Data storage device initializing read signal gain to detect servo seed pattern

Description

BACKGROUND

When manufacturing a data storage device such as 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 6₀-6_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 6₀-6_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, U.S. Pat. No. 5,668,679 teaches a disk drive which performs a self-servo writing operation by writing a plurality of spiral servo tracks to the disk which are then processed to write the concentric servo sectors along a circular path. Each spiral servo track is written to the disk as a high frequency signal (with missing bits), wherein the position error signal (PES) for tracking is generated relative to time shifts in the detected location of the spiral servo tracks. The read signal is rectified and low pass filtered to generate a triangular envelope signal representing a spiral servo track crossing, wherein the location of the spiral servo track is detected by detecting a peak in the triangular envelope signal relative to a clock synchronized to the rotation of the disk.

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 servo seed pattern.

FIG. 2B is a flow diagram according to an embodiment wherein a number of times an amplitude measurement exceeds a first threshold is first counted during a first revolution of the disk and second counted during a second revolution of the disk, wherein the servo seed pattern is detected based on the first and second count.

FIG. 2C shows control circuitry according to an embodiment for counting a number of times the amplitude measurement exceeds a first threshold.

FIG. 3A illustrates an embodiment wherein noise in the amplitude measurement exceeds the first threshold.

FIG. 3B illustrates an embodiment wherein a gain of the read signal is decreased until the noise in the amplitude measurement falls below the first threshold.

FIG. 3C illustrates an embodiment wherein the first threshold is increased until the noise in the amplitude measurement falls below the first threshold.

FIG. 4 is a flow diagram according to an embodiment wherein the first and second counts are re-measured until a delta between the counts falls below a second threshold.

FIG. 5A shows control circuitry according to an embodiment wherein after adjusting the gain of the read signal a servo seed pattern window is generated based on the rotation angle of the disk when the amplitude measurement exceeds the first threshold.

FIG. 5B illustrates an embodiment wherein the servo seed pattern window is opened to facilitate detecting the servo seed pattern on the disk.

FIG. 6 shows an embodiment wherein the servo seed pattern comprises a spiral track that spans multiple disk revolutions according to an embodiment.

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 16 comprising at least one servo seed pattern 18₀, 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 an amplitude measurement is generated based on a read signal emanating from the head while reading the disk (block 24). A number of times the amplitude measurement exceeds a first threshold is first counted during a first revolution of the disk (block 26), and a number of times the amplitude measurement exceeds the first threshold is second counted during a second revolution of the disk (block 28). The servo seed pattern is detected based on the first count and the second count (block 30).

In the embodiment of FIG. 2A, the control circuitry 22 processes a read signal 32 emanating from the head 20 to detect the servo seed patterns 18₀-18_N, and in one embodiment, generate a control signal 34 applied to a voice coil motor (VCM) 36 which rotates an actuator arm 38 about a pivot in order to actuate the head 20 radially over the disk 16. For example, in one embodiment the control circuitry 22 may actuate the head 20 over the disk 16 based on the servo seed patterns 18₀-18_N in order to write servo sectors that define concentric servo tracks such as shown in FIG. 1. At the beginning of the servo writing process, the control circuitry 22 may need to calibrate an initial gain for the read signal (e.g., determine a noise floor) as well as determine the initial circumferential location of the servo seed patterns 18₀-18_N relative to the head 20.

FIG. 2C shows control circuitry according to an embodiment wherein an amplifier 40 amplifies the read signal 32 based on a configurable gain control setting 42. Block 46 measures an amplitude of the amplified read signal 44 using any suitable technique which may include sampling, rectifying, averaging, filtering, and/or other suitable signal processing technique. The measured amplitude 48 is compared to a first threshold Th1 50 at comparator 52, and counter 54 counts the number of times the measured amplitude 48 exceeds the first threshold Th1 50 over a revolution of the disk, wherein in one embodiment the counter 54 is reset by reset signal 56 after each revolution.

FIG. 3A shows an example amplitude measurement over a revolution of the disk which illustrates operation of the control circuitry shown in FIG. 2C. In the example of FIG. 3A, the gain of amplifier 40 is initialized to a high setting such that the noise in the amplitude measurement randomly exceeds the first threshold Th1 over a revolution of the disk. That is, due to the random nature of the noise in the amplitude measurement, the value of the counter 54 after a first revolution of the disk will be different from the value of the counter 54 after a second revolution of the disk. FIG. 3B illustrates an embodiment wherein if the gain of the amplifier 40 is reduced, the noise in the amplitude measurement eventually falls below the first threshold Th1 leaving only the spikes in the amplitude measurement due to the head crossing the servo seed patterns 18₀-18_N. Accordingly, when the noise falls below the first threshold Th1, the delta in the counter value between a first and second revolution will fall below a second threshold (or be zero). In an alternative embodiment, instead of adjusting the gain of the amplifier 40, the first threshold Th1 is adjusted relative to the noise in the amplitude measurement. FIG. 3C illustrates an example of this embodiment wherein the first threshold Th1 is incrementally increased until the delta in the counter values between a first and second revolution falls below a second threshold indicating that the counter is driven by the spikes in the amplitude measurement corresponding to the periodic servo seed patterns 18₀-18_N rather than by the noise. In one embodiment, after adjusting the first threshold Th1 as shown in FIG. 3C, the control circuitry may make a corresponding adjustment to the gain of the read signal amplifier 40.

FIG. 4 is a flow diagram according to an embodiment wherein when initially detecting the servo seed patterns, the control circuitry 22 controls the VCM 36 to press the actuator arm 38 against an inner diameter (ID) crash stop (not shown), thereby maintaining the head 20 at a substantially constant radial position as the disk rotates (block 58). An amplitude measurement is generated based on the read signal (block 60), and the control circuitry first counts a number of times the amplitude measurement exceeds the first threshold Th1 during a first revolution of the disk (block 62), and counts a number of times the amplitude measurement exceeds the first threshold Th1 during a second revolution of the disk (block 64). A delta between the first and second counts is generated (block 66), and the delta is compared to a second threshold Th2 (block 68). If the delta is greater than the second threshold Th2, then the gain of the amplifier 40 and/or the first threshold Th1 is adjusted (block 70) and the flow diagram is repeated from block 60. This process is repeated until the delta falls below the second threshold Th2 at block 68, after which the counter values may be used to detect the servo seed patterns (block 72), such as by reading the servo seed patterns using the final gain adjustment.

In one embodiment, the control circuitry 22 is further configured to detect the servo seed patterns by opening a servo seed pattern window based on when the amplitude measurement exceeds the first threshold relative to a rotation angle of the disk. FIGS. 5A and 5B illustrate an example of this embodiment, wherein FIG. 5A shows control circuitry similar to FIG. 2C. A first set of registers 74 store the output of the first counter 54 after each revolution of the disk in order to generate the delta at block 66 of FIG. 4. A second counter 76 is clocked at a frequency based on the rotation speed of the disk, which in one embodiment is a clock 80 generated by the zero-crossings in a back electromotive force (BEMF) voltage generated by a spindle motor that rotates the disk. When the amplitude measurement 48 exceeds the first threshold Th1 50 at comparator 52 due to the head crossing a servo seed pattern, the value of the second counter 76 is stored in a corresponding register of a bank of registers 78. That is, each time the comparator 52 detects a servo seed pattern, the corresponding rotation angle of the disk is tracked by the second counter 76 is stored in a register 78. In one embodiment, the bank of registers 78 stores the second counter values generated over each revolution of the disk, which are then used to open a servo seed pattern window at the rotation angle where the register values are substantially the same across multiple revolutions (thereby ignoring noise that may trigger a false detection of a servo seed pattern). In one embodiment, the correlation of the detected servo seed patterns by the comparator 52 across multiple disk revolutions may also be used to adjust the gain and/or first threshold Th1 in the flow diagram of FIG. 4. For example, the gain and/or first threshold Th1 may be adjusted until the correlation of the detected servo seed patterns across multiple revolutions exceeds a threshold.

FIG. 5B illustrates an embodiment wherein the servo seed pattern window is opened based on the counter values stored in registers 78. As the disk rotates and the rotation angle changes as determined by the spindle BEMF clock 80, when the second counter 76 reaches a value previously stored in the registers 78, the servo seed pattern window is opened and the read signal processed to demodulate the servo seed pattern (e.g., to generate a PES for servoing the head). Once the servo seed patterns 18₀-18_N have been detected at a particular radial location (e.g., at the ID crash stop), the servo seed pattern windows may be adjusted as the head is moved radially over the disk in order to track variations in the circumferential location of the servo seed patterns.

Any suitable servo seed pattern may be recorded on the disk 16, and in one embodiment the area on the disk between the servo seed patterns may be erased (AC or DC) or comprise random magnetic transitions. In the embodiment of FIG. 2A, the servo seed pattern comprises a spiral track that spans a partial revolution of the disk 16. For example, the spiral track may comprise a high frequency signal (periodically interrupted by sync marks) that is written while moving the head radially across the disk 16 at a predetermined velocity. FIG. 6 shows an embodiment wherein each spiral track shown in FIG. 2A may be written over multiple disk revolutions by decreasing the radial velocity of the head relative to the rotation speed of the disk when writing each spiral track.

In one embodiment, the servo seed patterns 18₀-18_N may be self-written to the disk 16 by the control circuitry 22 internal to the disk drive. An example embodiment for writing servo seed patterns 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 servo seed patterns 18₀-18_N may be written to the disk 16 using an external servo writer prior to installing the disk into the disk drive. In either case, it may be necessary to calibrate the gain of the read signal amplifier 40 prior to detecting the servo seed patterns 18₀-18_N as described above.

In the embodiment of FIG. 3B, the gain of the amplifier 40 (FIG. 2C) is decreased until the delta between the counter values falls below the second threshold at block 68 of FIG. 4. In another embodiment, the gain of the amplifier 40 may be initialized to a low value and then increased until the delta between the counter values exceeds the second threshold. In another similar embodiment, the first threshold Th1 may be initialized to a high value and then decreased at block 68 of FIG. 4 until the delta between the counter values exceeds the second threshold. In general, these embodiments attempt to discover the noise floor in the amplitude measurement so that the servo seed patterns may be accurately detected when initially synchronizing to the servo seed patterns.

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.