A phase-locked loop FM detector is used in applications requiring what kind of synchronization?

A phase-locked loop (PLL) FM detector is primarily designed to achieve phase synchronization. The key function of a PLL is to match the phase of its output signal to the phase of the input signal. In the context of FM detection, this allows the PLL to effectively track the frequency of the modulated wave, thus ensuring that the output accurately reflects the frequency and phase of the incoming frequency-modulated signal.

Frequency synchronization occurs because the PLL adjusts its output frequency to match that of the input signal, allowing it to maintain lock on the incoming signal's frequency variations. While amplitude synchronization is important in some contexts, the core operation of the PLL emphasizes aligning phase and, consequently, frequency. Phase synchronization is crucial in applications like communications, where maintaining the correct phase relationship between signals is essential for coherent demodulation and minimizing distortion.

While the concept of all three types of synchronization may be relevant in broader scenarios, the PLL's functioning is specifically tailored to frequency synchronization by locking onto the phase of the incoming signal, making it the most appropriate choice in this case.