Phase lock loop is used in analog and digital communications to keep the phase of the output signal the same as the input signal.

The LM565 is a phase locked loop.

Nikolaos I. Margaris has written:

'Theory of the non-linear analog phase locked loop' -- subject(s): Nonlinear theories, Phase-locked loops

An ADPLL is an all-digital phase locked loop - a control system that generates an output signal whose phase is related to the phase of an input signal.

PLL stands Phase Locked Loop . It consists of phase detector,low pass filter,voltage controlled oscillator,error amplifier