Browse Prior Art Database

Narrow Bandwidth Gray Code Pattern

IP.com Disclosure Number: IPCOM000117247D
Original Publication Date: 1996-Jan-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 4 page(s) / 88K

Publishing Venue

IBM

Related People

Flynn, DT: AUTHOR [+2]

Abstract

The disclosed magnetic recording servo pattern improves the detection of Gray code fields when implemented with a narrow bandwidth channel. Baseline disturbances are minimized by limiting the maximum time between magnetic transitions. The pattern discussed limits magnet lengths to a ratio of 2 to 1.

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Narrow Bandwidth Gray Code Pattern

      The disclosed magnetic recording servo pattern improves the
detection of Gray code fields when implemented with a narrow
bandwidth channel.  Baseline disturbances are minimized by limiting
the maximum time between magnetic transitions.  The pattern discussed
limits magnet lengths to a ratio of 2 to 1.

      Gray code is typically used in magnetic recording servo systems
to encode track type information.  This form of encoding is ideal for
servo patterns because only one bit changes between consecutive
codes.  As the servo transducer straddles the boundary between two
tracks, the decoder resolves only two values based on this one bit
change.  Standard binary encoding cannot be used since multiple bit
changes might result in more than two decode possibilities.  These
additional decodes create errors because they do not represent either
of the two tracks on the boundary.

      Fig. 1 shows the magnetization pattern for the first eight
tracks of a 6 bit traditional Gray code.  The labels b0 through b5
indicate pairs of transitions that correspond to each encoded bit.
Assume negative to positive transitions are notated as {+1}, positive
to negative transitions are notated as {-1}, and the absence of a
transition is notated as {0}.  For the pattern shown, a "1 bit" is
encoded as a {+1, -1} pair and a " 0 bit" is encoded as a {0, 0}
pair.  Note that magnet lengths can be very long.  In the case of an
encoded "000000",...