JP2008004189A - Perpendicular magnetic disk device and its offset control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the reliability of data read by a perpendicular head by improving the error rate of a perpendicular magnetic disk device. <P>SOLUTION: The perpendicular magnetic disk device having a perpendicular magnetic recording medium 1 and a perpendicular head 2 is provided with an offset adjusting circuit 5 for receiving an input differential signal from the perpendicular head to adjust the offset amount of the input differential signal. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a perpendicular magnetic disk device and an offset control method thereof, and more particularly to an offset control technique for a perpendicular magnetic disk device having a perpendicular magnetic recording medium and a perpendicular head.

  In recent years, perpendicular magnetic disk devices have been put into practical use. However, a perpendicular magnetic recording disk (perpendicular magnetic recording medium, medium) for a hard disk drive (HDD) is used from a perpendicular magnetic recording head (vertical head) by using a backing layer. Information can be recorded even if the generated magnetic field is weakened, and the coercive force can be increased more than double that of a perpendicular recording medium or a longitudinal (planar) recording medium having no backing layer. Further, the perpendicular head has a narrow core width and a small leakage magnetic field, and a high recording density cannot be achieved unless a high recording magnetic field is generated.

  FIG. 1 is a block diagram schematically showing an example of a conventional perpendicular magnetic disk apparatus. In FIG. 1, reference numeral 101 denotes a perpendicular magnetic recording medium, 102 denotes a vertical head, 103 denotes a head amplifier, and 104 denotes a read channel circuit (RDC).

  As shown in FIG. 1, the conventional perpendicular magnetic disk apparatus reads data recorded on a perpendicular magnetic recording medium 101 with a vertical head 102, amplifies an input differential signal from the vertical head 102 with a head amplifier 103, The read channel circuit 104 converts the digital signal into “0” and “1” digital signals and outputs them.

  FIG. 2 is a view schematically showing an example of a vertical head in the perpendicular magnetic disk apparatus of FIG. 1 together with a recording medium, and shows a vertical head with a trailing shield. In FIG. 1, reference numeral 1011 is a recording layer, 1012 is an intermediate layer, 1013 is a soft under layer (SUL), 1021 is a GMR (Giant-Magneto Resistive) element, 1022 and 1023 are magnetic shields for GMR, 1024 is the main pole, 1025 is the trailing shield and return yoke, 1026 is the coil, 1027 is the leading edge of the main pole, and 1028 is the trailing edge of the main pole.

  As shown in FIG. 1, the perpendicular magnetic recording medium 101 includes a recording layer 1011, an intermediate layer 1012, and a soft magnetic underlayer (SUL) 1013. Here, the backing layer 1013 needs to be thin in order to manufacture and mass-produce the perpendicular magnetic recording medium 101. However, since the backing layer 1013 functions as a part of the vertical head 102, it is thinned. In this case, the magnetic field generated from the vertical head 102 is greatly reduced.

  Therefore, the vertical head 102 shown in FIG. 1 is provided with a trailing shield 1025 to introduce not only a vertical magnetic field but also a horizontal magnetic field to facilitate switching of magnetization of the recording layer 1011 by an oblique magnetic field. It is designed to improve performance. The present invention is applicable not only to a vertical head with a trailing shield shown in FIG. 2, but also to a perpendicular magnetic disk apparatus using a single-pole type vertical head that does not use a conventional trailing shield. Needless to say, you can.

  By the way, conventionally related to an optical disk reproducing apparatus, it is assumed that even if light having a wavelength shorter than the conventional light source wavelength is used, the reproduction signal SN ratio is prevented from deteriorating and a high quality reproduced signal is obtained. The output voltage from the current / voltage conversion unit is differentially amplified as a P-polarized and S-polarized voltage corresponding to each beam obtained by the differential amplification unit 42 for each beam, and each of these outputs is a timing adjustment adding unit. Have been proposed (see Patent Document 1, for example).

  Conventionally, this also relates to the magneto-optical reproducing apparatus, but adds the first and second differential output signals corresponding to the P-polarized component and the S-polarized component detected from two sets of two-divided photodetectors. It has also been proposed to obtain a tracking signal obtained by offset-correcting a track error caused by a magneto-optical pit obtained by differentiating both signals from a push-pull track error signal obtained by the groove (see, for example, Patent Document 2).

Japanese Patent Application Laid-Open No. 07-296437 JP 05-325304 A

  FIG. 3 is a diagram schematically showing an example of a sector configuration applied to the perpendicular magnetic disk apparatus of FIG.

  As shown in FIG. 3, for example, one sector is used by a user for a preamble area PRE for positioning the vertical head 102 such as a training pattern and an f2 signal, a sync byte area SB for synchronizing the sector, and a user. The data area DATA that is actual data and a gap area GAP for synchronization are configured. Note that FIG. 3 shows an example of a mere sector configuration, and other areas such as CRC (Cyclic Redundancy Check) for checking transfer data errors and ECC (Error Check and Correct) for correcting errors may be included. Needless to say.

  4 and 5 are waveform diagrams for explaining an example of the waveform of the differential signal input to the head amplifier of the perpendicular magnetic disk apparatus. 4 and 5, reference signs Sin + and Sin− indicate input differential signals from the vertical head 102, and Sin indicates a combined waveform of the input differential signals Sin + and Sin− in the head amplifier 103. Here, the input differential signals Sin + and Sin− are, for example, signals output when the vertical head 102 reads the f2 signal in the preamble region PRE having the sector configuration shown in FIG.

  As shown in FIG. 4, when there is no offset in the input differential signals Sin + and Sin−, both the positive (+) side and the negative (−) side are grounded at 50% of the upper and lower waveforms, that is, at exactly half the position. There is a level (zero level), and the combined waveform Sin, which is the result of adding the input differential signals Sin + and Sin−, also has a zero level at the half position of the + side and − side waveforms.

  In a perpendicular magnetic disk apparatus having a perpendicular magnetic recording medium and a perpendicular head, an offset having a reverse polarity occurs in relation to the magnetization state on the medium 101 during perpendicular recording, or in the perpendicular head 102 or the head amplifier 102, or Different offsets may occur on the + and − sides.

  That is, as shown in FIG. 5, when the input differential signals Sin + and Sin− have opposite phase offsets Los + and Los−, the combined waveform Sin includes the offsets Loss + and Sin + of the input differential signals Sin + and Sin−. An offset Los obtained by adding Los- is generated.

  As described with reference to FIG. 1, the conventional perpendicular magnetic disk apparatus is provided with a function of measuring an offset in input differential signals Sin + and Sin− from the vertical head 102 or controlling the offset. It wasn't.

FIG. 6 is a diagram for explaining a problem in a conventional perpendicular magnetic disk apparatus.
As shown in FIG. 6, a reproduction waveform W102 that is an output of the vertical head 102 is supplied to a head amplifier (head IC) 103, and a low-frequency component is cut and waveform-equalized by the head amplifier 103. Is supplied to an RDC (read channel circuit) 104.

  By the way, in a conventional in-plane recording type magnetic disk apparatus (horizontal magnetic disk apparatus), since the reproduction waveform is obtained as a Lorentz type signal, the zero level can be clearly determined by recording at a low frequency. It was. However, in a perpendicular recording type magnetic disk apparatus (perpendicular magnetic disk apparatus), since the reproduction waveform is a rectangular waveform, the zero level may not be clear even when recording at a low frequency.

  That is, in magnetic recording, a multilevel value is used as a reproduction signal equalization target (hereinafter referred to as a target), which is detected as “0” and “1” as digital information by a detector. Among them, there is a specific target whose error rate is better than other targets in perpendicular recording. Among these specific targets, the low frequency components are currently cut by the head IC (head amplifier), so that sufficient characteristics cannot be obtained and the loss is caused at the error rate. was there.

  An object of the present invention is to improve the reliability of read data by a vertical head by improving the error rate of a perpendicular magnetic disk device in view of the above-described problems of the prior art.

  According to the first aspect of the present invention, there is provided a perpendicular magnetic disk device having a perpendicular magnetic recording medium and a perpendicular head, each receiving an input differential signal from the perpendicular head, and each offset amount of the input differential signal. There is provided a perpendicular magnetic disk drive comprising an offset adjustment circuit for adjusting each of the above.

  According to a second aspect of the present invention, there is provided an offset control method for a perpendicular magnetic disk device having a perpendicular magnetic recording medium and a perpendicular head, each receiving an input differential signal from the perpendicular head, There is provided an offset control method for a perpendicular magnetic disk drive, wherein each offset amount of a signal is adjusted.

  According to the present invention, it is possible to improve the error rate of the perpendicular magnetic disk device and improve the reliability of read data by the perpendicular head.

  Hereinafter, embodiments of a perpendicular magnetic disk device and an offset control method for the perpendicular magnetic disk device according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 7 is a block diagram schematically showing an embodiment of the perpendicular magnetic disk apparatus according to the present invention. In FIG. 7, 1 is a perpendicular magnetic recording medium, 2 is a perpendicular head (perpendicular magnetic recording head), 3 is a head amplifier, 4 is a read channel circuit (RDC), and 5 is an offset adjustment circuit.

  As shown in FIG. 7, the perpendicular magnetic disk apparatus of the present embodiment is basically similar to the conventional perpendicular magnetic disk apparatus of FIG. 2, the input differential signal from the vertical head 2 is amplified by the head amplifier 3, converted into “0” and “1” digital signals by the read channel circuit 4, and output.

  The head amplifier 3 includes an input stage circuit 31 that amplifies an input differential signal from the vertical head 2, an output stage circuit 32, and adders 51 and 52, and the offset adjustment circuit 5 includes adders 51 and 52. , An integration circuit 53, a selection circuit 54, a determination circuit 55, and a memory 56. Here, the adders 51 and 52 are for removing the offset in the + side and − side signals of the input differential signal from the vertical head 2 and constitute a part of the offset adjustment circuit 5. In the embodiment shown in FIG. 7, it is provided in the head amplifier (head IC) 3 in order to reduce the influence of noise in the input differential signal from the vertical head 2 having a low signal level.

  That is, the adders 51 and 52 are respectively supplied with the + side and − side signals of the input differential signal from the vertical head 2 and the output signal of the selection circuit 54, and the + side and − side of the input differential signal. The input differential signal from which the offset is removed (the ground level is adjusted to the optimum offset value (zero level)) is supplied to the input stage circuit 31. Here, the selection circuit 54 is set in the memory 56 by the output of the determination circuit 55 that determines each offset amount of the input differential signal using the MSE signal (minimum square error signal) from the read channel circuit 4. Either the offset value obtained or the offset value obtained by integration by the integration circuit 53 is selected and output to the adders 51 and 52.

FIG. 8 is a diagram for explaining the operation of the perpendicular magnetic disk apparatus according to the present invention.
As shown in FIG. 8, for example, when an input differential signal W2 from the vertical head 2 has an offset of +100 μV, for example, −100 μV by the offset adjustment circuit 5 using the MSE signal from the read channel circuit 4 Thus, the input differential signal W2 ′ from which the offset has been removed is supplied to the input stage circuit 31. A specific operation will be described in detail later with reference to FIGS. 11 and 12.

  Here, as is clear from the comparison with the conventional perpendicular magnetic disk apparatus shown in FIG. 6 described above, the signal output from the head amplifier 3 in this embodiment is also effective in the low frequency, so the low frequency is cut off. A waveform W3 not supplied is supplied to an RDC (read channel circuit) 4.

  FIG. 9 is a diagram for explaining Kp (T50 / bit period) used in the present invention, and FIG. 10 is a diagram for explaining the effect of the present invention in relation to the bit period. Here, FIGS. 10A to 10C show the simulation results of the error rate of the specific target “5-6-0-F”.

  As shown in FIG. 9, Kp used in the following description is defined as, for example, a value obtained by dividing a time region T50 in which a signal output level is 25% to 75% by a bit period (Kp = T50 / bit). Period) and the value of Kp increases as the linear recording density in the track direction increases.

  Then, regarding the error rate of the specific target “5-6-0-F”, for example, as shown in FIG. 10A, when a low-frequency cut is performed (high-pass filter (HPF: low-frequency cut frequency fc)) 10) and a case where low-frequency cut is not performed (when considering up to a direct current (DC) region) as shown in FIG. 10B, an error occurs in a region where the value of Kp is large. It can be seen that the rate can be improved.

  That is, as shown in FIG. 10 (c), when Kp = 1.0, the error rate is 0.51 (−4.18 − (− 4.69 = 0.51) in consideration of the DC region. (−4.18), the difference in error rate (−4.69) when the high-pass filter is passed), whereas when Kp = 1.25, the difference is −0.18 (−5. 03 − (− 4.85) = − 0.18 digit error rate can be improved), and further, when Kp = 1.5, the difference is −0.3 (−5.81 − (− 5. 51) = − 0.3 digit error rate can be improved), and the error rate can be improved in a region where the value of Kp is large (for example, Kp = 1.25, 1.5) (this embodiment). The effect of the example is great), and the higher the linear recording density in the track direction, The effect of the improvement of the layer large error rate can be expected.

  FIG. 11 is a flowchart for explaining an embodiment of the offset control method of the perpendicular magnetic disk apparatus according to the present invention. Here, to simplify the explanation, it is assumed that the adders 51 and 52 are controlled with the same value, and the width of the offset amount is ± 100 mV. Therefore, δ = 2 mV.

  First, in step ST11, for example, when a read execution command (READ) is given from the hard disk controller (HDC: host) in FIG. 7, the process proceeds to step ST12, and a signal of a certain sector is read. Here, the normal correction value is a value set in the memory 56, and the offset adjustment in the adders 51 and 52 is performed by the offset value set in the memory 56. However, if the error rate becomes worse due to noise, changes with time, etc., and retry operation is performed, it is considered necessary to optimize the offset.

  In step ST12, it is determined whether or not there is a signal in the data area (for example, DATA in FIG. 3). If it is determined that there is no data area signal, the reading process ends, and if it is determined that there is a data area signal. That is, if it is determined that the data area is not the servo area, the process proceeds to step ST13 to determine whether n is greater than 100. Here, n indicates the number of times of performing processing, and when the number of times is limited to 100 (that is, assuming δ = 2 mV, by repeating 100 times, the offset value initially set in the memory 56 is −100 mV to 100 mV. Change within the range).

  If it is determined in step ST13 that n is greater than 100, the reading process ends. If it is determined that n is 100 or less, the process proceeds to step ST16, where n = n + 1 and offset. The value n1 is set to n1 + δ, and the process proceeds to step ST15.

  In step ST15, the MSE value (MSE (n)) calculated by the read channel circuit 4 when changed by the offset value in step ST16 is compared with the MSE-min value that minimizes the offset value. Steps ST13, ST14, and ST15 are repeated until the offset value initially set in the memory 56 is changed within the range of −100 mV to 100 mV (repeated only 100 times). At this time, if the value of the MSE minimum value MSE-min becomes smaller by the next offset value n1 in step ST14, the offset value n1 at that time is updated and set in the memory 56. In this way, the offset value initially set in the memory 56 is changed within the range of −100 mV to 100 mV, and in step ST14, the offset value n1 that makes the MSE value the smallest (the error rate is the highest). Is set in the memory 56 as a new offset value.

  FIG. 12 is a flow chart for explaining another embodiment of the offset control method of the perpendicular magnetic disk apparatus according to the present invention. The preamble pattern at the head of the data area (for example, the f2 signal of the preamble area PRE shown in FIG. 3). Etc.) and an approximate offset value at present is calculated.

  That is, first, in step ST11, for example, when a read execution command (READ) is given from the upper level, the process proceeds to step ST17, and a signal of a certain sector is read.

  In step ST17, the presence / absence of a preamble pattern signal (for example, the f2 signal in the preamble region PRE in FIG. 3) is determined. If it is determined that there is no preamble pattern, the process proceeds to step ST12 and is the same as described in FIG. Perform proper processing. If it is determined in step ST17 that there is a preamble pattern signal, the process proceeds to step ST18, where the integration circuit 53 integrates the input signal (output signal of the input stage circuit 31), and whether or not this integration value is zero. Is determined. In step ST18, the offset value is changed (n1 = n1 + Δ) in step 19 until the integral value of the input signal becomes zero. Here, for example, the offset value n1 initially set in the memory 56 is in increments of −100 mV, and Δ is about 0.1 mV.

  If it is determined in step ST18 that the integral value of the input signal is zero, the process proceeds to step ST12 and the same processing as described in FIG. 11 is performed. In this embodiment, after the approximate value is calculated first, the sequence of steps ST12 to ST16 in FIG. 11 described above is entered, so that further fine adjustment can be performed. That is, in the embodiment of FIG. 12, for example, even when the processes in steps ST13, ST16, and ST15 are performed 100 times, for example, by setting the value of δ in step ST16 to 1 mV, −50 mV to 50 mV with an accuracy of 1 mV An offset value that is optimal within the range of can be obtained.

  As shown in FIG. 7, a selection circuit 54 is provided, and the integration value obtained by integrating the input signal by the integration circuit 53 and the integration value becomes zero and the offset value set in the memory 56 are MSE. An appropriate one may be selected and supplied to the adders 51 and 52 based on the output of the determination circuit 55 determined by the signal.

  In the above description, the offset values in the adders 51 and 52 are assumed to be the same. However, if they are different, the same processing is independently performed on each of the adders 51 and 52 to perform the offset. The amount (offset value) is adjusted.

  As described above in detail, according to the embodiment of the perpendicular magnetic disk device and the offset control method of the perpendicular magnetic disk device according to the present invention, the error rate of the perpendicular magnetic disk device is improved and the read data of the perpendicular head is read. Reliability can be improved.

(Appendix 1)
A perpendicular magnetic disk drive having a perpendicular magnetic recording medium and a perpendicular head,
A perpendicular magnetic disk drive, comprising: an offset adjustment circuit for receiving each input differential signal from the vertical head and adjusting each offset amount of the input differential signal.

(Appendix 2)
2. The perpendicular magnetic disk drive according to claim 1, wherein the offset adjustment circuit includes an adder that adds an offset adjustment value to the input differential signal.

(Appendix 3)
The perpendicular magnetic disk device according to appendix 1, further comprising a determination circuit that determines each offset amount of the input differential signal using a minimum square error signal in a read channel circuit. Disk unit.

(Appendix 4)
The perpendicular magnetic disk device according to attachment 3, further comprising an integration circuit for integrating the waveforms of the input differential signals, and adjusting each offset amount of the input differential signals using the integration circuit. Then, the perpendicular magnetic disk apparatus is characterized in that each offset amount is finely adjusted by the determination circuit.

(Appendix 5)
2. The perpendicular magnetic disk drive according to claim 1, further comprising a memory for storing a reference value for adjusting each offset amount of the input differential signal.

(Appendix 6)
The perpendicular magnetic disk drive according to appendix 5, wherein a default value at which an error rate measured in advance is an optimum value is recorded in the memory.

(Appendix 7)
An offset control method for a perpendicular magnetic disk drive having a perpendicular magnetic recording medium and a perpendicular head,
An offset control method for a perpendicular magnetic disk drive, wherein each input differential signal from the vertical head is received and each offset amount of the input differential signal is adjusted.

(Appendix 8)
The offset control method for a perpendicular magnetic disk device according to appendix 7, wherein each offset amount of the input differential signal is adjusted by adding an offset adjustment value to the input differential signal. An offset control method for a perpendicular magnetic disk drive.

(Appendix 9)
In the offset control method for a perpendicular magnetic disk device according to appendix 7, adjustment of each offset amount of the input differential signal is performed by determining each offset amount of the input differential signal using a minimum square error signal. An offset control method for a perpendicular magnetic disk drive, characterized by:

(Appendix 10)
In the offset control method for a perpendicular magnetic disk device according to attachment 9, the adjustment of each offset amount of the input differential signal is performed by integrating the waveform of the input differential signal and using the integrated signal. An offset control method for a perpendicular magnetic disk drive, wherein each offset amount of an input differential signal is adjusted, and then each offset amount is finely adjusted using the minimum square error signal.

(Appendix 11)
The offset control method for a perpendicular magnetic disk apparatus according to appendix 7, wherein a reference value for adjusting each offset amount of the input differential signal is stored in a memory.

(Appendix 12)
The offset control method for a perpendicular magnetic disk apparatus according to appendix 11, wherein a default value at which an error rate measured in advance is an optimum value is recorded in the memory. Method.

  The present invention can be widely applied to a perpendicular magnetic recording medium and a perpendicular magnetic disk apparatus using various perpendicular heads such as a trailing shield or a single pole type.

It is a block diagram which shows roughly an example of the conventional perpendicular magnetic disc apparatus. FIG. 2 is a diagram schematically illustrating an example of a vertical head in the perpendicular magnetic disk apparatus of FIG. 1 together with a recording medium. FIG. 2 is a diagram schematically showing an example of a sector configuration applied to the perpendicular magnetic disk device of FIG. 1. FIG. 6 is a waveform diagram (part 1) for explaining an example of a waveform of a differential signal input to a head amplifier of a perpendicular magnetic disk device. FIG. 12 is a waveform diagram (No. 2) for explaining another example of the waveform of the differential signal input to the head amplifier of the perpendicular magnetic disk device. It is a figure for demonstrating the problem in the conventional perpendicular magnetic disc apparatus. 1 is a block diagram schematically showing an embodiment of a perpendicular magnetic disk apparatus according to the present invention. It is a figure for demonstrating operation | movement of the perpendicular magnetic disc apparatus based on this invention. It is a figure for demonstrating Kp (T50 / bit period) used by this invention. It is a figure for demonstrating the effect of this invention in relation to a bit period. 3 is a flowchart for explaining an embodiment of an offset control method for a perpendicular magnetic disk apparatus according to the present invention. 6 is a flowchart for explaining another embodiment of the offset control method of the perpendicular magnetic disk apparatus according to the present invention.

Explanation of symbols

1,101 Perpendicular magnetic recording medium 2,102 Perpendicular head 3,103 Head amplifier 4,104 Read channel circuit (RDC)
5 Offset adjustment circuit 31 Input stage circuit 32 Output stage circuit 51, 52 Adder 53 Integration circuit 54 Selection circuit 55 Determination circuit 56 Memory

Claims (5)

A perpendicular magnetic disk drive having a perpendicular magnetic recording medium and a perpendicular head,
A perpendicular magnetic disk drive, comprising: an offset adjustment circuit for receiving each input differential signal from the vertical head and adjusting each offset amount of the input differential signal.   2. The perpendicular magnetic disk apparatus according to claim 1, wherein the offset adjustment circuit includes an adder that adds an offset adjustment value to the input differential signal.   2. The perpendicular magnetic disk apparatus according to claim 1, further comprising a determination circuit that determines each offset amount of the input differential signal using a minimum square error signal in a read channel circuit. Magnetic disk unit.   4. The perpendicular magnetic disk drive according to claim 3, further comprising an integrating circuit that integrates each waveform of the input differential signal, and adjusting each offset amount of the input differential signal using the integrating circuit. After that, the perpendicular magnetic disk device is characterized in that the offset amount is finely adjusted by the determination circuit. An offset control method for a perpendicular magnetic disk drive having a perpendicular magnetic recording medium and a perpendicular head,
An offset control method for a perpendicular magnetic disk drive, wherein each input differential signal from the vertical head is received and each offset amount of the input differential signal is adjusted.

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