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A phase-locked loop (PLL) is a type of electronic circuitry that consists of a voltage/current driven oscillator paired with a phase detector that constantly keeps its input and output in phase with each other. The function of a phase detector is to match the phase of the oscillator’s periodic signal with that of the input signal and correct the oscillator if it goes slightly out of phase. This is called a feedback loop, as output is fed back to the input.
A phase-locked loop ensures a telecommunication signal in real time is locked at a certain frequency, if not, it tries to correct the frequency by constant comparing and feedback. PLLs are found in telecommunication channels as stabilizers, modulators, demodulators, noise removers and frequency dividers. They are used in wireless communication, especially in amplitude modulation (AM), frequency modulation (FM) as well as phase modulation (PM). Most commonly designed in the form of an integrated circuit (IC) that can handle digital communication, PLLs are one of the most important components for communication, both digital and analog. Wireless communication-aiding equipment utilizing phase-locked loop frequency control are also said to be frequency-synthesized.