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Browse Prior Art Database

Pattern and Demodulator for Burst with Digital Beat Demodulation

IP.com Disclosure Number: IPCOM000115758D
Original Publication Date: 1995-Jun-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 92K

Publishing Venue

IBM

Related People

Mueller, E: AUTHOR

Abstract

Disclosed is a method that allows non-coherent bursts of pulses on adjacent tracks to be digitized and demodulated by a Digital Processor (DSP).

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Pattern and Demodulator for Burst with Digital Beat Demodulation

      Disclosed is a method that allows non-coherent bursts of pulses
on adjacent tracks to be digitized and demodulated by a Digital
Processor (DSP).

      Conventional PES patterns require 1) alignment of transitions
between adjacent tracks, so that they may be added in the servo head
as they are read; and 2) peak detection of non-coherent bursts of
pulses on adjacent tracks.

      The evolution of disk files toward high data rates, high track
density and high accessing performance may require modification of
the servo patterns to take advantage of this increased, tangential
jitter and may make it impossible to write conventional servo
patterns with good enough accuracy to be read by a head spanning the
two tracks.

      An obvious solution is  to write bursts of transitions at a
high frequency on adjacent tracks in such a way that they never occur
at the same time.  That way their amplitudes can be independently
measured.  This is done on some low cost (PC grade) files using peak
detection.  Chip sets are available which implement this method.  But
this method suffers from the noise sensitivity of peak detectors, and
the result must be converted to a digital value for use with a
digital servo.

      Disclosed is the use of the PRML ADC to convert the servo PES
to digital values before demodulation.  Since there cannot be many
samples per measured transition, the values measured will be
dependant on the exact instant in the waveform that the conversion
occurs.  Since the waveforms  of the bursts on two adjacent tracks
cannot be assumed to be in phase with each other, the values measured
when the head is exactly centered (spanning 50% of each servo burst)
will appear unequal; so the servo will move off track to the point
where the values are equal.  The magnitude of this error is
intolerable.  A method is proposed to solve the problem of alignment
of pulses on adjacent tracks as required by conventional amplitude
and phase encoded PES patterns.  It is as follows:
  1.  Let the servo bursts be written on adjacent tracks such that
they
       may be read independently.  The burst on one track is written
       next to an erased zone on its neighbor tracks.
  2.  The burst frequency is chosen such that its frequency is an
       integer ratio to the sampling frequency;  for example, 16/17
or
       8/9.  The close ratios mean that  16 (or 8) cycles of the
burst
       frequency will be sampled with 17 (or 9) values.  Thus the
       samples will be measured at constantly changing phases.  The
       result is that...