JP4877933B2 - Information playback device - Google Patents

Description

The present invention relates to information reproducing equipment, more particularly, it relates to information reproducing equipment you reproduce information recorded on the optical disk.

  As digital technology advances and data compression technology improves, optical discs such as DVDs (digital versatile discs) have attracted attention as media for recording information such as music, movies, photos, and computer software. Along with the reduction in price, optical disk devices have come into wide use as information reproducing devices for reproducing information recorded on optical disks.

  In this optical disk apparatus, a reproducing light beam is condensed on an optical disk, and information is reproduced based on the reflected light (see, for example, Patent Document 1).

  In recent years, in the field of optical recording, optical discs (hereinafter also referred to as “super-resolution optical discs”) capable of reproducing information whose recording mark pitch is smaller than the diffraction limit (hereinafter referred to as “super-resolution playback”) have been proposed. (For example, see Patent Documents 2 to 5). This super-resolution optical disc has a layer containing a material whose optical constants (for example, the real part of refractive index n and the imaginary part of refractive index k) change when light is collected (hereinafter referred to as “super-resolution layer”). ”).

  As a result, when the reproducing light beam is condensed on the super-resolution layer, a micro mask area or a micro aperture area is generated in the light spot due to the change in the optical constant, thereby enabling super-resolution reproduction. Yes.

  However, when the information recorded on the super-resolution optical disk is reproduced using the optical disk device disclosed in Patent Document 1, the frequency distortion occurs in the RF signal obtained from the reflected light, resulting in a frequency of occurrence of a reproduction error. There was an inconvenience that it was expensive.

  Thus, for example, Patent Document 6 discloses a method of correcting asymmetry of a reproduction signal caused by super-resolution reproduction of a magneto-optical disk by using a waveform equalizer that performs phase correction in a reproduction system using a slicer. It is disclosed.

  However, this method does not use a PRML (Partial response maximum likelihood) method that can improve the decoding performance of a recording mark with a short pitch, so that even if super-resolution reproduction is used, it is difficult to increase the density.

  By the way, even in a normal optical disk, phase distortion may occur in a reproduction signal due to optical aberration caused by tangential tilt, and as a countermeasure, a PR (Partial Response) filter is used for phase correction in the PRML system. The method used is described in Patent Document 7 and the like.

  This Patent Document 7 discloses a method using an adaptive PR filter as a PR (Partial Response) filter that gives a predetermined intersymbol interference.

  This adaptive PR filter is composed of a digitally-configured FIR filter. In order to increase the accuracy of the waveform equivalent, the reproduction signal shaped at the clock timing after the clock extraction of the reproduction signal is given to the adaptive PR filter. . As a result, it is possible to perform phase correction while avoiding the influence of rotation unevenness and the like, and waveform equivalence to accurate PR characteristics is possible.

  However, phase correction is required for super-resolution reproduction that generates a very large phase distortion compared to super-resolution using magnetic transfer on magneto-optical disks and light spot asymmetry caused by tangential tilt. Therefore, it is difficult to extract the clock in the previous stage of the adaptive PR filter that performs the above function, and normal reproduction cannot be performed.

JP 2002-319137 A JP-A-6-183152 JP-A-5-205314 JP-A-11-250493 JP 2001-250274 A Japanese Patent Laid-Open No. 1996-221839 JP 2002-32919 A

The present invention has been made under such circumstances, purpose of that is, provide information reproducing apparatus capable of pitch of recording marks recorded on the optical disk to reproduce accurately a smaller information than the diffraction limit There is to do.

According to a first aspect of the present invention, there is provided an information reproducing apparatus for reproducing information recorded on an optical disk by using a PRML method, and condenses light emitted from the light source and the light on the optical disk. An optical head including an optical system including an objective lens, and a photodetector that receives reflected light from the optical disc; a signal generation circuit that generates an RF signal from an output signal of the photodetector; and a recording mark in the information A phase correction circuit that corrects phase distortion of the RF signal when the pitch of the RF signal is smaller than a diffraction limit; a clock extraction circuit that extracts a clock from the RF signal in which the phase distortion is corrected; and in synchronization with the clock; a decoding circuit for decoding the information from the RF signal the phase distortion is corrected; wherein the phase correction circuit, equivalence is asymmetrical central as the origin non When the nominal FIR filter and the optical disc are not super-resolution optical discs, the tap coefficient of any one multiplier is set to 1 and the tap coefficients of the remaining multipliers are all 0 so that the asymmetric FIR filter is invalid. a first information reproducing apparatus that have a coefficient changing circuit to.

  According to this, the phase correction circuit corrects the phase distortion of the RF signal when the pitch of the recording mark in the information is smaller than the diffraction limit, and the clock extraction circuit clocks out the RF signal whose phase distortion has been corrected. Is extracted. Therefore, in the decoding circuit, information is decoded in synchronization with an accurate clock. Accordingly, it is possible to accurately reproduce information in which the pitch of the recording marks recorded on the optical disc is smaller than the diffraction limit.

According to a second aspect of the present invention, there is provided an information reproducing apparatus for reproducing information recorded on an optical disc using a PRML system, and condenses light emitted from the light source and the optical disc on the optical disc. An optical head including an optical system including an objective lens, and a photodetector that receives reflected light from the optical disc; a signal generation circuit that generates an RF signal from an output signal of the photodetector; and a recording mark in the information A phase correction circuit that corrects phase distortion of the RF signal when the pitch of the RF signal is smaller than a diffraction limit; a clock extraction circuit that extracts a clock from the RF signal in which the phase distortion is corrected; and in synchronization with the clock; a decoding circuit for decoding the information from the RF signal; wherein the phase correction circuit, and asymmetric FIR filter equivalence is asymmetrical central as the origin A coefficient changing circuit in which tap coefficients of any one multiplier are set to 1 and all remaining tap coefficients are set to 0 so that the asymmetric FIR filter becomes invalid when the optical disc is not a super-resolution optical disc. preparative a second information reproducing apparatus that have a.

  According to this, the phase correction circuit corrects the phase distortion of the RF signal when the pitch of the recording mark in the information is smaller than the diffraction limit, and the clock extraction circuit clocks out the RF signal whose phase distortion has been corrected. Is extracted. Therefore, in the decoding circuit, information is decoded in synchronization with an accurate clock. Accordingly, it is possible to accurately reproduce information in which the pitch of the recording marks recorded on the optical disc is smaller than the diffraction limit.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a schematic configuration of an optical disc apparatus 20 according to an embodiment of the present invention.

  The optical disk device 20 shown in FIG. 1 includes a spindle motor 22 for rotating the optical disk 15, an optical pickup device 23, a seek motor 21 for driving the optical pickup device 23 in the radial direction of the optical disk 15, and laser control. A circuit 24, a drive control circuit 26, a reproduction signal processing circuit 28, a buffer RAM 34, a buffer manager 37, an interface 38, a flash memory 39, a CPU 40, a RAM 41, and the like are provided. Note that the arrows in FIG. 1 indicate the flow of typical signals and information, and do not represent the entire connection relationship of each block. In the present embodiment, as shown in FIG. 2 as an example, the optical disk 15 is sandwiched between transparent substrates, a recording layer on which information is recorded, a reflective layer that reflects light, and an optical constant depending on temperature. It is assumed that the super-resolution optical disc has a super-resolution layer including a material whose refractive index real part n and refractive index imaginary part k change and is capable of super-resolution reproduction.

  The optical pickup device 23 is a device for irradiating the optical disc 15 with laser light and receiving reflected light from the optical disc 15. The optical pickup device 23 includes a light source that emits laser light having a wavelength corresponding to the optical disk 15 and an objective lens that condenses the light from the light source on the optical disk 15, and is reflected by the optical disk 15 and returned via the objective lens. An optical system that guides light to a predetermined position, a light receiver that has a plurality of light receiving regions that are arranged at the predetermined position and receive the return light, a drive system that drives the objective lens minutely (all not shown), and the like. Yes. Each light receiving region of the light receiver outputs a signal (photoelectric conversion signal) corresponding to the amount of received light to the reproduction signal processing circuit 28. The drive system also includes a focusing actuator for driving the objective lens in the focus direction and a tracking actuator for driving the objective lens in the tracking direction. Here, as an example, the wavelength of laser light emitted from the light source (hereinafter also referred to as “light source wavelength”) is 635 nm, and the numerical aperture (NA) of the objective lens is 0.6. In this case, the diffraction limit is about 530 nm (≈light source wavelength / 2NA).

  By the way, the relationship between the CNR (carrier / noise ratio) and the reproduction power Pr when reproducing the pits (pit length = 200 nm) formed on the optical disk 15 by using the optical pickup device 23 as an example is shown in FIG. Is shown in In FIG. 3, it can be seen that when the reproduction power Pr is 2 mW or more, the CNR exceeds 30 dB, and super-resolution reproduction is possible. Hereinafter, the reproduction power capable of super-resolution reproduction is also referred to as “super-resolution reproduction power”.

  When a laser beam with super-resolution reproduction power is focused on the optical disk 15, the temperature of that portion rises, and in the light spot, as an example, a minute aperture region as shown in FIG. As a result, a micro mask region as shown in FIG. Each of the micro mask region and the micro aperture region has a shape with a tail in the direction opposite to the traveling direction of the light spot. Note that whether a minute mask region or a minute opening region is generated depends on the material and the layer configuration of the super-resolution layer.

  Therefore, when a minute opening region is generated, the amount of return light greatly varies depending on whether or not a pit is included in the minute opening region. On the other hand, when a minute mask area is generated, the amount of return light greatly varies depending on whether or not the pit is masked by the minute mask area.

  For example, when a mask region is generated, as shown in FIG. 5 as an example, the optical constant of the super-resolution layer is changed due to heating by the light spot, and the reflectance at the rear portion of the spot is lowered. Therefore, considering the light intensity distribution on the light incident side surface PL of the super-resolution layer, the incident light has a symmetric light spot shape, but the reflected light has an asymmetric light spot shape (state). Therefore, information from the recording layer is read out with an asymmetrical light spot, and phase distortion occurs in the RF signal.

  In addition, the reproduction power dependence of the light intensity distribution of the reflected light on the light incident side surface PL of the super-resolution layer is shown as an example in FIG. According to this, when the reproduction power Pr is increased to the super-resolution reproduction power, the rear of the light spot is masked, and the light intensity distribution of the reflected light is changed to a shape that is shaved from the rear part. In FIG. 6, the center position of the light spot is used as the reference (origin).

  Also, as an example, a Bode diagram of a reading system (including an optical disk) in the optical system obtained by Fourier transforming the light intensity distribution in FIG. 6 is shown in FIGS. 7A and 7B. . When the reproduction power Pr is 2.5 mW, the gain is maintained to some extent up to the high frequency region exceeding the diffraction limit, but phase distortion occurs from a frequency lower than the diffraction limit. This phase distortion becomes a phase distortion in the RF signal and adversely affects the decoding result of information included in the RF signal.

  Returning to FIG. 1, the reproduction signal processing circuit 28 includes an amplifier 28a, a servo signal generation circuit 28b, a wobble signal generation circuit 28c, an RF signal generation circuit 28d, a decoder 28e, and the like.

  The amplifier 28a converts each of a plurality of photoelectric conversion signals from the light receiver of the optical pickup device 23 into a voltage signal and amplifies it with a predetermined gain.

  The servo signal generation circuit 28b generates a servo signal (focus error signal, track error signal, etc.) based on each output signal of the amplifier 28a. The servo signal generated here is output to the drive control circuit 26.

  The wobble signal generation circuit 28c generates a wobble signal based on each output signal of the amplifier 28a.

  The RF signal generation circuit 28d generates an RF signal based on each output signal of the amplifier 28a.

  The decoder 28e extracts address information and a synchronization signal from the wobble signal. The address information extracted here is output to the CPU 40, and the synchronization signal is output to the drive control circuit 26.

  The decoder 28e performs a decoding process and an error detection process on the RF signal. When an error is detected, the decoder 28e performs an error correction process, and then stores the reproduced data in the buffer RAM 34 via the buffer manager 37. To do. Here, as shown in FIG. 8 as an example, as a circuit for obtaining binarized data from an RF signal (hereinafter also referred to as “binarized data acquisition circuit”), a high-pass filter (HPF) 60, an equivalent circuit 61, an AD converter (ADC) 62, an asymmetric FIR filter 63, an interpolator 64, an equivalent circuit 65, a Viterbi decoder 66, a PLL 67, a switching circuit 68, and the like.

  The HPF 60 removes low frequency noise included in the RF signal. The equivalent circuit 61 is arranged at the subsequent stage of the HPF 60, emphasizes a high frequency component attenuated by a decrease in MTF (modulation transfer function) by the optical system, and reduces intersymbol interference. The equivalent circuit 61 also serves as a low-pass filter (LPF) that cuts high-frequency components so that aliasing noise does not occur during AD conversion in the ADC 62.

  The ADC 62 is arranged at the subsequent stage of the equivalent circuit 61 and converts the output signal of the equivalent circuit 61 into a digital signal (AD conversion). The switching circuit 68 is arranged at the subsequent stage of the ADC 62 and outputs the output signal of the ADC 62 to either the asymmetric FIR filter 63 or the interpolator 64 in accordance with an instruction from the CPU 40.

  The asymmetric FIR filter 63 performs filter processing on the output signal of the ADC 62 and corrects phase distortion in the RF signal. Details of the asymmetric FIR filter 63 will be described later.

  The interpolator 64 receives the output signal of the ADC 62 or the output signal of the asymmetric FIR filter 63, and interpolates the sample value at the clock timing from the sample values of two or more times before and after.

  The PLL 67 reproduces the clock of the recording signal recorded on the optical disk 15 from the output signal of the interpolator 64 (hereinafter also referred to as “recording clock”), and instructs the interpolator 64 of the clock timing. That is, sampling in synchronization with the recording clock is performed by the combination of the interpolator 64 and the PLL 67. The recording clock cycle is 1T.

  The equivalent circuit 65 is arranged at the subsequent stage of the interpolator 64, and performs waveform equivalence to the output signal of the interpolator 64 so that a response corresponding to a desired PR (Partial Response) characteristic is obtained. The desired PR characteristic may be, for example, PR (1, 2, 2, 2, 1).

  The Viterbi decoder 66 is arranged at the subsequent stage of the equivalent circuit 65, and performs binarization by performing a decoding process on the output signal of the equivalent circuit 65 by a Viterbi decoding method which is a maximum likelihood decoding method. Output data. That is, here, a PRML (Partial Response Maximum Likelihood) signal processing method is used.

  Returning to FIG. 1, the drive control circuit 26 generates a drive signal for the drive system of the optical pickup device 23 based on the servo signal from the reproduction signal processing circuit 28 in order to correct the displacement of the objective lens 60. Thereby, tracking control and focus control are performed. Furthermore, the drive control circuit 26 generates a drive signal for driving the seek motor 21 and a drive signal for driving the spindle motor 22 based on an instruction from the CPU 40. The drive signal of each motor is output to the seek motor 21 and the spindle motor 22, respectively.

  The buffer RAM 34 temporarily stores data reproduced from the optical disc 15 (reproduced data) and the like. Data input / output to / from the buffer RAM 34 is managed by the buffer manager 37.

  The laser control circuit 24 controls the light emission power of the light source of the optical pickup device 23.

  The interface 38 is a bidirectional communication interface with a host device 90 (for example, a personal computer), and is a standard interface such as ATAPI (AT Attachment Packet Interface), SCSI (Small Computer System Interface), and USB (Universal Serial Bus). It is compliant.

  The flash memory 39 stores various programs described in codes readable by the CPU 40, light emission characteristics of the light source of the optical pickup device 23, equivalent coefficient information described later, and the like.

  The CPU 40 controls the operation of each unit in accordance with the program stored in the flash memory 39 and stores data necessary for control in the RAM 41 and the buffer RAM 34.

<< Details of Asymmetric FIR Filter >>
Here, the details of the asymmetric FIR filter 63 will be described.

  As shown in FIG. 9 as an example, the asymmetric FIR filter 63 includes 20 delay elements (D1 to D20), 21 multipliers (h1 to h21), a coefficient setting circuit 100, an adder 102, and the like. Have. That is, the asymmetric FIR filter 63 includes a 21-tap FIR filter. The multiplication coefficient (kn; n = 1 to 21) in each multiplier is also called a tap coefficient. A combination of multiplication coefficients in each multiplier is also called an equivalent coefficient. In FIG. 9, the delay elements and some of the multipliers are not shown. Note that the delay time of each delay element is 1T (one period of the recording clock).

  Adder 102 adds the output signals of the multipliers and outputs the result to interpolator 64.

  The coefficient setting circuit 100 is equivalent based on the configuration of the super-resolution layer, the recording density, the reproduction power, the linear velocity during reproduction, the driving waveform of the light source, and the like (hereinafter also referred to as “coefficient setting conditions” for convenience). Set the coefficient. Here, an appropriate equivalent coefficient for each coefficient setting condition is acquired in advance and stored in the flash memory 39 as the equivalent coefficient information. Therefore, the coefficient setting circuit 100 extracts the equivalent coefficient corresponding to the coefficient setting condition from the flash memory 39 and sets it in each multiplier.

  Here, as an example, a known pit sequence recorded on the optical disc 15 is reproduced, and the above-described method is performed using a least mean square (LMS) algorithm, a recursive least squares (RLS) algorithm, or the like. An equivalent coefficient that minimizes the difference between the target signal from which the recording clock can be reliably extracted by the PLL 67 and the output signal of the asymmetric FIR filter 63 is obtained, and the obtained equivalent coefficient is set to an equivalent coefficient suitable for the coefficient setting condition at that time. . Note that the convergence of computation can be accelerated by using an asymmetric equivalent coefficient as an initial value.

  Examples of equivalent coefficients set by the coefficient setting circuit 100 are shown below. Here, as shown in FIG. 10, the coefficient setting condition 1 is that the type of the recording medium is A, the reproduction power is 2.5 mW, the linear velocity is 4.30 m / s, and the shortest pit length is 0.193 μm. The coefficient setting condition 2 is that the type of the recording medium is A, the reproduction power is 2.1 mW, the linear velocity is 4.30 m / s, and the shortest pit length is 0.193 μm. The coefficient setting condition 3 is that the type of the recording medium is B, the reproduction power is 2.7 mW, the linear velocity is 4.30 m / s, and the shortest pit length is 0.193 μm. The type is B, the reproduction power is 2.7 mW, the linear velocity is 4.30 m / s, and the shortest pit length is 0.130 μm. Further, the coefficient setting condition 5 is that the type of the recording medium is A, the reproduction power is 2.7 mW, the linear velocity is 3.00 m / s, and the shortest pit length is 0.193 μm. Note that the recording medium A is a super-resolution optical disk in which a minute mask area is generated, and the recording medium B is a super-resolution optical disk in which a minute opening area is generated.

  FIG. 11 shows the light intensity distribution of the reflected light on the surface PL when the coefficient setting condition is 1. The reflected light intensity behind the spot is reduced by the micro mask generated by heat, and has an asymmetric shape. The equivalent coefficient at this time is shown in FIG. The equivalent coefficient is also asymmetric with the center tap coefficient (here, k11) as the origin.

  FIG. 13 shows the light intensity distribution of the reflected light on the surface PL when the coefficient setting condition 2 is satisfied. Compared with the coefficient setting condition 1, since the reproduction power is reduced, the area of the minute mask region is reduced, and the light intensity distribution is close to symmetry. And the equivalent coefficient at this time is shown in FIG. The equivalent coefficient is different from that in the coefficient setting condition 1, indicating that the equivalent coefficient needs to be changed according to the reproduction power.

  FIG. 15 shows the light intensity distribution of the reflected light on the surface PL when the coefficient setting condition 3 is satisfied. The reflected light intensity behind the spot becomes larger due to the minute aperture region caused by the heat and has an asymmetric shape. The equivalent coefficient at this time is shown in FIG. The equivalent coefficient is different from that in the coefficient setting condition 1, indicating that it is necessary to change the equivalent coefficient depending on the type of the super-resolution layer.

  FIG. 17 shows an equivalent coefficient under the coefficient setting condition 4. The equivalent coefficient is different from that in the case of the coefficient setting condition 3, indicating that it is necessary to change the equivalent coefficient according to the shortest mark length (recording density). Note that the coefficient setting condition 4 and the coefficient setting condition 3 are different only in the recording density, so the reflected light intensity distribution under the coefficient setting condition 4 is the same as that in FIG.

  The light intensity distribution of the reflected light on the surface PL when the coefficient setting condition is 5 is shown in FIG. Since the linear velocity is reduced as compared with the coefficient setting condition 1, the super-resolution layer becomes higher in temperature and the reflected light intensity behind the spot is reduced. The equivalent coefficient at this time is shown in FIG. The equivalent coefficient is different from that in the case of the coefficient setting condition 1, indicating that it is necessary to change the equivalent coefficient depending on the linear velocity.

  Next, processing when the optical disc 15 is loaded on the optical disc apparatus 20 will be briefly described with reference to FIG. The flowchart in FIG. 20 corresponds to a series of processing algorithms executed by the CPU 40.

  In the first step 401, the drive control circuit 26 is instructed to rotate the optical disc 15 at a predetermined linear velocity (or angular velocity).

  In the next step 403, the coefficient setting conditions and disc information recorded on the optical disc 15 are read out.

  In the next step 405, it is determined whether or not the optical disk 15 is a super-resolution optical disk based on the read disk information. Here, since the optical disk 15 is a super-resolution optical disk, the determination here is affirmed and the routine proceeds to step 407.

  In this step 407, a value “1”, which means that the loaded optical disk is a super-resolution optical disk, is set in the flag F.

  In the next step 411, the read coefficient setting condition, disk information, flag F value, and the like are stored in the RAM 41.

  In the next step 413, the read coefficient setting condition and the value of the flag F are notified to each unit that needs them. Then, the process when the optical disk 15 is loaded is terminated.

  In step 405, if the optical disk 15 is not a super-resolution optical disk, the determination in step 405 is denied and the process proceeds to step 409. In this step 409, a value “0”, which means that the loaded optical disk is not a super-resolution optical disk, is set in the flag F. Then, the process proceeds to step 411.

《Reproduction processing》
Next, a process (playback process) in the optical disk device 20 when a playback request for the optical disk 15 is received from the host device 90 will be briefly described with reference to FIG. The flowchart in FIG. 21 corresponds to a series of processing algorithms executed by the CPU 40.

  In the first step 501, the reproduction signal processing circuit 28, the laser control circuit 24, etc. are notified that the reproduction request command has been received from the host device 90. Thereby, the coefficient setting circuit 100 sets the equivalent coefficient as described above based on the equivalent coefficient information stored in the flash memory 39 and the coefficient setting condition stored in the RAM 41.

  In the next step 503, the flag F stored in the RAM 41 is read.

  In the next step 505, it is determined whether or not the value of the flag F is “1”. Here, since the value of the flag F is “1”, the determination here is affirmed and the routine proceeds to step 507.

  In step 507, the switching circuit 100 is instructed so that the output signal of the ADC 62 is input to the asymmetric FIR filter 63.

  In the next step 511, the drive control circuit 26 is instructed to form a light spot near the target position corresponding to the designated address included in the reproduction request command. Thereby, a seek operation is performed. When the seek operation is completed, the process proceeds to step 513. If the seek operation is unnecessary, the process here is skipped.

  In the next step 513, reproduction is started.

  In the next step 515, it is determined whether or not the reproduction is completed. If it is not completed, the determination here is denied and the determination is made again after a predetermined time has elapsed. If completed, the determination here is affirmed and the reproduction process is terminated.

  In step 505, if the value of the flag F is “0”, the determination in step 505 is denied and the process proceeds to step 509. In step 509, the switching circuit 100 is instructed so that the output signal of the ADC 62 is input to the interpolator 64. Then, the process proceeds to step 511.

  In other words, the optical disk device 20 is compatible with both a super-resolution optical disk and a conventional optical disk (here, DVD).

  Incidentally, FIG. 22 shows an example of an eye pattern of an input signal of the interpolator 64 through the asymmetric FIR filter 63 in the reproduction processing. In this case, the eye is open, and the PLL 67 can accurately extract the recording clock. In particular, the eye is firmly open even at the shortest pit, and the recording clock can be easily extracted. FIG. 23 shows an example of an eye pattern of the input signal of the interpolator 64 when not passing through the asymmetric FIR filter 63 for comparison. In this case, the eye is not open, and it is difficult for the PLL 67 to extract the recording clock with high accuracy. In particular, since the eye is not open at the shortest pit, the recording clock cannot be extracted. That is, the phase distortion in the RF signal is corrected by the asymmetric FIR filter 63.

  FIG. 24 shows the bit error rate when a 193 nm long pit recorded on the optical disk 15 is reproduced. The reproduction conditions are a reproduction power Pr of 2.5 mW and a linear velocity during reproduction of 2.5 m / s. Further, as the equivalent coefficient of the asymmetric FIR filter 63, each tap coefficient shown in FIG. 12 is used. When the asymmetric FIR filter 63 is not used, the bit error rate is about 0.5 and decoding is not possible at all. However, when the asymmetric FIR filter 63 is used, the bit error rate is drastically reduced to 0.0020. And normal decoding is performed.

  As described above, according to the optical disc apparatus according to the present embodiment, the RF signal is low-frequency noise removed by the HPF 60, the intersymbol interference is reduced by the equivalent circuit 61, and AD conversion is performed by the ADC 62. If the loaded optical disk is a super-resolution optical disk, the output signal of the ADC 62 is input to the asymmetric FIR filter 63. In the asymmetric FIR filter 63, the coefficient setting circuit 100 extracts the equivalent coefficient corresponding to the coefficient setting condition from the flash memory 39 and sets it in each multiplier. It is corrected by. The output signal of the asymmetric FIR filter 63 is supplied to the PLL 67 via the interpolator 64. Here, since the phase distortion is corrected, the recording clock is extracted with high accuracy. Therefore, the interpolator 64 performs sampling with high accuracy in synchronization with the recording clock. The output signal of the interpolator 64 is decoded by the equivalent circuit 65 and the Viterbi decoder 66 by the PRML signal processing method. Therefore, it is possible to accurately reproduce information in which the pitch of the recording marks recorded on the optical disc is smaller than the diffraction limit.

  In the above embodiment, as shown in FIG. 25 as an example, the switching circuit 68 is omitted and the output signal of the ADC 62 is input to the asymmetric FIR filter 63. As shown in FIG. A coefficient changing circuit 104 that instructs the coefficient setting circuit 100 to change the equivalent coefficient may be added to the asymmetric FIR filter 63. When the optical disk 15 is not a super-resolution optical disk, the coefficient changing circuit 104 changes the coefficient so that the equivalent coefficient is composed of a plurality of symmetric tap coefficients with the tap coefficient (here, k11) as the origin. In this case, the coefficient changing circuit 104 may change the equivalent coefficient so that the asymmetric FIR filter 63 becomes an FIR filter for the purpose of reducing or adjusting intersymbol interference (see FIG. 27). Further, the coefficient changing circuit 104 sets the tap coefficient of any one multiplier to 1 so that the asymmetric FIR filter 63 becomes invalid when the optical disk 15 is not a super-resolution optical disk, and tap coefficients of the remaining multipliers. May be all zero.

  In the above embodiment, the wobble information (see FIG. 33) of the optical disc 15 and the TOC (Table Of Contents) information area (see FIG. 34) located in the inner periphery of the optical disc 15 include information on the equivalent coefficient. In step 403, the CPU 40 also reads out information related to the equivalent coefficient from the optical disk 15 and stores it in the RAM 41, and the coefficient setting circuit 100 is notified that the playback request command has been received from the host device 90. The equivalent coefficient may be set based on the information on the equivalent coefficient stored in the RAM 41 and the coefficient setting condition.

  In this case, for example, when the information about the equivalent coefficient recorded on the optical disc 15 corresponds to the reproduction at 4 × speed and the user requests the reproduction at 16 × speed, FIG. 28 shows an example as an example. As described above, a coefficient arithmetic circuit 106 for calculating an equivalent coefficient corresponding to reproduction at 16 × speed from information on the equivalent coefficient recorded on the optical disc 15 may be added to the asymmetric FIR filter 63. The equivalent coefficient calculated by the coefficient calculation circuit 106 is preferably recorded in a predetermined area of the RAM 41 or the optical disc 15 and used for the next calculation. In this case, the convergence of computation can be accelerated by using an asymmetric equivalent coefficient as an initial value.

  Moreover, although the said embodiment demonstrated the case where the said asymmetrical FIR filter 63 contains a 21-tap FIR filter, it is not limited to this, For example, you may include a 5-tap FIR filter. The number of taps of the FIR filter may be an even number.

  Further, in the above embodiment, when the equivalent circuit 61 is a linear circuit, the HPF 60 is also a linear circuit, and thus the configuration of the HPF 60 and the equivalent circuit 61 may be switched.

  In the above embodiment, as shown in FIG. 29, the ADC 62 may perform sampling in synchronization with the recording clock. In this case, the recording clock extracted by the PLL 67 is supplied to the ADC 62. The interpolator 64 is not necessary.

  Further, in the above embodiment, when the asymmetric FIR filter 63 is configured by an analog circuit, the ADC 62 may be disposed in front of the interpolator 64 as shown in FIG.

  In the above embodiment, as shown in FIG. 31, the output signal of the ADC 62 is directly input to the interpolator 64, and the signal via the asymmetric FIR filter 63 is input only to the PLL 67. good. In this case, a conventional circuit for decoding an RF signal can be used as it is.

  Further, in the above embodiment, instead of the asymmetric FIR filter 63, as shown in FIG. 32, the phase distortion during super-resolution reproduction (in the above embodiment, at reproduction power of 2.5 mW) (see FIG. A phase compensation analog filter 73 having a phase characteristic opposite to that of (see FIG. 7B) and a function of canceling phase distortion may be used. In this case, the ADC 62 is arranged in front of the interpolator 64.

  In the above embodiment, the optical disk apparatus capable of only reproducing information has been described. However, the present invention is not limited to this, and any optical disk apparatus capable of reproducing at least information among recording, reproducing, and erasing of information may be used.

  In the above-described embodiment, the case where the optical pickup device includes one light source has been described. However, the present invention is not limited to this.

  As described above, the information reproducing method of the present invention is suitable for accurately reproducing information in which the pitch of the recording marks recorded on the optical disc is smaller than the diffraction limit. The information reproducing apparatus of the present invention is suitable for accurately reproducing information in which the pitch of the recording marks recorded on the optical disc is smaller than the diffraction limit. The optical disk of the present invention is suitable for accurately reproducing information whose recording mark pitch is smaller than the diffraction limit using the PRML method.

1 is a block diagram showing a configuration of an optical disc device according to an embodiment of the present invention. It is a figure for demonstrating a super-resolution optical disk. It is a figure for demonstrating the relationship between the reproduction power and CNR in a super-resolution optical disk. FIG. 4A is a diagram for explaining a minute opening region, and FIG. 4B is a diagram for explaining a minute mask region. It is a figure for demonstrating the effect | action of a micro mask area | region. It is a figure for demonstrating the relationship between the light intensity distribution of the reflected light in a super-resolution optical disk, and reproduction power. FIG. 7A is a Bode diagram for explaining the frequency characteristics of the gain, and FIG. 7B is a Bode diagram for explaining the frequency characteristics of the phase. It is a figure for demonstrating the binarized data acquisition circuit of the decoder in FIG. It is a figure for demonstrating the asymmetrical FIR filter in FIG. It is a figure for demonstrating the coefficient setting conditions 1-5. It is a figure for demonstrating the light intensity distribution of the reflected light on the coefficient setting conditions 1. FIG. It is a figure for demonstrating the equivalent coefficient of the asymmetric FIR filter in the coefficient setting condition 1. FIG. It is a figure for demonstrating the light intensity distribution of the reflected light on the coefficient setting conditions 2. FIG. It is a figure for demonstrating the equivalent coefficient of the asymmetric FIR filter in the coefficient setting condition 2. FIG. It is a figure for demonstrating the light intensity distribution of the reflected light on the coefficient setting conditions 3. FIG. 6 is a diagram for explaining an equivalent coefficient of an asymmetric FIR filter under a coefficient setting condition 3. FIG. 6 is a diagram for explaining an equivalent coefficient of an asymmetric FIR filter under a coefficient setting condition 4. FIG. It is a figure for demonstrating the light intensity distribution of the reflected light on the coefficient setting conditions 5. FIG. 10 is a diagram for explaining an equivalent coefficient of an asymmetric FIR filter under a coefficient setting condition 6. FIG. It is a flowchart for demonstrating a process when an optical disk is loaded. It is a flowchart for demonstrating reproduction | regeneration processing. It is a figure for demonstrating an eye pattern when phase distortion is correct | amended. It is a figure for demonstrating an eye pattern when a phase distortion is not correct | amended. It is a figure for demonstrating the relationship between the presence or absence of an asymmetric FIR filter, and a bit error rate. It is a figure for demonstrating the modification 1 of a binarization data acquisition circuit. It is a figure for demonstrating the asymmetrical FIR filter in FIG. FIG. 27 is a diagram for explaining an equivalent coefficient of the asymmetric FIR filter of FIG. 26 changed when the optical disc is not a super-resolution optical disc. It is a figure for demonstrating the asymmetrical FIR filter provided with the coefficient calculating circuit. It is a figure for demonstrating the modification 2 of a binarization data acquisition circuit. It is a figure for demonstrating the modification 3 of a binarization data acquisition circuit. It is a figure for demonstrating the modification 4 of a binarization data acquisition circuit. It is a figure for demonstrating the modification 5 of a binarization data acquisition circuit. It is a figure for demonstrating Example 1 of the storage area of the information regarding an equivalent coefficient. It is a figure for demonstrating Example 2 of the storage area of the information regarding an equivalent coefficient.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 15 ... Optical disk, 20 ... Optical disk apparatus (information reproducing apparatus), 23 ... Optical pick-up apparatus (optical head), 28d ... RF signal generation circuit (signal generation circuit), 28e ... Decoder (phase correction circuit, clock extraction circuit, decoding circuit) ).

Claims (2)

An information reproducing apparatus for reproducing information recorded on an optical disc using a PRML system,
An optical head including a light source, an optical system including an objective lens that condenses the light emitted from the light source onto the optical disc, and a photodetector that receives reflected light from the optical disc;
A signal generation circuit for generating an RF signal from an output signal of the photodetector;
A phase correction circuit for correcting phase distortion of the RF signal when the pitch of the recording mark in the information is smaller than a diffraction limit;
A clock extraction circuit for extracting a clock from the RF signal in which the phase distortion is corrected;
Comprising a; in synchronism with the clock, a decoding circuit for the phase distortion is decoding the information from the corrected RF signal
The phase correction circuit includes an asymmetric FIR filter whose equivalent coefficient is asymmetric with the center as an origin, and any one multiplier so that the asymmetric FIR filter is invalid when the optical disc is not a super-resolution optical disc. the tap coefficient is 1, the information reproducing apparatus that have a coefficient changing circuit for all the tap coefficients of the remaining multiplier 0. An information reproducing apparatus for reproducing information recorded on an optical disc using a PRML system,
An optical head including a light source, an optical system including an objective lens that condenses the light emitted from the light source onto the optical disc, and a photodetector that receives reflected light from the optical disc;
A signal generation circuit for generating an RF signal from an output signal of the photodetector;
A phase correction circuit for correcting phase distortion of the RF signal when the pitch of the recording mark in the information is smaller than a diffraction limit;
A clock extraction circuit for extracting a clock from the RF signal in which the phase distortion is corrected;
Comprising a; in synchronism with the clock, a decoding circuit for decoding the information from the RF signal
The phase correction circuit includes an asymmetric FIR filter whose equivalent coefficient is asymmetric with the center as an origin, and any one multiplier so that the asymmetric FIR filter is invalid when the optical disc is not a super-resolution optical disc. the tap coefficient is 1, the information reproducing apparatus that have a coefficient changing circuit for all the tap coefficients of the remaining multiplier 0.