U.S. patent application number 11/456852 was filed with the patent office on 2006-11-02 for method for selecting optimal recording and erasing powers for an optical disk drive.
Invention is credited to Han-Wen Hsu, Ming-Hsien Tsai.
Application Number | 20060245337 11/456852 |
Document ID | / |
Family ID | 32770062 |
Filed Date | 2006-11-02 |
United States Patent
Application |
20060245337 |
Kind Code |
A1 |
Hsu; Han-Wen ; et
al. |
November 2, 2006 |
METHOD FOR SELECTING OPTIMAL RECORDING AND ERASING POWERS FOR AN
OPTICAL DISK DRIVE
Abstract
A method in which, during an optimal power calibration (OPC)
process, an optical disk drive performs a plurality of write tests
to an optical disk at a plurality of test powers and measures a
corresponding plurality of modulation signal strength values of the
optical disk for the plurality of write tests to generate a
modulation signal strength versus power curve. The method then
determines possible gamma lines corresponding to considered powers,
and selects a considered power as a target power of the optical
disk drive when a possible gamma line is substantially tangential
to the modulation signal strength versus power curve at the
considered power. According to the method, powers within a domain
of the plurality of test powers are considered until a considered
power is selected as the target power for the optical disk.
Inventors: |
Hsu; Han-Wen; (Hsin-Chu
City, TW) ; Tsai; Ming-Hsien; (Kao-Hsiung City,
TW) |
Correspondence
Address: |
NORTH AMERICA INTELLECTUAL PROPERTY CORPORATION
P.O. BOX 506
MERRIFIELD
VA
22116
US
|
Family ID: |
32770062 |
Appl. No.: |
11/456852 |
Filed: |
July 11, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10249042 |
Mar 12, 2003 |
7099249 |
|
|
11456852 |
Jul 11, 2006 |
|
|
|
Current U.S.
Class: |
369/116 ;
G9B/7.099 |
Current CPC
Class: |
G11B 7/126 20130101 |
Class at
Publication: |
369/116 |
International
Class: |
G11B 7/00 20060101
G11B007/00 |
Claims
1. A method for selecting a target power for writing to an optical
disk with an optical disk drive, the method comprising: reading a
target gamma value, wherein a gamma value is a ratio of a change in
modulation signal to change in power normalized by a ratio of
modulation signal strength to power, and the target gamma value
identifies the target power of the optical disk; performing a
plurality of write tests to the optical disk at a plurality of test
powers using the optical disk drive; measuring a corresponding
plurality of modulation signal strength values of the optical disk
for the plurality of write tests using the optical disk drive, and
generating a modulation signal strength versus power curve;
determining a possible gamma line for a considered power within the
domain of the plurality of test powers, wherein the possible gamma
line has a slope equal to the target gamma value multiplied by a
ratio of the considered modulation signal strength to the
considered power; and selecting the considered power as the target
power of the optical disk drive when the possible gamma line is
substantially tangential to the modulation signal strength versus
power curve at the considered power; wherein powers within the
domain of the plurality of test powers are considered until a
considered power is selected as the target power for the optical
disk.
2. The method of claim 1 wherein a possible gamma line is
substantially tangential to the modulation signal strength versus
power curve when it has modulating strength values at two test
powers bracketing the considered power that are both greater than
or both less than the modulation signal strength versus power curve
at the two test powers bracketing the considered power.
3. The method of claim 1 further comprising when no possible gamma
line is substantially tangential to the modulation signal strength
versus power curve at each considered power, interpolating between
at least two possible gamma lines that are nearly substantially
tangential to the modulation signal strength versus power curve to
determine the target power of the optical disk drive.
4. The method of claim 1 wherein the considered powers are the test
powers.
5. The method of claim 4 wherein performing the plurality of write
tests and measuring the plurality of modulation signal strength
values are performed for at least three test powers before
considering each considered power.
6. The method of claim 1 wherein performing the plurality of write
tests and measuring the plurality of modulation signal strength
values are performed for all test powers prior to considering each
considered power.
7. The method of claim 1 further comprising setting a recording
power of the optical disk drive based on the target power.
8. The method of claim 1 further comprising setting an erasing
power of the optical disk drive based on the target power.
9. The method of claim 1 further comprising low pass filtering or
curve fitting the modulation signal before measuring modulation
signal strength values.
10. The method of claim 1 further comprising low pass filtering or
curve fitting the modulation signal after measuring modulation
signal strength values.
11. The method of claim 1 wherein the optical disk drive is a
recordable or rewritable CD, DVD, or HD-DVD drive.
12. An optical disk drive comprising a microcontroller, a memory,
and related circuitry for performing the method of claim 1.
13. A method for selecting a target power for writing to an optical
disk with an optical disk drive, the method comprising: reading a
target gamma value, wherein a gamma value is a ratio of a change in
modulation signal to change in power normalized by a ratio of
modulation signal strength to power, and the target gamma value
identifies the target power of the optical disk; performing a
plurality of write tests to the optical disk at a plurality of test
powers using the optical disk drive; measuring a corresponding
plurality of modulation signal strength values of the optical disk
for the plurality of write tests using the optical disk drive, and
generating a modulation signal strength versus power curve;
successively generating possible gamma lines for considered powers
within the domain of the plurality of test powers, wherein each
possible gamma line has a slope equal to the target gamma value
multiplied by a ratio of the considered modulation signal strength
to each considered power; and selecting a considered power as the
target power of the optical disk drive and ceasing possible gamma
line generation, when the corresponding possible gamma line is
substantially tangential to the modulation signal strength versus
power curve at the considered power; and interpolating between at
least two possible gamma lines that are nearly substantially
tangential to the modulation signal strength versus power curve to
determine the target power of the optical disk drive when no single
possible gamma line is substantially tangential to the modulation
signal strength versus power curve.
14. The method of claim 12 wherein a possible gamma line is
substantially tangential to the modulation signal strength versus
power curve when it has modulating strength values at two test
powers bracketing the considered power that are both greater than
or both less than the modulation signal strength versus power curve
at the two test powers bracketing the considered power.
15. The method of claim 12 wherein the considered powers are the
test powers.
16. The method of claim 14 wherein performing the plurality of
write tests and measuring the plurality of modulation signal
strength values are performed for at least three test powers before
considering each considered power.
17. The method of claim 12 wherein performing the plurality of
write tests and measuring the plurality of modulation signal
strength values are performed for all test powers prior to
considering each considered power.
18. The method of claim 12 further comprising setting a recording
power of the optical disk drive based on the target power.
19. The method of claim 12 further comprising setting an erasing
power of the optical disk drive based on the target power.
20. The method of claim 12 further comprising low pass filtering or
curve fitting the modulation signal before measuring modulation
signal strength values.
21. The method of claim 12 further comprising low pass filtering or
curve fitting the modulation signal after measuring modulation
signal strength values.
22. The method of claim 12 wherein the optical disk drive is a
recordable or rewritable CD, DVD, or HD-DVD drive.
23. An optical disk drive comprising a microcontroller, a memory,
and related circuitry for performing the method of claim 12.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This is a continuation-in-part of U.S. application Ser. No.
10/249,042, which was filed on Mar. 12, 2003 and is included herein
by reference.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The present invention relates to a digital electronic
device, and more specifically, to an optical storage device capable
of writing to an optical disk.
[0004] 2. Description of the Prior Art
[0005] Optical media is a popular data storage means having high
storage density, reliable data stability, and good portability.
Compact disks (CDs) and digital versatile disks (DVDs) have all but
replaced traditional competing storage devices such as magnetic
floppy disks and audio and video tapes. While digital devices used
to read and write optical media, such as CD-ROM drives and DVD
players, are complicated and highly precise, technological
innovation has made these devices reliable and practical.
[0006] In the past, optical disk drives were mainly available to
end users as read only devices. Most users were satisfied with
simply receiving software, music, or movies on CDs or DVDs and gave
little thought to using the devices as storage for themselves.
Optical disk drives capable of writing were specialized and
expensive pieces of equipment used mainly by media publishers to
produce their products. More recently, writable optical disk
drives, such as common CD-RW drives for use with computer systems,
have become widely available to individuals. And as a result, the
need to improve performance of these devices has increased
considerably.
[0007] FIG. 1 shows a typical CD-RW drive 10 that is commonly used
in computer systems. The CD-RW drive 10 is capable of reading,
writing, and erasing data on a CD 12. The basic operations of CD-RW
drives are well known in the art. Additionally, Van Der Zande et
al. teaches operation of a writable optical drive in detail in U.S.
Pat. No. 4,901,300, which is incorporated herein by reference.
[0008] A fundamental operation of the CD-RW drive 10 is an optimal
power calibration (OPC) process in which the optimal recording
power for a given CD is determined. The OPC process must be
completed before recording to the CD can begin. The optimal
recording power is determined by performing a series of recording
tests to a power calibration area of the CD. A crucial value in the
OPC process is the Orange Book gamma (.gamma.) value, which relates
recorded RF quality to recording power as follows: .gamma. = ( d m
d P W ) ( m P W ) ( Eqn . .times. 1 ) ##EQU1## where, [0009] m
represents the modulation amplitude of the RF signal; [0010]
P.sub.w is recording power; and [0011] dm/dP.sub.w is a
differential of modulation amplitude with respect to recoding
power;
[0012] An optimal or target gamma value is written to a blank CD at
the time of manufacture, and is read by the optical drive when
recording is to be performed. Conventionally, during the OPC
process, several recording powers as tested by writing to the power
calibration area of the CD. The modulation amplitude of each test
power is measured, the derivative of the modulation amplitude with
respect to recording power is numerically determined along with
other calculations according to Eqn. 1, and a gamma curve is
generated. The target power is then determined from the gamma curve
referencing the target gamma value.
[0013] The previously described procedure is illustrated in FIG. 2
showing a graph of measured modulation amplitude m and gamma value
.gamma. versus recording power. When performing the OPC procedure,
microprocessors and control circuitry of a conventional optical
disk drive first measure modulation amplitudes for a series of
recording powers to generate the modulation amplitude curve as
indicated by numeral 20 in FIG. 2 (the 4 points shown being
representative). The optical disk drive then calculates a gamma
curve from the measured modulation data, as indicated by numeral
22. Then, to obtain the target power the optical disk drive
references the target gamma and calculates or looks up the target
power. Finally, optimal write and erase powers are determined as
follows: P.sub.W0=.rho. P.sub.T P.sub.E0=.epsilon. P.sub.W0 (Eqns.
2) where, [0014] P.sub.W0 is the optimal recording power; [0015]
.rho. is a recording constant; [0016] P.sub.T is the target power;
[0017] P.sub.E0 is the optimal erasing power; and [0018] .epsilon.
is an erasing constant;
[0019] The constants .rho. and .epsilon. for respectively
determining the optimal recording and erasing powers are written to
the blank disk at the time of manufacture and read by the optical
disk drive during the OPC process. During the OPC process,
operations of a CD-R drive differ from a CD-RW drive mainly in that
erasing power is irrelevant for the CD-R drive.
[0020] Conventional optical disk drives determine the optimal
recording and erasing powers using circuitry incorporating Eqn. 1
and Eqns. 2. However, this method is highly sensitive to
measurement noise. Specifically, as the gamma curve is related to
measured modulation amplitudes by a differential function (Egn. 1)
and modulation amplitude measurement is susceptible to noise, the
calculated gamma curve can contain serious errors. Errors in the
gamma curve show up in determination of the target power and the
recording and erasing powers. Curve fitting is usually employed to
reduce the effects of this problem, however, at the cost of program
space and computation time. Higher order curve fitting yields
better results, but at the cost of optical drive processing
resources and time. In conventional drives, lower order curve
fitting is preferred, with the risk of determining erroneous
recording and erasing powers being accepted for sake of recording
speed. Another method of reducing errors in the gamma curve is to
use a low pass filter to smooth the measured modulation signals.
Generally, curve fitting and low pass filter smoothing require
additional hardware and additional costs. Hence, the conventional
method for determining optimal recording and erasing powers for an
optical disk drive is inefficient.
SUMMARY OF THE INVENTION
[0021] It is therefore a primary objective of the present invention
to provide an efficient method for selecting a target power for an
optical disk with an optical disk drive for determining the optimal
recording and erasing powers to reduce errors originating from
measured modulation signal noise, and to reduce required hardware
and OPC processing time.
[0022] Briefly summarized, the present invention includes reading a
target gamma value, performing a plurality of write tests to the
optical disk at a plurality of test powers, measuring a
corresponding plurality of modulation signal strength values of the
optical disk for the plurality of write tests and generating a
modulation signal strength versus power curve, determining a
possible gamma line for a considered power within the domain of the
plurality of test powers, and selecting the considered power as the
target power of the optical disk drive when the possible gamma line
is substantially tangential to the modulation signal strength
versus power curve at the considered power. A gamma value is a
ratio of a change in modulation signal to change in power
normalized by a ratio of modulation signal strength to power, and
the target gamma value identifies the target power of the optical
disk. A possible gamma line has a slope equal to the target gamma
value multiplied by a ratio of the considered modulation signal
strength to the considered power. According to the method, powers
within the domain of the plurality of test powers are considered
until a considered power is selected as the target power for the
optical disk.
[0023] According to the present invention, a possible gamma line is
substantially tangential to the modulation signal strength versus
power curve when it has modulating strength values at two test
powers bracketing the considered power that are both greater than
or both less than the modulation signal strength versus power curve
at the two test powers bracketing the considered power.
[0024] According to the present invention, when no possible gamma
line is substantially tangential to the modulation signal strength
versus power curve at each considered power, the method further
includes interpolating between two possible gamma lines that are
nearly substantially tangential to the modulation signal strength
versus power curve to determine the target power of the optical
disk drive.
[0025] It is an advantage of the present invention that selecting
the considered power as the target power of the optical disk drive
when the possible gamma line is substantially tangential to the
modulation signal strength versus power curve at the considered
power reduces errors originating from noise in the modulation
signal strength versus power curve.
[0026] It is a further advantage of the present invention that
determining possible gamma lines rather than differentiating the
modulation signal strength versus power curve allows the method to
be performed quickly and reduces processing time in the optical
disk drive.
[0027] It is a further advantage of the present invention that
determining possible gamma lines rather than differentiating the
modulation signal strength versus power curve reduces memory
required in the optical disk drive for determining the target
power.
[0028] These and other objectives of the present invention will no
doubt become obvious to those of ordinary skill in the art after
reading the following detailed description of the preferred
embodiment that is illustrated in the various figures and
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIG. 1 is a perspective view of an optical disk drive.
[0030] FIG. 2 is a graph relating to a method of performing an OPC
process according to the prior art.
[0031] FIG. 3a and FIG. 3b are graphs of gamma curve calculations
according to the present invention.
[0032] FIG. 4 is a graph of possible gamma lines according to the
present invention.
[0033] FIG. 5 is a flowchart of a method for determining a target
power according to the present invention.
[0034] FIG. 6 is a graph of a numerical method for performing a
tangent test according to the present invention
DETAILED DESCRIPTION
[0035] The present invention method can be realized with hardware
and programming of an optical disk drive, such as the CR-RW drive
shown in FIG. 1. The present invention also applies to other
writable optical disk systems such as CD-R, DVD-R, DVD-RW, DVD+RW,
and HD-DVD.
[0036] The following is a short mathematical derivation that is
required to implement the present invention method. Referring to
Eqn. 1, if gamma is assumed to be the target value, a
pseudo-modulation amplitude curve m.sub.1 can be defined as: d m 1
d P W = .gamma. T .function. ( m 1 P W ) ( Eqn . .times. 3 )
##EQU2## where, [0037] .gamma..sub.T is a target gamma value read
from an optical disk by the optical disk drive; [0038] m.sub.1
represents a pseudo-modulation amplitude; [0039] P.sub.w is
recording power of the optical drive; and [0040] dm/dP.sub.w is a
differential of pseudo-modulation amplitude with respect to
recording power;
[0041] FIG. 3a shows a modulation curve m according to Eqn. 1 and a
pseudo-modulation curve m.sub.1 according to Eqn. 3. The point at
which the curves m and m.sub.1 intersect (i.e. m=m.sub.1) is
designated by a numeral 30. At this point Eqn. 1 and Eqn. 3 can be
combined and rearranged to form Eqn. 4 as follows: d m d P W = d m
1 d P W .times. ( .gamma. .gamma. T ) ( Eqn . .times. 4 )
##EQU3##
[0042] Clearly, if the gamma value of the actual measured
modulation curve m at the point of intersection is equal to the
target gamma value, then the slopes of the modulation curves m and
m.sub.1 (represented by the derivatives in Eqn. 4) will also be
equal. In the same way, as illustrated in FIG. 3a, when the
modulation curves m and m.sub.1 do not have equal slopes where they
intersect, the gamma value of the actual measured modulation curve
m is not equal to the target gamma value and consequently the
corresponding power is not the target power. FIG. 3b illustrates a
case where the m and m.sub.1 curves are tangential and consequently
the gamma value and the target gamma value are equal, the
corresponding power being the target power.
[0043] Please refer to FIG. 4, showing a simplification of the
relationship illustrated in Eqn. 4. At points 40a-e along the
actual measured modulation curve m, lines 42a-e, termed "possible
gamma lines", represent the slopes of each pseudo-modulation curve
m.sub.1 intersecting these points 40a-e. Thus, at a point where the
slope of a line 42a-e is equal to the slope of the measured
modulation curve m, the power is the target power. In the example
illustrated in FIG. 4, point 40e meets this condition. The points
40a-e can be actual sample points where test recording powers were
used to write to the OPC area of a CD and the corresponding
modulation signals were measured, or can be interpolated or
extrapolated points of the measured modulation curve m. In
practical application, the modulation amplitude curves and possible
gamma lines described are stored and processed by the optical disk
drive as discrete data and arithmetic functions, and are described
graphically for clarity.
[0044] The present invention method for determining the target
power and the corresponding optimal writing and erasing powers is
realized with conventional hardware, such as microcontrollers,
memory chips, and logic circuits, and associated software of the
optical disk drive. The method is illustrated in a flowchart of
FIG. 5 and is described in detail as follows:
[0045] Step 100: Start;
[0046] Step 102: Initialization. The optical disk drive reads the
target gamma value from the optical disk, performs a predetermined
number of write tests at a predetermined number of test powers, and
measures the corresponding modulation amplitudes. A modulation
amplitude curve similar to the curve m of FIG. 4 can be generated,
and discrete numerical values and related defining functions can be
stored in the memory of the optical drive. A first considered
power, or point of the modulation curve, is selected;
[0047] Step 104: The optical disk drive generates a possible gamma
line at the currently considered test power using the target gamma
value;
[0048] Step 106: The optical disk drive performs a tangent test on
the possible gamma line with respect to the modulation curve to
determine if the possible gamma line is tangential within error to
the modulation curve at the considered power. If the possible gamma
line is tangent to the modulation curve go to step 114, otherwise,
go to step 108;
[0049] Step 108: The optical disk drive determines if the last
point of the modulation curve, i.e. the last considered power, has
been considered. If the last considered power has been processed go
to step 112, if not, go to step 110;
[0050] Step 110: The optical disk drive selects a next power, and
corresponding point on the modulation curve, for consideration;
[0051] Step 112: No possible gamma line meets the tangent criteria
of step 106. The optical disk drive selects at least two possible
gamma lines that nearly met the criteria and interpolates between
them to determine an interpolated considered power;
[0052] Step 114: The considered power is selected as the target
power and output;
[0053] Step 116: End.
[0054] In the method described above, a predetermined number of
write tests at a predetermined number of test powers should be
selected in sufficient quantity to accurately perform the tangent
test. The predetermined number of test powers can also be all the
test powers in a specific domain. If the predetermined number of
test powers is less than all the test powers in a specific domain,
the optical disk drive must perform additional writing tests and
reading of modulation amplitudes as necessary. Specifically, the
present invention method can be performed after all the modulation
amplitudes have been measured or during the testing/measuring
process. Furthermore, the considered powers can be, however need
not be, the actual test powers. Of course, it may be convenient to
consider only the test powers if the method is applied as the
writing tests and modulation signal measurements are performed. On
the contrary, if all writing tests and modulation amplitude
measurements are performed ahead of time, it may be timesaving to
select considered powers independent of the actual test powers. In
addition, low pass filtering or curve fitting can be performed on
the modulation signal to remove noise before or after modulation
signal strength values are measured, thereby smoothing the
modulation amplitude curve and improving the overall effectiveness
of the present invention.
[0055] Referencing FIG. 6, determining if a possible gamma line 50
is tangent to the modulation curve can be performed by the
following numerical method: S i = .gamma. T .function. ( m i P Wi )
.times. .times. .DELTA. 1 = m i + S i .function. ( P Wi + 1 - P Wi
) - m i + 1 .times. .times. .DELTA. 2 = m i - S i .function. ( P Wi
- P Wi - 1 ) - m i - 1 ( Eqns . .times. 5 ) ##EQU4##
[0056] where,
[0057] S.sub.i is a slope of a possible gamma line;
[0058] i is an index of the considered power and corresponding
considered possible gamma line, and i+1 and i-1 are indexes of
powers that bracket the considered power and are normally the
adjacent powers;
[0059] .DELTA..sub.1 and .DELTA..sub.2 are differences between the
possible gamma line and the modulation curve at points bracketing
to the power under consideration;
[0060] According to the present invention, if .DELTA..sub.1 and
.DELTA..sub.2 are both greater than zero or both less than zero,
the possible gamma line under consideration is tangent to the
modulation curve and the considered power P.sub.Wi is the target
power. At least three points, that is, three considered powers, are
required to implement Eqns. 5. Naturally, another numerical method
could be used to test whether each possible gamma line is tangent
to the modulation curve, however, the aim of the procedure
described in FIG. 6 and Eqns. 5 is to reduce memory requirements
and processing time while increasing accuracy.
[0061] When no possible gamma line is found to be tangent to the
modulation curve, the optical disk drive performs interpolation
between at least two possible gamma lines that are close to being
tangent to the modulation curve. The interpolation can be linear or
higher order, taking into consideration program space requirements
and processing speed. The target power is then selected based on
the result of the interpolation.
[0062] After the target power is determined by directly selecting a
suitable considered power or by interpolation using the method as
described above, the optical drive executes Eqns. 2 to determine
the optimal recording and erasing powers for the optical disk drive
and the optical disk to be written or erased.
[0063] In contrast to the prior art, the present invention compares
possible gamma lines with a measured modulation amplitude curve to
determine a target power and corresponding optimal recording and
erasing powers. The present invention method results in less error
in the optimal recording and erasing powers, as noise from
modulation measurements is inherently compensated for rather than
being amplified as in the prior art. The present invention method
requires less program space and memory, can be processed faster
than conventional methods, and accordingly has a less costly
implementation. More specifically, complicated hardware and
algorithms for performing numerical differentiations are not
required. Furthermore, the present invention method does not
require complicated curve fitting or low pass filtering as is
required in the prior art.
[0064] Those skilled in the art will readily observe that numerous
modifications and alterations of the device and method may be made
while retaining the teachings of the invention. Accordingly, the
above disclosure should be construed as limited only by the metes
and bounds of the appended claims.
* * * * *