JPH0466055B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical disc player that uses a light beam to reproduce information signals recorded on a disc from a disc.

BACKGROUND TECHNOLOGY AND PROBLEMS In an optical disc player that uses a light beam to reproduce information signals such as audio signals and video signals recorded on a disc from, for example, a spiral track, when reproducing the information signal, The light beam is required to be incident on the recording surface of the disk in a proper focused state and to trace the center of the track, and for this purpose a focus servo and a tracking servo are essential.

A tracking servo is an optical pickup that detects the deviation of the light beam incident on the disk from the center of the track, so-called tracking error, and makes the light beam incident on the disk based on the tracking error signal that is the detection signal. The focusing lens or the entire optical pickup is moved in the radial direction of the disk in order to reduce the tracking error to zero. As a tracking error detection method, there is a so-called three-beam method.

As shown in FIG. 1, this method consists of a main beam 11 for reading information signals and two auxiliary beams 12E and 12F for detecting tracking errors.
However, the auxiliary beams 12E and 12F are made incident on the disk so that they are at symmetrical positions with respect to the direction along the recording track T and the direction orthogonal to the recording track T, with the main beam 11 as the center. The reflected light from the disk is the second
The reflected light from the disk of the auxiliary beams 12E and 12F is detected by four photodetectors 21A to 21D arranged around one point as shown in the figure.
The outputs Ie and If of the photodetectors 22E and 22F are supplied to the subtraction circuit 23, whereby Ie-If is When the main beam 11 is located at the center of the track T as shown in FIG. 1, the amounts of light received by the photodetectors 22E and 22F are equal, Outputs Ie and If of photodetectors 22E and 22F
become equal, the tracking error signal Et becomes zero, and the main beam 11 deviates from the center of the track T. Depending on the direction of the deviation, a difference occurs in the amount of light received by the photodetectors 22E and 22F, and the light A difference is generated between the outputs Ie and If of the detectors 22E and 22F, so that the tracking error signal Et becomes positive or negative.

This tracking error signal Et is transmitted to the amplifier circuit 2.
4 to a movable coil 25 of a tracking drive means for moving the focusing lens of the optical pickup or the entire optical pickup in the radial direction of the disk, and the main beam 11 and the auxiliary beams 12E and 12F are controlled in accordance with the tracking error signal Et. They are moved together in the radial direction of the disk.

Although not shown, the photodetectors 21A to 21
The outputs Ia to Id of D are supplied to the arithmetic circuit, and Ia+Ib
The reproduction information signal represented by +Ic+Id and (Ia+Ib)
A focus error signal expressed as -(Ic+Id) is obtained.

However, due to the characteristics of the diffraction grating plate that divides the light beam emitted from the light source into the main beam 11 and the auxiliary beams 12E and 12F in the optical pickup, the amounts of light incident on the disk of the auxiliary beams 12E and 12F are not equal. Or, because the light-receiving sensitivities of the photodetectors 22E and 22F are different, or even because the installation positions of the photodetectors 22E and 22F are shifted, when the main beam 11 is located at the center of the track T, the photodetector 22E
A difference may occur between the outputs Ie and If of 22F and the tracking error signal Et may not become zero.

Therefore, conventionally, a variable resistor for level adjustment is provided on the output side of one of the photodetectors 22E, and a reference disk is used in the manufacturing process of the player.
This variable resistor adjusts the level of the output Ie of one of the photodetectors 22E so that when the main beam 11 is located at the center of the track T, the tracking error signal Et output from the subtraction circuit 23 becomes zero. There is. However, this method has the disadvantage of requiring a complicated adjustment process. Moreover, commercially available disks have variations in optical conditions, and the outputs Ie and If of the photodetectors 22E and 22F are also affected by the optical conditions of the disk, so this method Now, depending on the disc to be reproduced, the tracking error signal Et may not become zero when the main beam 11 is located at the center of the track T, so stable tracking servo can be expected regardless of the disc. It is difficult.

Purpose of the Invention In view of the above, the present invention provides that, when a user attempts to playback, the outputs of two photodetectors for tracking error detection are determined based on the optical conditions of the disc and the conditions of the optical system of the player. An object of the present invention is to provide an optical disc player that is automatically set to an appropriate level according to the situation, and always performs stable tracking servo.

Summary of the Invention The optical disc player according to the present invention includes first and second auxiliary beams that are incident on the disc together with the main beam for reading information signals and are used to detect tracking errors of the main beam.
first and second photodetectors that detect reflected light from the disk; a voltage generation circuit that generates a voltage to which the output of the first photodetector is multiplied; A multiplication circuit for multiplying the output of the photodetector, and a subtraction circuit for obtaining a main beam tracking error signal from the difference between the output of the multiplication circuit and the output of the second photodetector. When the disc is attached to the player, its output voltage increases or decreases stepwise or continuously from the initial value, and when the disc is attached to the player, the first and second auxiliary beams are connected to the disc. When the output of the multiplier circuit and the output of the second photodetector become approximately equal in level, the output voltage of the voltage generating circuit stops rising or falling. After that, the output voltage is held at the value at which it stopped.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 3 shows an example of an optical disc player according to the present invention.

The output Ie of the photodetector 22E mentioned above is sent to the multiplication circuit 30.
is supplied to the photodetector 22 in the multiplication circuit 30.
The output Ie of E is multiplied by the voltage X obtained from the digital-to-analog conversion circuit described later, and the output
Ie is supplied to one input terminal of the subtraction circuit 23, and the output If of the photodetector 22F is supplied to the other input terminal of the subtraction circuit 23.
A tracking error signal Et represented by -If is obtained. Subtraction circuit 23 and amplifier circuit 2
A switch 31 is inserted between the switches 4 and 4.

Further, the output X·Ie of the multiplication circuit 30 is supplied to a peak hold circuit 32 to hold its peak value, and the output _S1 of this peak hold circuit 32 is supplied to one input end of the voltage comparison circuit 33, and the output The output If of the detector 22F is the peak hold circuit 34
The output S ₂ of the peak hold circuit 34 is supplied to the other input terminal of the voltage comparison circuit 33 . The voltage comparator circuit 33 outputs an output S ₃ when the output S ₁ of the peak hold circuit 32 is less than the output S ₂ of the peak hold circuit 34.
becomes a low level, and when the output S ₁ of the peak hold circuit 32 becomes larger than the output S ₂ of the peak hold circuit 34, the output S ₃ becomes a high level. The output S ₃ of this voltage comparator circuit 33 is supplied to the switch 31 as its on/off control signal, and when the output S ₃ is at a low level, the switch 31 is turned off and the output S ₃
When the level is high, the switch 31 is turned on.

On the other hand, a binary counter 35 is provided to count the clock CK. The output _S3 of the voltage comparator circuit 33 is given to the counter 35 as a stop signal, and when the output _S3 is at a low level, the counter 35 is clocked.
Counts CK, but stops counting when output _S3 goes high. The output data of counter 35 is supplied to memory 36. The output _S3 of the voltage comparison circuit 33 is given to the memory 36 as a control signal, and when the output _S3 is at a low level, the counter 35
The output data of the counter 35 is taken out as is to the output of the memory 36, but when the output _S3 becomes a high level, the memory 36 stores and holds the output data of the counter 35 at that time, and thereafter continues to take out that data as an output. . The output data of the memory 36 is supplied to a digital-to-analog conversion circuit 37 and converted into an analog voltage, and the analog voltage is supplied as the aforementioned voltage X to the multiplication circuit 30.

To describe the operation of the above example, the counter 35 is initially set to a certain initial value. This initial value is determined when the data is supplied to the digital-to-analog conversion circuit 37 through the memory 36 and converted into an analog voltage, and when the analog voltage is multiplied by the output Ie of the photodetector 22E in the multiplication circuit 30, the output Ie of the photodetector 22E is multiplied by the multiplication circuit. The level of the output of the photodetector 22F is set to be smaller than the level of the output of the photodetector 22F. Therefore, at the beginning, the output S ₃ of the voltage comparator circuit 33
is at a low level, the switch 31 is turned off, and the tracking servo is not applied. In this state, when the disc is mounted on the player, the entire optical pickup is sent in the radial direction of the disc by the pickup feeding means, and the main beam 11 and auxiliary beams 12E and 12F from the pickup are rapidly moved in a direction across the recording track T. be moved by As a result, the output of photodetectors 22E and 22F
Ie and If are auxiliary beams 12E and 12F, respectively
When passing through the center of the recording track T, the waveform becomes a sinusoidal wave that takes a minimum value.

On the other hand, the counter 35 counts the clock CK from the above-mentioned initial value. The output data of the counter 35 is supplied to the digital-to-analog conversion circuit 37 through the memory 36 and converted into an analog voltage.
The output voltage X of the multiplication circuit 30 rises stepwise, and the peak value of the output X·Ie of the multiplication circuit 30 rises stepwise as shown in FIG. 4A. Therefore, the level of the output _S1 of the peak hold circuit 32 also increases stepwise as shown in FIG. 4B. On the other hand, the peak value of the output If of the photodetector 22F remains unchanged as shown in FIG.
The level of S ₂ is constant as shown in FIG. 4D.

Then, as shown in FIG. 4F, the counter 35
When the count value changes from a certain value n to n+1, the peak value of the output X·Ie of the multiplication circuit 30 exceeds the peak value of the output If of the photodetector 22F, and the output S ₁ of the peak hold circuit 32 becomes higher than that of the output S ₂ of the peak hold circuit 34, and the output S ₃ of the voltage comparison circuit 33 changes from a low level L to a high level H as shown in FIG. 4E. As a result, the counting of the clock CK in the counter 35 is stopped, and the data of the count value n+1 of the counter 35 at this time is recorded and held in the memory 36, and from now on, the voltage applied from the digital-to-analog conversion circuit 37 to the multiplication circuit 30 is X becomes a constant value corresponding to this n+1 data. As a result, the peak value of the output X·Ie of the multiplication circuit 30 and the peak value of the output If of the photodetector 22F are held at approximately the same value, and the subtraction circuit 23
When the main beam 11 is located at the center of the track T, the tracking error signal Et output from the track T becomes almost zero.

Then, when the output _S3 of the voltage comparison circuit 33 becomes a high level H, the switch 31 is turned on, and the tracking error signal Et output from the subtraction circuit 23 is applied to the movable coil 25 of the tracking drive means through the amplifier circuit 24. The tracking servo will now be applied.

The above-mentioned operation is performed every time a disc is attached to a player. Furthermore, since the contents of the memory 36 are erased when the power is turned off, the above-mentioned operation is performed even when the power is turned off and then turned on again. Ru.

Effects of the Invention As is clear from the above description, according to the optical disc player according to the present invention, the main beam for reading information signals is incident on the disc, and the main beam is used for detecting tracking errors of the main beam. The outputs of the two photodetectors that detect the reflected light from the disc of the two auxiliary beams are automatically set to an appropriate level according to the optical conditions of the disc and the conditions of the player's optical system. Therefore, the tracking servo is always stable, and a complicated level adjustment process is no longer necessary in the manufacturing process of the player.

[Brief explanation of the drawing]

Figure 1 is a diagram for explaining the three-beam method, Figure 2
3 is a connection diagram showing an example of a conventional optical disc player, FIG. 3 is a connection diagram showing an example of an optical disc player according to the present invention, and FIG. 4 is a connection diagram showing an example of an optical disc player according to the present invention.
FIG. 3 is a waveform diagram used to explain the operation of the example shown in the figure. In the figure, 11 is a main beam, 12E and 12F are auxiliary beams, 22E and 22F are photodetectors, 23 is a subtraction circuit, 30 is a multiplication circuit, 32 and 34 are peak hold circuits, 33 is a voltage comparison circuit, and 35 is a counter. , 36 is a memory, and 37 is a digital-to-analog conversion circuit.

Claims (1)

[Claims] 1. First and second auxiliary beams that are incident on the disk together with the main beam for reading information signals and used to detect tracking errors of the main beam, which detect reflected light from the disk. a voltage generating circuit that generates a voltage to be multiplied by the output of the first photodetector; and a multiplication circuit that multiplies the output voltage of the voltage generating circuit by the output of the first photodetector. , a subtraction circuit that obtains a tracking error signal of the main beam based on the difference between the output of the multiplication circuit and the output of the second photodetector, and the voltage generation circuit calculates the output of the main beam when the disk is attached. The voltage is raised or lowered stepwise or continuously from an initial value, and the first and second auxiliary beams are moved across the track over the disc when the disc is mounted. In this state, when the level of the output of the multiplication circuit and the output of the second photodetector become approximately equal, the rise or fall of the output voltage of the voltage generation circuit is stopped, and from then on, the output voltage is An optical disc player in which the voltage retains the value it had when it stopped.