JP2008027568A - Optical disk apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that focus sensitivities are different between a land and a groove, so that in focus control with the same gain, optimal gain is not obtained, focus offset is changed during focus learning of focus position adjustment, and in the land or the groove with lower sensitivity, a defocus amount increases, destabilizing a focus servo. <P>SOLUTION: Focus dependence of RF amplitude is measured in a land and a groove (S104 and S106). Focus widths of a range where an amplitude is reduced to a predetermined value from a largest amplitude focus point are compared with each other between the land and the groove (S107). The defocus amounts of the land and the groove are corrected based on an amplitude change with respect to defocusing. By using this correction coefficient, gains of focus servo are set for the land and the groove (S108). Thus, a gain difference between the land and the groove is measured more easily than when the gain of the focus servo is directly measured. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical disc apparatus characterized by a focus control method performed during recording / reproduction with respect to an optical disc.

  FIG. 10 is a block diagram illustrating a configuration example of a general optical disc recording / reproducing apparatus. As shown in FIG. 10, light emitted from a laser serving as a light source on a laser unit (hereinafter referred to as LDU) 102 is converted into parallel light through a collimator lens 103, transmitted through a polarization hologram 104, and then a quarter wavelength plate 105. Thus, the light is converted from linearly polarized light into circularly polarized light, and is condensed on the surface of the optical disk 101 rotated by the spindle motor 108 by the objective lens 106 driven by the actuator 107. The objective lens 106 can be moved in the focus direction F and the tracking direction (track crossing direction) T by an actuator 107. The light reflected from the optical disc 101 passes through the objective lens 106 again, and the circularly polarized light at the quarter wavelength plate 105 is polarized with the polarization direction of the linearly polarized light that has reached the quarter wavelength plate 105 by the polarization hologram 104. After being converted into orthogonal linearly polarized light and diffracted by the polarization hologram 104, the light is incident on and received by a photodetector serving as a light receiving element on the LDU 102 via the collimating lens 103, and the photodetector detects a signal corresponding to the incident light. Is output to the preamplifier 121. As described in detail below, the preamplifier 121 generates a focus error signal (hereinafter referred to as FE signal), a tracking error signal (hereinafter referred to as TE signal), and an RF signal from the detection signal. The FE signal and the TE signal indicate that the beam spot formed on the information recording layer of the optical disc 101 has a predetermined condensing state when the objective lens 106 is deviated from an appropriate position in the focus direction F and the tracking direction T. It indicates that it is not shown or is shifted in the tracking direction T. The RF signal includes data information recorded in the form of pits and marks on the information recording layer of the optical disc 101 and address information on a track on which data is recorded or reproduced. The signal processing unit 122 receives the RF signal, extracts the recorded data information and address information, and reproduces them. The servo unit 123 receives the FE signal and the TE signal, generates a control signal for controlling the actuator 107, and controls the objective lens 106 based on the control signal. Similarly, the spindle motor 108 is also controlled. The laser driver 125 controls the laser emission power on the LDU 102 used for recording or reproduction. Information reproduced by the signal processing unit 122 is transmitted to the controller 124. The servo unit 123 and the laser driving unit 125 are driven under the control of the controller 124.

  FIG. 8 shows an FE signal detection unit by general spot size detection (hereinafter, SSD). The photodetector 201 is a detector for detecting an FE signal on the LDU 102, and an FE signal is generated based on this output. In this figure, the subtractor 204 generates an FE signal of (b + c) − (a + d). Further, the adder 205 generates an FS signal as an addition signal of a + b + c + d, and an RF signal is detected from this signal. 202 indicates detection light from the optical disc at the front focal point (in a state where the focal point is on the front side of the detection surface of the photodetector 201), and 203 indicates the rear focal point (in a state where the focal point is on the rear side of the detection surface of the photodetector 201). A condensed spot is shown. When the distance between the optical disk and the objective lens changes, the spot size of 202 and 203 changes such that if one side becomes larger, the other becomes smaller, thereby generating an FE signal.

  When a disk with a groove such as DVD ± R or DVD-RAM is reproduced, zero-order light and first-order light are generated by diffraction by the groove. The guide groove of this type of optical disc has a convex portion (land) and a concave portion (groove). FIG. 3 shows a schematic diagram of the light amount distribution of the detection light from the optical disk on the polarization hologram 104. Reference numeral 301 denotes a case where a land is reproduced, and reference numeral 302 denotes a case where a groove is reproduced. As shown in FIG. 3, the light amount distribution is reversed during Land and Groove reproduction. In addition to this phenomenon, for example, the light used for focus control is not a full circle shown in 301 or 302, but a part thereof, for example, as shown in FIG. Depending on the positional relationship between the photodetector and the spot, the degree of change in the amplitude of the FE signal with respect to defocus may change between Land and Groove.

  FIG. 4 shows an FE signal when the distance between the optical disk and the objective lens is changed at the center of the track of Land or Groove. The wavy line in the figure shows the FE signal at the focal point.

  FIG. 5 shows a graph of the open loop characteristics of the focus servo when the defocus is changed while the same circuit gain is set in Land and Groove for a specific servo band frequency. If there is an inflection point in the FE signal near the in-focus point as shown in FIG. 4, the gain of the focus varies between Land and Groove as shown in FIG. 5, and changes in jitter and RF amplitude with respect to FE signal changes are measured. Then, as shown in FIG. 6, the sensitivity differs between Land and Groove. In FIG. 6, the concave characteristic is the jitter characteristic, and the convex characteristic is the RF amplitude characteristic.

  In this way, when there is an optical gain difference in the focus servo between the Land and the Groove, if the focus control is performed with the same circuit gain setting between the Land and the Groove, the gain is high in the Land depending on the setting. In some cases, the focus servo oscillates or the focus control residual becomes large because the gain is low in Groove. Therefore, it is desirable to set the gain individually for Land and Groove.

  In Patent Document 1 and Patent Document 2, a land and a groove are provided with a gain switching unit for a focus error signal and a track error signal.

  Japanese Patent Application Laid-Open No. 2004-228561 proposes that a sensitivity is calculated by taking a focus error signal or a tracking error signal while driving an objective lens, and setting the gain of a land and a groove using the value.

Generally, for gain measurement by open loop of servo, it is necessary to prepare an expensive measuring instrument such as a frequency characteristic analyzer or a circuit that realizes the same function as using a frequency characteristic analyzer. This leads to an increase in area, circuit scale and cost.
JP-A-7-129975 JP-A-8-329484 Japanese Patent Laid-Open No. 10-91976

  According to the present invention, the gain difference between the land and the groove can be measured with a simple operation by the optical disc apparatus without increasing the installation area, circuit scale and cost as described above, and the gain setting of the focus servo can be realized quickly. Objective.

  In order to solve the above problems, the present invention performs an optical pickup that reads information recorded on an optical disc, a demodulation circuit that demodulates digital data from an output signal of the optical pickup, and performs servo control from the output signal of the optical pickup An optical disc apparatus including a control unit, wherein the control unit performs a focus / tracking control on the concave portion and the convex portion of the guide groove of the optical disc, and a signal from the optical disc with respect to a focus offset at each of the concave and convex portions. The gain difference of the focus control at each of the concave and convex portions is acquired by comparing the amplitude change degrees of the concave and convex portions.

  Furthermore, a gain of focus control is set in each of the concave and convex portions by comparing the amplitude change degree of the signal from the optical disc with respect to the focus offset in each of the concave and convex portions.

  The signal from the optical disk is an addition signal.

  Alternatively, when the focus offset range of the amplitude obtained by subtracting a certain ratio from the maximum amplitude of the signal from the optical disc at each of the concave convex portions is ΔVg and ΔVl, and the gain of the focus control circuit of each concave convex portion is Gg and Gl, Gg = Gl−20 * log (ΔVg / ΔVl) is set.

  The present invention also includes an optical pickup that reads information recorded on an optical disc, a demodulation circuit that demodulates digital data from the output signal of the optical pickup, and a control unit that performs servo control from the output signal of the optical pickup. In the optical disc apparatus, the control unit performs focus and tracking control on the concave portion and the convex portion of the guide groove of the optical disc, and focuses on each of the concave portion of the guide groove and the flat portion without the convex groove and the guide groove. The gain value of the focus control in the concave portion and the convex portion is obtained by comparing the amplitude change degree of the signal from the optical disc with respect to the offset.

  Further, the gain of the focus control circuit at the concave and convex portions is compared by comparing the amplitude change degree of the signal from the optical disc with respect to the focus offset in the concave portion of the guide groove and the flat portion without the convex groove and the guide groove, respectively. It is characterized by setting a value.

  The signal from the optical disk is an addition signal.

  Alternatively, the focus offset ranges of amplitudes obtained by subtracting a certain ratio from the maximum amplitude of the signal from the optical disc in the concave portion of the guide groove and the flat portion without the convex portion and the guide groove are ΔVg, ΔVl, and ΔVm, respectively. When the gain of the focus control circuit of each flat part is Gg, Gl, Gm, Gg = Gm-20 * log (ΔVg / ΔVm) and Gl = Gm-20 * log (ΔVl / ΔVm) are set. And

  The present invention also includes an optical pickup that reads information recorded on an optical disc, a demodulation circuit that demodulates digital data from the output signal of the optical pickup, and a control unit that performs servo control from the output signal of the pickup. In the optical disc apparatus, the control unit performs an adjustment step of a focus offset having a lower focus control gain of the concave portion or the convex portion when setting the optimum focus position in the concave portion and the convex portion of the guide groove of the optical disc. It is characterized by being made smaller than the other.

  According to the present invention, in the FE signal, which is a differential signal detected in FIGS. 3 and 9, an inflection point occurs when the unevenness of the light amount distribution on the photodetector crosses the dividing line of the photodetector. In addition, since the RF signal (or FS signal) that is the addition signal is not affected by this, the focus servo gain difference between the convex portion and the concave portion is specified from the degree of amplitude fluctuation with respect to the defocusing of the RF amplitude of the optical disc, and focus control is performed. By setting the gain of the circuit section, it is possible to easily reduce the open-loop gain difference between the convex part and concave part and stabilize the optical disc focus control without preparing a frequency characteristic analyzer or a circuit that realizes its function. can do. Further, in the focus position learning, the optimum focus position learning can be performed by reducing the focus offset adjustment step when the optical gain of the focus control of the convex portion or the concave portion is small.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the optical configuration of the optical pickup device is the same as that of the conventional example, and a description thereof will be omitted.

(Embodiment 1)
In this embodiment, the focus servo gain difference between Land and Groove of the optical disk is measured, and the amplitude of the RF signal or FS signal from the optical disk is used to set the gain. A control procedure using the RF signal will be described below with reference to the flowchart of FIG.

  First, focus control for the optical disc is started (ON) (step S101).

  Next, tracking control is started (ON) to Land of the optical disc (step S102). Here, for convenience, tracking with respect to Land is performed first, but Groove may be performed first.

  The Land focus control gain is set to a specified value or so that the focus control residual is less than or equal to an allowable amount (step S103).

  Next, as shown in FIG. 7, a focus offset range in which the RF signal decreases at a certain rate from the focus point at which the RF signal has the maximum amplitude is obtained (step S104). More specifically, the RF signal is reproduced, a focus point where the amplitude is maximum is searched, and, for example, positive and negative focus offsets at which the RF signal is 90% of the maximum amplitude are obtained, and the offset width ( Hereinafter, ΔVl) is recorded.

  Next, tracking control for Groove is started (ON) (step S105).

  Next, in the same manner as in step S104, a focus offset range (hereinafter referred to as ΔVg) in which the RF signal amplitude decreases at a certain rate is also obtained in Groove (step S106).

  Thus, the optical focus gain difference between Land and Groove is obtained as 20 * log (ΔVl / ΔVg) (step S107). For example, since the gain difference between Land and Groove is different at points a and b with different focus offsets in FIG. 5, the average gain difference between Land and Groove is calculated using a frequency characteristic analyzer or a circuit that implements the function. In order to determine, it is necessary to measure at a large number of measurement points. However, according to this measurement method, the average gain difference in the measurement range can be easily obtained by simply measuring the amplitude of the RF signal in each of Land and Groove. I want.

  Further, the gains of Land and Groove are set (step S108). Specifically, when the gain in Land of the focus control circuit unit (here, one function of the servo unit 123 and the controller 124 in FIG. 10) is G1, and the gain in Groove is Gg, the optical gain difference is canceled. Thus, it is set to (Equation 1).

Gg = Gl-20 * log (ΔVg / ΔVl) (Formula 1)
As described above, if the gain is set, the gain difference caused by the focus error signal between the Land and the Groove can be corrected by the focus control circuit unit. As a result, the gain of the focus servo control including the pickup and the circuit of the Land and the Groove is increased. Can be aligned. According to this method, there is no need to separately prepare a circuit for measuring the open loop characteristic of the focus servo, and the degree of amplitude fluctuation with respect to the defocusing of the RF amplitude can be measured with a simple operation of Land and Groove. Gain correction can be performed. Since (Equation 1) shows only the relative relationship between Gg and Gl, the focus control residual is not more than a predetermined amount, and is separately adjusted so that the optimum Gg (or Gl) is obtained within a range where oscillation does not occur. Must.

(Embodiment 2)
In the present embodiment, the amplitude difference of the RF signal and the FS signal from the optical disk is used to measure the gain difference of the focus servo at the flat part without the guide groove and the Land and Groove of the optical disk. According to this embodiment, the flatness of a disc with a guide groove such as a DVD-RAM is set based on the gain setting of the focus servo when reproducing a disc without a guide groove such as a DVD-ROM held by the optical disc drive. The gain setting of the concave and convex portions can be quickly obtained from the focus offset amount with respect to the degree of amplitude change of the RF signal or the like in the convex portion, concave portion or convex portion. A control procedure using the RF signal will be described below with reference to the flowchart of FIG.

  First, focus control is started (ON) on the optical disc (step S201).

  Next, the optical pickup (OPU) is driven in a radial position direction (not shown) using a feed motor and moved to a radial position without a guide groove (step S202). In a DVD-RAM or the like, even if it is an unrecorded disc, an RF signal due to pre-pits exists in a flat portion without a guide groove on the innermost peripheral portion, and this signal may be used. Similar to the DVD-ROM, tracking control is applied with a phase difference (hereinafter referred to as DPD).

  Next, the focus control gain of the flat portion is set so that the specified value or the focus control residual is less than the allowable amount (step S203).

  Next, although not shown, as in the example of Land and Groove shown in FIG. 7, the focus offset range in which the RF signal decreases at a certain rate from the focus point at which the RF signal has the maximum amplitude is obtained. . More specifically, the RF signal is reproduced, a focus point where the amplitude is maximum is searched, and, for example, positive and negative focus offsets at which the RF signal is 90% of the maximum amplitude are obtained, and the offset width ( Hereinafter, ΔVm) is recorded (step S204).

  Next, the optical pickup is moved to a radial position with a guide groove by the feed motor (step S205).

  Next, tracking control is started (ON) to Land (step S206).

  Next, as in step S204, as shown in FIG. 7, a focus offset range (hereinafter referred to as ΔVl) in which the RF signal decreases at a certain rate from the focus point at which the RF signal has the maximum amplitude is obtained (step S204). S207).

  Next, tracking control is started (ON) in Groove (step S208).

  Next, as in step S204, as shown in FIG. 7, the focus offset range (hereinafter referred to as ΔVg) in which the RF signal amplitude decreases at a certain rate also in the groove is obtained (step S209). .

  As described above, the optical focus gain difference with respect to the flat portion without the guide groove of Land and Groove is obtained from 20 * log (ΔVl / ΔVm) and 20 * log (ΔVg / ΔVm) (step S210). For example, since the gain difference between Land and Groove is different at points a and b with different focus offsets in FIG. 5, the average gain difference between Land and Groove is determined by a frequency characteristic analyzer or a circuit that implements the function. In order to achieve this, it is necessary to measure at a large number of measurement points, but according to this measurement method, an average gain difference in the measurement range can be easily obtained simply by measuring the amplitude of the RF signal.

Based on the obtained gain difference, the gain of the focus control circuit in Land and Groove is set (step S211). Specifically, when the gain in the flat part without the groove of the focus control circuit part is G1, Gg, and Gm, respectively, the optical gain difference is canceled.
Gg = Gm-20 * log (ΔVg / ΔVm) (Formula 2)
Gl = Gm-20 * log (ΔVl / ΔVm) (Formula 3)
Set to.

  If the setting is made as described above, the gain difference generated by the focus error signal between the Land and the Groove can be corrected by the focus control circuit unit, and as a result, the gain of the focus servo control including the Land and the Groove pickup and circuit can be aligned. it can. Further, according to this method, it is not necessary to separately prepare a circuit for measuring the open-loop characteristic of the focus servo. Further, the degree of amplitude fluctuation with respect to the defocusing of the RF amplitude is simply measured by Land and Groove. Gain correction can be performed by operation. Further, the gain setting values of Land and Groove are based on the gain setting value Gm in a flat portion without a groove. The gain of Land and Groove varies depending on the width and depth of the guide groove of the optical disk to be reproduced, but there is no groove in the flat part, that is, there is no ± first-order diffracted light, so there is no significant fluctuation. If the gain setting value Gm of the focus control circuit is set to an optimum value by a unit or the like and then stored in a memory (not shown) in the optical disc apparatus, the gain setting values Gl and Gg of the Land and Groove focus control circuits are set. Can be determined quickly.

(Embodiment 3)
In the present embodiment, in order to perform optimum focus position learning by using Land or Groove of the optical disc, the signal offset (RF signal, FS signal, etc.) from the optical disc and the signal quality (RF signal or address signal) are changed by changing the focus offset. Jitter and error rate). At this time, the focus offset adjustment step is made smaller than the other when the focus gain is optically lower. In the case of FIG. 6, since the fluctuation of the RF amplitude and jitter with respect to the FE signal is steeper in Groove, if the focus offset adjustment step in Groove is reduced, the learning error is reduced in both Groove and Land, which is optimal. Focus position learning can be performed.

  The optical disc apparatus according to the present invention has an effect that the gain setting of the focus control can be performed without using a device or a circuit for frequency characteristic analysis, and the focus control can be stabilized. It is useful as a disk drive device for recording and reproducing.

7 is a flowchart showing the operation of the optical disc device according to the first embodiment of the present invention. Flowchart showing the operation of the optical disc apparatus according to the second embodiment Schematic diagram showing the light intensity distribution of the detection light from the optical disc FE signal characteristic diagram when the distance between the optical disk and the objective lens changes at the center of the Land or Groove track Characteristic diagram showing the open loop characteristics of the focus servo when the defocus is changed for a specific frequency Characteristic diagram showing change of jitter and RF amplitude with respect to change of FE signal A characteristic diagram showing a focus offset range in which the RF signal decreases at a certain rate from the focus point at which the RF signal has the maximum amplitude. Schematic diagram showing the configuration of a conventional SSD FE signal detector Conceptual diagram of FE signal detection unit by SSD using a part of opening Conceptual diagram showing a configuration example of a general optical disc recording / reproducing apparatus

Explanation of symbols

101 optical disk 102 LDU
DESCRIPTION OF SYMBOLS 103 Collimating lens 104 Polarization hologram 105 1/4 wavelength plate 106 Objective lens 107 Actuator 108 Spindle motor 121 Preamplifier 122 Signal processing part 123 Servo part 124 Controller 125 Laser drive part 201, 901 Photodetector 202, 902 Pre-focus spot 203, 903 Back focal spot 204 Subtractor 205 Adder 301 Light distribution during Land reproduction 302 Light distribution during Groove reproduction

Claims (9)

An optical disc apparatus comprising: an optical pickup that reads information recorded on an optical disc; a demodulation circuit that demodulates digital data from an output signal of the optical pickup; and a control unit that performs servo control from the output signal of the optical pickup. ,
The control unit, when performing focus / tracking control in the concave and convex portions of the guide groove of the optical disc, compares the focus offset with respect to the amplitude change degree of the signal from the optical disc in each of the concave and convex portions, thereby calculating the concave and convex portions. An optical disc apparatus characterized by acquiring a gain difference of focus control in each unit. 2. The optical disc apparatus according to claim 1, wherein a focus control gain is set in each of the concave and convex portions by comparing a focus offset with respect to the amplitude change degree of the signal from the optical disc in each of the concave and convex portions. The optical disk apparatus according to claim 2, wherein the signal from the optical disk is an addition signal. When the focus offset ranges of the amplitudes obtained by subtracting a certain ratio from the maximum amplitude of the signal from the optical disc at each of the concave convex portions are ΔVg and ΔVl, and the gain of the focus control circuit of each concave convex portion is Gg and Gl, Gg = 4. The optical disk apparatus according to claim 1, wherein the optical disk apparatus is set to Gl-20 * log (ΔVg / ΔVl). An optical disc apparatus comprising: an optical pickup that reads information recorded on an optical disc; a demodulation circuit that demodulates digital data from an output signal of the optical pickup; and a control unit that performs servo control from the output signal of the optical pickup. ,
When the control unit performs focus / tracking control on the concave portion and the convex portion of the guide groove of the optical disc, the amplitude change degree of the signal from the optical disc at each of the concave portion and the convex portion of the guide groove and the flat portion without the guide groove is controlled. An optical disc apparatus characterized in that a gain difference in focus control between the concave portion and the convex portion is obtained by comparing a focus offset with respect to the optical disc device. The gain value of the focus control circuit at the concave and convex portions is set by comparing the focus offset with respect to the amplitude change degree of the signal from the optical disc in each of the concave portion of the guide groove and the flat portion without the convex portion and the guide groove. The optical disc apparatus according to claim 5, wherein 7. The optical disc apparatus according to claim 6, wherein the signal from the optical disc is an addition signal. The focus offset ranges of the amplitude obtained by subtracting a certain ratio from the maximum amplitude of the signal from the optical disc in each of the concave portion of the guide groove and the flat portion without the convex portion and the guide groove are ΔVg, ΔVl, and ΔVm. Gg = Gm−20 * log (ΔVg / ΔVm) and Gl = Gm−20 * log (ΔVl / ΔVm) when Gg, Gl, and Gm are set as gains of the focus control circuits of the respective units. The optical disc apparatus according to claim 5. An optical disc apparatus comprising: an optical pickup that reads information recorded on an optical disc; a demodulation circuit that demodulates digital data from an output signal of the optical pickup; and a control unit that performs servo control from the output signal of the pickup,
When setting the optimal focus position in the concave and convex portions of the guide groove of the optical disc, the control unit reduces the focus offset adjustment step of the lower concave or convex portion of the focus control gain compared to the other. An optical disc device characterized by the above.

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