JPH04372724A - Optical disk reproducer - Google Patents

Abstract

PURPOSE:To reduce a cross talk at the time of narrowing a track pitch. CONSTITUTION:A sine wave is generated in a sine wave generating circuit 7 synchronously with a wobble clock generated in a wobble clock generating circuit 6. The wobbling of a galvano mirror 4 is operated corresponding to this sine wave. An A/D converter 10 samples the level of an RF signal inputted from a head amplifier 9 synchronously with the wobble clock, and the sampling value is A/D converted. An arithmetic circuit 11 searches the data of a prescribed track by an arithmetic operation from this sampling value.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a disc reproducing apparatus suitable for use, for example, in reproducing information recorded on an optical disc.

0002

2. Description of the Related Art Since optical disks have a larger capacity than magnetic disks, they have recently come to be used in various fields. When reproducing recorded data from this optical disk, the reproduction light beam is caused to trace the center of the track by tracking control using a continuity servo method or a sample servo method.

0003

By the way, there is also a demand for further improving the recording density of optical discs, and it is being considered to make the track pitch narrower. However, when the track pitch is narrowed, data from adjacent tracks leaks into the signal and appears as crosstalk with respect to the signal from the target track.

The present invention was made in view of the above situation, and is an object of the present invention to suppress crosstalk from adjacent tracks and to enable correct reading of data even when the track pitch is narrowed. be.

[0005]

[Means for Solving the Problems] A major feature of the optical disc reproducing apparatus of the present invention is that it is equipped with calculation means for calculating data recorded on the disc in correspondence with the output of the reading means and the output of the wobbling means. It is said that In the embodiment, the reading means is composed of an optical unit 3, an objective lens 5, and a head amplifier 9, and the wobbling means is composed of a galvanometer mirror 4, a wobble clock generation circuit 6, and a sine wave generation circuit 7. Also,
The calculation means is constituted by a calculation circuit 10 in the embodiment.

[0006]

[Operation] In the optical disc playback device configured as described above, the data recorded on the optical disc is calculated by calculating the output of the reading means such as an optical head and the output of the wobbling means such as a wobble clock generating circuit. It will be done. Therefore, even if the track pitch is narrowed, it is possible to suppress interference due to crosstalk.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing the configuration of an embodiment of an optical disc reproducing apparatus of the present invention. The optical disk 1 is rotated by a spindle motor 2, and a laser beam emitted from a laser diode included in an optical unit 3 is reflected by a galvanometer mirror 4, and is focused and irradiated by an objective lens 5. A wobble clock generating circuit 6 generates a clock of a constant frequency, and a sine wave generating circuit 7 generates a sine wave signal synchronized with this wobble clock. This sine wave signal is input to a drive amplifier 8 to drive the galvanometer mirror 4. The head amplifier 9 amplifies the RF signal output from the optical unit 3 and supplies it to the A/D converter 10. A/D converter 10
A/D converts the wobble clock input from the wobble clock generation circuit 6 and the RF signal input from the head amplifier 9, and outputs the result to the arithmetic circuit 11.

Next, its operation will be explained. The laser light emitted by the laser diode built into the optical unit 3 is incident on the galvanometer mirror 4, where it is reflected.
The light is incident on the objective lens 5. The objective lens 5 focuses the incident laser light and irradiates it onto the optical disc 1. The laser beam reflected on the optical disc 1 is transmitted through an objective lens 5,
The light enters the optical unit 3 via the galvanometer mirror 4. Optical unit 3 has a built-in photodiode.
The photodiode receives the incident laser light and outputs a reproduced RF signal. This reproduced RF signal is amplified by the head amplifier 9 and input to the A/D converter 10.

On the other hand, the wobble clock generating circuit 6 generates a wobble clock of a constant frequency (for example, a frequency four times or more of the clock of data recorded on the optical disk 1), and outputs it to the sine wave generating circuit 7. The sine wave generating circuit 7 generates a sine wave signal in synchronization with the input wobble clock. The drive amplifier 8 drives the galvanometer mirror 4 using this sine wave signal. As a result, the galvanometer mirror 4 is periodically rotated, and the spot of the laser beam on the optical disk 1 is periodically moved (wobbled) in a direction perpendicular to the track, as shown in FIG.
.

Therefore, for example, if the galvanometer mirror 4 is displaced as shown in FIG. 3(a) in response to a sine wave signal and a wobble clock is generated as shown in FIG. 3(b), this wobble clock If the displacement of the galvanometer mirror 4 is 0 at the timing of the rising edge of
Sampling the level of the reproduced RF signal when it has a positive peak and when it has a negative peak, Figure 3
The result is as shown in (c). The A/D converter 10 samples the reproduced RF signal inputted from the head amplifier 9 in synchronization with the wobble clock inputted from the wobble clock generation circuit 6, converts the sampled value into A/D, and outputs it to the arithmetic circuit 11. Output to. The arithmetic circuit 11 reads data recorded on the optical disc 1 from input data in the following manner.

That is, if wobbling is performed centering on track 0 as shown in FIG. 4, and when the amount of displacement due to wobbling from track 0 is x, the output level of the reproduced RF signal is as shown in FIG. It can be expressed as a function I(x) of the displacement x as follows. In this embodiment, the function I(x) is 1 when the amount of displacement x is 0, and is 0 when the amount of displacement x is larger than x1. Then, when the displacement x is from 0 to x1, it gradually decreases from 1 to 0.

As shown in FIG. 6, if the level of the reproduced RF signal when the amount of displacement x from the track is 0 is D, then the level when the amount of displacement is x is DI(x).

According to this principle, position A on track 0 in FIG. 4, position B displaced from track 0 by a displacement amount X toward the track +1 side on the right side in the figure, and position B displaced by a displacement amount X in the track -1 direction. The levels A, B, and C of the reproduced RF signal at C are (1) to (1) to (
3) It becomes as shown in the formula. A=I(0)D0+I(P)D1+I(P)D-1
...(1) B=I(X)D
0+I(P-X)D1+I(P+X)D-1...
(2) C=I(X)D0+I(P+X)D1+I(
P-X)D-1...(3)

[0014] Here, D
0, D1, and D-1 represent the levels of the reproduced RF signal when the spotlight is located on track 0, +1, or -1, respectively. Further, P represents the track pitch, and X represents the maximum value of the displacement amount x.

These equations (1) to (3) represent the function I(x
) are constants, so these can be expressed as α, β
, ε, γ, and ρ, it becomes as shown by the following equations (4) to (6). A=αD0+βD1+βD-1
...(4)
B=γD0+εD1+ρD−1
...(5)
C=γD0+ρD1+εD-1
...(6)

[0016] When these equations (4) to (6) are solved for D0, the following equation (7) is obtained. D0=[ρ(ε2-ρ2)]A/[(ε2-ρ2)(ρ
α−βγ) +(ε−ρ)2γβ]+[(ρ
2-ε2)β-(ρ-ε)εβ]B/[(
ε2−ρ2)(ρα−βγ)+(ε−ρ)2αβ]
+[(ρ-ε)βρC] /[(ε2-ρ2)(ρα-βγ)+(ε
−ρ)2αβ] =K1A+K2B+K3C

...(7)

Here, K1 to K3 are constants, and A to C are the levels of the reproduced RF signals at positions A to C in FIG. 4, so the levels at positions A to C are determined in synchronization with the wobble clock, and this Coefficient K to level
The data in track 0 can be read by multiplying by 1 to K3. The arithmetic circuit 11 performs this (
7) The calculation shown in the formula will be performed.

[0018]

As described above, according to the optical disk reproducing apparatus of the present invention, the optical beam is wobbled, and the data recorded on the optical disk can be obtained by calculation in accordance with the output of the reading means and the output of the wobbling means. Therefore, even when the track pitch is narrowed, it is possible to reduce the influence of crosstalk and read recorded data accurately.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of an optical disc playback device of the present invention.

FIG. 2 is a diagram illustrating a state in which a light beam is wobbled.

FIG. 3 is a timing chart illustrating the operation of the embodiment in FIG. 1;

FIG. 4 is a diagram illustrating a trace locus when a light beam is wobbled.

FIG. 5 is a graph showing changes in the level of a reproduced RF signal when a light beam is displaced from a predetermined track.

FIG. 6 is a diagram illustrating changes in the level of a reproduced RF signal when the light beam is displaced and when the light beam is not displaced.

[Explanation of symbols]

1 Optical disc 3 Optical unit 4 Galvano mirror 5 Objective lens 6 Wobble clock generation circuit 7 Sine wave generation circuit 10 A/D converter 11 Arithmetic circuit

Claims (1)

[Claims] 1. Reading means for irradiating an optical disk with a light beam and reading data recorded on the optical disk; wobbling means for wobbling the light beam irradiated on the optical disk at a predetermined cycle; An optical disc reproducing apparatus characterized by comprising: an arithmetic means for calculating data recorded on the optical disc in accordance with an output and an output of the wobbling means.