Synchronous detector
In electronics, a synchronous detector is a device that recovers information from a modulated signal by mixing the signal with a replica of the un-modulated carrier. This can be locally generated using a phase-locked loop or other techniques. Synchronous detection preserves any phase information originally present in the modulating signal. Synchronous detection is a necessary component of any analog television receiver, where it allows recovery of the phase information that conveys hue. <ref> Donald G. Fink (ed.)., Electronics Engineers' Handbook, McGraw Hill, 1975 ISBN 0-07-020980-4 page20-57 <./ref>