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Browse Prior Art Database

Track Error Signal Offset Calibration Using Interrupt and Intermittent Grooves

IP.com Disclosure Number: IPCOM000121440D
Original Publication Date: 1991-Sep-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 2 page(s) / 80K

Publishing Venue

IBM

Related People

Chow, WW: AUTHOR [+2]

Abstract

Adding di-bits and mirror marks onto grooved disks can provide calibration of the tracking error signal (TES) offset error, and disk tilt. This improves the placement of optical data at the center of the land or data track, and reduces positioning uncertainty associated with alignment problems in the drive, the optical head and electronic offsets.

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This is the abbreviated version, containing approximately 54% of the total text.

Track Error Signal Offset Calibration Using Interrupt and Intermittent
Grooves

      Adding di-bits and mirror marks onto grooved disks can
provide calibration of the tracking error signal (TES) offset error,
and disk tilt.  This improves the placement of optical data at the
center of the land or data track, and reduces positioning uncertainty
associated with alignment problems in the drive, the optical head and
electronic offsets.

      To implement the standard di-bits design complicates disk
manufacturing.  Groove depth is in the range of 1/16 to 3/16 of the
wavelength (lambda) which gives the best differential tracking error
signal.  Di-bits are optimized at a depth of 1/4 lambda and with a
width of over 1/5 microns.  Such design gives the best reflectivity
signal. Using both depths adds cost to the manufacture of stampers
for 2P or injection-molded disks.  If a direct etch technology is
used, fabrication with two different depths is nearly impossible.

      The mirror marks are easy to create on the disk.  They are
simply the absence of grooving.  There is no requirement for a second
depth or feature width.

      From our experience with prototype disk fabrication using the
master writer, we feel a simplified method can be used to create
mirror marks and di-bits.  The essence of the method is to stagger
the breaks in grooving.  In general, two adjacent groove walls are
sensed by the laser spot while tracking the land.  Sensing a di-bit
is e...