| 摘要 |
In the context of a DVD-RAM read-type architecture in which an optical storage medium ( 20 ) makes use of an eccentric wobble ( 164 ) to attain synchronisation information, a wobble PLL ( 179 ) is held in an acquired state whenever header regions ( 32, 33 ) embossed at regular intervals across the optical storage medium ( 20 ) are detected. More specifically, large dc variations associated with voltage spikes caused by header regions ( 32, 33 ) are scaled ( 260 ) relative to a dynamically varying amplitude envelope of the extracted wobble signal ( 164 ), such as to identify a start location ( 300 ) for each header region. The wobble PLL ( 179 ) is effectively allowed to free-run and hold state during periods of header, thereby mitigating the likelihood that the wobble PLL will loose lock during the header regions. Also, with suspension of the wobble PLL triggered by a first spike ( 300 ), a counter is initiated to over-sample wobble clock periods to pre-empt a successive header and such that the PLL can be disabled immediately prior to the successive header region. Use of a bandpass filter ( 156 ) to extract the wobble signal ( 164 ) benefits from generation of a spike at each transition of the header dc level, which spike can be used as a definitive marker for a header region.
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