JPH09120542A - Reproducing method of optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the amount of data which are recordable by reducing the length of the servo area of a sample servo system optical disk. SOLUTION: One sector is constituted of a header area and thirty-one data segments. The header area and the data segments have respective servo areas. The servo areas include pits 4A and 4B which are offset to the inner side and the outer side with respect to a track center and pits 5 provided on the track center. Note that a tracking error is detected by the pits 4A and 4B. Moreover, the pits 4A serve as clock pits. The pits 4B and 5 serve as one bit of a gray code 1 which is an access code. The position of the pits 4B and 5 vary in accordance with the track numbers.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk reproducing method, and more particularly to a sample servo type optical disk reproducing method.

[0002]

2. Description of the Related Art As a method of tracking servo for a rewritable optical disk, a sample servo for pre-formatting (or pre-recording) the servo area shown in FIG. 4 has been proposed. In the sample servo, a servo area is provided for each data segment obtained by further dividing one sector. The length of the servo area is 2 bytes. Since 1 byte is digitally modulated to be converted into a predetermined pattern of 11 channel bits, 2 bytes have a length of 22 channel bits on the optical disc.

When the pit position is determined corresponding to 22 channel bits, the pit positions 3 to 8 are the access code area 1. The access code recorded in the access code area 1 is 16 as shown in FIG.
This is a Gray code that repeatedly changes every two tracks with one track as a cycle. The Gray code is used to facilitate the interpolation by utilizing the adjacency. In FIG. 5, x indicates that there is a pit. The access code area 1 is used to seek a target track at a high speed, and the seek speed becomes faster as the access code change cycle becomes longer, that is, the number of tracks included in the access code change cycle increases. it can.

Further, in the sample servo, a pair of tracking pits 2A and 2B are formed at pit positions 11 and 17. These tracking pits 2A and 2B
The clock pit 3 is formed at the pit position 14 in the center between the two. One tracking pit 2A is offset inward by about 1/4 track pitch with respect to the track center indicated by the alternate long and short dash line, and the other tracking pit 2B is about 1/4 track pitch with respect to the track center. Offset to the outside. Since the offset directions are different, the tracking pits 2A and 2B are also called wobble pits. Further, the clock pit 3 is formed on the track center.

When the reading beam applied to the optical disk scans the track center, the level of the reproduction signal generated in the tracking pit 2A and the level of the reproduction signal generated in the tracking pit 2B become equal.
If the reading beam is displaced inward from the track center, the level change of the reproduction signal generated in the tracking pit 2A becomes larger than the level change of the reproduction signal generated in the tracking pit 2B. When a tracking error occurs in the opposite direction, the tracking pit 2B
Tracking pit 2 changes the level of the playback signal
It is larger than that of A. Therefore, the tracking error can be detected from the level difference between the reproduced signals generated in the tracking pits 2A and 2B. The clock for sampling and extracting the reproduction signal generated in the tracking pits 2A and 2B is formed by the PLL so as to be synchronized with the reproduction signal of the clock pit 3.

[0006]

When reading a pit, the distance that guarantees that the pit will not be correctly read due to intersymbol interference is T (unit is the length of formation of one pit), Let C be the length of the access code. In the conventional configuration shown in FIG. 4, the length of the servo area is (T + C + T + 1 + T + 1 + T + 1 + T = C
+ 5T + 3) is the minimum required. FIG. 4 shows (T =
It is an example of 2). In the access code area 1, since the code can be read even if inter-code interference occurs due to the regularity of the Gray code, the minimum distance between pits is 1.

The previously proposed tracking servo has the drawback that the required servo area becomes long and the proportion of the tracking pits and clock pits in the amount of data that can be recorded on the disk surface increases. Assuming that the servo area length is the same as before,
There is a problem in that the number of pits in the access code cannot be increased and the seek operation cannot be performed at a sufficiently high speed.

Therefore, an object of the present invention is to shorten the length of the servo area composed of tracking pits and clock pits to increase the amount of data that can be recorded / reproduced or increase the number of bits of the access code. An object of the present invention is to provide an optical disc reproducing method capable of increasing the seek speed.

[0009]

According to the present invention, there is provided a method for reproducing an optical disc, wherein a pair of tracking pits, which are offset inward and outward, are provided in a servo area with respect to a center position of the track. First and second pits (4A, 4B) provided to be offset inward and outward from the center position, and a third pit provided near the first and second pits (4A, 4B) Pits (5) are formed in the servo area, and the first and second
Tracking error is detected by the pits (4A, 4B) of the first, second, and third pits (4A, 4B, 5)
The method for reproducing an optical disk is characterized in that the timing of the reproduction signal of the pit is detected by one of the above. In addition, this invention, with respect to the center position of the track,
In a reproducing method of an optical disc having a pair of tracking pits, which are offset inside and outside, in a servo area, first and second offsets are provided inside and outside with respect to a center position of a track. Pits (4A, 4B) are formed in the servo area, the tracking error is detected by the first and second pits (4A, 4B), and the pit is formed by one of the first and second pits (4A, 4B). The method for reproducing an optical disk is characterized in that the timing of the reproduction signal is detected.

A tracking pit and a clock pit are required in the servo area. Two pits are required as tracking pits. Since these two pits have not only the function of tracking but also the function of clock pits, the length of the servo area can be shortened. Since the length of the servo area is short, the amount of data that can be recorded can be increased.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. This embodiment is one in which the present invention is applied to a magneto-optical disc which is one of rewritable optical discs, and FIG. 1 shows the overall configuration of a disc drive of this embodiment.

In FIG. 1, reference numeral 10 indicates an optical pickup. The optical pickup 10 is provided so as to face a magneto-optical disk (not shown) that rotates at a CAV (constant angular velocity) by a spindle motor 11. The optical pickup 10 is
It is sent by the linear motor 12 in the radial direction of the disk.

Reference numeral 13 indicates an interface between the host computer and the drive, and reference numeral 14 indicates a data buffer. The recording data is supplied from the data buffer 14 to the laser control circuit 16 via the data modulation circuit 15, and the data is recorded as a spiral track or a concentric circle track on the disk. Optical pickup from disc 1
The reproduction data read by 0 is reproduced signal processing circuit 17
Is supplied to the data demodulation circuit 18 via. Since an error correction code, for example, a product code is encoded with respect to the data, an error correction processing unit 19 for encoding and decoding the error correction code is provided. Further, for the magneto-optical disk, an external magnetic field generation unit 20 provided near the disk is provided. A system controller 21 for controlling the operation of the entire drive is provided. A drive controller 22 that controls the operations of the optical pickup 10, the spindle motor 11, the linear motor 12, and the external magnetic field generator 20 is provided. 23 is
7 shows a focus servo for controlling the focus of the optical pickup.

A pre-format decoder 24 is provided in association with the data demodulation circuit 18. As described below,
In addition to the rewritable area, the magneto-optical disk is provided with a pre-formatted area in which information cannot be rewritten and a pit pattern is used to record information in advance. The preformatted area includes a header area and a servo area. The pre-format decoder 24 is
It is provided to decode information in the pre-formatted area and to form a clock synchronized with clock pits in the servo area by, for example, a PLL. The clock generated by the preformat decoder 24 is supplied to the tracking control circuit 26, and the read data of the preformat area is supplied to the address decoder 25. The address decoder 25 decodes the sector address and the track address from the reproduction signal of the header and also decodes the access code of the servo area. The address information decoded by the address decoder 25 is also supplied to the tracking control circuit 26.

The tracking control circuit 26 controls the seek operation for accessing the target track and the tracking control for controlling the beam scanning so that the center of the track coincides with the center of the spot of the laser beam. To do. During a seek operation, the sector address and track address read from the header are used as the current address, the difference between the target address and the current address is calculated, and the drive signal for the linear motor 12 is formed so that this difference becomes zero. . In order to correctly position the laser beam on the track during recording or reproduction, a drive signal for finely moving the optical pickup 10 in the direction orthogonal to the track is formed based on the tracking error signal formed from the tracking pits in the servo area. . The linear motor 12 can also perform control to position the center of the laser beam spot on the center of the track.

An example of the data format in this embodiment will be described with reference to FIG. On the magneto-optical disk, 9760 tracks are formed with a track pitch of 1.6 μm. As shown in FIG. 2A, one sector is composed of a header area and 31 data segments. The length of the header area and each data segment is
It is 24 bytes.

As shown in FIG. 2B, the header area has a 5-byte servo area at the beginning, followed by a 1-byte sector address SA, followed by a 5-byte track address TA. A 6-byte check code for error detection and / or correction code is added to the sector address SA and the track address TA. Furthermore, 6 bytes long ALPC (Automatic Laser Power Control) via 1 byte margin
Area is provided. As described above, the header area is preformatted and cannot be rewritten.

As shown in FIG. 2C, the data segment has a servo area of 5 bytes similar to the header area, and a length of 19 bytes is set as a data area after that. Data is recorded in and reproduced from the data area by the magneto-optical effect. Therefore, the rewritable data amount of one sector is (19 ×
31 = 589 bytes).

Details of the servo area are shown in FIG. 2D. 1 for a 5-byte (40-bit) servo area
To 40 pit positions are defined. Of course, when digital modulation is performed, the number of bits changes after the original data and the modulation. In FIG. 2D, the increase in the number of bits due to digital modulation is ignored for simplicity.

A pit 4A having an offset of about 1/4 track pitch is formed inside a predetermined pit position 13 with respect to the track center (shown by a chain line). The pit 4A is a pit that has the functions of both a clock pit and a tracking pit. The position of the pit 4A is at least a distance T from the pit of the previous data segment so as not to cause intersymbol interference with the pit of the data segment of the previous sector.

For example, a pit 4B having an offset of about 1/4 track pitch is formed outside the track center (shown by a chain line) at the pit position 17.
The pit 4B doubles as a tracking pit and 1 bit of the gray code 1 forming the access code. A pit 5 is formed on the track center at a pit position 24, for example, in association with another 1 bit of the gray code 1.
The positions of these pits 4B and 5 are tracks (N + 0,
N + 1, ..., N + 63), as shown in FIG. 2E. However, a space corresponding to at least three pits is provided between the pits 4A and 4B and between the pits 4B and 5. That is, in this example, the minimum distance T for avoiding intersymbol interference is (T = 3).

Pits 6 and 7 corresponding to 1 bit forming the gray code 2 are formed at, for example, pit positions 26 and 31, respectively. These pits 6 and 7 change according to the bit pattern of the gray code 2 as shown in FIG. 2E. 64 with Gray code 1 and Gray code 2
Book tracks (N + 0, N + 1, ..., N + 63) are identified. However, in FIG. 2E, (N +
The pattern of the code up to the track of 6) is shown, and (N +
7) ... Patterns for (N + 63) tracks are omitted. Since 64 tracks can be identified by the Gray code 1 and the Gray code 2, the seek operation can be performed at a higher speed than the conventional method that can identify 16 tracks.

Between the pit 5 and the pit 6, the interval corresponding to one pit is set to be the minimum interval.
It is said that there is a similar relationship between the two. Therefore, intersymbol interference may occur between these two pits. In the case of a tracking pit, the analog level (peak value) of the reproduced signal corresponds to the amount of tracking error, and therefore intersymbol interference must be avoided. However, in the case of each of the gray code 1 and the gray code 2, there is the regularity that only the position of one pit changes in the adjacent tracks, so even if intersymbol interference occurs, the gray code 1 and the gray code 1 It is possible to decode Code 2 respectively. For this reason, the minimum distance between pits is 1 as described above.

A space of at least T is required between the pit 7 forming the Gray code 2 and the next data segment. Actually, the servo area shown in FIG. 2D is an area in which pre-recording is performed, and a rewritable data area (data segment) is located before and after the servo area,
Margins of T or more necessary to prevent intersymbol interference are provided in front of the pit 4A and behind the pit 7, respectively.

In this embodiment described above, the minimum required length of the servo area is determined. However, the gray code 2 is not provided in order to facilitate comparison with the conventional method. As shown in FIG. 2D, in front of pit 4A, in pit 5
After that, an interval of T is required between each of the pits 4A and 4B. A space of (C + T-1) is required between the pits 4B and 5. The reason (-1) is given here is that the minimum interval between Gray codes is generally 1 and there is a relationship of (T> 1). Therefore, in this embodiment, the minimum required length of the servo area is (T + 1 + T + (C
+ T-1) + T = C + 4T). This length is (T + 3) shorter than (C + 5T + 3) in the conventional example.

In this embodiment, first, the pit 4A
A clock synchronized with is formed so that each pit position can be detected. The levels of the reproduced signals at all pit positions are detected, and the access codes (Gray codes 1 and 2) are decoded from the positions of the pits 4B, 5, 6, 7. Further, a tracking error is detected from the difference between the peak levels of the reproduced signals of the pits 4A and 4B.

In the above-described embodiment, the following is done. Pit 4A: Functions as a clock pit and a tracking pit. Pit 4B: Functions as a tracking pit and a gray code pit. Pit 5: Gray code pit.

However, various modifications other than this are possible. FIG. 3A shows one of the modified examples. That is, the following is done. Pit 4A: Clock pit. Pit 4B: Functions as a tracking pit and a gray code pit. Pit 5: Functions as a tracking pit and a gray code pit. In this modification, the minimum required length of the servo area is the same as that in the first embodiment.

Further, the modification shown in FIG. 3B is as follows. Pit 4A: Functions as a clock pit and a tracking pit. Pit 4B: Functions as a tracking pit and a gray code pit. In the method of FIG. 3B, the minimum required length of the servo area is (C + 3T-1), which is
The length of the servo area is (2T + 4) short.

The access code is not limited to the Gray code, but a code such as a natural binary code can be used.
Alternatively, the track may be identified by the position of 1 bit.

The present invention is not limited to a rewritable disc such as a magneto-optical disc, but can be a write-once disc,
It is also applicable to non-rewritable ROM disks and the like.

[0032]

According to the present invention, the length of the servo area in which the tracking pit and the clock pit are inserted can be shortened as compared with the conventional method. Therefore, the proportion of the servo area on the disk can be reduced and the amount of recordable data can be increased. Further, when the length of the servo area is the same as the conventional one, the number of bits of the access code can be increased, and the number of tracks that can be identified by this access code increases. Therefore, the optical pickup can be sled at high speed during seek, and the seek operation can be made faster. Furthermore, since the pit for clock reproduction is not separately provided, it is not necessary to generate the window signal for detecting the read signal in order to detect the pit for clock reproduction, and the circuit configuration and signal processing are simplified. can do.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a drive system in an embodiment of the present invention.

FIG. 2 is a schematic diagram for explaining a data format of an embodiment of the present invention.

FIG. 3 is a schematic diagram used to describe a modified example of the present invention.

FIG. 4 is a schematic diagram showing a configuration of a conventional servo area.

FIG. 5 is a schematic diagram used to describe a conventional access code.

[Explanation of symbols]

4A, 4B, 5, 6, 7 ... Pits formed in the servo area

Claims (2)

[Claims] 1. A reproducing method of an optical disc having a pair of tracking pits, which are offset inside and outside with respect to a center position of a track, in a servo area. The first and second pits provided offset to the outside and the third pit provided near the first and second pits are formed in the servo area, and the first and second pits are formed. A method of reproducing an optical disk, wherein a tracking error is detected by a pit, and the timing of a reproduction signal of the pit is detected by one of the first, second and third pits. 2. A reproducing method of an optical disc having a pair of tracking pits, which are offset inside and outside with respect to a center position of a track, in a servo area. The first and second pits offset outward are formed in the servo area, the tracking error is detected by the first and second pits, and the pit is formed by one of the first and second pits. The method for reproducing an optical disc is characterized in that the timing of the reproduction signal of the above is detected.