Patent Application
20190279661
Embodiments of the present disclosure generally relate to data storage devices, such as disk drives.
Data storage devices such as disk drives comprise a disk and a head connected to a distal end of an actuator arm which is rotated about a pivot by a voice coil motor (VCM) to position the head radially over the disk. The disk comprises a plurality of radially spaced, concentric tracks for recording user data sectors and servo sectors. The servo sectors comprise head positioning information (e.g., a track address) which is read by the head and processed by a servo control system to control the actuator arm as it seeks from track to track.
Data is typically written to the disk by modulating a write current in an inductive coil to record magnetic transitions onto the disk surface in a process referred to as saturation recording. During read-back, the magnetic transitions are sensed by a read element (e.g., a magneto-resistive element) and the resulting read signal demodulated by a suitable read channel. Microwave assisted magnetic recording (MAMR) is a recent development that improves the quality of written data by using a spin torque oscillator (STO) to apply a high frequency auxiliary magnetic field to the media close to the resonant frequency of the magnetic grains, thereby enabling the magnetic field generated by the write coil to more readily magnetize the disk surface.
A data storage device is disclosed comprising a head actuated over a disk, wherein the head comprises a spin torque oscillator (STO) element. The data storage device further comprises a differential amplifier comprising a first input coupled to a first end of the STO element and a second input coupled to a second end of the STO element. A bias current is applied to the STO element, and the bias current is adjusted. A resistance delta of the STO element is detected based on an output of the differential amplifier, wherein the resistance delta corresponds to a bias current level when the STO begins to oscillate.
In one embodiment, a data storage device comprises a disk; a head actuated over the disk, wherein the head comprises a spin torque oscillator (STO) element; and control circuitry comprising a differential amplifier comprising a first input coupled to a first end of the STO element and a second input coupled to a second end of the STO element, wherein the control circuitry is configured to: apply a bias current to the STO element; adjust the bias current; and detect a resistance delta of the STO element based on an output of the differential amplifier, wherein the resistance delta corresponds to a bias current level when the STO begins to oscillate.
In another embodiment, a method of operating a data storage device, the method comprises applying a bias current to a spin torque oscillator (STO) element of a head actuated over a disk; adjusting the bias current; and detecting a resistance delta of the STO element based on an output of a differential amplifier comprising a first input coupled to a first end of the STO element and a second input coupled to a second end of the STO element, wherein the resistance delta corresponds to a bias current level when the STO begins to oscillate.
So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation.
In the following, reference is made to embodiments of the disclosure. However, it should be understood that the disclosure is not limited to specific described embodiments. Instead, any combination of the following features and elements, whether related to different embodiments or not, is contemplated to implement and practice the disclosure. Furthermore, although embodiments of the disclosure may achieve advantages over other possible solutions and/or over the prior art, whether or not a particular advantage is achieved by a given embodiment is not limiting of the disclosure. Thus, the following aspects, features, embodiments and advantages are merely illustrative and are not considered elements or limitations of the appended claims except where explicitly recited in a claim(s). Likewise, reference to “the disclosure” shall not be construed as a generalization of any inventive subject matter disclosed herein and shall not be considered to be an element or limitation of the appended claims except where explicitly recited in a claim(s).
Any suitable technique may be employed in block 20 of
The fine bias current is initialized to zero (block 46) and the output of the differential amplifier is processed to determine whether the resistance delta of the STO element has been detected (block 48). If the resistance delta is not detected, and the fine bias current has not reached its last fine step (block 50), the fine bias current is increased by the fine step (block 52). The flow diagram is then repeated until either the resistance delta of the STO element is detected at block 48, or the fine bias current reaches the last fine step at block 50. If the last fine step is reached, and the last coarse step has not been reached (block 54), the coarse bias current is increased by the coarse step (block 58) and the flow diagram is repeated from block 34. If the resistance delta of the STO element is detected at block 48, the coarse bias current and the fine bias current may be saved and used, for example, to configure an operating bias current for the STO element or to determine whether the resistance delta has shifted indicating a degrading STO element. If the resistance delta of the STO element is not detected after testing all of the coarse bias current steps at block 54, the control circuitry may determine the STO element is defective (block 56) and take appropriate remedial action, such as depopulating the corresponding head.
In one embodiment, the range of the fine bias current is configured so as to achieve overlap between consecutive coarse steps of the coarse bias current. An example of this embodiment is illustrated in
In one embodiment, employing a differential amplifier 10 such as shown in
In one embodiment, the gain of the differential amplifier 10 may be adjustable over multiple settings such as shown in
In one embodiment, the resistance delta of the STO element may be measured periodically to determine whether there has been a shift in the bias current that causes the STO to oscillate. If a shift is detected, the operating bias current may be adjusted to ensure the STO element is oscillating normally during subsequent write operations. In one embodiment, when a shift in the bias current is detected (by detecting a shift in the resistance delta), the control circuitry may update a field in a Self-Monitoring, Analysis, and Reporting Technology (SMART) database to indicate the STO element may be degrading toward failure so that appropriate remedial action may be taken.
Any suitable control circuitry may be employed to implement the flow diagrams in the above embodiments, such as any suitable integrated circuit or circuits. For example, the control circuitry may be implemented within a read channel integrated circuit, or in a component separate from the read channel, such as a disk controller, or certain operations described above may be performed by a read channel and others by a disk controller. In one embodiment, the read channel and disk controller are implemented as separate integrated circuits, and in an alternative embodiment they are fabricated into a single integrated circuit or system on a chip (SOC). In addition, the control circuitry may include a suitable preamp circuit implemented as a separate integrated circuit, integrated into the read channel or disk controller circuit, or integrated into a SOC.
In one embodiment, the control circuitry comprises a microprocessor executing instructions, the instructions being operable to cause the microprocessor to perform the flow diagrams described herein. The instructions may be stored in any computer-readable medium. In one embodiment, they may be stored on a non-volatile semiconductor memory external to the microprocessor, or integrated with the microprocessor in a SOC. In another embodiment, the instructions are stored on the disk and read into a volatile semiconductor memory when the disk drive is powered on. In yet another embodiment, the control circuitry comprises suitable logic circuitry, such as state machine circuitry.
In various embodiments, a disk drive may include a magnetic disk drive, an optical disk drive, etc. In addition, while the above examples concern a disk drive, the various embodiments are not limited to a disk drive and can be applied to other data storage devices and systems, such as magnetic tape drives, hybrid drives, etc. In addition, some embodiments may include electronic devices such as computing devices, data server devices, media content storage devices, etc. that comprise the storage media and/or control circuitry as described above.
The various features and processes described above may be used independently of one another, or may be combined in various ways. All possible combinations and subcombinations are intended to fall within the scope of this disclosure. In addition, certain method, event or process blocks may be omitted in some implementations. The methods and processes described herein are also not limited to any particular sequence, and the blocks or states relating thereto can be performed in other sequences that are appropriate. For example, described tasks or events may be performed in an order other than that specifically disclosed, or multiple may be combined in a single block or state. The example tasks or events may be performed in serial, in parallel, or in some other manner. Tasks or events may be added to or removed from the disclosed example embodiments. The example systems and components described herein may be configured differently than described. For example, elements may be added to, removed from, or rearranged compared to the disclosed example embodiments.
While certain example embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions disclosed herein. Thus, nothing in the foregoing description is intended to imply that any particular feature, characteristic, step, module, or block is necessary or indispensable. Indeed, the novel methods and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the embodiments disclosed herein.
While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
This application claims benefit of U.S. Provisional Patent Application Ser. No. 62/640,315, filed Mar. 8, 2018, which is herein incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62640315 | Mar 2018 | US |
