Dynamic information storage or retrieval – Control of storage or retrieval operation by a control... – Mechanism control by the control signal
Reexamination Certificate
2001-04-10
2003-06-10
Edun, Muhammad (Department: 2655)
Dynamic information storage or retrieval
Control of storage or retrieval operation by a control...
Mechanism control by the control signal
C369S047500, C369S053100, C369S059110, C369S116000
Reexamination Certificate
active
06577571
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to optical disk recording apparatuses and methods of recording data on optical disks, and more particularly to an optical disk recording apparatus that records data on an erasable optical disk and a method of recording data on an erasable optical disk.
2. Description of the Related Art
Direct-read-after-write optical disks are of two general types: write-once and erasable. In overwriting an erasable optical disk, a laser beam having a laser power alternating between a write power Pw and an erase power Pe is employed. In this case, the write power Pw forms pits on the recording film of the optical disk by changing the state of the recording film from a crystalline state to an amorphous state, and the erase power Pe erases the pits by changing the state of the recording film from the amorphous state to the crystalline state.
The Optimum levels of the write and erase powers Pw and Pe (optimum write and erase powers Pwo and Peo) of the laser beam at a time of recording data on an optical disk differ depending on a type of the optical disk, a recording apparatus, and a recording rate. Therefore, in order to set the optimum write and erase powers Pwo and Peo based on the combination of a type of the optical disk, a recording apparatus, and a recording rate employed in a practical recording, a recording power calibration called OPC (Optimum Power Control) is performed prior to the recording of data.
A description will be given of an OPC operation in a conventional optical disk recording apparatus for an erasable optical disk.
FIG. 1
is a diagram for illustrating the test recording area of the optical disk.
As shown in
FIG. 1
, a data area for storing a variety of data and a PCA (Power Calibration Area) that is a test recording area for setting the optimum write power of a laser beam are formed on the recording surface of the optical disk. The PCA, which is formed along a track closest to a disk center, includes a test area and a count area. The test area is formed of 100 partitions, and each partition is formed of 15 frames. In one OPC operation, one partition is used so that each frame of the partition is recorded with a test signal with a different level of the laser power. That is, the laser power has the 15 levels. Each test signal is an EFM-modulated signal formed of a pulse train having a pulse width three to ten times a reference pulse width T, and is recorded on each frame with pits of nine types of lengths. The reference pulse width T is for one cycle of a pulse signal having a frequency of 4.32 MHz, and is 230 nsec at a normal rate (1×).
The laser beam is emitted onto each frame so that each test signal is reproduced by detecting a light reflected back therefrom. At the same time, a modulation degree m as an index indicating the magnitude of the amplitude of each reproduced HF (high frequency) signal is measured by using the following equation
m
=I
11
/Itop
(1)
where I
11
is an amplitude of a reproduced HF signal based on pits and lands (regions between pits) of a pulse width 11 times the reference pulse width T, and Itop is the optical reflectivity of the lands as shown in FIG.
2
. In
FIG. 2
, I
3
is an amplitude of the reproduced HF signal based on pits and lands of a pulse width three times the reference pulse width T. The modulation degree m differs depending on the level of the write power Pw. As shown in
FIG. 3
, as the level of the write power Pw becomes lowers, the modulation degree m becomes smaller because the amplitude of the reproduced HF signal becomes smaller. On the other hand, as the level of the write power Pw becomes higher, the modulation degree m becomes larger because the amplitude of the reproduced HF signal becomes larger.
In the case of determining the optimum write power Pwo by the modulation degree m, a method using a parameter &ggr; obtained from the characteristic of the modulation degree m is employed. The parameter &ggr; is given by the following equation
&ggr;=(
dm/dPw
)×(
Pw/m
) (2)
That is, the parameter &ggr; is the differential of the characteristic of the modulation degree m. The optical disk is prerecorded with the target value &ggr;target of the parameter &ggr; as ATIP (Absolute Time In Pregroove) information. Therefore, as show in
FIG. 4
, the characteristic of the parameter &ggr; is obtained from the characteristic of the modulation degree m according to the above-described equation (2), and then a write power level Ptarget that realizes the target value &ggr;target is obtained. Since the optical disk is prerecorded with a coefficient &rgr; for obtaining the optimum write power Pwo from the write power level Ptarget as the ATIP information, the optimum write power Pwo is obtained, by using the coefficient &rgr;, from the following equation
Pwo=&rgr;×Ptarget
(3)
The optimum write power Pwo obtained from the above-described equation (3) is set and used as a write power at the time of a signal recording. The optimum erase power Peo is set, by using the optimum write power Pwo and a coefficient &egr; (a Pe/Pw ratio) recorded on the optical disk as the ATIP information, based on the following equation
Peo=&egr;×Pwo
(4)
FIG. 5
is a flowchart of a conventional OPC operation. In
FIG. 5
, in step S
10
, a recording rate is set to a value specified by a write command, and in step S
12
, a medium (optical disk) type is determined by obtaining an ID number recorded on the optical disk as the ATIP information.
Next, in step S
14
, a table storing a start power and a step power which table is prerecorded in memory is selected based on the recording rate. In step S
16
, the write power Pw is successively changed from the start power by the amount of the step power to have 15 different levels so that test signals are recorded in the test recording area of the optical disk.
Next, in step S
18
, the test signals are reproduced, and in step S
20
, the modulation degree m is measured with respect to each of the 15 levels of the write power Pw so that the characteristic of the modulation degree m indicated by a solid line in
FIG. 4
is obtained. The characteristic of the modulation degree m is a relation between the modulation degree m and the write power Pw of the 15 levels. Then, in step S
22
, the parameter &ggr; is obtained with respect to each of the 15 levels of the write power Pw from the characteristic of the modulation degree m by using the equation (2). The parameter &ggr; with respect to the modulation degree m is indicated by a dot-dash line in FIG.
4
.
Next, in step S
24
, the write power level Ptarget realizing the target value &ggr;target included in the ATIP information of the optical disk is obtained from the characteristic of the parameter &ggr; indicated by the dot-dash line in FIG.
4
. Then, in step S
26
, the optimum write power Pwo is obtained by multiplying the write power level Ptarget by the coefficient &rgr; (a real number larger than or equal to one) included in the ATIP information, and in step S
28
, the optimum write power Pwo is stored in memory. Thereafter, in step S
30
, the OPC operation ends, and in step s
32
, a recording is started with the above-described optimum write power Pwo.
With respect to an erasable optical disk, since a saturated laser power deteriorates the durability of the optical disk, a laser power of a point at which a modulation degree starts to be saturated becomes an optimum laser power. However, a change in a modulation degree change rate (the parameter &ggr;) is small at the point at which the modulation degree starts to be saturated. Therefore, a point at which a change in the modulation degree change rate is great (a point corresponding to a laser power smaller than the optimum power) is set as the target value &ggr;target, and the optimum write power Pwo is obtained by multiplying a power of the point by the coefficient &rgr;.
The characteristic of the modulation degree changes based on a
Hayasaka Kaname
Takeda Naoto
Anderson Kill & Olick
Edun Muhammad
Lieberstein Eugene
Meller Michael N.
TEAC Corporation
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