Patent ID: 7209314

Claim:
A magnetic recording disk drive comprising: a rotatable magnetic recording disk having a plurality of concentric circular data tracks and generally circumferentially-spaced servo sectors extending generally radially across the data tracks, each servo sector comprising a plurality of radially-spaced servo tracks, wherein each servo track comprises a phase quadrature pattern of servo blocks, said pattern having a first band and a second band spaced circumferentially from the first band; a read head that generates a clocked data stream that includes an analog servo signal from detection of the phase quadrature pattern of servo blocks, said analog servo signal being generally the sum of a sine function and a cosine function; an actuator connected to the head for positioning the head to different data tracks and maintaining the head on the tracks; servo electronics for digitizing the analog servo signal from the head; and a servo control processor comprising a demodulator for calculating a head position error signal (PES) from the digital servo signal and a controller for generating an actuator control signal from the PES, the demodulator comprising a program of instructions readable by the processor for undertaking method acts comprising: calculating the sine and cosine measured amplitudes of the digitized servo signal from the first and second bands, said measured amplitudes representing the radial position of the head in the presence of any circumferential misalignment in the pattern of servo blocks and in the presence of any clock error during detection of the servo blocks by the read head; and calculating from said measured amplitudes the sine and cosine true amplitudes of the digitized servo signal, said true amplitudes representing the radial position the head without any of said misalignment and any of said clock error.