JPS62185259A - Optical information reproducing device - Google Patents

Abstract

PURPOSE:To prevent an adverse influence from being exercised on tracking control of the reproducing device, even if it is shifted to a vertical direction to the direction in which an information track is mapped by extracting a tracking error signal caused by the phase difference of an output signal of the specific light-receiving cell provided on a photoelectric detector. CONSTITUTION:A photoelectric detector 1 is provided where a far-field pattern of a light spot, which is divided into four light receiving cells by a split line in the mapping direction of the information track and a split line vertical to the said split lines, and is formed on a recording medium, is formed by straddling the light-receiving cell. From the phase difference in the output signal between the two light-receiving cells provided at one side which is divided by the split line vertical to extrapolate of the information track mapped on the photoelectric detector 1, and two light receiving cells provided on the other side, a tracking error signal is extracted. Thus, even if the far-field pattern of the light spot on the photoelectric detector 1 shifts to the vertical direction to the mapping direction of the information track, no adverse influence will be exercised on tracking control.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an optical information reproducing device that optically reads information from a recording medium, and particularly relates to tracking control thereof.

2. Description of the Related Art In recent years, optical information reproducing devices that optically read information from recording media such as video discs and digital audio discs have been widely used.

Information is recorded on information tracks with a minute width, and accurate tracking control is generally required in order to reproduce the information. In order to perform tracking control, it is necessary to detect a tracking error, and this is normally performed using optical means. In order to detect this tracking error optically, a method (hereinafter referred to as This method (called a phase difference method) is already well known.

An example of the above-mentioned conventional optical information reproducing device will be described below with reference to the drawings.

FIG. 3 shows tracking error detection means using a phase difference method in a conventional optical information reproducing apparatus. In FIG. 3, 1 is a photoelectric detector, 3a is a first addition means, 3b is a second addition means, 4a is a first waveform shaping means, 4b is a second waveform shaping means, and 5 is a phase comparison means. ,
6 is a low pass filter. The operation of the tracking error detection means configured as described above will be explained below.

It is assumed that the photoelectric detector 1 consists of four light receiving cells A, B, C and D as shown in the figure. The first adding means 3a outputs a sum signal obtained by adding the output signals from the two light receiving cells A and C arranged diagonally, and the second adding means 3
b outputs a sum signal obtained by adding the output signals from two light receiving cells B and D disposed at other diagonal positions. It is already known that when there is no tracking error, there is no phase difference between these sum signals, but when a tracking error occurs, a phase difference occurs between them. (see official bulletin). Therefore, after the output signals from the first addition means 3a and the second addition means 3b are waveform-shaped by the first waveform shaping means 4a and the second waveform shaping means 4b, respectively, the phases of these signals are compared by the phase comparison means 5. A tracking error signal can be obtained by removing ripple components from the output using a low-pass filter 6. (For example, Japanese Unexamined Patent Publication No. 57-181433) Problems to be Solved by the Invention However, in the above configuration, information is recorded on the recording medium in a concave and convex manner, and the phase depth is an integer of a quarter wavelength. When the far-field image on the photoelectric detector moves in a direction perpendicular to the information track mapping direction due to tracking control, etc., the offset value of the tracking error detection signal changes, causing tracking The problem was that the control became unstable.

In view of the above-mentioned problems, the present invention provides optical information reproduction that does not adversely affect tracking control even if the far-field image on the photoelectric detector moves in a direction perpendicular to the direction in which the information track is mapped. It provides equipment.

Means for Solving the Problems In order to solve the above problems, the optical information reproducing device of the present invention is divided into four light receiving cells by a dividing line in the direction in which the information track is mapped and a dividing line perpendicular to the dividing line. is,
A far-field image of the light spot formed on the recording medium is formed across the light receiving cell, and has a photoelectric detector that is mapped onto the photoelectric detector in a direction perpendicular to the extending direction of the information track. The structure is such that a tracking error signal is extracted from the phase difference between output signals from two light receiving cells arranged on one side separated by a dividing line.

Effect of the present invention With the above-described configuration, even if the far-field image of the light spot on the photoelectric detector moves in a direction perpendicular to the direction in which the information track is mapped due to movement of the objective lens for tracking control, etc. Fluctuations in the offset of the tracking control signal no longer adversely affect tracking control. This is due to the following reasons. Two light receiving cells arranged on one side and two light receiving cells arranged on the other side separated by a dividing line perpendicular to the extending direction of the information track mapped on the photoelectric detector. The phase difference between the output signal and the cell when it is focused changes depending on the focus state of the light spot focused on the recording medium. Hereinafter, such a phase difference will be referred to as a focus phase difference. Recesses formed in the recording medium (hereinafter referred to as bits)
When the phase depth is an integral multiple of a quarter wavelength, this focus phase difference becomes zero during focusing, and when defocusing occurs, a phase difference corresponding to the direction and amount of defocusing occurs. However, if the focus phase depth deviates from an integral multiple of a quarter wavelength, the focus phase difference will not be zero even during focus. That is, an offset occurs in the focus phase difference.

The sign and magnitude of the focus phase difference offset change depending on the direction and magnitude of the shift in the phase depth of the bits. If the far-field image is formed symmetrically with respect to a dividing line parallel to the extending direction of the information track mapped on the photoelectric detector, the phase difference between the sum signals of the diagonal light receiving cells is detected. When this happens, the focus phase difference described above is canceled out and does not become an offset of the tracking error signal.

However, if the far-field image formed on the photoelectric detector is
If the displacement is asymmetrical with respect to the dividing line, the focus phase difference described above will not be canceled when detecting the phase difference of the sum signal of the diagonal light receiving cells, and tracking will be based on the phase difference of the sum signal. When detecting the error signal, this becomes the offset of the tracking error signal. Moreover, if the phase depth of the bit deviates from an integer multiple of a quarter wavelength to a shallower direction, the direction of the offset will change when the objective lens is displaced by tracking control to follow the eccentricity of the recording medium. In addition, when the objective lens loses its tracking control and crosses the track when the objective lens is deflected, a driving force is generated that further deflects the objective lens, and in some cases, the tracking control goes out of control. Sometimes. On the other hand, if the phase depth of the bit deviates from an integer multiple of a quarter wavelength in a deeper direction, the offset of the tracking error signal that occurs when the far-field image is displaced is opposite to the above case.

In this case, the above-mentioned disadvantages are small, but if the offset amount of the tracking error signal increases, tracking control becomes inaccurate and disadvantages occur.

The present invention eliminates the influence of the offset of the tracking error signal due to the residual offset of the focus phase difference described above.

Embodiments Hereinafter, optical information reproducing apparatuses according to embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a tracking control means of an optical information reproducing apparatus according to an embodiment of the present invention, and FIG. 2 is a characteristic diagram showing the improvement effect of this embodiment. In FIG. 1, 2a is a first low-pass filter, and 2b is a second low-pass filter, which remove information signal components from the output signals from the light-receiving cells C and D of the photoelectric detector 1, respectively. . 3a is a first addition means that adds the output signal from the first low-pass filter 2a and the output signal from the light receiving cell A located diagonally to the light receiving cell C; 3b is a second addition means; The means 3b adds the output signal from the second low-pass filter 2b and the output signal from the light-receiving cell B located diagonally to the light-receiving cell D. 8 is a differential amplifier, which is connected to the first
A focus error signal is detected from the difference signal between the output signal from the addition means 3a and the output signal from the second addition means 3b. Other configurations are the same as the conventional example shown in FIG.

The first waveform shaping means 4a, the second waveform shaping means 4b, the phase comparison means 5, and the low-pass filter 6 constitute a tracking error detection means 7.

The operation of the tracking control means of the optical information reproducing apparatus constructed as described above will be explained below with reference to FIG.

Information is recorded on the information track on the recording medium depending on the presence or absence of depressions or protrusions, and when the light spot accurately tracks this information track, the far-field image formed on the photoelectric detector 1 is It is symmetrical with respect to the direction in which the information track mapped onto this photoelectric detector 1 extends. Therefore, light receiving cells A and B or light receiving cells D and C
A small amount of light is always incident on the . That is, light receiving cell A
The signals output from C and B or the light receiving cells C and D are in phase. However, when the light spot tracks a position away from the center of the information track, that is, when a tracking error occurs, the light receiving cells A and C
It is already known that a phase difference occurs between the sum signal of the light receiving cells B and D and the sum signal of the light receiving cells B and D. This means that a phase difference also occurs between the output signals from the light receiving cells A and C or between the output signals from the light receiving cells B and D. Therefore, it is possible to detect a tracking error based only on the phase difference between the output signals from the light receiving cells A and C or only on the phase difference between the output signals from the light receiving cells B and D. In this way, the influence of the phase difference in the extending direction of the mapping of the information track, that is, the focus phase difference, as described in the description of the conventional example, is eliminated, and the offset of the tracking error signal due to this is eliminated. In this way, as shown in FIG. 2, even if the far-field image on the photoelectric detector 1 moves in a direction perpendicular to the direction in which the information track mapping extends, fluctuations in the offset of the tracking error signal can be reduced. can do. In FIG. 2, A shows the offset variation when the far-field image moves in the conventional example, and B shows the offset variation when the far-field image moves in the present invention. In this embodiment, a sum signal of a signal obtained by removing high frequency components from the output signal from the light receiving cell C by the first low-pass filter 2a, an output signal from the light receiving cell A, and an output signal from the light receiving cell D are used. The sum signal of the high-frequency signal removed by the second low-pass filter 2b and the output signal from the light-receiving cell B is waveform-shaped by the first adding means 3a and the second adding means 3b, respectively, and then the phase is determined. The comparator 5 is configured to detect a phase difference. Therefore, substantially the output signal from light receiving cell A and the light receiving cell B
This is equivalent to detecting the phase difference with the output signal from
From this phase difference, a tracking error signal with little offset fluctuation due to movement of the far-field image can be obtained. In addition, since the first low-pass filter 2a and the second low-pass filter 2b pass the band necessary for detecting the focus error signal, the far-field image on the photoelectric detector 1 has astigmatism. If the differential amplifier 8 includes the output signal from the first addition means 3a and the second addition means 3b,
A focus error signal can be detected by taking a difference signal between the output signal and the output signal.

Note that the first addition means 3a or the second addition means 3b
The input signal from the first waveform shaping means 4a or the second waveform shaping means 4a
It is an input signal to the waveform shaping means 4b, and is also an input signal to the differential amplifier 8 for obtaining a focus error signal. This is because the first addition means 3a and the second addition means 3
This is to reduce the number of input pins for the output signals from the four light receiving cells to two when the circuits after b are made into an integrated circuit.
When output signals from two light receiving cells are input independently from four input pins, the output signals from light receiving cells A and B are directly input to the first waveform shaping means 4a and the second waveform shaping means 4b. The first low-pass filter 2a and the second low-pass filter 2b can be omitted.

As described above, according to this embodiment, the light-receiving cells are divided into four light-receiving cells by the dividing line approximately parallel to the direction in which the mapping of the information track extends and the dividing line approximately perpendicular thereto, and formed on the recording medium. a photoelectric detector in which a far-field image of a light spot is formed astride the light receiving cells, one of which is separated by a dividing line perpendicular to the direction of extension of the information track mapped onto the photoelectric detector; By extracting the tracking error signal from the phase difference between the output signals from two light-receiving cells arranged on the side, the optical axis on the photoelectric detector due to movement of the objective lens for tracking control, etc. Even if the far-field image of the object moves in a direction perpendicular to the direction in which the mapping of the information track extends, it is possible to prevent fluctuations in the offset of the tracking control signal from adversely affecting the tracking control.

Effects of the Invention As described above, the present invention provides a far-field image of a light spot formed on a recording medium that is divided into four light-receiving cells by a dividing line in the direction in which an information track is mapped and a dividing line perpendicular thereto. has a photoelectric detector formed astride the light receiving cell, and is disposed on one side divided by a dividing line perpendicular to the extending direction of the information track to be mapped onto the frost detector. By extracting the trunking error signal from the phase difference between the output signals from the two light receiving cells and the two light receiving cells disposed on the other side, the tracking error signal can be extracted from the phase difference between the two light receiving cells and the two light receiving cells disposed on the other side. Even if the far-field image of the light spot on the photoelectric detector moves in a direction perpendicular to the direction in which the information track is mapped, fluctuations in the offset of the tracking control signal do not adversely affect tracking control. can get.

Further, output signals from respective light receiving cells arranged on one side separated by a dividing line perpendicular to the extending direction of the information track mapped on the photoelectric detector;
2 obtained by adding the low frequency components of the output signals from the light receiving cells arranged diagonally to each of the above light receiving cells.
By detecting the tracking error signal from the phase difference between the two sum signals, the tracking error signal can be detected from the phase difference between the output signals from the two light-receiving cells arranged on one side divided by the dividing line. Since the signal can be detected and the focus error signal can also be detected from the difference between the two sum signals, it is possible to reduce the number of input bins when integrated into an integrated circuit.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the main parts of an optical information reproducing device according to an embodiment of the present invention, FIG. 2 is a characteristic diagram showing the effects of the above embodiment, and FIG. 3 is a main part of a conventional optical information reproducing device. It is a block diagram of a part. 2a...first low pass filter, 2b...
...Second low-pass filter, 3a...First
Adding means, 3b...Second adding means, 4a.
...First waveform shaping means, 4b...Second
waveform shaping means, 5... phase comparison means, 7...
. . . Tracking error detection means, 8 . . . Differential amplifier.

Claims (2)

[Claims] (1) It has a light-receiving cell divided into four by a dividing line that is approximately parallel to the direction in which the mapping of the information track of the recording medium on which information is recorded in an uneven manner and a dividing line that is approximately perpendicular to the dividing line;
a photoelectric detector on which a far-field image of a converged light spot is formed on the recording medium across two light-receiving cells, and a dividing line perpendicular to the direction in which the information track is mapped onto the photoelectric detector; and tracking error detection means for detecting a tracking error from the phase difference between the output signals from two light receiving cells arranged on one side separated by and outputting a tracking error signal corresponding to the tracking error. Characteristic optical information reproducing device. (2) The tracking error detection means detects an output signal from each light receiving cell arranged on one side divided by a dividing line perpendicular to the extending direction of the information track mapped on the photoelectric detector. , a tracking error signal is detected from the phase difference of two sum signals obtained by adding the low frequency components of the output signals from the light receiving cells arranged diagonally to each of the light receiving cells, and the above photoelectric detection is performed. The far-field image of the light spot formed on the device includes astigmatism, and further comprises a focus error detection means for detecting a focus error signal from the difference signal between the two sum signals. The optical information reproducing device according to item (1).