JPS6079537A - Focus error signal generating device of optical disk player - Google Patents

Abstract

PURPOSE:To obtain a focus error signal having no error even if mechanical and positional shift of an optical system are generated, by correcting the positional shift to four photodetecting elements of a beam spot on a photodetector due to the mechanical and positional shifts, etc., by electrical and circuital processings. CONSTITUTION:Outputs of four photodetecting elemens 4A, 4B, 4C and 4D of a photodetector 4 are fetched as outputs A, B, C and D through pre-amplifiers 5A-5D, and supplied to a correcting circuit 10. The correcting circuit 10 amplifies separately the outputs of 4C and 4D so that the sum of outputs of the elements 4A, 4B is equalized to the sum of outputs of 4C and 4D. That is to say, the gain of a gain cotrol amplifier 11 and 12 is controlled by a voltage being proportional to S=(A+B)/(C+D), so that the sum (C'+D') of its outputs C', D' is equalized to (A+B). A, B, C' and D' and supplied to an operating circuit 20, and focus error signal F'=(A+C')-(B+D') is obtained. However, when the gain of the amplifier 11 and 12 is varied, the gain of a signal F' is also varied, therefore, in reality, a signal F'=F'/R' is fetched as a focus error signal.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is directed to recording information signals on a disc using a light beam and obtaining a focus error signal for the focus servo of an optical disc player that plays back from the disc. The present invention relates to a focus error signal generating device.

BACKGROUND TECHNOLOGY AND PROBLEMS In an optical disc player, which uses a light beam from an optical head to record information signals such as video signals and audio signals onto spiral or concentric tracks on a disc, and to reproduce them from the tracks, it is difficult to record information signals. During reproduction, it is necessary for the light beam incident on the disk to focus on the recording surface of the disk and trace the center of the track, and for this purpose, focus servo and tracking servo are essential.

The focus servo detects the shift of the focal point of the light beam incident on the disk relative to the recording surface of the disk, so-called focus error, and based on the detection signal, the focus error signal, focuses the focusing lens of the optical head or the entire optical head on the disk. Focus error when moving in the direction of the rotation axis.

The tracking servo detects the deviation of the spot on the disk of the light beam incident on the disk from the track, so-called tracking error, and based on the detection signal, the tracking error signal, The focusing lens of the optical head or the entire optical head is moved in the radial direction of the disk so that the tracking error becomes zero.

There are various methods for detecting focus errors, and a typical one is the astigmatism method. Figure 1 shows the basic configuration of an optical system for detecting shift focus errors using the astigmatism method. The light beam incident and reflected by this recording surface passes through a focusing lens λ, optical components such as a single wavelength plate (not shown in the figure), and further passes through a cylindrical lens 3 to reach a photodetector. be made into As shown in FIG. 2, the photodetector≠ is composed of seven photodetecting elements 1I-A, ≠B, ≠C1 arranged around one point, and the elements ≠A, 4' B,≠C
The outputs of 1≠D are A and B, respectively.

C, D,! : When, F − (A0C) L ('B+
D) A focus error is detected by the o operation.

When the recording surface / of the disk is located at the focal point of the focusing lens 2 as shown by the solid line, the light beam reflected from the recording surface / focuses at point X in the direction parallel to the plane of the paper in FIG. For a direction perpendicular to
≠If it is a perfect circle that evenly occupies the area on D, F=0. When the recording surface / approaches the focusing lens 2 as indicated by the broken line, the light beams reflected from the recording surface / become cylindrical at points X and Z, respectively, and are focused at a point distant from the lens 3 .

The spot on the photodetector μ is thinner in the direction parallel to the plane of the paper in FIG. 1 and thicker in the direction perpendicular to the plane of the paper, forming an ellipse as shown in FIG. 2A, F>0.

When the recording surface / moves away from the focusing lens 2 as indicated by the chain line, the light beams reflected on the recording surface / focus on points close to the cylindrical lens 3 in points X and Z, respectively, and the photodetector ≠ on the The spot is thicker in the direction parallel to the plane of the paper in FIG. 1 and thinner in the direction perpendicular to the plane of the paper, forming an ellipse as shown in FIG. 2C, with F<0.

There are various methods for detecting tracking errors, but when using the astigmatism method for detecting focus errors, it is convenient to use the push-pull method for detecting tracking errors. In that case, the number of photodetecting elements II-A, ≠B of the aforementioned photodetector t.

From the outputs A, B, C, and D of ≠C, 4'D, T -=,
A tracking error is detected by calculating CA+D>-(B+C).

When the recording surface / of the disk is located at the focal point of the focusing lens 2 as shown by the solid line in FIG. As shown in Figure 3B, the light intensity distribution of the upper spot is on the element ≠ A and ≠ D side and on the element ≠ B and ≠ C side.
If the spot is symmetrical on both sides, T = 0, but if the spot on the disk shifts in either direction with respect to the center of the disc, depending on the direction of the shift, the photodetector ≠ on the The light intensity distribution of the spot is as shown in Figure 3 A or C.
There is no asymmetrical relationship between the A and 41-D sides and the element 4'B and +C sides, so that T>υ or T<0.

By the way, when using the astigmatism method to detect focus errors, if the position of the spot on the photodetector ≠ elements ≠ A to tD deviates due to mechanical or positional deviation of the optical system, the direction of the deviation is In some cases, the focus stop signal F = (A10) - (B + D) is affected and errors occur, and the focus is adjusted so that the light beam incident on the disc is focused at a position that is shifted from the recording surface of the disc. If the servo is applied, in some cases, the focus servo may not be applied.

That is, when the recording surface of the disk is located at the focal point of the focusing lens, the spot above the photodetector is located on the element I as shown in FIG.
When the spot evenly occupies I-A-Il-D, regardless of the tracking error, the light intensity distribution of the spot above the photodetector is as shown in FIG. 3A.

A=D regardless of whether it becomes B or C.

B=C and F −(A+C)−(B+,D) −〇.

Furthermore, as shown in Fig. , regardless of the tracking error, the light intensity distribution of the spot above the photodetector will therefore be as shown in Figures A, B, and C.
Regardless of which one becomes, yahashi, A=D, B
=C, and F-(A10)-(B+D)=0, so the focus error signal F is not affected and no error occurs.

On the other hand, as shown in FIG.
If there is a tracking error, an error will occur in the focus error signal F depending on the direction of the spot shift on the photodetector and the tracking error if there is a tracking error. For example, the fifth
As shown in the figure, when the spot shifts in a direction that largely occupies the area on element ≠ C and jD, when the tracking error is in the - direction as in Figure j, A, D-A>C-H becomes F.
If = (A + C) - (B + D) < 0, p, and when the tracking error is in the opposite direction as shown in Figure J, then p - A
<C-H, so F=(A+C)-(B+D)>0
become.

Purpose of the Invention In view of this, the present invention provides that when the astigmatism method is used to detect focus errors, the beam spot on the photodetector may be ≠ due to mechanical or positional deviation of the optical system.
Even if the position of each photodetecting element is shifted, an error-free focus error signal can be obtained and the focus servo can be stably applied.

SUMMARY OF THE INVENTION In the present invention, the element 4? The relationship is maintained such that the sum of the outputs of A and 4tB is equal to the sum of the outputs of element + C and QD, so that the photodetector ≠ the element at the spot above! A focus error signal is generated by creating a state in which the position with respect to A-ID is shifted but is equivalent to not being shifted, and performing calculations using the astigmatism method in this state.

Embodiment FIG. 3 shows an example of the circuit portion of the focus error signal generating device of the present invention, in which t photodetecting elements of the aforementioned photodetector≠
A,! The outputs of B, 4'C, ≠D are preamplifiers! ;h, 3
;B, 3; Output A, B, C, through C, jD, respectively.
These outputs A-D are output to the correction circuit IO.
supplied to The correction circuit 10 includes elements 1l-A and ll
The outputs of elements +C and jD are amplified separately so that the sum of the outputs of elements B and the sum of the outputs of elements C and jD are equal. That is, the outputs C and D of the element≠C, 4'D are the gain control amplifier/
/.

/2, respectively, and the output A of elements FA and 1I-B
, B are added by the adder circuit/3 to obtain the output A + B,
Outputs C and D of elements 1I-C and 4'D are adder circuit/ll-
are added to obtain the output C+D, and the output A+B of the adder circuit/3 is divided by the output C+D of the adder circuit/g by the divider circuit/j to obtain the voltage C+D proportional to S=m. This voltage controls the gains of gain control amplifiers // and /2, but when A0B>C00 and S>/, the gains of amplifiers // and /2 are also controlled. ,A+B
When = C + and S = /, the gain of amplifier // and /2 is also set to /, and when A + B < C + D and S = /, the gain of amplifier // and /2 is set to /.
The gains of amplifiers // and /2 are also made smaller so that the sum C'+D' of the outputs c/ and D/ of amplifiers // and /2 is equal to A+B.

Then, the output A w B of the element ≠A, ≠B and the correction circuit I
Element 4'C amplified by gain control amplifier //, /2 of O
, 4'D are supplied to the arithmetic circuit 20. In the arithmetic circuit 20, the output A of element≠A and the amplifier/
The output C' of element≠C amplified by ' are added in the adding circuit 22 to obtain the output B+p/, and in the subtracting circuit 23, the output B+D' of the adding circuit λ is subtracted from the output A+C' of the adding circuit 2/, resulting in a focus error signal 1>'
=(A+C')-(B+D') is obtained. However, the gain of amplifier // and /2 is actually the elements 4AA, 4'B.
outputs A, B and the element tC amplified by the amplifier //, /2
The outputs C'ID' of 1≠D are all added in the adder circuit 30 to obtain the signal R'=A+B+C'+D', and the signal F'=(A 10C'
)-(B+D') is the output signal R' of the adder circuit 30 =
A 10B 10'+D' divided by the output signal F
"==F//R/ is taken out as a focus error signal.

Note that this example is a case where a tracking error is simultaneously detected by the push-pull method, and the output A of elements +4 to ≠D
-D is supplied to the arithmetic circuit 1.10, and in the arithmetic circuit tto, the outputs A of the elements l/LA and lLD.

D is added in addition circuit≠l to obtain output A+D, outputs B and C of element 4ZB, ≠C are added in addition circuit t2 to obtain output B10, and addition circuit is added in subtraction circuit I/L3. The output B+C of the adder circuit 412 is subtracted from the output A+D of the tracking error signal T=(A+D)-(B+
C) is obtained.

When the recording surface of the disk is located at the focal point of the focusing lens,
When the spot on the photodetector≠ does not shift as shown in Fig. 3, or when the spot on the photodetector≠ is not shifted as shown in Fig.
'When it deviates in a direction that occupies a large area on A and llD,
Regardless of the tracking error, the tracking error signal T = obtained by the arithmetic circuit 110 is therefore
Regardless of whether (A+D) - (B+C) is positive, zero, or negative, A=D, B=C, and A+B=C+
D becomes S=/. Therefore, when the gain of the gain control amplifier // and 7.2 of the correction circuit IO is / nil, the output c', D' of the amplifier / / , /j is C'=
C, D'=Dte, C'+D'=A+B, and the focus error signal F'=(A10') −(B +D') obtained from the subtraction circuit 23 of the arithmetic circuit 20 causes an error. do not have.

When the spot on the photodetector≠ shifts in a direction that largely occupies the areas on elements≠C and ≠・D or on elements FA and 4'B as shown in Fig. 5, A\D, B\C, and A+B< C+D
Or A+B>C+D, and S</or S>/. At this time, as mentioned above, if there is a tracking error, the gain of the gain control amplifiers /l and /2 of the correction circuit IO is made smaller or larger depending on the value of A+C<B. As a result, C'<C,
D'<D or C') C, D'>D, then C'+D'=A+B. Therefore, it is equivalent to the spot on the photodetector not being shifted as shown in Figure 3,
The focus error signal F'=(A+C')-(B+D') obtained by the subtraction circuit 23 of the arithmetic circuit 20 no longer causes any error.

However, in this way, the output C' +D of amplifier //, /2
If ' is changed, the gain of the signal F' also changes, so as mentioned above, the output signal of the adder circuit 30 is R' = A + B + C'
The gain of signal F' is adjusted by D'.

Effects of the Invention According to the present invention, when using the astigmatism method to detect focus errors, electrical and circuit processing allows By maintaining the same relationship between the beam spot and the large number of photodetector elements as when the device is not misaligned, it is possible to prevent the beam spot on the photodetector from expanding due to mechanical or positional misalignment of the optical system. Even if the position relative to the photodetector element shifts, it is equivalent to not shifting. By performing calculations using the astigmatism method in this state, focus error signals are generated. Even if the position of a beam spot on a photodetector with respect to a large number of photodetecting elements deviates, a focus error signal without error can be obtained and the focus servo can be applied stably. Therefore, there is no need to strictly adjust the optical system, and the burden on manufacturing the apparatus is reduced.

[Brief explanation of drawings]

Claims (1)

[Claims] 7th. Second. Third. The ≠th photodetecting element has photodetectors arranged around one point, and the first and third photodetecting elements have photodetectors arranged around one point.
A shift focus error is detected by the difference between the sum of the outputs of the first and tth photodetecting elements and the sum of the outputs of the second and tth photodetecting elements, and the difference between the outputs of the first and tth photodetecting elements an optical system configured to detect a tracking error based on the difference between the sum of outputs of the second and third photodetecting elements, and the sum of the outputs of the first and second photodetecting elements; and a correction circuit that amplifies the outputs of the third and third photodetecting elements separately so that the sum of the outputs of the third and ≠ photodetecting elements becomes equal; and the output of the first photodetecting element. and the difference between the sum of the outputs of the third photodetector element amplified by the correction circuit and the sum of the outputs of the second photodetector element and the output of the ≠th photodetector element amplified by the correction circuit. A focus error signal generating device for an optical disc player, comprising an arithmetic circuit that obtains a focus error signal.