Title: Optical disc apparatus
Abstract: An optical disc apparatus for recording test data on a predetermined area of an optical disc under varied recording powers to determine an optimum recording power based on the quality of a signal obtained by reproducing the recorded test data. The test data is recorded under adverse recording conditions so as to evaluate the amount of change in quality of the reproduction signal. In order to create adverse recording conditions, the optical disc is tilted or the laser is defocused. A recording power for which the change in signal quality due to the deteriorated recording conditions is sufficiently small is determined as an optimum recording power capable of providing adequate recording margin.
Patent Number: 6,898,163 Issued on 05/24/2005 to Takeda
| Inventors:
|
Takeda; Naoto (Tokyo, JP)
|
| Assignee:
|
TEAC Corporation (Musashino, JP)
|
| Appl. No.:
|
231303 |
| Filed:
|
August 28, 2002 |
Foreign Application Priority Data
| Aug 28, 2001[JP] | 2001-258545 |
| Current U.S. Class: |
369/47.53; 369/53.19 |
| Intern'l Class: |
G11B 007/00 |
| Field of Search: |
369/4432,475.3,531.8,531.9,533.5,591.1,116
|
References Cited [Referenced By]
U.S. Patent Documents
| 5475666 | Dec., 1995 | Ito et al.
| |
| 6404713 | Jun., 2002 | Ueki.
| |
| 6414922 | Jul., 2002 | Akiyama et al.
| |
| 6765850 | Jul., 2004 | Shiozawa et al.
| |
| 6813107 | Nov., 2004 | Lee.
| |
| Foreign Patent Documents |
| 6036285 | Feb., 1994 | JP.
| |
| 2000/-137918 | May., 2000 | JP.
| |
| 2001052351 | Feb., 2001 | JP.
| |
Primary Examiner: Tran; Thang V.
Assistant Examiner: Vuong; Bach Q.
Attorney, Agent or Firm: Christensen O'Connor Johnson Kindness PLLC
Claims
1. An optical disc apparatus comprising:
recording means for recording test data on a predetermined area of an optical
disc by irradiating laser light while changing recording power in a plurality of
levels,
reproducing means for reproducing said test data, and
setting means for determining an optimum recording power by evaluating signal
quality of a reproduction signal, wherein
said recording means deteriorate recording conditions and then records said test
data under deteriorated recording conditions,
said reproducing means recovers said recording conditions from the deteriorated
state and then reproduces said test data, and
said setting means determines said optimum recording power based on an amount
of change in said signal quality from each recording power to another recording
power.
2. The optical disc apparatus according to claim 1, wherein said recording conditions
are deteriorated by tilting said optical disc relative to said laser light.
3. The optical disc apparatus according to claim 1, wherein said recording conditions
are deteriorated by tilting said optical disc against relative to laser light in
either radius or circumference direction.
4. The optical disc apparatus according to claim 1, wherein said recording conditions
are deteriorated by shifting a focus position of said laser light.
5. The optical disc apparatus according to claim 1, wherein said recording conditions
are deteriorated by shifting a focus offset value which specifies a focus position
of said laser light.
6. The optical disc apparatus according to claim 1, wherein said recording conditions
are deteriorated by increasing rotation speed of said optical disc.
7. The optical disc apparatus according to claim 1, wherein jitter is used to
indicate signal quality of said reproduction signal.
8. The optical disc apparatus according to claim 1, wherein error rate is used
to indicate signal quality of said reproduction signal.
9. The optical disc apparatus according to claim 7, wherein said setting means
determines said optimum recording power by comparing the amount of change in jitter
from each recording power to another recording power with a reference value.
10. The optical disc apparatus according to claim 7, wherein said setting means
compares each amount of change in jitter between two neighboring recording powers
with a reference value so as to set the optimum recording power at either one of
two recording powers under which the minimum amount of change in jitter among the
amounts of change in jitter greater than or equal to said reference value is obtained.
11. The optical disc apparatus according to claim 7, wherein said setting means
compares each amount of change in jitter between two neighboring recording powers
with a reference value so as to set the optimum recording power at either one of
two recording powers under which the maximum amount of change in jitter among the
amounts of change in jitter smaller than or equal to said reference value is obtained.
12. The optical disc apparatus according to claim 7, wherein said setting means
compares the amount of change in jitter between a recording power to which attention
is given and a reference recording power with a reference value so as to set the
optimum recording power at a recording power under which said amount of change
in jitter matches the reference value.
13. The optical disc apparatus according to claim 8, wherein said setting means
compares the amount of change in error rate between each recording power and another
recording power with a reference value so as to determine said optimum recording power.
14. The optical disc apparatus according to claim 8, wherein said setting means
compares the amount of change in error rate between each pair of neighboring recording
powers with a reference value so as to set said optimum recording power at either
one of two recording powers under which the minimum amount of change in error rate
among the amounts of change in error rate greater than or equal to said reference
value is obtained.
15. The optical disc apparatus according to claim 8, wherein said setting means
compares the amount of change in error rate between each pair of neighboring recording
powers with a reference value so as to set said optimum recording power at either
one of two recording powers under which the maximum amount of change in error rate
among the amounts of change in error rate smaller than or equal to said reference
value is obtained.
16. The optical disc apparatus according to claim 8, wherein said setting means
compares the amount of change in error rate between a recording power to which
attention is given and a reference recording power with a reference value so as
to set said optimum recording power at a recording power under which the amount
of change in error rate matches the reference value.
17. The optical disc apparatus according to claim 1, further comprising overwrite
means for overwriting said test data while changing erasing power in a plurality
of levels, wherein
said overwrite means deteriorates recording conditions and then executes overwrite
under the deteriorated recording conditions, and
said setting means determines an optimum erasing power based on each amount of
change in said signal quality from a erasing power to another erasing power.
18. The optical disc apparatus comprising:
an optical pick-up unit for recording test data on a predetermined area of an
optical disc while changing recording power of laser light in a plurality of levels
and reproducing said test data,
a drive circuit for tilting said optical disc by a given angle at the time of
recording said test data and recovering said optical disc from tilting at the time
of reproducing said test data,
a signal processing circuit for detecting signal quality of a reproduction signal
provided from said optical pick-up unit and
a control circuit for computing the amount of change in signal quality from each
recording power to another recording power and selecting a recording power under
which the amount of change becomes smaller than or equal to a threshold value to
set the selected recording power as a recording power of said optical pick-up unit.
19. An optical disc apparatus comprising:
an optical pick-up unit for recording test data on a predetermined area of an
optical disc while changing recording power of laser light in a plurality of levels
and reproducing said test data,
a drive circuit for defocusing said laser light at the time of recording said
test data and recovering said laser light into focus at the time of reproducing
said test data,
a signal processing circuit for detecting signal quality of a reproduction signal
provided from said optical pick-up unit and
a control circuit for computing the amount of change in signal quality from each
recording power to another recording power and selecting a recording power under
which the amount of change becomes smaller than or equal to a threshold value to
set the selected recording power as a recording power of said optical pick-up unit.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to power optimization of an optical disc apparatus
and more particularly to power optimization when data is recorded on a recordable
optical disc.
2. Description of the Related Art
OPC (Optimum Power Control) is a publicly known technology for optimizing recording
power when data is recorded on an optical disc. With OPC, test data is recorded
on a predetermined area PCA of an optical disc at various power levels. Each set
of test data recorded at a different recording power is then reproduced so as to
determine the optimum power by selecting the recording power at which jitter or
error rate becomes minimum, or the power level at which jitter or error rate becomes
less than or equal to a threshold value.
An alternate method for determining the optimum recording power without performing
test recording has also been known. According to this alternate method, data on
an optimum recording power prestored in a control data zone of an optical disc
is initially retrieved and then recording under the retrieved optimum recording
power is performed on DVD-RAM or the like.
A method using data concerning the optimum recording power previously recorded
on the control data zone of the optical disc, however, is problematic in that data
recording under the optimum recording power is not always achieved optimally when
a combination of an optical disc and an optical disc driver (optical disc apparatus)
is changed. That is, because optical properties such as optical pickup and the
like will vary among different optical disc apparatuses, an optimum recording power
obtained by one optical disc apparatus under a certain standard is not always optimum
for another optical disc apparatus. This method has another problem in that it
is incapable of supporting variations in optimum recording power resulting from
changes in recording characteristics due to degradation of the optical disc by aging.
Although these problems can be avoided by using OPC to determine the optimum
recording power, with such a composite method there is a problem that it cannot
be known whether or not the determined recording power is capable of providing
sufficient margin of recording conditions. This uncertainty of recording margin
raises the possibility of recording instability. As a solution to secure recording
margin when optimum recording power is determined by OPC, it is possible to select
a recording power higher than the needed optimum recording power. However, excessively
increasing the recording power may decrease the number of recordings that can be
made on a disk, leading to a durability problem.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an optical disc
apparatus wherein an adequate recording margin is secured.
An optical disc apparatus according to the present invention comprises recording
means for recording test data on a predetermined area of an optical disc by irradiating
laser light while changing recording power in a plurality of levels, reproducing
means for reproducing said test data, and setting means for determining an optical
recording power by evaluating signal quality of a reproduction signal. In the optical
disc apparatus, the recording means deteriorates recording conditions (intentionally
creates adverse or less than ideal recording conditions) and then records said
test data, the reproducing means recovers said recording conditions from the deteriorated
state and then reproduces the test data, and the setting means determines an optimum
recording power based on each amount of change in signal quality from a recording
power to another recording power. When the test data is recorded under adverse
(deteriorated) recording conditions, reproduction signal quality of the test data
is substantially degraded when a recording power with small recording margin is
employed, but only slightly degraded when a recording power capable of securing
adequate recording margin is employed. By evaluating the amount of change in reproduction
signal quality, it becomes possible to determine the optimum recording power with
which adequate recording margin is secured.
According to an embodiment of the present invention, recording conditions
are deteriorated through methods for tilting the optical disc and/or defocusing
laser light irradiated onto the optical disc. The test data is recorded in a tilted
state or a defocused state and reproduction signal quality, for example, jitter
or error rate of the recorded test data is evaluated. In an example described in
the embodiment, the amount of each change in jitter or error rate is compared with
a reference value to set the optimum recording power at a recording power under
which the amount of change in jitter or error rate close to the reference value
is obtained.
The present invention may be applied to a CD-R drive, a CD-RW drive, a DVD-R
drive, a DVD-RAM drive, and similar devices.
Although the present invention will be clearly understood by reference to
the following embodiment, the scope of this invention is not limited to the embodiment.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a graph showing a relationship between tilt and jitters.
FIG. 2 is a graph showing a relationship between tilt and error rates.
FIG. 3 is a graph showing a relationship between focus offset and jitters.
FIG. 4 is a graph showing a relationship between focus offset and error rates.
FIG. 5 is a block diagram showing a configuration of an optical disc apparatus.
FIG. 6 is a drawing to explain tilt of an optical disc.
FIG. 7 is a drawing to explain positive tilt in a radius direction.
FIG. 8 is a drawing to explain negative tilt in a radius direction.
FIG. 9 is a flowchart showing a process performed in a controller.
FIG. 10 is a graphical representation showing the amount of change in jitters
between neighboring two recording powers.
FIG. 11 is a flowchart showing another process performed in the controller.
FIG. 12 is a flowchart showing still another process performed in the controller.
FIG. 13 is a flowchart showing a further process performed in the controller.
FIG. 14 is a flowchart showing a further process performed in the controller.
DESCRIPTION OF THE PREFERRED EMBODIMENT
A preferred embodiment of the present invention will be described below with
reference
to the drawings, beginning with a description of a basic principle of this embodiment.
According to the present embodiment, when test data is recorded while varying
recording powers so as to perform OPC, test recording is executed not under normal,
presumably ideal recording conditions, but under intentionally deteriorated conditions.
During recording, reproduction signal quality significantly declines when a recording
power providing a small recording margin is used. On the contrary, the reproduction
signal quality declines only slightly when a recording power providing a large
recording margin is used. Therefore, by evaluating the reproduction signal quality
of test data recorded under intentionally set imperfect recording conditions, it
becomes possible to estimate recording margin of the recording power under which
the test data is recorded. A recording power with adequate recording margin is
determined based on the obtained estimate.
To create deficient recording conditions, for example, a slope (tilt) of an optical
disc against optical pickup or focus offset of the optical pickup may be shifted
from the best conditions thereof.
FIG. 1 shows changes in reproduction signal quality (jitter) of test data when
the amount of tilt is changed from 0 (not tilted state), in other words, the changes
in jitter between when the test data is recorded on condition that tilt is changed
from 0 to another value and when the test data is reproduced on condition that
tilt is returned back to 0 after recording. In FIG. 1, plotting the amounts of
tilt in abscissa and the amounts of jitter in a reproduction signal in ordinate,
three recording powers A, B and C (A<B<C) are shown. Each difference
between two neighboring recording powers among A, B, and C is equal and represented
by a constant value k, that is, B-A=C-B=k. For recording power A, the amount of
jitter in a reproduction signal increases, i.e. reproduction signal quality decreases
as the increase in tilt angle in either positive or negative direction causing
deterioration in recording conditions. The amount of jitter associated with recording
power B, which is larger than the recording power A, also increases as tilt angle
increases, but to a lesser degree. That is, the decline in the reproduction signal
quality under the recording power B is smaller than the decline in the reproduction
signal quality under the recording power A. Further, for recording power C, the
amount of jitter changes only slightly, i.e. the reproduction signal quality declines
only slightly as tilt angle increases in either the positive or negative direction.
Because the recording power A provides small recording margin and the recording
power B or C provides a larger recording margin, the recording powers B and C are
preferable in view of recording margin. When attention is focused on a certain
tilt angle, it can be shown that the amount of change in jitter between the recording
powers A and B is large and the amount of change in jitter between the recording
powers B and C is small, or almost equal, even though the recording powers A, B
and C are established at regular intervals.
Referring to FIG. 2, a relationship between tilt angles and error rates
of reproduction signal quality is shown.
More specifically, changes in the error rate occur between when test data is
recorded on condition that a tilt angle is changed from 0 to another angle and
when the test data is reproduced on condition that the tilt angle is returned back
to 0 are shown in the figure. In FIG. 2, tilt angles are plotted along the abscissa
as with FIG.
1 and error rates of the generative signal quality are plotted
along the ordinate. Also as with FIG. 1, three recording powers A, B and C (A<B<C)
are represented. As to the recording power A, an error rate sharply increases,
i.e. the reproduction signal quality decreases as the increase in tilt angle in
either positive or negative direction. With recording power B or C, the error rate
also increases with an increase of tilt angle, yet not to the same extent as with
recording power A. This demonstrates that decline in the reproduction signal quality
under the recording power B or C is small. Accordingly, it can be seen that the
recording powers B and C are superior to the recording power A in terms of both
error rate and recording margin. Further, from a small variation in the amounts
of change between the recording powers B and C, it also can be understood that
the recording power B is capable of providing almost the same amount of recording
margin as the recording power C.
The reproduction signal quality, that is jitter and an error rate are shown in
FIGS. 3 and 4, respectively, when recording conditions are made to deteriorate
by changing focus offset of optical pickup, in other words, by shifting a focus
position from the optimum position instead of changing the tilt angle. In still
other words, changes in jitter and error rate between when test data is recorded
on condition that the focus offset is shifted and when the test data is reproduced
after recording on condition that the focus offset is returned back to the original
state are shown in the figure. In both of the figures, the focus offset of the
optical pickup is plotted along abscissa and designated as being at the normal
condition when the focus offset is set at an optimum offset Fsw. Under the recording
power A, both the amount of jitter and error rate sharply increase when the focus
offset is shifted from the optimum point in either positive or negative direction.
On the other hand, under the recording power B or C, the amount of change in both
jitter and error rate are relatively small when the focus offset is shifted. For
a case where the focus offset is shifted, it also can be seen from the figures
that the recording powers B and C are capable of providing superior recording margin
for the recording power A, and that recording power B is capable of providing a
volume of recording margin almost equal to that associated with the recording power C.
Adverse recording conditions can be intentionally created by changing the
tilt angle from 0 or by changing the focus offset from the optimum point (shifting
a focus position from the optimum position). By recording test data under imperfect
recording conditions and evaluating the reproduction signal quality in the test
data recorded under such conditions, it becomes possible to estimate the size of
the recording margin. Based on the results of this estimation, a value for the
optimum recording power which is obtained which is not excessively increased to
secure adequate recording margin, yet under which the adequate recording margin
is obtained.
FIG. 5 shows a block diagram depicting a main configuration of an optical disc
apparatus according to the present embodiment. An optical disc
10 is subjected
to CAV or CLV control executed by a spindle motor
12.
An optical pickup unit
14 placed to be opposed to the optical disc
10
irradiates laser light of recording power from a laser diode so as to record data
on the optical disc
10. In order to record data, a recording film of the
optical disc
10 may be partly fused and sublimated to form a pit, or a crystalline
state of the optical disc
10 may be heated and cooled to transit to an amorphous state.
In a process of data recording, recording data is supplied to an encoder
18
and then encoded therein. The encoded data is passed to an LD driver
16
which generates a driving signal according to the encoded data and sends the driving
signal to the optical pickup unit
14. The control signal from the controller
24 is provided to the LD driver
16. A value for the drive current,
that is, a recording power, is determined according to the control signal.
In a process of data reproduction, the LD driver
16 of the optical pickup
unit
14 irradiates laser light with reproducing power (reproducing power<recording
power), then receives the reflected laser light, and then converts the reflected
laser light into an electric signal to obtain a reproduction RF signal. The reproduction
RF signal is provided to an RF signal processor
20.
The RF signal processor
20, which comprising an amplifier, an equalizer,
a binarizer, a PLL section, binarizes the reproduction RF signal and generates
a synchronous clock signal to provide these signals to a decoder
22. The
decoder
22 decodes data according to the provided signals and then outputs
the signals as reproduction data.
The reproduction RF signal received from the RF signal processor
22 is
also provided to the controller
24 for evaluating signal quality. When recorded
data is reproduced, a circuit to control a focus servo or a tracking servo by generating
a tracking error signal or focus error signal, and a circuit to regenerate a wobble
signal formed on the optical disc
10 in order to use the signal for address
demodulation or for controlling of the number of revolutions are used in conjunction
with the above-noted components. These circuits are equivalent to those in conventional
technology, and are therefore not described in detail herein.
In order to determine the optimum recording power, the controller
24 estimates
the signal quality of all recorded test data and activates the LD driver
16
to execute OPC. The data used for determining the optimum recording power is not
merely recorded on the optical disc
10 while changing recording power in
a plurality of, 15 for example, levels so as to calculate the amounts of jitter
and error rates from the reproduction RF signal of the recorded test data and then
select a recording power under which the amount of jitter and the error rate become
smallest. Instead, a control signal is provided to the spindle motor
12
or the optical pickup unit
14 to create adverse recording conditions and
test data is test recorded under the adverse recording conditions. Such conditions
are created by, for example, tilting the optical disc
10 relative to the
optical pickup unit
14. Tilt of the optical disc
10 may be introduced
by inclining either or both of the spindle motor
12 or the optical pickup
unit
14.
FIG. 6 shows how the controller
24 tilts the optical disc
10.
Referring to tilting directions, the tilt may be introduced in either a radius
direction (r direction) of the optical disc
10 or in a perimeter direction
(θ direction or tracking direction) of the optical disc
10 may be
considered. In order to tilt the disc in the radial direction, the optical disc
10 is rotated about axis (a) shown in FIG. 6 by a very small angle γ.
On the other hand, in order to introduce the tilt in the perimeter direction, the
optical disc
10 is rotated about axis (b) by a very small angle θ.
Positive and negative directions of tilt angle may be arbitrarily determined according
to the rotating direction. FIGS. 7 and 8 shows a state in which the tilt is introduced
in the radial direction. In FIG. 7, the optical disc
10 is tilted in a direction
away from the optical pickup unit
14, which is designated as a positive
direction in the present embodiment. On the other hand, in FIG. 8, the optical
disc
10 is tilted in a direction toward to the optical pickup unit
14,
which is designated as a negative direction in the present embodiment.
FIG. 9 shows a flowchart of a process performed in the controller
24
when OPC is executed by tilting the optical disc
10 in the radial direction.
First, the controller
24 is transited to an OPC control mode (S
101).
Then, the controller
24 activates the spindle motor
12 or the optical
pickup unit
14 in order to introduce a given amount of tilt angle at the
time of recording the test data (S
102: tilt angle shifting by a given degree).
This tilt setting contributes to deterioration in recording conditions.
Next, the controller
24 records test data while successively changing
recording power in a plurality of levels, for example 15 levels (S
103).
After the test data is recorded at a plurality of levels of recording power,
controller
24 reactivates the spindle motor
12 or the optical pickup
unit
14 in order to return the tilt angle back to the normal state, in other
words, to a state of tilt angle=0 (not tilted state) (S
104). In the normal
state, the test data recorded under each of the different recording powers is reproduced
to input a reproduction RF signal. The amount of jitter in the reproduction RF
signal is measured according to the input (S
105). The amount of jitter may
be obtained by measuring, for example, the amount of jitter in a 3T signal, but
not limited to the 3T signal. It is also preferable to measure the amount of jitter
of other frequencies. As a result of this process, sets of data regarding the amount
of jitter are obtained in a number equal to that of the number of recording powers.
After completing measurement of the amount of jitter, the controller
24
computes the amount of change in jitter between neighboring recording powers, in
other words, jitter differences (S
106). For example, when the following
pairs of (recording power, the amount of jitter) are taken: (10 mw, 20%), (11 mw,
15%), (12 mw, 12%), (13 mw, 11%), (14 mw, 10%) and (15 mw, 9%), the below-listed
jitter difference values are obtained.
The jitter difference between 10 mw and 11 mw is:
The jitter difference between 11 mw and 12 mw is:
The jitter difference between 12 mw and 13 mw is:
The jitter difference between 13 mw and 14 mw is:
The jitter difference between 14 mw and 15 mw is:
After calculating each of the amounts of change in jitter (jitter differences)
between the neighboring recording powers, all jitter differences grater than or
equal to a target value J
0 prestored in a memory of the controller
24
are extracted and from among these the smallest jitter difference is selected (S
107).
When the target value J
0 is, for example, 2%, the following two jitter differences
are obtained as the jitter differences greater than or equal to the target value
among the above listed five jitter differences:
The smallest jitter difference between the above two jitter differences is
Once the jitter difference satisfying the condition is selected, the controller
24 determines the optimum recording power based on the selected jitter difference
(S
108). More specifically, the recording powers associated with the selected
jitter difference are 11 mw and 12 mw. Either one of these recording powers, for
example, the higher recording power of 12 mw, is determined as the optimum recording
power with enough recording margin.
Referring to FIG. 10 schematically showing the above-described process,
jitter difference values for Δ
1=J(10 mw)-J(11 mw), Δ
2=J(11
mw)-J(12 mw), . . . are plotted along the abscissa and the amounts of change in
jitter (jitter differences) are plotted along the ordinate. The jitter differences
greater than or equal to the target value J
0 among the jitter differences
associated with each of the recording powers are the jitter differences corresponding
to Δ
1 and Δ
2. The smallest jitter difference of Δ
2,
in other words, the jitter difference closest to the target value is selected so
that the optimum recording power is determined from the recording power associated
with Δ
2. Because the jitter differences at Δ
1 and Δ
2
are large, as is evident from FIG. 10, it can be understood that at Δ
1
and Δ
2, the reproduction RF signal quality substantially deteriorates
with variations in recording power. At Δ
3, Δ
4, and Δ
5,
on the other hand, because the jitter differences thereof do not vary largely regardless
of a change in recording power, that deterioration in the reproduction signal quality
is small. From the figure, it can be concluded that the recording powers corresponding
to Δ
3, Δ
4, and Δ
5 are adequate for each
providing enough recording margin, and Δ
1 and Δ
2 locates
on a border between the recording power adequate for providing the enough recording
margin and the recording power inadequate for providing the enough recording margin.
Accordingly, by selecting the higher recording power associated with Δ
2,
the lowest recording power among the recording powers capable of providing the
largest recording margin can be determined as the optimum recording power.
In the above-described embodiment, it is also possible to determine the optimum
recording power by selecting the jitter difference closest to the target value
among jitter differences smaller than or equal to the target value depending on
a setting of the target value. For the example of FIG. 10, either one of the recording
powers 12 mw and 13 mw associated with Δ
3, for example, the smaller
recording power 12 mw may be determined as the optimum recording power.
The target value previously retained in a control data zone of the optical disc
may be retrieved and then stored in the memory of the optical disc. It is, of course,
possible to prestore the target value in the memory during the drive (optical disc
apparatus) manufacturing process.
In the above example, an optimum recording power capable of providing the enough
recording margin, that is, capable of executing stable recording regardless of
deterioration in recording conditions is determined based on the amounts of change
in jitter between neighboring recording powers. It is also possible to evaluate
the amounts of change in jitter according to another method.
For example, the size of recording margin may be evaluated using differences
in jitter subtracted from a given reference instead of using the amounts of change
in jitter between neighboring recording powers.
FIG. 11 shows a flowchart of another process performed in the controller
24.
Process steps from S
101 to S
105 indicated in FIG. 9 (referred to
as process A) are identical with the above-described process. After the completion
of process A, the best recording power (i.e. a recording power associated with
the smallest amount of jitter) is selected from the obtained amounts of jitter
(S
206). In the above example, when a recording power Pw is 15 mw, jitter
J assumes a minimum value of 9%. Therefore, the recording power Pw=15 mw is selected.
It is also preferable to select the smallest amount of jitter instead of recording
power. After selection, differences in the amounts of jitter between the best jitter
and the other jitters are calculated (S
207). More specifically, the differences
are as follows:
J(13 mw)-
J(15 mw)=2%
After calculating the differences in the amounts of jitter by subtraction of
the reference amount of jitter, recording powers under which the target value J
0
(a target value for the amount of change from the best jitter (the reference amount
of jitter)) prestored in the memory of the controller
24 is achieved are
computed by linear approximation or the like (S
208). When J
0=4% is
taken in the above case, values close to this target value are as follows:
By linearly approximating these values, 11.66 mw is obtained as a recording power
under which a value of 4% is achieved. The value of 11.66 mw obtained by linear
approximation is determined as the optimum recording power capable of providing
enough recording margin (S
209).
According to this method, it is also possible to determine the optimum
recording power capable of providing sufficient recording margin.
Alternatively, the size of recording margin may be evaluated using
error rates of reproduction signals instead of the amount of jitter as the reproduction
signal quality as shown in FIG.
2. The error rates may be calculated from
the number of correction bits used for correcting the data decoded by the decoder
22 in an error correction circuit (not illustrated).
FIG. 12 shows a flowchart of still another process performed in the controller
24. In contrast to the example shown in FIG. 9, error rates are used as
a substitute for the amounts of jitter. More specifically, process steps from S
301
to S
304 are identical to the steps from S
101 to S
104 shown
in FIG.
9. Error rates of reproduction signals are calculated at step S
305
and each amount of change in error rate (error rate differences) between neighboring
recording powers is computed at step S
306. Further, two recording powers
under which the smallest error rate difference among the error rate differences
greater than or equal to a target error rate difference is obtained are extracted
at step S
307 and then at step S
308 the larger recording power among
the two recording powers is selected as the optimum recording power.
Also in this method, the size of the recording margin may be evaluated by calculating
differences in error rate between an error rate and a reference error rate. A flowchart
of the controller
24 regarding this case is shown in FIG. 13 for reference.
First, process steps identical to process A shown in FIG. 12 are executed. Next,
a minimum error rate is selected (S
406). Next, differences between the minimum
error rate and each of the other error rates, in other words, the amount of change
in error rate is calculated (S
407) and then a recording power under which
the target value of error rate differences is obtained is calculated by linear
approximation (S
408) so as to determine the calculated recording power as
the optimum recording power (S
409).
Although the optical disc
10 is tilted against the optical pick-up
14 so as to create adverse recording conditions under OPC in the above-described
embodiment, it is possible to shift the focus (FS) offset of the optical pick-up
14 from the best point to another point, that is, the optical pick-up
14
is defocused so as to intentionally deteriorate the recording conditions.
FIG. 14 shows a flowchart of a process performed in the controller
24
in such a case. In contrast to the process shown in FIG. 9, test data is recorded
under a state that the FS offset is shifted from the best point Fsw by a given
amount (S
502) based on a control signal provided from the controller
24
to the optical pick-up unit
14.
This method also makes it possible to determine the optimum recording power
capable of providing sufficient recording margin under OPC.
Up to this point, determination of the optimum recording power has been described.
When the optical disc
10 is rewritable, it is also possible to erase data
using a laser light of an erasing power (reproducing power<erasing power<recording
power) irradiated from the optical pick-up unit
14. In such a case, optimization
of the erasing power may be desired.
For example, after determination of the optimum recording power according to
either one of the methods described above, the optimum erasing power can be determined
by multiplying the determined optimum recording power Pwo by an established coefficient
ε (ε<1).
It is also possible to determine the optimum erasing power directly according
to either one of the above-described methods. In FIG. 9, for example, the optical
disc
10 is tilted to overwrite test data while changing erasing powers.
At this time, the amount of jitter in the overwritten data is measured. When the
margin of the erasing power is insufficient, the stored data is not completely
deleted during overwriting, and, as a result, the amount of jitter increases sharply.
Therefore, by evaluating the margin of erasing power based on the amount of change
in jitter, it becomes possible to determine a value for the optimum erasing power
with a larger margin.
Although the present invention has been described as related to the illustrative
embodiment, it is understood that various changes and modifications may be made
in the invention without departing from the spirit and scope thereof. For example,
when data is recorded on both a land and a groove on the optical disc
10,
it is possible to determine the respective optimum recording powers (and the optimum
erasing powers) for both land recording and groove recording by specifying the
separate target values.
Further, although examples of tilt and FS offset changed to deteriorate
recording conditions in the preferred embodiment were described, all conditions
which deteriorate recording conditions when they are changed are intended to be
embraced by the present invention. Such conditions include, for example, rotation
speed. For example, it is possible to evaluate the recording margin by executing
test recording with increased rotation speed faster than normal speed.
Although in the examples of the embodiment, either tilt or FS offset is
changed to deteriorate recording conditions, both tilt and FS offset may be changed
to obtain deteriorated recording conditions.
In addition, it is possible to determine the optimum recording power by changing
tilt and FS offset as a target for the deteriorated recording conditions, using
values for jitter and error rate as the reproduction signal quality, selecting
candidates for the optimum recording power based on results of executing all combinations,
and then specifying the smallest (or largest) power among the candidates as the
optimum recording power. It is obvious that combinations other than those described
in the embodiment may be employed. For example, the optimum recording power may
be determined by using both jitter and error rate values as indicators for the
reproduction signal quality in addition to tilting the optical disc
10 in
a circumferential direction. The amount of tilt or offset may be changed in a plurality
of steps to perform the same procedure as described above.
*
