The phase-locked loop FM detector can be used for which type of modulation?

The phase-locked loop (PLL) FM detector is specifically designed to demodulate frequency-modulated (FM) signals. In FM modulation, the frequency of the carrier wave is varied in accordance with the amplitude of the input signal, allowing for the transmission of information. The PLL technique is effective in capturing the instantaneous frequency changes of the incoming signal, thus allowing for accurate reconstruction of the original message.

The PLL works by locking onto the frequency of the incoming FM signal and replicating it within the circuit. As the frequency of the incoming signal changes, the PLL adjusts its output to maintain synchronization. This capability makes PLLs especially suited for demodulating FM signals, where frequency variations carry the information.

While phase modulation is also closely related to frequency modulation, the specific mechanism of the PLL is optimized for FM detection, making it the best choice among the options provided.