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ENDED LAB
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SUBJECT:
ASSIGNED BY:
COURSE:
COURSE CODE:
DATED:
BATCH:
SEMESTER:
SECTION:
GROUP MEMBERS:
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AREEBA NOOR
AREEBA HAMID
JAVERIA
MEHWISH ALEEM
Shakaib Akhtar Khan
EL-21106
EL-21138
EL-21134
EL-21137
EL-21136
Mam Saba
Communication Systems
TC-307
4th July 2023
2021
Fifth
C
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ABSTRACT
This project involves creating an AM modulator and demodulator circuit without relying on modulator
and demodulator ICs. The circuit, designed on a breadboard or Vero board, includes strategically placed
test points for waveform visualization. The lab report covers AM modulation theory, circuit design, and
waveform observations, offering students practical insights into AM modulation and demodulation
principles.
This hands-on learning experience enhances students' proficiency in circuit design, analysis, and
troubleshooting. By synthesizing theoretical knowledge with real-world applications, the project fosters
a practical understanding of AM modulation and demodulation, concluding with a consolidation of
insights gained from the immersive endeavor.
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OBJECTIVES ................................................................................................................................................................... 5
THEORETICAL BACKGROUND........................................................................................................................................ 5
1. Introduction to Modulation: ................................................................................................................................. 5
Types of Modulation: ............................................................................................................................................ 5
2. Understanding AM Modulation: ........................................................................................................................... 6
Definition of AM Modulation:............................................................................................................................... 6
Characteristics of AM Signals:............................................................................................................................... 6
Types of AM Modulation: ..................................................................................................................................... 7
3. AM Modulator and It’s Types: .............................................................................................................................. 7
Linear Modulators: ............................................................................................................................................... 7
Non-Linear Modulators: ....................................................................................................................................... 7
Transistor-Based AM Modulators: ........................................................................................................................ 7
4. Understanding AM Demodulation:....................................................................................................................... 8
Definition and Importance of AM Demodulation in Signal Reception: ................................................................ 8
Methods of AM Demodulation: ............................................................................................................................ 8
5. Advantages & Disadvantages of Amplitude Modulation ..................................................................................... 8
Advantages ........................................................................................................................................................... 8
Disadvantages ....................................................................................................................................................... 8
6. Our Focus .............................................................................................................................................................. 9
Square Law Modulator: ........................................................................................................................................ 9
Envelope Detector: ............................................................................................................................................... 9
LITRATURE REVIEW ....................................................................................................................................................... 9
SIMULATION ............................................................................................................................................................... 11
Circuit diagrams: ..................................................................................................................................................... 11
Waveforms:............................................................................................................................................................. 12
1.
Time Domain ............................................................................................................................................... 12
2.
Frequency Spectrum: .................................................................................................................................. 13
HARDWARE PICTURES ................................................................................................... Error! Bookmark not defined.
Observations ............................................................................................................................................................... 13
Calculation for ckt design ........................................................................................................................................... 14
Summary and Reflections ........................................................................................................................................... 15
References .................................................................................................................................................................. 15
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Table of Figures:
FIGURE 1: MODULATION AND ITS TYPES [2] ............................................................................................................................................. 5
FIGURE 2: TYPES OF MODULATION. [5] ................................................................................................................................................... 5
FIGURE 3: AM WAVEFORM [4] ............................................................................................................................................................. 6
FIGURE 4 BLOCK DIAGRAM OF AN AM MODULATOR ................................................................................................................................. 7
FIGURE 5: BLOCK DIAGRAM OF AM DEMODULATOR .................................................................................................................................. 8
FIGURE 6: CIRCUIT DIAGRAM OF AM MODULATION & DEMODULATION ....................................................................................................... 9
FIGURE 7: SIMULATION SQUARE LAW AM MODULATOR .......................................................................................................................... 11
FIGURE 8: SIMULATION OF ENVELOPE DETECTOR AM DEMODULATION....................................................................................................... 11
FIGURE 9: AM MODULATED WAVEFORM
FIGURE 10: DEMODULATED ORIGINAL INFORMATION SIGNAL ..................................................... 12
FIGURE 11: FREQUENCY SPECTRUM OF MODULATED WAVE ..................................................................................................................... 13
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OBJECTIVES
1. Design and implement an AM modulator and demodulator using a breadboard/Vero board.
• Circuit must be able to successfully transmit and receive a message
• Use of modulator and demodulator IC is not allowed
• The circuit must contain test points to visualize waveforms as seen in earlier lab sessions
THEORETICAL BACKGROUND
1. Introduction to Modulation:
Modulation is the process of changing one or more characteristics (amplitude, frequency, or phase) of a carrier
wave to encode information for transmission. This technique allows the integration of signals with different
frequencies, ensuring effective communication across various distances and technologies. [1]
Figure 1: Modulation and its types [2]
Types of Modulation:
Modulation comes in various forms, each altering different aspects of
the carrier signal. The primary types include:
1. Amplitude Modulation (AM): Involves varying the amplitude
of the carrier wave to encode information. Widely used in
broadcasting for audio signals.
2. Frequency Modulation (FM): Modifies the frequency of the
carrier wave in proportion to the information signal.
Commonly employed in radio broadcasting for high-fidelity
audio transmission.
3. Phase Modulation (PM): Alters the phase of the carrier wave
based on the information signal. Often utilized in
communication systems with specific bandwidth
requirements.
pg. 5
Figure 2: Types of modulation. [5]
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2. Understanding AM Modulation:
Definition of AM Modulation:
Amplitude Modulation (AM) is a communication technique where the carrier wave's amplitude varies with the
modulating signal's instantaneous amplitude. It is crucial for analog signal transmission, commonly used in AM
radio broadcasting and certain two-way radio systems. [4]
Characteristics of AM Signals:
Amplitude Modulation (AM) signals exhibit distinct characteristics that define their behavior in communication
systems. These include:
4.
5.
6.
7.
Carrier and Sidebands: AM signals consist of a carrier wave and two sidebands.
Carrier wave: Unmodulated signal frequency.
Sidebands: Frequencies above and below the carrier, carrying the modulating signal information.
Bandwidth Usage: AM signals typically occupy more bandwidth than the original modulating signal. The
bandwidth is directly related to the highest frequency in the modulating signal.
8. Signal-to-Noise Ratio (SNR): AM signals are susceptible to noise and interference. Maintaining a good
Signal-to-Noise Ratio (SNR) is crucial for signal clarity.
9. Simple Demodulation: AM signals are relatively easy to demodulate. The demodulation process involves
separating the carrier from the modulating signal.
10. Power Efficiency: AM transmitters require more power compared to other modulation techniques. The
power consumption is mainly due to the transmission of carrier and both sidebands.
Understanding these characteristics is essential for designing and optimizing AM modulation systems for effective
communication.
Figure 3: AM Waveform [4]
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Types of AM Modulation:
There are five types of amplitude modulation, such as:
1. Double sideband-suppressed carrier modulation: The transmitted waves consist of upper and lower
sidebands but the bandwidth of the channel remains the same.
2. Single sideband modulation: The modulated wave will consist of either the upper sideband or the lower
sideband and is used for translating the spectrum into a new frequency domain.
3. Vestigial sideband modulation: Only one sideband is used and is passed, retaining the other sideband.
4. Double sideband full carrier modulation: The message signal obtained from the modulated signal should
not go below zero. The message signal is stored in the modulated signal.
5. Quadrature amplitude modulation: Two different message signals are transmitted on the same
frequency carrier but the phase shift will be different. [3]
3. AM Modulator and It’s Types:
In Amplitude Modulation (AM), the modulator manipulates the amplitude of the carrier signal based on the
varying amplitudes of the information signal, suitable for transmission over a communication channel. [1]
Linear Modulators:
Linear modulators maintain a direct
relationship between the input signal and the
output modulation. [1]
1. Amplitude Modulation with Linear
Amplifiers
2. Frequency Modulation with Linear
Modulators
Non-Linear Modulators:
Figure 4 Block Diagram of an AM Modulator
Non-Linear modulators does not maintain a
direct relationship between the input signal and the output modulation. [1]
1. Class C Amplifiers for AM
2. Diode Modulators
Transistor-Based AM Modulators:
Transistor-based AM modulators use transistors to achieve amplitude modulation. [1]
1.
pg. 7
Common Emitter AM Modulator
2. Class A Transistor Modulators
3. Class C Transistor Modulators
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4. Understanding AM Demodulation:
Definition and Importance of AM
Demodulation in Signal Reception:
AM Demodulation is the vital process of
extracting the original modulating signal
from an amplitude-modulated carrier wave.
It plays a crucial role in signal reception,
ensuring accurate retrieval of transmitted
information, be it audio, video, or data, and
is essential for successful content
understanding.
Figure 5: Block diagram of AM Demodulator
Methods of AM Demodulation:
The simplest form of AM demodulator consists of a diode which is configured to act as envelope detector.
Another type of demodulator, the product detector, can provide better-quality demodulation with additional
circuit complexity. [2]
1. Envelope Detection 2. Coherent Detection 3. Square-Law Detector
5. Advantages & Disadvantages of Amplitude Modulation
Advantages
1. Amplitude modulation is economical as well as easily obtainable
2. It is so simple to implement, and by using a circuit with fewer components it can be demodulated.
3. The receivers of AM are inexpensive because it doesn’t require any specialized components.
Disadvantages
1.
2.
3.
4.
5.
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The efficiency of this modulation is very low because it uses a lot of power
This modulation uses amplitude frequency several times to modulate the signal by a carrier signal.
This declines the original signal quality on the receiving end & causes troubles in the signal quality.
AM systems are susceptible toward the generation of noise generation.
The applications of amplitude modulation limits to VHF, radios, & applicable one to one communication
only.
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6. Our Focus
As we were required to design an AM Modulator and Demodulator, we chose SQUARE LAW MODULATOR to
generate a DSBFC- Double Side Band Full Carrier AM-Modulated wave which would be transmitted through a
channel and when received will be Demodulated by using an ENVELOPE DETECTOR. We chose DSBFC for its easy
to generate and implement circuit design.
Square Law Modulator:
A Square Law Modulator utilizes the non-linear
relationship between input voltage and output current
or voltage in a transistor's saturation region. Operating
with a square law equation, it introduces amplitude
modulation to the output signal. This simple and
efficient modulator is used for generating AM signals in
communication systems, though careful tuning is
necessary to manage harmonic distortions. [1]
V2(t)= aVc cos wct + 2bx(t) Vc cos wct
𝟐𝐛
V2(t)= aVc cos wct (1+ 𝐚 x(t) )
Envelope Detector:
An envelope detector is a circuit used in amplitude
Figure 6: Circuit Diagram of AM Modulation & Demodulation
demodulation to extract the envelope of a modulated
signal. It typically consists of a diode and capacitor,
rectifying and smoothing the signal to recover the original message signal in applications such as AM
demodulation. [1]
LITRATURE REVIEW
Research Title: On the Implementation of Carrier-less Amplitude and Phase Modulation in Visible Light
Communication
Introduction:
Visible Light Communication (VLC) is a promising technology that utilizes existing lighting fixtures to provide
wireless data communication. However, the limited modulation bandwidth of commercially available white LEDs
used in VLC systems restricts the achievable data rate. To overcome this challenge, Carrier-less Amplitude and
Phase Modulation (CAP) has been proposed as a spectrally efficient modulation scheme for VLC. CAP offers
implementation simplicity and high spectral efficiency, making it suitable for VLC applications. This literature
review aims to provide a comprehensive overview of the implementation of CAP in LED-based VLC systems,
highlighting its unique features, challenges, and mitigation techniques.
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Implementation of CAP in LED-based VLC Systems
CAP is employed in LED-based VLC systems to improve the achievable data rate due to its implementation
simplicity and high spectral efficiency [5]. CAP can be implemented as a single band or a multiband scheme,
providing design flexibility [5]. The use of CAP modulation in VLC systems has the potential to achieve high data
rates with low complexity [6].
Challenges of CAP in LED-based VLC Systems
Despite its advantages, CAP modulation faces certain challenges in LED-based VLC systems. One major challenge is
the severe intersymbol interference (ISI) in bandlimited VLC systems, which degrades the performance of CAP [6].
Additionally, CAP is highly sensitive to timing jitter, further impacting its performance [6]. To address these
challenges, separate synchronization circuits or fractionally-spaced equalizers (FSE) can be used to mitigate timing
jitter sensitivity and equalization requirements [6].
Multi-band CAP (m-CAP) for VLC Systems
Multi-band CAP (m-CAP) offers the flexibility of tailoring the transmitted CAP signal to the frequency
characteristics of the VLC channel, reducing ISI [7]. However, the implementation of m-CAP increases
computational complexity and peak-to-average power ratio (PAPR) [7]. While m-CAP implementation results in
improved bit error rate (BER) performance, the increased complexity and PAPR pose implementation challenges.
Mitigation Techniques for CAP-based VLC Systems
To address the challenges of implementing CAP in LED-based VLC systems, various mitigation techniques have
been proposed. Low complexity synchronization and equalization techniques, as well as spatial and subband index
CAP schemes, are required to maintain the attractive features of CAP [8]. These techniques aim to improve the
performance of CAP-based VLC systems while minimizing complexity and power requirements [8].
Knowledge Gaps and Future Research Directions
Although significant progress has been made in the implementation of CAP in LED-based VLC systems, there are
still knowledge gaps and areas for future research. Theoretical analysis of CAP and its real-time implementation
require further investigation. Additionally, more research is needed to explore the potential of CAP in achieving
higher data rates and addressing the challenges of complexity and PAPR in m-CAP implementation [7]. Future
studies should focus on developing advanced synchronization and equalization techniques to enhance the
performance of CAP-based VLC systems [6] [8].
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Conclusion
In conclusion, Carrierless Amplitude and Phase Modulation (CAP) is a competitive and spectrally efficient
modulation scheme for LED-based VLC systems. CAP offers implementation simplicity and high data rates with
low complexity. However, CAP faces challenges such as severe ISI and sensitivity to timing jitter. Multi-band CAP
(m-CAP) provides design flexibility but increases computational complexity and PAPR. Mitigation techniques,
including low complexity synchronization and equalization techniques, as well as spatial and subband index CAP
schemes, have been proposed to address these challenges. Further research is recommended to explore the
theoretical analysis and real-time implementation of CAP, as well as to enhance the performance of m-CAP and
develop advanced synchronization and equalization techniques.
Overall, this literature review provides a comprehensive overview of the implementation of CAP in LED-based VLC
applications, highlighting its unique features, challenges, and potential future research directions.
SIMULATION
Circuit diagrams:
Figure 7: Simulation Square Law AM Modulator
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Figure 8: Simulation of Envelope Detector AM Demodulation
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Waveforms:
1. Time Domain
Figure 9: AM Modulated Waveform
Figure 10: Demodulated Original Information Signal
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2. Frequency Spectrum:
Figure 11: Frequency Spectrum of Modulated Wave
Observations
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Vm
6v
Vmax
19 V
Vc
15v
Vmin
9.8 V
FC
10kHz
Fm
500Hz
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Calculation for ckt design
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Summary and Reflections
In our exploration of AM modulation and demodulation, we utilized a BC107BP transistor for a square law
modulator, generating a Double-Sideband Suppressed Carrier (DSBSC) waveform. This modulation technique is
vital for transmitting various signals over communication channels. Additionally, employing an envelope detector
showcased the precision required for extracting the modulating signal from the carrier wave. This hands-on
experience deepened our understanding of AM modulation and demodulation processes, emphasizing the
practical applications in communication systems. The use of BC107BP and the envelope detector highlighted their
efficiency in analog signal processing. This journey exemplifies the synergy of theoretical knowledge and practical
experimentation in advancing communication technologies.
References
[1] 2. OpenAI. "Parallel operation of single-phase transformers." OpenAI Knowledge Base. [Online].
[2] M. Bakni, "en.wikipedia.or," 4 September 2021. [Online]. Available:
https://en.wikipedia.org/wiki/Amplitude_modulation#/media/File:Modulation_categorization.svg.
[3] "elprocus," [Online]. Available: https://www.elprocus.com/what-is-amplitude-modulation-derivationstypesand-applications/.
[4] "byjus," [Online]. Available: https://byjus.com/jee/amplitude-modulation/#need-for-modulation.
[5] "Ouzounis, T., Rosenqvist, E., & Ottosen, C. (2015). Spectral Effects of Artificial Light on Plant Physiology and
Secondary Metabolism: A Review. Hortscience, 50, 1128-1135.".
[6] "Mei, S., Liu, X., Zhang, W., Liu, R., Zheng, L., Guo, R., & Tian, P. (2018). High-Bandwidth White-Light System
Combining a Micro-LED with Perovskite Quantum Dots for Visible Light Communication. ACS Applied
Materials & Interfaces, 10(6), 5641-5648.".
[7] "Wang, Y., Tao, L., Huang, X., Shi, J., & Chi, N. (2015). 8-Gb/s RGBY LED-Based WDM VLC System Employing
High-Order CAP Modulation and Hybrid Post Equalizer. IEEE Photonics Journal, 7, 1-7.".
[8] "Dursun, I., Shen, C., Parida, M. R., Pan, J., Sarmah, S., Priante, D., ... Bakr, O. (2016). Perovskite Nanocrystals
as a Color Converter for Visible Light Communication. ACS Photonics, 3, 1150-1156.".
[9] "Wu, F. M., Lin, C. T., Wei, C. C., Chen, C. W., Chen, Z. Y., Huang, H. T., & Chi, S. (2013). Performance
Comparison of OFDM Signal and CAP Signal Over High Capacity RGB-LED-Based WDM Visible Light
Communication. IEEE Photonics Journal, 5, 7901507-7901507.".
[10] "rfwireless," [Online]. Available: https://www.rfwireless-world.com/images/AM-FM-PM.webp.
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