Seagate Technology Incorporated

Drew Michael Mader

Alfredo Sam Chu

Tim Rausch

Wenzhong Zhu

Jason Wayne Riddering

James E Angelo

Walter Richard Eppler

Steven J Kimble

Franklin P Martens

Michael A Cordle

Jason Charles Jury

Huazhou Lou

Joshua Ward Christensen

Raman Venkataramani

Ian James Gilbert

Christopher James Rea

Pu-Ling Lu

Josh Ward Christensen

A method for reducing noise in a read signal due attributable to read element asymmetry provides for transmitting a write signal through a write precompensation circuit that shifts rising edges and falling edges of each of pulse in the write signal by a select magnitude and in opposite directions. After the write signal is encoded on a media, a corresponding read signal is read, with a read element, from the media. The method further provides for transmitting the read signal through a magnetoresistive asymmetry compensation (MRAC) block that is tuned to correct second-order non-linearities characterized by a particular set of distortion signatures. The select magnitude of the waveform shift applied by the write precompensation circuit introduces a non-linear signal characteristic that combines with non-linear signal characteristics introduced by the read element to generate one of the particular distortion signatures that is correctable by the MRAC block.

Partial pulse pairing for improved read signal quality

A controller extracts a distortion component of a readback signal from a magnetic read head. The distortion component may be found using a finite length Volterra series, for example. The controller estimates a clearance between the read head and a recording medium based on the distortion component. This clearance measurement can be used for closed loop fly-height control of the read head.

Determining fly height using readback signal distortion

A read channel is configured to obtain an analog readback waveform from a magnetic recording medium of a disk drive at a sampling rate of one sample per one written bit. A buffer is coupled the read channel. Circuitry is configured to inject a plurality of different phase offsets into the read channel for each of a plurality of revolutions of the medium. The circuitry is also configured to store, in a buffer, an amplitude of the readback waveform for each of the different phase offsets. The circuitry is further configured to generate an oversampled readback waveform using the amplitudes stored in the buffer.

Readback waveform oversampling method and apparatus

A method includes generating, during manufacture of a heat-assisted magnetic recording (HAMR) disk drive, a temperature compensation equation for a compensation factor using initial operating currents supplied to a laser diode of the disk drive at different initial operating temperatures and an efficiency value based on the initial operating temperatures. The operating currents are representative of currents for recording data to or erasing data from a magnetic recording medium. The temperature compensation equation is stored in the disk drive. A subsequent efficiency value is determined based on at least one of the initial operating temperatures and an operating temperature differing from the initial operating temperatures. An updated compensation factor at the operating temperature is determined during field operation using the temperature compensation equation and the subsequent efficiency value. An updated operating current is calculated using the updated compensation factor and the operating temperature. A current supplied to the laser diode for a subsequent write operation is adjusted to the updated operating current.

Laser calibration using temperature compensation equation for heat-assisted magnetic recording device

A heat-assisted recording head is moved onto a ramp such that the recording head is thermally isolated from a moving disk. A heating device is activated on the recording head to cause the recording head to obtain a high temperature that is not obtainable when proximate to the moving disk. The recording head is moved over the moving disk such that the recording head reaches an operating temperature that is below the high temperature. One or more temperatures between the high temperature and the operational temperature are determined at which a laser of the recording head experiences mode-hopping. The one or more temperatures are stored and accessed by a controller to mitigate mode hopes during an operation of the recording head.

System and method using on-ramp heating to detect laser mode hopping in heat assisted recording

Stability or instability zones are determined for ambient temperatures and one or more operational parameters applied to a heat-assisted magnetic recording head. Operations within the stability or instability zones resulting in respective stable or unstable operation of a laser of the recording head. During operation of the recording head, it is determining that a current ambient temperature and currently applied values of the one or more operational parameters are at or near one of the instability zones, and a write operation of the recording head is modified in response.

Determining instability zones of a laser of a heat-assisted magnetic recording head

A temperature compensation equation is generated during manufacture of a heat-assisted magnetic recording (HAMR) disk drive using initial total currents supplied to a laser diode of the disk drive at different initial operating temperatures. The total currents represent currents for recording data to or erasing data from the medium. The temperature compensation equation is stored in the disk drive, and updated, during field operation, using a subsequent total current associated with an operating temperature differing from the initial operating temperatures. The total current supplied to the laser diode for a subsequent write operation is adjusted using the updated temperature compensation equation in response to the operating temperature at the time of the subsequent write operation.

In-field laser calibration for heat-assisted magnetic recording head using temperature compensation equation

Pseudorandom bit sequences are recorded to a heat-assisted recording medium at a laser power that is stepped while recording the pseudorandom bit sequences. The pseudorandom bit sequences are read from the heat-assisted recording medium to determine timing differences between bits written before and after the laser power is stepped. A thermal gradient of bits written to the heat-assisted recording medium is determined based on the timing differences.

Determining thermal gradient of a HAMR hotspot using pseudo-random bit sequences recorded at a stepped laser power

A heat-assisted magnetic recording head is moved relative to a magnetic recording medium. The medium comprises a plurality of sectors. The sectors define a plurality of sector groups distributed around a circumference of the medium. The sectors of each sector group are written using different operational currents supplied to a laser diode of the head such that at least one sector from each sector group is written using one of the different operational currents. For each of the different operational currents, an average write performance metric is calculated for all sectors written at each of the different operational currents. A particular operational current of the different operational currents is determined that results in a best average write performance metric.

Laser calibration for heat-assisted magnetic recording head using interleaved laser current

An apparatus comprises a slider configured for heat-assisted magnetic coupled to a controller. The slider comprises a writer, a heater, a near-field transducer, and an optical waveguide for communicating light from a laser diode to the near-field transducer. The controller is configured to set a target pre-write clearance of the slider prior to performing a write operation, set a target write clearance of the slider for performing the write operation, and determine a difference between the target pre-write and write clearances to define a target pre-write clearance offset. The controller is also configured to measure, for a plurality of different target pre-write clearance offsets, a writability metric for the slider while sweeping a laser diode current, and adjust the target pre-write clearance offset so that the writability metric reaches a predetermined threshold. The controller is further configured to perform subsequent write operations using the adjusted target pre-write clearance offset.

Calibration and adjusting target pre-write clearance offset for a heat-assisted magnetic recording device

An optical power level applied via a laser when recording data to a track of a heat-assisted recording medium is determined. In response to the optical power level being too low or too high, remedial action is taken to prevent loss of data on one or more of the track and an adjacent track.

Method and apparatus for detecting and remediating in response to insufficient or excessive HAMR optical power

An apparatus determines that phase errors have exceeded a threshold when reading data previously recorded to a heat-assisted recording medium. In response to the phase errors exceeding the threshold, remedial action is taken to prevent loss of data due changes in power applied to heat the heat-assisted recording medium when recording.

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Minneapolis, MN, United States of America

Drew Michael Mader