This document discusses different types of modulation including amplitude modulation (AM), frequency modulation (FM), phase modulation (PM), and pulse width modulation (PWM). It defines each type of modulation and compares their characteristics. It also discusses the needs for modulation, advantages and disadvantages of PM, and the relationship between PM and FM.

1. By:
Engr.Yasir Ali
Engr.Ashfaq Ali
Engr. Aamir Khan
(QUEST, Nawabshah)

2. MODULATION
NEEDS OF MODULATION
DEFINITION OF AM
DEFINITION OF FM
PM AND FM ARE RELATED
DEFINITION OF PHASE MODULATION
ADVANTAGES AND DISADVANTAGES OF PM
DEFINATION OF PHASE WIDTH MODULATION
ADVANTAGES AND DISADVANTAGES OF PWM

3. The process of altering the characteristics of the
amplitude, frequency, or phase angle of the highfrequency signal in accordance with the instantaneous
value of the modulating wave is called modulation.

4. Need for Modulation
• The antenna needed for transmitting signals should have
size at least λ/4.The information signal is of low frequency
(and therefore the wavelength is high). If we need to
transmit such a signal directly, the size of the antenna will
be very large and impossible to build. Hence direct
transmission is not practical.
• If we transmit the information signals directly, the signals
from different transmitters will get mixed up and the
information will be lost.
• When a wave has a large frequency, the energy
associated with it will also be large.

5. Amplitude Modulation (AM):
1Changes the amplitude of the carrier signal according
to the amplitude of the message signal.
2All information is carried in the amplitude of the carrier.
3AM systems usually occupy less bandwidth then FM
systems.
4AM carrier signal has time-varying envelope.

6. Frequency Modulation (FM)
 In telecommunications and processing of the
signal, frequency modulation (FM) conveys
information over a carrier wave by varying its
instantaneous frequency. This contrasts with the
modulation amplitude, which varies the amplitude of
the carrier, while its frequency remains constant.
Frequency modulation tends to be used in the
transmission of music.

7. Frequency versus Amplitude Modulation
AM
FM

8. Phase modulation (PM) is a form of modulation that
represents information as variations in the instantaneous
phase of a carrier wave. Modification in phase according to
low frequency will give phase modulation.
PM is not widely used for radio transmissions. This is
because it tends to require more complex receiving hardware
and there can be ambiguity problems in determining whether,
for example, the signal has changed phase by +180° or
-180°

9. What are the advantages and
disadvantages of phase modulation?
Advantage –
1.
2.
3.
Phase modulation & demodulation is easy compared to
Frequency modulation.
Phase modulator is used in determining velocity of moving
target by extracting Doppler information.
Doppler information needs stable carrier which is possible in
phase modulation but not in frequency modulation.
Disadvantage –
1.
2.
Phase ambiguity comes if we exceed its modulation
index pi radian(180 degree).
we need frequency multiplier to increase phase
modulation index.

10. PM and FM modulation are related
PM
FM
 PM is the time integral of FM.
 The PM carrier phase
deviation is proportional to
the amplitude of the
modulating signal, constant
with respect to the frequency
of the modulating signal.
 FM is the time derivative of
PM.
 The FM carrier frequency
deviation is proportional to
the amplitude of the
modulating signal and is
constant with respect to the
frequency of the modulating
signal.
 The FM carrier phase
deviation is proportional to its
frequency deviation and
inversely proportional to the
modulating frequency
 The PM carrier frequency
deviation is proportional to
the frequency of the
modulating signal.

11.  Pulse width modulation (PWM), also known as
pulse duration modulation (PDM), is a digital
modulation technique.
 PWM is a commonly used technique for
controlling power of electrical devices, made ​
practical by modern electronic power switches.
 PWM also works well with digital controls,
which, because of their on/off nature, can easily
set the needed duty cycle

12. Pulse width modulation:

13. Advantages & disadvantage of pulse
width modulation?
Advantages
o
o
o
o
o
o
o
Cheap to make.
Little heat whilst working
Low power consumption.
Can utilize very high frequencies (50-100 KHz is not uncommon.)
Very energy-efficient when used to convert voltages or to dim light bulbs.
High power handling capability
Efficiency up to 90%
Disadvantages
•
•
•
•
Complexity of circuit
Radio Frequency Interference
Voltage spikes
Electromagnetic noise

14. • ANY
•
•
QUESTION?