The sampling theorem can be explained as follows: 1. According to the sampling theorem, a continuous-time signal x(t) that has no frequency components higher than B Hz can be perfectly reconstructed from its samples if it is sampled at a frequency fs that is greater than 2B samples/second. This minimum sampling frequency fs is called the Nyquist rate. 2. The sampling theorem states that for a bandlimited signal with maximum frequency B Hz, the signal must be sampled at a frequency fs that is greater than 2B samples/second in order to avoid aliasing and allow perfect reconstruction of the original continuous-time signal from the samples. 3. Aliasing occurs when the signal is sampled at a rate lower than

1. MATRUSRI ENGINEERING COLLEGE
DEPARTMENT OF ELECTRONICS AND COMMUNICATION
ENGINEERING
SUBJECT NAME: ANALOG COMMUNICATIONS
FACULTY NAME: Dr. M.NARESH
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2. ANALOG COMMUNICATIONS
COURSE OBJECTIVES:
1. To Analyze the Analog communication system requirements
2.To understand the Generation and Detection of various analog modulation
techniques
3.To Analyze the noise performance of analog modulation techniques
4.To understand AM and FM Receivers.
5. To Understand the Pulse modulation techniques
COURSE OUTCOMES:
CO1: Describe basic concepts of linear and non-linear modulation and
demodulation schemes
CO2: Compare analog modulation schemes in terms of modulation index,
transmission bandwidth, TX power etc.
CO3: Explaining various aspects of sampling theorem to produce various
pulse modulation schemes
CO4: Appreciate the structures of various AM and FM transmitters and
receivers and understand design parameters.
CO5: Estimate electronic noise parameters on various analog modulation
schemes.
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3. SYLLABUS
UNIT I- Linear Modulation schemes: Need for modulation,
conventional Amplitude Modulation (AM). Double side band
suppressed carrier (DSB –SC)modulation ,Hilbert transform,
properties of Hilbert transform. Pre-envelop. Complex envelope
representation of band pass signals, In-phase and Quadrature
component representation of band pass signals. Low pass
representation of band pass systems. Single side band (SSB)
modulation and Vestigial-sideband (VSB) modulation. Modulation
and demodulation of all the modulation schemes, COSTAS loop.
UNIT II- Angle modulation schemes: Frequency Modulation (FM)
and Phase modulation (PM), Concept of instantaneous phase and
frequency. Types of FM modulation: Narrow band FM and wide
band FM. FM spectrum in terms of Bessel functions. Direct and
indirect (Armstrong's) methods of FM generation. Balanced
discriminator, Foster–Seeley discriminator ,Zero crossing detector
and Ratio detector for FM demodulation. Amplitude Limiter in FM.
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4. UNIT IV- Analog pulse modulation schemes: Sampling of
continuous time signals. Sampling of low pass and band pass signals.
Types of sampling. Pulse Amplitude Modulation (PAM) generation
and demodulation. Pulse time modulation schemes: PWM and PPM
generation and detection. Time Division Multiplexing.
UNIT III- Transmitters and Receivers: Classification of
transmitters. High level and low level AM transmitters. FM
transmitters. Principle of operation of Tuned radio frequency (TRF)
and super heterodyne receivers. Selection of RF amplifier. Choice of
Intermediate frequency. Image frequency and its rejection ratio
Receiver characteristics: Sensitivity, Selectivity, Fidelity, Double
spotting, Automatic Gain Control.
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UNIT V- Noise Sources and types: Atmospheric noise, Shot noise
and thermal noise. Noise temperature. Noise in two-port network:
noise figure, equivalent noise temperature and noise bandwidth.
Noise figure and equivalent noise temperature of cascade stages.
Narrow band noise representation. S/N ratio and Figure of merit
calculations in AM, DSB-SC, SSB and FM systems, Pre-Emphasis and
De-Emphasis

5. TEXT BOOKS /REFERENCES
TEXT BOOKS:
1. Simon Haykin, “Communication Systems,” 2/e, Wiley India, 2011.,
2. B.P. Lathi, Zhi Ding, “Modern Digital and Analog Communication
Systems”, 4/e, Oxford University Press, 2016
3. P. Ramakrishna Rao, “Analog Communication,” 1/e, TMH, 2011.
REFERENCES:
1.Taub, Schilling, “Principles of Communication Systems”, Tata
McGraw‐Hill, 4th Edition, 2013.
2. John G. Proakis, Masond, Salehi, “Fundamentals of Communication
Systems”, PEA, 1st Edition,2006
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6. LESSON PLAN:
UNIT IV- Analog pulse modulation schemes
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S. No. Topic(S)
No.
of Hrs
Relevant
COs
Text Book/
Reference
Book
1. Analog pulse modulation schemes: Sampling of
continuous time signals.
2 CO3 T1,T2,T3
2. Sampling of low pass and band pass signals. 2 CO3 T1,T2,T3
3. Types of sampling. Pulse Amplitude Modulation
(PAM) generation and demodulation
1 CO3 T1,T2,T3
4. Pulse time modulation schemes: PWM and PPM
generation and detection.
2 CO3 T1,T2,T3
5. Time Division Multiplexing 1 CO3 T1,T2,T3
TOTAL 08

7. PRE-REQUISITES FOR THIS COURSE:
PTSP III-SEM 3-Credits
ES215EC :SS IV-SEM 3-Credits
EXTERNAL SOURCES FOR ADDITIONAL LEARNING:
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Description Proposed Actions Relevance With POs
Relevance
With PSOs
Modulation &
Demodulation of all
Techniques including
multiplexing .
Communication Lab PO3, PO4, PO5 PSO2
CONTENT BEYOND SYLLABUS:
S. No. Topic Relevance with POs and
PSOs
1. Advanced Communication system PSO1

8. INTRODUCTION:
Pulse modulation schemes aim at transferring a narrowband analog signal over an
analog baseband channel as a two-level signal by modulating a pulse wave . Some pulse
modulation schemes also allow the narrowband analog signal to be transferred as a
digital signal (i.e., As a quantized discrete time signal) with a fixed bit rate, which can be
transferred over an underlying digital transmission system, for example, some line code
. These are not modulation schemes in the conventional sense since they are
not channel coding schemes, but should be considered as source coding schemes, and
in some cases analog-to-digital conversion techniques..
UNIT IV- Analog pulse modulation schemes
OUTCOMES:
Interpret with different types of receivers and study different
pulse modulation and demodulationtechniques
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9. CONTENTS:
4.1. Analog pulse modulation schemes:
4.2. sampling of continuous time signals.
4.3. Sampling of low pass and band pass signals.
4.4. Types of sampling.
4.5. Pulse amplitude modulation (PAM) generation and demodulation.
4.6. Pulse time modulation schemes:
PWM and PPM generation and detection.
4.7. Time division multiplexing.
OUTCOMES:
Interpret with different types of receivers and study different
pulse modulation and demodulationtechniques
UNIT IV- Analog pulse modulation schemes
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10. CONTENTS:
4.1. Analog pulse modulation schemes
4.2. Sampling of continuous time signals
OUTCOMES:
Explaining various aspects of sampling theorem to produce various pulse modulation
schemes
MODULE-1
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11. Sampling & reconstruction:
this section is concerned with digital signal processing systems capable of operating on
Analog signals which must first be sampled and digitised. The resulting digital signals
often need to be converted back to analogue form or “reconstructed”. Before starting, we
review some facts about analogue signals
Nyquist Rate:
It is the minimum sampling rate at which signal can be converted into samples and can
be recovered back without distortion.
Nyquist rate fs = 2fm hz
4.1. Analog pulse modulation schemes
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12. 4.1. Analog pulse modulation schemes
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13. SAMPLING OF CONTINUOUS TIME SIGNALS:
The process of converting continuous time signals into equivalent discrete time signals,
can be termed as sampling. A certain instant of data is continually sampled in the
sampling process.
The following figure indicates a continuous-time signal x(t) and a sampled signal xs(t).
When x(t) is multiplied by a periodic impulse train, the sampled signal xs(t) is obtained
A sampling signal is
a periodic train of pulses,
having unit amplitude,
sampled at equal intervals
of time Ts, which is called
as the Sampling time.
This data is transmitted at
the time instants Ts and the
carrier signal is transmitted
at the remaining time.
4.2. sampling of continuous time signals
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14. SAMPLING OF CONTINUOUS TIME SIGNAL:
Sampling of input signal x(t) can be obtained by multiplying x(t) with an impulse train
δ(t) of period Ts. The output of multiplier is a discrete signal called sampled signal which
is represented with y(t) the sampled signal takes the period of impulse
4.2. sampling of continuous time signals
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15. CONTENTS:
4.3 samplings of band pass signals
4.4. Types of sampling
OUTCOMES:
Discussing about types of sampling
MODULE-2
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16. 4.3 sampling of continuous time signals
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17. In case of band pass signals, the spectrum of band pass signal x[ω] = 0 for the frequencies outside
the range f1 ≤ f ≤ f2. The frequency f1 is always greater than zero. Plus, there is no aliasing effect when
fs > 2f2. But it has two disadvantages:
The sampling rate is large in proportion with f2. This has practical limitations. The sampled signal
spectrum has spectral gaps.
4.3 Samplings of Band Pass Signals
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18. 4.3 Samplings of Band Pass Signals
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19. The overlapped region in case of under sampling represents aliasing effect, which can be
removed by considering fs >2fm by using anti aliasing filters.
Types of SAMPLING:
4.4. Types of sampling
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1. Impulse sampling
2. Natural sampling
3. Flat –TOP sampling

20. CONTENTS:
4.4. Types of Pulse Modulation
4.5. Pulse amplitude modulation generation and demodulation
OUTCOMES:
Discussing about types of Pulse Modulation and PAM
MODULE-3
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21. Pulse modulation is a type of modulation in which the signal is transmitted in the form
of pulses. It can be used to transmit analogue information. In pulse modulation,
continuous signals are sampled at regular intervals:
1.Pulse amplitude modulation (PAM) generation and demodulation
2. Pulse width modulation (PWM) generation and demodulation
3. Pulse position modulation (PPM) generation and demodulation
4.4.Types of Pulse Modulation
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22. Generation:
4.5. Pulse amplitude modulation generation and demodulation
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23. 4.5. Pulse amplitude modulation generation and demodulation.
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24. DEMODULATION OF PAM;
Frequency range and provides sufficient attenuation at the pulse rate frequency. A simple low pass
filter (LPF) shown in the above Fig. can work as a PAM demodulator.
A low pass filter is basically an integrator. It filters out the high frequency sampling pulses of the
rectangular wave generator. Each pulse gets integrated, the amplitude of the integrated output being
proportional to the input pulse amplitude.
The capacitor will get charged at every pulse output and will keep on supplying this charged voltage
at the output during the off time of the pulse. This restores the fidelity of the message. The only
precaution to be observed is to ensure that the LPF has a flat frequency response over the entire base
band frequency.
4.5. Pulse amplitude modulation generation and demodulation
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25. CONTENTS:
4.6. Pulse Width and Pulse Position modulation generation and demodulation
OUTCOMES:
Discussing about PWM and PPM
MODULE-4
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26. 4.6 Pulse Width Modulation (PWM)
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In pulse width modulation (PWM), the width of each pulse is made directly proportional to the each pulse is made
directly proportional to the amplitude of the information signal. In pulse position modulation, constant -width pulses
are used, and the position or time of occurrence of each pulse from some reference time is made directly proportional
to the amplitude of the information signal.

27. 4.6 Pulse Width Modulation (PWM)
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A sawtooth generator generates a sawtooth signal
of frequency fs, and this sawtooth signal in this
case is used as a sampling signal. It is applied to
the inverting terminal of a comparator.
The modulating signal x (t) is applied to the non-
inverting terminal of the same comparator.
The comparator output will remain high as long
as the instantaneous amplitude of x (t) is higher
than that of the ramp signal. This gives rise to a
PWM signal at the comparator output
Here, it may be noted that the leading edges
of the PWM waveform coincide with the
falling edges of the ramp signal. Thus, the
leading edges of PWM signal are always
generated at fixed time instants.
However, the occurance of its trailing edges
will be dependent on the instantaneous
amplitude of x(t). Therefore, this PWM signal
is said to be trail edge modulated PWM.

28. The basic theory behind pulse width demodulation is that converting the PWM signal to PAM (pulse
amplitude modulation) signal. PAM can be easily detected by suitable low pass filter.
4.6 PWM Demodulation
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Input PWM wave is applied to ramp generator and synchronous pulse generator

29. 4.6 PWM Demodulation
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30. In pulse position modulation, constant -width pulses are used, and the position or time of occurrence
of each pulse from some reference time is made directly proportional to the amplitude of the
information signal.
4.6. Pulse Position Modulation (PPM)
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31. The output of the comparator is fed to a monostable multivibrator. It is negative edge triggered.
Hence, with the trailing edge of the PWM signal, the output of the monostable goes high.
This is why a pulse of PPM signal begins with the trailing edge of the PWM signal.
It is to be noted in case of PPM that the duration for which the output will be high depends on the RC
components of the multivibrator. This is the reason why a constant width pulse is obtained in case of
the PPM signal.
4.6. Pulse Position Modulation (PPM) Generation
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32. The PPM signal transmitted from the modulation circuit gets distorted by the noise during
transmission. This distorted PPM signal reaches the demodulator circuit. The pulse generator
employed in the circuit generates a pulsed waveform. This waveform is of fixed duration which is fed
to the reset pin (R) of the SR flip-flop.
The reference pulse generator generates, reference pulse of a fixed period when transmitted PPM
signal is applied to it. This reference pulse is used to set the flip-flop.
These set and reset signals generate a PWM signal at the output of the flip-flop. This PWM signal is
then further processed in order to provide the original message signal.
4.6 Pulse Position Demodulation (PPM)
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33. Comparison between PAM, PWM, and PPM
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PAM PWM PPM
Amplitude is varied Width is varied Position is varied
Bandwidth depends
on the width of the
pulse
Bandwidth depends
on the rise time of
the pulse
Bandwidth depends
on the rise time of
the pulse
Instantaneous
transmitter power
varies with the
amplitude of the
pulses
Instantaneous
transmitter power
varies with the
amplitude and the
width of the pulses
Instantaneous
transmitter power
remains constant
with the width of
the pulses
System complexity
is high
System complexity
is low
System complexity
is low
Noise interference
is high
Noise interference
is low
Noise interference
is low
It is similar to
amplitude
modulation (AM)
It is similar to
frequency
modulation
(FM)
It is similar to phase
modulation
(PM)

34. CONTENTS:
4.7. Time Division Multiplexing
OUTCOMES:
Discussing about TDM
MODULE-5
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35. Time division multiplexing (TDM): is the time interleaving of samples from several sources so that
the information from these source can be transmitted serially over a single communication channel.
4.7 Time Division Multiplexing (TDM)
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Inputs
Outputs

36. 4.7 Time Division Multiplexing (TDM)
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37. 1. Explain the sampling Theorem.
2. Draw and explain about PWM and PPM signals generation and detection.
3. Write about Time Division Multiplexing.
4. What are differences between PAM, PWM and PPM.
5. How PDM wave converted into PPM system?
Assignment Question
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38. Short answer questions
Questions & Answers
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S.NO QUESTION
Blooms
Taxonomy
Level
Course
Outcome
1. Define Nyquist rate? CO4
2. What is the need of pulse modulation? CO4
3. How PDM wave converted into PPM system? CO4
4. What do you mean by aliasing? CO4
5. Why flat-top sampling required? CO4

39. Long answer questions
Questions & Answers
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S.NO QUESTION
Blooms
Taxonomy
Level
Course
Outcome
1. State and prove the sampling theorem for the low pass
signal
CO4
2. Draw and Explain about PWM signals generation and
detection
CO4
3. Explain about Pulse amplitude modulation. CO4
4. Draw and Explain about PPM signals generation and
detection
CO4
5. Explain (a) Explain in brief about bit interleaving in TDM.
(b) How PDM wave converted into PPM system
CO4

40. THE-END
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