Dynamic information storage or retrieval – Binary pulse train information signal – Including sampling or a/d converting
Reexamination Certificate
1998-09-30
2002-06-11
Tran, Thang V. (Department: 2653)
Dynamic information storage or retrieval
Binary pulse train information signal
Including sampling or a/d converting
C369S059200, C369S047270, C369S047280, C369S047350
Reexamination Certificate
active
06404717
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an optical reproducing device, which projects a light beam onto an optical memory medium such as a magneto-optical disk which uses the magnetic ultra high resolution method, and which controls the quantity of light of the light beam so as to bring close to a predetermined value the quantity of a reproducing signal from recorded marks, and to an optical memory medium for use therein.
BACKGROUND OF THE INVENTION
Recent years have seen prolific development of high-density recording by means of magneto-optical disks which use the magnetic ultra high resolution method, provided with a recording layer and a reproducing layer. In magneto-optical disks of this type, a light beam is projected onto the reproducing layer of the disk, and in an area of the reproducing layer within the light beam spot which is heated to above a predetermined temperature (hereinafter referred to as the “aperture”), the magnetization of the recording layer is copied to the reproducing layer. Thus recorded marks smaller in diameter than the light beam spot can be reproduced.
In devices for reproducing magneto-optical disks of this type, even if the driving current for producing the light beam is held constant, there are cases in which the reproducing power of the light beam fluctuates with changes in the ambient temperature at the time of reproducing. If reproducing power is too strong, the aperture becomes too large, which increases crosstalk from reproducing signals from adjacent tracks, and reading errors occur. Again, if reproducing power is too weak, reproducing signal output from the target track is reduced, and again reading errors occur.
In a “Recording and Reproducing Device for Magneto-Optical Memory Medium and Magneto-Optical Memory Medium” disclosed in Japanese Unexamined Patent Publication No. 8-63817/1996 (Tokukaihei 8-63817) (U.S. Pat. No. 5,617,400), the aperture is maintained at a fixed size, and accurate data reproducing is performed, by reproducing a control pattern of repeated long marks and repeated short marks on a magneto-optical disk, and controlling reproducing light quantity so as to bring close to a predetermined value a ratio of the reproducing signal quantities of the two types of marks.
FIG. 11
explains the general structure of a magneto-optical disk reproducing device according to the foregoing conventional art. When projected light f′ from a semiconductor laser
202
is projected onto a magneto-optical disk
212
, reflected light g′ from recorded marks for reproducing power control on the magneto-optical disk
212
is converted into a reproducing signal a′ by a photodiode
203
. The reproducing signal a′ is sent to an A/D (Analog/Digital) converter
205
and to a clock producing circuit
204
. By means of PLL (Phase Locked Loop), the clock producing circuit
204
produces a clock signal c′ synchronized with the reproducing signal a′. Then, in accordance with the clock signal c′, the A/D converter
205
converts the reproducing signal a′ into digital data d′. On the basis of the digital data d′ sampled according to the clock signal c′, an amplitude ratio detecting circuit
213
calculates and outputs a ratio between an amplitude of the reproducing signal a′ of the long marks and an amplitude of the recording signal a′ of the short marks (amplitude ratio r′). A differential amplifier
210
then compares the amplitude ratio r′ with a standard value, producing a difference e′ therebetween. A reproducing light quantity control circuit
211
then outputs a driving current i′ for the semiconductor laser
202
in such a way that feedback reduces the difference e′, thus controlling the driving current i′ of the laser light in such a manner that an optimum reproducing light quantity is always applied.
However, in calculating the amplitude of the reproducing signal a′ from each type of mark, the amplitude ratio detecting circuit
213
calculates the amplitude based on digital data d′ sampled at a single upper peak position and digital data d′ sampled at a single lower peak position. Accordingly, it is difficult to improve the precision of the amplitude, and the precision of the amplitude ratio r′ calculated from the respective amplitudes may also be impaired. This results in the problem that accurate control of reproducing light quantity is difficult.
Here, sufficiently precise control of the reproducing light quantity is particularly necessary when using the foregoing magnetic ultra high resolution magneto-optical disks, because of their high recording density. Again, since the short marks are set to be shorter than the long marks, the reproducing signal a′ from the short marks has a smaller amplitude, and fluctuates with a shorter cycle, than the reproducing signal a′ from the long marks. Consequently, it is particularly difficult to improve the precision of the amplitude of the short marks.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an optical reproducing device and an optical memory medium which are capable of precisely detecting the amplitude of a reproducing signal from recorded marks.
In order to attain the foregoing object, an optical reproducing device according to the present invention includes a reproducing signal producing section, which outputs a reproducing signal obtained from recorded marks recorded in an optical memory medium; a signal quantity detecting section, which samples the reproducing signal at indicated sampling points, and outputs a reproducing signal quantity; a timing producing section, which indicates to the signal quantity detecting section sampling points having a phase offset from peak positions of the reproducing signal; and an amplitude calculating section, which, based on a plurality of the reproducing signal quantities, outputs an amplitude signal showing the amplitude of the reproducing signal.
With the foregoing structure, the reproducing signal from the recorded marks is sampled with a phase offset from peak positions of the reproducing signal, and the amplitude calculating section outputs an amplitude signal based on a plurality of reproducing signal quantities. Accordingly, an amplitude signal can be produced more precisely than when an amplitude signal is produced on the basis of reproducing signal quantities sampled from a reproducing signal only at peak positions within each period thereof.
Further, since the sampling points are not limited to peak positions, the timing producing section can indicate sampling points (for example at shoulder portions of the reproducing signal) with a timing suited to production of the amplitude signal. Accordingly, precision of the amplitude signal can be improved even in comparison with a case of averaging a plurality of reproducing signal quantities sampled only at peak positions.
In addition, in order to improve the precision of the amplitude signal, it is preferable to produce the amplitude signal based on reproducing signal quantities obtained from a plurality of periods of the reproducing signal, or to make more samplings per period of the recorded marks.
In addition to the foregoing structure, it is preferable if the sampling points indicated by the timing producing section are sampling points offset to precede upper or lower peak positions of the reproducing signal, and sampling points offset to follow upper or lower peak positions of the reproducing signal.
With this structure, even if the phase indicated by the timing producing section for use as the sampling points differs somewhat from the most suitable sampling points, the variation in the preceding and following sampling points creates fluctuations in the amplitude signal in mutually opposite directions, which thus cancel each other out. Consequently, even if the instructions of the timing producing section include error, the amplitude calculating section can produce a precise amplitude signal. Moreover, if the
Fuji Hiroshi
Maeda Shigemi
Okumura Tetsuya
Neuner George W.
Sharp Kabushiki Kaisha
Tran Thang V.
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