Dynamic information storage or retrieval – Condition indicating – monitoring – or testing – Including radiation storage or retrieval
Reexamination Certificate
2001-12-10
2004-09-21
Young, W. R. (Department: 2652)
Dynamic information storage or retrieval
Condition indicating, monitoring, or testing
Including radiation storage or retrieval
C369S059160, C369S124130
Reexamination Certificate
active
06795386
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to laser noise removal in an optical disk apparatus using various optical disks such as a DVD (Digital Versatile Disk) and a CD (Compact Disk) as a recording medium, for example.
Playback apparatus as well as recording and playback apparatus using an optical disk as a recording medium have come into wide use. For example, DVD players and CD players are widely used in ordinary households. Optical disk recording and playback apparatus capable of recording on a DVD-R (DVD Recordable), a DVD-RW (DVD Rewritable), a CD-R (CD Recordable), a CD-RW (CD Rewritable) and the like are widely used as a data recording apparatus for a personal computer, for example.
In such an optical disk apparatus as an optical disk playback apparatus or an optical disk recording and playback apparatus, a reproduced radio-frequency signal (reproduced RF signal) obtained from an optical disk includes so-called laser noise caused by laser light applied to the optical disk. Therefore, for highly accurate reproduction, methods for removing the laser noise from the reproduced RF signal have been proposed.
For example, Japanese Patent Laid-Open No. Hei 10-124919 proposes a method for removing the laser noise from the reproduced RF signal by subtracting a monitoring output signal for APC (Automatic Power Control) from the reproduced RF signal. An optical disk playback apparatus using this method is shown in FIG.
16
.
As shown in
FIG. 16
, laser light is applied from a laser light source (semiconductor laser device)
1
through a beam splitter
2
to an optical disk
100
. The light reflected from the optical disk
100
is supplied to a photodetector (light receiving device)
3
via the beam splitter
2
, and then converted into an electric signal by the photodetector
3
The output signal from the light receiving device
3
is amplified by an amplifier
4
, and then supplied to an arithmetic unit (adder)
5
as a reproduced RF signal rf(t).
In the meantime, the laser light emitted from the laser light source
1
is also supplied to a photodetector (light receiving device)
6
via the beam splitter
2
, and then converted into an electric signal by the photodetector
6
. The output signal from the light receiving device
6
is an APC monitoring output signal used for automatically adjusting power (light intensity) of the laser light. The APC monitoring output signal is supplied to a power control signal generating unit
7
. The APC monitoring output signal is also supplied to an amplifier
8
having a gain adjusting function, then adjusted in gain by the amplifier
8
, and supplied to the arithmetic unit
5
as an APC monitoring output signal m(t).
The arithmetic unit
5
subtracts the APC monitoring output signal m(t) from the reproduced RF signal rf(t) (antiphase addition). Thus, a so-called additive laser noise component (additive noise component) possessed by the laser light itself is subtracted and hence removed from the reproduced RF signal rf(t) including the laser noise component.
The reproduced RF signal rf(t) from which the additive noise component is removed is supplied to an equalizer
9
to be subjected to predetermined equalizing processing. Thereafter, a data discriminating unit
10
discriminates (distinguishes) data of the reproduced RF signal rf(t). The discriminated data is decoded by a decoding unit
12
and then reproduced. A clock reproducing unit
11
reproduces a clock signal used in discriminating the data.
Thus, by removing the additive noise component possessed by the laser light itself from the reproduced RF signal rf(t), it is possible to reduce jitter of the reproduced RF signal rf(t) around zero crossing level (shaking of the reproduced RF signal in a direction of a time axis), and to thereby improve a reproduction margin. Therefore, an optical disk apparatus with a reproducing system performing binary detection can make favorable reproduction.
Although the above-described conventional method for canceling the laser noise can cancel laser noise around zero crossing level, the method cannot cancel laser noise in other parts. The reproduced RF signal rf(t) is formed from the laser light applied to the optical disk and reflected from the optical disk. The light reflected from the optical disk is a product of the laser light applied to the optical disk multiplied by a recorded signal recorded on the optical disk (signal recorded on the optical disk by marks and spaces).
Hence, the reproduced RF signal rf(t) includes not only the so-called additive noise component possessed by the laser light itself but also a modulated noise component resulting from the additive noise component being modulated by the recorded signal of the optical disk.
Thus, even when the APC monitoring output signal m(t) formed from the laser light itself from the laser light source
1
and including only the additive noise component as shown in
FIG. 17B
is subtracted from the reproduced RF signal rf(t) including the additive noise component and the modulated noise component as shown in
FIG. 17A
, the laser noise around zero crossing level can be removed but the modulated noise component remains, as shown in FIG.
17
C.
The mainstream of reproduced signal processing by a reproducing system of an optical disk apparatus has recently been shifting from the conventional binary detection processing to PRML (Partial Response equalization and Maximum Likelihood detection) signal processing.
In the PRML signal processing, the reproduced RF signal uses multiple decision levels, and a Viterbi detector having multiple reference levels is used. It is therefore desirable that an optical disk apparatus having a reproducing system performing PRML signal processing reduce laser noise not only around zero crossing level of the reproduced RF signal but also around each of the reference levels.
Although the conventional method for canceling laser noise as described with reference to FIG.
16
and
FIGS. 17A
,
17
B, and
17
C is effective in the reproducing system that performs the conventional binary detection processing, the conventional method is not adequate for use in the optical disk apparatus performing the PRML reproduced signal processing because the conventional method cannot remove the modulated noise component from the reproduced RF signal rf(t).
In addition, the conventional method for canceling laser noise as described with reference to FIG.
16
and
FIGS. 17A
,
17
B, and
17
C is required to adjust the amplitude of laser noise dynamically depending on variation in the reflectivity of the optical disk (medium), variation in the gain of the I/V amplifier, variation in laser power and the like. This amplitude adjustment (gain adjustment) is made by the amplifier
8
having a gain adjusting function shown in FIG.
16
.
Thus, the conventional method for canceling laser noise requires an AGC (Automatic Gain Control) circuit, and it is extremely difficult for the AGC circuit to perform proper processing because the foregoing various variation factors in laser noise need to be considered.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an optical disk playback apparatus, an optical disk recording and playback apparatus, and a laser noise canceling circuit applied to an optical disk apparatus that can reliably and readily remove all laser noise components from the reproduced RF signal.
To achieve the above object according to first aspect, there is provided an optical disk playback apparatus including: a generating unit for generating laser light to be applied to an optical disk; a first light receiving unit for receiving the laser light applied from the generating unit to the optical disk and reflected from the optical disk, and converting the reflected light into an electric signal; a second light receiving unit for receiving at least part of the laser light applied from the generating unit to the optical disk, and converting the part of the laser light into an electric signal; a low-pass filter for extracting a direct-current component
Battaglia M. V.
Frommer William S.
Frommer & Lawrence & Haug LLP
Sony Corporation
Young W. R.
LandOfFree
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