US 4,544,838 A · Method and apparatus for detecting tracking error

Abstract

A tracking error of a light spot focused on an optical record disc by means of an objective lens with respect to an information track recorded on the disc is detected by processing outputs from a light detector arranged in a far field of the track and having four light receiving regions on which a light reflected by the disc is incident. A tracking error signal of a differential detection system, i.e. a difference between two sums of outputs from two pairs of two regions aligned in a direction tangential to the track is derived, and a push-pull signal, i.e. a difference between two sums of outputs of two pairs of two light receiving regions aligned in a radial direction is also obtained. Zero crossings of the push-pull signal are detected to produce sampling pulses and the tracking error signal of differential system is sampled by the sampling pulses to derive a tracking error signal which is substantially free from disturbance due to a possible shift of the light impinging upon the light detector with respect to the optical axis of objective lens.

Claims15

Dependent claims

A method for detecting a tracking error in a light spot projected by an objective lens onto a record medium with respect to an information track formed by a pit array extending along a tangential direction and viewed in a direction perpendicular to an optical axis of the objective lens as well as to the information track comprising:

introducing a light flux, which is derived from the light spot projected onto the record medium, onto a light detector arranged in a far field of the information track and having at least two light receiving regions divided along a direction corresponding to the tangential direction of the information track to produce photoelectrically converted outputs;
deriving a difference signal between said outputs;
and
producing a tracking error signal by sampling said difference signal in response to a timing signal representing the positioning of said light spot at substantially the center of a pit along said tangential direction of the information track, to extract those portions of the difference signal which occur during time intervals that correspond in time to said light spot being located at substantially the center of a pit in said tangential direction.

1 more element

An apparatus for detecting a tracking error of a light spot projected by an objective lens onto a record medium with respect to an information track formed by a pit array extending along a tangential direction and viewed in a direction perpendicular to an optical axis of the objective lens as well as to the information track comprising:

a light detector arranged in a far field of the information track and having at least two light receiving regions divided along a direction corresponding to the tangential direction of the information track, said light detector being arranged to receive a light flux, which is derived from the record medium in response to the projection of the light spot onto the record medium, to produce photoelectrically converted outputs;
means for producing a different signal between said outputs;
and
means for producing a tracking error signal from said difference signal by extracting those portions of the difference signal which occur during time intervals that correspond in time to the location of the light spot at substantially the center of a pit along the tangential direction of the information track.

1 more element

Dependencies are inferred from the claim text.

Method and apparatus for detecting tracking error

Life of this patent

Method and apparatus for detecting tracking error

Life of this patent

Abstract

Claims15