JPH10208262A - Optical information reproducing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the precision of detection of a tracking error by detecting the phase difference between two detection signals which change in phase relation according to the quantity of displacement of a light spot from the center of a track when one detection signal is state-inverted in the same direction within a prescribed time after the other detection signal is state-inverted. SOLUTION: An optical head 3 detects information recorded on an optical disk 1 and outputs detection signals (a) and (b). If the irradiation position of a light beam deviates from the information track center, the optical head 3 generates a phase difference between the two signals. Then 2nd waveform shaping means 41 and 42 remove low-frequency components from the detection signals (a) and (b), binarizes them, and outputs digital detection signals (c) and (d). A phase difference decision means 46 decides that both the signals are effective and outputs edge information when one of the two detection signals is state-inverted in the same direction within the prescribed time after the other detection signal is state-inverted. A tracking control means 5 cancels an error to make the light beam travel normally.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information reproducing apparatus, and more particularly, to a tracking control means for causing a light beam focused on a medium to travel along the center of a track.

[0002]

2. Description of the Related Art In recent years, optical disks for optically recording and reproducing information, such as digital video disks (hereinafter referred to as "DVDs"), have attracted attention as means for storing large amounts of video information and data information. Tracks are formed on this optical disc at a pitch of about 1 μm concentrically or spirally, and information is recorded on the track by utilizing a local optical constant or a change in physical shape.

In order to reproduce information from an optical disk having such a recording form with high quality, an optical disk apparatus controls the focusing position of a light spot for reading information with high precision, and this light spot always traces on a track. I am trying to do it. The positioning control of the light spot is performed two-dimensionally, and the control in the optical axis direction is performed by the focus control means, and the control in the radial direction is performed by the tracking control means. In such control, generally, the difference between the target position of the light spot and the current position, that is, the amount of error, is obtained,
A method of performing feedback control so that this error amount becomes zero is adopted.

The detection of the error amount is usually performed using optical means. As a detection method of a tracking error signal necessary for tracking control, there are a one-spot method using a main beam for reproducing information and a three-spot method using an auxiliary beam. In the one-spot method, a push-pull method and a phase difference method are employed in an actual device.

When the one-spot method is compared with the three-spot method, the one-spot method can simplify the optical system,
It is also advantageous in terms of light use efficiency. Reproducing a tracking error and information from a medium in which information is recorded in the form of uneven pits (hereinafter, referred to as "information pits") on a track using the one-spot method occurs due to the information pits. The purpose is to detect the degree of light diffraction as a signal.

It is known that the degree of the diffraction varies depending on the pit depth of the information pit. However,
The condition of the pit depth at which the tracking error signal is maximum is different from the condition of the pit depth at which the reproduction signal from the information pit is maximum. Taking the push-pull method as an example, the pit depth (λ / 4, λ:
(Wavelength of light), a tracking error cannot be detected in principle.

In addition, when the light spot diameter is constant, as the recording density on the medium increases, waveform interference caused by interference of reproduced waveforms from adjacent pits and crosstalk from adjacent tracks usually occur. As a result, the reproduction signal quality is degraded. For an apparatus that reproduces such a medium, it is necessary to secure an SNR that is a ratio between a signal level and a noise level from the viewpoint of signal detection performance.

The fact that the SNR is large means that the jitter of the detection signal is small and the detection error rate is low. In order to increase the SNR, assuming that the apparatus noise and the medium noise are constant, there is no other way than to set the parameters of each section so that the reproduced signal level is as high as possible.

Therefore, as a method for detecting a tracking error by the one-spot method, the tracking error can be detected even for a medium having a pit depth of λ / 4 in which the signal amplitude reproduced from the information pit becomes the maximum in principle. Some devices employ a possible phase difference method. The principle of this method is disclosed in Japanese Patent Publication No. 56-30610. Next, the principle of tracking error detection by the phase difference method will be described conceptually.

FIG. 13 is a diagram for explaining the principle of detecting a tracking error by the phase difference method. In the figure, (1) is a diagram showing the positional relationship between the information pits and the light spot, and shows how the light spot moves from t0 to t4. In the figure, the traveling position N of the light spot indicates the center of the reproduction target track. Point L indicates an intermediate position between the reproduction target track and the left adjacent track. Further, the point R indicates an intermediate position between the reproduction target track and the right adjacent track.

FIG. 13B shows a photodetector for detecting reflected light from a medium and converting it into an electric signal. This photodetector is divided into four parts (A, B, C, and D) by a dividing line in the track tangential direction and a dividing line in the radial direction perpendicular to the track. The optical system is designed to be formed at the center of the light detector. A phase difference occurs between two detection signals (A + C) and (B + D) obtained by adding the diagonal components of the four divided photodetectors in proportion to the tracking error amount. This is shown in (3), (4),
It is shown in (5).

FIG. 13C is a schematic diagram showing a state where the phase relationship between the two detection signals changes according to the scanning position of the light spot. The waveform on the left is a detection signal waveform when the light spot travels at point L in FIG. 13A, and shows a state in which the detection signal (A + C) has a phase advanced from the detection signal (B + D). The middle waveform is a detection signal waveform when the light spot travels at the point N, that is, the center of the track, and shows that the detection signal (A + C) and the detection signal (B + D) have the same phase. Further, the waveform on the right side is a detection signal waveform when the light spot travels at the point R, and shows a state in which the detection signal (A + C) is delayed in phase from the detection signal (B + D).

FIG. 13D shows the phase difference between the detection signal (A + C) and the detection signal (B + D) according to the scanning position of the light spot. In the figure, the phase difference is indicated by the pulse width. A pulse on the plus side indicates a case where the detection signal (A + C) is ahead of the detection signal (B + D), and a pulse on the minus side indicates a case where the detection signal (A + C) is later than the detection signal (B + D). Show. When the detection signal (A + C) and the detection signal (B + D) have the same phase, no pulse is output on both the + and-sides.

FIG. 13 (5) shows the pulse width, that is, the amount of phase difference, with respect to the travel position of the light spot, and it can be understood that the pulse width changes in proportion to the tracking error amount. A conventional optical information reproducing apparatus for detecting a tracking error using the phase difference method is disclosed in Japanese Patent Publication No. 5-80054.

Next, the configuration of a conventional optical information reproducing apparatus will be described with reference to FIG. In the figure, 1 is an optical disk, 2 is a spindle motor, 3 is an optical head, 4
Is a tracking error detecting means for detecting tracking error information from a signal output from the optical head, and 5 is a radius of a light beam emitted from the optical head to the medium so as to cancel the tracking error detected by the tracking error detecting means 4. Tracking control means for controlling the directional position. Further, the tracking error detecting means 4 includes a first waveform shaping means 41 and a second waveform shaping means 4.
2, a first phase comparing means 43, a validity determining means 44, and a phase difference-voltage converting means 45.

The operation of the conventional optical information reproducing apparatus configured as described above will be described with reference to FIG. The optical head 3 detects information recorded on the optical disk 1 and outputs detection signals (a) and (b). These two detection signals correspond to the detection signal (A + C) and the detection signal (B + D) described in FIG. As described above, the optical system of the optical head 3 is designed such that when the irradiation position of the light beam is displaced from the center of the information track, a phase difference occurs between the two detection signals. I have.

The first waveform shaping means 41 removes low-frequency components from the detection signal (a), binarizes the signal, and outputs a digital detection signal (c). Similarly, the second waveform shaping means 42 removes low-frequency components from the above-mentioned detection signal (b), binarizes it, and outputs a digital detection signal (d).

The validity determining means 44 determines that the two digital detection signals (c) and (d) are "Low" or "Hi".
gh ", the state of only one digital detection signal is inverted twice successively and becomes the same state again.
An invalid signal (e) is output. As described above, the case where one digital detection signal does not change but the other digital detection signal continuously inverts the state may occur when a large noise due to a flaw or the like is mixed in the detection signal. The first phase comparing means 43 compares the phases between the two digital detection signals (c) and (d) in a state where the invalid signal (e) is not output, and outputs a phase difference signal (f).

The phase difference-voltage conversion means 45 generates a tracking error signal by converting the phase difference signal (f) detected as time information into a voltage signal. The tracking control means 5 controls the radial position of the light beam emitted from the optical head 3 to the optical disc 1 so as to cancel the tracking error indicated by the above-mentioned tracking error signal, and the light beam always runs on the track center. To do.

FIG. 15 shows signal waveforms at various points in FIG. 14, and waveforms (a) to (f) are (a) to (f) in FIG.
This corresponds to (f). Hereinafter, the operation of the conventional optical information reproducing apparatus will be described in more detail with reference to FIG.

The two detection signals (a) and (b) output from the optical head 3 are binarized by a first waveform shaping means 41 and a second waveform shaping means 42, and a digital detection signal (c) And (d). The state inversion portions of the digital detection signal (c) are represented by c1, c2 and c5.
And The state inversion portions of the digital detection signal (d) are d1, d2, d3, d4 and d5.

At this time, state inversions c1, c2 and c5
Are paired with state inversions d1, d2 and d5. In these state inversion parts, the phase of the digital detection signal (c) is advanced as compared with the phase of the digital detection signal (d). Therefore, the phase difference signal (f) is output to the plus side as a pulse having a time width corresponding to the phase difference.

On the other hand, in the state inversion d3 of the digital detection signal (d), the digital detection signal (d) first inverts the state from the state where both the digital detection signals (c) and (d) are "Low". The first phase comparing means 43 determines that the phase of the digital detection signal (d) is ahead of the phase of the digital detection signal (c), and tries to output a phase difference signal to the minus side. However, since there is no state inversion of the digital detection signal (c) corresponding to the state inversion d3 and the state inversion d4 of the digital detection signal (d) appears continuously, the validity determination means 44 determines that the state inversions d3 and d4 are invalid. And raises an invalid signal (e). By this invalid signal, the first phase comparing means 43 causes the portion f based on the state inversion d3 and d4 to be
Process so that is not output.

As described above, in the conventional optical information reproducing apparatus, the two digital detection signals (c) and (d) are in the same state and only one of the digital detection signals is continuously inverted twice, and then again. When the same state occurs, it is determined that an abnormal state due to a defect such as a scratch has occurred and the output of the phase difference signal is stopped, so that a large detection error is prevented from being mixed into the phase difference signal, and tracking is performed. Control is stabilized.

[0025]

As described above, in the conventional optical information reproducing apparatus, even if the state inversion of one of the two digital detection signals is changed from the state in which the two digital detection signals are equivalent to each other, the effective state is obtained. The determination of the gender is unknown until the next state inversion appears in which digital detection signal. Therefore, the time until the completion of the validity determination varies depending on the length of a mark recorded on the medium or the length of an abnormal state caused by a defect or the like. Therefore, it is necessary to accumulate the phase difference signal until the determination of the validity of the state inversion is completed or to delay the operation of the phase comparison by the delay means.

In the method of electrically storing the phase difference signal using a capacitor or the like until the validity of the state inversion can be determined, the longer the time until the determination of the validity is completed, the more the capacitor and the like are stored. There is a problem that the accumulated value fluctuates due to a leak current of the circuit or the like, and the fluctuation becomes an error.

In the method of delaying the operation of the phase comparison by the delay means, depending on the setting of the delay time,
In some cases, the next state inversion does not appear within the set time, and in this case, the phase comparator cannot stop outputting the phase difference signal, and a large detection error is mixed in the tracking error signal in an abnormal state. There is also a problem that the reliability of the device is significantly reduced.

Next, another problem in the conventional optical reproducing apparatus will be described. FIG. 16 shows the relationship between the length of a recording mark and the phase difference generated between the two detection signals by optical simulation. However, the recording pit depth is ５ of the laser wavelength λ, and the track offset is の of the track pitch. In the figure, the horizontal axis represents the length of the recording mark normalized by the recording pit length Tch. This recording pit length Tch corresponds to one bit length of data recorded on the disk. The vertical axis represents the phase difference generated between the two detection signals, normalized by the recording pit length Tch. In this optical simulation, written by Takashi Yamada, "Special Issue: Searching for the Current State of DVD Technology-DVD Technology", O plus EN
o. 199 (1996) pp. The parameters described in paragraphs 70-79 were used. Parameter is laser wavelength 650
nm, NA0.6, recording pit length Tch0.133u
m, and the track pitch Tp is 0.74 μm. Also, the length of the recording mark on the horizontal axis in the figure is CD (Comp).
(act disk) or a value based on a modulation rule used in DVD. For this modulation rule, see K.K. A. S.
Imlink, "EFMPlus, a recording coding method to increase the recording capacity of a dissertation DVD," Nikkei Electronics N
o. 675 (1996); 161-165 describes the details. This modulation rule is characterized in that the run length (referred to as the number of consecutive identical symbols "1" or "0") is limited to a range of 2 to 10. Therefore, the length of the recording mark is 3Tch at the shortest and 1T at the longest.
1Tch. From the result of the optical simulation, it is found that when the length of the recording mark is as short as 3 Tch, no phase difference occurs between the two detection signals. In an actual apparatus, a reproduction mark length (record mark length is 3) which cannot be generated due to a modulation rule due to a medium defect or the like.
(Less than Tch or more than 12 Tch) may be detected.

However, the conventional optical reproducing apparatus does not have a function of judging such a pattern as abnormal and removing it. Therefore, in the case where such a pattern is continuous, even if a track shift occurs, a tracking error signal is generated. However, there is also a problem that a defect due to a defect cannot be obtained or disturbance due to a defect is mixed.

Further, since the time setting for determining the validity is fixed, there is a problem that it is difficult to cope with variable speed reproduction in which the data rate changes.

The present invention has been made to solve the above problems, and relates to an optical information reproducing apparatus for constructing a tracking servo system using a tracking error signal by a phase difference method, which is caused by a flaw or the like. It is an object of the present invention to provide a tracking error detecting means that can generate a good tracking error signal even when an abnormal state occurs and when the data rate changes.

A first object is to obtain means for improving the accuracy of tracking error detection by the phase difference method by determining the validity without depending on the length of a recording mark or the length of an abnormal state.

A second object is to eliminate disturbance to a tracking error signal due to information from a pattern having a short recording mark period or a pattern violating a modulation rule in which phase difference information between two digital detection signals has no meaning. Therefore, a means for improving the accuracy of tracking error detection by the phase difference method is obtained.

A third object is to provide a tracking error detecting means capable of responding to a change in data rate.

[0035]

In the optical information reproducing apparatus according to the first aspect of the present invention, two detection signals whose phase relationship changes in accordance with the amount of displacement of the light spot from the track center are generated. When one of the two digital detection signals obtained by analog processing and then binarized by the comparator is inverted, then the other digital detection signal is inverted in the same direction within a predetermined time after the other digital detection signal is inverted. The tracking error signal is obtained by detecting the phase difference between the two digital detection signals.

Further, in the optical information reproducing apparatus according to the second aspect of the present invention, two detection signals whose phase relationship changes according to the amount of displacement of the light spot from the track center are processed in an analog manner. After that, the positive and negative pulse widths of the two digital detection signals obtained by binarization by the comparator are within a predetermined range, and one of the two digital detection signals is inverted in state. Thereafter, when the state of the other digital detection signal is inverted in the same direction within a predetermined time, the tracking error signal is obtained by detecting the phase difference between the two digital detection signals.

Further, in the optical information reproducing apparatus according to the third aspect of the present invention, the predetermined time for detecting the state inversion between the two digital detection signals is set to be equal to or less than the reproduction time of the shortest mark. Is set to.

Further, in the optical information reproducing apparatus according to the fourth aspect of the present invention, the predetermined time is made variable according to a data rate.

Further, in the optical information reproducing apparatus according to the fifth aspect of the present invention, the condition for determining the pulse width of the digital detection signal is set to be not less than 5 times the channel bit period and not more than the longest mark length. It is something to set.

[0040]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In an optical information reproducing apparatus according to an embodiment of the present invention, two detection signals whose phase relationship changes in accordance with the amount of displacement of the light spot from the center of the track correspond to two corresponding detection signals. Generate two digital signals,
After extracting a pair of edges in which the two digital signals are inverted in the same direction within a predetermined time, a phase difference between the pair of edges is detected to obtain a tracking error signal. This is to suppress the incorporation of disturbance into the error signal and improve the tracking error detection ability.

Further, in an optical information reproducing apparatus according to another embodiment of the present invention, two detection signals generated from two detection signals whose phase relationship changes according to the amount of displacement of the light spot from the track center. As means for extracting a tracking error by detecting a phase difference between digital detection signals, a digital detection signal detected in principle from a short-period mark having no phase difference between the two digital detection signals, and a modulation rule After removing a digital detection signal from a recording mark having a length that cannot be generated, a pair of edges where the two digital signals are inverted in the same direction within a predetermined time is extracted, and the phase difference between the pair of edges is determined. The detection suppresses disturbance in the tracking error signal and improves the tracking error detection capability.

Furthermore, in the case of a CD or DVD, the two detection signals overlap with a plurality of record mark lengths that can be taken according to the modulation rule, so that the predetermined time is shorter than the pulse width reproduced from the shortest record mark. It is something to set.

Further, since the pulse width reproduced from the shortest recording mark changes according to the data rate, the function of changing the setting of the predetermined time according to the data rate is added, so that the rotation speed of the disk motor is increased. In this case, the tracking error can be detected with high precision even in variable-speed reproduction in which information is reproduced from the medium before the settling is performed, or in high-speed reproduction at a double speed or higher.

Further, under the condition that the recording pit depth is １ ／ of the laser wavelength λ and the track offset is の of the track pitch, the positive and negative pulse widths are at least five times the channel bit period as the digital detection signal. By setting the length to be equal to or less than the longest mark length, information from a short-period recording mark in which a phase difference does not occur in principle between the two digital detection signals, and a recording mark having a length that cannot be generated due to a modulation rule Is suppressed from being mixed in the tracking error signal as disturbance.

Hereinafter, the present invention will be described in detail with reference to the drawings showing the embodiments. However, in the embodiment, blocks with the same numbers as those of the conventional example are shown in FIG.
Is basically the same as the conventional optical information reproducing apparatus shown in FIG.

Embodiment 1 FIG. 1 is a diagram showing an optical information reproducing apparatus according to Embodiment 1 of the present invention. In the figure, 1 is an optical disk, 2 is a spindle motor, 3 is an optical head, 4 is a tracking error detecting means for detecting tracking error information from a signal output from the optical head,
Reference numeral 5 denotes tracking control means for controlling the radial position of the light beam emitted from the optical head to the medium so as to cancel the tracking error detected by the tracking error detection means 4. Further, the tracking error detecting means 4 includes a first waveform shaping means 41, a second waveform shaping means 42, a phase difference judging means 46, a second phase comparing means 47, and a phase difference-voltage converting means 45. . Furthermore, the phase difference-voltage conversion unit 45 includes a charge pump unit 451 and a low-pass filter (hereinafter, referred to as “LPF”) 452.

The operation of the optical information reproducing apparatus of the embodiment configured as described above will be described with reference to FIG. Optical head 3
Detects information recorded on the optical disc 1 and outputs detection signals (a) and (b). These two detection signals correspond to the detection signal (A + C) and the detection signal (B + D) described in FIG. The optical system of the optical head 3 is designed so that when the irradiation position of the light beam is shifted from the center of the information track, a phase difference occurs between the two detection signals.

The first waveform shaping means 41 removes low frequency components from the detection signal (a), binarizes the signal, and outputs a digital detection signal (c). Similarly, the second waveform shaping means 42 removes low-frequency components from the above-mentioned detection signal (b), binarizes it, and outputs a digital detection signal (d).

The phase difference judging means 46 sets the state of the other digital detection signal in the same direction within a predetermined time after one of the two digital detection signals (c) and (d) is inverted. When inverted, the two digital detection signals are determined to be valid, and the edge information (h) and (i) are output.

The second phase comparing means 47 detects a phase difference between edges from the two pieces of edge information (h) and (i), and outputs two driving signals (PUs) for driving the next-stage charge pump means 451. ) And (PN). Here, the drive signal (PU) is a signal indicating that the edge information (h) is advanced compared to the edge information (i), and the pulse width thereof corresponds to the advance time. In addition, the drive signal (P
N) is a signal indicating that the edge information (h) is behind the edge information (i), and the pulse width thereof corresponds to the delay time.

The charge pump means 451 drives the current source for the duration of the pulse width of the drive signal (PU) to accumulate (charge) electric charge in the capacitor constituting the LPF 452, and to drive the drive signal (PN). By driving the sink current source for the pulse width of (1) and extracting (discharging) the electric charge from the capacitor, the phase difference, which is time information, is converted into a voltage, which is an electric signal.

The LPF 452 removes high frequency components unnecessary for the tracking servo means by smoothing the pulse output of the charge pump means 451 to generate a tracking error signal (TES).

The tracking control means 5 controls the radial position of the light beam emitted from the optical head 3 to the optical disc 1 so as to cancel the tracking error indicated by the tracking error signal (TES). Always drive in the center of the truck.

FIG. 2 shows the signal waveforms of the respective parts denoted by the same symbols in FIG. The symbols (a) to (se) are
4 shows an internal signal of the phase difference determination means 46. Hereinafter, the operation of the optical information reproducing apparatus according to the first embodiment will be described in more detail with reference to FIG.

The two detection signals (a) and (b) output from the optical head 3 are binarized by the first waveform shaping means 41 and the second waveform shaping means 42, and the digital detection signal (c) And (d). The state inversion part of the digital detection signal (c) is represented by c1, c2, c5, c
6, c7 and c8. The state inversion part of the digital detection signal (d) is represented by d1, d2, d3, d4, d
5, d6, d7 and d8.

At this time, state inversion c1, c2, c5, c
6, c7 and c8 are state inversions d1, d2, d5, d
6, d7 and d8. Here, the state inversion c1, c2 and c5 of the digital detection signal (c) are
Indicates a state in which the phase is advanced as compared with the state inversion d1, d2 and d5 of the digital detection signal (d). The state inversions c6, c7 and c8 of the digital detection signal (c) are the state inversion d of the digital detection signal (d).
6 shows a state in which the phase is delayed as compared with d7 and d8.

Next, the operation when the above-mentioned digital detection signal is input to the phase difference judging means 46 will be described. When a state inversion (edge) occurs in the digital detection signal, the phase difference determination means 46 generates a gate for a predetermined time T starting from each rising edge and each falling edge. FIG. 2A shows a gate signal starting from the rising edge of the digital detection signal (c). FIG. 2 shows a gate signal starting from the falling edge of the digital detection signal (c). FIG. 2D shows a gate signal starting from the rising edge of the digital detection signal (d). FIG. 2T shows a gate signal starting from the falling edge of the digital detection signal (d).

The operation of the phase judging means 46 will be described for a state where the rising edge of the digital detection signal (c) is ahead of the rising edge of the digital detection signal (d) (portions c1 and d1, c5 and d5). The enable period of the gate signal shown in FIG.
h), the rising edge of the digital detection signal (d) occurs, that is, the digital detection signal (d) inverts in the same direction within a predetermined time T after the state of the digital detection signal (c) inverts. At the rising edge of the gate signal shown in FIG.
1 ") and reset to" Low "(or" 0 ") at the falling edge of the gate signal in FIG.
The signal shown in (g) is generated. This is because when the digital detection signal (d) reverses the state in the same direction within a predetermined time T after the state of the digital detection signal (c) reverses from "Low" to "High", the falling edge of FIG. This means that the position information of the rising edge of the digital detection signal (c) is projected on the edge. Also, a state where the rising edge of the digital detection signal (c) is delayed as compared with the rising edge of the digital detection signal (d) (portions c7 and d7).
The operation of the phase determination means 46 will be described. FIG.
When the rising edge of the digital detection signal (c) occurs during the "High" period of the gate signal shown in (d), that is, the digital detection signal (c) is within a predetermined time T after the state of the digital detection signal (d) is inverted. Are set to "High" (or "1") at the falling edge of the gate signal in FIG.
The signal is reset to “Low” (or “0”) at the falling edge of the gate signal in (A), and the signal shown in FIG.

In the same manner, the digital detection signal (c)
FIG. 2C shows the result of processing the rising edge of the digital detection signal (d), which has a paired relationship with the rising edge of FIG. When the rising edge of the digital detection signal (c) is more advanced than the rising edge of the digital detection signal (d) (portions c1 and d1, c5 and d5), this signal is the gate shown in FIG. When the rising edge of the digital detection signal (d) occurs during the period when the signal is “High”, “High” occurs at the timing of the falling edge in FIG.
h), and is reset to “Low” at the timing of the falling edge in FIG.
In the state (c7 and d7) in which the rising edge of the digital detection signal (c) is later than the rising edge of the digital detection signal (d), the signal "High" of the gate signal shown in FIG. If the rising edge of the digital detection signal (c) occurs during the “period”, it is set to “High” at the timing of the rising edge in FIG. 2A, and “Low” at the timing of the falling edge in FIG. Is reset to

The result of processing the falling edge of the digital detection signal (c) is shown in FIG. FIG. 2C shows the result of processing the falling edge of the digital detection signal (d), which has a paired relationship with the falling edge of the digital detection signal (c).

The position information of the rising edge and the falling edge of the digital detection signal (c) when the two digital detection signals are inverted in the same direction within the predetermined time T are shown in FIGS. By taking the logical sum of the signals shown, the signal is projected on the falling edge of the signal shown in FIG.

When the two digital detection signals are inverted in the same direction within the predetermined time T, the position information of the rising edge and the falling edge of the digital detection signal (d) is shown in FIGS. 2) is projected onto the falling edge of the signal shown in FIG.

In the case where an output appears only in one digital detection signal due to a medium defect or the like due to the above processing,
In the case where the two digital detection signals do not reverse in the same direction within the predetermined time T, the phase difference determination means 46 determines that an abnormal state has occurred and stops outputting the signals (h) and (i). This prevents the second phase comparison means 47 from erroneously detecting the phase difference.

FIG. 2 shows an example of the operation in the abnormal state.
Description will be made using the pulse portion between the state inversions d3 and d4 in (d). In this state, there is a detection pulse only in the digital detection signal (d), and a detection pulse corresponding thereto is not detected in the digital detection signal (c). In this case, since the state inversion of the digital detection signal (c) with respect to the state inversions d3 and d4 cannot occur within the fixed time T, the phase difference determination means 46 does not output a pulse to the signals (h) and (i).

The second phase comparing means 47 detects a phase difference between the falling edges of the outputs (h) and (i) of the phase difference judging means 46, and drives two charge pump means 451 of the next stage. It outputs drive signals (PU) and (PN). Here, the drive signal (PU) is a signal indicating that the falling edge of the signal (h) is ahead of the falling edge of the signal (i), and the pulse width thereof corresponds to the leading time. The drive signal (PN) is a signal indicating that the falling edge of the signal (h) is delayed compared to the falling edge of the signal (i), and the pulse width thereof corresponds to the delay time.

The charge pump means 451 drives the current source for the source for the duration of the pulse width of the drive signal (PU), thereby accumulating (charging) electric charge in the capacitor constituting the LPF 452, and also driving the drive signal (PN). By driving the sink current source for the pulse width of (1) and extracting (discharging) the electric charge from the capacitor, the phase difference, which is time information, is converted into a voltage, which is an electric signal.

The LPF 452 removes high frequency components unnecessary for the tracking servo means by smoothing the pulse output of the charge pump means 451, and generates a tracking error signal (TES).

The tracking control means 5 controls the radial position of the light beam emitted from the optical head 3 to the optical disc 1 so as to cancel the tracking error indicated by the tracking error signal (TES). Always drive in the center of the truck.

As described above, in the optical information reproducing apparatus according to the first embodiment, when an abnormal state occurs due to a defect such as a scratch, a signal for detecting a phase difference is transmitted to the second phase comparing means. Since it is not input to the block 47, erroneous detection of the phase difference can be prevented. As a result, disturbance can be suppressed from being mixed into the tracking error signal, and the tracking control can be stabilized.

Next, FIG. 3 shows a specific circuit example of the phase difference judging means 46. In the figure, 461 is a rising edge phase difference judging means, 462 is a falling edge phase difference judging means,
3 is a first inverter, 464 is a second inverter, 4
65 indicates a first OR means, and 466 indicates a second OR means.

Here, the rising edge phase difference judging means 46
1, 100 is the first flip-flop (FF), 10
1 is a first delay unit, 102 is a second FF, 103 is a second delay unit, 104 is a third FF, and 105 is a fourth FF.
F, 106 are third OR means, 107 is fifth FF, 1
08 is a sixth FF, and 109 is a fourth OR means. Further, the falling edge phase difference determining means 462
Is the same circuit as the rising edge phase difference determining means 461.

FIG. 4 is a diagram showing signal waveforms at various parts in FIG. The signal waveform of each symbol shown in FIG. 4 indicates a signal waveform of a portion given the same symbol in FIG. Hereinafter, the operation of the phase difference determination means 46 will be described with reference to FIG.

The two detection signals (a) and (b) output from the optical head 3 are binarized by a first waveform shaping means 41 and a second waveform shaping means 42, and a digital detection signal (c) And (d). The state inversion part of the digital detection signal (c) is represented by c1, c2, c5, c
6, c7 and c8. The state inversion part of the digital detection signal (d) is represented by d1, d2, d3, d4, d
5, d6, d7 and d8.

At this time, state inversions c1, c2, c5, c
6, c7 and c8 are state inversions d1, d2, d5, d
6, d7 and d8. Here, the state inversion c1, c2 and c5 of the digital detection signal (c) are
Indicates a state in which the phase is advanced as compared with the state inversion d1, d2 and d5 of the digital detection signal (d). The state inversions c6, c7 and c8 of the digital detection signal (c) are the state inversion d of the digital detection signal (d).
6 shows a state in which the phase is delayed as compared with d7 and d8.

The state inversions d3 and d4 of the digital detection signal (d) indicate abnormal states in which there is no corresponding state inversion of the digital detection signal (c).

First, the rising edge phase difference judging means 461
Will be described. The Q output (A) of the first FF 100 changes to “High” (or “1”) at the timing of the rising edge of the output pulse (c) of the first waveform shaping means 41 input to the clock input terminal. . The / Q output (A) is "Low" at the same timing.
(Or “0”). First delay means 101
Delays the / Q output (a) for a predetermined time T, and produces a waveform (c)
Is output. The first FF 100 changes the Q output (A) from “High” to “Low” at the timing of the falling edge of the waveform (C). Thereby, the first FF1
At the output of 00, a gate signal having a pulse width T starting from the rising edge of the digital detection signal (c) is output.

The second FF 102 is also the first FF 10
The same operation as 0 is performed, and a gate signal having a pulse width T starting from the rising edge of the digital detection signal (d) is output to the outputs (D) and (E). The second delay means 103 delays the / Q output (e) by a predetermined time T and outputs a waveform (f).

The Q output (g) of the third FF 104 is
When the Q output (a) of the second FF 102 has a rising edge within a predetermined period T from the rising edge of the digital detection signal (c) during the period when the Q output (a) of the FF 100 is "High", this edge At the timing of "Hig
After that, the Q output (G) of the third FF 104 changes to “Low” at the timing of the falling edge of the output (C) of the first delay unit 101.

The meaning of the Q output (g) signal of the third FF 104 is that the digital detection signal (c) is “Lo”
The digital detection signal (d) is changed from “Low” to “High” within a predetermined time T after changing from “w” to “High”.
h "indicates that the state inversion of the two digital detection signals is determined to be normal, and information on the rising edge of the digital detection signal (c) is output with a delay of T for a predetermined time.

A similar operation is performed by the fourth FF 105 and the fifth F
F107 and the sixth FF are also executed. The meaning of the output signal of each FF is as follows.
Within a predetermined time T after the digital detection signal (d) changes from "Low" to "High", the Q output (h) of the fourth FF 105 shows the digital detection signal (c) at "Lo".
When the signal changes from "w" to "High", a signal obtained by delaying the information of the rising edge of the digital detection signal (c) by a predetermined time T is output.

The digital output signal (d) is changed from “Low” to “Hi” to the Q output (K) of the fifth FF 107.
When the digital detection signal (c) changes from "Low" to "High" within a predetermined time T after changing to "gh", the information of the rising edge of the digital detection signal (d) delayed by a predetermined time T is output. Is done.

Further, the Q output (f) of the sixth FF 108
The digital detection signal (c) changes from “Low” to “H”.
When the digital detection signal (d) changes from "Low" to "High" within a certain time T after changing to "high", a signal obtained by delaying the information of the rising edge of the digital detection signal (d) by a certain time T is output. Is done.

The third OR means 106 outputs the third FF 10
4 and the Q output (h) of the fourth FF 105 are ORed to obtain the digital detection signal (c) when the rising edges of the two digital detection signals are within a predetermined time T. Outputs rising edge information (q).

The fourth OR means 109 outputs the fifth F
By taking the logical sum of the Q output (F) of F107 and the Q output (S) of the sixth FF 108, the digital detection signal (d) when the rising edges of the two digital detection signals are within the predetermined time T is obtained. Outputs rising edge information (S).

Next, the falling edge phase difference judging means 46
Operation 2 will be described. The two digital detection signals (c) and (d) are inverted and input by the first inverter 463 and the second inverter 464 to the falling edge phase difference determination means 462. The circuit configuration of the falling edge phase difference judging means 462 is the same as that of the above-mentioned rising edge phase difference judging means 461.
The falling edge information (s) of the digital detection signal (c) and the falling edge information (s) of the digital detection signal (d) when the falling edges of the two digital detection signals are within the predetermined time T are output. .

The first OR means 465 calculates the logical sum of the rising edge information (k) and the falling edge information (s) of the digital detection signal (c) to obtain one of the two digital detection signals. If the state of the other digital detection signal is inverted in the same direction within a predetermined time T after the detection signal is inverted, edge information (h) of the digital detection signal (c) is output.

The second OR means 466 calculates the logical sum of the rising edge information (S) and the falling edge information (S) of the digital detection signal (d), thereby obtaining one of the two digital detection signals. When the state of the other digital detection signal is inverted in the same direction within a predetermined time T after the state of the digital detection signal is inverted, the digital detection signal (d)
Is output as edge information (i).

According to the above processing, in the case where an output appears only in one digital detection signal due to a medium defect or the like, or in the case where the two digital detection signals do not invert in the same direction within a predetermined time T, the phase difference determination The means 46 stops outputting the signals (h) and (i) on the assumption that an abnormal condition has occurred, and prevents the second phase comparing means 47 in the next stage from erroneously detecting the phase difference.

FIG. 4 shows an example of the operation in the abnormal state.
Description will be made using the pulse portion between the state inversions d3 and d4 in (d). In this state, there is a detection pulse only in the digital detection signal (d), and a detection pulse corresponding thereto is not detected in the digital detection signal (c). In this case, since the state inversion of the digital detection signal (c) with respect to the state inversions d3 and d4 cannot occur within the fixed time T, the phase difference determination means 46 does not output a pulse to the signals (h) and (i).

Next, FIG. 5 shows the phase difference judging means 46 and the second
A specific example of a circuit in which the phase comparison means 47 of FIG.
In the figure, reference numeral 200 denotes a rising edge phase difference determination-comparison means;
01 denotes a falling edge phase difference determination / comparison means, 463 denotes a first inverter, 464 denotes a second inverter, 202 denotes a fifth OR means, and 203 denotes a sixth OR means.

Here, the rising edge phase difference determining / comparing means 200 includes a first flip-flop (F
F), 101 is a first delay means, 102 is a second FF,
103 is a second delay means, 114 is a seventh OR means, 1
15 is an eighth OR means, 116 is a seventh FF, 117 is an eighth FF, 118 is a NAND, and 119 is a third FF.
The delay means 120 comprises a fourth delay means. Also, a falling edge phase difference determination-comparing means 201
Is the same circuit as the rising edge phase difference determination and comparison means 200.

FIG. 6 is a diagram showing signal waveforms at various parts in FIG. The signal waveform of each symbol shown in FIG. 6 indicates the signal waveform of the portion given the same symbol in FIG. Hereinafter, the operation of the rising edge phase difference determining / comparing means 200 will be described with reference to FIG.

The Q output (A) of the first FF 100 is “Hig” at the rising edge of the output pulse (c) of the first waveform shaping means 41 input to the clock input terminal.
h ”, and the / Q output changes to“ Low ”at the same timing.
The output is delayed for a certain time T. The first FF 100 changes the Q output (A) from “High” to “Low” at the timing of the falling edge of the output of the first delay unit 101. As a result, a gate signal having a pulse width T starting from the rising edge of the digital detection signal (c) is output to the Q output (A) and / Q output of the first FF 100.

The second FF 102 is also the first FF 10
The same operation as 0 is performed, and a gate signal having a pulse width T starting from the rising edge of the digital detection signal (d) is output to its Q output (d) and / Q output.

The Q output (A) of the first FF 100 is input to one input terminal of the eighth OR means 115. The Q output (SO) of the seventh FF 116 is input to the other input terminal of the OR means 115. The Q output (d) of the second FF 102 is input to one input terminal of the seventh OR means 114. The Q output of the eighth FF 117 is input to the other input terminal of the seventh OR means 114.

The output of the seventh OR means 114 is input to the D input terminal of the seventh FF 116, and the / Q output of the first FF 100 is input to the clock input terminal of the third delay means 119.
And the reset input terminal is connected to the NAND means 1
18 outputs are input. Also, the D of the eighth FF 117
The input terminal receives the output of the eighth OR means 115,
The / Q output of the second FF 102 is input to the clock input terminal via the fourth delay means 120, and the output of the NAND means 118 is input to the reset input terminal. here,
The third delay unit 119 adjusts the timing of a signal input to the D input terminal and the clock input terminal of the seventh FF 116. Further, the fourth delay means 12
0 is arranged for the same purpose.

The Q output (SO) of the seventh FF 116 is one input terminal of the fifth OR means 202 and the NAND means 118
And one input terminal of the eighth OR means 115 as described above. Also, the eighth F
The Q output of F117 is input to one input terminal of the sixth OR means 203, the other input terminal of the NAND means 118, and one input terminal of the seventh OR means 114 as described above.

With the above configuration, the phase difference between the rising edges of the two digital detection signals (c) and (d) is detected. If the digital detection signal (c) is ahead of the digital detection signal (d), the seventh FF
The pulse width of the Q output signal (SO) 116 is the eighth FF 11
7 is wider than the pulse width of the Q output signal (ta), and the difference between these two pulse widths indicates the phase difference. Also,
Conversely, when the digital detection signal (d) is advanced compared to the digital detection signal (c), the pulse width of the Q output (ta) of the eighth FF 117 is equal to the pulse width of the Q output signal (g) of the seventh FF 116. It becomes wider than the pulse width, and the difference between these two pulse widths indicates the phase difference.

The feature of this circuit is that the dead band (region where no detection signal is output even if there is a phase difference between two signals in the process of phase difference comparison) caused by delay in the circuit is reduced. It is. That is, by delaying the reset signals of the seventh FF 116 and the eighth FF 117 by the NAND means 118, the Q output (SO) of the seventh FF 116 and the eighth FF 11
7, the minimum pulse of the delay time width is output to the Q output (ta).

Falling edge phase difference judging / comparing means 201
Is a circuit having the same configuration as the above-described rising edge phase difference determination / comparison means 200, and has the same operation. However, the input signals are different, and the two digital detection signals (c) and (d) are inverted and input by the first inverter 463 and the second inverter 464, respectively. That is, the falling edge phase difference determination / comparison means 201 detects the phase difference between the falling edges of the two digital detection signals (c) and (d), and outputs the output signals (g) and (n). Is output.

Rising edge phase difference judging / comparing means 200
Output signals (G) and (G) and the output signals (G) and (N) of the falling edge phase difference determination / comparison means 201 are
By the fifth OR means 202 and the sixth OR means 203,
Output signals (G) and (G) and output signals (G) and (G)
Are logically added to each other, and the next stage charge pump means 4
51 are converted into two driving signals (PU) and (PN) for driving the driving signal 51.

According to the circuit configuration described above, when one digital detection signal of two digital detection signals is inverted in state and then the other digital detection signal is inverted in the same direction within a predetermined time T, the digital detection signal is output. The phase difference between (c) and (d) can be detected.
Furthermore, the reduction of the dead zone that occurs during the phase difference comparison can also be realized.

Next, specific examples of the first delay means 101 and the second delay means 103 constituting the phase difference judgment means 46 will be described. In the following description, the operation of the first delay unit 101 will be described for convenience. The first delay means 101 includes 301
Is a transistor (TR), 302 is a first current source, 30
Reference numeral 3 denotes a second capacitor, and reference numeral 304 denotes a comparator. Reference numeral 100 denotes the first FF. The operation of this circuit will be described with reference to FIG. 8 showing waveforms at various parts in FIG.

The first FF 100 outputs Q at the timing of the rising edge of the output signal (c) of the first waveform shaping means 41.
The output is set to "High" and the / Q output is set to "Low" (FIGS. 8A and 8B). This / Q output is input to the base of the transistor 301. When the / Q output becomes “Low”, the emitter potential of the transistor 301 becomes
The current gradually decreases with a time constant determined by the current of the first current source 302 and the capacity of the second capacitor 303. Fig. 8 (d)
Shown in

The comparator 304 is a transistor 301
Is compared with a comparison voltage Vth, and the signal becomes “Low” in a region where the emitter potential is equal to or lower than the comparison voltage Vth. This state is shown in FIG. The output (C) of the comparator 304 is connected to the reset terminal of the first FF 100, and the output (C) of the comparator 304 is output.
Is "Low", the Q output of the first FF 100 is "Low".
w, and the / Q output becomes “High” (FIG. 8A)
(I)).

The Q output of the first FF 100 and / Q
The output pulse width indicates the amount of delay generated by the first delay means 101. This delay amount can be arbitrarily set according to the amount of current of the first current source 302 or the capacity of the second capacitor 303.

Here, as shown in FIG. 9, by making the first current source 302 a variable current type in which the amount of current can be controlled by an external control signal, the amount of delay of the delay means can be set arbitrarily. Become. By using this function, the amount of delay can be optimized according to the playback speed, and variable speed playback becomes possible.

The amount of current of the first current source 302 is controlled by D /
It can be easily realized by using an A converter (DAC). The control signal can be easily generated by processing the data reproduction clock frequency as information by a controller such as a microprocessor or a digital signal processor. That is, the controller may determine the reproduction speed from the data reproduction clock frequency, and derive a control signal for setting the optimum amount of current for the reproduction speed by calculating or referring to a table. When reproducing a medium in which header information indicating a track address or a sector address is recorded separately from user information,
The cycle of the header section may be used as an information source for the controller to obtain the control signal.

Next, a more specific example of the phase difference-voltage conversion means 45 is shown in FIG. Here, a description will be given of a case where a function for coping with the above-mentioned variable speed reproduction and a function for adjusting the balance of the tracking error signal are added. In the figure, 451 is a charge pump means, 452 is LP
F and 453 denote balance determination means, 454 denotes a controller, and 455 denotes reference current generation means. The charge pump unit 451 includes a second current source 400, a first switch unit 401, a second switch unit 402, and a third current source 403.

The operation of the phase difference-to-voltage converter 45 configured as described above will be described. Charge pump means 451
Are the first switching means 401 and the second switching means 4 based on the output signals PU and PN of the second phase comparing means 47.
By driving 03, a capacitor constituting the LPF 452 is charged and discharged. That is, the first switch unit 401
Short-circuits the switch for the duration of the pulse width of the drive signal (PU), and flows a current from the second current source 400 into the capacitor to charge it. Also, the second switch means 40
2 short-circuits the switch for the duration of the pulse width of the drive signal (PN), and the third current source 403 absorbs the current from the capacitor and discharges it.

Further, the LPF 452 smoothes the output pulse of the charge pump means 451 and converts it into a tracking error signal (TES).
Output to Here, the tracking error signal (TE
The ideal state of S) is, as shown in FIG. 11A, a waveform which is vertically symmetric with respect to a reference level (shown by a chain line in the figure). However, the balance of the optical system constituting the optical head 1 is deviated, and the second current source 400 and the third current source 4
11 (b) due to the imbalance in the amount of current between 03 and the like.
As shown in (c), the tracking error signal (TES) is vertically asymmetric. When the tracking error signal (TES) has an asymmetric waveform in this manner, the control margin on the side with the smaller amplitude level decreases, and the tracking performance deteriorates.

The balance determination means 453 detects a balance deviation of the tracking error signal (TES) and outputs the information to the controller 454. Controller 454
Processes the balance deviation information from the balance determination unit 453, and outputs a signal for correcting the balance deviation to the reference current generation unit 455. The reference current generating means 455 responds to a signal from the controller 454 by using the second current source 40.
The balance between the tracking error signal (TES) is corrected by varying the current balance between 0 and the third current source 403. At this time, the sum of the current amount of the second current source 400 and the current amount of the third current source 403 is constant.

Further, the reference current generating means 455 responds to a control signal from the controller 454 by using the second current source 400.
And the sum of the current amount of the third current source 403 and the current amount of the third current source 403 can be controlled. The sum of the current amounts needs to be optimized according to the reproduction speed, similarly to the delay amount of the delay means described above. The reason is that the relationship between the track shift amount and the phase difference amount generated between the two detection signals changes according to the reproduction speed even when the track shift amount is the same.

For example, assuming that the sum of the current amounts of the two current sources is constant and the track shift amount is constant, the phase difference generated between the two detection signals increases as the reproduction speed increases. Is reduced, and as a result, the signal level of the tracking error signal (TES) is reduced. Conversely, if the reproduction speed decreases, the amount of phase difference generated between the two detection signals increases, and as a result, the signal level of the tracking error signal (TES) increases.

However, the tracking error signal (TES) does not depend on the reproduction speed, and it is necessary to keep the relationship between the track shift amount and the signal level constant. Therefore, the controller 454 receives information from outside (hereinafter, “INFO”).
Called. ) Is used to determine the reproduction speed, and the reference current generating means 455 is controlled to control the sum of the current amounts of the two current sources in proportion to the reproduction speed. As the INFO, the reproduction clock frequency and the frequency of the header section may be used as described above.

By using the above-described configuration of the phase difference-voltage conversion means 45, it is possible to correct the asymmetry of the tracking error signal waveform caused by the imbalance between the optical system and the current source, and to correct the track irrespective of the change in the reproduction speed. The deviation amount and the amplitude of the tracking error signal (TES) can be made constant, and the tracking performance can be stabilized and variable speed reproduction can be performed.

Embodiment 2 FIG. 12 is a diagram showing an optical information reproducing apparatus according to Embodiment 2 of the present invention. In the figure, 1 is an optical disk, 2 is a spindle motor, 3 is an optical head, 4 is a tracking error detecting means for detecting tracking error information from a signal output from the optical head,
Reference numeral 5 denotes tracking control means for controlling the radial position of the light beam emitted from the optical head to the medium so as to cancel the tracking error detected by the tracking error detection means 4. Further, the tracking error detecting means 4 includes a first waveform shaping means 41, a second waveform shaping means 42, a pulse width determining means 48, and a phase difference determining means 4.
6. Second phase comparing means 47, phase difference-voltage converting means 4
5 is comprised.

The operation of the optical information reproducing apparatus of the embodiment configured as described above will be described with reference to FIG. This is basically the same as the description of FIG. However, the difference from the configuration of FIG. 1 is that the pulse width determining means 4 is provided between the first waveform shaping means 41 and the second waveform shaping means 42 and the phase difference determining means 46.
8 has been inserted.

The optical head 3 detects information recorded on the optical disk 1 and outputs detection signals (a) and (b). These two detection signals correspond to the detection signal (A + C) and the detection signal (B + D) described in FIG. When the irradiation position of the light beam deviates from the center of the information track, the optical head 3 detects the two detection signals (a).
The optical system is designed so that a phase difference occurs between (b) and (b).

The first waveform shaping means 41 removes low-frequency components from the detection signal (a), binarizes the signal, and outputs a digital detection signal (c). Similarly, the second waveform shaping means 42 removes low-frequency components from the above-mentioned detection signal (b), binarizes it, and outputs a digital detection signal (d).

The pulse width judging means 48 detects, for each of the two digital detection signals (c) and (d), a short-period mark in which no phase difference occurs between the two digital detection signals due to optical characteristics in principle. After removing the digital detection signal from the mark and the digital detection signal from the mark that cannot be generated due to the modulation rule, the signal (c ′)
And (d ') to the phase difference determination means 46.

The phase difference judging means 46 outputs the signal (c ′)
If one of the signals in (d) and (d ') is inverted, and the other signal is inverted in the same direction within a predetermined time after the signal is inverted, it is determined that the signals (c') and (d ') are valid.
The edge information (h) and (i) are output.

The second phase comparing means 47 detects a phase difference between edges from the two pieces of edge information (h) and (i), and drives two phase difference-voltage converting means 45 at the next stage. Output signals (PU) and (PN). Here, the drive signal (PU) is a signal indicating that the edge information (h) is advanced compared to the edge information (i), and the pulse width thereof corresponds to the advance time. In addition, the drive signal (P
N) is a signal indicating that the edge information (h) is behind the edge information (i), and the pulse width thereof corresponds to the delay time.

The LPF 452 removes high frequency components unnecessary for the tracking servo means by smoothing the pulse output of the charge pump means 451 and generates a tracking error signal (TES).

When the phase difference / voltage conversion means 45 is constituted by, for example, the charge pump means described with reference to FIG. 1, the LPF is driven by driving the source current source for the time of the pulse width of the drive signal (PU). Is accumulated (charged) in a capacitor constituting the circuit, and a sink current source is driven for the pulse width of the drive signal (PN) to extract (discharge) the charge from the capacitor, thereby obtaining time information. The phase difference is converted into a voltage which is an electric signal.

The LPF removes high frequency components unnecessary for the tracking servo means by smoothing the pulse output of the charge pump means, and generates a tracking error signal (TES).

The tracking control means 5 controls the radial position of the light beam emitted from the optical head 3 to the optical disc 1 so as to cancel the tracking error indicated by the above-mentioned tracking error signal (TES). Always drive in the center of the truck.

With the above configuration, in principle, a digital detection signal from a short-period recording mark in which no phase difference occurs between the two digital detection signals and a digital detection signal from a recording mark having a length that cannot be generated due to the modulation rule. After the detection signal is removed, an edge pair in which the two digital signals are inverted in the same direction is determined and extracted within a certain period of time, and the phase difference between the edge pair is detected to detect a tracking error signal. In this method, disturbance is suppressed and tracking error detection capability is improved.

[0129]

Since the present invention is configured as described above, it has the following effects.

In the optical information reproducing apparatus according to the first aspect of the present invention, two detection signals whose phase relationship changes according to the displacement amount of the light spot from the track center are two corresponding to each detection signal. Generate a digital signal. Then, after extracting an edge pair in which these two digital signals invert in the same direction within a predetermined time, a phase difference between the edge pair is detected to obtain a tracking error signal.
By doing so, the abnormal state can be determined more accurately, and disturbances can be suppressed from being mixed into the tracking error signal caused by a medium defect or the like, so that the tracking error detection accuracy by the phase difference method is improved. I do.

In the optical information reproducing apparatus according to the second aspect of the present invention, two digital signals generated from two detection signals whose phase relationship changes according to the amount of displacement of the light spot from the track center. A tracking error is generated by detecting a phase difference between the detection signals. At this time, in principle, a digital detection signal detected from a short-period mark where no phase difference occurs between the two digital detection signals, and a digital detection signal from a recording mark having a length that cannot be generated due to a modulation rule. After the removal, a pair of edges in which the two digital signals are inverted in the same direction is extracted within a predetermined time, and a phase difference between the pair of edges is detected to generate a tracking error signal. By doing so, in addition to suppressing the incorporation of disturbance into the tracking error signal caused by a medium defect or the like, the incorporation of unnecessary information into the tracking error signal which occurs even in a normal reproduction state can be suppressed. The detection ability is improved.

In the optical information reproducing apparatus according to the third aspect of the present invention, by setting the predetermined time to be equal to or less than the pulse width reproduced from the shortest recording mark that can be taken according to the modulation rule, the normal time can be set. An abnormal time can be accurately determined. Also, even if an abnormal state for a set time or less occurs, such a time does not cause a large disturbance to the tracking error signal and does not significantly reduce the reliability of the device.

In the optical information reproducing apparatus according to the fourth aspect of the present invention, the rotation speed of the disk motor can be reduced by variably setting the fixed time which varies according to the data rate according to the data rate. The tracking error detection accuracy can be maintained even in variable-speed reproduction in which information is reproduced from a medium before settling, or in high-speed reproduction at twice or higher speed.

In the optical information reproducing apparatus according to the fifth aspect of the present invention, the positive and negative pulse widths of the digital detection signal used for detecting the phase difference are at least five times the channel bit period and the longest. By setting the length to be equal to or less than the mark length, information from a short-period recording mark in which a phase difference does not occur in principle between the two digital detection signals, and information from a recording mark having a length that cannot be generated due to a modulation rule. It is possible to prevent information from being mixed into the tracking error signal as a disturbance, and it is possible to detect a tracking error with high accuracy.

[Brief description of the drawings]

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

FIG. 2 is a diagram showing output waveforms of respective units in FIG.

FIG. 3 is a diagram illustrating a specific example of a phase difference determination unit included in the optical information reproducing device according to the first embodiment of the present invention.

FIG. 4 is a diagram illustrating output waveforms of respective units in FIG. 3;

FIG. 5 is a diagram showing a specific example in which a phase difference determination unit and a phase comparison unit constituting the optical information reproducing apparatus according to the first embodiment of the present invention are integrated;

FIG. 6 is a diagram showing output waveforms of respective units in FIG.

FIG. 7 is a diagram showing a specific example of a delay unit.

FIG. 8 is a diagram showing output waveforms of respective units in FIG. 7;

FIG. 9 is a diagram showing another specific example of the delay unit.

FIG. 10 is a diagram showing output waveforms of respective units in FIG. 9;

FIG. 11 is a diagram showing a tracking error signal.

FIG. 12 is a block diagram of an optical information reproducing apparatus according to an embodiment of the present invention.

FIG. 13 is a diagram illustrating a principle of detecting a tracking error by a phase difference method.

FIG. 14 is a diagram showing a conventional optical information reproducing apparatus.

FIG. 15 is a diagram showing output waveforms of each unit in FIG. 14;

FIG. 16 is a diagram illustrating a relationship between a recording mark cycle and a generated phase difference.

[Explanation of symbols]

Reference Signs List 1 optical disk, 2 spindle motor, 3 optical head, 4 tracking error detecting means, 5 tracking control means, 41 first waveform shaping means, 42 second waveform shaping means, 43 first phase comparing means, 44 validity discrimination Means, 45 phase difference-voltage conversion means, 46 phase difference determination means, 47 second phase comparison means, 48 pulse width determination means, 100 first flip-flop (FF), 1
01 first delay means, 102 second FF, 103 second delay means, 104 third FF, 105 fourth F
F, 106 third OR means, 107 fifth FF, 1
08 sixth FF, 109 fourth OR means, 114
Seventh OR means, 115 Eighth OR means, 116 Seventh FF, 117 Eighth FF means, 118 NAND means, 119 Third delay means, 120 Fourth delay means, 200 Rising edge phase difference determination- Comparison means, 20
1 Falling Edge Phase Difference Judgment-Comparing Means, 202 Fifth
OR means, 203 sixth OR means, 301 transistor (TR), 302 first current source, 303 second capacitor, 304 comparator, 400 second
Current source, 401 first switch means, 402 second
Switch means, 403 third current source, 451 charge pump means, 452 LPF, 453 balance determination means, 454 controller, 455 reference current generation means, 461 rising edge phase difference determination means, 462 falling edge phase difference determination means, 463 First inverter, 464 second inverter, 465 first OR means, 466 second OR means

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Koji Yano, Inventor, Mitsubishi Electric Engineering Co., Ltd. 2-6-1 Otemachi, Chiyoda-ku, Tokyo

Claims (5)

[Claims] 1. A device for converging a light beam on an information track on a medium to form a light spot, and reproducing information recorded on the information track from the reflected light, comprising: An optical head that outputs at least two detection signals whose phase relationship changes according to a displacement amount (a tracking error amount) of the optical head; and a tracking error detection unit that detects a phase difference between the detection signals and outputs a tracking error signal. Tracking control means for controlling the light spot to travel along the center of the track in accordance with the tracking error signal, wherein the tracking error detection means is a digital detection signal obtained by binarizing the two detection signals. After one of the digital detection signals is inverted, the other detection signal is inverted in the same direction within a predetermined time. In case, the optical information reproducing apparatus characterized by obtaining a tracking error signal by detecting the phase difference between the detection signal. 2. An apparatus for converging a light beam on an information track on a medium to form a light spot and reproducing information recorded on the information track from the reflected light, comprising: An optical head that outputs at least two detection signals whose phase relationship changes according to a displacement amount (a tracking error amount); a tracking error detection unit that detects a phase difference between the detection signals and outputs a tracking error signal; Tracking control means for controlling the light spot to travel around the center of the track in accordance with the tracking error signal, wherein the tracking error detection means converts a digital detection signal obtained by binarizing the two detection signals. Each of the positive and negative pulse widths is within a predetermined range, and one of the two digital detection signals is When the state of the other digital detection signal is inverted in the same direction within a predetermined time after the state of the digital detection signal is inverted, a tracking error signal is obtained by detecting a phase difference between the digital detection signals. Information reproducing device. 3. The method according to claim 1, wherein the predetermined time is not more than a shortest mark length.
Item 6. The optical information reproducing apparatus according to any one of the above items. 4. The optical information reproducing apparatus according to claim 1, wherein the predetermined time is variable in accordance with a data rate. 5. The optical information according to claim 2, wherein the positive and negative pulse widths of each of the digital detection signals are not less than 5 times the channel bit period and not more than the longest mark length. Playback device.