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Head-Write Current Capacitive Compensation Technique

IP.com Disclosure Number: IPCOM000106367D
Original Publication Date: 1993-Oct-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 2 page(s) / 99K

Publishing Venue

IBM

Related People

Thompson, GA: AUTHOR [+2]

Abstract

This report describes a write current compensation technique, for application in magnetic tape drives with magneto-resistive or thin-film heads. The technique can reduce distortion and increase speeds of the head write current pulse if impedance mismatches occur between head and head cable. Traditionally, compensation was achieved as a result of custom tailoring of the head cable's electrical and mechanical properties. The limitations of this latter method are discussed.

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Head-Write Current Capacitive Compensation Technique

      This report describes a write current compensation technique,
for application in magnetic tape drives with magneto-resistive or
thin-film heads.  The technique can reduce distortion and increase
speeds of the head write current pulse if impedance mismatches occur
between head and head cable.  Traditionally, compensation was
achieved as a result of custom tailoring of the head cable's
electrical and mechanical properties.  The limitations of this latter
method are discussed.

      The power needed to successfully write a pattern of "one's" and
"zero's" to magnetic tape depends upon several parameters, one of
which is the electrical pulse width of the write head current.  A
decrease in the current pulse width will decrease power consumption,
and can provide for faster channel data rates.  Unfortunately, this
decrease also requires a corresponding reduction in the current pulse
rise and fall times in order to properly record the signal onto the
tape.  Fast-edge pulses are more likely to suffer from various
waveform distortions such as edge degradation, undershoot/overshoot,
ringing, and transmission-line effects.  Generally, these undesirable
effects are aggravated by impedance mismatches between driver, head
cable, and the head write element.

      Usually the head cable is a custom-designed flexible
interconnection circuit, or flex cable.  This cable, consisting of
one or more layers of dielectric material and copper conductors,
provides the electrical connection between head and read/write
circuits.  Compact, high-performance tape drives require miniaturized
head/cable assemblies that limit the physical size of the individual
components.  Also, as its name implies, the flex cable may require a
high degree of flexibility and low mass when used in moving-head
applications.  This may require the elimination of shielding layers.

      The physical design constraints of small signal-line geometries
and the absence of shields increases the electrical characteristic
impedance of the flex cable.  As a consequence, distortion of the
head write current pulse occurs when the flex cable impedance is much
greater than that of the head.  Typically, the flex cable is
electrically short in comparison to signal propagation delay times,
and the distortion occurs during the transition of the write current
pulse.  This can increase the pulse rise and fall times considerably.

      In the past, the design of the flex cable was optimized to
minimize the distortion of the write current pulse.  This
optimization required careful tailoring of certain physical
param...