Patent ID: 7787337

Claim:
A method for detecting a data defect, comprising: detecting a data signal including a master signal generated by a master part of an optical pickup head and a side signal generated by a side part of the optical pickup head, wherein the master part of the optical pickup head has four light-receiving portions A, B, C and D, the side part has two light-receiving portions E and G at a first side of the master part and two light-receiving portions F and H at a second side of the master part opposite to the first side, the master signal is the sum of each main-beam signal generated by the light-receiving portions A, B, C and D in response to the received light intensities, and the side signal is the sum of each sub-beam signal generated by the light-receiving portions E F, G and H in response to the received light intensities; subtracting the master signal from the side signal to obtain a discriminating signal; and detecting whether a data defect is existent according to the discriminating signal.