Browse Prior Art Database

Digital Thermal Asperity Detection

IP.com Disclosure Number: IPCOM000122244D
Original Publication Date: 1991-Nov-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 2 page(s) / 84K

Publishing Venue

IBM

Related People

Galbraith, RL: AUTHOR [+3]

Abstract

Described is a method of defining a read signal anomaly that is caused by an additive transient signal in terms of the relative amplitude of the sample values exiting an analog-to-digital (A/D) converter of a sampling detector. A sequence of sample values are defined that are indicative of the effective samples that would be present for thermal (additive) transient of a specific amplitude. Since a thermal asperity causes a shift in the baseline of the read signal, at some TA amplitude A/D samples will saturate. As the amplitude of the TA increases, the length of the sample burst containing saturated values also increases. The magnitude of a TA can then be categorized by the length of the burst of samples that contain saturated values.

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Digital Thermal Asperity Detection

      Described is a method of defining a read signal anomaly
that is caused by an additive transient signal in terms of the
relative amplitude of the sample values exiting an analog-to-digital
(A/D) converter of a sampling detector.  A sequence of sample values
are defined that are indicative of the effective samples that would
be present for thermal (additive) transient of a specific amplitude.
Since a thermal asperity causes a shift in the baseline of the read
signal, at some TA amplitude A/D samples will saturate.  As the
amplitude of the TA increases, the length of the sample burst
containing saturated values also increases.  The magnitude of a TA
can then be categorized by the length of the burst of samples that
contain saturated values.  The TA magnitude that will be declared by
the channel can be varied by varying the allowable length of the
sample burst containing saturated values that can occur before
declaring the anomaly a TA.  If a small burst is required, then a
relatively small amplitude TA will be sensed.  This will also result
in a higher probability of declaring a TA when the saturated sample
values were a result of some other effect.  Conversely, a large TA
declaration will more assuredly be correctly made if the allowable
burst is long indicating a larger TA.  The chances of this large
burst being the result of some other effect other than a TA will be
small.

      The following description of an embodiment of the invention
shows how thermal asperities are detected by digital logic.  The
figure shows a block diagram of the Thermal Asperity Detector.  The
'Adjustable Threshold Detector' takes in the A/D samples and senses
whether the samples have saturated in either the positive or negative
direction.  (The 'Adjustable Threshold Detector' can be adjusted to
accommodate changes in the...