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MULTIPLE POLE HIGH PASS THERMAL SPIKE FILTER FOR TAPE CHANNELS

IP.com Disclosure Number: IPCOM000014453D
Original Publication Date: 2000-Feb-01
Included in the Prior Art Database: 2003-Jun-19
Document File: 3 page(s) / 58K

Publishing Venue

IBM

Abstract

Thermal spikes (or thermal asperities) occur in magnetic tape and disk channels which use MR heads when a defect or debris on the media hits the MR head. This causes localized heating of the MR element which changes its resistance to increase and results in a transient in the detected signal. The transient is characterized by fast rise times and slow decay times as the localized heating dissipates. The transient causes the baseline of the signal to shift, often to levels several times the amplitude of the signal. Such shifts cause the data detector in the channel to make errors. The filter described here attenuates the low frequency energy associated with the thermal spike minimizing its effect on the error rate of the channel.

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MULTIPLE POLE HIGH PASS THERMAL SPIKE FILTER FOR TAPE CHANNELS

   Thermal spikes (or thermal asperities) occur in magnetic tape and disk
channels which use MR heads when a defect or debris on the media hits the MR
head. This causes localized heating of the MR element which changes its
resistance to increase and results in a transient in the detected signal. The
transient is characterized by fast rise times and slow decay times as the
localized heating dissipates. The transient causes the baseline of the signal to
shift, often to levels several times the amplitude of the signal. Such shifts
cause the data detector in the channel to make errors. The filter described here
attenuates the low frequency energy associated with the thermal spike minimizing
its effect on the error rate of the channel.

Tape and disk channels typically have a single pole high pass filter to
attenuate thermal spikes. Typically this is a simple RC filter formed by the
coupling capacitors into the preamplifier and the input resistance of the
preamplifier.

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The figure below shows the wave form from an analog simulation showing the
effect of a single and a double pole high pass filter on the output wave form
during a thermal spike.

The input to the simulation is the middle trace. This is the signal at the MR
head. It was constructed to approximate the typical thermal spike seen in
tape products. The shift in the wave form will clearly cause significant
errors since the output wave form completely crosses the baseline. The
negative threshold tracker will stick at the baseline. The effect of the high
pass pole at the input to the preamplifier is apparent in the bottom trace
which is the wave form at the preamplifier inputs after the first high pass

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pole. The baseline shift is reduced, but still very pronounced. The effect
of the...