JP3669905B2 - Dropout detection circuit - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a dropout detection circuit for detecting a dropout of an RF signal reproduced from an optical disc such as a compact disc as a recording medium.
[0002]
[Prior art]
Conventionally, in an optical disc system that reproduces recorded information from an optical disc such as a compact disc (CD) or a compact disc-rom (CD-ROM) as a recording medium, a dropout of an RF signal reproduced from the optical disc is performed. Dropout detection circuits for detection are widely used.
[0003]
Such a dropout detection system using a conventional dropout detection circuit will be described below with reference to FIGS. 5, 6, 7 and 8. FIG.
FIG. 8 shows a general block configuration of an optical disc system such as a CD. Here, a part of preprocessing necessary for extracting a data signal (recording data) based on CD recording information will be described. In FIG. 8, 36 is an optical pickup, 37 is a head amplifier block, and 38 is an optical disk signal processing / control block.
[0004]
In an optical disk system such as a CD, an analog RF signal is extracted from a reflected signal such as a laser applied to the optical disk by an optical pickup 36, and the analog RF signal is amplified to a certain level by a head amplifier block 37 composed of an analog circuit. The data is input to the optical disk signal processing / control block 38 constituted by a digital circuit, and the recording data is extracted from the analog RF signal.
[0005]
In addition to the amplification of the analog RF signal from the optical pickup 36, the head amplifier block 37 also generates a dropout signal and a track deviation signal necessary for stable reproduction of the optical disc. By adjusting the reading using these dropout signals and off-track signals, the data signal can be stably extracted from the analog RF signal of the optical disk.
[0006]
Here, a method for generating a dropout signal from an analog RF signal will be described.
Dropout generally refers to a state in which read data from an optical disk is missing due to scratches on the surface of the optical disk, etc. FIG. 6 shows an analog RF signal 1 (FIG. 6A), a high-speed detection signal 27. (FIG. 6 (b-1)), the low-speed detection signal 28 (FIG. 6 (b-2)), and the waveform diagrams of the dropout detection signal 9 (FIG. 6 (c)) are shown.
[0007]
When the bright side of the analog RF signal, that is, the side where the reflection from the optical disk is large, is set to a high level of the analog RF signal, and the dark side, ie, the side where the reflection of the optical disk is low, is set to a low level of the RF signal, as shown in FIG. In the non-dropout state, since the optical pickup 36 reads the reflection of the portion of the optical disk where data exists, both the bright side and dark side states exist, and the bright side and dark side envelopes have substantially constant values. Become.
[0008]
However, in the dropout state, since the optical pickup 36 reads the data missing portion, reflection from the optical disk is reduced and the level of the bright side envelope signal is lowered. Using this property, dropout detection can be performed.
[0009]
A dropout detection circuit for performing such dropout detection will be described below.
FIG. 5 is a block diagram showing a configuration of a conventional dropout detection circuit. In FIG. 5, 20 is a high-speed detection circuit, 21 is an external circuit (I), 22 is a low-speed detection circuit, 23 is an external circuit (II), 24 is a shift circuit, 25 is a comparison circuit, 1 is an analog RF signal, 27 is a high-speed detection signal, 28 is a low-speed detection signal, 29 is a shift signal, 9 is a dropout detection signal, and 26 is a current switching signal.
[0010]
The high-speed detection circuit 20 is configured to allow an arbitrary predetermined current to flow between its output terminal and GND, and the external circuit (I) 21 is used to obtain a detection speed for high-speed detection with respect to the high-speed detection circuit 20. In order to give a detection time constant, it has a capacitance connected between the output terminal of the high-speed detection circuit 20 and GND, and a current source for flowing a predetermined current between the output terminal of the high-speed detection circuit 20 and GND. Yes.
[0011]
The low-speed detection circuit 22 is configured such that an arbitrary current can flow between the output terminal and GND, and the amount of current can be controlled by the current switching signal 26. The external circuit (II) 23 includes a low-speed detection circuit. In order to give a detection time constant for obtaining a detection speed for low-speed detection to the circuit 22, an electrostatic capacity connected between the output terminal of the low-speed detection circuit 22 and GND, an output terminal of the low-speed detection circuit 22, and GND A current source for passing an arbitrary current therebetween. Here, the current switching signal 26 is a repetitive signal of a level H (high) section and a level L (low) section, and the output terminal in the low-speed detection circuit 22 is changed by changing the ratio of the H section and the L section. And the amount of current between GND and GND can be changed.
[0012]
In the dropout detection circuit configured as described above, in the high-speed detection circuit 20, the detection speed obtained by the capacitance of the external circuit (I) 21 and the current source is used, and the analog RF signal 1 is analogized. High-speed detection is performed, and a high-speed detection signal 27 is generated. On the other hand, in the low-speed detection circuit 22, analog low-speed detection is performed on the analog RF signal 1 by using the capacitance of the external circuit (II) 23, the detection speed obtained from the current source and the current switching signal 26, and the low-speed detection signal. 28 is generated.
[0013]
Next, the shift circuit 24 generates a shift signal 29 by level-shifting the low-speed detection signal 28, and the comparison circuit 25 compares the high-speed detection signal 27 with the shift signal 29, so that the level of the shift signal 29 is high. A section higher than the level of the detection signal 27 is set in a dropout state, a dropout detection signal 9 is generated as a signal in which this dropout state is detected, and this dropout detection signal 9 is used as an output of the dropout detection circuit.
[0014]
By configuring as described above, when the level of the bright side envelope signal becomes low as shown in FIG. 6A (dropout state), the low-speed detection signal 28 is shifted as shown in FIG. 6B. Although the shift signal 29 has a small change, the high-speed detection signal 27 has a large change, so that the level of the high-speed detection signal 27 becomes lower than that of the shift signal 29 and the level of the bright side envelope signal can be detected. And we were doing dropout detection.
[0015]
Further, when the playback speed changes, for example, as shown in FIG. 7, when the playback speed becomes double speed, the width of the dropout is actually ½ that of the single speed of FIG. However, when the followability by the time constant of the low speed detection circuit 22 is constant from the followability at the 1 × speed of FIG. 7A as shown in FIG. 7B, the level of the low speed detection signal 28 is changed. 6B, the level of the shift signal 29 also rises and the level of the high-speed detection signal 27 is lower than the shift signal 29 (dotted line period), that is, the period detected as a dropout state. Becomes wider than the actual width of the dropout, and the dropout detection signal 9 having a desired width cannot be obtained as shown in FIG.
[0016]
In the conventional configuration, the amount of current between the output terminal and GND in the low-speed detection circuit 22 is switched by the current switching signal 26 in response to the change in the reproduction speed as described above, and the electrostatic capacitance of the external circuit (II) 23 is switched. The low-speed detection signal 28 is controlled by changing the detection time constant by controlling the discharge current from the capacity and changing the follow-up property of the low-speed detection circuit 22 as shown in FIG. Further, by adjusting (lowering here) the level of the shift signal 29, a dropout detection signal 9 having a desired width is obtained as shown in FIG.
[0017]
[Problems to be solved by the invention]
However, in the conventional dropout detection circuit as described above, the low-speed detection circuit 22 and the high-speed detection circuit 20 require external circuits 23 and 21 for obtaining envelope signals, respectively. A terminal is required. In addition, the change in the reproduction speed is realized by switching the amount of low-speed detection current by the low-speed detection circuit 22 to change the follow-up property. However, this change in follow-up property is not flexible and therefore Detection accuracy is poor, and switching the amount of current leads to a change in external circuits and an increase in the number of analog circuits, resulting in an increase in circuit scale.
[0018]
In the future, when considering integration into the optical disk signal processing / control block 38, etc., the analog circuit will require many external circuits, and circuit design will be difficult because it is easily affected by manufacturing variations. However, even if the process is further miniaturized in the future, there is a problem that it is difficult to reduce the area.
[0019]
The present invention solves the above-mentioned conventional problems, and can easily change parameters such as a detection time constant and a detection current amount without the need for an external circuit or an analog circuit. And a dropout detection circuit capable of performing optimum dropout detection.
[0020]
[Means for Solving the Problems]
In order to solve the above problems, the dropout detection circuit according to the present invention enables setting of a tilt level parameter corresponding to a reproduction speed by rotating a disk in a digital manner at the time of dropout detection. By using this inclination level parameter, the optimum dropout detection can be easily performed for any reproduction speed.
[0021]
As described above, it is possible to flexibly cope with changes in playback speed when detecting dropouts, and it is possible to reduce the number of external circuits required by conventional analog circuits and to scale like an analog circuit by digitalization. It is possible to reduce the circuit configuration with a large size, making the detection accuracy less susceptible to manufacturing variations, improving the detection accuracy for dropout, and reducing the overall circuit scale. it can.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
The dropout detection circuit according to claim 1 of the present invention is a dropout detection circuit that detects a dropout state in which data is missing from an RF signal reproduced from an optical disk that is a recording medium. A / D converter for converting into a format, a peak detection circuit for extracting a bright side envelope signal composed of the peak value from the digital RF signal from the A / D converter, and a bright side envelope signal from the peak detection circuit An inclination detection circuit that detects an inclination caused by an increase / decrease change in the output and outputs an inclination signal indicating the degree of inclination, and an inclination of the bright-side envelope signal detected by the inclination detection circuit as a reference inclination level parameter for the dropout state The slope up reference signal and the slope down reference signal for A parameter switching circuit that switches and outputs the optical disk so as to change according to the reproduction speed of the optical disc, a tilt down comparison circuit that compares the tilt signal from the tilt detection circuit with the tilt down reference signal, and the tilt detection circuit Is set by the output signal of the slope down comparison circuit, and is reset by the output signal of the slope up comparison circuit. A section is provided with a set / reset flip-flop that sets a section as the dropout state and outputs a dropout detection signal having a time length corresponding to the section .
A dropout detection circuit according to a second aspect is the dropout detection circuit according to the first aspect, wherein the dropout detection circuit corresponds to the switching of the slope-up reference signal and the slope-down reference signal according to the reproduction speed by the parameter switching circuit. The A / D converter has a clock switching circuit for switching the frequency of the sampling clock when converting the RF signal to a real number multiple of the reproduction clock corresponding to the reproduction speed.
4. The dropout detection circuit according to claim 3, wherein the dropout detection circuit detects a dropout state in which data is missing from an RF signal reproduced from a recording medium, and a bright side envelope of a bright side RF signal of the RF signal. The peak detection circuit for detecting the inclination, the inclination detection circuit for detecting the inclination of the bright envelope detected by the peak detection circuit, and the inclination detected by the inclination detection circuit are below the first reference value It is configured to include dropout detection means for detecting as a dropout state from the time until the second reference value is exceeded.
A dropout detection circuit according to a fourth aspect is the dropout detection circuit according to the third aspect, wherein the first reference value and the second reference value are changed according to the reproduction speed of the recording medium. The parameter switching circuit is provided.
The dropout detection circuit according to claim 5 is the dropout detection circuit according to claim 4, comprising an A / D converter that converts an RF signal reproduced from the recording medium from an analog format to a digital format, The peak detection circuit is configured to detect a bright-side envelope of the digital RF signal .
[0024]
According to these configurations, it is possible to set the tilt level parameter corresponding to the playback speed by the rotational drive of the disc in the digital method when the dropout is detected, and facilitate the setting, and use the tilt level parameter. This makes it possible to easily perform optimum dropout detection for any playback speed.
[0025]
Hereinafter, a dropout detection circuit according to an embodiment of the present invention will be specifically described with reference to the drawings.
(Embodiment 1)
A dropout detection circuit according to the first embodiment of the present invention will be described.
[0026]
FIG. 1 is a block diagram showing the configuration of the dropout detection circuit according to the first embodiment. In FIG. 1, 1 is an analog RF signal read from a disk, 2 is an A / D converter, 3 is a peak detection circuit, 4 is an inclination detection circuit, 5 is a parameter switching circuit, 6 is an inclination down comparison circuit, and 7 is an inclination. Up comparison circuit, 8 is a set / reset flip-flop (FF), 9 is a dropout detection signal, 10 is a reproduction speed setting signal, 11 is a digital RF signal, 12 is a bright side envelope signal, 13 is a tilt signal, and 14 is a tilt A down reference signal, 15 is a tilt up reference signal, 16 is a tilt down detection signal, and 17 is a tilt up detection signal.
[0027]
The operation of the dropout detection circuit including the above components will be described below.
The analog RF signal 1 shown in FIG. 2A is converted into a digital RF signal 11 by the A / D converter 2 and input to the peak detection circuit 3. The peak detection circuit 3 detects the peak value for each peak from the digital RF signal 11, and as shown in FIG. 2B, the bright side envelope signal in which the peak value is sequentially changed and connected in a staircase pattern. 12 is extracted, and the extracted bright side envelope signal 12 is input to the inclination detection circuit 4.
[0028]
The inclination detection circuit 4 samples the bright side envelope signal 12 at an arbitrary period, holds the data of the bright side envelope signal 12 before one sampling, and inputs the bright side envelope signal sampled and inputted this time. By taking a difference from the 12 data, an increase / decrease change in the bright side envelope signal 12 is detected, and an inclination signal 13 indicating the increase change or decrease change is generated. The generated slope signal 13 is input to both the slope down comparison circuit 6 and the slope up comparison circuit 7 regardless of an increase change or a decrease change.
[0029]
On the other hand, as shown in FIGS. 3A and 3B, the slope of the RF signal at the time of dropout differs depending on the reproduction speed (here, 1 × speed and 2 × speed). For each of the playback speeds described above, the slope down reference is used for the slope signal 13 indicating the decrease change 12a of the bright side envelope signal 12 for dropout determination according to the slope of the RF signal at the time of dropout. In addition, a tilt-up criterion is set for the tilt signal 13 indicating the increase change 12b, and a playback speed setting signal 10 set for each playback speed is input to each of these standards, thereby reproducing the playback speed. And the slope down reference signal 14 and the slope up reference signal 15 corresponding to the increase / decrease change of the bright side envelope signal 12 are output. Is input to the down comparator circuit 6, the tilt-up reference signal 15 is inputted to the tilt-up comparator circuit 7.
[0030]
The slope down comparison circuit 6 detects whether or not the level of the analog RF signal 1 has dropped by comparing the magnitude of the signal slope. That is, the inclination signal 13 and the inclination down reference signal 14 are compared, and if the value of the inclination signal 13 is larger, it is considered that the level of the analog RF signal 1 has dropped, and the inclination as shown in FIG. The down detection signal 16 is set to H. Conversely, if the value of the slope signal 13 is smaller, the slope down detection signal 16 is set to L.
[0031]
On the other hand, the slope-up comparison circuit 7 detects whether the level of the analog RF signal 1 is rising by comparing the magnitudes of the signal slopes. That is, the inclination signal 13 and the inclination up reference signal 15 are compared, and if the value of the inclination signal 13 is smaller, it is considered that the level of the RF signal has increased, and the inclination up detection is performed as shown in FIG. Let signal 17 be H. On the contrary, if the value of the inclination signal 13 is larger, the inclination up detection signal 17 is set to L.
[0032]
The slope down detection signal 16 and the slope up detection signal 17 that change in this way are input to the set / reset FF 8. In the set / reset FF 8, as shown in FIG. 2E, the slope down detection signal 16 in FIG. 2C is set to H and the dropout detection signal 9 is set, and the slope up detection signal 17 in FIG. By resetting the dropout detection signal 9 with H, the dropout state is detected using the H section of the dropout detection signal 9 as the dropout section.
[0033]
As described above, the slope parameter corresponding to the reproduction speed can be set digitally by changing the analog circuit to the digital circuit and providing the parameter switching circuit 5, so that flexible setting is possible. It is possible to perform optimum dropout detection with respect to the playback speed.
(Embodiment 2)
A dropout detection circuit according to a second embodiment of the present invention will be described.
[0034]
FIG. 4 is a block diagram showing the configuration of the dropout detection circuit according to the second embodiment. In FIG. 4, 1 is an analog RF signal read from a disk, 2 is an A / D converter, 3 is a peak detection circuit, 4 is an inclination detection circuit, 5 is a parameter switching circuit, 6 is an inclination down comparison circuit, and 7 is an inclination. Up comparison circuit, 8 is a set / reset FF, 9 is a dropout detection signal, 10 is a reproduction speed setting signal, 11 is a digital RF signal, 12 is a bright side envelope signal, 13 is a tilt signal, 14 is a tilt down reference signal, Reference numeral 15 is an inclination up reference signal, 16 is an inclination down detection signal, 17 is an inclination up detection signal, 18 is a clock switching circuit, and 19 is an A / D sampling clock.
[0035]
The operation of the dropout detection circuit including the above-described components will be described below. Note that only parts different from the case of the first embodiment will be described here.
[0036]
By setting the reproduction speed setting signal 10 in accordance with the reproduction speed, a clock that is a real number multiple (for example, twice) of the reproduction clock is output from the clock switching circuit 18 as an A / D sampling clock 19, and this A / D sampling clock At 19 cycle timings, the A / D converter 2 samples the analog RF signal 1 and converts it to the digital RF signal 11.
[0037]
Since the subsequent operation is the same as that of the first embodiment, description thereof is omitted here.
As described above, in the second embodiment, the A / D converter 2 is provided by providing the clock switching circuit 18 and switching the period of the A / D sampling clock 19 from the clock switching circuit 18 according to the reproduction speed. The sampling clock can be switched for each reproduction speed, and since the A / D sampling clock 19 is synchronized with the reproduction clock, power consumption can be reduced.
[0038]
【The invention's effect】
As described above, according to the present invention, it is possible to set the tilt level parameter corresponding to the playback speed by the rotational drive of the disc in the digital method when the dropout is detected, and the setting is facilitated. By using parameters, it is possible to easily perform optimum dropout detection for any reproduction speed.
[0039]
As a result, it is possible to flexibly cope with changes in playback speed when detecting dropouts, while reducing the number of external circuits required in conventional analog circuits and the scale of analog circuits with digital circuits. Large circuit configuration can be reduced, detection accuracy is less affected by manufacturing variations, detection accuracy for dropout can be improved, and the overall circuit scale can be reduced. .
[0040]
Also, as the sampling clock of the A / D converter, the timing of the clock is switched for each playback speed so as to be synchronized with the playback clock, so that the playback clock can be used, and these clocks are generated. By sharing the circuit configuration, the entire circuit scale can be reduced, and the power consumption of the entire circuit can be reduced.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a dropout detection circuit according to a first embodiment of the present invention. FIG. 2 is a waveform diagram of each part for explaining operations in the first embodiment. FIG. 4 is a block diagram showing a configuration of a dropout detection circuit according to a second embodiment of the present invention. FIG. 5 is a block diagram showing a configuration of a conventional dropout detection circuit. FIG. 6 is a waveform diagram of each part for explaining the operation in the conventional example. FIG. 7 is a waveform diagram showing a difference between an RF signal and a dropout detection signal depending on a reproduction speed in the conventional example. Block diagram showing the basic configuration [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Analog RF signal 2 A / D converter 3 Peak detection circuit 4 Inclination detection circuit 5 Parameter switching circuit 6 Inclination down comparison circuit 7 Inclination up comparison circuit 8 Set / reset FF (BDO generation circuit)
9 Dropout detection signal 10 Playback speed setting signal 11 Digital RF signal 12 Bright side envelope signal 13 Tilt signal 14 Tilt down reference signal 15 Tilt up reference signal 16 Tilt down detection signal 17 Tilt up detection signal 18 Clock switching circuit 19 A / D Sampling clock 20 High-speed detection circuit 21 External circuit (I)
22 Low-speed detection circuit 23 External circuit (II)
24 shift circuit 25 comparison circuit 26 current switching signal 27 high-speed detection signal 28 low-speed detection signal 29 shift signal 36 optical pickup 37 head amplifier block 38 optical disk signal processing / control block

Claims (5)

  In a dropout detection circuit for detecting a dropout state in which data is missing from an RF signal reproduced from an optical disc as a recording medium, an A / D converter for converting the RF signal from an analog format to a digital format, and the A / D A peak detection circuit for extracting a bright side envelope signal having a peak value from a digital RF signal from the converter, and a slope due to an increase / decrease change of the bright side envelope signal from the peak detection circuit is detected, and the degree of the slope is indicated. An inclination detection circuit for outputting an inclination signal, and an inclination up reference signal and an inclination down reference signal for the inclination of the bright side envelope signal detected by the inclination detection circuit as reference inclination level parameters for the dropout state, Change the value so that it changes according to the playback speed of the optical disc. A parameter switching circuit for output, a slope down comparison circuit for comparing the slope signal from the slope detection circuit with the slope down reference signal, and a slope signal from the slope detection circuit and the slope up reference signal are compared. It is set by the output signal of the slope-up comparison circuit and the slope-down comparison circuit, reset by the output signal of the slope-up comparison circuit, and the section from the set to the reset is set as the dropout state and corresponds to the section A dropout detection circuit comprising: a set / reset flip-flop that outputs a dropout detection signal having a time length.   Corresponding to the switching of the tilt-up reference signal and the tilt-down reference signal according to the reproduction speed by the parameter switching circuit, the frequency of the sampling clock when converting the RF signal of the A / D converter according to the reproduction speed 2. The dropout detection circuit according to claim 1, further comprising a clock switching circuit for switching to a real number multiple of the reproduction clock. A dropout detection circuit for detecting a dropout state in which data is lost from an RF signal reproduced from a recording medium, the peak detection circuit detecting a bright side envelope of a bright side RF signal of the RF signal, and the peak detection circuit An inclination detection circuit for detecting the inclination of the bright envelope detected in step (b), and when the inclination detected by the inclination detection circuit becomes equal to or greater than the second reference value from when the inclination is equal to or less than the first reference value. A dropout detection circuit comprising: a dropout detection means for detecting the above as a dropout state. 4. The dropout detection circuit according to claim 3, further comprising a parameter switching circuit capable of changing the first reference value and the second reference value according to a reproduction speed of the recording medium. An A / D converter for converting an RF signal reproduced from the recording medium from an analog format to a digital format, wherein the peak detection circuit detects a bright-side envelope of the digital format RF signal. 4. The dropout detection circuit according to 4.

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