Browse Prior Art Database

Linearizer for Magneto-Resistive Head Output

IP.com Disclosure Number: IPCOM000111020D
Original Publication Date: 1994-Feb-01
Included in the Prior Art Database: 2005-Mar-26
Document File: 2 page(s) / 114K

Publishing Venue

IBM

Related People

Cunningham, EA: AUTHOR

Abstract

A method is disclosed that can linearize the output of an MR head that has been distorted by the non-linear transfer curve of output voltage versus flux level of input.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 49% of the total text.

Linearizer for Magneto-Resistive Head Output

      A method is disclosed that can linearize the output of an MR
head that has been distorted by the non-linear transfer curve of
output voltage versus flux level of input.

      A Magneto-Resistive (MR) read head is normally constructed with
some bias mechanisms that cause the operating point to be on one side
of the Lorentzian shaped transfer curve of resistance versus flux
from the recording medium.  The preferred operating point is where
the curve is most linear with high gain, so there is low distortion
and high output of the readback signal.  Due to deviations from the
optimum, some heads are biased closer or further from the peak of the
resistance curve.  If biased closer to the peak, then when an input
flux moves the resistance closer to the peak, the amplitude change
will be less than for the optimum bias, and the positive peak (higher
resistance) will be rounded off more than the negative peak.  If the
bias position is further from the peak than optimum, the negative
peak will be rounded off more than the positive peak.  Even with
proper bias, both peaks are slightly rounded.

      The solution is to provide a nonlinear circuit in an inverse
relationship to the transfer function of the MR head, so that the
overall transfer function is linear.  The circuit is to have a fixed
gain for low amplitude inputs, and then have higher incremental gain
for larger positive or negative signal peaks.  The increased
incremental gain thus compensates the lower incremental gain produced
where the MR transfer function has lower slope.

      Such a circuit can be designed using the non-linear
current/voltage characteristics of semiconductor diodes in
combination with resistors and other gain and offset controls.  The
direction of increasing gain with increased signal can be obtained by
applying a voltage related to the head signal, to a diode, and
measuring the current.  A resistor placed in series with the diode
can moderate the amount of increase in gain.  A resistor in parallel
with these can provide the fixed gain at low voltages, where the
diode has negligible conduction.  A second diode and series resistor
can be placed in parallel to the first diode and series resistor,
except with the opposite polarity connection of the diodes.  Thus,
one diode increases the current with increased voltage of one
polarity, and the other diode increases the current in the opposite
direction with more voltage in that direction.

      The three branch circuit described above can be used as the
emitter impedance of a differential pair of NPN transistors.  Two
equal current sources provide bias, each pulling a fixed current from
each emitter, to a negative supply.  A signal level of near 1 volt
peak-to-peak is applied between the input bases.  The collectors have
equal load resistors from the collectors to a positive supply
voltage, and a differential output signal is produced bet...