JPH0445893B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a tracking servo circuit for a disc playback device, and in particular to a loop gain adjustment capable of automatically adjusting its loop gain to an optimal value with the least tracking deviation. It is related to circuits.

[Conventional technology]

Conventionally, information recording disc playback devices that use a pick-up playback element that uses a light beam,
The tracking error signal controls the tracking of the pick-up reproducing element so that the pick-up reproducing element accurately follows and scans the recorded track. The loop gain adjustment circuit in such a tracking servo circuit detects level fluctuations in the tracking error signal that occur in response to disturbances applied to the pickup playback element and its playback device, and increases the loop gain of the tracking servo circuit. There are known things that can be configured to do this.

A conventional example of such a tracking servo circuit is shown in FIG. In the figure, 1 is a light emitter such as a laser diode, 2 is a light beam emitted from the light emitter 1, 3 is a lens, 4 is a beam splitter for distributing the laser beam into a main spot and an auxiliary spot, 5 is a prism, 6 is a λ/4 plate, 7 is a tracking mirror, and 8 and 11 are lenses. Further, numeral 9 is a transparent resin that covers the recording surface of the disk, and numeral 10 is a protruding pit forming a track.

Further, 12 is a photodetector that outputs a current of a magnitude corresponding to the amount of incident light; 24 and 25 are the photodetectors 12;
preamplifier for converting the output current into voltage,
26 is a summing amplifier that adds the outputs of both preamplifiers 24 and 25 to form an information signal 31 recorded on the disk.

Reference numerals 13 and 14 are preamplifiers for tracking control, which convert currents outputted from the photodetector 12 and corresponding to the amount of incident light into portions A and D of the photodetector 12 into voltages, respectively. . 15 is a differential amplifier that receives the outputs of these amplifiers 13 and 14 and outputs a tracking error signal; 17 and 1;
8 is a low-pass filter attached to the servo amplifier 16 for gain adjustment, and 21 is a drive circuit that receives the output of the servo amplifier 16 and drives the tracking mirror 7. Further, 22 is a level detector that detects level fluctuations of the tracking error signal output from the differential amplifier 15, and 23 is a selection switch that controls the switch 20 for switching the loop gain according to the output of the level detector 22. It is a circuit.

Next, the tracking control operation of the above device will be explained.

A laser beam 2 emitted from a light emitter 1 passes through a lens 3, a beam splitter 4, a prism 5, and a λ/
The light is irradiated onto the information recording disk through an optical system including four plates 6 and the like. The reflected light is guided to a photodetector 12 via a lens 8, a tracking mirror 7, a prism 5, and a lens 11. Tracking control is performed according to the intensity of the light incident on portions A and D of the light incident on the photodetector 12. That is, the photodetector 12 outputs a current whose size corresponds to the intensity of the incident light, and among these, the current whose size corresponds to the intensity of the incident light to the A part and the D part is outputted from the photodetector 12. The currents are input to amplifiers 13 and 14, where each current is converted into a voltage. The outputs of these amplifiers 13 and 14 are then sent to a differential amplifier 15.
A tracking error signal representing the deviation from the track center is obtained. In normal tracking without disturbance, the switch 20 is connected to contact a, and the loop gain of the control loop is
The low-pass filter 17 and servo amplifier 16 set the optimum value for tracking control. In this way, the tracking error signal is amplified and phase compensated optimally for tracking control by the low-pass filter 17 and the servo amplifier 16, and is applied to the drive circuit 21. The tracking mirror 7 is driven by this drive circuit 21, and the spot of the light beam on the disk is controlled to follow and scan on the track.

In such a circuit, when a disturbance is added and the beam spot on the disk begins to deviate from the track, the tracking error signal output from the differential amplifier 15 increases, and the level detector 22 detects the level fluctuation of this tracking error signal. The switch 20 is connected to contact b by the selection circuit 23, and the loop gain is set to be large by the low-pass filter 18 and servo amplifier 16 to prevent the beam spot on the disk from deviating from the track. It works like that.

[Problem that the invention seeks to solve]

By the way, as mentioned above, the disk has a structure in which the recording surface is covered with transparent resin 9, and air bubbles or opaque foreign matter may get mixed in therein.
In such a case, the bubble causes a kind of lens effect, and the refractive index in the bubble part of the disk is different from that in the transparent part, so that the light beam appears to have moved. Therefore, the tracking error signal becomes large, the loop gain is set to a large value, and the beam spot works to follow the track. However, in the case of an opaque foreign object, a phenomenon occurs that distorts the light intensity distribution, so even though the spot is not out of track, the tracking error signal becomes large, so the loop gain also becomes large, and the circuit continues to track the spot. Work to bring it back up. However, since the spot is actually not off the track, the spot will be off the track due to the above-mentioned operation, and the reproduction characteristics will be significantly degraded.

Therefore, the loop gain adjustment circuit of this tracking servo circuit increases the loop gain when the spot actually deviates from the track and the tracking error signal increases and detectable disturbances, such as vibrations and bubbles on the disk. However, in the same way, the tracking error increases, but in reality, for disturbances that do not cause the spot to be out of track, i.e., scratches on the disk and opaque foreign objects, the loop gain should be increased compared to normal tracking control without disturbances. It is desirable to lower the loop gain, and in this case too, conventional loop gain adjustment circuits that adjust the loop gain to increase the loop gain have had the problem of aggravating such disturbances.

This invention has been made in view of the above points, and is capable of automatically adjusting the loop gain of a tracking servo circuit to an appropriate amount for various disturbances.
It is an object of the present invention to provide a tracking servo circuit for an information recording disk reproducing device that eliminates the drawbacks of the conventional loop gain adjustment circuit as described above and prevents malfunctions.

[Means for solving problems]

A tracking servo circuit for a disc playback device according to the present invention includes a disturbance detection means for detecting the type of disturbance by detecting a level fluctuation of a playback information signal caused by a disturbance, and a control circuit based on the detection result of the disturbance detection means. A gain variable means for setting the loop gain of the loop to an optimum value is provided.

[Effect]

In this invention, level fluctuations in the reproduced information signal caused by disturbances are detected, and the type of the disturbance, that is, whether the disturbance causes a deviation from the track of the pickup element or not, is detected. Based on the results, an appropriate loop gain is automatically selected for the above disturbance.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Here, to summarize this embodiment, the low-pass filter attached to the servo amplifier for gain adjustment provided in the control loop has three stages, and the reproduced information signal generated by the disturbance of the information signal by the detector is level fluctuation is detected, and it is determined whether the above-mentioned disturbance causes the beam spot to deviate from the track and the tracking error signal increases, and an appropriate loop gain is set for the disturbance based on the determination result. The above-mentioned three-stage low-pass filter, that is, the loop gain, is automatically selected, and comfortable servo operation can be obtained by the selected loop gain.

A detailed explanation will be given below with reference to the drawings. 1st
FIG. 1 is a block diagram schematically showing an information recording disk reproducing apparatus equipped with a tracking servo circuit according to an embodiment of the present invention, and the same parts as in FIG. 1 are given the same reference numerals. 27 is a bottom detector for detecting the lower envelope of the reproduced information signal output from the summing amplifier 26; 29 is a peak detector for detecting the upper envelope of the reproduced information signal; 28 and 30 are the bottom detectors 27, respectively. , is a level detector that detects fluctuations in the output level of the peak detector 29, and each of the detectors 27, 29 and the level detectors 28, 3
0 constitutes a disturbance detection means that detects the level fluctuation of the reproduced information signal and detects the type of disturbance.

Further, 23 is a selection circuit that controls the switch 20 and selects the loop gain based on the output from the level detectors 28 and 30, and 17, 18, and 19 are low-pass filters that, together with the servo amplifier 16, set the loop gain. , the above selection circuit 2
3, switch 20, low pass filter 17,1
8, 19, and the servo amplifier 16 constitute a gain variable means for setting the loop gain to an optimal value according to the type of disturbance.

Next, the operation will be explained.

Since the operation of the control loop is similar to the conventional operation, a detailed explanation will be omitted here, and the operation of the information signal fluctuation detecting section, that is, the disturbance detecting means will be explained below.

The operation from the time when the laser beam emitted from the light emitter 1 is irradiated onto the disk until the reflected light reaches the photodetector 12 is the same as the conventional one. Then, the current output with a magnitude corresponding to the intensity of the light incident on the B part and C part of the photodetector 12 is transmitted to the preamplifier 2.
4, 25 into a voltage, and these amplifiers 24,
The outputs of 25 are summed by a summing amplifier 26,
An information signal 31 recorded on the disc is formed.

Here, the amount of light incident on the photodetector 12 is small because the light beam is diffusely reflected on the protruding pits 10 forming the track, and most of the amount of emitted light is reflected on the other mirror surfaces of the disk. A lot to come back to. Fig. 2a shows the light reflection intensity with respect to the spot position, and the amount of incident light when the main spot β shown in Fig. 2b follows the track center is point P, and as it goes to both sides of the point, That is, as the spot moves away from the track, the amount of incident light increases. Note that α and γ in FIG. 2b indicate auxiliary spots. In addition, in the same figure, the pit 10 is shown by a two-dot chain line, but the pit 10
are formed intermittently within the range shown by the two-dot chain line.

When the light beam is following the track, the minimum amount of incident light when the main spot β is on the pit and the maximum amount of incident light when the main spot β is on the mirror surface do not change. That is, the waveform of the information signal, its envelope, and the level of the tracking error signal are as shown in FIG. 3a. However, in the presence of disturbances, here vibrations and air bubbles on the disk, the maximum incident light intensity when the spot is on a mirror surface does not change, but when the spot is out of track, for example as shown in Figure 2b. When spot β moves in the direction of arrow
The amount of incident light increases as shown by the arrow in figure a, and in figure 3 b
As shown in , the information signal envelope is missing at the bottom. In this case, the level of the tracking error signal also fluctuates as shown in the figure.

On the other hand, when there are scratches and opaque foreign matter on the disk, the scratches and opaque foreign matter distort the light intensity distribution, and the amount of light incident on the photodetector 12 decreases.
The rate of decrease is the same whether the spot β is on the pit 10 or on the mirror surface. Therefore, the amount of change changes in proportion to the absolute amount of incident light, so when spot β is on bit 10, the minimum amount of incident light does not change, but when spot β is on the mirror surface, the maximum amount of incident light changes significantly. The information signal envelope becomes truncated at the top as shown in FIG. 3c. Furthermore, the level of the tracking error signal also varies as shown in the figure.

In this embodiment, the above-described fluctuations in the information signal envelope that change depending on the type of disturbance are detected, and an optimal loop gain is obtained accordingly. That is, the normal loop gain is
0 makes the a contact, that is, the low pass filter 17
A loop gain suitable for the spot to follow and scan on the track is provided. If the added vibration and bubbles on the disk cause the information signal to be outputted from the summing amplifier 26 with the bottom portion missing, the bottom detector 27,
The output of the bottom detector 27 of the peak detector 29 fluctuates. The level fluctuation is detected by the level detector 28.
As a result, the selection circuit 23 connects the switch 20 to the b contact, that is, the low-pass filter 18, to increase the loop gain.

Also, if the upper part of the information signal is lost due to scratches or opaque foreign matter on the disk, the summing amplifier 26
When the output from the peak detector 29 changes, and the level detector 30 detects the change, the selection circuit 23 connects the switch 20 to the c contact, that is, the low-pass filter 19, to lower the loop gain. . In this way, the loop gain is automatically adjusted to an appropriate value depending on the type of disturbance.

In this way, in this embodiment, disturbances are identified based on level fluctuations of the information signal, and one of the three low-pass filters 17, 18, 19 is selected depending on the type of disturbance, and the loop gain is automatically set to the optimum value. Since the adjustment is made, stable tracking can always be performed against various disturbances without complicated operations.

Although the above embodiment shows a loop gain adjustment circuit that adjusts the loop gain to be suitable for disturbances based on level fluctuations of the reproduced information signal, the tracking error signal shown in the conventional example is as shown in FIG. c.
As shown in FIG. 2, there is a large variation with respect to each disturbance, so this may be used to select the loop gain according to the disturbance. An example of such a circuit is shown in FIG. In this example,
The level detector 22 detects level fluctuations in the tracking error signal output from the differential amplifier 15, and detects disturbances that are difficult to distinguish from only the level fluctuations in the tracking error signal, such as scratches and opaque foreign objects on the disk. A level detector 30 detects the output of the peak detector 29, which is the amount of signal fluctuation. That is, when a fluctuation is detected only by the level detector 22, the selection circuit 23 selects the low-pass filter 18 to increase the loop gain, and when a fluctuation is detected by both the level detector 22 and the level detector 29, the selection circuit 23 selects the low-pass filter 18 to increase the loop gain. The selection circuit 23 selects the low-pass filter 19 to reduce the loop gain, thereby automatically adjusting the optimum loop gain according to the disturbance.

It goes without saying that the same effects as those of the above embodiment can also be obtained in such an embodiment.

Furthermore, in each of the above embodiments, the amount of total reflection light emitted from the disk is detected by adding the amount of light incident on portions B and C, which are four-part detectors in the photodetector. The detection method is not limited to this, for example, the amount of side beam reflected light for track servo, that is, the amount of light reflected by the side beam of the photodetector A and D.
It is also possible to add the amounts of incident light for each part. Alternatively, since the photodetector 12 normally has a common cathode, the entire photocurrent flowing through the cathode may be taken out by appropriate means to detect a change in the amount of light.

〔Effect of the invention〕

As described above, according to the present invention, the disturbance is identified based on the level fluctuation of the reproduced information signal that occurs in response to the disturbance, that is, the type of disturbance is detected, and the loop gain of the tracking servo loop is determined based on the detection result. Since it is automatically adjusted to the optimum value, it has the effect of always being able to perform stable tracking against disturbances without any complicated operations.

[Brief explanation of drawings]

FIG. 1 is a block configuration diagram of a tracking servo circuit of a disc playback device according to an embodiment of the present invention, FIG. 2 is a diagram for explaining changes in the amount of incident light due to movement of a light beam, and FIG. 3 is a diagram according to the present invention. FIG. 4 is a block diagram showing another embodiment of the present invention, and FIG. 5 is a block diagram of a tracking servo circuit of a conventional disc playback device. 9... Transparent resin of disk, 10... Track (pit), 16... Servo amplifier, 17, 18,
19...Low pass filter, 20...Switch,
22, 28, 30... Level detector, 23... Selection circuit, 27... Bottom detector, 29... Peak detector. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Scope of Claims] 1. A tracking servo circuit of a disk playback device that obtains a tracking error signal by scanning a track of a disk on which information is recorded, and controls tracking of a pick-up playback element using this tracking error signal. It consists of a peak detector that detects the upper envelope of the information signal, a bottom detector that detects the lower envelope of the information signal, and a level detector that detects fluctuations in the output level of each of these detectors. a disturbance detection means for detecting the type of disturbance by detecting a level fluctuation of the disturbance; A tracking servo circuit for a disc playback device, characterized in that the tracking servo circuit is equipped with a gain variable means for setting an optimal value according to the requirements. 2. In a tracking servo circuit of a disk playback device that obtains a tracking error signal by scanning a track of a disk on which information is recorded and controls tracking of a pick-up playback element using this tracking error signal, the upper envelope of the playback information signal , a level detector that detects output level fluctuations of the peak detector, and a tracking error signal level detector that detects the level of the tracking error signal, and detects level fluctuations of the reproduced information signal. a disturbance detection means for detecting the type of disturbance; and a disturbance detection means provided in a part of the tracking servo loop, which adjusts the loop gain of the tracking servo loop to an optimal value according to the type of disturbance, based on the detection result of the disturbance detection means. A tracking servo circuit for a disc playback device, characterized in that it is equipped with gain variable means for setting a value.