JPS6182336A - Tracking servo circuit for disc playback device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

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 circuit that can automatically adjust its loop gain to an optimal value with the least tracking deviation. It is related to.

[Conventional technology]

Conventionally, in an information recording disk reproducing apparatus using a pickup reproducing element using a light beam, tracking control of the pickup reproducing element is performed using a tracking error signal, so that the pickup reproducing element accurately follows and scans under the recorded track. I have to. The loop gain control circuit in such a tracking servo circuit detects level fluctuations in the tracking error signal that occur in response to disturbances applied to the big amplifier reproducing element and its reproducing device, and increases the loop gain of the tracking servo circuit. It is known what is set to do.

A conventional example of such a tracking servo circuit is shown in FIG. In the figure, ■ 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 and 6 are beam splitters for dividing the laser beam into a main spot and an auxiliary spot, 5 is a prism, and 7
is an I-ranking mirror, and 8 and 11 are lenses. Further, 9 is a transparent resin that covers the recording surface of the disk, and 10 is a protruding pin i. forming a track.

Further, 12 is a photodetector that outputs a current of a magnitude corresponding to the amount of incident light, 24.25 is a preamplifier for converting the output current of the photodetector 12 into a voltage, and 26 is a width of both the preamplifiers. 24 and 25 to form an information signal 31 recorded on the disc.

13.14 is a preamplifier for tracking control,
This converts the current outputted from the photodetector 12 into a voltage according to the amount of incident light on the A and D portions of the photodetector 12, respectively. 15 is a differential amplifier that receives the output of these amplifiers 13 and 14 and outputs a tracking error signal; 17 and 18 are low-pass filters attached to the servo amplifier 16 for gain adjustment; and 21 is a differential amplifier that receives the output of the servo amplifier 16 and outputs a tracking error signal. This is a drive circuit that drives the tracking mirror 7. Further, 22 is a level detector for detecting the level fluctuation of the tracking error signal output from the differential amplifier 15, and 23 is a selection for controlling the switch 20 for switching the loop gain according to the output of the level detector 22. It is a circuit.

Next, the operation of the 1 ranking control of the 112 system will be explained.

A laser beam 2 emitted from a light emitter 1 passes through a lens 3.
Beam splitter 4.6. The information recording disk is irradiated with the light through an optical system such as a prism 5.

The reflected light is reflected by the lens 8. tracking mirror 7,
Prism 5. and is guided to a photodetector 12 via 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 light)*detector 12 outputs a current whose magnitude corresponds to the intensity of the incident light, of which the A portion.

A current whose magnitude corresponds to the intensity of the light incident on the D section is input to the preamplifier 13.14, where the valley current is converted into a voltage. The outputs of these amplifiers 13 and 14 are calculated by a differential amplifier 15, and become a tracking error signal representing the deviation from the center of the transformer. In normal tracking without disturbance, the switch 20 is at contact a.
The loop gain of the control loop is set to a mid value for tracking control by a low pass filter 17 and a servo amplifier 16. In this way, the tracking error signal is amplified and two-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 l-rank.

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

[Problem that the invention seeks to solve]

As mentioned above, the disk has a structure in which the recording surface is covered with a 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 the light beam appears to have moved. For this reason, the tracking error signal becomes large, the loop gain is set to a large value, and the beam switch works to follow the track. However, in the case of opaque foreign objects, a phenomenon occurs that distorts the light intensity distribution, so the tracking error signal becomes large, and therefore the loop gain becomes large, even though the suboso I・does not deviate from the track. Work to get it back on the track. However, since the spot was not actually off the track, the spot is off the track due to the above operation, and the reproduction characteristics are significantly degraded.

Therefore, the loop gain adjustment circuit of this tracking servo circuit increases the loop gain when the spot actually deviates from one rank higher 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 for disturbances that do not actually cause the spot to deviate from the track, such as scratches on the disk and opaque foreign objects, the loop gain is changed to normal tracking control without disturbance. It is preferable to lower the loop gain than the current value, and in this case as well, conventional loop gain adjustment circuits that adjust the loop gain to increase it have the problem of aggravating the disturbance in response to such disturbances.

This invention has been made in view of the above points, and the loop gain of the tracking servo circuit is adjusted to i! It is an object of the present invention to provide a tracking servo circuit for a device for recording information recording discs, which can be automatically adjusted without a li, eliminates the drawbacks of the conventional loop gain adjustment circuit as described above, and prevents malfunctions. purpose.

[Means for solving problems]

A tracking servo circuit for a disk 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 the disturbance, and a control loop loop based on the detection result of the disturbance detection means. A gain variable means for setting the gain to an optimum value is provided.

[Effect]

In this invention, the level fluctuation of the reproduced information signal caused by the disturbance is detected, the type of the disturbance, that is, whether the disturbance causes a deviation from the track of the pickup element or not, is detected, and the detection result is Based on this, 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 level fluctuation of the reproduced information signal caused by the disturbance of the information signal is detected by the detector. The above three steps are performed to detect the disturbance and determine whether or not the above-mentioned disturbance is such that the beam spot 1- is off the track and the tracking error signal becomes large. The 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. 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 lower envelope of the reproduced information signal; 28 and 30 are bottom detectors, respectively. Vessel 27. This is a level detector that detects fluctuations in the output level of the peak detector 29, and detects the type of disturbance by detecting the level fluctuations of the reproduced information signal using each of the detectors 27, 29 and level detectors 28, 30. A detection means is configured.

Further, 23 is a selection circuit that controls the switch 20 and selects the loop gain based on the output from the level detector 28.30, and 17, 18.19 is a low-pass filter for setting the loop gain together with the servo amplifier 16. , the selection circuit 23° switch 20. The low-pass filters 17.1B and 19 and the servo amplifier 16 constitute a variable gain means that sets the loop gain to an optimum value depending on 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. And part B of the photodetector 12, part C
The output current corresponding to the intensity of the light incident on the section is converted into a voltage by preamplifiers 24 and 25, and the outputs of these amplifiers 24 and 25 are summed by a summing amplifier 26 and recorded on the disk. An information signal 31 is formed.

Here, the amount of light incident on the photodetector 12 is small because the light beam is diffusely reflected on the protruding bits 10 forming the track, and most of the amount of emitted light is reflected on the other mirror surfaces of the disk. There are a lot of things that come back. FIG. 2 fat shows the light reflection intensity with respect to the spot position,
The amount of incident light when the main spot β shown in fb) in the same figure follows the center of the track is point 1), and the amount of incident light increases as it goes to either side of the point, that is, as the spot deviates from the track. Note that α and γ in Fig. 2 (bl) indicate the auxiliary slot 1.
71-10 is shown by a two-dot chain line, and the pins 10 are formed intermittently within the range shown by this 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 pin 1- 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. 3+al. However, in the case 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 off track, for example in Figure 2 (shown in bl) When spot β moves in the direction of arrow X as shown in Fig. 2 fa
The amount of incident light increases as indicated by the arrow 1, resulting in an information signal envelope with a missing bottom portion, as shown in FIG. 3 (1). In this case, the level of the tracking error signal also fluctuates as shown in the figure.

On the other hand, if 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 reduction ratio is the same whether the spot β is on the focal point 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 the focal point 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 one in which the upper part is missing as shown in FIG. 3 (C1).The level of the 1-racking error signal also changes 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 connected to the a contact point, that is, the low-pass filter 17, by the switch 2o, and is given a loop gain suitable for the follow-up scan of the sub-so l- one rank above. Then, due to the applied vibrations and the bubbles in the disk, the bottom part of the information signal is lost, and the information signal is transferred to the summing amplifier 2.
6, 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, and the selection circuit 23 connects the switch 20 to the b contact, that is, the low-pass filter 18, so as to increase the loop gain.

Furthermore, if the -L portion of the information signal is lost due to scratches or opaque foreign matter on the disk, and the summing amplifier 26 outputs the information signal, the output of the peak detector 29 will fluctuate, and the level detector 30 will detect this fluctuation. Accordingly, the selection circuit 23 connects the switch 20 to the C contact, that is, the low-pass filter 19, so as 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 in the information signal, and one of the three low-pass filters 17, 18, and 19 is selected depending on the type of disturbance, and the loop gain is automatically set to the optimal value. Since the adjustment is made, stable tracking can always be performed against various disturbances without complicated operations.

In the above embodiment, a loop gain adjustment circuit was shown which adjusts the loop gain to be suitable for disturbances by the level fluctuation of the reproduced information signal, but the tracking error signal number shown in the conventional example, As shown by +c+, each disturbance exhibits a large fluctuation, so this may be used to select the loop gain according to the disturbance.One embodiment of such a circuit is shown in Fig. 4. In this embodiment, 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, that is, the disc. For scratches and opaque foreign matter on the top, the level detector 30 detects the output of the peak detector 29, which is the amount of variation in information.
If a fluctuation is detected in only the level detector 22 and the level detector 29, the selection circuit 23 selects the low-pass filter 18 to increase the loop gain, and if the fluctuation is detected in both the level detector 22 and the level detector 29, the selection circuit 23 The low-pass filter 19 is selected to reduce the gain, and the optimum loop gain is automatically adjusted depending on the disturbance.

Of course, such an embodiment can also provide the same effects as the dual embodiment.

In addition, in each example described in -11, it is reflected from the disk (
Detection of total internal reflection is performed by adding the amount of light incident on the 4-part detector 13 and C portions in the photodetector, but the method of light detection is not limited to this.
For example, the amount of light reflected from the side beam for track servo, ie, the amount of light incident on portions A and D of the photodetector, may be added. 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, that is, the type of disturbance is detected based on the level fluctuation of the reproduced information signal that occurs in response to the disturbance, and the loop gain of the tracking servo loop is optimized based on the detection result. Since the tracking is automatically adjusted to a suitable value, it is possible to always perform stable tracking against disturbances without having to perform complicated operations.

[Brief explanation of the drawing]

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, and FIG. 2 is a diagram for explaining changes in the amount of incident light due to movement of a light beam.
FIG. 3 is a diagram for explaining the disturbance detecting means of the present invention, FIG. 4 is a block diagram showing an embodiment of the present invention, and FIG.
The figure 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. 1
9...Ll-bus filter, 20...switch, 2
2.28.30 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 (3)

[Claims] (1) In a tracking servo circuit of a disc playback device that obtains a tracking error signal using a tracking control reference signal obtained from a track to be scanned on a disc on which information is recorded, and controls tracking of a pickup playback element using this tracking error signal. , a disturbance detection means for detecting the type of disturbance by detecting the level fluctuation of the reproduced information signal; and a disturbance detection means provided in a part of the tracking servo loop, which adjusts the loop gain of the tracking servo loop based on the detection result of the disturbance detection means. A tracking servo circuit for a disc playback device, comprising: a gain variable means for setting an optimal value according to the type. (2) The disturbance detection means includes a peak detector that detects the upper envelope of the reproduced information signal, a bottom detector that detects the lower envelope of the reproduced information signal, and detects fluctuations in the output level of each of these detectors. 2. A tracking servo circuit for a disc reproducing apparatus according to claim 1, further comprising a level detector. (3) The disturbance detection means includes a peak detector that detects the upper envelope of the reproduced information signal, a level detector that detects fluctuations in the output level of the peak detector, and a level detector that detects the level of the tracking error signal. A tracking servo circuit for a disk reproducing apparatus according to claim 1, characterized in that the tracking servo circuit comprises a tracking error signal level detector.