Magnetic disk drive

Abstract

To provide a magnetic disk device capable of suitably writing signals capable of taking on three or more levels to a magnetic disk. [Solution] The magnetic head comprises a light element and a light-emitting element that irradiates a laser beam onto the light position of the light element. The processing circuit is capable of performing any of the following light operations: a first light operation, a second light operation, and a third light operation. In the first light operation, the processing circuit supplies a positive recording current with an amplitude of the fourth value to the light element while the laser beam is output. In the second light operation, the processing circuit supplies a negative recording current with an amplitude of the fifth value to the light element while the laser beam is output. In the third light operation, the processing circuit supplies a recording current with an amplitude of a non-zero sixth value, which is smaller than either the fourth or fifth value, to the light element while the laser beam is output.

Description

Technical Field

[0001] This embodiment relates to a magnetic disk device.

Background Art

[0002] In recent years, technologies for writing signals with three or more levels on magnetic disks have been under development.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] One embodiment aims to provide a magnetic disk device that can suitably write a signal with three or more levels on a magnetic disk.

Means for Solving the Problems

[0005] According to one embodiment, a magnetic disk device comprises a magnetic disk, a magnetic head, and a processing circuit. The magnetic disk has tracks composed of a plurality of unit recording areas arranged in a row in the circumferential direction. The magnetic head includes a light element that writes data to the tracks and a light-emitting element that irradiates laser light onto the positions on the magnetic disk that are written by the light element. The processing circuit is capable of performing any of the following write operations: a first write operation that writes a first value to a first unit recording area, a second write operation that writes a second value to a first unit recording area, and a third write operation that writes a third value to a first unit recording area. The first unit recording area is one of the plurality of unit recording areas. The second value is different from the first value. The third value is different from both the first and second values. The first write operation is an operation that sets the magnetization state of the first unit recording area to a first state by supplying a positive recording current with an amplitude of a fourth value to the light element while causing the light-emitting element to output laser light. The second light operation is performed by supplying a negative recording current with an amplitude of the fifth value to the light element while outputting laser light to the light-emitting element, thereby changing the magnetization state of the first unit recording area to a second state, which is different from the first state. The third light operation is performed by supplying a recording current to the light element, which includes a non-zero recording current with an amplitude smaller than either the fourth or fifth value, while outputting laser light to the light-emitting element, thereby changing the magnetization state of the first unit recording area to a third state, which is different from both the first and second states. [Brief explanation of the drawing]

[0006] [Figure 1] Figure 1 shows an example of the configuration of a magnetic disk device according to the first embodiment. [Figure 2] Figure 2 is a schematic diagram showing an example of the configuration of a magnetic disk according to the first embodiment. [Figure 3] Figure 3 shows an example of the relationship between the amplitude of the recording current corresponding to the 0 state and the bit error rate when reading the digit region of the 0 state. [Figure 4]Figure 4 shows an example of a detailed configuration of the processing circuit according to the first embodiment. [Figure 5] Figure 5 is a diagram illustrating a specific example of the recording method according to the first embodiment. [Figure 6] Figure 6 is a diagram illustrating a specific example of the recording method according to Modification Example 1. [Figure 7] Figure 7 is a diagram illustrating a specific example of the recording method according to Modification Example 2. [Figure 8] Figure 8 shows an example of a detailed configuration of a processing circuit to which the PBW method is applied, according to Modification 3. [Figure 9] Figure 9 is a diagram illustrating a specific example of a recording method to which the PBW method is applied, according to Modification Example 3. [Figure 10] Figure 10 shows an example of a detailed configuration of a processing circuit to which the MPRZ method is applied, according to Modification 3. [Figure 11] Figure 11 is a diagram illustrating a specific example of a recording method to which the NPRZ method is applied, according to Modification Example 3. [Figure 12] Figure 12 shows an example of a detailed configuration of a processing circuit to which the MPRZ method is applied, according to Modification 4. [Figure 13] Figure 13 is a diagram illustrating a specific example of the recording method according to Modification 4. [Figure 14] Figure 14 is a diagram illustrating a specific example of the recording method according to Modification Example 5. [Figure 15] Figure 15 shows the relationship between the laser drive current when writing "0" and the amplitude variation of the regenerated signal when reading multiple digit regions where "0" is written, for the case where the data length of the written "0" is 1T and the case where the data length of the written "0" is 2T. [Figure 16] Figure 16 is a diagram illustrating a specific example of the recording method according to the second embodiment. [Figure 17]FIG. 17 is a diagram showing the relationship between the laser drive current at the time of writing "0" and the variation in the amplitude of the reproduction signal when reading a large number of digit areas where "0" has been written, for each of the cases where the length of the pre-written data is 2T and the case where the length of the pre-written data is 6T. [Figure 18] FIG. 18 is a diagram for explaining a specific example of the recording method according to the third embodiment. [Figure 19] FIG. 19 is a diagram for explaining a specific example of the recording method according to the fourth embodiment. [Figure 20] FIG. 20 is a diagram for explaining a specific example of the recording method according to Modification 6. [Figure 21] FIG. 21 is a diagram for explaining another specific example of the recording method according to Modification 6. [Figure 22] FIG. 22 is a diagram for explaining a specific example of the recording method according to Modification 7. [Figure 23] FIG. 23 is a diagram for explaining an example of the configuration for realizing the recording method according to Modification 7.

MODE FOR CARRYING OUT THE INVENTION

[0007] Hereinafter, a magnetic disk device according to an embodiment will be described in detail with reference to the accompanying drawings. Note that the present invention is not limited by these embodiments.

[0008] (First Embodiment) FIG. 1 is a diagram showing an example of the configuration of a magnetic disk device 1 according to the first embodiment.

[0009] The magnetic disk device 1 is connected to the host 2. The magnetic disk device 1 can receive an access command such as a write command or a read command from the host 2.

[0010] The magnetic disk drive 1 comprises a magnetic disk 11 having a magnetic layer formed on its surface. The magnetic disk drive 1 accesses the magnetic disk 11 in response to access commands. Access includes writing data and reading data. Although the magnetic disk drive 1 may have multiple magnetic disks 11, in the first embodiment, for the sake of simplicity in explanation and illustration, the magnetic disk drive 1 comprises only one magnetic disk 11.

[0011] Data is written and read by the magnetic head 22. Specifically, in addition to the magnetic disk 11, the magnetic disk device 1 includes a spindle motor (SPM) 12, a lamp 13, an actuator arm 15, a voice coil motor (VCM) 16, a servo controller (SVC) 21, a magnetic head 22, a hard disk controller (HDC) 23, a preamplifier 24, a read / write channel (RWC) 25, a processor 26, a FROM (Flash Read Only Memory) 28, and a DRAM (Dynamic Random Access Memory) 29.

[0012] The magnetic disk 11 is rotated at a predetermined rotational speed by the SPM 12, which is mounted coaxially.

[0013] SVC21 is an integrated circuit that functions as a driver for SPM12 and VCM16. The processor 26 controls the rotation of SPM12 and VCM16 via SVC21.

[0014] The magnetic head 22 includes a write element 22w and a read element 22r. The magnetic head 22 writes data to the magnetic disk 11 using the write element 22w. The magnetic head 22 reads data from the magnetic disk 11 using the read element 22r.

[0015] Furthermore, the magnetic head 22 is equipped with a laser diode 22ld. When data is written by the light element 22w, the laser diode 22ld irradiates the light location on the surface of the magnetic disk 11 with laser light, such as near-field light, thereby locally heating the light location. This reduces the coercivity of the light location, making it possible to reduce the amount of current (hereinafter referred to as recording current) supplied to the light element 22w to generate the magnetic field. This type of recording method, which assists magnetization with thermal energy, is known as heat-assisted magnetic recording (HAMR). In other words, according to this embodiment, the laser diode 22ld performs writing using the heat-assisted magnetic recording method.

[0016] Note that the laser diode 22ld is an example of a light-emitting element. The light-emitting element is not limited to a laser diode as long as thermal energy can be transferred to the light-emitting position by irradiating it with laser light.

[0017] The magnetic head 22 is attached to the tip of the actuator arm 15. The magnetic head 22 is moved radially across the magnetic disk 11 by the VCM 16 driven by the SVC 21. Note that either one or both of the write element 22w and the read element 22r on the magnetic head 22 may be provided in multiple quantities on a single magnetic head 22.

[0018] When the rotation of the magnetic disk 11 is stopped, the magnetic head 22 is moved onto the ramp 13. The ramp 13 holds the magnetic head 22 in a position away from the magnetic disk 11.

[0019] The preamplifier 24 is an integrated circuit that performs data writing and reading via the magnetic head 22. During writing, the preamplifier 24 amplifies the signal corresponding to the data to be written (the write data signal described later) supplied from the RWC 25 and supplies it to the writing element 22w. Also during writing, the preamplifier 24 controls the output of the laser light from the laser diode 22ld based on the signal supplied from the RWC 25 (the laser control signal described later). During reading, the preamplifier 24 amplifies the regeneration signal sent from the reading element 22r and supplies it to the RWC 25.

[0020] DRAM29 is used as a buffer for data transferred to and from host 2. For example, DRAM29 is used to temporarily store data to be written or data read from magnetic disk 11.

[0021] Furthermore, DRAM 29 is used by the processor 26 as operating memory. DRAM 29 is used as an area where the firmware program is loaded and an area where various management data is temporarily stored.

[0022] HDC23 controls the transfer of data between it and host 2 via the I / F bus. HDC23 supplies the data to be written, received from host 2, to RWC25 via DRAM29. HDC23 receives the read data output from RWC25 via DRAM29 and transmits that read data to host 2.

[0023] The RWC25 modulates the data to be written, supplied from the HDC23, and provides it to the preamplifier 24. The RWC25 also performs demodulation, including error correction, on the signal read from the magnetic disk 11 and supplied from the preamplifier 24, and then outputs the signal as digital data to the HDC23.

[0024] The processor 26 is, for example, a CPU (Central Processing Unit). FROM 28 and DRAM 29 are connected to the processor 26.

[0025] FROM28 stores the firmware program and various configuration information. The firmware program may also be stored on the magnetic disk 11.

[0026] The processor 26 performs overall control of the magnetic disk device 1 according to the firmware program stored in FROM 28 or the magnetic disk 11.

[0027] The HDC23, RWC25, and processor 26 may be configured as a System-On-a-Chip (SoC) 30. The SoC 30 may also include other elements (e.g., FROM 28 or DRAM 29).

[0028] Figure 2 is a schematic diagram showing an example of the configuration of a magnetic disk 11 according to the first embodiment. This figure shows an example of the rotation direction of the magnetic disk 11. The magnetic head 22 moves relative to the magnetic disk 11 as the magnetic disk 11 rotates. Therefore, the write / read direction, i.e., the direction in which data is written or read by the magnetic head 22 along the circumferential direction, is opposite to the rotation direction of the magnetic disk 11.

[0029] During the manufacturing process, servo information is written to the magnetic disk 11, for example, by a servo writer or by self-servo writing (SSW). As shown in Figure 2, a radial arrangement of servo regions 42 is shown as an example of the arrangement of servo regions to which servo information has been written. Between the servo regions 42, data regions 43 to which data can be written are provided.

[0030] Multiple concentric tracks 41 are arranged in the radial direction of the magnetic disk 11. Multiple data areas 43 are arranged along the tracks 41, with multiple sectors on which data is written.

[0031] The servo information includes servo marks, Gray codes, burst patterns, and postcodes. When writing data to or reading data from a sector, the SoC30 obtains information about the current position of the magnetic head 22 based on the servo information read by the magnetic head 22 from the servo area 42. Then, based on the calculated current position information, the SoC30 performs positioning control to bring the magnetic head 22 closer to the target position.

[0032] Data can be considered as a column consisting of multiple values. Each track 41 (more precisely, each sector of each track 41) has a column of multiple single-digit values ​​written along it. In other words, each track 41 (more precisely, each sector of each track 41) can be thought of as having a structure in which multiple unit recording areas, each capable of holding a single-digit value, are arranged in a row along the track 41. Each of these unit recording areas capable of holding a single-digit value is denoted as a digit area.

[0033] In the first embodiment, a signal that can take three levels is recorded in the digit area. That is, a single-digit value represented in ternary is written to each digit area.

[0034] Specifically, in light operation, the light element 22w is controlled as follows: When a positive recording current with an amplitude of a predetermined value or more is supplied while laser light is irradiated onto the digit region where the light element 22w is located, the light element 22w generates a magnetic field corresponding to the recording current, thereby magnetizing the digit region where the light element 22w is located to positive polarity. When a negative recording current with an amplitude of a predetermined value or more is supplied while laser light is irradiated onto the digit region where the light element 22w is located, the light element 22w generates a magnetic field corresponding to the recording current, thereby magnetizing the digit region where the light element 22w is located to negative polarity.

[0035] Furthermore, during light operation, when the amplitude of the recording current is suppressed to nearly zero while the digit region where the light element 22w is located is irradiated with laser light, the polarity of the magnetization of the digit region where the light element 22w is located becomes nonpolar. This is based on the fact that when only thermal energy is applied to raise the temperature of the digit region above the Curie temperature without applying a magnetic field, the polarity of the magnetization of many magnetic particles within the digit region changes randomly, and the overall polarity of the magnetization of that digit region appears to be nonpolar.

[0036] Thus, the light operation magnetizes the digit region to either positive, negative, or nonpolar. Each of the magnetization states of the digit region—that is, the positive, negative, and nonpolar states—is associated with a different value.

[0037] During the lead operation, when the lead element 22r passes over a digit region, the lead element 22r obtains a regenerated signal with an amplitude corresponding to the polarity of the magnetization in that digit region. If the polarity of the magnetization in the digit region is positive, a regenerated signal with a predetermined positive amplitude is obtained. If the polarity of the magnetization in the digit region is negative, a regenerated signal with a predetermined negative amplitude is obtained. If the polarity of the magnetization in the digit region is nonpolar, a regenerated signal with zero amplitude is obtained. The RWC25 acquires a value corresponding to the magnetization state of the digit region based on the amplitude of the regenerated signal obtained from the lead element 22r.

[0038] The correspondence between magnetization states and values ​​is designed arbitrarily. Hereafter, as an example, we will assume that the positive polarity state is associated with "+1", the negative polarity state is associated with "-1", and the nonpolar state is associated with "0". The positive polarity state, that is, the state where "+1" is lit, will be denoted as the +1 state. The negative polarity state, that is, the state where "-1" is lit, will be denoted as the -1 state. The nonpolar state, that is, the state where "0" is lit, will be denoted as the 0 state.

[0039] Furthermore, the amplitude of the recording current required to bring the digit region to a +1 state is denoted as the amplitude of the recording current corresponding to the +1 state. The amplitude of the recording current required to bring the digit region to a -1 state is denoted as the amplitude of the recording current corresponding to the -1 state. The amplitude of the recording current required to bring the digit region to a 0 state is denoted as the amplitude of the recording current corresponding to the 0 state.

[0040] When the correspondence between magnetization states and values ​​is defined as described above, "+1" is an example of the first value. "-1" is an example of the second value. "0" is an example of the third value. Writing "+1" to the digit region is an example of the first write operation. Writing "-1" to the digit region is an example of the second write operation. Writing "0" to the digit region is an example of the third write operation. The amplitude value of the recording current required to bring the digit region to a +1 state (AW1, described later) is an example of the fourth value. The amplitude value of the recording current required to bring the digit region to a -1 state (AW2, described later) is an example of the fifth value. The amplitude value of the recording current required to bring the digit region to a 0 state (AW3, described later) is an example of the sixth value. Positive polarity is an example of the first state. Negative polarity is an example of the second state. Nonpolarity is an example of the third state.

[0041] During write operation, if the amplitude of the recording current corresponding to the 0 state is set to zero, the magnetization state of the target digit region will be determined by thermal noise or the induced magnetic field from the surrounding digit regions. As a result, a polarity bias occurs in the magnetization of many magnetic particles within the target digit region. Since this bias occurs randomly for each digit region, variations occur in the amplitude of the regenerated signal when reading from many 0-state digit regions, and the bit error rate deteriorates accordingly.

[0042] Therefore, in the first embodiment, the amplitude of the recording current corresponding to the 0 state is controlled to a small non-zero value. This intentionally suppresses polarity bias in the magnetization of the numerous magnetic particles within the target digit region, thereby suppressing the variation in the amplitude of the regenerated signal when read against the 0 state digit region.

[0043] Naturally, if the amplitude of the recording current corresponding to the 0 state is too large, the recording method for that 0 state becomes equivalent to a normal saturated magnetic recording method, that is, a recording method that makes almost all magnetic particles in the digit region either positive or negative. Therefore, the amplitude of the recording current corresponding to the 0 state must be sufficiently smaller than the amplitude of the recording current corresponding to the -1 state and the +1 state.

[0044] Figure 3 shows an example of the relationship between the amplitude of the recording current corresponding to the 0 state and the bit error rate when reading from the digit region in the 0 state. The horizontal axis shows the amplitude of the recording current. The vertical axis shows the bit error rate when reading from the digit region in the 0 state, expressed on a common logarithmic scale. Hereafter, the bit error rate when reading from the digit region in the 0 state will be simply referred to as the bit error rate.

[0045] In the example shown in Figure 3, the bit error rate is minimized when the recording current amplitude is around 4 mA. In other words, when the recording current amplitude is 0 mA, the bit error rate worsens compared to when the recording current amplitude is 4 mA.

[0046] In the example shown in Figure 3, the amplitude of the recording current for saturation magnetic recording, i.e., the amplitude of the recording current corresponding to the -1 and +1 states, is set to 100 mA or more. If the amplitude of the recording current is greater than 4 mA, the bit error rate gradually worsens as the amplitude of the recording current approaches the amplitude of the recording current for saturation magnetic recording.

[0047] Therefore, following the example shown in Figure 3, the amplitude of the recording current corresponding to the 0 state is set to 4mA.

[0048] However, the amplitude value of the recording current corresponding to the 0 state, which minimizes the bit error rate, may depend on the setting of the laser light output by the laser diode 22ld, the characteristics of the magnetic head 22, and the characteristics of the magnetic film of the magnetic disk 11, etc. Therefore, regarding the amplitude of the recording current corresponding to the 0 state, for example, an optimal value is searched during the manufacturing process, and the value obtained through this search is determined as the amplitude of the recording current corresponding to the 0 state.

[0049] Hereafter, the setting value for the amplitude of the recording current corresponding to the 0 state will be referred to as the 0 state amplitude setting value.

[0050] To enable the control of the recording current as described above, the RWC25 and preamplifier 24 have the configuration described below. Hereafter, the RWC25 and preamplifier 24 will be referred to as the processing circuit 50.

[0051] Figure 4 shows an example of a detailed configuration of the processing circuit 50 according to the first embodiment.

[0052] The RWC25 comprises a media write data generation circuit 251, an encoder 252, a first driver 253, a second driver 254, and a third driver 255. The encoder 252 comprises a binary data generation circuit 61, a control signal generation circuit 62, and an LD control circuit 63.

[0053] The preamplifier 24 includes a fourth driver 241, a fifth driver 242, and a sixth driver 243.

[0054] The media write data generation circuit 251 is supplied with ternary write data from the HDC23. The ternary write data is a sequence of values ​​that can take the values ​​"+1", "-1", and "0".

[0055] The ternary write data supplied to the media write data generation circuit 251 may be transmitted from the host 2 to the magnetic disk drive 1. Alternatively, the host 2 may transmit binary data to the magnetic disk drive 1, and the binary data may be converted to ternary by the HDC 23 or other components of the magnetic disk drive star to generate the ternary write data supplied to the media write data generation circuit 251.

[0056] The media write data generation circuit 251 performs various modulations, including error correction coding, on the ternary write data. The media write data generation circuit 251 supplies the modulated ternary write data to the encoder 252. Hereafter, unless otherwise specified, ternary write data refers to the modulated ternary write data.

[0057] The binary data generation circuit 61 generates a write data signal that transitions between "H" level and "L" level from ternary write data. The binary data generation circuit 61 sets the write data signal to "H" level for the value "+1" in the sequence of ternary write data. The binary data generation circuit 61 sets the write data signal to "L" level for the value "-1" in the sequence of ternary write data.

[0058] The binary data generation circuit 61 sets the value "0" in the ternary write data sequence to a level opposite to the level corresponding to the value immediately following a sequence of one or more consecutive "0s" that includes the value "0". For example, if the value immediately following a sequence of one or more consecutive "0s" is "+1", the binary data generation circuit 61 sets the write data signal to the "L" level for that sequence of one or more consecutive "0s". If the value immediately following a sequence of one or more consecutive "0s" is "-1", the binary data generation circuit 61 sets the write data signal to the "H" level for that sequence of one or more consecutive "0s".

[0059] The control signal generation circuit 62 generates an amplitude control signal in synchronization with the write data signal generated by the binary data generation circuit 61. The amplitude control signal is a signal for controlling the amplitude of the recording current to the 0 state amplitude setting value. The control signal generation circuit 62 transitions the amplitude control signal from the "L" level to the "H" level when it starts writing a sequence of one or more consecutive "0"s, and maintains the amplitude control signal at the "H" level for a period of 1T. Outside of the above period, the control signal generation circuit 62 maintains the amplitude control signal at the "L" level.

[0060] "T" is a unit that represents the time or length of data based on the time required to write a single-digit data or the length of a single-digit data. For example, the time required to write N (where N is an integer greater than or equal to 1) digits of data or the length of N digits of data is expressed as NT.

[0061] The LD control circuit 63 outputs a laser control signal, which is a signal for controlling the drive current supplied to the laser diode 22ld.

[0062] The write data signal generated by the binary data generation circuit 61 is transferred to the preamplifier 24 via the first driver 253. The amplitude control signal generated by the control signal generation circuit 62 is transferred to the preamplifier 24 via the second driver 254. The laser control signal generated by the LD control circuit 63 is transferred to the preamplifier 24 via the third driver 255. Here, each signal is assumed to be transferred as a differential signal, but the configuration of each signal is not limited to a differential signal.

[0063] In the preamplifier 24, the fourth driver 241 receives the write data signal. The fifth driver 242 receives the amplitude control signal. The sixth driver 243 receives the laser control signal.

[0064] The fifth driver 242 transfers the amplitude control signal to the fourth driver 241.

[0065] The fourth driver 241 generates a recording current with a waveform corresponding to the write data signal. When generating the recording current, the fourth driver 241 switches the amplitude of the recording current between a value for saturated magnetic recording and the zero-state amplitude setting value, based on the amplitude control signal received from the fifth driver 242. More specifically, the fourth driver 241 starts generating a recording current with the amplitude of the zero-state amplitude setting value when the amplitude control signal transitions from the "L" level to the "H" level. When the signal transitions from the "H" level to the "L" level, the fourth driver 241 starts generating a recording current for saturated magnetic recording. The recording current generated by the fourth driver 241 is supplied to the write element 22w.

[0066] The sixth driver 243 generates a current (hereinafter referred to as the laser drive current) that drives the laser diode 22ld based on the laser control signal. The laser drive current is supplied to the laser diode 22ld, and the laser diode 22ld emits laser light based on the laser drive current.

[0067] Figure 5 is a diagram illustrating a specific example of the recording method according to the first embodiment.

[0068] Figure 5 shows a sequence of values ​​that make up the light data, and the magnetization state of the target track 41 after it has been magnetized by the light of that light data. In this figure, the magnetization state is indicated by dot hatching, diagonal hatching, and white hatching. Dot hatching indicates positive polarity, diagonal hatching indicates negative polarity, and white hatching indicates no polarity.

[0069] Additionally, the circumferential boundaries of the multiple digit regions DG aligned along track 41 are indicated by dotted lines.

[0070] Furthermore, the waveforms of the amplitude control signal, the output of the laser light from the laser diode 22ld, and the recording current are shown. Each waveform is shown such that its time axis corresponds to its circumferential position on track 41.

[0071] In the example shown in Figure 5, the column "-1, -1, -1, 0, -1, -1, +1, -1, 0, 0, +1, +1, +1, 0, 0, +1, -1" is shown as an example of ternary write data. In this specification, the columns of values ​​are presented in chronological order.

[0072] The laser output is controlled to remain constant at a value Pc during the illumination of the light data, so as to ensure that the temperature at the illumination site is above the Curie temperature.

[0073] The amplitude of the recording current corresponding to the +1 state is given by value AW1. The amplitude of the recording current corresponding to the -1 state is given by value AW2. Saturated magnetic recording is achieved with recording currents of these amplitudes.

[0074] When writing multiple values ​​that constitute the write data sequentially, at the timing of writing "+1" or "-1" after writing other values, the amplitude of the recording current is temporarily made larger than values ​​AW1 and AW2 in order to quickly stabilize the magnetic field of the writing element 22w. In this recording current waveform, the portion in which the amplitude of the recording current is temporarily increased immediately after the data value changes is known as OSA (OverShoot Amplitude). From the end of OSA until the next data change, the amplitude of the recording current is maintained at a constant value in order to maintain the magnetic field of the writing element 22w. This portion in which the amplitude of the recording current is maintained at a constant value is called IW.

[0075] The amplitude of the recording current corresponding to the 0 state is set to value AW3. Value AW3 is the value set as the amplitude setting value for the 0 state. Therefore, it is smaller than both value AW1 and value AW2, and is a non-zero value.

[0076] The amplitude control signal is transitioned from the "L" level to the "H" level when a sequence of one or more consecutive "0"s is lit. The amplitude control signal is maintained at the "H" level for the duration of the sequence of "0"s being lit, and then transitioned to the "L" level.

[0077] As the amplitude control signal transitions from the "L" level to the "H" level, the supply of a positive recording current with amplitude value AW3 to the light element 22w begins. After the supply of a positive recording current with amplitude value AW3 to the light element 22w begins, the supply of a positive recording current with amplitude value AW3 to the light element 22w ends when a sequence of one or more "0"s is finished, and the lighting with recording currents of amplitude values ​​AW1 and AW2 resumes.

[0078] In the example shown in Figure 5, a "0" is written by a positive recording current with an amplitude of value AW3. The sign of the recording current is not limited to positive. The RWC25 and preamplifier 24 may be configured so that a "0" is written by a negative recording current with an amplitude of value AW3. However, the sign of the recording current for writing a "0" is fixed to either positive or negative.

[0079] Thus, according to the first embodiment, the processing circuit 50 is configured to be able to write any of "+1", "-1", or "0" to the digit region DG. Specifically, the operation of writing "+1" to the digit region DG involves the processing circuit 50 supplying a positive recording current with an amplitude of value AW1 to the light element 22w while outputting laser light from the laser diode 22ld, thereby magnetizing the digit region DG to a positive polarity. Specifically, the operation of writing "-1" to the digit region DG involves the processing circuit 50 supplying a negative recording current with an amplitude of value AW2 to the light element 22w while outputting laser light from the laser diode 22ld, thereby magnetizing the digit region DG to a negative polarity. The operation of writing "0" to the digit region DG specifically involves the processing circuit 50 outputting laser light to the laser diode 22ld while supplying a recording current with a preset sign of positive and negative amplitude of value AW3 to the light element 22w, thereby making the magnetization state of the digit region DG nonpolar. Value AW3 is smaller than both value AW1 and value AW2, and is a non-zero value.

[0080] When writing "0" to the digit area DG, a recording current of a preset sign (either positive or negative) with a non-zero amplitude is supplied to the write element 22w, thereby suppressing amplitude variations in the regenerated signal when reading from the digit area DG in the 0 state. As a result, the bit error rate when reading from the digit area DG in the 0 state is suppressed. In other words, it is possible to suitably write signals that can take on three levels to the magnetic disk 11.

[0081] In the above description, an example was given in which a signal that can take on three levels is written to the magnetic disk 11. The technology of the first embodiment is also applicable to magnetic disk devices in which a signal that can take on four or more levels is written to the magnetic disk. The writing of one specific level of the signal corresponding to the non-polar state among the four or more levels that the signal can take is achieved by the processing circuit supplying a recording current of a preset sign of positive and negative amplitude of value AW3 to the writing element while causing the laser diode 22ld to output laser light. This suppresses the bit error rate when reading a signal of a specific level. In other words, it is possible to suitably write a signal that can take on three or more levels to the magnetic disk.

[0082] (Variation 1) Modification 1 will be described as one variation of the first embodiment. According to Modification 1, for example, as shown in Figure 6, the amplitude control signal is transitioned from the "L" level to the "H" level at a time Td earlier than the timing at which a sequence of one or more consecutive "0"s is started to light.

[0083] A write element has an area that is recorded on the magnetic disk at one time due to the effect of the size of its magnetic poles. This area is called the footprint. If the timing of switching the amplitude of the recording current to the 0 state amplitude setting is equal to the timing when the write element reaches the digit area DG, then due to the effect of the footprint, there is a risk that saturation magnetic recording will occur in a part of the digit area DG beyond the boundary of the digit area DG to which the "0" write target is located.

[0084] According to Modification 1, the timing of the amplitude control signal transition is continuously adjustable. The switching of the recording current amplitude to the 0 state amplitude setting occurs at a timing that is earlier than the timing at which the write element 22w reaches the digit region DG of the "0" write destination by a time Td corresponding to the footprint length. This prevents saturation magnetic recording from occurring in a part of the digit region DG beyond the boundary of the digit region DG of the "0" write destination. As a result, the recording quality of the 0 state is improved.

[0085] (Modification 2) As another variation of the first embodiment, Variation 2 will be described. The technology of Variation 2 can be used in conjunction with the technology of Variation 1.

[0086] According to Modification 2, in the RWC25, the control signal generation circuit 62 instructs the preamplifier 24 to set the amplitude of the recording current to the 0 state amplitude setting value by amplitude control signal during the period of writing one or more consecutive sequences of "0". In the preamplifier 24, the fourth driver 241 switches the amplitude of the recording current between values ​​AW1, AW2 and value AW3 under the control of the fifth driver 242. The fourth driver 241 sets the amplitude of the recording current to value AW3 while the amplitude control signal is at the "H" level, and sets the amplitude of the recording current to values ​​AW1, AW2 while the amplitude control signal is at the "L" level.

[0087] Therefore, as shown in Figure 7, for example, the amplitude control signal is maintained at the "H" level during the period when one or more consecutive "0"s are written. As a result, during this period, the amplitude of the recording current is set to value AW3, and the digit area DG where the "0"s are recorded is set to a 0 state.

[0088] (Variation 3) As yet another variation of the first embodiment, Variation 3 will be described. The technique of Variation 3 can be used in combination with either Variation 1 or Variation 2.

[0089] Two known methods for controlling the amplitude of the recording current are the PBW (Pulse Based Writing) method and the MPRZ (Main Pole Relaxation Zone) method. Modification 3 describes a technique for achieving three states—+1, 0, and -1—when these methods are applied.

[0090] Figure 8 shows an example of a detailed configuration of the processing circuit 50a to which the PBW method is applied, according to Modification 3. Note that the same components of the processing circuit 50a as those in the first embodiment will be omitted from explanation or explained briefly.

[0091] The RWC25 comprises a media write data generation circuit 251a, an encoder 252, a first driver 253, a second driver 254, and a third driver 255. The encoder 252 comprises a binary data generation circuit 61a, a PBW signal generation circuit 64, and an LD control circuit 63.

[0092] The preamplifier 24 includes a fourth driver 241a, a fifth driver 242a, and a sixth driver 243.

[0093] With respect to the ternary write data output by the media write data generation circuit 251a, the value of a sequence of one or more zeros is the same as the value immediately following it. For example, if the value immediately preceding a sequence of one or more zeros is "-1", the value immediately following that sequence of one or more zeros is "-1". If the value immediately preceding a sequence of one or more zeros is "+1", the value immediately following that sequence of one or more zeros is "+1". The media write data generation circuit 251a may generate ternary write data that satisfies the above constraints by modulation. Alternatively, the HDC23 or host 2 may generate ternary write data that satisfies the above constraints.

[0094] The binary data generation circuit 61a generates a write data signal that transitions between "H" and "L" levels from ternary write data. The binary data generation circuit 61a sets the write data signal to "H" level for the value "+1" in the sequence of ternary write data. The binary data generation circuit 61a sets the write data signal to "L" level for the value "-1" in the sequence of ternary write data.

[0095] The binary data generation circuit 61a sets the write data signal to the opposite level to the level corresponding to the value immediately preceding the sequence of consecutive zeros in the ternary write data sequence. For example, if the ternary write data sequence is "-1, 0, -1", the binary data generation circuit 61a generates a write data signal that transitions in the order "L, H, L". If the ternary write data sequence is "+1, 0, +1", the binary data generation circuit 61a generates a write data signal that transitions in the order "H, L, H". The write data signal generated by the binary data generation circuit 61a is transferred to the preamplifier 24 via the first driver 253.

[0096] The PBW signal generation circuit 64 generates a PBW signal. The PBW signal is a signal for controlling the pulse light. A pulse light is a lighting method in which a recording current of a pulse waveform with a predetermined amplitude is passed through the light element 22w. In the modified example 3, the pulse light is used as a light with a recording current of an amplitude set to the 0 state amplitude value.

[0097] A pulsed light is initiated when the PBW signal is at the "H" level at the timing of the edge of the light data signal. The pulsed light is then terminated at the next edge of the light data signal. Therefore, the PBW signal generation circuit 64 transitions the PBW signal from the "L" level to the "H" level slightly earlier than the timing to initiate the lighting of a sequence of one or more "0"s, and maintains the PBW signal at the "H" level for a period of 1T. Outside of the above period, the PBW signal generation circuit 64 maintains the PBW signal at the "L" level. The PBW signal generated by the PBW signal generation circuit 64 is transferred to the preamplifier 24 via the second driver 254.

[0098] In the preamplifier 24, the fourth driver 241a receives the write data signal. The fifth driver 242a receives the PBW signal.

[0099] The fifth driver 242a forwards the received PBW signal to the fourth driver 241a. The fourth driver 241a controls the enable and disable of pulsed light based on the PBW signal received from the fifth driver 242a. If the PBW signal is at the "H" level at the timing of the edge of the write data signal, the fourth driver 241a starts generating a recording current with an amplitude of the 0 state amplitude setpoint. Subsequently, the fourth driver 241a stops generating the recording current with an amplitude of the 0 state amplitude setpoint at the timing of the edge of the write data signal and starts generating a recording current for saturation magnetic recording.

[0100] Figure 9 is a diagram illustrating a specific example of a recording method to which the PBW method is applied, according to Modification Example 3.

[0101] Figure 9 shows a sequence of light data and the magnetization state of the target track 41 as a result of the light in that sequence of light data. It also shows the waveforms of the light data signal, the PBW signal, the laser light output, and the recording current.

[0102] As shown in Figure 9, the write data signal is set to the opposite level to the level corresponding to the value immediately preceding a sequence of consecutive zeros during the period in which one or more consecutive zeros are written. For example, if the sequence of write data is "-1, 0, -1", the write data signal transitions to "L, H, L". Similarly, if the sequence of write data is "-1, 0, 0, -1", the write data signal transitions to "L, H, H, L". Furthermore, the PBW signal is maintained at the "H" level for a period of 1T, slightly earlier than the timing at which the writing of one or more consecutive zeros begins.

[0103] Then, at the timing of the edge of the write data signal, when the PBW signal is at the "H" level, the amplitude of the recording current changes from AW1 and AW2 (AW2 in the example in Figure 9), which are the amplitudes for saturation magnetic recording, to AW3. Subsequently, at the timing of the next edge of the write data signal, the amplitude of the recording current is returned from AW3 to AW1 and AW2 (AW2 in the example in Figure 9). In this way, 1T "0" data and 2T "0" data are written.

[0104] Figure 10 shows an example of a detailed configuration of the processing circuit 50b to which the MPRZ method is applied, according to Modification 3.

[0105] The RWC25 comprises a media write data generation circuit 251b, an encoder 252, a first driver 253, a second driver 254, and a third driver 255. The encoder 252 comprises a binary data generation circuit 61b, an MPRZ signal generation circuit 65, and an LD control circuit 63.

[0106] The preamplifier 24 includes a fourth driver 241b, a fifth driver 242b, and a sixth driver 243.

[0107] The media write data generation circuit 251b generates binary data from ternary write data and generates a write data signal corresponding to the binary data. However, in ternary write data, the value immediately preceding and immediately following a sequence of 1 or more zeros are considered to be different values. For example, if the value immediately preceding a sequence of 1 or more zeros is "-1", the value immediately following that sequence of 1 or more zeros is "+1". If the value immediately preceding a sequence of 1 or more zeros is "-1", the value immediately following that sequence of 1 or more zeros is "+1".

[0108] The binary data generation circuit 61b generates a write data signal that transitions between "H" and "L" levels from ternary write data. The binary data generation circuit 61b sets the write data signal to "H" level for the value "+1" in the sequence of ternary write data. The binary data generation circuit 61b sets the write data signal to "L" level for the value "-1" in the sequence of ternary write data.

[0109] The binary data generation circuit 61b sets the write data signal to the same level as the value immediately preceding a sequence of consecutive zeros in the ternary write data sequence. For example, if the ternary write data sequence is "-1, 0, +1", the binary data generation circuit 61b generates a write data signal that transitions in the order "L, L, H". If the ternary write data sequence is "+1, 0, -1", the binary data generation circuit 61b generates a write data signal that transitions in the order "H, H, L". The write data signal generated by the binary data generation circuit 61b is transferred to the preamplifier 24 via the first driver 253.

[0110] The MPRZ signal generation circuit 65 generates an MPRZ signal. The MPRZ signal is a signal for controlling MPRZ writing. MPRZ writing involves changing the amplitude to a predetermined value during the writing process. In modified example 3, in MPRZ writing, the amplitude of the recording current is set to the 0 state amplitude setting value.

[0111] The MPRZ signal generation circuit 65 maintains the MPRZ signal at an "H" level for a period of 1T from the time it starts writing a sequence of one or more consecutive "0"s. Outside of the above period, the MPRZ signal generation circuit 65 maintains the MPRZ signal at an "L" level. The MPRZ signal generated by the MPRZ signal generation circuit 65 is transferred to the preamplifier 24 via the second driver 254.

[0112] In the preamplifier 24, the fourth driver 241b receives the write data signal. The fifth driver 242b receives the MPRZ signal.

[0113] The fifth driver 242b forwards the received MPRZ signal to the fourth driver 241b. The fourth driver 241b controls the enable and disable of MPRZ writing based on the MPRZ signal received from the fifth driver 242b. The fourth driver 241b starts generating a recording current with an amplitude equal to the 0-state amplitude setpoint when the MPRZ signal transitions from the "L" level to the "H" level. Subsequently, the fourth driver 241b terminates the generation of the recording current with an amplitude equal to the 0-state amplitude setpoint at the timing of the write data signal edge and generates a recording current for saturation magnetic recording.

[0114] Figure 11 is a diagram illustrating a specific example of a recording method to which the NPRZ method is applied, according to Modification Example 3.

[0115] Figure 11 shows a sequence of light data and the magnetization state of the target track 41 as a result of the light in that sequence of light data. It also shows the waveforms of the light data signal, the NPRZ signal, the laser light output, and the recording current.

[0116] As shown in Figure 11, the write data signal is set to the same level as the value immediately preceding a sequence of consecutive zeros during the period in which one or more consecutive zeros are written. Additionally, the MPRZ signal is maintained at an "H" level for a period of 1T from the moment the writing of the sequence of consecutive zeros begins.

[0117] Regardless of the level of the write data signal, at the timing when the MPRZ signal transitions from the "L" level to the "H" level, the amplitude of the recording current changes from AW1 and AW2, which are the amplitudes for saturation magnetic recording, to AW3. Subsequently, at the timing of the next edge of the write data signal, the amplitude of the recording current is returned from AW3 to AW1 and AW2. In this way, 1T "0" data and 2T "0" data are written.

[0118] (Modification 4) In Modification 3, only one of the PBR method or the MPRZ method was applied. As a result, a constraint arose on the relationship between the value immediately preceding a sequence of one or more consecutive "0"s and the value immediately following a sequence of one or more consecutive "0"s for ternary write data. By applying both the PBR method and the MPRZ method, it is possible to eliminate this constraint. Modification 4 describes a magnetic disk device 1 to which both the PBR method and the MPRZ method are applied. Modification 4 can be used in conjunction with Modification 1.

[0119] Figure 12 shows an example of a detailed configuration of the processing circuit 50c to which the MPRZ method is applied, according to Modification 4.

[0120] The RWC25 comprises a media write data generation circuit 251, an encoder 252, a first driver 253, a second driver 254c1, a second driver 254c2, and a third driver 255. The encoder 252 comprises a binary data generation circuit 61c, a PBW signal generation circuit 64c, an MPRZ signal generation circuit 65c, and an LD control circuit 63.

[0121] The preamplifier 24 includes a fourth driver 241c, a fifth driver 242a, a fifth driver 242b, and a sixth driver 243.

[0122] The binary data generation circuit 61c generates a write data signal that transitions between "H" and "L" levels from ternary write data. The binary data generation circuit 61c sets the write data signal to "H" level for the value "+1" in the sequence of ternary write data. The binary data generation circuit 61c sets the write data signal to "L" level for the value "-1" in the sequence of ternary write data.

[0123] The binary data generation circuit 61c determines the level of the write data signal for consecutive sequences of one or more "0"s in the sequence of ternary write data, according to the value immediately preceding the sequence of one or more "0"s and the value immediately following the sequence of one or more "0"s.

[0124] If the value immediately preceding a sequence of one or more zeros is the same as the value immediately following that sequence of one or more zeros, the binary data generation circuit 61c sets the write data signal to a level opposite to the level corresponding to the value immediately preceding that sequence of one or more zeros. In other words, the binary data generation circuit 61c operates in the same manner as the binary data generation circuit 61a in Modification 3.

[0125] If the value immediately preceding a sequence of one or more zeros is different from the value immediately following that sequence of one or more zeros, the binary data generation circuit 61c sets the write data signal to the same level as the value immediately preceding that sequence of one or more zeros. In other words, the binary data generation circuit 61c operates in the same manner as the binary data generation circuit 61b in Modification 3.

[0126] The PBW signal generation circuit 64c generates a PBW signal. If the value immediately preceding a sequence of one or more "0"s is the same as the value immediately preceding that sequence of one or more "0"s, the PBW signal generation circuit 64c transitions the PBW signal from the "L" level to the "H" level slightly earlier than the timing at which the writing of that sequence of one or more "0"s begins, and maintains the PBW signal at the "H" level for a period of 1T. Outside of the above period, the PBW signal generation circuit 64c maintains the PBW signal at the "L" level. The PBW signal generated by the PBW signal generation circuit 64c is transferred to the preamplifier 24 via the second driver 254c1.

[0127] The MPRZ signal generation circuit 65c generates an MPRZ signal. When the value immediately preceding a sequence of one or more "0"s is different from the value immediately following that sequence of one or more "0"s, the MPRZ signal generation circuit 65c maintains the MPRZ signal at an "H" level for a period of 1T from the time the writing of that sequence of one or more "0"s begins. Outside of the above period, the MPRZ signal generation circuit 65c maintains the MPRZ signal at an "L" level. The MPRZ signal generated by the MPRZ signal generation circuit 65c is transferred to the preamplifier 24 via the second driver 254c2.

[0128] In the preamplifier 24, the fourth driver 241c receives the write data signal. The fifth driver 242a receives the PBW signal. The fifth driver 242b receives the MPRZ signal.

[0129] The fifth driver 242a performs the same operation as the fifth driver 242a in Modification 3. The fifth driver 242b performs the same operation as the fifth driver 242b in Modification 3. The fourth driver 241c performs the same operation as the fourth driver 241a in Modification 3, and the same operation as the fourth driver 241b in Modification 3.

[0130] Figure 13 is a diagram illustrating a specific example of the recording method according to Modification 4.

[0131] Figure 13 shows a sequence of light data and the magnetization state of the target track 41 as a result of the light in that sequence of light data. It also shows the waveforms of the light data signal, the PBW signal, the MPRZ signal, the laser light output, and the recording current.

[0132] As shown in Figure 13, if the value immediately preceding a sequence of one or more "0"s is the same as the value immediately following that sequence of one or more "0"s, the write of "0" is achieved using the PBW method. If the values ​​immediately preceding a sequence of one or more "0"s are different from each other, the write of "0" is achieved using the MPRZ method. Therefore, with respect to ternary write data, the write of "0" is possible regardless of the relationship between the value immediately preceding a "0" and the value immediately preceding a "0".

[0133] (Variation 5) In addition to the PBW and MPRZ recording methods, the Advanced PBW method is also known. In the Advanced PBW method, a pulsed waveform recording current is used individually for each digit region (DG). The Advanced PBW method can also be applied as a recording method.

[0134] Figure 14 is a diagram illustrating a specific example of the recording method according to Modification 5. In Modification 5, the AdvancedPBW method is applied. Therefore, as shown in Figure 14, writing is performed individually for each digit region DG by a pulsed waveform recording current. The WCPC signal is a signal transferred from RWC25 to the preamplifier 24, and is a signal for changing the amplitude of a specific pulsed recording current.

[0135] As shown in Figure 14, when the AdvancedPBW method is applied, it becomes possible to write "0" to ternary write data, regardless of the relationship between the value immediately preceding "0" and the value immediately preceding "0".

[0136] (Second embodiment) In the first embodiment and its variations, the laser light output was controlled to be constant regardless of the value lit in the digit region DG. The laser light output may be controlled dynamically. The technique of the second embodiment can be used in conjunction with the techniques of the first embodiment and its variations.

[0137] The relationship between the amplitude variation of the regenerated signal when read from a large number of zero-state digit regions DG and the laser light output can vary depending on the length of a sequence of one or more consecutive "0"s. This sequence of one or more consecutive "0"s is denoted as the "0" data length. The "0" data length can also be considered as the number of digit regions DG that are written to in a circumferential direction.

[0138] Figure 15 shows the relationship between the laser drive current when writing "0" and the amplitude variation of the regenerated signal when reading multiple digit regions DG on which "0" is written, for two cases: one where the data length of the written "0" is 1T, and another where the data length of the written "0" is 2T. The horizontal axis shows the laser drive current when writing "0". The vertical axis shows the amplitude variation of the regenerated signal when reading multiple digit regions DG on which "0" is written. The laser drive current corresponds to the output of the laser light from the laser diode 22ld.

[0139] Hereafter, the amplitude variation of the reproduced signal will refer to the amplitude variation of the reproduced signal when read across a large number of digit regions DG where "0" is written.

[0140] If the laser beam output is too high, tracks 41 adjacent to the target track 41 may be affected, or the lifespan of the laser diode 22ld may be shortened. Conversely, if the laser beam output is too low, the amplitude variation of the regenerated signal will increase, and the bit error rate will increase. Therefore, it is desirable to suppress the laser beam output as much as possible while appropriately suppressing the amplitude variation of the regenerated signal.

[0141] Figure 15 shows that when the laser light output is reduced, even if the laser light output is the same, the variation in the amplitude of the regenerated signal is greater when the data length of the written "0" is 1T compared to when the data length of the written "0" is 2T.

[0142] Therefore, in the second embodiment, the processing circuit 50d controls the output of the laser light to be higher when the data length of the "0" to be written is 1T, as shown in Figure 16, for example, compared to when the data length of the "0" to be written is 2T. This suppresses the deterioration of the amplitude variation of the regenerated signal caused by the data length of the "0" to be written when a "0" with a data length of 1T is written.

[0143] When the data length of the "0" to be lit is 3T or more, the laser output may be the same as when the data length of the "0" to be lit is 2T, or it may be smaller than when the data length of the "0" to be lit is 2T. The longer the data length of the "0" to be lit, the smaller the laser output may be.

[0144] Thus, according to the second embodiment, the processing circuit 50d changes the output of the laser light when writing "0" according to the data length of the "0" to be written, that is, the number of consecutive digit regions DG in which "0" is written. More specifically, from the standpoint of the number of consecutive digit regions DG in which "0" is written, the processing circuit 50d increases the output of the laser light when the number of consecutive digit regions DG in which "0" is written is a first number, compared to when the number of consecutive digit regions DG in which "0" is written is a second number, which is greater than the first number.

[0145] Therefore, the deterioration of amplitude variations in the playback signal caused by the length of the written "0" data is suppressed. As a result, the deterioration of the bit error rate caused by the length of the written "0" data is suppressed.

[0146] (Third embodiment) When writing "0" data to a digit region DG that has old data written to it, the relationship between the amplitude variation of the regenerated signal and the output of the laser light can change depending on the length of the old data. The length of the old data here is the length of a sequence of identical values ​​written to one or more consecutive digit regions DG in the circumferential direction. In other words, it is equivalent to the number of consecutive digit regions DG in the same state among the +1, -1, and 0 states.

[0147] Hereafter, the old data that was written to a digit area DG before the data "0" was written to that digit area DG will be referred to as pre-written data. The length of the pre-written data will be the number of consecutive digit areas DG that are in the same state as the digit area DG to which the "0" data was written, among the +1, -1, and 0 states, including the digit area DG to which the "0" data was written.

[0148] Figure 17 shows the relationship between the laser drive current when "0" is lit and the amplitude variation of the regenerated signal when read for multiple digit regions DG where "0" is lit, for the case where the background data length is 2T and the case where the background data length is 6T, respectively.

[0149] Figure 17 shows that when the laser output is reduced, even if the laser output is the same, the amplitude variation of the reproduced signal is greater when the length of the background data is short compared to when the length of the background data is long.

[0150] Therefore, in the third embodiment, the processing circuit 50e controls the output of the laser light to be higher when the length of the background data is short compared to when the length of the background data is long, as shown in Figure 18, for example. This suppresses the deterioration of the amplitude variation of the regenerated signal caused by the length of the background data.

[0151] In Figure 18, the substrate data is shown as the magnetization state of the digit region DG. To make the substrate data easier to understand, the magnetization state of the digit region DG corresponding to the substrate data is shown shifted from the track center.

[0152] Figure 18 also shows the waveform of the laser drive current (in other words, the waveform of the laser light output) for two cases: one where the base data length is 3T, representing an example of a long base data length, and another where the base data length is 1T, representing an example of a short base data length. The relationship between the specific numerical value of the base data length and the laser light output is not limited to these. The base data length can be set arbitrarily, as long as the laser light output is higher when the base data length is the first length compared to when the base data length is a second length which is longer than the first length.

[0153] Thus, the processing circuit 50e changes the output of the laser light when "0" is lit, according to the length of the background data immediately before the "0" light, that is, the number of consecutive digit regions DG that include the digit region DG that is in the same state as the digit region DG that is lit at "0" among the +1 state, -1 state, and 0 state immediately before the "0" light. More specifically, considering the number of consecutive digit regions DG that include the digit region DG that is in the same state as the digit region DG that is lit at "0" among the +1 state, -1 state, and 0 state immediately before the "0" light, the processing circuit 50e increases the output of the laser light when the number of such consecutive digit regions DG is the third number compared to when the number of such consecutive digit regions DG is the fourth number, which is greater than the third number.

[0154] Therefore, the deterioration of amplitude variations in the playback signal caused by the length of the underlying data is suppressed. As a result, the deterioration of the bit error rate caused by the length of the underlying data is suppressed.

[0155] (Fourth embodiment) As mentioned above, if the amplitude of the recording current corresponding to the 0 state is set to zero during the write operation, the magnetization state of the target digit region will be determined by thermal noise or the induced magnetic field from the surrounding digit region. This induced magnetic field from the surrounding digit region includes the effect of the demagnetizing field from the digit region that the magnetic head passes through immediately before the consecutive digit region where "0" is written. In other words, the consecutive digit region where "0" is written is induced to have a polarity opposite to that of the digit region that the magnetic head passes through immediately before it. Hereafter, the digit region that the magnetic head passes through immediately before the consecutive digit region where "0" is written will be referred to as the forward adjacent digit region.

[0156] Due to the influence of the demagnetizing field from the adjacent forward digit region, it may not be possible to completely erase the background data when "0" is lit. In other words, the stability of the state when "0" is lit may be insufficient.

[0157] In the fourth embodiment, when a "0" is written, the processing circuit 50 (denoted as processing circuit 50f) supplies a small recording current to the writing element 22w with the same sign as the recording current when writing to the forward adjacent digit region DG. As a result, when a "0" is written, the writing element 22w generates a magnetic field that cancels out the demagnetizing field from the forward adjacent digit region DG. This makes it possible to erase the background data without the influence of the demagnetizing field from the forward adjacent digit region DG. As a result, the state in which a "0" is written can be stabilized.

[0158] Figure 19 is a diagram illustrating a specific example of the recording method according to the fourth embodiment.

[0159] In the example shown in Figure 19, the amplitude of the recording current corresponding to the +1 state is given by value AW1. The amplitude of the recording current corresponding to the -1 state is given by value AW2. Saturated magnetic recording is achieved with recording currents of these amplitudes.

[0160] In contrast, the amplitude of the recording current corresponding to the 0 state is given by value AW10 or value AW11. Values ​​AW10 and AW11 are smaller than either value AW1 or value AW2, and are non-zero values.

[0161] When writing to the forward adjacent digit region DG, the processing circuit 50f supplies a positive recording current with amplitude value AW1 to the writing element 22w. In other words, when writing "+1" to the forward adjacent digit region DG, it supplies a positive recording current with amplitude value AW11 to the writing element 22w when writing "0".

[0162] When writing to the forward adjacent digit region DG, the processing circuit 50f supplies a negative recording current with amplitude value AW2 to the writing element 22w, in other words, when writing "-1" to the forward adjacent digit region DG, it supplies a negative recording current with amplitude value AW10 to the writing element 22w when writing "0".

[0163] A recording current with a positive sign and an amplitude of value AW11 is an example of the eighth value. A recording current with a negative sign and an amplitude of value AW10 is an example of the ninth value. In other words, according to the fourth embodiment, a recording current with an amplitude of value 6 includes the recording current of value 8 and the recording current of value 9.

[0164] More specifically, when the processing circuit 50f writes "+1" to the front adjacent digit region DG and then writes "0", it supplies a positive recording current of the 8th value to the writing element 22w when writing "0". When the processing circuit 50f writes "-1" to the front adjacent digit region DG and then writes "0", it supplies a negative recording current of the 9th value to the writing element 22w when writing "0".

[0165] Therefore, the state in which "0" is written can be stabilized. In other words, signals that can take on a level of 3 or higher can be suitably written to the magnetic disk.

[0166] (Experimental variation 6) The effect of the demagnetizing field from the forward adjacent digit region DG is thought to increase as the length of the consecutive digit region DGs (hereinafter referred to as the length of the forward adjacent data) including the forward adjacent digit region DG that is in the same state as the forward adjacent digit region DG in the +1 and -1 states increases. Therefore, the processing circuit 50f may be configured to vary the recording current when writing "0" depending on the length of the forward adjacent data.

[0167] Figure 20 is a diagram illustrating a specific example of the recording method according to Modification 6. In the example shown in this figure, when "-1" is written to the forward adjacent digit region DG, followed by the writing of "0", and the length of the forward adjacent data is 3T, the processing circuit 50f supplies a negative recording current with an amplitude of AM12 to the writing element 22w when writing "0". When "-1" is written to the forward adjacent digit region DG, followed by the writing of "0", and the length of the forward adjacent data is 1T, the processing circuit 50f supplies a negative recording current with an amplitude of AM13 to the writing element 22w when writing "0". AM13 is smaller than AM12.

[0168] In other words, the shorter the length of the preceding adjacent data, the smaller the amplitude when writing "0" in the processing circuit 50f. In the example shown in Figure 20, when "-1" is written to the preceding adjacent digit region DG and then "0" is written, the amplitude when writing "0" is varied according to the length of the preceding adjacent data. Similarly, when "+1" is written to the preceding adjacent digit region DG and then "0" is written, the processing circuit 50f makes the amplitude when writing "0" vary according to the length of the preceding adjacent data.

[0169] Furthermore, the amplitude of the recording current corresponding to the 0 state, which minimizes the bit error rate, can be influenced by various factors in addition to the demagnetic field from the forward adjacent digit region (DG). Therefore, the optimal value for the amplitude of the recording current corresponding to the 0 state is searched for during the manufacturing process, for example, and the value obtained through this search is determined as the amplitude of the recording current corresponding to the 0 state.

[0170] Figure 21 is a diagram illustrating another specific example of the recording method according to Modification 6. When the length of the forward adjacent data is short (for example, when the length of the forward adjacent data is 1T), the effect of the demagnetic field from the forward adjacent digit region DG can be considered negligibly small. In such cases, as shown in Figure 21, when the length of the forward adjacent data is 1T, the processing circuit 50f may set the recording current to zero when writing "0".

[0171] Thus, the processing circuit 50f may be configured to vary the recording current when writing "0" depending on the length of the preceding adjacent data.

[0172] Furthermore, if the length of the preceding adjacent data is a first specific value (for example, 1T), the processing circuit 50f may set the recording current supplied to the light element 22w to zero when "0" is written.

[0173] (Example 7) In a series of one or more digit regions DG where "0" is written, the influence of the demagnetizing field from the adjacent forward digit region DG is attenuated according to the distance to the adjacent forward digit region DG. Therefore, according to Modification 7, while the magnetic head 22 passes through a predetermined section from the boundary between the adjacent forward digit region DG and the digit region DG where "0" is written until it passes through a section where it is strongly influenced by the demagnetizing field from the adjacent forward digit region DG, the processing circuit 50f supplies a recording current with a non-zero amplitude to the writing element 22w. After the magnetic head 22 has passed through this section, the processing circuit 50f reduces the recording current supplied to the writing element 22w to zero.

[0174] Figure 22 is a diagram illustrating a specific example of the recording method according to Modification 7. As shown in this figure, when "0" is written, the processing circuit 50f supplies a recording current with an amplitude of AW15 and a sign of positive or negative to the light element 22w for a time Td1 after the start of the "0" light. However, the value AW15 is smaller than either the value AW1 or the value AW2, and is a non-zero value. When "+1" is written to the forward adjacent digit region DG and then "0" is written, the sign of the recording current with an amplitude of AM15 supplied to the light element 22w is positive. When "-1" is written to the forward adjacent digit region DG and then "0" is written, the sign of the recording current with an amplitude of AM15 supplied to the light element 22w is negative.

[0175] When time Td1 has elapsed since the start of the "0" light, the processing circuit 50f reduces the recording current supplied to the light element 22w to zero.

[0176] Time Td1 corresponds to the time required for the magnetic head 22 to pass through a predetermined section where it is strongly affected by the demagnetizing field. With the above configuration, a "0" light is achieved, canceling the influence of the demagnetizing field from the forward adjacent digit region DG, only while the magnetic head 22 is passing through the section where it is strongly affected by the demagnetizing field. Note that time Td1 is an example of the first time length.

[0177] Figure 23 is a diagram illustrating an example of a configuration for realizing the recording method according to Modification 7. In the example shown in this figure, the processing circuit 50f can control the recording current described above using two control signals (control signal #1 and control signal #2). In the processing circuit 50f, the RWC25 uses control signal #1 to instruct the preamplifier 24 on the timing of writing "0". The RWC25 also generates control signal #2 by shifting the phase of control signal #1. The RWC25 transmits a signal obtained by shifting the phase of control signal #1 by an amount corresponding to time Td1 as control signal #2 to the preamplifier 24.

[0178] The preamplifier 24 starts supplying a recording current with an amplitude of AW15 and a sign of either positive or negative to the writing element 22w at the rising edge of the control signal #1. The preamplifier 24 also reduces the recording current supplied to the writing element 22w to zero at the rising edge of the control signal #1.

[0179] With the above configuration, the designer can continuously change time Td1 by setting the phase difference between control signal #1 and control signal #2. The phase difference between control signal #1 and control signal #2 may be set as a parameter by the designer or may be changed by the SoC30 (e.g., processor 26).

[0180] Note that the configuration for realizing the recording method according to Modification 7 is not limited to the examples described above. The preamplifier 24 may be equipped with a timer and configured to measure the time Td1 after the start of the "0" light.

[0181] Furthermore, in the description of Modification 7, the amplitude of the recording current at the start of the "0" light was set to value AW15. The amplitude of the recording current at the start of the "0" light can vary in various ways, as in Modification 6. Also, the amplitude of the recording current at the start of the "0" light can vary depending on the polarity of the front adjacent digit region DG, as in the fourth embodiment.

[0182] While several embodiments of the present invention have been described, these embodiments are presented as examples only and are not intended to limit the scope of the invention. These novel embodiments can be carried out in a variety of other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. [Explanation of Symbols]

[0183] 1 Magnetic disk drive, 2 Host, 11 Magnetic disk, 12 Spindle motor (SPM), 13 Ramp, 15 Actuator arm, 16 Voice coil motor (VCM), 21 Servo controller (SVC), 22 Magnetic head, 22ld Laser diode, 22r Read element, 22w Write element, 23 Hard disk controller (HDC), 24 Preamplifier, 25 Read / Write channel (RWC), 26 Processor, 28 FROM, 29 DRAM, 30 SoC, 41 Track, 42 ​​Servo area, 43 Data area, 50, 50a, 50b, 50c, 50d, 50e Processing circuit, 61, 61a, 61b, 61c Binary data generation circuit, 62 Control signal generation circuit, 63 LD control circuit, 64, 64c PBW signal generation circuit, 65, 65c MPRZ signal generation circuit, 241, 241a, 241b, 241c 4th driver, 242, 242a, 242b 5th driver, 243 6th driver, 251, 251a, 251b media write data generation circuit, 252 encoder, 253 1st driver, 254, 254c1, 254c2 2nd driver, 255 3rd driver.

Claims

1. A magnetic disk having tracks composed of multiple unit recording areas arranged in a line in the circumferential direction, A magnetic head comprising a light element that writes data to the track, and a light-emitting element that irradiates laser light onto the light position of the magnetic disk by the light element, It is possible to perform any of the following write operations: a first write operation which writes a first value to a first unit recording area which is one of the plurality of unit recording areas; a second write operation which writes a second value different from the first value to the first unit recording area; and a third write operation which writes a third value different from both the first and second values ​​to the first unit recording area, wherein the first write operation is an operation which sets the magnetization state of the first unit recording area to a first state by supplying a positive recording current with an amplitude of a fourth value to the light element while outputting the laser light to the light element, and The processing circuit comprises: a second light operation which causes the light-emitting element to output the laser light and supplies a negative recording current with an amplitude of the fifth value to the light element, thereby changing the magnetization state of the first unit recording area to a second state different from the first state; and a third light operation which causes the light-emitting element to output the laser light and supplies a recording current to the light element that includes a recording current with an amplitude of a non-zero sixth value which is smaller than either the fourth or fifth value, thereby changing the magnetization state of the first unit recording area to a third state different from both the first and second states. A magnetic disk drive equipped with the following features.

2. In the third light operation, the processing circuit supplies a recording current to the light element whose amplitude is a preset sign among positive and negative values, which is the sixth value. The magnetic disk device according to claim 1.

3. The processing circuit changes the output of the laser light in the third write operation according to the number of consecutive unit recording areas in which the third value, including the first unit recording area, is written. The magnetic disk device according to claim 2.

4. The processing circuit increases the output of the laser light when the number of consecutive unit recording areas on which the third value is written, including the first unit recording area, is a first number, compared to when the number of consecutive unit recording areas on which the third value is written, including the first unit recording area, is a second number greater than the first number. The magnetic disk device according to claim 3.

5. The processing circuit changes the output of the laser light during the third light operation according to the number of consecutive unit recording areas that include the first unit recording area which is in the same state as the first unit recording area among the first state, second state, and third state immediately before the third light operation. The magnetic disk device according to claim 2.

6. The processing circuit increases the output of the laser light when the number of consecutive unit recording areas is a third number, compared to when the number of consecutive unit recording areas is a fourth number greater than the third number. The magnetic disk device according to claim 5.

7. When the processing circuit performs the third write operation on the first unit recording area immediately after performing the first write operation or the second write operation on the second unit recording area, it sets the amplitude of the recording current to the sixth value at a timing earlier than the timing at which the write element reaches the first unit recording area. The second unit recording area is a unit recording area that the magnetic head passes through immediately before the first unit recording area among the plurality of unit recording areas. A magnetic disk device according to any one of claims 1 to 6.

8. In the third light operation, the recording current supplied to the light element has an amplitude of the sixth value, and there are multiple recording currents with a seventh value. The magnetic disk device according to claim 1.

9. The aforementioned plurality of seventh-value recording currents include an eighth-value positive recording current and a ninth-value negative recording current. The magnetic disk device according to claim 8.

10. The aforementioned processing circuit is When the third write operation is performed on the first unit recording area after the first write operation is performed on the second unit recording area, the write element is supplied with a positive recording current of the eighth value during the third write operation. When the second write operation is performed on the second unit recording area and then the third write operation is performed on the first unit recording area, the third write operation supplies a negative recording current of the ninth value to the write element. The second unit recording area is a unit recording area that the magnetic head passes through immediately before the first unit recording area among the plurality of unit recording areas. The magnetic disk device according to claim 9.

11. The aforementioned processing circuit is If the number of consecutive unit recording areas including the second unit recording area that is in the same state as the second unit recording area is the tenth value, the recording current supplied to the light element in the third light operation is set to zero. If the number of consecutive unit recording areas including the second unit recording area that is in the same state as the second unit recording area is greater than the tenth value, then in the third write operation, a positive recording current of the eighth value or a negative recording current of the ninth value is supplied to the write element. The magnetic disk device according to claim 10.

12. The aforementioned processing circuit is In the third light operation, for a first time period after the start of the third light operation, the light element is supplied with a positive recording current of the eighth value or a negative recording current of the ninth value. In the third light operation, after the first time period has elapsed since the start of the third light operation, the recording current supplied to the light element is reduced to zero. A magnetic disk device according to any one of claims 9 to 11.

13. In the third light operation, the recording current supplied to the light element includes a positive recording current, a negative recording current, and a zero recording current. The magnetic disk device according to claim 1.

14. The aforementioned processing circuit is Depending on the number of consecutive unit recording areas including the second unit recording area which is in the same state as the second unit recording area, the recording current supplied to the light element in the third light operation is varied. The second unit recording area is a unit recording area that the magnetic head passes through immediately before the first unit recording area among the plurality of unit recording areas. The magnetic disk device according to claim 13.

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