JPH0154783B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical disc reproducing apparatus such as an optical digital audio disc reproducing apparatus or an optical video disc reproducing apparatus, and particularly to a tracking device and a focusing device thereof. .

As a conventional tracking device and focusing device for an optical digital audio disc playback device, there is a device as shown in FIG. In the figure, 1 is a laser light source, 2 is a laser beam emitted from it, 3 is a diffraction grating that divides this laser beam into three laser beams, 4 is a beam splitter, 5 is a quarter wavelength plate, 6 is the objective lens system,
7 is a disk which is a disc-shaped recording medium; 8 is an information track on which information is recorded; 9a, 9b, 9c are photodetectors; 10a,
10a', 10b, and 10c are preamplifiers that amplify the small current output from this detector and convert it into voltage; 11 is a summing amplifier that takes out the reproduced high frequency signal HF; 12 is a differential amplifier that takes out the tracking error signal TE;
13 is a phase compensation circuit for the tracking error signal, 14 is a power amplifier for the tracking error signal, 15 is a tracking actuator, 16 is a differential amplifier for taking out the focus error signal FE, 1
7 is a phase compensation circuit for focus error signal, 1
8 is a power amplifier for a focus error signal, and 19 is a focusing actuator.

The tracking operation is as follows. A laser light beam 2 output from a laser light source 1 is divided into three laser light beams, first, second, and third, by a diffraction grating, and a beam splitter 4 and a quarter-wave plate 5.
The light is collected by an objective lens and focused on an information track 8 on a disk 7. If the track tracking is performed at the correct position at this time, the second
As shown in FIG. m, the light spot 20a formed by the first light beam is located on the track 8, and the spots 20b and 20c formed by the second and third light beams are respectively shifted in the left-right direction. 2K shows the case where the light beam shifts to the right, and FIG. 2N shows the case where the light beam shifts to the left.
The three reflected laser light beams reflected from the above-mentioned light spot position follow a course opposite to that described above, are changed in direction by 90 degrees by the beam splitter 4, and are incident on photodetectors 9a, 9b, and 9c. The central photodetector 9a which receives the first reflected laser beam is used for reading the high frequency signal HF recorded on the information track 8 and for focus servo for focusing the optical spot. In other words, the photodetector 9a has two outputs, and if the focus is correct, both outputs are equal, and if the focus is out of focus, one of the outputs becomes larger depending on the direction of the shift. , If these outputs are summed and amplified by the summing amplifier 11, a reproduced high frequency signal HF is obtained, and the differential amplifier 1
By taking the difference in 6, the focus error signal FE can be obtained. On the other hand, the two outer photodetectors 9b and 9c receive the second and third reflected laser beams and are used for tracking servo. That is, if the three optical spots 20a to 20c are positioned as shown in FIG. The king error signal TE becomes zero potential. In addition, when three light spots 20a to 20c are located as shown in h and n in FIG.
Since the amounts of light incident on the photodetectors 9b and 9c are different, the tracking error signal TE, which is the output of the differential amplifier 12, has a positive or negative potential.

FIG. 3 shows the tracking error signal TE (FIG. 3 Q) which is the output of the differential amplifier 12 and the output of the summing amplifier 11 when the optical spot 20a moves in the direction perpendicular to the track, that is, in the radial direction of the disk. The reproduced high frequency signal HF (FIG. 3R) is shown. In an actual disk, the information tracks 8 are lined up very closely, so the tracking error signal TE is output in the form shown in Figure 3Q, and a certain track is selected and tracked. The tracking servo is working. Also reproduces high frequency signals
HF is the envelope EV when the optical spot 20a is located at the center of the information track.
The amplitude of is maximum. Based on the principle described above, deviation from the tracking center is detected, and the tracking error signal TE is applied to the tracking actuator 15 via the phase compensation circuit 13 and the power amplifier 14, which is energized to generate the signal TE. A tracking servo operation is performed by moving the objective lens system 6 in the direction of the radius X of the disk 7 so that the distance becomes zero.

On the other hand, the focus error signal FE, which is the output of the differential amplifier 16, becomes zero potential if the objective lens system 6 correctly focuses the first laser beam onto the track 8 of the disk 7 as described above. This focusing error signal FE is applied to the focusing actuator 19 through the phase compensation circuit 17 and the power amplifier 18, and energizes the focusing actuator 19 so that the objective lens system 6 is moved along the optical axis Y so that the signal FE becomes zero. focus servo operation is performed.

Conventional tracking devices as explained above,
The focusing device is based on the assumption that the information track 8 on the disk 7 is accurately recorded and that the disk protective film that protects the recording surface is free from scratches and dirt. If the recording surface or protective film of the disk is scratched or if there is dirt on the surface, the reflected light from the disk will not enter the photodetectors 9a to 9c normally.
It becomes impossible to obtain the tracking error signal TE as shown in Figure Q, and as a result, it becomes impossible to track the track, and in the worst case, the track jumps, resulting in a pause state in which the track continues to follow the same track. Also, there was a drawback that it could be fast forwarded or reversed. Furthermore, scratches and stains on the recording surface and protective film of the disk have an adverse effect on the focus servo operation, causing inconveniences such as out-of-focus.

This invention has been made in view of the above points, and is an optical disc that has a tracking device that does not cause malfunctions such as track skipping even if a light spot enters a scratched or dirty part on the disk and the tracking error signal is disturbed. The present invention provides a type disc playback device.

The present invention also provides an optical disc playback device having a focusing device that eliminates inconveniences such as out-of-focus caused by disturbance of the focus error signal caused by a light spot entering a scratched or dirty area on the disc. It also provides.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 4 is a block diagram showing one embodiment of the invention applied to a tracking device, and FIG. 5 shows operating waveforms of each part. In FIG. 4, numerals 1 to 15 are equivalent to the conventional device shown in FIG. 1, and their operations are as explained in the conventional example. Note that the focusing circuit will be described later, so it is omitted.
21 is an envelope detector, 22 is a voltage comparator,
23 is a low-pass filter, 24 is a slicer, and 25 is an analog switch circuit.

The envelope EV of the reproduced high frequency signal HF read out from the information track 8 of the disk 7 decreases as the spot 20a shifts from the center of the information track 8 as shown in FIG. 3R. Similarly, if there are scratches or dirt on the disk surface or recording surface, the reflected light will not enter the photodetectors 9a to 9c normally, so the envelope EV of the high frequency signal HF will decrease and accurate tracking will not be possible. King error signal TE and focus error signal FE cannot be obtained. Therefore, the present invention focuses on this point, detects a drop in the envelope EV, and slices the large level fluctuations in the tracking error signal TE that are disturbed by scratches, dirt, etc. during the period when the envelope EV drops. By limiting the amplitude and inputting it to the phase compensation circuit 13 at the subsequent stage, the movement of the tracking actuator 15 is reduced, thereby preventing problems such as track skipping. The above will be explained with reference to FIGS. 4 and 5. The reproduced high frequency signal HF (FIG. 5A) detected by the central one 9a of the three photodetectors is amplified by the preamplifier 10a and the summing amplifier 11, and input to the information reading circuit. The envelope signal EV is input to the detector 21 and detected. This envelope signal EV is input to the voltage comparator 22, where it is compared with the reference voltage Vref (FIG. 5B). When the envelope signal EV falls below the reference voltage Vref, the output CP of the voltage comparator 22 changes from low level to high level (FIG. 5c). On/off of the analog switch circuit 25 is controlled by the output state of the voltage comparator 22, and when the output CP of the voltage comparator 22 is at a high level, it becomes on, that is, conductive. On the other hand, differential amplifier 12
The tracking error signal TE, which is the output signal of
The signal is input to the slicer 24 and the low-pass filter 21 (FIG. 5D). The low-pass filter 23 removes high-frequency components included in the tracking error signal TE and passes frequencies below the disk rotation frequency component, and its output signal TL is sent to the analog switch circuit 2.
5 (FIG. 5E).
This signal TL becomes a bias voltage for the slicer 24 when the analog switch circuit 25 is turned on. When the envelope signal EV does not decrease, the analog switch circuit 25 is off, that is, in a non-conducting state, so the slicer 24 does not operate, and passes the tracking error signal TE from the differential amplifier 12 directly to the phase compensation circuit 13. Let it pass. envelope signal
When EV decreases, the analog switch circuit 25 becomes conductive, so the slicer 24 becomes operational, and the level of the output signal TL of the low-pass filter 23 is used as a bias point to limit the amplitude of the tracking error signal TE. . Therefore, the disturbance in the tracking error signal TE is minimized from the broken line to the solid line in FIG.
4, so tracking actuator 1
The runout of 5 is reduced, and problems such as track skipping are no longer caused.

FIG. 6 is a block diagram showing one embodiment of the present invention applied to a focusing device, in which numerals 1 to 11 and 16 to 19 are equivalent to the conventional device shown in FIG. The operation is as explained in the conventional example. Note that the tracking device has been described above, so it is omitted here. Reference numerals 21 and 22 are the same envelope detectors and voltage comparators as in the embodiment shown in FIG. The output signal FL is obtained by removing the high frequency components included in the disc rotation frequency components and passing the components below the rotational frequency component of the disk. Similar to 25 in FIG. 4, 28 is an analog switch 27 that becomes conductive when the output CP of the voltage comparator 22 is at a high level.
is in operation when the analog switch 28 is conductive, and the focus error signal is set using the level of the output signal FL of the low-pass filter 26 as a bias point.
This is a slicer that limits the amplitude of FE.

This focusing device also operates in the same manner as the tracking device shown in FIG. 4, and detects a decrease in reflected light due to scratches or dirt on the disk surface or recording surface as a decrease in the envelope signal EV using the voltage comparator 22.
The analog switch circuit 28 is turned on and off by the output CP. That is, if the envelope signal EV does not decrease, the analog switch circuit is off, the slicer 27 does not operate, and the focus error signal FE is
The signal passes through the phase compensation circuit 17 as it is, is amplified by the power amplifier 18, and drives the focusing actuator 19 to perform normal focusing. When the envelope signal EV decreases,
The analog switch 28 becomes conductive and the slicer 27
limits amplitude changes in the focus error signal FE that are disturbed by scratches, dirt, etc., suppresses deflection of the focusing actuator 19, and eliminates undesirable operations such as defocusing.

As described above, according to the present invention, reflected light does not return to normal due to scratches on the recording surface of the disk, scratches on the protective film, dirt attached to the disk surface, etc.
Even if the tracking error signal or focus error signal is greatly disturbed, these disturbances are sufficiently limited and the large swing of the actuator is suppressed.
Normal track tracking can be performed without causing problems such as track skipping or defocusing.

The tracking device or focusing device described in the above embodiments is merely an example, and the present invention can also be applied to devices that obtain tracking error signals or focusing error signals by other means. Of course.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the tracking device and focusing device of a conventional optical disc playback device, FIG. 2 is a diagram showing the positional relationship of three light spots that illuminate the track of the disc, and FIG. Tracking error signal TE obtained when the light spot crosses the disk in the radial direction
4 is a block diaphragm showing one embodiment of the present invention applied to a tracking device, and FIG. 5 is a waveform diagram showing a reproduced high frequency signal.
FIG. 6 is a time chart of signal waveforms at various parts of the block diagram shown in the figure. FIG. 6 is a block diagram showing an embodiment in which the present invention is applied to a focusing device. In the figure, numerals 1, 3, 4, and 5 are a laser light source, a diffraction grating, a beam splitter, and a quarter-wave plate for generating the light beam 2. 6 is the objective lens system,
7 is a disk which is a disk-shaped recording medium; 8 is an information track; 9a, 9b, 9c are photodetectors; 11 is a summing amplifier that outputs a reproduced high frequency signal HF; 12 is a differential amplifier that outputs a tracking error signal TE;
15 is a tracking actuator, 16 is a differential amplifier for extracting the focus error signal FE, 19 is a focusing actuator, 21 is an envelope detector, 22 is a voltage comparator, 23 and 26 are low-pass filters, 24, 27 is a slicer, and 25 and 28 are analog switch circuits.

Claims (1)

[Scope of Claims] 1. A disc-shaped recording medium having a track on which information is recorded, a device for generating a light beam, an objective lens system for focusing the light beam from this device onto the track of the recording medium, and a device for generating a light beam from the track. A device that detects the reflected light beam of the track, reads out the information recorded on the track, and extracts a reproduced high-frequency signal; An optical disc playback device comprising a device for extracting a tracking error signal, and a tracking actuator that is energized by the tracking error signal and drives the objective lens system so that the light beam is always correctly positioned on the track, an envelope detector that detects the envelope of the reproduced high-frequency signal;
A voltage comparator that compares the output voltage of this detector with a reference voltage, a low-pass filter that removes high frequency components from the tracking error signal and passes frequencies below the recording medium rotation frequency, and limits the amplitude of the tracking error signal. a switch circuit that is connected between the slicer and the low-pass filter and becomes conductive when the voltage comparator output voltage is applied when the envelope detector output voltage is less than a reference voltage; and tracking via the slicer. A circuit is provided that compensates the phase of the error signal voltage, amplifies it, and applies it to the tracking actuator, and when the switch circuit is turned on, the slicer is activated and the low-pass filter output voltage is biased to output the tracking error signal. An optical disk device characterized in that the amplitude of the signal is limited. 2. A disc-shaped recording medium having a track on which information is recorded, a device for generating a light beam, an objective lens system for focusing the light beam from this device onto the track of the recording medium, and detecting the reflected light beam from this track. A device that reads out the information recorded on the track and extracts a reproduction high-frequency signal, a device that detects the reflected light beam and extracts a focus error signal corresponding to the focal shift of the focused light on the track, and In an optical disc playback device equipped with a focusing actuator that is energized by a cast error signal and drives the objective lens system so that the light beam always focuses correctly on the track, the envelope of the playback high-frequency signal is an envelope detector for detection, a voltage comparator for comparing the output voltage of this detector with a reference voltage, a low-pass filter that removes high frequency components from the focus error signal and passes frequencies below the recording medium rotation frequency component;
A slicer that limits the amplitude of the focus error signal, and a switch that is connected between the slicer and the low-pass filter and becomes conductive when the voltage comparator output voltage is applied, which occurs when the envelope detector output voltage is below the reference voltage. and a circuit for phase-compensating the focus error signal voltage that has passed through the slicer, amplifying it, and applying it to the focusing actuator, and when the switch circuit is conductive, the slicer is brought into operation and the low-pass filter is activated. An optical disk device characterized in that the amplitude of the focus error signal is limited by using an output voltage as a bias.