JP2957400B2 - Optical disk tracking error signal detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tracking error signal detecting device for an optical disk, and more particularly, to a tracking error signal detecting device using a heterodyne system.

[0002]

2. Description of the Related Art As an optical disc reproducing apparatus, there are a CD player (CD-ROM drive) and a video disc player. In this type of reproducing apparatus, a focus servo system and a tracking servo system are required to perform a reproducing operation favorably. The focus servo system is
The control is performed so that the light beam irradiated on the signal surface of the optical disk via the objective lens always falls within a predetermined depth of focus range following the surface deflection of the optical disk.

The tracking servo system controls the above-mentioned light beam so as to always follow a predetermined track accurately by following the eccentricity of the optical disk.
Various types of detection of a tracking error signal required for the tracking servo system, such as a three-beam system and a one-beam system, are conventionally known.

As one type of the one-beam system, there is a technology called a heterodyne system or a phase difference (time difference) system described in Japanese Patent Application Laid-Open No. 59-94249. This is a more effective means for tilting and warping of the optical disc than the push-pull method which is the same one-beam method.

FIG. 5 is a block diagram showing a conventional example of a tracking error signal detecting device using the heterodyne system. Hereinafter, description will be made with reference to this drawing.

A conventional tracking error signal detecting device is:
The reflected light 50 from the optical disk is received and the electric signals a,
Four light receiving elements 52a, 52b, which convert to b, c, d
52c, 52d, an analog reproduction signal output means 54 for synthesizing an analog reproduction signal B from the electric signals a,..., And a waveform shaping circuit 56 as a digital reproduction signal output means for converting the analog reproduction signal B into a digital reproduction signal C. , A heterodyne signal F from the electrical signals a,..., And a tracking error signal output unit 58 from the heterodyne signal F and the digital reproduction signal C to synthesize a tracking error signal I.

FIG. 6 is a waveform chart showing the operation of the conventional tracking error signal detecting device. Hereinafter, the operation of the tracking error signal detection device will be described with reference to FIGS.

[0008] The reflected light 50 from the optical disk is incident on substantially the center of the light receiving elements 52a,... The reflected light 50 is transmitted to the light receiving element 52a,
Are converted into electric signals a, b, c, and d, respectively. Then, the electric signals a and c output from the light receiving elements 52a and 52c on the diagonal line are added (a + c) by the adder 60, and the electric signals b and d output from the light receiving elements 52b and 52d are similarly added. At 62, the addition is performed (b + d). Further, the output signals of the adders 60 and 62 are added (a + b + c + d) by the adder 64 to extract the analog reproduced signal B. Further, the difference {(a + c) − (b + d)} between the output signals of the adders 60 and 62 is calculated by the adder 66 to extract the heterodyne signal F.

As shown in FIG. 6, an analog reproduction signal B and a heterodyne signal F are generated from the relationship between the pits P on the optical disk and the laser beam L applied to the pits P as shown in FIG. The analog reproduction signal B is supplied to a waveform shaping circuit 56.
Are converted into digital reproduction signals C, and the edge detection circuits 68 and 70 detect a rising edge signal D and a falling edge signal E. Hold circuit 7
In steps 2 and 74, the hold signals G and H are generated by holding the potential of the heterodyne signal F by the rising edge signal D and the falling edge signal E, and the difference between the hold signals G and H is generated by the differential amplifier 76. , A desired tracking error signal I is generated.

[0010]

FIG. 7 is a plan view showing the relationship between pits on an optical disk and a laser beam.
In the conventional tracking error signal detecting apparatus, FIG. 7 (J)
As shown in (1), when the data recording density of the optical disk is low, the size of the pit P1 has no problem compared to the laser beam L.

However, as shown in FIG. 7 ( K ), when the recording density is improved, the pit P2 recorded on the optical disk becomes smaller than the size of the laser beam L irradiated on the optical disk. . Therefore, the analog reproduction signal B and the heterodyne signal F cannot be correctly detected due to the interference between the pits P2 (hereinafter referred to as “intersymbol interference”). As a result, there is a problem that the reliability of the tracking error signal I is reduced.

[0012]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a tracking error signal detecting device for an optical disk, which has improved ability to detect a tracking error signal for a high recording density optical disk.

[0013]

SUMMARY OF THE INVENTION The present invention has been made to achieve the above object, and comprises a plurality of photosensitive elements for receiving reflected light from an optical disc and converting the reflected light into an electric signal.
Analog reproduction signal output means for synthesizing an analog reproduction signal from the electric signals output from the plurality of photosensitive elements; and a digital reproduction signal output for converting the analog reproduction signal output from the analog reproduction signal output means into a digital reproduction signal. Means, a heterodyne signal output means for synthesizing a heterodyne signal from the electric signals output from the plurality of photosensitive elements, a heterodyne signal output from the heterodyne signal output means, and a digital reproduction output from the digital reproduction signal output means. A tracking error signal detection device for an optical disk, comprising: a tracking error signal output unit that synthesizes a tracking error signal from a signal.

The improvement is that the analog reproduction signal output means is provided with a first waveform equalizing circuit for eliminating the attenuation and distortion of the analog reproduction signal, and the heterodyne signal output means is provided with the heterodyne signal output means. A second waveform equalizing circuit for eliminating attenuation and distortion is provided , and the first and second waveform equalizing circuits are provided .
The waveform equalization circuit 2 is composed of a transversal filter.
That is what we did .

[0015]

The light reflected from the optical disk is received by a plurality of photosensitive elements and converted into an electric signal. These electric signals are input to analog reproduction signal output means and are synthesized as analog reproduction signals, and are also input to heterodyne signal output means and are synthesized as heterodyne signals.
The analog reproduction signal is converted into a digital reproduction signal by digital reproduction signal output means. The digital reproduction signal and the heterodyne signal are input to a tracking error signal output unit, and are combined as a tracking error signal. At this time, in the analog reproduction signal output means, the attenuation and distortion of the analog reproduction signal are eliminated by the first waveform equalization circuit. In the heterodyne signal output means, the attenuation and distortion of the heterodyne signal are eliminated by the second waveform equalizing circuit.

[0016]

FIG. 1 is a block diagram showing an embodiment of a tracking error signal detecting device according to the present invention. Hereinafter, description will be made with reference to FIG. However, the same parts as those in FIGS. 5 and 6 are denoted by the same reference numerals, and description thereof will be omitted.

The tracking error signal detecting device according to the present invention comprises four photosensitive elements 52a and 52 for receiving reflected light 50 from an optical disk and converting the reflected light 50 into electric signals a, b, c and d.
, 52c, 52d, an analog reproduction signal output means 10 for synthesizing an analog reproduction signal B from the electric signals a,... output from the photosensitive elements 52a,. A waveform shaping circuit 56 as a digital reproduction signal output means for converting B into a digital reproduction signal C; a heterodyne signal output means 12 for synthesizing a heterodyne signal F from the electric signals a,... Output from the photosensitive elements 52a,. A tracking error signal output means 14 for synthesizing a tracking error signal I from the heterodyne signal F output from the heterodyne signal output means 12 and the digital reproduction signal C output from the waveform shaping circuit 56 is provided.

The analog reproduction signal output means 10 is provided with a waveform equalization circuit 16 for eliminating the attenuation and distortion of the analog reproduction signal B. The heterodyne signal output means 12 is provided with a waveform equalization circuit 18 for eliminating attenuation and distortion of the heterodyne signal F. The waveform equalizing circuits 16 and 18 have the same circuit configuration.

The analog reproduced signal B and the heterodyne signal F decrease in amplitude and cause distortion due to intersymbol interference in short pits (or between pits), so that they are input to the waveform equalizing circuits 16 and 18.

Since the waveform equalizing circuits 16 and 18 are for correcting intersymbol interference, a digital or analog transversal filter is used for this purpose, and several stages (3 to 15) are used as shown in FIG. Delay element 20 and coefficient unit 22
And an adder 24. Also transversal
The filter is based on the interval and size of the pits on the
The diameter of the light beam applied to the
Amplitude decay or distortion that changes with the speed of movement on the disk
Tap delay amount and tap coefficient can be selected according to
Wear.

The analog reproduction signal B corrected by the waveform equalization circuit 16 is binarized by a waveform shaping circuit 56 and converted into a digital reproduction signal C, and then the edge detection circuits 26 and 28
As a result, a rising edge signal D and a falling edge signal E are detected. The hold circuits 30 and 32 hold the potential of the heterodyne signal F corrected by the waveform equalization circuit 18 using the rising edge signal D and the falling edge signal E. A desired tracking error signal I is generated by calculating a difference between the two hold signals G and H generated by the hold circuits 30 and 32 by the differential image width circuit 76.

FIG. 3 is a circuit diagram showing the tracking error signal output means in this embodiment. Hereinafter, description will be made based on FIG.

The digital reproduction signal C is input to an edge detection circuit 26 for detecting a rising edge signal D and an edge detection circuit 28 for detecting a falling edge signal E. In the edge detection circuit 26, the digital reproduction signal C and
The rising edge signal D is detected by inputting the digital reproduction signal C delayed by the delay element 261 for a short time and then inverted by the inverter 262 to the AND gate 263. Further, in the edge detection circuit 28, after the digital reproduction signal C is inverted in advance by the inverter 280, the falling edge is thereafter passed through the delay element 281, the inverter 282, the logical product gate 283, and the like, similarly to the edge detection circuit 26. The signal E is detected.

The hold circuits 30 and 32 have the same configuration, and the heterodyne signal F whose waveform has been equalized is input to both of them. The hold circuits 30 and 32 include switch circuits 301 and 321 and capacitors 302 and 322, respectively.
And differential amplifiers 303 and 323. The switch circuits 301 and 321 are preferably semiconductor switches, and conduct only for a short time when the rising edge signal D or the falling edge signal E is detected. Capacitor 30
2, 322 are charged quickly during a short time while the switch circuits 301, 321 are conducting, and the heterodyne signal F
And the same potential as. Since the differential amplifiers 303 and 323 are configured as voltage followers, the input impedance is high. Therefore, when the switch circuits 301 and 321 conduct, the potentials of the capacitors 302 and 322 are maintained, and the outputs of the differential amplifiers 303 and 323 become equal to the potentials of the capacitors 302 and 322. Differential amplifier 3
The output signals 03 and 323 (hold signals G and H) are subtracted by the differential amplifier circuit 76 to generate a tracking error signal I.

FIG. 4 is a circuit diagram showing a tracking error signal output means in another embodiment of the tracking error signal detecting device according to the present invention. Hereinafter, description will be made with reference to FIG. However, the same parts as those in FIG. 1 or FIG.

In this example, A / D converters 40 and 42 and D / A converters 44 and 46 are used instead of the edge detection circuits 26 and 28 and the hold circuits 30 and 32 in FIG. 1 or FIG.
Is used. The A / D converters 40 and 42 take in analog data (heterodyne signal F) at the edge of the read clock signal (for example, digital reproduction signal C), so that edge detection and hold are possible. Therefore, the charge time and the discharge time are not affected by the capacitance values of the capacitors 302 and 322 in the analog hold circuits 30 and 32. In this example, the tracking error signal I is generated by converting the digitized signal into an analog signal. However, since the digital servo is performed today due to the improvement in DSP processing capability, the D / A converter 44 is not necessarily used. , 46 are not required. Therefore, since there is no influence of the charging / discharging time of the capacitors 302 and 322, the reliability of the tracking error signal I can be improved, and the connection with the digital servo DSP can be easily performed.

[0027]

According to the present invention, attenuation and distortion of the analog reproduced signal and the heterodyne signal can be eliminated by providing a waveform equalizing circuit in each of the analog reproduced signal output means and the heterodyne signal output means. Intersymbol interference can be reduced. Therefore, the ability to detect a tracking error signal with respect to an optical disk having a high recording density can be improved.

The tracking error signal output means A
When the / D converter is provided, since it is not affected by the charge / discharge time of the capacitor, the detection capability of the tracking error signal can be improved, and the DSP for digital servo can be improved.
Connection with the device can be facilitated.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention.

FIG. 2 is a block diagram of a waveform equalization circuit according to one embodiment of the present invention.

FIG. 3 is a circuit diagram showing a tracking error signal output means in one embodiment of the present invention.

FIG. 4 is a circuit diagram showing a tracking error signal output unit according to another embodiment of the present invention.

FIG. 5 is a block diagram showing a conventional example.

FIG. 6 is a timing chart showing the operation of the tracking error signal output device using the heterodyne method.

7A and 7B are plan views showing the relationship between pits and a laser beam on an optical disk; FIG. 7J shows a case where the recording density of the optical disk is low, and FIG. 7K shows a case where the recording density of the optical disk is high; Is shown.

[Explanation of symbols]

 Reference Signs List 10 analog reproduction signal output means 12 heterodyne signal output means 14 tracking error signal output means 16 first waveform equalization circuit 18 second waveform equalization circuit 50 reflected light 52a, 52b, 52c, 52d from optical disk photosensitive element 56 waveform Shaping circuit (digital playback signal output means)

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G11B 7/095

Claims (3)

(57) [Claims] 1. A plurality of photosensitive elements for receiving reflected light from an optical disc and converting them into electric signals, and an analog reproduction signal output means for synthesizing an analog reproduction signal from the electric signals output from the plurality of photosensitive elements. Digital reproduction signal output means for converting the analog reproduction signal output from the analog reproduction signal output means into a digital reproduction signal, and heterodyne signal output means for synthesizing a heterodyne signal from the electric signals output from the plurality of photosensitive elements. A tracking error signal output means for synthesizing a tracking error signal from the heterodyne signal output from the heterodyne signal output means and the digital reproduction signal output from the digital reproduction signal output means; In the apparatus, the analog reproduction signal output means The, of the optical disk
Intersymbol interference caused by pit spacing and size
A first waveform equalizing circuit that eliminates attenuation and distortion of the analog reproduction signal due to the following.
Intersymbol interference caused by pit spacing and size
A second waveform equalizing circuit for eliminating the attenuation and distortion of the heterodyne signal due to the first and second waveform equalizing circuits.
Optical disc tracking, characterized by comprising a filter.
King error signal detection device. 2. The optical disk tracking error signal detecting device according to claim 1, wherein said first and second waveform equalizing circuits have the same circuit configuration. 3. The tracking error signal output means,
3. An A / D converter for holding a heterodyne signal output from the heterodyne signal output means at rising and falling edges of the digital reproduction signal output from the digital reproduction signal output means. 2. An optical disk tracking error signal detection device according to claim 1.