Browse Prior Art Database

Compensation of Servo Burst Noise Level/Compensation of Magnetic Widths

IP.com Disclosure Number: IPCOM000123339D
Original Publication Date: 1998-Sep-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 3 page(s) / 109K

Publishing Venue

IBM

Related People

Cunningham, EA: AUTHOR

Abstract

Servo patterns written in Hard Disk Drives (HDD) using sector servo are typically written with the data write element and read by the data read element. The width of the written patterns and/or the read widths may not be of the correct size for optimum servo signal processing. In addition, the noise in the servo processing may change the apparent widths of the written and read widths, for which compensation should be done. The descriptions below show the effect of detection noise and how the compensation may be done. Also is shown, how the addition of artificial noise, or DC thresholds can be used to modify the apparent written and read widths, which adds an additional degree of freedom to better optimize the servo signals along with the required signal processing widths.

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Compensation of Servo Burst Noise Level/Compensation of Magnetic
Widths

   Servo patterns written in Hard Disk Drives (HDD) using
sector servo are typically written with the data write element and
read by the data read element.  The width of the written patterns
and/or the read widths may not be of the correct size for optimum
servo signal processing.  In addition, the noise in the servo
processing may change the apparent widths of the written and read
widths, for which compensation should be done.  The descriptions
below show the effect of detection noise and how the compensation may
be done.  Also is shown, how the addition of artificial noise, or DC
thresholds can be used to modify the apparent written and read
widths, which adds an additional degree of freedom to better optimize
the servo signals along with the required signal processing widths.

   There are many methods to write servo patterns in Hard
Disk Drives.  Some use phase aligned patterns written adjacent to one
another to simulate a single written track wider than the width of
that written by the data write head.  Some use tracks written
radially offset, but also with timing offset, and then the magnitude
of the signals are electrically added to simulate a signal from a
wider written width.  Regardless of the method, the patterns of the
commonly used sector servo patterns are written with the data write
element, and read with the data read element.  This adds
restrictions, since the elements must be tuned for the best use in
the data signal processing.

   The first aspect of this disclosure is that noise in the
detection system of the servo processing changes the apparent write
and read widths compared to the actual magnetic widths.  Figure 1
illustrates the theoretical radial displacement curves for uniform
head sensitivity with abrupt edges, and written widths of uniform
magnetization strength and abrupt edges.  The displacement curves are
for a case of a read head with a magnetic width of 0.6 of the pitch
of the written data tracks.  The written magnetization is for a width
of 0.5 of the data track pitch, as might be achieved by writing with
a wider write head, but then trimming off the edge by erasing with
the write element offset, so that some of the magnetization on one
side is erased, leaving a width of 0.5 of the written data track
pitch.  The pattern shown is one in which four equal bursts are
written with 0.5 of a track pitch offset from each other and
circumferentially of...