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US 5,844,870 AGranted
Device for scanning an optically readable record carrier
AssigneeU.S. Philips Corporation
InventorJosephus J. M. Braat
Life of this patent
Estimating the term…
Abstract
A device for optically scanning an information layer by means of a focused radiation beam. Radiation reflected from the information layer is made astigmatic by an oblique plane parallel plate and subsequently detected by a detection system. An electronic circuit derives a focus error signal, representing the distance between the focal point of the radiation beam and the information plane, from the electrical detector signals by using the high-frequency components in the detector signals. The influence of stray light falling on the detection system on the focus error signal is thereby reduced.
Claims17
A device for optically scanning an information layer on which information is stored, which device comprises:
- a radiation source;
- an objective system for converging radiation emitted by the radiation source on the information layer;
- a beam splitter positioned for forming a sub-beam from substantially one half of a cross-section of a radiation beam from the information layer;
- a radiation-sensitive detection system comprising two detectors arranged in the sub-beam and providing two detector signals;
- and
- first electronic circuit means for forming a first focus error signal from the detector signals by subtracting the two detector signals, and including:
- at least one high-pass filter means for filtering at least one of the detector signals to form the first focus error signal from high-frequency components of the detector signals, with a filter pass frequency for removing the effects of stray light;
- and
- means for forming an information signal representing the information stored in the information layer, with a frequency substantially equal to the frequency of the pass band of the high-pass filter means.
6 more elements
A device for optically scanning an information layer on which information is stored, which device comprises:
- a radiation source;
- an objective system for converging radiation emitted by the radiation source on the information layer;
- a radiation-sensitive detection system arranged in the path of a radiation beam from the information layer, including four detectors arranged in four separate quadrants, each detector providing a detector signal;
- astigmatizing means arranged in the radiation beam between the information layer and the detection system;
- and
- first electronic circuit means for forming a first focus error signal from the detector signals by adding the detector signals of diagonally arranged detectors and subtracting the resulting two differences, and including at least one high-pass filter means for filtering at least one of the detector signals to form the first focus error signal from high-frequency components of the detector signals, with a filter pass frequency for removing the effects of stray light;
- and
- means for forming an information signal representing the information stored in the information layer, with a frequency substantially equal to the frequency of the pass band of the high-pass filter means.
5 more elements
A device for optically scanning an information layer on which information is stored, which device comprises;
- a radiation source;
- an objective system for converging radiation emitted by the radiation source on the information layer;
- a beam splitter positioned for forming two sub-beams from a radiation beam from the information layer;
- a radiation-sensitive detection system comprising two detection sub-systems, each detection sub-system being arranged in a sub-beam and providing detector signals;
- and
- first electronic circuit means for forming a first focus error signal from the detector signals by subtracting two signals derived from the detector signals and each signal representing the diameter of one of the sub-beams, and including:
- at least one high-pass filter means for filtering at least one of the detector signals to form the first focus error signal from high-frequency components of the detector signals, with a filter pass frequency for removing the effects of stray light;
- and
- means for forming an information signal representing the information stored in the information layer, with a frequency substantially equal to the frequency of the pass band of the high-pass filter means.
6 more elements
A device for optically scanning an information layer on which information is stored, which device comprises:
- a radiation source;
- an objective system for converging radiation emitted by the radiation source on the information layer to form a reflected beam containing the information;
- a radiation-sensitive detection system positioned in the reflected beam and including one or more pairs of detectors, each detector providing a respective detector signal;
- and
- first electronic circuit means for forming a first focus error signal from the detector signals by subtracting the detector signals, and including:
- at least one high-pass filter means for filtering at least one of the detector signals to form the first focus error signal from high-frequency components of the detector signals, with a filter pass frequency for removing the effects of stray light;
- and
- means for forming an information signal representing the information stored in the information layer, with a frequency substantially equal to the frequency of the pass band of the high-pass filter means.
5 more elements
Apparatus for playing and/or recording information on a record carrier with at least tracking information in an information layer, comprising:
- a radiation source;
- an objective system for converging radiation emitted by the radiation source on the information layer;
- a radiation-sensitive detection system including pairs of detectors arranged in the sub-beam and providing detector signals;
- and
- first electronic circuit means for forming a first focus error signal from the detector signals by subtracting the detector signals, and including:
- at least one high-pass filter means for filtering at least one of the detector signals to form the first focus error signal from high-frequency components of the detector signals, with a filter pass frequency for removing the effects of stray light;
- and
- means for forming an information signal representing the information stored in the information layer, with a frequency substantially equal to the frequency of the pass band of the high-pass filter means;
- servo means for adjusting the relative positions of the objective system and the information carrier;
- means for moving the radiation beam with respect to the information carrier for reading and/or recording information on the record carrier.
7 more elements
A process for producing pre-recorded computer media, comprising the steps of:
- producing emmitted radiation;
- converging the emitted radiation onto an information layer using an objective system to produce a reflected beam;
- sensing the reflected beam using pairs of detectors arranged in the reflected beam, each detector providing a respective detector signal;
- and
- forming a first focus error signal from the detector signals using the sub-steps of:
- subtracting detector signals;
- filtering at least one of the detector signals using a high pass filter to form the first focus error signal from high-frequency components of the detector signals, with a filter pass frequency for removing the effects of stray light;
- and
- forming an information signal representing the information stored in the information layer, with a frequency substantially equal to the frequency of the pass band of the high-pass filter means.
6 more elements
Dependencies are inferred from the claim text.