Browse Prior Art Database

Adaptive Read Bias by Servo Stability

IP.com Disclosure Number: IPCOM000123148D
Original Publication Date: 1998-Jun-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 1 page(s) / 28K

Publishing Venue

IBM

Related People

Fukushima, Y: AUTHOR [+4]

Abstract

Disclosed is a servo stability improvement method by changing the read bias of MR (magnetoresistive) or GMR (giant MR) head. By improving servo stability, write error can be reduced.

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Adaptive Read Bias by Servo Stability

   Disclosed is a servo stability improvement method by
changing the read bias of MR (magnetoresistive) or GMR (giant MR)
head.  By improving servo stability, write error can be reduced.

   To get a read back signal, MR or GMR head uses a sense
current which is called read bias.  Some head has possibility to
show noise on its read back signal, if the read bias is bigger or
smaller.  This noise is called 'instability'.  Following table shows
an example.
  Read bias   PES stability (sigma)
  ---------   ---------------------
    100%         16.4
    110%         14.7
    120%         13.5
    130%         11.3

   In this case, read bias means % of standard current.  PES
(position error signal) stability means standard deviation of
position error signal.  So smaller value shows better positioning.
Next example shows opposite case.
  Read bias   PES stability (sigma)
  ---------   ---------------------
    100%         13.5
    110%         14.9
    120%         24.9
    130%        (seek error)

To achieve this function, following steps are necessary.
  1.  Measure PES standard deviations of each head by changing
       read bias.
  2.  Get the read biases of each head which shows smallest PES
       standard deviation.
  3.  Save the read bias values of each head into nonvolatile
       memory or Disk.
 ...