JP3941166B2 - Optical disc playback apparatus and signal playback circuit used for optical disc playback apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical disc playback apparatus that can appropriately cope with a sudden (local) amplitude change of a playback signal, and a signal playback circuit used in the optical disc playback apparatus .
[0002]
[Prior art]
In recent years, in magneto-optical and write-once optical disks for recording digital data, modulation codes having a DC component and a low-frequency component such as run-length code RLL (1, 7) have been adopted to improve recording linear density. .
By the way, the reproduction signal of the optical disk has low frequency due to dirt and dust on the surface of the optical disk, media (recording medium) defects, non-uniformity of reflectance, non-uniformity of recording sensitivity fluctuation, residual error of focus and tracking servo, etc. In order to prevent data detection errors due to the presence of noise, it is necessary to remove such low-frequency noise.
Conventionally, in order to remove such low-frequency noise, a low-frequency cutoff filter, that is, a high-pass filter is used.
[0003]
[Problems to be solved by the invention]
However, the low-frequency noise as described above and the low-frequency component of the modulation code have a common band, and if a high-pass filter is used to remove the low-frequency noise, the low-frequency of the modulation code There is a problem that the components are also removed together with noise, and detection errors increase.
[0004]
The present invention has been made in view of the above-described prior art, and includes an optical disc reproducing apparatus capable of detecting data with high accuracy without being affected by a low frequency component of a modulation code, and a signal reproducing circuit used in the optical disc reproducing apparatus. The purpose is to provide.
[ 0005 ]
[Means for Solving the Problems]
According to the present invention, a high-pass filter that inputs a reproduction signal read from an optical disc on which data having a low-frequency component is recorded, and blocks the low-frequency component included in the reproduction signal at a predetermined cutoff frequency; An adder circuit connected to a subsequent stage of the high-pass filter, and a binarization circuit connected to a subsequent stage of the adder circuit to generate a binarized signal by comparing the output signal of the adder circuit with a predetermined comparison level A circuit, a gain control circuit for controlling the gain of the amplitude of the output signal of the binarization circuit, connected to the subsequent stage of the binarization circuit, and connected to a subsequent stage of the gain control circuit, by the high-pass filter In order to compensate for the cut frequency component, the high frequency component included in the signal output from the gain control circuit is cut off at a predetermined cutoff frequency, and the low frequency component is passed through and output to the adder circuit. Filter and A reproduction signal said read envelope detection, and a envelope detection circuit for detecting the amplitude of the envelope detection signal,
The cutoff frequency of the high-pass filter is equal to the cutoff frequency of the low-pass filter, and the high-pass filter and the low-pass filter have complementary frequency characteristics,
The gain control circuit is responsive to the amplitude of the envelope detection signal detected by the envelope detection signal so that the amplitude of the gain control signal from the gain control circuit is equal to the amplitude of the read reproduction signal. Controlling the amplitude of the gain control signal from the gain control circuit;
A signal reproduction circuit for use in an optical disk reproduction apparatus is provided.
[ 0006 ]
According to the present invention, there is provided an optical disc reproducing apparatus having the signal reproducing circuit.
[ 0007 ]
Preferably, the gain control circuit includes at least two resistors connected in series and parallel, and a switch circuit that changes a resistance value of the two series and parallel resistors,
The envelope detection circuit compares the amplitude of the envelope detected signal with a predetermined level. When the amplitude of the envelope detected signal is equal to or lower than a predetermined level, the first logic level and the amplitude of the envelope detected signal are predetermined. A circuit for outputting a signal of the second logic level when the level is equal to or higher than the level;
The switch circuit of the gain control circuit is turned on when a signal output from the envelope detection circuit is at the first logic level, is turned off when the signal is at the second logic level, and when the switch circuit is on, the gain control is performed. The gain control circuit is configured so that the amplitude of the gain control signal from the circuit is equal to the amplitude of the read reproduction signal.
[ 0008 ]
In the signal reproduction circuit used in the optical disk reproduction apparatus of the present invention, the low-frequency noise included in the reproduction signal is removed by the high-pass filter, and the low-frequency component of the reproduction signal lost at that time is converted from the binarized signal. By feeding back the low-frequency component of the extracted reproduction signal and adding it to the output of the high-pass filter, a signal in which the low-frequency component is reproduced can be generated.
Furthermore, for sudden amplitude changes in the playback signal, the envelope of the playback signal is detected to detect when the detected envelope level is below a predetermined level. During the detected period, the gain control circuit changes the amplitude. The feedback amount of the feedback loop is controlled in accordance with.
As a result, it is possible to stably and accurately detect data even in a large signal missing portion without being affected by low-frequency noise.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an optical disk reproducing apparatus and a signal reproducing circuit used for the optical disk reproducing apparatus according to the embodiment of the present invention will be described.
FIG. 1 is a configuration diagram of a signal reproduction circuit 10 used in the optical disk reproduction apparatus of the present embodiment.
As shown in FIG. 1, a signal regeneration circuit 10 includes a high-pass filter (HPF , high-pass filter ) 1, an adder (adder circuit) 2, a comparator circuit (binarization circuit) 3, a gain control circuit (gain control circuit). ) 4, and a low pass filter (LPF, the low-pass filter) 5, an envelope detection circuit 6 and the pulse generation circuit 7.
The high-pass filter 1 performs high-pass filtering on the reproduction signal S0 at a cutoff frequency 1 / (2πRC) [Hz], and outputs the filtered reproduction signal S1 to the adder 2. By this filtering, the low frequency noise included in the reproduction signal S0 is removed. At the same time, the low frequency component of the reproduction signal S0 is also removed. For example, when the reproduction signal S0 as shown in FIG. 2 (A) is input, the reproduction signal S1 as shown in FIG. 2 (B) is output.
As shown in FIG. 4, the high-pass filter 1 provides a function as a high-pass filter for the reproduced signal S0 by disposing a capacitor 11 and a resistor 12.
[0010]
The adder 2 adds the reproduction signal S1 from which the low-frequency noise and the low-frequency component are removed and the feedback signal S5 from the low-pass filter 5 and outputs the addition signal S2 to the comparator circuit 3. The addition signal S2 is a reproduction signal obtained by adding the feedback signal S5 including the removed low-frequency component to the reproduction signal S1 from which the low-frequency component is removed, and reproducing the low-frequency component.
For example, in the case of the reproduction signal S0 and the feedback signal S5 as shown in FIGS. 2A and 2D, the addition signal S2 as shown in FIG.
The comparator circuit 3 is a circuit for encoding the addition signal S2. Specifically, the comparator circuit 3 binarizes the addition signal S2 at a predetermined comparison level, outputs the binarized signal S3 as a reproduction output of the optical disc reproduction apparatus 10, and controls the gain as a feedback signal S3. Also output to the circuit 4. For example, when the waveform of the addition signal S2 is as shown in FIG. 2E, the waveform of the binarized signal S3 is as shown in FIG.
[0011]
The gain control circuit (gain control circuit) 4 controls the gain of the feedback signal S3 to an appropriate value based on the pulse signal S7, and outputs the controlled feedback signal S4 to the low-pass filter 5.
Here, the aptitude value is a value that makes the amplitudes of the reproduction signal S0 and the feedback signal S4 equal.
The gain control circuit 4 is configured by using fixed resistors 21, 22, 23 and a switch 24 connected to a series-parallel circuit , for example, as shown in FIG. In this example, when the pulse signal S7 shown in FIG. 5C becomes a low level, the switch 24 is closed and the gain attenuation amount ( attenuation amount of the amplitude of the output signal of the gain control circuit 4) is opened. Larger than At this time, the pulse signal S7 is at a low level when the level of the reproduction signal S0 is lowered. Accordingly, the amplitude of the feedback signal S4 is made smaller than the amplitude of the reproduction signal S0 in response to this reduction, and feedback is performed. Prevent loop divergence. A sufficient effect can be obtained even if the resistance value of the fixed resistor 23 shown in FIG. This is because the frequency of the decrease in amplitude occurring in a portion where the low frequency component of the signal is large is not so high in practice.
For example, when the level of the pulse signal S7 changes as shown in FIG. 5C, the level of the feedback signal S4 changes as shown in FIG. 5D.
[0012]
The low-pass filter 5 performs low-pass filtering on the feedback signal S4 at a cutoff frequency 1 / (2πRC) [Hz], and outputs the filtered feedback signal S5 to the adder 2. Here, the cutoff frequencies of the high-pass filter 1 and the low-pass filter 5 are both set to 1 / (2πRC) [Hz]. That is, since the low-pass filter 5 has a frequency characteristic complementary to the high-pass filter 1, the reproduced signal S 0 lost in the high-pass filter 1 is included in the feedback signal S 5 output from the low-pass filter 5. The low frequency component is included.
As shown in FIG. 4, the low-pass filter 5 provides a function as a low-pass filter for the feedback signal S4 by disposing a capacitor 11 and a resistor 12.
For example, when the waveform of the binarized signal S3 is as shown in FIG. 2C, the waveform of the feedback signal S5 is as shown in FIG.
[0013]
The envelope detection circuit 6 receives the reproduction signal S 0, performs envelope (envelope) detection, and outputs the detection signal S 6 to the pulse generation circuit 7.
For example, when the waveform of the reproduction signal S0 is as shown in FIG. 5A, the waveform of the envelope detection signal S6 is as shown in FIG.
[0014]
The pulse generation circuit 7 outputs a pulse signal S7 obtained by pulsing the envelope detection signal S6 to the gain control circuit 4 at a predetermined comparison level.
For example, when the waveform of the envelope detection signal S6 is as shown in FIG. 5B, the waveform of the pulse signal S7 is as shown in FIG.
[0015]
Next, a method for removing a low frequency component of a reproduction signal using a signal reproduction circuit in the optical disk apparatus shown in FIG. 1 will be described with reference to FIGS.
First, a reproduction signal S0 from an optical disk as shown in FIG. 2A is supplied to a signal reproduction circuit 10 used in the optical disk reproduction apparatus shown in FIG. The low frequency component of the reproduction signal S0 is removed from the supplied reproduction signal S0 by the high-pass filter 1. For example, when the reproduction signal S0 as shown in FIG. 2 (A) is supplied to the high-pass filter 1, low-frequency components as shown in FIG. 2 (B) are removed from the high-pass filter 1. The reproduced signal S1 is output. Next, the reproduction signal S1 is output to the comparator circuit 3. The comparator circuit 3 encodes the input reproduction signal S1 by comparing it with a predetermined level. For example, when the reproduction signal S1 as shown in FIG. 2B is input to the comparator circuit 3, the reproduction signal S1 is encoded from the comparator circuit 3 as shown in FIG. The signal S3 is output. The encoded signal S3 is supplied to the gain control circuit 4.
[0016]
The gain control circuit 4 controls the gain of the encoded signal S3 in response to the pulse signal S7 from the pulse generation circuit 7. In the description of this low-frequency component removal method, for the sake of explanation, it is assumed that the gain of the encoded signal S3 is not controlled at all in the gain control circuit 4. Therefore, in this case, the output signal S4 from the gain control circuit 4 is supplied to the low-pass filter 5. A specific control operation of the gain control circuit 4 will be described later.
[0017]
The low-pass filter 5 passes only the low frequency component of the output signal S4 (in the example described above, the output signal S4 is the same signal as the signal S3). For example, when an output signal S4 as shown in FIG. 2C is supplied, the low-pass filter 5 outputs an output signal S5 as shown in FIG. Since this low-pass filter 5 has complementary frequency characteristics of the same cutoff frequency as the high-pass filter 1, the portion of the output signal S5 output from this low-pass filter in the period T2 has been removed by the high-pass filter 1. This is exactly the same as the portion of the signal having a low frequency component in the period T2. The output signal 5 of the low-pass filter 5 is supplied to the adding circuit 2.
[0018]
The adder circuit 2 adds the reproduction signal S1 from the high-pass filter 1 and the output signal S5 from the low-pass filter 5. The addition signal S2 added in the addition circuit 2 is a signal that is not affected by the low-pass filter 5 in the period T2, as shown in FIG.
Here, the reason why the low-pass filter 5 is provided will be described again with reference to FIG.
[0019]
First, in the example shown in FIG. 2, the period “T1” is defined as a period in which the reproduction signal S0 has a high frequency, and the period “T2” is defined as a period in which the reproduction signal S0 does not have a high frequency.
The high-pass filter 1 cuts low frequency components according to a predetermined frequency characteristic set in the filter regardless of the periods T1 and T2. Therefore, not only the low frequency component of the period T1 of the reproduction signal S1 is cut but also the low frequency component of the period T2 of the reproduction signal S1 that should not be cut.
[0020]
In the example shown in FIG. 2, no error signal is generated in the encoded signal. For example, if the playback signal level slightly decreases due to dust on the optical disk in the period T2, the high-pass signal is accordingly generated. The level of the reproduction output S1 from the filter 1 is lowered. As a result, the level of the reduced reproduction signal S1 becomes lower than the threshold (threshold) level of the comparator 3 for encoding the reproduction signal S1, and as a result, erroneous encoding is performed. Sometimes.
[0021]
In order to prevent this erroneous encoding, a low-pass filter 5 having the same cutoff frequency as that of the high-pass filter 1 and having a complementary frequency characteristic is provided, and the high-pass filter 1 is applied to the reproduction signal S1 in the period T2. The low-pass filter 5 compensates for the frequency component that has been cut by the above. Therefore, when only the period T2 of the final signal output from the signal reproduction circuit 10 is viewed, the low-frequency component of the reproduction signal S0 is removed by the high-pass filter 1, but the high-pass filter 5 and the addition circuit 2 provide high-pass. The low frequency components removed by the filter 1 are added again. As a result, the portion of the reproduction signal S0 during the period T2 is the same as not being subjected to any band limitation.
[0022]
As described above, the operation of the band limiting means including the high-pass filter 1 and the low-pass filter 5 is summarized as follows. In the period T1 in which the reproduction signal S0 has a high frequency, the band limiting means performs band limitation so as to remove a low frequency component included in the reproduction signal S0 by a high-pass filter, and the reproduction signal S0 has the high frequency. During the period T2, the band is not limited to the reproduction signal S0 by the high-pass filter.
[0023]
Next, the operation of the signal reproduction circuit 10 when the level of the reproduction signal from the optical disk fluctuates will be described with reference to FIG.
For example, as shown in FIG. 5A, when the amplitude of the reproduction signal S0 is A, the amplitude of the detection signal S6 detected by the envelope (envelope) detection by the envelope detection circuit 6 is larger than the comparison level C. The signal S7 becomes high level (second logic level) . As a result, the switch 24 of the gain control circuit 4 shown in FIG. 3 is in an open state, and the amplitude of the feedback signal S4 is an amplitude A equal to the amplitude of the reproduction signal S0.
[0024]
Thereafter, for example, due to dirt or dust on the surface of the optical disc, the reproduction signal S0 locally decreases to the amplitude B as shown in FIG.
As described above, when the amplitude of the reproduction signal S0 decreases, the pulse signal S7 becomes low level (first level ) when the amplitude of the detection signal S6 detected by the envelope detection circuit 6 reaches the comparison level C. The switch 24 shown in FIG. 4 is turned on.
When the switch 24 is turned on, the amplitude of the feedback signal S4 becomes the same amplitude B as that of the reproduction signal S0, as shown in FIG.
[0025]
As described above, according to the signal reproduction circuit 10 used in the optical disk reproduction apparatus of the present embodiment, even when the amplitude of the reproduction signal S0 is locally reduced due to dirt or dust on the surface of the optical disk, Correspondingly, the amplitude of the feedback signal S4 can be reduced. This effectively suppresses the feedback loop from diverging. Therefore, it is possible to perform data detection with high accuracy without being affected by low-frequency noise, even in a portion where the amplitude of the reproduction signal is reduced, and to increase the density of the recording medium (optical disk) .
[0026]
By the way, the signal reproduction circuit 10 used in the optical disk reproduction apparatus is provided with an AGC (automatic gain control) circuit (not shown) so as to maintain the amplitude constant even if the amplitude (gain) is lowered to some extent. The optical disc reproducing apparatus 10 can appropriately cope with a local amplitude decrease that cannot be handled by such an AGC circuit.
[0027]
The present invention is not limited to the embodiment described above. For example, in the embodiment described above, the gain switching of the gain control circuit 4 is set in two stages as shown in FIG. 3, but some fixed resistors and switches are further provided in parallel with the fixed resistors 22 and 23. The amplitude can be reduced in three or more stages. As a result, detection errors at the amplitude-decreasing portion of the reproduction signal can be reduced, and more accurate detection can be performed. Further, if necessary, it is possible to cope with not only a decrease in amplitude of the reproduction signal but also a partial increase. Further, the gain control circuit 4 shown in FIG. 3 may use a reversible resistance instead of switching the resistance value by the switch 24.
[0028]
In the above-described embodiment, the gain adjustment of the gain control circuit 4 is performed based on the pulse signal S7 as shown in FIG. 1, but the gain adjustment is performed based on the detection signal S6. Is also possible.
[0029]
【The invention's effect】
As described above, according to the present invention, even when the amplitude of the reproduction signal is locally reduced due to dirt or dust on the surface of the optical disk, the amplitude of the feedback signal can be reduced correspondingly. . This effectively suppresses the feedback loop from diverging. Accordingly, it is possible to perform data detection with high accuracy without being affected by low-frequency noise, even in a portion where the amplitude of the reproduction signal is reduced, and to increase the density of the recording medium .
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a signal reproduction circuit used in an optical disk reproduction apparatus according to an embodiment of the present invention.
2A is a waveform diagram of the reproduction signal S0, FIG. 2B is a waveform diagram of the reproduction signal S1 after passing through the high-pass filter, FIG. 2C is a waveform diagram of the binarized signal S3, and FIG. 2D is a feedback signal. A waveform diagram of S5, (E) is a waveform diagram of the addition signal S2.
FIG. 3 is a configuration diagram of a gain control circuit shown in FIG. 1;
4 is a specific configuration example of a high-pass filter and a low-pass filter shown in FIG.
5A is a waveform diagram of the reproduction signal S0, FIG. 5B is a waveform diagram of the detection signal S6, FIG. 5C is a waveform diagram of the pulse signal S7, and FIG. 5D is a waveform diagram of the feedback signal S4.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... High pass filter, 2 ... Adder 2, 3 ... Comparator circuit, 4 ... Gain control circuit, 5 ... Low pass filter, 6 ... Envelope detection circuit, 7 ... Pulse generation circuit, 10 ... Signal reproduction circuit used for optical disk reproduction apparatus , 11 ... capacitor, 12 ... resistance

Claims (4)

A high-pass filter that inputs a reproduction signal read from an optical disc on which data having a low-frequency component is recorded, and that blocks a low-frequency component included in the reproduction signal at a predetermined cutoff frequency;
An adder connected to a subsequent stage of the high-pass filter;
A binarization circuit that is connected to a subsequent stage of the adder circuit and generates a binarized signal by comparing an output signal of the adder circuit with a predetermined comparison level;
A gain control circuit connected to a subsequent stage of the binarization circuit and controlling the gain of the amplitude of the output signal of the binarization circuit;
In order to compensate for the frequency component that is connected to the subsequent stage of the gain control circuit and is cut by the high-pass filter, the high-frequency component included in the signal output from the gain control circuit is blocked at a predetermined cutoff frequency. A low-pass filter that passes a low-frequency component and outputs it to the adder circuit;
An envelope detection circuit for detecting an envelope of the read reproduction signal and detecting an amplitude of the envelope detected signal;
The cutoff frequency of the high-pass filter is equal to the cutoff frequency of the low-pass filter, and the high-pass filter and the low-pass filter have complementary frequency characteristics,
The gain control circuit is responsive to the amplitude of the envelope detection signal detected by the envelope detection signal so that the amplitude of the gain control signal from the gain control circuit is equal to the amplitude of the read reproduction signal. Controlling the amplitude of the gain control signal from the gain control circuit;
A signal reproducing circuit used in an optical disk reproducing apparatus. The gain control circuit includes:
At least two resistors connected in series and parallel;
A switch circuit that changes the resistance value of the two series-parallel resistors,
The envelope detection circuit compares the amplitude of the envelope detected signal with a predetermined level. When the amplitude of the envelope detected signal is equal to or lower than a predetermined level, the first logic level and the amplitude of the envelope detected signal are predetermined. A circuit for outputting a signal of the second logic level when the level is higher than
The switch circuit of the gain control circuit is turned on when a signal output from the envelope detection circuit is at the first logic level, is turned off when the signal is at the second logic level, and when the switch circuit is on, the gain control is performed. The gain control circuit is configured so that the amplitude of the gain control signal from the circuit is equal to the amplitude of the read reproduction signal.
The signal reproduction circuit according to claim 1. A high-pass filter that inputs a reproduction signal read from an optical disc on which data having a low-frequency component is recorded, and that blocks a low-frequency component included in the reproduction signal at a predetermined cutoff frequency;
An adder connected to a subsequent stage of the high-pass filter;
A binarization circuit that is connected to a subsequent stage of the adder circuit and generates a binarized signal by comparing an output signal of the adder circuit with a predetermined comparison level;
A gain control circuit connected to a subsequent stage of the binarization circuit and controlling the gain of the amplitude of the output signal of the binarization circuit;
In order to compensate for the frequency component that is connected to the subsequent stage of the gain control circuit and is cut by the high-pass filter, the high-frequency component included in the signal output from the gain control circuit is blocked at a predetermined cutoff frequency. A low-pass filter that passes a low-frequency component and outputs it to the adder circuit;
An envelope detection circuit for detecting an envelope of the read reproduction signal and detecting an amplitude of the envelope detected signal;
The cutoff frequency of the high-pass filter is equal to the cutoff frequency of the low-pass filter, and the high-pass filter and the low-pass filter have complementary frequency characteristics,
The gain control circuit is responsive to the amplitude of the envelope detection signal detected by the envelope detection signal so that the amplitude of the gain control signal from the gain control circuit is equal to the amplitude of the read reproduction signal. Controlling the amplitude of the gain control signal from the gain control circuit;
An optical disc reproducing apparatus provided with a signal reproducing circuit. The gain control circuit includes:
At least two resistors connected in series and parallel;
A switch circuit that changes the resistance value of the two series-parallel resistors,
The envelope detection circuit compares the amplitude of the envelope detected signal with a predetermined level. When the amplitude of the envelope detected signal is equal to or lower than a predetermined level, the first logic level and the amplitude of the envelope detected signal are predetermined. A circuit for outputting a signal of the second logic level when the level is equal to or higher than the level;
The switch circuit of the gain control circuit is turned on when a signal output from the envelope detection circuit is at the first logic level, is turned off when the signal is at the second logic level, and when the switch circuit is on, the gain control is performed. The gain control circuit is configured so that the amplitude of the gain control signal from the circuit is equal to the amplitude of the read reproduction signal.
The optical disk reproducing device according to claim 3.

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