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

Abstract

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.