WO2004097804A1

WO2004097804A1 - Non-linearity measuring method, non-linearity measuring device, magnetic recording/reproducing device, amd magnetic recording/reproducing lsi

Info

Publication number: WO2004097804A1
Application number: PCT/JP2003/005347
Authority: WO
Inventors: Hiroaki Ueno
Original assignee: Fujitsu Limited
Priority date: 2003-04-25
Filing date: 2003-04-25
Publication date: 2004-11-11
Also published as: JP3906226B2; JPWO2004097804A1

Abstract

A non-linearity measuring method capable of measuring NLTS with a high accuracy considering the magnetic inversion state of a preceding bit string. The NLTS depending on the magnetic inversion pattern string P1 can easily and quantitatively measured by constituting a device including a first measurement section (55) for measuring a first predetermined higher harmonic component from a reproduction signal of a reference signal magnetically recorded on a medium (2), a second measurement section (56) for measuring a second predetermined higher harmonic component from the reproduction signal for each of the signals of a plurality of types magnetically recorded on the medium (2) and to be measured, and a calculation section (57) for calculating the NLTS from the first predetermined higher harmonic component and the second predetermined higher harmonic component corresponding to the respective signals to be measured, wherein the signals of the plurality of types to be measured respectively have a magnetic inversion pattern string P1 preceding the bit to be subjected to the NLTS measurement.

Description

Nonlinearity measuring method, Nonlinearity measuring device, Magnetic recording / reproducing device and For magnetic recording / reproducing

L S I Technical Field

The present invention relates to a method for determining the nonlinearity of a magnetic field, and in particular, records and reproduces digital data on a recording medium such as a magnetic tape, a magnetic card, a flexible disk, a magnetic disk, a magneto-optical disk, and a magnetic drum as a change in magnetization polarity. The present invention relates to a magnetic recording / reproducing device and an LSI for magnetic recording / reproducing, and further relates to a method and a device for measuring nonlinearity in the magnetic recording / reproducing.

Background art

In recent years, as the density of magnetic recording / reproducing devices has increased and the data transfer speed has increased, NLTS has been developed to understand the non-linear transition shift (NLTS) that occurs in magnetic heads, recording media, and recording / reproducing transmission systems. Measurement is becoming essential. This NLTS is the data required to magnetically record the recording medium and accurately reproduce the recorded data, taking into account the transition shift (TS) so that the recorded data is not affected by the immediately preceding or succeeding recorded data. It is.

As a conventional NLTS measurement method, in 1994, IEEE Transactions on Magnetics, Vol. 30, No. 6, p. 4236, X. Che, MJ Peek and J. Fitzpai'tick's "AG eneralized frequency domain nonlinearity measurement method" (Non-Patent Document 1) is known. This paper describes a method for measuring the NLT S that occurs when a series of magnetization reversals is magnetically recorded on a medium with a bit string pattern signal containing two bits (Dibit).

This NLT S measurement method will be described below. This NLT S measurement method consists of the following three steps.

In step 1, the pulse width of one bit is T, and the polarity is inverted every 15 bits (at 15 T). Record the data on a medium, and measure the fifth harmonic signal (hereinafter referred to as the fifth-order component) of the reproduced signal. This fifth-order component is defined as V5ref. The above-mentioned reference signal is shown below by NRZ notation, in which the recording code of data recorded on the medium is indicated by a level, and NRZI notation, in which the recording code is indicated by inversion of the level.

NRZ notation: 111111111111111 000000000000000

NRZ I notation: 100000000000000 100000000000000

In step 2, data is recorded on the medium using the signal to be measured that repeats the 3OT bit string pattern including the Dibit pattern, and the fifth-order component V5pat of the reproduced signal is measured. The signals to be measured are shown below in NRZ notation and NRZ I notation.

NRZ notation: 100000001111111 011111110000000

NRZI notation: 110000001000000 110000001000000

In step 3, the ratio Vab2 V5pat / V5ref is calculated from V5ref and V5ref for the fifth-order component measured in step 1 and step 2. Next, NLTS (Dibit) generated by Dibit is calculated from the following equation. Here, 1 ^ 1 ^ 3 is a value normalized by one, that is, a value in which the pulse width of 1T is 1 (100%).

NLTS (Dibit) = acos [(2.Vab2) / 2] * 3 / π… (a)

The above equation (a) can be approximated by the following equation (b).

NLTS (Dibit) = Vab * 3 / (b)

The above paper also describes the NLT S measurement method when the magnetization reversal is further continuous.In addition to the author's author J. Fitzpatrick, A. Taratorin, SX Wang, B. Wilson In a paper entitled "Non-Linear Interactions in a Series of Transitions" published in IEEE Transactions on Magnetics, Vol. 33, No. 1, P956-961 in January 1996 (Non-Patent Document 2), It is stated that if MR (magnetoresistive) type is used, a large error will occur in the NLTS measurement value unless the nonlinearity of the reproduction head is removed.

In addition, one of the NLT S is a transition shift (HTS: Hard Transition Shift or O / W (Over Write) NLTS) by pre-recorded data. As a measurement method, a reference signal (f) that repeats a single bit string pattern And its 1Z2 frequency A method of calculating the NLTS from the signal under test (fZ2) is known.

In addition to dibits with two consecutive magnetization reversals, non-linear transition shifts (NLTS) caused by tribits with three consecutive magnetization reversals and signals repeating a 2T bit string pattern are troublesome. In addition to reducing the measurement error due to nonlinearities caused by MR (magnetoresistive) read heads as well as electromagnetic induction read heads, various types of NLTS can be used without changing the measurement method. A non-linearity measurement method for the purpose of easily measuring (see Patent Document 1) is also known.

However, in these conventional NLTS measurement methods, no consideration is given to the state of magnetization reversal of the bit string that precedes the NLTS measured pattern (bit string pattern), and the actual NLTS is measured. There is a problem that it is not a thing.

The present invention has been made in view of such a problem, and a non-linearity measuring method, a non-linearity measuring apparatus, and a magnetic recording / reproducing method capable of measuring NLTS with higher accuracy in consideration of the state of magnetization reversal of a preceding bit string. It is intended to provide a device and an LSI for magnetic recording and reproduction.

Patent Document 1

JP 2002-230709 A

Non-patent document 1

X. Che, M. J. Peek and J. Fitzpartick A Generalized frequency do main nonlinearity measurement method 1994, IEEE Transactions on Magnetics, Vol. 30, No. 6, p. 4236

Non-patent document 2

J. Fitzpatrick, A. Taratorin, SXWang and B. Wilson, "Non-Linear Interactions in a Series of Transitions", January 1996, IEEE Transactions on Magnetics, Vol. 33, No. 1, P956-961.

For this reason, the nonlinearity measuring method of the present invention can A non-linearity measurement method for calculating a nonlinear transition shift (NLTS), comprising a reference signal recording step of recording a reference signal on a medium, and a method of recording a plurality of types of signals to be measured on the medium. A measurement signal recording step, a first measurement step of measuring a first predetermined harmonic component from a reproduction signal of a reference signal magnetically recorded on the medium, and a plurality of types of signals to be measured magnetically recorded on the medium. A second measurement step of measuring a second predetermined harmonic component from the reproduced signal; and an NLTS from the first predetermined harmonic component and the second predetermined harmonic component corresponding to each signal under test. And a calculation step for calculating the NLTS. Each of the plurality of types of signals to be measured is provided with a magnetization reversal pattern sequence P1 prior to the measurement target bit of the NLTS. Note that the first predetermined harmonic component and the second predetermined harmonic component are the M-th harmonic components of order M, respectively, and the reference signal and the plurality of types of signals under test are all represented as a bit string having a bit period N. The bit period N may be a multiple of the order M of the predetermined harmonic component, and the ratio R (R = N / M) of the bit period N to the harmonic order M may be a multiple of two.

In addition, the signal to be measured is an NLT S measurement pattern sequence composed of the magnetization reversal pattern P1 and the non-linearity measurement bit; 2δ bits from the last bit of P (where δ is the previous bit on the medium) (Length negligible to the effect of NLTS from the following) At a subsequent position that is at least distant from the first bit of the NLTS measurement pattern sequence P (n1 + 0.5) Rth (where nl is a natural number) The bit sequence P2 excluding the last bit of the NLT S measurement pattern P is arranged starting from the subsequent position of the NLT S measurement pattern P, and the subsequent position at least δ bits away from the last bit of the magnetization reversal pattern P1 and the signal under test At the position preceding the last bit of the NLTS measurement pattern sequence P by more than 2δ bits, and at the (n2 + 0.5) Rth (where n2 is a natural number) succeeding position from the last bit of the NLTS measurement pattern sequence P. May have 1 magnetization reversal bit C 1 . '

Furthermore, the bit to be magnetized is represented by 1, and the signal to be measured is a 60-bit pattern 1J (bit period N = 60) of 000011000000000000000010000000000001 000000000000000000000000 where the magnetization reversal position is in the 4th, 5th, 22nd and 35th bits. The bit to be magnetized is represented by 1 and the signal to be measured has a magnetized reversal position at bits 4, 5, 6, 12, 22, 23, 36, and 42. 11000001000000000110000000000001000001000000000 A pattern of a 60-bit string of glue 00000 (bit period N = 60) may be used.

When the number of magnetization reversal bits in the NLTS measurement pattern sequence P is an odd number, the signal to be measured is a subsequent position at least δ bits away from the last bit of the NLTS measurement pattern sequence P, and the bit sequence Ρ 2 A second magnetization reversal bit C2 at a preceding position δ or more away from the first bit of the pattern, and a subsequent position at least δ bits away from the first magnetization reversal bit C1 and the last bit of the signal under measurement. At least δ bits from the second magnetization reversal bit, and a third magnetization reversal bit at the (R 3 (0.5), where η 3 is a natural number) succeeding position from the second magnetization reversal bit C 2 It may have C3.

Further, the bit to be inverted is represented by 1, and the signal to be measured is a 60-bit string of 0110110000 0000000 0011010000000000001000000000000000000000000 where the magnetization inversion position is in the first, second, fourth, fifth, fifth, fifth, ninth, twentieth, and thirty-fifth bits. The period of the magnetization reversal may be represented by 1 and the signal to be measured has the magnetization reversal position of 0, 2, 4, 5, 18, 20, 22, It may be a pattern of 35 bits, 1010110000 0000000010101000000000000100000000000000000 0000000, a 60-bit pattern IJ (bit period Ν = 60). Further, the bit to be magnetized is represented by 1 and the signal to be measured is represented by the magnetization reversal position at the 0th, 1, 2, 4, 5, 12, 18, 19, 20, 22, 35, and 42 bits. It may be a pattern of a 60-bit string (bit period Ν = 60) of 11101100000010000011101000000000000100000010000000 00000000 00, and the bit to be magnetized is represented by 1 so that the signal to be measured has the magnetization reversal position of the first, second, and fourth. , 5,6,12,19,20,22,23,36,42 bits may be a pattern of 01101110000 0100000011011000000 000100000100000000000000000 60-bit pattern (bit period N = 60).

Furthermore, the bit for magnetization reversal is represented by 1, and the signal to be measured is changed to the 0, 2, 4, 5, 6, 12, 12, 18, 20, 22, 23, 36, and 42 bits for the magnetization reversal position. There may be a pattern of a 60-bit string (bit period N = 60) of 10101110000010000010101100000000000010000010000000000000000 0, and magnetization The bit to be inverted is represented by 1, and the signal to be measured has the magnetization reversal position at the 0th, 1, 2, 4, 5, 6, 18, 18, 19, 20, 22, 23, and 36th bits 1110111000000 0000011101100000000000010000000000000000000000000000 May be a pattern of a 60-bit string (bit period N = 60).

In addition, the reference signal includes a first magnetization reversal bit R 1 at a head position, and a second magnetization reversal bit R 2 at a subsequent position at least δ bits away from the first magnetization reversal bit R 1, The third magnetization is located at a subsequent position at least δ bits away from the second magnetization reversal bit R 2 and at the η 4 XRth (where η 4 is a natural number) subsequent position from the first magnetization reversal bit R 1. An inversion bit R 3 and a subsequent position that is at least δ bits away from the third magnetization inversion bit R 3, a preceding position that is at least δ bits away from the last bit of the reference signal, and A fourth magnetization reversal bit R 4 may be provided at a position subsequent to the R-th (where η 5 is a natural number) from the magnetization reversal bit R 2 (η 5 +0.5).

Further, the bit for magnetization reversal is represented by 1, and the reference signal is the reference signal of the 60-bit string (bit cycle Ν = 60) of 100000000000000000100000100000000000 000000000000100000000000 where the magnetization reversal position is in the 0th, 18th, 24th, and 48th bits. It may be a turn.

In the calculation step, the NLTS may be calculated based on a ratio between the first predetermined harmonic component and the second predetermined harmonic component, and the NLTS is created by inverting the magnetization polarity of the signal under measurement. The inverted signal under measurement may be used as the signal under measurement.

Further, in the signal-under-measurement step, there is provided a change step capable of changing the recording position of the measurement target bit of the non-linearity in the signal-under-measurement, and in the second measurement step, based on the signal-under-measurement after moving the recording position. The second predetermined harmonic component may be measured.

In addition, a correction step is provided for correcting the second predetermined harmonic component based on the minimum value VpatMin of the second predetermined harmonic component measured based on the signal under measurement after moving the recording position. In this correction step, the second predetermined harmonic component Vpat measured based on the measured signal before moving the recording position and the second predetermined harmonic component Vpat measured based on the measured signal after moving the recording position may be used. When the predetermined harmonic component V pat 'of 2 To

V a '= s q r t (V at t "2-Vp a tM i n" 2)

It may be corrected so that

Further, each of the reference signal and the plurality of types of signals under test is a bit string having a bit period of 60 (N = 60), and the first predetermined harmonic component and the second predetermined harmonic component are of order 5 (M = 5), and the reference signal and the plurality of types of signals to be measured are each a bit string having a bit period of 50 (N = 50), and the first predetermined harmonic component. And the second predetermined harmonic component may be a fifth harmonic component of order 5 (M = 5).

The non-linearity measuring device of the present invention is a non-linearity measuring device for calculating a non-linear transition shift (NLTS) in magnetic recording / reproducing on a medium, wherein the reference signal magnetically recorded on the medium is A first measuring unit for measuring a first predetermined harmonic component from the reproduced signal of the first type, and measuring a second predetermined harmonic component from the reproduced signal for each of a plurality of types of signals to be measured magnetically recorded on a medium. A second measuring unit, and a calculating unit that calculates the NLTS from the first predetermined harmonic component and the second predetermined harmonic component corresponding to each of the signals under test. Each of them is characterized by having a magnetization reversal pattern sequence P1 preceding the measurement target bit of NLTS.

Further, the magnetic recording / reproducing apparatus of the present invention comprises: a first measuring section for measuring a first predetermined harmonic component from a reproduced signal of a reference signal magnetically recorded on the medium; and a plurality of types of devices to be measured magnetically recorded on the medium. A second measuring unit for measuring a second predetermined harmonic component from the reproduced signal for each of the signals; and a second predetermined harmonic component corresponding to each of the signals under measurement, and a second predetermined harmonic component corresponding to each of the signals to be measured. And a calculation unit that calculates a non-linear transition shift (NLTS) in magnetic recording / reproducing on a medium, and a plurality of types of signals to be measured are each switched in magnetization before a bit to be measured in NLTS. It is characterized by having a pattern sequence P1.

Also, the magnetic recording / reproducing LSI of the present invention comprises a first measuring unit for measuring a first predetermined harmonic component from a reproduction signal of a reference signal magnetically recorded on a medium, and a plurality of types of magnetic recording magnetically recorded on the medium. For each of the measured signals, a second predetermined harmonic component is measured from the reproduced signal. From the second measuring section to be determined, the first predetermined harmonic component and the second predetermined harmonic component corresponding to each signal under measurement, a nonlinear transition shift (NLTS) in magnetic recording / reproducing on a medium is obtained. ) Is calculated, and a plurality of types of signals to be measured are each provided with a magnetization reversal pattern sequence P1 prior to the measurement target bit of the NLTS.

According to the non-linearity measuring method, the non-linearity measuring device, the magnetic recording / reproducing device and the magnetic recording / reproducing LSI of the present invention, the following effects and advantages are obtained.

(1) NLTS that depends on the magnetization reversal pattern sequence P 1 is calculated by calculating the NLTS based on the predetermined harmonic component of the signal under measurement that includes the magnetization reversal pattern sequence P 1 prior to the NLTS measurement target bit. It can be easily and quantitatively measured, and is highly effective in the development of magnetic recording / reproducing devices (magnetic heads, transmission systems, etc.) and media.

(2) Correction can be easily made so that NLTS is minimized. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a diagram schematically showing a functional configuration of a nonlinearity measuring section (nonlinearity measuring device) provided in a magnetic disk device (magnetic recording / reproducing device) as one embodiment of the present invention.

FIG. 2 is a diagram showing an example of a reference pattern and a pattern to be measured used in the non-linearity measuring section of the magnetic disk device as one embodiment of the present invention.

FIG. 3 is a diagram schematically showing a hardware configuration of a magnetic disk device as one embodiment of the present invention.

FIG. 4 is a diagram schematically showing a configuration example of a pattern generation circuit used in a magnetic disk device as one embodiment of the present invention.

FIGS. 5 (a), 5 (b), 5 (c), 6 (a), 6 (b), and 6 (c) are magnetic disk drives as one embodiment of the present invention. FIG. 6 is a diagram showing an example of a measurement error due to simulation of NLT S for a plurality of types of NLT S patterns to be measured in FIG.

Figures 7 (a), 7 (b), 7 (c), 8 (a), 8 (b), and 8 (c) In the magnetic disk device as one embodiment of the present invention, a plurality of types of

FIG. 9 is a diagram showing an example of a measurement error by a simulation of the NLT S after correcting the NLT S pattern.

Figures 9 (a), 9 (b), 10 (a), 10 (b), 11 (a), 11 (b), 12 (a) and 12 (b) FIG. 3 is a diagram showing an actual measurement example of NLTS for a plurality of types of NLTS patterns to be measured in the magnetic disk device as one embodiment of the present invention.

FIG. 13 is a diagram showing an example of another reference pattern and a pattern to be measured used in the non-linearity measuring section of the magnetic disk device as one embodiment of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram schematically showing a functional configuration of a nonlinearity measuring unit (nonlinearity measuring device) provided in a magnetic disk device (magnetic recording / reproducing device) as one embodiment of the present invention.

The magnetic disk device (magnetic recording / reproducing device) 100 is used, for example, as a storage device in a computer system or the like, has a plurality of magnetic disks 2, and uses these magnetic disks 2 with a magnetic head 3 to transfer data. A non-linearity measuring unit 1 (see Fig. 1) that calculates the non-linear transition shift (NLTS) of magnetic recording / reproducing on the magnetic disk (medium) 2 (see Fig. 3). It is configured with.

As shown in FIG. 1, the non-linearity measuring section 1 of the magnetic disk device 100 includes a pattern generating section 51, a pattern recording section 52, a pattern reproducing section 54, a first measuring section 55, a second measuring section 56, and a calculating section. 57, a change unit 58 and a correction unit 59.

The pattern generating section 51 generates a reference pattern (reference signal) and a pattern to be measured (signal to be measured), and passes the reference pattern and the pattern to be measured to the pattern recording section 52.

FIG. 2 shows a non-linearity measuring unit of the magnetic disk drive 100 as one embodiment of the present invention. FIG. 3 is a diagram showing an example of a reference pattern and a pattern to be measured used in 1. The reference pattern and the pattern to be measured are both bit string patterns representing the states of magnetization and non-magnetization for magnetically recording data on the magnetic disk 2, and the pattern generation section 51 has a pattern as shown in FIG. A reference pattern and a pattern to be measured are generated.

In FIG. 2, the items in each column are shown in the upper row. In each item from the left, the first column shows the type of NLTS measurement, the second column shows the NLTS pattern to be measured, and the third column shows the bit position (Bit position). As the bit position, the above-mentioned reference pattern and the pattern to be measured are indicated by NRZI notation. Data selected from these patterns is supplied from the pattern generation section 51 as recording data.

In this embodiment, as shown in FIG. 2, the bit period N of each of the reference pattern and the pattern to be measured is 0 and 1 of 60 bits (60T; N = 60). , And is configured so that the magnetization reversal position is represented by 1. In FIG. 2, each of the reference pattern and the pattern to be measured is assigned a number from 0 to 59 as a bit position in order from the first to the last bit constituting each pattern, and The magnetization reversal position in the NLTS pattern to be measured is specified. Each pattern shown in FIG. 2 is for a case where the bit length δ = 4, where the influence from the previous bit can be ignored.

In the present embodiment, as shown in FIG. 2, the reference pattern is formed as a pattern of a bit string in which the magnetization reversal positions are in the 0th, 18th, 24th, and 48th bits. In the example shown in FIG. 2, two types of patterns to be measured are provided as NLTS types, a dibit pattern and a tribit pattern, and eight types of measured patterns are further provided as dibit patterns. It has an NLTS pattern and eight types of measured NLTS patterns as tribit patterns.

Here, the dibit pattern is a pattern (Di'001 fan 00) that includes two diversions in which two magnetization reversals are continuous, and the tribit pattern consists of three Patterns containing tribits with consecutive magnetization reversals (--- 0 0111000 ...).

In addition, each dibit pattern shown in FIG. 2 has a continuous magnetization reversal position (dibit) of two bits at the fourth and fifth bits from the beginning, and a 0 bit preceding each dibit. The 4th to 3rd bits each have a 4-bit magnetization reversal pattern sequence (preceding pattern) P1.

In the present embodiment, for convenience, a 6-bit portion (NLTS measurement pattern sequence P) of the 0th to 5th bits including the preceding pattern P1 and the dibit in each dibit pattern is used! The measured NLTS pattern shall be identified, for example, such as a measured NLT S pattern 0000 11 1, a measured NLT S pattern 00101 1, and a measured NLT S pattern 0100 11 1.

For example, in the measured NLT S pattern 0000 11 1, the magnetization reversal position is at the fourth, fifth, 22 and 35th bits, and in the measured NLT S pattern 01 10 11 1, the magnetization reversal position is the first, In 2, 4, 5, 19, 20, 22, and 35 bits, in the NLTS pattern 101 0 11 to be measured, the magnetization reversal position is 0, 2, 4, 5, 18, 18, 20, 22, In 35 bits, the measured reversal position is the 0th, 1st, 2nd, 4th, 5th, 12th, 18th, 19th, 20th, 22nd, 35th, and 42nd bits in the NLTS pattern 1 1 10 11 It is in.

In the present embodiment, it is assumed that the NLTS at the dibit position (the second bit of two consecutive magnetization reversal bits forming the dibit) in each measured NLTS pattern is measured. That is, the dibit position is the bit to be measured.

Similarly, each of the tribit patterns shown in FIG. 2 has a continuous magnetization reversal position (tribit) of three bits at the fourth to sixth bits from the beginning, and each tribit has The preceding 0th to 3rd bits have a 4-bit magnetization reversal pattern sequence (preceding pattern) P1, which is different from each other. In the present embodiment, for the sake of convenience, it is assumed that each measured NLTS pattern is identified using a 7-bit portion of the 0th to 6th bits consisting of the preceding pattern P1 and the tribit in each tribit pattern. , Measured NLT S pattern 00 00 1 1 1, measured NLTS pattern 00 101 1 1, measured NLTS pattern 01 001 1 1

For example, in the NLT S pattern to be measured 00001 11 1, the magnetization reversal position is at the fourth, fifth, sixth, twelve, 22, 23, 36, and 42 bits, and the NLT S pattern to be measured 01 10 1 In 1 1, the magnetization reversal position is in bits 1, 2, 4, 5, 6, 12, 2, 19, 20, 22, 23, 36, and 42. In the NLTS pattern 1010 11 1 1 Indicates that the magnetization reversal position is at bits 0, 2, 4, 5, 6, 12, 18, 18, 20, 22, 23, 36, and 42. In the NLTS pattern to be measured 1 1 101 11 1 The position is at bits 0, 1, 2, 4, 5, 6, 18, 19, 20, 22, 23, and 36.

Also, in the present embodiment, it is assumed that the NLTS at the tribit position (the third bit of three consecutive magnetization reversal bits forming the tribit) in each measured NLTS pattern is measured. That is, this tribit position is the bit to be measured.

The pattern recording section (reference signal recording section, measured signal recording section) 52 is for recording the reference pattern and the pattern to be measured generated by the pattern generating section 51 on the magnetic disk 2, and the pattern reproducing section 54 is for the magnetic disk 2. It reads and reproduces the reference pattern and the measured pattern recorded in 2.

The first measuring section 55 measures the first predetermined harmonic component (M-order component) from the reproduced signal of the reference signal magnetically recorded on the magnetic disk 2, and the reference pattern reproduced by the pattern reproducing section 54. , The fifth harmonic component (hereinafter sometimes referred to as the fifth-order component) Vref is measured.

The second measuring section 56 measures a second predetermined harmonic component (M-order component) from a reproduced signal of each of a plurality of types of signals to be measured magnetically recorded on the magnetic disk 2, and performs pattern reproduction. The fifth harmonic component Vpat is measured based on the pattern to be measured (NLTS pattern to be measured) reproduced by the unit 54.

Then, the reference pattern (reference signal) generated by the pattern generating section 51 is recorded on the magnetic disk 2 via the pattern recording section 52, and the data recorded on the magnetic disk 2 is transmitted via the pattern reproducing section 54. Input to the first measuring unit 55, Similarly, the pattern to be measured (signal to be measured) generated by the pattern generating section 51 is recorded on the magnetic disk 2 via the pattern recording section 52, and the data recorded on the magnetic disk 2 is transferred to the pattern reproducing section 54. Is input to the second measuring section 52 via the.

Hereinafter, in the present embodiment, both the first predetermined harmonic component measured by the first measuring unit 55 and the second predetermined harmonic component measured by the second measuring unit 56 are of order 5 (M = The case of the fifth harmonic component of 5) will be described.

The calculating unit 57 calculates the NLT from the first predetermined harmonic component measured by the first measuring unit 55 and the second predetermined harmonic component corresponding to each signal under measurement measured by the second measuring unit 56. This is to calculate S.

Specifically, the calculating unit 57 first calculates Vab according to the following equation (1), and then calculates NLTS according to the following equation (2).

Va b = V p a t / V r e f (1)

Here, Vpat is the Mth-order component of the measured pattern, and Vref is the Mth-order component of the reference pattern.

^{NLTS a cos ([- Vab 2} ) · · · (2)

π

Note that R is the ratio of the bit period Μ to the harmonic order （(R = NZM). For example, the bit period N is 60 bits (6 OT; N = 60), and the predetermined harmonic component is the order 5 ( If M = 5) then R = (60/5) = 12. That is, NLTS can be calculated by the following equation (3).

NLTS = -acos [l-Vab ² ).. '(3)

π

Here, NLTS is a value standardized by 1 、, that is, a value in which the pulse width of 1T is 1 (100%).

Next, the NLTS calculation formula of the above formula (3) will be described using a measured NLTS pattern 10 10 11 1 1 (pattern A) involving a tribit with a bit period (pattern period) of 60T.

(1) Calculation of 5th order component of pattern A The magnetization reversal positions of pattern A are the 0, 2, 4, 5, 6, 12, 18, 18, 20, 22, 23, 36, and 42 bits. Here, the NLTS of one bit before is normalized by the bit period T, tnl, the NLTS of two bits before magnetization reversal is normalized by the bit period T, tn2, and the NLTS of three bits previous magnetization reversal is the pit period. Let tn3 (= tnl-tn2) be the normalized value of T, and tow be the normalized value of NLTS based on the previous history. The previous history is the information immediately below before overwriting.

Va (t) = (t) -h (t-2T-tow + tn2)

+ h (t-4T-tn2) -h (t-5T-tow + tnl)

+ (t-6T + tn3) "(t-12T-tow)

+ (t-18T) -h (t-20T-tow)

+ h (t "22T + tn2) -h (t-23T-tow + tnl)

+ h (t-36T) -h (t-42T-tow)

Va (f) = H (£) [exp (0) -exp (-; j oT (2 + tow-tn2))

+ exp (-joT (4-tii2))-exp (-joT (5 + towtnl))

+ exp (-joT (6-tn3))-exp (-joT (l2 + tow))

+ exp (-jG) T (18))-exp (-jG) T (20 + tow-tn2))

+ exp (-jQT (22-tn2))-exp (-joT (23 + tow-tnl))

+ exp (-j ^ T (36))-exp (-joT (42 + tow))]

Since the 5th order component is 5f0 = 5 / T0 = 5 / (60T) = l / (12T), ωΤ = 2ττίΓ = 2π5ίΟΤ = π / 6. Here, f0 represents the repetition reference frequency.

Therefore, the fifth order component Va (5f0) of Va (f) can be expressed by the following equation.

Va (5fO) = H (5fO) [l-exp (-j 7t / 6 (2 + tow-tn2))

+ exp (-j 7T / 6 (4-tn2))-exp (-j 7t / 6 (5 + towtnl)) ⁷

+ exp (-j 7t / 6 (6-tn3))-exp (-j 7T / 6 (12 + tow))

+ exp ("j 7C / 6 (l8))-exp (-j 7C / 6 (20 + tow-tn2))

+ exp (-j 7t / 6 (22-tn2))-exp (-j 7t / 6 (23 + tow-tnl))

+ exp (-j 7t / 6 (36))-exp (-j 7T / 6 (42 + tow))]

Va (5fO) = H (5fO) [l_exp (_j 7t / 6 (2 + tow-tn2))

+ exp ("j 7T / 6 (4-tn2))-exp (-j 7t / 6 (5 + towtnl)) -exp (-j 7T / 6 (-tn3))-exp (-j 7T / 6 (tow))

-l + exp (-j 7T / 6 (2 + tow-tn2))

-exp (-j 7C / 6 (4-tn2)) + exp (-j 7r / 6 (5 + towtnl))

+ l + exp (-j 7T / 6 (tow))]

Va (5fO) = H (5fO) [l-exp j7r / 6 (tn3))]

(2) Calculation of the fifth order component of the reference pattern (pattern B) ''

Similarly, the fifth order component Vb (5f0) of the basic pattern is obtained.

The magnetization reversal positions of pattern B are the 0th, 18th, 24th, and 48th bits.

Vb (5fO) = H (5fO) [l-exp (-j t / 6 (l8 + tow))

+ exp (-j 7T / 6 (24))-exp (-j 7T / 6 (48 + tow))]

= H (5fO) 2

(3) Derivation of NLTS calculation formula

First, Vab = Va (5fO) / Vb (5fO) is calculated. Here, since Va (5f0) and Vb (5f0) are measured by a spectrum analyzer or the like, only absolute values are measured. Therefore, Vab is given by the above equations (4) and (5).

Vab = | Va (5fO) | / | Vb (5fO) |

= | l-exp (j'7r / 6 (tn3)) | / | 2 |

Here, if the real part of exp (j'7r / 6 * tn3) is Re and the imaginary part is Im,

Vab = sqrt [(1 -Re) ^A 2 + Im ^A 2] / 2

= sqrt (2-2Re) / 2 h

The real part Re is

Re = l-2Vab ^A 2

Therefore, the phase angle (M,

Φ = acos (Re) = acos (l-2Vab ^A 2)

Since の is π / 6 when viewed from the fifth-order component of fO, the amount of N LTS for 1 Τ is calculated by the following equation (6).

NLTS = 6 / 7C acos (l-2Vab ^A 2)

The NLTS calculation formula is the same for other measured NLTS patterns. The changing unit 58 arbitrarily changes (moves) the recording position of at least a part of the bits when the measured NLTS pattern (measured pattern) is recorded on the magnetic disk 2 by the pattern recording unit 52. This makes it possible to simulate the value of the NLTS by changing the dibit position and the trip position, and to simulate the value of the M-order component Vpat of the pattern to be measured.

The correction unit 59 corrects the value of the M-order component Vpat of the pattern to be measured, and uses the minimum value VpatMin of the value of Vpat based on the result of the simulation performed by the changing unit 58. The value of the M-order component Vpat of the measurement pattern is corrected. In the present embodiment, the correction unit 59 calculates and corrects the value Vpat ′ of the corrected Vpat based on the following equation (7), for example.

Note that the above equation (7) is

V a t '= s q r t (V p a t "2-V p a t M in" 2)

It can also be expressed as

The NLTS measurement method by the non-linearity measurement unit 1 of the magnetic disk drive 100 measures the non-linear shift of the magnetization transition point. However, in the case of magnetic recording, the non-linearity of the magnetic head (reproducing head) 3 p- Includes nonlinearity of playback amplitude due to H-curve nonlinearity. This non-linearity of the reproduction amplitude may cause a measurement error of the NLTS according to the present method, so it is desirable to correct it. FIG. 3 is a diagram schematically showing a hardware configuration of the magnetic disk device 100 as one embodiment of the present invention. As shown in FIG. 3, the magnetic disk device 100 includes a magnetic disk (medium) 2, a magnetic head, a turn recording unit, and a pattern reproducing unit) 3, an actuator 4, a head IC 5, a control circuit 6, an encoder 7 , A recording correction circuit 8, an AGC circuit 9, a signal detection circuit 10, a decoder 11, a servo demodulation circuit 12, a servo control circuit 13, a drive circuit 14, an FFT 15, and a pattern generation circuit 20.

The magnetic disk (medium) 2 uses a magnetic film with high coercive force to track onto a disk-shaped medium. The head is rotated by a spindle motor (not shown), and the magnetic head 3 can read information recorded on the surface or write information. It is like that.

The magnetic head (pattern recording unit, pattern reproducing unit) 3 reads various data recorded on the magnetic disk 2 and writes various information on the magnetic disk 3. Specifically, the magnetic head 3 is arranged to face the magnetic disk 2 and generates a magnetic field by supplying a recording current, and magnetizes the magnetic disk 2 in the track traveling direction. Thus, various data (a reference pattern, a pattern to be measured; details will be described later) are recorded on the magnetic disk 2.

That is, the magnetic head 3 functions as a pattern recording unit (reference signal recording unit, measured signal recording unit) 52 that writes the above-described reference pattern and pattern to be measured on the magnetic disk 2, and is recorded on the magnetic disk 2. It functions as a pattern reproducing section 54 that reads and reproduces the reference pattern and the pattern to be measured. The actuator 4 is for moving the magnetic head 3 in the radial direction of the magnetic disk 2 and includes, for example, a VCM (Voice Coil Motor) (not shown) used for positioning the magnetic head 3. . The actuator 4 is driven in accordance with a drive signal from the drive circuit 14 to move the magnetic head 3 to a predetermined position.

The head IC 5 controls reading / writing of data from / to the magnetic disk 2 by the magnetic head 3, and the encoder 7 generates the recording data supplied from the control circuit 6 and the data generated by the pattern generation circuit 20. The reference pattern and the pattern to be measured are converted into NRZ (Non-Return to Zero) data for recording on the magnetic disk 2 and output. Incidentally, NRZ is a so-called non-return-to-zero recording method, and is a recording method in which recording is performed with a pulse waveform in which a unit code interval length and a pulse length are the same in a binary signal pulse train. The output signal of the encoder 7 is supplied to the recording correction circuit 8.

The write correction circuit (WPC: Write Precompensation Circuit) 8 detects the bit arrangement of the output recording signal of the encoder 7 and performs correction according to the bit arrangement. The recording signal corrected by the recording correction circuit 8 is supplied to the head IC 5.

Further, the recording correction circuit 8 compensates for a recording signal in accordance with the calculation result of NLTS calculated by the control circuit 6, and supplies the recording signal to the head IC5. The recording and correction circuit 8 optimizes the compensation amount by correcting the compensation amount so as to be equal to the above-described ratio Vab = 1 or as close as possible to Vab = 1.

The head IC 5 supplies a recording current corresponding to the recording data supplied from the recording correction circuit 8 to the magnetic head 3. The head IC 5 amplifies the signal reproduced by the magnetic head 3 and supplies the amplified signal to the AGC circuit 9.

The AGC (Automatic Gain Control) circuit 9 is for controlling the amplitude of the signal supplied from the head IC 5 to be constant, and the control signal is transmitted to the FFT 15, the signal detection circuit 10, and the servo demodulation circuit 1 2 Output.

The signal detection circuit 10 detects the reproduced data from the output signal of the AGC circuit 9, and the decoder 11 decodes the signal detected by the signal detection circuit 10. The decoded signal is supplied to the control circuit 6.

The servo demodulation circuit 12 is for demodulating a servo signal from the signal supplied from the AGC circuit 9, and the demodulated signal is supplied to the servo control circuit 13.

The servo control circuit 13 determines the current position of the magnetic head 3 and the position where recording or reproduction is to be performed according to the servo signal supplied from the servo demodulation circuit 12 and the control signal supplied from the control circuit 6. Then, a drive control signal corresponding to the difference is generated and supplied to the drive circuit 14.

The drive circuit 14 generates a drive signal for driving the actuator 4 in accordance with the drive control signal supplied from the servo control circuit 13, and supplies the drive signal to the actuator 4. .

An FFT (Fast Fourier Transformer) 15 is provided downstream of the AGC circuit 9 to detect (measure) the 5th harmonic component from the reproduced signal output from the AGC circuit 9 and control it. The 5th harmonic component is output to the control circuit 6 etc. That is, the FFT 15 functions as the first measurement unit 55 and the second measurement unit 56 described above.

The control circuit 6 controls various processes in the magnetic disk drive 100, and controls the switching of the magnetic head 3, the positioning control of the magnetic head 3 with respect to the magnetic disk 2, the magnetic head 3 Data write / read is controlled by an external device, and the above-described recording data is received from the outside and supplied to the encoder 7.

When measuring the NLTS in the magnetic disk device 100, the control circuit 6 issues a command to select, for example, a reference pattern to be supplied to the encoder 7 or recording data of a bit string pattern forming a pattern to be measured. Is received from the outside and supplied to the pattern generation circuit 20, whereby the pattern generation circuit 20 generates a reference pattern and a pattern to be measured.

Further, the control circuit 6 calculates the NLTS based on the fifth-order component Vpat of the measured pattern measured by the FFT 15 and the Mth-order component fifth-order harmonic component Vref of the reference pattern and the like. ing. That is, the control circuit 6 includes a first predetermined harmonic component measured by the first measurement unit 55 and a second predetermined harmonic component corresponding to each signal to be measured measured by the second measurement unit 56. It functions as a calculation unit 57 that calculates the NLTS from the wave components. Further, the control circuit 6 supplies the calculated NLTS to the recording correction circuit 8.

Further, the control circuit 6 supplies the calculation result of the NLTS by the fifth harmonic method described above to the recording correction circuit 8, and the recording correction circuit 8 compensates according to the supplied NLTS calculation result. The recording signal is supplied to the head IC 5.

The pattern generation circuit 20 generates a reference pattern (reference signal) and a pattern to be measured (signal to be measured) based on the control of the control circuit 6, and supplies the reference pattern and the pattern to be measured to the encoder 7. And functions as the above-described pattern generation unit 51.

FIG. 4 shows a pattern used in the magnetic disk drive 100 as one embodiment of the present invention. FIG. 3 is a diagram schematically illustrating a configuration example of a power generation circuit 20. This pattern generation circuit 20 responds to a command supplied from the control circuit 6 and generates a reference pattern (reference signal (60 bits) stored in a non-volatile memory (not shown) in the selection circuit 30 as a reference signal composed of 60 bits each. One record data (pattern) is selected from a plurality of types of patterns under test (NLTS patterns under test) as the signal under test, and the 60-bit record data is stored in the shift register 31. Supply.

The shift register 31 is a 60-bit parallel input serial output shift register that writes 60-bit parallel recording data when the S / L mode is 0 and arbitrary data written when the S / L mode is 1. The bit is serially shifted one bit at a time, and supplied to the encoder 7.

Then, the encoder 7, the AGC circuit 9, the signal detection circuit 10, the decoder 11, the servo demodulation circuit 12, the servo control circuit 13, the drive circuit 14, the FFT 15, the control circuit 6, and the recording; In addition, at least a part of the pattern generation circuit 20 can be configured as a magnetic recording / reproducing LSI (Large Scale Integration).

A method of measuring NLTS by the fifth harmonic method in the magnetic disk device 100 according to an embodiment of the present invention configured as described above will be described. This NLTS measurement method consists of the following three steps.

First, a reference signal (reference pattern; see FIG. 2) is recorded on the magnetic disk 2 using the magnetic head 3, the reproduced signal is detected from the output of the AGC circuit 9, and the fifth harmonic is obtained by the FFT 15. Measure the wave signal (hereinafter referred to as 5th order component) (Step 1). In addition, let this 5th-order component be Vref.

Next, the pattern to be measured (see Fig. 2) is selected, recorded on the magnetic disk 2 as in step 1, and the fifth-order component Vpat of the reproduced signal is measured by the FFT 15 (step 2). ).

Then, after calculating the ratio Va b = Vp at / V ref based on the fifth-order components V ref and ぴ Vpat measured in steps 1 and 2, the NLTS is calculated from the above equation (2). (Step 3).

Then, the above steps 1 to 3 are sequentially changed for the pattern to be measured. Multiple NLTSs and measure multiple NLTSs.

FIGS. 5 (a), (b), (c) and FIGS. 6 (a), (b), (c) each show a plurality of types of measured objects in the magnetic disk device 100 according to an embodiment of the present invention. Measurement error by NLTS simulation for N LT S pattern (NLT S pattern to be measured 10101 1 1, NLT S pattern to be measured 1 1 101 11 1, NLTS pattern to be measured 01 101 1 1 and NLTS pattern to be measured 00001 1 1) It is a figure showing the example of. The simulations for Figs. 5 (a) to (c) and Figs. 6 (a) to (c) show that the bit period N is 60 bits (60T; N = 60) and the predetermined harmonic component 5 (M = 5), a bit length δ = 4T, R = N / M = 12, and a GMR p-H curve with negligible effects from the previous bit.

Figs. 5 (a) to 5 (c) are diagrams showing the relationship between the NLTS amount and the NLTS value at the tribit position, and (a) shows the vertical asymmetry ratio of the reproduced signal being 0% (A sym = 0%). The figure shows the simulation result in the case of (a), (b) is the figure showing the simulation result when the vertical asymmetry ratio of the reproduced signal is 10% (A sym = 10%), and (c) is the figure in which the vertical FIG. 9 is a diagram showing a simulation result in the case of 10% (A sym = -10%).

More specifically, FIGS. 6 (a) to 6 (c) are diagrams showing the relationship between the NLT Si and the NLTS value at the dibit position, respectively, and FIG. 6 (a) shows that the vertical asymmetry ratio of the reproduced signal is 0% (A sym = (B) is a diagram showing the simulation results when the vertical asymmetry ratio of the reproduced signal is 10% (A sym = 10%), and (c) is a diagram showing the simulation results when the vertical asymmetry ratio of the reproduced signal is 10% (A sym = 10%). FIG. 9 is a diagram illustrating a simulation result in a case where the up-down asymmetry ratio of a reproduced signal is 1 10% (A sym = —10%).

FIGS. 7 (a), (b), (c) and FIGS. 8 (a), (b), (c) each show a plurality of types of magnetic disk drives 100 according to an embodiment of the present invention. The corrected NLT S for the measured N LTS pattern (measured NLT S pattern 10101 11 1, measured NLTS pattern 1 1 101 11 1, measured NLTS pattern 01 101 1 1 and measured NLTS pattern 00001 1 1) FIG. 9 is a diagram showing an example of a measurement error by the simulation of FIG. The simulations in Figs. 7 (a) to (c) and Figs. 8 (a) to (c) show that the bit period N is 60 bits (60T; N = 60), order of the specified harmonic component 5 (M-5), negligible influence from the previous bit Bit length δ = 4Τ, R = N / M = 12, GMR p—with H curve Things.

More specifically, FIGS. 7A to 7C are diagrams showing the relationship between the NLTS amount and the NLTS value at the tribit position, and FIG. 7A shows that the upper and lower asymmetry ratio of the reproduced signal is 0% (A sym

= 0%), (b) shows the simulation result when the vertical asymmetry ratio of the reproduced signal is 10% (A sym = 10%), and (c) shows the vertical direction of the reproduced signal. FIG. 11 is a diagram showing simulation results when the asymmetry ratio is 1 10% (A sym = —10%).

Figures 8 (a) to 8 (c) show the NLTS amount and NLT at the dibit position, respectively.

FIG. 7A is a diagram showing a relationship with an LTS value. FIG. 7A is a diagram showing a simulation result when a vertical asymmetry ratio of a reproduced signal is 0% (A sym = 0%), and FIG. The figure shows the simulation results when the ratio is 10% (A sym = 10%), and (c) shows the simulation when the upper and lower asymmetry ratio of the reproduced signal is 1 10% (A sym =-10%). It is a figure showing a result.

9 (a), (1)), FIG. 10), (1, FIG. 11), (b) and FIGS. 12 (a), (b) each show a magnetic disk drive 100 according to an embodiment of the present invention. 5 is a diagram showing an example of actual measurement of NLT S relating to a plurality of types of NLT S patterns to be measured in FIG. More specifically, FIGS. 9A and 9B are diagrams showing an example in which the NLTS is measured without performing the nonlinear correction on the magnetic head 3 having a poor error rate, and FIG. (B) shows the measurement results for the measured NLTS pattern 10101 1 1, the measured NLTS pattern 00001 111, the measured NLTS pattern 01 101 11 1, and the measured NLTS pattern 1 1 101 1 1). FIG. 9 is a diagram showing measurement results of a plurality of dibits (measured NLT S pattern 10101 1, measured NLT S pattern 00001 1, measured NLTS pattern 01 101 1, and measured NLTS pattern 1 1 101 1).

FIGS. 10 (a) and 10 (b) are diagrams showing an example in which NLTS is measured without performing non-linear correction on a normal magnetic head 3, and FIG. 10 (a) shows a plurality of tribits (NLTS pattern 10101 to be measured). 1 1, NLT S pattern to be measured 00001 1 1, Figure showing the measurement results for the NLTS pattern to be measured 0 1 101 1 1 and the NLTS pattern to be measured 1 1 1 0 1 1 1), and (b) shows multiple dibits (NLTS pattern to be measured 1 0 10 1 1, NLT to be measured) FIG. 9 is a diagram illustrating measurement results of an S pattern 0000 1 1, a measured NLTS pattern 0 1 10 11 1 and a measured NLTS pattern 1 1 1 01 1).

FIGS. 11 (a) and 11 (b) are diagrams showing an example in which NLTS is measured by performing non-linear correction on a magnetic head 3 having a poor error rate. FIG. 11 (a) shows a plurality of tribits (measured NLT S Figure 10b shows the measurement results for pattern 1010 1 1 1, NLT S pattern to be measured 0000 1 1 1, N LTS pattern to be measured 01 101 1 1 and N LTS pattern to be measured 1 1 1 0 1 1 1). Shows the measurement results for multiple dibits (measured N LTS pattern 10 10 1 1, measured NLTS pattern 0000 11 1, measured N LTS pattern 0 1 101 1, and measured NLT S pattern 1 1 10 1 1) FIG.

FIGS. 12 (a) and 12 (b) are diagrams showing an example of a case where the NLTS is measured by performing a non-linear correction on a normal magnetic head 3, and FIG. Figure showing measurement results for 1 0 1 1 1, NL TS pattern to be measured 00001 11 1, NLTS pattern to be measured 0 1 10 1 1 1 and N LT S pattern to be measured 1 1 1 0 1 1 1), (b) Indicates the measurement results for multiple dibits (the NLTS pattern to be measured 101 01 1, the NLTS pattern to be measured 000011, the NLTS pattern to be measured 01 1 01 1 and the NLT S pattern to be measured 1 1 101 1) FIG.

9 (a), (b), 10 (a), (b), 11 (a), (b) and 12 (a), (b) show that the normal magnetic head 3 The difference in the amount of NLTS depending on the preceding pattern P1 is about 2%, but in the defective magnetic head 3, the difference in the amount of NLTS depending on the preceding pattern P1 is about 20%. .

In the actual measurement example, an example is shown in which the NLT S depends on the preceding pattern P1 and is caused by the magnetic head 3. However, the present invention is not limited to this. It is easy to guess that NLTS can occur in 2 and the recording transmission path (not shown). Next, an algorithm for generating a reference pattern (reference signal) and a pattern to be measured (signal to be measured) used in the non-linearity measuring section 1 of the magnetic disk device 100 will be described.

The reference pattern and the pattern to be measured used in the non-linearity measuring section 1 of the magnetic disk device 100 are not limited to those shown in FIG. 2, but other reference patterns and the pattern to be measured satisfying the following conditions. You can use. However, the bit length δ is such that the influence from the previous bit can be ignored.

(1) From the reproduction signal of the reference pattern magnetically recorded on the magnetic disk 2 and the reproduction signal of the pattern to be measured also magnetically recorded on the magnetic disk 2, obtain the Μ harmonic components of the order それぞれ, respectively. When both the reference pattern and the pattern under test are configured as a bit sequence with a bit period Ν, the bit period Ν is a multiple of the harmonic component order 、 and the bit period for the harmonic order Μ Ratio of Ν R (R = N / M) Force S multiple of S2.

(2) In the reference pattern, the first magnetization reversal bit R1 is provided at the head position, and the second magnetization reversal bit R2 is provided at a subsequent position at least δ bits away from the first magnetization reversal bit R1. In addition, a third position is located at a subsequent position at least δ bits away from the second magnetization reversal bit R2 and n4XRth (where n4 is a natural number) subsequent to the first magnetization reversal bit R1. And a δ bit from the last bit (Νth bit from the head) of the reference pattern at a subsequent position at least δ bits away from the third magnetization reversal bit R 3. The fourth magnetization reversal bit R 4 is located at the preceding position separated from the second magnetization reversal bit R 2 and at a position subsequent to the (η 5 +0.5) Rth (where η 5 is a natural number) from the second magnetization reversal bit R 2. It is provided.

(3) NLTS measurement pattern sequence composed of the preceding pattern Ρ1 and the non-linearity measurement bit in the pattern to be measured: 2δ bits from the last bit of カ (where δ is the previous bit on the medium) At the succeeding position that is at least distant from the first bit of the NLT S measurement pattern sequence Ρ (η 1 + 0.5) Rth (where η 1 Is a natural number), and a bit string Ρ2 excluding the last bit of the NLT S measurement pattern として A subsequent position that is at least δ bits away from the last bit of pattern P1 and is a preceding position that is at least 2δ bits away from the last bit (（th bit) of the pattern under test, and the NLTS measurement pattern The first magnetization reversal bit C 1 is provided at the position following the (η 2 + 0.5) Rth (where η 2 is a natural number) from the last bit of column Ρ.

(4) If the number of magnetization reversal bits in the NLT S measurement pattern sequence Ρ is odd in the pattern to be measured, furthermore, at a subsequent position at least δ bits away from the last bit of the NLT S measurement pattern sequence Ρ And the second magnetization reversal bit C 2 at a preceding position at least δ away from the first bit card of the bit string Ρ2 pattern, and at a subsequent position at least δ bits away from the first magnetization inversion bit c 1. It is a preceding position that is at least δ bits away from the last bit of the pattern to be measured, and is (η 3 +0.5) Rth (where η 3 is a natural number) from the second magnetization reversal bit C2 The third magnetization reversal bit C3 is provided at a position subsequent to.

The nonlinearity measurement unit 1 of the magnetic disk device 100 may measure the NLTS using any reference pattern or pattern to be measured that satisfies the above conditions (1) to (4).

FIG. 13 is a diagram showing an example of another reference pattern and a pattern to be measured used in the non-linearity measuring section 1 of the magnetic disk device 100 as one embodiment of the present invention. The reference pattern and the pattern to be measured shown in FIG. 13 satisfy the above conditions (1) to (4), and both the reference pattern and the pattern to be measured have a bit period 50 of 50 bits ( 50Τ; Ν = 50) is a bit string composed of 0s and 1s, and is configured to represent the magnetization reversal position by 1.

As described above, according to the magnetic disk drive 100 (nonlinearity measuring unit 1) as one embodiment of the present invention, the predetermined harmonic of the pattern to be measured having the preceding pattern Ρ1 preceding the bit to be measured of the NLTS. By calculating the NLTS based on the wave component (fifth-order component), the NLTS that depends on the preceding pattern Ρ1 can be easily and quantitatively measured, and the magnetic disk device (magnetic head, transmission system, etc.) It is very effective in media development.

In addition, correction can be easily performed so that NLTS is minimized. In order to optimize the write compensation circuit (WPC), it is possible to use the value of the ratio Vab of the fifth-order component between the reference signal and the signal under test without needing to calculate NLTS using a calculation formula. Correction can be easily performed.

Further, according to the present invention, it is possible to measure NLTS by using the magnetic disk device 100 alone.

The present invention is not limited to the above-described embodiment, and can be variously modified and implemented without departing from the gist of the present invention.

For example, in the above-described embodiment, the first predetermined harmonic component measured by the first measurement unit 55 and the second predetermined harmonic component measured by the second measurement unit 56 are of order 5 ( (M = 5) is described, but these predetermined harmonic components are not limited to the fifth harmonic component, but are harmonic components other than the fifth harmonic component. Is also good. Further, the first predetermined harmonic component and the second predetermined harmonic component may be harmonic components of different orders, and may be variously modified without departing from the spirit of the present invention. it can.

In addition, the pattern generating section 51 may output an inverted reference signal created by inverting the magnetization polarity of the above-described reference pattern (reference signal) as a reference signal, or may output the magnetization of the pattern to be measured (non-measurement signal). The inverted signal under test created by inverting the polarity may be output as the signal under test.Based on the inverted reference signal and the signal under test, the predetermined harmonic component is measured as described above, and the NLTS By calculating the NLTS polarity difference in the same preceding pattern can also be measured. In magnetic recording and reproduction, two polarities are output alternately depending on the direction of magnetization reversal. For example, in the reproduction signal of the dibit pattern, the first bit has a positive polarity and the second bit has a negative polarity, and the first bit has a negative polarity and the second bit has a positive polarity. You could think so. Since the measured pattern used in the non-linearity measuring section 1 of the magnetic disk drive 100 has an even number of magnetization reversal information, the measured pattern generated by reversing the magnetization polarity of the measured pattern is used. , It is possible to generate two polarities.

For the generation of the inverted reference signal and the inverted measured signal, the magnetization polarity of the reference pattern and the measured pattern generated from the pattern generator 51 is inverted. It is also possible to provide a reversing section and reverse the magnetization polarity by the reversing section.

In the above-described embodiment, the pattern of the reference signal or the signal to be measured (the reference pattern or the pattern to be measured) is generated by the pattern generating circuit 20 (pattern generating unit 51). However, the present invention is not limited to this. For example, the control circuit 6 receives a reference signal or a pattern signal of the signal under measurement from the outside, and converts the received pattern signal through the recording correction circuit 8 to the head IC 5. It can also be configured to be supplied to, recorded, and played back.

Furthermore, in the above-described embodiment, the FFT 15 is provided downstream of the AGC circuit 9; however, the configuration is not limited thereto. An FFT 15 may be provided at a position upstream of the circuit 9. Further, in the above-described embodiment, the control circuit 6 corresponds to the first predetermined harmonic component measured by the first measurement unit 55 and each signal to be measured measured by the second measurement unit 56. NLTS is calculated from the second predetermined harmonic component to be calculated, but the present invention is not limited to this. It may be provided separately.

Further, in the above-described embodiment, the first predetermined harmonic component measured based on the reproduced signal of the reference pattern and the second predetermined harmonic component measured based on the reproduced signal of the pattern under test are different from each other. Although the case where the M-th harmonic component has the same order M is described, the invention is not limited to this, and the first predetermined harmonic component and the second predetermined harmonic component have different orders. It may be a harmonic component.

If each embodiment of the present invention is disclosed, it can be manufactured by those skilled in the art. Industrial applicability

As described above, the nonlinearity measuring method, nonlinearity measuring apparatus, magnetic recording / reproducing apparatus, and magnetic recording / reproducing LSI of the present invention are useful for measuring the nonlinear transition shift in magnetic recording / reproducing on a medium. In particular, it is suitable for more accurate NLTS measurement considering the magnetization reversal state of the bit string preceding the pattern to be measured.

Claims

The scope of the claims

1. A non-linearity measurement method for calculating a non-linear transition shift (NLTS) in magnetic recording and reproduction on a medium,

A reference signal recording step for recording a reference signal on the medium;

A measured signal recording step of recording a plurality of types of measured signals on the medium; a first measuring step of measuring a first predetermined harmonic component from a reproduction signal of a reference signal magnetically recorded on the medium;

A second measurement step of measuring a second predetermined harmonic component from a reproduced signal of each of a plurality of types of signals to be measured magnetically recorded on the medium;

A calculating step of calculating the NLTS from the first predetermined harmonic component and the second predetermined harmonic component corresponding to each signal under test;

A non-linearity measurement method, wherein each of the plurality of types of signals to be measured includes a magnetization reversal pattern sequence P1 prior to the measurement target bit of the NLTS.

2. the first predetermined harmonic component and the second predetermined harmonic component are M-th harmonic components of order M, respectively;

The reference signal and the plurality of types of signals to be measured are each configured as a bit string having a bit period N, and the bit period N is a multiple of the order M of the predetermined harmonic component, and the harmonic order 2. The nonlinearity measuring method according to claim 1, wherein a ratio R (R = N / M) of the bit period N to M is a multiple of 2.

3. The measured signal is

2 δ bits from the last bit of the NLTS measurement pattern sequence P composed of the magnetization reversal pattern P 1 and the non-linearity measurement target bit (where δ is the number of bits from the previous bit on the medium) The subsequent position that is at least the bit length that can ignore the effect of NLT S) and the (nl + 0.5) Rth (where nl is a natural number) subsequent position from the first bit of the NLT S measurement pattern sequence Ρ As a starting point, a bit string P2 excluding the last bit of the NLTS measurement pattern P is arranged,

At a subsequent position at least δ bits away from the last bit of the magnetization reversal pattern P1 The preceding position is at least 2δ bits away from the last bit of the signal under measurement, and (η 2 + 0 · 5) Rth (where η 2) from the last bit of the NLTS measurement pattern sequence Ρ. 3. The non-linearity measuring method according to claim 2, wherein a first magnetization reversal bit C1 is provided at a position subsequent to a natural number.

4. The measured signal is

When the number of magnetization reversal bits in the NLTS measurement pattern sequence Ρ is an odd number, it is a subsequent position at least δ bits away from the last bit of the NLTS measurement pattern sequence Ρ, and the bit sequence 先頭 the first bit of the two patterns A second magnetization reversal bit C 2 at a preceding position at least δ away from

A subsequent position at least δ bits away from the first magnetization reversal bit C 1, a preceding position at least δ bits away from the last bit of the signal under measurement, and the ^second magnetization reversal bit C 2 4. The non-linearity according to claim 3, wherein a third magnetization reversal bit C 3 is provided at a position subsequent to the (η 3 +0.5) Rth (where η 3 is a natural number). Measuring method.

5. The reference signal is

A first magnetization reversal bit R 1 is provided at the head position,

A second magnetization reversal bit R 2 is provided at a subsequent position at least δ bits away from the first magnetization reversal bit R 1,

A third position is located at a position subsequent to the second magnetization reversal bit R2 by δ bits or more and at a position subsequent to the first magnetization reversal bit R1 at the η 4 XRth position (where η 4 is a natural number). The magnetization reversal bit R 3 of

A preceding position that is at least δ bits away from the third magnetization reversal bit R 3, a preceding position that is at least δ bits away from the last bit of the reference signal, and the second magnetization reversal bit R The second to (η 5 +0.5) R-th (where η 5 is a natural number) and a fourth magnetization reversal bit R 4 at a position subsequent to the R-th bit. The method for measuring nonlinearity according to any one of items 4.

6. The method according to claim 1, wherein in the calculating step, the NLTS is calculated based on a ratio between the first predetermined harmonic component and the second predetermined harmonic component. 6. The method for measuring nonlinearity according to any one of items 5 to 5.

7. The signal according to any one of claims 1 to 6, wherein an inverted signal under measurement created by inverting the magnetization polarity of the signal under measurement is used as the signal under measurement. Linearity measurement method.

8. In the measured signal recording step, a change step capable of changing a recording position of the measurement target bit of the non-linearity in the measured signal is provided,

8. The method according to claim 1, wherein in the second measuring step, the second predetermined harmonic component is measured based on the signal under measurement after moving the recording position. Or the method for measuring nonlinearity according to item 1.

9.The reference signal and the plurality of types of signals under test have a bit period of 60 (N

= 60), wherein the first predetermined harmonic component and the second predetermined harmonic component are fifth harmonic components of order 5 (M = 5), respectively. 9. The method for measuring nonlinearity according to any one of items 1 to 8.

10. The reference signal and the plurality of types of signals to be measured are all bit strings having a bit period of 50 (N = 50), and the first predetermined harmonic component and the second predetermined harmonic 9. The method for measuring nonlinearity according to claim 1, wherein the components are fifth harmonic components of order 5 (M = 5).

1 1. A non-linearity measuring device for calculating a non-linear transition shift (NLTS) in magnetic recording and reproduction on a medium,

A first measuring unit (55) for measuring a first predetermined harmonic component from a reproduction signal of a reference signal magnetically recorded on the medium;

Each of a plurality of types of signals to be measured magnetically recorded on the medium, A second measuring section (5 6) for measuring a predetermined harmonic component of 2,

A calculating unit (57) for calculating the N LTS from the first predetermined harmonic component and the second predetermined harmonic component corresponding to each signal under measurement;

A nonlinearity measuring apparatus, wherein the plurality of types of signals to be measured each include a magnetization reversal pattern sequence P1 prior to the measurement target bit of the NLTS.

1 2. The first predetermined harmonic component and the second predetermined harmonic component are M-th harmonic components of order M, respectively.

The reference signal and the plurality of types of signals to be measured are each configured as a bit string having a bit period N, and the bit period N is a multiple of the order M of the predetermined harmonic component, and the harmonic order 11. The nonlinearity measuring apparatus according to claim 11, wherein a ratio R (R = N / M) of the bit period N to M is a multiple of two.

13. A first measuring section (55) for measuring a first predetermined harmonic component from a reproduced signal of a reference signal magnetically recorded on a medium;

A second measuring unit (56) for measuring a second predetermined harmonic component from a reproduced signal of each of a plurality of types of signals to be measured magnetically recorded on the medium;

Calculation for calculating a non-linear transition shift (NLTS) in magnetic recording / reproducing on the medium from the first predetermined harmonic component and the second predetermined harmonic component corresponding to each signal to be measured. A magnetic recording / reproducing apparatus, comprising: a section (57), wherein the plurality of types of signals to be measured each include a magnetization reversal pattern sequence P1 prior to the measurement target bit of the NLTS.

14. The first predetermined harmonic component and the second predetermined harmonic component are M-th harmonic components of order M, respectively.

The reference signal and the plurality of types of signals to be measured are each configured as a bit string having a bit period N, and the bit period N is a multiple of the order M of the predetermined harmonic component, and the harmonic order 14. The magnetic recording / reproducing apparatus according to claim 13, wherein a ratio R (R = N / M) of the bit period N to M is a multiple of two.

15. The measured signal is

2 δ bits from the last bit of the NLTS measurement pattern sequence P composed of the magnetization reversal pattern P 1 and the non-linearity measurement target bit (where δ is the number of bits from the previous bit on the medium) Subsequent position that is at least distant from the first bit of the NLTS measurement pattern sequence P and that is the (n1 + 0.5) Rth (nl is a natural number) subsequent position , The bit string P2 excluding the last bit of the NLTS measurement pattern P is arranged,

A subsequent position that is at least δ bits away from the last bit of the magnetization reversal pattern P1, a preceding position that is at least 2δ bits away from the last bit of the signal under measurement, and the NLTS measurement pattern sequence The first magnetization reversal bit C 1 is provided at a position following the (ιι 2 +0.5) Rth (where η 2 is a natural number) from the last bit of the first magnetization reversal bit. The magnetic recording and reproducing apparatus according to claim 1.

16. The reference signal is

A first magnetization reversal bit R 1 is provided at the head position, and.

A subsequent position at least δ bits away from the third magnetization reversal bit R 3, a preceding position at least δ bits away from the last bit of the reference signal, and from the second magnetization reversal bit R 2 Claim 14 or Claim 15 wherein a fourth magnetization reversal bit R4 is provided at the position following the (η5 + 0.5) Rth (where η5 is a natural number). Item 6. A magnetic recording / reproducing apparatus according to Item 1.

1 7. A first measuring section (55) for measuring a first predetermined harmonic component from a reproduced signal of a reference signal magnetically recorded on a medium; Each of a plurality of types of signals to be measured magnetically recorded on the medium,

A second measuring unit (56) for measuring a predetermined harmonic component of 2,

Calculation for calculating a non-linear transition shift (NLTS) in magnetic recording / reproducing on the medium from the first predetermined harmonic component and the second predetermined harmonic component corresponding to each signal to be measured. (57), wherein each of the plurality of types of signals to be measured has a magnetic inverted pattern sequence P1 prior to the measurement target bit of the NLTS. Recording and playback LSI.

1 8. The first predetermined harmonic component and the second predetermined harmonic component are M-th harmonic components of order M, respectively.

The reference signal and the plurality of types of signals to be measured are each configured as a bit string having a bit period N, and the bit period N is a multiple of the order M of the predetermined harmonic component, and the harmonic order 18. The magnetic recording / reproducing L according to claim 17, wherein a ratio R (R = N / M) of the bit period N to M is a multiple of 2.

S I.

1 9. If the signal under measurement is

2δ bits from the last bit of the NLTS measurement pattern sequence P composed of the magnetization reversal pattern P1 and the non-linearity measurement target bit (where δ is the NLTS from the previous bit on the medium) Starting from the subsequent position that is at least the following position away from the first bit of the NLT S measurement pattern sequence P and that is the (nl + 0.5) Rth (where nl is a natural number) A bit string P2 excluding the last bit of the NLTS measurement pattern P is arranged, and

A subsequent position that is at least δ bits away from the last bit of the magnetization reversal pattern P1, a preceding position that is at least 2δ bits away from the last bit of the signal under measurement, and the NLTS measurement pattern sequence The first magnetization reversal bit C 1 is provided at a position following the (η 2 +0.5) Rth (where η 2 is a natural number) from the last bit of the first magnetization reversal bit. Magnetic recording / reproducing LSI as described.

20. The reference signal is

A first magnetization reversal bit R 1 is provided at the head position,

A second magnetization reversal bit R 2 at a subsequent position at least δ bits away from the first magnetization reversal bit R 1;

A third position at a subsequent position at least δ bits away from the second magnetization reversal bit R 2 and at a position subsequent to the η 4 XRth (where η 4 is a natural number) from the first magnetization reversal bit R 1 Magnetization reversal bit R 3

A subsequent position at least δ bits away from the third magnetization reversal bit R 3, a preceding position at least δ bits away from the last bit of the reference signal, and from the second magnetization reversal bit R 2 18. The method according to claim 18, wherein a fourth magnetization reversal bit R 4 is provided at a position following the (η 5 +0.5) Rth (where η 5 is a natural number). 10. The magnetic recording / reproducing LSI according to item 9.