JPH0384734A - Tracking servo for optical disk - Google Patents

Abstract

PURPOSE:To decrease the length of a servo area or to increase number of tracks corresponding to the period of a change in an access code by providing a pit having two functions or over such as those of a tracking pit and a clock pit of an access code. CONSTITUTION:First and 2nd pits 4A, 4B with an offset and a 3rd pit 5 in the vicinity of them are formed to a servo area and the 1st and 2nd pits 4A, 4B detect a tracking error. Moreover, a timing of a reproduction signal of a pit is detected by one of the 1st, 2nd and 3rd pits 4A, 4B and 5 and two of the 1st, 2nd and 3rd pits 4A, 4B, 5 constitute an access code. That is, since two tracking pits have a function of a clock pit or an access code pit, the length of the servo area is decreased. Thus, the data quantity to be recorded is increased and number of tracks to be identified by the access code is increased, then the seek operation is quickened.

Description

[Detailed Description of the Invention] (Industrial Application Field) This invention relates to a tracking servo for an optical disc, in particular,
Concerning improvement of sample servo.

[Summary of the invention]

This invention includes a pair of tracking pits that are offset to the inside and outside, respectively, with respect to the center position of the track, a pit that constitutes an access code that changes every predetermined number of tracks, and In an optical disk tracking servo in which the servo area has a clock pit for detecting timing, the tracking pit and the clock pit are not provided separately for access code pits, but instead serve two or more of these functions. By providing pits, the length of the servo area can be shortened or the number of trunks corresponding to the period of change of the access code can be increased.

[Conventional technology]

As a tracking servo system for a rewritable optical disc, a sample servo system has been proposed in which a servo area shown in FIG. 4 is preformatted (or pre-recorded) on the optical disc.

In sample servo, a servo area is further divided into one sector and is provided in a data segment.

The length of the servo area is 2 bytes. Since one byte is digitally modulated into a predetermined pattern of 11 channel bits, two bytes are the length of 22 channel pits on the optical disc.

When pit positions are determined in correspondence with channel pits 22, pit positions 3 to 8 are access code area 1.
It is said that As shown in FIG. 5, the access code recorded in the access code area 1 is a Gray code that changes repeatedly every two tracks with a cycle of 16 tracks. The Gray code is used to facilitate interpolation by utilizing adjacency. In FIG. 5, X indicates the presence of pits. Access code area 1 is used to seek a target track at high speed, and the longer the access code change cycle, that is, the greater the number of tracks included in the access code change cycle, the faster the seek speed. can.

Further, in the sample servo, a pair of tracking pits 2A and 2B are formed at pit positions 11 and 17.

A clock pit 3 is formed at a central pit position W14 between these tracking pits 2A and 2B. One tracking pit 2A is offset inward by approximately X track pitch from the track center indicated by the dashed line, and the other tracking pit 2B is offset approximately X track pitch outward from the track center. It is offset. Since the offset directions are different, the tracking pits 2A and 2B are also called wobble pits. Further, a clock pit 3 is formed on the track center.

When the reading beam irradiated onto the optical disc scans the track center, the tracking pit 2A
The level of the Isei signal generated at the tracking pit 2B becomes equal to the level of the reproduced signal generated at the tracking pit 2B. If the reading beam is shifted inward with respect to the track center, the level change of the reproduced signal occurring at the tracking pit 2A will be larger than the level change of the reproduced signal occurring at the tracking pit 2B. When a tracking error occurs in the opposite direction, the level change of the reproduced signal occurring at the tracking pit 2B becomes larger than that occurring at the tracking pit 2A. Therefore 1, tracking pit 2A
A tracking error can be detected from the level difference between the reproduced signals generated at 2B and 2B. A clock for sampling and extracting the reproduced signal from the tracking pits 2A and 2B is formed using a PLL so as to be synchronized with the reproduced signal from the clock pit 3.

[Problem to be solved by the invention]

T(
The unit is the length of one bit formed, and the length of the access code is C. 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+57+3) is required as a minimum. FIG. 4 is an example of (T-2). In access code area 1, the minimum distance between pits is set to 1 because the code can be read even if code amount interference occurs due to the regularity of the delay code.

The above-mentioned previously proposed tracking servo requires a long servo area, and has the disadvantage that tracking pits and clock pits account for a large proportion of the amount of data that can be recorded on a disk surface. When the length of the servo area is made equal to the conventional length, a problem arises in that the number of pits in the access code cannot be increased and a sufficiently high-speed seek operation cannot be performed.

Therefore, an object of the present invention is to increase the amount of data that can be recorded/played out by shortening the length of the servo area consisting of access codes, tracking pits, and clock pits, or to increase the number of access code pits. An object of the present invention is to provide a tracking servo for an optical disc that can increase the seek speed.

[Means to solve the problem]

This invention provides a pair of tracking pits that are offset to the inside and outside, respectively, with respect to the center position of the track, a pit that constitutes an access code that changes for each predetermined number of tracks, and a timing of a playback signal of the pit. In a tracking servo for an optical disk in which the servo area has clock pits to be detected, first and second pits (4A, 4B) are provided offset to the inside and outside with respect to the center position of the track. , first and second pits (4A.

A third pit (5) provided near the pit (4B) is formed in the servo area, and a tracking error is detected by the first and second pits (4A, 4B). pit (4A, 4B).

5), the timing of the pit playback signal is detected, and the first, second and third pits (4A, 4B) are detected.

The access code is configured by the two items 5).

Further, in the present invention, first and second pits (4A, 4B) provided inwardly and outwardly offset with respect to the center position of the track are formed in the servo area; A tracking error is detected by (4A, 4B), the timing of the reproduction signal of the pit is detected by one of (4A, 4B), and the timing of the reproduction signal of the pit is detected by one of (4A, 4B).
The access code is configured by at least one of the pits (4A, 4B).

[Effect]

The servo area requires a tracking pit, a clock pit, and a pit that constitutes an access code. Two pits are required as tracking pits. These two pits are not only for tracking,
Since it has the function of a clock pit or an access code pit, 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 increases, and the number of tracks that can be identified by the access code increases, so the seek operation becomes faster.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. In this embodiment, the present invention is applied to a magneto-optical disk, which is one type of rewritable optical disk, and FIG. 1 shows the overall configuration of a disk drive according to this embodiment.

In FIG. 1, 10 indicates an optical pickup. The optical pickup 10 is operated by a spindle motor l1.
It is provided opposite to a magneto-optical disk (not shown) that rotates at a constant angular velocity. The optical pickup 10 is sent by a linear motor 12 in the radial direction of the disk.

13 indicates an interface between the host computer and the drive, and 14 indicates a data buffer. Is the recording data from the data buffer 14 via the data modulation circuit 15 laser-based? 11 circuit 16, and data is recorded as a vortex@E rack or concentric tracks on the disk. Reproduction data read from the disc by the optical pickup 10 is supplied to a data demodulation circuit 18 via a reproduction signal processing circuit 17. Since the data is encoded with an error correction code, such as a product code, an error correction processing section 19 is provided that encodes and decodes the error correction code. Further, for the magneto-optical disk, an external magnetic field generating section 20 is provided close to the disk. A system controller 21 is provided to control the operation of the entire drive. A drive controller 22 is provided to control the operations of the optical pickup 10, spindle morph 111, linear morph 2, and external magnetic field generator 20. 23 indicates a focus servo for controlling the focus of the optical pickup.

A blitz/matte decoder 24 is provided in conjunction with the data demodulation circuit 18. As will be described later, the magneto-optical disk is provided with a preformat area in which information cannot be rewritten for each rewritable area ε and in which information has been previously recorded in a pattern of pits. This preformat area includes a header area, a servo area, etc. The preformat decoder 24 decodes the information in the preformat area and converts the clock synchronized with the clock pit in the servo area into, for example, P i
, ! , is provided for forming by. 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 information reader 25 decodes the sector address and track address from the header reproduction signal, as well as 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 a seek operation for accessing a target track, and performs tracking control so that the beam scans with the center of the track and the center of the laser beam spot aligned. 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 a drive signal for the linear motor 12 is formed so as to set this difference to 0. be done. In order to correctly position the laser beam on the track during recording or playback, a drive signal is used to slightly move the optical pickup 10 in a direction perpendicular to the track based on an I-racking error signal formed from a tracking pit in the servo area. It is formed. The linear motor 12 can also perform control to position the centers of the laser beams 1 to 41 on the center of the track.

An example of the data format in this embodiment will be explained with reference to FIG. On the magneto-optical disk, 9760 tracks are formed at a track pitch of 166 μm. As shown in FIG. 2A, one sector consists of a header area and 31 data segments. The length of the header area and each data segment is 24 bytes2.
It has a byte servo area, followed by a 1-byte sector address SA, followed by a track address TA as 5 bytes, and these sector addresses S.
A and track address TA are added with a check code of 6 bars 1F, which is an error detection and/or correction code. Additionally, a 6-byte long AI-PC (11-motion laser power control) area is provided via a 1-byte margin.As mentioned above, the header area is preformatted. , this is an area that cannot be rewritten.

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

Details of the servo area are shown in the second diagram.

Pit positions 1 to 40 are defined for a servo area of 5 bytes (40 bits). Of course, when digital modulation is performed, the number of bits changes from the original data after modulation. In the second diagram, for simplicity, the increase in the number of pits due to digital modulation is ignored.

A pit 4A is formed at a predetermined pit position 13 and is offset inward by approximately X track pitch with respect to the track center (indicated by a dashed line). This pit 4A is a pit that functions as both a clock pit and a tracking pit. The position of pit 4A is at least T
It has a distance of

For example, a pit 4B is formed at pit position 17 with an offset of approximately X track pitch outward from the track center (indicated by a dashed line). Pit 4B is
It serves both as a tracking pit and one bit of Gray code 1 constituting the access code. For example, a pit 5 is formed on the track center at a pit position 24 corresponding to the other bit of the gray code 1. The positions of these pits 4B and 5 are track (N+0, N+1,...
, N+63) as shown in FIG.

However, between the pits 4A and 4B and between the pits 4B and 5, there are provided intervals corresponding to at least three pits. That is, in this example, the minimum distance T to avoid code amount interference is (T-3).

Pit 6 corresponding to 1 bit constituting Gray code 2
and 7 are formed, for example, at pit positions 1126 and 31, respectively. These pits 6 and 7 change according to the pit pattern of the gray code 2 as shown in FIG. 2E.

64 tracks (N+0, N+1, . . . , N+63) are identified by Gray code 1 and Gray code 2. However, in Fig. 2E, for simplicity, the code pattern of the (N+6) track salt is shown, and (N+7) ・
... The pattern for track (N+63) is omitted. Since 64 tracks can be identified using Gray code 1 and Gray code 2, a faster seek operation is possible compared to the conventional method that allows 16 tracks to be identified.

The minimum distance between the pits 5 and 6 is the distance corresponding to one pit, and the same relationship exists between the pits 6 and 7. Therefore, code amount interference may occur between these two focal points. In the case of tracking pits, the analog level (peak value) of the reproduced signal corresponds to the amount of tracking error, so it is necessary to avoid code amount interference. In this case, since there is a regularity that the position of only one pit changes in adjacent tracks, it is possible to decode each of Gray code 1 and Gray code 2 even if code amount interference occurs. For this reason, as mentioned above, the minimum distance between pits is set to 1.

There must be an interval of at least T between the pit 7 constituting the Gray code 2 and the next data segment. In reality, the servo area shown in the second diagram is an area where blurring is recorded, and rewritable data areas (data segments) are located before and after it, so the T required to prevent code amount interference is The above margins are provided in front of the pit 4A and behind the pit 7, respectively.

In this embodiment described above, the minimum necessary length of the servo area is determined. However, in order to facilitate comparison of the conventional method ε, it is assumed that there is no Gray code 2. As shown in FIG. 2p, a distance T is required before the pit 4A, after the pit 5, and between the pits 4A and 4B. B) An interval of (C+T-1) is required between 4B and 5.

The reason why c-i> is set here is because the minimum interval of the Gray code is generally 1, and there is a relationship of (T>1). Therefore, in this embodiment, the minimum necessary length of the servo area is (T+1+'l'+ (C+T-1)+T-C+4T)
This length is (T+3) shorter than (C+5T+3) in the conventional example.

In this embodiment, first, a clock synchronized with the pit 4A is formed so that each pit position can be detected. The level of the reproduced signal at all pit positions is detected, and the access code (codes 1 and 2 for blurring) is decoded from the pit positions 4B, 5.6.7. Further, a tracking error is detected from the difference in peak levels of the reproduced signals of pits 4A and 4B.

In the embodiment described above, pit 4A: functions as a clock pit and a tracking pit.

Pit 4B = Functions as a tracking bit and gray code pit.

Pit 5: Gray code pit.

It is said that However, various other modifications are possible. FIG. 3A shows one modification. That is, Pit 4A: Clock pit.

Pit 4B Nidrucking bit and gray code pit filter function.

Pit 5 Functions as a Nidracking pit and a Gray Code pit.

It's good as well. In this modification, the required minimum length of the servo area is the same as in the first embodiment. Furthermore, the modified example shown in FIG. 3B is as follows: Pit 4A: Functions as a clock pit, a tracking pit, and a gray code pit.

Pit 4B Functions as a pit for the Nidorucking bit and gray code.

It is. In the method shown in FIG. 3B, the minimum required length of the servo area is (e+3T-1), and the length of the servo area is (2T+4'') shorter than in the conventional method.

Note that the access code is not limited to the Gray code, but may also be a natural binary code or the like, and tracks may be identified by the position of one bit.

Furthermore, the present invention is applicable not only to rewritable disks such as magneto-optical disks, but also to write-once disks, non-rewritable ROM disks, and the like.

〔Effect of the invention〕

According to the present invention, the length of the servo area in which the tracking pit and the access code are inserted can be made shorter than in the conventional method. Therefore, the ratio of servo areas available on the disk can be reduced, and the amount of data that can be recorded can be increased. Furthermore, when the length of the servo area is kept the same as before, the number of access code pits can be increased, and the number of tracks that can be identified by this access code is increased. Therefore, the optical pickup can be threaded at high speed during seek, and the seek operation can be made faster.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the configuration of a drive system in an embodiment of the present invention, Fig. 2 is a route diagram for explaining the data format of an embodiment of the invention, and Fig. 3 is a detailed diagram of the invention. FIG. 4 is a route map showing the configuration of a conventional servo area, and FIG. 5 is a route map used for explaining a conventional access code. Explanation of main symbols in the drawings 4A, 4B, 5.6.7: Pit formed in the servo area. Modifications Fig. 3 Fig. 4 Buo 'area afjin skort on the value Fig. 5

Claims (2)

[Claims] (1) Detecting a pair of tracking pits that are offset to the inside and outside of the center position of the track, the pits that make up the access code that changes every predetermined number of tracks, and the timing of the playback signal of the pits. In a tracking servo for an optical disk having clock pits in the servo area, first and second pits are provided offset to the inside and outside with respect to the center position of the track, and the first and second pits are offset from each other to the inside and outside of the track center position. A third pit provided near the second pit is formed in the servo area, a tracking error is detected by the first and second pits, and one of the first, second and third pits is detected. A tracking servo for an optical disc, characterized in that the timing of a reproduction signal of a pit is detected, and an access code is constituted by two of the first, second and third pits. (2) Detecting a pair of tracking pits that are offset to the inside and outside, respectively, with respect to the center position of the track, the pits that make up the access code that changes every predetermined number of tracks, and the timing of the playback signal of the pits. In a tracking servo for an optical disc having a clock pit in the servo area, first and second pits are formed in the servo area and are offset to the inside and outside with respect to the center position of the track. A tracking error is detected by the first and second pits, a timing of a playback signal of the pit is detected by one of the first and second pits, and at least one of the first and second pits detects a tracking error. A tracking servo for an optical disc, characterized in that an access code is configured.