Dynamic magnetic information storage or retrieval – Miscellaneous
Reexamination Certificate
1999-07-16
2002-05-21
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
Miscellaneous
C360S046000, C360S067000, C360S025000
Reexamination Certificate
active
06392841
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to data storage systems and, more particularly, to a system and method for restoring a thermal response of a magnetoresistive read transducer.
BACKGROUND OF THE INVENTION
A typical data storage system includes a magnetic medium for storing data in magnetic form and a transducer used to write and read magnetic data respectively to and from the medium. A typical disk storage device, for example, includes one or more data storage disks coaxially mounted on a hub of a spindle motor. The spindle motor rotates the disks at speeds typically on the order of several thousand revolutions-per-minute (RPM).
Digital information is typically stored in the form of magnetic transitions on a series of concentric, spaced tracks formatted on the surface of the magnetizable rigid data storage disks. The tracks are generally divided into a number of sectors, with each sector comprising a number of information fields, including fields for storing data, and sector identification and synchronization information, for example.
An actuator assembly typically includes a plurality of outwardly extending arms with one or more transducers and slider bodies being mounted on flexible suspensions. The slider body lifts the transducer head off the surface of the disk as the rate of spindle motor rotation increases, and causes the head to hover above the disk on an air bearing produced by high speed disk rotation. The distance between the head and the disk surface, which is typically on the order of 40-100 nanometers (nm), is commonly referred to as head-to-disk clearance or spacing.
Within the data storage system manufacturing industry, much attention is presently being focused on the use of a magnetoresistive (MR) element as a read transducer. A typical MR head, for example, incorporates an MR read element and a thin-film write element. MR element transducers, however, are known to introduce a distortion in the sensed magnetic signal, which typically represents user data or servo information stored on a magnetic storage disk. Such a distortion in a readback signal obtained by an MR transducer has heretofore been treated as undesirable low frequency noise, and as such, has been subject to high pass filtering in an attempt to mitigate the distortion.
It is well known, for example, that many data storage disk drive systems that employ MR heads utilize highpass filtering of the magnetic readback signals to block unwanted baseline modulation associated with the thermal response of the MR head. This undesirable thermal response generally interferes with the reliable operation of the recording channel, which is used for processing the magnetic signal portion of the readback signal. This “unwanted” thermal signal component of a magnetic readback signal, however, has been found to be quite useful for purposes of analyzing the flying characteristics of the airbearing slider and detecting disk surface defects, among other uses. The loss of the thermal response due to the blocking effect of the highpass filtering process generally renders the thermal component of a magnetic readback signal unusable.
There exists a need in the data storage system manufacturing community for an apparatus and method for restoring the thermal response of a highpass filtered magnetic readback signal. There exists a further need to obtain a highpass filtered thermal signal without interfering with the magnetic readback signal. The present invention is directed to these and other needs.
SUMMARY OF THE INVENTION
The present invention is directed to an apparatus and method for processing a readback signal obtained from a storage medium using a magnetoresistive element, and restoring a thermal signal component of the signal. A readback signal is obtained from the storage medium using an MR element. The readback signal comprises a thermal component representing a thermal response of the MR element, and may further comprise a magnetic component representing servo or user data. The readback signal is filtered so as to degrade the thermal component of the signal, typically by amplification circuitry exhibiting a highpass filtering behavior.
In one embodiment, the highpass filtered readback signal is subsequently filtered using a lowpass filter, such as by use of an anti-alias lowpass filter. The filtered signal is sampled to produce samples of the filtered signal. A sliding window comprising a series of binary values is applied to groups of the signal samples to produce a plurality of signal sample values for each of the signal sample groups. The signal sample values for each of the signal sample groups are summed to produce a restored thermal signal substantially representative of the thermal component of the signal obtained from the storage medium.
The sliding window comprises a series of binary zeros and binary ones, and the ordering of the series of binary zeros and binary ones differs for each of the groups of the signal samples to which the sliding window is applied. The sliding window has a preestablished length, and the signal sample groups are separated by a preestablished number of signal samples. The sliding window is applied to mask the sampled signal so as to progressively slide the window by a preestablished number of signal samples.
Applying the sliding window to the signal samples involves multiplying the series of binary values defining the sliding window with the signal samples of each of the signal sample groups. The summed signal sample values are arranged as a sequence of summed values, the summed values being representative of portions of the restored thermal signal. An interpolation operation is performed on the sequence of summed values to produce the restored thermal signal. The restored thermal signal may be used for a variety of operational and diagnostic functions, such as detecting a surface feature of the storage medium.
In accordance with another embodiment, a magnetic readback signal provided at an output of an amplification circuit that exhibits a highpass filtering behavior may be operated on to produce a restored thermal component. In this embodiment, the signal obtained from the storage medium comprises a magnetic component in addition to a thermal component. A ternary signal is produced using the signal obtained from the storage medium, such as by use of a recording channel analyzer coupled to the recording channel.
The ternary signal is sampled to produce samples of the ternary signal by the recording channel analyzer. A sliding window is applied to groups of the ternary signal samples to produce a plurality of signal sample values for each of the ternary signal sample groups. The signal sample values are summed for each of the ternary signal sample groups to produce a restored thermal signal substantially representative of the thermal component of the signal obtained from the storage medium.
An apparatus for restoring a thermal component of a readback signal employed in an information storage device includes a transducer comprising a magnetoresistive element for reading a signal from a storage medium. The readback signal comprises a thermal component representing a thermal response of the MR element. An amplification circuit, coupled to the transducer and preferably provided in an arm electronics module, alters the readback signal such that the thermal component is degraded. A sampling circuit, coupled to the amplification circuit, samples the altered signal to produce samples of the altered signal.
A processor, coupled to the sampling circuit, applies a sliding window comprising a series of binary values to groups of the signal samples to produce a plurality of signal sample values for each of the signal sample groups. The processor further sums the signal sample values for each of the signal sample groups to produce a restored thermal signal substantially representative of the thermal component of the signal obtained from the storage medium. The apparatus may be incorporated in-situ a disk drive system.
The above summary of the present invention is
Ottesen Hal Hjalmar
Smith Gordon James
Davidson Dan I.
Hollingsworth Mark A.
Hudspeth David
International Business Machines - Corporation
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