JPS6171424A - Tracking error detector in optical information reproducing device - Google Patents

Abstract

PURPOSE:To obtain a stable sampling point with a simple circuit by using a zero cross timing for leading/trailing of a difference signal of outputs of forward/backward photodetectors arranged in the track direction so as to detect the moment a light spot crosses the center of an information pit and the moment the spot crosses the center of the part having no information pit. CONSTITUTION:An output signal S5 of the 1st operation circuit 15 is a signal being always at a zero level when a light spot exists in the center of the track direction of the information pit 5. Thus, the sample pulse S6 produced at the leading zero cross of the signal S5 from a sample pulse generator 16 is produced nearly in coincidence with the moment the light spot 60 crosses the center of the information pit 5. An output signal S7 of the 2nd operation circuit 17 is equivalent to a signal S52. Thus, a signal S8 as a result of sampling the signal S7 by the signal S6 (a signal obtained from a sample and hold circuit 18) has less effect of the deviation component produced by moving the light spot for tracking control and is unchanged depending on the frequency of the information pit.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a tracking error detection device in an optical information reproducing device such as a video disc or a compact disc.

[Background of the invention]

In order to detect a tracking error in an optical information reproducing device, there is a conventional example of detecting an amount of asymmetry in a far field or a near field of diffracted light diffracted and reflected by information pits on a disk. Such a detection method is called a push-pull method. In this push-pull method, in order to detect the above-mentioned asymmetric amount, information bit strings (hereinafter referred to as tracks) are
A tracking error signal is detected by averaging the difference signals between the outputs of at least two light-receiving elements in the vertical direction. However, in such a method, the tracking error signal is small, and when the optical spot is moved due to the tracking error, the diffracted light beam on the light receiving element surface is also swayed, and this captured portion becomes the tracking error signal. It has the disadvantage that normal tracking cannot be performed because it appears as a deviation component in the image.

In order to alleviate the above drawback, the moment when the light spot crosses the center of the information pit is detected from the sum signal of the two light receiving elements, and the difference signal between the outputs of the two light receiving elements is sampled and held based on the output detected here. A device for detecting a tracking error signal using the above method is proposed in Japanese Patent Laid-Open No. 111133/1983.

This device will be explained and explained using Figures 5 and 6.

FIG. 5 is a diagram showing a schematic configuration of a track tracking device using diffracted light.
After passing through the beam splitter 2, the beam passes through the objective lens 3 and is focused onto the surface of the disk 4 in the form of a spot with a diameter of approximately 1.2 to 1.5 μm. On the surface of the disk 4, rows of information pits 5 having a length of about 0.9 to 3.3 μm perpendicular to the paper surface are provided in a direction perpendicular to the paper surface. The light spot is diffracted by the information pit 5, and this diffracted reflected light passes through the objective lens 3, is reflected by the beam splitter 2, and is received by two light receiving elements 50a and 50b arranged on both sides of the track. . The diffraction component of the reflected light causes an imbalance in the amount of light on both light-receiving elements due to the level relationship between the light spot and the track. Can detect location.

The photoelectric conversion outputs from the light receiving elements 50a and 50b are converted into a sum signal S+t by an adder circuit 51, and this sum signal S□ is divided into two parts, one of which passes through a delay line 53 and becomes a delay signal Sss. Con after becoming? The other signal enters the comparator 54, and the other signal directly enters the comparator 54. After the two signals are compared,
One-shot maru f55 to tl'i sample pulse signal s,.

is generated. In addition, two light receiving elements 50a, 50b
The difference signal 5 obtained by inputting the output of into the subtraction circuit rF652
52 is sampled and held by the sample hold circuit 56 using the sample pulse signal, and the sample hold circuit 56 outputs the output signal Sil! Get it. By amplifying this output signal Sss with the amplifier 57, the tracking difference signal can be taken out from the terminal S8.

FIGS. 6A to 6E show output signals in the electric circuit of the track tracking device shown in FIG. That is, FIG. 6(a) shows the light spot 60 moving in the direction of the arrow on a track consisting of 61 rows of light spots 60, and FIG. In the state, addition circuit 5
1 and the delay signal SSS obtained from the delay line 53.
c) shows the sample pulse signal SN obtained from the fun shot multi 55, Fig. 6) shows the difference signal 851 obtained from the subtraction circuit 52, and Fig. 6 f! '') indicates the output signal SSS of the sample and hold circuit 56.

According to the method described above, the tracking error signal becomes large, but in order to detect the point where the light spot crosses the information pit 9-1, the two light receiving elements 50a and 50b are used.
The processing circuit is complicated because it uses a tiller line 53 and a comparator 54 for processing the sum signal of , and obtaining a sample pulse. Furthermore, since the delay time of the delay line 53 is constant, the frequency of the information pit (
(Therefore, there was a drawback that the timing of generating sample pulses became unstable.

[Purpose of the invention]

In view of the above-mentioned drawbacks, it is an object of the present invention to obtain an accurate tracking error signal by simply and stably obtaining the interval in which the original spot crosses the center of the 171 signals.

[Summary of the invention]

The present invention provides an optical groove in the center of the information bit in the track direction.
Focusing on the fact that the return light from the disk becomes symmetrical in the track direction when there is a
゛ is detected by the difference signal of a pair of photoelectric conversion elements arranged in the track direction, and the return-following symmetry is detected in the difference signal of the pair of photoelectric conversion signals arranged in the direction orthogonal to the track direction. The tracking error signal is obtained from the signal when

〔Example〕

FIG. 1 is a first $stream side of a tracking error detection circuit according to the present invention.

In FIG. 1, a four-part light-receiving member (each element constituting this member is numbered 11 to 14) is arranged in place of the two light-receiving elements 50a and 50b in FIG.
It has the same configuration as a four-part light receiving member generally provided in a pull-7-pull type light receiving section, and is divided into a track direction and a direction perpendicular thereto. Note that the direction Y shown in the figure is the track direction υ, and the direction X is a direction perpendicular to the track direction.
4 (the intersection of arrows X and Y) is the center of objective lens 3 (
The reflected light of Fig. 5) coincides with the reflected light. The photoelectric conversion signals S1 to S4 obtained from the light receiving elements 11 to 14 are transmitted to the first circuit 15.
is input to the second arithmetic circuit 17. 15 first arithmetic circuits, between photoelectric conversion signal S8 and S4 (Ss + St)
CSs + 84) is calculated (7, a signal S corresponding to this difference signal is output (this difference signal also calculates the difference signal of each of the light receiving elements 11-14°12-13 arranged in the track direction (to)). It can also be seen as peace.

The output Ig S of the first calculation path 15 is input to the sample pulse generator 16, and the sample pulse generator 1G is input to the sample pulse generator 16.
Sampling at zero cross h at the rising edge of R No. S -
A sample pulse S6 of the hold circuit 18 is generated. On the other hand, the second arithmetic circuit 17 outputs the photoelectric conversion signals 81 to S.
(S%+S4) (S2+83) is calculated between 4 and outputs a signal S7 corresponding to this difference signal. .13-14 The output signal S7 of the second arithmetic circuit 17 can also be regarded as the sum of the respective difference signals.
becomes an input signal to the sample and hold circuit 18. The sample and hold circuit 18 converts the signal S into a sample pulse S6
and outputs a sample signal S8. The sample signal S8 is amplified by an amplifier 19, and a tracking error signal is obtained at a terminal 20.

Next, the operation shown in FIG. 1 will be explained using FIG. 2.

FIG. 2(A) is the same as FIG. 6(A), and shows as an example the case where the light spot 60 moves in the direction of the arrow on a track consisting of a row of information bits 5.

In reality, the light spot 60 remains stationary and the track moves, but since the two are in a relative relationship, the explanation is given assuming that the original spot 60 moves with respect to the track. When the light spot 60 is located at the center of the information bits 5 in the track direction, and when the light spot 60 is located at the center of the area between the information bits 5 in the track direction, the light from the disk 4 becomes symmetrical in the track direction. Therefore, the output signal Ss of the first arithmetic circuit 15 is generated when the light spot is located at the center of the information bits 5 in the track direction as shown in FIG. This signal is always at zero level when the optical spot 60 is located at the center of the signal.

Therefore, the sample pulse S generated from the sample pulse generator 16 at the zero crossing of the rising edge of the signal S.

As shown in FIG. 2(c), this occurs almost at the moment when the optical sub-toro 0 crosses the center of the information bit 5.

The output signal S7 of the second arithmetic circuit 17 is equivalent to the signal SS2 shown in FIG. 6), and is as shown in FIG. 2). Therefore, the signal SS shown in FIG. 2 (E) is obtained by sampling the signal S7 shown in FIG. 2 (C) with the signal S shown in FIG. ) is a signal that is not only less affected by the deviation component caused by moving the optical spot for tracking control, but also does not change depending on the frequency of the information bit.

Figure 3 shows a tracking error signal that reduces not only the deviation component that appears due to not moving the optical spot for tracking control, but also the deviation component that appears when the disc moves, and allows accurate track tracking. In the second embodiment, the signal S, , S, is obtained.
It is exactly the same as the figure.

The output signal S of the first arithmetic circuit 15 is input to the rising pulse generating circuit 16 and the falling pulse generating circuit 31, and the fourth
Figure 9. As shown in Figure 4 (B), the signal SS (Figure 4 (B))
A rising pulse S6 (FIG. 4(c)) is obtained at the zero-crossing point of the rising edge of signal S, and a falling pulse Sa+ (see FIG. 4) is obtained at the zero-crossing point of the falling edge of signal S. The first sample and hold circuit 18 receives the output signal S7 of the second arithmetic circuit 17.
Samples are taken at the timing of the rising signal S, and the output signal S is as shown in FIG. Figure 4 (to)
The signal S in is equivalent to the signal S in Fig. 2 (e), but
The signal shown in FIG. 4 is the output signal S of the second arithmetic circuit 17.
7 (Fig. 4 (e)) includes a deviation component due to the inclination of the disk. (the signal is not zero ζ), so it contains an error component. Second nailing circuit 17
The output signal S7 is also input to the second sample and hold circuit 32, and the second sample and hold circuit 32 samples and holds the output signal S7 at the timing of the falling pulse SSt. The output signal 832 of the second sample-and-hold circuit 32 obtained in this way is a signal that depends only on the deviation component. First sample and hold circuit 18. The output signals S@, S3□ of the second sample hall circuit 32 are input to a subtraction circuit 33, which subtracts the latter from the former and outputs a difference signal 83g (Fig. 4 (a)). This difference signal SaS is a signal that depends only on the tracking error obtained by removing the deviation component (FIG. 4 (g)) from the signal S in FIG.
Therefore, if the signal generated at this terminal 35 moves the optical spot in a direction perpendicular to the trunk, so-called tracking servo will be performed.

In the first embodiment described above, when the first arithmetic circuit 15 performs the calculation (S3+84) = (s, +s, ), the sample pulse generator 16 generates the sample pulse S6 at the zero cross of the falling edge of the signal S. All you have to do is make it happen.

〔Effect of the invention〕

As described above, according to the present invention, the moment when the correct spot crosses the center of the T-report bit and the moment when the optical spot crosses the center of the part where there is no clear-report bit are detected by the front and rear receivers arranged in the track direction. Detection from the zero-crossing timing of rising ↓ and falling ↓ and falling ↓ of the difference signal of the output of the 0 element.

[Brief explanation of drawings]

Figure 2gt shows the tracking error detection circuit of the first embodiment of the invention, Figure 2 is a time chart showing the signals in the circuit of Figure 1, and Figure 3 shows the tracking error of the second embodiment of the invention. Detection circuit, Figure 4 shows the signals in the circuit of Figure 3.
FIG. 5 is a diagram showing a schematic configuration of a conventional track tracking device using the push-pull method, and FIG. 6 is a time chart showing signals in the tracking error detection circuit of FIG. [Explanation of symbols of main parts] Semiconductor laser 2: Beam splitter 3: Objective lens 4: Disk 5: Information bits 11 to 14: Photodetector 15: First arithmetic circuit 16: Sample pulse generator 17: Second
Arithmetic circuit 18: Sample hold circuit

Claims (1)

[Claims] A beam emitted from a light source is focused by an objective lens, irradiated onto a disk having a track on which information is recorded, reflected from the disk, and modulated by the information recorded thereon. The reflected light beam is focused by the objective lens, and the focused reflected light is arranged in the far field or near field of the track with the reflected optical axis as the center, and is divided into the track direction and a direction perpendicular thereto. In an optical information reproducing device that makes light enter four light receiving elements, the amount and direction of deviation in the direction perpendicular to the track direction between the condensed light beam irradiated onto the disk and the information track recorded on the disk are calculated. In order to detect the tracking error represented by (
a first calculation means for calculating the sum of the difference signals of each of the light receiving elements (before and after); and a rise or rise of the signal calculated by the first calculation means corresponding to when the light spot is substantially in the center of the information pit. pulse generating means for detecting a downward zero crossing point and generating a sampling pulse; a second calculating means for calculating the sum of difference signals of each of the light receiving elements arranged in a direction perpendicular to the track; 2. A tracking error detection device for an optical information reproducing device, comprising: a sample hold means for sample-holding a signal obtained by two calculation means to obtain a sample value; and a tracking error detection device for an optical information reproducing device.