WO2002099802A1

WO2002099802A1 - Method for indicating a sector on a data medium and data medium adapted to said method

Info

Publication number: WO2002099802A1
Application number: PCT/FR2002/001836
Authority: WO
Inventors: Philippe Graffouliere
Original assignee: Stmicroelectronics S.A.
Priority date: 2001-06-07
Filing date: 2002-05-31
Publication date: 2002-12-12
Also published as: FR2825827A1; EP1399923A1

Abstract

The invention concerns a method for indicating on a data medium (9) a sector referenced by a binary word (16) consisting of M number of multiplets comprising each L number of bits, comprising operations which consist in engraving on the data medium locally at said sector, a succession of M multiplets corresponding each to a first multiplet, each second multiplet being equal to a vector of N components, each of value +1 or -1, such that N = 2L- 1 and such that the scalar product of said vector by any other vector to which is equal another second multiplet, is not more than a + 1. The data medium (9) is for example an optical disc.

Description

METHOD FOR INDICATING A SECTOR ON A MEDIUM

INFORMATION AND INFORMATION MEDIA

SUITABLE FOR THIS PROCESS

The field of the invention is that of writable information carriers such as optical disks and more particularly information carriers on which the information inscription is distributed by sectors. In the context of the invention, each sector is referenced by a binary word previously engraved on the information medium. Thus, to access a sector, a read or write head traverses the information medium until it detects this binary word.

Generally, a blank optical disc is not completely blank. A recording track is pre-matrixed on the disc. Often, this track is materialized by a spiral groove whose depth is equal to a quarter wavelength of laser beam emitted by a read head. During writing on the disc, the read head follows the groove so as to maintain a writing laser beam inside, next to or alternately inside and outside the groove.

The groove has the shape of a spiral on a macroscopic scale and a sinusoidal shape (called wobble in English) on a microscopic scale. The sinusoidal form is mainly used to measure a linear speed of passage of the disc under the read head so as to control this speed. According to a first known state of the art, a succession of pre-positioned holes (called prepit in English) locally in each sector, materializes the binary word which references this sector. These holes are pre-positioned inside or next to the groove so as to be able to locate an absolute position of the sector by means of the read head when it follows the groove. The frequency at which the succession of holes pre-positioned under the read head passes, makes this coding mode particularly sensitive to high frequency noise. This sensitivity to noise generates errors on the decoding of the succession of pre-positioned holes to obtain the binary word which references the sector. Another solution consists in coding the binary word by modifying certain alternations of the sinusoidal form of the furrow. For example, a modified alternation represents a first binary value and conversely a retained alternation represents a second binary value complementary to the first. The changes of alternation must be carried out so as not to disturb the detection of the original alternation by the read head in its servo-control functions intended to follow the groove and to calculate the speed of travel of the disc under the head.

Data writing to disk, such as NRZ (non-reset) data, is usually done by modulating the power of the laser beam from a writing head in the vicinity of the read head. When the signal resulting from the alternation changes is read while writing data to the disc, the signal read from the disc is disturbed by the writing laser beam. This generates errors on the decoding of the alternation modifications for the binary word which references the sector on which the data to be recorded are planned to be written.

In order to write the data on the correct sector as planned, it is necessary to compensate for the decoding errors in order to obtain the binary word which references the sector.

A solution could be envisaged which consists in placing an analog circuit between the read head and the decoding circuit, so as to filter the disturbances caused by power modulation of the writing laser beam. However, this solution has disadvantages of integration when it is desired to reduce the size of the electrical circuits in a read / write block on an optical disc. Logic circuits make it easier to achieve high integration than analog circuits.

To respond to the problem posed, a first object of the invention is a method for indicating on an information medium, a sector referenced by a binary word consisting of a number M of first bytes each comprising a number L of bits. The method is characterized in that it comprises actions consisting in engraving on the information medium locally in this sector, a succession of M second bytes each corresponding to a first byte, each second byte being equal to a vector of N components , each of value +1 or -1, such that N = 2 ^L - 1 and such that the scalar product of said vector by any other possible vector to which another second multiplet is equal, is at most equal to +1. The two values +1 and -1 taken as first and second binary value, have the effect of obtaining a scalar product equal to N when the vector is multiplied by itself. The decoding to obtain the binary word which references a sector is then achievable by means of a simple logic circuit. It is sufficient to match each second byte detected by a read head, to a first byte. The reference binary word then results directly from a concatenation of the first bytes thus obtained. In the absence of reading error of the second byte, the second byte is easily recognizable because it is the one whose scalar square is equal to N, greater than 1, the scalar product by other bytes being limited to 1. In the presence of reading errors on a few bits of the second byte, the second byte remains easily recognizable because it is the one whose scalar square is closest to N, the other scalar products being less than it. It is therefore sufficient to match the first byte to the second byte whose dot product with the second detected byte has the greatest value.

Different possibilities for engraving the succession of second bytes are possible.

Advantageously, the method according to the invention is further characterized in that one of the values +1 or -1 is etched by modifying an amplitude of a period of undulation of a groove on the information medium.

For example, the amplitude is increased to represent one of the binary values and kept to represent the other binary value. It is thus possible to use the groove for the second bytes without changing the period of the oscillations. This makes it possible to maintain the qualities of the groove which remains centered on the same average value for the servo in position of the read head and which remains of identical frequency for the servo in speed of the information medium.

The different possibilities are not limited to that previously stated. Differently, the method is still advantageous when it is characterized in that one of the values +1 or -1 is engraved by adding over a period of initial undulation of a groove on the information medium, three frequency alternations three times greater than an initial frequency of undulation of said groove.

Here again, the undulations of the groove remain centered around the average value of the initial undulations. This does not disturb the speed evaluation since it is mainly sensitive to a frequency three times lower. If the amplitude of the added sinusoidal oscillation is equal to half the amplitude of the basic sinusoidal oscillation, there is a single zero crossing at the center of a base period. When the resulting total amplitude is little modified, the entire space of the information carrier outside the initial ripple of the groove remains available for writing the data to be recorded.

For a smaller quantity of sectors on the information medium, it is possible to choose the number M of first bytes, equal to one, without departing from the scope of the invention. The number L is then equal to the number of bits of the binary word which references each sector. By dividing the binary word into at least two first bytes each comprising a number L of bits, at most equal to half the number of bits of the binary word, the size of each second byte is reduced in a substantially quadratic proportion. A size of the succession of M second bytes, less than the number of oscillations of the groove on a sector, makes it possible to use all or part of the remaining oscillations to improve the recognition of each sector.

According to an additional characteristic of the method, a third so-called synchronization byte is added at the head of the succession of M second bytes, said synchronization byte being made up of an acyclic sequence of P bits with P greater than N.

The synchronization byte offers the advantage of being able to precisely detect the start of the succession of M second bytes and therefore the start of the referenced sector, thus making it possible to use this sector to the maximum of its capacity. By choosing an acyclic sequence of P bits with P greater than N for the synchronization byte, synchronization is ensured, even with a high error rate while reducing the risk of confusion with a second byte. We can consider different solutions to associate with each value of first byte, a vector with N components, such that its scalar product by any other vector associated with another value of first byte, is at most equal to 1. For example, it is possible to obtain a Length Binary Sequence

Maximum (SBLM or MLBS for Maximum Length Binary Sequence in English), using a generator polynomial with L binary coefficients. An SBLM consists of N bits. A vector consisting of N components each associating the value -1 with a first bit value and the value +1 with a second bit value, has an interesting property. The scalar product of this vector by any other vector similarly constituted by means of a circular permutation of the SBLM, is equal to -1. There then exist N vectors whose scalar product with another vector is equal to -1, therefore less than 1. It is thus possible to make N vectors correspond to N different values of first multiplet of L bits. However, this only allows a distinct vector to correspond to N = 2 ^L -1 first bytes when there are 2 ^L possible values. The amount of sectors that can be referenced by the binary word is then reduced accordingly.

According to a particularly advantageous embodiment of the invention, the method is characterized in that the component values of each of 2 ^{L "1} first vectors, result from a different circular permutation on the same first binary sequence of maximum length of N values and in that the component values of each of 2 ^{L "1} other vectors are of opposite sign to the component values of one different from the first 2 ^{L" 1} vectors.

The dot product of two different first vectors is equal to -1. The dot product of two different second vectors is equal to -1. The scalar product of a first vector with a second vector whose components result from a sign inversion of those of the first, is equal to -N. The dot product of a first vector with any other second vector, is equal to +1. It is thus possible to make 2 ^L vectors correspond to 2 ^L first bytes. Each of all the possible values of the binary word can then reference a sector. Different choices are possible for the values of the numbers M, L, P. Considering an information medium configuration with a groove of 248 oscillations per sector, a particularly interesting choice consists in retaining the values M = 12, L = 4 and P = 63. The values of M and L make it possible to obtain a binary word of 48 bits which can then reference, taking into account 16 bits of correction for a Reed-Solomon code, up to 2 power 32 sectors. The value of L equal to 4 gives a value N of 15 bits for each second byte. It is then possible to engrave the succession of M second multiplets on 180 alternations of oscillation of the groove. Among the 68 remaining half-waves, 63 can be used to burn the synchronization byte.

The invention will be better understood from the description of an exemplary embodiment which follows with reference to the drawings in which:

- Figure 1 shows a means for generating vectors according to the invention;

- Figure 2 shows a correspondence table according to the invention;

- Figure 3 shows an information medium for implementing the invention;

- Figures 4 to 6 each show a local enlargement of the groove to highlight a possible change in alternation;

- Figures 7 and 8 show means of exploitation of the invention.

Referring to Figure 1, a means for generating a binary sequence of maximum length (SBLM) is shown in the form of an electrical diagram. It is possible to transcribe this diagram in the form of a program without any particular difficulty. This circuit or this program is implemented prior to the method according to the invention.

A register 1 to L fixed outputs, consists of L bits 10, 11, 12, 13 which each represent a coefficient of a generator polynomial of degree L-1. A shift register 2 consists of L bits 20, 21, 22, 23. AND logic gates 30, 31, 32, 33 combine two by two, respectively bits 10 and 20, 11 and 21, 12 and 22, 13 and 23. The output of each gate 30, 31, 32, 33 is received by a separate input of a register 4 of L bits 40, 41, 42, 43. A logic gate 5 combines the bits of register 4. The gate 5 is an XOR door, i.e. its output is 1 if one and only one bit of register 4 is 1. The output of gate 5 is 0 in all other cases. On the other hand, the output of gate 5 is looped back to the input of shift register 2.

Thus, for example, on a first phase of a two-phase clock, register 4 performs a bit-by-bit logical disjunction of registers 1 and 2. On a second phase of the two-phase clock, the first bit 20 at the input of the shift register 2 receives the exclusive OR of the bits of register 4, chasing the previous value of bit 20 towards bit 21 and so on until the last bit 23 receiving the previous value of bit 22. When in the example of FIG. 1, the number L is equal to four, the bits 10, 11, 12, 13 are each respectively equal to 1, 0, 0, 1. According to the results resulting from the theory of the bodies of Galois, the exit of the door 5 generates in steady state, a Binary Sequence of Maximum Length, ie of period N = 2 ^L -1 = 15. The output of gate 5 is also sent to the input of a shift register 6 to N bits 60 , 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74. The complement of the door exit 5 is sent to the input of a shift register 8 to N bits 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94. We can observe that the values 1, 0, 0, 1 of register 1 generate a sequence of bits 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, each respectively equal to 0, 1, 0, 1, 1, 0, 0, 1, 0, 0, 0, 1, 1, 1, 1 and simultaneously a sequence of bits 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, each respectively equal to 1, 0, 1, 0, 0, 1, 1, 0, 1, 1, 1, 0, 0, 0, 0. Each second phase of the two-phase clock causes a circular permutation of binary sequence of maximum length (SBLM) contained in registers 6 and 8.

By replacing the binary values 0 and 1 of an SBLM contained in register 6 or register 8, respectively by binary values -1 and +1, we obtain a vector with N components which has interesting properties. The dot product of two vectors obtained from two different SBLMs of the same register 6 or 8 is equal to +1. The scalar square of a vector is naturally equal to +15, the square of each component being equal to +1. The dot product of a vector by the same vector of opposite sign is equal to -15, this is the case for two vectors obtained from an SBLM of register 6 and the complementary SBLM of register 8. The scalar product of two vectors obtained from an SBLM of register 6 and a other SBLM of register 8 is equal to -1. The periodicity of the SBLM makes it possible to obtain 2N, ie thirty different vectors.

A four-bit byte can take sixteen different values. With reference to FIG. 2, a correspondence table 7 is established by means of which a different vector is made to correspond to each possible value of said first four-bit byte. The correspondence table comprises N + 1 lines, that is to say here sixteen lines with a first column containing on each line a value different from the byte ranging from 0000 on the first line to the value 1111 on the last line. A second column contains on each line a vector as previously described.

On the first eight lines, the second column contains a vector resulting from an SBLM of register 6. The first line contains for example the vector (-1, 1, -1, 1, 1, -1, -1, 1, -1, -1, -1, 1, 1, 1, 1) resulting from SBLM (0.1, 0.1, 1, 0.0.1, 0.0.0.1, 1, 1, 1). Each subsequent line repeats the previous line with a double circular permutation. The last eight lines repeat the first eight lines by reversing the sign of each component of the vector.

FIG. 3 shows an information medium on which the invention is implemented. Here, the information medium is an optical disc 9. A writing head 19 is provided for emitting a laser beam 26 whose power, controlled by a signal 29, makes it possible to engrave on the disc a groove 17 whose depth is equal to a quarter of the wavelength of the reflected laser beam 25, which can be received by a read head 18.

A micro motor 24 is provided for moving the read head 18, write head 19 assembly in a radial direction of the disc 9. An integrated circuit 15 for controlling the read head 18, write head 19 assembly , includes a servo block 27. The block 27 controls the motor 24 by means of a signal 28. The signal 28 starts from a first value which positions the read head 18, write head 19 assembly nearby from the center 14 of the disc, up to a last value which positions the read head 18, write head 19 assembly at the periphery of the disc 9.

While the disc 9 revolves around its center 14, the signal 28 changes from the first to the last value so as to engrave on the disc 9 the groove which, on a first scale called macroscopic, has the shape of a spiral which leaves from the center 14 towards the periphery of the disc 9.

While the signal 28 evolves from the first to the last value, the latter is modulated by an oscillation of first frequency and of first amplitude determined, so that on a second so-called microscopic scale, the groove 17 has a sinusoidal shape.

If during the etching of the groove 17, the disc 9 rotates at constant angular speed, the sinusoidal shape of the groove is of constant angular geometric period for the first determined frequency.

If during the engraving of the groove 17, the disc 9 rotates at an angular speed controlled by the radial position of the read head 18, write head 19 assembly, so as to maintain a constant linear speed of travel of the disc 9 under the writing head 19, the sinusoidal shape of the groove is of constant linear geometric period for the first determined frequency.

The oscillation on a microscopic scale of the groove then makes it possible to enslave subsequent rotations of the disc 9 at a speed homothetic to that of the engraving for the same radial position of the read head 18, write head 19 assembly.

The integrated circuit 15 comprises the correspondence table 7 and a logic write block 34. The write logic block 34 is designed to generate a signal 35 which modulates the signal 28.

The device which has just been described makes it possible to execute actions consisting in burning on the disc 9 a succession of bytes as explained now.

An element external to the integrated circuit 15, for example a computer, generates a binary word 16 whose value references a sector provided on the disk

9. The binary word 16 consists of a number M of first bytes each comprising L bits. In the embodiment described here, M is taken equal to twelve and L is taken equal to four. The write logic block 34 of the circuit integrated 15, receiving the value of the binary word 16, corresponds to each first byte a vector of the correspondence table 7, so as to constitute a second byte of N bits.

For each zero bit of a byte, the logic block 34 generates a signal 35 which reproduces an unmodified alternation, that is to say at the first frequency and at the first determined amplitude, so as to modulate the signal 28 For each one-bit of a byte, the logic block 34 generates a signal 35 which reproduces a modified alternation with respect to that at the first frequency and at the first determined amplitude. Different possible alternation modifications are described below.

The logic block 34 begins by modulating the signal 28 in order to engrave in the groove a third so-called synchronization byte, consisting of an SBLM of P bits. In the embodiment described here, P is taken equal to sixty three. Next, the logic block 34 modulates the signal 28 to engrave in the groove each of the second bytes. Each bit of the sequence made up of the third and M second bytes, is engraved on an alternation of the oscillation of the groove. In the example described here, this sequence is thus engraved on two hundred and forty three basic half-waves. Then, the logic block 34 modulates the signal 28 with five unmodified half-waves. During the engraving on two hundred and forty eight alternations of oscillation of the groove locally in a sector, the logic block 34 receives a new binary word value 16 to reference the next sector. As before, the logic block 34 makes M new second bytes correspond to the M first bytes of the new value of the binary word 16. As before, the logic block 34 modulates the signal 28 to burn a new sequence consisting of the byte of synchronization followed by the M new second bytes. This operation is repeated until reaching the end of the groove 17 or the last value of the binary word 16.

In a binary word 16 of forty eight bits where one byte is reserved for information for example on the type of disc and two bytes are dedicated to a correction of type Reed-Solomon on the binary word, there remain three bytes to identify the sector . This makes it possible to reference sixteen million sectors with high reliability. With two hundred and forty eight alternations of oscillation at the first frequency determined by sector and a possibility of writing one hundred and fifty six bits of data by alternation next to the groove, each sector can contain of the order of 4.7 mega bytes. Such a disc can contain around 75 gigabytes. Figures 4 to 6 show different possible alternation modifications.

FIG. 4 shows a change in alternation superimposing a triple frequency oscillation on an initial unmodified alternation frequency. An alternation 37 remains at the initial spatial frequency by absence of modulation of the signal 29 when a byte bit is at 0. An alternation 38 is modified at a triple spatial frequency by modulation of the signal 28 when a byte bit is at 1 By superimposing the triple frequency oscillation on the whole of an alternation period at the initial spatial frequency, the envelope of the oscillation at the initial frequency is preserved. At the speed of rotation of the disc 9, the spatial oscillation of the groove 17 modulates the laser beam 25 over the entire period and thus makes it possible to gain detection energy. Multiplying the spatial frequency by three over an initial period multiplies the temporal frequency accordingly. It is then necessary to provide a filter in the parts of the integrated circuit 15 which process clock signals so as to reduce the bandwidth around the initial frequency. When the parts of the integrated circuit 15 which process the clock signals essentially detect values on either side of zero on an alternation, it is observed in FIG. 4 that, the passage through zero of a modified alternation being preserved, the detection of the clock frequency is little disturbed. Figure 5 shows a change in alternation by increasing amplitude. An alternation 37 remains at the initial spatial amplitude by absence of modulation of the signal 29 when a byte bit is at 0. An alternation 38 is modified to a triple amplitude by modulation of the signal 29 when a byte bit is at 1 This change in alternation has the advantage of preserving the spatial frequency.

FIG. 6 shows a change in alternation superimposing a single oscillation alternation at a frequency five times over an initial unmodified alternation frequency. An alternation 37 remains at the spatial frequency initial by absence of modulation of signal 29 when a byte bit is at 0. An alternation 44 is modified by superposition in its center of an alternation at a spatial frequency five times greater, by modulation of signal 29 when a bit multiplet is at 1. By superimposing a single alternation of oscillation on a clearly higher frequency, the form of the alternation remains identical to the initial form on two fifths at the start of the period and two fifths at the end of the period of the initial form . This reduces the disturbances on the parts of the integrated circuit 34 responsible for following the initial oscillation of the groove 17. This change in alternation has the advantage of preserving the spatial amplitude but considerably reduces the window for detecting the change.

These three modulations are remarkable for the possibility of detecting them by suitable filtering. On the other hand, in each case, the modulation is orthogonal to the sinusoidal modulation, which facilitates detection. The optical disc thus endowed with premarks for referencing its data recording sectors can serve as a matrix for a large number of manufacturing of recordable information carriers.

Such an information medium comprises for each of its sectors referenced by a binary word consisting of M first bytes each comprising L bits, a succession of M second bytes each comprising N bits whose values can be interpreted as values + or -1 of N components of an associated vector such as the scalar product of said vector by any other vector associated with other values of second byte and at most equal to +1, with N = 2 ^L -1. These M second bytes, preceded by a synchronization byte for each sector, are preferably engraved on the groove by modification of the alternation of the micro spatial oscillations of the groove. As explained in the following description, these pre-marks allow a recording and or reading system to recognize a sector of the information medium for recording or reading computer data there.

FIG. 7 shows means of operating such a recording medium. These operating means include a device similar or different from the device of FIG. 3. With reference to FIG. 7, an optical disc 45 comprises a spiral groove 47 which leaves from the center 46 towards the periphery and whose depth is equal to a quarter of a wavelength of laser beam 49 receivable by a read head 48 When the disc 45 rotates around its center 46, the laser beam 49 received by the head 48 makes it possible to slave the latter in position to follow the center line of the groove. A writing head 50 mechanically linked to the reading head 48 is provided for engraving signals on the disc 45, next to the groove 47 by means of a laser beam 51.

A micro motor 52 is provided to move the read head 48, write head 50 assembly in a radial direction of the disc 45. An integrated circuit 53 for controlling the read head 48, write head 50 assembly , includes a servo block 54. The block 54 controls the motor 52 to keep constant a signal value 55 modulated by the power received from the laser beam 49. On a microscopic scale, the groove 17 has the form of a sinusoidal oscillation of which at least a first harmonic has a constant geometric period. The read head 48, write head 50 assembly is equipped with a pair of photo-detectors 60, 61 arranged perpendicular to the groove. The image of a task 62 (spot in English) of light reflected by the groove 47 on the two detectors 60, 61 generates a signal 63 of push-pull type (push-pull in English) by difference in light intensities received by each of the photodetectors 60, 61. The signal 63 contains the first harmonic which, detected by the integrated circuit 53, makes it possible to measure the linear speed of travel of the disc under the read head 48, write head 50 assembly. Among these oscillations, certain half-waves are identical to the first harmonic with a basic amplitude, others include a second harmonic or are of different amplitude, these are the modified half-waves described previously. Each modified half-wave causes an additional modulation of the push-pull type signal when it passes under the pair of photo-detectors 60, 61.

The integrated circuit 53 comprises the correspondence table 7 and a logical read write block 57. The logical read write block 57 is provided for generating a signal 58 for modulating the power of the laser beam 51 emitted by the writing head 50.

The device which has just been described makes it possible to execute actions consisting in positioning the read head 48, write head 50 assembly on a determined sector of the disc 45.

An element external to the integrated circuit 57, for example a computer, generates a binary word 56 whose value references the sector determined on the disk 45. The binary word 56 consists of a series of M first bytes each comprising L bits. In the embodiment described here, M is taken equal to twelve and L is taken equal to four.

On the other hand, the logic block 57 receives the signal 63. The logic block 57 interprets the signal 63 as being worth +1 when the signal 63 results from an additional modulation of the reflected laser beam 49 caused by a deformed alternation. The logic block 57 interprets the signal 63 as being equal to -1 in the other cases. Thus, the logic block 57 receives by the signal 63, a succession of binary values equal to + or -1.

When the logic block 57 receives a succession of binary values which correspond to the bits of the synchronization byte, the logic block 57 makes the scalar product of the N binary values which immediately follow the last bit of the synchronization byte, with each vector of the table of correspondence. The synchronization byte allows logic block 57 to accurately detect the first bit of the first of the second bytes of the series written on the disc.

Logic block 57 retains the vector of the correspondence table whose scalar product with the binary values received from signal 55 has the greatest value. This vector is the one which has the highest probability of corresponding to the second byte engraved on the groove at the place which passes under the read head 48. In the absence of error, this scalar product is equal to N. The logic block 57 then sends outwards, the first byte which corresponds in table 7 to the second byte.

In the absence of error, we saw previously that the scalar product of two equal vectors is equal to N, for example fifteen. The dot product of two different vectors is less than or equal to +1, for example -15, -1 or +1. A one-bit read error reduces the dot product by two vectors equal to N-2, for example thirteen. A one-bit read error increases the dot product of two different vectors by two units in the worst case. So that the dot product of two equal vectors is not greater than (N + 1) / 2, for example eight, at least (N + 1) / 4 errors which do not compensate each other, for example four errors for N = 15. For the dot product of two different vectors to be greater than (N + 1) / 2, for example eight, at least (N + 1) / 4 errors which do not compensate each other, for example four errors for N = 15. If the logic block 57 detects by the signal 63, a series of second bytes which all correspond, each to a first byte of the same rank from the binary word 56, the logic block 57 transmits in the signal 59 to the servo block 54, a command to keep the read head 48 in position on the sector detected as being that referenced by the binary word 56.

The integrated circuit 53 has read and / or write access to a register 36 intended to contain computer data to be recorded or recorded on the disc 45.

To control the writing of computer data on a determined sector of the disk 45, the element external to the integrated circuit 57, for example a computer, generates a binary word 56 whose value references the determined sector. The external element, not shown, stores in the register 36, the computer data to be written on the sector.

When the logic block 57 has positioned the write head 50 linked to the read head 48, on the referenced sector of the disc 45, the logic block 57 loads the data contained in the register 36 to modulate the signal 58 intended for the write head 50, so as to write the data from register 36 to the referenced sector of optical disc 45.

To control a reading of computer data on a determined sector of the disk 45, the element external to the integrated circuit 57, for example a computer, generates a binary word 56 whose value references the determined sector. When the logic block 57 has positioned the read head 48 on the referenced sector of the disc 45, the logic block 57 converts modulations of the signal 55 representative of data written on the referenced sector into bytes of computer data which it stores in the register 36. The external element, not shown, then reads in the register 36, the data written on the referenced sector of the optical disc 45.

The integrated circuit 53 which has just been described offers good qualities of reliability for recognizing a sector referenced on the optical disc 45.

The teaching of the invention is not limited to the example which has just been described. In particular, a person skilled in the art, based on the results from Galois body theory, can imagine other vector systems verifying the properties stated above without departing from the scope of the present invention, for example with d 'other values of M and L or with other modifications of alternation of oscillations of the guide groove on the information medium.

Those skilled in the art will appreciate that by making a different vector correspond to each possible value of a first multiplet of L bits, the properties of the dot product are advantageously used to detect a vector which has the highest probability of corresponding to a value. first multiplet.

Claims

1. Method for indicating on an information medium, a sector referenced by a binary word consisting of a number M of first bytes each comprising a number L of bits, characterized in that it comprises actions consisting in engraving on the information medium locally in this sector, a succession of M second bytes each corresponding to a first byte, each second byte being equal to a vector of N components, each of value +1 or -1, such that N = 2 ^L - 1 and such that the scalar product of said vector by any other vector to which another second byte is equal, is at most equal to +1.

2. Method according to claim 1, characterized in that one of the values +1 or -1 is engraved by modifying an amplitude of a period of undulation of a groove on the information medium.

3. Method according to claim 1 or 2, characterized in that one of the values +1 or -1 is etched by multiplying by three an initial frequency of ripple over the whole of an initial period of alternation.

4. Method according to one of the preceding claims, characterized in that a third so-called synchronization byte is added at the head of the succession of M second bytes, said synchronization byte being constituted by a binary sequence of maximum length of P bits with P greater than Ν.

5. Method according to one of the preceding claims, characterized in that the component values of each of 2 ^{L "1} first vectors, result from a different circular permutation on the same first binary sequence of maximum length of Ν values and in that the component values of each of 2 ^{L "1} other vectors are of opposite sign to the component values of one different from the first 2 ^{L" 1} vectors.

6. Method according to claim 4, characterized in that M = 12, L = 4 and P = 63.

7. Method according to claim 6, characterized in that the component values of each of the first eight vectors result from a different circular permutation on the same first binary sequence of maximum length of fifteen values and in that the component values of each of eight other vectors are of opposite sign to the component values of one different from the first eight vectors.

8. Information carrier (45) comprising several sectors for recording computer data, characterized in that it includes locally each sector referenced by a binary word consisting of a number M of first bytes each comprising a number L of bits , a succession of M second bytes each corresponding to a first byte, each second byte being equal to a vector of N components, each of value +1 or -1, such that N = 2 ^L - 1 and such that the scalar product of said vector by any other vector to which another second byte is equal, is at most equal to +1.

9. An information medium according to claim 8, characterized in that one of the values +1 or -1 is engraved in the form of a modified amplitude of period of undulation of a groove (47) on the medium d 'information.

10. Information carrier according to claim 8 or 9, characterized in that one of the values +1 or -1 is engraved in the form of three half-waves three times greater than an initial ripple frequency of a groove (47) on the information carrier, added over a period of undulation of said groove.

11. Information medium according to one of the preceding claims, characterized in that a third so-called synchronization byte is at the head of the succession of M second bytes, said byte of synchronization consisting of a binary sequence of maximum length of P bits with P greater than N.

12. Information medium according to one of the preceding claims, characterized in that the component values of each of 2 ^{L "1} first vectors, result from a different circular permutation on the same first binary sequence of maximum length of N values and in that the component values of each of 2 ^{L "1} other vectors are of opposite sign to the component values of one different from the first 2 ^{L" 1} vectors.

13. Information carrier according to claim 11, characterized in that M = 12, L = 4 and P = 63.

14. Information medium according to claim 13, characterized in that the component values of each of the first eight vectors result from a different circular permutation on the same first binary sequence of maximum length of fifteen values and in that the component values of each of the other eight vectors are of opposite sign to the component values of one different from the first eight vectors.

15. Integrated circuit (53) for detecting on a data medium (45), a recording sector referenced by a binary word (56), characterized in that it comprises:

- a correspondence table (7) which corresponds to a succession of M first bytes constituting the binary word (56) with each a number

L of bits, a succession of M second bytes each corresponding to a first byte, each second byte being equal to a vector of N components, each of value +1 or -1, such that N = 2 ^L - 1 and such that the scalar product of said vector by any other vector to which another second byte is equal, is at most equal to +1;

- a logic block (57) arranged to make the scalar product of a first vector of the correspondence table with a second vector originating from a signal (58) received at the input of the integrated circuit (53) and arranged to detect that the second vector corresponds to a first byte when the dot product of the first and second vector is significantly greater than +1.

16. Integrated circuit according to claim 15, characterized in that the logic block (57) is arranged to detect a synchronization byte from the signal (58).