Phase detectors are a type semiconductor device that acts as an analogue multiplier, frequency mixer or logic circuit that generates a voltage signal. This represents the difference in phase between two signal inputs. Phase detectors are an essential element of the PLL (phase-locked loop).
There are three main types of phase detectors, analogue phase detectors, digital phase detectors and phase frequency detectors.
Phase frequency detectors in particular are constructed of four flip flop circuits. The logic this circuit follows is that it determines which of the two signals has a zero crossing earlier, it also determines which of the signals more often has a zero crossing. Compared to simpler phase detector constructions such as multipliers, these phase frequency detectors are designed to improve lock time and pull in range and also prevent a "false lock" condition in PLL applications.
Phase detectors are widely used in applications such as