JP2011108324A - Method for evaluating characteristics of magnetic recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of evaluating nonlinear distortion by separating it into nonlinear transition shift and partial erasure without causing deterioration of measurement precision, even if the nonlinear transition shift becomes not negligible to a bit gap T. <P>SOLUTION: A plurality of bit patterns are recorded on a magnetic recording medium. A first bit pattern is of 42 bits length and has an isolated bit for each 21 bits. A second one is 42 bits length and has dibits at the head and an isolated bit for each of 10th bit, 17th bit, 20th bit, 25th bit, 29th bit and 34th bit. The other bit pattern is a pattern wherein phases of isolated bits of the 10th bit and the 25th bit of the second bit pattern is shifted as much as prescribed amount. The nonlinear transition shift and the partial erasure are computed by obtaining the seventh harmonic component of reproduced waveforms of each bit pattern, respectively. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for evaluating characteristics of a magnetic recording medium, and in particular, quantitatively analyzes non-linear distortion such as non-linear transition shift and partial erasure of a recording signal caused by adjacent recording of bits in high-density recording. On how to evaluate. The characteristic evaluation method of the present invention can be used for characteristic evaluation of a magnetic recording medium that performs magnetic recording, such as a magnetic disk medium or a magnetic tape for a fixed magnetic recording apparatus.

  In the current read channel signal processing of magnetic recording apparatuses, the PRML (Partial Response Maximum Likelihood) method is the mainstream instead of the conventional peak detection method. When the bit interval is narrowed due to an increase in the linear recording density, the peak detection method significantly reduces the bit detection performance due to waveform interference. However, the PRML method performs detection based on waveform interference, and therefore reduces performance degradation. be able to.

  However, when the bit interval is narrowed, nonlinear distortion due to the influence of adjacent bits also increases. In these nonlinear distortions, the transition position of the magnetization shifts back and forth with respect to the position where it should be originally formed, and the amplitude of the reproduced pulse waveform is larger than when the solitary wave is linearly superimposed. There is a partial erasure that decreases, but these all decrease the detection performance of the PRML system and cause the error rate to deteriorate. Therefore, in a magnetic recording apparatus, in order to reduce these nonlinear distortions as much as possible, it is general to estimate the amount of nonlinear distortion by some means and perform pre-compensation according to the estimated value.

  On the other hand, with the progress of higher recording density of magnetic recording, the importance of nonlinear distortion evaluation is increasing in the evaluation of magnetic recording media and magnetic recording heads, and more accurate and more efficient measurement methods. Is required.

  As a method for measuring nonlinear distortion of a magnetic recording medium, for example, there is a method using the periodicity of a pseudo random signal. This method utilizes the fact that when a pseudo-random signal is recorded, if there is a non-linear transition shift, an echo of the pseudo-random signal having a magnitude corresponding to the non-linear transition shift amount appears at a specific position of the read waveform. Among this type of measurement method, for example, the method disclosed in Non-Patent Document 1 obtains a dipulse response waveform by deconvolution of a reproduced waveform of a pseudo-random signal and a recording bit sequence, and echoes from this dipulse response waveform. Taking out the pulse.

  Another method called harmonic elimination method is that when a specific bit pattern is recorded and reproduced, if there is no nonlinear transition shift, the specific odd-order harmonic component becomes zero, and if there is a nonlinear transition shift, This utilizes the fact that odd harmonic components appear in proportion to the quantity.

  For example, the method disclosed in Non-Patent Document 2 is also a kind of this harmonic elimination method. The method discloses a generalized method of constructing a bit pattern that removes odd harmonics. The basis of this construction method is the following principle.

The fundamental frequency of a signal in which the pulse waveforms A and A ′ having the same polarity separated by the time interval qT repeat with a period NT is f ₀ = 1 / NT, and the voltage of the k-order harmonic is expressed as shown in Equation (1). Is done.

ここで、ｑは整数、Ｔはビット間隔、Ｎは整数、Ｐ（ｋｆ₀）は孤立波のフーリエ変換である。従って、パルス波形Ａ、Ａ’の時間間隔ｑＴのｑが式（２）の関係を満たす場合にｋ次高調波はゼロとなる。

Here, q is an integer, T is a bit interval, N is an integer, and P (kf ₀ ) is a Fourier transform of the solitary wave. Therefore, when the q of the time interval qT between the pulse waveforms A and A ′ satisfies the relationship of the expression (2), the k-order harmonic becomes zero.

ここで、ｍは整数である。今、パルス波形Ａ、Ａ’と反対極性のパルス波形Ｂ、Ｂ’の時間間隔ｑ’Ｔ（ｑ≠ｑ’）も上記関係を満足するとした場合、パルス波形Ａ、Ａ’とＢ、Ｂ’を重ね合わせた波形のｋ次高調波もゼロとなる。
従って例えば以下に示す３０ビットのパターン（ＮＲＺＩ表記である。）は、１ビット目と１０ビット目の間隔が９Ｔ、２ビット目と１７ビット目の間隔が１５Ｔであり、ｋ＝５とした場合、それぞれの間隔が上記条件を満足するので、その再生波形の５次高調波成分はゼロとなる。

110000000100000010000000000000

しかし非線形歪みがある場合は、５次高調波成分ははゼロにはならない。もし２ビット目が非線形遷移シフトによりΔだけ前方にシフトしたとすると、５次高調波電圧はΔがＴに対して極めて小さい場合は、近似的に式（３）のように表される。

Here, m is an integer. If the time interval q′T (q ≠ q ′) of the pulse waveforms B and B ′ having the opposite polarity to the pulse waveforms A and A ′ also satisfies the above relationship, the pulse waveforms A and A ′ and B and B ′ The k-order harmonics of the waveform obtained by superimposing are also zero.
Therefore, for example, in the following 30-bit pattern (in NRZI notation), the interval between the 1st and 10th bits is 9T, the interval between the 2nd and 17th bits is 15T, and k = 5 Since each interval satisfies the above condition, the fifth harmonic component of the reproduced waveform becomes zero.

110000000100000010000000000000

However, when there is nonlinear distortion, the fifth harmonic component does not become zero. If the second bit is shifted forward by Δ due to non-linear transition shift, the fifth-order harmonic voltage is approximately expressed as equation (3) when Δ is very small with respect to T.

ここでＰ（５ｆ₀）は、１５Ｔの孤立波パターンの再生信号の周波数スペクトラムから求めることができる。そのため５次高調波を測定することにより、非線形遷移シフトΔを求めることが出来る。

Here, P (5f ₀ ) can be obtained from the frequency spectrum of the reproduced signal of the 15T solitary wave pattern. Therefore, the nonlinear transition shift Δ can be obtained by measuring the fifth harmonic.

  However, none of the above methods can separate nonlinear transition shift and partial erasure. If there was a partial erasure, there was a problem that the amount of non-linear transition shift was estimated larger than the actual amount. Further, since the above harmonic elimination method assumes that the nonlinear transition shift is sufficiently smaller than the bit interval T, there is a problem that measurement error increases when this assumption is not satisfied.

  As a method of measuring the nonlinear transition shift and the partial erasure separately, for example, Non-Patent Document 3 first determines a partial erasure using a square wave signal that is not affected by the nonlinear transition shift, A method for obtaining a total nonlinear distortion by removing harmonics and obtaining a nonlinear transition shift amount from these results is disclosed. However, since this method also assumed that the nonlinear transition shift was sufficiently smaller than the bit interval T, there was a similar problem.

  As another method, Patent Document 1 discloses that a 30-bit measurement pattern including a dibit and an isolated bit performs pre-compensation on the bit interval of the dibit, and a fifth order with a reference pattern including only the isolated bit. The partial erasure is obtained from the compensation amount that minimizes the harmonic ratio, and further, the nonlinear transition shift amount is obtained using a predetermined expression that relates the fifth harmonic ratio, the partial erasure, and the nonlinear transition shift. A method is disclosed. However, this method requires pre-compensation means for continuously changing the interval between dibits, and such hardware has a complicated structure and requires high accuracy, so that it has not been easy to implement.

Japanese Patent Laid-Open No. 10-269511

IEEE Transactions on Magnetics, September 1987, Vol. MAG-23, no. 5, p. 2377-2379 IEEE Transactions on Magnetics, November 1994, Vol. 30, no. 6, p. 4236-4238, IEEE Transactions on Magnetics, November 1995, Vol. 31, no. 6). p. 3021-3026

  As described above, the conventional nonlinear distortion measurement method cannot measure the nonlinear transition shift and the partial erasure separately, or even if it can, the nonlinear transition shift is sufficiently smaller than the bit interval T. There is a problem that implementation is not easy because conditions are required, or complicated and highly accurate hardware is required.

  The present invention has been made in view of the above-described problems, and its object is to achieve non-linear transition of non-linear distortion without deteriorating measurement accuracy even when non-linear transition shift cannot be ignored with respect to the bit interval T. It is an object of the present invention to provide a method for evaluating the characteristics of a magnetic recording medium that can be separately evaluated for shift and partial erasure and can be implemented relatively easily.

  In order to achieve the above object, a method for evaluating characteristics of a magnetic recording medium according to the present invention records a plurality of bit patterns on a magnetic recording medium using a magnetic recording head and reads out the bit patterns to evaluate the characteristics of the magnetic recording medium. In the method, the plurality of bit patterns include a first bit pattern having a 42-bit length having an isolated bit every 21 bits, a dibit at the beginning, a 10th bit, a 17th bit, a 20th bit, a 25th bit, A second bit pattern having a 42-bit length having an isolated bit at each of the bit and the 34th bit, and the phases of the 10th and 25th isolated bits of the second bit pattern, respectively. A plurality of other bit patterns shifted by a predetermined amount are included, and a seventh-order harmonic component of the reproduced waveform of each bit pattern is obtained to obtain a nonlinear transition shift and a pattern. And calculates the Sharuireja respectively.

  The other bit patterns are third to fifth bit patterns, and the third bit pattern is obtained by advancing the phase of the 10th isolated bit of the second bit pattern by the predetermined amount B. The fourth bit pattern is a pattern obtained by delaying the phase of the 25th isolated bit of the second bit pattern by the predetermined amount B, and the fifth bit pattern is the second bit pattern. A pattern in which the phase of the 10th isolated bit of the pattern is advanced by a predetermined amount B, and the phase of the isolated bit of the 25th bit is delayed by the predetermined amount B, and the first to fifth bit patterns are reproduced. It is preferable to calculate the nonlinear transition shift and the partial erasure by obtaining the seventh harmonic component of the waveform.

  Alternatively, the other bit patterns are third to fifth bit patterns, and the third bit pattern delays the phase of the 10th isolated bit of the second bit pattern by a predetermined amount B. The fourth bit pattern is a pattern obtained by advancing the phase of the 25th isolated bit of the second bit pattern by the predetermined amount B, and the fifth bit pattern is the second bit pattern. This is a pattern in which the phase of the 10th isolated bit of the bit pattern is delayed by a predetermined amount B and the phase of the 25th isolated bit is advanced by the predetermined amount B, and the first to fifth bit patterns It is preferable to calculate the nonlinear transition shift and the partial erasure by obtaining the seventh harmonic component of the reproduced waveform.

  More preferably, a nonlinear transition shift and a partial gain are obtained by using a value obtained by dividing the seventh harmonic component of the second to fifth bit patterns by half the value of the seventh harmonic component of the first bit pattern. It is to calculate the rager.

  According to the characteristic evaluation method of the magnetic recording medium of the present invention, the seventh harmonic component becomes zero when there is no nonlinear distortion, and the seventh harmonic component according to the amount appears when there is nonlinear distortion. . Since the second pattern of the basic period 42T and the first pattern whose magnetization is reversed every 21T are used, and the phase compensation of predetermined bits of the second pattern is performed, the seventh order of the reproduced waveform of these patterns is performed. By measuring the harmonic component, the nonlinear transition shift and the partial erasure can be separated and measured.

  In addition, since it is not assumed that the nonlinear transition shift is sufficiently small with respect to the bit interval T, the measurement accuracy does not deteriorate even when the nonlinear transition shift cannot be ignored as compared with the bit interval T. The phase compensation amount may be a fixed value and does not require a mechanism for continuously changing. Therefore, there is no addition of complicated and highly accurate hardware, and it can be implemented relatively easily.

It is a block diagram which shows the structural example of the characteristic evaluation apparatus of the magnetic-recording medium for performing the characteristic evaluation of this invention. It is the flowchart which showed the example of the procedure of the characteristic evaluation method of the magnetic recording medium of this invention. It is a schematic diagram which shows the example of the reproduction waveform of the 2nd bit pattern used by this invention. It is a chart figure which shows the example of the recording current signal produced with the write amplifier 104 used by this invention. It is a schematic diagram which shows the example of the reproduction | regeneration waveform of the 1st bit pattern used by this invention.

Embodiments of a magnetic recording head characteristic evaluation method of the present invention will be described below with reference to the drawings.
FIG. 1 is a block diagram showing a schematic configuration of a characteristic evaluation apparatus 100 for carrying out a magnetic recording medium characteristic evaluation method according to the present invention. This characteristic evaluation apparatus 100 is configured as follows in order to evaluate the characteristic of a magnetic recording medium to be evaluated. That is, a data generator 103 that generates a predetermined data pattern, a write amplifier 104 that supplies a recording current corresponding to the data pattern to the magnetic recording head 101, and a predetermined track of the rotating magnetic recording medium 102 A magnetic recording head 101 for recording and reproducing, a read amplifier 105 for amplifying the read reproduction signal, a waveform measurement (Wave-Profile Measuring) unit 106 for measuring the amplified signal waveform, and An evaluation unit 108 is provided. The waveform measuring unit 106 measures the observed waveform, and measures and outputs a value as described later. The evaluation unit 108 inputs each measurement value, and finally calculates a nonlinear transition shift and a partial erasure based on each measurement value.

  Although details of the magnetic recording head 101 are not shown in FIG. 1, the recording element has a single-pole head that generates a magnetic field in the direction perpendicular to the recording surface or a ring head that generates a magnetic field in the in-plane direction. In addition, a giant magnetoresistive (GMR) element or a tunneling magnetoresistive (TMR) element is used as a reproducing element. As the magnetic recording medium 102, a perpendicular recording medium in which the magnetic anisotropy of the magnetic film is adjusted to be perpendicular to the recording surface or a longitudinal recording medium in which the in-plane direction is adjusted can be used.

  Further, as shown in the figure, this characteristic evaluation apparatus 100 further includes an oscilloscope 107 for the observer to visually observe the reproduced waveform in response to the signal from the waveform measuring unit 106, the calculated nonlinear transition shift and partial erase. A display 109 for displaying the J value, a disk drive unit 110, a control unit 111 for controlling the entire characteristic evaluation apparatus 100, and the like. Here, the oscilloscope 107 can be externally connected. The characteristic evaluation apparatus 100 can be connected to a PC (personal computer) 120 that stores measurement results including the calculated nonlinear transition shift and partial erasure. The control unit 111 can have a basic computer configuration including a microprocessor, a memory, an input / output interface, and the like. Although not shown in FIG. 1, the characteristic evaluation apparatus 100 includes an input / output user interface that is normally provided in the apparatus.

  Even in a configuration different from the configuration of FIG. 1 described above, a similar function can be provided. For example, the waveform measurement unit 106, the oscilloscope 107, and the evaluation unit 108 calculate a target measurement value by inputting data from the general-purpose waveform measurement device (Wave-Profile Measuring Machine) and the waveform measurement device. It is also possible to adopt a configuration including a non-linear transition shift from the measured values and a PC on which a shift program for calculating a partial erasure is mounted. In the case of this configuration, the functions of the display 109 and the PC 120 are also included. When such a PC connects the control unit 111 as an external device, the PC manages the procedure according to the present invention and controls the control unit 111. At the same time, a part of the procedure is directly executed. It becomes possible.

In the following, the characteristic evaluation method will be described based on the configuration of FIG. 1, but basic operations excluding detailed operations can be executed in the same manner with the other configurations described above.
The control unit 111 controls each component in the characteristic evaluation apparatus 100 by the program code built in the internal memory according to the setting and start instruction from the user, and finally executes the method of the present invention. The execution result is displayed on the display 109 and / or output to the PC 120.

  FIG. 2 is a flowchart showing an example of a procedure for carrying out the characteristic evaluation method according to the present invention, which will be described in detail below with reference to FIG. In this description, the case where the phase of the 10th bit of the second bit pattern is advanced by a predetermined amount B and the phase of the 25th bit is delayed by a predetermined amount B is taken as an example.

  First, in step 200, an operation of AC demagnetizing a measurement track (not shown) provided on the magnetic recording medium 102 by the magnetic recording head 101 is executed. Here, the purpose of AC demagnetization is to reduce the influence of nonlinear effects during writing due to the measurement track being magnetized in one direction.

Next, in step 201, first, the data generator 103 generates a second bit pattern at a bit interval T. Here, when the second bit pattern is represented by NRZI, it has an isolated bit at the beginning of each of the dibit, the 10th bit, the 17th bit, the 20th bit, the 25th bit, the 29th bit, and the 34th bit. The pattern shown next in the basic period 42T is a repeated pattern.

11000000010000001001000010001000100000000

Here, this pattern has bit intervals so that the 1st bit, 10th bit, 2nd bit and 17th bit, 20th bit and 29th bit, 25th bit and 34th bit respectively remove the 7th harmonic. And the polarity is set. Therefore, when there is no nonlinear distortion, the 7th harmonic of the reproduction signal of this pattern is zero.

This pattern is converted into a recording current signal by the write amplifier 104. FIG. 4 is a chart schematically showing an example of the recording current waveform, where the horizontal axis is the time axis, and 300 to 303 show the waveforms of four types of recording current signals. A recording current signal corresponding to the second bit pattern is indicated by 300. Recording is performed on the measurement track of the magnetic recording medium 102 by the magnetic recording head 101. Subsequently, reproduction is performed by the reproducing head of the magnetic recording head 101 and the read amplifier 105. FIG. 3 is a schematic diagram showing an example of the reproduction waveform of the second bit pattern, and shows an example of the reproduction waveform for one cycle. Next, the waveform measurement unit 106 performs frequency analysis of the reproduction signal to obtain a frequency spectrum, obtains a voltage value V ₁ of a harmonic component that is seven times the fundamental frequency f ₀ = 1 / 42T, and stores it.

Next, in step 202, the magnetic recording head 101 performs AC demagnetization again on the measurement track.
Next, in step 203, first, the data generator 103 generates a third bit pattern at a bit interval T. As shown in 301 of FIG. 4, the third bit pattern is phase-shifted by a predetermined amount B (B <T) with respect to the 10th bit of the second bit pattern by a phase compensation unit (not shown) of the data generator 103. The operation to advance is performed. As a result, the recording current signal indicated by 301 in FIG. The magnetic recording head 101 records / reproduces data on the measurement track of the magnetic recording medium 102. Similarly, the frequency analysis of the reproduction signal is performed, and the voltage value V ₂ of the seventh harmonic component is obtained and stored.

Next, in step 204, an operation of AC demagnetizing the measurement track again by the magnetic recording head 101 is executed.
Next, in step 205, first, a fourth bit pattern is generated at a bit interval T from the data generator 103. As shown in 302 of FIG. 4, the fourth bit pattern is phase-shifted by a predetermined amount B (B <T) with respect to the 25th bit of the second bit pattern by a phase compensation unit (not shown) of the data generator 103. The operation which delays is performed. As a result, the recording current signal indicated by 302 in FIG. The magnetic recording head 101 records / reproduces data on the measurement track of the magnetic recording medium 102. Similarly, the frequency analysis of the reproduction signal is performed, and the voltage value V ₃ of the seventh harmonic component is obtained and stored.

Next, in step 206, the magnetic recording head 101 performs AC demagnetization again on the measurement track.
Next, in step 207, the data generator 103 first generates a fifth bit pattern at a bit interval T. As shown in 303 of FIG. 4, the fifth bit pattern is phase-shifted by a predetermined amount B (B <T) with respect to the 10th bit of the second bit pattern by a phase compensation unit (not shown) of the data generator 103. And the phase is delayed by a predetermined amount B with respect to the 25th bit. As a result, the recording current signal indicated by 303 in FIG. The magnetic recording head 101 records / reproduces data on the measurement track of the magnetic recording medium 102. Similarly, the frequency analysis of the reproduction signal is performed, and the voltage value V ₄ of the seventh harmonic component is obtained and stored.

Next, at step 208, the magnetic recording head 101 performs an AC demagnetizing operation again on the measurement track.
Next, in step 209, first, the first bit pattern is generated from the data generator 103 at the bit interval T. Here, the first bit pattern is a pattern in which the following pattern repeats in the basic period 42T in which an isolated bit appears every 21T when represented by NRZI.

100000000000000000000100000000000000000000

This pattern is converted into a recording current signal by the write amplifier 104, and recorded / reproduced on the measurement track of the magnetic recording medium 102 by the magnetic recording head 101. FIG. 5 shows an example of a reproduction waveform for one period of the first bit pattern. Similarly, the frequency analysis of the reproduction signal is performed, and the voltage value V ₅ of the seventh harmonic component is obtained and stored.

Next, in step 210, the seventh harmonic voltage V _{1 to} V ₄ obtained in steps 200 to 207 by the evaluation unit 108 is a value obtained by multiplying the seventh harmonic voltage V ₅ obtained in steps 208 to 209 by 0.5. And the results are stored as parameters Y _{1 to} Y ₄ , respectively.

  Next, in step 211, the calculation described later is performed to calculate the partial erasure α. In step 212, the calculation described later is also performed to calculate the nonlinear transition shift Δ. Then, the obtained partial erasure α and the nonlinear transition shift Δ are displayed on the display 109, and the measurement process is terminated.

Hereinafter, a specific method for obtaining the partial erasure α and the nonlinear transition shift Δ will be described in more detail.
The reproduction waveform of the second bit pattern of the basic period 42T having an isolated bit at the beginning of the dibit, the 10th bit, the 17th bit, the 20th bit, the 25th bit, the 29th bit, and the 34th bit is represented by the formula ( It is expressed as 4).

式（４）において、ｐ（ｔ）は孤立波の再生波形であり、第１項と第２項は先頭のダイビットによるパルス波形、第３項〜第８項はそれぞれ１０ビット目、１７ビット目、２０ビット目、２５ビット目、２９ビット目及び、３４ビット目の孤立ビットによるパルス波形を表している。

In Expression (4), p (t) is a solitary wave reproduction waveform, the first and second terms are the pulse waveforms due to the first dibit, and the third to eighth terms are the 10th and 17th bits, respectively. , 20th bit, 25th bit, 29th bit, and 34th bit pulse waveforms are represented.

Here, consider a case where nonlinear distortion occurs in the leading dibit. For example, when the pulse waveform behind the dibit is shifted forward by Δ due to the non-linear transition shift, and further, the amplitude of the dibit pulse is (1−α) (0 ≦ α <1) times due to the partial erasure. The reproduced signal subjected to the distortion is expressed as shown in Equation (5).

また、１０ビット目の孤立パルスの位相をｂ₁だけ進ませ、２５ビット目の孤立パルスの位相をｂ₂だけ進ませた場合の再生信号は式（６）のように表される。

Also, the reproduction signal when the phase of the 10th bit isolated pulse is advanced by b _{1 and} the phase of the 25th bit isolated pulse is advanced by b ₂ is expressed as in equation (6).

さらに、周波数をωとして、周波数スペクトラムは式（７）のように表される。

Furthermore, the frequency spectrum is expressed as shown in Equation (7), where ω is the frequency.

ここで、Ｐ（ω）は孤立波のフーリエ変換である。

Here, P (ω) is the Fourier transform of the solitary wave.

The fundamental frequency of the reproduction signal is ω ₀ = π / 21T. Therefore, the 7th harmonic component is expressed as shown in Equation (8).

従って７次高調波成分の大きさは式（９）のように表される。

Therefore, the magnitude of the seventh harmonic component is expressed as shown in Equation (9).

ここで、式（１０）、式（１１）で表されるＹとβを定義する。

Here, Y and β represented by Expression (10) and Expression (11) are defined.

Ｙは、式（１２）のように表せる。

Y can be expressed as in equation (12).

ここで、１０ビット目と２５ビット目の位相補正量を共にゼロとした場合のＹの値Ｙ₁は、ｂ₁＝ｂ₂＝０と置くことにより、式（１３）のように表される。

Here, the Y value Y ₁ when the phase correction amounts of the 10th bit and the 25th bit are both zero is expressed as equation (13) by setting b ₁ = b ₂ = 0. .

１０ビット目の位相をＢ（Ｂ＜Ｔ）だけ進ませた場合のＹの値Ｙ₂は、ｂ₁＝Ｂ、ｂ₂＝０と置くことにより、式（１４）のように表される。

The Y value Y _{2 in} the case where the phase of the 10th bit is advanced by B (B <T) is expressed as in Expression (14) by setting b ₁ = B and b ₂ = 0.

２５ビット目の位相をＢ（Ｂ＜Ｔ）だけ遅らせた場合のＹの値Ｙ₃は、ｂ₁＝０、ｂ₂＝−Ｂと置くことにより、式（１５）のように表される。

The Y value Y ₃ when the phase of the 25th bit is delayed by B (B <T) is expressed as in Expression (15) by setting b ₁ = 0 and b ₂ = −B.

１０ビット目の位相をＢ（Ｂ＜Ｔ）だけ進ませ、２５ビット目の位相をＢ（Ｂ＜Ｔ）だけ遅らせた場合のＹの値Ｙ₄は、ｂ₁＝Ｂ、ｂ₂＝−Ｂと置くことにより、式（１６）のように表される。

The Y value Y ₄ when the 10th bit phase is advanced by B (B <T) and the 25th bit phase is delayed by B (B <T) is b ₁ = B, b ₂ = −B. Is expressed as in equation (16).

ここで、φを式（１７）で定義する。

Here, φ is defined by equation (17).

式（１３）、式（１６）より、

From Equation (13) and Equation (16),

式（１４）、式（１５）より、

From Equation (14) and Equation (15),

式（１８）より、

From equation (18)

式（１９）より、

From equation (19)

式（２０）、式（２１）と（ｃｏｓβ）²＋（ｓｉｎβ）²＝１の関係より、

Equation (20), and formula (21) (cos .beta) from ² + ^{(sinβ) 2} = 1 in the relationship,

式（２２）をαについて解くことにより、パーシャルイレージャαは式（２３）のように求められる。

By solving equation (22) for α, partial erasure α is obtained as shown in equation (23).

また、式（１１）、式（２１）より、非線形遷移シフトΔは式（２４）のように求められる。

Further, from the equations (11) and (21), the nonlinear transition shift Δ is obtained as in the equation (24).

また、２１Ｔ間隔で孤立ビットが繰り返す第１のビットパターンの再生波形は式（２５）のように表される。

Also, the reproduction waveform of the first bit pattern in which the isolated bits repeat at 21T intervals is expressed as in Expression (25).

従って、その周波数スペクトラムは式（２６）のように表される。

Therefore, the frequency spectrum is expressed as shown in Equation (26).

ここで、Ｐ（ω）は孤立波のフーリエ変換である。従って、その７次高調波電圧は、式（２７）のように表される。

Here, P (ω) is the Fourier transform of the solitary wave. Therefore, the seventh harmonic voltage is expressed as shown in Equation (27).

即ち、式（１３）〜式（１６）のＹ₁〜Ｙ₄はそれぞれ、第２のビットパターンをそのまま記録再生した場合、第２のビットパターンの１０ビット目の位相をＢ（Ｂ＜Ｔ）だけ進ませた第３のビットパターンを記録再生した場合、第２のビットパターンの２５ビット目の位相をＢ（Ｂ＜Ｔ）だけ遅らせた第４のビットパターンを記録再生した場合、及び第２のビットパターンの１０ビット目の位相をＢ（Ｂ＜Ｔ）だけ進ませ、２５ビット目の位相をＢ（Ｂ＜Ｔ）だけ遅らせた第５のビットパターンを記録再生した場合のそれぞれの７次高調波電圧を、第１のビットパターンを記録再生した場合の７次高調波電圧を０．５倍した値で割ることにより求めることができる。

That is, Y ₁ to Y ₄ in the equations (13) to (16) are respectively the phase of the 10th bit of the second bit pattern as B (B <T) when the second bit pattern is recorded and reproduced as it is. Recording / reproducing the third bit pattern advanced by a distance, recording / reproducing a fourth bit pattern in which the phase of the 25th bit of the second bit pattern is delayed by B (B <T), and second 7th order when the fifth bit pattern in which the phase of the 10th bit is advanced by B (B <T) and the phase of the 25th bit is delayed by B (B <T) is recorded and reproduced. The harmonic voltage can be obtained by dividing the seventh harmonic voltage when the first bit pattern is recorded / reproduced by 0.5.

And the value of Y ₁ to Y ₄ obtained, the partial erasure α can be calculated by equation (23). Further, the nonlinear transition shift Δ can be obtained from the equation (24) from the partial erasure α and the values of Y ₂ and Y ₃ .

  In the above example, the case where the phase of the 10th bit of the second bit pattern is advanced by a predetermined amount B and the phase of the 25th bit is delayed by a predetermined amount B has been described. May be delayed by a predetermined amount B, and the phase of the 25th bit may be advanced by a predetermined amount B. In that case, the equations (23) and (24) may be changed to B = −B.

As described above, according to the method for evaluating the characteristics of the magnetic recording medium of the present invention, the nonlinear transition shift and the partial erasure can be measured separately.
In addition, since it is not assumed that the nonlinear transition shift is sufficiently small with respect to the bit interval T, the measurement accuracy does not deteriorate even when the nonlinear transition shift cannot be ignored as compared with the bit interval T. Further, since the phase compensation amount can be implemented with a fixed value, a mechanism for changing the phase compensation amount is not required, and the characteristic evaluation can be performed with relatively simple hardware.

DESCRIPTION OF SYMBOLS 100 Magnetic recording medium characteristic evaluation apparatus 101 Magnetic recording head 102 Magnetic recording medium 103 Data generator 104 Write amplifier 105 Read amplifier 106 Waveform measurement part 107 Oscilloscope 108 Evaluation part 109 Display 110 Disk drive part 111 Control part 120 PC (personal) ·Computer)
300 Recording current signal 301 in step 201 Recording current signal 302 in step 203 Recording current signal 303 in step 205 Recording current signal in step 207

Claims (4)

In a method of recording a plurality of bit patterns on a magnetic recording medium using a magnetic recording head, and reading out this to evaluate the characteristics of the magnetic recording medium,
The plurality of bit patterns include a first bit pattern of 42 bits long having an isolated bit every 21 bits,
A second bit pattern having a 42-bit length having an isolated bit at the beginning of the dibit, 10th bit, 17th bit, 20th bit, 25th bit, 29th bit, and 34th bit,
Furthermore, it includes a plurality of other bit patterns in which the phases of the 10th bit and 25th isolated bit of the second bit pattern are respectively shifted by a predetermined amount,
A method for evaluating characteristics of a magnetic recording medium, wherein a nonlinear transition shift and a partial erasure are calculated by obtaining a seventh harmonic component of a reproduced waveform of each bit pattern. The other bit patterns are third to fifth bit patterns,
The third bit pattern is a pattern obtained by advancing the phase of the tenth isolated bit of the second bit pattern by the predetermined amount B,
The fourth bit pattern is a pattern obtained by delaying the phase of the 25th isolated bit of the second bit pattern by the predetermined amount B,
The fifth bit pattern is a pattern in which the phase of the 10th isolated bit of the second bit pattern is advanced by a predetermined amount B and the phase of the 25th isolated bit is delayed by the predetermined amount B. ,
2. The characteristic evaluation of a magnetic recording medium according to claim 1, wherein a seventh-order harmonic component of the reproduction waveform of the first to fifth bit patterns is obtained to calculate a nonlinear transition shift and a partial erasure, respectively. Method. The other bit patterns are third to fifth bit patterns,
The third bit pattern is a pattern obtained by delaying the phase of the tenth isolated bit of the second bit pattern by a predetermined amount B,
The fourth bit pattern is a pattern obtained by advancing the phase of the 25th isolated bit of the second bit pattern by the predetermined amount B,
The fifth bit pattern is a pattern in which the phase of the 10th isolated bit of the second bit pattern is delayed by a predetermined amount B and the phase of the 25th isolated bit is advanced by the predetermined amount B. ,
2. The characteristic evaluation of a magnetic recording medium according to claim 1, wherein a seventh-order harmonic component of the reproduction waveform of the first to fifth bit patterns is obtained to calculate a nonlinear transition shift and a partial erasure, respectively. Method. Nonlinear transition shift and partial erasure are calculated using a value obtained by dividing the seventh harmonic component of the second to fifth bit patterns by half of the seventh harmonic component of the first bit pattern. The method for evaluating characteristics of a magnetic recording medium according to claim 2, wherein:

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