junction is exposed to light, the reverse current increases with the
light intensity.
 When there is no incident light, the reverse current, is almost
negligible and is called the dark current.
 An increase in the amount of light intensity, expressed as irradiance
(mW/cm2), produces an increase in the reverse current,

Photodiode
34
 Applications:
 Smoke Detector Circuit, Compact disc player, TV
Remote, Camera light meter, Street Light,

Light Emitting Diode (LED)
35
 The increasing use of digital displays in
calculators, watches, and all forms of
instrumentation has contributed to an extensive
interest in structures that emit light when properly
biased.
 The light-emitting diode is a diode that gives off
visible or invisible (infrared) light when energized.
 The energy converted during recombination at the
junction is dissipated in the form of heat within the
structure, and the emitted light.
 Diodes constructed of GaAs emit light in the
infrared (invisible) zone during the recombination
process at the p–n junction.

36
 The below table provides a list of common
compound semiconductors and the light they
generate.

37
 Construction
Process of electroluminescence in the LED, graphic symbol and Parts of an
LED

38
 Construction
 The external metallic conducting surface
connected to the p -type material is smaller to
permit the emergence of the maximum number
of photons of light energy when the device is
forward-biased. Note in the figure that the
recombination of the injected carriers due to
the forward-biased junction results in emitted
light at the site of the recombination.

39
 When the device is forward-biased, electrons cross the pn junction from the n-type material and
recombine with holes in the p-type material.
 These free electrons are in the conduction band and at a higher energy than the holes in the
valence band.
 The difference in energy between the electrons and the holes corresponds to the energy of visible
light.
 When recombination takes place, the recombining electrons release energy in the form of
photons.
 The emitted light tends to be monochromatic (one color) that depends on the band gap (and other
factors).
 A large exposed surface area on one layer of the semiconductive material permits the photons to
be emitted as visible light.
 This process, called electroluminescence,

40
• The forward voltage across an LED is considerably greater than for a silicon
diode.
• Typically, the maximum VD for LEDs is between 1.2 V and 3.2 V, depending
on the material.
• Reverse breakdown for an LED is much less than for a silicon rectifier diode
(3 V to 10 V is typical).
• The LED emits light in response to a sufficient forward current.
• The amount of power output translated into light is directly proportional to the
forward current.
• An increase in ID corresponds proportionally to an increase in light output.
• The light output (both intensity and color) is also dependent on temperature.

41
 Applications
 TV Remote, Calculator, Traffic Signals,
Watches and Automotive Head Lamps

Photocoupler (Optocoupler)
42
 Construction
 An optocoupler (also called an optoisolator) combines
an LED and a photodiode in a single package.
 Figure shows an optocoupler.
 It has an LED on the input side and a photodiode on
the output side.
 The left source voltage and the series resistor set up a
current through the LED.

43
 Then the light from the LED hits the photodiode,
and this sets up a reverse current in the output
circuit.
 This reverse current produces a voltage across
the output resistor.
 The output voltage then equals the output supply
voltage minus the voltage across the resistor.
 When the input voltage is varying, the amount of
light is fluctuating. This means that the output
voltage is varying in step with the input voltage.
This is why the combination of an LED and a
photodiode is called an optocoupler.

44
 Applications:
 Switches, SMPS, Signal Isolation, Modem
Communication

Introduction
46
 The term biasing is an all-inclusive term for
the application of dc voltages to establish a
fixed level of current and voltage.
 For transistor amplifiers the resulting dc
current and voltage establish an operating
point on the characteristics that define the
region that will be employed for amplification
of the applied signal.
 Because the operating point is a fixed point on
the characteristics, it is also called the
quiescent point (abbreviated Q -point).

Introduction
47
 Following important basic relationships for a
transistor:
 VBE = 0.7 V
 IE = (β + 1)IB ≈ IC
 IC = βIB
 Types of Biasing
 Base Bias or Fixed Bias
 Collector to Base Bias
 Voltage Divider Bias

Base Bias or Fixed Bias
 Circuit Diagram  Apply KVL at input
side or Base Emitter
Side So,
 +VCC – IBRB – VBE =
0
 The current IB is :

 Now IC = βIB
48

Base Bias or Fixed Bias
 Circuit Diagram  Apply KVL at output side or
Collector Emitter Side So,
 VCE + ICRC – VCC = 0
 and
 VCE = VCC – ICRC
 From Circuit
 VCE = VC – VE
 VBE = VB – VE
 and VE = 0V
 So
 VCE = VC
 VBE = VB
49

Collector to Base Bias
 Circuit Diagram  The current through
RC is not IC , but
I’C. where I’C = IC +
IB.
 However, the level of
IC and I’C far
exceeds the usual
level of IB, and the
approximation IC≈I’C is
normally employed.
 Substituting IC ≈ IC =
βIB and IE ≈ IC
50

 Circuit Diagram  From input side of the circuit
 VCC – I’CRC – IBRF – VBE – IERE
= 0
 So
 VCC– βIBRC – IBRF – VBE –
βIBRE = 0
 VCC – IBRF – VBE – βIB(RE +
RC)= 0
 Now
51

 Circuit Diagram  Apply KVL at output side or
Collector Emitter Side So,
 IERE + VCE + I’CRC – VCC =
0
 I’C ≈ IC and IE ≈ IC
 We have
 IC(RC + RE) + VCE – VCC = 0
 and
 VCE = VCC – IC(RC + RE)
52

Voltage Divider Bias
 Circuit Diagram  Let I1 and I2 are
current through R1
and R2.
 From circuit (apply
KCL)
 I1 = IB + I2
 The current IB is much
smaller than I2.
 So I1 = I2
 The voltage across
R2, which is actually
the base voltage can
be determined using
the voltage-divider
53

 Circuit Diagram  VB is determined,
the level of VE can
be calculated from
 VBE = VB – VE
 VE = VB – VBE
 and the emitter
current can be
determined from
 and ICQ ≈ IE
54

 Circuit Diagram  The collector-to-emitter
voltage is determined by
 VCE = VCC – ICRC – IERE
 but because IE ≈ IC,
 VCEQ = VCC – IC(RC + RE)
55

INTRODUCTION TO
OPERATIONAL
AMPLIFIER
56

Introduction to Operational
Amplifier
Ideal v/s practical Op-amp
57
 Difference between Ideal and Practical Op-
Amp
Parameters Ideal Op-Amp
Practical Op-Amp
(E.g. LM 741)
Bandwidth (BW) Infinite 1MHz
Slew Rate (SR) Infinite 0.5 V / μs
Open loop gain (AOL) Infinite 200,000
Common Mode
Rejection Ratio (CMRR)
Infinite 90 dB
Power Supply Rejection
Ratio (PSRR)
Zero
120 dB (+Supply)
110 dB (-Supply)
Input impedance (Ri) Infinite 2 MΩ
Output impedance (Ro) Zero 75 Ω
Offset and Offset Drifts Zero 1mV, 20nA

Introduction to Operational
Amplifier
58
 The 741 Op Amp

OPERATIONAL
AMPLIFIER
APPLICATION
CIRCUITS
59

Peak Detector Circuit
 RC ≥ 10 T
60

Peak Detector Circuit
61
 During +ve half cycle when the input voltage is positive, the diode is
conducting/ON and capacitor charges to the peak of the input
voltage.
 Second, when the input voltage is negative during –ve half cycle,
the diode is non-conducting/OFF and the capacitor discharges
through the load resistor.
 As long as the discharging time constant is much greater than the
period of the input signal (T), the output voltage will be
approximately equal to the peak value of the input voltage.
 This can achieved by making discharging time constant RC can be
made much longer than the period of the input signal (RC ≥ 10 T),
will get almost perfect peak detection of low-level signals.
 If the peak-detected signal has to drive a small load, to avoid
loading effects by connecting the voltage follower (op-amp buffer)
isolates the small load resistor from the peak detector. This
prevents the small load resistor from discharging the capacitor too
quickly.

Comparator
62
 Comparator circuit compares a single voltage
on one input of op-amp with a known voltage
called reference voltage (Trip point or trigger
point) on the other input and produces high or
low output depending upon relative magnitude
of two input.
 Comparators with Zero Reference
 Comparators with Nonzero References
 Comparators with Hysteresis or Schmitt Trigger
 Window Comparator

Comparator
Comparators with Zero Reference
63
 Non-Inverting Comparator
 Because of the high open-loop voltage gain, a positive input voltage
produces positive saturation, and a negative input voltage produces
negative saturation.
 Above circuit is called a zero-crossing detector because the
output voltage ideally switches from low to high or vice versa
whenever the input voltage crosses zero (input compares with zero
reference voltage).

Comparator
64
 Non-Inverting Comparator

Comparator
65
 Inverting Comparator
 The input signal drives the inverting input of the comparator.
In this case, a positive input voltage produces a maximum
negative saturation, as shown in above diagram. On the other
hand, a negative input voltage produces a maximum positive
saturation.

Comparator
66
 Inverting Comparator

Comparator
Comparators with Nonzero
References
67
 Non-Inverting Comparator: Positive reference
 When Vin is greater than Vref, the differential input voltage is
positive and the output voltage is high (+Vsat). When Vin is less
than Vref, the differential input voltage is negative and the output
voltage is low (-Vsat).
 Vin > Vref then Vout = +Vsat
 Vin < Vref then Vout = - Vsat

Comparator
References
68
 Non-Inverting Comparator: Positive reference

Comparator
References
69
 Non-Inverting Comparator: Negative reference
 Vin > Vref then Vout = + Vsat
 Vin < Vref then Vout = - Vsat

Comparator
References
70
 Non-Inverting Comparator: Negative reference

Comparator
Schmitt Trigger or Regenerative Feedback
71
 If the input to a comparator contains a large amount of noise, the output will be
erratic when Vin is near the trip point.
 When the noise peaks are large enough, they produce unwanted changes in the
comparator output. In diagram observe that producing unwanted transitions from low
to high. When an input signal is present, the noise is superimposed on the input
signal and produces erratic triggering.
 One way to reduce the effect of noise is by using a comparator with positive
feedback.
 The positive feedback produces two separate trip points that prevent a noisy input
from producing false transitions.

Comparator
72
 Inverting Schmitt trigger
 When the comparator is positively saturated, a
positive voltage is fed back to the noninverting
input. This positive feedback voltage holds the
output in the high state.
 Similarly, when the output voltage is negatively
saturated, a negative voltage is fed back to the
noninverting input, holding the output in the
low state.

Comparator
73

Comparator
74

Comparator
75
 The output voltage will remain in a given state until the
input voltage exceeds the reference voltage for that
state.
 For instance, if the output is positively saturated, the
reference voltage is +BVsat. The input voltage must
be increased to slightly more than +BVsat to switch
the output voltage from positive to negative, as shown
in input/output response has hysteresis.
 Once the output is in the negative state, it will remain
there indefinitely until the input voltage becomes more
negative than -BVsat. Then, the output switches from
negative to positive shown in input/output response
has hysteresis.

Comparator
76
 The trip points are defined as the two input voltages
where the output voltage changes states. The upper
trip point (UTP) has the value:
 UTP = + BVsat
 and the lower trip point (LTP) has the value:
 LTP = - BVsat
 The difference between these trip points is defined as
the hysteresis (also called the deadband ):
 VH = UTP - LTP
 which equals:
 VH = 2BVsat

Comparator
77
 Lab experiment:
 a) Design and construct a Schmitt trigger using
Op-Amp for given UTP and LTP values and
demonstrate its working. (Wired Experiment)
 b) Design and implement a Schmitt trigger using
Op-Amp using a simulation package for two sets
of UTP and LTP values and demonstrate its
working. (Simulation Experiment)

Comparator
78
 Non-Inverting Schmitt trigger

Comparator
79
 Let current through the R1 is Iin (In coming) and R2 is Iout (Out
going)
 So Iin = Iout

Vin
R1
=
Vout
R2
 𝑉𝑖𝑛 =
𝑅1
𝑅2
𝑉𝑜𝑢𝑡
 When Vin becomes positive and greater that
𝑅1
𝑅2
𝑉𝑜𝑢𝑡 then the
output switches to +Vsat. Therefore UTP is
 𝑈𝑇𝑃 =
𝑅1
𝑅2
+𝑉𝑠𝑎𝑡
 Similarly
 𝐿𝑇𝑃 =
𝑅1
𝑅2
−𝑉𝑠𝑎𝑡

Comparator
80
 Assume that the output is negatively saturated.
The feedback voltage will hold the output in
negative saturation until the input voltage
becomes slightly more positive than UTP.
When this happens, the output switches from
negative to positive saturation.
 Once in positive saturation, the output stays
there until the input voltage becomes slightly
less than LTP. Then, the output can change
back to the negative state.

Comparator
81
 Application of Schmitt trigger
 Digital to analog conversion
 One bit DAC
 Level Detection
 Hysteresis voltage
 Line reception
 Output level is only changed as the data chnages

Comparator
Window Comparator
82
 An ordinary comparator indicates when the
input voltage exceeds a certain limit or
threshold.
 A window comparator (also called a double-
ended limit detector) detects when the input
voltage is between two limits called the
window. To create a window comparator, will
use two comparators with different thresholds.

Comparator
Window Comparator
83
 Low Output between Limits

Comparator
Window Comparator
84
 Low Output between Limits
 Circuit shows a window comparator that can produce a low
output voltage when the input voltage is between a lower and
an upper limit.
 When Vin is less than LTP or greater than UTP, the output is
high. When Vin is between LTP and UTP, the output is low.
 Operation:
 When Vin < LTP, comparator A1 has a positive output and A2
has a negative output. Diode D1 is on and D2 is off. Therefore,
the output voltage is high.
 Similarly, when Vin > UTP, comparator A1 has a negative output
and A2 has a positive output. Diode D1 is off, D2 is on, and the
output voltage is high.
 When LTP < Vin < UTP, A1 has a negative output, A2 has a
negative output, D1 is off, D2 is off, and the output voltage is low.

Active Filters
85
 An electric filter is often a frequency selective circuit that passes a
specified band of frequency and blocks or attenuates signals of
frequencies outside this band.
 Active filters employs transistor or op-amp in addition to resistor and
capacitor.
 RC network are used for filter.
 The most commonly used filters are follows:
 Low pass filters
 High pass filter
 Band pass filter
 Band reject filter.
 All pass filter
 Next slide shows the frequency response characteristics of the five
types of filter. The ideal response is shown by dashed line. While
the solid lines indicates the practical filter response.

Active Filters
87
 A filter that provides a constant output from dc up
to a cut-off frequency fH and then passes no signal
above that frequency is called an ideal low-pass
filter.
 A filter that provides or passes signals above a
cutoff frequency fL is a high-pass filter, as shown
in previous slide.
 When the filter circuit passes signals that are
above one ideal cutoff frequency (fL) and below a
second cutoff frequency, (fH) it is called a
bandpass filter.
 Two types of filters
 First Order Filter – One capacitor used
 Second Order Filter – Two or more capacitor used

Active Filters
88
 Attenuation refers to a loss of signal.
 The order of a passive filter equals the
number of inductors and capacitors in the filter.
 The quality factor (Q) is the measure of
“frequency selectivity" of a filter circuit.
 High the Q narrower the bandwidth
 Lower the Q wider the bandwidth

Active Filters- Low-pass filter
89
 Non-Inverting unity gain
 It is nothing more than an RC lag circuit and a voltage
follower. The voltage gain is: Av = 1.
 When the frequency increases above the cutoff frequency,
the capacitive reactance decreases and reduces the
noninverting input voltage.
 Since the R1C1 lag circuit is outside the feedback loop, the
output voltage rolls off. As the frequency approaches
infinity, the capacitor becomes a short and there is zero
input voltage.

90
 Non-Inverting with voltage gain
 Although it has two additional resistors, it has the
advantage of voltage gain.

91
 Inverting with voltage gain
 As the frequency increases, the capacitive reactance decreases
and reduces the impedance of the feedback branch. This implies
less voltage gain.
 As the frequency approaches infinity, the capacitor becomes a
short and there is no voltage gain.

Active Filters- High-pass filter
92
 Noninverting unity gain
 When the frequency decreases below the cutoff frequency,
the capacitive reactance increases and reduces the
noninverting input voltage.
 Since the R1C1 circuit is outside the feedback loop, the
output voltage rolls off. As the frequency approaches zero,
the capacitor becomes an open and there is zero input
voltage.

93
 Non-Inverting with voltage gain

94
 Inverting with voltage gain

Active Filters- Second Order Filter
Low Pass/High Pass Filter
95
 Generalized form of second order filter
 If Z1=Z2=R and Z3=Z4=C get second order low pass
filter
 If Z1=Z2=C and Z3=Z4=R get second order high pass
filter

Active Filters- Band-pass Filter
96
 Two types of band pass filter
 Wide band pass filter
 Narrow band pass filter

97
 Wide Band Pass Filters
 Cascade of low-pass and high-pass filter

98
 Narrow Band Pass Filters
 In the circuit the input signal goes to the inverting
input rather than the noninverting input. Also the
circuit has two feedback paths, one through a
capacitor and another through a resistor.

99
 Narrow Band Pass Filters
 At low frequencies, the capacitors appear to be
open. Therefore, the input signal cannot reach the
op amp, and the output is zero.
 At high frequencies, the capacitors appear to be
shorted. In this case, the voltage gain is zero
because the feedback capacitor has zero
impedance.
 Between the low and high extremes in frequency,
there is a band of frequencies where the circuit
acts like an inverting amplifier.

Active Filters- Band-Reject/Stop
Filter
100
 Two types of Band Reject Filter:
 Wide/Broad Band Reject filter
 Narrow/Notch Band Reject Filter
 Wide/Broad Band Reject filter
 Summing together the output of the low pass and
high pass filter produces broad reject filter.

Active Filters- Band-Reject/Stop/Notch
Filter
101
 Narrow/Notch Band Reject Filter

Active Filters- Band-Reject/Stop/Notch
Filter
102
 Narrow/Notch Band Reject Filter
 At low frequencies, all capacitors are open. As a
result, all the input signal reaches the noninverting
input of op-amp and passes to the output.
 At very high frequencies, the capacitors are
shorted. Again, all the input signal reaches the
noninverting input and passes to the output.
 Between the low and high extremes in frequency
the feedback signal returns with the correct
amplitude and phase to attenuate the signal on
the noninverting input. Because of this, the output
voltage drops to a very low value.

Active Filters- All Pass Filter
103
 Also called phase filter because the filter shifts
the phase of the output signal without
changing the magnitude.

104
 All-pass lag filter
 R<< (1/2πfC) then phase shift Ø= 0º
 R>> (1/2πfC) then phase shift Ø= -180º
 R= (1/2πfC) then phase shift Ø= -90º
 Where f is the input frequecy

105
 All-pass lead filter
 R<< (1/2πfC )then phase shift Ø= 90º
 R>> (1/2πfC )then phase shift Ø= 180º
 R= (1/2πfC) then phase shift Ø= 0º
 Where f is the input frequecy

Non-Linear Amplifier
106
 In this amplifier the gain value is non-linear
function of the amplitude of the input signal.
 The gain may be large for weak signal and
very small for large signal this can achieved
using non-linear device such as PN junction
diode as shown below. Also called log
amplifier.

Non-Linear Amplifier
107
 Working:
 For small value of input signal, diodes act as
open circuit and the gain is high due to minimum
feedback.
 When the amplitude of input signal is large,
diodes offer very small resistance and thus gain is
low.

Relaxation Oscillator
109
 In circuit, there is no input signal.
 Nevertheless, the circuit produces a rectangular output
signal. This output is a square wave that swings between –
Vsat and +Vsat. How is this possible?
 Assume that the output is in positive saturation. Because of
feedback resistor R, the capacitor will charge exponentially
toward +Vsat, as shown in waveform. But the capacitor
voltage never reaches +Vsat because the voltage crosses the
UTP. When this happens, the output square wave switches to
–Vsat.
 With the output now in negative saturation, the capacitor
discharges, as shown in waveform. When the capacitor
voltage crosses through zero, the capacitor starts charging
negatively toward –Vsat. When the capacitor voltage crosses
the LTP, the output square wave switches back to +Vsat. The
cycle then repeats.

Relaxation Oscillator
110
 Lab Experiment:
 a) Design and construct a square waveform
generator (Op-Amp relaxation oscillator) for given
frequency and demonstrate its working. (Wired
Experiment)
 b) Design and implement a square waveform
generator (Op-Amp relaxation oscillator) using a
simulation package and demonstrate the change
in frequency when all resistor values are doubled.
(Simulation Experiment)

Current-To-Voltage Converter
 Also called Transimpedance amplifier
 Fig-1can also be represent as Fig-2
 From Fig-2 Voltage gain of the
amplifier is
 𝐴 = −
𝑅𝑓
𝑅1
or
𝑉𝑂𝑢𝑡
𝑉𝑖𝑛
= −
𝑅𝑓
𝑅1
 𝑉𝑜𝑢𝑡 = −
𝑉𝑖𝑛
𝑅1
𝑅𝑓-------------------(1)
 From Fig-2 circuit
 𝑖𝑖𝑛 =
𝑉𝑖𝑛
𝑅1
 So equation (1) becomes
 𝑉𝑜𝑢𝑡 = −𝑖𝑖𝑛𝑅𝑓
 So input current converted to output
voltage.
 Application: DAC, Sensing Current from
photodetector
111
Fig-
1
Fig-
2

Voltage-To-Current Converter
 Also called
Transconductance
amplifier.
 Apply KVL at input side
 𝑉𝑖𝑛 − 𝑖𝑜𝑢𝑡𝑅1 = 0
 𝑉𝑖𝑛 = 𝑖𝑜𝑢𝑡𝑅1
 𝑖𝑜𝑢𝑡 =
𝑉𝑖𝑛
𝑅1
 Form equation the input
voltage is converted into
output current.
 Application: DC and AC
voltmeter, LED, Zener
Diode tester.
112

Integrated Circuit(IC)
Multivibrators
114
 A multivibrator circuit oscillates between a “HIGH” state and a
“LOW” state producing a continuous output.
 It generates square, rectangular, pulse waveforms, also
called nonlinear oscillators or function generators.
 There are basically three types of clock pulse generation
circuits:
 Astable – A free-running multivibrator that has NO stable
states but switches continuously between two states this
action produces a train of square/rectangular wave pulses
at a fixed frequency.
 Monostable – A one-shot multivibrator that has
only ONE stable state and is triggered externally with it
returning back to its first stable state.
 Bistable – A flip-flop that has TWO stable states that
produces a single pulse either positive or negative in value.

Multivibrators
115

Multivibrators
116
 The NE555 (also LM555, CA555) is a widely used IC
timer, a circuit that can run in either of two modes:
monostable (one stable state) or astable (no stable
states).

Multivibrators
 Functional Block
Diagram of IC 555
 The 555 timer contains a
voltage divider, two
comparators, an RS flip-
flop, and an npn transistor.
 Since the voltage divider
has equal resistors, the top
comparator (C1) has a trip
point of:
 𝐔𝐓𝐏 =
𝟐
𝟑
𝐕𝐂𝐂
 The lower comparator (C2)
has a trip point of:
 𝐋𝐓𝐏 =
𝟏
𝟑
𝐕𝐂𝐂
117

Multivibrators
118
 Pin-1 (Ground)
 Pin-2 (Trigger) Is connected to the lower comparator. The trigger voltage that is
used for the monostable operation of the 555 timer. When the timer is inactive,
the trigger voltage is high. When the trigger voltage falls to less than the LTP,
the lower comparator (C2) produces a high output.
 Pin-3 (Output)
 Pin-4 (Reset) Pin 4 may be used to reset the output voltage to zero. If Pin 4 is
not in used so it should connected to +VCC.
 Pin-5 (Control) Pin 5 may be used to control the output frequency when the 555
timer is used in the astable mode. If not in use then pin 5 is bypassed to ground
through a capacitor
 Pin-6 (Threshold) Pin 6 is connected to the upper comparator. The voltage on
pin 6 is called the threshold. When the threshold voltage is greater than the
UTP, the upper comparator (C1) has a high output.
 Pin-7 (Discharge) To discharge the external connected capacitor when
transistor in ON.
 Pin-8 (+VCC)

Multivibrators
119
 SR Flip-Flop
 Duty cycle (D) is the proportion of time during which the device is
operated.
 In terms of square wave signal it defines the percentage of time for
which signal is at logic high level.
 For square wave it can be calculated as (high time / (high time +
low time))
 Duty cycle of 50% means that the low time and high time of the
signal is same.
S R 𝑸 𝑸
0 0 No Change
0 1 0 1
1 0 1 0
1 1 Invalid

Integrated Circuit(IC) Multivibrators
Astable Operation of the 555
Timer
 Circuit Diagram  Charge time (High
Time)
 𝑡𝑐 = 0.693 𝑅1 + 𝑅2 𝐶
 Discharge time (Low
Time)
 𝑡𝑑 = 0.693𝑅2𝐶
 Total Time period T is
 𝑇 = 𝑡𝑐 + 𝑡𝑑
 The frequency is given
by
 𝑓𝑂 =
1
𝑇
 The duty cycle is
𝑡𝑐
120

Timer
121
Capacitor and output waveforms

Timer
122
When output 𝑄= High, so
the transistor is OFF and
capacitor C starts charging
through R1 and R2 till
reaches to UTP

Timer
123
When output 𝑄= Low, so
the transistor is ON and
capacitor C starts
discharging through R2 till
reaches to LTP

Timer
124
 When Q is low, the transistor is cut off and the capacitor is charging through R1
and R2 resistance. Because of this, the charging time constant is (R1+R2)C. As
the capacitor charges, the threshold voltage (pin 6) increases. Eventually, the
threshold voltage exceeds
2
3
VCC. Then, the upper comparator sets the flip-flop.
 With Q high, the transistor saturates and grounds pin 7. The capacitor now
discharges through R2. Therefore, the discharging time constant is R2C. When
the capacitor voltage drops to slightly less than
1
3
VCC, the lower comparator
resets the flip-flop.
 The output is a rectangular wave that swings between 0 and VCC. Since the
charging time constant is longer than the discharging time constant, the output
is nonsymmetrical. Depending on resistances R1 and R2, the duty cycle is
between 50 and 100 percent.
 When R1 is much smaller than R2, the duty cycle approaches 50 percent.
Conversely, when R1 is much greater than R2, the duty cycle approaches 100
percent.
 To make the duty cycle to become less than 50 percent. By placing a diode in
parallel with R2 (anode connected to pin 7), the capacitor will effectively charge
through R1 and the diode. The capacitor will discharge through R2.

Timer
125
 Lab Experiment:
 Design and implement an Astable multivibrator
circuit using 555 timer for a given frequency and
duty cycle.

Monostable Operation of the 555
Timer
 Circuit Diagram  Pulse Width is
 W=1.1RC
 The circuit has an
external resistor R and
a capacitor C.
 The voltage across the
capacitor is used for the
threshold voltage to pin
6.
 When the trigger
arrives at pin 2, the
circuit produces a
rectangular output
pulse from pin 3.
126

Timer
127

Timer
128
 Initially, the Q output of the RS flip-flop is high. This turn ON
the transistor and the capacitor discharge to ground through
pin 7. The circuit will remain in this state until a trigger arrives
at pin 2.
 When the trigger input falls to slightly less than
1
3
VCC the
lower comparator resets the flip-flop. Since Q has changed to
low, the transistor goes OFF, allowing the capacitor to charge.
At this time, 𝑄 has changed to high.
 The capacitor now charges exponentially through R as shown
in waveform. When the capacitor voltage is slightly greater
than
2
3
VCC, the upper comparator sets the flip-flop. The high
Q turns ON the transistor, which discharges the capacitor
almost instantly. At the same instant, 𝑄 returns to the low
state and the output pulse ends.
 𝑄 remains low until another input trigger arrives.

Objective
130
 Comprehend importance of voltage regulator
and its characteristics.
 Study IC based voltage regulator and its
analysis.

Introduction
131
 A voltage regulator provides a constant dc
output voltage that is essentially independent
of the input voltage, output load current, and
temperature.
 The voltage regulator is one part of a power
supply.
 Its input voltage comes from the filtered output
of a rectifier derived from an ac voltage or from
a battery in the case of portable systems.

Need for Regulator
132
 Power supply circuits built using filters, rectifiers,
and then voltage regulators.
 Starting with an ac voltage, we obtain a steady dc
voltage by rectifying the ac voltage, then filtering
to a dc level, and, finally, regulating to obtain a
desired fixed dc voltage.
 The regulation is usually obtained from an IC
voltage regulator unit, which takes a dc voltage
and provides a somewhat lower dc voltage, which
remains the same even if the input dc voltage
varies or the output load connected to the dc
voltage changes.

Need for Regulator
133
 Block Diagram of Regulated Power Supply

Need for Regulator
134
 The ac voltage, typically 230V, 50Hz, is connected to a
transformer, which steps that ac voltage down to the level for
the desired dc output.
 A diode rectifier then provides a full-wave rectified voltage,
which is initially filtered by a basic capacitor filter to produce a
dc voltage.
 This resulting dc voltage usually has some ripple or ac
voltage variation.
 A regulator circuit can use this dc input to provide a dc
voltage that not only has much less ripple voltage, but also
remains at the same dc value even if the input dc voltage
varies somewhat or the load connected to the output dc
voltage changes.
 Regulator keeps the output voltage constant under variable
load conditions and even in varying input voltage conditions.

Need for Regulator
135
 Factors Affecting the Load Voltage
 Load Current (IL)
 Load current is the current that the load is drawing at that
instant.
 The output voltage should remains constant in spite of the
change in the load current.
 Line Voltage
 Input AC 230V is line voltage
 The output voltage must remain constant irrespective of
any change in the line voltage.
 Temperature
 The overall performance of the power supply is
temperature dependent.

Need for Regulator
136
 Performance Parameters of Power Supply
 Line Regulation
 Load Regulation
 Voltage Stability factor (SV)
 Temperature Stability Factor (ST)
 Ripple Rejection (RR)

Need for Regulator
137
 Line Regulation (Source Regulation)
 Line regulation can be defined as the percentage
change in the output voltage for a given change in
the input voltage.
 Ideally the line regulation should be zero

Need for Regulator
138
 Load Regulation
 When the amount of current through a load
changes due to a varying load resistance, the
voltage regulator must maintain a nearly constant
output voltage across the load.
 Load regulation can be defined as the percentage
change in output voltage for a given change in
load current. One way to express load regulation
is as a percentage change in output voltage from
no-load (NL) to full-load (FL).

Need for Regulator
139
 Voltage Stability factor (SV)
 Dependency of output voltage on the input line
voltage is called Voltage Stability factor.
 Its is defined as percentage change in the output
voltage which occurs per volt change in input
voltage where load current and temperature are
constant.
 Ideally its should be zero.

Need for Regulator
140
 Temperature Stability Factor (ST)
 The stability of the power supply will be
determined by temperature coefficient of various
temperature sensitive semiconductor devices.
 Better choose the low temperature coefficient
devices.
 E.g. Zener Diodes

Need for Regulator
141
 Ripple Rejection (RR)
 It is defined as how effectively the regulator
rejects the ripples and attenuate it from input to
output.
 RR is very small and in dB

Adjustable voltage regulator
142
 Voltage regulators comprise a class of widely
used ICs.
 Regulator IC units contain the circuitry for
reference source, comparator amplifier, control
device, and overload protection all in a single
IC.
 IC units provide regulation of either a fixed
positive voltage, a fixed negative voltage, or
an adjustably set voltage.

143
 Voltage regulators are also available in circuit
configurations that allow the user to set the
output voltage to a desired regulated value.
 The LM317, for example, can be operated with
the output voltage regulated at any setting
over the range of voltage from 1.2 V to 37 V.

144
With typical IC values of VREF=1.25V and IADJ= 100 mA

145
 For LM317
 The load regulation is 0.1 %
 Line regulation is 0.01 %
 RR is 80dB
 LM337 is a Adjustable Negative Linear Voltage
Regulators
 Advantage of Adjustable Voltage Regulators is
 Voltage range from 1.2V to 37V
 Output current 0.1A to 1.5A
 Better load and line regulation
 Improve system performance, reliability and thermal
overloading
 Good overload protection

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