JPS59223941A - Reproducing device of information recording disc - Google Patents

Abstract

PURPOSE:To prevent the malfunction of a control loop due to a false control signal by providing a limiter circuit, which clips a control signal having a specific frequency range with a prescribed value, in the control loop of an optical disc device. CONSTITUTION:Limiter circuits 26 and 27 inserted to a track following-up control loop and a focus control loop respectively show limiter characteristics for high ferquency components but do not show limiter characteristics for high frequency components but do not show limiter characteristics for low frequency components. In case of surface shake or eccentricity of a disc, the relation between an essential control voltage Vt and a false control voltage Vf is shown by Fig. Since the frequency components of the voltage Vf are very higher than those of the voltage Vt, they can be discriminated with respect to a band. The clipping operation indicated by clip levels E1 and E1' is performed for the discriminated high-frequency false control voltage by a clipping circuit. Thus, the clipping of the essential control voltage is avoided to perform the sufficient clipping operation for the false control voltage Vf.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an information recording disc reproducing device, and in particular to an information recording disc reproducing apparatus, which irradiates a recording surface of a disc with light, reads recorded information from the reflected light, and uses the reflected light to read the recorded information from the irradiated light. This invention relates to information recording disc reproduction @exploration that controls the spot on the recording surface.

Such playback devices are known as compact disc players as audio equipment and C video disc players as video equipment, and their playback principle is based on the presence or absence of protrusions called bits on one side of a transparent polycarbonate base material. A disk-shaped disk with a metal film for reflecting the light beam formed on its pit surface is rotated at a constant linear velocity, and a light beam from a He-1-1e laser or a semiconductor laser as a light source is generally directed onto the disk. irradiate the pit surface (hereinafter referred to as "recording surface") through the base material of
Information is read by detecting the reflected light, and in this case, a spot of light narrowed to 2 μm or less is placed on the recording surface at the center of a track with a width of 1 μm or less made by the bit string. The light beam is controlled so that it is always tracked, and the spot is controlled so that it is at a focal position on the recording surface (so that the focus of the light beam is on the recording surface).

Next, a first example of a conventional information recording disk reproducing device will be described.
To explain according to the diagram, 1 is a light source made of a 1'' e-He laser or a semiconductor laser, and the light beam 2 generated from it is corrected into approximately parallel light by a collimating lens 3, and then It is split into three light beams by the diffraction grating 4. These three light beams pass through a beam splitter 5 and a 174 wavelength plate (hereinafter referred to as "λ/4 plate") 6, have their optical paths bent at right angles by a tracking mirror 7, and enter a condenser lens 8. The three light beams that passed through the condenser lens hit track 1 on the recording surface of disk 9.
The light beam is focused and reflected to form a tiny spot at zero. At this time, the intensity of the reflected light is modulated depending on the presence or absence of a bit (not shown) in the track 10. This reflected light passes through the disk 9 and the condensing lens 8 again, is bent at a right angle by the tracking mirror 7, and is incident on the λ/4 plate 6 and the beam splitter 5.

At this time, the path of the reflected light beam is bent at a right angle by the beam splitter 5, and is incident on the photodetector 14 through the next cylindrical lens 13.

The 2/4 plate 6 is made of anisotropic crystal, and has a refractive index that differs depending on the direction, and the light that passes through it has a phase difference of λ/4, that is, 90°, with respect to the vibration components in directions perpendicular to each other. occurs. Therefore, linearly polarized light can be changed to circularly polarized light, and circularly polarized light can be changed to linearly polarized light. On the other hand, the beam splitter 5 passes components parallel to the incident plane and reflects components perpendicular to the incident plane. Therefore, beam splitter 5 and λ
The reflected light and the irradiated light can be separated by the /4 plate 6. The photodetectors 14 are A and B.

It is composed of four components C and D, and the three reflected light beams are incident on A and D, respectively, at both ends, and the central beam is incident on portions B and C, respectively. Photodetector 1
The outputs of part A and part 8 of 4 are used for track following control, -5
The outputs of part 8 and part C are used for focus III'm.

The three light beams divided by the diffraction grating 4 produce three spots on the recording surface of the disk 9 as shown in FIG. 2(a). Here, β is the 5-main spot that generates signals for reading recorded information and focus control, α and γ are auxiliary spots for generating track following control signals, and auxiliary spots α and γ are the main spots. They are located in opposite directions centering on β. These spots α, β, and γ are moved in the direction of arrow X by the tracking mirror 7, and along with this movement, the values α' and γ' of the light reflection intensity by the auxiliary spots α and γ change as shown in FIG. 2(b). It moves in the direction of the arrow (not shown). In Fig. 2 (b), the horizontal axis represents the track center P and the auxiliary spot α.
, γ, and the vertical axis indicates the light reflection intensity. When the auxiliary spots α and γ move as described above and their light reflection intensities α′ and γ′ become unbalanced, the intensity difference becomes a signal corresponding to the deviation of the main spot β from the track center, i.e. This becomes a track error signal.

The signal for focus control is obtained by the curvature of the light intensity pattern on the photodetector shown in FIG. 3, and this pattern change is caused by the effect of the cylindrical lens 13. If the disk 9 is too fast, the amount of light incident on the C6- portion of the photodetector 14 will be large, as shown in FIG. +5- As shown, the amount of light entering the B portion of the photodetector 14 increases.

When the light is focused on the recording surface of the Z-C disk 9, the light y that enters the B part and the C part becomes equal as shown in the 'in3 diagram (opening 2). , by taking the difference between the outputs of portions B and C, a signal corresponding to the deviation of the spot from the in-focus point, that is, A-Casuela-1Δ (focus control signal) is obtained. Note that in FIG. 1, means for reading information from the anti-abrasive light beam of the main slot 1-β is not shown.

Now, to explain the track following control loop, the current outputted at a magnitude corresponding to the intensity of light incident on portions A and D of the photodetector 14 is transmitted to the preamplifiers 15 and 16.
is converted into voltage by

The outputs of these amplifiers are deduced by the @11 differential amplifier 17 and become a track error signal (track following control signal) St representing the deviation from the track center. The track error signal S is applied to the first drive circuit 19 after being subjected to processing such as amplification and phase compensation by the first servo amplifier 18 . One first drive circuit is a track actuator 12
The track actuator 12 rotates the tracking mirror 7, and the track actuator 12 rotates the tracking mirror 7. The spot on the disk 9 is moved in a direction perpendicular to the track 10. When the disk 9 rotates and moves from 1 to rack, a tracking error signal S is generated indicating the deviation of the spot position from the track center as described above, but this signal causes the tracking mirror 7 to rotate. Spot is track 10
Move in the direction you want to track.

The same applies to the focus control loop, and the current output according to the intensity of light incident on the B and C portions of the photodetector 14 is converted into voltage by the preamplifiers 20 and 21, and the The focus error signal S2 is output from the 12 differential amplifier 22 as a focus error signal S2. This focus error signal S2 is transmitted to the second servo amplifier 23 and the second drive circuit 24.
are sequentially applied to the force actuator 11.

The focus actuator 11 moves the condenser lens 8 in a direction perpendicular to the disk 9 in accordance with the focus error signal S2.

By the way, since the conventional information recording disk reproducing apparatus was only configured as described above, it had the following drawbacks. That is, since the disk 9 is made of transparent resin, there may be air bubbles or opaque foreign matter mixed in therein.The air bubbles have a kind of lens effect on the light beam, and the opaque foreign matter is This causes a phenomenon that distorts the distribution of optical marks, and has a significant effect on the sensor characteristics of the two types of control loops mentioned above. Conventional devices were completely immune to this kind of influence, so there is no possibility of track deviation or Pseudo-tilt that misidentifies the focal point position on the recording surface as having moved even though it has not moved.
There was a drawback that No. 1g occurred and the control system operated erroneously.

Therefore, a main object of the present invention is to provide an information recording disk reproducing apparatus that prevents malfunctions of the control loop due to pseudo control signals.

To summarize the present invention, by providing a limiter circuit in the I11 control loop that clips the control signal in the same specific wave number range at a predetermined value, the pseudo control signal is distinguished from the desired control signal in terms of frequency, and the level of the control signal is is clipped so that it does not essentially function as a control signal.

The above objects and other objects and features of the present invention will become more apparent from the detailed description given below with reference to the drawings.

FIG. 4 is a block diagram showing an outline of the information recording disk reproduction unit according to the present invention, and the same parts as in FIG. 1 are given the same reference numerals. 26 and 27 are limiter circuits inserted in each of the track following control loop and the focus control loop. Since the operating principle of each control loop has been described above, a detailed explanation thereof will be avoided here, and the operation and role of the limiter circuits 26 and 27, which are the main parts of the present invention, will be explained. The characteristics of the limiter circuits 26 and 27 are as shown in FIG. ] shows almost no limiter characteristics.

A limiter circuit exhibiting such characteristics includes a limiter section 28 and a bypass filter section 2, as shown in the block diagram of FIG.
9. When the frequency component of the input signal is low, the impedance of the bypass filter section 29 is high, so no limiter effect appears on the output even if the amplitude of the input signal is large. Next, when the frequency component of the human input signal becomes high and the impedance of the bypass filter section 29 becomes extremely low, the amplitude component exceeding the limit level of the limiter 28 is equivalently grounded, and the component does not appear in the output.

A specific circuit example is shown in FIG. The limiter section 28 is constructed by connecting diodes 01.02 in parallel in opposite directions, and the high pass filter section 29 is constructed from a capacitor C. In addition, the frequency at which the limiter is activated is selected using a resistor R and a capacitor C.

As mentioned above, the control system's hinge output is greatly affected by air bubbles, foreign matter, or scratches on the disk surface in the disk 9, and a large amplitude pseudo flilj is generated.This pseudo control The time the signal is generated is very short compared to the rotation period of the disk 9.
Usually, the size of air bubbles, foreign objects, scratches, etc. is large (at least 1+n
m, and the length of one circumference of the disc, for example, for a compact disc, C is 157111Im to 370Il1
m, 314 mn- in optical PidenojT isk
9421111> Compared to 2, it is very small at 1m. Since surface runout and eccentricity of the disk occur in synchronization with the rotation of the disk, focus control and 1 to easy tracking 1 are necessary.
The main component of the control signal for 1J III is the disk rotation frequency component or a frequency component twice that frequency.
The relationship between the 'original control voltage' vt and the 'pseudo control voltage' vt is as shown in FIG. 8. In this way, the frequency component 41 of the 'pseudo control voltage' Vf
Since the frequency component of the lN pressure "Vt" is very high, it can be discriminated in terms of band.For example, the clip levels E+ and E1' shown in FIG. Let us perform the lip motion as shown.

If such frequency discrimination is not performed, it will be necessary to widen the clipping range to the clipping level E21E2' shown in FIG. 8 in order to avoid clipping the "original control voltage". , ``Pseudo control voltage''
It is not possible to perform a rip operation on vr.

In addition, in the above embodiment, an example was shown in which the amplitude level of the "pseudo control signal" is clipped to a constant level after reaching the limit level, but even after the amplitude level reaches the limit level, the slope is made gentler. Even if the configuration is configured so that the human output 9 power is proportional and suppresses sudden changes in the signal level,
The specific characteristics in that case are shown in Box 9, and a circuit example is shown in Fig. 10. In this circuit example, diode D1. D
A resistor Ro is inserted between the parallel connection portion of 2 and the capacitor C. Therefore, the slope at which the limiter operation starts when the diode D or D2 becomes conductive is determined by R and RO. When the pseudo control voltage □ is considered as a variable, the slope for this variable is Re/13- (Ro+R>, but since RO is chosen small, the slope is small. The clip levels E1, E, ' in Fig. 8 are ,
This shows that the characteristic of the bypass filter section 29 is -16 dB/dec, but the characteristic of the bypass filter section 29 is -1
It is also possible to use a material having an attenuation characteristic of 2 dB/dec or more to separate the C band.

As described above, according to the present invention, a limiter circuit for selectively clipping a control signal band is provided in the focus control loop and/or track following control loop of an information recording disc reproducing device, so that damage to the disc can be avoided. This has the effect of being able to prevent malfunctions of the control loop due to pseudo control signals based on foreign objects, air bubbles, etc.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram for explaining a conventional information recording disk reproducing apparatus. FIG. 2 is a diagram for explaining the sensor principle of track following control. FIG. 3 is a diagram for explaining the sensor principle of focus control. FIG. 4 is a block diagram of a 14-information recording disc reproducing apparatus embodying the present invention. FIG. 5 is a characteristic diagram of a part of the configuration in FIG. 4, FIG. 6 is a block diagram of the configuration, and FIG. 7 is a specific circuit diagram of the configuration. Figure 8 shows the 41i! ! FIG. 9 is a characteristic diagram when a part of the configuration in FIG. 4 is implemented in another embodiment, and FIG. 10 is a circuit diagram for realizing it. In the figure, 9 is a disk, 10 is a track, 26.2
7 is a limiter circuit, 28 is a limit/litter part, 29 is a bypass filter part, β is a main spot, α and γ are auxiliary spots.
・Indicates. Agent Masuo Oiwa 15- 8z-ku, Figure 3, Figure 8, Figure t3, Figure 9, Figure 10, Procedural amendment (voluntary) 1. Indication of the case: Japanese Patent Application No. 1989-98906 2. Name of the invention Information recording disk reproducing device 3, Representative Hitoshi Katayama of the person making the amendment, Department 4, Agent 5, Column 6 for detailed explanation of the invention in the specification to be amended, Page 3, line 8 of the specification of the contents of the amendment. Correct “constant linear velocity J” to “constant angular velocity or constant linear velocity”. Above 2-

Claims (5)

[Claims] (1) A means for irradiating light onto the recording surface of a disk on which information is recorded and reading the information from the reflected light, and control for controlling the spot of the irradiated light on the recording surface using the reflected light. What is claimed is: 1. An information recording disc reproducing apparatus having a control loop, wherein a limiter circuit is provided in the control loop to clip a control signal in a specific frequency range to a predetermined value. (2) The limiter circuit includes a focus control loop that controls the spot so that it is located at a desired focal point;
2. The information recording disk reproducing apparatus according to claim 1, further comprising one or both track following control loops for causing the spot to follow a track on the recording surface. (3) The original control signal has a rotational frequency component of the disk as a main component, and the specific frequency range is a frequency range higher than the rotational frequency. Information recording disc playback device. (4) The original control signal has a main component of a frequency component twice the rotational frequency of the disk, and the specific frequency range is a frequency range higher than twice the rotational frequency. An information recording disc reproducing apparatus according to claim 1. (5) The information recording disk reproducing apparatus according to claim 1, wherein the limiter circuit generates an output proportional to the input with a small slope when the input exceeds a predetermined value.