U.S. patent application number 14/336610 was filed with the patent office on 2015-08-06 for laser controller for heat-assisted magnetic recording device.
The applicant listed for this patent is Kabushiki Kaisha Toshiba. Invention is credited to Hiroshi Isokawa.
Application Number | 20150221332 14/336610 |
Document ID | / |
Family ID | 53638505 |
Filed Date | 2015-08-06 |
United States Patent
Application |
20150221332 |
Kind Code |
A1 |
Isokawa; Hiroshi |
August 6, 2015 |
LASER CONTROLLER FOR HEAT-ASSISTED MAGNETIC RECORDING DEVICE
Abstract
According to one embodiment, there is provided a magnetic disk
device including a light source, a light irradiation element, and a
controller. The light irradiation element is configured to receive
light from the light source to irradiate light onto a magnetic
disk. The controller is configured to switch between a first
control and a second control according to a pulse width of data to
be written onto the magnetic disk. The first control keeps an
output of the light source at a first value. The second control
makes the output of the light source change periodically between
the first value and a second value lower than the first value.
Inventors: |
Isokawa; Hiroshi;
(Yokohama-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kabushiki Kaisha Toshiba |
Tokyo |
|
JP |
|
|
Family ID: |
53638505 |
Appl. No.: |
14/336610 |
Filed: |
July 21, 2014 |
Current U.S.
Class: |
369/13.26 |
Current CPC
Class: |
G11B 11/10595 20130101;
G11B 2005/0021 20130101; G11B 5/02 20130101; G11B 11/10506
20130101; G11B 11/1053 20130101 |
International
Class: |
G11B 7/1263 20060101
G11B007/1263 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 6, 2014 |
JP |
2014-021657 |
Claims
1. A magnetic disk device comprising: a light source; a light
irradiation element configured to receive light from the light
source to irradiate light onto a magnetic disk; and a controller
configured to keep an output of the light source at a first value
when a first time from an edge timing of pulse of data to be
written onto the magnetic disk until a next edge timing is less
than a first threshold, and to change the output of the light
source from the first value to a second value lower than the first
value when the first time is greater than or equal to the first
threshold.
2. The magnetic disk device according to claim 1, further
comprising a recording head configured to write data onto the
magnetic disk, wherein the light irradiation element irradiates
light onto an area of the magnetic disk onto which data is to be
written by the recording head.
3. The magnetic disk device according the claim 1, wherein the
second value is a value at which the output of the light source is
off, and wherein the controller controls the light source such that
light is output intermittently from the light source when the first
time is greater than or equal to the first threshold.
4. The magnetic disk device according to claim 1, wherein the
second value is a value between the first value and a value at
which the output of the light source is off.
5. (canceled)
6. (canceled)
7. The magnetic disk device according to claim 1, wherein the
controller keeps the output of the light source at the second value
when an elapsed time from timing when it has changed the output of
the light source from the first value to the second value is less
than a second threshold, and changes the output of the light source
from the second value to the first value when the elapsed time is
greater than or equal to the second threshold.
8. (canceled)
9. The magnetic disk device according to claim 1, wherein the
controller changes the output of the light source such that a
timing when the output of the light source becomes the second value
and an edge timing of pulse of data to be written onto the magnetic
disk do not overlap with each other.
10. The magnetic disk device according to claim 9, wherein the
controller delays the timing of the switching with respect to the
edge of the pulse.
11. The magnetic disk device according to claim 1, wherein the
controller comprises: a determining unit configured to compare a
pulse width of data to be written onto the magnetic disk with the
first threshold to determine whether the pulse width is greater
than or equal to the first threshold according to a comparison
result; and a control signal generating unit configured to generate
a control signal change the output of the light source according to
a determination result of the determining unit, the magnetic disk
device further comprising a preamp that generates a drive signal
for the light source according to the generated control signal.
12. (canceled)
13. A controller which controls a light source in a magnetic disk
device comprising a light irradiation element that receives light
from the light source to irradiate light onto a magnetic disk,
wherein the controller is configured to keep an output of the light
source at a first value when a first time from an edge timing of
pulse of data to be written onto the magnetic disk until a next
edge timing is less than a first threshold, and to change the
output of the light source from the first value to a second value
lower than the first value when the first time is greater than or
equal to the first threshold.
14. The controller according to claim 13, wherein the control
signal generating unit compares an elapsed time from timing when it
has changed the output of the light source from the first value to
the second value with a second threshold, and generates the control
signal so as to keep the output of the light source at the second
value when the elapsed time is less than the second threshold and
to change the output of the light source from the second value to
the first value when the elapsed time is greater than or equal to
the second threshold, according to the comparison result.
15. (canceled)
16. The controller according to claim 13, wherein the controller
generates a first clock, generates data to be written onto the
magnetic disk synchronously with the first clock, and compares a
pulse width of the generated data with the first threshold
synchronously with the first clock.
17. The controller according to claim 16, wherein the controller
frequency multiplies the first clock to generate a second clock,
and generates the control signal synchronously with the second
clock.
18. The controller according to claim 16, wherein the controller
delays timing of the switching with respect to the edge of the
pulse of the generated data.
19. (canceled)
20. A control method which controls a light source in a magnetic
disk device having the light source and a light irradiation element
that receives light from the light source to irradiate light onto a
magnetic disk, the control method comprising: keeping an output of
the light source at a first value when a first time from an edge
timing of pulse of data to be written onto the magnetic disk until
a next edge timing is less than a first threshold; and changing the
output of the light source from the first value to a second value
lower than the first value when the first time is greater than or
equal to the first threshold.
21. The control method according to claim 20, further comprising:
irradiating light onto an area of the magnetic disk onto which data
is to be written by a head.
22. The control method according to claim 20, wherein the second
value is a value at which the output of the light source is off,
and the control method further comprises controlling the light
source such that light is output intermittently from the light
source when the first time is greater than or equal to the first
threshold.
23. The control method according to claim 20, wherein the second
value is a value between the first value and a value at which the
output of the light source is off.
24. The control method according to claim 20, wherein the changing
the output of the light source includes changing the output of the
light source such that a timing when the output of the light source
becomes the second value and an edge timing of pulse of data to be
written onto the magnetic disk do not overlap with each other.
25. The control method according to claim 20, further comprising:
comparing a pulse width of data to be written onto the magnetic
disk with the first threshold to determine whether the pulse width
is greater than or equal to the first threshold according to a
comparison result; and generating a control signal to change the
output of the light source according to a determination result of
the determining unit, generating a drive signal for the light
source according to the generated control signal.
26. The control method according to claim 20, further comprising:
generating a first clock, generating data to be written onto the
magnetic disk synchronously with the first clock, and comparing a
pulse width of the generated data with the first threshold
synchronously with the first clock.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from Japanese Patent Application No. 2014-021657, filed on
Feb. 6, 2014; the entire contents of which are incorporated herein
by reference.
FIELD
[0002] Embodiments described herein relate generally to a magnetic
disk device and a control method.
BACKGROUND
[0003] In these years, a heat assist recording scheme is attracting
attention as a technology that enables high density magnetic
recording of a 1 Tbit/inch.sup.2 class. In the heat assist
recording scheme, laser light generated by a light source (laser
diode) is converted by a near field transducer into near-field
light to be irradiated onto part of the surface of a magnetic disk
so as to raise the temperature of the magnetic disk locally. Then,
by applying a magnetic field to the temperature-raised part of the
magnetic disk by a magnetic field generating element, data is
recorded magnetically. At this time, it is desired to improve data
reliability.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] FIG. 1 is a diagram showing configuration of the magnetic
disk device according to an embodiment;
[0005] FIG. 2 is a diagram showing configuration relating to an RDC
in the embodiment;
[0006] FIG. 3 is a diagram showing configuration of the RDC in the
embodiment;
[0007] FIG. 4 is a diagram showing configuration of a preamp in the
embodiment;
[0008] FIG. 5 is a waveform diagram showing operation of the
magnetic disk device according to the embodiment;
[0009] FIG. 6 is a flow chart showing operation of the magnetic
disk device according to the embodiment;
[0010] FIG. 7 is a diagram for explaining influence of a frequency
characteristic in the embodiment;
[0011] FIG. 8 is a graph for explaining an effect of the
embodiment;
[0012] FIG. 9 is a graph for explaining an effect of the
embodiment;
[0013] FIG. 10 is a graph for explaining an effect of the
embodiment;
[0014] FIG. 11 is a graph for explaining an effect of the
embodiment;
[0015] FIG. 12 is a waveform diagram showing operation of a
magnetic disk device according to a modified example of the
embodiment; and
[0016] FIG. 13 is a waveform diagram showing operation of a
magnetic disk device according to another modified example of the
embodiment.
DETAILED DESCRIPTION
[0017] In general, according to one embodiment, there is provided a
magnetic disk device including a light source, a light irradiation
element, and a controller. The light irradiation element is
configured to receive light from the light source to irradiate
light onto a magnetic disk. The controller is configured to switch
between a first control and a second control according to a pulse
width of data to be written onto the magnetic disk. The first
control keeps an output of the light source at a first value. The
second control makes the output of the light source change
periodically between the first value and a second value lower than
the first value.
[0018] Exemplary embodiments of a magnetic disk device will be
explained below in detail with reference to the accompanying
drawings. The present invention is not limited to the following
embodiments.
Embodiment
[0019] The magnetic disk device 100 according to the present
embodiment will be described in outline using FIGS. 1 and 2. FIG. 1
is a diagram showing configuration of the magnetic disk device
according to the embodiment. FIG. 2 is a diagram showing
configuration relating to data recording by the magnetic disk
device according to the embodiment.
[0020] A magnetic disk 50 is a disk-shaped recording medium on
which to record a variety of information and is rotationally driven
by a spindle motor 103. The magnetic disk 50 has a perpendicular
recording layer anisotropic in a direction perpendicular to the
surface thereof. The magnetic disk 50 has multiple tracks in a
concentric-circle shape with a point near the rotational center of
the spindle motor 103 as their center.
[0021] Reading from and writing onto the magnetic disk 50 is
performed by means of a magnetic head 5 provided on one end of an
arm 107 that is a head support mechanism via a head slider 104. The
magnetic head 5 includes a recording head 5w and a read head
5r.
[0022] The recording head 5w moves relative to the surface of the
magnetic disk 50 in a down track direction with keeping in a state
of being lifted slightly from the surface of the magnetic disk 50
by lift generated by the rotation of the magnetic disk 50 so as to
record information onto the magnetic disk 50 by a magnetic field
generating element 5d.
[0023] At this time, in the recording head 5w, according to the
heat assist recording scheme, laser light generated by a light
source (e.g., LD: Laser diode) 5a is guided by a waveguide 5b to a
near field transducer (light irradiation element) 5c, which
converts the laser light into near-field light. In the recording
head 5w, the converted near-field light is irradiated from the near
field transducer 5c onto part of the surface of the magnetic disk
50 to raise the temperature of the magnetic disk 50 locally, and a
magnetic field is applied to the temperature-raised part by the
magnetic field generating element 5d to record information
magnetically. For example, the magnetic field generating element 5d
writes data onto the magnetic disk 50 with reversing the direction
of the magnetic field for magnetization or not, depending on
whether the level of data to be written is 1 or 0. That is, the
recording head 5w is used for write operation for the magnetic disk
50 according to the heat assist recording scheme.
[0024] Note that the light source 5a may be provided outside the
magnetic head 5 as long as the configuration is made such that
laser light can be supplied to the near field transducer (light
irradiation element) 5c via the waveguide 5b.
[0025] The read head 5r moves relative to the surface of the
magnetic disk 50 in a down track direction with keeping in the
state of being lifted slightly from the surface of the magnetic
disk 50 by lift generated by the rotation of the magnetic disk 50
so as to read information recorded on the magnetic disk 50 by a
magnetoresistive element 5e. That is, the read head 5r is used for
read operation for the magnetic disk 50.
[0026] The arm 107 pivots on an arc with a shaft 108 as the center
by drive by a voice coil motor 102, which is a head drive
mechanism, provided at the other end of the arm 107 so that the
recording head 5w and the read head 5r seek in a cross-track
direction of the magnetic disk 50 to switch tracks subject to
reading or writing. The magnetic disk 50, the magnetic head 5, the
voice coil motor 102, and the spindle motor 103 are housed in a
case 101.
[0027] As shown in FIG. 1, the magnetic disk device 100 has a
magnetic recording control unit 120. The magnetic recording control
unit 120 has a head control unit (preamp) 123, a power control unit
121, a read write channel (RDC) 124, a hard disk control unit (HDC)
122, and a storage unit 125. The head control unit 123 has a write
current control unit 123a, a read signal detecting unit 123b, and a
heat assist control unit 123c. The power control unit 121 has a
spindle motor control unit 121a and a voice coil motor control unit
121b. The storage unit 125 is constituted by, e.g., a RAM, ROM, or
nonvolatile memory.
[0028] In the write operation according to the heat assist
recording scheme, control (first control) is applied which records
information onto the magnetic disk 50 by modulating the magnetic
field from the magnetic field generating element 5d with heating
the magnetic disk 50 by near-field light corresponding to constant
laser power. The first control is control which keeps the output of
the light source 5a at a first value OP1 as indicated by, e.g., the
dot-dashed line in 7D of FIG. 7. FIG. 7 is a diagram for explaining
influence of a frequency characteristic.
[0029] If the first control is performed in a fixed manner, at the
time of recording, constant light power continues to be supplied
from the light source 5a to the near field transducer 5c. Thus, the
light source 5a and the near field transducer 5c are likely to
degrade due to heat generation by themselves, and the reliability
of each of the light source 5a and the near field transducer 5c may
decrease (refer to FIGS. 10, 11). Further, since a constant drive
current needs to continue to be supplied to the light source 5a to
make the light source 5a generate laser light, power consumption by
the light source 5a is likely to increase.
[0030] As another control in the write operation according to the
heat assist recording scheme, control (second control) is applied
which makes laser light from the light source 5a change in pulses
(e.g., intermittently) synchronously with the polarity reversing of
the magnetic field generated from the magnetic field generating
element 5d while irradiating it. The second control is control
which makes the output of the light source 5a change periodically
between the first value OP1 and a second value OP2 as shown by,
e.g., the solid line in 7D of FIG. 7. The second value OP2 is lower
than the first value OP1.
[0031] If the second control is performed in a fixed manner, a
constant current need not be continuously applied to the light
source 5a. Thus, compared with the case of performing the first
control in a fixed manner, the degradation due to heat generation
of the near field transducer 5c receiving light from the light
source 5a can be suppressed, and hence the lifetime of the near
field transducer 5c can be elongated, thus suppressing a decrease
in the reliability of the near field transducer 5c. Further,
because the time-averaged amount of current supplied to the light
source 5a can be reduced, power consumption in the light source 5a
can be reduced.
[0032] However, if the second control is performed in a fixed
manner, the reliability of data written on the magnetic disk 50 may
be decreased.
[0033] In the second control, a control signal (Pulse Data) to
control the drive current of the light source 5a is supplied from
the RDC 124 to the preamp 123. The rectangular waveform output from
the RDC 124, shown in 7A of FIG. 7, has deteriorated in shape when
input into the preamp 123 as shown in 7B of FIG. 7 due to the
influence of the frequency characteristic (f characteristic A) of
the transmission path for laser drive control. Further, the
waveform of the drive current supplied from the preamp 123 to the
light source 5a has deteriorated in shape as shown in 7C of FIG. 7
due to the influence of the frequency characteristic (f
characteristic B) of the preamp 123. Also, the output waveform of
laser light emitted from the light source 5a has further
deteriorated in shape as shown in 7D of FIG. 7 due to the influence
of the frequency characteristic (f characteristic C) of the light
source 5a.
[0034] Hence, in the case where the second control is performed in
a fixed manner, if the finally-obtained frequency characteristic of
the transmission path for laser control is at or below that of the
signal transmission path for magnetic field control, then the
laser-control current value changes according to the control
frequency, and hence it is difficult to obtain signal quality
uniform across the entire frequency band of data to be recorded on
the magnetic disk device 100. For example, compared with an ideal
waveform, the output waveform of laser light is more likely to
decay in amplitude when the pulse width of data WDATA to be written
onto the magnetic disk 50 is shorter. Thus, as the pulse width of
data WDATA becomes shorter, the reliability of data actually
written on the magnetic disk 50 may decrease with respect to data
WDATA to be written (see FIG. 8).
[0035] Accordingly, in the present embodiment, the magnetic disk
device 100 switches between the first control and the second
control according to the pulse width of data to be written onto the
magnetic disk 50, thereby improving the reliability of data written
on the magnetic disk 50 while elongating the lifetimes of the light
source 5a and the near field transducer 5c and lowering the power
consumption of the light source 5a.
[0036] In the magnetic disk device 100, as shown in FIG. 2, the RDC
(controller) 124 switches between the first control and the second
control according to a command and/or data 51 received from the HDC
122.
[0037] Specifically, the HDC 122 generates the predetermined
command and/or data 51 according to a command and/or data 1
received from a host HS via a host I/F 122a and outputs to the RDC
124. The RDC 124 performs control according to the predetermined
command and/or data 51. For example, when receiving a write
command, the RDC 124 generates data .phi.54 to be written onto the
magnetic disk 50 and outputs to the preamp 123.
[0038] Further, the RDC 124 generates a heat assist control signal
.phi.200 and outputs to the preamp 123. The heat assist control
signal .phi.200 is a signal to control the drive current for the
light source 5a, which is to be generated in the preamp 123.
[0039] At this time, the RDC 124 generates the heat assist control
signal .phi.200 while switching between the first control and the
second control according to the pulse width of data .phi.54 to be
written. The first control is control which keeps the output of the
light source 5a at the first value OP1. The second control is
control which makes the output of the light source 5a change
periodically between the first value OP1 and the second value OP2.
The second value OP2 is lower than the first value OP1 and is,
e.g., a value at which the output of the light source 5a is off.
That is, in the second control the RDC 124 controls the light
source 5a such that light is intermittently output from the light
source 5a.
[0040] For example, when the pulse width of data .phi.54 to be
written onto the magnetic disk 50 is less than a first threshold,
the RDC 124 performs the first control. When the pulse width of
data .phi.54 is greater than or equal to the first threshold, the
RDC 124 performs the second control.
[0041] Here, a magnetic-field reversing period 139 is stored in the
storage unit 125, and the RDC 124 refers to the storage unit 125 to
acquire the magnetic-field reversing period 139. The RDC 124
obtains the first threshold according to the magnetic-field
reversing period 139. The RDC 124 compares the time (first time)
from an edge timing to the next edge timing of the pulse of data
.phi.53 subject to writing (see FIG. 3) with the first threshold.
According to the comparison result, when the first time is less
than the first threshold, the RDC 124 keeps the output of the light
source 5a at the first value OP1. On the other hand, when the first
time is greater than or equal to the first threshold, the RDC 124
switches the output of the light source 5a from the first value OP1
to the second value OP2.
[0042] Further, the storage unit 125 stores a heat assist period
133. The RDC 124 refers to the storage unit 125 to acquire the heat
assist period 133. The RDC 124 obtains the second threshold
according to the heat assist period 133. The RDC 124 compares the
elapsed time from the timing when it has switched the output of the
light source 5a from the first value OP1 to the second value OP2
with the second threshold. According to the comparison result, when
the elapsed time is less than the second threshold, the RDC 124
keeps the output of the light source 5a at the second value OP2.
When the elapsed time is greater than or equal to the second
threshold, the RDC 124 switches the output of the light source 5a
from the second value OP2 to the first value OP1.
[0043] Further, the RDC 124 can set a third threshold, and, for
example, the third threshold can be set to be twice the second
threshold. The RDC 124 compares the time (second time) from the
timing when it has switched the output of the light source 5a from
the second value OP2 to the first value OP1 until an edge timing of
the pulse of data .phi.53 subject to writing (see FIG. 3) with the
third threshold. According to the comparison result, when the
second time is less than the third threshold, the RDC 124 keeps the
output of the light source 5a at the first value OP1. When the
second time is greater than or equal to the third threshold, the
RDC 124 switches the output of the light source 5a from the first
value OP1 to the second value OP2.
[0044] Note that the storage unit 125 stores a clock
frequency-multiplication setting value 137 and that the RDC 124
refers to the storage unit 125 to acquire the clock
frequency-multiplication setting value 137. When generating the
heat assist control signal .phi.200, the RDC 124 can use the clock
frequency-multiplication setting value 137.
[0045] The preamp 123 generates a write current 56 according to
data .phi.54 to be written and supplies to the magnetic head 5.
Thus, the magnetic field generating element 5d generates the
magnetic field according to the write current 56 to write data onto
the magnetic disk 50. At this time, the preamp 123 acquires a heat
assist current setting 300 from the storage unit 125. The preamp
123 generates a drive current (drive signal) 58 according to the
heat assist control signal .phi.200 and the heat assist current
setting 300 and supplies to the magnetic head 5. Thus, laser light
generated by the light source 5a is guided by the waveguide 5b to
the near field transducer 5c, which converts the laser light into
near-field light. The converted near-field light is irradiated from
the near field transducer (light irradiation element) 5c onto part
of the surface of the magnetic disk 50 to raise the temperature of
the magnetic disk 50 locally, and a magnetic field is applied to
the temperature-raised part by the magnetic field generating
element 5d to record data magnetically.
[0046] Next, the configuration and operation of the RDC 124 will be
described using FIGS. 3 and 5. FIG. 3 is a diagram showing the
configuration of the RDC 124. FIG. 5 is a waveform diagram showing
operation of the magnetic disk device 100 including the RDC
124.
[0047] The RDC 124 mainly has a configuration for generating record
data to be recorded onto the magnetic disk 50, that is, data
.phi.54 to be written and a configuration for generating the heat
assist control signal .phi.200 to control a drive current to be
generated in the light source 5a. Specifically, the RDC 124 has a
clock generating circuit (first clock generating unit) 157, a data
generating circuit (data generating unit) 135, a
frequency-multiplied clock generating circuit (second clock
generating unit) 159, a magnetic-field reversing period determining
unit 161, a heat assist control signal generating circuit 163, a
delay circuit (delay unit) 140, and a delay circuit (delay unit)
142.
[0048] The clock generating circuit 157 generates a clock (first
clock) .phi.62 (period=t). The clock generating circuit 157
supplies the generated clock .phi.62 to the data generating circuit
135, the magnetic-field reversing period determining unit 161, and
the frequency-multiplied clock generating circuit 159.
[0049] The data generating circuit 135 receives a predetermined
command and/or data 51 from the HDC 122 and the clock .phi.62 from
the clock generating circuit 157. For example, the data generating
circuit 135 generates data .phi.53 subject to writing onto the
magnetic disk 50 synchronously with the clock .phi.62 according to
the write command and/or data 51 from the HDC 122. The data
generating circuit 135 supplies the generated data .phi.53 to the
delay circuit 140 and the magnetic-field reversing period
determining unit 161.
[0050] The frequency-multiplied clock generating circuit 159
receives the clock .phi.62 (period=t, frequency=1/t) from the clock
generating circuit 157. The frequency-multiplied clock generating
circuit 159 acquires the clock frequency-multiplication setting
value (N) 137 from the storage unit 125. The frequency-multiplied
clock generating circuit 159 frequency-multiplies the clock .phi.62
(e.g., by N) according to the clock frequency-multiplication
setting value (N) 137 to generate a frequency-multiplied clock
(second clock) .phi.64 (period=t/N, frequency=N/t). The
frequency-multiplied clock generating circuit 159 supplies the
frequency-multiplied clock .phi.64 to the heat assist control
signal generating circuit 163.
[0051] The magnetic-field reversing period determining unit 161
receives the data .phi.53 subject to writing onto the magnetic disk
50 from the data generating circuit 135 and the clock .phi.62 from
the clock generating circuit 157. The determining unit 161 acquires
the magnetic-field reversing period (M) 139 from the storage unit
125. The determining unit 161 obtains the first threshold according
to the magnetic-field reversing period (M) 139. For example, the
determining unit 161 multiplies the magnetic-field reversing period
(M) 139 by the period t of the clock .phi.62 to obtain the
multiplying result (Mt) as the first threshold. The determining
unit 161 compares the pulse width of the data .phi.53 subject to
writing with the first threshold (Mt) synchronously with the clock
.phi.62 to determine whether the pulse width of the data .phi.53 is
greater or equal to the first threshold (Mt) according to the
comparison result.
[0052] Further, the magnetic-field reversing period determining
unit 161 counts the number `m` of clocks during the time (first
time) from the timing when the magnetic field reverses until the
timing when the magnetic field reverses the next time based on the
clock .phi.62. The determining unit 161 multiplies the number `m`
of clocks by the period `t` of the clock .phi.62 to obtain the
multiplying result (mt) as the length of time until the magnetic
field reverses the next time. The determining unit 161 compares the
length of time (mt) until the magnetic field reverses the next time
with the first threshold (Mt) and determines whether the length of
time (mt) until the magnetic field reverses the next time is
greater than or equal to the first threshold (Mt) according to the
comparison result.
[0053] FIG. 5 shows, for example, the case where M=3, N=1, and
K=1.5.
[0054] At timing T1, the determining unit 161 counts the number `m`
(=2) of clocks during the first time from timing T2 until timing T3
and compares the first time (2t) with the first threshold (3t) to
determine that the first time (2t) is less than the first threshold
(3t).
[0055] At timing T4, the determining unit 161 counts the number `m`
(=4) of clocks during the first time from timing T5 until timing T8
and compares the first time (4t) with the first threshold (3t) to
determine that the first time (4t) is greater than or equal to the
first threshold (3t).
[0056] At timing T9, the determining unit 161 counts the number `m`
(=7) of clocks during the first time from timing T10 until timing
T18 and compares the first time (7t) with the first threshold (3t)
to determine that the first time (7t) is greater than or equal to
the first threshold (3t).
[0057] The magnetic-field reversing period determining unit 161
shown in FIG. 3 supplies a magnetic-field reversing period
determination value 66 as the determining result to the heat assist
control signal generating circuit 163. Further, if the length of
time (mt) until the magnetic field reverses the next time is
greater than or equal to the first threshold (Mt), the determining
unit 161 supplies the length of time (mt) until the magnetic field
reverses the next time to the generating circuit 163.
[0058] The heat assist control signal generating circuit 163
receives the frequency-multiplied clock .phi.64 from the
frequency-multiplied clock generating circuit 159 and the
magnetic-field reversing period determination value 66 from the
determining unit 161. The generating circuit 163 acquires the heat
assist period (K) 133 from the storage unit 125.
[0059] If the magnetic-field reversing period determination value
66 indicates that the time until the timing when the magnetic field
reverses the next time is greater than or equal to the specified
length (mt>Mt), the generating circuit 163 receives the length
of time (mt) until the magnetic field reverses the next time. In
response to the reception of the length of time (mt) until the
magnetic field reverses the next time, the generating circuit 163
changes the level of a heat assist control signal .phi.230 from
high (active) to low (inactive) to output to the delay circuit 142.
That is, the generating circuit 163 switches the control operation
of the RDC 124 from the first control to the second control.
[0060] For example, at each of timings T4, T9 in FIG. 5, the heat
assist control signal generating circuit 163 receives the length of
time (mt) until the magnetic field reverses the next time and in
response to this, sets an "LD OFF control" flag to be active.
[0061] At each of timings T5, T10, in response to the "LD OFF
control" flag being active, the generating circuit 163 changes the
level of the heat assist control signal .phi.230 from high (active)
to low (inactive). Also, the generating circuit 163 sets the "LD
OFF control" flag to be non-active.
[0062] The heat assist control signal generating circuit 163 shown
in FIG. 3 obtains the second threshold according to the heat assist
period (K) 133. For example, the generating circuit 163 multiplies
the period t/N of the frequency-multiplied clock .phi.64 by the
heat assist period (K) 133 to obtain the multiplying result
(K.times.t/N) as the second threshold.
[0063] The heat assist control signal generating circuit 163
compares the elapsed time from the timing when it has changed the
level of the heat assist control signal .phi.230 from high to low
with the second threshold. The generating circuit 163 counts the
number `k` of clocks during the elapsed time based on the
frequency-multiplied clock .phi.64. The generating circuit 163
multiplies the number `k` of clocks by the period t/N of the
frequency-multiplied clock .phi.64 to obtain the multiplying result
(k.times.t/N) as the elapsed time. The generating circuit 163
compares the elapsed time (k.times.t/N) with the second threshold
(K.times.t/N) and determines whether the elapsed time (k.times.t/N)
is greater than or equal to the second threshold (K.times.t/N)
according to the comparison result. That is, the second threshold
(K.times.t/N) is the time period for which the level of the heat
assist control signal .phi.230 should be kept low.
[0064] At the timing when the elapsed time (k.times.t/N) has become
greater than or equal to the second threshold (K.times.t/N), the
generating circuit 163 changes the level of the heat assist control
signal .phi.230 from low (inactive) to high (active) to output to
the delay circuit 142.
[0065] For example, at timing T6 shown in FIG. 5, the heat assist
control signal generating circuit 163 compares the elapsed time
(1.5.times.t/N) at timing T7 with the second threshold
(1.5.times.t/N) and determines that the elapsed time
(1.5.times.t/N) is greater than or equal to the second threshold
(1.5.times.t/N). Accordingly, the generating circuit 163 sets the
"LD ON control" flag to be active. Also at timing T11 shown in FIG.
5, the same process is executed.
[0066] At each of timings T7, T12, in response to the "LD ON
control" flag being active, the generating circuit 163 changes the
level of the heat assist control signal .phi.230 from low
(inactive) to high (active). Also, the generating circuit 163 sets
the "LD ON control" flag to be non-active.
[0067] Further, the heat assist control signal generating circuit
163 shown in FIG. 3 counts down from the length of time (mt) until
the magnetic field reverses the next time during the time from when
outputting low (inactive) as the heat assist control signal
.phi.230 to when outputting high (active) to calculate the
remaining time (second time) until the magnetic field reverses the
next time.
[0068] That is, the heat assist control signal generating circuit
163 subtracts the second threshold (K.times.t/N) from the length of
time (mt) until the magnetic field reverses the next time to obtain
the remaining time (second time) A (=mt-K.times.t/N) until the
magnetic field reverses the next time. The generating circuit 163
can set the third threshold and, for example, if the off-duty in
the second control is set at 50%, the third threshold can be set to
be twice the second threshold (2.times.K.times.t/N), the second
threshold being the time period for which the level of the heat
assist control signal .phi.230 should be kept low.
[0069] The heat assist control signal generating circuit 163
compares the second time with the third threshold and according to
the comparison result, if the second time is less than the third
threshold, keeps the level of the heat assist control signal
.phi.230 high to output to the delay circuit 142. That is, the
generating circuit 163 switches the control operation of the RDC
124 from the second operation to the first operation.
[0070] On the other hand, if the second time is greater than or
equal to the third threshold, at the timing when the second
threshold has elapsed from the timing when the heat assist control
signal .phi.230 changed from low to high, the generating circuit
163 changes the level of the heat assist control signal .phi.230
from high to low to output to the delay circuit 142. That is, the
generating circuit 163 keeps the control operation of the RDC 124
at the second operation.
[0071] For example, at timing T7 shown in FIG. 5, the heat assist
control signal generating circuit 163 compares the second time
(2.5t) with the third threshold (3t) and determines that the second
time (2.5t) is less than the third threshold (3t) according to the
comparison result. Accordingly, the generating circuit 163 keeps
the level of the heat assist control signal .phi.230 high.
[0072] At timing T11, the generating circuit 163 compares the
second time (5.5t) with the third threshold (3t) and determines
that the second time (5.5t) is greater than or equal to the third
threshold (3t) according to the comparison result. Accordingly, the
generating circuit 163 changes the level of the heat assist control
signal .phi.230 from high to low at timing T14, when the second
time (1.5t) has elapsed from timing T12.
[0073] If changing the level of the heat assist control signal
.phi.230 from high to low, the heat assist control signal
generating circuit 163 shown in FIG. 3, at the timing when the
second threshold has elapsed from the timing when it changed the
heat assist control signal .phi.230 from high to low, changes the
level of the heat assist control signal .phi.230 from low to high
to output to the delay circuit 142. Then, the generating circuit
163 compares the remaining time (second time) from the timing when
the heat assist control signal .phi.230 changed from low to high
until the magnetic field reverses the next time with the third
threshold again and according to the comparison result, if the
second time is less than the third threshold, keeps the level of
the heat assist control signal .phi.230 high to output to the delay
circuit 142. That is, the generating circuit 163 switches the
control operation of the RDC 124 from the second operation to the
first operation.
[0074] As shown in, e.g., FIG. 5, the heat assist control signal
generating circuit 163 changes the heat assist control signal
.phi.230 from low to high at timing T16, when the second threshold
(1.5t) has elapsed from timing T14.
[0075] At timing T17, the generating circuit 163 compares the
second time (2t) with the third threshold (3t) and determines that
the second time (2t) is less than the third threshold (3t)
according to the comparison result. Accordingly, the generating
circuit 163 keeps the level of the heat assist control signal
.phi.230 high.
[0076] The delay circuit 140 receives the data .phi.53 subject to
writing from the data generating circuit 135. The delay circuit 140
delays the data .phi.53 by a predetermined delay amount to generate
the data .phi.54 to be written. The delay circuit 140 outputs the
data .phi.54 to the preamp 123.
[0077] The delay circuit 142 receives the heat assist control
signal .phi.230 from the heat assist control signal generating
circuit 163. The delay circuit 142 delays the heat assist control
signal .phi.230 by a predetermined delay amount to generate the
heat assist control signal .phi.200. The delay circuit 142 outputs
the heat assist control signal .phi.200 to the preamp 123.
[0078] Note that the predetermined delay amount in the delay
circuit 140 and the predetermined delay amount in the delay circuit
142 are adjusted such that the data .phi.54 to be written and the
heat assist control signal .phi.200 are synchronous in a phase
relation shown in FIG. 5, taking into account the time required for
the processes in the magnetic-field reversing period determining
unit 161 and the heat assist control signal generating circuit 163
(e.g., time corresponding to the maximum pulse width in the data
.phi.53 subject to writing).
[0079] For example, while counting the pulse width of the data
.phi.53 subject to writing during the time from timing T10 to
timing T18 finishes at timing T18, the magnetic-field reversing
period determining unit 161 needs to realize the count at timing
T9. Hence, the predetermined delay amount in the delay circuit 140
is made greater than the predetermined delay amount in the delay
circuit 142 by an amount that can be made greater than or equal to
the time from timing T10 to timing T18. Thus, the determining unit
161 can realize the count value for the pulse width of the data
.phi.53 subject to writing from timing T10 to timing T18 at timing
T9 and can make the data .phi.54 to be written and the heat assist
control signal .phi.200 synchronous in a phase relation shown in
FIG. 5 when they are output from the RDC 124.
[0080] Next, the configuration and operation of the preamp 123 will
be described using FIGS. 4 and 5. FIG. 4 is a diagram showing
configuration of the preamp 123. FIG. 5 is a diagram showing
operation of the magnetic disk device 100 including the preamp
123.
[0081] The preamp 123 has a read/write processing unit 302 and a
heat assist current control unit 301.
[0082] The read/write processing unit 302 receives the data .phi.54
to be written from the RDC 124. The read/write processing unit 302
generates a write current 56 according to the data .phi.54 to
supply to the magnetic head 5. Thus, the magnetic field generating
element 5d generates a magnetic field according to the write
current 56 to write data onto the magnetic disk 50.
[0083] The heat assist current setting 300 is stored in the storage
unit 125, and the heat assist current control unit 301, referring
to the storage unit 125, acquires the heat assist current setting
300. The heat assist current setting 300 is setting information
denoting a relation between the level of the heat assist control
signal and the value of the drive current to be generated. In the
heat assist current setting 300, the high level of the heat assist
control signal .phi.200 is associated with the first value OP1 of
the output of the light source 5a, and the low level of the heat
assist control signal .phi.200 is associated with the second value
OP2 of the output of the light source 5a.
[0084] The heat assist current control unit 301 generates the drive
current 58 according to the heat assist control signal .phi.200 and
the heat assist current setting 300 to supply to the magnetic head
5. When the heat assist control signal .phi.200 is at the high
level, the heat assist current control unit 301 generates the drive
current 58 to supply to the light source 5a such that the output of
the light source 5a is at the first value OP1. When the heat assist
control signal .phi.200 is at the low level, the heat assist
current control unit 301 generates the drive current 58 to supply
to the light source 5a or turns off the drive current 58 not to
supply to the light source 5a such that the output of the light
source 5a is at the second value OP2.
[0085] For example, at timing T1 shown in FIG. 5, the heat assist
current control unit 301, according to the heat assist control
signal .phi.200 being kept at the high level, keeps the drive
current at a first current value I1 so that the output of the light
source 5a is kept at the first value OP1.
[0086] At timing T5, the heat assist current control unit 301,
according to the heat assist control signal .phi.200 changing from
the high level to the low level, changes the drive current from the
first current value I1 to a second current value I2 so that the
output of the light source 5a changes from the first value OP1 to
the second value OP2.
[0087] At timing T7, the heat assist current control unit 301,
according to the heat assist control signal .phi.200 changing from
the low level to the high level, changes the drive current from the
second current value I2 to the first current value I1 so that the
output of the light source 5a changes from the second value OP2 to
the first value OP1.
[0088] At timing T8, the heat assist current control unit 301,
according to the heat assist control signal .phi.200 being kept at
the high level, keeps the drive current at the first current value
I1 so that the output of the light source 5a is kept at the first
value OP1.
[0089] Next, the operation of the magnetic disk device 100 will be
described using FIG. 6. FIG. 6 is a flow chart showing operation of
the magnetic disk device 100.
[0090] The RDC 124 waits for a rise timing or fall timing of the
frequency-multiplied clock .phi.64 (No at step S1) and when a rise
timing or fall timing of the frequency-multiplied clock .phi.64 has
come (Yes at step S1), determines whether a heat assist counter
CNT1 exists (step S2).
[0091] The heat assist counter CNT1 is a counter that is created in
the RDC 124 (in the heat assist control signal generating circuit
163) to count the elapsed time from the timing when the heat assist
control signal .phi.230 is changed from the high level to the low
level (e.g., the elapsed time from timing T10 shown in FIG. 5). A
count value C in units of half the period of the
frequency-multiplied clock .phi.64 is set in the heat assist
counter CNT1.
[0092] If the heat assist counter CNT1 exists (Yes at step S2),
then the RDC 124 decrements the count value C of the heat assist
counter CNT1 (step S3). The RDC 124 determines whether the count
value C of the heat assist counter CNT1 is zero (step S4). If the
count value C of the heat assist counter CNT1 is not zero (No at
step S4), then the process returns to step S1. If the count value C
of the heat assist counter CNT1 is zero (Yes at step S4), then the
RDC 124 changes the heat assist control signal .phi.230 from the
low level (inactive) to the high level (active) (step S5) and
eliminates the heat assist counter CNT1. At the same time, the RDC
124 creates a heat assist counter CNT2 and sets the count value
temp_t of the heat assist counter CNT2 to an initial value (0).
[0093] The heat assist counter CNT2 is a counter that is virtually
created in the RDC 124 (in the heat assist control signal
generating circuit 163) to count the elapsed time from the timing
when the heat assist control signal .phi.230 is changed from the
low level to the high level (e.g., the elapsed time from timing T12
shown in FIG. 5). The count value temp_t in units of half the
period of the frequency-multiplied clock .phi.64 is set in the heat
assist counter CNT2.
[0094] The RDC 124 compares the time (second time) from the timing
when it has changed the heat assist control signal .phi.230 from
the low level to the high level until the timing when the magnetic
field reverses the next time with the third threshold
(1.5t.times.2) and determines whether the second time is greater
than or equal to the third threshold according to the comparison
result (step S6). If the second time is less than the third
threshold (No at step S6), the RDC 124 returns the process to step
S1.
[0095] On the other hand, if the heat assist counter CNT1 does not
exist (No at step S2), then the RDC 124 determines whether the
timing when the magnetic field is to be reversed has come (step
S7). If the timing when the magnetic field is to be reversed has
not come (No at step S7), the process returns to step S1. If the
timing when the magnetic field is to be reversed has come (Yes at
step S7), the RDC 124 compares the time (first time) until the
timing when the magnetic field is to be reversed the next time with
the first threshold and determines whether the first time is
greater than or equal to the first threshold according to the
comparison result (step S8). If the first time is less than the
first threshold (No at step S8), the RDC 124 returns the process to
step S1. If the first time is greater than or equal to the first
threshold (Yes at step S8), then the RDC 124 creates the heat
assist counter CNT1 and sets the count value C of the heat assist
counter CNT1 to an initial value (3) (step S9) and changes the heat
assist control signal .phi.230 from the high level (active) to the
low level (inactive) (step S10). Then, the process returns to step
S1.
[0096] If the second time is greater than or equal to the third
threshold (Yes at step S6), then the RDC 124 waits for a rise
timing or fall timing of the frequency-multiplied clock .phi.64 (No
at step S11). When a rise timing or fall timing of the
frequency-multiplied clock .phi.64 has come (Yes at step S11), then
the RDC 124 increments the count value temp_t of the heat assist
counter CNT2 (step S12). The RDC 124 determines whether the count
value temp_t of the heat assist counter CNT2 is at 3 (step S13). If
the count value temp_t of the heat assist counter CNT2 is not at 3
(No at step S13), then the process returns to step S11. If the
count value temp_t of the heat assist counter CNT2 is at 3 (Yes at
step S13), then the RDC 124 eliminates the heat assist counter
CNT2. Then, the RDC 124 creates the heat assist counter CNT1 and
sets the count value C of the heat assist counter CNT1 to an
initial value (3) (step S14) and then changes the heat assist
control signal .phi.230 from the high level (active) to the low
level (inactive) (step S15) and returns the process to step S1.
[0097] As described above, in the present embodiment, in the
magnetic disk device 100, the RDC 124 switches between the first
control and the second control according to the pulse width of data
to be written onto the magnetic disk 50. The first control is
control which keeps the output of the light source 5a at the first
value. The second control is control which makes the output of the
light source 5a change periodically between the first value and the
second value. The second value is lower than the first value. The
RDC 124 performs the first control when the pulse width of data to
be written onto the magnetic disk 50 is less than the first
threshold, and performs the second control when the pulse width of
data to be written onto the magnetic disk 50 is greater than or
equal to the first threshold.
[0098] With this performance, the reliability of data written on
the magnetic disk 50 can be improved as compared with the case of
performing the second control in a fixed manner. For example, as
shown in FIG. 8, when the pulse width of data to be written onto
the magnetic disk 50 is short, the amplitude of the data can be
secured as compared with the case of performing the second control
in a fixed manner, and hence the reliability of data written is
improved. Thus, as shown in 9A of FIG. 9, the error rate for the
same frequency can be decreased as compared with the case of
performing the second control in a fixed manner, and hence the
reliability of write operation can be improved. Further, as shown
in 9B of FIG. 9, the linear recording density for the same error
rate can be improved as compared with the case of performing the
second control in a fixed manner, and hence the recording density
in write operation can be improved. FIGS. 8 and 9 are graphs for
explaining effects of the present embodiment in comparison with the
case of performing the second control in a fixed manner.
[0099] Further, because the time-averaged amount of current
supplied to the light source 5a can be reduced as compared with the
case of performing the first control in a fixed manner, power
consumption in the light source 5a can be reduced. Yet further,
because constant light power need not continue to be supplied from
the light source 5a to the near field transducer 5c at recording,
the degradation due to heat generation of the light source 5a can
be suppressed, and the degradation due to heat generation of the
near field transducer 5c receiving light from the light source 5a
can be suppressed as compared with the case of performing the first
control in a fixed manner. Thus, as shown in FIGS. 10, 11, the
lifetimes of the light source 5a and the near field transducer 5c
can be elongated, thus suppressing a decrease in the reliability of
the light source 5a and the near field transducer 5c. FIGS. 10, 11
are graphs for explaining effects of the present embodiment in
comparison with the case of performing the first control in a fixed
manner.
[0100] Therefore, according to the present embodiment, the
reliability of data written on the magnetic disk 50 can be improved
while elongating the lifetimes of the light source 5a and the near
field transducer 5c and lowering the power consumption of the light
source 5a. Further, signal quality can be improved, and storage
capacity can be increased.
[0101] Note, although the above embodiment describes illustratively
the case where the output of the light source 5a is controlled by
controlling the drive current of the light source 5a, the output of
the light source 5a may be controlled by controlling the drive
voltage (drive signal) of the light source 5a.
[0102] Alternatively, although the above embodiment shows in FIG. 5
the operation in the case where the frequency-multiplier factor N
of the frequency-multiplied clock .phi.64 generated in the
frequency-multiplied clock generating circuit 159 equals 1, the
frequency-multiplier factor N of the frequency-multiplied clock
.phi.64 may be greater than 1. For example, as shown in FIG. 12,
the frequency-multiplier factor N of the frequency-multiplied clock
.phi.64 may equal 2. In this case, since the period t/N of the
frequency-multiplied clock .phi.64 is shorter than the period t of
the clock .phi.62 for generating the data .phi.53 subject to
writing, the off-duty of the heat assist control signal .phi.230
can be set more finely, and the off-duty of the heat assist control
signal .phi.230 can be made greater than 50%. For example, in the
example shown in FIG. 12, the off-duty of the heat assist control
signal .phi.230 in the second control can be set at 62.5%. Thus,
the power consumption in the light source 5a can be further reduced
as compared with the case of performing the first control in a
fixed manner.
[0103] Alternatively, although the above embodiment shows
illustratively the case where the data .phi.54 to be written and
the heat assist control signal .phi.200 are made synchronous in a
phase relation shown in FIG. 5, the RDC 124 may switch between the
first control and the second control such that the timings when the
output of the light source 5a becomes the second value and edge
timings of the pulses of data to be written onto the magnetic disk
50 do not coincide. For example, as shown in FIG. 13, the RDC 124
may delay the timing when to switch between the first control and
the second control with respect to the edge of the pulse of data to
be written onto the magnetic disk 50. In this case, the
predetermined delay amount in the delay circuit 140 shown in FIG. 3
and the predetermined delay amount in the delay circuit 142 should
be adjusted such that the data .phi.54 to be written and the heat
assist control signal .phi.200 are in a phase relation shown in
FIG. 13. That is, the amount by which the predetermined delay
amount in the delay circuit 140 is greater than the predetermined
delay amount in the delay circuit 142 can be made slightly smaller
than in this embodiment so that the data .phi.54 to be written and
the heat assist control signal .phi.200 are in a phase relation
shown in FIG. 13.
[0104] Alternatively, although the above embodiment shows
illustratively the case where the second value OP2 is at an off
level when the second control makes the output of the light source
5a change periodically between the first value OP1 and the second
value OP2, the second value OP2 may be a value between the first
value OP1 and the off level. Also in this case, because the
time-averaged amount of current supplied to the light source 5a can
be reduced, power consumption in the light source 5a can be reduced
as compared with the case of performing the first control in a
fixed manner.
[0105] While certain embodiments have been described, these
embodiments have been presented by way of example only, and are not
intended to limit the scope of the inventions. Indeed, the novel
embodiments described herein may be embodied in a variety of other
forms; furthermore, various omissions, substitutions and changes in
the form of the embodiments described herein may be made without
departing from the spirit of the inventions. The accompanying
claims and their equivalents are intended to cover such forms or
modifications as would fall within the scope and spirit of the
inventions.
* * * * *