A synchronous detector capable of detecting the position of a frame without a synchronous signal included in the frame

摘要

The synchronous detector has three registers for storing individual patterns of three consecutive frames. The decoder generates a frame position signal based on the individual pattern. The pointer circuit counts the number of frame position signals to generate a pointer signal. The decoder generates a count-up signal when it is able to decode an individual signal. The decoder generates a reset signal when it can not decode an individual signal. The counter counts the count-up signal and is reset by the reset signal. The register holds a predetermined value. The comparator compares the count value of the counter with the predetermined value. The comparator generates a comparison command signal when the predetermined value is smaller than the count value. The comparison circuit compares the frame position signal with the pointer signal. If the frame position signal is not equal to the pointer signal, the optical head skips several frames or slips to the next track.