Phase Modulation: Definition, Diagram, Application, Advantage and Disadvantage
Table of Contents
Phase modulation is the process of changing the carrier signal’s phase in a linear relationship with the current value of the message signal. Below are examples of a message signal’s and a phase-modulated signal’s waveforms:
The equation of a PM signal is represented by:
V(t) = A cos [ωct + ϕ (t)]
ωc is the carrier frequency constant
A is the amplitude constant
ϕ (t) is the phase angle, which is not constant. It is a function of the baseband signal.
Let’s first discuss the message signal and the carrier signal.
Information or a message is contained in a message signal. What needs to be sent from the transmitter to the receiver is the original signal. The signal is transformed by the transmitter into a usable format before being transmitted to the receiver via the communication channel. And The signal travels through a communication channel to get from one end to the other. The signal is converted back into its original form by the receiver before being perceived. There are several noise factors and attenuation that affect a message signal. To get rid of the noise, the message signal must be modulated. Additionally, it aids in enhancing the signal’s effectiveness. So a message signal is frequently referred to as a modulated signal. The baseband signal is another term for the message signal.
The carrier signal has a higher frequency and has the same sinusoidal waveform as the message signal. It indicates that the carrier signal has a higher frequency than the message signal. During the modulation process, the carrier signal is transmitted on the same communication channel as the message signal. The high-frequency carrier signal boosts the message signal’s frequency when it is transmitted alongside it. It is used in situations where a high-frequency output signal is needed but a low-frequency incoming message signal is present.
Modulation is the process of transforming an information signal into an effective transmission format. So Here, the signal from the incoming message is changed into radio waves, which is an effective mode of transmission for the communication system. With the exception of the integrator, the PM modulation process is similar to the FM modulation process. Before the modulated signal is applied to the balanced modulator in FM, an integrator is required. Prior to the balance modulator block in FM is the integrator block. However, no integrator block is necessary for PM modulation. The PM modulator’s block diagram is displayed below:
The circuit consists of a carrier signal source, balance modulator, adder, and a 90 degree phase shifter. The carrier signal source generates a carrier sinωct with the carrier frequency ωc. The 90 degree phase shifter converts the carrier signal sinωct to cosωct, which is the carrier with a phase shift of 90 °. So A balance modulator generates a double sideband amplitude modulated signal by superimposing the message and the carrier signal sinωct. The output signal is generally a suppressed carrier signal. The output of the balance modulator and the output of the phase shifter are sent to the adder, which adds these two outputs. The carrier shifted by a phase of 90° when added to the output of the balanced modulator forms a phase modulated signal.
By passing the FM signal through a differentiator and an FM modulator, we can also use a frequency modulator as a phase modulator.
The block diagram is shown below:
m(t) is the modulated signal
mi(t) is the instantaneous modulated signal, which is the output of the differentiator.
v(t) is the phase modulated signal, output of the frequency modulator.
The process of demodulation involves restoring the original signal. The recipient is doing its job. It restores the signal to its initial state. So The demodulation of FM and the demodulation of PM are related. Let y(t) represent the FM demodulator’s output. The FM demodulator’s output is directly proportional to the modulated signal.
m(t) ∝ y(t)
m(t) is the modulated signal
m(t) ∝ θ(t)
The message is inversely proportional to the modulating system’s phase angle. It is a requirement for a phase-modulated signal.
y(t) ∝ dθ(t)/dt
y(t) = kdθ(t)/dt
A constant is always substituted in place of the proportionality symbol.
K is the proportionality constant
So By placing the integrators after the frequency discriminator or frequency demodulators in FM, we are able to recover the message signal from the phase-modulated input.
Applications of Phase Modulation
The applications of Phase Modulation are listed as follows:
- Digital Synthesizers
Digital synthesizers employ PM to create signals and waveforms.
- Sound Synthesis
Compared to AM, PM is less sensitive to noise interference and popping sounds. As a result, it is appropriate for sound synthesis, also known as sound broadcasting.
- Telephone communication
PM’s high-speed transmission makes it a popular choice for telephone communication.
Advantages of Phase Modulation
The advantages of Phase Modulation are as follows:
- Low signal power consumption
PM requires a minimal amount of signal power because of its higher effectiveness and quick speed.
- High speed
One of the fastest modulation techniques is phase modulation. It results from the rapid pulse generation.
- Easy modulation and demodulation
Due to its straightforward circuit design, phase modulation and demodulation are simpler than with PM.
- Simple circuit design
In comparison to FM, the phase modulated circuit requires fewer components. Thus, it has a straightforward circuit design.
Disadvantages of Phase Modulation
The disadvantages of Phase Modulation are as follows:
- Low signal to noise ratio
Compared to FM, PM has a lower signal to noise ratio. It results from FM’s wider bandwidth.
- Low noise immunity
Compared to FM, PM is less noise-resistant. It’s because external disturbances have a smaller impact on frequencies than on phases. As a result, PM is less noise-resistant than FM.
- Complex circuitry during conversion from FM to PM
Phase modulation must be converted from frequency modulation through a complicated process. It is as a result of the extra parts needed for the conversion.