JP3847910B2 - Tracking control device for optical disk playback system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical disk reproduction system for reproducing an optical disk such as a CD (Compact Disk) and a DVD (Digital Video Disk), and more particularly to improvement of a tracking control device for performing tracking control on the optical pickup.
[0002]
[Prior art]
As is well known, in an optical disk reproduction system for reproducing an optical disk as described above, high-precision tracking control is performed on an optical pickup in order to read recorded information from a track formed with a small width on the optical disk. It is necessary to apply.
[0003]
As the tracking control means, apart from the light beam for reading the record information, a tracking error is detected by irradiating the optical disk with an auxiliary light beam dedicated to tracking control, and the record information using the same light beam. And a method for detecting tracking errors.
[0004]
Of these, the tracking control means based on the latter method allows the reflected light from the optical disk to be received by a photoelectric converter having a plurality of light receiving areas, and tracking based on the phase difference of the electrical signal output from each light receiving area. In general, a tracking error signal generating means by a so-called phase difference method, which generates an error signal, is used.
[0005]
By the way, regardless of which tracking control method described above is used, for example, the sensitivity difference of each light receiving area constituting the photoelectric converter, the variation in the light amount distribution of the light beam received in each light receiving area, the pit shape of the optical disk, etc. Due to the influence, the DC level of the tracking error signal generated in the optimum tracking state varies for each reproduction system or each optical disc.
[0006]
In short, the tracking control means uses the light beam even in a state where there is no tracking error that accurately traces the track formed on the optical disk, that is, even when the light beam is accurately on-track. Different DC offsets (hereinafter referred to as tracking residual errors) are generated in the generated tracking error signal for each optical disc reproducing system or each optical disc. For this reason, it is necessary to install a means for correcting the tracking residual error in the tracking control means.
[0007]
Further, in the tracking error signal generating means using the phase difference method described above, when the objective lens of the optical pickup is shifted in the radial direction of the optical disk, there is no tracking error after the shift, that is, the light beam is accurately on-track. Even if the state becomes a state, a tracking residual error is generated in the tracking error signal, so that a tracking residual error correcting means is necessary also in this respect.
[0008]
As a means for correcting this tracking residual error, conventionally, there is a method of correcting the reproduction signal with a difference in the degree of amplification of each reproduction signal output from a plurality of light receiving areas constituting the photoelectric converter, and the generated tracking error signal. In general, a method of correcting by adding a direct current level is used.
[0009]
However, in the correction means for making a difference in the amplification degree of each reproduction signal, in the case of the means for generating the tracking error signal by the phase difference method described above, the phase of the reproduction signal output from each light receiving region is compared. There is a problem that the tracking residual error cannot be corrected even if the level of each signal is changed.
[0010]
In addition, in the method of correcting by adding the DC level to the tracking error signal, it is necessary to add a circuit for adding the DC level separately, and the circuit is highly accurate to adjust a minute DC voltage. Because of the demand, there is a problem that the configuration becomes complicated and causes an economic disadvantage. Further, in the correction method by adding the DC level, since a DC voltage for correction is always given, there is a disadvantage that an offset voltage is output when there is no signal.
[0011]
[Problems to be solved by the invention]
As described above, the conventional tracking residual error correction means used in the tracking control means of the optical disk reproduction system cannot be used depending on the tracking error signal generation method, and there is a separate circuit with high accuracy. It has the problem of becoming necessary.
[0012]
Therefore, the present invention has been made in consideration of the above circumstances, and in the generation of a tracking error signal using a phase difference method, it is possible to easily correct a tracking residual error with a simple configuration. It is an object of the present invention to provide a tracking control device for an optical disk reproduction system.
[0015]
[Means for Solving the Problems]
A tracking control device for an optical disc reproduction system according to the present invention irradiates an optical disc with a light beam via an objective lens, and transmits light obtained from the optical disc to a tracking direction of the optical disc and a tangential direction of the optical disc. And an optical disk reproducing system provided with an optical pickup that receives light by a photodetector having a plurality of light receiving portions arranged in correspondence with each other.
[0016]
And first and second delay means for delaying the signal component obtained from each light receiving portion at one diagonal position of the photodetector in proportion to the level of the input control voltage, First addition means for adding the signals delayed by the first and second delay means, and control for inputting signal components obtained from the respective light receiving portions at the other diagonal position of the photodetector Third and fourth delay means for delaying in proportion to the voltage level, second addition means for adding the signals delayed by the third and fourth delay means, and the first Tracking error signal generation for generating a tracking error signal corresponding to the tracking error of the objective lens with respect to the track formed on the optical disk based on the phase difference between the output signal of the adding means and the output signal of the second adding means Means, Control means for correcting a DC offset included in the tracking error signal output from the tracking error signal generating means by adjusting the level of the control voltage input to the plurality of delay means. The fourth to fourth delay means have the same characteristic that the delay amount can be varied within a certain range, and the control means has a first control voltage applied to both the first and second delay means. And a second control voltage applied to both the third and fourth delay means, and the increase / decrease relationship of the first and second control voltages is set to be opposite to each other.
[0017]
According to the configuration as described above, the delay means for delaying the reproduction signal obtained from each light receiving portion at one diagonal position among the plurality of light receiving portions constituting the photodetector of the optical pickup, and the other Since the delay time difference with the delay means for delaying the reproduction signal obtained from each light receiving unit at the diagonal position of is appropriately adjusted, the tracking error signal generation method using the phase difference has a simple configuration. The tracking residual error can be easily corrected.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a first embodiment of the present invention will be described in detail with reference to the drawings. In FIG. 1, reference numeral 11 denotes an optical disk. The optical disk 11 is rotationally driven by a disk motor 12. An optical pickup 13 for reading information from the optical disk 11 is disposed on the signal recording surface side of the optical disk 11.
[0019]
The optical pickup 13 is supported so as to be movable in the tracking direction of the optical disk 11. The optical pickup 13 condenses the laser light on the signal recording surface of the optical disk 11 through an objective lens 13a supported so as to be finely driven in the tracking direction of the optical disk 11, and the reflected light is converted into a photoelectric converter. 13b receives light.
[0020]
The photoelectric converter 13b includes four photodetectors A, B, C, and D that generate electrical signals corresponding to the amount of received light. In this case, the horizontal direction in the figure, that is, the arrangement direction of the photodetectors A and B and the photodetectors C and D corresponds to the tracking direction of the optical disk 11, and the vertical direction in the figure, that is, the photodetectors A and D and the photodetectors B and C. The arrangement direction corresponds to the track direction (tangential direction) formed on the optical disc 11.
[0021]
The electrical signals output from the photodetectors A, B, C, and D are amplified by the preamplifier circuits 14a, 14b, 14c, and 14d, respectively, and then supplied to the waveform equalization circuits 15a, 15b, 15c, and 15d. Supplied and corrected to a signal whose edge position is fixed.
[0022]
The output signals of the waveform equalization circuits 15a and 15c are respectively supplied to and added to the addition circuit 16a. The output signals of the waveform equalization circuits 15b and 15d are respectively supplied to and added to the addition circuit 16b. That is, among the four photodetectors A, B, C, and D that constitute the photoelectric converter 13b, signals output from the photodetectors A and C and the photodetectors B and D that are in a diagonal position relationship are added to the adder circuit 16a. , 16b, respectively.
[0023]
Here, the output signal of the adder circuit 16a is supplied to the first delay circuit 17a and delayed. The output signal of the adder circuit 16b is supplied to the second delay circuit 17b and delayed. The delay amount, that is, the delay time of the first and second delay circuits 17a and 17b is variable according to the control voltage output from the delay control circuit 18, as will be described in detail later. The delay control circuit 18 is controlled by a system control circuit 19 that incorporates, for example, a microcomputer for comprehensively controlling the operation of the optical disc playback system.
[0024]
The output signals of the first and second delay circuits 17a and 17b are both supplied to the phase difference detection circuit 20. The phase difference detection circuit 20 detects the phase difference between both signals output from the first and second delay circuits 17a and 17b, and outputs a detection signal corresponding to the phase difference to the tracking error signal generation circuit 21. ing.
[0025]
The tracking error signal generation circuit 21 generates a tracking error signal corresponding to the tracking error based on the input detection signal, and a tracking error signal is generated by the phase difference method. The tracking error signal generated by the tracking error signal generation circuit 21 is supplied to the system control circuit 19 and used for control of the delay control circuit 18.
[0026]
FIG. 2 shows the relationship between the delay time of the first and second delay circuits 17 a and 17 b and the control voltage output from the delay control circuit 18. As shown by a straight line a in FIG. 2, the delay time of the first delay circuit 17a increases to d1 to d3 in proportion to the level of the control voltage output from the delay control circuit 18 increasing to V1 to V3. It has the characteristic to do. Further, the second delay circuit 17b has a delay time d3-3 proportional to the level of the control voltage output from the delay control circuit 18 being increased to V1 to V3 as shown by a straight line b in FIG. The characteristic is shortened to d1.
[0027]
Therefore, for example, if the control voltage level is set to V3, the delay time of the first delay circuit 17a is d3, and the delay time of the second delay circuit 17b is d1. That is, the phase of the signal obtained by adding the reproduction signals obtained from the photodetectors A and C is delayed with respect to the phase of the signal obtained by adding the reproduction signals obtained from the photodiodes B and D.
[0028]
As a result, the DC level is superimposed on the tracking error signal generated by the tracking error signal generation circuit 18. Further, the magnitude of the direct current level superimposed on the tracking error signal is determined by the delay time difference between the first and second delay circuits 17a and 17b.
[0029]
According to the first embodiment, an optical disk used with a simple configuration in which the delay times of the first and second delay circuits 17a and 17b are appropriately adjusted based on the generated tracking error signal. The tracking residual error generated in the tracking error signal for each reproduction system or each optical disk can be easily corrected.
[0030]
Next, FIG. 3 shows a second embodiment of the present invention. In FIG. 3, the same parts as those of FIG. That is, the output signals of the waveform equalization circuits 15a, 15b, 15c, and 15d are supplied to the delay circuits 22a, 22b, 22c, and 22d and are respectively delayed.
[0031]
Among these, the output signals of the delay circuits 22 a and 22 c are added by the adder circuit 23 a and then supplied to one input terminal of the phase difference detection circuit 20. The output signals of the delay circuits 22b and 22d are added by the adder circuit 23b and then supplied to the other input terminal of the phase difference detection circuit 20.
[0032]
In FIG. 3, reference numerals 24a, 24b, 24c and 24d denote input terminals to which first, second, third and fourth control voltages are applied, respectively. These first to fourth control voltages are generated from a delay control circuit 25 controlled by the system control circuit 19.
[0033]
The delay time of the delay circuit 22a is controlled by a control voltage obtained by adding the second and third control voltages applied to the input terminals 24b and 24c by the adder circuit 26a. The delay time of the delay circuit 22b is controlled by a control voltage obtained by adding the second and fourth control voltages applied to the input terminals 24b and 24d by the adder circuit 26b.
[0034]
Further, the delay time of the delay circuit 22c is controlled by a control voltage obtained by adding the first and third control voltages applied to the input terminals 24a and 24c by the adder circuit 26c. The delay time of the delay circuit 22d is controlled by a control voltage obtained by adding the first and fourth control voltages applied to the input terminals 24a and 24d by the adder circuit 26d.
[0035]
FIG. 4 shows the relationship between the delay times of the delay circuits 22a, 22b, 22c and 22d and their control voltages. These delay circuits 22a, 22b, 22c, and 22d all have delay times increased to d1 to d3 in proportion to the level of the input control voltage increasing from V1 to V3, as shown by the solid line in FIG. Have the same characteristics.
[0036]
FIG. 5 shows the relationship between the first control voltage and the second control voltage. That is, there is a characteristic that the level of the second control voltage is lowered to V3 to V1 in proportion to the level of the first control voltage being increased to V1 to V3. The relationship between the third control voltage and the fourth control voltage is also set similarly to FIG.
[0037]
According to the second embodiment, first, the third control voltage contributes to the control of the delay time of the delay circuits 22a and 22c, and the fourth control voltage controls the delay time of the delay circuits 22b and 22d. Has contributed. For example, if the level of the third control voltage is set to V3, the delay time of the delay circuits 22a and 22c is d3. At this time, the level of the fourth control voltage is V1, and therefore the delay of the delay circuits 22b and 22d. The time is d1.
[0038]
That is, as in the first embodiment, the phase of the signal obtained by adding the reproduction signals obtained from the photodetectors A and C is delayed with respect to the phase of the signal obtained by adding the reproduction signals obtained from the photodetectors B and D. Is done. For this reason, it becomes possible to easily correct the tracking residual error generated in the tracking error signal for each optical disc reproducing system or each optical disc 11 used.
[0039]
The first control voltage contributes to the control of the delay times of the delay circuits 22c and 22d, and the second control voltage contributes to the control of the delay times of the delay circuits 22a and 22b. For example, if the level of the second control voltage is set to V3, the delay time of the delay circuits 22a and 22b is d3. At this time, the level of the first control voltage is V1, and therefore the delay of the delay circuits 22c and 22d. The time is d1.
[0040]
That is, the phase of each reproduction signal obtained from the photodetectors A and B is delayed with respect to the phase of each reproduction signal obtained from the photodetectors C and D. For this reason, when the objective lens 13a is shifted in the radial direction of the optical disc 11 and thereafter has no tracking error, the tracking residual error generated in the tracking error signal can be easily corrected.
The present invention is not limited to the above-described embodiments, and can be variously modified and implemented without departing from the scope of the invention.
[0041]
【The invention's effect】
As described above in detail, according to the present invention, in the generation of the tracking error signal using the phase difference method, an extremely good optical disc reproducing system capable of easily correcting the tracking residual error with a simple configuration. A tracking control device can be provided.
[Brief description of the drawings]
FIG. 1 is a block configuration diagram showing a first embodiment of a tracking control device of an optical disk reproducing system according to the present invention.
FIG. 2 is a view for explaining the characteristics of first and second delay circuits in the first embodiment;
FIG. 3 is a block diagram showing a second embodiment of the tracking control device of the optical disk reproducing system according to the present invention.
FIG. 4 is a view for explaining the characteristics of each delay circuit in the second embodiment;
FIG. 5 is a view for explaining the relationship between a first control voltage and a second control voltage in the second embodiment;
[Explanation of symbols]
11 ... Optical disc,
12 ... disk motor,
13: Optical pickup,
14a-14d ... Preamplifier circuit,
15a to 15d: waveform equalization circuit,
16a, 16b ... addition circuit,
17a ... first delay circuit,
17b ... second delay circuit,
18 ... delay control circuit,
19 ... System control circuit,
20 ... Phase difference detection circuit,
21 ... Tracking error signal generation circuit,
22a to 22d ... delay circuit,
23a, 23b ... addition circuit,
24a to 24d ... input terminals,
25 ... delay control circuit,
26a to 26d: adder circuits.

Claims (2)

A plurality of light receiving units that irradiate the optical disc with a light beam through an objective lens and that arrange the light obtained from the optical disc in correspondence with the tracking direction of the optical disc and the tangential direction of the optical disc, respectively. In an optical disk reproduction system equipped with an optical pickup that receives light with a photodetector having
First and second delay means for respectively delaying signal components obtained from the respective light receiving portions at one diagonal position of the photodetector in proportion to the level of the input control voltage;
First addition means for adding the signals delayed by the first and second delay means ;
Third and fourth delay means for respectively delaying signal components obtained from the respective light receiving portions at the other diagonal position of the photodetector in proportion to the level of the input control voltage;
Second addition means for adding the signals delayed by the third and fourth delay means ;
Based on the phase difference between the output signal of the first addition means and the output signal of the second addition means, a tracking error signal corresponding to the tracking error of the objective lens with respect to the track formed on the optical disc is generated. Tracking error signal generating means;
Control means for correcting the DC offset included in the tracking error signal output from the tracking error signal generating means by adjusting the level of the control voltage input to the plurality of delay means ,
The first to fourth delay means have the same characteristic that the delay amount can be varied within a certain range,
The control means generates a first control voltage applied to both the first and second delay means and a second control voltage applied to both the third and fourth delay means, and And a tracking control device for an optical disk reproducing system, wherein the increase / decrease relationship of the second control voltage is set to be opposite to each other . Among the plurality of delay means, the delay means for delaying the reproduction signal of the light receiving unit corresponding to one tangential half surface of the photodetector, and the light receiving unit corresponding to the other tangential half surface of the photodetector. The delay means for delaying the reproduction signal is provided with a third control voltage and a fourth control voltage set in the same increasing / decreasing relationship as the first and second control voltages, respectively. The tracking control device for an optical disk reproducing system according to claim 1 .

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