Difference between Amplitude Modulation and Phase Modulation
Last Updated :
20 Dec, 2024
Amplitude Modulation (AM) and Phase Modulation (PM) are two different types of analog modulation techniques used to encode information onto a carrier wave. Both are used in telecommunications, broadcasting, and various forms of wireless communication. While AM varies the amplitude of the carrier signal, PM modulates the phase of the carrier wave in response to the information signal.
In this article, both Amplitude Modulation and Phase modulation will be explained in detail in relation to basic principles, uses, and the main difference between the two.
What is Amplitude Modulation(AM)?
Amplitude Modulation is a modulation in which the amplitude of the carrier wave changes according to the instantaneous amplitude of the modulating signal keeping phase and frequency constant. The amplitude of the carrier wave is modified to send the data or information.
It can transmit over long distances and has a large range. Its modulation index varies from 0 to 1. In Amplitude Modulation, the frequency and phase remain the same.
How Amplitude Modulation Works?
In Amplitude Modulation, the modulating signal which may be a voice or music signal changes the amplitude of a high-frequency carrier wave. The amplitude of the carrier wave is varied proportional to the strength of the modulating signal which contains the information to be transmitted within the wave. In contrast to the more complex cables that offer noise protection, AM is simpler and more commonly implemented and is far more prone to noise and interference that ends up distorting the signal.
Amplitude ModulationAdvantages of Amplitude Modulation(AM)
- Simplicity: AM is easy to implement with basic electronic components.
- Widespread Use: AM has been used for over a century in radio broadcasting and long-distance communication.
- Long-Distance Coverage: AM signals can travel far, especially at night, due to their ability to bounce off the ionosphere and cover large distances.
- Low-Cost Equipment: AM transmitters and receivers are less expensive than other modulation schemes.
Disadvantages of Amplitude Modulation(AM)
- Noise and Interference: AM is highly susceptible to interference from electrical equipment, weather conditions, and atmospheric noise, which can degrade signal quality.
- Poor Sound Quality: AM typically offers lower sound quality and narrower bandwidth compared to other modulation techniques like FM.
- Power Inefficiency: AM requires more transmission power because a significant portion of the signal energy is used by the carrier wave, which doesn’t carry any useful information.
- Bandwidth Consumption: AM signals occupy a relatively large bandwidth compared to the message signal, which can lead to inefficient use of the frequency spectrum.
What is Phase Modulation(PM)?
Phase Modulation is a modulation technique in which the phase of the carrier wave changes according to the instantaneous amplitude of the modulating signal keeping amplitude and frequency as constant. Phase Modulation and Frequency Modulation are similar, but in Phase Modulation frequency of the carrier signal is not increased. Phase Modulation is used in mobile system. The phase of the carrier wave is modified in order to send the data or information.
How Phase Modulation Works?
In Phase Modulation, the modulating signal results into a phase shift of the carrier wave. As seen in the above block diagram, the amount of phase shift is dependent on the amplitude of the modulating signal. Inasmuch as the phase of the wave is being modified then the frequency is retained as is the usual characteristic of an Amplitude Modulation wave. By Phase Modulation, it is meant a technique that is widely used in digital communication systems where data, noise and interferences are crucial factors.
Phase ModulationAdvantages of Phase Modulation(PM)
- Better Noise Immunity: PM is less susceptible to amplitude-based noise and interference (such as electrical noise), providing a more reliable signal.
- Improved Signal Quality: Since PM is less affected by noise, it generally provides higher quality transmission in noisy environments.
- More Efficient Use of Power: Unlike AM, PM does not require as much transmission power since the carrier amplitude remains constant.
- Better Bandwidth Efficiency: PM can achieve better bandwidth efficiency than AM, as the bandwidth required is closely related to the message signal’s frequency, and not wasted on the carrier wave.
Disadvantages of Phase Modulation(PM)
- More Complex Equipment: PM requires more advanced and expensive equipment for both modulation and demodulation, making it more costly than AM.
- Limited Range: PM signals generally have a shorter transmission range compared to AM, especially in free-space applications like radio broadcasting.
- Requires Precise Control: PM requires precise control of the phase changes to avoid signal distortion, which requires more sophisticated equipment.
- Bandwidth Usage: PM can consume more bandwidth than necessary, especially when the modulation index (degree of phase shift) is high.
Difference Between Amplitude Modulation and Phase Modulation
| Amplitude Modulation | Phase Modulation |
|---|
| In Amplitude Modulation, the frequency remains the same. | In Phase Modulation, the amplitude remains the same. |
| It has simple circuit. | It has complex circuit. |
| Its modulation index varies from 0 to 1. | Its modulation index is always greater than one. |
| Noise immunity is poor than in PM. | Noise immunity is better than in AM. |
| In Amplitude Modulation, the phase remains the same. | In Phase Modulation, the frequency remains the same. |
| Amplitude Modulation is widely used. | Phase Modulation is used in mobile system. |
Highly susceptible to noise, electrical interference, and atmospheric conditions | Less susceptible to interference, especially from amplitude-based noise |
| Signal to noise ratio is better than Phase Modulation. | Signal to noise ratio is poor than Amplitude Modulation. |
| The amplitude of the carrier wave is modified in order to send the data or information. | The phase of the carrier wave is modified in order to send the data or information. |
Simple equipment, easier to implement and maintain | Complex equipment, requires precise modulation and demodulation |
| In AM, received signal is of low quality. | In FM, received signal is of high quality. |
It has better sound quality.
| It has poor sound quality. |
Conclusion
Amplitude Modulation (AM) and Phase Modulation (PM) are two widely used modulation techniques, each with its own strengths and applications. AM is simpler and suitable for long-distance, cost-effective communication, but it suffers from poor sound quality and high noise susceptibility. PM, on the other hand, offers better noise immunity and higher signal quality, making it ideal for mobile and digital communication systems. The choice between AM and PM depends on the specific requirements of the communication system, such as range, sound quality, and equipment complexity.
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