What Is a Phase-Locked Loop?

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  • Written By: Malcolm Tatum
  • Edited By: Bronwyn Harris
  • Last Modified Date: 03 December 2019
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A phase-locked loop (PLL) is a type of balancing system that serves to regulate the frequency of an output signal so that it is comparable to the input signal generated by the same equipment. Accomplishing this process involves the use of what is known as a variable frequency oscillator coupled with a detector that is able to read both of the signals. Together, these components function as a single circuit to read and manage the signals so that a stable loop is created.

The process of creating a phase-locked loop involves tracking the two signals involved, identifying the frequencies and then modulating the frequencies so that are essentially functioning in step with one another. The ability to create this type of locked loop situation makes a number of electronic media applications possible. For example, the ability to establish a phase-locked loop aids in being able to establish a clear radio signal even if there is a lot of background noise and static in the transmission. In a sense, the loop makes it possible to modulate the input and output signals in the transmission so that the actual communication is clear.


A phase-locked loop is also utilized in other types of communication situations. With general telecommunications, including wired and wireless telephone communications, this process of manipulating the frequency results in avoiding or at least minimizing some of the audio issues that can occur. This includes echoing on the line, a phenomenon known as cutting in and out, and even sudden screeching noises that drown out any attempts at communication. With much of telecommunications making use of digital technology rather than the older analog technology, the need to establish a phase-locked loop in order to enhance reception is more important than ever.

Use of a phase-locked loop is also important to the function of a number of electronic devices, including computers of different types. By creating a stable loop, the level of efficiency is maintained while the potential for circuit overload is kept to a minimum. As long as the circuit is able to reconcile the input and output signals so they are comparable, the flow to and from the device will remain within reasonable safety parameters. This ensures efficient function as well as preventing an unreasonable amount of stress on the circuitry that could cause permanent damage to the device, requiring replacement of all or at least some of the components.


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