What is a phase-locked loop (PLL)?

A phase-locked loop (PLL) is defined as a control system that generates a signal that is synchronized to the phase of an input signal. This synchronization allows the output frequency to match the frequency of the input signal, which is particularly useful in various applications such as radio communications, where maintaining a steady signal phase is critical for demodulating received signals.

The PLL consists of several components, including a phase detector, a low-pass filter, and a voltage-controlled oscillator. The phase detector compares the phase of the input signal with that of the output signal, sending a control voltage to the voltage-controlled oscillator to adjust its frequency. This feedback mechanism ensures that the output signal remains aligned with the input signal, effectively "locking" onto its phase.

While options related to enhancing audio quality, preventing signal interference, or increasing transmission rates may involve PLL technology in certain contexts, they do not directly define what a PLL is. These other methods may utilize PLLs as part of their processes, but the fundamental characteristic of a phase-locked loop is its phase synchronization capability, which is critical for maintaining signal integrity in various electronic systems.