JPH10198981A - Optical information reproduction device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a tracking servo highly accurate by performing a tracking servo only by the tracking detection output obtained from pits whose signal-to- noise ratios are relatively satisfactory in a high-density disk DVD. SOLUTION: The phase comparision signal obtained by a phase comparating means 6 from values which are outputs of adders 2, 3, in which output signals of cells A, C and B, D being in diagonal positions on a photoelectric detector 1 consisting of quadripartite light receiving elements A, B, C, D are respectively added, is inputted to a holding means 9 via delaying means 8. Besides, after the added signal RF of (A+B+C+D) is shaped into a pulse shape to be inputted to a pit part detecting means 11 and then a 3T pit and a 4T pit are detected by using a master clock (f) to be inputted to the holding means 9. The holding means 9 does not output a tracking detection signal by annuling it when 3T and 4T pits whose signal-to-noise are relatively low are detected and output it when 5T∼14T pits, whose signal-to-noise are satisfactory are detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an optical information reproducing apparatus for optically reading information from a high-density information recording disk located above a compact disk (CD), and more particularly to a tracking servo thereof.

[0002]

2. Description of the Related Art Discs for recording and reproducing information such as music are CDs.
The technology is well known. Following the CD, 12cm in diameter,
The storage capacity is 4.7 by laminating two 0.6mm thick boards.
Development and commercialization of high-density discs capable of reproducing up to 17 GB have been promoted and are called digital versatile discs (DVDs).

In general, if the wavelength of a reading laser for optically reading information from such a disc is λ and the numerical aperture of a reading lens is NA, the size of a condensed reading light spot is expressed by λ / NA. In a DVD put into practical use in 1996, λ = 0.65 μm, NA = 0.
6 is a typical example, the size of the reading light spot is λ / NA = 1.08 μm. On the other hand, the track pitch of the pit row of the information signal tracks formed spirally or concentrically on the DVD is 0.74 μm, and the tracking servo operates at the target accuracy at a normal reproduction speed. An information signal can be reproduced well.

Incidentally, in order to perform tracking servo, it is necessary to detect a tracking error signal. An example of this detection is a phase difference detection method. Specifically, reflected light obtained by irradiating the reading laser to the information signal track position on the disk is received by the four-division light receiving element. The four-division light receiving element adds two detection signals output from one of two diagonally arranged light receiving parts. Similarly, two detection signals output from the other two light receiving units are added. Thus, the phase error is detected by the phase comparator between the two sets of the added signals. Thereafter, a signal obtained by removing unnecessary high frequency signal components from the phase error signal is used as a tracking error signal. FIG. 2 shows a conventional optical information reproducing apparatus using this phase difference detection method (for example, Japanese Patent Publication No. 6-3648).

FIG. 2 is a block diagram of a conventional optical information reproducing apparatus. As shown in FIG. 2, the optical information reproducing apparatus A includes a photoelectric detector 1 including four-division light receiving elements A to D,
Addition means 2 and 3, which are photocurrent-voltage conversion means, waveform shaping means 4 and 5, phase comparison means 6, low-pass filter (LP
F) 7. a is the reproduction scanning direction (track direction) of the optical pickup (not shown), and b is the radial direction of the optical disk (not shown).

Next, the operation of the optical information reproducing apparatus A will be described. A laser beam emitted from a reading laser constituting an optical pickup (not shown) irradiates an information signal track on an optical disc (not shown) via a known optical system (mainly, a collimator lens, a half mirror, and an objective lens). In response to this, reflected light from the information signal track irradiated with the laser light is again reflected by the above-described optical system (mainly an objective lens,
The light is converted into diffracted light via a half mirror and enters the photoelectric detector 1. The photoelectric detector 1 includes four light receiving cells A, B, C, and D (four-division light receiving elements). The adding means 2 outputs a sum signal (A + C) obtained by adding output signals from the two light receiving cells A and C arranged at diagonal positions.

On the other hand, the adding means 3 outputs a sum signal (B + D) obtained by adding output signals from the two light receiving cells B and D arranged at diagonal positions. When there is no tracking error, there is no phase error between these sum signals. However, when a tracking error occurs, a phase error occurs between these sum signals. Here, the output signals from the light receiving cells A, B, C, D are indicated as A, B, C, D. Then, the waveforms of the sum signals (A + C) and (B + D) from the adding means 2 and 3 are respectively shaped by the waveform shaping means 4 and 5, and the phases are compared by the phase comparing means 6. By removing unnecessary high frequency components, a stable tracking error signal can be obtained.

[0008]

Now, in DVD,
If the adverse conditions overlap, for example, the aberration becomes large due to the aging deterioration of the optical pickup, and the disk also becomes large due to the warpage, it becomes difficult for the above-described tracking servo to operate with the desired accuracy. If the track density is to be increased more than that of the DVD, it is difficult for the tracking servo to operate with the desired accuracy even in a normal reproduction speed state. The lack of accuracy of the tracking servo is due to the lack of signal quality of the tracking servo detection. More specifically, the tracking servo detection signal S versus noise N
This is because the ratio, that is, S / N is insufficient. The main cause of the noise N is crosstalk interference from a neighboring track.

In order to improve the S / N ratio of tracking servo detection, the present inventor has mainly investigated a known phase difference detection method as a typical tracking detection method for DVDs. As a result, there is clearly a significant difference in S / N between tracking detection in relatively short pits, ie, 3T and 4T pits, and tracking detection in relatively long pits, ie, 6T to 14T pits. I figured out the thing.

Incidentally, the master clock (channel frequency) f of the DVD is f = about 26.16 MHz and the period T
(= 1 / f) is T = about 38 nsec, and the length of each pit is defined in the range of 3T to 14T. The shortest pit length is 3T pits, 3T pit length = 0.4 μm, the longest pit length is 14T pits, 14T pit length =
1.87 μm.

On the other hand, when a DVD is reproduced by the optical information reproducing apparatus A having the above configuration, the photoelectric detector 1
A reproduction signal (RF output, A + B + C + D) obtained by adding all the output signals A to D from the two light receiving cells A to D has a well-known reproduction output waveform called an eye pattern. This eye pattern has a time-to-level characteristic in which the outputs of RF signals obtained by reproducing and scanning the 3T to 14T pits are all superimposed, and each RF signal output oscillates in a sine wave shape around the zero level. There is a relationship of RF output level of reproducing 3T pit <RF output level of reproducing 4T pit <RF output level of reproducing 5T pit, and RF output level of reproducing 6T pit to 14
It is known that all the RF output levels obtained by reproducing the T pits have the same relationship (the output level reaches a peak). This relationship is such that the 3T and 4T pits have a relatively shorter pit length than the 6T to 14T pits, so that the RF output level is relatively small, and as a result, the S / P ratio is relatively small.
N is considered to be inferior. The 5T pit is 3T,
It has intermediate properties between 4T pits and 6T-14T pits.

On the other hand, in the case of a DVD or a test disk having a higher density than this, the RF output level of the 3T and 4T pits based on the RF output level of the 7T to 14T pits is the RF output level of the 7T to 11T pit of the CD. Is relatively small as compared with the RF output level of the 3T and 4T pits based on. For example, in the size of a reading light spot, a CD is about 1.73 μm, while a DVD is about 1.08 μm, and the 3T pit length of a CD is 0.9 μm and the 3T pit length of a DVD is about 0.3 μm. 4 μm. As a result, it is clear that DVDs require higher precision than DVDs for tracking servo required to reproduce the same 3T pits.

By the way, near the zero cross in the eye pattern described above, RF outputs corresponding to the leading edge and the trailing edge of each pit are obtained. Many of the tracking detection methods using one beam, such as the above-described phase difference detection method and the known heterodyne detection method, use the RF near the zero cross.
A tracking detection output (tracking error signal) is obtained at the output reproduction timing. For this reason, the S / N of the tracking detection output becomes better as the RF output level near the zero cross becomes higher, but the tracking detection output becomes relatively S / N in the 3T and 4T pits where the RF output level is relatively small. Can be estimated to be inferior. By observing this, it was confirmed that the S / N was relatively inferior to the tracking detection in the 3T and 4T pit portions with a significant difference.

In order to improve the S / N ratio of the tracking detection output used for the tracking servo, the present invention positively utilizes the above-mentioned significant difference to improve the 3T, 4T.
The tracking detection output obtained by reproducing and scanning the pits is rejected, and the S / N of the tracking detection is relatively good.
An optical information reproducing apparatus capable of improving the S / N ratio of tracking servo detection by using only a tracking detection output obtained by reproducing and scanning T-14T pits as a tracking detection output used for tracking servo. The purpose is to provide.

[0015]

In order to solve the above problems and achieve the above object, the present invention provides an optical information reproducing apparatus having the following constitutions (1) to (3).

(1) As shown in FIG. 1, a reproducing scanner (mainly a reading laser collimator lens) for reproducing and scanning an optical disk (not shown) in which information signal tracks are formed as a large number of pit rows in a concentric or spiral manner. An optical information reproducing apparatus B for generating a tracking detection signal (a phase error signal and a tracking error signal output from the phase comparing means 6) for use in tracking control of a pickup comprising a half mirror and an objective lens. A pickup signal (RF signal (A
+ B + C + D)), based on the multi-pit row (3T
~ 14T pits), pits of specific length (3T,
Detecting means (3T, 4T pit detecting means, pit detecting means) for outputting a detection signal obtained by detecting the 4T pit)
And holding means 9 for controlling an output of a tracking detection signal generated based on the detection signal,
The detection signal from the detecting means 11 is applied to the holding means 9.
An optical information reproducing apparatus for outputting the tracking detection signal when the detection signal from the detection means 11 is not supplied to the holding means 9 when the detection signal is supplied to the holding means 9. .

(2) The reproduction scanner (pickup)
Assuming that the wavelength of the light source is λ, the numerical aperture of the condenser lens is NA, and the size of the reproduction light spot is λ / NA, the pit of a specific length detected by the detection means is 0.4 / λ / NA. 2. The optical information reproducing apparatus according to claim 1, wherein the pit is at least twice and at most 0.5 times. For example, the size λ / NA of the reproduction light spot in a DVD is 1.08 μm. The length of the 3T pit, which is the shortest pit of a DVD, is 0.
4 μm, which is 0.3 μm of the size of the reproduction light spot.
7 times. 4T pit length of DVD is 0.53μm
Which is 0.49 times the size of the reproduction light spot. From observation of these reproduced waveforms, it was found that the boundary between the passage of the tracking detection output and the passage of the tracking detection output was set to 0.4 to 0.5 times the size of the reproduced light spot. Since the numerical value of this magnification is normalized by the size of the light spot, the result of observation in this DVD system can be applied as it is to the numerical value of the magnification in other systems.

(3) The channel frequency used to generate an information signal to be recorded on the optical disk is f,
Assuming that the cycle of the channel frequency f is T and the range of the length of many pits constituting the information signal track is 3T to 14T, the pit having the specific length is a pit of 4T or less. Item 3. The optical information reproducing apparatus according to item 1 or 2.

The operation of the optical information reproducing apparatus according to the present invention is as follows. For example, a tracking detection circuit uses a circuit known in a tracking detection method using one beam such as a known phase difference detection method or a known heterodyne detection method, and performs tracking detection for all pits of 3T to 14T. Output a signal. The 3T and 4T pit detection circuits detect only 3T and 4T pit portions from the reproduced signal.
A circuit for rejecting the output of the tracking detection circuit at this time using pulses corresponding to the 3T and 4T pits can be constituted by a known circuit technology using, for example, an analog electronic switch, and the object of the present invention is 3T and 4T. The passage of the tracking detection output in the pit is prevented, and an operation using only the tracking detection output in the 5T to 14T pit is performed. According to the above operation, as a result of rejecting a tracking detection portion having a relatively inferior detection S / N, the tracking detection signal obtained according to the present invention improves the S / N as compared with the conventional example. be able to.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An optical information reproducing apparatus according to the present invention will be described below with reference to FIGS. FIG. 1 is a block diagram showing an optical information reproducing apparatus according to an embodiment of the present invention.
FIG. 3 is a diagram for explaining the operation of the optical information reproducing apparatus of the present invention.

As will be described later, the optical information reproducing apparatus of the present invention generally uses a circuit known in the tracking detection method using one beam, such as a known phase difference detection method or a time difference detection method (see FIG. Optical information reproducing apparatus shown in FIG. 2) A
A 3T, 4T pit detection circuit (3T, 4T pit portion detection means) 11; and a circuit for rejecting the output of the tracking detection circuit in accordance with the timing of the tracking detection output obtained by reproducing and scanning the 3T, 4T pit. When a relatively low S / N tracking detection output obtained by reproducing and scanning the 3T and 4T pits is detected by using the (hold means) 9, the tracking detection output is not output, and
A relatively high S / N tracking detection output obtained by reproducing and scanning the 5T to 14T pit detected immediately before is continuously output.

As shown in FIG. 1, the optical information reproducing apparatus B according to the present invention includes the phase comparing means 6 and the low-pass filter (LP) in the optical information reproducing apparatus A shown in FIG.
F), a delay means 8 and a hold means 9 are connected in cascade, and a waveform shaping means 10 and a pit detection means 1 are provided on the input side of the hold means 9.
1 has the same configuration as the one connected in cascade.

That is, as shown in FIG. 1, the optical information reproducing apparatus B includes a photoelectric detector 1 having four divided light receiving elements A to D, adding means 2 and 3, which are photocurrent-voltage converting means, and a waveform. Shaping means 4, 5, 10, phase comparing means 6, low-pass filter (LPF) 7, delay means 8, holding means 9, 3
T, 4T pit portion detecting means (pit portion detecting means) 11 is provided. a is the reproduction scanning direction (track direction) of the optical pickup (not shown), and b is the radial direction of the optical disk (not shown).

Next, the operation of the optical information reproducing apparatus B will be described. A laser beam emitted from a reading laser constituting an optical pickup (not shown) irradiates an information signal track on a DVD (not shown) via a known optical system (mainly, a collimator lens, a half mirror, and an objective lens). In response to this, the reflected light from the information signal track irradiated with the laser light is converted into diffracted light again through the above-mentioned optical system (mainly an objective lens and a half mirror) and enters the photoelectric detector 1. The photoelectric detector 1 includes four light receiving cells A, B, C, and D (four-division light receiving elements). The adding means 2 outputs a sum signal (A + C) obtained by adding output signals from the two light receiving cells A and C arranged at diagonal positions.

On the other hand, the adding means 3 outputs a sum signal (B + D) obtained by adding output signals from the two light receiving cells B and D arranged at diagonal positions. When there is no tracking error, there is no phase difference between these sum signals, but when a tracking error occurs, a phase difference occurs between these sum signals. Therefore, the sum signals (A + C) from the adding means 2 and 3
After waveform shaping of (B + D) by the waveform shaping means 4 and 5, respectively, a phase comparison signal whose phase is compared by the phase comparing means 6 is supplied to the delay means 8.

The delay means 8 outputs a phase comparison signal (ie, 3T-14) outputted from the phase comparison means 6 to the hold means 9.
A pulse obtained by detecting the leading edge and the trailing edge of the T pit, respectively;
This is provided in order to match the timing with a detection signal (only 3T and 4T pits have been detected) to be output to the CPU. As will be described later, the delay means 8 outputs a phase comparison signal output from the phase comparison means 6 with a delay time equal to the time Tb (shown in FIG. 3C) for five clocks of the master clock f required to detect the 4T pit. The signal is output with a delay. As described above, the output of the phase comparing means 6 is delayed by a time equivalent to five clocks by using the delay means 8. However, the delay of the five clock times is practically not practical from the viewpoint of the delay time of the tracking servo. It's not a problem.

The hold means 9 comprises a well-known sample hold circuit. During a period in which the detection signal is not supplied from the pit detection means 11, the hold means 9 is output from the phase comparison means 6 via the delay means 8 and 5T. The delayed phase comparison signal is output to the low-pass filter 7. On the other hand, during the period when the detection signal is supplied (3T, 4T pit detection period), the phase comparison signal is output from the phase comparison means 6 via the delay means 8. Also, without outputting the phase comparison signal delayed by 5T to the low-pass filter 7 (without outputting the phase comparison signal obtained by detecting the 3T and 4T pits),
The phase comparison signal (the phase comparison signal obtained by detecting the 5T to 14T pits) obtained by reproducing and scanning the １４14T pit is output to the low-pass filter 7. As a result, the hold means 9 can always output a phase comparison signal having a good S / N to the low-pass filter 7, and as a result, the low-pass filter 7 can output a tracking error signal having a good S / N. is there.

Next, the waveform shaping means 10 and the pit detecting means 11 will be described. In the optical information reproducing apparatus B, 1T (one clock cycle) is about 38 ns.
A master clock generating circuit (not shown) for generating a master clock of c (that is, a master clock f of DVD of about 26.16 MHz) is provided. The master clock f output from the master clock generation circuit is output to the pit detection means 11 (shown in FIG. 3A). On the other hand, an RF signal (A + B + C + D) obtained by adding all the output signals from the four-divided light receiving elements A to D of the photoelectric detector 1 described above.
Is output to the waveform shaping means 10, where the waveform is shaped into a rectangular pulse, and then output to the pit detecting means 11.

As a matter of course, the pulses output from the waveform shaping means 10 have a phase shift with respect to the above-mentioned master clock f. In this state, the pit detecting means 11 detects each of the 3T pit and the 3T pit as follows. That is, a reading laser beam (not shown) is applied to mirrors (reflection portions) to 3
As shown in FIG. 3B, the output pulse from the waveform shaping means 10 obtained by continuously irradiating the T pit to the mirror (reflection portion) changes from the "1" level (mirror, reflection portion) to "0". The falling change to the level (the leading edge of the 3T pit) is detected by the pit detecting means 11 in synchronization with the rising of the clock 1 of the master clock f. The subsequent rising transition from the “0” level (the trailing edge of the 3T pit) to the “1” level (mirror) is caused by the master clock f
Is detected in synchronization with the rise of the clock 4 of FIG. Therefore, the detection of the 3T pit by the pit detecting means 11 requires a time period Ta of four periods of the master clock f.

Similarly, the output pulse from the waveform shaping means 10 obtained by continuously irradiating the reading laser beam with the mirror (reflection portion) to the 4T pit to the mirror (reflection portion) of the information signal track is shown in FIG. ), The falling change from the “1” level (mirror) to the “0” level (the leading edge of the 4T pit) is detected in synchronization with the rising edge of the clock 1 of the master clock f. The subsequent rising change from the “0” level (the trailing edge of the 4T pit) to the “1” level (mirror) is detected in synchronization with the rising of the clock 5 of the master clock f. Therefore, the detection of the 4T pit by the pit detecting means 11 requires a time period Tb for five periods of the master clock f.

As a result, the pit detecting means 11 outputs 3T,
The detection signal obtained by detecting the 4T pit is output to the holding means 9. As described above, when the optical information reproducing apparatus of the present invention detects a relatively low S / N tracking detection output obtained by reproducing and scanning 3T and 4T pits, it outputs this tracking detection output. Instead, a relatively high S / N tracking detection output obtained by reproducing and scanning the 5T to 14T pit detected immediately before can be continuously output. In the present embodiment, the parameters such as the pit size of the optical disc and the size of the read light spot are configured so as not to use the detection output of the 3T and 4T pits. However, the present invention is not limited to this. It is of course possible to adopt a configuration in which the detection output of the 3T to 5T pits is not used according to the above. In the above-described embodiments of the present invention, a DVD has been described as an example. However, it is needless to say that the present invention can be applied to reproduction of a disk having a higher density than a DVD.

[0032]

As described above, the present invention mainly outputs a tracking detection signal from a pit (3T, 4T pit) of a specific length having a relatively low S / N relative to crosstalk interference. High S / N with no crosstalk resistance
Pits other than pits of a specific length (5T to 14T
Since the tracking detection signal from the pit is used, it is possible to provide a strong tracking detection against crosstalk interference from an adjacent track. Also, using this advantage, D
In VD, optical information suitable for high-precision tracking even under adverse conditions such as large aberration due to aging of the optical pickup and large aberration due to warpage of the disc, etc. A playback device can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of an optical information reproducing apparatus according to the present invention.

FIG. 2 is a block diagram of a conventional optical information reproducing apparatus.

FIG. 3 is a diagram for explaining the operation of the optical information reproducing device of the present invention.

[Explanation of symbols]

Reference Signs List 6 phase comparing means 9 holding means 11 3T, 4T pit detecting means, pit detecting means (detecting means) A, B Optical information reproducing apparatus

Claims (3)

[Claims] An optical information reproducing apparatus for reproducing and scanning an optical disk having information signal tracks formed as a large number of pit rows in a concentric or spiral manner, and for generating a tracking detection signal for use in tracking control of a reproducing scanner. Detecting means for outputting a detection signal obtained by detecting a pit having a specific length in the multiple pit row based on a reproduction signal obtained by performing the reproduction scan by the pickup; Holding means for controlling the output of a tracking detection signal generated based on the detection means, wherein when the detection signal from the detection means is supplied to the holding means, the output of the tracking detection signal is blocked, and And outputting the tracking detection signal when the detection signal is not supplied to the holding means. 2. The light source wavelength of the reproducing scanner is λ, the numerical aperture of the condenser lens is NA, the size of the reproducing light spot is λ / NA,
Then, the pit of a specific length detected by the detection means is λ /
2. The optical information reproducing apparatus according to claim 1, wherein the pits are 0.4 to 0.5 times NA. 3. The channel frequency used to generate an information signal to be recorded on the optical disk is f, the period of the channel frequency f is T, and the length of a large number of pits constituting an information signal track is 3T to 14T. 3. The optical information reproducing apparatus according to claim 1, wherein the pit having the specific length is a pit of 4T or less.