Dynamic magnetic information storage or retrieval – General recording or reproducing – Specifics of equalizing
Reexamination Certificate
1998-02-02
2001-12-04
Neal, Regina Y. (Department: 2651)
Dynamic magnetic information storage or retrieval
General recording or reproducing
Specifics of equalizing
C360S046000
Reexamination Certificate
active
06327108
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to disc drive servo systems. In particular, the present invention relates to filters in servo systems.
BACKGROUND OF THE INVENTION
Magnetic storage devices store data on magnetic media using write heads that generate small magnetic fields. As a write head passes over a medium, its small magnetic field alters localized magnetic moments on the medium. Data is retrieved from magnetic media using read heads that sense transitions in the localized magnetic fields generated by each of these magnetic moments. In response to each of these transitions, a read head generates electrical pulses that are part of a series of pulses forming a read signal. The pulses are either positive or negative depending on the direction of the magnetic moment transition.
Ideally, each pulse rises and falls quickly to provide a very sharp and large peak for detection. Unfortunately, capacitive and inductive effects and magneto-resistive head effects often cause shouldering just before or just after the peak. In extreme cases, this shouldering can be detected as a peak and can cause some data to be obscured. In addition, noise in the read channel often interferes with proper peak detection.
Prior art systems have attempted to remove noise and shouldering from the pulses using fixed filters that are designed to produce the best average pulses for an entire line of magnetic storage devices. However, these fixed filters are unable to accommodate pulse idiosyncracies that are found in individual data storage devices within a line of data storage devices. In addition, in disc drives, such fixed filters are unable to accommodate changes in the pulse shape that occur because the head has moved to different radial positions along the disc.
The present invention addresses these and other problems, and offers other advantages over the prior art.
SUMMARY OF THE INVENTION
A method and apparatus detects and filters pulse asymmetries in a read signal of a data storage device. A value indicative of the difference between the shape of a pulse from its first zero crossing to its peak and the shape of the pulse from its second zero crossing to its peak is determined. This value is minimized by adjusting at least one filter characteristic of a read signal filter.
In the present invention, a phase-locked loop clock signal is aligned with an input read signal such that the peaks of the read signal occur at transitions in the phase-locked loop clock signal. These two signals are then multiplied together. The resulting product is integrated to produce a series of integrands. If the pulses are symmetrically shaped about their peaks, the integrands will be equal to zero. However, if the pulses are asymmetrical, the integrands will have magnitudes greater than zero. A processor receives the integrands and attempts to minimize the magnitude of the integrands by adjusting the filter characteristics of a read signal filter.
REFERENCES:
patent: 5117408 (1992-05-01), Weispfenning et al.
patent: 5301080 (1994-04-01), Ottesen et al.
patent: 5367409 (1994-11-01), Ottesen et al.
patent: 5586144 (1996-12-01), Kahlman et al.
patent: 5592340 (1997-01-01), Minuhin et al.
patent: 5638225 (1997-06-01), Tsuboi et al.
patent: 5677802 (1997-10-01), Saiki et al.
patent: 6025712 (2000-02-01), Mian
patent: 59-33618 (1984-02-01), None
patent: 359033618A (1984-02-01), None
patent: 60-70552 (1985-04-01), None
patent: 360070552A (1985-04-01), None
Ellis Timothy F.
Sacks Alexei H.
Magee Theodore M.
Neal Regina Y.
Seagate Technology LLC
Westman, Champlin & Kellly, P.A.
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