Pulse or digital communications – Synchronizers – Synchronization failure prevention
Patent
1995-12-06
1998-04-07
Chin, Wellington
Pulse or digital communications
Synchronizers
Synchronization failure prevention
375373, 369 4432, 369 48, 369 59, 369124, 395439, G11B 1722, G11B 390
Patent
active
057373710
ABSTRACT:
An apparatus and method are provided for detecting and correcting data stream misalignments during read back of data in an optical drive unit. In a dual PLL system, after a data stream is divided into separate positive and negative data streams, correlations are made between the transitions in the even nibbles of a sync mark and the transitions in the odd nibbles. Proper and improper alignments can be detected. The resync marks are also employed to determine whether the two data streams are misaligned and, if they are, by how much. While the position of an alignment bit within a resync mark can be detected, realigning the data streams based upon this position can result in small defects causing false alignment and a continuous error until the next resync. Consequently, the present invention employs other bits in the resync mark and in the adjoining customer data field to validate the misalignment independent of the alignment bit itself. Moreover, if a suspected misalignment is not validated by the other bits, information about the misalignment is stored in a memory and the next resync mark is examined. Once any misalignment is validated, a realignment is performed by gating the positive data stream, with an appropriate delay, through a multiplexor to be OR'd with the negative data stream.
REFERENCES:
patent: Re33665 (1991-08-01), Ogawa
patent: 5351231 (1994-09-01), King et al.
patent: 5502711 (1996-03-01), Clark et al.
patent: 5559983 (1996-09-01), Masood
patent: 5563854 (1996-10-01), Kobunaya et al.
Chin Wellington
International Business Machines - Corporation
Luther William
Shifrin D. A.
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