Unit – 3:Data Conversion and display

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PHY C16 – T: Electronic Instrumentation & Sensors Unit – 3: Data Conversion and Display
Notes by Mr. Chandrakantha T S, Dept. of PG Studies & Research in Electronics Kuvempu University, Jnanasahyadri Shankaraghatta,2023-24
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PHY C16 – T: Electronic Instrumentation & Sensors(Theory)
Unit – 3: Data Conversion and Display
INTRODUCTION
Data Conversion
 Data conversion involves transforming data from one form to another, particularly in
digital and analog systems.
 Data conversion in the context of digital systems and human interaction focuses on
bridging the gap between the digital world (computers, digital devices) and the human
experience (perception and interaction).
 This involves transforming data into formats that can be understood and used by both
digital systems and humans.

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Need for Data Conversion
Data conversion is essential for various reasons across different domains, particularly in bridging
the gap between digital systems and human interaction.
1. Interoperability: Ensures compatibility and seamless communication between different
systems and formats.
2. Data Processing and Efficiency: Facilitates accurate, efficient processing and analysis of
data by converting it into digital formats.
3. Human Interaction: Translates digital data into formats that humans can perceive and
interact with, such as visual displays and audio.
4. Communication and Transmission: Enables successful data transfer and maintains
signal integrity across different mediums.
5. Storage and Quality Improvement: Optimizes storage, reduces noise, and enhances the
precision and reliability of data.
Types of Data Conversion
 Signals are mainly classified into two types i.e. Analog & Digital signal. The data or
information that we perceive in real world exists in analog form while the digital devices such
as cellphone, calculator & computer can only understand a data signal in digital domain.
 Analog to Digital (ADC) & Digital to analog converter (DAC) are the two types of converters
that we use in our daily life to convert the signals into each other.
There are two types of data conversion: 1) Analog-to-Digital (A/D) Conversion/ADC
2) Digital-to-Analog (D/A) Conversion/DAC

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1) Analog-to-Digital (A/D) Conversion/ADC
 ADC stands for analog to digital converter. It is an electronic device used for converting
an analog signal into a digital signal.
 In the real world, every real quantity such as voice, temperature, weight etc exists in the
analog state. And it cannot be processed by any digital device such as a computer or a cell
phone.
 These analog quantities are converted into digital form so that a digital device can process
it. This conversion is done using analog to digital converter.
Block Diagram of ADC
 The analog signal is first applied to the ‘sample‘ block where it is sampled at a specific
sampling frequency.
 The sample amplitude value is maintained and held in the ‘hold‘ block. It is an analog
value.
 The hold sample is quantized into discrete value by the ‘quantize‘ block. At last, the
‘encoder‘ converts the discrete amplitude into a binary number.

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Analog to Digital Conversion Steps
The conversion from analog signal to a digital signal in an analog to digital converter is explained
below
1. Sampling
 Sampling is the process of measuring and recording the value of a continuous analog
signal at discrete time intervals.
 It captures the analog signal at regular intervals to create a series of discrete data points
that can be processed digitally.
 The analog signal is sampled at a specific rate, known as the sampling frequency. The
frequency must be high enough to capture the signal accurately according to the
Nyquist theorem, which states it should be at least twice the highest frequency
component of the signal (fs >).

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2. Holding
 Holding is the process of maintaining the sampled value constant until the next
sampling point is taken.
 It ensures that the amplitude of the sampled signal remains stable during the
quantization and encoding stages of conversion.
 Once a sample is taken, a sample-and-hold circuit preserves that value for a brief period
to allow for accurate conversion by the subsequent stages.
3. Quantization
 Quantization is the process of converting the continuous amplitude values of the analog
signal into discrete amplitude levels.
 It maps the analog signal’s continuous range into a finite set of discrete values or levels,
which can be represented digitally.
 The continuous amplitude is divided into a number of discrete intervals. Each sample’s
amplitude is approximated to the nearest interval level, producing discrete output
values that correspond to those intervals.
4. Encoding
 Encoding is the process of converting the quantized discrete amplitude values into a
binary format.
 It translates the quantized levels into a binary code that can be processed, stored, or
transmitted by digital systems.
 Each quantized level is represented as a binary number (a sequence of bits) 3-bits in
above 001, 011, 100, 100, 010, 001, 011, 110, and 110.
All these steps are completed rapidly, typically within microseconds, ensuring quick conversion
from analog to digital form.

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8-Bit ADC Example
Suppose we have an analog signal that ranges from 0 to 5 volts, and we want to convert it into an
8-bit digital representation.
Sampling: Assume the analog signal value at a specific time is 3.2 volts.
Holding: The sampled value of 3.2 volts is held constant during the conversion process.
Quantization:
Range: With an 8-bit ADC, the analog range (0 to 5V) is divided into 28
=256 discrete levels.
Resolution: Each level represents a voltage step of
5
0.0195
256
v
V
 per step.
Quantization Process: The 3.2V sample is mapped to the nearest discrete level.
3.2
164.1
0.0195
v
Quantization Level
V
 
Rounding to the nearest integer, the quantized level is 164.
Encoding: Convert the quantized level (164) to an 8-bit binary number
Decimal 164 in binary is 2
10100100
A/D Converter with Preamplification and Filtering
 An Analog-to-Digital Converter (A/D converter or ADC) with preamplification and
filtering is designed to enhance the accuracy and quality of the analog-to-digital conversion
process.
 For low-resolution ADCs (8 or 10 bits) with single-ended inputs and normalized analog
input ranges of 5-10V (bipolar or unipolar), preamplification and filtering are important,
especially when dealing with low signal levels.

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1. Analog Signal Input: Two analog signals o
e and om
e are input to the system. These signals
may come from sensors or other analog sources.
2. Preamplification:
 Preamplification is the process of boosting the strength of the analog signal before it
reaches the ADC and optimizing accuracy and resolution.
 Improves signal-to-noise ratio, ensuring the signal is distinguishable from background
noise.
 Here A1 and A2 are operational amplifiers used for preamplification. They amplify
the input analog signals to a higher voltage level suitable for accurate conversion.
 Each amplifier has a positive and negative power supply ( )
cc EE
V and V
 
 The amplifiers have a gain set by the resistors R1R_1R1 and a variable gain resistor.
The total gain of the preamplification stage is 1000.
3. Differential Amplification(A3):
 This operational amplifier(A3) is configured to perform differential amplification.

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 It processes the difference between the outputs of A1 and A2 to improve the signal-
to-noise ratio and eliminate common-mode noise.
 The resistors R2, R3, R4 and RF set the gain and ensure accurate differential
amplification.
4. Filtering: The amplified signal passes through a filter (low-pass, band-pass, active filter,
or tracking filter) to remove noise and unwanted components.
5. Analog-to-Digital Converter (ADC): Converts the amplified and filtered analog signal
into a digital signal
 Sampling: Captures the amplitude of the analog signal at discrete intervals.
 Holding: Maintains the sampled value steady during quantization.
 Quantization: Converts the continuous amplitude into discrete levels.
 Encoding: Transforms the quantized levels into a binary format.
6. Buffer: Temporarily stores the digital data before it is sent to the computer or transmission
system.
7. Conversion Command and Status: Control signals that manage the data flow and
conversion process.
8. Output:
To Computer or Transmission System: The final digital output is sent to a computer or
another system for further processing, analysis, or transmission.
2) Digital-to-Analog (D/A) Conversion/DAC
 Digital to analog converter is an electronic circuit that converts any digital signal (such as
binary signal) into an analog signal (voltage or current).

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 The DAC has several digital inputs & a single analog output.
D/A Converter Types
Digital-to-Analog Converters (D/A converters or DACs) convert digital signals into analog
voltages. Various methods can be used for this conversion, including
1) Variable Resistor Network D/A Converter
2) Ladder Type (R-2R) D/A Converter
3) Op-Amp Based D/A Converter
1) Variable Resistor Network D/A Converter
 A Variable Resistor Network D/A Converter is one of the simplest methods to convert a
digital signal into an analog signal.
 It utilizes a network of resistors to generate an analog voltage corresponding to a given
digital input.
 This can be achieved most easily by designing a Variable Resistor Network which changes
each of the digital levels into an equivalent binary weight voltage (or current).
Example:
Suppose we wish to change the 8 possible states of digital signals into equivalent analog voltages.
The smallest number represented by 000 (0V) and the largest number represented is 111(5V)

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 Hence the resistive ladder must do two things in order to change the digital input into an
equivalent analog output.
1. 20
bit must be changed to +1 V, 21
bit to +2 V and 22
bit to + 4 V.
2. The three voltages representing the digital bits must be summed together to form the
analog output voltage.
 A resistive ladder which performs the above functions is shown below
 The resistors R0, R1 and R2 form the divider network. RL is the load to which the divider
is connected and is large enough not to load the divider network.
 Assume that the digital input signal 001 is applied to this Variable Resistor Network. Using
the levels as before, 0 = 0 V and 1 = +7 V. The equivalent circuit is shown below.RL. is
considered very large, and hence neglected.
 The analog output voltage VA can be easily determined by the use of Millman’s theorem.

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In general, the following hold.
1. There is one input resistance for each digital bit.
2. Beginning with the LSB, each following resistor is half the previous
3. The full scale output voltage is equal to the +ve voltage of the digital input signal
(negative voltages work equally well).
4. The change in output voltage due to a change in the LSB is equal to V/(2n
— 1), where V
is the digital input voltage level.
5. The LSB has a weight of 1/(2n
— 1), where n is the number of input bits.
6. The output voltage VA can be found for any digital input signal by using the following
modified form of Millman’s theorem.
where V0, V1, V2, …, Vn-1 are the digital input voltage levels (0 and + V) and n is the
number of input bits.
The Variable Resistor Network has two basic drawbacks.
 Each resistor must have a precise value, making the network costly due to precision
requirements.
 The resistor for the MSB handles much larger currents than the LSB resistor, potentially
leading to higher power dissipation and thermal issues.
To overcome the drawbacks of the Variable Resistor Network, an alternative approach called the
Ladder Network (R-2R Network) is often used.

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2) Ladder Type (R-2R) D/A Converter
 This method is more precise, accurate & easy to design then the variable resistor weighted
resistor method.
 The circuit uses resistors of two values: R and 2R.
 The resistors are arranged in a specific manner to create a ladder-like structure.
 The circuit takes a 4-bit binary input (D, C, B, A) where D is the Most Significant Bit
(MSB) and A is the Least Significant Bit (LSB).
 The output voltage is taken from the top of the ladder(VD) and ground.
 Each bit of the binary input can either be 0 or 1.
 A 1 means the corresponding switch is connected to a reference voltage (often 5V or a
similar voltage), and a 0 means the switch is connected to ground (0V).
 The resistors form a voltage divider network.
 Depending on the binary input, different combinations of switches will be connected to the
reference voltage or ground, changing the voltage at the various points in the ladder.
 The output voltage is the sum of the contributions from each bit, weighted according to its
position (MSB to LSB).
 The MSB has the highest weight (largest influence on VOUT), and the LSB has the smallest
weight.
 The output voltage VOUT is a weighted sum of the binary inputs. For a 4-bit DAC, the
formula can be expressed as:

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Where:
 VREF is the reference voltage.
 D, C, B, and A are the binary input bits (1 or 0).
Example:
Let's consider an example with a reference voltage VREF of 5V. We'll calculate the output analog
voltage for a 4-bit binary input of 1011.
Given binary input: 1011 D=1 (MSB), C=0, B=1, A=1 (LSB)

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3) Op-Amp Based D/A Converter
 A 4-bit Digital-to-Analog Converter (DAC) using an operational amplifier (op-amp) is a
circuit that converts a 4-bit digital input into a corresponding analog output voltage.
 This type of DAC uses an op-amp in a summing amplifier configuration to combine the
effects of binary-weighted inputs.
 Each resistor corresponds to a bit in the digital input.
 The resistors have values such that each subsequent resistor is double the value of the
previous one (e.g., R, 2R, 4R, 8R).
 Each digital bit controls a switch that connects the corresponding resistor to either the
reference voltage VREF or ground.
 For example, if D3=1, the switch connects the 8R resistor to VREF. If D3=0, it connects to
ground.
 A feedback resistor Rf is connected from the output of the op-amp to its inverting input.
 The op-amp sums the currents through the resistors, which are proportional to the digital
input bits.
 The inverting input of the op-amp sums the currents from each resistor, and the op-amp
output provides the weighted sum as an analog voltage.
 The analog output voltage VOUT is calculated using the principle of current summation at
the inverting input of the op-amp.

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Example:
Let us consider full-scale voltage of binary 1 is 5V and for binary 0 is 0V

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The output of this circuit for different digital inputs are given below:
A B C D Vout
0 0 0 0 0
0 0 0 1 -0.625
0 0 1 0 -1.250
0 0 1 1 -1.875
0 1 0 0 -2.500
0 1 0 1 -3.125
0 1 1 0 -3.750
0 1 1 1 -4.375
1 0 0 0 -5.000
1 0 0 1 -5.625
1 0 1 0 -6.250
1 0 1 1 -6.875
1 1 0 0 -7.500
1 1 0 1 -8.125
1 1 1 0 -8.750
1 1 1 1 -9.375
 Clearly, the output of this circuit is equal to the weighted sum of the digital inputs.
 Full-scale value of this circuit is (-9.375V).
 The output of this circuit depends on two factors, the first one is the value of the feedback
resistor and the second is the precision of the input voltage.
Digital display systems and Indicators
 Digital display systems and indicators are essential components in many electronic devices,
providing a visual interface for users to interact with the system.
 Display devices provide a visual display of numbers, letters, and symbols in response to
electrical input, and serve as constituents of an electronic display system.
 They can be classified into several types based on their technology and application.

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Classification of Displays
Commonly used displays in the digital electronic field are as follows.
1. Segment Displays
 Segment displays are a type of digital display that uses segments to represent numbers and,
in some cases, letters and symbols. Commonly used in digital clocks, calculators, and
meters.
 Consists of seven individual segments arranged in a pattern to form the digits 0-9.
 Each segment is typically an LED that can be illuminated in different combinations to
represent digits.

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2. Dot Matrix Displays:
 Comprise an array of LEDs or LCDs arranged in a matrix form (e.g., 5x7, 8x8).
 Each dot (or pixel) can be individually controlled to display characters or graphics.
3. Liquid Crystal Displays (LCDs):
 Character LCDs: Typically 16x2 or 20x4 character displays that show alphanumeric
characters.
 Graphic LCDs: Capable of displaying complex graphics, including images and text.
4. Organic Light Emitting Diode (OLED) Displays:
 OLED displays are a type of advanced display technology that uses organic compounds
to emit light when an electric current is applied.

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 OLEDs have gained popularity in a wide range of applications, from smartphones and
televisions to wearable devices and lighting solutions, due to their superior image quality,
flexibility, and efficiency.
5. Plasma Displays:
 Plasma displays are a type of flat-panel display technology that was widely used in large
television screens and monitors.
 They work by illuminating tiny cells containing ionized gases, which emit ultraviolet light
when electrically charged.
6. Light Emitting Diode (LED) Displays:
 LED displays are a type of flat-panel display that uses light-emitting diodes (LEDs)
as the light source.
 These displays are widely used in a variety of applications, from small devices like
digital watches to large-scale displays like billboards and stadium screens.
 LED technology offers several advantages over traditional display technologies,
including energy efficiency, brightness, and longevity.

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Light Emitting Diodes (LED)
 Light Emitting Diodes, commonly known as LEDs, are semiconductor devices that emit
light when an electric current passes through them.
 LEDs are widely used in various applications due to their energy efficiency, long lifespan,
and compact size.
 They are utilized in everything from indicator lights and displays to general lighting and
electronic devices.
Structure of an LED

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An LED consists of several key components:
1. Semiconductor Material: The core of an LED is a piece of semiconductor material,
typically composed of elements like gallium, arsenic, and phosphorous. This material is
what emits light when electrically stimulated.
2. P-N Junction: The semiconductor material is doped to create a p-n junction. One side of
the junction is doped with elements that provide extra electrons (n-type), while the other
side is doped with elements that create "holes" or the absence of electrons (p-type).
3. Anode and Cathode: The LED has two terminals: the anode (positive) and the cathode
(negative). When a voltage is applied across these terminals, it drives current through the
LED.
4. Encapsulation: The semiconductor and junction are encapsulated in a transparent or semi-
transparent case made of epoxy or plastic, which protects the internal components and
helps to direct the emitted light.
Working Principle of an LED
The operation of an LED is based on the principles of electroluminescence and the behavior of
the p-n junction:
1. Forward Bias: When a forward voltage is applied across the LED (positive to the anode
and negative to the cathode), electrons from the n-type region gain enough energy to cross
the junction and recombine with holes in the p-type region.

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2. Electron-Hole Recombination: As electrons recombine with holes, they release energy
in the form of photons. The wavelength (and therefore the color) of the emitted light
depends on the energy gap of the semiconductor material used.
3. Emission of Light: The emitted photons are what we perceive as light. The efficiency
and color of the light depend on the materials and design of the LED.
Color of LEDs
LEDs can emit light in various colors depending on the semiconductor material used and the
energy gap.
Color Wavelength Forward
Voltage
Semiconductor Material
White 395 – 530 nm 3V – 5V Gallium-indium-nitride (GaInN), Zinc Selenide (ZnSe)
Ultraviolet < 400 nm 3.1 – 4.4
V
Aluminum nitride (AlN), Aluminum gallium nitride
(AlGaN), Aluminum gallium indium nitride (AlGaInN)
Violet 400 – 450 nm 2.8 – 4.0
V
Indium gallium nitride (InGaN)
Blue 450 – 500 nm 2.5 – 3.7
V
Indium gallium nitride (InGaN), Silicon carbide (SiC)
Green 500 – 570 nm 1.9 – 4.0
V
Gallium phosphide (GaP), Aluminum gallium indium
phosphide (AlGaInP), Aluminum gallium phosphide
(AlGaP)
Yellow 570 – 590 nm 2.1 – 2.2
V
Gallium arsenide phosphide (GaAsP), Aluminum gallium
indium phosphide (AlGaInP), Gallium phosphide (GaP)
Orange 590 – 610 nm 2.0 – 2.1
V
Gallium arsenide phosphide (GaAsP), Aluminum gallium
indium phosphide (AlGaInP), Gallium phosphide (GaP)
Red 610 – 760 nm 1.6 – 2.0
V
Aluminum gallium arsenide (AlGaAs), Gallium arsenide
phosphide (GaAsP), Aluminum gallium indium phosphide
(AlGaInP), Gallium phosphide (GaP)
Infrared > 760 nm < 1.9 V Gallium arsenide (GaAs), Aluminum gallium arsenide
(AlGaAs)

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Advantages of LEDs
1. Energy Efficiency: LEDs convert a higher percentage of electrical energy into light
compared to traditional incandescent bulbs, making them more energy-efficient.
2. Long Lifespan: LEDs can last tens of thousands of hours, significantly longer than
incandescent or fluorescent lamps.
3. Durability: LEDs are solid-state devices with no moving parts, making them more
resistant to shocks and vibrations.
4. Environmental Impact: LEDs contain no hazardous materials like mercury, making them
more environmentally friendly.
5. Compact Size: The small size of LEDs allows for greater design flexibility in various
applications.
Applications of LEDs
 Indicator Lights: LEDs are used as indicator lights in electronic devices, dashboards, and
control panels.
 Displays: LED technology is used in digital displays, including televisions, computer
monitors, and mobile screens.
 Lighting: LEDs are increasingly used in general lighting solutions, including residential,
commercial, and street lighting.
 Automotive: LEDs are used in vehicle headlights, taillights, and interior lighting.

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Liquid Crystal Display (LCD)
 Liquid Crystal Displays (LCDs) are flat-panel displays that use the light-modulating
properties of liquid crystals.
 These displays are commonly found in devices such as televisions, computer monitors,
smartphones, and digital watches.
Structure of an LCD
An LCD consists of several key components:
1. Backlight: Provides the necessary illumination for the display. It can be made of LEDs or
fluorescent lights.
2. Polarizing Filters: There are typically two polarizing filters placed at the front and back
of the liquid crystal layer. These filters control the light passing through the display.

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3. Glass Substrates: Two glass plates sandwich the liquid crystal layer. The inner surfaces
of these glass plates are coated with a transparent conductive material, usually indium tin
oxide (ITO), to form electrodes.
4. Liquid Crystal Layer: This layer contains the liquid crystal molecules, which can align
in different orientations when an electric field is applied. The alignment of these molecules
controls the passage of light.
5. Electrodes: Transparent electrodes made of ITO are patterned on the inner surfaces of the
glass substrates. They apply an electric field across the liquid crystal layer.
6. Color Filters: For color displays, a matrix of red, green, and blue color filters is placed in
front of the liquid crystal layer to create the necessary colors.
Types of LCDs
LCDs can be classified based on their light interaction and illumination methods. The primary
types include Reflective LCDs, Transmissive LCDs, and Transflective LCDs.

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1) Reflective LCDs: Use ambient light reflected from a mirrored surface behind the liquid crystal
layer.
2) Transmissive LCDs: Use backlighting to illuminate the display, generally providing better
visual characteristics than reflective LCDs.
3) Transflective LCDs: Combines ambient light and a backlight
Working Principle of an LCD
LCDs utilize organic materials known as liquid crystals, which maintain a crystal-like structure
even when melted. The most commonly used liquid crystal structures in displays are nematic and
cholesteric:
Nematic Liquid Crystals (NLC): These are the most popular type of liquid crystals used in LCDs.
They are usually transparent, but when subjected to a strong electric field, the ions within the liquid
crystal move and disrupt the orderly structure, causing the liquid to become polarized and turn
opaque. Removing the electric field allows the liquid crystal to return to its transparent state.
1. Electric Field Application: When an electric field is applied across the liquid crystal layer,
it causes the ions in the liquid crystal to move, disrupting the ordered structure and turning
the liquid crystal layer opaque.

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2. Light Modulation: The degree of opacity can be controlled by varying the strength of the
electric field. In a transmissive LCD, light from the backlight passes through the liquid crystal
layer and the color filters to produce the desired image. In a reflective LCD, ambient light is
used.
3. Image Formation: By controlling the electric field applied to different segments of the LCD,
various patterns or characters can be displayed. Transparent electrodes and backlighting can
be used to enhance readability in low-light conditions.
4. Color Production: In color LCDs, the light passing through the liquid crystal layer then
passes through the color filters (red, green, and blue). By controlling the intensity of light
passing through each color filter, different colors can be produced.
Advantages of LCDs
1. Energy Efficiency: LCDs consume less power compared to traditional cathode ray tube
(CRT) displays.
2. Slim Profile: LCDs are much thinner and lighter than CRTs, making them suitable for a
wide range of applications.
3. Low Heat Generation: LCDs generate less heat compared to other display technologies.
4. High Resolution and Image Quality: LCDs offer high resolution and good image quality
with sharp and clear visuals.
5. No Geometric Distortion: LCDs do not suffer from geometric distortion issues that are
common in CRTs.
Applications of LCDs
 Televisions: LCDs are widely used in modern flat-screen TVs.
 Computer Monitors: LCD monitors are common for desktop computers and laptops.
 Mobile Devices: Smartphones, tablets, and handheld devices utilize LCD technology.
 Digital Watches and Clocks: LCDs are used in digital timepieces for their low power
consumption.
 Instrumentation: Many medical and scientific instruments feature LCDs for displaying
data.

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Data Transmission Systems
 Data transmission systems are the mechanisms and technologies used to convey
information from one place to another.
 This information can be in the form of voice, video, text, or other data types.
 Data transmission systems are critical in various applications, including
telecommunications, broadcasting, computer networking, and the internet.
Types of Data Transmission
1)Analog Transmission
Analog transmission involves sending continuous signals that vary in amplitude, frequency, or
phase to represent data. These signals can take any value within a given range and are typically
used in traditional forms of communication.

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Characteristics:
 Continuous Signals: Analog signals are continuous and can take an infinite number of
values within a range.
 Susceptibility to Noise: Analog signals are prone to noise and interference, which can
degrade the quality of the transmitted data over long distances.
 Signal Degradation: The quality of analog signals can deteriorate over distance due to
attenuation, requiring amplification which can further introduce noise.
Examples:
 Traditional Telephone Lines: Analog signals were used in the early days of telephony
to transmit voice over long distances.
 Radio Broadcasts: AM and FM radio transmissions use analog signals to broadcast
audio content.
 Analog Television: Early television systems used analog signals to transmit visual and
audio information.
2)Digital Transmission
Digital transmission involves sending discrete signals, typically in binary form (0s and 1s), to
represent data. These signals are used in modern communication systems due to their robustness
and efficiency.
Characteristics:
 Discrete Signals: Digital signals represent data as a series of discrete values, typically
binary, which makes them less prone to noise.
 Error Detection and Correction: Digital systems can use various techniques to detect
and correct errors, maintaining signal integrity over long distances.
 Efficient Bandwidth Usage: Digital transmission can be more efficient in using
bandwidth, supporting higher data rates and better quality of service.

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Examples:
 Computer Networks: Data transmission over Ethernet and Wi-Fi networks uses digital
signals to communicate between devices.
 Digital Telephony: Modern telephone systems, including VoIP (Voice over Internet
Protocol), use digital signals to transmit voice data.
 Digital Broadcasting: Digital TV and radio broadcasts use digital signals to deliver high-
quality audio and video content.
 Fiber Optic Communication: Fiber optic cables use light pulses, a form of digital
transmission, to transmit data over long distances with minimal loss and high speed
Advantages and Disadvantages of Digital Transmission over Analog
Transmission
Digital communication systems offer numerous benefits over analog systems, but they also
come with certain drawbacks.
Advantages of Digital Transmission
1. Noise Immunity: Digital signals are less susceptible to noise and interference compared
to analog signals. Errors due to noise can be detected and corrected using error detection
and correction techniques.
2. Signal Integrity: Digital signals maintain their quality over long distances without
degradation, as they can be easily regenerated using repeaters.
3. Data Compression: Digital transmission allows for efficient data compression techniques,
reducing the bandwidth required for transmission.
4. Multiplexing(Video+Audio): Multiple digital signals can be easily multiplexed on the
same channel, increasing the efficiency of bandwidth usage.
5. Security: Digital transmission offers better security features such as encryption, making it
harder for unauthorized parties to intercept or tamper with the data.
6. Storage: Digital data can be stored more efficiently and reliably, with the ability to be
copied without loss of quality.

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7. Compatibility: Digital systems are compatible with modern digital technology, including
computers, mobile devices, and the internet, facilitating integration and interoperability.
8. Error Detection and Correction: Digital systems can incorporate sophisticated error
detection and correction algorithms, improving the reliability of data transmission.
Disadvantages of Digital Transmission
1. Complexity: Digital systems are generally more complex and require sophisticated
hardware and software, leading to higher initial costs and complexity in design and
implementation.
2. Bandwidth Requirements: Digital signals often require higher bandwidth compared to
analog signals to transmit the same information, especially for high-quality audio and
video.
3. Quantization Errors: Analog signals need to be converted to digital form through
sampling and quantization, which can introduce quantization errors and affect the fidelity
of the signal.
4. Synchronization: Digital transmission requires precise synchronization between the
transmitter and receiver, which can be challenging to maintain over long distances or in the
presence of high noise levels.
5. Latency: Digital processing and transmission can introduce latency, which might be
critical in real-time applications such as live audio or video streaming.
6. Power Consumption: Digital circuits and processing units can consume more power
compared to analog circuits, which can be a limitation in battery-operated devices.

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Modulation
Modulation is the process of varying a carrier signal in order to transmit data. The carrier signal,
typically a high-frequency sinusoidal wave, is altered in some manner—such as its amplitude,
frequency, or phase—to encode information.
Need for Modulation
1. Efficient Transmission: Modulation allows the transmission of signals over long distances
without significant loss of quality or strength. High-frequency signals can travel longer
distances compared to low-frequency signals.
2. Multiplexing: Modulation enables the simultaneous transmission of multiple signals over
a single communication channel by using different carrier frequencies. This increases the
efficiency of the channel.
3. Noise Reduction: Modulated signals are more resistant to noise and interference, as they
can be transmitted at higher frequencies where the effect of noise is less severe.
4. Antenna Size: The size of the transmitting and receiving antennas is inversely proportional
to the frequency of the signal. Higher frequencies allow for smaller antennas, which are
more practical for various applications.

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Demodulation
Demodulation is the process of extracting the original message signal from the modulated carrier
wave. This is the reverse process of modulation and is essential for the receiver to recover the
transmitted information.
Pulse Modulation
 Pulse modulation is a form of modulation where the message signal is
encoded into a sequence of pulses.
 Instead of continuously varying a parameter of a sine wave, as in continuous-
wave modulation (e.g., AM or FM), pulse modulation varies specific
properties of a pulse train.
 These properties include amplitude, duration, position, and more.

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Types of Pulse Modulation
The key types of pulse modulation include Pulse Amplitude Modulation (PAM), Pulse Time
Modulation (PTM), and Pulse Width Modulation (PWM).
1)Pulse Amplitude Modulation (PAM)
 Pulse Amplitude Modulation is a technique where the amplitude of each pulse
is varied according to the instantaneous value of the message signal.
 As we can see in the figure shown above that the amplitude of the pulses is varying with
respect to the amplitude of analog modulating signal, like in case of amplitude modulation.
 But the major difference is that unlike AM, here the carrier wave is a pulse train rather than
continuous wave signal.

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PAM Modulator:
The key components of a PAM modulator are a Low Pass Filter (LPF), Pulse Generator,
Multiplexer (MUX), and Modulator.
 Low Pass Filter (LPF): The analog message signal is passed through the LPF to remove
any unwanted high-frequency components, resulting in a clean baseband signal.
 Pulse Generator: The pulse generator creates a series of pulses at regular intervals
(sampling rate). These pulses are used to sample the analog message signal.
 Multiplexer (MUX): The MUX combines the filtered message signal with the pulse train.
At each sampling instant, a pulse is generated that corresponds to the amplitude of the
message signal at that instant.
 Modulator: The modulator adjusts the amplitude of each pulse based on the amplitude of
the message signal at the corresponding sampling point, producing the PAM signal.
2) Pulse Time Modulation (PTM)
 Pulse Time Modulation (PTM) involves varying the timing characteristics of pulses to
encode the message signal.
 There are two primary types of PTM: Pulse Width Modulation (PWM), also known as
Pulse Duration Modulation (PDM), and Pulse Position Modulation (PPM).

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a) Pulse width modulation (PWM) /Pulse Duration Modulation (PDM)
 Pulse Width Modulation (PWM), or Pulse Duration Modulation (PDM), is a
technique where the width (duration) of each pulse is varied in proportion to
the amplitude of the message signal.

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 As we can see that unlike PAM, in this technique the amplitude of the signal
is constant and only the width is varying.
 PWM technique is similar to frequency modulation because, by the variation
in the width of the pulses, the frequency of the pulses in the PWM signal
shows variation.
PWM Modulator
1. Message Signal and Carrier Waveform:
 The message signal, which is the information to be transmitted, is fed into
the modulator.
 The carrier waveform, typically a sawtooth wave, is generated by the
ramp signal generator and fed to the inverting terminal of the comparator.
2. Pulse Amplitude Modulation:
 The modulator creates a PAM signal by sampling the message signal at
regular intervals defined by the carrier waveform.
 This PAM signal represents the amplitude of the message signal at
discrete points in time.

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3. Comparator Circuit:
 The comparator has two inputs: the PAM signal (non-inverting terminal)
and the ramp signal (inverting terminal).
 The comparator also has a reference voltage that determines the
threshold for the comparison.
4. Intersection and Pulse Width Determination:
 The comparator compares the PAM signal with the ramp signal.
 When the ramp signal exceeds the reference voltage, the comparator switches
its output state.
 The leading edge of the PWM pulse is aligned with the start of the ramp signal.
 The width of the PWM pulse is determined by the duration for which the ramp
signal is above the reference voltage.
5. Generation of PWM Signal:
 The width of each pulse in the PWM signal is directly proportional to the
amplitude of the message signal at each sampling point.
 This means that higher amplitude message signals result in wider pulses, and
lower amplitude signals result in narrower pulses.

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The figure below will help us to understand in a better way how PWM signal is
generated by the comparator:

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b) Pulse Position Modulation (PPM)
Pulse Position Modulation (PPM) is a technique where the position of each pulse, relative to a
reference pulse, is varied according to the instantaneous value of the message signal.
 Here the pulse amplitude and the pulse width are the two constant that does not show
variation with the amplitude of the modulating signal but only the position shows variation.
 It is to be noted here that the position of the pulse changes according to the reference pulses.
And these reference pulses are nothing but PWM pulses. Basically, the falling edge of
PWM pulses acts as the starting of the PPM pulses.

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PPM Modulator:
Pulse Position Modulation (PPM) can be generated using a combination of Pulse Width
Modulation (PWM) and a monostable multivibrator. This approach controls the time
characteristics of PWM to derive the position modulation required for PPM.
PWM Conversion to PPM Signal
 The input PWM signal has pulses with varying widths, corresponding to the amplitude of
the original message signal at each sampling point.
 The monostable multivibrator is triggered by the trailing edge of each PWM pulse.
 Upon triggering, the multivibrator generates a pulse of a fixed width.
 The output of the monostable multivibrator is the PPM signal, where the position of each
pulse corresponds to the width of the previous PWM pulse.

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Comparison of PAM, PWM, and PPM
Parameter PAM (Pulse Amplitude
Modulation)
PWM (Pulse Width
Modulation)
PPM (Pulse Position
Modulation)
Principle Amplitude of pulses varies
according to the message
signal.
Width of pulses varies
signal.
Position of pulses varies
signal.
Noise Immunity Low - susceptible to noise
and interference.
High - better noise
immunity than PAM.
Higher - very good noise
immunity.
Bandwidth
Requirement
Moderate - depends on the
number of samples and the
Nyquist rate.
High - requires more
bandwidth due to varying
pulse widths.
High - requires precise
timing and
synchronization.
Power Efficiency Moderate - power varies
with pulse amplitude.
High - more efficient
power usage.
High - efficient power
usage with fixed pulse
width.
Complexity Simple - easy to implement. Moderate - requires
precise timing and
control.
High - requires precise
synchronization and
timing.
Advantages - Simple to implement.
- Direct representation of the
analog signal.
- Better noise immunity.
- Efficient power delivery.
- Compatibility with
digital control systems.
- Very good noise
immunity.
- Efficient use of power.
- Suitable for optical and
wireless communications.
Disadvantages - Poor noise immunity.
- Limited to analog signals.
- Power varies with pulse
amplitude.
- Requires more
bandwidth.
- Can generate high-
frequency harmonics.
- More complex
generation and
demodulation.
- Requires precise timing
and synchronization.
- More complex
modulation and
demodulation.
- Requires more
bandwidth.
Applications - Basic communication
systems.
- Audio and video
broadcasting.
- Analog signal
transmission.
- Motor speed control.
- Light dimming.
- Power regulation.
- Audio signal
transmission.
- Optical communication
systems.
- Remote control systems.
- Wireless communication.
- Radar and navigation
systems.

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Principle of Phase Sensitive Detection (PSD)
 A Phase Sensitive Detector (PSD) or Phase Meter Circuit is used to compare
an AC signal with a reference signal.
 The output is a rectified signal that indicates both the magnitude and the phase
relationship between the input signal and the reference signal.
 This circuit is particularly useful for identifying the phase polarity and
magnitude of error signals in various applications.

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Circuit Description
 Reference Voltage (Vr): The AC signal used as a reference for phase comparison.
 Signal Voltage (Vs): The AC signal to be compared with the reference voltage.
 Rectifiers (D1, D2): Diodes used for rectifying the signal in phase with the reference
voltage.
 Resistors (R1, R2): Resistors across which the rectified voltages are developed.
 Zero-center Galvanometer: A meter that indicates the phase error and its direction.
Working Principle
 The PSD circuit involves rectifying the input signal in synchronization with a reference
signal. It uses a pair of diodes and resistors to achieve this.
 The key feature of this circuit is its ability to deflect a zero-center meter (galvanometer or
DC voltmeter) to indicate the direction and magnitude of the phase error between the input
and reference signals.
1. Initial Condition with Vs = 0:
o For the first half-cycle, the instantaneous polarity of Vr causes the rectified current to
flow through D1, producing a positive voltage across R1.
o On the second half-cycle, the polarity of Vr causes current to flow through D2,
producing a positive voltage across R2.
o These two equal and opposite currents average out over a full cycle, causing the
galvanometer to read zero.
2. With an Input Signal (Vs) Applied:
o In-Phase Condition:
 When Vs is in phase with Vr, it adds to Vr during the positive half-cycle,
causing a larger current through D1 and a higher voltage across R1.
 During the negative half-cycle, Vs opposes Vr, reducing the current through D2
and resulting in a lower voltage across R2.
 The galvanometer deflects to the right, proportional to the magnitude of Vs.

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o Out-of-Phase Condition (180°):
 When Vs is 180° out of phase with Vr, it opposes Vr during the positive half-
cycle, reducing the current through D1 and the voltage across R1.
 During the negative half-cycle, Vs adds to Vr, causing a larger current through
D2 and a higher voltage across R2.
 The galvanometer deflects to the left, proportional to the magnitude of Vs.
Lock-In Amplifier
A Lock-In Amplifier is an advanced instrument used to measure the amplitude and phase of a
signal with a specific known frequency, even when that signal is buried in noise. This device is
highly effective at extracting weak signals that are otherwise indistinguishable from noise.

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Working Principle
1. Reference Signal: The lock-in amplifier requires a reference signal, which is a pure sine
wave of the same frequency as the signal of interest.
2. Mixing: The input signal, containing the desired signal and noise, is mixed with the
reference signal. This process shifts the frequency of the desired signal to DC (zero
frequency) and the noise to higher frequencies.
3. Low-Pass Filtering: A low-pass filter removes the high-frequency noise components,
leaving only the DC component, which is the desired signal's amplitude and phase
information.
4. Phase Detection: The phase of the input signal relative to the reference signal can also be
determined. This is achieved by mixing the input signal with both the reference signal and
a 90-degree phase-shifted version of the reference signal.
Advantages
 High Sensitivity: Can detect extremely weak signals.
 Noise Rejection: Excellent at rejecting noise and interference.
 Precision: Provides accurate measurements of amplitude and phase.
Applications
 Spectroscopy: Used in various forms of spectroscopy to detect weak optical signals.
 Electrical Measurements: Used in precise electrical measurements such as impedance
and capacitance measurements.
 Biomedical Engineering: Employed in medical devices to detect physiological signals.
 Communications: Used in communication systems to extract signals from noise.

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Phase-Locked Loop (PLL)
A Phase-Locked Loop (PLL) is an electronic control system that generates a signal with a phase
that is related to the phase of an input signal. PLLs are widely used in communication systems for
synchronization purposes.
Working Principle
1. Phase Detector: Compares the phase of the input signal with the phase of the output signal
from the Voltage-Controlled Oscillator (VCO).
2. Low-Pass Filter: Filters the output of the phase detector to produce a DC voltage
proportional to the phase difference.
3. Voltage-Controlled Oscillator (VCO): Generates an output signal whose frequency is
controlled by the DC voltage from the low-pass filter.
4. Feedback Loop: The VCO output is fed back to the phase detector, forming a closed-loop
system.
When the PLL is in lock, the frequency of the VCO is identical to the frequency of the input signal,
and the phase difference between them is constant.
Types of PLLs
 Analog PLL: Uses analog components like resistors, capacitors, and operational
amplifiers.
 Digital PLL: Uses digital logic components and is implemented in software or hardware.

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Applications
 Frequency Synthesis: Used to generate precise frequencies for communication systems.
 Clock Generation and Recovery: Used in digital systems to synchronize clock signals.
 Demodulation: Used in demodulating frequency and phase modulated signals.
 Motor Speed Control: Used to control the speed of motors in various applications.
Comparison of Lock-In Amplifier and PLL
Parameter Lock-In Amplifier Phase-Locked Loop (PLL)
Purpose Extracts weak signals from noise Synchronizes the phase and
frequency of signals
Key
Components
Reference signal, mixer, low-pass
filter
Phase detector, low-pass filter, VCO
Output Amplitude and phase of the input
signal
Frequency and phase-locked output
signal
Noise Rejection Excellent Good
Common
Applications
Spectroscopy, biomedical signal
detection, communication
Frequency synthesis, clock recovery,
demodulation, motor control
Sensitivity High Moderate to high
Complexity Moderate to high Moderate
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Unit – 3:Data Conversion and display

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Unit – 3:Data Conversion and display