Patent EP0478298A2 successfully refreshed from Google Patents.
EP0478298A2
Expired / Lapsed
EP
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Low-noise preamplifier for magneto-resistive heads
Assignee: IMP Inc
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Filing: 1991-09-25
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Granted: —
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Expires: 2011-09-25
Abstract
Abstract A d.c. current source (17) provides current through a field effect transistor (12) and the effective resistance (18) of a magneto-resistive element to ground. A feedback loop including an operational transconductance amplifier (26) provides a bias voltage for the field-effect transistor (12) whereby the voltage across said effective resistance (18) of said magneto-resistive element is held constant while the resistance of said element changes. The resulting a.c. current flowing through the magneto-resistive element flows only through the feedback loop and an output resistor (25) connected across the inputs (22 and 24) of the operational transconductance amplifier (26). The amplification of the circuit is approximately the resistance of the output resistor divided by the resistance of the magneto-resistive element. <IMAGE>
Inventors
- 👤 Hans W. c/o Minnesota Mining and Klein
- 👤 Corey D. c/o Minnesota Mining and Petersen
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-02 22:24
CPC Classifications
H; H03; H03F; H03F3/00; H03F3/189; H03F3/19; H03F3/195; G; G11; G11B; G11B5/00; G11B2005/0002; G11B2005/0005; G11B2005/001; G11B2005/0013; G11B2005/0016; G11B2005/0018; G11B5/008; G11B5/00813
Claims Analysis
Total Claims: 5
Claim 1
Independent Claim
233 words
A preamplifier (10) for a magneto-resistive sensor having an effective resistance (18), said preamplifier comprising an input transistor (12) having input (13), output (14) and control (15) elements, the input and output elements being connected in series with said sensor element, means (22) coupled to said sensor (18) for providing an output signal indicative of varying magnetic fields at said sensor, and a feedback loop (30) for providing a control signal on the control element (15) of said transistor, such that a predetermined fraction of a constant current supplied to said preamplifier flows through said transistor (12) and sensor (18), thereby providing a fixed bias in said sensor and a different predetermined fraction of said constant current flows through said output signal providing means (22), said feedback loop including means (26) responsive to an error current in said output signal production means (22) when current other than said different fraction of said predetermined current flows therethrough, for providing a said control signal which changes the operating conditions of said transistor (12) in such a manner as to substantially eliminate said error current and maintain said predetermined fractional currents, and means (28) for blocking dynamic changes in said control signal such that the control element of the transistor responds only to static conditions, and an AC output voltage developed at said feedback providing means is proportional to varying magnetic fields present at said sensor.
Claim 2
Dependent Claim
19 words
A preamplifier according to claim 1, wherein said input transistor comprises a MOS having source drain and gate elements.
Claim 3
Dependent Claim
17 words
A preamplifier according to claim 1, wherein said control signal providing means comprises an operational transconductive amplifier.
Claim 4
Dependent Claim
31 words
A preamplifier according to claim 3, wherein said dynamic charge blocking means (28) comprises a capacitor coupled to said transconductance amplifier such that the loop gain rolls off at low frequencies.
Claim 5
Dependent Claim
237 words
A preamplifier (10) for a magneto-resistive sensor having an effective resistance (18), said preamplifier comprising an input field effect transistor (12) having source (13), drain (14), and gate (15) elements, means for maintaining a contact, a d.c. current (17), means serially connecting said d.c. current maintaining means (17), said source (13) and drain (14) elements of said transistor (12), and said magneto-resistive sensor (18) to a circuit ground (20), and a feed-back loop (30) for providing a control signal on said gate (15) element of said transistor (12), including an output resistor (25) serially connected (32) between said drain element (14) of said transistor (20) and a circuit reference voltage (21), an operational transconductance amplifier (26) having two input terminals (22 and 24) and an output terminal (27), means connecting said output resistor (25) across said two input terminals, capacitive means (28) connected between said output terminal (27) and a circuit ground (20), and means connecting said output terminal (27) to said gate element (15) of said input transistor (12), whereby d.c. bias current from said d.c. current maintaining means (17) is fully directed through said input transistor (12) and said magneto-resistive element (18) to ground (20) and d.c. voltage across said magneto-resistive element sensor is held constant, and wherein a.c. current flow through said input transistor (12) resulting from changes in the effective resistance (18) of said magneto-resistance element flows only through said output resistor (25).
References Cited (Backward Citations)
No citation records indexed.
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