Apparatus for generating tracking error signals in a differential phase detection system

DETAILED DESCRIPTION Accordingly, it is an object of the present invention to provide a tracking servo circuit for an optical pick-up that can eliminate the above-noted defects inherent in the prior art.
Another object of the invention is to provide an improved tracking servo circuit for an optical pick-up, wherein a beam spot jump and subsequent settling in a random access mode can be performed in a stable fashion and no oscillations occur in the tracking servo signal, even if an external mechanical shock acts on the tracking servo device.
A further object of this invention is to provide an improved tracking servo circuit for an optical pick-up, in which tracking servo signals are produced from a photo-detector having a number of separate active areas and which also provides the reproduced information signal.
In accordance with an aspect of the present invention, there is provided in a tracking servo circuit for an optical pick-up of the kind having a light source for transmitting a light beam through a focusing lens onto a surface of the optical record medium where the information tracks are arranged, a photo-detector for receiving the diffraction pattern formed by the light reflected from the surface of the record medium, and a tracking servo device for controlling the position of the focusing lens in a tracking direction in response to a tracking servo signal so as to trace the information tracks, in which the photo-detector comprises four separate light-receiving areas.
The tracking servo circuit comprises a first tracking-error detecting circuit to detect a first tracking error signal in response to the outputs of selected ones of the four light-receiving areas and a second tracking-error detecting circuit to detect a second tracking-error signal in response to outputs of selected other ones of the four light-receiving areas and an operational circuit that produces a tracking servo signal by a mathematical operation on the first and second tracking-error signals, such that any DC component included in the first tracking-error signal is removed