JP2001266373A - Tracking error signal detector and optical disk device using this - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tracking error signal detector capable of suppressing the deterioration of precision in the detection of a tracking error signal caused by high density and high linear velocity. SOLUTION: The center of a reproduction information track is irradiated with a main beam 302, and a position deviated outward from the center of the reproduction information track by a fixed quantity is irradiated with two sub-beams 303 and 304. The reflected light of the two sub-beams are photodetected by a quadrant photodetector 305 to detect tracking error signals by a DPD signal respectively, and the sum signal of them is detected as the tracking error signal of the main beam.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a tracking error signal detecting device in an apparatus for reproducing information by irradiating a laser beam onto an optical information recording medium such as an optical disk, and an optical disk apparatus having the apparatus.

[0002]

2. Description of the Related Art In recent years, the density of optical disks has been increasing, but there is a concern that the sensitivity of a tracking error signal may be reduced as the track pitch of an optical disk becomes narrower.

[0003] Hereinafter, a conventional tracking error signal detecting device using the DPD method will be described.

FIG. 1 shows a block diagram of a conventional tracking error signal detecting device. In FIG. 1, 12
Reference numeral 1 denotes a signal processing circuit, 101 denotes an information pit on an information track of the optical disk, and 102 denotes a beam spot emitted from the optical head to the disk surface. 103
A four-divided light receiving element which receives the reflected light from the disk, divided into four parts A, B, C, and D, and 104a and 104b are outputs A and C of each light receiving element of the four-divided light receiving element and a sum of B and D Adders 105a and 105b are high-frequency emphasizing circuits, 106a and
106b converts the output of the high frequency emphasis circuit into a binary signal.
A digitizer 107; a phase difference detector 107 for detecting a phase difference from outputs S2 and T2 of the binarizer; and 108a and 108b LPFs
(Low-pass filter), 109 is a subtractor.

Hereinafter, this operation will be described with reference to FIG.

FIG. 2 shows the signals S1 to S3 and T1 to T3 of FIG.
Is a schematic representation of the operation waveform of FIG. When a track offset exists in the sum outputs S1 (= A + C) and T1 (= B + D) of the four-division light receiving element, a phase difference depending on the track offset amount appears.

S1 and T1 are high frequency emphasizing circuits 105a and 105
After boosting the high range by b, the binarizer 106a,
The signals are converted into binary signals S2 and T2 by 106b. Thereafter, the phase difference detector 107 detects the phase difference from the signals of S2 and T2, and if S2 is ahead of T2, it is determined that the phase is advanced, and the advanced phase pulse S3 having a time width corresponding to the phase difference is determined. Is output. Conversely, when T2 is behind the phase of S2, a delayed phase pulse T3 is output.

After passing through LPF (low-pass filter) 108, S3 and T3 are input to a subtracter 109, and are subjected to subtraction processing to generate a tracking error signal.

[0009] With the recent increase in the density of optical discs and the increase in linear velocity accompanying the increase in transfer rates, phase difference pulses (leading phase pulses,
The time width of the lag phase pulse is short, and it is necessary to detect this with high accuracy.

In particular, in the next generation of high-density optical discs after DVD, it is expected that the track pitch will be further narrowed, and it is required that the beam spot follow the track center with high accuracy.

In the DPD method, if the beam spot is near the track center, the time width of the phase difference pulse to be detected becomes very small. There is a problem that the phase difference pulse cannot be detected and the accuracy of the tracking error signal is deteriorated due to the limit of the accuracy of the pulse width of the detection circuit.

In order to solve such a problem, Japanese Patent No.
No. 3859 proposes a tracking error signal detection device capable of detecting a minute pulse width.

In Patent No. 2743859, instead of directly detecting a short pulse width at the time of pulse width detection by devising a circuit configuration, two pulses having a pulse width difference corresponding to a phase difference are once generated. By subtracting the difference by a subtractor, a minute pulse width is detected by a method independent of the circuit operation speed.

[0014]

However, when the beam spot is scanning near the track center, the phase difference becomes very small, so it is weak to the influence of noise, and the direction of the phase difference due to noise is reversed. However, there is a problem in that the detection circuit tends to malfunction and the detection sensitivity and detection accuracy of the tracking error signal are reduced.

Accordingly, the present invention is to solve the above-mentioned problem in the conventional tracking error signal detecting device, and to provide a tracking error signal detecting device capable of suppressing a decrease in the accuracy of tracking error signal detection due to an increase in density and a high linear velocity. With the goal.

[0016]

In order to solve the above problem, a first tracking error signal detecting device according to the present invention comprises:
Means for irradiating the optical disk with the irradiation light by focusing on the information surface of the optical disk when the optical disk rotates, and reading the two sub-beams by the main beam when the main beam is irradiated on the center of the information track to be read Means for irradiating a position shifted by the same amount to both outer sides from the track center, means for receiving reflected light of the two sub-beams independently by a plurality of divided light-receiving elements, and output from the divided light-receiving elements Two means for detecting a mutual phase difference between the two output signals, and two means for respectively generating tracking error signals corresponding to the two sub beams from the phase difference. Is detected as a tracking error signal of the main beam.

Further, the second tracking error signal detecting device of the present invention is a device for irradiating irradiation light by focusing on the information surface of the optical disk when the optical disk is rotating, and the center of the information track from which the main beam reads. In the state where the main beam is read out, the center of each track adjacent to the information track from which the main beam reads the two sub-beams is located on the side of the track where the main beam reads or both of the two adjacent tracks. A means for irradiating a position shifted outward by the same amount, a means for receiving reflected light of two sub-beams independently by a plurality of divided light receiving elements, and a means for receiving two reflected light beams from the divided light receiving elements Two means for detecting a mutual phase difference between output signals, and two means for generating tracking error signals respectively corresponding to two sub beams from the phase difference. Comprising means, and detecting a sum signal of the tracking error signal corresponding to the two sub-beams as the main beam tracking error signal.

Further, in the first tracking error signal detecting device, in a state where the main beam is irradiated to the center of the information track to be read, the two sub-beams are located on both outer sides from the center of the track where the main beam is to be read. 1 /
Irradiation is performed at positions shifted within a range from 10 track pitches to less than 1/4 track pitch.

In the second tracking error signal detecting device, in a state where the main beam is irradiated on the center of the information track to be read out, two sub-beams are formed on both sides of the information track from which the main beam reads out. From the center of the track to the track side where the main beam reads out or to both outer sides of two adjacent tracks.
Irradiation is performed at positions shifted within a range from 0 track pitch or more to less than 1/4 track pitch.

Also, in the optical disc apparatus of the present invention, the second tracking error signal detecting device, the signal of the information track from which the main beam reads, and the main beam from which the sub beam reads are read. A crosstalk removing unit for removing a signal component of an adjacent track included in a signal of an information track whose main beam is read based on signals of tracks adjacent to the information track to be read out. And

[0021]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 is a block diagram of a first tracking error signal detecting device according to the present invention. The optical pickup is a general three-beam optical system. As shown in FIG. 3, the main beam 302 irradiates the center of the main track, and the left and right (first and second) sub-beams 303 and 304 are formed on the main track. Irradiation is performed to a position shifted from the center to the outside by the same amount (more than 1/10 track pitch to less than 1/4 track pitch). Reference numeral 301 denotes information pits formed on information tracks of the optical disc.

The reflected lights of the left and right sub-beams 303 and 304 are independently incident on general four-divided light receiving elements 305 corresponding to the left and right and upper and lower sides of the information track of the optical disk, respectively, and are tracked by the conventional DPD method described below. Error signals are detected independently.

That is, the left and right sub beams 303 and 304
Signal detection circuits 321 and 322 having the same configuration for processing the reflected light of
1, 322 are added by the adder 314. Here, the internal configuration of one detection circuit 321 is shown and described as a representative.

That is, the output A,
B, C, and D add the diagonal outputs of the light receiving elements by an adder 306 to generate two signals (A + C) and (B + D).

The outputs of (A + C) and (B + D) are boosted by high frequency emphasizing circuits 307a and 307b, respectively, and are binarized signals S2 and T2 by binarizers 308a and 308b to detect a phase difference. Is input to the device 309.

FIGS. 4 and 5 show a general phase difference detector 309.
Is a configuration example and an operation waveform example thereof. The phase difference is detected from the signals of S2 and T2, and when S2 is ahead of T2, it is determined that the phase is advanced, and the advance of the time width corresponding to the phase difference is performed. The phase pulse S3 is output. Conversely, if T2 is behind the phase of S2, a delayed phase pulse T3 is output.

That is, if a track offset exists in a certain direction and (A + C) is ahead of (B + D), a leading phase pulse S3 is output, and a track offset exists in the opposite direction. If the phase of (A + C) is later than that of (B + D), a delayed phase pulse T3 is output.

The leading phase S3 and the lagging phase T3 are respectively LPF
After passing through (low-pass filters) 310a and 310b, a subtractor 311 performs a subtraction process to generate a tracking error signal.

The phase difference detector 309 of FIG. 4 will be described. Signals S2 and T2 are input to input terminals 401 and 402, respectively. This signal is directly transmitted to the first,
The signal is supplied to the second input terminal and, after passing through the inverters 403 and 404, respectively, to the first and second input terminals of the NAND circuit 406. NAND circuit 405,
The output of 406 is supplied to the set terminal and the reset terminal of the flip-flop circuit 407. The output of the flip-flop circuit 407 is supplied to one input terminal of each of the EXOR circuits 408 and 409. The EXOR circuits 408 and 40
The outputs of the inverters 403 and 404 are respectively supplied to the other input terminals of No. 9. According to this circuit, the input and output signal waveforms are the operation waveforms as shown in the example of FIG.

In the configuration of the present invention, the tracking error signal (L) 312 and the tracking error signal (R) 313 corresponding to the reflected light of the left and right sub-beams obtained by the above-described method are added by the adder 314, and The result is output as a tracking error signal of the main beam.

Next, the operation of the tracking error signal detecting device according to the present invention will be described.

FIG. 6 is a graph showing track offset dependency showing the detection sensitivity of a tracking error signal by one conventional beam. The vertical axis indicates the ratio of the pulse phase difference amount (the sum of the leading phase pulse width and the lagging phase pulse width) detected when the beam spot scans the information track over a certain distance.

When the track offset is 0, the ratio of the phase difference of the detected pulse is 0, and the phase difference of the detected pulse increases as the track offset increases.

This is not a problem when the linear density of the optical disk is relatively low and the linear velocity is low. However, when the linear density and the linear velocity increase, the phase difference amount of the pulse detected with respect to the unit offset amount increases. Becomes very small, and it becomes difficult to perform high-precision detection due to the limitation of the operation speed of the pulse width detection circuit and the limitation of the accuracy of the phase difference detection time width.

FIG. 7 is a diagram showing the relationship between the pulse width of the phase difference pulse detected when the beam spot scans the center of the track and the detection frequency. As shown in FIG. 7, when the beam spot scans the center of the track, the frequency of the detected phase difference pulse is most frequent near zero.

Since the small area of the phase difference detection width indicated by the shaded area cannot be detected for the above-described reason, the actual detection sensitivity of the tracking error signal is as shown in FIG. Becomes dull.

In the configuration of the present invention, when the main beam irradiates the center of the track, the left and right sub-beams are irradiated symmetrically outward from the center of the track by the same amount, so that the tracking error signal shown in FIG. Are detected from the reflected light of the sub-beams, respectively.

FIG. 10 is a diagram showing the relationship between the pulse width of the detected phase difference pulse and the detection frequency when the left and right sub-beams irradiate a position offset symmetrically outward from the track center by the same amount.

As shown in FIG. 10, the phase difference pulse width having a higher detection frequency is not near zero but at a position having a certain amount of pulse width. In other words, the presence of a certain amount of track offset makes it possible to stably detect a phase difference pulse with a high detection frequency, reduce the influence of a small area of the undetectable phase difference detection width, and provide a highly accurate tracking error. A signal can be obtained.

The present invention takes advantage of this fact.
That is, the sum signal of the high-precision tracking error signals from the left and right sub-beams is used as the main beam tracking error signal, and a high-accuracy tracking error signal can be obtained with the configuration of the present invention.

FIG. 11 is a block diagram of a second tracking error signal detecting device according to the present invention.

The difference from FIG. 3 is that the main beam 302 irradiates the center of the main track to be reproduced and the two left and right sub-beams 303 and 304 are respectively adjacent to the information track from which the main beam 302 reads. With respect to the center of the track, the main beam 302 irradiates a position shifted by the same amount (more than 1/10 track pitch to less than 1/4 track pitch) to the track side to be read or to both outer sides of two adjacent tracks. The configuration of the other parts is the same as the block diagram of the first tracking error signal detection device. Therefore, parts corresponding to the blocks in FIG. 3 are denoted by the same reference numerals.

With respect to the center of each track adjacent to the information track from which the main beam reads the two left and right sub-beams, to the track side where the main beam reads or to the outside of the two adjacent tracks. Even when irradiation is performed at a position shifted by the same amount, a highly accurate tracking error signal can be obtained in the same manner as the operation of the first tracking error signal detection device.

In particular, in the configuration of the second tracking error signal detecting device, the left and right sub-beams are shifted from the center of the adjacent track by a distance not less than 1/10 track pitch to less than 1/4 track pitch. Since the irradiation is performed at the offset position, a crosstalk removing unit that removes a signal component of an adjacent track included in a signal of an information track from which a main beam is read by using the output is provided. Thus, the tilt detection and the crosstalk removal of the present invention can be realized by the same optical system. Therefore,
It is possible to reduce an increase in cost when the tracking error signal detecting device of the present invention is mounted on an optical disc device having a crosstalk removing function using a three-beam optical system.

[0046]

As described above, according to the structure of the present invention, the operation speed limit of the circuit for detecting the tracking error signal and the tracking error caused by the accuracy limit of the circuit are increased by increasing the density and the linear velocity of the optical disk. Deterioration of the error signal detection performance can be suppressed.

[Brief description of the drawings]

FIG. 1 is a block diagram of a conventional tracking error signal detection device.

FIG. 2 is a diagram showing an operation example of a conventional tracking error signal detection device.

FIG. 3 is a block diagram of a first tracking error signal detection device according to the present invention.

FIG. 4 is a configuration diagram of a general phase difference detector.

FIG. 5 is an operation waveform diagram of a general phase difference detector.

FIG. 6 is a diagram showing the track offset dependence of a tracking error signal at low density and low linear velocity.

FIG. 7 is a diagram showing a relationship between a pulse width of a phase difference pulse detected when a beam spot scans a track center and a detection frequency.

FIG. 8 is a diagram showing the track offset dependence of a tracking error signal at high density and high linear velocity.

FIG. 9 shows the output (X, Y) of the tracking error signal from the sub beam in the tracking error signal detection device of the present invention.
FIG.

FIG. 10 shows the relationship between the pulse width and the detection frequency of the phase difference pulse detected when the left and right sub-beams irradiate the position offset by the same amount symmetrically outward from the track center in the tracking error signal detection device of the present invention. FIG.

FIG. 11 is a block diagram of a first tracking error signal detection device according to the present invention.

[Explanation of symbols]

101, 301: information pit, 102: beam spot, 103, 305: four-division light receiving element, 104a, 10
4b, 306a, 306b... Adders, 105a, 105
b, 307a, 307b ... high frequency emphasis circuit, 106a, 1
06b, 308a, 308b ... binarizer, 107, 30
9 ... Phase difference detector, 108a, 108b, 310a, 3
10b: low-pass filter, 109, 311: subtractor,
302: main beam spot, 303, 304: sub beam spot, 312, 313: tracking error signal, 3
14 ... Adder.

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) DB18

Claims (5)

[Claims] A means for irradiating an information surface of the optical disc with an irradiation light including a main beam and first and second sub-beams while the optical head is rotating, the optical beam being read out; Means for irradiating the first and second sub-beams to positions shifted by the same amount to both outsides from the center of the track where the main beam reads, in a state where the center is illuminated at the center of the information track for performing reading; Means for receiving the reflected light of the first and second sub-beams independently by a plurality of divided light receiving elements, and detecting a mutual phase difference between two output signals output from the divided light receiving elements And two means for generating tracking error signals corresponding to the first and second sub-beams from the phase difference, respectively. Tracking error signal detecting apparatus characterized by detecting a sum signal of Kkingu error signal as a tracking error signal of the main beam. A means for irradiating the information surface of the optical disc with an irradiation light including a main beam and first and second sub-beams while focusing on the information surface of the optical disc during rotation of the optical disc; In a state where the center of the information track to be read is irradiated, the main beam reads the first and second sub beams with respect to the center of each track adjacent to the information track from which the main beam reads. Means for irradiating a position shifted by the same amount to the side of the track to be dipped or to both outer sides of two adjacent tracks, and a plurality of divided light receiving parts which respectively divide the reflected light of the first and second sub-beams independently. Means for receiving light by an element; two means for detecting a mutual phase difference between two output signals output from the divided light receiving element; and the first and second sub-beams based on the phase difference. And two means for generating a tracking error signal corresponding to the first and second sub-beams, respectively, wherein a sum signal of the tracking error signals corresponding to the first and second sub-beams is detected as a tracking error signal of the main beam. Tracking error signal detection device. 3. When the main beam is irradiated on the center of the information track to be read, the first and second sub-beams are 1/10 from the track center where the main beam is read to both outer sides. 2. The tracking error signal detection device according to claim 1, wherein the irradiation is performed to positions shifted from a track pitch to a track pitch less than 1/4 track pitch. 4. In a state where the main beam is irradiated on the center of an information track to be read, the first and second sub-beams of each track adjacent to the information track from which the main beam is to be read are used. With respect to the center, at least 1/10 track pitch to 1/1 / to the track side where the main beam reads out or both outer sides of two adjacent tracks.
2. The tracking error signal detection device according to claim 1, wherein the irradiation is performed at positions shifted within a range of less than four track pitches. 5. A tracking error signal detecting device according to claim 3, wherein: a signal of an information track from which the main beam reads out;
The first and second sub-beams are included in a signal of an information track to be read by the main beam based on signals of tracks adjacent to the information track to be read by the main beam. An optical disc device, comprising: a crosstalk removing unit that removes a signal component of both adjacent tracks.