Definitions for "Phase Locked Loop"
(PLL) A very efficient corrective circuit that acts as a phase detector. It compares the frequency of a known oscillator with a received signal and uses the output of the detector to keep the oscillator in phase with the incoming frequency.
a circuit designed to minimize the phase difference between two signals
A circuit in which a crystal oscillator is used as a time base for a voltage controlled oscillator maintaining frequency and phase lock between the two oscillators. This is a useful technique for achieving a frequency programmable crystal oscillator and output frequencies that are out of the range of a crystal manufactured to achieve certain performance specifications. However, short term frequency stability is one or two orders of magnitude worse than for a true crystal oscillator.