A Quick Guide to Understanding Phase Locked Loop

June 22, 2019

Phase-locked loops are discussed in a variety of contexts: demodulators, microcontrollers, serial communications, oscillator modules, etc.

But what is a phase-locked loop exactly?

An Introduction to Phase Locked Loop

In its most basic configuration, a phase locked loop (PLL) is a control system with a variable frequency oscillator that compares the phase of an input signal to the phase of an output signal and adjusts the oscillator to keep the phases matched.

What is the most common application of phase-locked loop?

Phase-locked loops have numerous applications in digital electronics, telecommunication and signal processing. However, they are most commonly used to recover signals from noisy communication channels where the data may have been interrupted.

How does the phase-locked loop work?

Let’s start with listing the components of phase-locked loop system.

A typical phase locked loop circuit has three main components:

• Phase detector
• Low pass filter
• Voltage controlled oscillator

The phase detector is actually a phase difference detector. Its function is to accept and compare two periodic input signals and to generate an output signal representing the phase difference between the two input signals. The output of the phase detector is a calibrated voltage signal.

The voltage signal, produced by the phase detector, needs to be conditioned before it can be used by voltage-controlled oscillator. For that, the signal is passed through a low pass filter. The low pass filter removes any high frequency content that may be mixed with the voltage signal.

Once the voltage signal has been conditioned and purified, it is then forwarded to the voltage controlled oscillator. The voltage controlled oscillator adjusts the phase of its oscillation depending on the value of the voltage signal.

The output from the voltage controlled oscillator is fed back to the phase detector, and so the system continues to run in a loop to optimize for better performance and signal fidelity.

Phase-locked loops are typically available in the form of ICs. To shop for high quality phase-locked loop ICs, visit ADSANTEC today.

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