International Business Machines Corporation

Jacobus C Van Peppen

Klaas Berend Klaassen

Stephen A Jove

Michael O Jenkins

John Thomas Contreras

Paul Wingshing Chung

Hung Liang Hu

Calvin Shizuo Nomura

Dale Brian Chapman

Walter Eugene Weresin

Paik Saber

Byron R Brown

Klaas B Klaasen

Joseph J Lum

A magnetic-head write-driver circuit includes a write-driver circuit and a by-pass driver circuit coupled in parallel to a signal path between the input and the output of the magnetic-head write-driver circuit. The write-driver circuit receives an input signal having transitions and outputs a first write signal related to the input signal. The by-pass driver circuit outputs an assist signal that is coupled to the first write signal to form an output write signal. The assist signal is related to transitions of the first write signal and assists in shortening reversal time of the transitions of a write signal by producing &ldquo;overshoots&rdquo; in the write signal at the time of the transitions. Additionally, the assist signal assists in charging and discharging a parasitic capacitance associated with an output of the magnetic-head write-driver circuit. The assist signal can add a current to, and/or enforce a voltage on, the first write signal to form the output write signal.

By-pass write drivers for high-performance data recording

A magnetoresistive transducer biasing technique that provides a uniform transducer biasing in a product. The technique provides biasing for transducer constant power dissipation, constant sensor current density biasing, constant sensor bias voltage, constant sensor temperature rise biasing, and constant effective magnetic biasing of a transducer.

Electronic magnetoresistive voltage biasing using a circuit and current

Electronic magnetoresistive sensor biasing using a transducer equivalent

A magnetoresistive transducer biasing technique that provides high common mode rejection ratio (CMRR) for a dual MR sensor head, while providing for short-circuit protection of the sensor elements within the head for short-circuits between the head and a disk.

High CMRR and sensor-disk short-circuit protection device for dual

A circuit is disclosed for pre-amplifying signals from an MR sensor in a disk drive without producing output voltage transients as the MR head changes its operational mode. In one preferred embodiment, the circuit includes a bias current source, an input stage, and a voltage clamp across the inputs of the OTA of the input stage. The input stage remains active in all modes of the MR head to avoid transients generated by the thermal responses of the MR sensor. In a second embodiment, the circuit allows the current from a first current source to bypass the input stage and flows directly to the MR sensor in write or idle mode. The bias current remains generally constant in all modes, thus avoiding output transients. In the third embodiment, upon switching to read state, the MR sensor is biased with an additional current source to quickly heat up the sensor. Upon reaching the normal read-mode temperature, the additional current is cut off and the sensor is again biased with only the first current source, thus avoiding voltage transients at the output of the circuit.

Magneto-resistive head pre-amplifying circuit for avoiding output

Circuitry for eliminating magnetic instability of an inductive magnetic transducer during sensing of data from a magnetic recording medium to prevent distortion of the readback signal by hysterically moving domain walls. An inductive sensing coil has an impedance constituting the output impedance of the transducer. Means connected to the coil amplifies a data signal generated by the magnetic flux changes and produces a selected input impedance. The sum of these input and output impedances is selected to be small enough to substantially eliminate motion of the domain walls in the yoke of the transducer while the transducer is sensing data from the medium.

Suppression of magnetic instability in inductive recording heads

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 magetic recording system includes a current-tapering circuit which gradually reduces the WRITE current in a magnetic recording head to zero over a time interval on the same order of magnitude as the characteristic relaxation time of the domain patterns in the magnetic recording head, rather than abruptly. Specific embodiments of the current-tapering circuit create a down-sloping ramp, a decaying exponential curve, and a high-frequency burst. The resultant magnetic recording system has reduced Barkhausen noise and reproducible READ performance as well as improved READ sensitivity following a WRITE operation.

Controlled magnetic recording head relaxation in a magnetic recording

A method and circuitry for suppressing additive transient disturbances in an analog differential input signal, such disturbances being due, for example, to thermal asperity transients caused by an MR transducer contacting a moving storage surface. The input data signal is algebraically summed with a corrective feedback signal for providing as output signal. The output signal is fed back to a circuit including an envelope detector and differentiator and converted into another signal that is the derivative of an amplitude envelope corresponding to the output signal. Nonlinear signal-adaptive filter means converts said other signal into the corrective feedback signal, which substantially replicates the additive transient disturbance and is subtracted from the data input signal to render the output signal substantially free of the transient disturbance. The input, output and corrective signals are preferably differential signals.

Method and circuitry to suppress additive disturbances in data channels

A method and circuitry are disclosed for suppressing additive transient disturbances in a data channel; e.g., due to thermal transients caused by an MR transducer contacting moving a storage surface. Positive and negative envelope detectors each have their inputs connected to the channel, and provide respective outputs which are summed and contain an envelope component and a residue component. A buffer interconnects the detectors to allow both detectors to follow rapid positive excursions of the data channel signal. A nonlinear signal-adaptive filter is connected to the summed output to further reduce the residue component. The data channel signal (or preferably the output from a delay means connected to the channel) is summed with the output from the filter. The relative amplitudes of these two outputs is set such that the resulting summed output signal is free of additive disturbances.

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

A method and apparatus for measuring the flying height of a slider supporting a magnetic transducer in-situ in a direct manner in an operational magnetic disk storage system. The method and apparatus produce relative motion between the magnetic transducer and a magnetic recording medium at a first velocity so that the resulting air bearing positions the magnetic transducer slider at a first flying height from the magnetic medium. A single signal of constant periodicity is written over a predetermined area of the recording medium by the magnetic transducer, and a readback signal is sensed from the predetermined area of the recording medium to produce a first signal. The flying height of the magnetic transducer slider is lowered to substantially zero, and a readback signal is sensed at the lowered flying height to produce a second signal. The first flying height is then calculated as the ratio, expressed in decibels, of the first and second signals times the wavelength divided by a constant. In an alternate embodiment a plurality of signals are recorded and readback signals are simultaneously sensed at two separate wavelengths. In a further embodiment, a signal is recorded which has a spectral content comprising a plurality of different frequencies, and readback signals are simultaneously sensed at two separate wavelengths.

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San Jose, CA, United States of America

Jacobus C Van Peppen