JPS5938939A - Optical disk - Google Patents

Abstract

PURPOSE:To compensate the output of a signal detector with an output of wave detection, by recording a bit of a specific depth which is prewobbled based on a fixed rule, detecting the reproduced waveform of the bit based on a wobble rule and sampling and holding the output of wave detection. CONSTITUTION:It is supposed that a lead light spot passes over a dotted line with the spot center shifted to either one side not the center 210 of a track to a bit train 300 which is prewobbled up to lambda/4 depth (lambda: wavelength of reproduced light). In such a case, a lead waveform is obtained as shown by (b). The lead waveform has an amplification difference DELTA to a shift amount delta from the center of the track. The synchronous wave detection is given to the amplification difference with reference timing as shown by (c) to obtain a DC signal corresponding to an amplitude difference DELTA. Both the reference timing of (c) and a gate signal can be easily produced from a synchronous signal. A gate signal of (d) is used as a control signal to extract a prewobbled region. This process can give an integrated compensation to an offset contained in an optical system of an electric system of a 2D circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical disc, and particularly to an optical disc with improved tracking control accuracy.

Optical discs and devices have been proposed in which guide grooves (referred to as groups) are provided as track information on an optical disc, and information is read and written while tracking based on signals from the groups.

Tracking signal detection in this method uses diffraction of a narrowed laser spot in a laser beam.
It is controlled by a servo system that guides the laser beam to a position where the intensity of the diffracted light on both sides of the group is balanced. The above method uses two detectors (21) etec to detect the diffracted light on both sides of the group.
tor ) and is controlled so that the differential value becomes zero, so it is called the 2D method. The problem with the 2D method is that when the relative angle between the optical spot and the disk changes, the symmetry of the reflected light distribution to the two detectors described above becomes poor, resulting in a non-negligible offset in tracking control. be. Since the above-mentioned relative angle is caused by the inclination or vibration of the disk, in order to keep the offset If within the above-mentioned allowable value, the mechanical precision of the device and the disk must be made even stricter. Therefore, there is a problem in that restrictions must be placed on the design and manufacturing of the device, or on the material of the disk medium.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical disk device capable of correcting an offset signal included in a tracking signal.

Offsets included in the tracking signal, such as offsets due to the inclination of the disk in the 2D system or offsets due to the detection system or amplifier, can be corrected if there is a reference signal that is guaranteed to be at the center of the track. The present invention uses a kota pit. The polarity of the correction signal is determined by the prewobble polarity of the reference signal.

The present invention will be explained in detail by way of examples below. FIG. 1 is a diagram schematically showing an optical disk device. The disk 20 is rotated by a motor 30. The head 10 is a head drive mechanism 4
0 positions the target track. The head 10 includes a laser 1. It includes an optical system 2, a photodetector 3, etc. A signal for positioning is transmitted from the photodetector 3 to a control signal for the drive mechanism 40 by the light spot control circuit 50. A modulation signal according to write information is applied to the laser 1 from a write circuit 70. The read signal from the disk is demodulated by the photodetector 3 and the serial read circuit 60. 80 is a read/write signal processing circuit. FIG. 2 schematically shows a disk 20, in which tracks 21 are formed concentrically or spirally. One lap of the track is divided into several sectors. An example format of each sector is shown in FIG. A sector is divided into a header part 100 and a data part 200.
In 0, the address of the track sector of that part is recorded. The data portion 200 records the true data on the disc. Furthermore, examples of recording in the header section 100 include a mark 110 (SM) indicating the start point of a sector, a section 120 (VFO) indicating a clock reference, and a synchronization signal 130 (8Y
NC), 7)"L/space 140 (ID), gap 150 (GAP) for header processing time, etc. are recorded.

Tracking control is performed to read or write data recorded on a track, so if there is an information pit created in advance at the center of the track, the best tracking state is when it can be read best. It's supposed to be.

Ru. Therefore, in a disc in which the header part is produced at the same time as a group, or in a disc in which the information pit in the header part itself is a track signal, it is guaranteed that the header part information pit is located at the center of the track. Therefore, if there is a difference between the best read condition of the header section signal and the state indicating the track center from the tracking signal detection circuit, the tracking detection signal can be corrected based on the best read condition of the header section. The best read conditions for header signals can be found from so-called pre-wobbled pits. In order to find the center of the trunk using the pre-wobbling method, information on how the trunk is wobbled is required in advance. Therefore, gap 15 in the format shown in Figure 3
If the 00 portion is wobbled by the same amount on the left and right sides of the track as shown in Figure 4, the gap 1
Since the exact position of 50 can be known from the synchronization signal 130 when reading, the serial read signal waveform is checked using the timing signal generated from the synchronization signal and a predetermined wobble rule, and the tracking state at that time is determined on either the left or right side. It is possible to detect the degree of deviation.

In FIG. 5, 210 is a group, and 300 is a pit. Therefore, a correct tracking signal can be obtained by correcting the tracking signal due to the amount of deviation.

However, the above correction cannot be made at all points on the track, so for example, the gap 15 of a certain sector
The correction amount at the 0 position must be held until the next sector gap arrives. An embodiment that realizes the above operation will be described below.

In Figure 5, for a pre-wobbled pit row as shown in (a), if the lead light spot is shifted to one side instead of the center of the track and the spot center passes on the dotted line, the lead waveform will be as shown in (b). .

That is, an amplitude difference of Δ occurs in the read waveform with respect to the amount of deviation δ of the optical spot from the track center. By synchronously detecting this at the reference timing as shown in (c), a DC signal corresponding to the amplitude difference Δ is obtained. The reference timing in (c) and the gate signal in (c) can be easily created from a synchronization signal. The gate signal in ) is used as a control signal for extracting the prewobbled region. FIG. 6 is a circuit diagram showing an embodiment of the above-mentioned corrected tracking signal circuit.

31 and 32 are two photodetectors for 2D signal detection, and the difference signal between them is produced by an amplifier 51 and becomes the source of a tracking signal. On the other hand, an amplifier 61 generates a sum signal of the 2D output. This is a normal data read signal. From now on, the peak detection circuit 62. Clock regeneration circuit 63. Synchronous signal detection circuit 64
The reference timing signal 650 shown in FIG. 5(c) and the gate signal 651 shown in FIG. From the output of the amplifier 61 and the timing signal 650, the synchronous detection circuit 66 detects △ in FIG.
Generate an amount corresponding to. This output is used as gate signal 65
1, the sample and hold circuit 67 samples the gate signal 651 in the "tl" interval and holds it in the '0' interval.The held signal value 670 is multiplied by an appropriate coefficient G'k and calculated as described above. The detection signal 52 from the 2D and the adder 53 are added to form a tracking control signal 55.

Here, the output 670 of the sample bold circuit 67 is the fifth
The polarity and absolute value change according to the direction and amount of deviation of the light spot from the track center shown in the figure. The relationship between the amount of deviation and the correction signal 54 can be changed by appropriately selecting the input/output characteristics of the function generator 68.

As described above, according to the present invention, it is possible not only to compensate for the offset of the tracking signal in the 2D detector due to the inclination of the disk, but also to comprehensively compensate for the offset included in the optical system and electric circuit system of the 2D circuit. Compensation is not continuous but zumbling, but the frequency that causes the offset is very low, and sampling about 10 times per track is sufficient, whereas normally one track is divided into several dozen sectors. Therefore, there is no problem at all as a sampling frequency. That is, there is no need to newly provide a reference focus area when implementing the present invention.

[Brief explanation of drawings]

Figure 1 is a diagram showing an overview of the configuration of an optical disc device, Figure 2 is a diagram showing the state of tracks on a disc, Figure 3 is a diagram showing an example of a sector format, and Figure 4 is a diagram showing a pre-wobbled reference pit. Figure 5 is a diagram showing an example, and Figure 5 is a diagram showing a signal waveform for generating a correction signal from the reference pit.
The figure shows the correction signal.

Claims (1)

[Claims] A track signal detector has a track guide groove formed in a concentric circle or a spiral shape on the disk, and detects the balance of diffracted light from the track, and a track signal detector that detects the balance of diffracted light from the track, and wavelength) or light and dark pits are recorded in a plurality of predetermined areas on the track, a means for detecting a reproduced waveform of the pits according to the wobble rule, and a means for sampling the detection output and recording the pits. a means for holding the section where the
An optical disc characterized in that the output of the track signal detector can be corrected based on the output of the holding means.