JPS59223977A - Reproducing device of information recorded disk - Google Patents

Abstract

PURPOSE:To limit sufficient by the unnecessary component of a control signal and realize a stable operation of a control loop by constituting that one end of a clipping circuit whose other end is fed with a control signal is controlled by a signal produced by removing a high frequency component form the control signal. CONSTITUTION:Since amplifiers 34 and 35 are invertional amplifiers and, when the gain of each amplifier is ''1'', a voltage at a point (a) becomes the same as the voltage of an output terminal 37 in intensity and phase to a signal having a low frequency like an original control signal, no limiter operation is performed to the control signal. However, since the gain of a low-pass filter 28 drops to a signal having a high frequency, a high frequency signal at the point (a) also becomes smaller. In this manner, the low-pass filter 28 acts for discriminating signal bands to be subjected to the limiter operation by passing the control signal after selecting their frequencies. Therefore, the control signal obtained at the output terminal 37 becomes one which is produced by sufficiently performing the limiter operation an a dummy control signal.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an information recording disk reproducing device, and more particularly to an information recording disk reproducing device that reads information from a disk on which information is recorded through a light beam or a reproducing needle, and detects a detection signal from the reflected light of the light beam or from the reproducing needle. The present invention relates to an information recording disc reproducing apparatus which uses the above to control the spot of the light beam or the reproducing needle on the recording track of the disc.

Among such reproducing apparatuses, a reproducing apparatus that reads information and controls spots through a light beam will be described below.

Such playback devices are known as compact disc players as audio equipment and optical 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 disc-shaped disk on which information is engraved and a metal film for reflecting a light beam is formed on the bit surface is rotated at a constant linear velocity, and a light beam from a He-@e laser or a semiconductor laser as a light source is generally directed onto the disk. Information is read by illuminating the bit surface (hereinafter referred to as "recording surface") through the base material and detecting the reflected light. The spot is controlled so that it always tracks the center of the track with a width of 1 μm or less made by the bit string, and the spot is controlled so that it becomes the focal position on the recording surface (the focus of the light beam is focused on the recording surface). control) is carried out.

Next, a first example of a conventional information recording disk reproducing apparatus will be described.
To explain according to the figure, reference numeral 1 denotes a light source made of the above-mentioned He-He laser or semiconductor laser, and a light beam 2 generated therefrom is corrected into approximately parallel light by a collimating lens 3, and then converted into a parallel beam by a next diffraction grating 4. The book is split into light beams. These three light beams are connected to a beam splitter 5 and a quarter wavelength plate (hereinafter referred to as "λ/4 plate").
6, the optical path is bent at a right angle by a tracking mirror 7, and the light enters a condenser lens 8. The three light beams that have passed through the condenser lens are directed to track 10 on the recording surface of disk 9.
The light beam is focused and reflected to form a tiny spot. 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 again, is bent at right angles 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 right angles by the beam splitter 5, and is incident on the photodetector 14 through the next cylindrical lens 13. The front λ/4 plate 6 is made of an anisotropic quartz crystal, and has a refractive index that differs depending on the direction, and the light that passes through it has a λ/4, that is, 90°, for vibration components in directions perpendicular to each other.
generates a phase difference. 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, the reflected light and the irradiated light can be separated by the beam splitter 5 and the λ/4 plate 6. The photodetectors 14 are A, B, and C.
, D, and of the three reflected light beams, the beams at both ends are incident on the A and 0 sections, respectively, and the central beam is incident on the B and C sections. The outputs of parts A and 8 of the photodetector 14 are used for track following control, while the outputs of parts B
, C portions are used for focus control.

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 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 5- 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 value α' of the light reflection intensity by the auxiliary spots α and γ is
, γ' shift in the direction of the arrow shown in FIG. 2(b). In FIG. 2(B), the horizontal axis indicates the relative position between the track center P and the auxiliary spots α and 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 changing the light intensity pattern on the photodetector shown in FIG.
This pattern change is caused by the effect of the cylindrical lens 13. As shown in FIG. 3(a), if the disk 9 returns too much, the amount of light incident on the C portion of the photodetector 14 will be large (
On the other hand, if the disk 9 is too close, the amount of light 6- incident on the 8 portions of the photodetector 14 increases as shown in FIG. 3(C). When the light is focused on the recording surface of the disk 9, the amount of light incident on portions B and C becomes equal, as shown in FIG. 3(D). therefore,
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 focus error signal, is obtained.

Note that in FIG. 1, means for reading information from the reflected light beam of the main spot β is not shown.

Now, to explain the track following control loop, the current outputted in a magnitude corresponding to the intensity of light incident on the A section and the D section of the photodetector 14 is converted into a voltage by the preamplifiers 15 and 16. The outputs of these amplifiers are calculated by the first differential amplifier 17, and a track error signal (track following control signal @) S representing the deviation from the track center is generated.
, becomes. 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 . The first drive circuit 19 is only for driving the track actuator 12,
The track actuator 12 rotates the tracking mirror 7 and moves the sub-boxes on the disk 9 in a direction perpendicular to the track 10. When the disk 9 rotates and the track moves, a track error signal S indicating the deviation of the spot position from the track center is generated as described above. 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 second differential amplifier circuit 22 outputs the focus error signal (focus control signal) 82 . This focus error signal S2 is sent to the second servo amplifier 23,
The signal passes sequentially through the second drive circuit 24 and is applied to the focus 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 disk 9 is made of transparent resin, air bubbles or opaque foreign matter may get mixed in therein. In such a case, bubbles have a kind of lens effect, and opaque foreign objects cause a phenomenon that distorts the light intensity distribution, which significantly affects the sensor characteristics of the two types of control loops mentioned above. In other words, a false signal is generated that is mistakenly recognized as having moved, even though the track has not actually shifted or the focal point has moved, causing the control loop to operate erroneously. As mentioned above, the sensor output in the control loop is significantly affected by air bubbles in the disk 9, foreign matter, or scratches on the disk surface, and a pseudo control signal with a large amplitude is generated. The time it takes is very short compared to the rotation period of the disk 9. Normally, the size of bubbles, defects, scratches, etc. is about 1111 mm at most, which is very large compared to the length of one circumference of a disc (for example, 157 mm to 370 mm for a compact disc, and 314 mm to 942 mm for an optical video disc). This is because it is small 9-. Since the surface runout and eccentricity of the disk 9 occur in synchronization with the rotation of the disk, the main component of the control signal for focus control and track following control is the disk rotation frequency component or a frequency component twice that frequency. The relationship between the "original control signal" Vt and the "pseudo control signal" vr is as shown in FIG. To remove such unnecessary large amplitude signals, a limiter circuit 26.
However, the limiter circuits 26 and 27 in conventional playback devices simply use diodes, and do not clip the original control signal. To avoid this, set the clip level to a fairly high level E2 as shown in Figure 4.
*E 2 ' must be set, resulting in
There is a drawback that a sufficient rip operation cannot be expected with respect to a pseudo control signal.

Therefore, the main object of the present invention is to provide an information recording disk reproducing apparatus that sufficiently limits the pseudo control signal to prevent malfunctions of the control loop.

10- To summarize the present invention, a limiter circuit provided in a control loop is connected in parallel with each other with opposite polarities, and includes a clip circuit consisting of a diode whose one end is connected to a control signal path, and By comprising a low-pass filter that removes the component, and a buffer circuit that inputs the output of the low-pass filter to the other end of the clip circuit in positive phase with respect to the control signal, only the pseudo control signal can be sufficiently maintained at a predetermined level. This signal is clipped so that it does not actually 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. 5 is a block diagram schematically showing an information recording disk reproducing apparatus embodying the present invention, and the same parts as in FIG. 1 are given the same reference numerals. 28.31 is a low pass filter,
29.32 is a buffer circuit that outputs the output of the low-pass filter 28.31 in positive phase with respect to the control signal from the differential amplifier 17.22, and 30.33 is the differential amplifier 17.22.
These low-pass filters 2B and 31, buffer circuits 29 and 32, and clip circuits 26 and 27 control the pseudo control l signal at a predetermined level. Limiter circuits 26 and 27 are formed to clip the signal so that it does not substantially function as a control signal.

Since the operation of each control loop has been described above, a detailed description thereof will be omitted here, and the configuration and operation of the limiter circuit, which is the main part of the present invention, will be explained.

FIG. 6 specifically shows a low-pass filter 28, a buffer circuit 29, and a clip circuit 30 that constitute the limiter circuit 26, and the low-pass filter 28 is composed of resistors R, R, capacitors C, and an amplifier 34. Further, the buffer circuit 29 is formed by an amplifier 35, and the clip circuit 30 is formed by parallel-connected diodes D7. It is composed of D2. A control signal as shown in FIG. 4 is input through the input terminal 36, and the control signal is applied to the output terminal 37 side through the resistor R' and is also applied to the low-pass filter 28.

Amplifiers 34 and 35 are inverting amplifiers, and assuming that the gain of each amplifier is 1, the voltage at point a is the same as the voltage at output terminal 37 for a low frequency signal such as an original control signal.

Since they are in the same phase, the potential difference between the ends of the diode r)+ and D2 becomes almost zero, and the diode DI.

D2 is held off. In such a state, no limiter action is performed on the control signal.

However, since the gain of the low-pass filter 28 decreases for high-frequency signals, the high-frequency signal at point a also becomes small, and a potential difference occurs between the ends of the diodes I)+ and D2, which turn them on alternatively. When the diodes D, , D2 are turned on, the signal level at the output terminal 37 becomes a value divided by the resistor R' and the output impedance Z of the buffer circuit 29. Since normally R'>> Z, the signal level at the output terminal 37 becomes a value divided by the resistor R' and the output impedance Z of the buffer circuit 29. The signal level becomes small.

Although FIG. 6 shows the limiter circuit 30 in the track following control loop, the limiter circuit 33 in the focus control loop is similarly constructed.

As described above, the low-pass filter 28 selects the frequency of the control signal and passes it through, thereby discriminating the signal band to be subjected to the limiter operation.

As a result, the control signal obtained at the output terminal 37 becomes one in which the limiter has sufficiently worked on the portion of the pseudo control signal Vf, as shown in FIG. In Figure 7, E.

,E,′ is the clip level.

Now, the original control signal Vt is 2 times the number of rotations of the disk 9.
Attenuation occurs with a slope of -40 dB/dec above a frequency that is about twice as high. For convenience of explanation, FIG. 8 shows the frequency characteristics of the original control signal Vt, with the vertical axis plotted linearly. In the clip circuit shown in Fig. 6, the dead zone is from the zero potential difference between the diodes D+ and D2 to the forward rising voltage Vo of the diode, so even if the voltage at point a in Fig. 6 is the stomach. , the limiter operation is not performed at iI3 above the frequency fO at which only a level corresponding to the dead zone occurs with respect to the original control signal. Utilizing this fact, the cutoff frequency of the Ll-bass filter 2B [. 4. That is, the above [, is set to match the above fo so that a potential difference is mainly present between both ends of the diodes D, D, and D only at a frequency f or higher. This way -), then f.

As described above, there is an advantage that the limiter operation is performed only on the pseudo control signal at J3, and the b1 limiter is not performed on the original control signal at f or above. Also, at frequency f, on IJ tin, diodes D, , D2
It is desirable to increase the voltage across both terminals of It shows things.

Although the track following control and focus control in an optical disc playback device have been explained above, the present invention can be similarly applied to a track following control loop and a jitter control loop in a playback stylus type disc playback device. it is obvious.

As described above, according to the present invention, the control signal in the control loop is clipped (one end of the clipping circuit receives the control signal, and the other end is controlled by a signal obtained by removing high frequency components from the control signal). This has the effect that unnecessary control signal components can be sufficiently limited, and stable operation of the control loop can be obtained.

[Brief explanation of the drawing]

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 1 to easy tracking control. FIG. 3 is a diagram for explaining the sensor principle of focus control. Fourth
The figure is a signal waveform diagram for explaining the drawbacks of a conventional information recording disk reproducing device. FIG. 5 is a block diagram of an information recording disc reproducing apparatus embodying the present invention. FIG. 6 is a circuit diagram of the main part of FIG. 5. FIG. 7 is a signal waveform diagram showing the effect of the first invention. FIG. 8 is a characteristic diagram for explaining the present invention. In the figure, 9 is a disk, 1o is a track, 26.2
7 is a limiter circuit, 28.31 is a low pass filter, 2
9.32 is a buffer circuit, 30°33 is a clip circuit%
D+ *Dt is a diode, α and γ are auxiliary spots, and β is the main spot. Agent Masuo Oiwa 17 - 2nd plate - 406 - Notification of amendments to the procedures (spontaneous) September 19, 1981 1, Indication of case Patent application No. 8-98907 No. 1 of 1983,
Name of the invention Information recording disk reproducing device 3, relationship with the case of the person making the amendment Patent applicant address 2-2-3 Marunouchi, Chiyoda-ku, Tokyo Name (601) Mitsubishi Electric Corporation Representative Kata 111 Nihachibe 4. Agent 5, in column 6 of the detailed description of the invention in the specification subject to amendment, in lines 6 to 7 of page 3 of the specification of contents of the amendment, set "constant linear velocity" to F.
Correct to "constant angular velocity or constant linear velocity." Above 2-

Claims (3)

[Claims] (1) means for reading information from a disc on which information is recorded via a light beam or a reproducing needle; a control loop for controlling the spot of the light beam or the reproducing needle in a recording track of the disc; and a control loop within the control loop. In an information recording disk reproducing apparatus having a limiter circuit provided for clipping a control signal, the limiter circuit is connected in parallel with each other with opposite polarities, and one end thereof is connected to a control signal path. The present invention is characterized by comprising a low-pass filter that removes high-frequency components of the control signal, and a buffer circuit that inputs the output of the low-pass filter to the other end of the clip circuit in positive phase with respect to the control signal. Information recording disc playback device. (2) The cutoff frequency of the low-pass filter is
2. The information recording disk reproducing apparatus according to claim 1, wherein the frequency is selected such that the control signal level is equal to the forward rising voltage of the diode. (3) The information recording disk reproducing apparatus according to claim 1, wherein the low-pass filter is selected to have a second-order low-pass filter characteristic.