KR100604927B1 - Method for determinging TPITrack Per Inch of harddisk drive and recording medium adapted 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.

TPI determination method of the hard disk drive according to the present invention comprises the steps of performing an ATW (Adjacent Track Write) test while changing the TPI to a predetermined write frequency to measure the change in the error rate according to the change in the TPI; Obtaining a plurality of TPI-BER curves by performing a plurality of times of measuring a change of a bit error rate (BER) according to the change of the TPI while changing the recording frequency; And obtaining a mean or worst TPI-BER curve among the plurality of TPI-BER curves, determining a difference (OFFt) between the TPI corresponding to the critical BER and the reference TPI in the obtained TPI-BER curve, and determining the determined difference (OFFt). And determining the TPI obtained by adjusting the reference TPI as a TPI suitable for the head.

The method of determining the TPI of a hard disk drive according to the present invention determines an appropriate TPI by considering not only the TPI but also the frequency of recording data, thereby increasing the reliability of the hard disk drive and reducing the process defect.

Description

Method for determinging TPI (Track Per Inch) of harddisk drive and recording medium adapted therefor}

Figure 1 shows a characteristic (TPI-BER) curve showing the change of BER with the change of TPI.

2 is a graph showing appropriate recording parameters according to zones.

3 is a graph showing the change of the error rate according to the zone.

4 is a flowchart showing a conventional TPI determination method.

5 is a flowchart showing an embodiment of a TPI determination method according to the present invention.

FIG. 6 shows examples of TPI-BER curves obtained as a result of the process s508 shown in FIG. 5.

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

FIG. 8 shows a block diagram of the controller 140 for controlling the hard disk drive 100 shown in FIG. 7.

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.

The manufacturing process of the hard disk drive includes the so-called 747 test, which performs an Adjacent Track Write (ATW) test while changing the track per inch (TPI), 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 performed while changing the TPI. As a result of the 747 test, a TPI-BER curve is obtained which shows the change of the error rate with the change of TPI. 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. This 747 test is based on the characteristic that the recording heads have different track widths that can effectively record data without affecting adjacent tracks.

Figure 1 shows a characteristic (TPI-BER) curve showing the change of BER with the change of TPI. In Fig. 1, the horizontal axis shows the TPI, and the vertical axis shows the error rate. Here, the change in the TPI is indicated by changing the degree of overlap with the target track in recording data on adjacent tracks. Specifically, in FIG. 1, where the TPI is 0, the data is recorded at a distance from the target track by the reference TPI in performing the ATW test, and the location where the TPI is 2 is 2% smaller than the reference TPI from the target track. In other words, recording data at a position further away from the reference TPI, where TPI is 2 means recording data at a position 2% larger than the reference TPI from the target track, that is, less than the reference TPI. The larger the TPI, the smaller the track width.

The error rate on the vertical axis is expressed as a logarithmic function.

Referring to the result shown in FIG. 1, the TPI suitable for the head is determined as a reference BER, that is, a TPI at a position falling below 85% (criteria BER) from the BER corresponding to the reference TPI. For example, if the reference BER is 8, the TPI at the position where the BER falls below 6.8 in the TPI-BER curve is selected as the appropriate TPI for the head. Applying this, a TPI that is 4% larger than the reference TPI is determined to be a suitable TPI for the head.

As can be seen with reference to Figure 1, the conventional TPI determination method for the head uses a method of measuring the error rate (BER) while changing the TPI. However, not only the track width but also the position on the disc and the frequency of data to be recorded affect the error rate.

2 is a graph showing appropriate recording parameters according to zones. Figure 2 shows the measurement results for the two samples. In Fig. 2, the horizontal axis represents the zone and the vertical axis represents the value of the recording parameter. In Fig. 2, the lower thick straight line shows the limit of the recording parameter. The limit value of the recording parameter represents a value that can generate an ATW above the allowable value.

Referring to FIG. 2, the sample # 1 has the proper recording parameter closer to the limit of the recording parameter in all zones than the sample # 2, and even lower than the limit of the recording parameter in some zones of the outer periphery as in section A. Located in That is, the sample # 1 has a smaller margin of ATW than the sample # 2, and is treated as defective due to the characteristics of the A portion.

3 is a graph showing the change of the error rate according to the zone. The graph shown in FIG. 3 shows the result of measuring the error rate (BER) according to each zone when the ATW test is performed with the same recording parameters. Referring to FIG. 3, it can be seen that the BER falls below the allowable value (bold straight line in FIG. 3) in some zones of the inner circumference. The reason why the BER falls below the allowable value in some zones is not because of the recording parameter but because of poor STW (Servo Track Write) in the zone or the frequency characteristic of the head. Although the TPI applied to a head in a hard disk drive is constant, the frequency of recording data, that is, the linear density, differs for each zone in a disk corresponding to the head. Referring to FIG. 3, in some zones on the inner circumferential side, an error below the allowable value occurs when data is recorded by the frequency assigned to the zone, which is treated as a defect.

Accordingly, it can be seen that the frequency of the recording data needs to be taken into account in setting the TPI suitable for the head.

Referring to FIG. 1, it can be seen that the BER changes greatly around the criteria BER in the ATE heads. The characteristics of the ATE heads can vary greatly depending on the position of the disk, the frequency characteristics of the head, and environmental changes. Indicates. Therefore, it can be seen that a TPI suitable for the head needs to be set in consideration of the position on the disk, the frequency characteristic of the head, and the environmental change.

The magnetic properties of the disks vary with environmental changes, such as temperature changes and the passage of time, and if these changes do not match the characteristics of the head, it can lead to poor reliability and poor process.

In the prior art, the method of determining the TPI suitable for the head depends only on the change in the BER according to the change in the TPI, and thus there is a problem in that it does not reflect the change in the BER due to the position on the disk, the frequency characteristic of the head, and the temperature change. . Accordingly, there is a potential risk that the BER may be greatly increased due to the position on the disk, the frequency characteristic of the head, environmental changes, and the like, thereby lowering the reliability.

It is an object of the present invention to provide a method for determining a TPI suitable for a head in consideration of the frequency characteristic of the head.

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 a ATW test while changing the TPI at a predetermined recording frequency to measure a change in the error rate according to the change in the TPI;

Performing a process of measuring a change of an error rate according to a change of the TPI while changing the recording frequency a plurality of times; And

And determining a TPI suitable for the head with reference to the measurement results performed the plurality of times.

Herein, in determining a TPI suitable for the head, it is preferable to refer to an average or worst result of the plurality of measurement results.

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

A computer-readable recording medium having recorded thereon a program for determining a TPI suitable for a head, comprising:

Performing a ATW test while changing the TPI at a predetermined recording frequency to measure a change in the error rate according to the change in the TPI;

Performing a plurality of steps of measuring a change in an error rate according to a change in the TPI while changing the recording frequency; And

A program including a process of determining a TPI suitable for a head is recorded by referring to the measurement results performed a plurality of times.

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

The burn-in test process of a hard disk drive includes a process of recording data while varying the TPI to set a track pitch suitable for each head, and measuring an error rate while reproducing the recorded data.

4 is a flowchart showing a conventional TPI determination method.

First, a TPI-BER curve having data having a predetermined frequency and showing a change in error rate according to a change in TPI is obtained (s402).

In the TPI-BER curve, the difference OFFt between the TPI corresponding to the criteria BER and the reference TPI is determined (s404). For example, as described with reference to FIG. 1, the difference between the TPI and 0 where the BER falls below 6.8 is determined. Is determined to be OFFt.

Determine the TPI suitable for the head according to the OFFt (s406).

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. .

Referring to FIG. 4, since the conventional method relies only on the change in the BER according to the change in the TPI in determining the TPI suitable for the head, the change in the BER according to the frequency characteristic of the head is not reflected.

5 is a flowchart showing an embodiment of a TPI determination method according to the present invention.

Initialize index N (s502).

First, a characteristic curve showing the change in the error rate according to the change in the TPI with data having a predetermined frequency is obtained (s504).

The TPI-BER curve as shown in FIG. 1 is obtained by measuring the error rate while varying the offtrack amount of the adjacent track based on the track width corresponding to the specifically set reference TPI. The error rate is measured by recording predetermined test data N times in the target track and both tracks adjacent to the target track and reading the data recorded in the target track N times. Here, the recording parameters are the same regardless of the change in the TPI, and the basic TPI is a value set by testing the representative normal heads. Here, the recording frequency is determined according to the index N.

On the other hand, changing the offtrack amount is achieved by adjusting the offset of the head from the center of the adjacent track. As the TPI increases to +, data is recorded at a position closer to the target track (N), so the adjacent track effect is increased. On the contrary, as the TPI increases to-, data is recorded at a position farther from the target track (N). Becomes smaller.

The index N is increased by 1 (s506). It is determined whether the index N is the maximum value Nmax. (S508) If the index N is smaller than the maximum value Nmax in step s508, the process proceeds to step s504. Otherwise, the process goes to step s510. Proceed.

That is, a process (s504) of obtaining a characteristic curve showing a change in error rate according to the change in TPI with data having a predetermined frequency is performed by Nmax times.

As a result of S508, Nmax TPI-BER curves are obtained.

Average the Nmax TPI-BER curves or select the worst characteristic curve (s510).

TPI and criterion corresponding to criteria BER in the TPI-BER curve obtained by S510 process, that is, the TPI-BER curve obtained by averaging Nmax TPI-BER curves or the TPI-BER curve having the worst characteristic among Nmax TPI-BER curves. The difference OFFt of the TPI is determined (s514). For example, as described with reference to FIG. 1, the difference between the TPI and 0 at the position where the BER falls below 6.8 is determined as OFFt.

Determine the TPI suitable for the head according to the OFFt (s514).

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. .

FIG. 6 shows examples of TPI-BER curves obtained as a result of the process s508 shown in FIG. 5. The TPI-BER curves shown in FIG. 6 show the result of performing a 747 test on various heads H1 to H4 with recording data having the same frequency. Referring to FIG. 6, it can be seen that TPI-BER characteristics are exhibited as the heads are different even though the recording frequencies are the same. This proves that even in the same head, different TPI-BER characteristics may be shown due to different recording frequencies.

Referring to FIG. 6, it can be seen that the slope of the TPI-BER curve for the H2 head is sharp while the slope of the TPI-BER curve for the H1 head is gentle. This indicates that the H1 head is a head with high WW (Weak Write) tendency, and the H2 head is a head with a high ATW tendency.

If the recording frequency is changed, the slope of the TPI-BER curve for the H1 head becomes smoother, and the slope of the TPI-BER curve for the H2 head becomes more sharp. This indicates that even if a TPI is set for the head based on the measurement results for a certain recording frequency, this TPI is not appropriate for other recording frequencies.

In the present invention, the TPI suitable for the head is determined by the TPI-BER curve having poor or average characteristics of the two TPI-BER curves. Therefore, the reliability of the hard disk drive is increased and the process defects are reduced.

7 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. 8 shows a block diagram of the controller 140 for controlling the hard disk drive 100 shown in FIG. 7.

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 invention as follows.

First, the controller 141 controls the head 120 to follow the target track. When the head follows the target track, the controller 141 records the data on the target track at a predetermined recording frequency, and also records the data on 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 TPI to obtain a TPI-BER curve. Here, changing the TPI is accomplished by controlling the offset of the head 120 when writing data to adjacent tracks. For example, the width at which the target track and the adjacent track overlap is controlled by controlling the offset of the head 120 when recording to the adjacent track.

The controller 141 repeats the above operation for Nmax times while changing the recording frequency to obtain Nmax TPI-BER curves. The controller 141 selects the averaged or worst-case Nmax TPI-BER curves obtained.

The controller 141 determines the TPI suitable for the head from the obtained TPI-BER curve as described with reference to FIG. 6.

As described above, the method of determining the TPI of the hard disk drive according to the present invention determines the TPI suitable for the head in consideration of the track width as well as the frequency of the recording data, thereby increasing the reliability of the hard disk drive and reducing the process defect. .

Claims (3)

Measuring a change in error rate according to a change in the TPI by performing an ATW (Adjacent Track Write) test while changing the TPI at a predetermined recording frequency; Obtaining a plurality of TPI-BER curves by performing a plurality of times of measuring a change of a bit error rate (BER) according to the change of the TPI while changing the recording frequency; And Obtain the average or worst TPI-BER curve among the plurality of TPI-BER curves, determine the difference (OFFt) between the TPI corresponding to the critical BER and the reference TPI in the obtained TPI-BER curve, and determine the determined difference (OFFt). Determining the TPI obtained by adjusting the reference TPI as much as the TPI suitable for the head. delete A computer-readable recording medium having recorded thereon a program for determining a TPI suitable for a head, comprising: Performing a ATW test while changing the TPI at a predetermined recording frequency to measure a change in the error rate according to the change in the TPI; Obtaining a plurality of TPI-BER curves by performing a plurality of times of measuring a change of an error rate (BER) according to the change of the TPI while changing the recording frequency; And Obtain the average or worst TPI-BER curve among the plurality of TPI-BER curves, determine the difference (OFFt) between the TPI corresponding to the critical BER and the reference TPI in the obtained TPI-BER curve, and determine the determined difference (OFFt). A recording medium recording a program comprising the step of determining the TPI obtained by adjusting the reference TPI as much as the TPI suitable for the head;

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