Patent ID: 7099243

Claim:
An optical pickup apparatus for recording information on a groove of an optical disc and/or reproducing the information from the groove by irradiating a main beam on the groove, irradiating an advanced side beam on the groove and an advanced land adjacent thereto, and irradiating a subsequent side beam on the groove and subsequent land adjacent thereto, said apparatus comprising: a light source; diffracting means for diffracting light emitted from said light source to form a main beam of zeroth-order light, and a pair of side beams of plus and minus first-order lights, said side beams being positioned at both sides of the main beam with the zeroth-order light being fitted between the first-order lights; light receiving means for receiving the main and side beams formed by said diffracting means and reflected by the optical disc, said light receiving means including a four-divided main beam photoreceptor for receiving and photoelectrically converting the main beam and a pair of two-divided side beam photoreceptors for receiving and photoelectrically converting the pair of side beams; first calculating means for calculating main push-pull signal MPP according to a formula, MPP=(A+D)−(B+C), where A, B, C, and D are electric signals photoelectrically converted by the four-divided main beam photoreceptor included in said light receiving means; second calculating means for calculating side push-pull signal SPP according to a formula, SPP=(F−αE)+(αH−G), where E, and F are electric signals photoelectrically converted by one of the two-divided side beam photoreceptors included in said light receiving means, and H, and G are electric signals photoelectrically converted by the other two-divided side beam photoreceptors included in said light receiving means; and third calculating means for calculating a differential push-pull signal DPP including a constant K according to a formula, DPP=MPP−K*SPP, said differential push-pull signal DPP forming a tracking error signal using the main push-pull signal calculated by said first calculating means and the side push-pull signals calculated by said second calculating means, wherein the constant α is previously set to adjust an MPP offset to zero when the main beam is positioned at the center of the four-divided main beam photoreceptor and the pair of side beams are positioned at both sides of the main beam and are symmetrical about the main beam by making (F−αE) and (αH−G) offsets equal to zero.