JPS63181126A - Optical information reproducing device - Google Patents

Abstract

PURPOSE:To reduce the fluctuation of an offset of a tracking error signal by obtaining a tracking error signal from the phase difference of output signals from two photodetection cells at the track direction and the other side respectively. CONSTITUTION:The phase difference of photodetector cells A, B is detected by a 1st phase comparator means 11 and the phase difference of photodetector cells C, D is detected by a 2nd phase comparator means 12 respectively and a tracking error detection means 13 detects the tracking error from the sum of the phase differences. In detecting the tracking error, the phase difference of the output signals among the photodetector cells before and after the moving direction of the information track, that is, the photodetector cells A, B and C, D is not affected. Thus, the objective lens is displaced by the tracking control, resulting that the fluctuation of the offset of the tracking error signal is minimized even if the remote visual image 2 is displaced on the photodetector 1.

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.

2. Description of the Related Art In recent years, optical information reproducing devices that optically read information from recording media such as video disks and digital audio disks 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. This is usually done using optical means. Specifically, this method detects a tracking error signal from the phase difference between the signals output from two parts of a photoelectric detector that receives detection light and outputs an electrical signal (hereinafter referred to as the phase difference method). ) is already known.

Hereinafter, an example of an optical information reproducing apparatus using the above-mentioned conventional phase difference method will be described with reference to the drawings.

FIG. 3 shows a block diagram of the main parts of a conventional optical information reproducing device. In FIG. 3, 1 is a photoelectric detector, 2 is a far-field image formed across four light-receiving cells that constitute this photoelectric detector 1, and 3a and 3b.
is an adder, 4a and 4b are waveform shapers, 5 is a phase comparator, and 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. Adder 3a outputs a sum signal by adding output signals from two light receiving cells A and C arranged diagonally, and adder 3b outputs a sum signal by adding output signals from two light receiving cells A and C arranged diagonally. A sum signal obtained by adding the output signals from B and D is output. It is assumed that the information track moves substantially in the direction of the arrow in the figure. It is already known that when there is no tracking error, there is no phase difference between the above sum signals, but when a tracking error occurs, a phase difference occurs between them (for details, see Japanese Patent Application Laid-Open No. 1983-1993).
(See Publication No. 93222). Therefore, the output signals from adder 3a and adder 3b are waveform-shaped by waveform shapers 4a and 4b, respectively, and then phase-compared by phase comparator 5, and ripple components are removed from the output by low-pass filter 6. By doing this, a tracking error signal can be obtained. (For example, JP-A-57-
181433 Publication) Problems to be Solved by the Invention - However, with the above configuration, information is recorded on the recording medium unevenly, and the phase depth seems to deviate from an integral multiple of a quarter wavelength. In some cases, when the far-field image on the photoelectric detector moves to follow the eccentricity of the recording medium, the offset value of the tracking error detection signal fluctuates, resulting in a problem that tracking control becomes unstable.

In view of the above-mentioned problems, the present invention provides an optical information reproducing device in which even if a far-field image on a photoelectric detector moves, the adverse effect on tracking control is small.

Means for Solving the Problems In order to solve the above problems, the optical information reproducing apparatus of the present invention is provided with the following features: The phase difference between the respective signals output from the two light-receiving cells arranged on one side separated by a dividing line perpendicular to The configuration is such that the tracking error is detected from the phase difference between the respective signals.

Effect of the Invention With the above-described configuration, the present invention can reduce fluctuations in the offset of the tracking control signal even if the objective lens follows the eccentricity □ of the recording medium and the far-field image on the photoelectric detector moves due to tracking control. can. This is due to the following reasons. An output signal from two light receiving cells arranged on one side and an output signal from two light receiving cells arranged on the other side separated by a dividing line perpendicular to the track direction on the photoelectric detector. There is a phase difference between them that changes depending on the focus state. If the phase depth of the unevenness formed on the recording medium is an integral multiple of a quarter wavelength, the phase difference according to the focus state becomes zero at the time of focusing, but if the phase depth is a quarter wavelength, If it deviates from an integral multiple of the wavelength, the phase difference will not be zero even when focused. When the far-field image formed on the photoelectric detector is symmetrical with respect to the dividing line parallel to the track direction on the photoelectric detector, the phase difference that changes depending on the focus state is the difference between the diagonal light receiving cells. It is canceled when detecting the phase difference between two sum signals obtained by adding the outputs. Therefore, in such a case, no offset occurs in the tracking error signal. However, if the far-field image 2 on the photoelectric detector 1 moves and becomes asymmetric with respect to the dividing line parallel to the track direction, the phase difference between the two sum signals will change depending on the focus state. The phase difference caused by the tracking error signal no longer cancels out, and therefore one offset of the tracking error signal fluctuates.

The present invention calculates the phase difference between the respective output signals from two light receiving cells on one side divided by a dividing line perpendicular to the track direction, and the position of each output signal from the two light receiving cells on the other side. By detecting phase differences and obtaining a tracking error signal from these phase differences, variations in the offset of the tracking error signal when the far-field image moves on the photoelectric detector are reduced.

Example Below, regarding an optical information reproducing device according to an example of the present invention,
This will be explained with reference to the drawings.

FIG. 1 shows a block diagram of the main parts of an optical information reproducing apparatus according to a first embodiment of the present invention. In FIG. 1, 1 is a photoelectric detector and 2 is a far-field image, which are the same as in the conventional example. ? a.

7b, 7c and 7d are current-voltage converters and photoelectric detector 1
Converts the output current output from the converter into voltage.

Waveform shapers 8a, 8b, 8c and 8d shape the waveforms of the output signals of the current-voltage converters 7a, 7b, 7c and 7d, respectively. 9a and 9b are phase comparators, the phase comparator 9 detects the respective output signals from the waveform shapers 8a and 8d, and the phase comparator 9b detects the phase difference between the respective output signals from the waveform shapers 8C and 8d. are detected and output phase difference detection signals respectively. 10 is an adder, 6
is a low-pass filter, and the adder 10 is a phase comparator 9a.
The low-pass filter 6 removes ripple components from the output signal and outputs a tracking error signal. Note that the waveform shaper 8a, waveform shaper 8b, and phase comparator 9a are used as the first phase comparison means 11, and the waveform shaper 8c, waveform shaper 8d, and phase comparator 9b are used as the second phase comparison means 12.
The adder 10 and the low-pass filter 6 constitute tracking error detection means 13, respectively.

Regarding the optical information reproducing device configured as above,
The operation will be explained below with reference to FIG.

Information is recorded on the information track on the recording medium as concave or convex marks (hereinafter referred to as pits), and a light spot is focused on this information trunk. The reflected or transmitted light from this light spot is received and forms a blurred image, that is, a far-field image, on the photoelectric detector 1. At this time, the photoelectric detector 1 includes four light-receiving cells A, B, C, and D as shown in the figure, and the direction in which the information trunk mapped onto these cells extends is the direction indicated by the arrow in the figure. shall be taken as a thing. If a tracking error occurs and the optical spot deviates from the center of the information track, as explained in the conventional example, the sum signal of the outputs of light receiving cells A and C and the sum signal of the outputs of light receiving cells B and D A phase difference occurs between the two. This means that a similar phase difference occurs between the output signals of the light receiving cells A and B or the light receiving cells C and D. Therefore, the first phase comparison means 11 detects the phase difference between the light receiving cells A and B, the second phase comparison means 12 detects the phase difference between the light receiving cells C and D, and the tracking error detection means 13 detects these positions. Tracking error is detected from the sum of phase differences. When a tracking error is detected in this manner, the phase difference in the output signal between the front and rear light receiving cells in the moving direction of the information track, that is, between the light receiving cells A, B and the light receiving cells C, D, has no effect.

Therefore, even if the objective lens is displaced for tracking control and, as a result, the far-field image 2 is displaced on the photoelectric detector 1, variations in the offset of the tracking error signal can be made extremely small. Figure 2 is a characteristic diagram showing this effect, showing the sum of the output signals of light receiving cells A and B and the light receiving cell C.
In the conventional example where the tracking error signal is obtained from the phase difference between the sum of the output signals of Accordingly, it is possible to reduce fluctuations in tracking offset as shown in characteristic B in the figure.

As described above, according to this embodiment, light converges on the recording medium across the light-receiving cells divided into four by the dividing line substantially parallel to the direction in which the mapping of the information trunk extends and the dividing line perpendicular to the dividing line. A far-field image of the spot is formed, and the phase difference between the respective signals output from two light-receiving cells arranged on one side separated by a dividing line perpendicular to the direction in which the information track extends and the above-mentioned division Tracking control is achieved by providing a tracking error detection means that substantially adds the phase difference between the respective signals output from the two light receiving cells arranged on the other side separated by the line and outputs a tracking error signal. Therefore, even if the objective lens is displaced, fluctuations in the offset of the tracking error signal can be suppressed to a small level.

In the above embodiment, the first phase comparison means 11 and the second phase comparison means 12 digitally detect the phase difference, but the present invention limits the phase difference detection means in principle. Rather, any method that can substantially detect a phase difference may be used.

Effects of the Invention As described above, the present invention provides light that is converged on a recording medium across light receiving cells divided into four by a dividing line that is substantially parallel to the direction in which the mapping of an information trunk extends and a dividing line that is perpendicular to the dividing line. A far-field image of the spot is formed, and the phase difference between the respective signals output from two light-receiving cells arranged on one side separated by a dividing line perpendicular to the direction in which the information track extends and the above-mentioned division Tracking control is achieved by providing a tracking error detection means that substantially adds the phase difference between the respective signals output from the two light receiving cells arranged on the other side separated by the line and outputs a tracking error signal. Therefore, even if the objective lens is displaced, fluctuations in the offset of the tracking error signal can be suppressed to a small level.

[Brief explanation of the drawing]

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 present invention, and FIG. 3 is a main part of an optical information reproducing device in a conventional example. It is a block diagram of a part. 6...Low pass filter, 8a, ab, 3c
. 8d... Waveform shaper, 9a, 9b...
Phase comparator, 10... Adder, 11...
- First phase comparison means, 12... Second phase comparison means 12.13... Tracking error detection means.

Claims (1)

[Claims] The light-receiving cell is divided into four by a dividing line that is substantially parallel to the direction in which the mapping of the information track of the recording medium on which information is recorded with unevenness and a dividing line that is perpendicular to the extending direction, and the light-receiving cell is divided into four by a dividing line that is perpendicular to the dividing line and a dividing line that is perpendicular to this. a photoelectric detector on which a far-field image of a converged light spot is formed on the recording medium; 2 placed on the side
a first phase comparison means for detecting the phase difference between the respective signals output from the two light receiving cells; a second phase comparison means for detecting a phase difference; and a tracking error detection means for detecting a position error of the optical spot with respect to the information track from the output signals of the first and second phase comparison means and outputting a tracking error signal. An optical information reproducing device comprising: