JPS61148636A - Tracking servo circuit of optical disc player - Google Patents

Abstract

PURPOSE:To perform a stable tracking servo for a disc in which a signal that contains low frequency component is recorded or a disc with many damages by eliminating the time difference (phase difference) of the detection signal obtained based on the distant beam spot. CONSTITUTION:The detection signal PE obtained based on the preceding spot S11 is supplied to an operational amplifier 32 via a delay circuit 31. In consequence, the time difference between the signal PE and the signal PF is made almost zero. Therefore, any component of the signal recorded in the disc is not superposed on the tracking-error signal TE outputted from the operational amplifier 32. In consequence, for cases of reproducing from the video disc with digital sound signal that includes low frequency component that extends to the frequency band of the tracking servo itself, or from the disc damaged in many places, a stable tracking servo can be performed without malfunction.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a tracking servo circuit for an optical disc player, particularly when a low frequency component signal that extends to the tracking servo frequency band is recorded on an optical disc. , or what is effective when the optical disc has many scratches.

[Conventional technology]

2. Description of the Related Art Conventionally, optical discs (hereinafter simply referred to as discs) on which video signals, audio signals, etc. are recorded as spiral pit rows are generally known. In order to reproduce signals recorded on this disc, for example, a video disc, a dedicated disc player is required, and the disc player is equipped with an optical pickup device configured as shown in FIG. 5, for example. That is, the laser beam output from the laser diode 1 is converted into three laser beams (0-order light, +1
After being split into second-order light and -first-order light, the light reaches a collimator lens 4 via a polarizing beam splitter 3. Among the three laser beams, the +1st-order light is used for tracking servo, and the 0th-order light is used for focus servo and detection of signals recorded on the disk 20. The three laser beams are collimated into parallel beams by a collimator lens 4, have their phases changed by 90° by a K wavelength plate 5, and then are irradiated onto a disk 20 via an objective lens 6.

By irradiating the disk 20 with the three laser beams, three spots 811 (+1st order light) and 812 are formed on the surface of the disk 20, as shown in FIG.
(0th order light) and 518 (1st order light) are respectively imaged.

Each of the spots 811 and Sta is the spot S12.
Pit rows 21, 21 . ... are spaced apart from each other by a distance l (so-called beam spacing) in the longitudinal direction of the track, and at a distance W corresponding to the width Wj of the track in the radial direction of the disk 20. That is, spot S12
is pit row 21.21. When located at the center of a track consisting of..., spot 811 and spot Seg are positioned so as to cover approximately the right half and approximately the left half of the track, respectively. Note that the spot S11 is located on the pit rows 21, 21 . For ..., spot 5i11
shall take precedence over.

The light based on the three laser beams reflected on the surface of the disk 20 passes through the objective lens 6, the % wavelength plate 5, and the collimator lens 4 again, and reaches the polarizing beam splitter 3. This light passes through the wavelength plate 5 twice,
Since the phase is 180° different from that of the original laser beam, it is deflected at right angles by the polarizing beam splitter 3 and is incident on the photodiode 10 via the concave lens 7 and the cylindrical lens 8.

formed by light reflected on the surface of the disk 20,
As shown in FIG. 7, each of the spots 821, S22, and Sza corresponding to the above-mentioned spots Stt, Stz, and Sta is a light-receiving area 11 provided on the light-receiving surface of the photodiode 10. A set of four light-receiving areas 12゜13
．． 14, 15, and the light receiving area 16, respectively. The spot 822 is used for focus servo and detection of signals recorded on the disk 20.

The spot S22 has a perfect circular shape as shown in the figure if the spot Su on the disk 20 is in focus, but if the spot S22 is out of focus, the light receiving area 12
．． It changes into an elliptical shape with the longer axis direction being in the 14th direction or the 13th and 15th directions of the light receiving area. Focus servo is performed based on this, and the light receiving area is 12°13.14
．． The detection signal obtained in step 15 was detected by two people, PnyP
c, Pa, a signal (PA0Pc)-(FB0PD) is formed, and focus control is performed so that this signal becomes zero.

Further, the detection of the signals recorded on the disk 20 is performed by forming the following signals: Ph, PB, PC+PD.

The spot 841 and the spot Sza are used for tracking servo, and detect the detection signal P obtained in the light receiving area 11 and the detection signal P obtained in the light receiving area 16.
The difference signal PE -PF of F is the tracking error signal TE
The tracking control is performed by, for example, moving the entire optical pickup device so that the tracking error signal TE becomes zero.

This causes the spot 8 to be imaged on the surface of the disk 20.
12 follows a track consisting of pit rows 21, 21, . . . and is always located at the center of the track.

[Problems to be Solved by the Invention] In the optical pickup device of the optical video disc player described above, the spots So and S1m on the disc 20 corresponding to the spots 821 + Sza used for the tracking servo, respectively, are the sixth spots. As shown in the figure, they are arranged at a distance l.Therefore, strictly speaking, the detection signal PE obtained in the light receiving area 11 of the photodiode 10 and the detection signal PE obtained in the light receiving area 16 If the linear velocity of the trunk during reading is V, then a time difference t (phase difference) corresponding to 1/V has occurred in the detection signal PF, and the tracking error signal TE is different from the original error signal on the disc. However, the frequency band that can be tracked by the tracking servo circuit is usually several kHz or less, and conventionally, optical video discs do not have frequency modulation ( The frequency band occupied by the recorded video and audio signals (FM) is approximately 2MHz~
Since the signal was as high as 14■i, this signal had almost no adverse effect on the tracking servo.

However, in recent years, optical video discs that additionally record digital audio signals in an empty frequency band of about 2 h or less have become commercially available, and when playing back these discs, the error signals are superimposed on the original error signals. Since the frequency component of the digital audio signal falls within the frequency band of the tracking servo, the tracking servo may malfunction and become unstable. For example, as shown in FIG. 8, the time difference t that occurs between the detection signal PE obtained at the light receiving area 11 of the photodiode and the detection signal PF obtained at the light receiving area 16 is the time difference t that occurs when the digital audio signal included in the signal PE is detected. and the component DF of the digital audio signal included in the signal PF.
In cases where a phase difference of 80°) is caused,
Since the amplitude of the digital audio signal component -DF included in the tracking error signal TF, which is a difference signal, is doubled, the drive amplifier of the tracking servo circuit becomes saturated, and the servo becomes unstable. It becomes something.

Furthermore, when playing back a disc with many scratches, the tracking servo may become unstable for the same reason.

The present invention has been proposed in view of the above-mentioned conventional problems, and is applicable to optical discs on which signals having low frequency components that extend into the frequency band of the tracking servo are recorded. An object of the present invention is to provide a tracking servo circuit for an optical disc player that can perform stable tracking servo even when the disc player has many scratches.

[Means for solving problems]

In order to achieve the above-mentioned object, a tracking servo circuit for an optical disc player according to the present invention is arranged at a distance j in the longitudinal direction of a recording track on an optical disc and is arranged at a distance j in the radial direction of the optical disc. light receiving means for detecting reflected light from the optical disk based on at least two beam spots arranged at a distance W corresponding to the width of the recording trunk; A signal that delays the detection signal obtained by the light receiving means based on the leading one of the two relatively moving beam spots by a delay time corresponding to the distance l between the two beam spots. and a difference signal forming means for forming a difference signal between the output signal from the signal delay means and the detection signal obtained by the light receiving means based on the other beam spot, the difference signal forming means The feature is that the tracking servo is performed based on the difference signal from the .

[Effect]

According to the present invention, the detection signal obtained by the light receiving means based on one of the preceding beam spots among at least two beam spots arranged on the optical disk is determined based on the distance between the two beam spots. The signal is delayed by a signal delaying means by a delay time corresponding to l, and a difference signal between this delayed signal and a detection signal obtained by the light receiving means based on the other beam spot is formed by a difference signal forming means.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a tracking servo circuit for an optical disc player according to the present invention will be described in detail below with reference to the drawings. In this embodiment, the present invention is applied to a tracking servo circuit for an optical video disc player. Regarding the optical pickup device of this optical video disc player, the above-mentioned FIGS.
The configuration is assumed to be similar to that shown in the figure, and description thereof will be omitted.

FIG. 1 is a block diagram showing the tracking servo circuit of this embodiment. In FIG. 1, a detection signal PE based on a preceding spot Sll obtained in a light receiving area 11 of a photodiode 10 as a light receiving means is transmitted to a delay circuit 3.
1 to a non-inverting input terminal of an operational amplifier 32 as a difference signal forming means, and a detection signal PF based on the spot Sla obtained in the light receiving area 16 is supplied to the inverting input terminal of the operational amplifier 32. The operational amplifier 32 forms and outputs a difference signal PE-Pp, that is, a tracking error signal TE. Based on this tracking error signal TE, tracking servo is performed to move the entire optical pink amplifier device, for example.

The delay time of the delay circuit 31 is the time difference t occurring between the detection signal PE and the detection signal Pv, that is, the above-mentioned #/V
(ratio of distance l between spot 811 and Sxa to scarlet speed V of the track being read). Note that when playing back a disc with constant linear velocity (CLV), the above delay time may be constant; however, when playing a disc with constant linear velocity (CLV),
When playing back an AV disc, it is desirable to automatically change the delay time between the outer and inner peripheries of the disc based on the position information obtained by the optical pink amplifier device. However, in reality, there is no practical problem even if the delay time is fixed in accordance with the innermost circumference of the disk where the linear velocity is the slowest.

In this way, the delay circuit 31 is provided and the preceding spot S
The detection signal PK obtained based on the delay circuit 31
By supplying the tracking error signal TE to the operational amplifier 32 via the operational amplifier 32, the time difference between the signal PE and the signal PF is almost eliminated, and the component of the signal recorded on the disk is superimposed on the tracking error signal TE output from the operational amplifier 32. There is no such thing. Therefore, even when playing a digital audio video disc that has low frequency components that extend into the tracking servo frequency band, or a disc that has many scratches, it is possible to perform stable tracking servo without malfunction. can.

For example, a phase shift filter as shown in FIG. 2 may be used as the delay circuit 31. This phase shift filter is 2
This is an all-pass filter using two operational amplifiers 41 and 42, and the output terminal of the operational amplifier 41 is connected to the non-inverting input terminal of the operational amplifier 42. Further, the input signal is supplied to the inverting input terminal of the operational amplifier 41 through a series circuit of a resistor 43 and a capacitor 44, and the connection point between the resistor 43 and the capacitor 44 and the operational amplifier A capacitor 45 is connected between the output terminal of 41 and the output terminal of 41. Furthermore, a resistor 46 is connected between the inverting input terminal and the output terminal of the operational amplifier 41.

That is, this filter is a second-order filter having capacitors 44 and 45, and can obtain a delay time of, for example, about 3.6 μm.

Additionally, since the frequency component of the signal recorded on the disk that is superimposed on the original error signal generally exists above the frequency band of the tracking servo, it is effective to simply delay only the high frequency band of the signal. There are many things. Therefore, as the delay circuit 31, for example, a low-pass filter consisting of a resistor 51 and a capacitor 52 as shown in FIG. 3, or an operational amplifier 61 as shown in FIG.
Resistance 62. An integral filter circuit comprising a parallel circuit of a capacitor 63 and a resistor 64 connected between the inverting input terminal and the output terminal of the operational amplifier 61 may also be used.

Note that the present invention is not limited to optical video discs, but can be widely applied to tracking servo circuits of optical disc players such as compact discs. It is also assumed that the focus on the disc includes bumps that are convex parts when viewed from the reading side. Furthermore, the recording track may be one in which signals are recorded based on differences in reflectance, polarization angle, etc.

〔Effect of the invention〕

As is clear from the description of the embodiments described above, in the tracking servo circuit for an optical TiSF player according to the present invention, of at least two beam spots disposed on the optical disk and used for tracking servo, the leading The detection signal obtained by the light receiving means based on one beam spot is delayed by the signal delay means by a delay time corresponding to the distance l between the two beam spots, and is supplied to the difference signal forming means, Difference signal (tracking error signal) with the detection signal obtained based on the spot
We are trying to form a Therefore, the time difference (phase difference) between the detection signal obtained based on one beam spot and the detection signal obtained based on the other beam spot is almost eliminated, and the difference signal is recorded on the optical disk. No signal components are superimposed. Therefore, according to the present invention, an optical disc to be reproduced has a signal having a low frequency component that extends within the frequency band of the tracking servo recorded thereon.
Alternatively, even if there are many scratches, stable tracking servo can be performed.

[Brief explanation of drawings]

Figure K1 is a block diagram showing an example of the tracking servo circuit of an optical Tisp player according to the present invention, Figure 2 is a circuit diagram showing an example of the delay circuit in the above embodiment, and Figure 3 is another example. FIG. 4 is a circuit diagram showing still another example. FIG. 5 is a configuration diagram schematically showing an example of an optical pickup device for an optical disc player that has been commonly used in the past, and FIG. 6 is an enlarged plane showing the arrangement position of the spot imaged on the optical disc. 7 is an enlarged plan view showing the light receiving area provided on the light receiving surface of the photodiode, and FIG. 8 is a waveform diagram showing an example of a signal superimposed on the original error signal. 10... Photodiode, 11. 16... Light receiving area 520... Disk, 21, 21. ... city pit row, 31 ... delay circuit, 32 ... operational amplifier, 81
1+8111...spot

Claims (1)

[Claims] At least two discs arranged at a distance l in the longitudinal direction of the recording track on the optical disc and arranged at a distance w in the radial direction of the optical disc according to the width of the recording track.
a light receiving means for detecting reflected light from the optical disc based on two beam spots;
a signal delay means for delaying a detection signal obtained by the light receiving means based on one of the two beam spots that precedes the beam spot by a delay time corresponding to a distance l between the two beam spots; a difference signal forming means for forming a difference signal between an output signal from the means and a detection signal obtained by the light receiving means based on the other beam spot; A tracking servo circuit for an optical disc player, characterized in that it performs tracking servo.