JPS5936333A - Automatic focus servo circuit - Google Patents

Abstract

PURPOSE:To simplify the control of a photodetector and other optical systems and at the same time to reduce the selection standard of a semiconductor laser, by using a tracking error signal to correct a focus error signal. CONSTITUTION:The outputs A and C, B and D, A and D and B and D are supplied to adding amplifiers 11, 12, 22 and 23 respectively among those outputs A-D of photodetecting elements 10A-10D of a 4-split photodetector 10. Then the sum outputs of amplifiers 11 and 12 and 22 and 23 are supplied to differential amplifiers 13 and 24, respectively. A focus error signal epsilon=(A+C)-(B+D) and a tracking error signal epsilont=(A+D)-(B+C) are delivered from amplifiers 13 and 14, respectively. The signal epsilon and signal muepsilont given from an amplifier 25 of a gain mu are sent to an adding amplifier 26. Thus a corrected focus error signal epsilon0 and signal epsilont are delivered to terminals 14 and 27, respectively. As a result, the control is simplified for the detector 10 and other optical systems. At the same time, the selection standard is reduced from a semiconductor laser which serves as a light source.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an autofocus servo circuit used in a device such as an optical disk that records or reproduces information on an information track using an optical method.

Figure 1 is an explanatory diagram showing an example of the optical system of an optical disc;
The figure is a circuit diagram of a conventional system for detecting focus errors. In FIG. 1, 1 is a semiconductor laser for reading information;
Reference numeral 2 denotes a Collinaut lens that converts the light beam emitted from the semiconductor laser 1 into a parallel light beam.

6 is a focusing lens, 4 is a disk that stores information, 5 is a beano splitter that reflects the reflected light from the disk 4, Ruri, 1 is a spherical lens that focuses the reflected light from the beano splitter 5, and 7 is in the X direction. It is a cylindrical lens that has a lens effect.

In FIG. 2, a photodetecting element 10A divided into 10 and 4 parts is shown.
10D, 811 which receives the light spot emitted from the cylindrical lens 7 in FIG. 1 is a summing amplifier which modulates the output signals of the photodetecting elements 10A and 10C, and 12 is the photodetecting element 10B. and 10D, and 16 is a double summing amplifier 11.
11j: an output terminal for the focus error signal ε.

The light emitted from the semiconductor laser 1 is passed through the collimating lens 2
The reflected light from the disk 4 passes through the condenser lens 6 and is irradiated onto the information track of the disk 4 by the condensing lens 6 into a spot with a diameter of, for example, 171)71. Reflected by splitter 5, spherical lens 6, cylindrical lens 7
]11, where the convergence point 15 in the X direction and
The convergence point 16 in the y direction perpendicular to the paper surface becomes different light beams,
The light is irradiated onto the photodetector 10 in FIG. Convergence points 15 and 1
The cross-sectional shapes (spot shapes) of the luminous flux at positions 8a, 8b, and 8c between 6 and 6 are respectively 9a and 9 shown in FIG.
b, as shown in 9c. Here, the photodetector 10 is installed at a position 8b where the shape of the light spot is circular, and when the distance between the lens 6 and the disk 4 is a predetermined value and the focus is on, the light A circular light spot is irradiated onto the photothermal surface of the detector 10. When the distance between the lens 6 and the disk 4 changes from a predetermined value and the focus shifts, this corresponds to a change in the installation of the photodetector 10 from 8b to 8a or 8c, and the light receiving surface of the photodetector 10 changes. The shape of the light spot irradiated on the top is 98 or 9c
The photodetector 10 is installed so that the boundaries of the photodetecting elements 10A to 1ON) are inclined at 45° with respect to the x and y directions, as shown in FIG. Electric signals corresponding to the shape (area) of the light spot irradiated thereon are obtained from each of the photodetecting elements 10A to IOD.

The summing amplifier 11 outputs the photodetecting element 10A and the output A of the IOC.
and C are added together, and the addition amplifier 12 adds the photodetector element 10.
Add B and IOD outputs B and D to 1? , -iru. The subtraction amplifier 16 subtracts the outputs of both the addition amplifiers 11 and 12, and outputs a focus error signal ε=(A+C)−(
11+D) 1. According to such a circuit, when the disk 4 approaches the lens 6, the spot shape on the photodetector 10 becomes an ellipse long in the y-axis direction as shown in 9a, and a positive voltage can be obtained. On the other hand, when the disk 4 moves away from the lens 3, the spot shape on the photodetector 11J becomes a dawn shape long in the X-axis direction as shown by 1d' and 9c, and a negative voltage is obtained from the output terminal 14. In this way, the focus error signal ε
indicates the +'A R at the 11-focus point, and the lens 6 is moved so that the value of the focus 1 color signal 6 becomes a constant value (for example, zero), and the lens 6 and the disc 4 is maintained at a predetermined 1F'+.

FIG. 6 is an explanatory diagram showing the relationship between the diffracted light by the second track of the disk 4 and the spot shape of the photodetector 10. (A) and (B) show the diffracted light from the track, ( /tsu.

(d) Photodetection The spot shape of p = 10-1- is calculated respectively. (A) is the 41st pattern when the spot hits the center of the track 17, and it becomes symmetrical as shown in 18. Create a symmetrical spot shape as shown. (b) This is the diffraction pattern when the spot appears on the edge of Hatrack 17, and as shown in 19, it is asymmetrical. In this case, the spot shape on the photodetector 10 is asymmetrical to the IE right, as shown in 21 of 2). Furthermore, if the radiation pattern (transverse mode) of the semiconductor laser 1 is biased (including the higher-order mode pattern), a corresponding bias will occur in the bright portion 28 as shown in ().

In this way, when the reproduction spot scans the track 17, the spot shape on the photodetector 10 is no longer circular, but as long as it is horizontally symmetrical or vertically symmetrical,
7) A two-tone combination whose spot shape is asymmetrical as shown in (→) does not cause a disturbance to the focus error signal ε from the reducing ζT amplifier 16.

Therefore, in the conventional focusing device of Mr. Kazutoshi, the shape of the spot that emits sound on the photodetector 10 is changed in order to reduce the disturbance caused by the reproduction spot cutting the track 114. Furthermore, it was necessary to precisely adjust and arrange the photodetector 10 and other optical elements so that iqJ was symmetrical. In addition, it is necessary to use a semiconductor laser 1 with less bias, or to use a dual optical system.

Here, the present invention aims to realize an autofocus servo circuit which can simplify the adjustment of the photodetector 10 and other optical systems, and which can make the selection criteria for semiconductor lasers looser. be.

The circuit according to the present invention converts the signal from the photodetector into a human input signal (1-7), includes a tracking error detection means (1-7) that outputs a dragging error signal indicating a tracking error of the light beam, and (1-7) provides a focusing error signal. The feature is that the correction is performed according to the tracking error signal.

FIG. 4 is a block diagram of an example of a circuit according to the present invention. In this figure, TE is the trailing error detection means featured in the present invention.

This means includes a photodetector 11oA, an optical amplifier 22 that adds signals from the ioD, and a photodetector element 10B.

The addition amplifier 72 which adds the signals from 10C is composed of a differential amplifier 24 which obtains the difference between the outputs of these two addition amplifiers 22 and 23, and an amplifier 25 with a gain of /7 (μ is normal or negative polarity). (teii). 26 is an additional amplifier that adds the outputs of the subtraction amplifier 16 and the amplifier 25, and 27 is an output terminal that takes out the tracking error signal output from the differential amplifier 24.

The other parts are the same as the circuit of FIG.

In this circuit, the output terminal 27 has (A+D)−
A tracking error signal 6t as represented by (B-1-C) is obtained. In addition, the output terminal 14 has (1)
As shown in the equation, a focus error signal 6° corrected by the tracking error signal 6t is obtained.

go=ε10μ・εt=(A+C)−(B+D)10μ((A+I))−(B
+C)l (1) Next, the operation of this circuit will be explained with reference to FIGS. 5 to 7.

Figure 5 (a), (b), and (c) are all track 17
These are the diffraction patterns of the reflected light from (A) - the left end of the track 17, (B) the center of the track 17, and (←→) the right end of the track 17, respectively. ni), (e), and (e) are all (i) and (b).
, (c) respectively show the shape of the light spot on the photodetector 10. Here, the photodetecting element 10A, IO
A case where there are bright portions 35, 36, and 37 on the H side will be illustrated.

When the spot hits the left end of the track 17 as shown in (A), as is clear from (A), the output signal A from the photodetecting element 10A is the strongest, followed by the output signal ■ from the photodetecting element 10D. ] is large, and the photodetector element IQB and 113
The output signal B of C has the same magnitude as Cfd. If the spot hits the center of the track 17 as shown in (B), then the light detection element 1
0A, IOH output signal A.

B is equal to 7, and the output signals C and D of the photodetecting elements 10C and 10D are also equal, and their thickness is smaller than A and B.

When the spot hits the right end of the track 17 as shown in 0), as is clear from 0), the photodetector element 1
Output signal B from 0B is the largest, followed by photodetector 1
Output signal from 0C Output signal C from 10C is large,
The output signals A and D of the photodetecting elements 10A and 10D have the same magnitude.

From this, the focus error signal obtained from the subtraction amplifier 16! =(A+C)-(B+D) changes as shown in FIG. 6 depending on the spot position. Also, l・racking error signal εt obtained from the differential amplifier 24=
(A+1))-(B+C) changes as shown in FIG. 7 depending on the spot position.

As is clear from FIGS. 6 and 7, the focus error signal 8 and the tracking error signal εt exhibit almost the same characteristics (tendencies) with respect to spot track deviation, although there is a difference in sensitivity. Therefore, in the addition amplifier 26 in FIG. 4, the focus error signal ε is corrected by adding (or subtracting 9) a tracking error (a signal μ·εt obtained by multiplying the M number εt by μ) to the focus error signal ε, and outputs the A focus error signal ε from which the influence of track deviation has been removed or reduced can be obtained at the terminal 14. This signal 60 is applied to a lens moving means (not shown), and the lens is moved so that ε becomes zero. 6 position is adjusted.

In the above embodiment, the focus error signal ε and the tracking error signal 6t are obtained by using the output signal from the same photodetector 10, but the tracking error signal εt f, (obtaining circuit As a means,
For example, it is possible to use circuit means that slightly vibrates the playback spot in the direction across the track at a constant frequency, and detects changes in the amplitude of the playback signal using the spot vibration signal to obtain a tracking error signal. The circuit means for obtaining the focus error signal t is also not limited to that of the embodiment. Furthermore, although the case where track information is reproduced is taken as an example here, the present invention can also be applied to the case where information is recorded on a track.8 As explained above, according to the present invention, the focus error signal can be reproduced. This is corrected using a tracking error signal, and disturbances in the focus servo when crossing the track can be reduced or eliminated by adding a simple electrical path 191, thereby improving stability and reliability. Moreover, the adjustment of the optical system can be simplified, and the selection criteria for the laser light source can be made more relaxed.

Therefore, yield can be improved2.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram showing an example of the optical system of an optical disc;
The figure is a circuit diagram of a conventional focus error detection device, part 6.
The figure is an explanatory diagram showing the relationship between the diffracted light from the track and the spot shape on the photodetector, FIG. 4 is a block IAI showing an example of the circuit according to the present invention, and FIG. 5 is the diffracted light from the track and the light Detector - (7) An explanatory diagram showing the relationship with the spot shape, No. 61/l is a diagram showing the relationship between the spot position and the focus error signal, and Fig. 7 is a diagram showing the relationship between the spot position and the tracking error signal. FIG. 10...Photodetector, 11,12.22,23゜26...Kason amplifier, 13.24...Differential amplifier, 25...Amplifier, TE・・・・・・
Tracking error detection means. Agent Makoto Kuzuno - Figure 1 1s2 (A) (~))T
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No. 2, Shikoaki's name Autofocus servo circuit:
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Saku1 person f1 place Heavy industry; profit■°dai I11 ward Marunouchi-1'l'+2 sound 35;・name (4, (6 (11)
'Ryodenki Ii Song Dynasty I1 Representative δ Piece 1 + V Cross Section 4 Generation 1111 85, ``Detailed Description of the Invention'' column of the specification to be amended. 6. Contents of correction (1) Correct "focus error" on line 4 of page 2 of the specification to "of focus error" 1. (2) 1. Subtract amplifier" on line 20 of page 2 of the specification. Correct as "differential amplifier." (3) “Light-curing surface” and “light-receiving surface” on page 6, line 18 of the specification
and correct it. (4) "Reduced door amplifier" on page 4, line 13 of the specification is corrected to "differential amplifier". (5) "l jt'" on page 5, line 4 of the specification is "matched"
and correct it. (6) Correct "-mounted amplifier" on page 6, line 7 of the specification to 1 - differential amplifier. (7) Subtract 1 a/no on page 7, lines 17-18 of the specification. is called a "differential amplifier" and corrected by 1. (8) "Reduced a amplifier" on page 9, line 16 of the specification is corrected to "differential amplifier."that's all

Claims (1)

[Claims] (1) A light beam scans an information rack to record information or record information. a force error detection means for detecting a deviation of the information track of the round beam;
'(tracking error detection means for detecting the deviation from the information track of B1), and the focus error error signal from the focus error detection means described in 111 is corrected at a predetermined rate by the tracking error signal from the tracking error detection means. An autofocus servo circuit characterized in that it has a means for correcting the correction, and outputs the corrected signal as a focus error signal.