JPS60145539A - Tracking error detecting device - Google Patents

Abstract

PURPOSE:To eliminate a position shift influence to an incident luminous flux in spite of a variation of amodulation degree by varying a ratio for adding a difference of an amplitude of both output signals and a difference of mean values, based on a modulation degree of the sum of output signals of photodetecting areas divided into the direction orothogonal to a track. CONSTITUTION:Reflected light from a disk 15 is made incident on a photodetector 17 having photodetecting areas 18a, 18b divided into the direction orothogonal to the direction of a track. Outputs S1, S2 of the areas 18a, 18b are supplied to amplitude detecting circuits 25, 27 and mean value detecting circuits 26, 28, and also supplied to an amplitude detecting circuit 34 and a peak value detecting circuit 35 through an adder 33. Outputs of the circuits 34, 35 are supplied to a substracter 37 through a divider 36, subtracted from a constant C and supplied to a multiplier 38. An output which has subtracted 29 outputs of the circuits 25, 27 is multiplied and supplied to an adder 39, and added to an output which has subtracted 30 outputs of the circuits 26, 28. In this way, in spite of a variation of a modulation degree, a detection can be executed stably without being influenced by a relative position shift of the photodetector 17 and a luminous flux which is made incident on this photodetector.

Description

Detailed Description of the Invention Technical Field The present invention relates to a tracking error detection device suitable for use in an optical disc recording and/or reproducing device.

2. Description of the Related Art In an optical disc recording and/or reproducing apparatus, there is a push-pull method as a method for detecting a relative positional deviation between a light spot and a track on a disc. Figure 1 A, t and B are diagrams for explaining the push-pull type IjiL ridge. , incident yt
The bundle 4cm is focused on the objective lens. As shown in FIG. 1A, if the light spot is irradiated onto the bit a with no horizontal deviation, the light 5 diffracted by the bit 3 will be symmetrical, but as shown in FIG. 1B, ni, W; Spot σ] Center is bit 8σ] Takumi U)
The diffracted light 1 and the diffracted light 5 that are off center are asymmetrical. In the push-pull method, by detecting this asymmetrical likelihood, information on the relative positional deviation between the optical spot and the track on the disk surface, that is, a tracking error signal, is obtained.

FIG. 2 shows the configuration of a typical optical system of the push-pull method. Light emitted from the semiconductor laser 11 is made into a parallel beam by a collimator lens 12, transmitted through a half mirror 13ffi, and then passed through an objective lens 14. A track article with bit 16 of disk 15 is converged. The reflected light from the disk 15 is focused by the objective lens 14, reflected by the half mirror 13, and received by the yt detector 17 arranged in the far field thereof. The photodetector 17 is perpendicular to the direction of the track in the incident light beam.
・Two light-receiving areas 18a divided into intersecting 10,000 and I-2.
.

181) as shown in Figure 3, the tracking error signal is obtained by supplying these output signals to the W reducer 20 through low-pass filters 19a and 191), respectively.

The push-pull method described above has the advantage that both the optical system and the No. 1 processing system are very simple in configuration, but the disk may be tilted with respect to the yC thread, and the objective lens may be affected by the tracking servo. Therefore, if the position of the light beam incident on the photodetector changes due to excessive movement relative to the photodetector, there is a drawback that an error occurs in the tracking error signal.

In order to eliminate the above-mentioned drawbacks, signal processing methods as described below have been proposed.

FIG. 4 A, B and C show the light receiving area 18a of the photodetector I7.
It shows how the outputs S and S2 of 18b and 18b change according to the shift J of the bit 16 due to the rotation of the disk. Here, the sum S of the outputs of the light receiving area 18 a + 18 b when there is no sub-bont 21 on the pi) 16,
+ 32K 1. When the tracking error is zero, the division of the change due to bit 16 of the light beam 22 incident on the photodetector 17, that is, the modulation degree, is spatially expressed as m (
o<+n<11. ) When the racking error is Δ, the luminous flux 2
The center of +t'TI redrack 28 is the light receiving area 18at on the side of 10,000 bordering on the center of 2 (G118t).
The modulation degree of is Q(Δ), where P(Δ)=Q(-Δ), P
[U)""Q(01:m. Figure 4A shows the case where both the tracking error and the positional deviation of the light beam are zero. In this case, the output S1.S is both between bits. The peak value becomes - and changes with an amplitude of +-m.

2 2 In Fig. 4B, there is a tracking error of Δ, but the luminous flux 22
shows the case where the positional deviation is zero. In this case, the peak value of the output S2 is i and the amplitude is 7P (Δ), and the peak value of the output S2 is i and the amplitude is 7Q (Δ).

Here, if the outputs S and S2 are each passed through appropriate low-pass filters to calculate the average light intensity, and the difference between them is S8(Δ), then S8(Δ1=-(Q(Δ)-P(Δ))... (1
). Since S8 becomes an odd function with respect to Δ due to the assumptions regarding P(Δ) and Q(Δ), it can be seen that it can be used as a tracking error signal.

This is exactly the push-pull method described earlier.

In FIG. ΦG, the tracking error is zero.

A case in which there is a positional shift of the light beam z20 is shown. In this case, when the peak value of the output S□ is A and the fG width is Am, the output direction 52 (
D Heary 6fi&i (1-A), m1MG! (
1-A)m. Here, the output S1. If we include the difference S8([1) in the average yC amount of S, we get S(υl=(1--1(2A-11...(2)2), but U(m(1,A~ -Dechirukara, 58(0)
~0. Therefore, if there is a positional deviation of the GeC bundle 22, an error occurs when the difference S8 in the average amount of light incident on both light receiving areas 1ga and 18b is used as a tracking error signal. Therefore, S(
Take the difference between the amplitudes of the outputs S□ and S2 as Δ), and further calculate S,
(Δ) is expressed by the following formula.

S (Δ)=S (Δ)+α・S (Δ) ... (
3) 5 8 4 1 Here, if α=---, then m 1 S (01=88(0)+ (,--gl 84([month...(4)1=(1-7) (2A-1)7(7--H)+2A-]
It will be 1m20. Moreover, the height when the positional deviation of the light beam 22 is zero is S, (
Δ)=7(Q(Δ)−P(Δl)+(7−stones)(1(Δ
l-7Q(Δ))=-(Q(Δ)-P(Δ))...
(5) m, and S is an odd function with respect to Δ. Even if the positional shift of the light beam 22 is not zero, if Δ changes and, for example, S, increases + JO, S, will decrease, so if α is a negative value, S, (Δ) will decrease. However, in the opposite case, S6(Δ) increases. Therefore, S, (Δ) becomes a valid tracking error signal even when the position of the light beam is misaligned.

FIG. 5 shows the configuration of a circuit that actually implements the signal processing method described above. Ten thousand light receiving areas 18a of the photodetector 17
The output s1 is supplied to the swing 1 detection circuit 25 and the average value detection circuit 26, and similarly the output S2 of the other light receiving area 18b is
is also supplied to the amplitude detection circuit 27 and the average value detection circuit 28. The amplitude detection circuits 25 and 27 determine whether there is a pit or not.
It detects the amplitude of a signal that changes over time, and is composed of, for example, a bypass filter, a detection circuit, and a low-pass filter. 't, the average value detection circuit 26.28 is p,
It detects the average value of a signal that changes depending on the presence or absence of a cut, and is configured with, for example, a low-pass filter.

The outputs of the amplitude detection circuits 25 and 27 are supplied to a subtracter 29 to calculate the amplitude difference S, and the outputs of the average value detection circuits 26 and 28 are supplied to a subtracter 8o to calculate the difference S8 between the average values. Ru. The output S of the subtracter 29 is supplied to an amplifier 81 and multiplied by α, and the output αS4 and the output S8 of the subtracter 80 are added by an adder 32 to obtain a tracking error signal S.

As explained above, according to 7S: signal processing method, the photodetector 17
It is possible to effectively eliminate the adverse effect on the tracking error signal due to variations in the position of the light beam incident on the tracking error signal. Therefore, if the modulation degree m is constant, an accurate tracking error signal can always be obtained. However, the degree of modulation m changes depending on the size, shape, and pitch of the pits. Particularly in a disk recorded at a constant angular velocity, the degree of modulation changes because the size of the pits differs between the inner and outer circumferences. For this reason, α is kept constant, that is, the difference between the average values s8 and the difference between the amplitudes S,
If the ratio of adding 2 and 2 is always kept constant, there is a problem that S5 (old to 0) will occur due to changes in the modulation degree m, resulting in an error.

OBJECTS OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide cheap tracking that is not affected by the relative positional deviation between the photodetector and the light beam incident thereon, regardless of changes in the degree of modulation. It is an object of the present invention to provide a tracking error detection device suitably configured to detect error signals.

Summary of the invention 4I: The invention converges light emitted from a light source to
i! A recording medium with a track recorder having 7 strips recorded thereon is irradiated with the reflected light, which is placed in the far field and 1 Jtl.
The track is divided into 7 sections perpendicular to the direction of the track.
In a device that detects a tracking error based on the sum of the difference in amplitude and the difference in average value of output signals of both light receiving regions by receiving light with a photodetector having a light receiving region, the phase of the output signal of the S orientation light receiving region is detected. The method further comprises means for changing the ratio of adding the difference in amplitude of the output signals of the two light-receiving areas and one difference in the average value based on the degree of modulation. This is a characteristic feature.

Example FIG. 6 shows a first embodiment of the invention.

In this example, the optical system shown in FIG.
The beam is incident on the detector 17. Light receiving area 18al...

The outputs S□ and S2 of 18b are the same as in FIG.
il detection circuit 25.27 and average value detection circuit 26°2
8 to calculate the amplitude 111M and the average value, respectively, and obtain the difference S in their amplitude and the difference S8 in the average value by subtractors 29 and 3o, respectively. In this example, the outputs S□+S2' of the receiving C areas 18a and 18b are
& is supplied to the adder 33 to add Ii, and its output S□+8
2 to the swing 1 failure detection circuit 84 and the peak value detection circuit 85, and ? 7+: In the width detection circuit 84, the amplitude of the input 7J signal □・signal S□+82, which changes depending on the presence or absence of pits, is calculated, and in the peak value detection circuit 85, the amplitude is calculated manually (g
Ji! Detect the maximum value of fS +82 within a suitable time. The outputs of the amplitude detection circuit 84 and the peak value detection circuit 85 are respectively supplied to the X and Y input terminals of the analog divider 6 to obtain Y/X, which is then supplied to the inverting input terminal of the subtracter 37. A counting constant O is supplied to the non-inverting input terminal of the subtracter 37, the output of the subtracter 37 and the output S of the subtracter 29 are multiplied by the analog multiplier 8B, and the multiplication result and the output of the subtracter 30 are The tracking error signal S6 is obtained by adding the sum of the outputs S and J1XH89.

According to a non-embodiment, the analog divider 86 calculates the ratio between the JM width detection circuit 34 and the peak value detection circuit 85, that is, the light receiving area 18a added by the adder 83.

The ratio of the amplitude of the sum of the outputs of 18b + 82 to the peak value?
Since the reciprocal of the modulation degree m is obtained as the output, the output of the analog divider 86 is subtracted from the constant C in the subtracter 87, and the value 2 is added to the subtracter 29 in the analog multiplier 8B. This IJ
The tracking error signal S6 obtained from the O calculator 39 has a value expressed by the following equation.

56=33+ (0-iii-IS, ...(6)
Here, if O = "/2 in the above equation (6), -
, its right-hand side becomes α=--- in equation (3), and this m α changes continuously according to the degree of modulation.

That is, conventionally, the output S of the light receiving area] 8a, 1Flb,
, the amplitude difference S of S2 and the average value difference S8 are always added at a constant ratio, but according to this example, the error always becomes zero depending on the modulation degree of Pitoy No. 5. It will be automatically adjusted to the optimal value.

Therefore, regardless of the change in the modulation degree, )'C detector I7
7. It is affected by the relative positional deviation between this and the incident light beam. j<, a stable tracking error signal can always be obtained.

FIG. 7 shows a second embodiment of the invention.

In exceptional cases, the output S of the light receiving area 18a, l'81)
Prepare two different ratios for adding the amplitude difference S of □, S, and the average value difference S8, and automatically select one of them - 10,000 according to the modulation degree m. This is different from Fig. 6 in this respect. Therefore, in exceptional cases, the output of the subtracter 29, that is, the difference in amplitude between the outputs S□ and S2 of the light receiving areas 18a and 18b output from the amplitude detection circuits 25 and 27°
, are supplied to two amplifiers 40 and 41 with different amplification factors α and β to amplify them, respectively, and their outputs α9 and βS4 are supplied to a switching circuit 42. Also,
Peak value 1: Output of the detection circuit 35, that is, output S of the light receiving areas 18a and 18b output from the IJO calculator 88
The peak value of the sum S+82 of S+82 is supplied to an attenuator 48 with an attenuation rate γ and is attenuated, and an amplitude detection I detects the amplitude of the output of the attenuator 43 and the output S+S2 of the adder 88.
Compare the output of the circuit 34 with the comparator 44. In this way, the comparator 44 compares the amplitude of the output S□+S of the adder 83 and γ times the peak value, and calculates the modulation degree m of S1+82.
is larger or smaller than γ, the switching circuit 42 is controlled based on the result, and the amplifier 40
'One output αS of either one of P5 and 41, or G or βS, is selected and supplied to the adder 39.
．． The tracking error signal S5 is obtained by adding the output Si of the EI optical regions 18a and 18b outputted from 28, and the difference S8 (S2), LJiitxσ).

In this practical example, the amplification factor α of the amplifier 40,4]
.

β is set appropriately under the condition of β<−−−<α, and 2
When the output of the γ comparator 44 becomes III, > γ, S selects the output αS4 of the amplifier 1...40 to obtain a tracking error signal of S5-88+αS4, and when m<γ is expressed. is the amplifier 41+/) output βS, which is expanded to s, =s
8+βS.

Obtain the tracking error signal. In this way, the one closest to (1-, 1, 2 γ) among α, βσ] is automatically selected according to the modulation degree m.

According to the present embodiment, without using an expensive analog multiplier as in the first embodiment, a stable tracking error of -1d with less error than before can be achieved due to the inexpensive circuit configuration.
I can ask about the number once.

In the second embodiment, two ratios to be added are prepared, but it is also possible to prepare three or more ratios to obtain a tracking error signal with even fewer errors.

As described in the Effects of the Invention, in the present invention, the sum of the outputs of both light receiving areas of a photodetector having light receiving areas divided into directions orthogonal to the track (based on the jJ modulation degree) , Since the ratio of adding the difference in amplitude of the output signal of these two light-receiving areas and the difference in the average value is changed, the relationship between the photodetector and the light flux incident on it is independent of the change in the modulation degree. A stable tracking error signal that is not affected by relative positional deviation can be obtained.

[Brief explanation of the drawing]

Figures 1A and B are diagrams for explaining the push-pull type original +111, Figure 2 is a diagram showing the configuration of its typical optical system, and Figure 3 is a diagram showing the configuration of the signal processing circuit as well. Figures 4A, B, and G are diagrams for explaining Ike's signal processing method; Figure 5 is a diagram showing a circuit configuration for implementing the signal processing method; FIG. 7 is a diagram showing the second $ i'fT4 example. 11... Semiconductor laser 12... Collimator lens 13... Half mirror 14... Objective lens 15...
・Disk 16...Bit 17...Photodetector 1
8a, 18b...', no light area 25.27.34
... Amplitude detection circuit 26.28 ... Average value detection circuit 29.80.37 ... Subtractor 38.89 ... Kato device 85 ... Peak value detection circuit 86 ... Analog divider 38 ... Analog multiplication u 40.4] ... Amplifier 42 ... Switching circuit 43 ... Attenuator, 4
4... Comparator. Patent Applicant Olympus Optical Industry Co., Ltd. No. 1) Figure 3 Figure 3 Procedural Amendment Document April 1981 181 1. Indication of the case Showa 5! J year special ・+7. Application No. 278 2, Name of the invention Drugging error detection device 3, Person making the correction '11a'] Relationship between Participant, N Applicant (0371'1 Linbus Optics - E-gyo 44, Expression company representative 1) "1 (Shi Sugi t" Akatsuki Ra (1, 1,...)
,. 1 other person 1'-

Claims (1)

[Claims] L Light emitted from a light source? j: 11y, bundle and irradiate the tracks on which information is recorded onto the recording medium,
The reflected light is received by a SoC detector arranged in a 7-foot field and has a light-receiving area divided in a direction perpendicular to the direction of the 1111 track, and the difference in the amplitude of the output ID number of both light-receiving areas is calculated and averaged. In a device that detects tracking errors one by one based on the sum of the difference between fi&, the J width of the output signal of both the front d1 light receiving areas is determined based on the modulation IW of the sum of the output signals of both the front d1 light receiving areas. JJ
II Means for changing the ratio to be calculated 'Ir: To provide (
Tracking error detection device Wa'