Patent ID: 7376054

Claim:
A disk playback device comprising a calculation processing circuit for determining an optimum value of offset for an error signal based on an amplitude value of the error signal in accordance with focus deviation or tracking deviation of an optical head or an amplitude value of an output signal of the optical head, and making an offset adjustment based on the optimum offset value, the calculation processing circuit approximating to a quadratic curve the relationship between offset values and the amplitude values in signal reproduction, and repeating calculation of the optimum offset values based on the quadratic curve, and comprising: calculation processing means for approximating to a quadratic curve the relationship between the offset values and the amplitude values with reference to three different offset values and three amplitude values at the respective offset values, and calculating an offset value corresponding to the peak of the quadratic curve as the optimum offset value, and value setting means for setting the three different offset values: a first offset value; a second offset value smaller than the first offset value and having an amplitude value smaller than an amplitude value at the first offset value by a predetermined value or more; a third offset value greater than the first offset value and having an amplitude value smaller than an amplitude value at the first offset value by a predetermined value or more, and setting the three amplitude values respectively at three amplitude values at the first to third offset values, the value setting means setting the first offset value at an optimum offset value obtained in a previous optimum offset value calculation processing, and setting the second and third offset values respectively at second and third offset values set in a previous optimum offset value calculation processing, wherein a maximum of three amplitude values of a maximum of three different offset values need to be measured to determine the optimum offset value and the determination of said second and said third offset values does not require the determination of amplitude values of at least five different offset values.