JP2894810B2 - Information playback device - Google Patents

Description

The present invention relates to an information reproducing apparatus for reproducing information recorded on an information recording medium, for example, used in an electronic filing system or the like. More specifically, the present invention relates to an information reproducing apparatus for reproducing information recorded on an information recording medium by multi-level recording.

(Prior Art) With the development of information and communication technology, there is a strong demand for an auxiliary storage device for storing information to have a large capacity, a high speed processing, a small size, a low cost, and the like. As an auxiliary storage device that meets such demands, for example, there is an electronic filing system.
It is widely used as an auxiliary storage device for computers.

An electronic filing system is a system for storing information by irradiating a recording portion of an information recording medium such as an optical disk or a magneto-optical disk with a light beam and causing a change in optical characteristics at the recording portion of the information recording medium. is there. For example, if an optical disc is used as an information recording medium, the information to be recorded is converted into binary information consisting of “0” and “1”, for example, corresponding to “1” of the amorphous layer of the optical disc. By irradiating the region to be irradiated with a light beam to perform crystallization and not irradiating the region corresponding to “0” with the light beam, information can be recorded on this optical disk. In addition, if the amount of reflected light is detected by irradiating a weak light beam that does not cause crystallization to the recording portion of such an optical disc, the difference in reflectance between the amorphous region and the crystallized region can be obtained. Thereby, the information recorded on the optical disc can be reproduced.

However, such electronic filing systems,
Although the storage capacity can be dramatically improved as compared with the case where another auxiliary storage device is used, it cannot be said that it is sufficient to answer the above demand. As a method for improving the storage capacity of an electronic filing system, a technique for reducing the diameter of a light beam applied to an information recording medium to increase the recording density is conventionally known, but the diameter of the light beam is limited by the diffraction limit of light. Therefore, miniaturization has a limit.

On the other hand, the information recorded on the information recording medium is "0".
And multi-valued information (3
(Above information equal to or greater than the value), an auxiliary storage device that increases the amount of recorded information per predetermined area of the information recording medium and thereby substantially improves the storage capacity is disclosed in, for example,
63-163962.

This comprises a signal processing means for converting an information signal into a signal having three or more stages, a light beam output means for outputting a light beam whose energy is modulated in multiple stages in accordance with the processed signal having three or more stages, and a light beam. And an optical system for converging and irradiating the information recording medium on the information recording medium, and the information recording apparatus performs multi-level recording on a recording area of the information recording medium. When reproducing recorded information from an information recording medium on which multi-level recording has been performed in this manner, a light beam for outputting a light beam to an information recording medium having a recording portion with a multi-level information recording level is formed. Beam output means, an optical system for condensing a light beam on the information recording medium, and a reproduction signal for generating a predetermined reproduction signal by detecting a multi-step optical characteristic of the recording portion obtained by irradiating the light beam The information reproducing apparatus constituted by the processing means is used.

(Problems to be Solved by the Invention) In the information reproducing apparatus as described above, a photoelectric conversion element is usually used as means for detecting multi-stage optical characteristics. That is, the reflected light of the light beam applied to the information recording medium by the light beam output means is received by the photoelectric conversion element, and the output of the photoelectric conversion element is used to create a reproduction signal corresponding to the multi-stage optical characteristics. . Here, in order to convert an analog output (hereinafter, referred to as a reproduction waveform) of the photoelectric conversion element when the reflected light is received into a digital signal as a reproduction signal, a clock (which gives a timing to capture a voltage value of the reproduction waveform) Hereinafter, referred to as a demodulation clock).

In an information reproducing apparatus that reproduces information recorded on an information recording medium by binary recording as described above, the demodulated clock is generally generated from a reproduced waveform.
This method is called a self-clock.

 Hereinafter, the self-clock will be described.

FIG. 6A is a diagram conceptually showing a state in which recording has been performed on a recording portion of the information recording medium. In the figure, the shaded area is the area where the optical characteristics have changed due to the irradiation of the light beam (the light beam output by the light beam output means of the information recording device). Hereinafter, this area is referred to as a recording mark. The recording mark corresponds to the binary information “0” or “1”, but is described here as corresponding to “1”. That is, when the recording information (binary information) is "0", no recording mark is formed, and when it is "1", a recording mark is formed.

FIG. 6 (b) is a diagram showing output pulses of the light beam output means when forming a recording mark as shown in FIG. 6 (a), and corresponds to recording information. Less than,
This pulse is called a recording pulse.

Here, when the recording mark shown in FIG. 6 (a) is reproduced using the photoelectric conversion element of the information reproducing apparatus, FIG. 6 (c)
The reproduced waveform shown in FIG. Also, a predetermined slice level is set for the reproduced waveform shown in FIG. 6C, and when the voltage value of the reproduced waveform is smaller than this slice level, it becomes “low”, and the voltage value of the reproduced waveform becomes When a binarized waveform that becomes “high” when the level is higher than the slice level is generated, the result is as shown in FIG. 6D. This binarized waveform is a demodulation clock. Recording information is taken in according to the rising or falling timing of the demodulated clock.

When the demodulated clock is generated in this manner, compared to the recording pulse shown in FIG. 6 (b), there is almost no time lag, so that the recorded information can be faithfully reproduced.

However, if such a self-clock is applied as it is to an information reproducing apparatus for reproducing information recorded on an information recording medium by multi-level recording, when reproducing the recorded information for the following reason, There has been a problem that a time shift, that is, a so-called reproduction jitter occurs.

FIG. 7A is a diagram conceptually showing a state in which four-level recording has been performed on a recording portion of the information recording medium. Here, it is assumed that the recording marks (quaternary information) correspond to “3”, “2”, and “1” in descending order of the recording mark area, and that the recording mark is not formed when the recording mark is “0”. . Also, the seventh
FIG. 7B is a diagram showing a recording pulse when forming a recording mark as shown in FIG. 7A, and FIG. 7C is a diagram showing an output timing of the light beam output means. When a heat mode optical disk is used, the area of the recording mark increases as the energy of the light beam during recording increases. Therefore, as can be understood from FIGS. 7A and 7B, the area of the recording mark increases as the signal level of the recording pulse increases.

When such recorded information is reproduced using the photoelectric conversion element of the information reproducing apparatus, a reproduced waveform as shown in FIG. 7D is obtained. Therefore, when a predetermined slice level is set for this reproduced waveform and a binarized waveform, that is, a demodulated clock is generated in the same manner as in the case of FIG. 6 (d), FIG. It becomes like. As described above, in the case of multi-level recording, the waveform of the demodulation clock changes depending on the signal level of the recording pulse. Therefore,
The deviation from the recording pulse increases, and the reproduction jitter increases. When the reproduction jitter is large as described above, when the voltage value of the reproduction waveform is acquired according to the timing of the demodulation clock, it is impossible to accurately reproduce the recorded information.

The present invention has been tried in view of the problems of the related art, and suppresses a reproduction jitter that occurs when reproducing information recorded by multi-level recording on an information recording medium to a range that does not hinder practical use. An object of the present invention is to provide an information reproducing apparatus capable of accurately reproducing recorded information.

[Means for Solving the Problems] An information reproducing apparatus of the present invention is an information reproducing apparatus for reproducing information recorded on an information recording medium by multi-value recording,
A light beam output means for outputting a light beam, an optical system for condensing the light beam output by the light beam output means on a recording portion of the information recording medium, and receiving the light beam reflected by the recording portion. Optical characteristic detecting means for outputting an electric signal corresponding to the optical characteristic of the recording portion, and differential operation means for differentiating the signal waveform of the electric signal output by the optical characteristic detecting means and outputting a differential waveform. A clock generating means for detecting a zero crossing of the differential waveform input from the differential calculating means and generating a demodulated clock; and detecting a signal level of the electric signal in synchronization with the demodulated clock obtained by the clock generating means. And a reproduction signal generating means.

(Operation) In the information reproducing apparatus of the present invention, when generating the demodulated clock from the reproduced waveform obtained by the optical characteristic detecting means, first, the reproduced waveform is differentiated, and then, the differentiated waveform is obtained. Since the zero crossing of the differentiated waveform is detected and the demodulated clock is generated in synchronization with the timing of the zero crossing, the demodulated clock is generated at the timing when the voltage value of the reproduced waveform reaches the peak value. Here, the timing at which the voltage value of the reproduced waveform reaches the peak value is substantially constant, regardless of the reproduced waveform (ie, irrespective of the size of the recording mark), so that the reproduction jitter does not hinder practical use. Range.

(Example) Hereinafter, one example of the present invention will be described. Here, the case where the information reproducing apparatus of the present invention is applied to an information recording / reproducing apparatus that records multi-valued information on an information recording medium (here, an optical disc) and reproduces the recorded multi-valued information is used in an electronic filing system. Will be described as an example.

FIG. 1 is a schematic configuration diagram showing such an information recording / reproducing apparatus.

When recording information in such a device, first, the recording signal processing device 10 converts an information signal input from a control circuit (not shown) of the electronic filing system into a signal of a plurality of levels (that is, a multi-level signal). The multi-valued processing signal is output to the semiconductor laser 11. The semiconductor laser 11 irradiates a recording laser beam having energy or wavelength according to the signal level of the processing signal output from the recording signal processing device 10. Here, in order to change the energy of the laser beam in multiple steps according to the signal level, the intensity or the pulse width of the light beam or both of them may be changed, or the wavelength of the light beam may be changed. . By irradiating the recording layer of the information recording medium (optical disc) 20 with the laser beam having the energy or the wavelength corresponding to such a signal level via the optical system 30, the irradiation part of the information recording medium 20 is irradiated with the laser beam. A state change corresponding to energy or wavelength (that is, corresponding to a signal level) occurs, a recording mark is formed, and multilevel information is recorded.

When reproducing the multi-valued information recorded in this way, the semiconductor laser 11 described above uses the information recording medium 20.
A laser beam for reproduction having a small energy and a constant wavelength is output so as not to cause a state change in the irradiated portion.
The reproduction laser beam output from the semiconductor laser 11 is
The information recording medium 20 is irradiated via the optical system 30, and the reflected light is guided to the photoelectric conversion element 12 via the optical system 30. The photoelectric conversion element 12 converts the received laser beam into an electric signal. This electric signal is guided to the reproduction signal processing device 40 via the processing circuit 14. The reproduction signal processing device 40 reproduces multi-valued information from the input electric signal and outputs it to the control circuit.

If the information recording medium 20 is of a rewritable type such as a phase change type, the laser beam is output from the semiconductor laser 11 at a lower intensity than during recording, and this laser beam is output through the optical system 30. The information can be erased by irradiating the information recording medium 20 to change the recording layer in this portion to a state before recording. When the information recording medium 20 is of a type that can be overwritten, when the information signal input by the recording signal processing device 10 is multi-valued, the signal level depends on the light intensity at the time of overwriting. The semiconductor laser 11 outputs a recording laser beam having an energy or a wavelength corresponding to the signal level, and irradiates the information recording medium 20 via the optical system 30 to perform overwriting.

In the optical system 30, the divergent laser beam output from the semiconductor laser 11 is converted into a parallel light beam by the collimator lens 31 and guided to the beam splitter 32. The beam reflected by the beam splitter 32 is condensed and irradiated on the information recording medium 20 by the condenser lens 36. During reproduction, a part of the laser beam applied to the information recording medium 20 is further reflected, and the reflected light travels straight through the beam splitter 32 and is guided to the half mirror 33. Here, the beam that has traveled straight through the half mirror 33 is guided to the photoelectric conversion element 13 via the lens 35. On the other hand, the light reflected by the half mirror 33 is guided to the photoelectric conversion element 12 via the lens.

The signal output from the photoelectric conversion element 12 is output to the reproduction signal processing device 40 via the processing circuit 14 as described above, and the tracking control device 19 is output via the amplification circuit 16.
The irradiation position of the beam is used as correction data for optimization. Further, the signal output from the photoelectric conversion element 13 passes through the processing circuit 15 and the amplification circuit 17,
It is guided to the focusing control device 18 and used as data for focus control.

Next, the recording signal processing device 10 will be specifically described.

In this embodiment, quaternary recording is performed on the information recording medium 20. FIG. 2 is a block diagram showing a schematic configuration of the recording signal processing device. As shown in FIG. 2, the recording signal processing device 10 includes a quaternary circuit 101,
A modulation circuit 102 and a semiconductor laser drive circuit 103 are provided. Input data (information signal) is binarized,
That is, it is input as a binary signal, which is first
The data is converted into 4-bit information, that is, 4-value data by the value conversion circuit 101. The quaternary data is converted by the modulation circuit 102 into a signal having one of four signal levels of “0”, “1”, “2”, and “3”, and is applied to the semiconductor laser drive circuit 103 as a voltage. You. Thus, the intensity of the light beam and the like are modulated in four stages according to the recording signal.

Next, the reproduction signal processing device 40 will be specifically described.

FIG. 3 is a block diagram showing a schematic configuration of the reproduction signal processing device 40. The reproduction signal processing device 40, as described above,
An electric signal is input from the processing circuit 14, and a reproduction signal corresponding to the information recorded on the information recording medium 20 is output. Also,
As shown in FIG. 3, the reproduction signal processing device 40 removes high-frequency components of the electric signal input from the processing circuit 14 and a low-pass filter (LPF) 401, and differentiates the signal waveform of the output signal of the LPF 41. Differential operation circuit 402 for outputting a differential waveform, a clock generation circuit 403 for detecting a zero crossing of the differential waveform input from the differential operation circuit 402 and generating a demodulated clock, and a demodulation signal obtained by the clock generation circuit 43. A reproduction signal generation circuit 404 for detecting a signal level of the electric signal in synchronization with a clock.

Hereinafter, signal processing in the reproduction signal processing device 40 will be described with reference to FIGS. 4 (a) to 4 (f).

FIG. 4 (a) is a diagram conceptually showing a state where quaternary recording has been performed on a recording portion of the information recording medium 20. FIG. In the figure, the hatched area is the recording mark. Also, the fourth
FIG. 4B is a diagram showing an output pulse (recording pulse) of the recording signal processing device 10 when a recording mark as shown in FIG. 4A is formed, and is recorded on the information recording medium 20. It supports multi-value information. As described above, when a heat mode optical disk is used, the area of the recording mark increases as the signal level of the recording pulse increases.

FIG. 4 (c) shows a photoelectric conversion element when reproducing multi-valued information.
The signal waveform (reproduced waveform) when the signal subjected to the photoelectric conversion in 12 is taken into the reproduced signal processing device 40 via the processing circuit 14 and the high-frequency component is removed by the LPF 401 is shown. Thus, the reproduction waveform changes according to the size of the area of the corresponding recording mark. When this reproduced waveform is input to the differential operation circuit 402 and differentiated, a differentiated waveform as shown in FIG. 4 (d) is obtained. As can be seen by comparing the reproduced waveform shown in FIG. 4 (c) with the differentiated waveform shown in FIG. 4 (d), when the reproduced waveform takes a peak value, a zero crossing of the differentiated waveform is obtained. .

Here, as shown in FIG. 4 (b), the signal level of the recording pulse varies depending on the recorded value of the multilevel information recorded on the information recording medium, but the pulse interval and pulse width are always constant. It is. Further, as shown in FIG. 4 (c), the peak value of the reproduced waveform substantially corresponds to the recording pulse and appears at regular intervals. On the other hand, since the zero crossing of the differential waveform corresponds to the peak value of the reproduction waveform as described above, it also corresponds to the recording pulse and appears at a constant interval. Therefore, by detecting the zero crossing of this differentiated waveform and generating a demodulated clock, a demodulated clock with almost no deviation from the recording pulse can be obtained, and the reproduction jitter can be kept within a range that does not hinder practical use. Becomes

FIG. 4 (e) shows an example of the demodulated clock generated by the clock generation circuit 403, in which the rising of the clock is synchronized with the zero crossing of the differential waveform shown in FIG. 4 (d). Is shown. FIG. 4 (f)
Using this demodulated clock, the reproduction signal generation circuit 404
It shows an example of a reproduced signal when reproducing multi-valued information recorded on the information recording medium 20, and shows a case where the signal level of the electric signal is detected in synchronization with the rise of the demodulation clock. . Thus, FIG. 4 (e)
Since the demodulated clock shown in FIG. 4 has almost no time lag as compared with the recording pulse shown in FIG. 4B, it is possible to faithfully reproduce the recorded information.

Note that, here, the LPF 401 removes the high-frequency noise of the electric signal input from the processing circuit 14 before performing the differentiation processing in the differentiation operation circuit 402, but this processing is not necessarily performed. Further, if necessary, after performing a delay process on the demodulated clock, the reproduction signal generation circuit 404 can reproduce the multi-valued information. In addition, this demodulated clock can be stabilized by locking the synchronization state using a PLL circuit.

In addition, here, the case where the demodulated clock is generated using the reproduction waveform of the information recorded on the information recording medium 20 has been described, but this information is a clock bit for obtaining a timing for reproducing other recorded information. Of course, it is possible. That is, separately from the recording information to be reproduced, multi-value information as clock bits is stored in the information recording medium 20.
The demodulated clock is generated from the multi-valued information as the clock bit by using the differential operation circuit 402 and the clock generation circuit 403 as described above, and the reproduction of the “recorded information to be reproduced” is performed using the demodulated clock. May be performed.

Next, the information recording medium 20 will be described in detail. Here, a phase change type optical disk will be described as an example. FIG. 5 is a sectional view showing a layer structure of the optical disc. As shown in FIG. 5, this optical disc comprises an optical disc substrate 201, a first protective layer 202, a recording layer 203, a second
, A reflective layer 205, and a third protective layer 206.

As a material for forming the optical disc substrate 201, a material that is transparent and has little change with time is suitable. For example, acrylic resin such as polymethyl methacrylate, polycarbonate resin, epoxy resin, styrene resin, glass, or the like. In addition, continuous grooves, sample servo marks, preformat marks, and the like are formed on the optical disk substrate 201 according to the recording format.

The recording layer 203 is formed of a material whose state changes when irradiated with a light beam. Such materials include, for example, GeTe, TeSe, GeSbSe, TeOx, In
There are chalcogenide amorphous semiconductor materials such as Se and GeSbTe, and compound semiconductor materials such as InSb, GeSb and InSbTe. This recording layer 203 can be formed by a vacuum evaporation method, a sputtering method, or the like. Further, the film thickness of the recording layer 203 is practically in the range of several nm to several μm.

The first protective layer 202 and the second protective layer 204 are formed in contact with the recording layer 203 on the upper surface and the lower surface, respectively, and are provided to protect the recording layer 203. The first protective layer 202 and the second protective layer 204 can prevent inconveniences such as the recording layer 203 being scattered or punctured by laser beam irradiation. As a material for forming the first protective layer 202 and the second protective layer 204, for example, SiO ₂ , SiO, Al
N, Al ₂ O ₃ , ZrO ₂ , TiO ₂ , Ta ₂ O ₃ , ZnS, Si, Ge or the like is suitable, and using such a material, it can be formed by, for example, a vacuum evaporation method or a sputtering method. . Note that the thickness of the first protective layer 202 and the second protective layer 204 is practically several nm to several μm.

The reflective layer 205 enhances the change in the characteristics of the reflected light due to the change in the optical characteristics of the recording layer 203, and also cools the recording layer 203 (that is, absorbs and dissipates the heat of the recording layer 203). This is provided to prevent the temperature of the recording layer 203 from rising. As a material for forming the reflection layer 205, for example, Au, Al, Cu or Ni-Cr
And the like, and can be formed using such a material by, for example, a vacuum evaporation method or a sputtering method. The thickness of the reflective layer 205 is suitably several nm to several μm in practical use.

The third protective layer 206 has scratches in handling the optical disc,
It is provided to prevent dust and the like. As a forming material, an ultraviolet curable resin or the like is generally used. For example, the ultraviolet curable resin is applied to the surface of the reflective layer 205 by a spin coating method, and then cured by irradiating ultraviolet light. This third protective layer 206
The film thickness is preferably in the range of several μm to several hundred μm for practical use.

When recording multi-valued information on such an optical disc, it is effective to control the cooling rate of the recording layer 203 during recording to adjust the shape of the recording mark. The control of the cooling rate is performed by controlling the first protective layer 202, the recording layer 203, and the second protective layer 20.
4. It can be performed by appropriately selecting a material and a film thickness of the reflective layer 205. For example, to increase the cooling rate, the thickness of the recording layer 203 should be reduced,
Using a material having high thermal conductivity as a material for forming
It is effective to use a material having a high thermal conductivity as a material for forming the first protective layer 202 and the second protective layer 204.

When recording multilevel information on an optical disc,
It is also effective to devise an output pulse profile of the semiconductor laser 11 during recording.

Here, the configuration example of the optical disk capable of recording on only one side has been described, but it is also possible to configure the optical disk such that double-sided recording is possible. The double-sided recording optical disk is obtained, for example, by bonding two optical disks shown in FIG. 5 with the recording layer 203 inside.

In addition, the first protective layer 202, the second protective layer 204, the reflective layer 205, and the third protective layer 206 shown in FIG. 5 can be omitted depending on the application.

As described above, in the present embodiment, the case where the multi-valued information recorded on the phase-change type optical disc is reproduced has been described as an example, but the information reproducing apparatus of the present invention is not limited to such a case, and the organic material, The same effect can be obtained when reproducing multi-valued information recorded on an optical disk formed of a shape-change material, a perforated material, or a composite material of these materials. Similar effects can be obtained when reproducing multi-valued information recorded on an information recording medium.

[Effects of the Invention] As described in detail above, according to the information reproducing apparatus of the present invention, a demodulated clock that accurately corresponds to a recording pulse can be generated. The reproduction jitter generated when reproducing the reproduced information can be kept within a practically acceptable range, and the recorded information can be reproduced accurately.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an information reproducing apparatus according to one embodiment of the present invention, FIG. 2 is a block diagram showing a schematic configuration of the recording signal processing device shown in FIG. 1, and FIG. 3 is FIG. 4 (a) to 4 (f) are diagrams for explaining signal processing of the reproduced signal processing apparatus shown in FIG. 3, and FIG. 5 is a block diagram showing a schematic configuration of the reproduced signal processing apparatus shown in FIG. FIGS. 6 (a) to 6 (d) and FIGS. 7 (a) to 7 (e) are schematic sectional views showing a layer structure of an example of the information recording medium shown in FIG. FIG. 3 is a diagram for explaining signal processing of the information reproducing device. 10 ... Recording signal processing device, 11 ... Semiconductor laser, 12,13
... Photoelectric conversion elements, 14, 15 processing circuit, 16, 17 amplification circuit, 18 focusing control device, 19 tracking control device, 20 information recording medium, 30 optical system, 31
…… Collimator lens, 32 …… Beam splitter, 33…
... half mirror, 34, 35 ... lens, 36 ... condensing lens, 40 ... reproduction signal processing device, 101 ... quaternary circuit, 102
…… Modulation circuit, 103 …… Semiconductor laser drive circuit, 201
… Optical disk substrate, 202… first protection layer, 203… recording layer, 204… second protection layer, 205… reflection layer, 206…
Third protective layer, 401 ... Low-pass filter (LPF), 402
…… Differential operation circuit, 403 …… Clock generation circuit, 404 ……
Reproduction signal generation circuit.

Claims (1)

(57) [Claims] An information reproducing apparatus for reproducing information recorded on an information recording medium by multi-level recording, comprising: a light beam output means for outputting a light beam; and a light beam output by the light beam output means. An optical system for condensing light on a recording portion of the information recording medium, an optical characteristic detecting means for receiving the light beam reflected by the recording portion and outputting an electric signal according to an optical characteristic of the recording portion; Differential operation means for differentiating the signal waveform of the electric signal output from the optical characteristic detection means to output a differential waveform, and detecting a zero crossing of the differential waveform input from the differential operation means to generate a demodulation clock. A clock generation unit; and a reproduction signal generation unit that detects a signal level of the electric signal in synchronization with a demodulated clock obtained by the clock generation unit. Information reproducing device.