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Browse Prior Art Database

Use of VFO Sync Fields for Servo Positioning Information in Disk Drives

IP.com Disclosure Number: IPCOM000038006D
Original Publication Date: 1989-Sep-01
Included in the Prior Art Database: 2005-Jan-31
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Brown, DH: AUTHOR [+3]

Abstract

Disclosed is a method of utilizing the pattern used to synchronize the file variable frequency oscillator (VFO) to the data field for both VFO synchronization and servo track following. The VFO sync field is a fixed frequency burst of information written on a disk file immediately ahead of the data field. The VFO is used to clock out the data in a disk drive when reading the data. This disclosure shows how that same VFO sync field can be used for the additional task of positioning the read/write heads. The VFO in the disk drive adjusts its phase to that of the VFO sync field so that the data that follows can be clocked out properly. Inverting the VFO sync field polarity can be done without affecting the ability to synchronize the VFO to readback the data.

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This is the abbreviated version, containing approximately 58% of the total text.

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Use of VFO Sync Fields for Servo Positioning Information in Disk Drives

Disclosed is a method of utilizing the pattern used to synchronize the file variable frequency oscillator (VFO) to the data field for both VFO synchronization and servo track following. The VFO sync field is a fixed frequency burst of information written on a disk file immediately ahead of the data field. The VFO is used to clock out the data in a disk drive when reading the data. This disclosure shows how that same VFO sync field can be used for the additional task of positioning the read/write heads. The VFO in the disk drive adjusts its phase to that of the VFO sync field so that the data that follows can be clocked out properly. Inverting the VFO sync field polarity can be done without affecting the ability to synchronize the VFO to readback the data. In fact, the polarity of the VFO sync field is not controlled in currently produced disk drives.

This disclosure states that by controlling the polarity of all VFO sync fields on even tracks to be one way and all odd tracks to be the opposite polarity, a null servo pattern occurs when the data head straddles the boundary between the two adjacent sync fields. Due to additive cancellation between the oppositely polarized fix frequency fields, head position can be obtained from this boundary between VFO sync fields on adjacent tracks. The amplitude of the VFO field is an indication of the head position, phase shift of the VFO signal (with respe...