JPS6212929A - Tracking error signal detector for optical information reproducing device - Google Patents

Abstract

PURPOSE:To obtain an always precise tracking error signal by detecting respective modulation degrees due to a pit from reflected beams of two tracking error detecting beams on an optical recording medium which are projected to one edge part and the other edge part of an information track respectively. CONSTITUTION:The reflected beams of two tracking error detecting subbeams irradiated from one edge part and the other edge part of an information track of the optical recording medium are detected by photodetectors 21a, 21b. The photoelectrically transduced outputs of the photodetectors 21a, 21b are amplified by amplifiers 22a, 22b and the amplified outputs are supplied to peak holding circuits 23a, 23b and low pass filters (LPFs) 24a, 24b. The outputs of the circuits 23a, 23b and the LPFs 24a, 24b are supplied to dividers 25a, 25b, the outputs of the LPFs 24a, 24b are divided by the outputs of the peak holding circuits 23a, 23b to remove the variation of the quantity of the subbeams themselves and signals corresponding only to the modulation degrees due to the pit are outputted, and a tracking error signal is outputted to an output terminal 27.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a tracking error signal detection device in an optical information reproducing device.

[Conventional technology]

The optical information reproducing device uses three light beams, one of which is positioned as the main beam on the information track to be read on the optical disk, and the reflected light is received by a corresponding photodetector to generate a reproduced signal. At the same time, a focusing error signal is obtained, and the other two sub-beams are positioned at one edge portion and the other edge portion of the information track to be read or an information track near the sub-beam, and the reflected light is transmitted to each photodetector. There is a so-called 3-beam system in which a tracking error signal is obtained based on the outputs of these photodetectors.

As shown in FIG. 5, a conventional tracking error signal detection device in such a 3-beam system detects the outputs of photodetectors la and lb, which respectively receive two sub-beams of reflected light from an optical disk. By amplifying with amplifiers 2a and 2b and supplying the outputs of these amplifiers 2a and 2b to a subtracter 4 through low-pass filters 3a and 3b, respectively, the subtracter 4 calculates the difference between the average values within a suitable time, that is, There is one in which the difference between the average values of the amounts of light reflected by the two sub-beams on the optical disk is outputted to the output terminal 5 as a tracking error signal.

[Problem that the invention seeks to solve]

However, in the three-beam system, since the two sub-beams follow different paths, the amount of light reflected on the optical disk fluctuates due to interference, and when the beams are obtained from different light sources, further due to fluctuations in the light sources. For this reason, in a configuration that detects the difference in the average amount of reflected light as a tracking error signal, as shown in Figure 5, it is not possible to obtain an accurate tracking error signal, and as a result, the accuracy of the tracking servo decreases. , there is a problem that accurate reproduction of information and stable random access become difficult.

The present invention was made by focusing on these conventional problems, and it is possible to always obtain accurate tracking error signals without being affected by fluctuations in the light intensity of the tracking error detection beam due to interference or the like. Therefore, it is an object of the present invention to provide a tracking error signal detection device in an optical information reproducing device that is appropriately configured so that information can always be accurately reproduced and stable random access can be easily performed using a high-precision tracking servo. .

[Means for solving problems]

In order to achieve the above object, in this invention, as shown in the conceptual diagram in FIG. The sub-beams reflected by the optical recording medium are received by photodetectors 11a and llb, respectively, and the outputs of these photodetectors 11a and llb are sent to amplifiers 12a and 12b and modulation degree detectors 13a and 13a.
3b to a subtracter 14, and the output of this subtracter 14 is supplied to an output terminal 15 as a tracking error signal.

[For production]

In the above configuration, the modulation degree detectors 13a and 13b detect the rate at which the reflected light of the corresponding subbinim is modulated by the pits of the information track, and the subtracter 14 detects the difference in the modulated rate as a tracking error signal. and outputs it to the output terminal 15.

〔Example〕

FIG. 2 is a block diagram showing a first embodiment of the invention. In this embodiment, in a 3-beam type optical information reproducing apparatus, two sub-beams for tracking error detection are reflected, which are irradiated onto one edge portion and the other edge portion of an information track of an optical recording medium. Light detector 21
The light is received by a and 21b, respectively. These photodetectors 2
The photoelectric conversion outputs of 1a and 21b are each sent to an amplifier 22a.
, 22b, and then the peak hold circuit 23a,
23b and a low-pass filter 24a,
24b.

Here, the hold time of the peak hold circuits 23a and 23b is set to be longer than the period of the longest pit of the information track, but sufficiently shorter than the fluctuation period of the sub-beam light quantity. By setting the hold time in this way, the peaks of the outputs of the peak hold circuits 23a and 23b correspond to the outputs of the photodetectors 21a and 21b when the sub-beams are in non-pit portions of the information track. The change in output corresponds to the amount of light reflected on the information track itself. Moreover, low-pass filters 24a, 24
The time constant b is set to such a value that the tracking error band is passed through and signal components due to the presence or absence of pits are cut.

By setting the time constants in this manner, the outputs of the low-pass filters 24a and 24b include level changes due to changes in the light quantity of the sub-beams themselves, and the modulation degree due to the pits changes in response to tracking errors.

The outputs of the peak hold circuits 23a, 23b and the low-pass filters 24a, 24b are sent to the dividers 25a and 2.
5b, and divides the outputs of the low-pass filters 24a and 24b by the outputs of the peak hold circuits 23a and 23b, respectively, thereby removing fluctuations in the light intensity of the sub-beam itself and obtaining a signal corresponding only to the modulation degree due to the pits. , the outputs of these dividers 25a and 25b are subtracted by subtracter 2.
6 and outputs a tracking error signal to the output terminal 27.

In this way, in this embodiment, the tracking error signal is obtained from the difference between the signals corresponding only to the modulation degree by the pits of both sub-beams, so even if the light intensity of the sub-beams fluctuates, it is always accurate without being affected by it. It is possible to obtain accurate tracking error signals. Therefore, since tracking servo can always be performed with high precision, information can always be reproduced accurately and stable random access can be easily performed.

FIG. 3 is a block diagram showing a second embodiment of the invention, and FIG. 4 is a signal waveform diagram of each part thereof.

In this embodiment, the output Sla+s of the photodetectors 31a and 31b which receive the reflected light of the sub-beams irradiated on one edge portion and the other edge portion of the information track, respectively.
Ib is supplied to peak hold circuits 33a and 33b via variable gain amplifiers 32a and 32b, respectively.

Here, the hold time in the peak hold circuits 33a and 33b is set to be longer than the period of the longest pit of the information track and sufficiently shorter than the period of fluctuation of the sub-beam light amount, as in the first embodiment.

In this embodiment, peak hold circuits 33a, 33b
The gains of the variable gain amplifiers 32a and 33b are controlled based on the outputs of the variable gain amplifiers 32a and 33b so that their output peaks are constant. That is, the peak hold circuit 33a.

Negative feedback is applied to lower the gain when the output of 33b increases, and to increase the gain when the output decreases. Thereby, the variable gain amplifier 32a.

The output S2a (521) of 32b has a constant peak and light amount fluctuations have been removed.

Output S2a of these variable gain amplifiers 32a and 32b
+S2b is supplied to low-pass filters 34a and 34b and averaged, thereby removing the signal component of the pits as in the first embodiment to obtain a signal S3a+S3b corresponding only to the modulation degree due to the pits. Output signals S3a +S3 of these low-pass filters 34a and 34b
b is supplied to a subtracter 35 for subtraction, and the difference signal S4 is outputted to an output terminal 36 as a tracking error signal.

Therefore, in this embodiment as well, as in the first embodiment,
An accurate tracking error signal can always be obtained without being affected by variations in the light intensity of the sub-beams.

〔Effect of the invention〕

As described above, according to the present invention, at least two tracking error detection beams projected onto one edge portion and the other edge portion of the information track of the optical recording medium are reflected on the optical recording medium. Since the degree of modulation by the pit is detected from the light and the tracking error signal is obtained from the difference between these degrees of modulation, it is possible to always obtain an accurate tracking error signal without being affected by fluctuations in the light intensity of the tracking error detection beam. Can be done. Therefore, since tracking servo can always be performed with high precision, information can always be reproduced accurately and stable access can be easily performed.

[Brief explanation of drawings]

Fig. 1 is a diagram explaining the present invention, Fig. 2 is a diagram showing a first embodiment of the invention, Fig. 3 is a diagram also showing a second embodiment, Fig. 4 is a signal waveform diagram of each part, FIG. 5 is a diagram showing a conventional technique. 111.11b...Photodetector 12a, 12b・
...Amplifiers 13a, 13b...Modulation degree detector 14...Subtractor 15...Output terminal 21
a, 21b... Photodetector 22a, 22b ---
・Amplifiers 23a, 23b...Peak hold circuit 2
4a, 24b...Low pass filters 25a, 25
b...Divider 26...Subtractor 27...Output terminal 31a, 31b...Photodetector 32a
, 32b...variable gain amplifier 33a, 33b.
...Peak hold circuit 34a, 34b...Low pass filter 35...Subtractor 36...Output terminal Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Procedure Correction Book 1. Indication of the case 1985 Patent Application No. 149113 2 Title of the invention Tracking error signal detection device in an optical information reproducing device 3 Person making the correction Relationship to the case Patent applicant (037) Olympus Optical Industry Co., Ltd. 4 Agent 1 changed "peak output" in lines 4-5 on page 7 of the specification to "
The output will be changed to ``, and the change in output will correspond to the amount of light reflected on the information track itself'' in lines 7 and 8 of the same page will be corrected to ``. Correct to. 2. Change "Rhydom Access" in the first line of page 11 of the specification to "
Corrected to "Random Access."

Claims (1)

[Claims] 1. Detection of a tracking error signal from reflected light of at least two light beams for tracking error detection irradiated on one edge portion and the other edge portion of an information track of an optical recording medium. A tracking error signal detection device for an optical information reproducing device includes a photodetector that receives each of the reflected lights of the at least two tracking error detection light beams, and a modulation degree due to the pit from the output of these photodetectors. A tracking error signal detection device in an optical information reproducing device, comprising modulation degree detection means for detecting the respective modulation degrees, and a subtracter for calculating the difference between the outputs of these modulation degree detection means and outputting a tracking error signal. . 2. The modulation degree detection means includes a peak hold circuit that holds the peak of the output of the photodetector for a predetermined hold time longer than the pit period, and a predetermined peak hold circuit that removes the pit signal component from the output of the photodetector. Tracking in the optical information reproducing device according to claim 1, characterized in that the tracking device comprises a low-pass filter having a time constant of , and a divider for dividing the output of the low-pass filter by the output of the peak hold circuit. Error signal detection device. 3. The modulation degree detection means includes a variable gain amplifier that amplifies the output of the photodetector, and a variable gain amplifier that holds the peak of the output of the variable gain amplifier for a predetermined hold time longer than the pit period. and a low-pass filter having a predetermined time constant that removes pit signal components from the output of the variable gain amplifier. A tracking error signal detection device in an optical information reproducing device according to claim 1.