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Browse Prior Art Database

Phase Locked Oscillator Generated Clock Track

IP.com Disclosure Number: IPCOM000082217D
Original Publication Date: 1974-Oct-01
Included in the Prior Art Database: 2005-Feb-28
Document File: 3 page(s) / 29K

Publishing Venue

IBM

Related People

Blythin, P: AUTHOR [+3]

Abstract

The figure shows apparatus for writing a clock track on a magnetic disk. The clock track, which consists of several thousand evenly spaced transitions around the disk, is derived iteratively from a single-index pulse previously written on the disk.

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Phase Locked Oscillator Generated Clock Track

The figure shows apparatus for writing a clock track on a magnetic disk. The clock track, which consists of several thousand evenly spaced transitions around the disk, is derived iteratively from a single-index pulse previously written on the disk.

The iterative technique requires two tracks on the disk each with its associated heads 1 and 2 and read write circuits 3 and 4. The read write circuits are controlled by a logic control block 5 to enable information to be written on one track of the disk with one head, whilst information is simultaneously read from the other track with the other head.

Information read from the disk is supplied by block 5 to a phase-locked loop consisting of phase-error detector 6, phase error to voltage converter 7, compensator circuit 8, voltage-controlled oscillator 9 and a multistage counter 10. The nominal frequency of the oscillator 9 is selected to be similar to the frequency of the required clock track.

The counter 10 has sufficient divide-by-two stages Sl to Sn, so that the frequency of the signal from the final stage is similar to the frequency of a signal derived from a single-index mark on the rotating disk. Output signals from all the stages of counter 10 are available to be written as information on the disk, and selection is by way of switch 11 under control of block 5. A single-shot 12 completes the apparatus and under control of block 5, provides the means by which the index pulse is written on the disk.

The process for writing the clock track is initiated by energizing single-shot 12 to write an index pulse on the disk surface with head 1. Head 1 is then used to read the index pulse from the disk and the...