JP2002288839A - Optical disk reproducing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that a dropout detection circuit operates erroneously in the case that no information is recorded on an optical disk in detecting a dropout of the optical disk such as a DVD-R(digital versatile disk recordable), and to provide an optical disk reproducing apparatus in which the erroneous detection of the dropout signal is few, for a recording type of the optical disk having an unrecorded portion. SOLUTION: An amplitude detecting means 12 which detects an amplitude of a reproduction signal from the front stage of an AGC(auto gain control) circuit 5 by comparing the level of the production signal from the optical disk 1 through a low band cut filter 4 and the AGC circuit 5 at the time of detecting the dropout and a comparison level setting means 13 which sets the comparison level of a level comparator 7 of a dropout detection means 6 in accordance with the output are provided, thereby the erroneous detection of the noise element of the unrecorded part, as the dropout, does not arise.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk reproducing apparatus for reproducing information recorded on an optical disk.

[0002]

2. Description of the Related Art In an optical disk reproducing apparatus, when reproducing an optical disk, the reproduction is performed while detecting the amplitude of the reproduction signal and detecting the dropout caused by the attachment of a scratch or dirt on the surface of the optical disk. I have.
When a dropout is detected, a PLL (Phase Look Up) used to hold the servo loop or to reproduce data is used.
edLoop), the servo system is skipped (disengaged) due to scratches on the optical disc, etc.
Is prevented from being skipped (disengaged) and cannot be reproduced, thereby improving the stability of the optical disc reproducing apparatus. Such a dropout detector is disclosed in, for example, Japanese Patent Application Laid-Open No. 54-118211.

Hereinafter, a conventional optical disk reproducing apparatus will be described with reference to the drawings.

FIG. 12 is a block diagram showing a configuration of an optical disk reproducing apparatus having a dropout detecting function in a conventional example.

In FIG. 12, reference numeral 1 denotes an optical disk;
The information recorded on the optical disc 1 is reproduced by the optical pickup 3 while being rotated by the rotating means 2.

A data signal output from the optical pickup 3 passes through a low-frequency cut filter 4 in the form of an analog signal, and an auto gain control circuit (hereinafter referred to as an AGC circuit) for compensating for a change in the reflectance of the optical disk 1. And 5). AGC during normal playback
The amplitude of the data signal output from the circuit 5 is constant.

[0007] The signal having the constant amplitude is binarized through binarizing means 11 and used for data reproduction, and is also input to the dropout detector 6, where the surface of the optical disk 1 is damaged or stained. Etc., the dropout is detected. That is, if the reflected light is interrupted by a scratch or dirt on the optical disk surface, the amplitude of the data signal locally decreases.
Is detected by the level comparator 7.

The level comparator 7 is a kind of a binarizing circuit for binarizing an input signal at the applied comparison level. The input signal is degraded due to scratches and dirt on the surface of the optical disk, and is smaller than the comparison level. Then, no binarized output is output. The output of the level comparator 7 is input to a monomultivibrator (hereinafter, referred to as a monomulti circuit) 9, and while the binarized output is output at a frequency equal to or less than a certain interval (as long as it does not output at a certain interval or less), The mono-multi circuit 9 does not output the signal, and when the output pulse of the level comparator 7 becomes equal to or longer than a predetermined interval, the mono-multi circuit 9 outputs the pulse as the output of the dropout detector 6.

Therefore, if the input signal is degraded due to scratches or dirt on the surface of the optical disc, becomes smaller than the comparison level, and a binarized output that is longer than a predetermined interval is detected as a dropout.

The dropout signal thus obtained is used as a signal for holding a servo loop and for holding data PLL.

[0011]

However, in such a conventional configuration, it is assumed that information is recorded on the optical disk and that the data signal (RF signal) has an amplitude. Is not taken into account (case where an unrecorded area exists) is not considered.

For example, as shown in the signal waveform diagram of FIG.
For example, in an optical disc such as a DVD-RAM in which a recording portion and an unrecorded portion are scattered, the amplitude of the data signal is smaller in the unrecorded portion than in the recording portion.
In this case, the noise component in the unrecorded portion is amplified. Therefore, the output of the AGC circuit 5 is, as shown in FIG.
In the unrecorded portion, a signal lower than the comparison level (broken line) for determining the deterioration of the data signal is generated, and the output of the level comparator 7 is, as shown in FIG. Outputs pulses at relatively wide intervals. As a result, as shown in FIG. 4C, the output of the mono-multi circuit 9 does not recognize the noise component of the unrecorded portion as data, and is therefore output as a dropout.

Therefore, in the case of an optical disk having an unrecorded portion, there is a problem that a noise component in the unrecorded portion is erroneously detected as a dropout.

As shown in the signal waveform diagram of FIG.
For example, in an optical disc such as a DVD-RAM, in which a recorded portion and an unrecorded portion can be scattered, and the reflectance of the recorded portion decreases when a signal is recorded, the data is transferred from the unrecorded portion to the recorded portion during reproduction. Since the DC level of the signal suddenly drops, a problem that the start portion of the recording unit is erroneously detected as dropout also occurs.

FIG. 13A is a signal waveform diagram showing a data signal of a portion which goes from an unrecorded portion to a recorded portion. In the unrecorded portion, the comparison level (broken line) is set slightly lower than the signal level. I have. However, when moving from an unrecorded portion to a recorded portion, the head of the recorded portion drops to a level lower than the comparison level, and as shown in FIG.
The output of the level comparator 7 outputs a long pulse at the head of the recording unit, and as shown in FIG.
Is also output as a dropout signal.

Further, as shown in the signal waveform diagram of FIG.
For example, in the case of an optical disc such as a DVD-RAM that sequentially reproduces tracks having different reflectivities such as a land track and a groove track, the DC level of the data signal is changed at the boundary between the land track and the groove track due to the difference in the reflectivity. Since the drop may occur abruptly, there is also a problem that the reflectance difference at the track boundary is erroneously detected as a dropout.

FIG. 8A is a diagram showing a data signal at a boundary between a land track and a groove track in an unrecorded portion of a DVD-RAM disk. In the land track, the comparison level (broken line) is slightly lower than the signal level. It is set below. However, when moving from the land track to the groove track, the level is lowered to a level lower than the comparison level near the track boundary due to the reflectance difference between the land track and the groove track. For this reason, as shown in FIG. 8B, the output of the level comparator 7 outputs a long pulse at the track boundary, and
As shown in (c), the output of the mono-multi circuit 9 also outputs a dropout signal at the boundary between tracks.

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical disk reproducing apparatus which can reduce the erroneous detection of a dropout signal even in a recording type optical disk having an unrecorded portion in order to solve the above problems. I do.

[0019]

In order to achieve this object, an optical disc reproducing apparatus according to the present invention comprises a low-frequency cut filter for inputting a reproduction signal from a recording medium and removing a low-frequency component of the reproduction signal. An automatic gain control circuit for controlling the gain of the output of the low-frequency cut filter, a dropout detector for detecting a dropout from the output of the automatic gain control circuit, and an amplitude detecting means for detecting the amplitude of the output of the low-frequency cut filter And comparison level setting means for setting a comparison level in the dropout detector in accordance with the output of the amplitude detection means.

Thus, for example, when the recording area is shifted from the recording section to the unrecorded section, the noise component in the unrecorded section is not detected as a dropout.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first aspect of the present invention provides a low-frequency cut filter for receiving a reproduction signal from a recording medium and removing a low-frequency component of the reproduction signal, and an output of the low-frequency cut filter. An auto gain control circuit for controlling the gain of the, and a dropout detector for detecting a dropout from the output of the auto gain control circuit,
An amplitude detecting means for detecting an amplitude of an output of the low-frequency cut filter, and a comparison level setting means for setting a comparison level in the dropout detector in accordance with an output of the amplitude detecting means.

Thus, by detecting the amplitude of the signal input to the auto gain control circuit by the amplitude detecting means, it is determined whether the signal is a recorded portion or a non-recorded portion. By lowering the comparison level of the dropout detector, a noise component generated in an unrecorded portion is not erroneously detected as a dropout.

According to a second aspect of the present invention, there is provided a low-frequency cut filter for receiving a reproduced signal from a recording medium and removing a low-frequency component of the reproduced signal, and a direct-current (DC) output of the low-frequency cut filter. In-line means for suppressing component fluctuation, an automatic gain control circuit for controlling the output gain of the in-line means, and a drop-out detector for detecting drop-out from the output of the auto gain control circuit. .

By using in-line means for suppressing the DC fluctuation of the reproduced signal before inputting the signal to the auto gain control circuit, the DC fluctuation of the unrecorded portion and the recorded portion can be suppressed. When moving from the recording unit to the recording unit, the head of the recording unit is not erroneously detected as a dropout.

According to a third aspect of the present invention, there is provided a low-frequency cut filter for receiving a reproduced signal from a recording medium and removing a low-frequency component of the reproduced signal, and an output gain of the low-frequency cut filter. And a dropout detector for detecting a dropout from the output of the autogain control circuit, wherein the low-pass cut filter has a cutoff when reproducing data from the recording medium. It has a band switching means for lowering the frequency and raising the cutoff frequency when data is not reproduced.

Thus, when the reproduction is not performed, the DC fluctuation of the signal caused by the reflectance difference in the unrecorded portion is suppressed by increasing the cutoff frequency of the low-frequency cut filter before inputting the signal to the auto gain control circuit. Therefore, even at the boundary between the land track and the groove track, the signal fluctuation due to the influence of the reflectance difference is not erroneously detected as a dropout.

The fourth invention of the present invention is directed to
In a third aspect, the dropout detector has means for binarizing an input signal, and means for outputting a signal corresponding to a pulse interval of the binarized signal. The dropout can be reliably detected by obtaining the output of the dropout detector using a monomultivibrator or the like which is output when the pulse output from the binarization unit continues for a predetermined interval or more. .

Further, the fifth invention of the present invention is directed to
In the third invention, the dropout detector has a comparison means for comparing a signal obtained by detecting the envelope of the input signal with a predetermined reference level at a desired comparison level. By using a dropout detector including a comparison means for comparing the envelope-detected signal with a reference level, the dropout can be reliably detected.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Embodiment 1) FIG. 1 is a block diagram showing a configuration of an optical disk reproducing apparatus according to Embodiment 1 of the present invention.

In FIG. 1, information is reproduced by an optical pickup 3 from an optical disk 1 rotated by a rotating means 2. From the data signal read by the optical pickup 3, the low-frequency component is removed by the low-frequency cut filter 4, and the data signal is read by the automatic gain control circuit (AGC).
Circuit 5).

The output of the AGC circuit 5 is used for signal reproduction via the binarizing means 11 and is also input to the dropout detector 6, which detects signal loss and outputs the signal as a dropout signal. It is used for controlling a servo circuit and a hold of a PLL circuit (not shown), etc., and improves the reading stability of the optical disk reproducing apparatus.

The configuration of the dropout detector 6 is the same as that described in the prior art, except that the comparison level set in the level comparison means 7 is different. This comparison level is set by the comparison level setting means 13, and the input of the comparison level setting means 13 is a result of the amplitude detection means 12 detecting the amplitude of the reproduced signal before being input to the AGC circuit 5. Therefore, the comparison level is set based on the amplitude of the reproduction signal.

The operation of the optical disk reproducing apparatus thus configured will be described below.

Since the AGC circuit 5 has a function of adjusting the amplitude of the input signal, the AGC circuit 5 keeps the amplitude of the data signal reproduced from the optical disk 1 at a constant amplitude. However, when the optical disc 1 has scratches or dirt and the reflected light is blocked, the output of the AGC circuit 5 also temporarily deteriorates in amplitude.

This amplitude deterioration is detected by the level comparator 7 in the dropout detector 6, at which time the AGC circuit 5
When the input amplitude is small, the output amplitude increases. Therefore, as described above, the AGC circuit 5 operates in the unrecorded portion to increase the amplitude of the data signal. For this reason, a noise component having a large amplitude is input to the dropout detector 6, so that the noise component is caught by the comparison level of the level comparator 7, and a dropout signal is output.

Therefore, the amplitude detecting means 12 detects the amplitude of the signal before being input to the AGC circuit 5, and determines whether there is a recording signal or not.

The amplitude detecting means 12 detects a signal before being input to the AGC circuit 5 by two envelope detectors, for example, and determines the presence or absence of the signal. That is, by detecting the upper envelope and the lower envelope of the input signal, and taking the difference between them, the presence or absence of the signal, that is, whether the signal is recorded or not recorded, is recorded / unrecorded. Has been determined.

If the amplitude detected by the amplitude detecting means 12 is small, it is considered that the data has not been recorded. Therefore, the comparison level setting means 13 lowers the detection level of the level comparator 7 in the dropout detecting circuit 6 by The dropout detection sensitivity is lowered, making dropout detection difficult.

As described above, the amplitude detecting means 12
At the preceding stage of the AGC circuit 5, the amplitude of the input signal is detected to determine whether the recording section is a recording section or an unrecorded section. In this case, it is possible to prevent a noise component from being erroneously detected as a dropout in an unrecorded portion.

(Embodiment 2) Next, Embodiment 2 of the present invention will be described in detail with reference to the drawings.
FIG. 2 is a block diagram showing a configuration of the optical disc reproducing apparatus according to the present embodiment.

In FIG. 2, components having the same functions as in the first embodiment are denoted by the same reference numerals. The difference from the first embodiment is that the dropout detector 6 includes an envelope detector 14, a reference level generator 15, and a level comparator 16.

As described above, the envelope of the input signal to the dropout detector 6 is detected by the envelope detector 14, and is compared at a fixed comparison level, and is output, thereby detecting signal amplitude deterioration due to dropout. can do.

Further, a comparison level setting means 13 is provided by an amplitude detection means 12 for detecting the amplitude before the AGC circuit 5.
By setting the comparison level of the level comparator 16 by adding an offset, the dropout detection sensitivity can be reduced in the unrecorded portion, and the noise component is mistaken for the dropout in the unrecorded portion. Detection can be prevented.

(Third Embodiment) Next, a third embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 3 is a block diagram showing a configuration of the optical disc reproducing apparatus according to the present embodiment.

In FIG. 3, the difference from the first or second embodiment is that the output of the optical pickup 3 passes through the low-pass cut filter 4 and then through the in-line unit 17 to the A
This is the point that is input to the GC circuit 5. The dropout detector 6 may have any of the configurations shown in FIG. 1, FIG. 2 or FIG. Further, there is no problem even in combination with the configuration shown in the first or second embodiment.

The operation of the inlining means 17 will be described below.

For example, an optical disk such as a DVD-RAM disk has a CAPA (Compliment
An address signal called "ary Allocated Pit Addressing" is formed by pre-pits.

In order to record a signal between the CAPA signal and the CAPA signal, as shown in FIG.
Regarding the DC level of each signal, the CAPA signal has the highest DC level, followed by the data portion of the unrecorded portion and the data portion of the recorded portion.

When this signal is directly input to the drop-out detector 6 described in the first or second embodiment, when the recording section moves from the unrecorded section to the recording section, the recording section has a higher DC voltage than the unrecorded section. Since the level is lowered, the recording unit is erroneously detected as a dropout, and a dropout signal is output as shown in FIG.

Therefore, as shown in FIG. 14, if a dropout is detected using a signal in which the fluctuation of the DC level between the recorded portion and the unrecorded portion is reduced, the recorded portion will not be erroneously detected as a dropout. Thus, the CAPA signal,
The one that works to align the unrecorded part signal and the recorded part signal is
This is the inline means 17.

FIGS. 5A and 5B are signal waveform charts for explaining the operation of the in-line conversion means 17, in which FIG. 5A is an input data signal, and FIG. FIG. 3C shows a data signal in which the fluctuation of the DC level is suppressed by the inlining means 17.

That is, as shown in FIG. 5, the in-line means 17 produces a CAPA section and an in-line pulse outputted at the head of the data section.
DC level fluctuation is suppressed.

The configuration of the inlining means 17 is, for example,
As shown in FIG. 6, the output of the capacitor 21 serving as a low-frequency cut filter can be short-circuited to the reference level by the analog switch 22 via the resistor 23 for each in-line pulse.

As described above, by inputting a signal whose DC level matches the desired reference level to the AGC circuit 5 and the dropout detector 6, the dropout detector 6 can be used when the data is transferred from the unrecorded portion to the recorded portion. A malfunction can be prevented.

Since the resistor 23 adjusts the response of the signal waveform, it may be 0Ω or not.

As described above, by providing the in-line means 17 in front of the AGC circuit 5, it is possible to prevent the head of the recording portion from being erroneously detected as a dropout even when the recording portion is moved from an unrecorded portion to a recording portion. it can.

Embodiment 4 Next, Embodiment 4 of the present invention will be described in detail with reference to the drawings.
FIG. 7 is a diagram showing a configuration of the optical disc reproducing apparatus according to the present embodiment.

FIG. 7 differs from the first to third embodiments in that a low-frequency cut filter provided with a band switching means is provided before the AGC circuit 5. In the drawing, it is simply shown as a band switching unit 18.

The operation of the band switching means 18 will be described below.

For example, an optical disk such as a DVD-RAM disk uses a land-groove recording method,
Recording is performed on both the land track of the groove and the groove track. Therefore, in order to reproduce both the land track and the groove track having different optical characteristics, as shown in FIG. 8A, the land track is moved to the groove track, or the groove track is moved to the land track. At that time, from the difference in reflectance, DC
Step occurs.

In particular, in an unrecorded portion, the effect of the reflectance difference between the land and the groove appears directly on the signal.

The dropout detector 6 erroneously detects this step as a dropout, and outputs a dropout signal as shown in FIG. 8B.

Therefore, as shown in FIG.
1 and a resistor 32, the output of a high-pass filter (low-pass cut filter) is short-circuited to a reference level by a non-read signal via a resistor 34 by an analog switch 33. Can be increased.

The non-read signal is a signal indicating whether the signal of the optical disk is to be reproduced or not, and is output when the signal is not reproduced.

As described above, by increasing the cutoff of the input high-pass filter during non-reading,
As shown in the signal diagram of FIG. 10A, the DC fluctuation between the land track and the groove track can be suppressed, and the difference in reflectance between the land track and the groove track is not erroneously detected as a dropout. As shown in b), it is possible to suppress the output width of the dropout signal in which the DC fluctuation due to the reflectance difference is erroneously detected as the dropout.

The output signal S from the optical pickup is
In order to increase the / N ratio, differential transmission may be performed using a signal whose polarity is inverted. In such a case, the band switching means 18 connects the differential input to the capacitor 4 as shown in FIG.
1 and 42, the outputs of which are connected to each other by a resistor 43, and an analog switch 44 and a resistor 45 which are short-circuited by a non-read signal in parallel with the resistor 43.
Depending on the connection method.

In the above embodiment, a DVD-RAM has been described as an example of a recording medium. However, it goes without saying that any optical disk having the same problems as the present invention may be used.

[0069]

As described above, according to the first aspect of the present invention, the amplitude of the signal input to the AGC circuit is detected by the signal detection means, so that the signal can be recorded in the recording section or the unrecorded section. Judgment is made, and if it is an unrecorded part,
By lowering the comparison level of the dropout detector, it is possible to prevent a noise component generated in an unrecorded portion from being erroneously detected as a dropout.

Further, in the second invention, the DC fluctuation of the unrecorded part and the recorded part can be suppressed by using the in-line means for suppressing the DC fluctuation of the reproduced signal before inputting the signal to the AGC circuit. Also, even when the recording section is shifted from the unrecorded section to the recording section, it is possible to prevent the head of the recording section from being erroneously detected as a dropout.

In the third invention, when no reproduction is performed,
By increasing the cutoff frequency of the low-frequency cut filter before inputting the signal to the AGC circuit, signal DC fluctuations caused by a reflectance difference in an unrecorded portion can be suppressed.
It is possible to prevent the reflectance difference at the boundary between tracks from being erroneously detected as dropout.

Further, in the fourth invention, when the pulse of the binarizing means is at a certain interval or more, the output of the dropout detector is obtained by the output mono-multi circuit, so that the dropout can be reliably detected. can do.

According to the fifth aspect of the present invention, the dropout detector is composed of a level comparison means for comparing the envelope-detected signal with the reference level generated by the reference level generator, so that the dropout can be reliably performed. It can be detected.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an optical disc reproducing device according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of an optical disc reproducing device according to the second embodiment;

FIG. 3 is a block diagram showing a configuration of an optical disc reproducing device according to the third embodiment;

FIG. 4 is a signal waveform diagram showing a problem of the conventional optical disc reproducing apparatus.

FIG. 5 is a signal waveform diagram illustrating an operation of the optical disc reproducing device according to the third embodiment of the present invention.

FIG. 6 is a circuit diagram showing a configuration of an in-line means of the optical disc reproducing apparatus.

FIG. 7 is a block diagram showing a configuration of an optical disc reproducing apparatus according to Embodiment 4 of the present invention.

FIG. 8 is a signal waveform diagram showing a problem of a conventional optical disc reproducing apparatus.

FIG. 9 is a circuit diagram showing a configuration of a band switching unit of the optical disc reproducing apparatus according to Embodiment 4 of the present invention.

FIG. 10 is a signal waveform diagram showing the operation of the optical disc reproducing apparatus.

FIG. 11 is a circuit diagram showing another configuration of the band switching means of the optical disc reproducing apparatus.

FIG. 12 is a block diagram showing a configuration of a conventional optical disc reproducing apparatus.

FIG. 13 is a signal waveform diagram showing a problem in a conventional optical disc reproducing apparatus.

FIG. 14 is a signal waveform diagram illustrating an operation of the optical disc reproducing device according to the third embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical disk 2 Rotating means 3 Optical pickup 4 Low-pass cut filter 5 AGC circuit 6 Dropout detector 7 Level comparing means 9 Mono multi circuit 11 Binarization means 12 Amplitude detecting means 13 Comparison level setting means 14 Envelope detector 15 Reference level Generator 16 Level comparator 17 Inline means 18 Band switching means

Claims (5)

[Claims] A low-frequency cut filter for receiving a reproduction signal from a recording medium and removing a low-frequency component of the reproduction signal; an auto gain control circuit for controlling a gain of an output of the low-frequency cut filter; A dropout detector that detects a dropout from an output of the auto gain control circuit; an amplitude detection unit that detects an amplitude of an output of the low-frequency cut filter; and the dropout detection according to an output of the amplitude detection unit. An optical disc reproducing apparatus comprising: a comparison level setting means for setting a comparison level in a disc. 2. A low-frequency cut filter that receives a reproduction signal from a recording medium and removes a low-frequency component of the reproduction signal, and an in-line unit that suppresses a change in a DC component of an output of the low-frequency cut filter. An optical disc reproducing apparatus comprising: an auto gain control circuit for controlling a gain of an output of the in-line unit; and a dropout detector for detecting a dropout from an output of the auto gain control circuit. 3. A low-frequency cut filter for receiving a reproduced signal from a recording medium and removing a low-frequency component of the reproduced signal; an auto-gain control circuit for controlling an output gain of the low-frequency cut filter; A dropout detector that detects dropout from the output of the auto gain control circuit, wherein the low-pass cut filter lowers the cutoff frequency when reproducing data on the recording medium, and when not reproducing data. An optical disc reproducing apparatus having a band switching means for increasing its cutoff frequency. 4. A drop-out detector according to claim 1, wherein
4. The optical disc reproducing apparatus according to claim 1, further comprising: means for converting the value into a signal; and means for outputting a signal corresponding to a pulse interval of the binarized signal. 5. The dropout detector according to claim 1, further comprising comparison means for comparing a signal obtained by detecting an envelope of the input signal with a predetermined reference level at a desired comparison level. An optical disc reproducing apparatus according to any of the above.