JP2637603B2 - Optical information recording / reproducing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention expresses and recognizes a plurality of pieces of information in one pit based on the difference in the amount of reflected light or transmitted light from a pit recorded on an optical recording medium. The present invention relates to an optical information recording / reproducing method which can be performed.

2. Description of the Related Art Conventionally, when information is recorded using light and when the recorded information is read, an optical recording medium used is in the form of a disk, card, or tape.
Some of these optical recording media can be recorded and reproduced, and others can be reproduced only.

At the time of reproduction, information is recorded on the medium by narrowing a light beam modulated in accordance with the recording information to a minute spot so as to form an optically detectable information pit row, and scanning the information track. Have done. Also,
Reproduction of information is realized by scanning an information track with a light beam spot having a constant power that does not allow recording on the medium, and reading the light with a difference in the amount of reflected light or transmitted light from the information bit string. I have.

In this case, the size of the light beam spot on the recording medium is controlled by an auto-focusing (AF) control unit, and the displacement of the information track arrangement is controlled by an auto-tracking (AT) control unit. In order to use such a control means, the size of the light beam spot is naturally restricted, and the size and pitch of the information pit row generated by the light beam spot are determined. Normally, the signals handled here are binarized, but the information capacity of one recording medium is determined by the size and pitch of the information pit row, and this is an obstacle to high density. It has become.

[Problems to be Solved by the Invention] Therefore, in order to optically recognize a plurality of recording states, one pit expresses a plurality of information. It has been proposed that multi-level recording be performed by recording on the recording medium. This can be expressed by generating each pit so that when a light spot is provided on a recording medium, the amount of reflected light or the amount of transmitted light is different.

FIG. 4 shows the difference between the amplitude of the reproduction signal corresponding to the recording power of the laser beam, in other words, the difference in the amount of reflected light or transmitted light. As is apparent from the figure, no pits are formed on the recording medium where the power of the laser beam does not reach a certain threshold A, and although it is non-linear from the point beyond the threshold A to the point B position, The reproduction signal level increases with the increase of the value. And
Beyond point B, a so-called saturated region where the amplitude of the reproduced signal hardly changes even when the laser power is changed.

Focusing on such characteristics, consideration is given to the signal-to-noise ratio (S / N) in the region from point A to point B, and up to what value accurate quantization (multi-level quantization) can be realized. Have been. At this time, by generating a pit using the divided slice level as a recording condition, multi-value information can be applied to one pit.
It is possible to realize high-density recording on one recording medium. That is, for example, when N recording states are created, log ₂ N
That is, the density is doubled. FIG. 5 shows the recording pit row 3 generated in this manner.
Here, in order to simplify the description, the case of quaternary recording is illustrated. That is, two bits of binary data correspond to one pit (“0” = (0
0), “1” = (01), “2” = (10), “3” = (11)).
Therefore, in the example of the illustrated pit example, the binary data represented by (123033001) is (011011001111000001). The reproduced signal waveform generated corresponding to this is as shown in FIG. 5 (b). Here, the small dent in the reproduced signal in the portion where "3" is continuous is caused by the presence of an unrecorded portion in the width direction generated in the portion where each figure pit is in contact.

However, as shown in FIG. 5 (b), when adjacent pits are in different recording states, the boundary of the pits can be determined as an edge on the reproduced signal, and the self-clock signal can be generated using this as an edge signal. However, when unrecorded states continue or pits in the same recorded state continue, edge signals are not detected for a long time during reproduction, and it becomes difficult to generate a self-clock signal.

In order to realize multi-level recording, the present applicant separately records an unrecorded area where no optical recording is performed between recording pits so as to leave at least an optically recognizable area. In addition, an optical information recording / reproducing method capable of reliably generating a self-clock signal and facilitating reproduction is proposed. Here, as shown in FIG. 6, the binary data to be recorded (see FIG. 6 (a)) is multi-valued (here, FIG. 6 (b)) weighted by the density of each recording bit.
Is recorded as four-valued) data. FIG. 6 (c) shows the amount of reflected light or the amount of transmitted light when reproduced with a light beam spot. The amount of reflected light is inversely proportional to the density of pits (the higher the density of pits, the smaller the amount of reflected light) ). By detecting the amount of reflected light or the amount of transmitted light at the positions of a plurality of thresholds, multi-value is realized. In addition, even if the signal at the same level continues, there is an unrecorded area between the recording pits, and each signal is divided into positions, so that the self-clock signal can be easily generated. This clock signal is generally generated by detecting a fundamental wave number component contained in the data signal and using a PLL circuit.

Here, the problem is that the size of the pits is usually set to the minimum value that can be detected optically in order to increase the recording density on the recording medium. The unrecorded area of becomes the size corresponding to this,
The density in the track direction is restricted to half the size including the unrecorded area. This greatly affects the multiplicity of each pit.

[Purpose of the Invention] The present invention has been made based on the above circumstances, and when multi-leveling is realized, a self-clock signal is reliably generated to facilitate reproduction, and at the same time, the number of pits in each pit is reduced. It is an object of the present invention to provide an optical information recording / reproducing method capable of achieving sufficient recording sophistication even when the multiplicity is kept low.

[Means for Solving the Problems] For this reason, according to the present invention, information is recorded on an optical recording medium in which a plurality of information is expressed per recording pit so that a plurality of recording states can be optically recognized. In the reproducing method, each recording pit is recorded in a recording state that can be recognized at a plurality of slice levels in the unsaturated state, and the length of each recording pit and the interval provided between each recording pit are determined. The length is used to represent a plurality of recording states, and the recording state of the recording pits, the length of the recording pits, and the length of the interval between the recording pits are determined by a predetermined conversion rule. Are determined in accordance with the different arrangements of the plurality of pits of the binary data in accordance with
Reading a signal modulated by recording pits from the recording medium; comparing the read signal with each of the plurality of slice levels; and determining a smallest one of the plurality of slice levels. Creating a clock signal from a signal indicating the result of the comparison with the read signal; and determining a length of a recording pit and an interval between recording pits from the read signal based on the created clock signal. Through the process of detecting the length of
As a result of the comparison with the plurality of slice levels, the arrangement of the binary data corresponds to the length of the detected recording pit and the length of the interval between the detected recording pits based on the predetermined conversion rule. By doing so, the information is reproduced.

[Operation] Therefore, since there is always a constant level (non-recording level) interval between the recording pits, it can be used to generate a self-clock signal. In addition, the length of each recording pit and each Since the information is expressed by the difference in the length of the interval between the recording pits, the above-mentioned interval can be used effectively, and the recording pit can express information by both the slice level and the pit length,
Sufficient high-density recording can be realized.

Embodiment An embodiment of the present invention will be specifically described below with reference to FIGS. 1 to 3. FIG. 1A shows an example of binary data recorded by the optical information recording / reproducing method of the present invention. FIG. 1 (b) shows the binary data obtained by multi-value recording by the reproducing method of the present invention, and the numerical value in the square frame indicates the density of each pit. The binary data string is 2
Separated for each bit, 3n + 1th (n = 0,1,2 ...)
Is converted according to the density of the pits, the 3n + 2nd set is converted according to the length of the pits, and further, 3n +
The third set is converted according to the length of the interval between pits. When multi-leveling is performed according to the density of each pit,
As in the case shown in the figure, this corresponds to the number of thresholds. That is, the signal levels correspond to “0” for “00”, “1” for “01”, “2” for “10”, and “3” for “11”. When multi-valued according to the pit length and the interval length between pits, conversion is performed as shown in the following table.

The pit length shown here indicates the length between both edges of the pit, and the pit interval indicates the length of an unrecorded area between the edges of the pit.

The present invention requires a 1-2.5 bit length to divide the binary data string into 6 bits and indicate the first 4 bits,
One to 2.5 bits are needed to indicate the last two bits. Since the generation probabilities of data “00” to “11” are all equal,
The average value required to represent 6 bits is 3.5 bits,
The high-density recording is about 1.7 times higher than the multi-valued recording shown in FIG.
In addition, since the unrecorded areas are alternately generated as information, the advantage that the generation of the self-clock signal can be ensured can be maintained.

FIG. 2 is a block diagram of a modulation circuit according to the embodiment of the present invention. Here, the binary data is temporarily stored in the buffer memory 1, and the MPU 2 sends a signal to the down counter circuit 3 when the information in the buffer memory 1 is in an unrecorded state.
At other slice levels, a signal corresponding to this is output to the D / A converter 4. When the count value becomes zero, the down counter circuit 3 issues a carry signal Cy to the MPU 2. Further, the down counter circuit 3 receives a clock signal (HCLK) with respect to its clock input terminal.
The above clock is a half cycle of the time corresponding to one pit width,
That is, the frequency is set to twice the fundamental frequency. The digital signal from the MPU 2 is converted into an analog value via the D / A converter 4 and input to the LD driver 5. The LD driver 5 supplies a current corresponding to the semiconductor laser (LD) 6 based on the input value to emit light.

Thus, the binary data to be modulated is stored in the temporary buffer memory 1 and read out by the MPU 2 every 6 bits. The 6 bits read to the MPU2 are divided into three every two bits, a value obtained by adding 2 to the value of the second two bits is loaded into the counter 3, and the first two bits are subjected to D / A conversion. The output of the LD 6 is controlled according to the binary data, and the pit density is changed. On the other hand, the counter 3 counts HCLK, and outputs a carry signal Cy to the MPU 2 when the count value becomes zero. MPU2 is the carry signal Cy
Is received from the counter 3, the input to the D / A converter 4 is stopped, and a value obtained by adding 2 to the third 2-bit value is loaded into the counter 3. After that, the MPU 2 reads the next 6 bits from the buffer memory 1. Since HCLK is a clock having a frequency twice as high as the fundamental frequency, the value loaded to the counter 3 is in the range of 2 to 5 based on binary data. Therefore, considering this as a unit of one pit length, HC
Since one of the LKs has 1/2 pit, a pit length or pit interval of 1 to 2.5 can be obtained.

The counter 3 counts HCLK as described above, and outputs a carry signal Cy to the MPU 2 when the count value becomes zero,
Upon receiving the carry signal Cy, the MPU 2 loads the counter 3 with a value obtained by adding 2 to the value of the second 2 bits of the next 6 bits previously read and placed, and also loads the first 2 bits.
The bits are input to the D / A converter 4. By repeating such an operation until there is no more binary data to be recorded, the recording of all data is completed.

FIG. 3 shows a demodulation circuit for reproducing information from a medium recorded by the information recording / reproducing method of the present invention. Here, the light irradiated on the recording medium is received by the light receiving element 7 via the optical system as a reflected light amount corresponding to the density of the pit. The output from the light receiving element 7 is compared by a comparator 8 having four thresholds (see FIG. 1 (c)). Here, a clock signal having a frequency twice the fundamental frequency is generated by the clock generation circuit 9 from the output signal of the threshold having the lowest absolute value.
It is supplied to the level detection circuit 10 and the signal width detection circuit 11. The output of the comparator 8 and the clock signal are input to the level detection circuit 10, and the levels of "0" to "3" are determined. On the other hand, the output of the light receiving element 7 is also supplied to a signal width detection circuit 11, and is detected based on a clock signal having a pit length and a next inter-pit interval having a frequency twice as high.
The detected pit length and pit interval are integer multiples of the 1-bit interval in FIG. 1 (b). The output of the level detection circuit 10 and the output of the signal width detection circuit 11 are
After being subtracted by 2 inside 2, it is halved and converted into the corresponding binary data according to the above table. In this way, MP
U12 reproduces the first two bits from the output of the level detection circuit 10 from the output of the level detection circuit 10, and reproduces the next two bits and the last two bits from the output of the signal width detection circuit 11, respectively. , And the operation of collectively storing the 6 bits in the buffer memory 13 is repeated as many times as necessary to reproduce all data.

The MPU 12 and the buffer memory 13 can be the same as the MPU 2 and the buffer memory 1 in the modulation circuit.

Further, in the above-described embodiment, the case where the density change of the pit is used as an example of the method of multi-value has been described. However, the present invention can also be applied to a method of multi-value corresponding to the polarization angle of the liquid crystal. . Further, the present invention mainly exemplifies the multi-valued data in units of 2 bits. However, it is needless to say that the multi-valued data may be converted into any number of bits as long as the S / N ratio of the recording medium allows. is there.

Further, in the above embodiment, the first two bits are converted to the pit density, the second two bits are converted to the pit length, and the third two bits are converted to the pit interval. The combination is only one example, and each of the first, second and third
Of course, the bits may be converted according to any of the pit density, pit length, and pit interval.

[Effects of the Invention] The present invention has been described in detail above. When reproducing recorded information, a result of comparison between the readout signal and the smallest slice level among a plurality of slice levels. A clock signal is created from the signal indicating the length of the recording pit and the length of the interval between the recording pits from the read signal based on the created clock signal.
High-density recording becomes possible, and the same value, for example,
Even for information in which "0" s are continuous, a clock signal can be generated by detecting the edge of a pit recorded on the recording medium for each predetermined amount of information, and information can be reproduced stably.

[Brief description of the drawings]

FIG. 1 is a signal schematic diagram showing an embodiment of the present invention, FIG. 2 is a block diagram of the modulation circuit, FIG. 3 is a block diagram of the demodulation circuit, and FIG. 4 is a reproduction signal corresponding to the optical power. FIGS. 5 (a) and 5 (b) are diagrams showing recording pits and reproduced signals in a conventional multi-level recording / reproducing method, and FIGS. 5 (a) and 5 (b) are diagrams showing a multi-valued information recording / reproducing method related to the present invention. It is a signal schematic diagram. DESCRIPTION OF SYMBOLS 1 ... Buffer memory, 2 ... MPU 3 ... Counter circuit 9 ... Clock generation circuit 10 ... Level detection circuit 11 ... Signal width detection circuit

Claims (1)

(57) [Claims] 1. A method for recording and reproducing information on an optical recording medium in which one recording pit expresses a plurality of information so that a plurality of recording states can be optically recognized. Is recorded in a recording state that can be recognized at a plurality of slice levels in the unsaturated state, and each of the plurality of recording states is expressed by a length of each recording pit and a length of an interval provided between each recording pit. The recording state of the recording pits, the length of the recording pits, and the length of the interval between the recording pits are different according to a predetermined conversion rule. And when reading recorded information, reading a signal modulated by recording pits from the recording medium; and Comparing the read signal with the plurality of slice levels, and generating a clock signal from a signal indicating a result of the comparison between the smallest slice level of the plurality of slice levels and the read signal. And comparing the plurality of slice levels with the plurality of slice levels through a step of detecting a length of a recording pit and a length of an interval between recording pits from the read signal based on the generated clock signal. As a result, it is possible to reproduce information by associating an array of binary data based on the length of the detected recording pit and the length of the interval between the detected recording pits based on the predetermined conversion rule. Characteristic optical information recording / reproducing method.