Review of Analog and digital modulation

1. Review of
Analog and Digital
Modulation
Prof. Manish Mishra
Department of Electronics
DDU Gorakhpur University

4. Basic Analog Communications System
Modulator
Demodulator
Transmission
Channel
Input
transducer
Transmitter
Receiver
Output
transducer
Carrier
EM waves (modulated
signal)
EM waves (modulated
signal)
Baseband signal
(electrical signal)
Baseband signal
(electrical signal)

5. • Information Source: Audio, Image, Text,
data
• Input Transducer: Converts source signal
to equivalent electric signal by means of:
 Microphone
 Camera
 Keyboard

6. • Output Transducer: Converts electrical
signal to human useable form by means
of:
 Speaker
 Monitor
• Transmitter: Converts electrical signal into
form suitable for channel
 Modulator
 Amplifier

7. • Channel: Medium used to transfer signal
from transmitter to receiver.
• Point to point or Broadcast
 Wire lines
 Fiber optic cable
 Atmosphere
 Often adds noise / weakens & distorts
the signal.

8. • Receiver: Extracts an estimate of the
original transducer output
 Demodulator
 Amplifier

11. Frequency Assignment
Frequency Division Multiplexing

12. Modulation
 The process of impressing low frequency information to
be transmitted on to a high-frequency wave, called the
carrier wave, by changing the characteristics of either its
amplitude, frequency, or phase angle is called
modulation.
 The process of altering the characteristics of the
amplitude, frequency, or phase angle of the high-
frequency signal in accordance with the instantaneous
value of the modulating wave is called modulation.

13. Types of Analog Modulation
 Amplitude Modulation
 Frequency Modulation
 Phase Modulation
The method of varying amplitude of a high
frequency carrier wave in accordance with the
information to be transmitted, keeping the
frequency and phase of the carrier wave
unchanged is called Amplitude Modulation.

14. Amplitude Modulation
Carrier wave
Baseband signal
Modulated wave
Amplitude varying-
frequency constant

15. Angle Modulation (frequency modulation and
phase modulation.)
• Angle modulation is the process by which the
angle (frequency or Phase)of the carrier signal
is changed in accordance with the
instantaneous amplitude of modulating or
message signal. It is also known as
“Exponential modulation”. The amplitudes of
the carrier remain constant in this process.

16. Frequency Modulation
Carrier wave
Baseband signal
Modulated wave
Frequency varying-
amplitude constant
Large amplitude:
high frequency
Small amplitude:
low frequency

17. Modulator
Demodulator
Transmission
Channel
Input
transducer
Transmitter
Receiver
Output
transducer
Carrier
EM waves (modulated
signal)
EM waves
(modulated signal)
Analog signal
analog signal
Digital signal
digital signal
Digital Modulation System

18. Elements of Digital Communication

24. Sampling Theorem and Its Importance
“A band limited signal can be reconstructed
exactly if it is sampled at a rate at least twice
the maximum frequency component in it”
𝒇𝒔 ≥ 𝟐𝒇𝒎
Here,
𝒇𝒔 = sampling frequency
𝒇𝒎 = maximum frequency component
in the signal

27. Pulse Amplitude Modulation
Pulse Amplitude Modulation (PAM) is an analog
modulating scheme in which the amplitude of the pulse
carrier varies proportional to the instantaneous
amplitude of the message signal.

29. Pulse Width Modulation(PWM)
 Pulse Width Modulation (PWM) or Pulse Duration
Modulation (PDM) or Pulse Time Modulation (PTM)
is an analog modulating scheme in which the
duration or width or time of the pulse carrier varies
proportional to the instantaneous amplitude of the
message signal.
 The width of the pulse varies in this method, but the
amplitude of the signal remains constant. Amplitude
limiters are used to make the amplitude of the signal
constant. These circuits clip off the amplitude, to a
desired level and hence the noise is limited.

30. PWM Signal

31. There are three variations of PWM. They are:
 The leading edge of the pulse being constant, the
trailing edge varies according to the message signal.
 The trailing edge of the pulse being constant, the
leading edge varies according to the message signal.
 The center of the pulse being constant, the leading
edge and the trailing edge varies according to the
message signal.

32. Pulse Position Modulation (PPM)
• Pulse Position Modulation (PPM) is an analog modulating
scheme in which the amplitude and width of the pulses
are kept constant, while the position of each pulse, with
reference to the position of a reference pulse varies
according to the instantaneous sampled value of the
message signal.
• The transmitter has to send synchronizing pulses (or
simply sync pulses) to keep the transmitter and receiver in
synchronism. These sync pulses help maintain the position
of the pulses. The following figures explain the Pulse
Position Modulation.

35. Pulse Code Modulation(PCM)

36. PCM Coding of Analog Signal

37. Amplitude Shift Keying(ASK)
 Amplitude Shift Keying (ASK) is a type of
Amplitude Modulation which represents the
binary data in the form of variations in the
amplitude of a signal.
 Any modulated signal has a high frequency
carrier. The binary signal when ASK
modulated, gives a zero value for Low input
while it gives the carrier output for High
input.

39. ASK Modulator

40. ASK Demodulator

41. Frequency Shift Keying (FSK)
 Frequency Shift Keying (FSK) is the digital
modulation technique in which the frequency of
the carrier signal varies according to the digital
signal changes. FSK is a scheme of frequency
modulation.
 The output of a FSK modulated wave is high in
frequency for a binary High input and is low in
frequency for a binary Low input. The binary 1s
and 0s are called Mark and Space frequencies.

44. Phase Shift Keying (PSK)
• Phase Shift Keying (PSK) is the digital
modulation technique in which the phase
of the carrier signal is changed by varying
the sine and cosine inputs at a particular
time. PSK technique is widely used for
wireless LANs, bio-metric, contactless
operations, along with Bluetooth
communications.

45. Binary Phase Shift Keying (BPSK)
 This is also called as 2-phase PSK or Phase Reversal Keying. In this
technique, the sine wave carrier takes two phase reversals such as
0° and 180°.
 BPSK is basically a Double Side Band Suppressed Carrier (DSBSC)
modulation scheme, for message being the digital information.
Quadrature Phase Shift Keying (QPSK)
 This is the phase shift keying technique, in which the sine wave
carrier takes four phase reversals such as 0°, 90°, 180°, and 270°.
 If this kind of techniques are further extended, PSK can be done
by eight or sixteen values also, depending upon the requirement.

46. BPSK Modulator
The block diagram of Binary Phase Shift Keying consists of the
balance modulator which has the carrier sine wave as one
input and the binary sequence as the other input.
The modulation of BPSK is done using a balance modulator, which multiplies the two signals
applied at the input. For a zero binary input, the phase will be 0° and for a high input, the
phase reversal is of 180°

47. The output sine wave of the modulator will be the direct
input carrier or the inverted (180° phase shifted) input carrier,
which is a function of the data signal.

48. Differential Phase Shift Keying (DPSK)
 In Differential Phase Shift Keying (DPSK) the phase of the
modulated signal is shifted relative to the previous signal element.
No reference signal is considered here. The signal phase follows the
high or low state of the previous element. This DPSK technique
doesn’t need a reference oscillator.
If the data bit is Low i.e., 0, then the phase of the signal is not reversed, but continued
as it was. If the data is a High i.e., 1, then the phase of the signal is reversed, as with
NRZI, invert on 1 (a form of differential encoding).

49. Stay at Home
Stay Safe