JP3231812B2 - Optical disk drive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk apparatus for recording or reproducing data on a disk by using a laser beam.

[0002]

2. Description of the Related Art Hitherto, there has been known an optical disk recording apparatus for recording data by heating a recording medium using the energy of a laser beam and changing its magneto-optical properties.

First, a conventional optical disk recording apparatus will be described with reference to FIGS. FIG. 2 shows a basic configuration example of a conventional optical disk recording apparatus. In FIG. 2, D is a guide sign type magneto-optical disk capable of rewriting (overwriting) data, in which a large number of recording tracks are divided into a plurality of sectors at an equal angle, and each sector has a plurality of sectors at an equal angle. And three guide marks Pa to Pc as shown in FIG. 3 are formed in a specific area (so-called servo area) of each segment.

An optical head 10 includes a laser diode 11, photodiodes 12 and 13, and an optical system represented by a beam splitter 14.
Data is written (or read) by a light beam radiated from the laser diode 11 disposed opposite to the magneto-optical disk D.

At the time of recording, digital data is input to the input terminal I.
N to the encoder 21 to be converted to a predetermined format and to a recording signal conforming to, for example, a pulse position modulation type modulation method. The output of the encoder 21 is supplied to a light intensity modulating circuit 22,
Output from the laser diode 1 via the drive amplifier 23.
1 to control the intensity of the emitted light intermittently.

[0006] A part of the light emitted from the laser diode 11 is separated by the beam splitter 14 and detected by one of the photodiodes 12, and the detected output is passed through an amplifier 24 and a low-pass filter 25 to a comparator 26. And is compared with the set reference value of the reference voltage source 27. The output of the comparator 26 is fed back to the light intensity modulation circuit 22, the light intensity (power level) of the laser diode 11 is controlled to a constant value, and so-called APC is performed. As a result, a recording layer (not shown) of the optical disc D, which is driven to rotate at a constant angular velocity (CAV), records a length corresponding to the irradiation pulse width of the laser beam under an external magnetic field by the electromagnet 15, for example. An area (mark) is formed.

At the time of recording (or at the time of reproduction), the reflected light from the optical disk D is detected by the other photodiode 13 via the beam splitter 14, and the detection output is supplied to the servo control circuit 30, Various servo controls of the optical head 10, such as focus control and tracking control, are performed.

As described above, the guide mark formed in the servo area of each sector of the disk D, as shown in FIG.
Control pit (so-called clock pit) Pc serving as a reference
Are provided on the center line of the track, and a pair of control pits (so-called servo pits) Pa and Pb are spaced from each other by a predetermined distance in the track direction and have a track pitch p with respect to the center line of the track. 1/4 each
(Offset).

At the time of recording or reproduction, for example, when the servo area of each sector is scanned by the light beam spot BS having a diameter of about 1/2 of the track pitch p, the photodiode 13 of the optical head 10 outputs the signal shown in FIG. As shown, a series of detection signals (reproduced RF signals) peaking at timings corresponding to the pits Pa, Pc, and Pb are obtained.

As is well known, the beam spot BS
Is a so-called on-track scanning on the center line of the track, the peak levels Apk and Bpk of the reproduced RF signals Sa and Sb respectively corresponding to the servo pits Pa and Pb are equal. Therefore, the tracking control includes the reproduction R
A difference signal between the F signals Sa and Sb can be used. Actually, the reproduced RF signals Sa and Sb are respectively sampled and held at the rising timing of the channel clock CKch as shown in FIG. 4B, and a difference signal for tracking control is formed.

Further, the above-mentioned channel clock CKch
Indicates that both servo pits P
a, the intermediate level of the reproduced RF signals Sa, Sb corresponding to Pb (level near the middle of the upper and lower peak levels)
m1, Am2; Bm1, Bm2 are sampled, and (Am1-Am2)
The operation of + (Bm1−Bm2) is performed, and the result of this operation is generated from the PLL circuit injected as the phase error signal. As shown in FIG. 4, the phase is accurately synchronized with both servo pits Pa and Pb. Can be. [JP-A-3-156
No. 774 (Japanese Patent Application No. 1-295141)]

[0012]

As described above, in the conventional optical disk recording apparatus, the laser diode 11 emits light of a constant intensity to the disk D. However, the reflectivity of the disk D is allowed to fluctuate in any part of each disk, for example, within a range of ± 12%.

Due to the change in the reflectivity of this disk, the reproduction R
When the level of the F signal fluctuates, the level of the difference signal for tracking control as described above and the level of the phase error signal of the PLL circuit also fluctuate. In other words, when scanning each part of an individual disk, there is a problem that the loop gain of the servo system fluctuates, the margin decreases, and jitter and tracking error increase, or inconvenience such as instability of the servo system occurs. there were.

When a disc is recorded in the CAV system, the spatial frequency characteristics (Modulation
Since the Transfer Function changes depending on the radius of the track, the level of the reproduced RF signal fluctuates between the inner and outer circumferences of the disk, for example, by about 20%, further aggravating the above-described problem.

In general, fluctuations in the signal level can be absorbed by using an automatic gain control amplifier. However, when the rotation speed of the optical disk is, for example, 3600 rpm, the frequency of the reproduced RF signal of the servo pit is, for example, about 8 MHz, and for example, in small steps of ± 25%.
It is difficult to obtain a program gain control amplifier having good phase characteristics.

In view of the foregoing, an object of the present invention is to eliminate the influence of uneven reflection of an optical disk and changes in spatial frequency characteristics, to easily obtain a reproduction RF signal of a constant level, and to stabilize the operation of a servo system. To provide an optical disk device capable of performing such operations.

[0017]

As shown in FIG. 1, for example, the optical disk apparatus according to the present invention includes a light receiving element 13 for detecting a reflected light of a light beam BS emitted from a laser light source 11 to an optical disk D, and a detecting means for detecting the light receiving element 13. Of the outputs, the detection output from a pair of control pits Pa and Pb provided at a predetermined distance in the track direction and at a predetermined distance from the center line of the track is used for tracking control. A sample-and-hold circuit 32, 33, 35 for obtaining a pair of peak level signals S32, S33; a subtractor 36 for subtracting the pair of peak level signals S32, S33 to obtain a tracking control signal _Stk ; Adder 37 for adding the peak level signals S32 and S33 of the above, and a comparator 26 for comparing the output of the adder 37 with the reference value 27.
And the output of the comparator 26 is
And the intensity of the light beam is controlled.

[0018]

According to this configuration, the influence of the uneven reflection of the optical disk and the change in the spatial frequency characteristic is eliminated, and a reproduced RF signal of a constant level is easily obtained, and the operation of the servo system is stabilized.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which an optical disk apparatus according to the present invention is applied to an optical disk recording apparatus for a guide sign type disk will be described below with reference to FIG.

FIG. 1 shows the configuration of an embodiment of the present invention.
In FIG. 1, portions corresponding to FIG. 2 described above are denoted by the same reference numerals, and redundant description will be omitted.

In FIG. 1, the optical head 10R does not have the photodiode 12 (see FIG. 2) for detecting the light emitted from the laser diode 11 as described above.
And a photodiode 13 for detecting light reflected from the light source. 30A is a servo control circuit, and its amplifier 31
, The output of the photodiode 13 is supplied to the pair of sample and hold circuits 32 and 33 and the PLL circuit 34 in common, and the output of the PLL circuit 34 is supplied to the timing signal generation circuit 35.

The timing signal from the generator 35 is supplied to the sample and hold circuits 32 and 33, respectively.
The outputs of the sample and hold circuits 32 and 33 are supplied to a subtractor 36, respectively, and the output of the subtracter 36 is derived as a tracking control signal Stk. Servo control circuit 30A
The configuration as described above is almost the same as the conventional one.

In this embodiment, an adder 37 is provided in parallel with the subtractor 36. The outputs of the sample hold circuits 32 and 33 are supplied to the adder 37, and the adder 3
7 is supplied to a comparator 26. Other configurations are the same as those in FIG.

Next, the operation of the embodiment of the present invention will be described with reference to FIGS. In this embodiment, an optical disk of a guide sign type as described above is used. During recording or playback, as shown in FIG.
When the servo pits Pa and Pb in each servo area of the optical disk are scanned by the beam spot BS having a diameter of p / 2, the photodiode 13 of the optical head 10R outputs
At timings corresponding to the pits Pa and Pb, reproduced RF signals Sa and Sb as shown in FIG. 4A are obtained.

In the sample and hold circuits 32 and 33, the reproduction R
The peak levels Apk and Bpk of the F signals Sa and Sb are sampled and held, and sample and hold circuits 32 and 33 are provided.
The output signals S32 and S33 are expressed by the following equation 1 with reference to when the light beam spot BS is on-track.

S32 ≒ αsin (2πx / p) + β S33 ≒ −αsin (2πx / p) + β where x is a shift in the radial (radial) direction (tracking offset), and the peak level Apk, Bpk and x =
Since it is 0, Apk = αsin (2πx / p) + β = β Bpk = −αsin (2πx / p) + β = β

As described above, the tracking control signal Stk is formed from the signals S32 and S33 in the subtractor 36. In the adder 37, a sum signal Ssm is formed from the output signals S32 and S33 of the sample and hold circuits 32 and 33. The value of the sum signal Ssm is, as apparent from the following equation, the offset of the beam spot BS. Regardless of the amount x, for example, it is substantially constant within a range of ± 10%. Ssm = S32 + S33 ≒ 2β

In the comparator 26, the sum signal Ssm is compared with a reference value set by the voltage source 27.
The output of 6 is fed back to the light intensity modulation circuit 22, and the power level of the laser diode 11 is controlled so that the level of the sum signal Ssm becomes constant in each part of the optical disk.

As is apparent from the above, the level of the sum signal Ssm directly depends on the peak levels of the reproduced RF signals Sa and Sb, which are affected by the uneven reflection of the optical disk and changes in the spatial frequency characteristics. Therefore, in this embodiment, the laser diode 1 is controlled so as to obtain a sum signal Ssm of a constant level.
By controlling the power level of 1, the effects of uneven reflection of the optical disk and changes in the spatial frequency characteristics can be easily removed, and the operation of the servo system can be stabilized.

Although the above-described embodiment uses an overwrite type recording medium, the present invention can be applied to a read-only type or write-once type recording medium.

[0030]

As described in detail above, according to the present invention,
In the optical disk device, a pair of reproduction RF signals for forming a tracking control signal is obtained from the reflected light receiving element of the optical head, and a power level control signal is generated based on a sum signal formed by adding the reproduction RF signals. Since the optical disk drive is formed and controls the power level of the light beam from the laser light source, an optical disk device that can eliminate the effects of uneven reflection of the optical disk and changes in the spatial frequency characteristics and stabilize the operation of the servo system has been developed. can get.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of an optical disk device according to the present invention.

FIG. 2 is a block diagram illustrating a configuration example of a conventional optical disc device.

FIG. 3 is a schematic diagram for explaining the present invention.

FIG. 4 is a waveform chart for explaining the operation of the conventional example.

[Explanation of symbols]

 10R, 10M Optical head 11 Laser diode 13, 16 Light receiving element 26 Comparator 27 Reference voltage source 32, 33 Sample hold circuit 34 PLL circuit 37 Adder

────────────────────────────────────────────────── ─── Continuing on the front page (72) Hiroshi Sumihiro 6-35, Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (72) Inventor Masaji Sato 6-35, Kita-Shinagawa, Shinagawa-ku, Tokyo No. Sony Corporation (56) References JP-A-61-255540 (JP, A) JP-A-59-72659 (JP, A) JP-A-60-258732 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G11B 7 / 005,7 / 125

Claims (1)

(57) [Claims] 1. A light-receiving element for detecting reflected light of a light beam emitted from a laser light source onto an optical disk, and a detection output of the light-receiving element, each of which has a predetermined distance in a track direction and a center line of a track. A sample-and-hold circuit for obtaining a pair of peak level signals for tracking control using detection outputs from a pair of control pits provided at a predetermined interval, and subtracting the pair of peak level signals A subtractor that obtains a tracking control signal by adding the pair of peak level signals; and a comparator that compares an output of the adder with a reference value. An optical disc device, wherein the intensity of the light beam is controlled by returning to a laser light source.