Electricity: measuring and testing – Magnetic – Magnetic information storage element testing
Patent
1994-03-30
1995-06-13
Snow, Walter E.
Electricity: measuring and testing
Magnetic
Magnetic information storage element testing
360 25, 369 58, 371 211, G01R 3312, G11B 2700, G01N 2782
Patent
active
054246385
ABSTRACT:
An apparatus and method for detecting defects in the magnetic medium of a disk drive system includes sampling the output signal of the read channel of the system to provide a sampled output signal. In one embodiment, the sampled output signals from the read channel is squared. A delayed sampled output signal is also provided. The squared sampled output signal is summed with the delayed squared output signal. The square of the expected value of the sum of the squared sampled output signal and the delayed squared output signal is subtracted from the sum to provide a difference output signal. A threshold detector determines when the difference output signal of the subtraction means exceeds a predetermined threshold to provide an output signal indicative of a defect in the medium. One threshold detector determines when the absolute value of the difference output signal exceeds a predetermined threshold value. Another threshold detector determines when the difference output signal of the subtraction means exceeds either a predetermined upper threshold value or a predetermined lower value. The expected value may be a constant. In another embodiment, the absolute value of the sampled output signal and a delayed sampled absolute-value output signal are summed together.
REFERENCES:
patent: 4881136 (1989-11-01), Shiraishi et al.
patent: 4929894 (1990-05-01), Monett
patent: 5121057 (1992-06-01), Huber et al.
patent: 5247254 (1993-09-01), Huber et al.
Magnetic Characterization Using Elements of a PRML Channel by Jonathan D. Coker, Richard L. Galbraith, Gregory J. Kerwin from IEEE Transactions Magazine, vol. 27, No. 6, Nov. 1991.
Heller III Edward P.
King Patrick T.
Seagate Technology Inc.
Snow Walter E.
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