Browse Prior Art Database

Using the Position Error Signal Burst Fields for Automatic Gain Control Input

IP.com Disclosure Number: IPCOM000118282D
Original Publication Date: 1996-Dec-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 4 page(s) / 149K

Publishing Venue

IBM

Related People

Greenberg, R: AUTHOR [+2]

Abstract

In order to read the Servo Identifier (SID), gray code, and Position Error Signal (PES) bursts in the servo field of a disk drive, the channel gain must be correctly set up. Typically, an Automatic Gain Control (AGC) field is used to set up this gain. This invention removes the need for a unique AGC field by allowing the channel gain to be adjusted through an interface driven by an external micro-processor. The micro-processor measures the amplitude of the PES bursts and adjusts the channel gain up or down appropriately.

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Using the Position Error Signal Burst Fields for Automatic Gain Control
Input

      In order to read the Servo Identifier (SID), gray code, and
Position Error Signal (PES) bursts in the servo field of a disk
drive, the channel gain must be correctly set up.  Typically, an
Automatic Gain Control (AGC) field is used to set up this gain.  This
invention removes the need for a unique AGC field by allowing the
channel gain to be adjusted through an interface driven by an
external micro-processor.  The micro-processor measures the amplitude
of the PES bursts and adjusts the channel gain up or down
appropriately.

      At present, the industry is using a Quad burst amplitude scheme
to generate PES.  This scheme typically uses four distinct fields
written "spaced out in time and also spaced radially."  These fields
are often written one track wide.  This disclosure shows an example
where these fields are a half track wide.  This invention will work
for any width burst and for fewer or more burst fields than four.

      The layout of a four-field burst is shown in the
Figure. 

                            (Image Omitted)

      The Figure above shows a four-burst layout as an example of how
the servo PES pattern might be written.  The track centerlines are
shown as track n-1, n, etc.  The width of each burst is 1/2 track.

This is achieved by erasing each burst on side 2 when the next burst
nearer the ID is written.

      In the present design, the "WRITE RECOVERY" and "AGC" fields
shown above are written with the AGC pattern from the Outer Diameter
(OD) to the Inner Diameter (ID) in a phase-aligned fashion.  A
phase-aligned SID and gray code is also written on each track.

      This invention eliminates the need for the AGC field.  The
write recovery field will still be needed and can be written with
phase-aligned AGC pattern if that's possible.  There would be two
methods of operation depending on whether there can exist a phase
aligned "WRITE RECOVERY" field or not.

      If phase alignment is possible, then the AGC operation would
proceed as described in SECTION A below.  If phase alignment is not
possible, then the AGC would operate as shown in SECTION B below.

      SECTION A (Phase alignment possible)

There are three conditions under which the AGC operates:
  1.  Trackfollow
  2.  Seeking
  3.  Recalibration.  This is the operation which brings the
       actuator from the crash stop to cylinder 0.

      TRACKFOLLOW AGC OPERATION AFTER A DATA READ OPERATION

      The "WRITE RECOVERY" field is unreadable immediately after a
write operation.  After data read operations, it is readable.
Therefore, after read operations, this field could serve exactly the
same purpose as the AGC field.  "WRITE RECOVERY" fields are normally
longer than AGC fields anyway.  Therefore, during write operations
the AGC would be updated differently.

      TRACKFOLL...