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Asynchronous Quadrature Burst Position Error Demodulation Technique

IP.com Disclosure Number: IPCOM000122013D
Original Publication Date: 1991-Oct-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 2 page(s) / 59K

Publishing Venue

IBM

Related People

Freitas, D: AUTHOR [+3]

Abstract

The position error signal (PES) channel provides a magnetic disk head- positioning servo system with information on the radial position of a head relative to a disk pattern. Any noise present in the system reduces positional accuracy, leading to degraded performance and possible instability of the system. This article presents a demodulation technique that reduces the noise produced by the coupling of tangential motion of a head in a quadrature burst-type PES channel.

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Asynchronous Quadrature Burst Position Error Demodulation Technique

      The position error signal (PES) channel provides a
magnetic disk head- positioning servo system with information on the
radial position of a head relative to a disk pattern.  Any noise
present in the system reduces positional accuracy, leading to
degraded performance and possible instability of the system.  This
article presents a demodulation technique that reduces the noise
produced by the coupling of tangential motion of a head in a
quadrature burst-type PES channel.

      A quadrature burst-type channel [1] operates by comparing the
relative amplitudes of signals recorded on adjacent tracks.  In a
synchronous demodulator, the amplitudes of the individual bursts are
obtained by multiplying the read-back signal by a rectification
clock; this signal is then low-pass filtered.  When skew exists
between the head and the pattern (see the figure), a timing error is
introduced between the rectification clock and the pattern.  If a
further timing jitter is introduced by mechanical motion or
electrical noise, the relative amplitudes of the bursts are affected,
and the position channel output represents this incorrectly as an
off-track motion.

      The asynchronous demodulation technique replaces the
multiplicative rectifiers with asynchronous rectifiers, one for each
quadrature burst.  To ensure that the rectification includes only a
single quadrature burst and none of the adjacent burs...