Browse Prior Art Database

Disk Drive Automatic Gain Control Gain Setting Method with High Frequency Patterns on Reference Tracks

IP.com Disclosure Number: IPCOM000122542D
Original Publication Date: 1991-Dec-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 3 page(s) / 153K

Publishing Venue

IBM

Related People

Brown, DH: AUTHOR [+2]

Abstract

Disclosed is a method of writing high frequency write recovery patterns on direct access storage devices (DASDs) without regard to transition position alignment between adjacent tracks. This is useful when the frequency of the write recovery pattern requires tighter track-to-track phase alignment than the file can provide. Files with high frequency data channels and low frequency servo channels are classes of files that can use this technique. Any servo patterns that are passed through the high frequency data channel will require a high frequency automatic gain control (AGC) recovery field ahead of the pattern to properly set the gains of the AGC for reading. EFFECTS OF MISALIGNMENT ON SIGNALS WITH VARIOUS FREQUENCIES

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Disk Drive Automatic Gain Control Gain Setting Method with High Frequency
Patterns on Reference Tracks

      Disclosed is a method of writing high frequency write
recovery patterns on direct access storage devices (DASDs) without
regard to transition position alignment between adjacent tracks.
This is useful when the frequency of the write recovery pattern
requires tighter track-to-track phase alignment than the file can
provide.  Files with high frequency data channels and low frequency
servo channels are classes of files that can use this technique.  Any
servo patterns that are passed through the high frequency data
channel will require a high frequency automatic gain control (AGC)
recovery field ahead of the pattern to properly set the gains of the
AGC for reading.
EFFECTS OF MISALIGNMENT ON SIGNALS WITH VARIOUS FREQUENCIES

      Fig. 1 shows the effects of misalignment and how it becomes
more significant with increasing frequency.  In the figure, the
shaded areas are regions of a track that are magnetized in one
direction and the unshaded areas are magnetized in the opposite.
Transitions occur between the shaded and unshaded regions.  Ideally,
the regions should line up exactly from track to track.  In example
A, a head that is designed with low resolution to perform at the
lower frequencies will see insignificant effects of the misalignment
between tracks N and N+1.  In example B, the misalignment is more
significant.  In example C, the frequency has been increased to the
point where the misalignment is large enough to cause complete
cancellation of a head signal for a head that straddles the two
tracks.

      In a DASD that requires a high frequency pattern for the AGC
write recovery field, it is difficult to write patterns with
insignificant track-to-track misalignment. The technique of this
disclosure is to write the high frequency pattern directly under the
head on the disk revolution prior to reading this pattern.  On the
next revolution of the disk, the head could then easily read back the
pattern since it will be centered over it and not have any problems
with interfering misaligned signals from adjacent tracks.

      Fig. 2 demonstrates this idea.  Part A shows two adjacent
misaligned tracks with the head position denoted by the marker to the
left.  In this situation, the head will straddle the two tracks, with
each track contributing additively a part of the readback signal.
Since the phase of the two tracks in this example is close to 180
degrees, the combined readback signal will be close to zero due to
the destructive cancellation.  The write recovery pattern is
unreadable and the AGC will set up the wrong gain.

      Part B shows the same situation with a newly written track
overwriting the two previous tracks.  This new track is perfect...