EP0241770A1
Expired / Lapsed
EP
⏱️ 0.0 years remaining
A circuit for biasing a magnetoresistive sensor and amplifying signals produced thereby
Assignee: International Business Machines Corp
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Filing: 1987-03-24
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Granted: —
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Expires: 2007-03-24
Abstract
Abstract A constant current source (J1) supplies a bias current to a magnetoresistive (MR) sensor (R h ) and amplifier means (11, 12, 13) is responsive to the current flowing through the MR sensor to produce an amplified output signal representing the change in resistance of the MR sensor arising from changes in the magnetic field to which the MR sensor is exposed. The circuit includes first means (14) coupled to the amplifier means to set the frequency response thereof and second means (15) for substantially eliminating DC offset voltage in the output signal. The resistance of the MR sensor can be disposed as degenerative feedback in the emitter circuit of a differential pair comprising the input stage of the amplifier. The constant current source (J1) that supplies bias current to the MR sensor also supplies current to the differential pair. DC feedback to the input stage balances current flow in both paths of the differential input stage to correct for DC offset arising in the output from variations in transistor characteristics and the steady-state value of the MR sensor.
Inventors
- 👤 Klaas Berend Klaassen
- 👤 Stephen Alan Jove
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-03 15:30
CPC Classifications
G; G11; G11B; G11B5/00; G11B5/02; G01; G01R; G01R33/00; G01R33/02; G01R33/06; G01R33/09; G11B19/00; G11B19/02; G11B2005/0002; G11B2005/0005; G11B2005/001; G11B2005/0013; G11B2005/0016
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
90 words
A circuit comprising means (J1) for supplying a bias current to a magnetoresistive (MR) sensor (R h ) and amplifier means (11, 12, 13) responsive to the current flowing through the MR sensor to produce an amplified output signal representing the change in resistance of the MR sensor arising from changes in the magnetic field to which the MR sensor is exposed, first means (14) coupled to the amplifier means to set the frequency response thereof and second means (15) for substantially eliminating DC offset voltage in said output signal.
Claim 2
Dependent Claim
90 words
A circuit comprising means (J1) for supplying a bias current to a magnetoresistive (MR) sensor (R h ) and amplifier means (11, 12, 13) responsive to the current flowing through the MR sensor to produce an amplified output signal representing the change in resistance of the MR sensor arising from changes in the magnetic field to which the MR sensor is exposed, first means (14) coupled to the amplifier means to set the frequency response thereof and second means (15) for substantially eliminating DC offset voltage in said output signal.
Claim 3
Dependent Claim
33 words
A circuit as claimed in claim 1, in which there is means to subtract an error signal produced by the first means from a signal representing the current flowing through the MR sensor.
Claim 4
Dependent Claim
23 words
A circuit as claimed in claim 1 or claim 2, in which the second means feeds forward a signal to the amplifier means.
Claim 5
Dependent Claim
35 words
A circuit as claimed in any preceding claim, in which the amplifier means divides the signal representing the current flowing through the MR sensor by a signal representing the stead-state resistance of the MR sensor.
Claim 6
Dependent Claim
147 words
A circuit as claimed in claim 1, comprising a constant current source (J1) coupled to the MR sensor for producing a current therethrough having a constant time average value; an input stage, having at least two transistors (T1, T2) coupled in a differential pair configuration and having the MR sensor (R h ) coupled to the emitter of one (T2) of the pair of transistors and coupled to the constant current source, for amplifying current deviations from said constant time average value of the current flowing through the MR sensor; and output means, coupled to the input stage, for correcting variations in input stage voltage levels and for amplifying and transmitting signals received therefrom; the collectors and bases of the pair of transistors being coupled to the output means, and the emitter of the other transistor (T1) of the pair being coupled to the constant current source.
Claim 7
Dependent Claim
91 words
A circuit as claimed in claim 5, wherein the output means includes: at least two transistors coupled in a second differential pair configuration for correcting the voltage at the bases of the first differential pair; and first and second follower transistors, coupled to the first differential pair, for coupling the variations in the voltage levels produced in the input stage to the second differential pair; said second differential pair being coupled to a second constant current source, and said follower transistors being coupled to third and fourth constant current sources, respectively.
Claim 8
Dependent Claim
36 words
A circuit as claimed in claim 6, further including: a plurality of input stages; and selection means for activating an individual one of the plurality of input stages and deactivating all of the remaining input stages.
Claim 9
Dependent Claim
28 words
A circuit as claimed in claim 7, further including: transient suppression means for suppressing transients produced by deactivating one and activating another of the plurality of input stages.
Claim 10
Dependent Claim
75 words
A circuit as claimed in claim 7 or claim 8, wherein the transient suppression means comprises: a fifth constant current source coupled to the emitter of one of said follower transistors; a resistor and first and second diodes, each coupled in parallel to each other and between the first and fifth constant current sources, the cathode of the first diode and the anode of the second diode being coupled to the fifth constant current source.
Claim 11
Dependent Claim
33 words
A circuit as claimed in any of claims 7 to 9, further including enhancing means for decreasing input impedance presented to the MR sensor and for increasing input impedance of the input stage.
Claim 12
Dependent Claim
44 words
A circuit as claimed in any of claims 7 to 10, further including settling means for reducing the time required for the circuit to settle into steady-stage operating after one of the input stages is deactivated and another of the input stages is activated.
References Cited (Backward Citations)
DE3308352A1
Cited
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