KR100594313B1 - Method for determinging tpi of harddisk drive and recording medium therefor - Google Patents

Abstract

The present invention relates to a hard disk drive, and more particularly, to a method for determining a TPI suitable for a head and a recording medium suitable for the same.

In the TPI determination method of a hard disk drive according to the present invention, a process of obtaining an offtrack curve showing a change in an error rate according to an offtrack amount is performed by performing an ATW (Adjacent Track Write) test while changing an offtrack amount of an adjacent track. ; A process of calculating a reference BER (BER) that does not change even when the offtrack amount changes in the offtrack curve

; Calculating an offtrack amount β at a position where an error rate is lowered by a predetermined ratio α between a reference BER and a measurement limit BER in the offtrack curve; And determining a TPI suitable for the head according to the value of β.

The TPI determination method of the hard disk drive according to the present invention has the effect that the TPI can be appropriately determined according to the variation of the head magnetic recording width.

Description

Method for determing TPI of harddisk drive and recording medium therefor}

1 is a graph showing the distribution of the magnetic recording width with respect to the head.

Figure 2 shows an example of the TPI-BER curve used in the conventional TPI determination method.

3 is a graph for schematically showing a TPI determination method according to the present invention.

4 shows an offtrack curve for a head having a magnetic recording width narrower than the target magnetic recording width.

5 shows an offtrack curve for a head having a magnetic recording width wider than the target magnetic recording width.

6 is a flowchart illustrating an embodiment of a TPI determination method according to the present invention.

Fig. 7 schematically shows the relationship between the offset and the erase position.

8 shows TPI values according to the value of β.

9 is a diagram illustrating a configuration of a hard disk drive to which the present invention is applied.

FIG. 10 is a block diagram of a controller for controlling the hard disk drive shown in FIG. 9.

The present invention relates to a hard disk drive, and more particularly, to a method for determining a TPI suitable for a head and a recording medium suitable for the same.

As the data storage capacity of hard disk drives increased, the track density increased. As track density increases, track margins inevitably decrease, and inter-track interference and adjacent track erase (ATE) problems become important.

On the other hand, due to the difficulty in managing the magnetic write width (MWW) in the head, it is difficult to cope with a wide distribution of the MWW only with a single track per inch (TPI).

For example, heads with magnetic write widths wider than the standard can cause ATE problems, whereas heads with magnetic write widths wider than the standard can cause weak write problems.

In the related art, a method of determining a TPI suitable for a head based on a characteristic curve (TPI-BER curve) showing a change in an error rate according to a change in off-track amount was used, but a reference BER (reference bit), which is a basic basis for determining TPI, was used. Since the error rate does not reflect the difference in performance of the head, there is a problem in that an optimal TPI cannot be determined.

It is an object of the present invention to provide a method of predicting a magnetic recording width of a head and determining a TPI suitable for the head according to the predicted magnetic recording width.

Another object of the present invention is to provide a recording medium suitable for the above method.

TPI determination method of the hard disk drive according to the present invention to achieve the above object

Performing an ATW (Adjacent Track Write) test while changing an off track amount of an adjacent track to obtain an off track curve showing a change in an error rate according to the off track amount;

Calculating a reference BER (BER) which does not change even if the offtrack amount changes in the offtrack curve;

Calculating an offtrack amount β at a position where an error rate is lowered by a predetermined ratio α between a reference BER and a measurement limit BER in the offtrack curve; And

And determining a TPI suitable for the head according to the value of β.

A computer-readable recording medium according to the present invention for achieving the above another object is

In a computer-readable recording medium in which a program for determining a TPI suitable for a head is recorded.

Performing an ATW (Adjacent Track Write) test while changing the offtrack amount of the head to obtain an offtrack curve showing a change in the error rate according to the offtrack amount;

Calculating a reference BER (BER) which does not change even if the offtrack amount changes in the offtrack curve;

Calculating an offtrack amount β at a position where an error rate is lowered by a predetermined ratio α between a reference BER and a measurement limit BER in the offtrack curve; And

A program including a process of determining a TPI suitable for a head according to the value of β is recorded.

Hereinafter, the configuration and operation of the present invention will be described in detail with reference to the accompanying drawings.

1 is a graph showing the distribution of the magnetic recording width with respect to the head. The graph shown in FIG. 1 shows the results of measuring the magnetic recording width using a Guzik Spinstand apparatus for a plurality of heads. In Fig. 1, the horizontal axis represents the magnetic recording width, and the vertical axis represents the overwrite capacity.

Referring to FIG. 1, it can be seen that the magnetic recording widths of the head are distributed over a wide range around the target magnetic recording width. The reference TPI is determined according to the target magnetic recording width.

Figure 2 shows an example of the TPI-BER curve used in the conventional TPI determination method. 2 shows TPI-BER curves for two different heads f1, f2.

During the manufacturing process of the hard disk drive, a so-called 747 test is performed that performs an Adjacent Track Write (ATW) test while varying the off-track amount, and determines the appropriate TPI for the head based on the result.

Specifically, in the 747 test, a predetermined test pattern is recorded in adjacent tracks adjacent to the target track, the data recorded in the target track is reproduced to measure an error rate, and the ATW test is repeatedly performed while changing the TPI. As a result of the 747 test, a TPI-BER curve as shown in FIG. 2 showing a change in error rate with a change in TPI is obtained. Here, the error rate is measured by a bit error rate (BER). In the measured TPI-BER curve, the TPI corresponding to the predetermined criteria BER is determined as the TPI suitable for the head.

The method of determining TPI using the TPI-BER curve of FIG. 2 is as follows.

Determine the difference OFFt between the TPI corresponding to the criteria BER and the reference TPI in the TPI-BER curve. Here, for example, as described with reference to FIG. 1, the difference between the TPI and the reference TPI at the position where the BER falls below 6.8 is determined as OFFt.

The OFFt determines the appropriate TPI for the head.

For example, an OFFt greater than 4% results in a 100K TPI greater than the reference TPI; an OFFt between 2% and 2% results in a 97K TPI, which is the reference TPI, and a value less than -2% results in a 94K TPI less than the reference TPI. .

However, in the conventional TPI determination method, the optimal TPI could not be determined because it does not reflect that the baseline BER, which is the basis for determining the criteria BER, depends on the performance of the head.

The present invention newly defines a reference BER and proposes a method of determining a TPI suitable for a head based on a ratio between a defined reference BER and a limit BER. Here, the reference BER is defined as BER in a region where the BER does not change even if the TPI changes when the BER is measured while changing the TPI.

3 is a graph for schematically showing a TPI determination method according to the present invention. The graph shown in FIG. 3 shows a change in the error rate of a target track obtained by performing an ATW test while changing the offtrack amount of an adjacent track, and is called an offtrack curve.

In the graph shown in FIG. 3, the vertical axis represents the offtrack amount of the adjacent track, and the vertical axis represents the error rate. A positive value in the off-track amount of the horizontal axis indicates that the off-track amount of the adjacent track increases, that is, the track width of the target track is narrowed or the TPI increases as the adjacent track approaches the target track further. The track's offtrack amount decreases, i.e., the adjacent track is further away from the target track, indicating that the target track becomes wider or the TPI decreases. On the other hand, the error rate of the vertical axis indicates that there is a large number of errors as 0 on the upper side, and that the error is small as a lower side on the lower side.

In the present invention, the reference BER is determined as the BER at the position where the BER does not change despite the change in the off track amount. For example, in FIG. 2, the BER where the offtrack amount is -12% is the reference BER. In practice, the reference BER is defined as the average of the BER in a range in which the off-track amount hardly changes. Referring to FIG. 3, it can be seen that as the TPI decreases, that is, as the track width increases, the error decreases. In addition, the reference BER is determined according to the magnetic recording width of the head.

α is a constant for determining the effective range of BER. For example, if α is 30%, the BER falling from the reference BER by 30% falls within the effective BER range. Thus, the α value is an important parameter for determining the appropriate TPI for the head.

On the other hand, β refers to the off-track amount corresponding to α * reference BER, the TPI is determined by this β.

Referring to FIG. 3, according to the TPI determining method according to the present invention, a TPI suitable for a head is determined by an off-track amount of a position where an error rate is increased by α * reference BER from a reference BER, which is an error rate not affected by an adjacent track. Is determined. Here, since the reference BER is determined according to the performance of the head, according to the TPI determination method according to the present invention it is possible to determine the TPI depending on the head characteristics.

4 shows an offtrack curve for a head having a magnetic recording width that is narrower than the target magnetic recording width, and FIG. 5 shows an offtrack curve for a head having a magnetic recording width that is wider than the target magnetic recording width.

When the offtrack curve is obtained around the reference TPI corresponding to the target magnetic recording width, the head having a magnetic recording width narrower than the target magnetic recording width is insensitive to the change of the offtrack amount, so that the slope of the offtrack curve is small. As a result, the amount of off-track corresponding to α * reference BER is large. That is, it can be seen that the TPI of the head having the magnetic recording width narrower than the target magnetic recording width may be larger than the reference TPI.

On the other hand, a head having a magnetic recording width wider than the target magnetic recording width is sensitive to a change in the offtrack amount, so that the slope of the offtrack curve is large. As a result, the amount of off-track corresponding to α * reference BER is small. In other words, it can be seen that the TPI of a head having a magnetic recording width wider than the target magnetic recording width cannot be made much larger than the reference TPI.

6 is a flowchart illustrating an embodiment of a TPI determination method according to the present invention.

First, the zone and the head are determined (s602).

The offtrack amount is determined (s604). The offtrack amount is changed in a predetermined unit, for example, 2% over a predetermined range, for example, from 12% to 16%. Here, the offtrack amount is calculated based on the track width corresponding to the reference TPI.

The test data is recorded while following the target track N (s606).

By applying the off-track amount determined in step s504, the tracks N + 1 and N-1 adjacent to the target track are DC-deleted M times, for example, 100 times.

Fig. 7 schematically shows the relationship between the offset and the erase position. If the offtrack amount is 0%, DC erases 100 times from the target track N in the radial direction of the disc by a track width corresponding to the reference TPI. If the offtrack amount is 16%, DC erases 100 times from the target track N in the radial direction of the disc by (track width corresponding to the reference TPI minus track width * (16%) corresponding to the reference TPI). If the offset amount is -12%, DC erases 100 times from the target track N in the radial direction of the disc by (track width corresponding to the reference TPI + track width * (12%) corresponding to the reference TPI). do.

In other words, as the offtrack amount increases to +, the positions close to the target track N are DC erased, so that the TPI increases and the adjacent track effect increases, so that the error rate of the test data read from the target track N increases. On the contrary, as the offtrack amount becomes-, positions far from the target track N are DC erased, so that the TPI is smaller and the adjacent track effect is smaller, so that the error rate of the test data read from the target track N is reduced.

The test data recorded in the target track N is read out a predetermined number of times, for example, 100 times (s610). At this time, the condition for reading the data recorded in the target track N is that there is no ECC correction and no retry. . That is, the test data recorded in the target track N is read as it is once (without retry) and without error correction.

The number of errors generated in the test data read from the target track N is counted. (S612) BER or CSM (Channel Statistical Measurement) corresponding to the counted error number is calculated. (S614) In the embodiment of the present invention, BER is used, but CSM or bit error number can be used. Here, the CSM is one of the indicators indicating the error rate generated from the data read from the disk. The CSM checks the bit error provided by the channel chip, which has an advantage of shortening the measurement time compared to the bit error rate (BER). . CSM and BER have a logarithmic relationship.

As a result of step s614, the BER corresponding to the off-track amount determined in step s604 is obtained.

It is determined whether the measurement is in the final stage (s616). That is, it is determined whether the measurement is performed while changing the off-track amount to the final stage of 16%. If it is not the measurement of the last step in step S616, the process from step s604 to s614 is repeated.

As a result of the processes S604 to S616, an off-track curve as shown in FIGS. 3 to 5 is obtained.

A reference BER is calculated (s618). In the exemplary embodiment of the present invention, the reference BER is determined as an average of BERs when the offtrack amount is 10% and 12%. Since the reference BER should be a value irrespective of the off track amount or the TPI, it is preferable to determine the BER that does not change despite the change in the off track amount. However, if the offtrack amount is increased without limit, it is beyond the purpose of determining the appropriate TPI for the head in consideration of the adjacent track effect, and the offtrack variation applied to prepare the offtrack curve should also be considered. The average value is applied where the track hardly changes, that is, in the range where the offtrack is 10% to 12% when referring to FIGS.

The off-track amount corresponding to the position where the error rate decreases by α * reference BER between the reference BER and the measurement limit BER calculated in S614 is calculated, i.e. (s620).

The TPI suitable for the head is determined according to the value of β (s622).

8 shows TPI values according to the value of β. It can be seen that the larger the value of β, that is, the narrower the magnetic recording width, the higher the TPI is assigned, and the smaller the value of the β, the larger the magnetic recording width, the lower the TPI is assigned. Here, the values of -12% and 16% refer to a range in which the reference BER is not saturated, and thus, a range of TPI that can satisfy a desired capacity. These values can vary depending on the model and the environment of each drive.

9 is a diagram illustrating a configuration of a hard disk drive to which the present invention is applied.

Hard disk drive 100 includes at least one disk 112 that is rotated by spindle motor 114. The hard disk drive 100 also includes a head 120 positioned adjacent to the surface of the disk 112.

The head 120 may read or write information from the rotating disk 112 by sensing a magnetic field formed on the surface of the disk 112 or by magnetizing the surface of the disk. Although shown as a single head in FIG. 6, it should be understood that it consists of a recording head for magnetizing the disc 112 and a separate reading head for sensing the magnetic field of the disc 112.

The head 120 is configured to create an air bearing between the head and the surface of the disk 112. Head 120 is coupled to a head stack assembly (HSA) 122. Head stack assembly 122 is attached to actuator arm 124 having voice coil 126. The voice coil 126 is located adjacent to the magnetic assembly 128 that specifies (supports) the voice coil motor 130 (VCM). The current supplied to the voice coil 126 generates a torque to rotate the actuator arm 124 relative to the bearing assembly 132. Rotation of the actuator arm 124 will move the head across the surface of the disk 112.

The information is stored in the annular track of the disc 112. In general, the disk 112 is composed of a data zone in which user data is recorded, a parking zone in which the head is located when the drive is not used, and a maintenance cylinder.

FIG. 10 shows a block diagram of the controller 140 controlling the hard disk drive 100 shown in FIG. 9.

The controller 140 includes a controller 141 coupled to the head 120 by a read / write (R / W) channel circuit 145 and a read preamp & write driver circuit 46. The controller 141 may be a digital signal processor (DSP), a microprocessor, a microcontroller, or the like.

The controller 141 supplies a control signal to the read / write channel 145 to read data from the disk 112 or to write data to the disk 112.

Information is typically sent from the R / W channel 145 to the host interface circuit 147. The host interface circuit 147 includes control circuitry that allows the disk drive to interface to a system such as a personal computer.

The R / W channel circuit 145 modulates the analog signal read from the head 120 in the regeneration mode and amplified by the read preamplifier circuit 146 into a digital signal that can be read by a host computer (not shown). Outputs to the interface circuit 147, and converts the user data from the host computer through the host interface circuit 147 into a write current so that the data can be written to the disk and output to the write driver circuit 416. Run

The controller 141 is also coupled to the VCM drive circuit 148 which supplies a drive current to the voice coil 126. The controller 141 supplies a control signal to the driving circuit 148 to control the excitation and movement of the head of the VCM.

The controller 141 is coupled to a nonvolatile memory and a random access memory (RAM) element 142-3, such as a read only memory (ROM) or flash memory element 142-1. . The memory elements 142-1 and 142-3 contain instructions and data used by the controller 141 to execute software routines.

One of the software routines is a seek routine for moving the head from one track to another and a following routine for finding a target sector within the track. The seek routine includes a servo control routine to ensure that the head is moved to the correct track.

In addition, the memory elements 142-1 and 142-3 store programs for determining a TPI suitable for the head. The buffer memory 143 stores the data to be recorded in the first buffer memory 143-1 when a recording command from the host computer is issued. The second buffer memory 143-3 is a place for temporarily storing data reproduced from the disc 112.

Referring to the operation of determining the TPI suitable for the head according to the present invention.

First, the controller 141 controls the head 120 to follow the target track. When the head follows the target track, the controller 141 writes predetermined test data on the target track and DC erases adjacent tracks. The error rate is measured by reading the data recorded in the target track. The controller 141 performs the above-described ATW test while changing the offtrack amount to obtain an offtrack curve.

The controller 141 determines the reference BER and β from the obtained off-track curve, and determines the TPI according to the value of β with reference to FIG. 8.

As described above, the TPI determination method of the hard disk drive according to the present invention has an effect that the TPI can be appropriately determined according to the variation of the head magnetic recording width.

Claims (4)

Performing an ATW (Adjacent Track Write) test while changing an off track amount of an adjacent track to obtain an off track curve showing a change in an error rate according to the off track amount; Calculating a reference BER (BER) which does not change even if the offtrack amount changes in the offtrack curve; Calculating an offtrack amount β at a position where an error rate decreases by a predetermined ratio α between a reference BER and a measurement limit BER in the offtrack curve; And And determining a TPI suitable for a head according to the value of β. The method of claim 1, wherein the ATW test Recording predetermined test data on a target track; DC-tracking tracks adjacent to the target track by a given off-track amount and DC erasing a predetermined number of times; And And reading out the test data recorded in the target track without error correction and counting the number of errors. The method of claim 2, wherein the ATW test reads test data recorded on a target track without error correction and retry to count the number of errors. In a recording medium that can be read by a computer on which a program for determining a track per inch (TPI) suitable for a head is recorded, Performing an ATW (Adjacent Track Write) test while changing an off track amount of an adjacent track to obtain an off track curve showing a change in an error rate according to the off track amount; Calculating a reference BER (BER) which does not change even if the offtrack amount changes in the offtrack curve; Calculating an offtrack amount β at a position where an error rate is lowered by a predetermined ratio α between a reference BER and a measurement limit BER in the offtrack curve; And A recording medium having a program recorded thereon, the method including determining a TPI suitable for a head according to the value of β;

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