JP4793993B2 - Optical disk device - Google Patents

Description

The present invention relates to an optical disk apparatus and, more particularly, to an optical disk apparatus having a Tilt detection device for detecting the tilt of the optical disk.

  In recent years, with the advancement of digital technology and the improvement of data compression technology, CDs (compact discs) and the like are used as information recording media for recording information (hereinafter also referred to as “contents”) such as music, movies, photographs, and computer software. Optical discs such as DVDs (digital versatile discs) have attracted attention, and along with the reduction in price, optical disc apparatuses that use optical discs as access target media including information recording and reproduction have become widespread.

  In an optical disc device, information is recorded by forming a laser light micro-spot on the recording surface of an optical disc on which spiral or concentric tracks are formed, and information is reproduced based on the reflected light from the recording surface. ing. The optical disk device is provided with an optical pickup device as a device for irradiating the recording surface with laser light and receiving reflected light from the recording surface.

  In general, an optical pickup device includes an objective lens and is disposed at a light receiving position and an optical system that guides light emitted from a light source to a recording surface and guides return light reflected by the recording surface to a predetermined light receiving position. Equipped with an optical detector. This photodetector outputs a signal including information necessary for position control of the objective lens as well as reproduction information of data recorded on the recording surface. Then, the optical disc apparatus performs various controls based on the output signal from the photodetector so that a light spot having a predetermined shape is formed at a predetermined position on the recording surface.

  In the optical pickup device, if there is a deviation (hereinafter also referred to as “tilt” for convenience) between the optical axis direction of the objective lens and the direction perpendicular to the recording surface, wavefront aberration occurs due to the tilt, and the light spot There is a possibility that the deterioration of the shape or the signal including the reproduction information and servo information output from the photodetector may be deteriorated. Hereinafter, a tilt in a direction orthogonal to the tangential direction of the track (hereinafter also referred to as “radial direction”) is referred to as “radial tilt”, and a tilt in the tangential direction of the track (hereinafter also referred to as “tangential direction”). Is called “tangential tilt”.

  Therefore, various methods and apparatuses for correcting the tilt have been proposed (see, for example, Patent Documents 1 to 3).

  However, in the devices disclosed in Patent Documents 1 to 3, if the recording density of the optical disc is further increased in the future, it may be difficult to ensure sufficient detection accuracy.

Japanese Utility Model Publication No. 3-29778 Japanese Patent No. 3777767 JP-A-8-45081 Japanese Patent No. 3498644 JP-A-11-110769

The present invention has been made under such circumstances, and an object thereof is to provide an optical disc apparatus capable of stably accessing an optical disc excellent in responsiveness.

The present invention relates to a recording of information on an optical disc, is divided at least reproducing optical disk apparatus capable of reproduction and erasing light source, the light from the light source into one main beam and two sub-beams An optical system that irradiates the access target track of the optical disc with the main beam from the grating and irradiates the two sub beams to tracks adjacent to one side and the other side of the access target track, respectively. A main beam light receiving element for receiving the main beam reflected by the optical disk, and a first sub beam light receiving element and a second sub beam for receiving the two sub beams reflected by the optical disk, respectively. A light receiver having a light receiving element; a first transversal filter to which an output signal of the light receiving element for the main beam is input; A second transversal filter having a structure in which an output signal of a beam receiving element is input and a tap coefficient is inverted with respect to the first transversal filter with the center of the tap coefficient as an origin, and the first transformer A tangential tilt detector having a subtractor for outputting a difference between a jitter value in the output signal of the versatile filter and a jitter value in the output signal of the second transversal filter; and an output signal of the light receiving element for the main beam; A third transversal filter to which an output signal of the first sub-beam light receiving element is input; an output signal of the main beam light-receiving element; and an output signal of the second sub-beam light receiving element; The tap coefficient is inverted with respect to the third transversal filter with the center of the tap coefficient as the origin. A radial tilt detector, and a subtractor that outputs a difference between a jitter value in the output signal of the third transversal filter and a jitter value in the output signal of the fourth transversal filter; A tilt that corrects a tangential tilt of the optical disc with respect to a reference surface based on an output signal of the tangential tilt detector, and corrects a radial tilt of the optical disc with respect to a reference surface based on an output signal of the radial tilt detector. a correction device, an optical disk device Ru comprising a.

According to this, it becomes possible to perform the access to the superior optical disk responsiveness stably.

  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.

  An 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 sledge direction, a laser control circuit 24, An encoder 25, a motor control circuit 26, a pickup control circuit 27, a reproduction signal processing circuit 28, a buffer RAM 34, a buffer manager 37, an interface 38, a flash memory 39, a CPU 40, and a RAM 41 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 an example, a DVD corresponding to light having a wavelength of 405 nm is used for the optical disc 15.

  As shown in FIG. 2, the optical pickup device 23 includes a light emitting / receiving module 51, a diffractive element 50, a collimating lens 52, an objective lens 60, and a driving system (focusing actuator, tracking actuator and tilt actuator (all not shown)). Etc. In this embodiment, the focus direction is the Z-axis direction, and the tracking direction is the X-axis direction.

  The light emitting / receiving module 51 includes a semiconductor laser LD that emits laser light having a wavelength of 405 nm, a light receiver PD that receives return light, and the like. Here, the maximum intensity emission direction of the light emitted from the light receiving and emitting module 51 is defined as the + Z direction.

  The light receiver PD is disposed in the vicinity of the semiconductor laser LD and receives the return light diffracted by the diffraction element 50. As shown in FIG. 3 as an example, this light receiver PD includes a four-part light receiving element Pd1 including four partial light receiving elements (Qa, Qb, Qc, Qd) and two partial light receiving elements (Qe, Qf). It is configured to include a two-divided light receiving element Pd2 and a two-divided light receiving element Pd3 composed of two partial light receiving elements (Qg, Qh).

  The four-divided light receiving element Pd1 includes a dividing line DL1 in a direction corresponding to the tangential direction of the track (here, the Y-axis direction) and a dividing line in a direction corresponding to the direction orthogonal to the tangential direction of the track (here, the X-axis direction). It is divided into four by DL2. The partial light receiving element Qa is located on the + X side of the dividing line DL1 and on the + Y side of the dividing line DL2. The partial light receiving element Qb is located on the −X side of the dividing line DL1 and on the + Y side of the dividing line DL2. The partial light receiving element Qc is located on the −X side of the dividing line DL1 and on the −Y side of the dividing line DL2. The partial light receiving element Qd is located on the + X side of the dividing line DL1 and on the −Y side of the dividing line DL2.

  The two-divided light receiving element Pd2 is divided into two by a dividing line DL3 in a direction corresponding to the tangential direction of the track. The partial light receiving element Qe is located on the −X side of the dividing line DL3. The partial light receiving element Qf is located on the + X side of the dividing line DL3.

  The two-divided light receiving element Pd3 is divided into two by a dividing line DL4 in a direction corresponding to the tangential direction of the track. The partial light receiving element Qg is located on the −X side of the dividing line DL4. The partial light receiving element Qh is located on the + X side of the dividing line DL4.

  Each of the partial light receiving elements performs photoelectric conversion to generate a current signal corresponding to the amount of received light. The current signals generated by the partial light receiving elements are output to the reproduction signal processing circuit 28, respectively.

  The diffraction element 50 is disposed on the + Z side of the light emitting / receiving module 51, and includes a grating 50a and a hologram 50b. In the present embodiment, as an example, the diffraction element 50 and the light emitting / receiving module 51 are integrated. Thereby, the number of parts at the time of an assembly | attachment reduces, and workability | operativity can be improved. In addition, the adjustment process can be simplified.

  The grating 50a includes light emitted from the light emitting / receiving module 51 (hereinafter, also referred to as “emitted light” for convenience) as zero-order light as a main beam and two first-order diffracted light (+ 1-order diffracted light and -1st order diffracted light). As an example, as shown in FIG. 4, two first-order diffracted light spots SP1 are formed on the recording surface at positions shifted from the center of the zero-order light spot SP0 by the track pitch Pt in the tracking direction. Is set to be. The magnitude of the tangential direction component of the line vector connecting the center of the light spot SP0 and the center of the light spot SP1 is L (hereinafter also referred to as “tangential direction deviation L” for convenience). In this embodiment, as an example, it is assumed that the amount of 0th-order light, the amount of + 1st-order diffracted light, and the amount of -1st-order diffracted light are substantially equal.

  Therefore, when the light spot SP0 is formed on an access target track (hereinafter also referred to as “target track” for convenience), a track adjacent to one side of the target track (hereinafter also referred to as “first adjacent track” for convenience). ) And a light spot SP1 is formed on a track adjacent to the other side of the target track (hereinafter also referred to as “second adjacent track” for convenience).

  The hologram 50b is disposed on the + Z side of the grating 50a, and diffracts the return light from the recording surface of the optical disc 15 in the direction of the light receiving surface of the light receiver PD. Here, as an example, as shown in FIG. 5, the return light of the zeroth order light is received by the four-divided light receiving element Pd1, and the return light of each first-order diffracted light is respectively received by the two-divided light receiving element Pd2 and the two-part received light element Pd3. It is set to receive light.

  The collimating lens 52 is disposed on the + Z side of the diffraction element 50, and each light beam that has been converted into three beams by the diffraction element 50 is substantially parallel light. The objective lens 60 is disposed on the + Z side of the collimating lens 52, collects each light transmitted through the collimating lens 52, and forms a light spot on the recording surface of the optical disc 15, respectively.

  The focusing actuator is an actuator for minutely driving the objective lens 60 in the focus direction that is the optical axis direction of the objective lens 60. The tracking actuator is an actuator for minutely driving the objective lens 60 in the tracking direction. The tilt actuator is an actuator for tilting the objective lens 60 in the tangential direction and the radial direction.

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

  The amplifier 28a converts each photoelectric conversion signal from the light receiver PD into a voltage signal and amplifies it with a predetermined gain. Here, as shown in FIG. 6, the output signal of the amplifier 28a corresponding to the output signal of the partial light receiving element Qa is Sa, the output signal of the amplifier 28a corresponding to the output signal of the partial light receiving element Qb is Sb, and the partial light receiving element. The output signal of the amplifier 28a corresponding to the output signal of Qc is Sc, the output signal of the amplifier 28a corresponding to the output signal of the partial light receiving element Qd is Sd, and the output signal of the amplifier 28a corresponding to the output signal of the partial light receiving element Qe is Se. The output signal of the amplifier 28a corresponding to the output signal of the partial light receiving element Qf is Sf, the output signal of the amplifier 28a corresponding to the output signal of the partial light receiving element Qg is Sg, and the output signal of the amplifier 28a corresponding to the output signal of the partial light receiving element Qh. The output signal is Sh.

  The servo signal detection circuit 28b detects a focus error signal and a track error signal based on the output signal of the amplifier 28a.

  Here, the focus error signal FE is obtained based on the following equation (1).

  FE = (Sa + Sb) − (Sc + Sd) (1)

  As shown by the following equation (2), for example, the track error signal TE is detected using a so-called differential push-pull method (DPP method).

TE = PP ₀ −k × PP ₁ (2)

PP ₀ in the above equation (2) is a push-pull signal of 0th order light, and is obtained by the following equation (3). Note that k is a constant.

PP ₀ = (Sb + Sc) − (Sa + Sd) (3)

Further, PP ₁ in the above equation (2) is a push-pull signal of ± primary light, and is obtained by the following equation (4).

PP ₁ = (Se−Sf) + (Sg−Sh) (4)

  The detected focus error signal and track error signal are output to the pickup control circuit 27.

  The wobble signal detection circuit 28c detects a wobble signal based on the output signal of the amplifier 28a. Here, the wobble signal Wb is obtained based on the following equation (5).

  Wb = (Sb + Sc)-(Sa + Sd) (5)

  The RF signal detection circuit 28d detects an RF signal based on the output signal of the amplifier 28a. Here, the RF signal RF is obtained based on the following equation (6).

  RF = (Sa + Sb + Sc + Sd) (6)

  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 encoder 25. 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.

  The tilt detection circuit 28f detects tangential tilt and radial tilt based on the output signal of the amplifier 28a, and generates a tangential tilt signal and radial tilt signal. As shown in FIG. 7 as an example, the tilt detection circuit 28f includes a signal generation circuit 151 that generates a wobble signal and an RF signal based on the output signal of the amplifier 28a, and a tangential based on the output signal of the signal generation circuit 151. A tangential tilt detection unit TT that generates a tilt signal and a radial tilt detection unit RT that generates a radial tilt signal based on an output signal of the signal generation circuit 151 are provided.

  The signal generation circuit 151 generates the wobble signal Wb based on the equation (5) or the RF signal RF based on the equation (6). The wobble signal Wb or the RF signal RF generated here is output to the tangential tilt detection unit TT and the radial tilt detection unit RT.

  The signal generation circuit 151 generates the wobble signal Wb1 in the first adjacent track based on the following equation (7) or the RF signal RF1 in the first adjacent track based on the following equation (8). The wobble signal Wb1 or the RF signal RF1 generated here is output to the radial tilt detector RT.

Wb1 = Se−Sf (7)
RF1 = Se + Sf (8)

  Further, the signal generation circuit 151 generates the wobble signal Wb2 in the second adjacent track based on the following equation (9) or the RF signal RF2 in the second adjacent track based on the following equation (10). The wobble signal Wb2 or the RF signal RF2 generated here is output to the radial tilt detector RT.

Wb2 = Sg−Sh (9)
RF2 = Sg + Sh (10)

  The tangential tilt detection unit TT includes two filters (f1, f2), two jitter value acquisition circuits (109, 119), and a subtractor 121.

  The filter f1 includes a delay element 101, two multipliers (103, 105), and an adder 107. The delay element 101 delays the wobble signal Wb or the RF signal RF by time t1. Multiplier 103 multiplies wobble signal Wb or RF signal RF by coefficient k01, and multiplier 105 multiplies the output signal of delay element 101 by coefficient k02. The time t1 and each coefficient described above are set in a register (not shown) by the CPU 40. Here, as an example, t1 = 18 ns, k01 = −0.1, and k02 = 1 are set (see FIG. 8). Adder 107 adds the output signal of multiplier 103 and the output signal of multiplier 105. That is, the filter f1 is a 2-tap transversal filter having k01 and k02 as tap coefficients.

  The filter f2 includes a delay element 111, two multipliers (113, 115), and an adder 117. The delay element 111 delays the wobble signal Wb or the RF signal RF by time t1. Multiplier 113 multiplies wobble signal Wb or RF signal RF by coefficient k11, and multiplier 115 multiplies the output signal of delay element 111 by coefficient k22. Each coefficient is set in a register by the CPU 40. Here, as an example, k11 = 1 and k12 = −0.1 are set (see FIG. 8). Adder 117 adds the output signal of multiplier 113 and the output signal of multiplier 115. That is, the filter f2 is a 2-tap transversal filter having k11 and k12 as tap coefficients. The filter f2 has a structure in which the tap coefficient is inverted with respect to the filter f1 with the center of the tap coefficient as the origin.

  When both the tangential tilt and the radial tilt are substantially 0, the radius of the ring-shaped first diffraction spot (r in FIG. 9A) including the main spot in the light spot SP0 of the 0th-order light is included. The CPU 40 registers the value obtained by dividing the radius of the first diffraction spot by the linear velocity of the optical disc 15 as the delay time t1 in the delay element 101 and the delay element 111, which is obtained in advance and stored in the flash memory 39. Set to.

  The jitter value acquisition circuit 109 acquires a jitter value based on the output signal of the adder 107, and generates a signal corresponding to the jitter value. The jitter value acquisition circuit 119 acquires a jitter value based on the output signal of the adder 117, and generates a signal corresponding to the jitter value.

  The subtractor 121 subtracts the output signal of the jitter value acquisition circuit 109 from the output signal of the jitter value acquisition circuit 119. The output signal of the subtractor 121 is the tangential tilt signal.

  The radial tilt detector RT includes two gain amplifiers (131, 133), three delay elements (135, 137, 139), three subtractors (141, 143, 149), and two jitter value acquisition circuits (145). 147).

  The gain amplifier 131 adjusts the wobble signal Wb1 or the RF signal RF1 based on the gain ka.

  The delay element 135 delays the wobble signal Wb or the RF signal RF by time t2. Thereby, the phase shift of Wb or RF with respect to Wb1 or RF1 can be corrected.

  The gain amplifier 133 adjusts the wobble signal Wb2 or the RF signal RF2 based on the gain kb.

  Each gain is set in a register by the CPU 40. Here, ka = 0.2 and kb = 0.2 are set as an example (see FIG. 8). Note that when there is a difference in the amount of light of the three beams, it is necessary to adjust the values of ka and kb.

  Delay element 137 delays the output signal of multiplier 133 by time t2. Then, the delay element 139 delays the output signal of the delay element 137 by time t2. Thereby, the phase shift of Wb2 or RF2 with respect to Wb1 or RF1 can be corrected.

  The delay time t2 in each delay element is set by the CPU 40 in a register (not shown) as a value obtained by dividing the tangential direction deviation L by the linear velocity of the optical disk 15. Here, as an example, t2 = 18 ns.

  The subtractor 141 subtracts the output signal of the multiplier 131 from the output signal of the delay element 135. The subtractor 143 subtracts the output signal of the delay element 139 from the output signal of the delay element 135.

  The jitter value acquisition circuit 145 acquires a jitter value based on the output signal of the subtractor 141, and generates a signal corresponding to the jitter value. The jitter value acquisition circuit 147 acquires a jitter value based on the output signal of the subtractor 143, and generates a signal corresponding to the jitter value.

  The subtractor 149 subtracts the output signal of the jitter value acquisition circuit 147 from the output signal of the jitter value acquisition circuit 145. The output signal of the subtracter 149 is the radial tilt signal.

  The tangential tilt signal and the radial tilt signal generated by the tilt detection circuit 28f as described above are output to the pickup control circuit 27, respectively.

  Returning to FIG. 1, the motor control circuit 26 generates a drive signal for driving the seek motor 21 based on an instruction from the CPU 40, and outputs the drive signal to the seek motor 21. The motor control circuit 26 generates a drive signal for driving the spindle motor 22 based on an instruction from the CPU 40 and outputs the drive signal to the spindle motor 22. The motor control circuit 26 adjusts the drive signal of the spindle motor 22 so that the linear velocity (or angular velocity) of the spindle motor 22 is maintained at the instructed speed during reproduction and recording.

  The pickup control circuit 27 includes a focus control circuit 27a, a tracking control circuit 27b, and a tilt control circuit 27c.

  The focus control circuit 27a generates a driving signal for the focusing actuator for correcting a focus shift based on the focus error signal.

  The tracking control circuit 27b generates a driving signal for the tracking actuator for correcting a track deviation based on the track error signal.

  The tilt control circuit 27c generates a drive signal for the tilt actuator for correcting the tangential tilt based on the tangential tilt signal. Further, the tilt control circuit 27c generates a drive signal for the tilt actuator for correcting the radial tilt based on the radial tilt signal.

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

  The encoder 25 takes out the recording data stored in the buffer RAM 34 based on an instruction from the CPU 40 via the buffer manager 37, modulates the data, adds an error correction code, and the like, and outputs a write signal to the optical disc 15. Generate. The write signal generated here is output to the laser control circuit 24.

  The laser control circuit 24 controls the power of laser light emitted from the semiconductor laser LD. For example, at the time of recording, the laser control circuit 24 generates a drive signal for the semiconductor laser LD based on the write signal, recording conditions, emission characteristics of the semiconductor laser LD, and the like.

  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. At the time of reproduction, the reproduction data stored in the buffer RAM 34 is output to the host device 90 via the interface 38 for each sector. At the time of recording, recording data is input from the host device 90 via the interface 38 and accumulated in the buffer RAM 34 via the buffer manager 37.

  In the flash memory 39, various programs written in a code readable by the CPU 40, the radius r of the first diffraction spot, the coefficient (tap coefficient) of each multiplier, the gain of each gain amplifier, the tanger The local direction deviation L, recording conditions, emission characteristics of the semiconductor laser LD, and the like are stored.

  The CPU 40 controls the operation of each unit according to a program stored in the flash memory 39 and saves data necessary for control in the RAM 41 and the buffer RAM 34.

About tangential tilt
The first diffraction spot in the zero-order light spot SP0 formed on the recording surface preferably has a ring shape including the main spot therein as shown in FIG. 9A as an example. By the way, when there is a tangential tilt, as shown in FIG. 9B and FIG. 9C as an example, the first diffraction spot has a crescent shape, and on the minus side or the plus side of the main spot with respect to the track direction. Will be formed. In this case, the light intensity of the first diffraction spot varies depending on the magnitude of the tangential tilt. Here, the direction in which the address in the track increases is referred to as “track direction”. In the present embodiment, as an example, the tangential tilt when the first diffraction spot is formed on the negative side of the main spot with respect to the track direction is referred to as a positive tangential tilt, and the first tangential tilt on the positive side of the main spot. The tangential tilt when the diffraction spot is formed is referred to as a negative tangential tilt.

  Further, in this specification, as shown in FIG. 10 as an example, in the track direction, the − side region of the main spot is the A region, the + side region is the B region, and the light intensity in the A region and the B region is This is called the crosstalk amount.

  FIG. 11 shows an example of the relationship between the measured A region crosstalk amount and jitter value. According to this, the relationship between the amount of crosstalk (Xa) and the jitter value (Ya) can be expressed by the following equation (11). Here, ka is the sensitivity to jitter crosstalk, and varies depending on the wavelength of light emitted from the light source, the numerical aperture of the objective lens, the track pitch, the pit length, and the like. ca is jitter caused by intersymbol interference, B region crosstalk, and the like. Note that Xa ≧ 0.

Ya = ka × Xa ² + ca (11)

  Similarly, the relationship between the B region crosstalk amount (Xb) and the jitter value (Yb) can be expressed by the following equation (12). Note that Xb ≧ 0.

^{Yb = kb × Xb 2 + cb} ...... (12)

  Therefore, the total crosstalk amount (Xt) is the sum of the crosstalk amount Xa in the A region and the crosstalk amount Xb in the B region, as shown by the following equation (13).

  Xt = Xa + Xb (13)

  Therefore, the relationship between the total crosstalk amount Xt and the jitter value (Yt) can be expressed by the following equation (14). Here, kt is the sensitivity to jitter crosstalk, and ct is the jitter caused by intersymbol interference or noise.

Yt = kt × Xt ² + ct (14)

  FIG. 12 shows an example of the relationship between the tangential tilt and the crosstalk amount. According to this, the relationship between the tangential tilt and the crosstalk amount can be expressed by a linear expression within the range of realistic tilt correction.

  FIG. 13A shows an example of the relationship between the crosstalk amount Xa in the area A and the tangential tilt. FIG. 13B shows an example of the relationship between the crosstalk amount Xb in the B region and the tangential tilt.

  FIG. 14 shows an example of the relationship between the total crosstalk amount Xt and the tangential tilt. The relationship between the jitter value Yt and the tangential tilt at this time is shown as an example in FIG. In this case, the tangential tilt can be obtained from the jitter value Yt, but the tangential tilt direction (+ or-) cannot be known.

  Therefore, as an example, as shown in FIG. 16A, if a filter that reduces the crosstalk amount Xa in the A region to Acancel (hereinafter referred to as “positive filter” for convenience) is used, the crosstalk amount in the A region | The overall crosstalk amount, which is the sum of Acancel | and the B region crosstalk amount Xb, increases as the tangential tilt increases toward the negative side, as shown in FIG. 18A as an example. Thus, the crosstalk amount can be converted.

  As an example, as shown in FIG. 17A, if a filter that reduces the crosstalk amount Xb in the B region to Bcancel (hereinafter referred to as “negative filter” for convenience) is used, the crosstalk amount in the A region | The overall crosstalk amount, which is the sum of Bcancel | and the B region crosstalk amount Xa, increases as the tangential tilt increases toward the + side, as shown in FIG. 18B as an example. Thus, the crosstalk amount can be converted.

  FIG. 19A shows an example of the relationship between the jitter value (Y1) and the tangential tilt (Tt) based on the crosstalk amount converted by the positive filter. The relationship between the jitter value Y1 and the tangential tilt Tt can be expressed by the following equation (15). Here, k is the sensitivity to jitter crosstalk, α is the crosstalk correction amount of the filter, and c is jitter due to intersymbol interference, noise, and the like.

Y1 = k × (Tt−α) ² + c (15)

  Similarly, the relationship between the jitter (value Y2) due to the crosstalk amount converted by the negative filter and the tangential tilt Tt is shown in FIG. 19B as an example. The relationship between the jitter value Y2 and the tangential tilt Tt can be expressed by the following equation (16).

Y2 = k × (Tt + α) ² + c (16)

  The relationship between the difference between the jitter value Y2 and the jitter value Y1 (assumed as ΔY) and the tangential tilt Tt is shown in FIG. 20 as an example. The relationship between ΔY and tangential tilt Tt can be expressed by the following equation (17).

  ΔY = Y2−Y1 = 4 × α × k × Tt (17)

  That is, the relationship between ΔY and tangential tilt Tt is a straight line passing through the origin. Note that the greater the crosstalk correction amount α, the higher the sensitivity to tangential tilt, but the jitter value saturates when the crosstalk amount exceeds a certain level, so the larger the crosstalk correction amount α, the more the tangential tilt measurable range is. Narrow.

  In the present embodiment, the filter f1 has the function of the positive filter, and the filter f2 has the function of the negative filter. Here, the output signal of the adder 107 is a signal including a signal corresponding to | Acancel | + Xb, and the output signal of the adder 117 is a signal including a signal corresponding to Xa + | Bcancel |. Therefore, based on the output signal of the subtractor 121, the magnitude and direction (+ or −) of the tangential tilt can be known at the same time. A specific relationship between the output signal (tangential tilt signal) of the subtractor 121 and the tangential tilt is shown in FIG. FIG. 22 shows the relationship between the output signal (tangential tilt signal) of the subtractor 121 and the radial tilt. In other words, the tangential tilt detection unit TT can accurately detect the tangential tilt even when the radial tilt exists at the same time.

  FIG. 23 shows an example of the relationship between the noise level (carrier / noise (C / N)) and the tangential tilt signal when the tangential tilt is small. According to this, the tangential tilt signal is almost constant regardless of the magnitude of noise. That is, the tangential tilt detection unit TT is resistant to noise and has high tangential tilt detection accuracy. Further, when the tangential tilt is 0, the tangential tilt detection unit TT can also use the tangential tilt signal as it is as a tangential tilt correction signal because the tangential tilt signal is also 0. Further, the tangential tilt detection unit TT can cope with so-called AC tilt in which the magnitude of the tangential tilt changes with time.

<About radial tilt>
When there is a radial tilt, as shown in FIGS. 24A and 24B as an example, the first diffraction spot in the light spot SP0 of the 0th order light has a crescent shape and is formed on a track adjacent to the target track. Will come to be. The light intensity of the first diffraction spot varies depending on the magnitude of the radial tilt. In the present embodiment, as an example, the radial tilt when the first diffraction spot is formed on the second adjacent track is referred to as a positive radial tilt, and the first diffraction spot is formed on the first adjacent track. The radial tilt is referred to as a negative radial tilt.

  A concrete relationship between the output signal (radial tilt signal) of the subtractor 149 and the radial tilt is shown in FIG. That is, based on the output signal of the subtractor 149, the magnitude and direction (+ or-) of the radial tilt can be known at the same time.

  FIG. 26 shows the relationship between the output signal (radial tilt signal) of the subtractor 149 and the tangential tilt. That is, the radial tilt detector RT can accurately detect the radial tilt even when tangential tilt is present at the same time.

  FIG. 27 shows an example of the relationship between the noise magnitude (C / N) and the radial tilt signal when the radial tilt is small. According to this, the radial tilt signal is almost constant regardless of the magnitude of noise. That is, the radial tilt detector RT is resistant to noise and has high detection accuracy of radial tilt. In addition, when the radial tilt is 0, the radial tilt detection unit RT can also use the radial tilt signal as it is as a radial tilt correction signal because the radial tilt signal is also 0. Furthermore, the radial tilt detector RT can cope with so-called AC tilt in which the magnitude of the radial tilt changes with time.

<Recording process>
Next, processing (recording processing) in the optical disc device 20 when a recording request is received from the host device 90 will be briefly described with reference to FIG. The flowchart in FIG. 28 corresponds to a series of processing algorithms executed by the CPU 40.

  When a recording request command is received from the host device 90, the start address of the program corresponding to the flowchart of FIG. 28 is set in the program counter of the CPU 40, and the recording process starts.

  In the first step 401, the motor control circuit 26 is instructed to rotate the optical disk 15 at a predetermined linear velocity (or angular velocity), and the reproduction signal processing circuit 28 is notified that a recording request command has been received from the host device 90. To do.

  In the next step 403, the motor control circuit 26 is instructed to form a light spot in the vicinity of the target position corresponding to the designated address included in the recording request command. Thereby, a seek operation is performed. When the seek operation is completed, the process proceeds to step 405. If the seek operation is unnecessary, the process here is skipped.

  In step 405, the tilt control is turned on. Thereby, the tangential tilt signal and the radial tilt signal are generated by the tilt detection circuit 28f as described above. Here, a tangential tilt signal is generated based on the wobble signal Wb. Further, a radial tilt signal is generated based on the wobble signals Wb, Wb1, and Wb2. A drive signal for the tilt actuator is output from the tilt control circuit 27c.

  In the next step 407, recording is permitted.

  In the next step 409, it is determined whether or not the recording 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 routine proceeds to step 411.

  In this step 411, the host device 90 is notified that the recording has been completed. Then, the recording process ends.

《Reproduction processing》
Next, a process (playback process) in the optical disc apparatus 20 when a playback request is received from the host apparatus 90 will be briefly described with reference to FIG. The flowchart in FIG. 29 corresponds to a series of processing algorithms executed by the CPU 40.

  When the reproduction request command is received from the host device 90, the start address of the program corresponding to the flowchart of FIG. 29 is set in the program counter of the CPU 40, and the reproduction process starts.

  In the first step 501, the motor control circuit 26 is instructed to rotate the optical disc 15 at a predetermined linear velocity (or angular velocity), and the reproduction signal processing circuit 28 is notified that a reproduction request command has been received from the host device 90. To do.

  In the next step 503, the motor 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 505. If the seek operation is unnecessary, the process here is skipped.

  In step 505, the tilt control is turned on. Thereby, the tangential tilt signal and the radial tilt signal are generated by the tilt detection circuit 28f as described above. Here, a tangential tilt signal is generated based on the RF signal RF. A radial tilt signal is generated based on the RF signals RF, RF1, and RF2. A drive signal for the tilt actuator is output from the tilt control circuit 27c.

  In the next step 507, reproduction is started.

  In the next step 509, 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.

  Note that the RF signal RF supplied from the tangential tilt detector TT may be a signal after waveform equivalence, or a signal before waveform equivalence.

  As is apparent from the above description, in the optical disc apparatus 20 according to the present embodiment, a tilt detection device is configured by the tilt detection circuit 28f, and a tilt correction device is configured by the tilt control circuit 27c and a tilt actuator (not shown). Yes.

  In the tangential tilt detection unit TT, a first signal generation circuit is configured by the filter f1, a second signal generation circuit is configured by the filter f2, and a signal is generated by the jitter value acquisition circuit 109 and the jitter value acquisition circuit 119. A quality acquisition circuit is configured.

  In the radial tilt detector RT, the multiplier 131, the delay element 135, and the subtractor 141 constitute a first signal generation circuit, and the multiplier 133, the delay element 135, the delay element 137, the delay element 139, and the subtractor. 143 constitutes a second signal generation circuit, and jitter value acquisition circuit 145 and jitter value acquisition circuit 147 constitute a signal quality acquisition circuit.

  In the recording process and the reproduction process, the tilt detection method according to the present invention is implemented.

  As described above, according to the tilt detection circuit 28f according to the present embodiment, when the tangential tilt is increased to the − side with respect to the reference plane based on the wobble signal or the RF signal by the filter f1, the tilt increases. When a signal (first signal) including a signal component is generated and the tangential tilt is increased to the + side with respect to the reference plane based on the wobble signal or the RF signal by the filter f2, the signal component that increases with the increase is added. A containing signal (second signal) is generated. The jitter value acquisition circuit 109 acquires a jitter value based on the output signal of the filter f1, and the jitter value acquisition circuit 119 acquires the jitter value based on the output signal of the filter f2. Then, the output signal of the jitter value acquisition circuit 109 is subtracted from the output signal of the jitter value acquisition circuit 119 by the subtractor 121 to generate a tangential tilt signal. Thereby, the magnitude and direction (+ side or − side) of the tangential tilt can be simultaneously obtained in real time. Accordingly, the tangential tilt of the optical disc with respect to the reference surface can be detected quickly and accurately.

  Further, according to the tilt detection circuit 28f according to the present embodiment, the multiplier 131, the delay element 135, and the subtracter 141 increase the radial tilt when the radial tilt is increased to the + side based on the wobble signal or the RF signal. A signal (first signal) including a signal component that increases with the frequency is generated, and the multiplier 133, the delay element 135, the delay element 137, the delay element 139, and the subtractor 143 generate a radial signal based on the wobble signal or the RF signal. When the tilt increases toward the − side with respect to the reference plane, a signal (second signal) including a signal component that increases with the increase is generated. The jitter value acquisition circuit 145 acquires a jitter value based on the output signal of the subtractor 141, and the jitter value acquisition circuit 147 acquires the jitter value based on the output signal of the subtractor 143. Then, the subtractor 149 subtracts the output signal of the jitter value acquisition circuit 1147 from the output signal of the jitter value acquisition circuit 145 to generate a radial tilt signal. Thereby, the magnitude and direction (+ side or − side) of the radial tilt can be simultaneously obtained in real time. Therefore, the radial tilt of the optical disc with respect to the reference surface can be detected quickly and accurately.

  Further, according to the optical disc apparatus 20 according to the present embodiment, both the tangential tilt and the radial tilt are accurately detected by the tilt detection circuit 28f, and the tangential tilt and the radial tilt are respectively detected by the tilt control circuit 27c and the tilt actuator. It is corrected. Therefore, it is possible to stably access an optical disc having excellent responsiveness.

  An example of the frequency characteristic of tangential tilt is shown in FIG. The tangential tilt value takes a maximum value in the vicinity of 2ω (ω: rotational frequency of the optical disk), and greatly attenuates at 3ω or more. That is, a great effect can be obtained if the DC to 2ω component of the tangential tilt can be corrected. Therefore, when the calculation of the jitter value is completed within a time corresponding to 1/4 or less of the rotation period of the optical disc, tangential tilt sampling can be performed four times per one rotation of the optical disc. Therefore, by providing an LPF (low-pass filter) having a cutoff frequency of 2ω in the subsequent stage of the subtractor 121 and the subtractor 149, tangential up to 2ω components, as is clear from the sampling theorem (sampling theorem). Tilt information can be faithfully reproduced, and more effective tangential tilt correction can be performed.

  In the above-described embodiment, the case where a 2-tap transversal filter is used for each of the filters f1 and f2 in the tangential tilt detection unit TT has been described. However, the present invention is not limited to this. For example, FIGS. As described above, a 5-tap transversal filter may be used.

  In this configuration, the light spot on the adjacent track is used to detect the crosstalk component, but the actual crosstalk component is a leakage component to the end portion of the light spot. Therefore, the frequency characteristic of the crosstalk component is different from the frequency characteristic of the reproduction signal of the adjacent track. Therefore, in order to subtract the crosstalk amount more strictly, each gain of the radial tilt detector RT in the above embodiment is used to convert the frequency characteristic of the reproduction signal of the adjacent track into the frequency characteristic of the crosstalk component. Instead of the amplifier, transversal filters may be used as shown in FIGS. Conversely, the gain amplifier can be considered as a kind of transversal filter in a broad sense.

  Moreover, although the said embodiment demonstrated the case where the value of the said coefficient k01 and k12 was respectively -0.1, it is not limited to this. Each value may be changed according to the required detection sensitivity and detection range. The smaller the absolute values of the coefficients k01 and k12, the wider the tangential tilt detectable range but the lower the detection sensitivity. On the other hand, the larger the absolute value of the coefficients k01 and k12, the narrower the tangential tilt detectable range but the higher the detection sensitivity. .

  Moreover, although the said embodiment demonstrated the case where the objective lens 60 was tilted with a tilt actuator and each tilt was correct | amended, it is not limited to this. For example, an optical element that includes an electro-optic crystal or a liquid crystal exhibiting an electro-optic effect and imparts an optical phase difference to light is disposed on the optical path between the light emitting / receiving module 51 and the objective lens 60, thereby tangentially. Wavefront aberration caused by tilt and radial tilt may be canceled out. In this case, the tilt control circuit 27c applies a driving voltage to the optical element that gives the optical phase difference in accordance with the tangential tilt signal and the radial tilt signal.

  Further, tilt correction may be performed by tilting the entire optical pickup device 23. In this case, a drive mechanism for tilting the entire optical pickup device 23 is further provided, and the tilt control circuit 27c supplies a drive voltage to the drive mechanism in accordance with a tangential tilt signal and a radial tilt signal. It becomes.

  In the above embodiment, a bit error rate acquisition circuit may be used instead of each jitter value acquisition circuit of the tilt detection circuit 28f. In particular, when the jitter value does not have a normal distribution, the detection accuracy can be further improved.

  In the above embodiment, when a PRML (Partial Response Maximum Likelihood) method is used as the recording modulation method, a PRSNR (Partial Response Signal- You may use each to-Noise Ratio) measuring instrument.

  In the above-described embodiment, the signal generation circuit 151 of the tilt detection device 28f may be included in the amplifier 28a.

  In the above embodiment, the optical disk apparatus capable of recording and 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 embodiment, the case where the tilt detection device 28f detects both tangential tilt and radial tilt has been described. For example, when the influence of radial tilt on recording and reproduction is small, the tangential tilt is detected. It may be detected only. In this case, the radial tilt detector RT is not necessary. Only the tangential tilt is corrected.

  In the above embodiment, the case where a so-called three-beam method is used has been described. However, when the tilt detection device 28f detects only a tangential tilt, a so-called one-beam method may be used. In this case, the grating 50a, the two-divided light receiving element Pd2, and the two-divided light receiving element Pd3 are not necessary. The track error signal is detected by a push-pull method (PP method) or a phase difference method (DPD method).

  Moreover, although the said embodiment demonstrated the case where the optical disk had one recording layer, it may have not only this but a several recording layer.

  Moreover, although the said embodiment demonstrated the case where the optical disk was DVD corresponding to the light of a wavelength of 405 nm, it is not limited to this. For example, the optical disk may be a DVD that supports a CD system and light having a wavelength of 660 nm.

  In the above embodiment, the case where the optical pickup device includes one semiconductor laser has been described. However, the present invention is not limited thereto, and for example, a plurality of semiconductor lasers that emit light having different wavelengths may be included. In this case, for example, at least one of a semiconductor laser emitting light having a wavelength of about 405 nm, a semiconductor laser emitting light having a wavelength of about 660 nm, and a semiconductor laser emitting light having a wavelength of about 780 nm is included. Also good. That is, the optical disk apparatus may be an optical disk apparatus that supports a plurality of types of optical disks that conform to different standards.

  In recent years, there has been proposed an optical disc system aiming at an increase in recording capacity by using an optical system in which the NA (numerical aperture) of the objective lens exceeds 1 using a solid immersion lens (SIL). In this optical disk system using SIL (hereinafter also referred to as “SIL optical disk system” for convenience), a transparent layer (hereinafter referred to as “reading side substrate”) between the laser light incident surface and the recording layer, for example, Even if there is no substrate (with a thickness of 0.6 mm for DVD) or there is a substrate on the readout side, the influence of coma aberration due to tilt is small. However, the tilt causes the gap between the SIL and the disk to change off-axis, that is, the gap between the SIL and the disk due to the tilt increases as the distance from the central axis of the objective lens increases, and so-called seepage from the tilt SIL occurs. The distribution of light (evanescent light) changes, leading to an increase in the diameter of the light spot in the recording layer, resulting in a decrease in recording quality and reproduction quality.

  An example of the change in the light spot shape with respect to the tilt in the SIL optical disk system is shown in FIGS. 38 (A) to 38 (C). Compared with FIG. 9 described above, the first diffraction spot does not change due to tilt because there is no coma, but the gap changes due to tilt, so the shape of the light spot in the recording layer is, for example, relative to tangential tilt. As shown in FIGS. 38B and 38C, the shape extends in the tangential direction (track direction) of the disc. As described above, also in the SIL optical disc system, the shape of the light spot in the recording layer is changed with the tilt, and the crosstalk amount is increased as in the case of the normal optical disc system. Therefore, even in the SIL optical disk system, tilt detection is possible by using the tilt detection method of the present invention.

  In particular, in the SIL optical disk system, the gap between the SIL and the disk is generally very small, such as several tens of nm. Therefore, even if the tilt amount changes slightly, the shape of the light spot in the recording layer changes greatly. Therefore, by using the tilt detection method of the present invention, it is possible to detect the tilt with very high sensitivity.

  As described above, according to the tilt detection method and tilt detection apparatus of the present invention, it is suitable for quickly and accurately detecting the tilt of the optical disc with respect to the reference plane. Further, the optical disc apparatus of the present invention is suitable for stably accessing an optical disc having excellent responsiveness.

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 the optical pick-up apparatus in FIG. It is a figure for demonstrating the light receiver in FIG. It is a figure for demonstrating the 3 beam method. It is a figure for demonstrating return light. It is a figure for demonstrating the amplifier in FIG. It is a figure for demonstrating the tilt detection circuit in FIG. It is a figure for demonstrating the tap number and delay time of each filter in FIG. FIGS. 9A to 9C are diagrams for explaining the relationship between the shape of the light spot by the main beam and the tangential tilt, respectively. It is a figure for demonstrating the amount of crosstalk. It is a figure for demonstrating the relationship between the crosstalk amount and jitter value in A area | region of FIG. It is a figure for demonstrating the relationship between the amount of crosstalk and a tangential tilt. FIG. 13A is a diagram for explaining the relationship between the crosstalk amount and the tangential tilt in the A region, and FIG. 13B shows the relationship between the crosstalk amount and the tangential tilt in the B region. It is a figure for demonstrating. It is a figure for demonstrating the relationship between the whole crosstalk amount and a tangential tilt. It is a figure for demonstrating the relationship between a jitter value and a tangential tilt corresponding to FIG. FIG. 16A is a diagram for explaining Acancel, and FIG. 16B is a diagram for explaining | Acancel |. FIG. 17A is a diagram for explaining Bcancel, and FIG. 17B is a diagram for explaining | Bcancel |. FIG. 18A is a diagram for explaining a signal included in the output signal of the filter f1, and FIG. 18B is a diagram for explaining a signal included in the output signal of the filter f2. FIG. 19A is a diagram for explaining the output signal of the jitter value acquisition unit 109, and FIG. 19B is a diagram for explaining the output signal of the jitter value acquisition unit 119. It is a figure for demonstrating the output signal of the subtractor 121. FIG. It is a figure for demonstrating the relationship between a tangential tilt signal and a tangential tilt. It is a figure for demonstrating the relationship between a tangential tilt signal and radial tilt. It is a figure for demonstrating the relationship between a tangential tilt signal and the magnitude | size of noise. 24A and 24B are diagrams for explaining the relationship between the shape of the light spot and the radial tilt, respectively. It is a figure for demonstrating the relationship between a radial tilt signal and radial tilt. It is a figure for demonstrating the relationship between a radial tilt signal and a tangential tilt. It is a figure for demonstrating the relationship between a radial tilt signal and the magnitude | size of noise. It is a flowchart for demonstrating a recording process. It is a flowchart for demonstrating reproduction | regeneration processing. It is a figure for demonstrating the frequency characteristic of a tangential tilt. It is a figure for demonstrating the modification of the filter f1 in FIG. It is a figure for demonstrating the modification of the filter f2 in FIG. It is a figure for demonstrating the number of taps of the filter f1 of FIG. 31, and the filter f2 of FIG. It is a figure for demonstrating the modification of the radial tilt detection part in FIG. It is a figure for demonstrating the filter 301 in FIG. It is a figure for demonstrating the filter 351 in FIG. It is a figure for demonstrating the number of taps of each filter in FIG. 38A to 38C are diagrams for explaining the relationship between the shape of the light spot by the main beam and the tangential tilt in the optical disc system using the SIL.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 15 ... Optical disk, 20 ... Optical disk apparatus, 23 ... Optical pick-up apparatus, 27c ... Tilt control circuit (a part of tilt correction apparatus), 28f ... Tilt detection circuit (tilt detection apparatus), 109 ... Jitter value acquisition circuit (Signal quality acquisition) Part of the circuit), 119... Jitter value acquisition circuit (part of the signal quality acquisition circuit), 121... Subtractor, 145... Jitter value acquisition circuit (part of the signal quality acquisition circuit), 147. Part of signal quality acquisition circuit), 149... Subtracter, f1... Filter (first signal generation circuit), f2... Filter (second signal generation circuit).

Claims (1)

An optical disk device capable of at least reproducing information recorded, reproduced and erased from an optical disk,
A light source;
A grating that splits light from the light source into one main beam and two sub-beams;
An optical system for irradiating the access target track of the optical disk with the main beam from the grating, and irradiating the two sub beams on tracks adjacent to one side and the other side of the access target track;
A main beam light receiving element for receiving the main beam reflected by the optical disk, a first sub beam light receiving element and a second sub beam light receiving element for receiving the two sub beams reflected by the optical disk, respectively. A receiver having an element;
A first transversal filter to which an output signal of the main beam light receiving element is input, and an output signal of the main beam light receiving element is input, and the tap coefficient is a tap coefficient for the first transversal filter. And a difference between a jitter value in the output signal of the first transversal filter and a jitter value in the output signal of the second transversal filter. A tangential tilt detector having a subtractor that performs
A third transversal filter to which an output signal from the main beam light-receiving element and an output signal from the first sub-beam light-receiving element are input; an output signal from the main beam light-receiving element; and the second sub-beam A fourth transversal filter having a structure in which the tap coefficient is inverted with respect to the third transversal filter, with the center of the tap coefficient as the origin, and the third transversal filter. A radial tilt detector having a subtractor for outputting a difference between a jitter value in the output signal of the filter and a jitter value in the output signal of the fourth transversal filter;
A tilt that corrects a tangential tilt of the optical disc with respect to a reference surface based on an output signal of the tangential tilt detector, and corrects a radial tilt of the optical disc with respect to a reference surface based on an output signal of the radial tilt detector. a correction device, an optical disk device Ru comprising a.

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