In a communication system, the modulation is an important step. Modulation is the process of transmitting a message signal (Baseband signal with low frequency) from transmitter to receiver without changing its characteristics (like amplitude, frequency, phase) by using a carrier signal (high frequency) which varies in accordance with the instantaneous values of the low frequency wave by keeping its frequency and phase constant.

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The modulation techniques are classified into two major types: analog and digital or pulse modulation. We have discussed previously the different types of modulation techniques, let us understand the basic difference between PAM, PWM, and PPM.

Types of Modulation Techniques

Before going to discuss the difference between PAM, PWM, and PPM, let us discuss individually each. All these are pulse analog modulation techniques.

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Pulse Amplitude Modulation

By varying the amplitude of the pulses (the carrier signal) in proportion to the instantaneous values of the analog signal (the message signal).

Pulse Amplitude Modulation (PAM) Signals

The above figure illustrates the time domain representation of the PAM technique which mentions analog message and PAM modulated signal as an output.

Pulse amplitude modulation is used in the popular Ethernet communication standard. The PAM modulator and demodulator circuits simple compared to other kinds of modulation and demodulation techniques.

There are two categories of PAM techniques, one is the pulses have the same polarity and the other in which the pulses can have both positive and negative polarities according to the amplitude of the modulating signal.

Pulse Width Modulation

The Pulse width Modulation– By varying the width of the pulses (the carrier signal) in proportion to the instantaneous values of the analog signal (the message signal).




The width of the pulse varies, but the amplitude of the pulse remains constant. Amplitude limiters are used to make the amplitude constant. These circuits clip-off the amplitude, to a preferred level and hence the noise is limited.

There are three types 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.



Pulse Position Modulation

By varying the position of the pulses (the carrier signal) in proportion to the instantaneous values of the analog signal (the message signal).

Pulse position modulation is done in accordance with the pulse width modulated signal. Each trailing of the pulse width modulated signal becomes the starting point for pulses in PPM signal.

Hence, the position of these pulses is proportional to the width of the PWM pulses. But the main disadvantage of the PPM modulation technique is, The synchronization between transmitter and receiver must be needed.






Difference between PAM, PWM, and PPM

In all the above cases, we detect the message of the pulse modulated signal and reconstruct the original analog signal.

Difference between PAM, PWM, and PPM of the Analog Modulation

The below table gives the detailed difference between PWM, PAM, and PPM.

Sr. No.

Parameter

PAM

PWM

PPM

1

Type of Carrier

Train of Pulses

Train of Pulses

Train of Pulses

2

Variable Characteristic of the Pulsed Carrier

Amplitude

Width

Position

3

Bandwidth Requirement

Low

High

High

4

Noise Immunity

Low

High

High

5

Information Contained in

Amplitude Variations

Width Variations

Position Variations

6

Power efficiency (SNR)

Low

Moderate

High

7

Transmitted Power

Varies with amplitude of pulses

Varies with variation in width

Remains Constant

8

Need to transmit synchronizing pulses

Not needed

Not needed

Necessary

9

Bandwidth depends on

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

10

Transmitter power

Instantaneous transmitter power varies with the amplitude of the pulses

Instantaneous transmitter power varies with the amplitude and width of the pulses

Instantaneous transmitter power remains constant with the width of the pulses

11

Complexity of generation and detection

Complex

Easy

Complex

12

Similarity with other Modulation Systems

Similar to AM

Similar to FM

Similar to PM



This article is all about the difference between PAM, PWM, and PPM techniques. Furthermore, for any help on Electronic projects or doubts regarding this article, you can contact us by commenting in the comment section given below.



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Source：elprocus