JP2004071035A - Optical disk drive - Google Patents

Abstract

Provided is an optical disk device that can prevent a malfunction of a dropout detection device and a malfunction of a servo even when a WDO occurs.
A high-speed peak detection circuit for detecting the bright side of a reproduced signal obtained by reproducing information recorded on an optical disk, and a low-speed peak detection circuit for detecting the bright side of the reproduced signal with a time constant different from that of the high-speed peak detection circuit. Comparing the high-speed peak detection signal detected by the high-speed peak detection circuit with the low-speed peak detection signal detected by the low-speed peak detection circuit, and when the potential of the low-speed peak detection signal is larger than the potential of the high-speed peak detection signal. And a comparator which outputs a dropout detection signal when it is determined to be in a dropout state, a limiter circuit is provided after the low speed peak detection circuit, and the low speed peak detection signal is clipped to a predetermined potential.
[Selection diagram] Fig. 1

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical disc device that can prevent erroneous detection from occurring in dropout detection and can prevent erroneous servo operation before it occurs.
[0002]
[Prior art]
In recent years, recording and reproduction of a compact disk (hereinafter, referred to as “CD”) have been put to practical use. In order to perform recording and reproduction on a CD with high accuracy, it is necessary to accurately detect a dropout. Here, the dropout detection in the optical disk device refers to a phenomenon that when foreign matter such as dust or dirt adheres to the disk surface, a phenomenon occurs in which a signal cannot be detected and a part that is interrupted occurs, and such a signal is interrupted. This means detecting the part.
[0003]
Hereinafter, a dropout detection method in a conventional optical disk device will be described with reference to the drawings. FIG. 16 is a block diagram of a dropout detection device in a conventional optical disk device.
[0004]
In FIG. 16, reference numeral 1 denotes a reproduced signal reproduced from the optical disk, 2 denotes a high-speed peak detection circuit for detecting the bright side of the reproduced signal 1, and 3 denotes a case where the bright side of the reproduced signal 1 is slower than the high-speed peak detection circuit 2. Reference numeral 4 denotes a low-speed peak detection circuit that performs detection with a constant, and reference numeral 4 denotes a comparator that compares outputs obtained from the high-speed peak detection circuit 2 and the low-speed peak detection circuit 3.
[0005]
A conventional dropout detection method will be described with reference to FIG. 17 based on an actual operation signal waveform in the thus configured dropout detection device.
[0006]
In FIG. 17, waveforms a to e show waveforms at the same time and at the same point. A waveform a is a reproduction signal from the optical disk, and the reproduction signal 1 is indicated by oblique lines. Waveform b is a high-speed peak detection signal obtained by the high-speed peak detection circuit 2, waveform c is a low-speed peak detection signal obtained by the low-speed peak detection circuit 3, d is a waveform obtained by lowering the potential of the output waveform c, e indicates a dropout detection signal which is an output waveform of the comparator 4.
[0007]
A section T1 in FIG. 17 shows a normal reproduction state in which no dropout has occurred. In this state, since the potential of the output waveform b is higher than the potential of the waveform d, the comparator 4 outputs a low level, and the dropout detection signal e indicates a low level.
[0008]
In the section T2, dropout occurs, and the light side of the waveform a sharply drops. The output waveform b also drops sharply following the bright side of the waveform a, but the output waveform d drops at a gentler slope than the output waveform b due to the large time constant. Therefore, since the potential of the waveform b is lower than the potential of the waveform d at the input of the comparator 4, the output of the comparator 4 outputs a high level as indicated by the dropout detection signal e, and a dropout occurs. Can be detected.
[0009]
On the other hand, since the section T3 shows the waveform at the point in time after the dropout section, the potential of the output waveform b is higher than the potential of the waveform d, and the waveform returns to the normal reproduction state. Also returns to the original low level.
[0010]
[Problems to be solved by the invention]
However, in recent years, compact discs having various recording states, such as CD-R and CD-RW, have become widespread. Therefore, for example, in a recordable area on a disc such as a CD-R or a CD-RW that can not only reproduce but also record data, an unrecorded portion may be present in a recorded area due to a buffer under run error.
[0011]
In the above-described configuration, when playing back a disc in which an unrecorded portion exists in the recorded area, unlike the normal dropout, the bright side of the reproduced signal is temporarily A phenomenon called white drop out (hereinafter, referred to as “WDO”), which increases in size, occurs.
[0012]
Due to such a phenomenon, even though dropout has not actually occurred, the dropout detection device malfunctions, and the dropout detection signal becomes high level, so that the servo is disconnected during the reproduction or the sound skips. Or the problem that it occurs. Further, after the occurrence of WDO, the dropout detection device malfunctions, and the problem remains that the original dropout signal cannot be detected while the dropout detection signal is at a high level.
[0013]
Hereinafter, an embodiment of the high-speed peak detection circuit 2 and the low-speed peak detection circuit 3 is shown in FIG. 19, and their operations will be described with reference to FIG.
[0014]
In FIG. 19, the high-speed peak detection circuit 2 includes a diode 7, a current source 8, and a capacitor 9. The diode 7 and the capacitor 9 hold the bright side value of the reproduction signal 1 from the optical disk. The source 8 is for discharging the capacitor 9. The low-speed peak detection circuit 3 is composed of a diode 10, a current source 11, a capacitor 12 having a larger capacitance value than the capacitor 9, and a level shift circuit 13. The diode 10 and the capacitor 12 are provided in the reproduction signal 1 from the optical disk. And the current source 11 is for discharging the capacitor 12. The level shift circuit 13 shifts the level of the output voltage.
[0015]
In FIG. 18, a section T4 indicates an unrecorded portion. In the section T4, the reflected light amount of the RF signal waveform a increases, and WDO occurs. At this time, since the waveform b obtained by the high-speed peak detection circuit 2 in FIG. 19 is charged in the capacitor 9, the potential of the waveform b rises and becomes a waveform following the light side of the waveform a. Similarly, the waveform c obtained by the low-speed peak detection circuit 3 follows the bright side of the waveform a. However, since the capacitance value of the capacitor 12 is larger than that of the capacitor 9, the low-speed peak detection follows the high-speed peak detection more. It is slow and follows only to a potential lower than the waveform b. Note that the waveform d is a waveform that has passed through the level shift circuit 13, and is a waveform obtained by level shifting the waveform c.
[0016]
Since the WDO ends when the unrecorded portion ends, the light side of the waveform a returns to the normal position in the section T5. However, for the waveforms b and c, the discharge of the charges charged in the capacitor 9 or the capacitor 12, respectively, is started. Since the waveform b discharges faster than the waveform c, the potential of the waveform b obtained by the high-speed peak detection circuit 2 is higher than the potential of the waveform d obtained by the low-speed peak detection circuit 3 in this section. The output of the comparator 4 is at a low level.
[0017]
In the section T6, since the discharge speed of the waveform b and the waveform d is different due to the difference in the time constant of the high-speed peak detection circuit 2 and the low-speed peak detection circuit 3, the potential of the waveform d is higher than the potential of the waveform b. The dropout detection signal shown by the waveform e in the output of the comparator 4 keeps outputting a high level for a long time.
[0018]
In the section T3, since the potential of the discharged waveform d becomes smaller than the potential of the waveform b, the output of the comparator 4 becomes low as shown by the waveform e.
[0019]
As described above, when the dropout detection signal indicates the high level for a long time, a problem occurs in that the servo control of the tracking system and the focus system is not performed.
[0020]
SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical disk device capable of preventing a malfunction of a dropout detection device and preventing a malfunction of a servo even when WDO occurs, in order to solve the above problems. .
[0021]
[Means for Solving the Problems]
In order to achieve the above object, an optical disc apparatus according to the present invention includes a high-speed peak detection circuit that detects a bright side of a reproduction signal obtained by reproducing information recorded on an optical disc, and a high-speed peak detection circuit that detects a light side of the reproduction signal. A low-speed peak detection circuit that detects signals with different time constants, a high-speed peak detection signal detected by the high-speed peak detection circuit, and a low-speed peak detection signal detected by the low-speed peak detection circuit are compared. A comparator that determines a dropout state and outputs a dropout detection signal when the potential is greater than the potential of the high speed peak detection signal, including a limiter circuit after the low speed peak detection circuit, Is clipped to a predetermined potential.
[0022]
With this configuration, when a WDO occurs, the high-speed peak detection signal follows the WDO and falls from the peak potential by a certain time constant, but the low-speed peak detection signal is clipped to a certain potential, so that it is kept at a predetermined potential. After that, the time constant of the low-speed peak detection is large, and it falls at a gentle slope. Therefore, the potential of the level-shifted low-speed peak detection signal does not become higher than the potential of the high-speed peak detection signal, so that an erroneous detection signal of dropout due to WDO does not occur, and malfunction of the servo is prevented beforehand. Becomes possible.
[0023]
Further, the optical disk device according to the present invention preferably includes a limiter circuit after the high-speed peak detection circuit, and the high-speed peak detection signal is preferably clipped to a predetermined potential. By doing so, when WDO occurs, both the high-speed peak detection signal and the low-speed peak detection signal are clipped to a certain potential, so that the discharge time of the high-speed peak detection signal by WDO is shortened, and the original BDO after WDO is generated. This prevents the occurrence of a dead zone in which BDO cannot be detected even if the error occurs. In addition, since the low-speed peak detection signal is also clipped to a certain potential when WDO occurs, the potential gradually decreases with a gentle slope due to a large time constant, and the potential of the level-shifted low-speed peak detection signal becomes higher than that of the high-speed peak detection signal. The potential does not become higher than the potential, an erroneous detection signal of dropout due to WDO is not generated, and an optical disk device in which servo does not malfunction can be obtained.
[0024]
Also, an optical disc apparatus according to the present invention includes a high-speed peak detection circuit for detecting a bright side of a reproduced signal obtained by reproducing information recorded on an optical disc, and a high-speed peak detection circuit for detecting the bright side of the reproduced signal with a time constant different from that of the high-speed peak detection circuit. A low-speed peak detection circuit, a high-speed peak detection signal detected by the high-speed peak detection circuit, and a low-speed peak detection signal detected by the low-speed peak detection circuit. A comparator that outputs a drop-out detection signal when the potential is higher than the potential and outputs a drop-out detection signal; a drop-out caused by an increase in the amount of reflected light before the high-speed peak detection circuit and the low-speed peak detection circuit; A limiter circuit for clipping a signal to a predetermined potential is inserted.
[0025]
With such a configuration, when WDO occurs, the reproduced signal from the optical disc is clipped to a certain potential, so that both the high-speed peak detection signal and the low-speed peak detection signal are clipped to a certain potential. The same effect can be expected.
[0026]
Also, an optical disc apparatus according to the present invention includes a high-speed peak detection circuit for detecting a bright side of a reproduced signal obtained by reproducing information recorded on an optical disc, and a high-speed peak detection circuit for detecting the bright side of the reproduced signal with a time constant different from that of the high-speed peak detection circuit. A low-speed peak detection circuit, a high-speed peak detection signal detected by the high-speed peak detection circuit, and a low-speed peak detection signal detected by the low-speed peak detection circuit. When the potential is higher than the potential, a comparator that determines that the device is in a dropout state and outputs a dropout detection signal, and an unrecorded portion exists in a reproduction signal obtained by reproducing information recorded on the optical disc. An unrecorded portion detection circuit for detecting an unrecorded portion in a case where And wherein the sul.
[0027]
With this configuration, when a WDO occurs, the high-speed peak detection signal follows the WDO and falls from the peak potential by a certain time constant. However, since the unrecorded portion is detected, the low-speed peak detection signal is not detected during the unrecorded portion. Since the potential is held, the potential of the level-shifted low-speed peak detection signal does not become higher than the potential of the high-speed peak detection signal, and the dropout signal due to WDO is not erroneously detected. Obtainable.
[0028]
Further, in the optical disk device according to the present invention, when an unrecorded portion is detected, it is preferable to hold not only the potential of the low-speed peak detection signal but also the potential of the high-speed peak detection signal. In this way, when WDO occurs, the unrecorded portion is detected by the unrecorded portion detection circuit, so that the potential of the high-speed peak detection signal and the potential of the low-speed peak detection signal are both held during the unrecorded portion. You. Therefore, it is expected that the same effect as the above-described effect can be obtained.
[0029]
BEST MODE FOR CARRYING OUT THE INVENTION
(Embodiment 1)
Hereinafter, an optical disc device according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram illustrating a configuration of the optical disc device according to the first embodiment of the present invention.
[0030]
In FIG. 1, reference numeral 1 denotes a reproduced signal from an optical disk. A high-speed peak detection signal can be obtained by a high-speed peak detection circuit 2 for detecting the bright side of the reproduced signal 1 at high speed. A low-speed peak detection signal can be obtained by the low-speed peak detection circuit 3 that detects a time constant different from that of the high-speed peak detection circuit 2. Then, by inserting the limiter circuit 5 after the low-speed peak detection circuit 3, it is possible to obtain a low-speed peak detection signal clipped to a certain potential when WDO occurs.
[0031]
Next, the comparator 4 compares the high-speed peak detection signal with the low-speed peak detection signal. When the potential of the low-speed peak detection signal is higher than the potential of the high-speed peak detection signal, a drop-out detection signal indicating that the device is in a drop-out state is output.
[0032]
The operation of each signal waveform when WDO actually occurs will be described with reference to FIG. In FIG. 2, waveforms a to e show waveforms at the same time and at the same point. Similarly, in the following explanatory diagrams, the waveforms a to e all indicate waveforms at the same time and at the same point.
[0033]
FIG. 3 is an exemplary diagram in which a limiter circuit 5 is inserted into the low-speed peak detection circuit 3 shown in FIG. The limiter circuit 5 includes a PNP transistor 14 and a reference voltage 15, and the low-speed peak detection signal is clipped by the limiter circuit 5 to a certain potential.
[0034]
In FIG. 2, in the section T7, the reproduction signal waveform a is in a normal reproduction state, and the waveforms b and c are waveforms obtained by detecting the light side of the waveform a. The waveform d is a waveform obtained by lowering the potential of the waveform c.
[0035]
Section T8 shows an unrecorded portion on the disk surface, and WDO occurs in waveform a. Waveform b follows WDO to be charged by capacitor 9 of FIG. The waveform c does not follow WDO, but is clipped to a certain potential by the limiter circuit 5.
[0036]
Further, after the section T9, WDO ends, and the light-side level of the waveform a returns to the normal reproduction state. In the waveforms b and c, the discharge of the capacitor 9 and the capacitor 12 starts after the end of the WDO. The waveform b drops to the normal potential, and the waveform c drops from the clipped potential to the normal potential with a gentler slope than the waveform b in the section T10 because the capacity of the capacitor 12 is larger than the capacity of the capacitor 9. In the subsequent section T11, the waveform c returns to the normal reproduction state.
[0037]
Comparing the waveform b and the waveform d, the potential of the waveform d is always smaller than the potential of the waveform b by inserting the limiter circuit 5 after the low-speed peak detection circuit 3, and the output waveform e is always at the low level. Become.
[0038]
As described above, according to the first embodiment, even when WDO occurs, there is an effect that erroneous detection of dropout does not occur and a situation in which servo is disengaged does not occur.
[0039]
(Embodiment 2)
An operation waveform in the case where the original dropout occurs after the occurrence of WDO in the first embodiment will be described with reference to FIG. In the sections T7 to T9 in FIG. 4, each waveform operates in the same manner as in FIG. 2, but the original dropout occurs after the occurrence of WDO, so that the waveform b has a high-speed peak detection up to the dark side of the waveform a. , And then follows the dropout of the waveform a.
[0040]
Therefore, in the section T12, since the potential of the waveform b is smaller than the potential of the waveform d, the drop-out detection signal shown in the waveform e is detected. Is a dead zone where the dropout cannot be completely detected. Also, in the waveform d, since the discharge is performed at a low speed after the occurrence of the WDO, the detection sensitivity for detecting the dropout detection signal varies.
[0041]
Such a section in which the original dropout cannot be detected is called a “dead zone area”, and specifically means a discharge period of the high-speed peak detection signal b as shown in a section T9 shown in FIG. That is, the occurrence of WDO causes the waveform b to follow WDO. In the section T9, since the WDO ends, the discharge of the waveform b starts. Therefore, when the original dropout occurs in the section T9, since the discharge action of the high-speed peak detection circuit by the WDO has started, the dropout cannot follow the dropout despite the occurrence of the dropout. The original dropout cannot be detected.
[0042]
An optical disk device according to a second embodiment of the present invention will be described with reference to the drawings in order to make such a dead zone smaller. FIG. 5 is a block diagram illustrating a configuration of the optical disc device according to the second embodiment of the present invention.
[0043]
In FIG. 5, reference numeral 1 denotes a reproduced signal from the optical disk, and a high-speed peak detection signal can be obtained by a high-speed peak detection circuit 2 for detecting the bright side of the reproduced signal 1 at high speed. A low-speed peak detection signal can be obtained by the low-speed peak detection circuit 3 that detects a time constant different from that of the high-speed peak detection circuit 2.
[0044]
By inserting a limiter circuit 5 after the high-speed peak detection circuit 2 and the low-speed peak detection circuit 3, when a WDO occurs, the high-speed peak detection signal and the low-speed peak detection signal clipped to a certain potential. Can be obtained.
[0045]
Next, the comparator 4 compares the high-speed peak detection signal with the low-speed peak detection signal. If the potential of the low-speed detection peak signal is higher than the potential of the high-speed detection peak signal, a dropout detection signal indicating a dropout state is output.
[0046]
FIG. 6 shows an example in which a limiter circuit 5 is inserted into the high-speed peak detection circuit 2 shown in FIG. The limiter circuit 5 includes a PNP transistor 16 and a reference voltage 17, and the high-speed peak detection signal is clipped to a certain potential by the limiter circuit 5. Therefore, the high-speed peak detection signal and the low-speed peak detection signal are clipped to a certain potential.
[0047]
The operation of each signal waveform when WDO actually occurs will be described with reference to FIG. In FIG. 7, a section T7 is in a normal reproduction state, and shows the same operation as in FIG.
[0048]
The section T8 indicates an unrecorded portion on the disk surface, and WDO occurs in the reproduced signal waveform a. The waveforms b and c do not follow WDO, but are clipped to a certain potential by the limiter circuit 5 shown in FIG. After the section T9, WDO ends, and the light-side level of the waveform a returns to the normal reproduction state.
[0049]
In the section T9, the waveform b falls to the normal potential because the discharge of the capacitor 9 starts at the same time when the WDO ends. In the section T10 including the section T9, the discharge of the capacitor 12 of the waveform c starts simultaneously with the end of the WDO. In the waveform c, since the capacitance of the capacitor 12 is larger than the capacitance of the capacitor 9, the potential drops from the clipped potential to a normal potential with a gentler slope than the waveform b. In the subsequent section T11, the waveform c also returns to the normal state.
[0050]
Comparing the waveform b and the waveform d, the potential of the waveform d is always smaller than the potential of the waveform b by inserting the limiter circuit 5 into the low-speed peak detection circuit 3. Therefore, since the waveform e is always at the low level, there is no erroneous detection of the dropout, and the situation in which the servo is disconnected does not occur. Furthermore, by inserting the limiter circuit 5 also in the high-speed peak detection circuit 2, the dead zone region after WDO corresponding to the period T9 also becomes narrow.
[0051]
Here, an operation waveform when an original BDO actually occurs after the WDO will be described with reference to FIG. 8, in a section T7 to a section T9, each waveform performs the same operation as in FIG. When the original dropout occurs after WDO, the waveform b is discharged with the time constant of the high-speed peak detection, and thereafter follows the light side (dropout) of the waveform a. Therefore, in the section T12, since the potential of the waveform b is smaller than the potential of the waveform d, the dropout detection signal shown in the waveform e is detected. In the waveform d, since the discharge is performed at a low speed after WDO, the detection sensitivity tends to be slightly different from the normal state, and the dropout detection signal equivalent to the original state is not detected. There is no problem as long as the waveform e shown in FIG. In the section T11, all the waveforms return to the normal reproduction state.
[0052]
As described above, according to the second embodiment, there is no erroneous detection of dropout, and there is no occurrence of a situation where the servo is disconnected. Further, since the dead zone is narrower than in the first embodiment, a dropout detection signal can be detected even when an original dropout occurs after WDO.
[0053]
(Embodiment 3)
Hereinafter, an optical disc device according to a third embodiment of the present invention will be described with reference to the drawings. FIG. 9 is a block diagram illustrating a configuration of the optical disc device according to the third embodiment of the present invention.
[0054]
In FIG. 9, reference numeral 1 denotes a reproduced signal from the optical disc. A high-speed peak detection signal can be obtained by a high-speed peak detection circuit 2 for detecting the bright side of the reproduced signal 1 at high speed. A low-speed peak detection signal can be obtained by a low-speed peak detection circuit 3 that detects a time constant different from that of the high-speed peak detection circuit 2. By inserting a limiter circuit 5 in front of the high-speed peak detection circuit 2 and the low-speed peak detection circuit 3, when a WDO occurs, the high-speed peak detection signal and the low-speed peak detection signal clipped to a certain potential can be obtained. Obtainable.
[0055]
Next, the comparator 4 compares the high-speed peak detection signal with the low-speed peak detection signal. When the potential of the low-speed peak detection signal is higher than the potential of the high-speed peak detection signal, a dropout detection signal indicating a dropout state is output.
[0056]
The operation of each signal waveform when WDO actually occurs will be described with reference to FIG. As shown in FIG. 10, the operation of each signal waveform that can be obtained in the third embodiment is the same as the operation of the optical disk device according to the second embodiment in all the waveforms other than the waveform a.
[0057]
The waveform a is in a normal reproduction state in the section T7. WDO occurs in the unrecorded portion of the section T8, but is clipped to a certain potential by the limiter circuit 5. After the section T9, the state returns to the normal reproduction state.
[0058]
Therefore, as shown by the waveform e in FIG. 10, the dropout is not erroneously detected, and the servo is not disconnected. Further, since the dead zone region after WDO corresponding to the section T9 is also narrowed, there is an advantage that the same effect as in the second embodiment can be obtained only by adding one limiter circuit.
[0059]
(Embodiment 4)
In the above-described first to third embodiments, when the reproduction signal 1 has a large DC offset, a circuit for generating the reproduction signal 1 needs to have high accuracy so that the DC offset does not occur.
[0060]
For example, in the third embodiment of the present invention, an operation of each signal waveform when a large negative DC offset actually occurs in the reproduction signal 1 will be described with reference to FIG.
[0061]
In FIG. 11, when a large DC offset occurs on the negative side, the reference level of the reproduced signal waveform a 'decreases, but since the potential clipped to a certain potential by the limiter circuit 5 does not change, dropout detection after WDO is performed. The signal goes high for a long time. Therefore, the operation is the same as that of the conventional method shown in FIG. 18, and the larger the DC offset is, the more erroneously the dropout detection signal is detected by the WDO for a longer time.
[0062]
Hereinafter, an optical disc device according to a fourth embodiment of the present invention will be described with reference to the drawings. FIG. 12 is a block diagram illustrating a configuration of the optical disc device according to the fourth embodiment of the present invention.
[0063]
In FIG. 12, reference numeral 1 denotes a reproduction signal from the optical disk, and a high-speed peak detection signal can be obtained by a high-speed peak detection circuit 2 for detecting the bright side of the reproduction signal 1 at high speed. A low-speed peak detection signal can be obtained by the low-speed peak detection circuit 3 that detects a time constant different from that of the high-speed peak detection circuit 2.
[0064]
Further, in order to cope with a case where an unrecorded portion exists in the reproduction signal 1, an unrecorded portion detection circuit 6 for detecting the unrecorded portion is provided. That is, when WDO occurs due to an unrecorded portion, the unrecorded portion detection circuit 6 controls the low-speed peak detection circuit 3 to hold a normal value.
[0065]
Next, in the unrecorded portion, the comparator 4 compares the high-speed peak detection signal with the low-speed peak detection signal controlled by the unrecorded portion detection circuit 6. When the potential of the low-speed peak detection signal is higher than the potential of the high-speed peak detection signal, a dropout detection signal indicating a dropout state is output.
[0066]
The operation of each signal waveform when WDO actually occurs will be described with reference to FIG. Here, the waveform f is a signal for detecting an unrecorded portion, and is a binary signal. Further, like the waveforms a to e, the waveforms on the same time axis are shown.
[0067]
In FIG. 13, in the section T7, each waveform is in a normal reproduction state. The waveform f indicates a low level because the waveform a is in a normal reproduction state. Section T8 shows an unrecorded portion, and WDO occurs in waveform a. The waveform b follows WDO by the capacitor 9 shown in FIG. In the waveform f, an unrecorded portion is detected and is at a high level. Therefore, with the waveform c, the unrecorded portion detection circuit 6 keeps the normal potential without following the WDO.
[0068]
After the section T9, WDO ends, and the light-side level of the waveform a returns to the normal reproduction state. The waveform b starts discharging the capacitor 9 at the same time as the end of the WDO, and drops to a normal potential. Since the waveform a is in a normal reproduction state, the waveform c is a waveform in which the light side of the waveform a is peak-detected at a low speed. In a section T11 after the section T9, all the waveforms are in a normal reproduction state.
[0069]
When the waveform b and the waveform d are compared with each other, the potential of the waveform d is always lower than the potential of the waveform b by inserting the unrecorded portion detection circuit 6, so that the waveform e is always at the low level. Therefore, there is no erroneous detection of the dropout detection signal, and there is no occurrence of a situation where the servo is disconnected.
[0070]
(Embodiment 5)
Hereinafter, an optical disc device according to a fifth embodiment of the present invention will be described with reference to the drawings. FIG. 14 is a block diagram illustrating a configuration of the optical disc device according to the fifth embodiment of the present invention.
[0071]
In FIG. 14, reference numeral 1 denotes a reproduced signal from the optical disk. A high-speed peak detection signal can be obtained by a high-speed peak detection circuit 2 for detecting the bright side of the reproduced signal 1 at high speed. A low-speed peak detection signal can be obtained by the low-speed peak detection circuit 3 that detects a time constant different from that of the high-speed peak detection circuit 2. Further, when an unrecorded portion exists in the reproduction signal 1, an unrecorded portion detection circuit 6 is provided to detect the unrecorded portion. When WDO occurs due to an unrecorded portion, the unrecorded portion detection circuit 6 controls the high-speed peak detection circuit 2 and the low-speed peak detection circuit 3 to hold normal values.
[0072]
Next, in the unrecorded portion, the comparator 4 compares the high-speed peak detection signal and the low-speed peak detection signal controlled by the unrecorded portion detection circuit 6. Then, when the potential of the low-speed peak detection signal is higher than the potential of the high-speed peak detection signal, a dropout detection signal indicating a dropout state is output.
[0073]
The operation of each signal waveform when WDO actually occurs will be described with reference to FIG. In FIG. 15, in the section T7, each waveform is in a normal reproduction state. Section T8 shows an unrecorded portion, and WDO occurs in waveform a. In the waveform f, an unrecorded portion is detected and is at a high level.
[0074]
Therefore, the waveforms b and c do not follow WDO, and are kept at the normal potential by the unrecorded portion detection circuit 6. After the section T9, the WDO ends, and the light-side level of the waveform a also returns to the normal reproduction state. Since the waveform a is in the normal reproduction state, the waveforms b and c are waveforms obtained by detecting the peak of the light side of the waveform a at a low speed. In a section T11 after the section T9, all waveforms are in a normal reproduction state.
[0075]
When the waveform b and the waveform d are compared with each other, the potential of the waveform d is always lower than the potential of the waveform b by inserting the unrecorded portion detection circuit 6, so that the waveform e is always at the low level. Therefore, there is no erroneous detection of the dropout detection signal, and there is no occurrence of a situation where the servo is disconnected.
[0076]
In addition, by controlling both the high-speed peak detection circuit and the low-speed peak detection circuit, the dead zone region generated in the fourth embodiment is also eliminated, so that the detection sensitivity does not change even when the original dropout occurs after WDO. Absent.
[0077]
Furthermore, in the fourth and fifth embodiments, even when a DC offset occurs in the reproduced signal 1, the influence of the DC offset is not exerted. The operation is equivalent to that of FIG. 11 or FIG.
[0078]
【The invention's effect】
As described above, according to the optical disk device of the present invention, even when an unrecorded portion exists in a reproduction signal from an optical disk, a method of inserting a limiter circuit or inserting an unrecorded portion detection circuit By using the method, erroneous detection of the dropout detection signal is prevented, and a situation in which the servo is disengaged does not occur.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of an optical disk device according to a first embodiment of the present invention.
FIG. 2 is a signal waveform diagram illustrating an operation when WDO occurs in an input signal according to the first embodiment of the present invention.
FIG. 3 is a configuration example of a high-speed peak detection circuit and a low-speed peak detection circuit according to the first embodiment of the present invention;
FIG. 4 is a signal waveform diagram for explaining an operation in a case where WDO occurs in an input signal and then an original dropout occurs in the first embodiment of the present invention;
FIG. 5 is a block diagram showing a configuration of an optical disk device according to a second embodiment of the present invention;
FIG. 6 is a diagram illustrating a configuration example of a high-speed peak detection circuit and a low-speed peak detection circuit according to the second embodiment of the present invention;
FIG. 7 is a signal waveform diagram illustrating an operation when WDO occurs in an input signal according to the second embodiment of the present invention.
FIG. 8 is a signal waveform diagram illustrating an operation when WDO occurs in an input signal and an original dropout occurs thereafter in the second embodiment of the present invention.
FIG. 9 is a block diagram illustrating a configuration of an optical disc device according to a third embodiment of the present invention;
FIG. 10 is a signal waveform diagram illustrating an operation when WDO occurs in an input signal according to Embodiment 3 of the present invention.
FIG. 11 is a signal waveform diagram illustrating an operation in a case where an input signal has a large DC offset on the negative side in the third embodiment of the present invention.
FIG. 12 is a block diagram showing a configuration of an optical disk device according to a fourth embodiment of the present invention.
FIG. 13 is a signal waveform diagram illustrating an operation when WDO occurs in an input signal according to Embodiment 4 of the present invention.
FIG. 14 is a block diagram showing a configuration of an optical disk device according to a fifth embodiment of the present invention.
FIG. 15 is a signal waveform diagram illustrating an operation when WDO occurs in an input signal according to an embodiment of the present invention.
FIG. 16 is a block diagram showing a configuration of a conventional optical disk device.
FIG. 17 is a signal waveform diagram illustrating an operation when a normal dropout occurs in a conventional optical disk device.
FIG. 18 is a signal waveform diagram illustrating an operation when a WDO occurs in an input signal in a conventional optical disc device.
FIG. 19 is a diagram illustrating a configuration example of a high-speed peak detection circuit and a low-speed peak detection circuit.
[Explanation of symbols]
1 playback signal
2 High-speed peak detection circuit
3 Low-speed peak detection circuit
4 Comparator
5 Limiter circuit
6 Unrecorded part detection circuit
7, 10 diode
8,11 Current source
9,12 Capacitor
13 Level shift circuit
14, 16 PNP transistor
15, 17 Reference power supply
a, a 'playback signal waveform
b, b 'High-speed peak detection signal waveform
c, c 'Low-speed peak detection signal waveform
d, d 'Level shifted low-speed peak detection signal waveform
e Dropout detection signal waveform
f Unrecorded part detection signal waveform

Claims (5)

A high-speed peak detection circuit for detecting the bright side of a reproduction signal obtained by reproducing information recorded on an optical disc;
A low-speed peak detection circuit that detects the bright side of the reproduced signal with a time constant different from the high-speed peak detection circuit,
The high-speed peak detection signal detected by the high-speed peak detection circuit is compared with the low-speed peak detection signal detected by the low-speed peak detection circuit, and the potential of the low-speed peak detection signal is higher than the potential of the high-speed peak detection signal. A comparator that outputs a dropout detection signal by determining that the state is a dropout state,
An optical disc device comprising the limiter circuit after the low-speed peak detection circuit, wherein the low-speed peak detection signal is clipped to a predetermined potential. 2. The optical disk device according to claim 1, wherein the limiter circuit is provided after the high-speed peak detection circuit, and the high-speed peak detection signal is also clipped to a predetermined potential. A high-speed peak detection circuit for detecting the bright side of a reproduction signal obtained by reproducing information recorded on an optical disc;
A low-speed peak detection circuit that detects the bright side of the reproduced signal with a time constant different from the high-speed peak detection circuit,
The high-speed peak detection signal detected by the high-speed peak detection circuit is compared with the low-speed peak detection signal detected by the low-speed peak detection circuit, and the potential of the low-speed peak detection signal is higher than the potential of the high-speed peak detection signal. A comparator that outputs a dropout detection signal by determining that the state is a dropout state,
An optical disc device, wherein a limiter circuit is inserted before the high-speed peak detection circuit and the low-speed peak detection circuit to clip a dropout signal generated by an increase in the amount of reflected light to a predetermined potential. A high-speed peak detection circuit for detecting the bright side of a reproduction signal obtained by reproducing information recorded on an optical disc;
A low-speed peak detection circuit that detects the bright side of the reproduced signal with a time constant different from the high-speed peak detection circuit,
The high-speed peak detection signal detected by the high-speed peak detection circuit is compared with the low-speed peak detection signal detected by the low-speed peak detection circuit, and the potential of the low-speed peak detection signal is higher than the potential of the high-speed peak detection signal. A comparator that, when larger, determines that it is in a dropout state and outputs a dropout detection signal;
An unrecorded portion detection circuit for detecting the unrecorded portion when an unrecorded portion is present in a reproduced signal obtained by reproducing information recorded on the optical disc,
An optical disc device, wherein when the unrecorded portion is detected, the potential of the low-speed peak detection signal is held. 5. The optical disc apparatus according to claim 4, wherein when the unrecorded portion is detected, not only the potential of the low-speed peak detection signal but also the potential of the high-speed peak detection signal is held.

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