Magnetoresistive head amplifier

Claim 2

A circuit for biasing a magnetoresistive element and amplifying signals produced by said magnetoresistive element, said circuit comprising: a first current source coupled to said magnetoresistive element and to a power supply; an input stage, comprising a plurality of transistors coupled in a first differential pair configuration wherein an emitter of a first transistor of said first differential pair of transistors is coupled to said magnetoresistive element, for amplifying current deviations resulting from variation of resistance of said magnetoresistive element; and a voltage source coupled to the bases of said first differential pair of transistors for providing a bias voltage; a second current source coupled to an emitter of a second transistor of said differential pair of transistors.

Claim 3

The circuit of claim 1 further comprising: a capacitor coupled to said differential pair of transistors and to said first and second current sources.

Claim 4

The circuit of claim 1 further comprising: selection means coupled to said voltage source for selecting a first one of a plurality of magnetoresistive elements and deactivating a remainder of said plurality of magnetoresistive elements.

Claim 5

The circuit of claim 3 wherein said selection means comprises a switching element for selectably coupling said voltage source to said input stage.

Claim 6

Apparatus for biasing a magnetoresistive sensor and amplifying signals produced by a magnetoresistive sensor when exposed to a changing magnetic field, said sensor having a steady-state resistance value, said apparatus comprising: current receiving means for receiving current from said magnetoresistive sensor, and for producing, in response thereto, signals representing a change in sensor resistance arising from changes in a magnetic field to which the sensor is exposed; amplifying means coupled to said current receiving means for amplifying said signals produced thereby, and having an output for transmitting said amplified signals therefrom, said amplifying means having a differential configuration with a first side of said differential configuration coupled to a second side of said differential configuration, wherein said magnetoresistive sensor is coupled between said amplifying means and a capacitor; biasing means for providing a bias signal to said amplifying means independent of said output.

Claim 7

Apparatus for biasing a magnetoresistive sensor and amplifying signals produced by a magnetoresistive sensor when exposed to a changing magnetic field, said sensor having a steady-state resistance value, said apparatus comprising: current receiving means for receiving current from said magnetoresistive sensor, and for producing, in response thereto, signals representing a change in sensor resistance arising from changes in a magnetic field to which the sensor is exposed; amplifying means coupled to said current receiving means for amplifying said signals produced thereby, and having an output for transmitting said amplified signals therefrom, said amplifying means having a differential configuration with a first side of said differential configuration coupled to a second side of said differential configuration, wherein said magnetoresistive sensor is coupled between said amplifying means and a capacitor; biasing means for providing a bias signal to said amplifying means independent of said output.

Claim 8

The apparatus of claim 5 further comprising: selecting means coupled to said current receiving means for selecting one of a plurality of magnetoresistive sensors.

Claim 9

The apparatus of claim 6 further comprising: bandwidth increasing means for increasing a bandwidth of said amplifying means.

Claim 10

A circuit for biasing a magnetoresistive element and amplifying signals produced by said magnetoresistive element, said circuit comprising: first amplifying means coupled to said magnetoresistive element; second amplifying means coupled to said first amplifying means in a differential amplifier configuration; a first current source for providing a first current through said first amplifying means; a second current source for providing a second current through said second amplifying means; and coupling means comprising a capacitor for coupling said signals to said second amplifying means.

Claim 11

A circuit for biasing a magnetoresistive element and amplifying signals produced by said magnetoresistive element, said circuit comprising: first amplifying means coupled to said magnetoresistive element; second amplifying means coupled to said first amplifying means in a differential amplifier configuration; a first current source for providing a first current through said first amplifying means; a second current source for providing a second current through said second amplifying means; and coupling means comprising a capacitor for coupling said signals to said second amplifying means.

Claim 12

The circuit of claim 8 wherein said first amplifying means comprises a first transistor and said second amplifying means comprises a second transistor.

Claim 13

The circuit of claim 9 wherein a third transistor is coupled to said first transistor in a cascode configuration and a fourth transistor is coupled to said second transistor in a cascode configuration.

Claim 14

The circuit of claim 8 further comprising: third amplifying means for amplifying second signals produced by a second magnetoresistive element; and fourth amplifying means coupled to said third amplifying means in a second differential amplifier configuration.

Claim 15

The circuit of claim 8 wherein said first amplifying means comprises a first plurality of transistors coupled to each other and said second amplifying means comprises a second plurality of transistors coupled to each other.

Claim 16

The circuit of claim 8 wherein said first current and said second current are of an equal magnitude.

Claim 17

A circuit for biasing a magnetoresistive element and amplifying signals produced by said magnetoresistive element, said circuit comprising: a first current source coupled to said magnetoresistive element and to a power supply; an input stage, comprising a plurality of transistors coupled in a first differential pair configuration wherein an emitter of a first transistor of said first differential pair of transistors is coupled to said magnetoresistive element, for amplifying current deviations resulting from variation of resistance of said magnetoresistive element; and a voltage source coupled to the bases of said first differential pair of transistors for providing a bias voltage; output means coupled to collectors of said first differential pair of transistors for transmitting output signals; a second current source coupled to an emitter of a second transistor of said differential pair of transistors.

Claim 18

A circuit for biasing a magnetoresistive element and amplifying signals produced by said magnetoresistive element, said circuit comprising: a first current source coupled to said magnetoresistive element and to a power supply; an input stage, comprising a plurality of transistors coupled in a first differential pair configuration wherein an emitter of a first transistor of said first differential pair of transistors is coupled to said magnetoresistive element, for amplifying current deviations resulting from variation of resistance of said magnetoresistive element; and a voltage source coupled to the bases of said first differential pair of transistors for providing a bias voltage; output means coupled to collectors of said first differential pair of transistors for transmitting output signals; a second current source coupled to an emitter of a second transistor of said differential pair of transistors.

Claim 19

The circuit of claim 14 further comprising: a capacitor coupled to said differential pair of transistors and to said first and second current sources.