Patent ID: 8023219

Claim:
A storage device, comprising: an area demodulator configured to demodulate a first demodulation signal and a second demodulation signal having a phase difference of 90° from a read signal by a head of an area demodulation pattern recorded on a medium: a head position demodulator configured to receive the first demodulation signal and the second demodulation signal and output a phase angle indicating a direction of a vector formed in a phase plane by the first demodulation signal and the second demodulation signal as a head position signal; and a function correction module configured to correct an arctangent function set to the head position demodulator for each head, wherein the function correction module comprises: a measurement holding module configured to hold, as a measurement point, a set of the first demodulation signal and the second demodulation signal output from the area demodulator by moving the head in a direction transversing a track of the medium; a litharge generator configured to set the measurement point held in the measurement holding module on the phase plane and generate a position litharge; a probability density measuring module configured to divide a zone in which a ratio of the first demodulation signal and the second demodulation signal providing the measurement point in the position litharge changes from zero to 1 into a predetermined number of zones and measure number of measurement points for each of the zones as a probability density; and a correction function generator configured to obtain a cumulative probability density by sequentially cumulating the probability density of the zones with respect to the zone in which the ratio changes from zero to 1, and set a function based on the cumulative probability density to the head position demodulator as a corrected arctangent function for each head.