# Difference between Amplitude and Phase Modulations

In data communication, modulation is a process of changing the characteristics of a data carrier signal so that it can travel the desired distance for data transmission. Modulation is a necessary process in communication systems to increase the reliability of data communication.

In the modulation process, an additional signal, called carrier signal, is generated that can go up to long distances, then the message signal is superimposed with this carrier signal, so that the carrier signal transmit the message signal over a long distance without getting affected by the external disturbances. This process is known as modulation.

There are several types of modulations present such as amplitude modulation (AM), phase modulation (PM), frequency modulation (FM), etc. In this article, we will discuss the amplitude modulation (AM) and phase modulation (PM), and the important differences between them. So, let us begin with the introduction of AM and PM.

## What is Amplitude Modulation (AM)?

The modulation processing in which the amplitude of the high frequency carrier signal is altered in accordance with the instantaneous amplitude of the modulating signal, then this type of modulation technique is called as Amplitude Modulation (AM).

In the case of amplitude modulation, the phase and frequency of the carrier signal kept constant, but only amplitude is varied. The amplitude of the carrier signal is changed according to the distance and nature of data or information to be sent. Amplitude modulation generally can transmit data and information over long distances.

For a perfect amplitude modulation, the modulation index should be equal to 1 that means the modulation depth should be 100%. Generally, the modulation index of amplitude modulation varies from 0 to 1. Amplitude modulation is used in electronic communication such as in modems in computers, VHF aircraft radios, portable two-way radios, etc.

## What is Phase Modulation (PM)?

In communication, phase modulation (PM) is a subtype of the angle modulation technique. Phase modulation can be defined as the modulation process in which the phase of the carrier signal is changed in accordance with the instantaneous amplitude of the modulating signal.

In the case of phase modulation, the amplitude and frequency of the carrier signal remains constant while only the phase of the carrier signal is changed. In the case of phase modulation, the modulation index is always more than 1. Phase modulation is widely used in several digital data transmission systems such as in WIFI, GSM, Satellite Communication, mobile communication, etc.

After getting insights into the basics of amplitude modulation and phase modulation, let us now discuss the important differences between them.

## Differences between Amplitude Modulation and Phase Modulation

The following table highlights all the significant differences between amplitude modulation (AM) and phase modulation (PM) −

Parameter

Amplitude Modulation

Phase Modulation

Abbreviation

Amplitude modulation is abbreviated as AM.

Phase modulation is abbreviated as PM.

Definition

The modulation process in which the amplitude of the carrier signal is varied according to the instantaneous amplitude of the modulating signal is known as amplitude modulation.

The modulation process in which the phase of the carrier signal is varied according to the instantaneous amplitude of the modulating signal is known as phase modulation.

Modulation index

The modulation index for the amplitude modulation varies from 0 to 1. For perfect amplitude modulation, it is 1.

The modulation index for the phase modulation is always greater than 1.

Variable parameter

In amplitude modulation, the variable parameter of the carrier signal is its amplitude.

In phase modulation, the variable parameter of the carrier signal is its phase.

Constant parameter

In amplitude modulation, the frequency and phase of the carrier signal are kept constant.

In phase modulation, the amplitude and frequency of the carrier signal are kept constant.

Effect of noise

Amplitude modulation is greatly affected by noise.

Phase modulation is relatively more immune to noise.

Signal to noise ratio

Amplitude modulation has better signal to noise ratio.

For phase modulation, signal to noise ratio is poor.

The received signal is of low quality in the case of amplitude modulation due to poor immunity to noise.

In the phase modulation, the high quality signal is received.

System fidelity

For amplitude modulation, the system fidelity is poor.

Phase modulation has improved system fidelity.

Amplitude modulation is a linear modulation.

Phase modulation is a non-linear modulation.

Types

Types of amplitude modulation include – Double Sideband Suppressed Carrier Modulation (DSB-SC), Single Sideband Modulation (SSB), Vestigial Sideband Modulation (VSB), etc.

Types of phase modulation include - Quadrature Phase Shift Keying (QPSK), Binary Phase-shift keying (BPSK), etc.

Modulation circuit

The modulator circuit for amplitude modulation is relatively simple.

The modulator circuit used for phase modulation is complex

Applications

Amplitude modulation is widely used in TV video transmission, short and medium wave band broadcasting, aircraft communication, etc.

Phase modulation is widely used in mobile and telephone communication, sound synthesis systems, digital synthesizers, etc.

## Conclusion

Both AM and PM are the types of continuous-wave modulation techniques. Amplitude modulation is a modulation technique in which the amplitude of the carrier signal is changed by keeping the frequency and phase of the signal constant. On the other hand, in phase modulation, the phase of the carrier wave is varied according to the modulating signal by keeping the amplitude and frequency constant.

Another significant difference between amplitude modulation and phase modulation is that the amplitude modulation is a linear modulation technique, while the phase modulation is a non-linear modulation technique.

Updated on: 27-Mar-2023

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