Patent Application
20120281304
The present inventions are related to systems and methods sensing data, and more particularly to systems and methods for characterizing a data sensor.
Data storage devices often include a read head that senses information stored on a storage medium. The data is often arranged in tracks of a particular width. As the sensing characteristics of the read head change, there is a possibility to sense data from tracks on either side of the track being read and/or to unduly limit the width of the tracks established on a storage medium. Existing approaches for characterizing such sensors have been signal amplitude based methods and/or variable gain amplifier based methods. Such methods, however, are not as accurate as the width of data tracks is decreased resulting in smaller signal to noise ratios.
Hence, for at least the aforementioned reasons, there exists a need in the art for advanced systems and methods for characterizing data sensors.
The present inventions are related to systems and methods sensing data, and more particularly to systems and methods for characterizing a data sensor.
Various embodiments of the present invention provide data storage devices that include: a storage medium, a read/write head assembly disposed in relation to the storage medium, and a track width setting circuit. The track width setting circuit is operable to: write data to at least a first track and a second track on the storage medium, read data from the second track, determine an estimated track offset where interference from the data written to the first track is insubstantial, and modify at least the second track width based at least in part on the estimated track offset. The first track is a first track width and the second track is a second track width. In some cases, the first track width and the second track width are the same. In other cases, the first track width is different from the second track width.
In some instances of the aforementioned embodiments, determining the estimated track offset where interference from the data written to the first track is insubstantial includes: comparing a value read from the target track to a threshold value to yield a comparison value; and indicating the interference from the data written to the first track is insubstantial based on the comparison value. In other instances of the aforementioned embodiments, determining the estimated track offset where interference from the data written to the first track is insubstantial includes: reading the target track at a first adjusted track offset to yield a first value, and reading the target track at a second adjusted track offset to yield a second value. The first adjusted track offset is closer to the first track than the second adjusted track offset. The instance further includes comparing the first value to a threshold value to yield a first comparison value. The first comparison value indicates that the interference from the data written to the first track is not insubstantial. The instance further includes comparing the second value to the threshold value to yield a second comparison value. The second comparison value indicates that the interference from the data written to the first track is insubstantial. In some such instances, the estimated track offset is the second adjusted track offset.
In other instances of the aforementioned embodiments, the estimated track offset is a first estimated track offset, and the track width setting circuit is further operable to write data to a third track on the storage medium. The third track is adjacent the second track and separated from the first track by the second track. The track width setting circuit is further operable to: determine a second estimated track offset where interference from the data written to the third track is insubstantial; and modify at least the second track width based at least in part on a distance between the first estimated track offset and the second estimated track offset.
Other embodiments of the present invention provide methods for determining a track width corresponding to a read sensor. Such methods include writing data to at least a first track, a second track, and a third track on a storage medium. The second track exhibits a track width, and the third track is adjacent the second track and separated from the first track by the second track. The methods further include: reading data from the second track; determining a first estimated track offset where interference from the data written to the first track is insubstantial; determining a second estimated track offset where interference from the data written to the third track is insubstantial; calculating a distance between the first estimated track offset and the second estimated track offset; and modifying the track width based at least in part on a distance between the first estimated track offset and the second estimated track offset.
This summary provides only a general outline of some embodiments of the invention. Many other objects, features, advantages and other embodiments of the invention will become more fully apparent from the following detailed description, the appended claims and the accompanying drawings.
A further understanding of the various embodiments of the present invention may be realized by reference to the figures which are described in remaining portions of the specification. In the figures, like reference numerals are used throughout several figures to refer to similar components. In some instances, a sub-label consisting of a lower case letter is associated with a reference numeral to denote one of multiple similar components. When reference is made to a reference numeral without specification to an existing sub-label, it is intended to refer to all such multiple similar components.
a-1b are block diagrams of a known magnetic storage medium and track storage scheme;
a-5c depict example interim outputs relative to track width settings in accordance with some embodiments of the present invention; and
The present inventions are related to systems and methods sensing data, and more particularly to systems and methods for characterizing a data sensor.
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In a typical read operation, read/write head assembly 276 is accurately positioned by motor controller 268 over a desired data track on disk platter 278. The desired track is identified in part using the enhanced servo data processing circuit. Motor controller 268 both positions read/write head assembly 276 in relation to disk platter 278 and drives spindle motor 272 by moving read/write head assembly to the proper data track on disk platter 278 under the direction of hard disk controller 266. Spindle motor 272 spins disk platter 278 at a determined spin rate (RPMs). Once read/write head assembly 276 is positioned adjacent the proper data track, magnetic signals representing data on disk platter 278 are sensed by read/write head assembly 276 as disk platter 278 is rotated by spindle motor 272. The sensed magnetic signals are provided as a continuous, minute analog signal representative of the magnetic data on disk platter 278. This minute analog signal is transferred from read/write head assembly 276 to read channel module 264 via preamplifier 270. Preamplifier 270 is operable to amplify the minute analog signals accessed from disk platter 278. In turn, read channel circuit 210 decodes and digitizes the received analog signal to recreate the information originally written to disk platter 278. This data is provided as read data 203 to a receiving circuit. A write operation is substantially the opposite of the preceding read operation with write data 201 being provided to read channel circuit 210. This data is then encoded and written to disk platter 278.
The width of the tracks being written and read by read/write head assembly 276 is variable, and may be varied based upon an amount of inter-track interference sensed by read/write head assembly 276. The amount of interference is determined by and the track width modified by the inter-track interference based track width setting circuit included as part of read channel circuit 210. The inter-track interference based track width setting circuit may be implemented similar to that described below in relation to
It should be noted that storage system 200 may be integrated into a larger storage system such as, for example, a RAID (redundant array of inexpensive disks or redundant array of independent disks) based storage system. It should also be noted that various functions or blocks of storage system 200 may be implemented in either software or firmware, while other functions or blocks are implemented in hardware.
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In operation, data is written to tracks on test disk 378 that exhibit a width controlled by test controller 320 (i.e., test controller 32 controls the radial location of read head 376 during writes to test disk 378). Test controller 320 then positions read head 376 over a track to be read. The data on test disk 378 consists of groups of magnetic signals that may be detected by read head 376 when the assembly is properly positioned over disk platter 378. As test disk 378 is spun relative to read head 376, read head 376 senses the data and transfers minute analog signals representative of the data to head characterization circuit 310 via preamplifier circuit 370. Preamplifier 270 is operable to amplify the minute analog signals accessed from test disk 378. In turn, head characterization circuit 310 determines an amount of interference caused by tracks adjacent to that being read. This process is repeated for different track widths under the control of test controller 320 until a read width of read head 376 is established. This read width is provided as a characteristic of read head 376. The amount of interference is determined by and guidance on modifying the track width is provided the inter-track interference based track width setting circuit included as part of head characterization circuit 310. The inter-track interference based track width setting circuit may be implemented similar to that described below in relation to
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In addition, setting circuit 400 includes a track width register 406 that stores a track width input 404, and provides the stored track width as a track width output 408 to a head location and disk rotation controller circuit 410. Head location and disk rotation controller circuit 410 is shown in dashed lines as it may include a number of elements including, but not limited to, a hard disk controller, a motor controller, and/or a spindle motor similar to those discussed above in relation to
In controlling the position of read/write head assembly 476 relative to disk platter 478, read/write head assembly 476 is positioned a distance away from a previous track that corresponds to track width output 408. In addition, head location and disk rotation controller circuit 410 receives a head offset control value 420 that controls an offset from an expected track centerline. In particular, in positioning read/write head assembly 476 relative to disk platter 478, head location and disk rotation controller circuit 410 adjusts the location of read/write head assembly 476 a positive or negative offset from the location set by track width output 408.
Setting circuit 400 also includes an analog front end circuit 434 that receives an analog signal 430 from read/write head assembly 476 during read operations, and provides a corresponding analog output signal 436. Analog front end circuit 434 may include any circuitry known in the art that is capable of receiving an analog input signal and providing a modified analog signal as an output. In one particular instance, analog front end circuit 434 includes an amplifier (not shown) that receives and amplifies analog input signal 430 and an analog filter (not shown) that reduces any noise exhibited at the output of the amplifier. Based upon the disclosure provided herein, one of ordinary skill in the art will recognize a variety of circuitry that may be included in analog front end circuit 434 in accordance with different embodiments of the present invention.
Analog output signal 436 is provided to an analog to digital converter circuit 438. Analog to digital converter circuit 438 provides a series of digital samples 440 representing analog output signal 436. Digital samples 440 are synchronized to a sample clock (not shown) that is provided to analog to digital converter circuit 438. Analog to digital converter circuit 438 may be any circuit or system known in the art that is capable of converting a continuous signal into a series of digital samples. Analog input signal 436 is a continuous signal representing a number of bit periods. The bit periods recur with a periodicity of T, and the sample clock causes analog to digital converter circuit 438 to generate a number of samples of analog input signal 430 for each period T. In one particular embodiment of the present invention, four samples are generated for each period T. In another embodiment of the present invention, eight samples are generated for each period T. It should be noted that other numbers of samples per period may be generated. Based upon the disclosure provided herein, one of ordinary skill in the art will recognize a variety of sampling frequencies and corresponding bit periods that may be used in relation to different embodiments of the present invention.
Digital samples 440 are provided to a track width controller circuit 402, and track width controller circuit 402 provides track width input 404 to track width register 406, and data input 414 to write controller circuit 416. Track width controller circuit 402 is operable to perform a stepwise approach to determining a track width on disk platter 478 that optimizes the operation of the read element included in read/write head assembly 476. In particular, track width controller circuit 402 sets an initial track width by writing a value corresponding to the initial track width to track width register 406. Once head location and disk rotation controller circuit 410 causes read/write head assembly 476 to position over an adjacent track of a track width corresponding to track width output 408, track location controller circuit 402 provides an adjacent data pattern as data input 414 to write data controller circuit 416 that in turn causes a signal corresponding to data input 414 to be stored to disk platter 478 via read/write head assembly 476. As used herein, the phrase “adjacent track” is used in its broadest sense to mean a location on a storage medium that is adjacent to another location that will be the target of a read (i.e., a target track”). As an example, Track N−1 and Track N+1 of
Head location and disk rotation controller circuit 410 additionally causes read/write head assembly 476 to position over a target track next to the previously discussed adjacent track and also having a track width corresponding to track width output 408, track location controller circuit 402 provides a target data pattern as data input 414 to write data controller circuit 416 that in turn causes a signal corresponding to data input 414 to be stored to disk platter 478 via read/write head assembly 476. As used herein, the phrases “target data pattern” and “adjacent data pattern” are used in their broadest senses to mean any data pattern distinguishable from the other (i.e., a target data pattern is any data pattern that is distinguishable from an adjacent data pattern, and vice versa). Thus, for example, an adjacent target data pattern may be a series of data that causes relatively high values to be written to disk platter 478 and a corresponding target data pattern may be a series of data that causes relatively low values to be written to disk platter 478. Based upon the disclosure provided herein, one of ordinary skill in the art will recognize a variety of possible target and adjacent data patterns that may be used in relation to different embodiments of the present invention. In addition, head location and disk rotation controller circuit 410 causes read/write head assembly 476 to position over another adjacent track next to the previously discussed target track and also having a track width corresponding to track width output 408. Once positioned, track location controller circuit 402 provides an adjacent data pattern as data input 414 to write data controller circuit 416 that in turn causes a signal corresponding to data input 414 to be stored to disk platter 478 via read/write head assembly 476.
After the aforementioned writes, track width controller circuit 402 causes write controller circuit 410 to position read/write head assembly 476 over the target track with an offset from the centerline of the target track defined by an initial offset value provided by track width controller circuit 402 as head offset control value 420. In some cases, the initial offset is set to make interference from one of the adjacent tracks likely (i.e., read/write head assembly 476 is positioned far enough from the center line of the target track such that it senses both the target track and the adjacent track on the side of the target track corresponding to the offset). Once positioned, read/write head assembly 476 senses the previously stored target data and provides the sensed information as analog signal 430. In turn, digital samples 440 corresponding to analog signal 430 are provided to track width control circuit 402. Track width control circuit analyzes digital samples 403 to determine if there is any impact from the adjacent track on the side of target track corresponding to the offset.
On the initial pass, it is likely that interference from the adjacent track occurs. Where this is the case, the offset value provided by track width controller circuit 402 as head offset control value 420 is adjusted such that read/write head assembly 476 moves stepwise away from the adjacent track from which the interference is sensed. This stepwise process is continued until the interference from the adjacent track drops below a threshold level. The threshold level may be programmable. The offset corresponding to the step where the interference the adjacent track drops below a threshold level is identified as a first non-interference point. The stepwise process of adjusting the offset value provided by track width controller circuit 402 as head offset control value 420 is continued until interference from the adjacent track on the opposite side of the target track exceeds the threshold level. The offset corresponding to this step preceding the step where the interference is detected is identified as a second non-interference point. As used herein, the phrase “non-interference point” is used in its broadest sense to mean a point where interference from an adjacent track is less than or equal to a given level or percentage.
The previously described case is graphically depicted in
Returning to
b shows an example situation where the distance between non-interference points is acceptable. In this case shown as a graph 511, the tracks have a width of 571 resulting in a first non-interference point 595 nearer to a second non-interference point 597 than what occurred in graph 510.
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The read/write head assembly is positioned over the target track (Track N) with an initial offset in a positive direction from the center of the target track (block 625). Such positioning may be done in part by providing an initial offset to a write controller circuit. In some cases, the initial offset is selected to be sufficient to assure interference from one of the adjacent tracks (e.g., Track N−1). Data is then read from the target track by passing the read/write head assembly over the track as the selected offset to yield a data output (block 630). It is determined whether the data output is affected by the defined pattern maintained in the adjacent track (e.g., Track N−1) (block 635). This may be determined by comparing the data output with a threshold level. Where the data output is greater than the threshold level (or less then for a reversed pattern contrast), the data output may be considered interfered with by the defined pattern in the adjacent track. Where the data output is affected by the adjacent track (block 635), the offset is modified in a negative direction (decreasing the positive offset or increasing a negative offset) from the center of the target track, and the read/write head assembly is aligned with the updated offset (block 645). At this juncture, the processes of blocks 630-665 are repeated for the updated offset.
Alternatively, where the data output is not affected by the defined pattern maintained in the adjacent track (e.g., Track N−1) (block 635), it is determined whether a prior read of the target track at a different offset resulted in an affect by the same adjacent track (block 640). Where the target track was not previously affected by the same adjacent track (block 640), the offset is modified in a positive direction (i.e., to increase a positive offset or decrease a negative offset) from the center of the target track, and the read/write head assembly is aligned with the updated offset (block 650). At this juncture, the processes of blocks 630-665 are repeated for the updated offset. In contrast, where the target track was previously affected by the same adjacent track (block 640), it is determined whether the data output is affected by the defined pattern of the opposite adjacent track (e.g., Track N+1) (block 655). Again, this may be determined by comparing the data output with a threshold level. Where the data output is greater than the threshold level (or less then for a reversed pattern contrast), the data output may be considered interfered with by the defined pattern in the adjacent track. Where the data output is not affected by the adjacent track (block 655), the offset is identified as a center region or area (i.e., an area with limited or no interference from adjacent tracks), the offset is modified in a negative direction (decreasing the positive offset or increasing a negative offset) from the center of the target track, and the read/write head assembly is aligned with the updated offset (block 660). At this juncture, the processes of blocks 630-665 are repeated for the updated offset.
Alternatively, where the data output is affected by the adjacent track (block 655), the extent of the center area or non-interference region has been determined and a width of the center area is calculated by subtracting a point corresponding to one extreme of the center area from a point corresponding from the other extreme of the center area (block 665). At this juncture, it is determined whether the calculated width is too large (block 670). This may be done, for example, by comparing the calculated width to threshold value. A calculated width that is too large indicates a lower storage density (i.e., too wide of tracks) than can be supported by the read/write head assembly. Where the calculated width is too large (block 670), the track width is decreased (block 675). This may be done, for example, by writing a reduced value to the track width register. At this juncture, the processes of blocks 610-690 are repeated for the updated track width.
Otherwise, where the track width is not determined to be too large (block 670), it is determined whether the calculated width is too small (block 680). Again, this may be done, for example, by comparing the calculated width to threshold value. A calculated width that is too small indicates a storage density that is too great (i.e., too narrow of tracks) than can be supported by the read/write head assembly. Where the calculated width is too small (block 680), the track width is increased (block 685). This may be done, for example, by writing an increased value to the track width register. At this juncture, the processes of blocks 610-690 are repeated for the updated track width. Alternatively, where the calculated width is not too small (block 680), the calculated track width is stored (block 690). This stored track width may be used for operation of a storage device where the method is implemented in relation to a storage device, or may be used to characterize a read head where the method is implemented in relation to a test stand.
It should be noted that the various blocks discussed in the above application may be implemented in integrated circuits along with other functionality. Such integrated circuits may include all of the functions of a given block, system or circuit, or only a subset of the block, system or circuit. Further, elements of the blocks, systems or circuits may be implemented across multiple integrated circuits. Such integrated circuits may be any type of integrated circuit known in the art including, but are not limited to, a monolithic integrated circuit, a flip chip integrated circuit, a multichip module integrated circuit, and/or a mixed signal integrated circuit. It should also be noted that various functions of the blocks, systems or circuits discussed herein may be implemented in either software or firmware. In some such cases, the entire system, block or circuit may be implemented using its software or firmware equivalent. In other cases, the one part of a given system, block or circuit may be implemented in software or firmware, while other parts are implemented in hardware.
In conclusion, the invention provides novel systems, devices, methods and arrangements for characterizing read sensors and/or for setting track width. While detailed descriptions of one or more embodiments of the invention have been given above, various alternatives, modifications, and equivalents will be apparent to those skilled in the art without varying from the spirit of the invention. Therefore, the above description should not be taken as limiting the scope of the invention, which is defined by the appended claims.
