International Business Machines Corporation

Hitachi Global Storage Technologies Netherlands B.v.

Calvin Shizuo Nomura

Klaas Berend Klaassen

Stephen A Jove

John Thomas Contreras

Paul Wingshing Chung

Glen A Garfunkel

Jacobus C Van Peppen

Kevin Roy Vannorsdel

Michael L Workman

Michael M Siverling

Charles R Nielsen

Jacobus C Leonardus Van Peppen

Jacobus C VanPeppen

Steven Alan Jove

Dewey Earl Brownback

Dennis Patrick Sheehan

Arm electronics (AE) suitable for use in a disk drive are disclosed. The AE has write circuitry configured to operate the AE in a write mode during which a write mode supply current is drawn, and read circuitry configured to operate the AE in a read mode during which a read mode supply current is drawn. The AE uses a decaying current pulse generator that generates a decaying current pulse at the beginning of each write-to-read mode transition. The decaying current pulse has an initial value that is equal to the difference between the write mode supply current and the read mode supply current. This controlled load forces the AE to draw a gradually decreasing supply current for each write-to-read mode transition such that supply voltage transients (otherwise present due to parasitics in cabling between the AE and power supply) are reduced. Thus, the undesirable effects of such transients in the read circuitry are reduced so that write-to-read mode recovery times can be shortened.

Methods and apparatus for gradually decreasing supply current demand in arm electronics for write-to-read transitions

A method and apparatus for re-initializing a GMR head after losing initialization is disclosed. The invention may use a voltage controlled waveform, which allows the current to vary with the resistance of the GMR head. Furthermore, according to a further aspect of the invention a stack of GMR heads may be reinitialized having the same orientation to preclude inversion of the reset magnetic fields on half of the heads. In addition, improvements in re-initializing GMR heads is provided by implementing wave shaping. The invention can also provide re-initialization of GMR heads at different points in the manufacturing process.

Preamplifier bias mode to re-initialize a GMR head after losing

An FET write driver providing high rates of data transfer to a magnetic storage medium by effectively utilizing the voltage swing provided by supply voltage. A first and a second p-channel FET power switch are coupled between the voltage supply and the inductive head, each having a high aspect ratio for low resistance. A first and a second current mirror are coupled at their inputs to the inductive head and a current source, each current mirror having a reference arm coupled to the current source and a mirror arm coupled to the inductive head. Each current mirror has an output coupled respectively to a first and a second mirror enabling FET switch, each having a high aspect ratio for low resistance. A pair of differential signals dp and dn selects the ON and OFF states of the FET switches to provide either a first current path through the first FET power switch and the second current mirror to provide a write current in a first direction or a second current path through the second FET power switch and the first current mirror to provide a write current in a second opposite direction. During operation, the low voltage drops across the FET switches allow for a substantial portion of the voltage supply to be available for writing using the inductive head. The circuit is inherently stable and avoids ringing and overshoot, which results in improved timing and maintains signal integrity. The write driver can operate with low voltage power supplies for cost reduction or low power consumption in products such as portable computers while still retaining a high data transfer rate. For multiple head disk drive units, a plurality of write drivers are provided that include an additional switch at the current source input, which allows a single current source to be utilized as a reference current and a single set of differential signals to control all of the write circuits.

High speed FET write driver for an inductive head

A circuit forming part of an arm electronics module installed on an actuator arm that measures the voltage across an MR head A control unit supplies a measurement enable signal that enables a measurement enable circuit. A current bias circuit, responsive to the control unit, supplies a bias current to the MR head. A common node in the circuit provides a voltage signal responsive to the voltage across the MR head, with an added diode V.sub.BE drop across an input transistor. A voltage measurement amplifier has an input node and an output node that supplies an output voltage reduced in voltage by one diode drop (V.sub.BE). An input switch, responsive to the measurement enable signal is coupled between the input node and the common node. An output switch, responsive to the measurement enable signal is coupled between the output node and an output terminal. The output terminal is connected to a connector pin in an electrical connector via a flex cable to provide a convenient point for test and calibration apparatus to sample the MR head voltage. The circuit advantageously allows the MR head's voltage to be measured during assembly of and after merging into a disk enclosure, providing essential information for optimizing each MR head's operating point. Furthermore, an electrical short circuit may be provided across the MR head during the manufacturing process to prevent damage to the MR head due to electro-static discharge (ESD). The short can be left in place until merging into the disk enclosure and then, after merging, the voltage measurement circuit can be utilized to measure the voltage of the head with the short removed. Furthermore, the voltage measurement circuit can be enabled some time after normal operation of the disk drive begins, for purposes such as reoptimizing the bias currents through the MR heads or for failure analysis.

Voltage measurement circuit for a magnetoresistive head installed in a

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).

Low noise voltage-biasing amplifier for magnetoresistive element

An amplifier circuit is disclosed for simultaneously producing electrical output signals whose magnitude is representative of signals produced by a magnetoresistive (MR) element and protecting said MR element from electrical short circuits between said element and its environment. A means including a first feedback loop biases the MR element with a bias current and amplifies a signal current for causing the MR element to produce a circuit output signal corresponding to dRh/Rh and in which any dc offset error is minimized. Rh is the resistance of the MR element and dRh is the magnetic-signal-induced change in the resistance of the MR element. A second feedback loop insures that the MR element is held at a preselected reference potential and concurrently insures that no current will flow sufficient to damage the element in event of a short circuit between the element and its environment. The feedback loops are interconnected by outputs of the respective feedback loops being commonly connected to the bases of a pair of input bipolar transistors, whose respective emitters are connected to opposite terminals of the MR element.

Low noise amplifier with short circuit protection for signals from

A protective circuit for a magnetoresistive (MR) element having a first and a second terminal in which a first current source is coupled to the first terminal of the MR element to produce a bias current through the MR element and a second current source is coupled to the second terminal of the MR element to produce a reference current. Circuit means coupled across the MR element senses the center potential of the MR element substantially midway between the first and second terminals, and a feedback circuit responsive to the sensed center potential is coupled to adjust the current output of the first current source to maintain the center potential to a selected reference voltage to protect the MR element from short circuits to a conductive area of the magnetic recording medium. A second feedback circuit is provided which comprises a pair of transistors coupled in a differential pair configuration and a transconductance stage which feeds back a signal as a current to the transistors which keeps the dc currents through each of the transistors equal, and the transistors provide an amplified output signal which is a function of the magnetic flux being sensed by the MR element.

Protective circuit for a magnetoresistive element

An amplifier for voltage biasing and amplifying the signals produced by a magnetic sensor is provided. Electrically, the resistance of the sensor is disposed between the bases of a differential pair comprising the input stage of the amplifier. Constant bias voltage for the sensor is provided independently of sensor resistance. 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 input stage emitter resistor. The amplified signal, representing .DELTA.R.sub.h /R.sub.h, is sensed as a voltage across the magnetoresistive sensor, where .DELTA.R.sub.h is the change in steady-state resistance, R.sub.h, of the sensor.

Voltage amplifier for constant voltage biasing and amplifying signals

Circuitry for providing a high speed access by a swingable arm and a transducer carried thereby across a plurality of tracks on a rotatable data storage device to a target track on the rotatable device including a speed indicating circuit connected with the transducer for indicating the speed of the transducer in crossing tracks on the rotatable device and a switchable filter effectively between the transducer and said speed indicating circuit which has a high roll off as the transducer crosses the tracks at a high speed and has a low roll off as the transducer approaches the target track at a relatively low speed so as to thereby cause the speed indicating circuit to accurately indicate the speed of the transducer in moving across the tracks of the rotatable device.

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San Jose, CA, United States of America

Calvin Shizuo Nomura