JP2010055671A - Defect detection circuit, optical disk device, and defect detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve response speeds of entering and exiting a defect area. <P>SOLUTION: A defect detection circuit which detects a defect of an optical disk includes: a decoding processing part which decodes an RF signal read from the optical disk and generates state information of the RF signal; an envelope signal generation circuit which extracts the RF signal on the basis of the state information and generates an envelope signal; and a defect determination part which determines a defect area on the basis of the envelope signal and outputs a control signal. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical disc defect detection circuit, an optical disc apparatus including the same, and a defect detection method.

  In recent years, optical disks such as CDs (Compact Discs), DVDs (Digital Versatile Disks), and BDs (Blu-ray Discs) are often used as information storage media. The rotation of the optical disk is controlled by servo control. Further, the position of the pickup for reading / writing information from / to the optical disc is also controlled by servo control. By this servo control, the optical disc apparatus can stably read and write information. However, an optical disk has a defective area due to dirt or scratches such as fingerprints attached to the disk surface. In such a defective area, appropriate reflected light cannot be obtained from the optical disk, and servo control becomes unstable. For this reason, there is a possibility of causing a problem in reading / writing data.

  Therefore, when the pickup passes over the defective area, the servo control is fixed immediately before the defective area. In such servo control, it is necessary to detect a defective area. Patent Document 1 discloses a defect detection circuit for detecting a defective area of an optical disc.

  A block diagram of the optical disc apparatus 1 disclosed in Patent Document 1 is shown in FIG. As shown in FIG. 4, the optical disc apparatus 1 includes an optical disc rotation motor 10, a pickup 20, a servo control circuit 30, an AGC (Automatic Gain Control) circuit 40, and a defect detection circuit 50.

  The optical disk rotation motor 10 is a motor that rotates an optical disk. The pickup 20 generates an RF (Radio Frequency) input signal X having an amplitude corresponding to the output of laser light to the optical disc and the amount of reflected light from the optical disc. The servo control circuit 30 outputs a control signal for controlling the rotational speed of the rotary motor 10 and the position of the pickup 20 according to the state of the RF input signal X. The servo control circuit 30 fixes the amplification factor based on the hold enable signal output from the defect detection circuit 50.

  The AGC circuit 40 amplifies the RF input signal X whose amplitude varies to a signal having a substantially constant amplitude, and outputs the amplified signal as an AGC output signal Z to an internal circuit (not shown). In the internal circuit, signal processing is performed based on the AGC output signal Z. The AGC circuit 40 fixes the amplification factor based on the hold enable signal output from the defect detection circuit 50.

  The defect detection circuit 50 includes a peak hold detection circuit 51, an inclination detection circuit 52, a comparison circuit 53, and a comparison voltage control circuit 54, and detects a defect area based on the amplitude of the RF input signal X.

The peak hold detection circuit 51 generates an envelope signal whose signal level varies according to the variation of the peak level of the RF input signal X. The inclination detection circuit 52 detects the inclination of the envelope signal based on the rate of change in the signal level of the envelope signal, and outputs an inclination detection signal. The comparison circuit 53 compares the inclination detection signal with a predetermined range specified by the reference voltage, and outputs a defect detection signal Y. The comparison voltage control circuit 54 compares the RF input signal X with the amplitude reference value Vref, and supplies the comparison voltage Vcomp to the comparison circuit 53 based on the comparison result.
In the defect area, the amplitude of the signal is smaller than that in the normal area, and the slope of the envelope signal increases when entering the defect area and exiting from the defect area. Therefore, a defective area can be detected with the above configuration.
JP 2008-047164 A

  Incidentally, the time length of the mark / space recorded on the optical disc has a length that is an integral multiple of the period T of the channel clock. Here, the space means a portion where no mark is formed in the track. The shortest length of the mark / space is 3T for DVD, for example. Here, the amplitude of the RF signal corresponding to the short mark and space of 3T to 5T gradually increases with the length thereof, and the amplitude of the RF signal corresponding to the mark and space of 6T or more becomes a constant value.

  Therefore, in the peak hold circuit 51, it is necessary to set the time constant of the detection circuit for performing the peak hold of the RF signal to a certain extent so as not to detect the mark / space of 3 to 5T as a defect. On the other hand, the larger the time constant, the smaller the differential signal (the slope of the RF envelope signal) generated by the slope detection circuit 52. Therefore, there has been a problem that the response speed of entering the defect area and escaping from the defect area becomes slow.

One embodiment of the present invention provides:
A defect detection circuit for detecting an optical disc defect,
A decoding processor that decodes an RF signal read from the optical disc and generates state information of the RF signal;
An envelope signal generation circuit that extracts the RF signal based on the state information and generates an envelope signal;
The defect detection circuit includes a defect determination unit that determines whether or not the defect region is based on the envelope signal and outputs a control signal.

Another aspect of the present invention is:
A decoding processor that decodes an RF signal read from the optical disc and generates state information of the RF signal;
An envelope signal generation circuit that extracts the RF signal based on the state information and generates an envelope signal;
An optical disc apparatus comprising: a defect determination unit that determines whether or not a defect area is present based on the envelope signal and outputs a control signal.

Another aspect of the present invention is:
The RF signal read from the optical disc is decoded to generate state information of the RF signal,
Based on the state information, the RF signal is extracted to generate an envelope signal;
This is a defect detection method for determining whether or not it is a defect area based on the envelope signal.

  With the defect detection circuit according to the present invention, the response speed of the entry into the defect area and the escape from the defect area is increased.

Embodiment 1
Embodiments of the present invention will be described below with reference to the drawings. The optical disc apparatus according to Embodiment 1 reproduces and records information from an optical disc (for example, CD, DVD, BD, etc.) using laser light. Reproduction is performed by irradiating the recording surface with laser light and detecting a change in the amount of reflected light.

  FIG. 1 shows a block diagram of the optical disc apparatus according to the first embodiment. As shown in FIG. 1, the optical disk apparatus according to Embodiment 1 includes an optical disk rotating motor 110, a pickup 120, a servo control circuit 130, an AGC circuit 140, a defect detection circuit 150, and a PRML (Partial Response Maximum Likelihood) processing circuit 160. Have.

  The optical disk rotation motor 110 is a motor that rotates the optical disk, and controls the rotation speed of the optical disk based on a control signal input from the servo control circuit 130. The pickup 120 generates an RF input signal X having an amplitude corresponding to the output of laser light to the optical disc and the amount of reflected light from the optical disc. The pickup 120 can be moved along the surface of the optical disk by, for example, a servo motor. A servo motor that controls the position of the pickup 120 is controlled by a servo control circuit 130.

  The servo control circuit 130 outputs a control signal for controlling the rotational speed of the optical disc and the position of the pickup in accordance with the RF input signal X. The servo control circuit 130 fixes the amplification factor based on the hold enable signal output from the defect detection circuit 150.

In an optical disc apparatus, tracking servo control, focus servo control, spindle servo control, and thread servo control are performed when information recording or information reproduction from an optical disc is performed.
The tracking servo control detects a positional deviation between the center of the light spot and the center of the groove of the optical disk using the reflected light from the optical disk, and controls the position of the pickup so as to correct this positional deviation. This maintains the center of the light spot at the center of the groove on the optical disc.
The focus servo control detects a shift of the focal position of the objective lens that collects the laser light using the reflected light from the optical disc, and controls the position of the pickup so as to correct this focus shift. As a result, the focal position of the objective lens for condensing the laser light is maintained on the surface of the optical disk following the vertical movement of the optical disk.
The spindle servo control controls the rotation speed of the optical disk rotation motor so that the data rate and wobble frequency of the reproduction RF signal are constant.
The sled servo control enables long-distance seek by controlling the inclination of the pickup so as to follow the DC component of tracking.

  The AGC circuit 140 amplifies the RF input signal X whose amplitude varies to a signal having a substantially constant amplitude, and outputs the amplified signal to the PRML processing circuit 160 as an AGC output signal Z. Note that fluctuations in the amplitude of the RF input signal X occur due to, for example, fluctuations in the amount of laser light or defects (defects) such as fingerprints or scratches on the optical disk surface. The AGC circuit 140 fixes the amplification factor based on the hold enable signal output from the defect detection circuit 150.

  In the PRML processing circuit 160, PRML processing of the signal, that is, decoding processing is performed based on the AGC output signal Z.

  The defect detection circuit 150 detects a defect area based on the amplitude of the RF input signal X. The defect detection circuit 150 will be described in detail. The defect detection circuit 150 includes an RF signal level extraction circuit 151, an inclination detection circuit 152, a comparison circuit 153, a comparison voltage control circuit 154, a subtractor 155, and a state determination circuit 156.

  The state determination circuit 156 determines the number of consecutive specific states from among the transition states in the PRML processing performed by the PRML processing circuit 160. For example, when PR (1221) is used for a DVD, the number of continuous states S0 (000) indicating the bottom level or the number of continuous states S5 (111) indicating the top level is determined. From this, a mark (top level) / space (bottom level) of 6T or more can be extracted.

  Based on the determination result of the state determination circuit 156, the RF signal level extraction circuit 151 extracts only the RF input signal X in a specific state protected by a predetermined number of consecutive times, and connects the maximum values of the RF input signal X. A bottom envelope signal obtained by connecting the minimum values of the top envelope signal and the RF input signal X is generated. In the case of PR (1221), the bottom envelope signal is generated by extracting the RF input signal X in the state S0 (000) in which protection is applied for a predetermined number of consecutive times. Further, the top envelope signal is generated by extracting the RF input signal X in the state S5 (111) protected by the continuous number of times.

  In this embodiment, both a top envelope signal and a bottom envelope signal are generated. Therefore, both the dark defect area and the bright defect area can be detected with high accuracy, which is preferable. Here, the defect area may be detected from only one of the envelope signals. In that case, the subtractor 155 is unnecessary.

The subtractor 155 obtains the difference between the peak envelope signal and the bottom envelope signal and outputs the amplitude / envelope signal.
The inclination detection circuit 152 differentiates the amplitude / envelope signal generated by the subtractor 155, detects the inclination of the envelope signal from the differential value (change rate of the amplitude / envelope signal), and outputs an inclination detection signal. For example, when there is no change in the signal level of the envelope signal, the inclination detection signal maintains a predetermined signal level. On the other hand, when the signal level of the envelope signal varies, the signal level of the inclination detection signal is varied according to the rate of change of the envelope signal. The fluctuation in the signal level of the inclination detection signal becomes larger as the change rate of the envelope signal is larger. In the present embodiment, the inclination detection signal is generated from the amplitude / envelope signal, but the inclination detection signal may be generated from each of the top envelope signal and the bottom envelope signal.

  The comparison circuit 153 compares the inclination detection signal with a predetermined range specified by the reference voltage Vcomp, and outputs a defect detection signal Y. For example, when the inclination detection circuit 152 detects a drop (negative change rate) in the signal level of the envelope signal and the signal level of the inclination detection signal that fluctuates according to the change rate falls outside a predetermined range, The signal level changes from the low level to the high level. On the other hand, when the inclination detection circuit 152 detects an increase (positive change rate) of the signal level of the envelope signal, and the signal level of the inclination detection signal that fluctuates according to the change rate falls outside the predetermined range, The signal level changes from high level to low level.

  For example, the predetermined range is obtained by setting an upper limit value and a lower limit value above and below the signal level of the inclination detection signal when the inclination is 0 in the envelope signal. The upper limit value and the lower limit value can be set so that the amplitude change of the RF input signal X generated by the defect can be detected and does not react to the amplitude change of the RF input signal X generated by the fluctuation of the laser beam. preferable. The comparison voltage Vcomp that sets the predetermined range is generated by the comparison voltage control circuit 154.

  The comparison voltage control circuit 154 compares the amplitude / envelope signal generated by the subtractor 155 with the amplitude reference value, and supplies a comparison voltage Vcomp obtained by multiplying the reference voltage Vref by a coefficient based on the comparison result to the comparison circuit 153. The coefficient can be set arbitrarily. The coefficient may be changed based on a comparison result between the amplitude / envelope signal and the amplitude reference value. The operation of the comparison voltage control circuit 154 will be described in more detail. When the comparison voltage control circuit 154 determines that the amplitude / envelope signal is smaller than the amplitude reference value, the comparison voltage control circuit 154 decreases the coefficient applied to the reference voltage Vref. As a result, the voltage level of the comparison voltage Vcomp is reduced. On the other hand, when it is determined that the amplitude / envelope signal is larger than the amplitude reference value, the coefficient applied to the reference voltage Vref is reduced. As a result, the voltage level of the comparison voltage Vcomp increases.

  In this way, by changing the voltage level of the comparison voltage Vcomp in accordance with the amplitude / envelope signal, it becomes possible to detect a defect having a smaller inclination due to a decrease in the amplitude / envelope signal. On the other hand, when the amplitude / envelope signal is large, it is possible to selectively detect the defect area in accordance with the gradient that has increased as the amplitude level has increased.

  The reference voltage Vref is set in advance as a voltage level at which the defect region can be selectively detected when the amplitude / envelope signal is an arbitrarily set amplitude level. As the amplitude reference value, a value corresponding to the amplitude level used when setting the reference voltage Vref is set in advance. The reference voltage Vref and the amplitude reference value can be arbitrarily set, and the above setting method shows an example.

  The defect detection signal Y is input to the servo control circuit 130 and the AGC circuit 140 as a hold enable signal. The servo control circuit 130 and the AGC circuit 140 maintain the previous control state and amplification factor during a period in which the hold enable signal is at a high level, for example. On the other hand, during the period in which the hold enable signal is at the low level, the servo control circuit 130 performs various controls so that the reproduction of information from the optical disk is stable, and the AGC circuit 140 increases the amplification factor according to the amplitude of the RF input signal X. change.

  Next, a timing chart showing an example of the operation of the defect detection circuit 150 is shown in FIG. 2, and the operation of the defect detection circuit 150 will be described with reference to this figure. When the RF input signal X is input, the RF signal level extraction circuit 151 generates a top envelope signal and a bottom envelope signal according to the state information generated by the state determination circuit 156. Subsequently, the subtractor 155 generates an amplitude / envelope signal from both envelope signals. The inclination detection circuit 152 generates an inclination detection signal according to the inclination of the amplitude / envelope signal. Then, when the signal level of the inclination detection signal becomes equal to or greater than a predetermined range, the comparison circuit 153 changes the signal level of the defect detection signal Y. In the example illustrated in FIG. 2, the predetermined range is a range between the upper limit value Vth_H and the lower limit value Vth_L.

  In the example shown in FIG. 2, the amplitude of the RF input signal X decreases at the timing t3 when the pickup reaches the upper part of the defect area. At this time, the signal level of the envelope signal decreases according to the change in the signal level of the RF input signal X. Since the rate of change of the envelope signal is negative, the signal level of the inclination detection signal decreases. Further, the signal level of the inclination detection signal at the timing t3 is lower than the lower limit value Vth_L of the predetermined range. As a result, the defect detection signal Y changes from the low level to the high level.

  Further, when the pickup escapes from the upper part of the defect area at timing t4, the amplitude of the RF input signal X increases. At this time, the signal level of the envelope signal rises according to the change in the signal level of the RF input signal X. Since the rate of change of the envelope signal is positive, the signal level of the tilt detection signal increases. Further, the signal level of the inclination detection signal at the timing t4 exceeds the upper limit value Vth_H within a predetermined range. As a result, the defect detection signal Y changes from the high level to the low level.

  On the other hand, the amplitude of the RF input signal X also decreases at timings t1 to t2 and timings t5 to t6. The change in the amplitude of the RF input signal X during this period is, for example, due to fluctuations in the laser beam, and is smaller than the decrease in amplitude at timings t3 to t4. Therefore, the decrease in the signal level of the envelope signal and the change in the signal level of the tilt detection signal are small compared to the period from timing t3 to t4. At this time, the fluctuation of the signal level of the inclination detection signal is sufficiently within a predetermined range. Therefore, the signal level of the defect detection signal Y does not change.

  Next, the effect of the present invention will be described with reference to FIG. A curve indicated by a solid line is a signal curve according to Embodiment 1, and a curve indicated by a broken line is a signal curve in the configuration described in Patent Document 1.

  In the peak hold detection circuit described in Patent Document 1, for example, a time constant of a detection circuit for performing peak hold of an RF signal so as not to detect a 3 to 5T mark / space on a DVD as a defect (for example, in a low-pass filter) RC time constant) had to be set large to some extent. Therefore, as shown by a broken line in FIG. 3, the fluctuations of the generated top / bottom envelope signal and the amplitude / envelope signal are gentler than the amplitude fluctuation of the actual RF input signal X. Therefore, the response speed of entering the defect area and escaping from the defect area is slow.

  On the other hand, in the defect detection circuit 150 according to the first embodiment, the RF signal level extraction circuit 151 extracts only the RF input signal X in the specific state determined by the state determination circuit 156 from the RF input signals. Then, a top envelope signal connecting the maximum value of the RF input signal X and a bottom envelope signal connecting the minimum value of the RF input signal X are generated. In other words, the peak hold detection circuit is unnecessary and it is not necessary to provide a time constant.

  Therefore, as shown by a solid line in FIG. 3, fluctuations in the generated top / bottom envelope signal and amplitude / envelope signal approach the amplitude fluctuation of the actual RF input signal X. Therefore, the change of the inclination detection signal is also steep, and the response speed of switching of the defect detection signal Y, that is, the entry into the defect area and the escape from the defect area is also increased. Thus, better servo control can be realized when there is a defective area. In the configuration according to the first embodiment, it is not necessary to set a time constant for generating the bottom envelope signal, but, of course, a time constant smaller than the conventional one may be set.

  Further, the peak hold detection circuit described in Patent Document 1 requires a circuit for optimizing the time constant. Furthermore, since the optimum time constant varies depending on the reproduction bit rate, a circuit for setting the optimum time constant according to the reproduction bit rate is also required. Therefore, the peak hold detection circuit described in Patent Document 1 tends to be large in circuit scale. On the other hand, in the present invention, since the state information by the PRML process is effectively used, the circuit scale can be extremely reduced as compared with Patent Document 1.

  Further, in the configuration described in Patent Document 1, in order to generate the amplitude / envelope signal from the top envelope signal and the bottom envelope signal, the circuit scale is increased for the above reason. On the other hand, in the present invention, since the state information by the PRML process is effectively used, the amplitude / envelope signal can be easily generated without increasing the circuit scale. As a result, the response speed of entering the defect area and escaping from the defect area can be made faster than detecting the inclination from one of the top envelope signal and the bottom envelope signal. In addition, both the dark defect area and the bright defect area can be detected with high accuracy.

1 is a block diagram of an optical disc device according to Embodiment 1. FIG. 3 is a timing chart illustrating an operation of the defect detection circuit according to the first embodiment. It is a figure which shows the relationship of the detection result of the defect of Embodiment 1 and a comparative example. FIG. 1 of Patent Document 1.

Explanation of symbols

110 Optical disk rotation motor 120 Pickup 130 Servo control circuit 140 AGC circuit 150 Defect detection circuit 151 RF signal level extraction circuit 152 Inclination detection circuit 153 Comparison circuit 154 Comparison voltage control circuit 155 Subtractor 156 State determination circuit 160 PRML processing circuit Vcomp Comparison voltage Vref Reference voltage X RF input signal Y Defect detection signal Z AGC output signal

Claims (12)

A defect detection circuit for detecting an optical disc defect,
A decoding processor that decodes an RF signal read from the optical disc and generates state information of the RF signal;
An envelope signal generation circuit that extracts the RF signal based on the state information and generates an envelope signal;
A defect detection circuit comprising: a defect determination unit that determines whether or not the defect region is based on the envelope signal and outputs a control signal.   The defect detection circuit according to claim 1, wherein the decoding process is a PRML process.   The defect detection circuit according to claim 1, wherein the defect determination unit determines whether or not the defect region is based on a change amount of the envelope signal with respect to time. The envelope signal generation circuit generates a top envelope signal and a bottom envelope signal,
The defect detection circuit according to claim 3, wherein the defect determination unit determines whether or not the defect region is based on a change amount with respect to time of a difference between the top envelope signal and the bottom envelope signal. A decoding processor that decodes an RF signal read from the optical disc and generates state information of the RF signal;
An envelope signal generation circuit that extracts the RF signal based on the state information and generates an envelope signal;
An optical disc apparatus comprising: a defect determination unit that determines whether or not a defect area is based on the envelope signal and outputs a control signal.   6. The optical disc apparatus according to claim 5, wherein the decoding process is a PRML process.   7. The optical disc apparatus according to claim 5, wherein the defect determination unit determines whether or not the defect area is based on a change amount of the envelope signal with respect to time. The envelope signal generation circuit generates a top envelope signal and a bottom envelope signal,
8. The optical disc apparatus according to claim 7, wherein the defect determination unit determines whether or not the defect area is based on a change amount with respect to time of a difference between the top envelope signal and the bottom envelope signal. The RF signal read from the optical disc is decoded to generate state information of the RF signal,
Based on the state information, the RF signal is extracted to generate an envelope signal;
A defect detection method for determining whether or not a defect area is based on the envelope signal.   The defect detection method according to claim 9, wherein the decoding process is a PRML process.   The defect detection method according to claim 9 or 10, wherein it is determined whether or not the defect region is based on a change amount of the envelope signal with respect to time.   The envelope signal has a top envelope signal and a bottom envelope signal, and determines whether or not the defect region is based on a change amount with respect to time of a difference between the top envelope signal and the bottom envelope signal. The defect detection method according to claim 11.

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