JPH0520707A - Tracking controller - Google Patents

Abstract

PURPOSE:To provide a tracking controller hardly generating the pulselike noise in a tracking control system. CONSTITUTION:The reflected light received from an optical disk 6 of a leading light beam 6b is received by a 1st photodiode 7. The output of the photodiode 7 undergoes the current/voltage conversion through a 1st current/voltage converter means 9. Then the current/voltage conversion output is delayed by a delay means 15 having a delay element larger than at least the primary value. The reflected light received from the disk 6 of a follower light beam 6d is received by a 2nd photodiode 8, and the output of the photodiode 8 undergoes the current/voltage conversion through a 2nd current/voltage converter means 10. A subtractor means 11 carries out the substantial subtraction between the current/voltage conversion output and the output of the means 15. Then the phase and the low band of the subtraction output are compensated by a loop filter means 12. A tracking actuator 14 is displaced by a tracking drive means 13 in accordance with the output of the means 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk reproducing apparatus, and more particularly to a tracking control apparatus used for reproducing compact disks and laser disks.

[0002]

2. Description of the Related Art In recent years, tracking control devices using the three-beam method have been widely used in compact disc players and laser disc players.

A conventional tracking control device will be described below. FIG. 6 is a block diagram of this conventional tracking control device. In FIG. 6, the light beam emitted from the laser diode 1 is converted into parallel light by the first lens 2 and is converted into parallel light by the diffraction grating 3.
It is split into two light beams. These three light beams are passed through the beam splitter 4 and the objective lens 5 to the optical disc 6
Incident on the upper information track 6a, the preceding sub-beam 6b,
A main beam 6c and a trailing sub beam 6d are formed.
These three light beams again pass through the objective lens 5 and the beam splitter 4, and the preceding sub beam 2b is incident on the first photodiode 7 and the succeeding sub beam 2d is incident on the second photodiode 8, respectively.

The first photo diode 7 is an optical disk 6
The preceding sub-beam 6b reflected from the
Convert to ₁ . The second photo diode 8 receives the trailing sub beam 6d reflected from the optical disc 6 and converts it into a photocurrent I ₂ . The first current-voltage converting means 9 includes a first operational amplifier 9a and a first resistor 9b having a resistance value R ₁ .
Converts the photocurrent I ₁ into a voltage V ₁ . Meanwhile, the second
The current-voltage converting means 10 converts the photocurrent I ₂ into the voltage V ₂ by the second operational amplifier 10a and the second resistor 10b having the resistance value R ₁ . The subtracting means 11 includes a third operational amplifier 11a and resistors 11b, 11c, 11 having a resistance value R _2.
The voltages V ₁ and V ₂ are subtracted by 1: 1 by d and 11e and output as a tracking error signal TE. The tracking error signal TE is linearly proportional to the relative positional deviation between the information track 6a on the optical disc and the light beam irradiated on it.

This tracking error signal TE is sent to the loop filter means 12 and multiplied by a linearly proportional gain,
Phase compensation and low frequency compensation are performed. The output of the loop filter circuit 12 is voltage-current converted in the next tracking drive means 13, and the tracking actuator 1
4 is driven, and the position of the objective lens 5 is controlled so that the tracking error signal TE becomes zero.

[0006]

However, in the above-mentioned conventional configuration, when there is a defect on the disk, a time difference occurs when the preceding sub-beam 6b and the succeeding sub-beam 6d pass through the defect, so that the tracking control system is pulsed. However, there is a problem in that the stability of tracking control is apt to be impaired due to the generation of noise. The cause is as follows.

Now, the leading sub beam 6b and the trailing sub beam 6b
If the distance difference between the frames 6d is l and the scanning linear velocity is v,
Transit time that occurs when these two beams pass through a defect
Difference τ ₁Is   τ₁= l / v (1) Becomes At this time, the
The transfer function G (s) of the racking error signal is as follows.
It

G (s) = 1-exp (-sτ ₁ ) (2) The frequency characteristic of the gain of this transfer function G (s) is | G (s) | = (2-2cosωτ ₁ ) ^1/2 ( 3) The expression (3) is due to the fact that the gain is doubled for each angular frequency ω of (2n-1) π / τ ₁ and the noise is amplified. Here, n is a natural number.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a tracking control device in which pulse noise is unlikely to occur in the tracking control system.

[0010]

In order to achieve this object, a tracking controller of the present invention comprises an optical system for dividing a light beam emitted from a laser light source into three along an information track on an optical disk. And a tracking control device having an optical pickup equipped with a tracking actuator movable in the radial direction of the optical disc, wherein a first photo diode receives a reflected light in which the preceding light beam is reflected from the optical disc, The first to current-voltage conversion of the output of the first photo diode
Current-voltage converting means, delay means for delaying the output of the first current-voltage converting means by at least a first-order delay element, and a following light beam receiving reflected light reflected from the optical disk. A second photo-diode, a second current-voltage converting means for converting the output of the second photo-diode into current-voltage, an output of the second current-voltage converting means and an output of the delay means. Subtraction means for substantially subtracting, loop filter means for performing phase compensation and low-frequency compensation on the output of the subtraction means, and tracking drive means for displacing the tracking actuator according to the output of the loop filter means. It has a different configuration.

[0011]

According to the present invention, since the preceding sub-light beam is delayed by, for example, the first-order lag element, the crest value of the pulse noise is alleviated by the above-described structure.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a tracking control device according to the first embodiment of the present invention. Figure 1
At, the laser diode 1, the first lens 2, the diffraction grating 3, the beam splitter 4, the objective lens 5, the optical disk 6, the loop filter means 12, the tracking drive means 13, and the tracking actuator 14 are
The laser diode 1, the first lens 2, the diffraction grating 3, the beam splitter 4, the objective lens 5, the optical disk 6, the loop filter means 12, the tracking drive means 13, and the tracking actuator 14 shown in the conventional example of FIG. Since they are the same, the description is omitted.

The first photo diode 7 is the optical disk 6
The preceding sub-beam 6b reflected from the
Convert to ₁ . The second photo diode 8 receives the trailing sub beam 6d reflected from the optical disc 6 and converts it into a photocurrent I ₂ .

The first current-voltage converting means 9 converts the photocurrent I ₁ into a voltage V ₁ by the first operational amplifier 9a and the resistor 9b having the resistance value R ₁ . This voltage V ₁ has a resistance value R ₃
Is supplied to the delay means 15 including a resistor 15b, a capacitor 15c having a capacitance value C _1, and a fourth operational amplifier 15a. The delay means 15 causes a first-order phase delay in the voltage V ₁ with a time constant τ ₂ = C ₁ · R ₃ determined by the resistance value R ₃ and the capacitance value C ₁ , and a low transfer function 1 / (1 + sτ ₂ ). The voltage V ₁ is converted to a voltage V ₃ via a pass filter. here,
s represents a Laplace operator. On the other hand, the second current-voltage converting means 10 includes the second operational amplifier 10 and the resistance value R.
_The photocurrent I ₂ is converted into the voltage V ₂ by the resistor 10b of ₁ .

The voltages V ₂ and V ₃ thus obtained are
Third operational amplifier 11 and resistor 11 having resistance value R ₂
It is sent to the subtracting means 11 composed of b, 11c, 11d and 11e, and is subtracted 1: 1. As a result, the tracking error signal TE is obtained.

When the delay means 15 as described above is added between the first current-voltage converting means 9 on the preceding sub-beam side and the resistor 11d, the tracking error signal TE when passing through the defect on the disk is shown. The transfer function G '(s) is
When the passing time difference between the preceding sub beam 6b and the following sub beam 6d is τ ₁ , it is as follows.

G '(s) = 1 / (1 + sτ ₂ ) -exp (-sτ ₁ ) (4) The frequency characteristic of the gain of this transfer function G' (s) is | G '(s) | = [2-2 ・ (cosωτ ₁ + ωτ ₂ sinωτ ₁ ) / (1 + ω ² τ ₂ ² )] ^1/2 (5). Here, when τ ₁ = τ ₂ is set and the equation (5) is calculated, the frequency characteristic shown by the solid line 20 in FIG. 2 is obtained. The waveform indicated by the broken line 21 in FIG.
The frequency characteristics of equation (3) are shown.

As is apparent from FIG. 2, the peak of the gain for amplifying noise is suppressed as compared with the case of the conventional example, and the maximum gain is about 1.56 times, which is 0.78 times that of the conventional example. The angular frequency that forms the first peak is approximately ω = 1.4π.
/ τ ₁ and the angular frequency that causes the peak shifts by 40%.

As a result, the defective portion is identified as the preceding sub beam 6
b and the noise component generated when the succeeding sub-beam 6d passes are suppressed, and the peak position moves to a high frequency component as shown in FIG. 2. Therefore, when a low pass filter is further installed in the subsequent stage, There is an advantage that it can be easily removed.

FIG. 3 is a block diagram of a tracking control device according to the second embodiment of the present invention. Figure 3
In, a laser diode 1, a first lens 2, a diffraction grating 3, a beam splitter 4, an objective lens 5, an optical disk 6, a first current-voltage conversion means 9, and a second current-
Voltage conversion means 10, subtraction means 11, loop filter means 12, tracking drive means 13, and tracking
The actuator 14 is the laser diode 1, the first lens 2, the diffraction grating 3, the beam splitter 4, the objective lens 5, the optical disk 6, and the first current-voltage converting means shown in the first embodiment of FIG. The second current-voltage converting means 10, the subtracting means 11, the tracking driving means 13, the loop filter means 12 and the tracking actuator 14 are the same as those in FIG.

There are two types of read-only optical discs, a compact disc (abbreviated as CD) and a laser disc (abbreviated as LD), and the difference in reproduction linear velocity reaches about 10 times.
Therefore, according to the equation (1), the time difference τ ₁ generated when the preceding sub-beam 6b and the succeeding sub-beam 6d pass through the defect on the disk due to the difference in the scanning linear velocity is significantly different when reproducing the both. It will be.

The difference between the shapes of CD and LD lies in the difference in disk radius. In the case of CD, the diameter is 12 cm, and LD
In the case of, the diameter is 20 cm or 30 cm. Therefore, the disc type discriminating means 17 uses the difference in the diameters, for example, a photo sensor or the like, to determine the boundary region of the disc diameters, that is, the diameter
By providing the area between 2 cm and 20 cm in diameter, it is possible to determine the type of disk by the presence or absence of reflected light.

In the case of a CD, the switch 16a is closed according to the output of the disc type discriminating means and the delay means 1 is operated.
The capacitor 16c is connected in parallel to the capacitor 15c of No. 5, and in the case of the LD, the switch 16a is released and only the capacitor 15c is used as the capacitor of the delay means 15.

As described above, by providing the switching means 16 for switching the time constant of the delay means in response to the difference in the time taken for the preceding sub-beam 6b and the succeeding sub-beam 6d to pass through the defect depending on the type of the disc. The stable tracking operation is possible even when reproducing different types of discs.

FIG. 4 is a block diagram of a tracking controller according to the third embodiment of the present invention. Figure 4
In FIG. 6, the laser diode 1, the first lens 2, the diffraction grating 3, the beam splitter 4, the objective lens 5, the optical disk 6, the tracking driving means 13, and the tracking actuator 14 are the laser diode shown in the conventional example of FIG. The diode 1, the first lens 2, the diffraction grating 3, the beam splitter 4, the objective lens 5, the optical disk 6, the tracking driving means 13, and the tracking actuator 14 are the same as those of the first embodiment, and therefore the description thereof will be omitted.

The first photo diode 7 is the optical disk 6
The preceding sub-beam 6b reflected from the
Convert to ₁ . The second photo diode 8 receives the trailing sub beam 6d reflected from the optical disc 6 and converts it into a photocurrent I ₂ .

The second current-voltage converting means 10 is added.
Resistance value R₁Resistor 10b and first operational amplifier
Photocurrent I₂The voltage V₂Convert to output
It The second delay means 19 has a resistance value R₃Resistor 19b
And capacity C₁Capacitor 19c and fifth operational amplifier
19a constitutes a first-order low-pass filter,
V ₂The voltage V_FourConvert to. This low pass filter is
Resistance value R₃And capacity C₁Time constant τ determined by₂= C₁・ R₃Have
A first order delay element. This second delay means 1
The transfer function of 9 is 1 / (1 + sτ₂).

Similarly, the first current-voltage converting means 9 is
It is converted into the voltage V ₁ by the added resistor 9 b having the resistance value R ₁ . This voltage V ₁ is a resistor 18b having a resistance value R _3.
And 18d, a capacitor 18c having a capacitance value C _1, a capacitor 18c having a capacitance value C _3, and a fourth operational amplifier 18a, a second-order delay having time constants τ ₃ = C ₃ · R ₃ and τ ₂ = C ₁ · R _3. Voltage V applied to the element and with high-frequency components removed
_{Get 5} The transfer function of this second-order low-pass filter is 1 / {(1 + sτ ₃ ) · (1 + sτ ₂ )}.

The voltages V ₄ and V ₅ thus obtained are
The subtracting means 11 is a third operational amplifier 11a which constitutes the subtracting means 11.
And the resistance R ₂ becomes resistors 11b, 11c, 11d,
Subtract 1: 1 with 11e. As a result, the tracking error signal TE is obtained.

The transfer function G "(s) of the tracking error signal TE when passing through a defect on the disk when the above low-pass characteristics are added to both the leading sub-beam 6b side and the trailing sub-beam 6d side. Is the preceding sub-beam 6
It is as follows when the transit time difference between b and the trailing sub-beam 6d is τ ₁ .

G "(s) = [1 / (1 + sτ ₃ ) -exp (-sτ ₁ )] / (1 + sτ ₂ ) (6) The frequency characteristic of the gain of this transfer function G" (s) is , ｜ G "(s) ｜ = [{2-2 ・ (cosωτ ₁ + ωτ ₃ sinωτ ₁ ) / (1 + ω ² τ ₃ ² )} / (1 + ω ² τ ₂ ² ] ^1/2 (7 Here, if τ ₁ = τ ₂ = τ ₃ and equation (7) is calculated, the frequency characteristic shown by the solid line 40 in Fig. 5 is obtained, which is indicated by the broken line 41 in Fig. 5. The waveform is
The frequency characteristics of equation (3) are shown. As is apparent from FIG. 5, the peak of the gain that amplifies the noise is suppressed as compared with the case of the conventional example, and the maximum gain is about 0.57 times.
0.28 times. The angular frequency that forms the first peak is approximately ω = 0.4π / τ ₁ , and compared with the peak frequency of the conventional example, the angular frequency at which the peak occurs moves to 40% lower angular frequency, but Is a sufficiently small value, so there is no practical problem. As a result, the noise component generated when the preceding sub-beam 6b and the succeeding sub-beam 6d pass through the defective portion is further suppressed as compared with the first embodiment, so that the amplitude of the pulse noise is reduced.

On the other hand, the loop filter means 16 is composed of a digital filter. At this time, in order to sample the tracking error signal TE with an analog / digital converter (not shown), an anti-alias filter for preventing aliasing noise caused by sampling is necessary. In the present embodiment, the anti-alias filter is configured so that each low-pass filter composed of the first delay means 18 and the second delay means 19 also serves. Therefore, there is an advantage that it is not necessary to separately provide a low-pass filter.

In the first and second embodiments described above, the first current-voltage conversion means 9 and the delay means 15 are used.
However, the first current-voltage converting means 9
A capacitor may be connected in parallel to the resistor 9b attached to the same and used also.

In the third embodiment, the first current-voltage converting means 9 and the first delay means 18 are separated from each other, and the second current-voltage converting means 10 and the second delay means 19 are separated from each other. However, a capacitor may be connected in parallel to the resistor 9b attached to the first current-voltage converting means 9 and the resistor 10b attached to the second current-voltage converting means 10 to serve also.

Further, the characteristics of the low-pass filter in the delay means 15 of the first and second embodiments are first-order, but if the order is second or higher, the effect of noise reduction is
Further improve.

In the second embodiment, the switching means is
Although the capacitance of the capacitor of the delay unit 15 is switched, it may be switched to a plurality of low pass filters.

Further, the characteristic of the low-pass filter in the delay means 18 of the third embodiment is second-order, but if the order is third or higher, the noise reduction effect is further improved.

A low-pass filter is mounted on both the first operational amplifier 9a and the second operational amplifier 10a, and the cut-off frequency of the low-pass filter formed on the first operational amplifier 9a is calculated by the second operation. It may be set to be lower than the cutoff frequency of the low pass filter configured by the amplifier 10a.

In addition, the present invention is not limited to the above embodiment, but various modifications can be made.

[0041]

As described above, according to the present invention, by providing the low-pass filter for delaying the preceding sub-beam, noise generated when scanning the defect on the disk can be reduced. This enables stable tracking control.

Further, since the low-pass filter forming the first and second delay means has a structure which also functions as an anti-alias filter required when the loop filter circuit is digitized, the cost is further reduced. There is an advantage that the tracking control device can be configured.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a tracking control device according to a first embodiment of the present invention.

FIG. 2 is a frequency characteristic diagram showing a gain improving effect in the first embodiment.

FIG. 3 is a block diagram showing the configuration of a tracking control device according to a second embodiment of the present invention.

FIG. 4 is a block diagram showing a configuration of a tracking control device according to a third embodiment of the present invention.

FIG. 5 is a frequency characteristic diagram showing a gain improving effect in the third embodiment.

FIG. 6 is a block diagram showing a configuration of a conventional tracking control device.

[Explanation of symbols]

7 First Photo Diode 8 Second photo diode 9 First current-voltage conversion means 10 Second current-voltage conversion means 11 Subtraction means 12 loop filter means 13 Tracking drive means 14 Tracking actuator 15 Delay means

Claims (4)

[Claims] 1. A light comprising an optical system for dividing a light beam emitted from a laser light source into three along an information track on an optical disc, and a tracking actuator movable in the radial direction of the optical disc. In a tracking control device having a pickup, a first photo diode for receiving a reflected light of a preceding light beam reflected from the optical disc, and a first current for current-voltage converting the output of the first photo diode. A voltage converting means, a delaying means for delaying the output of the first current-voltage converting circuit by at least a first-order or more delay element, and a second light beam for receiving the reflected light reflected from the optical disk. And a second current-voltage converting means for converting the output of the second photo-diode into current-voltage. Subtracting means for substantially subtracting the output of the second current-voltage converting means and the output of the delaying means, loop filter means for performing phase compensation and low frequency compensation on the output of the subtracting means, and this loop filter means. And a tracking drive device that displaces the tracking actuator according to the output of the tracking control device. 2. A light having an optical system for dividing a light beam emitted from a laser light source into three along an information track on the optical disc, and a tracking actuator movable in the radial direction of the optical disc. In a tracking control device having a pickup, a disc type discriminating means for discriminating a reproduction linear velocity of the mounted optical disc, a first photo diode for receiving a reflected light of a preceding light beam reflected from the optical disc, First current-voltage converting means for converting the output of the first photo diode into current-voltage, and delay means for delaying the output of the first current-voltage converting circuit by at least a first-order or more delay element, Switching means for switching the time constant of the delay means in accordance with the output of the disc type discrimination means, and the last optical beam A second photo diode for receiving the reflected light reflected from the optical disk; second current-voltage converting means for converting the output of the second photo diode into a current-voltage; and a second current- Subtracting means for substantially subtracting the output of the voltage converting means and the output of the delay means, loop filter means for subjecting the output of the subtracting means to phase compensation and low-frequency compensation, and the above-mentioned depending on the output of the loop filter means. A tracking control device comprising: a tracking drive means for displacing a tracking actuator. 3. A light comprising an optical system for dividing a light beam emitted from a laser light source into three along an information track on an optical disk, and a tracking actuator movable in the radial direction of the optical disk. In a tracking control device having a pickup, a first photo diode for receiving a reflected light of a preceding light beam reflected from the optical disc, and a first current for current-voltage converting the output of the first photo diode. -Voltage conversion means, first delay means for delaying the output of the first current-voltage conversion circuit by at least a first-order delay element, and the last-going light beam receives the reflected light reflected from the optical disk. A second photo diode, and a second current-voltage converting means for converting the output of the second photo diode into a current-voltage. Second delay means for delaying the output of the second current-voltage conversion circuit by at least a first-order delay element, and substantially subtracting the output of the second delay means and the output of the first delay means. And a loop drive means for sampling the output of the subtraction means to perform phase compensation and low frequency compensation, and a tracking drive means for displacing the tracking actuator according to the output of the loop filter means. A tracking control device characterized in that the order of the first delay means is made larger than the order of the second delay means and also serves as an anti-alias filter. 4. A light comprising an optical system for dividing a light beam emitted from a laser light source into three along an information track on an optical disc, and a tracking actuator movable in the radial direction of the optical disc. In a tracking control device having a pickup, a disc type discriminating means for discriminating the type of the loaded optical disc, a first photo diode for receiving a reflected light of a preceding light beam reflected from the optical disc, and a first photo diode. First current-voltage converting means for converting the output of the photodiode of the present invention into current-voltage, and first delaying means for delaying the output of the first current-voltage converting circuit by at least a first-order delay element, Switching means for switching the time constant of the first delay means in accordance with the output of the disc type discrimination means, and the optical line for the last line. A second photodiode for receiving the reflected light reflected from the optical disk; second current-voltage converting means for converting the output of the second photodiode into current-voltage; and the second current. Second delay means for delaying the output of the voltage conversion circuit by at least a first-order delay element, and subtraction means for substantially subtracting the output of the second delay means and the output of the first delay means, The first delay means includes loop filter means for sampling the output of the subtracting means and performing phase compensation and low-frequency compensation, and tracking driving means for displacing the tracking actuator according to the output of the loop filter means. Is larger than the order of the second delay means and also functions as an anti-alias filter.