JPS63131334A - Optical information reproducing device - Google Patents

Abstract

PURPOSE:To always stabilize the tracking control even with the variance of pit phase depth of a recording medium by using a delay means whose delay varies with an output signal from a delay control means so as to adjust the delay to cancel the focus error. CONSTITUTION:When the phase difference between an output signal from a 3rd adder means 9a and an output signal from a 4th adder means 9b is not zero, the phase difference is an offset of a tracking error signal and when the phase difference is zero, the offset of the tracking error signal is eliminated. Then the delay control means 10 outputs the delay control signal to a 1st delay means 2a and a 2nd delay means 2b in response to the phase difference to adjust the delay thereby canceling the focus phase difference completely. Thus, even when the phase depth of the pit of the recording medium is varied and the offset of the focus phase difference is fluctuated, the tracking control is always made stable.

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 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. 2 shows tracking error detection means using a phase difference method in a conventional optical information reproducing apparatus. In FIG. 2, 1 is a photoelectric detector, 3a is a first addition means, 3b is a second addition means, 41L is a first waveform shaping means, and 4! L is a second waveform shaping means, 6 is a phase comparison means, and 6 is a low-pass filter. The operation of the tracking error detection means configured as described above will be explained below.

The photoelectric detector 1 has four parts, M, B, O, and D, as shown in the figure.
It shall consist of two light receiving cells. First addition means 3&
outputs a sum signal obtained by adding output signals from two light-receiving cells arranged at diagonal positions; A sum signal obtained by adding the output signals from B and D is output. 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 41L and the second waveform shaping means 4b, respectively, the phases of these signals are compared by the phase comparison means 6. , 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 trunk 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. After the phase difference between the two light-receiving cells arranged on one side separated by the dividing line and the two light-receiving cells arranged on the other side when the output signals are focused is canceled by the delay means. , two sum signals are obtained by adding the output signals of two diagonal light receiving cells, and a tracking error signal is extracted from the phase difference between these sum signals.

Further, the delay amount of the delay means is variable according to the output signal from the delay amount control means, and the delay amount is adjusted so as to cancel out the phase difference.

The present invention has the above-described configuration, so that 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 signals varies depending on the focus state of the light spot converged on the recording medium.

Hereinafter, such a phase difference will be referred to as a focus phase difference. If the phase depth of the concavities (hereinafter referred to as pits) formed on the recording medium is an integral multiple of a quarter wavelength, this focus phase difference will be zero at the time of focusing, and when defocusing, the phase depth will change in that direction. A phase difference occurs depending on the amount of defocus.

However, if the phase depth of the pit deviates from an integer multiple of a quarter wavelength, the focus phase difference will not be zero even at the time of one focus. That is, an offset occurs in the focus phase difference. The sign and magnitude of this focus phase difference offset change depending on the direction and magnitude of the shift in the phase depth of the pit. If the far-field image is formed symmetrically with respect to the dividing line parallel to the direction in which the information track is 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 displaced asymmetrically with respect to the dividing line, when detecting the phase difference between the sum signals of the diagonal receiving cells, The focus phase difference described above is not canceled out, and when a tracking error signal is detected from the phase difference of the sum signal, this becomes an offset of the tracking error signal. Moreover, if the phase depth of the pit 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 tracking control is lost and the object crosses the track with the objective lens eccentric, a driving force is generated that further eccentricizes 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 pit is an integer multiple of a quarter wavelength or is shifted in the deeper direction, the offset of the tracking error signal that occurs when the far-field image is displaced is opposite to that in 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 adjusts the amount of delay so as to cancel out the focus phase difference described above by using a delay means whose delay amount changes according to the output signal from the delay amount control means, and eliminates the tracking error caused by the residual offset of the focus phase difference. This eliminates the effects of offset.

Embodiment Hereinafter, an optical information reproducing apparatus according to a first embodiment of the present invention will be explained with reference to the drawings.

FIG. 1 shows a tracking control means of an optical information reproducing apparatus according to a first embodiment of the present invention. In FIG. 1, 2& is a first delay means, and 2b is a second delay means, which delay the output signals from the light receiving cell C and the light receiving cell D of the photoelectric detector 1, respectively. The amount of delay is variable by a delay amount control signal. 31L is a first addition means that adds the output signal from the first delay means 2a and the output signal from the light receiving cell located diagonally to the light receiving cell C, and 3b is a second adding means. , the output signal from the second delay means 2b and the output signal from the light receiving cell B located diagonally to the light receiving cell D are added. 91L is a third addition means that adds the output signal from the first delay means 2IL and the output signal from the second delay means 2b. 9b is a fourth adding means that adds the output signal from the light receiving cell and the output signal from the light receiving cell B. Reference numeral 110 denotes a delay amount control means, which outputs the output signal from the third addition means 91L and the fourth addition means 9.
A signal corresponding to the phase difference with the output signal from the second delay means 21L and 2b is outputted to the first and second delay means 21L and 2b. 8 is a preamplifier that amplifies the read signal from the recording medium. Other configurations are the same as the conventional example shown in FIG. Note that the first waveform shaping means 4j and the second waveform shaping means 4
The b0 phase comparison means 6 and the low-pass filter e constitute the 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.

When the phase depth of the pits formed on the recording medium deviates from an integer multiple of a quarter wavelength, when the information track extends in the direction of the arrow in the figure (vertical direction in the figure), when focused The far-field image formed on the photoelectric detector 1 changes in brightness and darkness as it moves in the vertical direction. That is, an offset of the focus phase difference occurs. Here, for example, it is assumed that the output signals from the light receiving cells C and D lead the output signals from the light receiving cells B and B in phase. First delay means 2
& and the second delay means 2b delay the output signals from the light receiving cell C and the light receiving cell D so as to cancel out the offset of these focus phase differences. After delaying the output signals from the light receiving cells C and D in this way, the first adding means 3a (C adds the output signals of the light receiving cells B and C, and the second adding means 3b adds the output signals from the light receiving cells B and D.
Add the output signals from. These first addition means 31
A tracking error signal can be obtained by shaping the output signals from L and the second adding means 3b by the first waveform shaping means 4b and comparing the phases with the phase comparing means 6. In this way, the far-field image on the photoelectric detector 1 moves in the left-right direction in the figure, and the output signals from the two light-receiving cells on either the left or right side of the figure are transferred to the other two light-receiving cells. Even if the output signal from the first waveform shaping means 4IL becomes larger than the output signal from the second waveform shaping means 4IL, the offset of the focus phase difference is substantially canceled. There is no phase difference between the output signal from the waveform shaping means 4b and the output signal from the waveform shaping means 4b.

On the other hand, since the preamplifier 8 obtains a read signal by amplifying the sum signal of the four light receiving cells from the change in the current injected into the common substrate of the photoelectric detector 1, the first delay means 2a and the second Even if the delay means 2b is constituted by a low-pass filter or the like, the frequency characteristics of the read signal will not be deteriorated, and a conventional read signal can be obtained. The other operations are the same as those of the conventional example, so the explanation will be omitted.

Further, in the above embodiment, the offset of the focus phase difference is completely canceled out, and the operation thereof will be explained below. If the phase difference between the output signal from the third addition means gt and the output signal from the fourth addition means 9b is not zero, this phase difference becomes an offset of the tracking error signal, but if this phase difference is zero, There is no offset in the tracking error signal. Therefore, the delay amount control means 10 outputs a delay amount control signal to the first delay means 21L and the second delay means 2b according to this phase difference, and adjusts the delay amount so as to completely cancel out the focus phase difference. By doing so, even if the phase depth of the bit of the recording medium fluctuates and the offset of the focus phase difference fluctuates, the tracking control can always be made stable.

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; After canceling out the phase difference between the two light-receiving cells arranged on one side and the two light-receiving cells arranged on the other side at the time of focusing the output signals, the two light-receiving cells on the diagonal By creating a configuration in which two sum signals are obtained by adding the output signals of the light-receiving cells, and a tracking error signal is extracted from the phase difference between these sum signals, the photoelectric detector can be controlled by moving the objective lens for tracking control. Even if the far-field image of the light spot above moves in the direction perpendicular to the direction in which the information track mapping extends,
Tracking control can always be performed stably without fluctuations in the offset of the tracking control signal.

Effects of the Invention As described above, the present invention is divided into four light-receiving cells by a dividing line parallel to the direction in which an information track is mapped and a dividing line perpendicular to the dividing line, and the distance of a light spot formed on a recording medium is improved. a photoelectric detector whose visual field image is formed across the light-receiving cells, and arranged on one side separated by a dividing line perpendicular to the direction in which the information track is mapped onto the photoelectric detector; After canceling out the phase difference when the output signals are focused between the two light-receiving cells disposed on the other side and the two light-receiving cells disposed on the other side, the outputs of the two diagonal light-receiving cells are By adding up the signals to obtain two sum signals and extracting the tracking error signal from the phase difference between these sum signals, the light spot on the photoelectric detector due to movement of the objective lens for tracking control, etc. Even if the far-field image moves in a direction perpendicular to the direction in which the information track is mapped, there is no fluctuation in the offset of the tracking control signal, resulting in the effect that tracking control is always stable.

Furthermore, if the read signal is detected from the current injected into the common substrate of the photoelectric detector and the first delay means 2a and the second delay means 2b are configured with a low-pass filter or the like, the read signal will be adversely affected. The above effects can be obtained without any problems.

Furthermore, by adjusting the delay amounts of the first delay means and the second delay means by the delay amount control means 10 and completely canceling out the offset of the focus phase difference, the phase depth of the pits of the recording medium can be prevented from varying. Therefore, the tracking control can be made stable at all times even when the tracking control is performed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the main parts of an optical information reproducing apparatus according to an embodiment of the present invention, and FIG. 2 is a block diagram of the main parts of a conventional optical information reproducing apparatus. 21L...first delay means, 2b...
Second delay means, 3! L...first addition means,
3b...Second addition means, 4a...First waveform shaping means, 4b...Second waveform shaping means, 6...Phase comparison Means, 7... Tracking error detection means, 8... Preamplifier, 9
1L... Third addition means, 9b... Fourth addition means, 10... Delay amount control means.

Claims (3)

[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; on either side in the direction of canceling the phase difference when the output signal is focused between the two light receiving cells arranged on one side and the two light receiving cells arranged on the other side separated by first and second delay means that delay respective signals output from the two light receiving cells and whose delay amount is variable according to a control signal; and an output signal from the first delay means and the corresponding light receiving cell. The first one adds the output signals from the light receiving cells arranged at diagonal positions of the cells.
a second adding means for adding an output signal from the second delay means and an output signal from a light receiving cell disposed at a diagonal position of the corresponding light receiving cell; a third addition means for adding the output signal from the first delay means and the output signal from the second delay means; and a light receiving device disposed at a diagonal position of the light receiving cell corresponding to the first delay means. a fourth adding means for adding the output signal from the cell and the output signal from the light receiving cell disposed diagonally to the light receiving cell corresponding to the second delay means; the third adding means and the fourth adding means; delay amount control means for detecting a phase difference between the output signals from the addition means of No. 4 and outputting a delay amount control signal to the first and second delay means in a direction to cancel this phase difference; and tracking error detection means for outputting a tracking error signal from the phase difference of the output signal from the second addition means. (2) The photoelectric detector has four light receiving cells formed on a common substrate, and the delay amount of the first and second delay means changes depending on the input of a control signal, and the output from the common substrate is The optical information reproducing apparatus according to claim 1, wherein an information signal is reproduced by a signal. (3) The phase depth of the unevenness recorded and formed on the recording medium is shallower than a quarter wavelength, and the amount of delay of the first delay means and the second delay means is mapped onto the photoelectric detector. The first delay is equal to the phase difference between the two light receiving cells on one side and the two light receiving cells on the other side separated by a dividing line in a direction substantially perpendicular to the direction in which the information track extends. The optical information reproducing apparatus according to claim 1, wherein the delay amount of the means and the second delay means is controlled by a signal from the delay amount control means so as to cancel out the phase difference. .