Browse Prior Art Database

Low-Noise High-Bandwidth Current-Biasing Magnetoresistive-Element Preamplifier

IP.com Disclosure Number: IPCOM000115825D
Original Publication Date: 1995-Jun-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 59K

Publishing Venue

IBM

Related People

Contreras, JT: AUTHOR [+2]

Abstract

Disclosed is a high input impedance (relative to present state-of-the-art low noise preamplifiers for Magnetoresistive (MR) transducers) circuit that eliminates the high frequency response limitations caused by parasitic input lead inductance from transducer to amplifier. This circuit allows operation for high data rates with no changes to current electronic packaging requirements.

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Low-Noise High-Bandwidth Current-Biasing Magnetoresistive-Element
Preamplifier

      Disclosed is a high input impedance (relative to present
state-of-the-art low noise preamplifiers for Magnetoresistive (MR)
transducers) circuit that eliminates the high frequency response
limitations caused by parasitic input lead inductance from transducer
to amplifier.  This circuit allows operation for high data rates with
no changes to current electronic packaging requirements.

      The figure shows a low noise amplifier with common mode voltage
control for the MR head and a high input impedance so that the system
bandwidth is independent of the parasitic input inductance and
resistance.  Here, two power supplies +V and -V are used.  The MR
element Rmr is connected between the bases of input devices Q1 and
Q2.  Constant current Jref provides a bias current for the MR
element.  Resistors R1 and R2 are equal and provide a means of
determining the common mode voltage of the MR element.  Resistor R3
provides a means to convert a first-error current into a first-error
voltage at the input of the transconductance stage g1.  This
first-error current would be proportional to the difference in
potential between the common mode voltage of the MR element and a
reference voltage Vref.  Therefore, this first-error current is
minimized when the output of g1 is equivalent to the intended biasing
current of the MR element Jref.  The high frequency bandwidth of the
transconductance s...