JPH04111229A - Information reproducing device - Google Patents

Abstract

PURPOSE:To accurately reproduce recorded information by receiving a light beam reflected by a recording part position of an information recording medium, outputting an electric signal according to an optical characteristic of the recording part position, sampling this electric signal with a prescribed demodulation clock, detecting a peak value of the sampled electric signal and outputting a regenerative signal. CONSTITUTION:The device possesses a recorded signal processing device 10, processing circuits 14 and 15 and a regenerative signal processing device 40, and the electric signal outputted from an optical characteristic detecting means is sampled with the demodulation clock, and then the peak value of this electric signal is detected, so that a recorded signal is regenerated based on this peak value. In this case, the timing for making a voltage value of the electric signal outputted from the optical characteristic detecting means become a peak value is not dependent upon the waveform of the electric signal (that is, irrespective of the size of a recording mark), and is set to be approximately constant intervals. By this method, reproducing jutters are suppressed to a range which is not detrimental to practical use by detecting the peak value after sampling this electric signal with the demodulation clock.

Description

[Detailed Description of the Invention] [Object of the Invention (Industrial Application Field) The present invention relates to an information reproducing device for reproducing information recorded on an information recording medium, which is used, for example, in an electronic filing system. More specifically, the present invention relates to an information reproducing apparatus that reproduces information recorded on an information recording medium by multilevel recording.

(Prior Art) With the development of information and communication technology, there is a strong demand for auxiliary storage devices that store information to have a larger capacity, faster processing speed, smaller size, and lower cost. An example of an auxiliary storage device that meets this demand is an electronic filing system, which has become popular as an auxiliary storage device for computers.

An electronic filing system is a system that stores information by irradiating the recording area of an information recording medium such as an optical disk or magneto-optical disk with a light beam to cause a change in the optical characteristics of the recording area of the information recording medium. be. For example, when using an optical disc as an information recording medium, the information to be recorded is converted into binary information consisting of "0" and "1", and corresponds to "1" in the amorphous layer of the optical disc, for example. By irradiating the area corresponding to the rOJ with a light beam to effect crystallization, and not irradiating the area corresponding to the rOJ with the light beam, information can be recorded on this optical disc. Furthermore, if a weak light beam that does not cause crystallization is irradiated onto the recording area of such an optical disk and the amount of reflected light is detected, it is possible to determine the reflectance between the amorphous area and the crystallized area. Depending on the difference, the information recorded on this optical disc can be reproduced.

However, although such electronic filing systems can dramatically improve storage capacity compared to the use of other auxiliary storage devices, they are not sufficient to meet the above-mentioned demands. As a method to improve the storage capacity of electronic filing systems, there is a known technique to increase the recording density by reducing the diameter of the light beam irradiated onto the information recording medium, but the diameter of the light beam is
There is a limit to miniaturization because it is limited by the diffraction limit of light.

On the other hand, by making the information recorded on the information recording medium not binary information consisting of "0" and "1" but multi-valued information (information with three or more values), the predetermined area of the information recording medium can be An auxiliary storage device that increased the amount of recorded information per unit and thereby substantially improved the storage capacity was developed, for example, in Japanese Patent Application Laid-Open No. 6
3-163962.

This includes a signal processing means that converts an information signal into a signal of three or more stages, a light beam output means that outputs a light beam whose energy is modulated in multiple stages according to the processed signal of three or more stages, and a light beam An information recording apparatus is constituted by an optical system that condenses and irradiates the information recording medium onto the information recording medium, and this information recording apparatus performs multilevel recording on the recording area of the information recording medium. In addition, when reproducing recorded information from an information recording medium on which multilevel recording has been performed in this way, a light beam is outputted to the information recording medium in which recording parts with multiple levels of information recording are formed. a beam output means, an optical system for focusing a light beam on the information recording medium, and a reproduction signal for generating a predetermined reproduction signal by detecting multi-stage optical characteristics of the recording area obtained by irradiating the light beam. An information reproducing device configured with a processing means is used.

(Problems to be Solved by the Invention) In the information reproducing device as described above, a photoelectric conversion element is usually used as a means for detecting multi-stage optical characteristics. That is, a photoelectric conversion element receives the reflected light of the light beam irradiated onto the information recording medium by the light beam output means, and uses the output of this photoelectric conversion element to create a reproduction signal according to multi-stage optical characteristics. . Here, in order to convert the analog output (hereinafter referred to as a reproduced waveform) of the photoelectric conversion element upon receiving reflected light into a digital signal as a reproduced signal, a clock ( (hereinafter referred to as demodulation clock) is required.

In an information reproducing apparatus that reproduces information recorded on an information recording medium by binary recording as described above, it has been common to generate this demodulated clock from a reproduced waveform. This method is called self-clocking.

This self-clock will be explained below.

FIG. 6(a) is a diagram conceptually showing a state in which recording is performed on a recording site of an information recording medium. In the figure, the shaded area is the area where the optical characteristics have changed due to irradiation with the light beam (the first beam output by the light beam output means of the information recording device). Hereinafter, this area will be referred to as a recording mark. Recording marks are binary information “0” or “1”.
", but here it will be explained 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.

Further, 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. Hereinafter, this pulse will be referred to as a recording pulse.

Here, when the recording mark shown in FIG. 6(a) is reproduced using a photoelectric conversion element of an information reproducing apparatus, a reproduced waveform as shown in FIG. 6(C) is obtained.

In addition, a predetermined slice level is set for the reproduced waveform shown in FIG. 6(C), and when the voltage value of the reproduced waveform is smaller than this slice level, it becomes "low", When a binarized waveform is generated that becomes "high" when it is larger than the slice level, the result shown in Fig. 6 (d
). This binarized waveform is the demodulated clock.

Recorded information is taken in according to the rising or falling timing of this demodulated clock.

When the demodulated clock is generated in this way, as shown in Fig. 6 (
Compared to the recording pulse shown in b), since there is almost no time lag, it is possible to faithfully reproduce recorded information.

However, if such a self-clock is applied as it is to an information reproducing device that reproduces information recorded on an information recording medium by multilevel recording, the reproduction signal will be affected when reproducing the recorded information for the following reasons. There is a problem in that a time lag occurs, that is, so-called playback jitter.

FIG. 7(a) is a diagram conceptually showing a state in which four-value recording has been performed on a recording portion of an information recording medium.

Here, the recording information (
It corresponds to "3", "2", and "1" of four-value information), and when it is "0", no recording mark is formed. In addition, FIG. 7(b) is a diagram showing recording pulses when forming recording marks as shown in FIG. 7(a), and FIG.
c) is a diagram showing the timing of the output of the light beam output means. When using a heat mode optical disc, the larger the energy of the light beam during recording, the larger the area of the recording mark. Therefore, as can be seen from FIGS. 7(a) and 7(b), the larger the signal level of the recording pulse, the larger the area of the recording mark.

When such recorded information is reproduced using a photoelectric conversion element of an information reproducing apparatus, a reproduced waveform as shown in FIG. 7(d) is obtained. Therefore, if 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) above, the result is shown in FIG. 7(e). It becomes like that. In this way, in the case of multilevel recording, the waveform of the demodulated clock changes depending on the signal level of the recording pulse. Therefore, the deviation from the recording pulse becomes large, and the reproduction jitter becomes large. If the reproduction jitter is large as described above, it becomes impossible to accurately reproduce recorded information when the voltage value of the reproduced waveform is captured in accordance with the timing of this demodulation clock.

The present invention has been attempted in view of the problems of the prior art, and aims to suppress reproduction jitter that occurs when reproducing information recorded on an information recording medium by multilevel recording to a range that does not cause any practical problems. An object of the present invention is to provide an information reproducing device that can accurately reproduce recorded information.

[Structure of the Invention] (Means for Solving the Problems) An information reproducing apparatus of the present invention is an information reproducing apparatus that reproduces information recorded on an information recording medium by multilevel recording, and is an information reproducing apparatus that reproduces information recorded on an information recording medium by multilevel recording. a beam output means; an optical system that focuses the light beam outputted by the light beam output means on a recording site of the information recording medium; optical property detection means for outputting an electrical signal according to the characteristics of the optical property; sampling means for sampling the electrical signal output by the optical property detection means at a predetermined demodulation clock; and sampling means for sampling the electrical signal sampled by the sampling means. and reproduced signal generating means for detecting a peak value and outputting the reproduced signal.

(Function) The information reproducing device of the present invention samples the electrical signal output from the optical characteristic detection means using a demodulation clock, detects the peak value of this electrical signal, and reproduces the recorded signal based on the peak value. It is. The timing at which the voltage value of the electrical signal output from the optical characteristic detection means reaches its peak value is at approximately constant intervals regardless of the waveform of the electrical signal (that is, regardless of the size of the recording mark). By sampling the electrical signal using a demodulated clock and detecting the peak value, it is possible to suppress reproduction jitter to a range that does not cause any practical problems.

(Example) Hereinafter, one embodiment of the present invention will be described.

Here, the information reproducing apparatus of the present invention is applied to an information recording and reproducing apparatus for recording multi-value information on an information recording medium (here, an optical disk) and reproducing the recorded multi-value information in an electronic filing system. will be explained using an example.

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

When recording information with such a device, first,
A recording signal processing device 10 converts an information signal input from a control circuit (not shown) of an electronic filing system into a multi-level signal (that is, converts it into a multi-value signal), and converts this multi-value processed signal into a semiconductor laser. Output to 11. The semiconductor laser 11 irradiates a recording laser beam with energy or wavelength depending on the signal level of the processed signal output from the recording signal processing device 10. Here, in order to change the energy of the laser beam in multiple stages according to the signal level, it is sufficient to change the intensity or pulse width of the light beam, or both, or to change the wavelength of the light beam. . By irradiating the recording layer of the information recording medium (optical disk) 20 with a laser beam having energy or wavelength corresponding to the signal level through the optical system 30, the laser beam is applied to the irradiated portion of the information recording medium 20. A recording mark is formed by a change in state depending on the energy or wavelength (that is, depending on the signal level), and multi-level information is recorded.

Furthermore, when reproducing the multivalued information recorded in this way, the semiconductor laser 11 described above is connected to the information recording medium 2.
A reproducing laser beam with a constant wavelength and low energy so that no state change occurs in the irradiated portion of 0 is output. The reproduction laser beam output from the semiconductor laser 11 is irradiated onto the information recording medium 20 via the optical system 30,
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 electrical signal. This electrical signal is transmitted to the processing circuit 14
The signal is guided to the reproduced signal processing device 40 via. The reproduced signal processing device 40 reproduces multivalued information from the input electrical signal and outputs it to a control circuit (not shown).

Note that when the information recording medium 20 is of a write type, such as a phase change type, a laser beam with a lower intensity than that during recording is output from the semiconductor laser 11, and this laser beam is passed through the optical system 30. Information can be erased by irradiating the information recording medium 20 and changing the recording layer in this portion to the state before recording. In addition, if the information recording medium 20 is of a type that allows override, the signal level is set according to the light intensity at the time of override when the information signal inputted to the recording signal processing device 10 is multivalued. Then, overriding is performed by outputting a recording laser beam of energy or wavelength corresponding to this signal level from the semiconductor laser 11 and irradiating the information recording medium 20 via the optical system 30.

In the optical system 30 , the diverging laser beam output from the semiconductor laser 11 is converted into a parallel beam by a collimator lens 31 and guided to a beam splitter 32 .

The beam reflected by the beam splitter 32 is condensed and irradiated onto the information recording medium 20 by a condensing lens 36 . During reproduction, a portion of the laser beam irradiated onto 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 passed 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 34.

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 is also guided to the tracking control device 19 via the amplifier circuit 16, where it is converted into a beam. The irradiation position is used as correction data for optimization. In addition, photoelectric conversion element 1
The signal output from 3 is guided to the focusing control device 18 via the processing circuit 15 and the amplification circuit 17.
Used as data for focus control.

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

In this embodiment, it is assumed that four-value 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 10
3. Input data (information signal) is input in a binarized state, that is, as a binary signal, and this signal is first converted into information in units of 4 bits, that is, 4-valued data, in a 4-value conversion circuit 101. . This quaternary data is converted into a signal with one of four signal levels of "0", "1", "2", and "3" in the modulation circuit 102, and is sent to the semiconductor laser drive circuit 103 as a recording pulse (voltage). pulse) applied as rel. This modulates the intensity of the light beam in four stages depending on the recording signal. Moreover, the modulation circuit 10
2 modulates the recording pulse according to a predetermined modulation clock so that recording is performed at a constant recording timing.

Next, the reproduced signal processing device 40 will be specifically explained.

FIG. 3 is a block diagram showing a schematic configuration of the reproduced signal processing device 40. As shown in FIG. As described above, the reproduction signal processing device 40 receives the electrical signal from the processing circuit 14 and outputs a reproduction signal corresponding to the information recorded on the information recording medium 20.

Further, as shown in FIG. 3, this reproduced signal processing device 40 includes a low-pass filter (LPF) 401 that removes high frequency components of an electrical signal manually inputted from the processing circuit 14, and an electrical signal outputted from an optical characteristic detection means. A sampling circuit 402 samples the electrical signal using a predetermined demodulation clock, and a reproduction signal generation circuit 403 detects the peak value of the electrical signal sampled by the sampling circuit 402 and outputs the reproduction signal.

The signal processing in this reproduced signal processing device 40 will be explained below with reference to FIGS. 4(a) to 4(e).

FIG. 4(a) is a diagram conceptually showing a state in which four-value recording has been performed on the recording portion of the information recording medium 20. In the figure, the shaded areas are recording marks. Moreover, FIG. 4(b) is a diagram showing the output pulses (recording pulses) of the recording signal processing device 10 when forming recording marks as shown in FIG. This corresponds to multivalued information recorded in 20. Note that, as described above, when using a heat mode optical disk, the larger the signal level of the recording pulse, the larger the area of the recording mark.

FIG. 4(c) is a diagram showing an example of a demodulated clock.

In this embodiment, it is assumed that a demodulation clock corresponding to a modulation clock during recording is generated in synchronization with a reproduction signal. Moreover, FIG. 4(d) shows the signal when the signal photoelectrically converted by the photoelectric conversion element 12 is taken into the reproduction signal processing device 40 via the processing circuit 14 and the high frequency component is removed by the LPF 401 during reproduction of multilevel information. This shows the signal waveform (reproduced waveform). In this way, the reproduced waveform changes depending on the area of the corresponding recording mark.

Here, in the sampling circuit 402, as shown in FIG.
) is sampled at a predetermined sampling time using the rising edge of the demodulation clock shown in FIG.
When the peak value of the sampled reproduced waveform is detected in step 03, this peak value differs depending on the width of the reproduced waveform, that is, the area of the corresponding recording mark. Therefore, by detecting this peak value, the value recorded on the information recording medium can be determined.

In this way, by generating a reproduction signal (multilevel information bit) as shown in FIG. 4(e), the influence of reproduction jitter can be removed, so that recorded information can be reproduced faithfully. It's coming. When generating multilevel information bits from the peak values of the reproduced waveforms, the signal level of the multilevel information bits may be set to be proportional to the peak values of the reproduced waveforms, or other methods may be used. . For example, three types of slice levels SI 52 are set for the peak value of the reproduced waveform.
, S3 (Sl < 52 < 53), and if the peak value is less than 81, "0", if it is 81 or more and less than 82, "1", if it is 82 or more and less than 53, "2", 83
If it is above, it may be set to "3".

Note that the pulse width of the demodulated clock is the reproduced signal waveform of the recording mark with the smallest level of the reproduced signal excluding the non-recorded portion (here, the recording mark corresponding to "1" of multi-level information)
It is desirable that the pulse width be smaller than the pulse width of .

Further, here, high-frequency noise of the electrical signal input from the processing circuit 14 is removed by the LPF 401, but this processing does not necessarily need to be performed.

Furthermore, in order to make the recording pulse correspond to the demodulation clock, we decided to generate the demodulation clock using the modulation clock for modulating the recording pulse. Of course, the demodulated clock may be generated using bits. That is, in addition to the recorded information to be reproduced, multi-value information as a clock bit is transmitted to the information recording medium 2.
0, a demodulated clock is generated from this multi-level information as a clock bit using the clock generation circuit 403 as described above, and the above-mentioned "recorded information to be reproduced" is reproduced using this demodulated clock. It may also be a thing.

Additionally, a synchronization bit may be stored in the information recording medium in advance, and the demodulated clock and the reproduced signal may be synchronized using this synchronization bit.

Also, it is preferable to use the rising edge of the demodulation clock as a trigger for sampling the reproduced waveform.
It is also possible to use other timings, such as the falling edge. On the other hand, the sampling time may be sufficient as long as it is sufficient to detect the peak of each multilevel level of the reproduced waveform.

Therefore, in this embodiment, a certain amount of jitter margin can be provided between the demodulated clock and each multilevel signal peak.

Next, the information recording medium 20 will be explained in detail. Note that a phase change type optical disc will be explained here as an example. FIG. 5 is a sectional view showing the layer structure of this optical disc. As shown in FIG. 5, this optical disc includes an optical disc substrate 201, a first protective layer 202, a recording layer 203,
, a second protective layer 204, a reflective layer 205, and a third protective layer 206.

As a material for forming the optical disk substrate 201, a material that is transparent and has little change over time is suitable. Examples include acrylic resin such as polymethyl methacrylate, polycarbonate resin, epoxy resin, styrene resin, or glass. Furthermore, continuous grooves, sample servo marks, preformat marks, etc. are formed on this optical disk substrate 201 depending on the recording format.

The recording layer 203 is made of a material whose state changes when irradiated with a light beam. Examples of such materials include GeTe, TeSe, and Ge5bSe.
Examples include chalcokenide-based amorphous semiconductor materials such as TeOx-based, InSe-based, Ge5bTe-based, and compound semiconductor materials such as InSb-based, GeSb-based, and In5bTe-based.

This recording layer 203 can be formed by a vacuum deposition method, a sputtering method, or the like. Further, the film thickness of this recording layer 203 is practically suitable 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 upper and lower surfaces of the recording layer 203, 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 scattering or holes in the recording layer 203 due to laser beam irradiation, for example. First protective layer 20
2 and the second protective layer 204 are as follows:
For example, S I O2, S 10, AgN.

A1203, Zr02s TiO2, Ta, +03
. Note that the film thicknesses of the first protective layer 202 and the second protective layer 204 are practically
Several nanometers to several micrometers are suitable.

The reflective layer 205 enhances changes in the characteristics of reflected light due to changes in the optical characteristics of the recording layer 203, and
This is provided to prevent the temperature of the recording layer 203 from rising by cooling the recording layer 203 (that is, by absorbing and dissipating the heat of the recording layer 203). The material forming this reflective layer 205 is, for example, Au5AI.
SCu, Ni-Cr, or the like is suitable, and can be formed using such a material by, for example, a vacuum evaporation method or a sputtering method. Note that the thickness of the reflective layer 205 is suitably several nanometers to several micrometers in practice.

The third protective layer 206 protects against scratches from handling the optical disc.
This is provided to prevent lumps, etc. Further, as a forming material, an ultraviolet curable resin or the like is usually used. For example, the ultraviolet curable resin is applied to the surface of the reflective layer 205 by a spin code method and then cured by irradiation with ultraviolet rays. This third protective layer 20
The film thickness of No. 6 is practically suitable in the range of several μm to several hundred μm.

When recording multivalued 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. This cooling rate can be controlled by appropriately selecting the materials and film thicknesses of the first protective layer 202, recording layer 203, second protective layer 204, and reflective layer 205. For example, if you want to increase the cooling rate, you can reduce the thickness of the recording layer 203, use a material with high thermal conductivity as the material for forming the reflective layer 205, and It is effective to use a material with high thermal conductivity as the material for forming the protective layer 204.

Furthermore, when recording multilevel information on an optical disk, it is also effective to devise a profile of the output pulse of the semiconductor laser 11 during recording.

Although an example of the configuration of an optical disc that allows recording on only one side has been described here, it is also possible to configure the optical disc so that recording can be performed on both sides. A double-sided recording optical disc can be obtained, for example, by laminating two optical discs shown in FIG. 5 with the recording layer 203 facing inside.

Furthermore, the first protective layer 202, second protective layer 204, reflective layer 205, and third protective layer 206 shown in FIG.
It may be omitted depending on the application.

As described above, although the present embodiment has been described with reference to the case of reproducing multilevel information recorded on a phase change type optical disc, the information reproducing apparatus of the present invention is not limited to such a case.
A similar effect can be obtained when reproducing multilevel information recorded on an optical disk made of an organic material, a shape-changing material, a perforated material, or a composite material thereof. Similar effects can be obtained when reproducing multivalued information recorded on other information recording media.

[Effects of the Invention] As explained in detail above, the information reproducing apparatus of the present invention can eliminate the influence of reproduction jitter that occurs when reproducing information recorded on an information recording medium by multilevel recording. The recorded information can be reproduced accurately.

[Brief explanation of drawings]

Sasa Figure 1 is a schematic configuration diagram showing an information reproducing device according to an 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. 4(a) to (e) 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. A schematic cross-sectional view showing the layer structure of an example of the information recording medium shown in FIG. 1, and FIG.
a) to FIG. 6(d) and FIG. 7(a) to FIG. 7(e)
FIG. 2 is a diagram for explaining signal processing of a conventional information reproducing device. 10... Recording signal processing device, 11... Semiconductor laser, 12.13... Photoelectric conversion element, 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
...Huff Mirror 3435...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 protective layer, 203... Recording layer, 2
04... Second protective layer, 205... Reflective layer, 206
...Third protective layer, 401...Low pass filter (
LPF), 402... sampling circuit, 403...
...Reproduction signal generation circuit. Applicant's agent Patent attorney Takehiko Suzue

Claims (1)

[Claims] An information reproducing device for reproducing information recorded on an information recording medium by multilevel recording, comprising a light beam output means for outputting a light beam, and a light beam outputted by the light beam output means. an optical system that focuses the light beam on a recording site of the information recording medium; and an optical characteristic detection means that receives the light beam reflected at the recording site and outputs an electrical signal according to the optical characteristic of the recording site. Sampling means for sampling the electrical signal output by the optical characteristic detection means at a predetermined demodulation clock, and reproduction signal generation means for detecting the peak value of the electrical signal sampled by the sampling means and outputting the reproduction signal. An information reproducing device comprising: