Apparatus for reproducing information from an optically readable record carrier

Claim 1

An apparatus for reproducing information from an optically readable record carrier on which information is stored in the form of a track of optically detectable areas which alternate with intermediate areas, which apparatus comprises an optical system for projecting a light beam onto an optical detector via the record carrier, which detector comprises four sub-detectors situated in four separate quadrants of an imaginary X-Y-coordinate system whose origin is situated on the optical axis of the optical system, the X-axis of the coordinate system extending effectively in the track direction and the Y-axis extending effectively transversely of the track direction, a first adder circuit for adding the signals supplied by diagonally disposed first and third sub-detectors to form a first signal, a second adder circuit for adding the signals supplied by at least the other two sub-detectors to form a second signal, and a tracking-error signal generator for deriving a tracking-error signal from the first and the second signal, the tracking-error signal generator comprising means for measuring the time interval between a given zero crossing of the first signal and a corresponding zero crossing of the second signal, said time interval measuring means generating a third signal representative of the time interval between said given and corresponding zero crossings and direction-detection means for detecting the sequence in which said zero crossings of the first and the second signal occur and in response thereto inverting or not inverting the polarity of the third signal to thereby form the tracking-error signal.

Claim 2

An apparatus for reproducing information from an optically readable record carrier on which information is stored in the form of a track of optically detectable areas which alternate with intermediate areas, which apparatus comprises an optical system for projecting a light beam onto an optical detector via the record carrier, which detector comprises four sub-detectors situated in four separate quadrants of an imaginary X-Y-coordinate system whose origin is situated on the optical axis of the optical system, the X-axis of the coordinate system extending effectively in the track direction and the Y-axis extending effectively transversely of the track direction, a first adder circuit for adding the signals supplied by diagonally disposed first and third sub-detectors to form a first signal, a second adder circuit for adding the signals supplied by at least the other two sub-detectors to form a second signal, and a tracking-error signal generator for deriving a tracking-error signal from the first and the second signal, the tracking-error signal generator comprising means for measuring the time interval between a given zero crossing of the first signal and a corresponding zero crossing of the second signal, said time interval measuring means generating a third signal representative of the time interval between said given and corresponding zero crossings and direction-detection means for detecting the sequence in which said zero crossings of the first and the second signal occur and in response thereto inverting or not inverting the polarity of the third signal to thereby form the tracking-error signal.

Claim 6

An apparatus for reproducing information from an optically readable record carrier on which information of a substantially fixed bit frequency is stored in the form of a track of optically detectable areas which alternate with intermediate areas, said apparatus comprising an optical system for projecting a light beam onto an optical detector via the record carrier, said detector having four sub-detectors disposed in four separate quadrants of an imaginary X-Y coordinate system whose origin is on the optical axis of the optical system, the X axis of said coordinate system effectively extending in the track direction and the Y axis effectively extending transversely of the track direction, first means for adding signals supplied by diagonally disposed first and third sub-detectors to form a first signal, second means for adding signals supplied by at least the other two sub-detectors to form a second signal, and means responsive to zero crossings of said first and second signals for generating a tracking error signal in dependence on the time interval between corresponding zero crossings of said first and second signals, said generating means comprising a first and second zero crossing detector for supplying first and second pulses, respectively, at the zero crossings of the first and second signals, respectively, first and second tuned circuits which are tuned to the bit frequency or upper harmonics thereof and which are excited by said first and said second zero crossing detectors, respectively, and means for detecting the phase difference between the signals supplied by said first and second tuned circuits.

Claim 7

An apparatus for reproducing information from an optically readable record carrier on which information of a substantially fixed bit frequency is stored in the form of a track of optically detectable areas which alternate with intermediate areas, said apparatus comprising an optical system for projecting a light beam onto an optical detector via the record carrier, said detector having four sub-detectors disposed in four separate quadrants of an imaginary X-Y coordinate system whose origin is on the optical axis of the optical system, the X axis of said coordinate system effectively extending in the track direction and the Y axis effectively extending transversely of the track direction, first means for adding signals supplied by diagonally disposed first and third sub-detectors to form a first signal, second means for adding signals supplied by at least the other two sub-detectors to form a second signal, and means responsive to zero crossings of said first and second signals for generating a tracking error signal in dependence on the time interval between corresponding zero crossings of said first and second signals, said generating means comprising a first and second zero crossing detector for supplying first and second pulses, respectively, at the zero crossings of the first and second signals, respectively, first and second tuned circuits which are tuned to the bit frequency or upper harmonics thereof and which are excited by said first and said second zero crossing detectors, respectively, and means for detecting the phase difference between the signals supplied by said first and second tuned circuits.