Methods and apparatus for regenerating track crossing signals for searches across unrecorded areas on read/write optical discs

Apparatus for regenerating quadrature-phase track crossing signals for searches across blank data areas on read/write compact discs, such apparatus comprising:

• circuitry for receiving in-phase and quadrature-phase track crossing signals from an optical pickup unit and supplying the crossing signals to a track crossing counter mechanism;
• circuitry for comparing the in-phase and quadrature-phase track crossing signals for generating a blank signal when no quadrature signal transition occurs between two successive in-phase signal transitions;
• circuitry responsive to the in-phase signals for generating fake quadrature-phase signals;
• and
• circuitry responsive to the blank signal for supplying a fake quadrature-phase signal to the track crossing counter mechanism during the occurrence of the blank signal.

Apparatus for comparing two sets of pulse signals having the same frequency and offset in time relative to one another and producing a missing transition signal when a signal transition in one set of the pulse signals is missing, the apparatus comprising:

• a bistable circuit;
• circuitry for supplying the two sets of pulse signals to the bistable circuit for alternately setting and resetting the bistable circuit;
• and
• circuitry for comparing the output of the bistable circuit with one of the sets of pulse signals for producing a missing transition signal when the bi-stable circuit fails to alternate between set and reset conditions.

Apparatus for comparing first and second sets of pulse signals having the same frequency and offset in time relative to one another and producing a missing transition signal when a signal transition in the second set of pulse signals is missing, the apparatus comprising:

• a first bistable circuit having set and reset input terminals and an output terminal;
• a second bistable circuit having a data input terminal an enable data read-in terminal and an output terminal for producing a missing transition signal;
• circuitry for supplying the first set of pulse signals to the set input terminal of the first bistable circuit and to the enable data read-in terminal of the second bistable circuit;
• circuitry for supplying the second set of pulse signals to the reset input terminal of the first bistable circuit;
• and
• circuitry for coupling the output of the first bistable circuit to the data input terminal of the second bistable circuit.