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Low Voltage Preamp Front End Stage for Magneto-Resistive Heads

IP.com Disclosure Number: IPCOM000104182D
Original Publication Date: 1993-Mar-01
Included in the Prior Art Database: 2005-Mar-18
Document File: 4 page(s) / 73K

Publishing Venue

IBM

Related People

Swart, DP: AUTHOR

Abstract

This invention provides a means to implement a first amplification stage for the magneto-resistive (MR) head in a disk file, where the power supply voltage available is as low as 3.6 volts.

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

Low Voltage Preamp Front End Stage for Magneto-Resistive Heads

      This invention provides a means to implement a first
amplification stage for the magneto-resistive (MR) head in a disk
file, where the power supply voltage available is as low as 3.6
volts.

      In this circuit, one end of the MR head is tied to GND, and the
read bias current is driven into the other end by a PNP current
source.  The readback signal developed is coupled into the
preamplifier at the emitters of a pair of low noise NPN transistors
(Fig. 1).

      The PNP current source QS1 supplies, the required read bias
current to the MR element.  This current must be as free of noise as
possible.  Hence, the external base capacitor, CB, is required.

      The emitters of low noise input transistors QL1 and QL2 are
connected one to each end of the MR head.  The collectors drive the
common base stage, QC1 and QC2.

      The collectors of QC1 and QC2 drive load resistors RC1 and RC2.
The difference in voltage developed across these resistors is the
output voltage of this front end stage.

      Voltage divider RD1 and RD2 provides a measure of the DC
voltage with respect to GND at the collectors of QC1 and QC2.  This
voltage, at node CT, is fed to feedback amplifier A1.

      To control the voltage at node CT and to keep QC1 and QC2 from
saturating, the DC operating current of QL1 and QL2 must be tightly
controlled.  Amplifier A1 compares the voltage at node CT with
reference voltage VREF, and adjusts the common...