Phase Modulation (PM)

Phase Modulation (PM) is a type of modulation technique where the phase of a high-frequency carrier wave is varied in proportion to the amplitude of a low-frequency modulating signal. This results in a modulated signal that contains the original signal at a higher frequency.

The basic block diagram of a PM transmitter includes three main blocks: a modulating signal source, a high-frequency carrier wave source, and a modulator. The modulating signal source generates the low-frequency signal that is to be transmitted. The carrier wave source generates a high-frequency carrier signal that is typically several times the frequency of the modulating signal. The modulator combines the modulating signal with the carrier wave to produce the modulated signal.

Phase Modulation (PM)

The modulated signal can be expressed as:

s(t) = A_c cos[2πf_c t + φ(t)]

where A_c is the amplitude of the carrier wave, f_c is the frequency of the carrier wave, and φ(t) is the phase deviation of the carrier wave caused by the modulating signal.

Phase modulation is closely related to frequency modulation, and in fact, FM can be seen as a special case of PM. The difference between the two is that in PM, the phase of the carrier wave is directly proportional to the modulating signal, while in FM, the frequency of the carrier wave is directly proportional to the modulating signal.

At the receiver, the modulated signal is demodulated to extract the original low-frequency signal. The demodulation process typically involves the use of a phase detector, which compares the phase of the modulated signal with a reference signal to recover the original signal.

PM has some advantages over FM, including simplicity and better resistance to amplitude noise. However, FM is more commonly used in practical applications due to its higher bandwidth efficiency and wider frequency range.