Browse Prior Art Database

Quad Burst Servo Needing No Sync Id And Having Added Information

IP.com Disclosure Number: IPCOM000101641D
Original Publication Date: 1990-Aug-01
Included in the Prior Art Database: 2005-Mar-16
Document File: 3 page(s) / 126K

Publishing Venue

IBM

Related People

Cunningham, EA: AUTHOR

Abstract

Disclosed is an improvement in writing and detecting quad-burst servo that requires no synchronization or identification fields and allows several bits of information to be added to the basic burst.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Quad Burst Servo Needing No Sync Id And Having Added Information

       Disclosed is an improvement in writing and detecting
quad-burst servo that requires no synchronization or identification
fields and allows several bits of information to be added to the
basic burst.

      A typical quad burst servo pattern is usually written with a
single frequency pattern that is recorded in bursts with four types
of offtrack positions separated in time, as shown in Fig. 1.  Each
burst is recorded with a given width and each successive burst is
offset by one half of that width.  The normal procedure used in
obtaining the servo signal is to use the magnitude of burst B minus
the magnitude of burst A to develop the primary Position Error Signal
(PES) or the P signal.  The magnitude of burst D minus the magnitude
of burst C is used for the quadrature PES signal, or Q signal.  The P
and Q signals are shown in Fig. 2.

      In addition to the fields shown, some timing information
patterns are normally required to identify which pattern is which.
Additional information may also be included in such fields.

      The disclosed improvement described below allows the quad burst
servo pattern to be written without any separate identification
fields.  This allows the actual servo information patterns to be more
continuous.  The method can also be used for the older two-burst
servo system.

      This is done by modifying the recorded pattern so as to contain
some binary information, without changing the fundamental frequency
content for the servo system.  In this way, each of the four bursts
can be self-identifying.  In addition, more information can be
recorded in each burst than just the two bits needed to identify four
types, the amount depending on the length of the burst.  Thus, some
information, such as some of the lower bits of the track number or
sector number, could be included.

      A short example pattern is shown in Fig. 3, consisting of four
periods.  Note that just before the indicated point in each period of
six clock cells, there is a positive pulse, and then a corresponding
negative pulse at the same spacing.  Also, the spacing of the pair
from the indicated point is either  1 clock cell, as in the first
two indicated points, or  2 clock cells as in the last two
indicated points.  The symmetry of the pattern causes the phase of
the fundamental to have a zero crossing at the indicated points. The
position of  1 clock cell represents  60 degrees of angle for
the fundamental.  The position of a pulse pair at this spacing
provided the fourier content of sin(60 deg) or 0.866 of the amplitude
if it was at  1.5 clock cells, or 90 degrees.  For the spacing of
 2 clock cells, the corresponding angle is  120 degrees.  Note
that sin(120 deg)=si...