Browse Prior Art Database

Multiple Automatic Gain Control for Servo Information

IP.com Disclosure Number: IPCOM000117736D
Original Publication Date: 1996-May-01
Included in the Prior Art Database: 2005-Mar-31
Document File: 2 page(s) / 47K

Publishing Venue

IBM

Related People

Ohsawa, T: AUTHOR

Abstract

This article describes a Hard Disk Drive which has multiple Automatic_Gain_Control (ACTIVE/HOLD) capability. If there are large missing bits and/or large extra bits at the AGC recovery location, it causes Automatic_Gain_Control malfunction and causes SERVO missing error. This method is to HOLD the Automatic_Gain_Control at the error location in Error Recovery Procedure (ERP), and ACTIVATE the AGC at the previous AGC recovery location.

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Multiple Automatic Gain Control for Servo Information

      This article describes a Hard Disk Drive which has multiple
Automatic_Gain_Control (ACTIVE/HOLD) capability.  If there are large
missing bits and/or large extra bits at the AGC recovery location, it
causes Automatic_Gain_Control malfunction and causes SERVO missing
error.  This method is to HOLD the Automatic_Gain_Control at the
error location in Error Recovery Procedure (ERP), and ACTIVATE the
AGC at the previous AGC recovery location.

The Figure shows one of the implementations of this algorithm:
       (1) step_1

      If there are large extra bits, Hard Disk Controller (HDC)
cannot find the SRV_M and Data(N) information because of the AGC
recovery problem.  HDC can make the dummy sector pulse from previous
SRV_M-1 information; however, data cannot be recovered.
       (2) step_2 (During ERP)

      During the next revolution, AGC recovery has been done at the
SRV_M-1, and AGC is held at the AGC recovery location of SRV_M.  By
this method, Data(N) can be recovered because the read back signal
bad location is terminated at the large extra bit location only.
Read gate which defines the Data(N) start point has been asserted
using the dummy sector pulse from the previous servo information
(SRV_M-1), even if the SRV_M information cannot be read.

      The benefit of this method is minimizing the disturbance of the
read back signal which causes the malfunction of AGC.