Data storage device employing different frequency preambles in adjacent data tracks

Description

BACKGROUND

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.

FIG. 1 shows a prior art disk format 2 as comprising a number of servo tracks 4 defined by servo sectors 6₀-6_N recorded around the circumference of each servo track. Each servo sector 6_i comprises a preamble 8 for storing a periodic pattern, which allows proper gain adjustment and timing synchronization of the read signal, and a sync mark 10 for storing a special pattern used to symbol synchronize to a servo data field 12. The servo data field 12 stores coarse head positioning information, such as a servo track address, used to position the head over a target data track during a seek operation. Each servo sector 6_i further comprises groups of servo bursts 14 (e.g., N and Q servo bursts), which are recorded with a predetermined phase relative to one another and relative to the servo track centerlines. The phase based servo bursts 14 provide fine head position information used for centerline tracking while accessing a data track during write/read operations. A position error signal (PES) is generated by reading the servo bursts 14, wherein the PES represents a measured position of the head relative to a centerline of a target servo track. A servo controller processes the PES to generate a control signal applied to a head actuator (e.g., a voice coil motor) in order to actuate the head radially over the disk in a direction that reduces the PES.

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 comprising a plurality of data tracks defined by servo tracks.

FIG. 2B is a flow diagram according to an embodiment wherein a first frequency preamble is written to a first data sector in a first data track, and a second frequency preamble is written to a second data sector of a second data track adjacent to the first data track.

FIG. 2C illustrates an embodiment wherein a third frequency preamble is written to a third data sector in a third data track adjacent to the first data track.

FIGS. 3A-3C illustrate an embodiment wherein the frequency components of the different frequency preambles are evaluated to generate a jog value used during a retry read operation.

FIG. 4 is a flow diagram according to an embodiment wherein a retry read operation is executed by jogging the head away from an interfering data track as determined by the frequency components of the different frequency preambles.

FIG. 5 is a flow diagram according to an embodiment wherein the jog value used during retry operations may be adjusted incrementally based on the frequency components of the different frequency preambles.

FIG. 6 is a flow diagram according to an embodiment wherein the frequency components of the different frequency preambles may be used to generate a preamble position error signal (PES) used to servo the head over the disk during a read operation.

FIG. 7 is a flow diagram according to an embodiment wherein the servo burst PES may be disabled after settling onto the target data track and the preamble PES used to servo the head while tracking the target data track during a read operation.

FIG. 8 is a flow diagram according to an embodiment wherein when a difference between the preamble PES and the servo burst PES exceeds a threshold during a read operation, the target data track is rewritten to compensate for an off-track write due, for example, to a vibration during the write operation.

DETAILED DESCRIPTION

FIG. 2A shows a data storage device in the form of a disk drive according to an embodiment comprising a disk 16 comprising a plurality of data tracks 18 each comprising a plurality of data sectors, and a head 20 actuated over the disk 16. The disk drive further comprises control circuitry 22 configured to execute the flow diagram of FIG. 2B, wherein a first frequency preamble is written to a first data sector of a first data track (block 24) and a second frequency preamble is written to a second data sector of a second data track (block 26), wherein the first frequency is different from the second frequency and the first data track is adjacent to the second data track.

In the embodiment of FIG. 2A, the disk 16 comprises a plurality of servo sectors 28₀-28_N that define a plurality of servo tracks, wherein the data tracks 18 are defined relative to the servo tracks at the same or different radial density. The control circuitry 22 processes a read signal 30 emanating from the head 20 to demodulate the servo sectors 28₀-28_N and generate a position error signal (PES) representing an error between the actual position of the head and a target position relative to a target track. A servo control system in the control circuitry 22 filters the PES using a suitable compensation filter to generate a control signal 32 applied to a voice coil motor (VCM) 34 which rotates an actuator arm 36 about a pivot in order to actuate the head 20 radially over the disk 16 in a direction that reduces the PES. The servo sectors 28₀-28_N may comprise any suitable head position information, such as a track address for coarse positioning and servo bursts for fine positioning. The servo bursts may comprise any suitable pattern, such as an amplitude based servo pattern or a phase based servo pattern (FIG. 1).

In one embodiment, when writing to a data sector of a target data track a preamble is written to the data sector which may comprise a periodic signal having a predetermined frequency (e.g., a 2T preamble where “T” represents a bit cell period of the recorded data). When reading the data sector, the preamble may be processed, for example, to synchronize timing recovery and/or to adjust the gain of the read signal. The preamble may be written at any suitable location such as at the beginning of the data sector, and in some embodiments the preamble may be written at multiple locations such as a primary preamble written at the beginning of the data sector and a secondary preamble written between data segments and/or at the end of the data sector. In one embodiment illustrated in FIG. 2C, the preambles of adjacent data tracks may be written using different frequency periodic signals, wherein in the example of FIG. 2C the preambles of adjacent data tracks may be written as a 2T preamble, a 3T preamble, or a 4T preamble. Recording different frequency preambles in adjacent data tracks such as shown in FIG. 2C may be used advantageously for any suitable purpose, example embodiments of which are described below.

FIG. 3A illustrates an embodiment wherein when writing to data track N+1 an off-track write may occur due, for example, to a vibration that causes the write element to deviate toward track N. Referring to the flow diagram of FIG. 4, when subsequently attempting to read a data sector from data track N (block 38) by processing the resulting read signal (block 40), the data sector may be unrecoverable due to the intertrack interference from track N+1. If the data sector is unrecoverable (block 42), a frequency component of the read signal is evaluated (block 44) in order to generate a jog value (block 46). A retry read of the data sector is then executed while offsetting the head by the jog value (block 48). FIG. 3B illustrates the frequency components of the read signal when initially reading the 3T preamble of the data sector in data track N. Since the magnitude of the 4T frequency component is relatively large due to the intertrack interference from data track N+1, a jog value is generated that jogs the head toward data track N−1 during the retry read of data track N. As illustrated in FIG. 3C, during the retry read the resulting 4T frequency component is reduced as is the intertrack interference from data track N+1, thereby enabling the recovery of the data sector in data track N. The jog value may be generated in any suitable manner, such as based on the magnitude of the adjacent track preamble frequencies and/or based on the magnitude of the adjacent track preamble frequencies relative to the magnitude of the target track preamble frequency.

In one embodiment, generating the sign and magnitude of the jog value based on the magnitude of the preamble frequencies reduces the time required to recover a data sector as compared to the prior art technique of selecting an arbitrary sign and incrementally increasing the magnitude of the jog value until the data sector is recovered. That is, in one embodiment the magnitude of the preamble frequencies helps determine the correct sign (radial direction) of the jog value as well as an accurate estimate of the jog magnitude that will result in a successful retry read rather than arbitrarily scanning through a number of jog magnitudes in both radial directions until the data sector is recovered.

FIG. 5 is a flow diagram according to an embodiment wherein the jog value is initialized to zero (block 50). When a data sector is unrecoverable at block 42, a frequency component of the read signal is evaluated to select a sign for a jog delta (block 52). The jog value is then adjusted by the jog delta (block 54) and the data sector reread while offsetting the head radially away from the target track based on the jog value (block 56). The resulting read signal is processed to recover the data sector (block 58), and if the retry read fails (block 60), the process is repeated after incrementally increasing the magnitude of the jog value at block 54. If the data sector is unrecoverable at block 60 and the magnitude of the preamble frequency (in this example the 3T frequency) of the target data sector begins to decrease at block 62, it indicates that the head has been offset too far away from the target data track. Accordingly, the polarity of the jog delta is reversed and the magnitude of the jog delta is halved (block 64) so that the head is incrementally stepped back toward the target data track during subsequent retry reads. Although not shown, the flow diagram of FIG. 5 may terminate after a predetermined number of iterations if the data sector in the target data track cannot be recovered, in which case the host may be notified of a fatal error or other heroic error recovery procedures executed.

FIG. 6 is a flow diagram that illustrates another use for writing different frequency preambles to adjacent data tracks according to another embodiment. In this embodiment, when reading the data sector from data track N (block 66) as shown in FIG. 3A, a frequency component of the read signal is evaluated (block 68) in order to generate a preamble position error signal (PES) (block 70). The head is then servoed over data track N based on the preamble PES (block 72), for example, in order to read one or more data sectors from data track N. This embodiment may help the head track the actual centerline of the data track as compared to the centerline of the data track defined by the servo sectors 28₀-28_N. For example, if a data track is written off-track due to a vibration during a write operation, the preamble PES may improve the ability to recover data sectors from the data track during read operations. The preamble PES may be generated in any suitable manner, such as based on the magnitude of the target data track preamble frequency in the read signal, and/or based on the relative magnitudes of the adjacent track preamble frequencies in the read signal. Referring again to the example of FIG. 3A, when attempting to read a data sector from track N the preamble PES may be generated based on a difference between the measured magnitudes of the preamble frequencies and target magnitudes, wherein the relative magnitude of the 4T preamble frequency (from data track N+1) and the 2T preamble frequency (from data track N−1) may determine the sign of the preamble PES. In another embodiment, the preamble PES may be incrementally adjusted at each data sector so as to maximize the magnitude of the target data track preamble frequency (e.g., the 3T frequency when reading data from data track N).

FIG. 7 is a flow diagram that extends on the flow diagram of FIG. 6, wherein when executing a read operation the control circuitry seeks the head to the target data track based on the servo sectors (block 74) and then settles the head onto the target data track based on the servo burst PES (block 76). Once the head has settled onto the target data track, the servo burst PES may be disabled for at least part of the data track (block 78) so that the head may be servoed over the target data track based on the preamble PES. That is, in one embodiment the preamble PES may provide a more accurate tracking of the target data track during at least part of a read operation, particularly if at least part of the target data track was written off-track due, for example, to a vibration during the write operation.

The preamble PES may be used to servo the head over the disk during an initial read of a data track, and/or it may be used during a retry read as part of an error recovery procedure. In some embodiments, the preamble PES and the servo burst PES may be weighted differently and then combined to generate a different servo system PES during each retry read. That is, there may be a particular weighting of the preamble PES and the servo burst PES that may enable the successful recovery of a data sector.

FIG. 8 is a flow diagram that illustrates another use for writing different frequency preambles to adjacent data tracks according to another embodiment. When executing a read operation the control circuitry seeks the head to the target data track based on the servo sectors (block 80) and then settles the head onto the target data track based on the servo burst PES (block 82). While tracking the target data track based on the servo burst PES, a data sector is read to generate a read signal (block 84) and a frequency component of the read signal is evaluated (block 86) to generate a preamble PES (block 88) as described above. A delta between the servo burst PES and the preamble PES is generated (block 90), and when the delta exceeds a threshold (block 92), at least part of the target data track is rewritten and optionally at least part of at least one of the data tracks adjacent to the target data track is rewritten (block 94). In this embodiment, the preamble PES operates as a metric for indicating when a data track is written off-track due, for example, to a vibration during a write operation. That is, the preamble PES may indicate when a written data track deviates from the target data track as defined by the servo sectors, and therefore may be used to trigger a rewrite in order to re-align the data track. Prior to rewriting a misaligned data track, the adjacent data tracks may also be read and then rewritten together with the target data track so that the rewrite does not corrupt the previously written adjacent data tracks.

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, 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.