JPS59223945A - Track error detector of optical disc - Google Patents

Abstract

PURPOSE:To detect a track error signal where an offset component is eliminated by forming a projecting part and recessed part alternately in the lengthwise direction of track and obtaining a difference signal between the first and the second track error signals obtained from the reflected light. CONSTITUTION:The projecting parts 11a and recessed parts 11b are formed alternately in the lengthwise direction on each track, and pits P are formed on these parts. The detecting elements of a two-divided detector 14 are provided in accordance with the breadthwise direction of the track. The difference signal of the output of a differential amplifier 15 is the track error signal, and this signal has an opposite polarity to the deviation direction as shown in Fig. (a) and (b). A changeover switch 16 switches the signals from the projecting parts and recessed parts. Both signals are sample-held, and the difference between signals shown in Fig. (a) and (b) is outputted as the final track error signal from a differential amplifier 22. Since the offset is shown by broken lines in Fig. (a) and (b), the offset components are cancelled in said output. Signal levels are maximum and have opposite polarities because of the reflected light from the projecting parts and recessed parts having the height and the depth of + or -lambda/8, and therefore, the S/N ratio is high.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a track error detection device for an optical disc, which focuses a light beam from a light source onto an optical disc and detects a track error signal from the reflected light. .

[Technical Background of the Invention and Problems Therewith] As a conventional track error detection device of this type, there is a so-called push-pull type track error detection device. This type of device receives the reflected light from the optical disc with a two-split detector installed in the far field of the optical system, and uses a differential amplifier to obtain the difference between the output signals of each detection element of the two-split detector. It detects signals.

This type of apparatus has the advantage of simplifying the configuration of the optical system since it is possible to obtain a track error signal with a single light beam, but it has the following problems.

That is, when the disk 1 is tilted by θ as shown in FIG. , 2fθ occurs,
One turn of light reception on the detector 4 is shifted.

Furthermore, as shown in FIG. 1(b), when the objective lens 2 deviates by d during tracking, the two-part detector 4
A positional shift of 2d occurs in the reflected light from the disk 1 that is incident on the disc 1, resulting in a shift of the light reception pattern as in the case of (&). If the light receiving pattern on the detector 4 is shifted in this way, a track error signal with a different amplitude should be obtained from the track output from the differential amplifier 5, whereas the light receiving pattern is shifted. Humiliation′
As a result, the amplitudes in the positive and negative directions become different, as shown in FIG. For this reason, the tracking control is carried out properly, which has a disadvantage.[Object of the Invention] The object of the present invention is to receive the reflected light from the optical disc with a two-split detector installed in the far field of the optical system. By obtaining a track error signal from the difference signal, it is possible to obtain an accurate track error signal that is not affected by shifts in the light receiving pattern due to the tilt of the optical disk or the deviation of the objective lens. An object of the present invention is to provide a track error detection device for an optical disc that enables one racking control.

[Invention Fence Key]

In order to achieve the above object, the present invention is characterized by the following configuration. Specifically, convex portions and concave portions are alternately formed along the track longitudinal direction on the recording surface of the optical disc, and a $1 track error signal and a second track error signal are generated based on the reflected light from the convex portions and the four portions. A final track error signal from which an offset component has been removed is detected by detecting a track error signal and obtaining a difference signal between the first track error signal and the second track error signal. It is said that

[Embodiments of the invention]

3 is a diagram showing the overall configuration of an embodiment of the present invention, FIG. 4 is a partially enlarged perspective view showing the state of the recording surface of an optical disc, and FIG. ) and (b) are the first. FIG. 7 is a diagram showing a second track error signal.

In FIG. 3, reference numeral 1 indicates an optical disk, onto which a light beam from a light source (not shown) passes through a polarizing beam splitter 13 and is focused by an objective lens 12. There is. This optical disc 11
As shown in FIG. 4, each track TI, T2 is recorded on the recording surface of
. . . Convex portions 11a and convex portions 11b are alternately formed extending in the longitudinal direction of the track, and information recording pins (P) are formed on these convex portions and the four portions.

The pitch of the convex portion 11m and the fourth portion 11b is set so that the switching frequency thereof is lower than the frequency of the information recording pitch (P) and is in a frequency band that is worse than the servo band.

Further, the height and depth of the convex portion 11a and the concave portion 11b are ±λ/ based on m(0) from the surface of the optical disk 110.
8 (λ=wavelength of the light beam).

The reflected light from the optical disk 11 passes through an objective lens 12 and a polarizing beam splitter 13, and enters a two-split detector 14, where it is converted into an electrical signal. The two-split detector 14 connects a pair of detection elements 14m and 14b to the tracks TI and T.
It is installed in the far field of the optical system in correspondence with the width direction of z. Each detection signal output from each detection element 14&, 14b of the two-part detector 14 is
This becomes the differential input of the zero differential amplifier 15. Thus, the first differential amplifier 15 amplifies and outputs the difference signal between the output signals of the detection elements 14m and 14b. This is the track error signal. This track error signal is a first track error signal based on the reflected light from the convex portion 11a and a second track error signal based on the reflected light from the concave portion 11b, which are arranged in series in time. It has become. Above 1. As shown in FIGS. 5(a) and 5(b), the second track error signal has a signal polarity opposite to the direction of the track deviation. 1st. The second track error signal is transferred to the first track error signal, which will be described later, by the changeover switch 16. The signal is distributed and supplied to the second sampling and hold circuits xom and zobK, respectively.

The changeover switch 16 is controlled by a changeover control means 17. This switching control means detects the rotation angle of the optical disc 11, for example, by detecting an index mark provided in a non-recording area of the disc, using a sensor 18, and controls the switching of this detection signal 16. That is, during the period in which the first track error signal based on the light reflected from the convex portion 11a is obtained, the selector switch 16 is switched to the terminal 16a side, and the second track error signal based on the light reflected from the concave portion 11b is obtained. During this period, the selector switch 16 is switched to the terminal 16b side.

The first track error signal output from the differential amplifier 15 is thus supplied to the first sampling and hold circuit 20a via the terminal 16a side of the changeover switch 16.
The second track error signal output from the differential amplifier 15 is supplied to the second sampling and hold circuit 20b via the terminal 16b side of the changeover switch 16.

1st. Second sampling and holding circuit 20*, I!
Ob samples and holds each input signal.

The first sample was held. The second track error signals are each filtered through a low-pass filter 21m.
, 21b to the second differential amplifier 22.

As a result, the second differential amplifier 22 outputs a final track error signal obtained by subtracting the second track error signal shown in FIG. 5(b) from the first track error signal shown in FIG. 5(a). Output.

Incidentally, the offset due to the tilt of the optical disk 11 or the deviation of the objective lens is caused by the first . It is applied in the same direction as the second track error signal. Therefore, the output of the differential amplifier 22, which is the output of the difference between the two signals, provides only the track error signal in which the offset component has been canceled. Also number 1. Since the second track error signal is a signal obtained based on the reflected light from the convex portion 11a and the concave portion 11b whose height and depth are set to ±λ/8, the signal level is the maximum. Moreover, since it is designed to obtain the difference between signals of opposite polarity, the signal level becomes even greater. Therefore, it becomes a signal with a large S/N ratio. Thus, a track error signal containing an offset component and having a sufficiently large 8/N ratio is sent out from the output terminal 23 as the final track error signal. As a result, the optical disc 11 is controlled by the tracking control system (not shown).
Tracking control of optical pickup can be performed accurately.

Note that the present invention is not limited to the above-mentioned embodiment. For example, the convex portions and concave portions formed on the optical disk 110 may be formed as shown in FIG. 6. That is, in the case shown in FIG. 6, tracks TI, T2, etc. are continuously provided without providing a guard band between the tracks, and in the odd-numbered tracks TI, T8, T5... 33, 35... are provided intermittently at a constant pitch in the longitudinal direction of the tracks, and in the even-numbered tracks Tj, T(, T6t..., the recesses 32,
By providing 34, 36... with a phase difference of one pitch from the recesses in the odd-numbered tracks, the portion of each track where no recesses are not provided can be used as a relative protrusion with respect to the recesses. This is what I did. With this structure, the pitch in the track width direction is reduced to 1/2 compared to that of the above embodiment, so recording density can be improved, and there is no need to particularly form convex portions on the optical disk. This has the advantage that the optical disc can be operated easily.

Further, as shown in FIG. 7, each track TJ.

T2... is intermittently provided with unevenness formation@tang M, and a non-irregularity formation area N is interposed between the above-mentioned area steepness and M, and the above-mentioned area fi
A switching signal for controlling the changeover switch 16 may be obtained from the relationship between M and N. That is, for example, T of each track TI, T2, . . . formed as described above.
When a pick-up operation is performed using a beam spot B having a diameter larger than the track width for I, the sum signal of the output signals of each detection signature 14m and 14b in the optical detector 14 is divided into an area M as shown at 81 in FIG. In the case of the signal N, the signal level becomes different like Ll and L2. Therefore, if the frequency band containing the information signal component is cut by passing the signal S through a low-pass filter, the signal level shown in Fig. 8 is obtained. 8
Binary signals corresponding to regions M and N such as 2 are obtained.

By performing signal processing using the rising edges and falling edges of this binary signal, it is possible to obtain a cut suppression control pulse signal as shown at S3 in FIG. 8.

Furthermore, in the above embodiment, the height of the convex portion and the depth of the four portions were set to λ/8 with reference to O, but λ/4
It may be set to ±λ/8 with reference to . In short, it is sufficient to set it to ±λ/8 based on a ship that is an integral multiple of λ/4.

〔Effect of the invention〕

According to the present invention, in an apparatus in which reflected light from an optical disc is received by a two-split detector installed in the far field of an optical system and a track error signal is detected from the difference signal, a track error signal is detected on the recording surface of the optical disc in the longitudinal direction of the track. Convex portions and concave portions are provided alternately along the ridges, and the first. Second
Since the final track error signal is obtained by obtaining the difference between the track error signals of Accordingly, it is possible to provide a tracking error detection device for an optical disc that enables accurate tracking control.

[Brief explanation of the drawing]

Figures 1 (a) and (b) and Figures 2 (a) and (b) are diagrams for explaining the shortcomings of conventional tracking error detection means, and Figures 3 to 5 (a) and (b). 3 is a block diagram showing the overall configuration, FIG. 4 is a perspective view showing an enlarged state of the recording surface of an optical disk, and FIG. 5(a), ( b) is a diagram showing the first and second track error signals, FIG. 6 is a perspective view showing the main part of another embodiment of the present invention, and FIGS. 7 and 8 are still another embodiment of the present invention. FIG. 2 is a diagram for explaining an example of a middle-aged woman. 1.1... Optical disc, 11a... Convex portion, 11b
. . . concavity, 2.12 . . . objective lens, 3. Is...
・Polarizing beam splitter, 4.14... Two-split dip 2, 5.15... Differential amplifier, 16... Changeover switch, 17... Switching control system, 18... Sensor,
19... Switching signal generator, 20a, 20b... Sampling hold circuit, 21h, 21b°... Low pass filter, 22... Differential amplifier, P... Information recording pit, B... Beam spot , TI, T2...truck.

Claims (1)

[Claims] Convex portions and concave portions are formed alternately in the longitudinal direction of the recording track on the recording surface of an optical disk, and a light beam from a light source is focused and irradiated onto these convex portions and four portions to extract reflected light. an optical system, and a two-split detector installed in the far field of the optical system with a pair of detection elements corresponding to the width direction of the track so as to receive the reflected light extracted by the optical system and convert it into an electric signal. By obtaining the difference between the output signals from each detection element of this two-part detector, a first track error signal based on the light reflected from the convex portion and a second track error signal based on the light reflected from the four portions are obtained. a first differential amplifier for obtaining a track error signal; a means for individually extracting a first track error signal and a second track error signal output from the first differential amplifier; The eagle 2 sniffed out the first one. A track error detection device for an optical disc, comprising: a second differential amplifier that obtains a differential output of a second track error signal.