U.S. patent application number 11/976709 was filed with the patent office on 2008-03-20 for laser power control technique and apparatus for recording and reproducing data in and from optical disk under laser power control.
Invention is credited to TERUYASU WATABE.
Application Number | 20080069158 11/976709 |
Document ID | / |
Family ID | 33518565 |
Filed Date | 2008-03-20 |
United States Patent
Application |
20080069158 |
Kind Code |
A1 |
WATABE; TERUYASU |
March 20, 2008 |
Laser power control technique and apparatus for recording and
reproducing data in and from optical disk under laser power
control
Abstract
A laser power control apparatus for controlling the output power
of a semiconductor laser used to record and reproduce data in and
from a recording medium is provided. The laser power control
apparatus includes a controller configured to vary the peak output
power level of the semiconductor laser in a stepwise manner,
calculate a differential efficiency at each of the varied peak
output power levels, and determine a laser driving current based on
a relation between the differential efficiency and the peak output
power level. In addition, a laser driving unit is configured to
drive the semiconductor laser using the laser driving current
determined by the controller.
Inventors: |
WATABE; TERUYASU; (Kanagawa,
JP) |
Correspondence
Address: |
DICKSTEIN SHAPIRO LLP
1825 EYE STREET NW
Washington
DC
20006-5403
US
|
Family ID: |
33518565 |
Appl. No.: |
11/976709 |
Filed: |
October 26, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10845410 |
May 14, 2004 |
7304928 |
|
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11976709 |
Oct 26, 2007 |
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Current U.S.
Class: |
372/29.015 ;
G9B/7.101 |
Current CPC
Class: |
G11B 7/1267 20130101;
G11B 7/0062 20130101 |
Class at
Publication: |
372/029.015 |
International
Class: |
H01S 5/06 20060101
H01S005/06 |
Foreign Application Data
Date |
Code |
Application Number |
May 16, 2003 |
JP |
2003-138897 |
May 16, 2003 |
JP |
2003-138910 |
Claims
1-4. (canceled)
5. A laser power control apparatus for controlling an output power
level of a semiconductor laser used to record and reproduce data in
and from a recording medium, comprising: a controller configured to
cause the semiconductor laser to output the laser beam with
different irradiation waveforms corresponding to different
recording speeds, calculate a differential efficiency for each of
the recording speeds, and determine a laser driving current based
on a relation between the differential efficiency and the recording
speed; and a laser driving unit configured to drive the
semiconductor laser using the laser driving current determined by
the controller.
6. The laser power control apparatus of claim 5, wherein the
controller is configured to derive a formula defining the
differential efficiency as a function of recording speed based on
the calculated differential efficiencies.
7. The laser power control apparatus of claim 6, wherein the
controller derives the formula prior to a recording operation
carried out using the laser beam, and the controller is further
configured to determine a laser driving current corresponding to a
target recording power level and a target recording speed for the
recording operation based on the formula.
8. The laser power control apparatus of claim 6, wherein the
controller derives the formula prior to test writing carried out
for determining an optimum recording power level for a recording
operation, and the controller is further configured to determines
the laser driving current corresponding to the optimum recording
power level based on the formula.
9. (canceled)
10. A laser power control method for controlling an output power
level of a semiconductor laser used to record and reproduce data in
and from a recording medium, comprising the steps of: causing the
semiconductor laser to output the laser beam with different
irradiation waveforms corresponding to different recording speeds;
calculating a differential efficiency for each of the recording
speeds; deriving a formula defining the differential efficiency as
a function of recording speed based on the calculated differential
efficiencies; and determining a laser driving current suitable for
a target recording power level and a target recording speed for a
recording operation based on the formula.
11. (canceled)
12. An apparatus for recording and reproducing data in and from a
recording medium, comprising: a semiconductor laser configured to
emit a laser beam at two or more levels of output power; an optical
system configured to guide the laser beam onto the recording
medium; a controller configured to cause the semiconductor laser to
output the laser beam with different irradiation waveforms
corresponding to different recording speeds to calculate a
differential efficiency for each of the recording speeds prior to a
recording operation and determine a laser driving current suitable
to a target recording power level based on a relation between the
differential efficiency and the recording speed; and a laser
driving unit configured to drive the semiconductor laser using the
laser driving current determined by the controller.
13-25. (canceled)
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a laser power control
technique required when recording and reproducing data in and from
optical recording media, such as DVD disks, with a laser beam.
[0003] 2. Description of Related Art
[0004] Along with wide use of multimedia, various types of
read-only storage media (such as music CDs, CD-ROMs, and DVD-ROMs),
as well as playback equipment, are in practical use. Recently,
phase-change recording media have come to the front, in addition to
recordable disks using dye-type media and rewritable MOs using
magneto-optical (MO) media. Especially, rewritable DVDs are
attracting a great deal of attention as the next-generation
multimedia recording media and as large-capacity storage media.
[0005] In phase-change media of optical data storage, the phase of
the recording layer changes in a reversible manner between the
crystalline state and the amorphous state when recording and
reproducing data. Unlike MO media, phase-change media do not
require an external magnetic field. Data can be recorded and
reproduced using only a laser beam emitted from a laser diode (LD),
and overwrite recording can be performed by erasing recording data
with a laser beam in one pass.
[0006] FIG. 1 is a timing chart showing an ordinary multipulse
waveform used to record data in dye-type recording media. For
dye-type media, a single pulse waveform is generated based on, for
example, eight-to-sixteen modulation to record data on the dye-type
recording layer. However, a single pulse recording method has such
a problem that the recording mark written on the recording layer
deforms into a tear-drop shape due to heat accumulation. To
overcome this problem, it is proposed to produce a multipulse
waveform of a laser beam based on EFM modulation, as an LD output
waveform strategy, when forming marks on the recording layer. The 8
to 16 EFM signal and the multipulse waveform are indicated by
symbols (b) and (c), respectively, in FIG. 1.
[0007] As an example of the multipulse irradiation, it is proposed
to produce a head pulse and subsequent pulses for heating the
recording layer to define a mark.
[0008] FIG. 2 is a timing chart showing an ordinary multipulse
waveform used to record data in phase-change recording media.
Again, a laser beam with a multipulse waveform is produced to form
a mark, but this waveform has multiple levels of recording power,
as indicated by symbol (c).
[0009] For recording data in dye-type or phase-change recording
media, it is necessary to correctly control the output power of the
laser diode (LD). However, the driving current vs. output power
characteristic of a laser diode easily fluctuates due to
self-heating. In order to stabilize the output power, automatic
power control (APC) is performed generally. In automatic power
control, a portion of the laser beam emitted from the laser diode
is guided onto a photo detector (PD), and laser driving current is
controlled using a monitor current generated by the photo detector
in proportion to the output power of the laser diode.
[0010] In general, a radio frequency electric current is superposed
on the laser driving current to reduce noise. Considering only the
data reproducing aspect, the APC can be realized easily by
constructing a feedback loop of a relatively low frequency band
because the laser driving current itself is a direct current.
[0011] On the other hand, when conducting the APC during the
recording operation, laser power control becomes more difficult
because the laser output power has to be changed at high speed to
form marks and spaces. The recording power may be controlled to
some extent with a simple structure as in data reproduction, by
constructing a feedback loop of a low frequency band making use of
the fact that the digital sum value (DSV) of the recorded data
becomes zero in CD or DVD disks. However, the recording power
cannot be controlled accurately.
[0012] To improve the control accuracy of the recording power, a
sample and hold circuit may be used. For example, when data of the
maximum length of 11 T consisting of marks and spaces are recorded
in a CD-R (dye-type) medium using the strategy indicated by symbol
(c) in FIG. 3, the output power is sampled and held for each mark
and each space. With this method, the recording power can be
controlled more accurately at relatively low cost.
[0013] However, multipulse laser output is desired to record data
in DVD disks of both dye-type and phase-change type, as has been
explained above. For this reason, using a sample and hold circuit
is unrealistic because high-frequency control is required for the
light-receiving system and the subsequent stages.
[0014] To overcome this problem, JP 9-171631A proposes to
appropriately insert a non-pulse driving period in the laser output
waveform to control the output level of the laser between the
amorphous level (at peak power) and the reading level (at bottom
power) during the data recording operation in a phase-change
medium.
[0015] However, if this technique is applied to the recording power
control for mark formation in a dye-type medium based on the
recording strategy shown in FIG. 1, a correct recording mark cannot
be formed due to consecutive heating, and consequently, an area in
which the recording operation is conducted during the non-pulse
period results in a defective spot. This defective spot has little
effect on the reproducing operation as long as error correction is
carried out because automatic power control (APC) is implemented at
a relatively long interval.
[0016] As to power control for space formation, the output power
for forming a space is generally a constant power, and it can be
controlled without causing defect in the recorded data by sampling
and holding the output power at the timing of writing relatively
long space data. This means that the space recording power can be
controlled at a shorter interval as compared with the mark
recording power.
[0017] Since the optimum level of the recording power varies
depending on the surrounding temperature, as well as on type of the
recording medium and the linear velocity, the recording power is
optimized through test writing in the optimum power control (OPC)
process. The OPC process is carried out by recording and
reproducing prescribed test data on and from a power calibration
area (PCA) in the recording medium.
[0018] To be more precise, test data of a prescribed pattern formed
by marks and spaces with lengths of three times to fourteen times
as long as the channel clock T (3T-14T) are recorded at several
different levels of laser output power. Then, the test data are
reproduced, and DC modulations of the RF signal and RF signal
asymmetry after DC coupling are calculated as evaluation parameters
at each level of output power.
[0019] The modulation M is calculated using equation (1), which is
expressed by the ratio of maximum peak-to-peak amplitude I.sub.p-p
of the RF signal to the maximum level Imax of the RF signal.
M=I.sub.p-p/I.sub.max (1)
[0020] The asymmetry .beta. after DC coupling is expressed by
equation (2) using a positive peak level X1 and a negative peak
level X2 of the RF signal after AC coupling. .beta.=(X1+X2)/(X1-X2)
(2) where X1+X2 denotes the difference between the positive and
negative peaks of the RF signal after AC coupling, and X1-X2
denotes the peak-to-peak value of the RF signal after AC
coupling.
[0021] The optimum recording power is determined based on the
modulation M and/or the asymmetry .beta. after AC coupling.
[0022] To conduct actual recording operations, it is necessary to
calculate the differential efficiency of the laser diode (LD) in
advance and determine the driving current for each power level. In
general, pre-recording is implemented in the focus-off state prior
to the recording operation, and the recording output power levels
are sampled to calculate the differential efficiency.
[0023] Conventionally, it has been considered that the driving
current vs. laser output power characteristic (I-L characteristic)
of a laser is substantially linear. However, to be more exact, the
I-L characteristic exhibits a slightly a non-linear property. In
addition, when outputting a laser pulse, the I-L characteristic
varies in a short period of time due to abrupt change from low
power to high power. As a result, the peak level of each pulse
declines, as illustrated in FIG. 4. The peak drop becomes
conspicuous as the output power becomes high. This is because the
laser heats up more rapidly when the output power becomes
higher.
[0024] In general, the higher the recording speed, the shorter the
recording pulse. Accordingly, the quantity of peak drop increases
when the recording speed becomes slower, as illustrated in FIG. 5A
and FIG. 5B. The peak drop B of a long-width pulse shown in FIG. 5B
is greater than the peak drop A of a short-width pulse shown in
FIG. 5A (B>A).
[0025] If the laser driving current is determined on the assumption
that that the I-L characteristic is linear, with little regard to
the non-linear characteristic of the laser diode, output power
error will occur and the recording quality will be degraded.
[0026] Another problem caused in conventional optical disk
recording/reproducing apparatuses due to variation in peak drop
phenomenon is deviation from the optimum full-scale value of the
digital-to-analog converter.
[0027] Some kinds of optically recording and reproducing
apparatuses employ a laser power control system that uses a
digital-to-analog converter (DAC) as the current source for driving
the peak power of the laser diode (LD), while digitally controlling
the peak level. In such type of apparatus, another
digital-to-analog converter is used to set the maximum driving
current for the former DAC.
[0028] The latter DAC is called a full-scale DAC. The full-scale
DAC adjusts the quantity of the maximum current required to drive
the laser so as to optimize the resolution of the former DAC (for
driving the peak level).
[0029] If a large amount of laser driving current is not so
required, the value of the full-scale DAC is set small to increase
the resolution of the peak-level driving DAC. For determining the
full-scale DAC value, the differential efficiency of the laser has
to be estimated in advance to determine how much driving current is
required with respect to the maximum output power required under
the given recording condition.
[0030] However, if the laser diode (LD) has such a characteristic
that the peak drop becomes conspicuous along with increase of laser
output power, the differential efficiency of the laser diode
fluctuates depending on the output power. With such fluctuation,
the optimum full-scale DAC value cannot be determined, and
therefore, the resolution of the peak-level driving DAC cannot be
set to the optimum.
SUMMARY OF THE INVENTION
[0031] It is therefore an object of the present invention to
overcome the above-described problem, and to provide a laser power
control technique capable of controlling the laser output power
precisely during the recording operation based on an accurate
differential efficiency, taking into consideration the non-linear
characteristic of a laser diode.
[0032] It is another object of the invention to provide a laser
power control technique capable of controlling the laser output
power more precisely by calculating differential efficiency
accurately and setting the resolution of the laser driving DAC.
[0033] It is still another object of the invention to provide an
apparatus for recording and reproducing data in and from an optical
recording medium using a laser beam under improved laser power
control.
[0034] To achieve the objects, in one aspect of the invention, a
laser power control apparatus for controlling an output power level
of a semiconductor laser used to record and reproduce data in and
from a recording medium is provided. This laser power control
apparatus comprises:
[0035] a controller configured to vary a peak output power level of
the semiconductor laser in a stepwise manner, calculate a
differential efficiency at each of the varied peak output power
levels, and determine a laser driving current based on a relation
between the differential efficiency and the peak output power
level; and
[0036] a laser driving unit configured to drive the semiconductor
laser using the laser driving current determined by the
controller.
[0037] With this laser control apparatus, the output power level of
the laser can be controlled accurately in the recording operation,
taking into the non-linearity of the driving current vs. output
power characteristic of the laser.
[0038] In another aspect of the invention, a laser power control
apparatus for controlling an output power level of a semiconductor
laser used to record and reproduce data in and from a recording
medium comprises:
[0039] a controller configured to cause the semiconductor laser to
output the laser beam with different irradiation waveforms
corresponding to different recording speeds, calculate a
differential efficiency for each of the recording speeds, and
determine a laser driving current based on a relation between the
differential efficiency and the recording speed; and
[0040] a laser driving unit configured to drive the semiconductor
laser using the laser driving current determined by the
controller.
[0041] With this laser power control apparatuses, the output power
level of the laser can be controlled further accurately depending
on the waveform of the output pulse (or the recording speed).
[0042] In still another aspect of the invention, an apparatus for
recording and reproducing data in and from a recording medium is
provided. The apparatus comprises:
[0043] a semiconductor laser configured to emit a laser beam at two
or more levels of output power;
[0044] an optical system configured to guide the laser beam onto
the recording medium;
[0045] a controller configured to vary a peak output power level of
the semiconductor laser in a stepwise manner to calculate a
differential efficiency at each of the varied peak output power
levels prior to a recording operation and determine a laser driving
current suitable for a target recording power level based on a
relation between the differential efficiency and the peak output
power level; and
[0046] a laser driving unit configured to drive the semiconductor
laser using the laser driving current determined by the
controller.
[0047] In yet another aspect of the invention, an apparatus for
recording and reproducing data in and from a recording medium
comprises:
[0048] a semiconductor laser configured to emit a laser beam at two
or more levels of output power;
[0049] an optical system configured to guide the laser beam onto
the recording medium;
[0050] a controller configured to cause the semiconductor laser to
output the laser beam with different irradiation waveforms
corresponding to different recording speeds to calculate a
differential efficiency for each of the recording speeds prior to a
recording operation and determine a laser driving current suitable
to a target recording power level based on a relation between the
differential efficiency and the recording speed; and
[0051] a laser driving unit configured to drive the semiconductor
laser using the laser driving current determined by the
controller.
[0052] In yet another aspect of the invention, a laser power
control apparatus for controlling an output power level of a
semiconductor laser used to record and reproduce data in and from a
recording medium comprises:
[0053] a laser driving unit configured to drive the semiconductor
laser; and
[0054] a controller configured to vary a peak output power level of
the semiconductor laser in a stepwise manner to calculate a
differential efficiency at each of the varied peak output power
levels prior to a recording operation, and determine a maximum
driving current for the laser driving unit based on a relation
between the differential efficiency and the peak output power
level.
[0055] With this laser power control apparatus, the output power
level of the laser can be controlled accurately by determining the
maximum driving current for the laser driving unit.
[0056] In yet another aspect of the invention, an apparatus for
recording and reproducing data in and from a recording medium is
provided. This apparatus comprises:
[0057] a semiconductor laser configured to emit a laser beam at two
or more levels of output power;
[0058] an optical system configured to guide the laser beam onto
the recording medium;
[0059] a controller configured to vary a peak output power level of
the semiconductor laser in a stepwise manner to calculate a
differential efficiency at each of the varied peak output power
levels prior to a recording operation and determine a maximum
driving current required to drive the semiconductor laser at a
target recording power, based on a relation between the
differential efficiency and the peak output power level; and
[0060] a laser driving unit configured to drive the semiconductor
laser using the maximum driving current determined by the
controller.
BRIEF DESCRIPTION OF THE DRAWINGS
[0061] Other objects, features, and advantages of the present
invention will become more apparent from the following detailed
description when read in conjunction with the accompanying
drawings, in which:
[0062] FIG. 1 is a timing chart showing an example of a multipulse
waveform of a laser beam used to record data in a dye-type
recording medium;
[0063] FIG. 2 is a timing chart showing an example of a multipulse
waveform of a laser beam used to record data in a phase-change
recording medium;
[0064] FIG. 3 is a timing chart showing an example of a recording
strategy employed when recording data in a CD-R (dye-type)
recording medium;
[0065] FIG. 4 is a diagram showing peak drop in a laser output
pulse;
[0066] FIG. 5A and FIG. 5B are pulse shapes showing the relation
between recording speed and peak drop;
[0067] FIG. 6 is a block diagram showing the major part of a data
recording and reproducing apparatus to which the present invention
is applied;
[0068] FIG. 7 is a schematic diagram showing the structure of the
optical pickup according to the first embodiment of the
invention;
[0069] FIG. 8 is a block diagram of the system controller used in
the optical pickup shown in FIG. 7;
[0070] FIG. 9 is a block diagram of the LD driving unit used in the
optical pickup shown in FIG. 7;
[0071] FIG. 10A through FIG. 10C show LD driving timing according
to the first embodiment of the invention;
[0072] FIG. 11 is a flowchart of calculation of the differential
efficiency and determination of peak level driving current
according to the first embodiment of the invention;
[0073] FIG. 12 is a graph of LD output power as a function of LD
driving current, showing the non-linear I-L characteristic;
[0074] FIG. 13 is a graph used to explain stepwise change of the
peak level output power to calculate differential efficiencies at
different peak levels taking the non-linear I-L characteristic into
account according to the first embodiment of the invention;
[0075] FIG. 14 is a flowchart of calculation of differential
efficiency at different recording speeds according to another
example of the first embodiment of the invention;
[0076] FIG. 15 shows LD driving timing at different recording
speeds;
[0077] FIG. 16 is a block diagram of the optical pickup according
to the second embodiment of the invention;
[0078] FIG. 17 is a block diagram of the system controller used in
the optical pickup shown in FIG. 16;
[0079] FIG. 18 is a block diagram of the LD driving unit used in
the optical pickup shown in FIG. 16;
[0080] FIG. 19 is a flowchart of calculation of differential
efficiency and determination of full-scale setting value according
to the second embodiment of the invention; and
[0081] FIG. 20 is a graph for explaining rotational control of the
spindle using zone constant linear velocity (ZCLV) for increasing
the recording speed.
DETAILED DESCRIPTION OF THE INVENTION
[0082] The preferred embodiments of the present invention are
described below with reference to the attached drawings.
[0083] FIG. 6 is a block diagram of an apparatus for optically
recording and reproducing data in and from a recording medium
(hereinafter, simply referred to as an "optical disk apparatus"),
to which the present invention is applied. In the preferred
embodiments, DVD-ROM formatted code data are recorded in a dye-type
recording medium through eight to sixteen (8 to 16) modulation, by
implementing mark edge/pulse width recording. A semiconductor laser
diode (LD) is driven so as to output multipulse irradiation to form
recording marks in the recording medium in accordance with the
DVD-ROM formatted code data.
[0084] The optical disk apparatus includes a spindle motor 2 for
rotating an optical disk 1, an optical pickup 3, a motor driver 4,
a read amplifier 5, a servo processor 6, a DVD decoder 7, an ADIP
decoder 8, a laser controller 9, a DVD encoder 10, a DVD-ROM
encoder 11, a buffer RAM 12, a buffer manager 13, a DVD-ROM decoder
14, an ATAPI/SCSI interface 15, a digital-to-analog converter (DAC)
16, a ROM 17, a CPU 18, and a RAM 19. LB denotes laser beam, which
is emitted from the optical pickup 3 toward the optical disk 1, and
audio signals are output from the digital-to-analog converter
16.
[0085] The arrows connected between blocks indicate data flow. To
simplify the figure, connection between each block and the CPU 18
that controls the operation of the block is omitted. Control
programs described by codes readable by the CPU 18 are stored in
the ROM 17. When the optical disk apparatus is turned on, the
control programs are loaded in the main memory (not shown), and the
CPU 18 controls the operation of each component (block) according
to the control programs, while temporarily saving data required for
control coordination in the RAM 19.
[0086] A more detailed explanation is made next on the structure
and the operation of the optical disk apparatus shown in FIG. 6.
The optical disk 1 is rotated by the spindle motor 2. The spindle
motor 2 is controlled by the motor driver 4 and the servo processor
6 such that the linear velocity or the angular velocity becomes
constant. The linear velocity or the angular velocity can be varied
in a stepwise manner.
[0087] The optical pickup 3 guides the laser beam LB emitted from
the semiconductor laser onto the optical disk 1 so as to form a
light spot S on the recording layer. The optical pickup 3 is
movable by means of a seek motor (not shown) along the sledge. The
seek motor, together with the focus actuator and the track actuator
provided in the optical pickup 3, bring the light spot S of the
laser beam LB to a target position, via the motor driver 4 and the
servo processor 6, based on the signal acquired from the
light-receiving element and the position sensor.
[0088] When reading data from the optical disk 1, reproducing
signals acquired by the optical pickup 3 are amplified and
binarized by the read amplifier 5, and then supplied to the DVD
decoder 7. The binary data, which have been encoded through
eight-to-sixteen modulation converting eight-bit data to
sixteen-bit data, are demodulated by the DVD decoder 7. A binding
bit is added to the modulated code such that the number of "1"s and
the number of "0"s become equal to each other on average. This is
called "suppression of DC component", and the slice level
fluctuation of the DC-cut reproducing signal is suppressed.
[0089] The demodulated data are then subjected to deinterleaving
and error correction, and supplied to the DVD-ROM decoder 14, in
which further error correction is implemented to improve the
reliability of data. The data, which have been subjected to error
correction twice, are temporarily saved in the buffer RAM 12 by the
buffer manager 13. When the data are accumulated sufficient to
define sector data, the data are transferred to the host computer
(not shown) at a time via the ATAPI/SCSI interface 15. If the
reproduced data are audio (music) data, the data output from the
DVD decoder 7 are supplied to the digital-to-analog converter (D/A
converter) 16, and analog audio signal "Audio" is output.
[0090] When writing data, the data supplied from the host computer
via the ATAPI/SCSI interface 15 are temporarily saved in the buffer
RAM 12 by the buffer manager 13. Before the writing operation is
started, the laser spot has to be positioned at a writing start
position. For DVD+RW media or DVD+R media, the writing start
position is determined by the wobble signal reproduced from the
wobbling groove of the track, which is marked in advance on the
optical disk 1. For DVD-RW and DVD-R media, the writing start
position is determined from the land prepit area, instead of the
wobble signal. For DVD-RAM media and DVD-RAM.cndot.WO media, the
writing start position is determined from the prepit area.
[0091] The wobble signal reproduced from DVD+RW or DVD+R disks
contains address information called an "Address in Pregroove
(ADIP)", which is extracted by the ADIP decoder 8. The sync signal
produced by the ADIP decoder 8 is supplied to the DVD encoder 10 to
allow data to be written in an accurate position on the optical
disk 1. The data saved in the buffer RAM 12 are supplied to the
DVD-ROM encoder 11 or DVD encoder 10, which adds an error
correction code to or implements interleaving of the data. Then,
the data are written in the optical disk 1 by the laser controller
9 and the optical pickup 3.
[0092] The address information is also extracted from the land
prepit area or prepit area.
[0093] FIG. 7 is a schematic diagram illustrating the optical
pickup 3A according to the first embodiment of the invention. The
optical pickup 3A includes an optical system including a laser
diode (LD) 21 functioning as the light source, a beam splitter 22,
a set of lenses 23-26, and a pair of light-receiving elements 27
and 28. The laser diode 21 is driven by the LD driving unit 29A.
The optical pickup 3A also includes current-to-voltage converter
amplifiers (I/V amplifiers) 30 and 31, and a system controller 32A.
The system controller 32A supplies bias-level current driving
signal 101, peak-level current superposing signal 102, power
sampling timing signal 106, pulse control signal 107, and write
gate signal 108 to the LD driving unit 29A.
[0094] FIG. 8 is a block diagram of the system controller 32A used
in the optical pickup 3A. The system controller 32A includes a
sample-and-hold circuit 33, a peak and bottom detection circuit 34,
a host controller 35A, an APC circuit 36, a data decoder 37, a data
decoder 38, and an LD waveform control circuit 39.
[0095] FIG. 9 is a block diagram of the LD driving unit 29A shown
in FIG. 7. The LD driving unit 29A has a bias level driving circuit
40, a peak level superposing circuit 41, and an adder 42.
[0096] In playback, the LD driving unit 29A drives the laser diode
(LD) 21 so as to output a laser beam at a reproducing power (or
reading power). The laser beam at a reproducing power is guided by
the optical system of the optical pickup 3 onto the optical disk 1.
The light-receiving element 27 receives a return beam reflected
from the optical disk 1 and converts the light quantity into an
electric current signal. The electric current is converted to a
voltage and amplified by the I/V amplifier 30. This IV-converted
signal is output as the RF signal 105.
[0097] A portion of the laser beam emitted from the LD 21 is guided
to the monitoring light-receiving element 28, and a monitoring
current detected in proportion to the output power is converted to
a voltage and amplified by the I/V amplifier 31, which is then
output as the power monitoring signal 104.
[0098] The APC circuit 36 (FIG. 8) in the system controller 32A
receives the power monitoring signal 104, and outputs a bias-level
current driving signal 101 to the LD driving unit 29A. (It should
be noted that the sample and hold circuit 33 is always in the
sampling mode in the playback mode.) The APC circuit 36 is
structured by an inverting amplifier, and accordingly, a feedback
loop is formed by the APC circuit 36, the LD driving unit 29A, and
I/V amplifier 31 in order to implements automatic power control
(APC) for keeping the reproducing power constant.
[0099] In general, to record data in a dye-type recording medium,
two different levels of recording power, namely, peak level and
space level (bias level) are required. In this example, the bottom
level of the multipulse irradiation for forming a mark is at the
same level as the bias level. However, the bottom level may be set
separately from the bias level.
[0100] In the recording mode, the host controller 35A generates a
pulse control signal 107 based on the input data (consisting of
eight-to-sixteen modulated data) and supplies the pulse control
signal 107 to the LD driving unit 29A, as shown in FIG. 7. The LD
driving unit 29A drives the laser diode (LD) 21 by a driving
current according to the pulse control signal 107 to cause the
laser diode 21 to output multipulse irradiation shown in FIG. 1
(indicated by symbol (c)). The laser beam emitted from the laser
diode 21 is guided onto the optical disk 1 to form recording marks
on the recording layer.
[0101] The host controller 35A supplies bias-level current driving
signal 101 and peak-level current superposing signal 102 to the LD
driving unit 29A in order to control the space level and the peak
level of the laser output power.
[0102] In the LD driving unit 29A, the bias level driving circuit
40 (FIG. 9) generates a bias current according to the bias-level
current driving signal 101. The peak level superposing circuit 41
generates an electric current according to the peak-level current
superposing signal 102, which is added to the bias current by the
adder 42. The superposed driving signal is supplied to the laser
diode 21. In this example, the peak level superposing circuit 41 is
a digital-to-analog converter (first DAC), which converts the
peak-level current superposing signal 102 supplied in a digital
form from the host controller 35A to an analog form (electric
current).
[0103] The host controller 35A outputs a power sampling timing
signal 106 when long space data (for example, space data of 10 T or
longer) are output. The sample and hold circuit 33 samples and
holds the power monitoring signal 104 at the falling edge (changing
from H to L) of the power sampling timing signal 106, as
illustrated in FIG. 10C, in order to execute bias level power
control.
[0104] The peak output power level of the laser diode 21 is
regulated by superposing an electric current calculated from the
differential efficiency of the laser output power to the bias level
driving current and by supplying the resultant driving signal to
the laser diode (LD) 21.
[0105] The laser diode 21 is driven to implement dummy writing in
period A shown in FIG. 10A, prior to (or immediately before) the
actual recording operation, and the differential efficiency of the
laser beam is calculated based on the peak level sampled in the
dummy writing period A. During the dummy writing, the system is set
in the defocusing state so as not to record data in the recording
medium.
[0106] In the ordinary writing operation, multipulse irradiation is
conducted between the peak power level and the bottom power level
to record the data based on the waveform indicated by symbol (c) in
FIG. 1. It is not practical to sample the peak level during
irradiation with such a waveform. Accordingly, in the dummy writing
period A, the peak level is maintained for a certain period of time
(non-pulse peak period) to allow the peak level to be sampled for
calculation of the differential efficiency, as illustrated in FIG.
10B. The non-pulse peak period is inserted at the timing of
occurrence of long mark data (longer than or equal to 10 T, for
example).
[0107] In the ordinary writing operation, the power sampling timing
signal 106 becomes H-level when long space data come up. To the
contrary, during the dummy irradiation for calculation of the
differential efficiency, the power sampling timing signal 106 rises
to the H level when long mark data come out, at which timing
non-pulse irradiation is conducted to allow the peak level to be
sampled. Based on the two sampling levels, that is, the peak level
sampled at the occurrence of long mark data and the bias level
sampled at the occurrence of long space data as illustrated in FIG.
10B, the differential efficiency of laser output is calculated.
[0108] FIG. 11 is a flowchart showing calculation of differential
efficiencies at different peak power levels and determination of
the laser driving current according to the first embodiment of the
invention.
[0109] First, the peak output power level is set to several levels
(Pw1 in S1-1, Pw2 in S1-3, and Pw3 in S1-5), and dummy writing is
carried out at the respective levels to calculate the corresponding
differential efficiencies (S1-2, S1-4, and S1-6). As illustrated in
FIG. 12 and FIG. 13, the relation between the peak output power
level of the laser diode 21 and the LD driving current is
non-linear. Accordingly, the optimum LD driving current is
determined taking the non-linear characteristic into account
according to the preferred embodiments.
[0110] The differential efficiency 77 (Pw) at each output power is
estimated from equation (3).
.eta.(Pw)=(Pw-Pb)/.DELTA.Iw=(Pw-Pb)/(Iw-Ib) (3) where Ib denotes
the bias level driving current, Pb denotes the bias output power
level, Iw denotes the peak level driving current, Pw denotes the
peak output power level, and .DELTA.Iw denotes the peak level
superposing current representing the difference between Iw and
Ib.
[0111] Then, an approximate expression defining the relation
between output power Pw and differential efficiency .eta. is
derived from the differential efficiencies and the associated peak
power levels (S1-7 of FIG. 11). The expression may be a linear
expression; however, quadratic expression (4) is preferably
employed in this embodiment for a more accurate definition of the
function. .eta.(Pw)=a*Pw 2+b*Pw+c (4)
[0112] If no test writing is carried out, the differential
efficiency .eta.(Pw) is determined by substituting a peak power Pw
used in the actual recording operation in formula (4). Then, the
peak level superposing current .DELTA.Iw is calculated from
equation (5) (S1-8), which current is extracted as the peak-level
current superposing signal 102. .DELTA.Iw(Pw)=Pw/.eta.(Pw) (5)
[0113] If test writing is carried out in the test writing period B
as shown in FIG. 10A, the host controller 35A generates a sector
sync signal 211 (see FIG. 8) every time the sector is switched in
the test writing period. In writing test data, the write gate
signal 108 is at a High level. For example, when DVD-formatted
eight-to-sixteen modulation codes are employed, sector sync signal
211 is generated every 38,688 channel clocks (1,488*26=38,688).
Every time the sector sync signal 211 is generated, the peak-level
current superposing signal 102 is updated to change the peak output
power level of the laser diode in a stepwise manner, as indicated
by period B in FIG. 10A.
[0114] At each peak output power level, the differential efficiency
.eta. and the associated peak-level current superposing signal 102
are calculated using equations (4) and (5).
[0115] When test writing with the output power varied stepwise is
finished, the recorded data are reproduced, and RF signal 105 is
sampled at each sector and asymmetry .beta. is calculated for each
sector using equation (2). Based on the calculated asymmetry
.beta., the output power of the laser diode (LD) 21 is determined
for the actual recording operation. The .beta. value that
represents the highest recording quality has been estimated in
advance depending on the type of the recording medium (disk).
[0116] FIG. 14 and FIG. 15 illustrate a modification of the
calculation of the differential efficiency according to the first
embodiment of the invention. In the modification, differential
efficiencies are calculated at different recording speeds.
[0117] FIG. 14 is a flowchart of calculation of differential
efficiency and determination of laser driving current, and FIG. 15
is a timing chart showing channel clocks (a) for different
recording speeds and the multipulse waveform of the laser diode. An
appropriate correction is made on differential efficiency .eta.
depending on the recording speed. Other portions are the same as
those explained in the first embodiment.
[0118] During the dummy writing period, which is carried out prior
to (or immediately before) the recording operation in order to
calculate differential efficiency, the recording speed is varied to
several levels. In this example, multipulse irradiation is
conducted with waveforms for three different recording speeds
(S2-1, S2-3, and S2-5). The recording speed is increased from
recording speed 1, to recording speed 2, and to recording speed 3,
as shown in FIG. 15. At each recording speed, the differential
efficiency is calculated using equation (3) (S2-2, S2-4, and
S2-6).
[0119] Then, an approximate expression defining the relation
between recording speed (linear velocity) V1 and differential
efficiency .eta. is derived from the differential efficiencies and
the associated recording speeds (S2-7). The expression is quadratic
expression (6), as in the first embodiment. .eta.(V1)=a*V1 2+b*V1+c
(6)
[0120] If no test writing is carried out, the differential
efficiency .eta.(V1) is determined by substituting a recording
speed V1 used in the actual recording operation in formula (6).
Then, the peak level superposing current .DELTA.Iw is calculated
from equation (7) (S2-8), which current is extracted as the
peak-level current superposing signal 102.
.DELTA.Iw(V1)=Pw/.eta.(V1) (7)
[0121] If test writing is carried out in the second embodiment, the
host controller 35 executes the same sequence as in the first
embodiment, in this case, at each peak level test
[0122] At each peak output power level, the differential efficiency
.eta. and the associated peak-level current superposing signal 102
are calculated using equations (6) and (7).
[0123] Next, the second embodiment of the invention is explained
with reference to FIG. 16 through FIG. 20. FIG. 16 is a block
diagram of the optical pickup 3B according to the second
embodiment, and FIG. 17 is a block diagram of the system controller
32B used in the optical pickup 3B. The host computer 35B of the
system controller 32B generates and supplies a full-scale setting
signal 103, in addition to bias-level current driving signal 101,
peak-level current superposing signal 102, power sampling timing
signal 106, pulse control signal 107, and write gate signal 108, to
the LD driving unit 29B.
[0124] FIG. 18 is a block diagram of the LD driving unit 29B, which
includes a bias level driving circuit 40, a peak level superposing
circuit 41, and a full-scale setting circuit 43. The bias level
driving circuit 40 generates bias current according to the
bias-level current driving signal 101 supplied from the system
controller 32B. The peak level superposing circuit 41 generates
electric current corresponding to the peak-level current
superposing signal 102, which current is superposed on the bias
current through the adder 42. The peak-level superposing circuit 41
is formed by a digital-to-analog converter referred to as the first
DAC.
[0125] The full-scale setting circuit 43 is also formed by a
digital-to-analog converter (referred to as the second DAC) and it
determines the full-scale of the peak level superposing circuit
(the first DAC) 41 based on the full-scale setting signal supplied
from the host controller 35B of the system controller 32B.
[0126] FIG. 19 is a flowchart showing the operation of calculation
of differential efficiency and determination of full-scale setting
value, which is executed by the host controller 35B.
[0127] First, the peak output power level is set to several levels
(Pw1 in S3-1, Pw2 in S3-3, and Pw3 in S3-5), and dummy writing is
carried out at the respective levels to calculate the corresponding
differential efficiencies (S3-2, S3-4, and S3-6). The differential
efficiency .eta.(Pw) at each output power level is estimated from
equation (3). .eta.(Pw)=(Pw-Pb)/.DELTA.Iw=(Pw-Pb)/(Iw-Ib) (3) where
Ib denotes the bias level driving current, Pb denotes the bias
output power level, Iw denotes the peak level driving current, Pw
denotes the peak output power level, and .DELTA.Iw denotes the peak
level superposing current representing the difference between Iw
and Ib.
[0128] Then, an approximate expression defining the relation
between output power Pw and differential efficiency .eta. is
derived from the differential efficiencies and the associated peak
power levels (S3-7). The approximate expression is quadratic
expression (4). .eta.(Pw)=a*Pw 2+b*Pw+c (4)
[0129] If no test writing is carried out, the differential
efficiency .eta.(Pw) is determined by substituting a peak power Pw
used in the actual recording operation in formula (4). Then, the
full-scale setting value is determined (S3-8) for the full-scale
setting circuit 43 of the LD driving unit 29B. The full-scale
setting value (FS) is determined by estimating the maximum driving
current from the maximum power required under the current condition
and the differential efficiency.
[0130] To be more precise, the Full-Scale setting value (FS) is
determined from equations (8) and (9).
.DELTA.Iw(Pw_max)=(Pw_max-Pb)/.eta.(Pw_max) (8)
FS=[.DELTA.Iw(Pw_max)/.DELTA.Iw_max]*255 (9) where Pw_max is the
maximum output level, .DELTA.Iw(Pw_max) is the peak-level
superposing current at the maximum output power, and .DELTA.Iw_max
is the maximum driving current generated by the peak level
superposing circuit 41. In equation (9), it is assumed that the
full-scale setting value (RS) is represented by 8 bits. When
.DELTA.Iw(Pw_max) is equal to .DELTA.Iw_max, the full-scale setting
value (FS) becomes 255. This full-scale setting value is extracted
as the full-scale setting signal 103 to be supplied to the LD
driving circuit 29B.
[0131] Then, the peak-level superposing current .DELTA.Iw is
calculated from equation (5), as in the first embodiment, which
current is extracted as the peak-level current superposing signal
102. .DELTA.Iw(Pw)=Pw/.eta.(Pw) (5)
[0132] If test writing is carried out in the test writing period B
(FIG. 10A), the host controller 35B generates a sector sync signal
211 (see FIG. 8) every time the sector is switched in the test
writing period. In writing test data, the write gate signal 108 is
at a High level. For example, when DVD-formatted eight-to-sixteen
modulation codes are employed, sector sync signal 211 is generated
every 38,688 channel clocks (1,488*26=38,688). Every time the
sector sync signal 211 is generated, the peak-level current
superposing signal 102 is updated to change the peak level output
power of the laser diode in a stepwise manner, as indicated by
period B in FIG. 10A.
[0133] At each peak output power level, the differential efficiency
.eta. and the associated peak-level current superposing signal 102
are calculated using equations (4) and (5).
[0134] When test writing with the output power varied stepwise is
finished, the recorded data are reproduced, and RF signal 105 is
sampled at each sector and asymmetry .beta. is calculated for each
sector using equation (2). Based on the calculated asymmetry
.beta., the output power of the laser diode (LD) 21 is determined
for the actual recording operation. The .beta. value that
represents the highest recording quality has been estimated in
advance depending on the type of the recording medium (disk).
[0135] After the optimum power is set through test writing, actual
recording operations are carried out. If the recording power (peak
power level) changes greatly, the differential efficiency also
changes, and therefore, the full-scale setting value changes. In
the same recording medium, one of the conditions that causes the
recording power to change is change in recording speed. In general,
as the recording speed increases, the required recording power also
increases.
[0136] Under the circumstances where data are recorded repeatedly,
the differential efficiency and the full-scale setting value are
newly calculated when the recording output power level changes from
the output power level for the previously performed recording
operation by a prescribed quantity or more, or when the recording
speed is changed. With this arrangement, the full-scale setting
value can be updated to the optimum value according to the
circumstances.
[0137] To further increase the recording speed, the rotation of the
spindle motor 2 is controlled in the zone constant linear velocity
mode, as illustrated in FIG. 20 during the recording operation.
Under this rotational control, the recording speed is increased in
a stepwise manner, as the recording position on the optical disk
shifts to the outer periphery in the radial direction. This
arrangement can prevent the revolution rate of the spindle motor 2
from increasing excessively when data are being recorded near the
center portion of the disk.
[0138] When the recording position on the optical disk 1 reaches a
prescribed position along the radius, a higher recording power
level (peak output power level) is required in order to increase
the recording speed. If the recording operation is carried out
continuously in the ZCLV mode, a new differential efficiency and a
new full-scale value are calculated upon change of the recording
speed to update the full-scale value to the optimum.
[0139] As has been described above, the laser driving current can
be set accurately based on the differential efficiencies at
different peak power levels or different recording speeds.
Consequently, the laser output power in the recording operation can
be controlled precisely, taking the non-linear I-L characteristic
into account. In addition, by determining the maximum driving
current for the laser driving source, the laser output power in the
recording operation can be controlled precisely.
[0140] As a result, the recording quality is improved.
[0141] This patent application is based on and claims the benefit
of the earlier filing date of Japanese Patent Application Nos.
2003-138897 and 2003-138910, both filed May 16, 2003, the entire
contents of which are hereby incorporated by reference.
* * * * *