JP4566934B2 - Defect detection apparatus, optical disc apparatus, and defect detection method - Google Patents

Description

  The present invention is used in an information recording / reproducing apparatus such as an optical disk apparatus that performs at least one of information reproduction and information recording using a laser beam, and has a defect in the information recording medium using a signal reproduced from the information recording medium such as an optical disk. The present invention relates to a defect detection apparatus for detecting a defect.

  The optical disc apparatus reproduces information stored in the optical disc by irradiating the optical disc with laser light and detecting a change in reflected light from the optical disc. The optical disk device includes a device that only reproduces information from a read-only optical disk such as a CD-ROM or DVD-ROM, and a write-once optical disk such as a CD-R or DVD-R, or a CD-RW or DVD- There is an apparatus for recording and reproducing information on a rewritable optical disk such as a RAM.

  When performing information recording on an optical disc or reproducing information from an optical disc, tracking servo control, focus servo control, spindle servo control, and thread servo control are performed. The tracking servo control is a method for detecting the positional deviation between the center of the light spot and the center of the groove of the optical disk by using the reflected light from the optical disk, and controlling the drive unit to correct the positional deviation, thereby controlling the groove center on the optical disk. This is the control to maintain the center of the light spot. The focus servo control detects the deviation of the focal position of the objective lens that collects the laser light using the reflected light from the optical disc, and controls the drive unit to correct this focal deviation. In this control, the focal position of the objective lens that collects the laser light is maintained on the surface of the optical disc following the blur. In the spindle servo control, the spindle rotation speed is controlled so that the data rate and wobble frequency of the reproduction RF signal are constant. Further, the sled servo control is a control for tracking the DC component of the tracking error signal, suppressing the lens tilt, and performing a long distance seek.

  An optical disk may have a defective area such as dust or fingerprints attached to the optical disk surface or scratches on the optical disk surface. In such a defective area, accurate reflected light cannot be obtained from the optical disc, and the servo control described above cannot be performed normally. For this reason, a defective area of the optical disk is detected based on a change in the reflected light reflected by the optical disk, and measures such as fixing the servo control to the state before the defective area in the defective area are taken to prevent servo control problems. This has been done conventionally. An apparatus and a method for detecting a defective area of an optical disc are disclosed in, for example, Patent Documents 1 and 2.

  Patent Document 1 discloses a defect detection apparatus that detects a defect by performing threshold determination on the signal amplitude of an RF signal reproduced from an optical disc. Specifically, a region where the top peak level of the RF signal is below a predetermined threshold is determined as a defective region, and when it is in the defective region, the gain of a variable gain amplifier (VGA) that amplifies the RF signal is suppressed. This prevents the tracking servo control malfunction caused by fluctuations in the reproduction signal level due to overamplification after escape from the defective area.

  Patent Document 2 discloses an optical disc apparatus that detects a defective area by performing threshold determination on the top peak level of a sub beam (± first order diffracted light) in the three beam method.

Further, not only a defect detection method that directly determines a threshold value for a top peak level of a reproduction signal such as an RF signal, but also a threshold value determination for a difference between the top peak level of the RF signal and the bottom peak level of the RF signal. However, there is also a method in which two peak hold signals are generated by holding the top peak level of the RF signal by two peak hold circuits having different attenuation rates, and a threshold is determined for the difference between the two peak hold signals. Yes.
JP 2005-166151 A Japanese Patent Laid-Open No. 2004-146013

  Defects due to fingerprints attached to the optical disk surface are smaller than other defects such as scratches on the optical disk surface, and the attenuation of the amplitude of the reproduction signal is small, and the reflectance varies within the defect area. There is a feature that the amount of attenuation of the amplitude is not uniform. When such a defect exists, the threshold determination for the top peak level of the reproduction signal as disclosed in Patent Documents 1 and 2 or the threshold determination for the difference between the top peak level of the reproduction signal and another signal is performed. When a defect is detected, the top peak level of the reproduction signal fluctuates due to uneven reflectance in the defect region, so that the top peak level of the reproduction signal exceeds the threshold for determining the defect region escape, thereby causing the defect region. There is a possibility of misjudging as an escape.

  As described above, the conventional defect detection apparatus and the defect detection method have a problem that a signal amplitude attenuation amount such as fingerprint attachment is relatively small, and a defect having a characteristic that the amplitude level fluctuates in the defect region cannot be detected correctly. is there.

  A defect detection apparatus according to the present invention is a defect detection apparatus that detects a defect area of an information recording medium using a reproduction signal obtained by detecting reflected light from the information recording medium. Specifically, the defect area is detected based on the fluctuation of the signal level of the first bottom hold signal obtained by detecting the bottom level of the first peak hold signal in which the peak level of the reproduction signal is detected. And the attenuation rate of the first bottom hold signal is smaller than the attenuation rate of the signal level of the first peak hold signal.

  Here, the reproduction signal is, for example, an RF signal or a wobble signal reproduced from an optical disc. The signal (first bottom hold signal) obtained by further holding the signal (first peak hold signal) holding the peak level of the reproduction signal further suppresses minute amplitude fluctuations of the first peak hold signal. It will be a thing. Therefore, by determining the defect area using the first bottom hold signal, it is possible to suppress the erroneous detection of the defect area escape caused by the minute amplitude fluctuation of the reproduction signal or the first peak hold signal in the defect area. Can do. As a result, the amount of attenuation of the signal amplitude, such as fingerprint attachment, is relatively small, and it is possible to improve the detection accuracy of the defect having the characteristic that the amplitude level fluctuates in the defect region.

  An optical disk apparatus according to the present invention includes the above-described defect detection apparatus according to the present invention, and detects a defective area of an optical disk by the defect detection apparatus. As described above, by using the defect detection apparatus according to the present invention, it is possible to improve the detection accuracy of the defect area. For this reason, the stability of servo control can be improved by performing tracking servo control using the defect detection signal output from the defect detection apparatus according to the present invention. Furthermore, gain control of an AGC amplification unit that amplifies an RF signal reproduced from the optical disk may be performed based on a defect detection result by the defect detection apparatus according to the present invention.

  According to the present invention, it is possible to provide a defect detection apparatus and a defect detection method with high defect detection accuracy, and an optical disc apparatus with improved servo control stability using these defect detection apparatus or defect detection method.

  Hereinafter, specific embodiments to which the present invention is applied will be described in detail with reference to the drawings. In the drawings, the same elements are denoted by the same reference numerals, and redundant description will be omitted as necessary for the sake of clarity.

Embodiment 1 of the Invention
FIG. 1 shows a configuration of the defect detection apparatus 1 according to the present embodiment. The defect detection apparatus 1 receives an RF signal reproduced from an optical disk, detects a defect of the optical disk using the input RF signal, and outputs a defect detection signal to the outside.

  In FIG. 1, a high-speed peak hold circuit 10 detects the top peak level of an input RF signal and outputs a peak hold signal S1. Thus, the high-speed peak hold circuit 10 is a circuit that detects the envelope of the top peak level of the input RF signal. The high-speed peak hold circuit 10 has a tracking capability to a peak level that can detect a defect entry in a sufficiently early time after removing a high-frequency superimposed component of the input RF signal, and the output signal. It has an attenuation characteristic that the attenuation rate of S1 is larger than the attenuation rate of the output signal S2 of the low-speed bottom hold circuit 11 described later.

  The low speed bottom hold circuit 11 receives the output signal S1 of the high speed peak hold circuit 10, detects the bottom peak level of the input signal S1, and outputs the bottom hold signal S2. As described above, the attenuation rate of the output signal S2 of the low-speed bottom hold circuit 11 has an attenuation characteristic that is lower than the attenuation rate of the output signal S1 of the high-speed peak hold circuit 10.

  The comparison circuit 12 compares the output signal S2 of the low-speed bottom hold circuit 12 with the voltage threshold value Vth, and if the value of the signal S2 is equal to or less than the voltage threshold value Vth, a defect detection signal indicating that the defect area of the optical disk is present. Output. That is, the voltage threshold Vth is a reference value for determining entry into and exit from the defect area.

  The D / A converter (DAC) 13 outputs a voltage threshold Vth to the comparison circuit 12. The voltage threshold Vth can be changed by changing the input digital value of the D / A converter (DAC) 13.

  The relationship among the RF signal, the signal S1, the signal S2, and the defect detection signal will be described with reference to the waveform diagram of FIG. The waveform shown at the top of FIG. 2 is an example of an RF signal reproduced from the optical disc. A region where the signal amplitude is reduced in the RF signal in FIG. 2 indicates a defective region due to adhesion of a fingerprint or the like.

  The waveform of the signal S1 obtained by inputting the RF signal in FIG. 2 to the high-speed peak hold circuit 10 is the waveform in the second stage from the top in FIG. Furthermore, the waveform of the signal S2 obtained by inputting the signal S1 of FIG. 2 to the low-speed bottom hold circuit 11 is the waveform of the third stage from the top of FIG.

  As shown in FIG. 2, the output signal S2 of the low-speed bottom hold circuit 11 suppresses a minute amplitude fluctuation of the signal S1 indicating the envelope of the top peak level of the RF signal. More specifically, when the value of signal S1 decreases, signal S2 quickly follows signal S1. On the other hand, when the value of the signal S1 increases, the signal S2 does not follow the signal S1, but increases at a speed determined by the attenuation characteristic of the low-speed bottom hold circuit 11. That is, by further holding the bottom after the peak hold of the RF signal, the waveform change when the RF signal peak level rises can be blunted. If such a signal S2 is compared with the voltage threshold value Vth in FIG. 2, the value of the signal S2 does not exceed the threshold value Vth in the defect region, and the waveform of the defect detection signal output by the defect detection apparatus 1 is as shown in FIG. As shown in the bottom row. A high level of the defect detection signal indicates a defective area, and a low level indicates that the defect area is not a defective area.

  As described above, the defect due to the fingerprint adhering to the surface of the optical disk has a smaller attenuation of the amplitude of the reproduction signal than other defects such as scratches on the optical disk surface, and the reflectance variation within the defect area. Therefore, there is a feature that the attenuation amount of the signal amplitude is not uniform. With respect to such a defect, the conventional defect detection apparatus detects the defect region by comparing the signal S1, which is the top envelope signal of the RF signal, with the voltage threshold value Vth. FIG. 9 shows a waveform of a conventional defect detection signal obtained by comparing the value of the signal S1 shown in FIG. 2 with the voltage threshold Vth. As described above, in the conventional defect detection method, if the amplitude variation of the RF signal is present in the defect region, the value of the signal S1 exceeds the voltage threshold Vth, and it is erroneously determined that the defect is not a defect despite being in the defect region. There is a case.

  On the other hand, the defect detection apparatus 1 according to the present embodiment detects a defect region using a signal S2 obtained by further bottom-holding the signal S1 obtained by holding the top peak of the RF signal. For this reason, it is possible to suppress erroneous detection of escape from the defective area due to minute amplitude fluctuations of the RF signal in the defective area.

  By suppressing erroneous detection in this manner, it is possible to detect a defect with a small decrease in the signal amplitude of the RF signal, which has been difficult to detect as a defect region in the past. For this reason, by using the defect detection apparatus 1, it is possible to detect a defect by setting the voltage threshold Vth to be higher than that in the prior art, and it is possible to improve the detection sensitivity for a small defect. Furthermore, since the voltage threshold value Vth can be set higher than in the prior art, the responsiveness of the entry determination to the defect area can be improved. For this reason, the servo control stability can be improved by performing the tracking servo control of the optical disk apparatus using the defect detection signal output from the defect detection apparatus 1 and the gain control of the amplification circuit for amplifying the RF signal. .

  Since the defect detection apparatus 1 determines the escape from the defect area by the threshold determination for the signal S2 after the bottom hold, compared to the case of determining the escape of the defect area by the threshold determination for the signal S1, The determination timing is delayed. However, when a defect area is entered, a high-speed response is required to quickly hold servo control such as tracking servo control and gain control during RF signal amplification, whereas a high-speed response request for the determination of defect area escape is not big. This is because the servo control is held while the defect area is determined, and therefore the influence on the servo control due to the delay in the defect recovery determination is small.

  A specific configuration example of the defect detection apparatus 1 according to the present embodiment is shown in FIG. FIG. 3 shows a configuration example of an analog circuit. The peak hold circuit 10 of FIG. 3 includes an operational amplifier 101 that operates as a comparator for an input voltage (RF signal), an NPN transistor 102 that operates as a switch for controlling charge / discharge of the capacitor C1, and a resistor R1 that determines the discharge speed of the capacitor C1. And an operational amplifier 103 that operates as a voltage follower that performs impedance conversion. When the negative feedback from the operational amplifier 103 to the operational amplifier 101 detects that the capacitor C1 is charged to the input voltage (RF signal level), the charging of the capacitor C1 is stopped. When the top peak level of the RF signal rises, the output level from the operational amplifier 103 follows the change in the peak level by charging the capacitor C1. Further, when the top peak level of the RF signal is lowered, the change in the peak level is followed by the voltage drop due to the discharge of the capacitor C1.

  3 determines the discharge rate of the operational amplifier 111 that operates as a comparator for the input voltage (signal S1), the PNP transistor 112 that operates as a switch that controls charging and discharging of the capacitor C2, and the capacitor C2. The resistor R2 and the operational amplifier 113 that operates as a voltage follower that performs impedance conversion are included. When the level of the input signal S1 falls, the PNP transistor 112 is turned on and the capacitor C2 is charged, so that the output level from the operational amplifier 113 follows the change in the input signal S1. Further, when the level of the input signal S1 rises, the output level from the operational amplifier 113 gradually increases as the capacitor C2 is discharged.

  The comparison circuit 12 in FIG. 3 is configured using an operational amplifier 121. Note that the description of the DAC 13 that provides the threshold voltage Vth is omitted.

  In the configuration of FIG. 3, the decay time constant C1 × R1 of the high-speed peak hold circuit 10 and the decay time constant C2 × R2 of the low-speed bottom hold circuit 11 are determined so that the relational expression C1 × R1 <C2 × R2 holds. To do. Note that the configuration of FIG. 3 is an example, and the defect detection apparatus 1 can be realized by other circuit configurations and also by a digital circuit.

  Next, FIG. 4 shows a configuration example of an optical disc apparatus using the defect detection apparatus 1 according to the present embodiment. The optical disc apparatus 100 shown in FIG. 4 performs recording and reproduction with respect to the optical disc 40. The spindle motor (SPM) 41 is a motor that rotationally drives the optical disc 40 at a predetermined speed. The optical head 42 receives a laser light source that irradiates the recording surface of the optical disc 40 with laser light, an objective lens that focuses the laser light on the recording surface of the optical disc 40, and laser light reflected by the recording surface of the optical disc 40. , A six-divided photodetector that outputs main signals (A, B, C, D) and auxiliary signals (E, F), and a fine actuator for correcting tracking errors and focus errors.

  The drive unit 43 performs driving of the SPM 41, driving of the coarse actuator that moves the optical head 42 in the radial direction of the optical disc 40, and driving of the fine actuator in accordance with a control signal from the servo control unit 44.

  The servo controller 44 detects the tracking error and the focus error using the main signals (A, B, C, D) and the auxiliary signals (E, F) output from the optical head 42, and finely corrects them. A control signal for operating the actuator is generated and output to the drive unit 43.

  The AGC amplifier is an amplifier having an automatic gain control (AGC) function, and amplifies an RF signal obtained by adding the main signals (A, B, C, D) output from the optical head 42 to a predetermined level. Output.

  The signal processing unit 46 performs synchronization, demodulation, and decoding processing on the RF signal read from the optical disc 40, and outputs the decoded data to an interface with an external host. Further, data to be recorded on the optical disk 40 is input from an external host, and is output to the laser drive unit 47 as a recording pulse after encoding and modulation.

  The laser driving unit 47 drives the laser light source provided in the optical head 42 with a power setting value corresponding to the writing position of the optical disc 40.

  The defect detection apparatus 1 included in the optical disc apparatus 100 receives the RF signal obtained by adding the main signals (A, B, C, D) output from the optical head 42, and performs the above-described defect area detection operation. Do. When the defect detection apparatus 1 detects a defect, a defect detection signal (DEF signal in FIG. 4) is output to the servo control unit 44 and the AGC amplification unit 45. The servo control unit 44 that has received the defect detection signal prevents the tracking servo control from running away by holding the tracking servo control in a state before the defect detection. In addition, the AGC amplification unit 45 that has received the defect detection signal holds the gain for the RF signal at the gain before the defect detection, thereby preventing overamplification of the RF signal.

  As described above, according to the defect detection apparatus 1 according to the present embodiment, it is possible to improve the detection accuracy of the defect area. For this reason, the servo control unit 44 performs tracking servo control using the defect detection signal output from the defect detection apparatus 1 and gain control of the AGC amplification unit 45 that amplifies the RF signal, thereby performing servo control of the optical disc apparatus 100. Stability can be improved.

  The configuration of the optical disc apparatus 1 shown in FIG. 4 is an example. The defect detection circuit 1 may be provided at a subsequent stage of the AGC amplification unit 45, or may be provided between a plurality of amplification circuits constituting the AGC amplification unit 45. Further, the control performed using the defect detection signal output from the defect detection circuit 1 may be at least one of the tracking servo control and the gain control of the AGC amplification unit 45 described above, and further, writing processing to a DVD-RAM disk or the like You may utilize for the detection of the defect area | region performed before.

Other embodiments.
The defect detection apparatus 1 according to the first embodiment of the invention has a configuration in which a defect region is detected by threshold determination on a signal S2 obtained by further bottom-holding the signal S1 obtained by holding the top peak of the RF signal. However, the signal to be subjected to threshold determination for detecting the defective area is not limited to the signal S2. For example, the defect detection apparatus 2 shown in FIG. 5 generates two peak hold signals by holding the top peak level of the RF signal by two peak hold circuits having different attenuation rates, and the difference between these two peak hold signals. Is a threshold judgment.

  The low-speed peak hold circuit 21 provided in the defect detection apparatus 2 holds the top peak level of the RF signal and has a lower attenuation speed than the high-speed peak hold circuit 10. The difference circuit 22 generates a difference signal S4 (S4 = S3-S2) between the signal S2 generated by the low-speed bottom hold circuit 11 and the peak hold signal S3 generated by the low-speed peak hold circuit 21. The defective area can also be detected by comparing the obtained signal S4 with the voltage threshold Vth in the comparison circuit 12. FIG. 6 shows waveform diagrams of the RF signal, the signals S1 to S4, and the defect detection signal.

  Moreover, the defect detection apparatus 3 shown in FIG. 6 detects a defect region by performing threshold determination on the difference between the top peak level of the RF signal and the bottom peak level of the RF signal. The bottom hold circuit 31 provided in the defect detection device 3 holds the bottom peak level of the RF signal. Further, the difference circuit 32 generates a difference signal S6 (S6 = S2-S5) between the signal S2 generated by the low-speed bottom hold circuit 11 and the bottom hold signal S5 generated by the bottom hold circuit 31. The defective area can also be detected by comparing the signal S6 thus obtained with the voltage threshold Vth in the comparison circuit 12. FIG. 8 shows waveform diagrams of the RF signal, the signals S1, S2, S5 and S6, and the defect detection signal.

  As described above, various signals can be used for threshold determination for detecting the defective area. However, the signal S2 obtained by further bottom-holding the signal S1 obtained by holding the top peak of the RF signal, or the signal By detecting a defective area by a determination using the signal S2, such as a threshold determination for a difference between S2 and another signal, the detection accuracy of the defective area can be increased.

  In the embodiment of the invention described above, the case where the defect area is detected using the RF signal as an input signal has been described. However, it is also possible to detect a defective area by inputting another reproduction signal reflecting information on the defective area of the optical disc instead of the RF signal. For example, when detecting a defective area of an unrecorded DVD-RAM disc, a wobble signal reproduced from a wobbling pre-groove is input to the defect detection apparatus according to the present invention to detect the defective area. Also good.

  In the above-described embodiment of the present invention, the case where the entry into the defect area and the escape from the defect area are determined by one threshold value determination for one signal (signal S2, S4, or S6) has been described. Such a configuration is effective in that the circuit scale of the defect detection apparatus 1 can be reduced. However, the entry into the defect area and the escape from the defect area may be determined by separate threshold values. Further, the entry into the defect area and the escape from the defect area may be determined using separate signals.

  For example, in the defect detection apparatus 1 according to the first embodiment of the present invention, the entry into the defect area may be determined using the signal S1, and the escape from the defect area may be determined using the signal S2. Since the signal S1 has a smaller delay from the peak level fluctuation of the RF signal than the signal S2, the responsiveness of the determination to enter the defect area is improved. Note that, by performing determination using the signal S2 at least for determination of escape from the defective area, it is possible to suppress erroneous determination of escape from the defective area, so that the detection accuracy of the defective area can be improved.

  Furthermore, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the gist of the present invention described above.

It is a block diagram of the defect detection apparatus concerning Embodiment 1 of invention. It is a wave form diagram which shows operation | movement of the defect detection apparatus concerning Embodiment 1 of invention. It is a figure which shows the Example of the defect detection apparatus concerning Embodiment 1 of invention. It is a figure which shows the structural example of a magnetic disc apparatus provided with the defect detection apparatus concerning Embodiment 1 of invention. It is a block diagram of the defect detection apparatus concerning this invention. It is a wave form diagram which shows operation | movement of the defect detection apparatus concerning this invention. It is a block diagram of the defect detection apparatus concerning this invention. It is a wave form diagram which shows operation | movement of the defect detection apparatus concerning this invention. It is a wave form diagram which shows operation | movement of the conventional defect detection apparatus.

Explanation of symbols

1, 2, 3 Defect detection device 10 High-speed peak hold circuit 11 Low-speed bottom hold circuit 12 Comparison circuit 13 D / A converter (DAC)
DESCRIPTION OF SYMBOLS 100 Optical disk apparatus 40 Optical disk 41 Optical head 42 Spindle motor (SPM)
43 Drive unit 44 Servo control unit 45 AGC amplification unit 46 Signal processing unit 47 Laser drive unit

Claims (11)

A defect detection device for detecting a defect area of an information recording medium using a reproduction signal obtained by detecting reflected light from the information recording medium,
A defect region is detected by threshold determination using a first bottom hold signal obtained by detecting a bottom level of a first peak hold signal in which the peak level of the reproduction signal is detected;
The defect detection apparatus according to claim 1, wherein the signal level attenuation rate of the first bottom hold signal is smaller than the signal level attenuation rate of the first peak hold signal. A first peak hold unit that detects a peak level of the reproduction signal and generates the first peak hold signal;
A first bottom hold unit that detects a bottom level of the first peak hold signal and generates the first bottom hold signal;
A comparison unit that performs threshold determination using the first bottom hold signal;
A defect detection apparatus according to claim 1.   The defect detection apparatus according to claim 2, wherein an attenuation time constant of the first peak hold unit is smaller than an attenuation time constant of the first bottom hold unit.   The defect detection apparatus according to claim 1, wherein escape from the defect area is detected by threshold determination using the first bottom hold signal.   The defect detection apparatus according to claim 4, wherein an entry into the defect area is detected by threshold determination using the first bottom hold signal.   The defect detection apparatus according to claim 4, wherein an entry into the defect area is detected by threshold determination using the first peak hold signal. A second peak hold unit that detects a peak level of the reproduction signal and generates a second peak hold signal having a lower decay rate than the first peak hold signal;
The defect detection apparatus according to claim 2, wherein the detection unit determines escape from the defect region by threshold determination for a difference signal between the second peak hold signal and the first bottom hold signal. A second bottom hold unit that detects a bottom level of the reproduction signal and generates a second bottom hold signal;
The defect detection device according to claim 2, wherein the detection unit determines escape from the defect region by threshold determination for a difference signal between the first bottom hold signal and the second bottom hold signal. An optical disc apparatus that performs at least one of information recording on an optical disc or information reproduction from an optical disc,
A defect detection signal is generated based on a threshold determination using a bottom hold signal obtained by inputting a reproduction signal from the optical disc and detecting a bottom level of a peak hold signal obtained by detecting a peak level of the reproduction signal; and And a defect detection device in which the signal level attenuation rate of the bottom hold signal is smaller than the signal level attenuation rate of the peak hold signal,
An optical disc apparatus that switches a control state of tracking servo for the optical disc in accordance with the defect detection signal.   The optical disc apparatus according to claim 9, wherein the reproduction signal is an RF signal or a wobble signal. A defect detection method for detecting a defect area of an information recording medium using a reproduction signal obtained by detecting reflected light from the information recording medium,
A peak hold signal is generated by a peak hold on the reproduction signal,
A bottom hold signal with a lower decay rate than the decay rate of the peak hold signal is generated by bottom hold with respect to the peak hold signal,
A defect detection method for detecting the defect area by threshold determination using the bottom hold signal.

Images