International Business Machines Corporation

Hitachi Global Storage Technologies Netherlands B.v.

Stephen A Jove

Klaas Berend Klaassen

Paul Wingshing Chung

Jacobus C Van Peppen

John Thomas Contreras

Calvin Shizuo Nomura

Jacobus C Leonardus Van Peppen

Michael O Jenkins

Wayne Leung Cheung

Kevin Roy Vannorsdel

Jacobus C VanPeppen

Albert John Wallash

Michael L Workman

Jacobus Cornelis Leonardus Van Peppen

Charles R Nielsen

Dale Brian Chapman

Long Tran

Paik Saber

John Thomas Conteras

Julian Edgar Vaughn

Klaas B Klassen

Chon N Vo

Paul Wingshung Chung

A preamplifier system is provided for use with a magneto-resistive (MR) sensor. Included is an alternating current (AC) coupling module connected to the MR sensor for blocking a direct current (DC) voltage associated with an input signal, and filtering low frequency noise associated with the input signal. Also provided is a gain stage module coupled to the AC coupling module. The gain stage module includes a plurality of cascode field effect transistors (FETs) configured for amplifying the input signal, while reducing intrinsic noise and increasing operational bandwidth. Coupled to the gain stage module is a control circuit for feeding back an output of the gain stage module for bias regulation and disturbance rejection.

CMOS low-noise MR read head pre-amplifier circuit

A method and apparatus for providing quadrature biasing for coupled-pair circuits. A QBCP-circuit for quadrature amplifiers provides a new input common-mode sense point that separates the inputs for the differential-and-common mode feedback-control loops. The QBCP circuit biases all four transistors equivalently and reduces the feedback-loop interaction, thereby simplifying the bias control system and improves the voltage-transfer frequency-response performance.

Method and apparatus for providing quadrature biasing for coupled-pair circuits

A method and apparatus for providing matched differential MR biasing and pre-amplification. Tightly matched and well centered low-level MR bias voltage is provided directly to the sensing element for controlled input-impedance differential pre-amplification without common-mode voltage level control with loops.

Method and apparatus for providing matched differential MR biasing and pre-amplification

Bi-Variant Coupled Pair (BVCP) circuits suitable for use in channel front-end low noise preamplifiers of magnetic storage devices are described. In a magnetic storage device, a BVCP circuit provides a DC bias voltage for a read transducer, low-noise amplification performance, and relatively small AC coupling capacitor values for reducing the cost of an integrated circuit (IC) in which the BVCP circuit may be embodied. The BVCP circuit also has a controllable input impedance for matching a transmission line impedance for high data rate applications.

Preamplifier circuit suitable for use in magnetic storage devices

A method and system for providing a current-sensing preamplifier for use with a magnetoresistive sensor is disclosed. The method includes providing at least one input device coupled with the magnetoresistive sensor, providing a gain stage, and providing a feedback circuit. In a system aspect, the current-sensing preamplifier includes at least one input device. The at least one input device is coupled with the magnetoresistive sensor through an interconnect having a characteristic impedance. The at least one input device provides an input impedance for the current-sensing preamplifier. The current-sensing preamplifier also includes a gain stage coupled with the at least one input device and a feedback circuit coupled with the gain stage and the at least one input device. The feedback circuit provides at least one signal to the at least one input device. The at least one signal controls the input impedance based on at least one error signal.

Quasi-current sensing input impedance controlled preamplifier for magnetoresistive elements

A multi-state preamplifier having a first detector and a second detector provides voltage-sensing and current-sensing signal amplification, respectively. Either the first detector or the second detector is selected and switched active at any given time, producing an amplified signal representing either the signal voltage developed across the MR element or the signal current flowing through the MR element, respectively. The switching process to activate either the first detector or the second detector is carried out by a detector determining circuit connected to a disk drive control unit. The detector giving the optimum high frequency bandwidth for the preamplifier is chosen based on the resistance of the MR element coupled with the input interconnect network characteristic and parasitic impedances.

Multi-state preamplifier for disk drives

A method and system for providing a voltage-sensing preamplifier for use with a magnetoresistive sensor is disclosed. The method includes providing a gain stage and providing a control circuit. The system includes the gain stage and the control circuit. The gain stage includes at least one input device that is coupled with the magnetoresistive sensor through an interconnect having a characteristic impedance. The at least one input device has a first input impedance. The control circuit provides at least one signal to the at least one input device. The at least one signal controls the first input impedance of the at least one input device to control a second input impedance of the voltage-sensing preamplifier, such that the preamplifier input impedance is modified toward the characteristic impedance of the interconnect to improve the bandwidth of the signal amplified by the system.

Quasi-voltage sensing input impedance controlled preamplifier for magnetoresistive elements

A voltage-biasing, voltage-sensing differential preamplifier having a high input impedance preamplifier circuit to amplify magnetic data readback signals from a magnetoresistive (MR) sensor and feedback circuits to simultaneously hold the electrical center of the MR sensor at a prescribed potential (usually ground) while applying a predetermined constant differential voltage-bias across the MR element. The feedback circuits provide a stable operating point for the MR sensor at the desired bias-voltage, and maintain the average potential on the MR sensor at or near the disk substrate potential to limit the destructive effects of MR sensor contact with conducting asperities.

Voltage-biasing, voltage-sensing differential preamplifier for magnetoresistive elements

The present invention is a preampifier circuit for magnetoresistive (MR) elements which has a high imput impedance with respect to the MR resistance so that the resultant system would not be sensitive to the series input inductance of the leads necessary to connect the MR element with the preamplifier. With former preamplifiers, nearly all are low impedance types, (using either BiCMOS or BiPolar technology), or differential (using BiPolar technology). The present invention fills a need in the prior art by providing a preamplifier curcuit using BiCMOS technology with a high input impedance, and single ended (SE) topology for minimum power dissipation.

High input impedance single ended, low supply voltage magnetoresistive preamplifier circuits

In a magnetoresistive read/inductive write magnetic transducer, magnetic stability of the magnetoresistive read sensor is improved by reducing the bias current to the magnetoresistive read sensor to a predetermined value during a period when a write current signal is applied to the inductive write head. The reduced bias current is greater than zero, but less than that required for reading data stored in a magnetic storage media. The reduced bias current is about 30% of the full bias current applied during the read operation of the magnetoresistive head.

Partial MR sensor bias current during write

A data storage system comprises magnetoresistive (MR) sensing elements for sensing data from a recording medium that is referenced to ground, and an amplifier circuit including a biasing stage, an amplifying stage, and a matching stage, each referenced to a common supply voltage source and to ground. The biasing stage includes a reference current source for selectively biasing each MR element with a constant current and, in so doing, developing a single-ended voltage signal having a first dc component. The amplifying stage converts the single-ended voltage signal into an amplified single-ended output voltage signal having a second dc component but in which the first dc component is eliminated. The matching stage creates a bias and imposes said bias on the amplifying stage for converting the single-ended output voltage signal to a differential output voltage signal in which the second dc component is eliminated.

Low noise amplifier circuit for magnetoresistive sensors for fast

Writing of data on a storage disk by an inductive magnetic transducer is modulated by write driver circuitry that includes a supply voltage as low as three volts provided by a source referenced to ground, and a bias current source connected to either the supply voltage source or ground. Two bias control switches respectively direct the bias current to one or the other of two current gain circuits according to whether a positive or a negative input terminal has a preselected polarity. The gain circuits selectively respond to the bias currents supplied by the associated control switch for amplifying the bias current to remove a write current from a respective associated terminal of the transducer. Two current source switches connected to a respective one of the input terminals and to a respective one of the terminals of the transducer selectively allow and prevent the write current from flowing into the respective associated terminal of the transducer depending upon which of the input terminals has the preselected polarity. When data is not being written by the transducer, a controllable reference voltage circuit maintains the transducer at a potential at least as negative as ground to prevent electro-erosion of the transducer; and this circuit also is preferably connected to both gain circuits to prevent them from saturating.

High-transition-rate, low-supply-voltage write driver circuitry for

An optical data storage system including an amplifier which (i) provides a differential current input having a low impedance over the full range of frequencies for which amplification is required in an optical detector that includes a photodiode that senses the intensity of an optical signal generated by data on the optical storage medium; (ii) reverse biases the photodiode; (iii) amplifies the signal current from both sides of the photodiode to improve signal-to-noise ratio; and (iv) is isolated from and unaffected by power supply noise.

Differential amplifier for optical detectors in an optical data storage

Low noise, low power, low voltage amplifier circuits with a single ended input having no common mode rejection for concurrently biasing and amplifying signals generated by magnetoresistive (MR) elements in a disk file. The amplifier circuits comprise a single (grounded) supply voltage source. One terminal of each MR element and the conductive substrate of each MR element and the conductive substrate of each disk in the disk file are grounded to minimize transient conductive asperity currents. The head/disk assembly of the disk file is completely enclosed by a highly conductive electrostatically shielded metallic enclosure that operates as a Faraday cage and isolates leads connecting the MR elements with the amplifier circuit from large, fast rise/fall time voltage transients.

Low-voltage, low-power amplifier for magnetoresistive sensor

A circuit for concurrently producing low noise electrical output signals which are amplified representations of signals produced by a magnetoresistive (MR) element and protecting said element from electrical short circuits which can occur between said element and its environment. A first feedback loop comprises (a) an input amplifier for amplifying a signal current from the MR element and (b) a source of bias current for biasing the MR element with a bias voltage. An input amplifier is concurrently biased by said current and amplifies a signal current from the MR element for producing a circuit output signal corresponding to dRh/RhRh and in which any differential direct current (dc) output offset error is minimized. (RhRh is the square of the time-averaged resistance of the MR element and dRh is the magnetic-signal-induced change in the resistance of the MR element.) A second feedback loop, electrically in series with the first feedback loop, biases the MR element toward a preselected reference potential and concurrently prevents flow of a current sufficient to damage the MR element in the event of a short circuit occurring between the MR element and its environment (e.g. the recording surface of a magnetic recording disk).

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Watsonville, CA, United States of America

Stephen A Jove