Data storage device attenuating interference from first spiral track when reading second spiral track

Description

This application is a continuation-in-part of U.S. patent application Ser. No. 14/260,503, filed on Apr. 24, 2014, entitled “DATA STORAGE DEVICE READING FIRST SPIRAL TRACK WHILE SIMULTANEOUSLY WRITING SECOND SPIRAL TRACK” to Charles A. Park et al., the disclosure of which is incorporated herein by reference.

BACKGROUND

When manufacturing a disk drive, concentric servo sectors 6₀-6_N are written to a disk 2 which define a plurality of radially-spaced, concentric servo tracks 6 as shown in the prior art disk format of FIG. 1. A plurality of concentric data tracks are defined relative to the servo tracks 4, wherein the data tracks may have the same or a different radial density (tracks per inch (TPI)) than the servo tracks 4. Each servo sector (e.g., servo sector 6₄) comprises a preamble 8 for synchronizing gain control and timing recovery, a sync mark 10 for synchronizing to a data field 12 comprising coarse head positioning information such as a track number, and servo bursts 14 which provide fine head positioning information. The coarse head position information is processed to position a head over a target data track during a seek operation, and the servo bursts 14 are processed to maintain the head over a centerline of the target data track while writing or reading data during a tracking operation.

In the past, external servo writers have been used to write the concentric servo sectors 2₀-2_N to the disk surface during manufacturing. External servo writers employ extremely accurate head positioning mechanics, such as a laser interferometer, to ensure the concentric servo sectors 2₀-2_N are written at the proper radial location from the outer diameter of the disk to the inner diameter of the disk. However, external servo writers are expensive and require a clean room environment so that a head positioning pin can be inserted into the head disk assembly (HDA) without contaminating the disk. Thus, external servo writers have become an expensive bottleneck in the disk drive manufacturing process.

The prior art has suggested various “self-servo” writing methods wherein the internal electronics of the disk drive are used to write the concentric servo sectors independent of an external servo writer. For example, a known technique for self-servo writing a disk drive is to first write a plurality of spiral tracks to the disk, and then to servo on the spiral tracks while writing a plurality of servo sectors that define concentric servo tracks such as shown in FIG. 1.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a prior art disk format comprising a plurality of servo tracks defined by servo sectors.

FIG. 2A shows a data storage device in the form of a disk drive according to an embodiment comprising a head actuated over a disk surface.

FIG. 2B is a flow diagram according to an embodiment wherein while reading a first spiral track on the disk surface a second spiral track is simultaneously written on the disk surface.

FIG. 2C illustrates the writing of a second spiral track while simultaneous reading a first spiral track according to an embodiment, wherein the second spiral track is written in an opposite radial direction as the first spiral track.

FIG. 3 illustrates the writing of a second spiral track while simultaneous reading a first spiral track according to an embodiment, wherein the second spiral track is written in the same radial direction as the first spiral track.

FIG. 4A illustrates an embodiment wherein the first spiral track comprises a periodic pattern written at a first frequency, and the second spiral track comprises a periodic pattern written at a second frequency different from the first frequency.

FIG. 4B shows an embodiment wherein a read signal generated while reading the first spiral track is bandpass filtered based on the frequency of the first spiral track to attenuate crosstalk caused by simultaneously writing the second spiral track on the disk surface at the second frequency.

FIG. 5A shows a data storage device in the form of a disk drive comprising a head actuated over a disk surface comprising a first spiral track at least partially overwritten by a second spiral track.

FIG. 5B is a flow diagram according to an embodiment wherein the head is servoed over the disk surface based on the second spiral track.

FIG. 5C illustrates an embodiment wherein the read element of the head passes over the second spiral track as well as part of the first spiral track.

FIG. 6 illustrates an embodiment wherein a ratio of frequencies between the first and second spiral tracks attenuates interference from the first spiral track when demodulating the read signal generated while reading the second spiral track.

FIG. 7 shows an embodiment wherein the read signal is filtered with a bandpass filter to attenuate interference from the first spiral track.

FIG. 8A shows an embodiment wherein sync marks in the first spiral track may interfere with the spectral signature of the second spiral track.

FIG. 8B shows an embodiment wherein the first spiral track consists primarily of a periodic pattern without sync marks, whereas the second spiral track comprises a periodic pattern with sync marks.

FIG. 8C shows an embodiment wherein recording the first spiral tracks without sync marks removes the interference from the spectral signature of the second spiral track as compared to FIG. 8A.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

FIG. 2A shows a data storage device in the form of a disk drive according to an embodiment comprising a disk surface 16 comprising a first spiral track 18, and a head 20 actuated over the disk surface 16. The disk drive further comprises control circuitry 22 configured to execute the flow diagram of FIG. 2B, wherein while reading the first spiral track 18 a second spiral track 24 is simultaneously written on the disk surface (block 25).

In one embodiment, the first spiral track 18 may be considered a “bootstrap” spiral track from which the head 20 may be servoed in order to write the second spiral track 24 which may be considered a servo spiral track. In one embodiment, the disk surface 16 may comprise a plurality of bootstrap spiral tracks which may be read in order to write a plurality of servo spiral tracks. The servo spiral tracks may then be processed in order to servo the head 20 radially over the disk surface 16 in order to write servo sectors that define concentric servo tracks. In another embodiment, the servo spiral tracks may be used as a final servo pattern for servoing the head during normal access operations without needing to write servo sectors to the disk surface.

In one embodiment, the first spiral track 18 (as well as other similar spiral tracks if needed) may be self-written to the disk surface 16 by the control circuitry 22 internal to the disk drive. An example embodiment for self-writing spiral tracks is disclosed in U.S. Pat. No. 8,634,283 entitled “DISK DRIVE PERFORMING IN-DRIVE SPIRAL TRACK WRITING” the disclosure of which is incorporated herein by reference. In another embodiment, the first spiral track 18 (e.g., bootstrap spiral track) may be written to the disk surface 16 using an external servo writer prior to installing the disk into the disk drive.

FIGS. 2A and 2C illustrate an example embodiment wherein the second spiral track 24 is written in an opposite radial direction as the first spiral track 18. That is, the first spiral track 18 is written from the inner diameter (ID) of the disk surface 16 toward the outer diameter (OD) of the disk surface 16, and the second spiral track 24 is written from the OD to the ID of the disk surface 16. FIG. 2C also illustrates an embodiment wherein the head 20 comprises a read element 26 that is offset circumferentially from a write element 28 by a reader/writer gap. Accordingly in this embodiment while writing the second spiral track 24 the read element 26 travels along trajectory 30A and reaches the first spiral track 18 before the write element 28 overwrites the first spiral track 18 while travelling along trajectory 30B. In this manner, even if the read element 26 and the write element 28 are aligned so as to both travel along trajectory 30B, the read element 26 reads the first spiral track 18 before it is overwritten by the write element 28.

In another embodiment illustrated in FIG. 3, the second spiral track 32 is written in the same radial direction as the first spiral track 34 (e.g., from the OD to the ID). In this embodiment, the second spiral track 32 is written at a different radial velocity than the first spiral track 34 such that the slope of the second spiral track 32 is different from the slope of the first spiral track 34. This ensures the head 20 will cross over the first spiral track 34 when writing the second spiral track 32 as illustrated in FIG. 3. In the example of FIG. 3, the second spiral track 32 is written at a higher radial velocity than the first spiral track 34 such that the slope of the second spiral track 32 is greater than the slope of the first spiral track 34. In another embodiment, the second spiral track 32 may be written at a lower radial velocity than the first spiral track 34.

FIG. 4A illustrates an embodiment wherein the first spiral track 18 comprises a periodic pattern written at a first frequency (periodically interrupted by a sync mark), and the second spiral track 24 comprises a periodic pattern written at a second frequency (periodically interrupted by a sync mark) different from the first frequency. This embodiment may help attenuate crosstalk in the read signal generated while reading the first spiral track 18 while simultaneously writing the second spiral track 24. In one embodiment, the control circuitry may filter the read signal generated while reading the first spiral track 18 based on the frequency of the periodic pattern in the first spiral track 18. FIG. 4B illustrates an example of this embodiment wherein the control circuitry may bandpass filter the read signal to extract the frequency component in the read signal corresponding to the periodic pattern in the first spiral track 18.

In the example of FIGS. 4A and 4B, the periodic pattern in the first spiral track 18 comprises a lower frequency than the periodic pattern in the second spiral track 24. However, in other embodiments the periodic pattern in the first spiral track 18 may comprise a higher frequency than the periodic pattern in the second spiral track 24. Any suitable delta between the frequencies may be employed, and in one embodiment the frequencies and the delta are selected to reduce the implementation cost and complexity of the bandpass filter.

In the embodiment of FIG. 2C, the second spiral track 24 is written continuously so as to eventually overwrite the first spiral track 18 as the write element 28 passes over the first spiral track 18. This embodiment may improve performance while servoing on the second spiral track 24 since in one embodiment there are no gaps (or a reduced number of gaps) in the second spiral track 24. In one embodiment, when reading the second spiral track 24, for example to servo the head 20 over the disk surface 16 while writing servo sectors of concentric servo tracks, the resulting read signal may be filtered based on the frequency of the periodic pattern in the second spiral track 24. For example, the read signal may be bandpass filtered so as to extract the frequency component corresponding to the second spiral track 24, thereby attenuating interference from the periodic pattern in the first spiral track 18 near the locations where the second spiral track 24 overwrites the first spiral track 18.

FIG. 5A shows a data storage device in the form of a disk drive according to an embodiment comprising a disk surface 16 comprising a first spiral track 18 at least partially overwritten by a second spiral track 24. The disk drive further comprises control circuitry 22 configured to execute the flow diagram of FIG. 5B, wherein a head 20 is actuated over the disk surface 16 based on the second spiral track 24 (block 35).

FIGS. 5A and 5C illustrates an example embodiment wherein the second spiral track 24 is written in an opposite radial direction as the first spiral track 18 similar to the embodiment described above with reference to FIG. 2C. In one embodiment, the control circuitry 22 servos the head 20 in a substantially concentric path 36, for example, while writing concentric servo sectors to the disk such as shown in FIG. 1. As illustrated in FIG. 5C, the read element 26 may pass over the second spiral track 24 at a radial location where the second spiral track 24 overwrites the first spiral track 18, and therefore there may be interference in the read signal due to reading at least part of the first spiral track 18. This interference may reduce the accuracy of the resulting position signal generated based on demodulating the second spiral track 24. Accordingly, in order to reduce this interference, in one embodiment the first spiral track 18 comprises a periodic pattern written at a first frequency, and the second spiral track 24 comprises a periodic pattern written at a second frequency different from the first frequency. In the embodiment shown in FIG. 5C, the second frequency is higher than the first frequency; however in another embodiment the second frequency may be lower than the first frequency.

In one embodiment, the second spiral track 24 may be demodulated by processing the read signal samples to compute a discrete Fourier transform (DFT) at the second frequency using any suitable technique. When demodulating the second spiral track 24 using a DFT, the interference from the first spiral track 18 may be attenuated when the ratio between the second frequency and the first frequency is substantially an integer plus one-half as shown in FIG. 6. The ratio may be inverted in the embodiment where the second frequency is lower than the first frequency (i.e., the interference from the first spiral track 18 may be attenuated when the ratio between the first frequency and the second frequency is substantially an integer plus one-half). In another embodiment shown in FIG. 7, the control circuitry 22 may bandpass filter the read signal proximate the second frequency, thereby attenuating interference from the first spiral track 18. The bandpass filtering may be implemented in any suitable manner, including in the analog domain and/or in the digital domain.

In the embodiment of FIG. 4A, the first spiral track 18 may comprise a periodic pattern written at a first frequency as well as sync marks which may facilitate demodulating the spiral track when writing the second spiral track 24. However, in one embodiment the sync marks in the first spiral track 18 may interfere with the demodulation of the second spiral track 24 when attempting to servo on the second spiral track 24 (e.g., when writing concentric servo sectors). This embodiment is illustrated in FIG. 8A wherein the frequency spectrum of the first spiral track 18 may comprise a peak at the frequency of the periodic pattern, as well as a frequency component 38 due to the sync marks that may overlap with the peak frequency component of the second spiral track 24. Accordingly, in one embodiment illustrated in FIG. 8B the first spiral track 18 may be written without sync marks (i.e., consist primarily of the periodic pattern written at the first frequency), thereby avoiding the interference when demodulating the second spiral track 24 by removing the frequency component as illustrated in FIG. 8C. In one embodiment, the first spiral track 18 may be demodulated using other techniques not based on sync marks. For example, the first spiral track 18 may be demodulated by evaluating a peak in the read signal generated when reading the first spiral track 18.

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.

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, solid state 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.