JP2007149147A - Modulating method, modulating device, information recording medium and demodulating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a modulating method, a modulating device, an information recording medium and a demodulating method which can improve a reliability by introducing a RLL (Run-Length Limited) signal so that a LSB (Least Significant Bit) signal does not repeat 0 and 1, grasping the LSB of each cell as one signal string, preventing the LSB signal from being the highest frequency by encoding a run-length limited code to the position of the LSB and eliminating a signal (with small amplitude) of a weak power in high pass by making the LSB signal a low pass signal. <P>SOLUTION: In the modulating method for information recording for recording information as multivalued information of a ternary or more in an information recording medium, when the number of bits of the multivalued information is defined as n bits, information in n-1 bits of a higher-order is set as it is, and in the least significant bits, encoding is performed with a run-length limited code in which the minimum reversal interval is two or more. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a modulation / demodulation method and modulation / demodulation apparatus for recording / reproducing information on / from a recording medium, particularly when information is recorded / reproduced in multiple values (three or more values). The present invention relates to a modulation method, a modulation apparatus, an information recording medium, and a demodulation method that improve reliability.

When information is recorded on an information recording medium in multiple values (three or more values), especially when the amplitude is expressed in multiple values, the noise, error, or error of the reproduced signal affects the lower bits compared to the upper bits. (For example, see Patent Document 1).
In Patent Document 1, a plurality of continuous multi-value recordings (one multi-value recording unit is called a cell), that is, an error is detected by providing an intersymbol distance in the LSB (Least Significant Bit) of a plurality of cells. It is disclosed that a signal having a large amplitude deviation from a value is treated as an error.
As described above, when the amplitude is expressed in multiple values on the information recording medium, the noise, error, or error of the reproduction signal affects the lower bits compared to the upper bits. As an example, when the amplitude is divided into eight values and recorded, the whole amplitude is divided into eight, and each is set to V0 to V7 from the smaller amplitude.
Normally, this is expressed in 2-bit representation, V0 is expressed as 000, V1 as 001, V6 as 110, and V7 as 111. In addition, a bit having a large weight (usually the left side) in the 2-bit representation is called an MSB (Most Significant Bit), and a bit having a small weight (usually the right side) is called an LSB (Least Significant Bit).
This weight indicates the amplitude value indicated by each bit. For simplicity, if V0 is 0 and V7 is 7, the MSB has a weight of 4, and the LSB has a weight of 1. That is, if the 2-bit representation is changed from MSB to B2, B1, B0, the amplitude Vs can be expressed by the following equation.
Vs = B2 * 4 + B1 * 2 + B0
Here, for the sake of simplicity, the interval between the bits is made constant, and the weight is also expressed as a power of 1, 2, 4 and 2. However, this may be a different interval or non-linear.
Here, when the noise, error, or error generated during recording / reproduction is Vn, the SN ratio is shown in the following equation.
SN = Vs / Vn
= B2 * 4 / Vn + B1 * 2 / Vn + B0 / Vn
As can be seen from this equation, LSB is more susceptible to noise than MSB. In other words, the reliability of the LSB is lower than that of other bits, and the overall reliability is lowered.
Therefore, in Patent Document 1, as described above, a plurality of continuous multi-value recordings (one multi-value recording unit is called a cell), that is, an intersymbol distance is provided in the LSBs of a plurality of cells, and an error is detected. A signal having a large amplitude deviation from the reference value was treated as an error.
FIG. 13 is a characteristic diagram showing signal transmission characteristics in recording / reproduction. Considering signal transmission, as shown in FIG. 13, the signal transmission is relatively flat or sluggishly lowered to a certain frequency, but has a characteristic that it rapidly deteriorates when a certain frequency is exceeded ( It gets worse at higher frequencies). That is, a signal having a high frequency has a small reproduction signal amplitude during reproduction and is weak against noise.
JP 2003-168980 A

However, the maximum frequency in the case of multilevel recording is a signal that changes in units of cells. For example, in the case of the above eight values, 0, 7, 0, 7 and 0, 1, 0, 1 are repeated.
Here, the 0 and 7 signals have a larger amplitude and allowance for noise than the 0 and 1 signals. Therefore, if a signal that repeats 0 and 1, that is, a signal in which the LSB changes alternately between 0 and 1 is removed, the signal can be made resistant to noise. Patent Document 1 does not take measures to prevent this change in LSB from repeating 0 and 1.
Therefore, in view of the above situation, an object of the present invention is to introduce an RLL signal so that the LSB signal does not repeat 0 and 1, and to catch the LSB of each cell as one signal string, and to run length limited ( By encoding the (RLL) code at this LSB position, the LSB signal is prevented from reaching the highest frequency, and the low frequency signal is eliminated by eliminating the high frequency weak power (small amplitude) signal. It is an object to provide a modulation method, a modulation apparatus, an information recording medium, and a demodulation method that improve the performance.
Another object of the present invention is to introduce a modulation rule from a signal recorded in a modulation system that avoids the LSB signal from reaching the highest frequency by introducing the RLL signal so that the LSB signal does not repeat 0 and 1. It is an object to provide a demodulation method that further improves reliability by performing maximum likelihood decoding using.

In order to solve the above-mentioned problem, the invention according to claim 1 is a modulation method for information recording in which information is recorded on an information recording medium as multi-value information of three or more values. When the number is n bits, the modulation method is characterized in that the information is set as it is in the upper n-1 bits and the least significant bit is encoded with a run-length limited code having a minimum inversion interval of 2 or more.
The invention according to claim 2 is characterized by the modulation method according to claim 1, wherein when the least significant bit is modulated, the modulation is performed with a fixed number of cells.
In the invention of claim 3, when 0 is a symbol that is not inverted and 1 is a symbol that is inverted, modulation is performed in units of four cells, and four of 0001, 0010, 0100, 0101, or left and right are inverted. The modulation method according to claim 2, wherein 1000, 0100, 0010, and 1010 are modulation signals and correspond to 2-bit information, respectively.
According to a fourth aspect of the present invention, there is provided a modulation apparatus for recording information in which information is recorded on an information recording medium as multi-value information of three or more values, wherein the number of bits of the multi-value information is n bits. , Information is set as it is in the upper n-1 bits, and the least significant bit sequentially inputs data to the first memory means for encoding with a run-length limited code having a minimum inversion interval of 2 or more, The information from the first memory means is input to the second and third memory means corresponding to the bits to output information, and further information for generating parity is selected, and the least significant bit is a run-length limited code. The modulation apparatus outputs the information from the memory means corresponding to each bit in accordance with the order of input to the run length limited encoding circuit and output.
The invention according to claim 5 is characterized by the modulation device according to claim 4 using a modulation circuit that performs encoding of the run-length limited code in a certain cell unit.

The invention according to claim 6 is that when the modulation circuit uses a symbol that does not invert 0 and a symbol that inverts 1 for 2 bits of input, 0001, 0010, 0100, 0101, or 5. The modulation device according to claim 4, wherein 1000, 0100, 0010, and 1010 inverted left and right are output as modulation signals.
According to a seventh aspect of the present invention, in the information recording medium for recording information on the information recording medium, the information is recorded as multi-value information of three or more values, and the number of bits of the multi-value information is n bits. The information recording medium is characterized in that information is set as it is in the upper n-1 bits, and the least significant bit is encoded with a run-length limited code having a minimum inversion interval of 2 or more.
The invention according to claim 8 is the information recording medium according to claim 7, wherein when the least significant bit is modulated, the modulation is performed with a certain number of cells.
According to the ninth aspect of the present invention, when 0 is a non-inverted symbol and 1 is an inverted symbol, modulation is performed in units of four cells, and four of 0001, 0010, 0100, 0101 or left / right inversion are performed. 9. The information recording medium according to claim 8, wherein 1000, 0100, 0010, and 1010 are modulation signals and correspond to 2-bit information, respectively.
In the invention according to claim 10, when the information is recorded on the information recording medium as multi-value information of three or more values and the number of bits of the multi-value information is n bits, In the demodulation method for decoding the information recording medium in which the information is set as it is and the least significant bit is encoded with a run-length limited code with an integer m having a minimum inversion interval of 2 or more, the least significant bit “0” is decoded. And “1” information, the state is determined from m + 1 consecutive “0” and “1” states, and the error is cumulatively calculated according to the transition of the state state, and the paths connecting the states merge. The demodulating method is characterized in that the one with the smaller total error at the point survives and finally the path with the smaller error is selected as a decoded word.

The invention according to claim 11 is characterized by the demodulation method according to claim 10, wherein a difference from each multilevel reference signal is used as the error signal.
The invention according to claim 12 is the demodulation method according to claim 10, wherein an error value is relatively obtained from the difference between a difference signal between two multilevel reference signals close to the reproduction signal and the reproduction signal. It is characterized by.
In the invention according to claim 13, when the reproduction signal is larger than the maximum level or smaller than the minimum level, the maximum level and the next level of the maximum or the minimum level and the next level of the minimum level are two points. 13. The demodulation method according to claim 12, wherein an error value is relatively obtained from a difference from a multilevel reference signal and the reproduced signal.
The invention according to claim 14 is the demodulation method according to any one of claims 10 to 13, wherein a multi-value corresponding to the least significant bit corresponding to "0" and "1" is recorded simultaneously. Features.
According to the fifteenth aspect of the present invention, in order to demodulate the lowest-order modulation performed at a constant interval k, information of “0” and “1” in the lowest-order bits is converted into k consecutive “0”. The state is determined from the state of “1” and “1”, and the error is cumulatively calculated according to the transition of the state of the state, and the one with the smaller total error at the point where the path connecting the states joins is survived. 15. The demodulation method according to claim 10, wherein a path with a small error is selected as a decoded word.
The invention according to claim 16 is characterized by the demodulation method according to claim 15, wherein the state not in the modulation rule is discarded at the time of performing modulation in units of k.

  According to the present invention, in the modulation method, since the least significant bit with a small amplitude of the reproduction signal is not changed alternately by 0 and 1, reliability can be improved. Further, in the demodulation method, maximum likelihood decoding can be performed by a modulation rule, and reliability can be improved.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a waveform diagram showing a reproduction waveform of multilevel recording. As shown in FIG. 1, the upper stage is the ideal value of the reproduced waveform, and the middle stage is the ideal reproduced clock. The voltage of the reproduction waveform changes to a rectangular wave at the rise of the reproduction clock, and the level can be determined stably at the fall of the reproduction clock. On the other hand, the actual waveform is shown in the lower part.
FIG. 2 is a schematic diagram showing a configuration example of a general optical disc apparatus. In this description, an optical disk is taken as an example of the recording medium, but the present invention does not depend on the recording method of the medium. That is, the same effect can be obtained with a magneto-optical, write-once medium, and rewritable medium. FIG. 2 shows the minimum configuration necessary for the description. This apparatus is illustrated mainly with respect to parts related to the present invention.
When a command is sent from an external device (for example, a personal computer) 1 to the optical disk drive (spindle motor) 2, the interface controller 3 receives the command and reports to the controller 4 that the command has been received. The controller 4 interprets this command, causes the optical disc drive 2 to perform the operation requested by the command, and reports to the external device 1 through the interface controller 3.
Further, when recording information, the information is temporarily stored in the buffer memory 6 from the external device 1 through the interface controller 3 through the digital circuit 5. The digital circuit 5 performs operations such as adding an error correction code, adding a synchronization signal, and converting the data into a modulation code to a multilevel level. The address to be written is recorded at the address indicated by reading the address written in advance on the information recording medium (optical disk) 7.

Next, the current is controlled so that the LD on the pickup 9 emits light so as to be recorded on the optical disk 7 by the analog circuit 8, and recording is performed at a multilevel level. Further, the pickup 9 receives the reflected light from the optical disc 7 and processes the reflected light by the PD, and processes it by the analog circuit 8 to generate a focus error signal, a tracking error signal, and the like, and inputs them to the servo circuit 10. This servo circuit 10 controls the position of the pickup 9 and the position of the lens.
At this time, the optical information recording medium 7 usually has a spiral groove or data array. Therefore, it moves from the inner circumference to the outer circumference with the passage of time (for example, from the outer circumference to the inner circumference), and exceeds the range where tracking control is possible. Therefore, the whole PU is moved from the tracking servo signal, and a control called a caliper is performed so that the lens position can always be kept close to neutral.
In the case of reproduction, the output of the pickup 9 is quantized by the analog circuit 8 and clock extracted using a PLL or the like, the digital circuit 5 performs synchronization detection, demodulation, error correction, etc., and is stored in the buffer memory 6. Thereafter, information is transferred to the external device 1 through the interface controller 3.
The present invention relates to the part of the digital circuit 5 described above, which is a part of the operation of demodulating the data sent from the external device 1 into a modulation code to a multi-level or returning from a reproduction signal to data.

FIG. 3 is a schematic diagram illustrating a conventional modulation method as a comparison. First, for comparison, a conventional modulation scheme will be described here. In this example, the multi-value number is 8 and the unit for modulation is 4 cells.
Eleven bits are extracted from the data sent from the external device. This corresponds to D0 to D11 at the top in FIG. Dn indicates the nth bit. In the modulation circuit, D0 to D10 are arranged in a matrix of 3 rows and 4 columns, and a parity P is provided at the last location in the third row.
This parity is set such that the inter-code distance of the four values D2, D5, D8, and P in the third row is 2. As an example, P is defined by the following equation.
P = D2 + D5 + D8
Here, the operator “+” means exclusive OR, EXOR. Here, the data of 3 rows and 4 columns is divided into 4 cells from cell 0 to cell 3 and recorded. This corresponds to the lowermost part of FIG.
Then, the syndrome S is calculated at the time of reproduction and demodulation, and if S is not 0, it is assumed that there is an error, and an error is processed if the deviation of the amplitude from the reference value of the reproduction signal of the four cells is large.
S = D2 + D5 + D8 + P
However, in such a conventional modulation system as shown in FIG. 3, since the lower bits are allowed to change alternately between 1 and 0, this portion of the signal is easily buried in noise.
Therefore, in the present invention, a run-length limited code is used in order to prevent the lower bits from alternately changing between 1 and 0. Every 5 bits from the data sent from the external device, 4 bits are set as they are on the upper bit side, and 1 bit is prepared separately to create a lower bit.

表１の左側が元データであり、それを変調すると右側の２倍のビット列に変換する。この際、１，０は元データの１，０とは意味が異なり、０は前の符号の状態を保持し、１は反転させる。このときの最小反転のパターンは１００１であり、反転間隔は３である。この最小反転間隔が２以上であれば１，０が交互になることはない。
復調の際には下位ビットは従来の（２，７）ＲＬＬの復調を行えば良い。また、（２，７）ＲＬＬの変わりに（１，７）ＲＬＬやＥＦＭなどでもよい。
（２，７）ＲＬＬなどは規則性を保つため、データの前と後ろに整合ビットが必要となる。そこで、或る単位でデータを変換する方式を用いると、この整合ビットの必要が無くなる。 FIG. 4 is a schematic diagram for explaining the first embodiment of the modulation system according to the present invention. In FIG. 4, D0 to D3 and D5 to D8 at the top correspond to upper bits, and D4 and D9 on the left side are data for lower bits.
The lower bits D4, D9, D14, and D19, for example, perform (2, 7) RLL modulation shown in Table 1 to generate R0 to R7. Note that (2, 7) RLL in Table 1 is a generally well-known modulation method, and is a code in which the inversion interval is limited to 3 to 8.

The left side of Table 1 is the original data, and when it is modulated, it is converted into a bit string twice as large as the right side. At this time, 1 and 0 have different meanings from 1 and 0 of the original data, 0 holds the state of the previous code, and 1 is inverted. At this time, the minimum inversion pattern is 1001 and the inversion interval is 3. If this minimum inversion interval is 2 or more, 1 and 0 do not alternate.
At the time of demodulation, the lower bits may be demodulated in the conventional (2,7) RLL. Further, (1,7) RLL or EFM may be used instead of (2,7) RLL.
For (2, 7) RLL and the like, regularity bits are required before and after data in order to maintain regularity. Therefore, if a method of converting data in a certain unit is used, the need for this matching bit is eliminated.

Tables 2 and 3 show examples of conversion in units of 4 cells. This has a minimum run of 2 cells and a maximum of 6 cells. Tables 2 and 3 are obtained by inverting the left and right sides of the modulation signal. It is free to associate which modulation signal with which data.

FIG. 5 is a schematic diagram for explaining a second embodiment of the modulation system according to the present invention. In the second embodiment of FIG. 5, D4 and D9 are converted in units of four cells using a conversion table.
FIG. 6 is a circuit diagram showing a first embodiment of a modulation device according to the present invention. In the modulation device of FIG. 6, the input data is temporarily input to the first memory means (shift register 1) 11, and when all the data is input, the second and third memory means (corresponding to each bit of the output) Data is input in the shift registers 2 (MSB), 3) 12 and 13.
At this time, in the LSB, the run length limited encoding circuit 14 performs run length limited encoding such as (2, 7) RLL. The reliability can be improved because the least significant bit having a small amplitude of the reproduction signal is not changed by 0 and 1 alternately.

図８は最尤復号における状態の遷移を説明する状態遷移図である。図８では、この状態ごとに誤差情報を計算し、パスの合流点で誤差が小さい方を生き残らせ、大きい方を放棄する。これを繰り返すと最も近いものが生き残る。
この時、誤差情報を用いるが、２値記録の場合では実際の再生信号の再生値を用いることができるが、多値記録では、さらに下位１ビットのみの場合は誤差を簡単に求められない。 FIG. 7 is a circuit diagram showing a second embodiment of the modulation device according to the present invention. In FIG. 7, the inputted data is once inputted to the first memory means (shift register 1) 11, and when all the data is inputted, the second, third and fourth memory means (corresponding to each bit of the output) ( Data is input in shift registers 2 (MSB), 3, 4 (LSB)) 12, 13, 15.
At this time, the LSB performs conversion according to the rules in Tables 2 and 3. By performing modulation in units of a certain cell, it is possible to omit extra matching bits. By using this modulation rule, a code having a minimum inversion interval of 2 can be easily generated.
Tables 2 and 3 are obtained by inverting the left and right of the modulation signal. Also, which modulation signal is associated with which data is free. Maximum likelihood decoding is performed to improve the reliability of code reproduction.
For example, using the examples in Tables 2 and 3, since the minimum inversion interval is 2, maximum likelihood decoding is performed while viewing three consecutive signals (minimum inversion interval + 1). Since the minimum inversion interval is 2, “010” and “101” do not exist. Here, “010” indicates that the LSB decoded data continues in the order of 0, 1, 0. This is shown in Table 4.

FIG. 8 is a state transition diagram illustrating state transition in maximum likelihood decoding. In FIG. 8, error information is calculated for each state, the one with the smaller error at the junction of the paths survives, and the larger one is discarded. If this is repeated, the closest one will survive.
At this time, error information is used, but in the case of binary recording, the reproduction value of an actual reproduction signal can be used. However, in multi-level recording, the error cannot be easily obtained when only the lower one bit is used.

FIG. 9 is a schematic diagram showing an example of a reproduction signal. Therefore, first, the reference value of each level is obtained by recording and reproducing. For example, taking FIG. 1 as an example, level 0 is 7V and level 7 is 0V. At this time, the difference between the two levels close to the reproduction value is taken as an error.
As shown in FIG. 9, they are 1.7, −0.3, 0.3, and 1.2 in order of time from the left side. From this, the error when LSB is 1, 0 is obtained as shown in Table 5. That is, the difference between the nearest odd level and the even level is taken as an error level, and a value obtained by adding the higher ranks after decoding is determined.

そこで、図８の状態遷移をサンプルごとに考えると図１０の形状になる。ここに表６の距離を、各ステートを示す丸の右側に示し、次の“０”，“１”の値の誤差を矢印の傍に示す。２つの矢印が交わるステートで生き残りパスが決定する。このときの生き残りを太線で示す。
各レベルの基準値がリニアでない場合が考えられる。この場合には、各レベル間の距離を１として相対的に決めることができる。或る再生値がＶｘである場合に、この再生値がレベルｎとレベルｎ＋１の間にある場合は各レベルの基準値をＶｎ，Ｖｎ＋１とすると、レベルｎとの誤差Ｅｎ、レベルｎ＋１の誤差Ｅｎ＋１は次式で求めることができる。
Ｅｎ＝（Ｖｎ−Ｖｘ）／（Ｖｎ−Ｖｎ＋１）
Ｅｎ＋１＝（Ｖｎ＋１−Ｖｘ）／（Ｖｎ−Ｖｎ＋１）
また、最大レベル及び最小レベルの外側の再生値には、例えば、最大レベルが０とし、次に大きいレベルが１であるとすると、次式で求め、同様に計算することができる。
Ｅ０＝（Ｖ０−Ｖｘ）／（Ｖ０−Ｖ１）
Ｅ１＝（Ｖ１−Ｖｘ）／（Ｖ−Ｖ１）
これは最小の場合も同様であり、再生信号が、最大レベル及び最小レベルの範囲を超えた場合の処理が可能となる。
また、ＬＳＢを０から１にする場合は、多値が３ビットの場合、例えば、２から３になるだけでなく、２から１になる場合もある（図９、表５参照。）そこで、生き残りパスの計算中のパスメモリにこの復号した際の値から変化させる多値記録の値を同時に記録させればよい。 FIG. 10 is a diagram showing the state transition of FIG. 8 for each sample. In this case, “111” is the closest to the first three LSBs. The sum of squares of each error is 0.27. Similarly, when distances from all states are obtained, the distance of # 1 in Table 6 is obtained.

Therefore, when the state transition of FIG. 8 is considered for each sample, the shape of FIG. 10 is obtained. Here, the distance in Table 6 is shown on the right side of the circle indicating each state, and the error of the next “0” and “1” values is shown beside the arrow. The survival path is determined by the state where the two arrows cross. Survival at this time is indicated by a bold line.
A case where the reference value of each level is not linear can be considered. In this case, the distance between each level can be relatively determined as 1. When a certain reproduction value is Vx and this reproduction value is between level n and level n + 1, assuming that the reference value of each level is Vn, Vn + 1, an error En with level n and an error En + 1 with level n + 1 Can be obtained by the following equation.
En = (Vn−Vx) / (Vn−Vn + 1)
En + 1 = (Vn + 1−Vx) / (Vn−Vn + 1)
In addition, the reproduction values outside the maximum level and the minimum level can be obtained by the following equation and calculated in the same manner, assuming that the maximum level is 0 and the next highest level is 1, for example.
E0 = (V0−Vx) / (V0−V1)
E1 = (V1-Vx) / (V-V1)
The same applies to the minimum case, and processing when the reproduction signal exceeds the range of the maximum level and the minimum level becomes possible.
Further, when the LSB is changed from 0 to 1, when the multi-value is 3 bits, for example, not only from 2 to 3, but also from 2 to 1 (see FIG. 9, Table 5). What is necessary is just to record simultaneously the value of the multi-value recording which changes from the value at the time of this decoding in the path memory which is calculating the survival path.

FIG. 11 is a state transition diagram showing state transitions when maximum likelihood decoding is performed. As a modulation method, there is a method of converting in units of a certain cell as shown in Tables 2 and 3 and FIG. In this case, maximum likelihood decoding can be performed with this number of cells even when reproduction is demodulated.
At this time, in the example, the unit is 4 cells, and if the modulation rules shown in Tables 2 and 3 are used, the unit to be modulated must be in a bold line state. Therefore, when a unit of modulation is obtained during demodulation, states other than this thick line can be discarded.
FIG. 12 is a state transition diagram showing a state that changes for each cell. As shown in FIG. 12, the modulation rule is in the third state from the left, the thin line “0000” and “1111” states are excluded, and the thin line path is also excluded. Thus, the reliability can be improved by combining the modulation rule and the unit for performing the maximum likelihood code, and the reliability can be improved by discarding the state in the unit of the modulation rule.

It is a wave form diagram which shows the reproduction waveform of multi-value recording. 1 is a schematic diagram illustrating a configuration example of a general optical disc device. It is the schematic explaining the conventional modulation system as a comparison. It is the schematic explaining 1st Embodiment of the modulation system by this invention. It is the schematic explaining 2nd Embodiment of the modulation system by this invention. 1 is a circuit diagram showing a first embodiment of a modulation device according to the present invention. FIG. It is a circuit diagram which shows 2nd Embodiment of the modulation apparatus by this invention. It is a state transition diagram explaining the transition of the state in maximum likelihood decoding. It is the schematic which shows the example of a reproduction signal. It is the figure which represented the state transition of FIG. 8 for every sample. It is a state transition diagram which shows the transition of the state at the time of maximum likelihood decoding. It is a state transition diagram which shows the state which changes for every cell. FIG. 6 is a characteristic diagram showing signal transmission characteristics in recording / reproduction.

Explanation of symbols

11 First memory means (shift register 1)
12 Second memory means (shift register 2)
13 Third memory means (shift register 3)
14 Run-length limited encoding circuit 15 Fourth memory means (shift register 4)

Claims (16)

  In a modulation method for information recording in which information is recorded on an information recording medium as multi-value information of three or more values, when the number of bits of the multi-value information is n bits, information is stored in the upper n-1 bits. A modulation method characterized in that the encoding is performed as it is, and the least significant bit is encoded by a run length limited code having a minimum inversion interval of 2 or more.   The modulation method according to claim 1, wherein when the least significant bit is modulated, the modulation is performed with a fixed number of cells.   When 0 is a non-inverted symbol and 1 is an inverted symbol, modulation is performed in units of four cells, and four of 0001, 0010, 0100, 0101, or 1000,0100,0010,1010 inverted left and right are used as modulation signals. 3. The modulation method according to claim 2, wherein each of the modulation methods corresponds to 2-bit information.   In an information recording modulation apparatus for recording information on an information recording medium as multi-value information of three or more values, when the number of bits of the multi-value information is n bits, information is stored in the upper n-1 bits. As it is, the least significant bit is sequentially input to the first memory means for encoding with a run-length limited code having a minimum inversion interval of 2 or more, and information is output from the first memory means. Input to the second and third memory means corresponding to the bit, further select information for generating parity, and the least significant bit is input to the run-length limited encoding circuit of the run-length limited code, and output A modulation apparatus for outputting information from the memory means corresponding to each bit in accordance with the order of performing the steps.   5. The modulation apparatus according to claim 4, wherein a modulation circuit that performs encoding of the run-length limited code in a certain cell unit is used.   When the modulation circuit has a symbol that does not invert 0 and a symbol that inverts 1 with respect to 2 bits of input, four of 0001, 0010, 0100, 0101, or 1000, 0100, 0010, 1010 that are horizontally inverted are obtained. 5. The modulation device according to claim 4, wherein the modulation device outputs the signal as a modulation signal.   In an information recording medium for information recording in which information is recorded as multi-value information of three or more values on an information recording medium, when the number of bits of the multi-value information is n bits, the upper n-1 bits are information. Is set as it is, and the least significant bit is encoded by a run-length limited code having a minimum inversion interval of 2 or more.   8. The information recording medium according to claim 7, wherein when the least significant bit is modulated, modulation is performed with a certain number of cells.   When 0 is a non-inverted symbol and 1 is an inverted symbol, modulation is performed in units of four cells, and four of 0001, 0010, 0100, 0101 or 1000,0100,0010,1010 inverted left and right are modulated signals. 9. The information recording medium according to claim 8, wherein each of the information recording media corresponds to 2-bit information.   When information is modulated on an information recording medium as multi-value information of three or more values and the number of bits of multi-value information is n bits, the information is set as it is in the upper n-1 bits and the least significant bit is used as the least significant bit. In a demodulation method for decoding the information recording medium encoded with a run-length limited code having an integer m having a minimum inversion interval of 2 or more, the information of the least significant bits “0” and “1” is m + 1 pieces. The state is determined from the consecutive “0” and “1” states, and the error is accumulated according to the transition of the state state, and the one with the smaller error at the point where the path connecting the states joins survives. And, finally, selecting a path with a small error as a decoded word.   11. The demodulation method according to claim 10, wherein a difference from each multi-level reference signal is used as the error signal.   11. The demodulating method according to claim 10, wherein an error value is relatively obtained from a difference between two multi-level reference signals close to the reproduction signal and the reproduction signal as the error signal.   When the reproduction signal is larger than the maximum level or smaller than the minimum level, the difference between the maximum level and the maximum next level or the difference between the two-level multilevel reference signal of the minimum level and the next level of the minimum level is 13. The demodulation method according to claim 12, wherein an error value is relatively obtained from the reproduction signal.   The demodulation method according to any one of claims 10 to 13, wherein a multi-value corresponding to the least significant bit corresponding to "0" and "1" is recorded simultaneously.   In order to demodulate the lowest-order modulation performed at a constant interval k, the state of the lowest-order bits “0” and “1” is determined from k consecutive “0” and “1” states. In accordance with the state transition, cumulatively calculate the error, survive the one with the smaller total error at the point where the paths connecting the states merge, and finally select the path with the smaller error as the decoded word The demodulation method according to any one of claims 10 to 14, wherein:   16. The demodulation method according to claim 15, wherein a state not included in the modulation rule is discarded at the time of performing modulation in k units.

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