Dynamic information storage or retrieval – Control of storage or retrieval operation by a control... – Control of information signal processing channel
Reexamination Certificate
2001-04-11
2004-08-03
Tran, Thang V. (Department: 2653)
Dynamic information storage or retrieval
Control of storage or retrieval operation by a control...
Control of information signal processing channel
C369S047500, C369S053260, C369S059150, C369S116000
Reexamination Certificate
active
06771576
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an optical reproduction apparatus which carries out the reproduction with respect to an optical recording medium, especially relates to an optical reproduction apparatus that simultaneously carries out (a) an AGC (automatic gain control) in which the gain of an amplifier circuit that amplifies a reproduction signal is controlled and (b) a control of the reproduction power of a light beam.
BACKGROUND OF THE INVENTION
In an optical disk reproduction apparatus, a reproduction signal detected by an optical pickup is processed such as amplified and wave-form-equalized by a wave form process circuit. The reproduction signal thus processed is sent to a binary circuit or a PRML process circuit so as to be converted into a digital signal. The amplitude of the reproduction signal varies due to the change such as the change in the reflectance of a recording layer. For this problem, in the wave form process circuit, so called an AGC (automatic gain control) is generally carried out so as to stably amplify the reproduction signal and have a predetermined amplitude (see, for example, Japanese unexamined patent publication No. 58-73022 (publication data: May 2, 1983).
FIG. 8
is a diagram showing a structure of a conventional optical reproduction apparatus. The following description deals with the operation of such a conventional apparatus. A reproduction signal read out from an optical disk
30
a
by an optical head
31
is sent to an AGC amplifier
32
so as to be amplified, and then is sent to an amplitude detection circuit
33
. The amplitude of the reproduction signal outputted from the amplitude detection circuit
33
is sent to a gain control circuit
34
which compares the amplitude with a reference amplitude, calculates a gain by which the amplitude of the reproduction signal is made to be equal to the reference amplitude, and returns to the AGC amplifier
32
. The reproduction signal thus amplified by the AGC amplifier
32
, that has a stable predetermined amplitude, is sent to a digital data reproduction circuit
35
. This allows to realize a reproduction of the digital data with high reliance and small reading error. The response speed of the amplifier
32
is usually set to be high so as to swiftly follow the change in the amplitudes of the reproduction signal.
In the mean time, according to a conventional rewritable magneto-optical disk reproduction apparatus of magnetic super-resolution type, two kinds of marks having respective different lengths are reproduced. The reproduction power is controlled so that the ratio of the two reproduction signals becomes close to a predetermined value, thereby ensuring that the reproduction power is always maintained optimal and the reading error is reduced (see, for example, Japanese unexamined patent publication No. 8-63817 (publication date: Mar. 8, 1996).
FIG. 9
is a schematic diagram showing a structure of such a conventional rewritable magneto-optical disk reproduction apparatus.
FIG. 10
is an explanatory view illustrating a structure of the magneto-optical disk
30
. In
FIG. 10
, a sector
50
is composed of a short mark recording region
51
and a long mark recording region
52
that are provided for controlling the reproduction power, and a data recording region
53
. A pattern in which short marks are repeated is recorded in the short mark recording region
51
. A pattern in which long marks are repeated is recorded in the long mark recording region
52
. Digital data are recorded in the data recording region
53
.
In
FIG. 9
, the light projected from a semiconductor laser
36
is converged onto the sector
50
. When the light is converged onto the short mark recording region
51
, the light reflected from the pattern in which the short marks are repeated is directed to a photo diode
37
by which the reflected light is converted to a reproduction signal. In a similar manner, the reproduction signal of the pattern in which the long marks are repeated is reproduced from the long mark recording region
52
. The reproduction signals are sent to an amplitude ratio detection circuit
38
. The amplitude ratio detected by the amplitude ratio detection circuit
38
and a target amplitude ratio are compared with each other by a differential amplifier
39
. And, a feedback control is made, i.e., a laser power control circuit
40
controls a driving electric current of the semiconductor laser
36
so that the difference between the above ratios becomes small. Thus, the driving electric current of the laser light is controlled so that the optimal reproduction power is provided. Thereafter, the projected light is converged onto the data recording region
53
. The reproduction signal read out from the data recording region
53
is sent to a digital data reproduction circuit
41
which reproduces the digital data having a low error rate. Thereafter, when converging the projected light onto the next sector, the processing is repeated in a similar manner so that an optimal reproduction power is newly set. Thus, the recording regions for the marks of a reproduction power control use are provided in a dispersion manner, and the amount of the reproduction signal is detected for each sector so as to control the reproduction power. This allows to control the reproduction power in a short time interval and to follow the change in the optimal reproduction power in a short time.
By the way, in the reproduction power control, the error is generated in the process of the detection of the amplitude ratio. More specifically, even when reproducing the mark pattern of the reproduction power control use under the same reproduction power and the same conditions, generated is the unevenness of the amplitude ratio that is reproduced by the noise contained in the reproduction signal. This causes the error in the differential signal of the detected amplitude ratio and the target amplitude ratio. The error is generated in the reproduction power to be controlled, accordingly. Even when the reproduction is made under the same conditions, since the reproduction power to be controlled has the unevenness due to the error. The amplitudes of the reproduction signal have also the unevenness, accordingly. For example, in the case where the reproduction power is controlled for each sector like the reproduction apparatus shown in
FIG. 9
, the reproduction conditions should be almost the same among the adjoining sectors. However, in actual, the amplitudes of the reproduction signals obtained for each sector have the unevenness due to the above-mentioned reason. Note that the amount of the unevenness is not so large. The error rate in the digital data reproduction is little affected.
However, in the case where the reproduction power control and the AGC are simultaneously carried out, when the response speed of the AGC is so fast as to carry out the AGC for each sector, as has been discussed, the gain of the AGC is found in accordance with the amplitude that varies depending on the unevenness of the reproduction power. This causes the problem that the unevenness of the amplitudes becomes larger so as to adversely affect the digital data reproduction.
FIG. 11
shows the results of the change in the amplitudes of the long mark that has actually been measured when controlling the reproduction power for a single sector under a constant condition. The horizontal axis indicates how many times the controlling has been carried out (how long the time has passed). The vertical axis indicates the amplitudes of the reproduction signal of the long mark. FIG.
11
(
a
) shows the change in the amplitudes when only the reproduction power control is carried out. FIG.
11
(
b
) shows the change in the amplitudes when the reproduction power control and the AGC for each sector are simultaneously carried out. As is clear from FIGS.
11
(
a
) and
11
(
b
), when the reproduction power control and the AGC for each sector are simultaneously carried out, the unevenness of the amplitudes became large. When comparing the both cases in accordance w
Maeda Shigemi
Okumura Tetsuya
Conlin David G.
Daley, Jr. William J.
Edwards & Angell LLP
Sharp Kabushiki Kaisha
Tran Thang V.
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