Optical disk reproducing device

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to a disc device, and more particularly to a mark edge recording type optical disc playback device.

【0002】

[Previous technology]

There are two types of recording methods for optical disks such as magneto-optical disks: mark pit recording method and mark edge recording method. In the mark pit recording method, the NRZ code used for information processing is recorded on the optical disc as it is (1 has pits and 0 has no pits), so there are few errors, but when 1 continues, it is adjacent to 1. Since it is necessary to electrically classify 1 , there is a drawback that the recording density cannot be increased.

【0003】

On the other hand, in the mark edge recording method, the NRZ code is converted to a code in which "1" is not continuous (for example, 1/7 byte code), the edge position of the pit corresponds to "1", and the distance between edges corresponds to zero. It is a recording method that allows the number of zeros to be determined according to the length between "1" and "1". According to this method, the recording density can be increased by increasing the frequency of the drive clock, so that the mark pit method is being used in place of the above-mentioned mark pit method.

【0004】

However, when this method is used, the position of "1" and the lengths of "1" and "1" correspond to the recorded data and the reproduced data, so that the arrangement state of "1" and "0" of the recorded data can be changed. It is necessary not only to accurately reflect the recording state on the disk surface, but also to electrically and accurately reproduce the recorded edge position of the pit.

【0005】

When recording with the mark edge recording method, when the medium is irradiated with a laser beam of a predetermined power (level 1), as shown in Fig. 6 (b), the space between 1 and 1 is simply shown in Fig. 6. Since the domain Ds formed as shown in (a) is far from the ideal state Dp, the pulse train method shown in FIG. 7 is used.

【0006】

That is, as shown in Fig. 7 (c), when no pits are formed, the output of the writing laser is held at an extremely low assist level (level 0), and when pits are formed, it is relatively high enough to form pits. It shifts to a level (level 1) (about 2/3 of level 3 described later) and longer (3/2 cycle of the drive pulse shown in Fig. 7 (b)), and then higher and shorter (about 2/3 of the drive pulse). Writing is performed with a pulse (level 2) (1/2 cycle). According to this method, as shown in Fig. 7 (a), domain Ds having a shape relatively close to the ideal domain Dp shape is formed, and the consistency between the recorded data and the recorded domain can be maintained.

【0007】

FIG. 8 is a block diagram showing an example of a mark edge recording type optical disc playback device. Optical disk 1 For example, the reflected light from a magneto-optical disk is converted into an electric signal by an optical detector (not shown) provided in the optical head 11, then amplified by an amplifier 12, and further obtained by a low-pass filter 13 to obtain a signal envelope. Then, the analog signal as shown in FIG. 9A is obtained, the peak level and the bottom level of the analog signal obtained from a predetermined track (or a specific time) are confirmed, and the values are held in the peak bottom holder 14. Then, slice the intermediate value to the slice level L.₀To determine as. Then, in the binarization circuit 15, as shown in FIG. 9 (b), the slice level L₀The higher part is set to 1 and the lower part is set to 0 (binarized), and as shown in FIGS. 9 (c) and 9 (d), the rising and falling edges of the above binarized signal are set. Obtain the dual data (PDATA) and (NDATA) to be displayed. By ORing this dual data, the reproduced data of the recorded data can be obtained, and the signal thus obtained is decoded into the NRZ data required for normal data processing by the decoder 16 and used. become.

【0008】

[Problems to be Solved by the Invention]

As described above, the mark edge recording method is advantageous in that the recording density is high, but the position of "1" represented by the recording signal and the interval between "1" and "1" are recorded so as to correspond to the recording signal. It needs to be done and regenerated.

【0009】

By the way, when only a predetermined type of optical disc of a predetermined manufacturer is used, the optimum recording conditions with few errors can be uniquely determined, but the thickness of the material, magnetic film, etc. used for the optical disc is determined by the manufacturer. The state of the pits formed is slightly different depending on the type and manufacturer of the optical disc, even if each level (level 0 to 2) of the laser beam during recording by the above pulse train method is the same. The optimum write conditions cannot be uniquely determined.

【0010】

That is, according to the pulse train recording method, it is necessary to adjust each of the levels of the laser beam in the above three stages in order to obtain an appropriate recording, and it takes time to determine an appropriate light power.

【0011】

On the other hand, various methods for reducing reproduction errors on the reproduction side have also been proposed. For example, Japanese Patent Application Laid-Open No. 3-91135 proposes a method of determining the amplification factor of the amplifier circuit and the delay amount of the delay circuit to the optimum state according to the reproduction state. It also has a change in the reproduced waveform corresponding to (a), and it cannot be dealt with by a simple idea that, for example, increasing the amplification factor reduces the error rate, and it is necessary to adjust the two factors of the delay amount and the amplification factor. , Further processing becomes complicated.

【0012】

Further, in the above-mentioned conventional configuration, when determining the slice level at the time of binarization, the midpoint between the peak level and the bottom level of the analog data reproduced from a specific track is taken. However, the method of simply taking the midpoint in this way is the data in which the domain part and the non-domain part are relatively uniformly distributed as shown in Fig. 10 (a) or (b) (1/7 data in this case). In the case of), the fluctuations of the slice levels La and Lb are small, and the error rate is small, but as shown in Fig. 10 (c), the density of the domain-forming portion is high, and the density of the domain-forming portion is low. If it changes, it may cause fluctuations in the slice level Lc, and this fluctuation in the slice level will increase the error rate.

【0013】

The present invention has been proposed in view of the above-mentioned conventional circumstances, and an optical disc reproduction device capable of more accurate reproduction with less error rate by optimizing the slice level at the time of reproduction of the optical disk device. It is intended to be provided.

【0014】

[Means for solving problems]

In general, the error rate when slicing analog playback data as shown in Fig. 5 at each level of A, B, C, D, and E, which gradually increases, becomes a parabolic curve as shown in Fig. 4, and the curve. At the tip of, and the error rate is 10^-6Ideally, the slice level is set as follows, and this slice level does not necessarily coincide with the midpoint between the peak level and the bottom level of the reproduced signal described above. Therefore, the midpoint between the peak level and the bottom level is level P.₀When was, the correction value V₀It is necessary to add the offset of to the optimum slice level C.

【0015】

FIG. 1 is a principle block diagram for obtaining the optimum slice level C. As described in FIG. 8, an analog reproduction signal is input to the binarization circuit 15 of the reproduction means 10, and the midpoint between the peak level and the bottom level of the analog reproduction signal is input as a slice level. ing. Further, in the present invention, the slice level changing means 20 inputs an offset value for changing the slice level to a plurality of stages to the binarization circuit 15, and a specific pattern predetermined by the plurality of slice levels is input. Is read.

【0016】

Then, the error rate calculation means 30 calculates the error rate for the reproduction / demodulation signal read for each of the slice levels. In the slice level correction means 40, the upper and lower limits of the slice level equal to or less than the permissible value are obtained from the error rates calculated in this way, and the midpoint thereof is set as the optimum slice level. When the optimum slice level is determined in this way, a correction value (offset value) for the slice level from the peak bottom holder 14 corresponding to the optimum slice level can be determined and input to the binarization circuit.

【0017】

When the upper and lower margins of the slice level whose error rate is equal to or less than the allowable value are wide, the narrower the margin, the easier it is to determine the optimum slice level. Therefore, the reproduction condition control means 50 intentionally forms a reproduction signal having a bad error rate by changing the transmission frequency of the low-pass filter (not shown) of the reproduction circuit or the boost value of the electronic filter (not shown), and the above margin. To make it easier to determine the optimum slice level.

【0018】

[Embodiment]

FIG. 2 is a functional block diagram showing an embodiment of the present invention, and FIG. 3 is a flow diagram showing an operation procedure thereof.

【0019】

First, when the power is turned on, the initial setting means 60 of the MPU 100 operates, and default values such as the amplification factor of the amplifier 12 corresponding to the optical disk 1 originally supported by the optical disk device and the transmission frequency of the low-pass filter 13 are set. To do. Of course, at this time, not only the playback system but also the default value of the recording system (that is, the assist level shown in FIG. 7, the three levels of level 1 and level 2, etc.) is set (Fig. 3, step S1).

【0020】

When the optical disk 1 is mounted on the disk device, the medium determination means 70 determines whether or not the optical disk is of the type supported by the device (FIG. 3, step S2). Here, if the device supports the optical disc 1, recording / playback is performed according to the above default value.

【0021】

If the optical disc is not supported, the write control means 80 is activated to write a specific pattern stored in the test pattern memory 90 to a predetermined area of the optical disc (FIG. 3, step S3). The above assist level at the time of this writing, or the writing conditions such as level 1 and level 2 (see FIG. 7) follow the default values. Also, here, write a pattern with the highest error rate as shown in Fig. 10 (c).

【0022】

When this writing is completed, the reproduction control means (not shown) is activated, the reproduction laser of the optical head is turned on, and the written test pattern is test-leaded. At this time, the operation of each circuit of the reproduction means 10 is the same as that of the conventional case shown in FIG. 8. From the peak bottom holder 14, the peak level and the center value of the bottom level of the analog reproduction signal are binarized as the slice level. It has been entered.

【0023】

Further, in the present invention, the slice level changing means 20 of the MPU 100 is activated during the reproduction, and the offset value is set to two values with respect to the slice level input from the peak bottom holder 14, for example, so as to be level A in FIG. Input to the conversion circuit 15 and try to reproduce at the slice level A (Fig. 3, step S4). The binarized signal obtained in this way is converted into the dual data shown in FIGS. 9 (c) and 9 (d), and converted into the NRZ data required for information processing by the decoder 16.

【0024】

The error rate calculation means 30 calculates the error rate Era by comparing it with the test pattern stored in the test pattern memory 90 in advance at the output of the decoder 16, and stores this result in the register Ra together with the slice level A ( Figure 3, step S5). Next, the error rate Erb is calculated in the same manner as above at the slurry level B higher than the above level A, and stored in the register Rb. In this way, while increasing the slice level sequentially from A to B to C to D to E, the error rates Era, Erb, Erc, Erd, and Ere at each slice level are set to the corresponding registers Ra, Rb, Rc, Rd, and so on. Store in Re (Fig. 3, step S4 S5 S6 repeated).

【0025】

Next, the slice level means 40 compares the error rates stored in the registers Ra to Re, and determines the upper limit value and the lower limit value of the slice level whose error rate is equal to or less than the allowable value (FIG. 3, step S7).

【0026】

Further, the value between the upper limit value and the lower limit value is set as the optimum slice level, and the correction value in which the midpoint between the peak level and the bottom level output from the peak bottom holder 14 is the optimum slice level is set as the offset value with respect to the midpoint. Offset value Stored in memory 41. As a result, the optimum slice level is obtained (Fig. 3, step S9), and in the subsequent normal playback, the above correction value is always applied to the midpoint between the peak level and the bottom level output from the peak bottom holder 14. Playback is done at the offset slice level.

【0027】

The optimum slice level can be determined as described above, but even if the test pattern has a high error occurrence rate, the actual error rate will differ depending on the type of medium. Therefore, in the curve shown in FIG. 4, the margins between the upper limit value and the lower limit value of the slice level (Fig. 4, margin V).₁(See) will vary from medium to medium, and if this margin is wide, the curve will also be gentle and it may be difficult to determine its central level.

【0028】

Therefore, the reproduction condition control means 50 changes the set value of the electronic filter 17 to change the boost value to create a waveform in which an error is likely to occur, and narrows the range of the upper and lower limit levels. Instead of changing the boost value of the electronic filter 17 as described above, the transmission frequency of the low-pass filter 13 may be changed (FIG. 3, steps S8 S10).

【0029】

When the slice level and other read conditions are determined for the specific type of optical disc as described above, the conditions are stored in the storage means together with the type of the optical disc, and are used as the determination conditions in the medium determination means 70. Here, when the optimum slice level has been determined by test writing in the past and the medium is not the medium for which the default value is set in the step S1, the default value written in the step S1 is usually rewritten. Perform processing (Fig. 3, step S10 S11).

【0030】

If the procedure for calculating the error rate and determining the correction value (offset value) described above is performed based on the calculation of the error rate a plurality of times, more accurate reproduction can be performed. Further, the optimum slice level is set as the midpoint between the upper limit value and the lower limit value of the slice level whose error rate is equal to or less than the permissible value. The slice level corresponding to the lowest error rate of the curve may be found.

【0031】

[Effect of the invention]

As described above, in the reproduction of an optical disc, the present invention determines the slice level for an analog signal by correcting the midpoint between the peak value and the bottom value of the analog signal so that the error rate is the lowest. Moreover, since the slice level is determined for each type of optical disc, it is possible to ensure a playback state with few errors at all times even if different types of optical discs are used.

[Simple explanation of drawings]

[Figure 1]

It is a principle block diagram of this invention.

[Figure 2]

It is a functional block diagram of 1 Example of this invention.

[Fig. 3]

It is a flow chart which shows the procedure of this invention.

[Fig. 4]

It is a graph which shows the relationship between an error rate and a slice level.

[Fig. 5]

It is a relationship diagram of an analog reproduction signal and a slice level.

[Fig. 6]

The recording domain of an optical disc.

[Fig. 7]

The recording domain of an optical disc.

[Fig. 8]

It is a conventional functional block diagram.

[Fig. 9]

It is a waveform diagram of FIG.

[Fig. 10]

It is a relationship diagram of NRZ code, 1/7 byte, recording pattern, and reproduction analog signal.

[Explanation of symbols]

1 optical disc 10 Reproduction means 20 Slice level change method 30 Error rate calculation method 40 Slice level correction means and 50 Playback condition control means