Browse Prior Art Database

Prevention of Seeking and Tracking Errors Due to Media Data

IP.com Disclosure Number: IPCOM000113501D
Original Publication Date: 1994-Aug-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 39K

Publishing Venue

IBM

Related People

Bui, NX: AUTHOR [+2]

Abstract

The information stored on an optical disk can introduce noise into the tracking error signal that indicates the laser spot position on the disk. The impact of this noise can be minimized by adjusting the cutoff of a low pass filter when moving between tracks, terminating a track seek operation, and following a given track.

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Prevention of Seeking and Tracking Errors Due to Media Data

      The information stored on an optical disk can introduce noise
into the tracking error signal that indicates the laser spot position
on the disk.  The impact of this noise can be minimized by adjusting
the cutoff of a low pass filter when moving between tracks,
terminating a track seek operation, and following a given track.

      During a seek operation, the track crossing rate and therefore
the frequency of the Tracking Error Signal (TES) varies from zero to
perhaps 500 kHz, depending on the details of the system.  To limit
the noise entering the system, a low pass filter is commonly added
with a cutoff frequency slightly above the highest TES frequency
encountered.  The media noise often has considerable energy below the
cutoff frequency.

      The system shown in the Figure reduces the bandwidth of the low
pass filter by an order of magnitude as the head mechanism slows.
The filter bandwidth is only lowered when the track crossing rate is
well below the new cutoff frequency to prevent signal transients due
to phase delay.

      The low frequency cutoff point of the filter (about 50 kHz) is
maintained during the termination of the seek and throughout track
following, greatly reducing the effect of the majority of media
induced errors.  The filter is returned to its high cutoff point as a
new seek begins, again avoiding glitches in the TES due to the filter
switching, while allowing th...