International Business Machines Corporation

Chung Chuan Liu

Francis Edward Mueller

Wayne Leung Cheung

Martin H Dost

A digital servo control system for a disk drive provides asynchronous servo information signal demodulation. The system includes a digital demodulator having a digital squarer that removes any phase component of the digitized servo information signal and includes a burst signal accumulator that accumulates the squared terms according to respective burst timing intervals to produce a digital, quadrature position error signal (PES). The demodulator also can include a filter comprising a harmonic notch filter preferably implemented as a Hilbert Transform filter. Alternatively, the demodulator does not include a filter and squarer and, instead, the squarer comprises a sum-and-squarer that sums the squares of odd and even digitized samples. A split burst servo pattern for the servo control system is comprised of half-width transitions that can be written in a single pass of a recording head and therefore has no phase misalignment between adjacent flux patterns.

Quadrature servo pattern disk providing asynchronous digital PES

Asynchronous digital PES demodulation disk drive servo control system

A track-seeking and track-following servo encodement and detection system employs a servo pattern using a reference signal and control signals, the control signals having an orthogonal phase relationship to each other by cyclically revolving in phase by 90.degree., 180.degree., 270.degree., and repeating this pattern every four tracks.

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San Jose, CA, United States of America

Chung Chuan Liu