Magnetic disk drive read channel with digital thermal asperity d

Details Magnetic disk drive read channel with digital thermal asperity d Magnetic disk drive read channel with digital thermal asperity d

1997-10-06

2000-03-14

Kim, W. Chris

Dynamic magnetic information storage or retrieval

General processing of a digital signal

Head amplifier circuit

360 25, 360 65, 360 61, G11B 509, G11B 502, G11B 5035, G11B 1512

Patent

active

060380918

ABSTRACT:
A thermal asperity-tolerant read channel is provided for a magnetic disk drive. Thermal asperities are detected by a digital detector which includes a pre-filter, a first threshold comparator and, optionally, a second threshold comparator. The pre-filter reduces noise and signal variation in the analog-to-digital converter output to enable better detection of a DC shift caused by a thermal asperity. The first threshold comparator compares the pre-filter output to a predetermined level; if the predetermined level is exceeded, the comparator output is set to one state, providing an initial indication of the presence of a thermal asperity. The optional second threshold comparator determines whether, out of a predetermined number of comparator outputs, the number in the one state exceeds programmed value; if so, the second threshold comparator outputs a final indication of the presence of a thermal asperity. In such a manner, accurate detection of thermal asperities is enhanced while reducing the likelihood of false detection. When a thermal asperity is detected, one or more of the following features can be activated to reduce the adverse effects of the thermal asperity: a squelch connected to the inputs of the variable gain amplifier; a loop-hold feature to maintain channel parameters such as timing, offset and gain until the effects of the thermal asperity have dissipated; and a user data erasure pointer to flag data which has been corrupted by the thermal asperity and which needs to be corrected by ECC circuitry.

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"Slider-Disk Asperity Hit Detector", IBM Technical Disclosure Bulletin, vol. 34, No. 7B, pp. 11-13, Dec. 1991.

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