Patent ID: 8705191

Claim:
A disk drive controller system that reads information from a disk that is rotating relative to a read head, the information being previously recorded in a plurality of tracks, the disk having at least one short null servo position error signal (“PES”) wedge recorded on the disk, the at least one short null servo PES wedge including a calibration field and a position error signal field, the disk drive controller system comprising: circuitry that reads the calibration field to produce a calibration field signal; circuitry that reads the position error signal field to produce a position error field signal; and control circuitry that uses information from the calibration field signal and the position error field signal to produce a signal for use in controlling a radial position of the read head relative to the disk; wherein: the information from the position error field signal is indicative of an amount by which the read head is radially displaced from a center of a track being read; and the control circuitry adjusts the information from the position error field signal based at least in part on the information from the calibration field signal to compensate for phase error in the position error field signal.