Lsi Logic Corporation

Mitel Semiconductor Limited

David I Boddy

Stephen Williams

Nicholas Mihailovits

Philip J Armitage

Trevor P Beatson

Nicholas A I Mihailovits

Brendan P Fenney

In the context of a DVD-RAM read-type architecture in which an optical storage medium () makes use of an eccentric wobble () to attain synchronisation information, a wobble PLL () is held in an acquired state whenever header regions () embossed at regular intervals across the optical storage medium () are detected. More specifically, large dc variations associated with voltage spikes caused by header regions () are scaled () relative to a dynamically varying amplitude envelope of the extracted wobble signal (), such as to identify a start location () for each header region. The wobble PLL () 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 (), 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 () to extract the wobble signal () 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.

Header detect configuration within a DVD-RAM read device and methods of acquiring and maintaining phase lock in a wobble phase lock loop

In the context of mirror modulation ( ) extraction during track seek or jump modes of an optical disc reading device ( ), such as a DVD ROM, a mirror averaged level (i.e. the dc level ( ) of the RF envelope ( )) is held so that the mirror modulation ( ) is seen as a swing below a set mirror rebias level ( ) at an output of a mirror amplifier ( ), as shown in FIG. . With the holding of the dc level ( ) by a ground-referred capacitor ( ) during seek operation of the device ( ), a first input (n ) to the mirror amplifier varies with the mirror modulation, whereas a second input (p ) to the mirror amplifier ( ) does not vary. This phenomenon enables the top level of a RFRP signal ( ) to be defined by the mirror rebias level ( ) and the mirror component swing (during seek operation) to be optimized and always to occur below the mirror rebias level ( ). During on-track operation, the first input (n ) and the second input (p ) are essentially equal and so the RFRP signal ( ) sits at the dc level ( ). Being able both to define the mirror rebias level ( ) and to vary a gain ( ) of the mirror amplifier ( ) allows a swing, arising from the mirror modulation, in the RFRP signal ( ) to be optimally positioned in relation to top and bottom hold circuits ( ) used for definition of a slice level ( ) for mirror recovery purposes.

Apparatus and method providing a mirror averaging function to generate a mirror signal from optical data on an optical disc

A frequency tracking arrangement in which a frequency tracking circuit utilizes a continuously variable analogue first order all-pass filter circuit as a controllable phase-shift element in a closed-loop system which produces a control signal to control the phase shift circuit to introduce a 90.degree. phase shift of a received reference frequency signal when the circuit is tracking that reference frequency. The control signal may then be utilized to slave the cut-off frequency of a filter and/or the delay time introduced by a delay line.

Frequency tracking arrangements

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Rawtenstall, United Kingdom

David I Boddy