Read-Write Channel for Optical Recording

Generally optical discs are divided into several sectors in which an amount of data is stored. Each sector starts with a header which contains an address and synchronization information. If, because of aging of the disc, this sync-info is destroyed, one needs a backup for having access to the data in that sector. A convenient way of attaining this is to have a prerecorded clock (a depth modulation of the pregroove) in the disc. Using this clock, a defect-insensitive phase lock loop and a counter, the sync-info of previous sectors can be used to reach the data in the damaged sector.