Browse Prior Art Database

Digital Sector Mark Channel for Optical Disk Drives

IP.com Disclosure Number: IPCOM000116559D
Original Publication Date: 1995-Oct-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 64K

Publishing Venue

IBM

Related People

Clark, AR: AUTHOR [+4]

Abstract

Every sector in an optical disk starts with a sector mark. If the channel does not recognize the sector mark, then the whole sector may be lost. An all digital method for detection of the sector mark is presented that is robust against transients in the readback waveform, requires no acquisition time, and is programmable and simple to implement.

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Digital Sector Mark Channel for Optical Disk Drives

      Every sector in an optical disk starts with a sector mark.  If
the channel does not recognize the sector mark, then the whole sector
may be lost.  An all digital method for detection of the sector mark
is presented that is robust against transients in the readback
waveform, requires no acquisition time, and is programmable and
simple to implement.

      The proposed channel is shown in Fig. 1 and the associated
waveforms are shown in Fig. 2.  It is based on a double derivative
threshold qualified peak detection channel.  A double derivitive
channel is used because it is nearly immune to baseline offsets of
the input waveform and requires virtually no time to acquire an
initial threshold.

      In the detection of the sector mark, the digitized preamplifier
output is sent to the sector mark channel (A).  The input is
differentiated (1 - D when done digitally) which maps the edges of
the sector mark to peaks.  The peaks are sent to a detector and a
tracking threshold for threshold qualified peak detection.  In the
tracking threshold (D), the peaks are rectified and passed through a
low-pass filter which has a programmable coefficient.  This derives a
reference that is used by the detector to reject any small peaks that
are due to noise.  In the detector (C), the peaks are differentiated
again.  If a zero-crossing occurs and the associated peak is greater
than the tracking threshold, then a secto...