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Magneto-Resistive Head Bias For Symmetrical Output

IP.com Disclosure Number: IPCOM000106331D
Original Publication Date: 1993-Oct-01
Included in the Prior Art Database: 2005-Mar-21
Document File: 2 page(s) / 62K

Publishing Venue

IBM

Related People

Bonaccio, AR: AUTHOR [+2]

Abstract

The circuit described below dynamically optimizes the dc bias current in a magneto-resistive (MR) head used for reading digital information stored on magnetic recording media. The criterion for adjustment is the minimization of dissymmetry in the amplified output signal voltage.

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Magneto-Resistive Head Bias For Symmetrical Output

      The circuit described below dynamically optimizes the dc bias
current in a magneto-resistive (MR) head used for reading digital
information stored on magnetic recording media.  The criterion for
adjustment is the minimization of dissymmetry in the amplified output
signal voltage.

      The (magnetic flux)-to-(output voltage) transfer function of an
MR head may exhibit non-linearity over portions of its range.  The
optimum dc bias current for the transfer function occurs at the
operating point where equal positive and negative flux changes
produce equal positive and negative voltage changes.  The figure
shows a MR head bias current source that uses negative feedback to
drive the bias current toward its optimum value in response to the
degree of symmetry in the output signal voltage.

      The MR head bias current source, consisting of NPN transistor
T1 and resistor R3, has a T1 collector current that divides between
the two input terminals of amplifier A1.  A1 has a very low input
impedance and has internal feedback to cause precisely enough dc
voltage to appear across the MR head so that a predictable fraction
(usually one-half) of the T1 collector current flows through the MR
head.  The dc offset of A1 must be very small or of a known value so
that the dc component of the signal can be separated from the dc
offset of A1.  The gain of A1 must be sufficient to produce a good
signal-to-noise ratio, b...