Dynamic magnetic information storage or retrieval – General processing of a digital signal – Head amplifier circuit
Reexamination Certificate
1998-10-06
2001-01-16
Kim, W. Chris (Department: 2753)
Dynamic magnetic information storage or retrieval
General processing of a digital signal
Head amplifier circuit
C360S025000
Reexamination Certificate
active
06175457
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to methods and apparatus for detecting data, and more particularly to, a method and apparatus for dual polarity thermal asperity detection in a direct access storage device.
DESCRIPTION OF THE RELATED ART
Direct access storage devices (DASDs) often incorporating stacked, commonly rotated rigid magnetic disks are used for storage of data in magnetic form on the disk surfaces. Data is recorded in concentric, radially spaced data information tracks arrayed on the surfaces of the disks. Transducer heads driven in a path toward and away from the drive axis write data to the disks and read data from the disks. Typically servo information is provided on one or more disk surfaces for reading by the transducer heads for accurately and reliably positioning transducer heads on the disk surfaces to read and write data.
A partial-response maximum-likelihood (PRML) detection channel advantageously is used to achieve high data density in writing and reading digital data on the disks. U.S. Pat. No. 4,786,890 discloses a class-IV PRML channel using a run-length limited (RLL) code. The disclosed class-IV partial response channel polynomial equals (1−D
2
), where D is a one-bit interval delay operator and D
2
is a two-bit interval delay operator and the channel response output waveform is described by taking the input waveform and subtracting from it the same waveform delayed by a two-bit interval. A (0,k=3/k1=5) PRML modulation code is utilized to encode 8 bit binary data into codewords comprised of
9
bit code sequences, where the maximum number k of consecutive zeroes allowed within a code sequence is 3 and the maximum number k1 of consecutive zeroes in the all-even or all-odd sequences is 5. Various improvements have been implemented in PRML detection channels in disk drives.
For example, U.S. Pat. No. 5,196,849 issued Mar. 23, 1993 to Richard L. Galbraith and assigned to the present assignee, discloses apparatus and a method for encoding a predefined number of bits of binary data into codewords having a predefined number of bits for PRML data channels. Rate 8/9 block codes having maximum ones and run length constraints (0,8,12,∞) and (0,8,6,∞) are disclosed for providing timing and gain control and reduced susceptibility to misequalization effects in PRML detection channels.
U.S. Pat. No. 5,233,482 to Richard L. Galbraith, Gregory J. Kerwin and Joe M. Poss, issued Aug. 3, 1995 to the present assignee, discloses thermal asperity compensation methods and apparatus for data detection in a PRML data channel.
In hard disk drives, a thermal asperity (TA) detector identifies readback signal anomalies, for example that result from the heating of the read element's magnetoresistive stripe as it strikes a disk defect.
An important aspect of the detector design is how to identify events of either positive or negative polarity without having two separate detectors and therefore doubling the hardware. Detectors which utilize an initial saturation level to dynamically switch the polarity of the level threshold can make incorrect decisions as the result of noise or signal shaping from equalization. The response of discrete time equalization can in fact cause the first sample of the TA event to be opposite in sign of the actual TA. This initial sample can cause the detector to commit to the wrong polarity with no chance of correcting in time to qualify the event.
SUMMARY OF THE INVENTION
A principal object of the present invention is to provide a method and apparatus for dual polarity thermal asperity detection in a direct access storage device. Other important objects of the present invention are to provide such method and apparatus substantially without negative effects; and to provide such method and apparatus that overcome some of the disadvantages of prior art arrangements.
In brief, a method and apparatus are provided for dual polarity thermal asperity detection in a direct access storage device. A level threshold comparator receives a data signal from a data channel in the direct access storage device and compares data samples of the data signal with a positive level threshold and a negative level threshold. Responsive to each identified consecutive data sample above the positive level threshold and responsive to each identified consecutive data sample less than the negative level threshold, a counter value is incremented. A count comparator compares the counter value with a predefined count threshold and identifies a thermal asperity event responsive to a counter value above the predefined count threshold.
REFERENCES:
patent: 4786890 (1988-11-01), Marcus et al.
patent: 5196849 (1993-03-01), Galbraith
patent: 5233482 (1993-08-01), Galbraith et al.
patent: 6018428 (2000-01-01), Okamura
patent: 6038091 (2000-03-01), Reed et al.
patent: 9-231505 (1997-09-01), None
International Business Machines - Corporation
Kim W. Chris
Pennington Joan
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