JPH03260914A - Optical disk reproducing system - Google Patents

Abstract

PURPOSE:To narrow the track pitch and to enhance the recording density and then to highly speed up the read of data by irradiating over two tracks with a light beam spot. CONSTITUTION:Scanning is performed when the center of the beam spot SP is positioned at a middle point between the tracks as under the just tracking state. A middle position between the tracks is irradiated by the spot SP. By this method, information by pots P on the tracks TKn and TKn+1 can be read out by scanning them in one revolution. As a result, the data read-out speed is approximately doubled.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an optical disc playback method.

[Summary of the Invention] The optical disc playback method of the present invention performs playback scanning with a light beam by setting the intermediate position between a track and its adjacent track as the proper center position of the beam spot, and This allows the data recorded on the two tracks to be read simultaneously.

[Prior Art] When reproducing an optical disk (including a magneto-optical disk) using a light beam, as is well known, uneven pits (in the case of a magneto-optical disk, vertical six in the N direction or the S direction) are formed.
As shown in FIG. 6, a track on which digital data is recorded by R field is scanned while performing tracking control so that the beam spot SP follows the track center Tc. By always performing on-track scanning in this manner, information on pits P formed on the track can be accurately read.

[Problems to be Solved by the Invention] In recent years, among various technical issues in data recording systems that use optical discs as recording media, there has been an increase in recording density and read speed (transmission speed of digital information).
Increasing the speed of this process is a particularly important issue, and various research is being carried out.

Regarding recording density, the track pitch is usually set to (1,61
Increasing the number of tracks on a disk by making the tracks narrower (approximately 500 m) is one of the most effective ways to improve recording density, but it is important to prevent crosstalk from adjacent tracks when scanning tracks for playback. Therefore, it is difficult to further narrow the track pitch, and there is a problem in that it is difficult to realize this.

In addition, regarding data transmission speed, since only one track's worth of data can be read in -circular scanning (scanning for one rotation of the disk), various improvements have been made in the playback signal processing circuit system, data recording density, disk rotation speed, etc. Even if we do so, there is a problem that there are limitations. In other words,
Of course, as long as one track is scanned with one beam spot, the light beam will scan digital data read from one track of an optical disc, for example.
It is impossible to read and transmit in less time than it takes to read and scan a track.

[Means for Solving the Problems] The present invention has been made in view of the above problems, and has two objectives: to improve the recording density by making it possible to narrow the track pitch, and to improve the data reading speed. The purpose is to speed up the process more effectively.

That is, tracking control is performed using the center position of the beam spot of the light beam as the center position between two adjacent tracks, and reproduction scanning is performed so that the beam spot of the light beam is irradiated over the two tracks. This is an optical disc playback method that allows two tracks of recorded data to be read in one round scan.

[Function] Since data for two tracks can be read in one scan, the data transmission speed can be almost doubled, and since two tracks are irradiated with a light beam at the same time, the track pitch can be reduced to less than half of the conventional one. It becomes necessary to fill up the
This allows the number of tracks to be more than doubled.

[Example] FIG. 1 is a schematic diagram for explaining the reproduction method of the present invention, where TKn, TK, . . . indicate tracks formed on the recording surface of an optical disc, and each track contains data. is recorded as bit P.

Further, SP indicates a beam spot of a reproduction light beam, and reproduction scanning is performed in the direction of the arrow by rotation of the disk. As shown in the figure, the beam spot SP is irradiated at an intermediate position between the tracks (that is, a state where tracking is completely off in the conventional tracking method), but in the reproduction method of this embodiment, this state is A just tracking state is set, and tracking control is performed so that the optical spot SP follows the intermediate position between the tracks and performs reproduction scanning.

In addition, the track pitch W is set so that when the beam spot SP is irradiated to the middle position of the track to perform scanning, each bit P on the tracks TK, , TK, . . . on both sides of the beam spot SP can be read. The length is set to less than half that of a normal optical disc (approximately 1.611 m).

That is, in this embodiment, scanning is performed with the center of the beam spot SP positioned at the midpoint between the tracks as the just tracking state, and both tracks TK.

Since the information from bit P above TK can be read in one round scan, the data reading speed is almost doubled compared to the normal playback method, which can read only one track's worth of data in one round scan. You will be able to do that.

Actual scanning on the optical disc is performed as shown in FIG.

A solid line TKn-TKn+5 indicates the center of a track formed concentrically on the recording surface of the optical disk, and data is recorded on this track TK as a bit P as shown in FIG. 1 above.

Note that this track may be formed in a spiral shape. In addition, in the optical disc to which the playback method of this embodiment is applied, each track TK includes:
As shown in the figure, a non-recorded portion is provided as a traverse area AT.

Scanning by the light beam in this embodiment is performed as shown by the dotted line in the figure. That is, the beam spot SP is first placed on the track TK, .

TKn+1 is scanned at the same time, and the data of tracks TKn, TK, . . . 1 is read in one round scan. Then, a track jump is performed when the traverse area hole 〇 is reached, and the beam spot SP is on the track T K 11+2+
It is controlled to an intermediate position of T K n,3. Then, in one round scan, the tracks T K n, 2. After reading the data on the tracks T K , , 3, a track jump is performed when the traverse area AT is reached, and the beam spot sp is set on the tracks T K , , 4 . Move to the intermediate position of T K n,5. Thereafter, reproduction scanning is performed in the same manner.

The above-described reproducing operation allows data reading to be performed at approximately twice the speed as compared to normal track scanning for each track.

43. The track jump in the traverse area AT described above requires 60QI including the settling time after the jump.
About Lsec is required, but for example, if the disk rotation is 3
In the case of 600 rpm, the average track length used as the traverse area hole 0 is about 5% of one track length. For this reason, the amount of data that can be recorded in one track is reduced by about 5%, but as described above, in this embodiment, the track pitch is set so that the beam spot SP is irradiated on two tracks at the same time. must be set to less than half of the
Since the total number of tracks can be doubled or more, the overall recording density can be greatly improved.

By the way, in this embodiment, as described above, two tracks are simultaneously read by one beam spot SP, so that the reproduced output is a combination of the recorded data of both tracks.

Therefore, the data of the two scanned tracks must be extracted separately from the reproduced output.

One method for making this possible is to use a data recording method such that bit positions on even-numbered tracks and odd-numbered tracks, that is, on adjacent tracks, are never adjacent to each other.

To do this, for example, as shown in Figure 3, in a normal optical disc recording system, the reference clock CK, which is used as the channel clock during recording, is divided by half, and two clocks with opposite phases are created. CK2. Generate CK3. And this clock CK2. CK3 is used as a recording channel clock and is switched between even-numbered tracks and odd-numbered tracks.

For example, as shown in the figure, track TKn uses channel clock CK2 to modulate recorded data to form bits using the position recording method described later, and tracks TK, . . . use channel clock CK3. If bits are formed by modulating recorded data using the position recording method, the bits P in adjacent tracks will not be adjacent to each other in the disk radial direction (perpendicular to beam scanning).

Note that the position recording method adopted as the data modulation method is, as shown in FIG.
Bit P as shown on track TK for 1°
The pit lengths of all bits P are uniform until they are formed. On the other hand, in the case of the edge recording method shown in FIG. 4(b), as shown in the figure, there is a characteristic that the pit lengths are long and short, so even if two channel clocks with opposite phases are used, bit P is Since it is impossible to prevent radially adjacent portions from forming, this embodiment cannot be said to be suitable.

As described above, the reproduction method of the present invention is made possible by preventing the bits P from adjoining between adjacent tracks.

That is, as shown in FIG. 3, the tracks TKn, TK, .
When P scans, a reproduced RF signal as shown is obtained from the optical head.

This reproduced RF signal is a composite of the recorded data on tracks TKn, TKn, .
For the F signal, the above channel clocks CKa, CK
RF++ by extracting the signal components using
11, RFfn*+l, it is possible to accurately separate the reproduced data into tracks. Therefore, by scanning two tracks at once,
There are no problems such as not being able to obtain accurate playback data or problems such as crosstalk occurring.

Note that, as a tracking control method for carrying out this embodiment, for example, a method using a gray code can be considered.

When adopting the sampled support method as a control method during recording and playback of an optical disc, in each block, which is the minimum unit recording division in each track, as shown in FIG. A control information area ARs is provided in the clock bit Q used for generating the channel clock. As soon as the is formed,
16 to identify the track number (0 to F in the diagram) in detail
Gray code Q for each track. , Ql is area AR6
It is formed in the part of

When such a gray code area is scanned with the optical spot SP, a relatively large level of amplitude is obtained as an RF signal component in the areas where the bits are adjacent, and a relatively small level of amplitude is obtained in the areas where the bits are not adjacent. can get. For example, as shown in the figure, when the optical spot SP scans between tracks 2 and 3 in the direction of the arrow, the gray code bits Q D2 located next to each other on the reproduced RF signal appear.
A relatively large level of amplitude appears with 1Q a, 1 2 , a relatively small level of amplitude is obtained with Gray code bit Q, :3, and then a similar comparison is made with Gray code bit Q E2. A small-scale amplitude can be obtained.

In other words, among the amplitudes obtained on the RF signal by scanning the Gray code area, the second and third amplitudes are the parts where bits are not adjacent between the two tracks being scanned. Therefore, by detecting the amplitudes at the second and third levels and performing subtraction processing on these two amplitude levels, information on which track the beam spot has shifted toward the center, that is, a tracking error signal, can be obtained. Obtainable.

In this embodiment, if a tracking error signal is generated by such a method, for example, it becomes possible to perform scanning by controlling the beam spot to an intermediate position between tracks, as described above.

[Effects of the Invention] As explained above, in the optical disc playback method of the present invention, the case where the beam spot is irradiated at the intermediate position between tracks is controlled as the just tracking state, and two tracks on both sides are simultaneously scanned. By doing so, data for two tracks can be read in one round scan, and the reading speed (data transmission speed) can be almost doubled.

Furthermore, since the track pitch needs to be narrowed, the number of tracks can be increased, and the recording density can also be significantly improved.

[Brief explanation of drawings]

Fig. Y is an explanatory diagram of an embodiment of the reproduction method of the present invention, Fig. 2 is an explanatory diagram of the scanning method of the embodiment of the reproduction method of the present invention, and Fig. 3 is a diagram of the recording method and reproduction applied in this embodiment. 4(a) and 4(b) are explanatory diagrams of the position recording method and edge recording method. Section 5 is a schematic diagram of the control information area for explaining the tracking method that can be adopted in this embodiment. FIG. 6 is an explanatory diagram of scanning using a conventional beam spot. T K n to T K r, -s represents a track, SP represents a beam spot, P represents a bit, and AT represents a traverse area. Field H 10 tough sugar

Claims (1)

[Claims] By setting the center position of the beam spot of the light beam at the middle position between two adjacent tracks on the optical disk and performing reproduction scanning so that the beam spot of the light beam is irradiated over the two tracks, the reproduction can be performed in one round scan. An optical disc playback method characterized by being able to read two tracks of recorded data.