Phase Locked Loops - PLL
A phase-locked loop (PLL) is an electronic circuit with a voltage or current-driven feedback source that is used to control the frequency and/or phase of an associated oscillator. It is one of the basic components of modern telecommunications and also widespread in modern electronic systems. In essence, the circuit locks onto a reference frequency, and despite changes in the signal's input parameters, the output stays locked to the reference input frequency. The PLL can be used to demodulate the amplitude, frequency and phase of a signal, as well as modulating it. It is used mainly in radio and television equipment and other radio-frequency (RF) applications.