JP2878416B2 - Tracking error signal generator for optical disc player - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a tracking error signal generating device for an optical disc player.

2. Description of the Related Art In an optical disk player that plays a disk-shaped recording medium (hereinafter, simply referred to as a disk) such as a video disk or a digital audio disk, an optical spot for reading information of a pickup has a recording track regardless of the eccentricity of the disk. A tracking servo device for controlling so as to always accurately track is indispensable.

This tracking servo device generates a tracking error signal corresponding to the amount of deviation of the information reading light spot with respect to the recording track of the disk in the disk radial direction, and provides a tracking actuator for biasing the information reading light spot in the disk radial direction. Performing position control of the information reading light spot with respect to the recording track by driving according to the tracking error signal,
This is a so-called closed servo control system.

Further, in such a servo device, at the time of a so-called jump operation in which the information reading light spot jumps over the recording track, the servo loop is opened (opened), and an acceleration signal having a polarity corresponding to the jump direction is supplied to the tracking actuator. At the time of zero crossing of the tracking error signal level during operation, a deceleration signal of the opposite polarity to the acceleration signal is supplied to the actuator for a certain period of time to apply a certain braking force, then the servo loop is closed (closed) and the servo is closed. Is controlled (see Japanese Patent Application Laid-Open No. 2-79228).

As a method of generating a tracking error signal, a three-beam method, a push-pull method, a time difference detection method, and the like are known.
Among these generation methods, the time difference detection method is disclosed in Japanese Patent Application Laid-Open No. 57-18143.
As is apparent from the description of Japanese Patent Publication No. 3 (1993), as a light receiving means for receiving the reflected light beam from the disk, a so-called four-split photodetector composed of four photoelectric conversion elements arranged so that the light-receiving surface is split into four is used. Used. Assuming that the output signals of the quadrant photodetector are Sa, Sb, Sc, and Sd, the sum total of the output signals Sa + S
b + Sc + Sd is used for signal reproduction as a read RF signal. Sum signals Sa + Sc and Sb + Sd of the output signals from the photoelectric conversion elements having a diagonal relationship with respect to the intersection of the two division lines on the light receiving surface are obtained by an adder, and the order of the two diagonal sum signals Sa + Sc, Sb + Sd is further obtained. A phase difference is determined. The amount of this phase difference corresponds to the amount of tracking deviation,
Whether the phase difference is advanced or delayed corresponds to the direction of tracking deviation. That is, of the phase difference between the outputs of the photoelectric conversion elements, a phase change component that changes according to the amount of deviation of the information reading light spot with respect to the recording track in the disk radial direction is detected and derived as a tracking error signal. Things.

Thus, two diagonal sum signals are used to detect the phase difference.
Sa + Sc and Sb + Sd are separately supplied to a phase comparator via limiters as waveform shaping means, and a tracking error signal is obtained from a phase difference output of the phase comparator. The limiter sets a limiter level to obtain a zero cross point of the diagonal sum signals Sa + Sc and Sb + Sd. In order to determine the limiter level, an AC coupling capacitor is inserted at the output of each of the adders to cut off the DC component of the read RF signal.

By the way, in a video disk such as an LD (laser disk), a read RF signal contains an FM audio component in addition to a video signal, and may further contain an EFM audio signal component. Also reads RF signals containing low frequency components. FIG. 4A shows the format of a recording signal in the case of a video disk of the NTSC system. When recording each of the above-mentioned signals on the disk, the waveform is shaped by a limiter and recorded. This is shown in FIG. 4 (B). When the frequency characteristics of the recording system and the reproduction system are sufficiently high, an RF signal having a spectrum shown in FIG. 4B (shown in FIG. 4D)
Is input to the limiter, but in the actual case, for example, CLV
Due to the influence of the MTF of the optical system such as the inner circumference of the disc or CAV disc, the high-frequency component is removed due to the low-pass characteristic shown by the broken line LP in FIG. 4C. Therefore, an RF signal (shown in FIG. 4 (E)) having a spectrum as shown by a solid line in FIG. 4 (C) is obtained. As a result, the limiter level of the limiter is no longer based on the original zero-cross point of the diagonal sum signals Sa + Sc and Sb + Sd, and an appropriate tracking error signal cannot be obtained because a large amount of the EFM audio signal leaks into the tracking error signal. There was a problem.

SUMMARY OF THE INVENTION [Object of the Invention] Accordingly, an object of the present invention is to provide a tracking error signal generation device for an optical disc player that can obtain a correct tracking error signal for any disc.

[Constitution of the Invention] A tracking error signal generating apparatus for an optical disc player according to the present invention comprises an objective lens for converging an irradiation light beam on an information recording surface of a disc-shaped recording medium and reflection from the information recording surface via the objective lens. A light detector for receiving the light beam, and the light detector further divides the two regions divided into two along the tangential direction of the recording track into two along the track orthogonal direction, thereby dividing the light receiving surface into four parts A tracking error signal generating apparatus for an optical disc player having a pickup composed of four photoelectric conversion elements arranged in such a manner that the output signals of the four photoelectric conversion elements have a diagonal relationship with each other. Means for adding each of them and removing each of the DC components by an AC coupling element and outputting each of them, and individually passing a predetermined high frequency component of each output signal of the adding means. Filter means for shaping, first waveform shaping means for individually shaping each output signal of the filter means, second waveform shaping means for individually shaping each output signal of the adding means, and a disc set in the player. Determining means for determining whether or not a video signal is recorded; and relaying each output signal of the first waveform shaping means when the determining means determines that the video signal is recorded, wherein no video signal is recorded. Switching means for relaying each output signal of the second waveform shaping means when the discriminating means discriminates, and phase comparing means for detecting a phase difference between the respective relay output signals by the switching means and outputting it as a tracking error signal. It is characterized by.

[Operation of the Invention] In the tracking error generating apparatus of the present invention, when a video disc is set, a tracking error signal is obtained by a time difference detection method with respect to a read RF signal of only a video signal component that has passed through an HPF. When a disc such as a CD other than a video disc is set, the read RF
The tracking error signal is obtained by the time difference detection method using the signal as it is. Therefore, a correct tracking error signal can be obtained for any disk.

Embodiment Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view showing an example of the configuration of a pickup P used in an optical disc player having a tracking error generating device according to the present invention. In the pickup P, a laser light source 2 that emits a laser light beam, a mirror 3 that reflects the laser light beam in the direction of the disk D, and an incident light beam converge on the information recording surface of the disk D inside the body 1. An objective lens 4 to be driven and a photodetector 5 for receiving a reflected light beam from the disk D passing through the objective lens 4 are housed, and are driven by a tracking actuator (not shown).
The body 1 including the objective lens 4 and the photodetector 5 is configured to be integrally movable in the disk radial direction (direction). The body 1 is integrally movable in the optical axis direction by a focus actuator (not shown). The specific configuration of the pickup P is described in detail in Japanese Patent Application No. 2-135726 filed by the present applicant.

Next, an example of the configuration of the tracking error generation device according to the present invention will be described with reference to FIG. The disc player provided with the tracking error generating device is a so-called compatible player capable of playing LD, LDD, CDV and CD. The compatible player itself is disclosed in, for example, JP-A-61-73274.

First, the built-in optical detector 5 to the pickup P is, as apparent from the figure, arranged as the light receiving surface is divided into four by division lines L ₂ perpendicular to the dividing line L ₁ and which along the track tangential direction A four-divided photodetector comprising four photoelectric conversion elements 5a to 5d, arranged so that the center 0 of the light receiving surface coincides with the optical axis of the light beam reflected from the disk D when the tracking state is proper. ing. Of these four photoelectric conversion elements 5a to 5d, the photoelectric conversion elements arranged diagonally
The outputs Sa, Sc of 5a, 5c and the outputs Sb, Sd of the photoelectric conversion elements 5b, 5d are added by adders 6 and 7, respectively.

HPFs (high-pass filters) 10, 11 and zero-cross comparators 12, 13 are connected to the added outputs (Sa + Sc), (Sb + Sd) of the adders 6, 7, respectively. The output signals of the HPFs 10 and 11 are supplied to limiters (LIMs) 16 and 17 via amplifiers 14 and 15. The outputs of the zero cross comparator 12 and the limiter 16 are connected to a changeover switch 18. The changeover switch 18 selectively outputs one of the output signals of the zero-cross comparator 12 and the limiter 16 according to the changeover signal. Similarly, the outputs of the zero cross comparator 13 and the limiter 17 are connected to a changeover switch 19. These changeover switches
18 and 19 are linked. Selector switch 18
And 19 are supplied to a phase comparator (PC) 20. The phase comparator 20 is configured to output a voltage having a magnitude proportional to the phase difference between the two inputs. The phase difference output of the phase comparator 20 is derived as a tracking error signal via an LPF (low-pass filter) 21.

The switching signal is output from the disc determination circuit 22. The disc discriminating circuit 22 is, for example, the diameter of the disc D set on the turntable of the player, or the TOC of the disc D.
Disk D set from (Table of Contents) is L
It discriminates between D (including the LDD and the video section of the CDV) and CD (including the audio section of the CDV), and generates a switching signal of a level according to the discrimination result.

In addition, the sum total output of each output of the photoelectric conversion elements 5a to 5d (Sa +
Sb + Sc + Sd) is taken by the adders 8, 9 and 23 and is derived as a read RF signal for reproduction. Although not shown, AC coupling capacitors are inserted into the outputs of the adders 6 and 7, respectively. However, this AC coupling capacitor may be inserted into each output of the photoelectric conversion elements 5a to 5d.

In this configuration, when the disc discrimination circuit 22 determines that the disc D set on the turntable is an LD, the changeover switches 18 and 19 compare the phases of the output signals of the limiters 16 and 17 according to the changeover signal. Relay output to the device 20. That is, in the case of LD, the HPF 10 extracts only the high frequency component, which is the video signal component in the output signal (Sa + Sc) of the adder 6. Thereby, the FM audio signal component and the EFM audio signal component in the read RF signal are deleted. The output signal of the HPF 10 is amplified by the amplifier 14 and supplied to the limiter 16. The limiter 16 shapes the output signal of the amplifier 14 to a signal in the range of ± Vs [V] with ± Vs [V] as the limiter level around the zero cross point. The signal (Sa + Sc) thus processed is supplied to the phase comparator 20. Similarly, the output signal of the adder 7 (Sb + S
d) is also supplied to the phase comparator 20 via the HPF 11, the amplifier 15, the limiter 17, and the switch 19.

On the other hand, the disc D set on the turntable is CD
In the case where the discrimination circuit 22 determines that this is the case, the changeover switches 18 and 19 relay the output signals of the zero-cross comparators 12 and 13 to the phase comparator 20 in accordance with the switching signal. In this case, the output signal of the adder 6 (Sa + Sc)
Is an EFM audio signal component, and the output signal (Sa + Sc) is shaped by the zero cross comparator 12 into a square wave signal whose level is inverted with the zero cross point as a comparison reference level. The signal (Sa + Sc) thus processed is supplied to the phase comparator 20. Similarly, the output signal (Sb
+ Sd) is also a phase comparator via the zero-cross comparator 13.
Supplied to 20.

When the signal (Sa + Sc) is ahead of the signal (Sb + Sd) in phase, the signal ac supplied via the switch 18 and the signal bd supplied via the switch 19 are shown in FIG. Assuming such a waveform, the phase comparator 20 outputs a positive pulse signal as shown by PC in FIG. 3 (A). If the signal (Sa + Sc) is ahead of the signal (Sb + Sd), the signal supplied via the switch 18
Assuming that ac and the signal bd supplied through the switch 19 have waveforms as shown in FIG.
Outputs a pulse signal of negative polarity as shown by PC in FIG. 3 (B).

The output signal from the phase comparator 20 becomes a tracking error signal via the LPF 21. The polarity and level of the tracking error signal indicate the direction and amount of deviation of the information reading beam spot with respect to the recording track of the disk D in the disk radial direction. This tracking error signal is supplied to a tracking actuator (not shown).

In the above-described embodiment, the zero-cross comparators 12 and 13 and the limiters 16 and 17 are provided as waveform shaping means, respectively.However, the zero-cross comparators 12 and 13 are not provided, and the limiters 16 and 17 are switched to the switches 18 and 19. And the phase comparator 20.

Further, in the above-described embodiment, a straight line is used as the dividing line of the photodetector. However, the present invention is not limited to this. For example, as described in Japanese Patent Application Laid-Open No. Alternatively, the photodetector may be divided by a curve projected on the photodetector through an objective lens and an optical component for generating astigmatism for focusing, with a straight line parallel or orthogonal to the track.

As described above, in the tracking error signal generation device according to the present invention, the output signals of the four photoelectric conversion elements of the photodetector of the pickup which are in a diagonal relationship are added, and the video disk ( (Including the video section of CDV)
When it is determined that a disc is set, each high-frequency component is passed through the HPF through the HPF and supplied to the waveform shaping means.On the other hand, when it is determined that a disc other than a video disc is set, each sum output signal is output. The signal is supplied as it is to the waveform shaping means, and the phase difference between the output signals of the waveform shaping means is detected by the phase comparing means and output as a tracking error signal.
That is, when a video disc is set, a tracking error signal is obtained by a time difference detection method with respect to a read RF signal of only a video signal component that has passed through the HPF.
When a disc such as a CD other than a video disc is set, the read RF signal is used as it is, and a tracking error signal is obtained by a time difference detection method. Therefore, a correct tracking error signal can be obtained for any disk.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of the configuration of a pickup used in an optical disc player provided with the apparatus of the present invention.
2 is a block diagram showing an embodiment of the present invention, FIG. 3 is a waveform diagram showing the operation of the phase comparator in the apparatus of FIG. 2, and FIG. 4 is a read RF signal and a read RF after AC coupling. FIG. 4 is a waveform chart showing signals. Explanation of Signs of Main Parts P ... Pickup D ... Disk 2 ... Laser Light Source 4 ... Objective Lens 5 ... Photodetector 10,11 ... HPF 16,17 ... Limiter 20 ... Phase Comparator

Continued on the front page (72) Inventor Nobuko Kobitsu 4-2610 Hanazono, Tokorozawa-shi, Saitama Pref. Pioneer Co., Ltd. Tokorozawa Plant (58) Field surveyed (Int. Cl. ⁶ , DB name) G11B 7/09-7 / 095

Claims (1)

(57) [Claims] An object lens for converging an irradiation light beam on an information recording surface of a disk-shaped recording medium, and a photodetector for receiving a reflected light beam from the information recording surface passing through the objective lens, The photodetector further divides the two areas divided into two along the tangential direction of the recording track into two along the orthogonal direction of the track, so that the light receiving surface is divided into four parts. A tracking error signal generating apparatus for an optical disc player having a pickup comprising: a sum of output signals of diagonal relations among the four photoelectric conversion elements; and a DC component by an AC coupling element. Adding means for removing each of the signals, filtering means for individually passing a predetermined high frequency component of each output signal of the adding means, and each output signal of the filtering means. First waveform shaping means for individually shaping waveforms, second waveform shaping means for individually shaping each output signal of the adding means, and whether or not a video signal is recorded on a disc set in the player Determining means for determining whether a video signal has been recorded, and relaying each output signal of the first waveform shaping means when the determining means determines that a video signal has been recorded, and determining that the video signal has not been recorded. A switching means for relaying each output signal of the second waveform shaping means; and a phase comparing means for detecting a phase difference between the relay output signals by the switching means and outputting it as a tracking error signal. Tracking error signal generation device.