Phase Locked Loop Basics

A phase-locked loop (PLL) is an electronic circuit with a voltage or voltage-driven oscillator that constantly adjusts to match the frequency of an input signal. PLLs are used to generate, stabilize, modulate, demodulate, filter or recover a signal from a "noisy" communications channel where data has been interrupted.

1. What are the basic components of the phase-locked loop?
2. What is the principle of PLL?
3. Why do we use PLL?
4. How does VCO work in PLL?

What are the basic components of the phase-locked loop?

A PLL typically consists of a phase detector, a loop filter, and a voltage-controlled oscillator (VCO). The phase detector compares the reference signal with the oscillator frequency and outputs an error signal. The loop filter (usually a low-pass filter) then generates an error voltage from the error signal.

What is the principle of PLL?

A phase-locked loop or phase lock loop (PLL) is a control system that generates an output signal whose phase is related to the phase of an input signal. There are several different types; the simplest is an electronic circuit consisting of a variable frequency oscillator and a phase detector in a feedback loop.

Why do we use PLL?

The main purpose of a PLL circuit is to synchronize an output oscillator signal with a reference signal. When the phase difference between the two signals is zero, the system is “locked.” A PLL is a closed-loop system with a control mechanism to reduce any phase error that may occur.

How does VCO work in PLL?

A phase-locked loop (PLL) circuit is a feedback system that combines a voltage controlled oscillator (VCO) and a phase detector in such a way that the oscillator signal tracks an applied frequency or phase modulated signal with the correct frequency and phase.