Dynamic information storage or retrieval – Control of storage or retrieval operation by a control... – Control of information signal processing channel
Reexamination Certificate
2000-11-13
2003-04-08
Huber, Paul W. (Department: 2653)
Dynamic information storage or retrieval
Control of storage or retrieval operation by a control...
Control of information signal processing channel
C369S044260, C369S044410
Reexamination Certificate
active
06545959
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical disc recording and reproducing apparatus preferable when used for a writable optical disc such as a write once optical disc (CD-R) and a rewritable optical disc (CD-RW), and a method for reading information.
Specifically, in the present invention, a photodetector detects a return light of a light beam applied to an optical disc in such a manner that a target pre-format address and recorded information are distinguished from interference information by the pre-format addresses adjacent to the target pre-format address at its inner and outer peripheral sides. With this arrangement, the target pre-format address and the recorded information can be read from the optical disc with excellent reproducibility, and the crosstalk between adjacent pregrooves can be prevented, even if the light beam is applied across adjacent information recording layers in accordance with the increase in a storage density of the optical disc.
2. Description of the Related Art
In recent years, as information media for editing and recording audio information in such a manner as to suit the preferences of listeners, writable optical discs such as write once optical discs (CD-R) and rewritable optical discs (CD-RW) standardized in ISO/IEC13490-1 are increasingly used. In each of these optical discs
10
, as shown in
FIG. 1A
, grooves
1
for guiding a light beam (hereinafter, referred to as pregrooves) are formed, and a positioning method referred to as a tracking servo is employed. The tracking servo is a mechanism where pits and projections constituting lands
2
formed on both sides of each pregroove
1
are detected to decide the position of an optical pickup, so that the desired pre-format address is accurately irradiated with a laser beam.
Sloped surfaces of the land, which coincide to side surfaces of the pregroove
1
, are for med with a slight wobble in the form of sine wave in-phase with each other as shown in FIG.
1
B. The wobble signal indicating the wobble component has been subjected to FM modulation. In the wobble signal, time axis information which indicates the position on the optical disc
10
, and a recommended value of the power of the laser beam optimum for recording are encoded.
This time axis information is referred to as MTIP (Absolute Time In Pregroove) information, and is written as an absolute time in the signal recording region (i.e. a program region) of the optical disc
10
along a direction from the starting point at its inner peripheral side toward its outer peripheral side. The ATIP information is written in the processing of the CD-R an d CD-RW. The ATIP information is written in the optical disc
10
such as CD-R and CD-RW in a modulation mode referred to as bi-phase modulation mode. In this mode, a baseband modulation is conducted where, depending on whether the waveform of the last pulse signal constituting the error correction information of the immediately preceding pre-format address ends at a high level or low level, the pre-format address in the next frame is connected without being inverted, or the pre-format address is inverted and connected.
The ATIP information is written, for example, in the side surfaces Us, Ut of the pregroove
1
between two lands
2
a
,
2
b
shown in FIG.
1
B. That is, the ATIP information is written in the side surface Us of the land
2
a
located at the inner peripheral side of the pregroove
1
in which data is recorded, and in the side surface Ut of the land
2
b
located at the outer peripheral side of the pregroove
1
in such a manner that the ATIP information written in the side surface Us is synchronous to the ATIP information written in the side surface Ut.
Therefore, the ATIP information can be read as a wobble signal by detecting the reflected light from the main spot
4
on the wobble formed in the lands
2
a
,
2
b
by two light receiving elements split in the direction of track. The broken double line circles in
FIG. 1B
show spot diameters of the light beam applied to the optical disc having a standard density. The two-dot long and two short dashes line circles show a light beam of which irradiation diameter is relatively enlarged as the pregrooves are formed so as to be closer to each other in accordance with the increase in a storage density of the optical disc
10
. This problem arises because there is a limitation on enlarging the spot diameters of the light beam.
The wobble signal is produced in such a manner that its center frequency becomes 22.05 kHz for example, when the optical disc
10
is rotated at a standard velocity (CLV) of a compact disc (CD). One sector of the ATIP information is constituted in such a manner as to coincide to one data sector after the signal is recorded. Therefore, at the time of recording information, the pregrooves
1
are irradiated with a light beam with a predetermined intensity and information is written therein while the sector of the ATIP information is synchronous with the data sector.
In a conventional method, when a signal is recorded in the optical disc
10
, as shown by a broken line in
FIG. 1B
for example, a pit
61
is formed at a main spot
4
created in a three-beam method, and in this state, the return light from the main spot
4
is split and received in the photodetecting section
71
shown in FIG.
2
. In the photodetecting section
71
, a light receiving signal A from the light receiving element PD
1
such as a photodiode which constitutes a four split photodetector
711
, and a light receiving signal D from the light receiving element PD
4
similar to the light receiving element PD
1
are added to each other to produce an addition signal A+D. At the same time, a light receiving signal B from the light receiving element PD
2
, and a light receiving signal C from the light receiving element PD
3
are added to each other to produce an addition signal B+C. In the photodetecting section
71
, the latter addition signal B+C is subtracted from the former addition signal A+D to obtain a wobble signal.
In the above-described method, furthermore, the light receiving signals A to D from the four light receiving elements PD
1
to PD
4
in the photodetector
711
are also added to each other to produce an RF signal (A+B+C+D). At the same time, a tracking servo is controlled by use of a light receiving signal E from the light receiving element PD
5
, a light receiving signal F from the light receiving element PD
6
of the two split photodetector
712
, and a light receiving signal G from the light receiving element PD
7
, and a light receiving signal H from the light receiving element PD
8
of the two split photodetector
713
.
When the return light from the main spot
4
is employed, there arises a problem that the degree of reflection is changed in the process of forming the pit
61
, and the amount of light of the return light from the main spot
4
is fluctuated. In an attempt to avoid such a problem, the signal levels of the light receiving signals A to H from the photodetecting section
71
are adjusted by use of a high speed AGC, so as to eliminate the influence of the fluctuation of the amount of light. Alternatively, the ratio between the addition value of the light receiving signal A from the light receiving element PD
1
and the light receiving signal D from the light receiving element PD
4
, and the addition value of the light receiving signal B from the light receiving element PD
2
and the light receiving signal C from the light receiving element PD
3
by use of a divider, so as to eliminate the influence of the fluctuation of the amount of light. In the state where the influence of the fluctuation of the amount of light is eliminated in these manners, a wobble component is taken out to obtain time axis information and the like. Furthermore, in the information reading method according to the conventional example, time axis information and the like is obtained by sampling and holding an RF signal when the power of the laser beam is
Huber Paul W.
Sony Corporation
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