Patent ID: 7468939

Claim:
An optical disk apparatus comprising: a motor for rotating an optical disk; a light source; diffraction means for diffracting a portion of light emitted from the light source to form a main beam of 0 th order light and a pair of sub beams composed of +1 st order light and −1 st order light which are formed on both sides of the 0 th order light; an objective lens for converging the main beam onto a recording track of the optical disk and the pair of sub beams onto two tracks that are positioned at both sides of the recording track of the optical disk; light receiving means for receiving the main beam and the sub beams reflected from the optical disk, and outputting electrical signals through photoelectric conversion; a calculation section for, based on the electrical signals output from the light receiving means, providing a main push-pull signal MPP, a sub push-pull signal SPP, and a differential signal between the main push-pull signal MPP and the sub push-pull signal SPP; and phase difference detection means for detecting a phase difference between the main push-pull signal MPP and the sub push-pull signal SPP, wherein, in accordance with an output from the phase difference detection means, an offset is applied in a tracking control of the main beam with respect to the optical disk to compensate for an off-tracking caused by a phase shift of the differential signal, and comprising: signal amplitude calculation means for adjusting amplitudes of the main push-pull signal MPP and/or the sub push-pull signal SPP so that the amplitude of the main push-pull signal MPP and the amplitude of the sub push-pull signal SPP become equal; signal summation means for calculating a sum of the main push-pull signal MPP and the sub push-pull signal SPP which are output from the signal amplitude calculation means; and phase difference calculation means for, based on an output from the signal summation means, calculating a phase difference between the main push-pull signal MPP and the sub push-pull signal SPP.