Introduction to PLLs
Chapter 1 of Phase-Locked Loops: Design, Simulation, and Applications provides an introduction to phase-locked loops (PLLs). The PLL helps keep parts of our world orderly. If we turn on a television set, a PLL will keep heads at the top of the screen and feet at the bottom. In color television, another PLL makes sure that green remains green and red remains red (even if the politicians claim that the reverse is true).
A PLL is a circuit that causes a particular system to track with another one. More precisely, a PLL is a circuit synchronizing an output signal (generated by an oscillator) with a reference or input signal in frequency as well as in phase. In the synchronizedoften called lockedstate the phase error between the oscillator's output signal and the reference signal is zero, or remains constant.