JP2008090975A - Focus bias adjustment circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To properly adjust a focus bias value by considering defects of an optical disk. <P>SOLUTION: The focus bias adjustment circuit adjusting the focus bias value for focus servo control of an optical pickup includes: an amplitude variation measurement part applying an external disturbance signal having periodicity to the optical pickup and measuring amplitude variation in an RF signal read from the optical disk; an external disturbance response arithmetic part calculating an index value of the external disturbance response to the external disturbance signal on the basis of the amplitude variation of the RF signal; and a focus bias adjustment part obtaining the focus bias value to be set on the basis of the index value and a prescribed evaluation function. The external disturbance response arithmetic part retains the amplitude variation of the RF signal before defect detection during a period when the defect of the optical disk is detected. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a focus bias adjustment circuit.

  In an optical disk recording / reproducing apparatus such as a CD or a DVD, it is necessary to focus the laser beam on the information surface of the optical disk. In order to keep the distance between the objective lens and the information surface of the optical disk in focus, a focus error signal FE is used. Focus servo control based on The basic operation of focus servo control is to drive the objective lens in the optical pickup in the focus direction (the direction parallel to the optical axis), and the laser beam reflected by the optical disk is electrically output by a photodetector provided in the optical pickup. After being converted into a signal, it is extracted as a focus error signal FE. The state where the focus error signal FE becomes the reference value (VREF) is set as the focal point.

  However, even in a state where the focus error signal FE is at the reference value (VREF), optimal recording / reproduction is not always possible due to the defocused state. For example, the DC offset (center level) of the focus error signal FE is adjusted due to variations in the characteristics of the optical disc, variations in the characteristics of the optical system in the optical pickup, and the position of the objective lens naturally dropping due to its own weight. It is necessary. Therefore, an optical disk recording / reproducing apparatus is generally provided with a mechanism for adjusting the focus bias value FBIAS applied to the focus error signal FE to arbitrarily change the distance between the objective lens and the information surface of the optical disk.

As a conventional mechanism for adjusting the focus bias value FBIAS, for example, in Patent Document 1 shown below, a reciprocating motion parallel to the optical axis is given to the objective lens under the control of a sinusoidal pilot signal P. As a result, a periodic change appearing on the envelope of the read signal V is observed (see FIG. 11), and a mechanism for correcting the position of the objective lens by a focusing error signal obtained by comparison with the pilot signal P is disclosed. Yes. In addition, a mechanism for performing adjustment so that the amplitude of the RF signal read from the optical disk is maximized, a mechanism for performing adjustment so that the reproduction jitter of the optical disk is minimized, and the like are generally known. .
JP 50-85348 A

  By the way, in the conventional mechanism for adjusting the focus bias value FBIAS, a method of searching for an optimum focus bias value FBIAS based on a predetermined index value obtained from a signal optically read from an optical disc is used to detect scratches, dirt, It has not been able to cope with various defects (defects) of optical disks such as dust and fingerprints. For this reason, with the conventional mechanism, the search for the optimum focus bias value FBIAS may be temporarily delayed or headed in the wrong direction due to the influence of the defect location of the optical disk.

  A main aspect of the present invention for solving the above-described problem is that a focus bias adjustment circuit that adjusts a focus bias value for focus servo control of an optical pickup applies a disturbance signal having periodicity to the optical pickup, and An amplitude fluctuation measuring section for measuring the amplitude fluctuation of the read RF signal, a disturbance response calculating section for calculating an index value of a disturbance response to the disturbance signal based on the amplitude fluctuation of the RF signal, the index value and a predetermined evaluation function A focus bias adjustment unit that obtains a focus bias value to be set based on the above, and the disturbance response calculation unit is configured to detect the RF signal before the defect detection during a period in which the defect of the optical disc is detected. It is assumed that amplitude fluctuation is maintained.

  According to the present invention, it is possible to appropriately adjust the focus bias value in consideration of the defect of the optical disc.

<< Optical disk device >>
FIG. 1 is a diagram showing a configuration of an optical disc apparatus according to an embodiment of the present invention.

  The optical disk 10 is a medium that conforms to an optical disk standard such as CD, DVD, or HD-DVD, and is driven to rotate by a spindle motor 300.

  The optical pickup 400 includes an objective lens 410 for condensing laser light emitted from a semiconductor laser (not shown) as a light spot on the optical disk 10, other optical lenses, and an eight-divided diode that receives reflected light from the optical disk 10. And a servo mechanism 430 for focus / tracking servo.

  The servo mechanism 430 includes a lens holder that holds the objective lens 410, a substrate that elastically supports the lens holder with a suspension wire, a drive coil provided on the lens holder, a magnet that works magnetically by driving the drive coil, a yoke, and the like. It is comprised by a magnetic member etc. That is, by driving the drive coil, the objective lens 410 is driven in the focus direction (direction parallel to the optical axis) and the tracking direction (direction orthogonal to the optical axis) by magnetic action.

  The analog signal processing circuit 200 includes an RF generation circuit 210, an FE generation circuit 220, a TE generation circuit 230, and a defect determination circuit 240.

  The RF generation circuit 210 generates an analog RF signal based on the reflected light from the optical disc 10 detected by the photodetector 420. Note that the RF generation circuit 210 includes a binarization circuit and a peak hold / bottom hold circuit, and the digital signal processing circuit 100 has a binarized signal, a peak level PH of the RF signal, and a peak level PH of the RF signal. Supply the bottom level BH.

  The FE generation circuit 220 generates a focus error signal FE based on the reflected light from the optical disc 10 received by the photodetector 420. For example, the focus error signal FE is obtained from the optical disc 10 according to the astigmatism method or the Foucault method.

  The TE generation circuit 230 generates a tracking servo tracking error signal TE based on the reflected light from the optical disk 10 received by the photodetector 420. For example, the tracking error signal TE is obtained from the optical disc 10 according to a three-beam method, a differential push-pull method, or a DPD (Differential Phase Detection) method.

  The defect determination circuit 240 generates a defect signal indicating that a defect (defect) on the optical disk 10 such as a flaw, dirt, dust or fingerprint attachment has been detected. The defect determination circuit 240 generates a dark defect signal D1 indicating that a dark defect has been detected and a bright defect signal D2 indicating that a bright defect has been detected as a defect signal.

  FIG. 2 is a diagram for explaining a mechanism for detecting a dark defect. As shown in FIG. 2A, the envelope of the RF signal has a waveform that swings between the maximum peak level PH_MAX and the minimum bottom level BH_MIN. For example, when the surface of the optical disk 10 is scratched, the optical disk 10 The intensity of reflected light from the information surface decreases. As a result, when the upper envelope of the RF signal becomes equal to or lower than the first detection reference level Vth1, it is determined that it is a dark defect. As shown in FIG. A defect signal D1 is generated.

  FIG. 3 is a diagram for explaining a mechanism for detecting a bright defect. As shown in FIG. 3A, the envelope of the RF signal has a waveform that oscillates between the maximum peak level PH_MAX and the minimum bottom level BH_MIN. For example, if there is a scratch in the label of the optical disk 10, the optical disk The reflected light intensity from the 10 information surfaces increases. As a result, when the lower envelope of the RF signal becomes equal to or higher than the second detection reference level Vth2, it is determined that there is a bright defect, and as shown in FIG. A bright defect signal D2 is generated.

  The digital signal processing circuit 100 includes a spindle servo control circuit 110, a focus servo control circuit 120, a tracking servo control circuit 130, and an encoder / decoder 140. The digital signal processing circuit 100 may be an analog / digital mixed LSI integrated with the analog signal processing circuit 200.

  The spindle servo control circuit 110 generates a bit clock signal having a frequency proportional to the rotation speed of the optical disc 10 based on the binarized RF signal generated by the RF generation circuit 210. Then, the spindle servo control circuit 110 performs control so that the rotation speed of the spindle motor 300 becomes the specified rotation speed based on the result of comparing the bit clock signal with the reference clock signal corresponding to the specified rotation speed of the spindle motor 300. I do.

  The focus servo control circuit 120 generates a drive voltage for driving a drive coil for focus servo control in the servo mechanism 430 based on the focus error signal FE generated by the FE generation circuit 220, and focuses the focus of the light spot. Perform focus servo control.

  The focus servo control circuit 120 has a focus bias adjustment circuit 125 that adjusts the DC offset of the focus error signal FE, in other words, adjusts the focus bias value FBIAS applied to the focus error signal FE. Note that the adjustment of the focus bias value FBIAS is necessary for each characteristic variation of the optical disc 10 and each characteristic variation of the optical system in the optical pickup 400. Further, the adjustment of the focus bias value FBIAS is performed while the double speed related to recording / reproduction is halfway every time various types of the optical disc 10 are recorded / reproduced, for example, because the position of the objective lens 410 is naturally lowered by its own weight. This is necessary every time a change is made or when retrying because the recording / reproducing state is poor.

  The tracking servo control circuit 130 generates a driving voltage for driving the tracking servo control driving coil in the servo mechanism 430 based on the tracking error signal TE generated by the TE generation circuit 220, and the light spot S is set to the target scanning track. Tracking servo control to follow.

  The encoder / decoder 140 performs an encoding process or a decoding process according to the standard of the optical disc 10. For example, when the optical disc 10 is a DVD, the encoding process includes a scramble process, an error correction code and an error detection code generation and assignment, an EFM + modulation process, and the like for the write data transmitted from the host computer 600. The decoding processing includes EFM + demodulation processing, error correction, error detection, descrambling processing, and the like for the read data (binarized RF signal) read from the optical disc 10.

  The microcomputer 500 is a system controller that controls the entire optical disk device, such as the digital signal processing circuit 100, the analog signal processing circuit 200, and the optical pickup 400.

  The host computer 600 is, for example, an external device such as a personal computer equipped with an optical disk device. The host computer 600 issues a recording command and a reproduction command to the optical disk device, transmits write data before encoding processing, and read data after decoding processing. Receive.

<< Focus bias adjustment circuit >>
=== Adjustment principle ===
The adjustment principle of the focus bias value FBIAS by the focus bias adjustment circuit 125 will be described with reference to FIGS. 4 and 5 and the flowchart shown in FIG. The following main body is the focus bias adjustment circuit 125 unless otherwise specified.

  First, the focus bias adjustment circuit 125 sets an initial value FB_INI (corresponding to the center level FOFF that is a DC offset of the disturbance signal X) of the focus bias value FBIAS (S600), as shown in FIG. In addition, during the calculation period in which focus servo control is performed by applying a sinusoidal disturbance signal X having an amplitude with reference to the center level FOFF to the focus servo loop, the RF signal amplitude fluctuation Y is measured (S601). .

  That is, during the calculation period, the objective lens 410 is vibrated in the focus direction by the disturbance signal X, and the amplitude variation Y of the RF signal is measured based on the reflected light from the optical disc 10 detected by the photodetector 420 at that time. I will do it.

  Then, as shown in FIG. 4B, the focus bias adjustment circuit 125 multiplies the disturbance signal X and the amplitude variation Y of the RF signal, and further, the multiplication value (= X · Y) is calculated during the calculation period. Is integrated over time, the disturbance response index value W (= E (X · Y)) for the disturbance signal X is calculated (S602). The index value is not limited to the index value W described above, and any index value can be used as long as the disturbance response corresponding to each center level FOFF of the disturbance signal X can be verified.

  Here, a reference value W ′ of disturbance response to a plurality of center levels FOFF is obtained in advance for each type or double speed of the optical disc 10 or for each model of the optical pickup 400 using a standard machine of the optical disc apparatus. Then, the reference value W ′ of the disturbance response with respect to the plurality of center levels FOFF is statistically processed, for example, as shown in FIG. 4C, the focus bias value FBIAS (center level FOFF) and the reference value W of the disturbance response. An evaluation function (W = F (FBIAS)) that is associated with 'is obtained in advance for each type of optical disc 10, each double speed, or the like. Further, the focus bias value FBIAS when the reference value W ′ is “0” in the evaluation function F () is obtained as the optimum value FB_BEST.

  The focus bias adjustment circuit 125 performs the following adjustment of the focus bias value FBIAS based on the evaluation function F () and the optimum value FB_BEST. That is, as shown in FIG. 5, first, the calculated value Wt obtained for the disturbance response index value W is applied to the evaluation function F () to thereby obtain the reference value F ^ {− 1} () of the focus bias value FBIAS. Wt) is obtained (S603).

  Further, a deviation amount ΔFB between the obtained reference value F ^ {− 1} (Wt) and the optimum value FB_BEST is obtained (S604). The focus bias adjustment circuit 125 adjusts the current focus bias value FBIAS by the determined deviation amount ΔFB (S605). In addition, since the case where the disturbance response index value W indicates a non-specified value is considered, it is possible to determine the predetermined convergence condition, for example, until the disturbance response index value W falls within a predetermined specified range (S606: YES). It is preferable to repeat the processing (S600 to S605).

=== Circuit configuration ===
FIG. 7 is a diagram showing the configuration of the focus servo control circuit 120 and its peripheral circuits according to an embodiment of the present invention. Peripheral circuits of the focus servo control circuit 120 include an RF generation circuit 210 that is a source of the RF signal peak level PH and bottom level BH, an FE generation circuit 220 that is a source of the focus error signal FE, a dark defect signal D1, and a bright signal. There is a defect determination circuit 240 that is a supply source of the defect signal D2, and a focus drive signal generation circuit 435 that generates a focus drive signal for driving a focus servo drive coil of the servo mechanism 430.

  The focus servo control loop is mainly formed by the optical pickup 400, the FE generation circuit 220, the focus servo control circuit 120, and the focus drive signal generation circuit 435.

  As shown in FIG. 7, the focus bias adjustment circuit 125 includes a disturbance generation unit 1251, a disturbance response calculation unit 1252, an evaluation function setting unit 1253, an FBIAS adjustment unit 1254, an FBIAS setting unit 1255, A switch unit 1256, an FOFF setting unit 1257, and an addition unit 1258 are included.

  The disturbance generation unit 1251 generates a disturbance signal X and supplies it to one input terminal of the switch unit 1256 and the disturbance response calculation unit 1252. The disturbance signal X is a signal having periodicity such as a sine wave signal, a triangular wave signal, a rectangular wave signal, and the like, and needs to have a frequency with which the focus servo control by the focus servo control circuit 120 can follow. The disturbance signal X needs to be set to a gain that does not affect the servo gain of the focus servo control circuit 120.

  The disturbance response calculation unit 1252 calculates a disturbance response index value W for the disturbance signal X during a calculation period in which the disturbance signal X is applied to the focus servo control loop to perform focus servo control. The index value W is calculated by measuring the amplitude fluctuation ΔR of the RF signal based on the difference between the peak level PH and the bottom level BH of the RF signal and performing a predetermined calculation on the measured amplitude fluctuation ΔR of the RF signal. It is done by carrying out. Further, in order to prevent bias in measurement of the amplitude fluctuation ΔR of the RF signal, the disturbance response calculation unit 1252 is set to the calculation period described above, and a period extending over a predetermined circumference of the optical disc 10 (for example, one round of the disc). Is preferred.

  Further, when the disturbance response calculation unit 1252 calculates the disturbance response index value W using the dark defect signal D1, the bright defect signal D2, and the like from the defect determination circuit 240, the defect of the optical disc 10 is detected. During this period, processing for maintaining the amplitude fluctuation ΔR of the RF signal measured before the detection of the defect is performed.

  That is, when a defect occurs, the amplitude fluctuation ΔR of the RF signal becomes meaningless data, and thus the disturbance response index value W is not correctly calculated.

  The evaluation function setting unit 1253 sets the evaluation function F () of the index value W of the focus bias value FBIAS versus disturbance response for each type of the optical disc 10 and the type of the optical pickup 400. In the present embodiment, the evaluation function F () is a linear function that can be easily calculated and approximated, but a quadratic or higher-order function may be used.

  The FBIAS adjustment unit 1254 determines the focus bias optimum value FB_BEST by applying the disturbance response index value W calculated by the disturbance response calculation unit 1252 to the evaluation function F () set by the evaluation function setting unit 1253.

  The FBIAS setting unit 1255 supplies the focus bias initial value FB_INI set by the microcomputer 500 and the focus bias optimum value FB_BEST obtained by the FBIAS adjustment unit 1254 to the other input terminal of the switch unit 1256. .

  The switch unit 1256 selects the disturbance signal X supplied from the disturbance generation unit 1251 or the focus bias initial value FB_INI or the focus bias optimum value FB_BEST supplied from the FBIAS setting unit 1255 and outputs it to the addition unit 1258.

  The FOFF setting unit 1257 sets the center level FOFF of the disturbance signal X. The center level FOFF is changed every time the microcomputer 500 obtains a plurality of disturbance response index values W.

  The addition unit 1258 superimposes the difference between the selection output of the switch unit 1256 and the reference value OFF set in the FOFF setting unit 1257 on the focus error signal FE supplied from the FE generation circuit 220 and outputs the result. A focus drive signal FD is generated in the focus drive signal generation circuit 435 by the output FE ′ of the adder 1258.

<< Disturbance response calculation circuit to cope with defects >>
FIG. 8 is a diagram showing a configuration of the disturbance response calculation circuit 1252 according to an embodiment of the present invention.

  The disturbance response calculation circuit 1252 includes an amplitude fluctuation measurement unit 150, an LPF 160, a first defect detection unit 170, a second defect detection unit 180, a logical sum calculation unit 190, a switch unit 200, a multiplication unit 210, an addition unit 211, and a delay. Part 212.

  The amplitude fluctuation measuring unit 150 calculates the level difference between the peak level PH in the upper envelope of the RF signal and the bottom level BH in the lower envelope of the RF signal, that is, the amplitude fluctuation ΔR (= PH−BH) of the RF signal. This is an adder that measures.

  An LPF (Low Pass Filter) 160 converts the amplitude fluctuation ΔR of the RF signal output from the amplitude fluctuation measuring unit 150 into a direct current by a weighted moving average, and as a result, a direct current component E (ΔR) of the amplitude fluctuation ΔR of the RF signal. Ask. Note that the LPF 160 of this embodiment includes a multiplier 161 that multiplies the amplitude variation ΔR of the RF signal by the filter coefficient a1, a delay unit 162 that delays the amplitude variation ΔR of the RF signal by unit time, and a filter that filters the output of the delay unit 162. A multiplier 163 that multiplies by the coefficient a2, a delay unit 164 that delays the output of the adder 166 by unit time, a multiplier 165 that multiplies the output of the delay unit 164 by the filter count b1, and multipliers 161, 163, and 165 It is configured by an IIR (Infinite Impulse Response) filter including an adder 166 that adds the outputs and a switch unit 167 provided between the adder 166 and the delay unit 164.

  The switch unit 167 is turned on / off based on a switching signal SW output from a later-described OR operation unit 190. When the switch unit 167 is turned on, DC conversion of the amplitude fluctuation ΔR by the LPF 160 is continuously performed. However, when the switch unit 167 is turned off, DC conversion of the amplitude fluctuation ΔR by the LPF 160 is stopped. In the present embodiment, the switch unit 167 is turned on when the switching signal SW is “0”, and the switch unit 167 is turned off when the switching signal SW is “1”.

  The first defect detection unit 170 performs dark defects based on the dark defect signal D1 and the bright defect signal D2 generated by the defect determination unit 240 due to cuts on the surface of the optical disc 10, adhesion of dust, scratches in the label, or the like. Alternatively, it is detected that a bright defect (hereinafter referred to as “first defect”) has occurred.

  Specifically, the first defect detection unit 170 includes an AND operation unit 171 that calculates the logical product of the dark defect signal D1 and the third enable signal ENB3, and the bright defect signal D2 and the fourth enable signal ENB4. An AND operation unit 172 that calculates an AND, an OR operation unit 173 that calculates the logical sum of the output of the AND operation unit 171 and the output of the AND operation unit 172, the output of the OR operation unit 173, and the first And an AND operation unit 174 that calculates the logical product of the enable signal ENB1 and outputs the operation result as the first error signal ERR1. In the present embodiment, the case where the first error signal ERR1 is “1” means that the detection of the first defect is effective and the first defect is detected.

  The second defect detection unit 180 is a minute defect (hereinafter referred to as “second defect”) that is difficult to detect by the defect determination unit 240 or the first defect detection unit 170 due to a fingerprint or the like attached to the surface of the optical disc 10. ) Is detected. That is, as shown in FIG. 9, when a fingerprint or the like is attached to the surface of the optical disc 10, a minute amplitude fluctuation ΔR appears in the envelope of the RF signal, but the upper envelope of the RF signal is the first detection reference. It does not drop to the level Vth1, and the lower envelope of the RF signal does not rise to the second detection reference level Vth2. Therefore, the second defect detection unit 180 detects the minute amplitude variation of the RF signal as described above as a second defect, in a complementary role of the first defect detection unit 170.

  Specifically, the second defect detection unit 180 is set in the detection reference level setting unit 181 based on the detection reference level setting unit 181 that sets the third detection reference level Vth3 and the second enable signal ENB2. The comparison unit 182 that compares the third detection reference level Vth3 with the amplitude variation ΔR of the RF signal output from the amplitude variation measurement unit 150 to detect the magnitude relationship between the two, and detects the output edge of the comparison unit 182 An edge detection unit 183 that outputs a second error signal ERR2 indicating that the error has occurred. In the present embodiment, the case where the second error signal ERR2 is “1” means that the detection of the second defect is effective and the second defect is detected.

  The OR operation unit 190 calculates the logical sum of the first error signal ERR1 and the second error signal ERR2, and outputs the calculation result to the switch unit 200 as a switching signal SW. In the present embodiment, the case where the switching signal SW is “1” is a case where the first error signal ERR1 or the second error signal ERR2 is “1”.

  In the switch unit 200, the amplitude variation ΔR of the RF signal output from the amplitude variation measuring unit 150 is input to one input terminal a, and the DC component E (ΔR) of the amplitude variation ΔR output from the LPF 160 to the other input terminal b. ) And one of the input terminals a and b is selected by the switching signal SW from the OR operation unit 190. In this embodiment, when the cut-off signal SW is “0”, the amplitude variation ΔR of the RF signal input to the input terminal a is selected, and when the switching signal SW is “1”, the input is input to the input terminal b. The DC component E (ΔR) of the amplitude fluctuation ΔR thus selected is selected.

  The multiplication unit 210 multiplies the selection output of the switch unit 200 and the disturbance signal X.

  A cumulative adder composed of the adder 211 and the delay unit 212 performs cumulative addition (integration) on the output of the multiplier 210. The result of the cumulative addition is a disturbance response index value W for the disturbance signal X, which can be extracted from the delay unit 212.

  With this configuration, the disturbance response calculation circuit 1252 performs the operation shown in the flowchart of FIG.

  That is, when the first defect and the second defect are not detected (S100: NO, S101: NO), the disturbance response calculation circuit 1252 becomes “0”, so that the input terminal of the switch unit 200 While a is selected, the switch unit 167 of the LPF 160 is turned on (S102, S103). In this case, the multiplication unit 210 multiplies the amplitude variation ΔR of the RF signal and the disturbance signal X, and using the multiplication result, cumulative addition is performed in the addition unit 211 and the delay unit 212 (S104). Until the predetermined convergence condition is reached (S105: YES), the calculation of the index value W of the disturbance response is continued.

  On the other hand, when one of the first defect and the second defect is detected (S100: YES, S101: YES), the switching signal SW becomes “1”, so that the input terminal b of the switch unit 200 is At the same time, the switch unit 167 of the LPF 160 is turned off (S106, S107). In this case, the multiplication unit 210 multiplies the output of the LPF 160 (DC component E (ΔR) of the amplitude fluctuation ΔR) just before the detection of the first defect or the second defect and the disturbance signal X, and performs such multiplication. Using the result, cumulative addition in the adding unit 211 and the delay unit 212 is performed (S108).

  When the detection of the first defect or the second defect is completed, the switching signal SW becomes “0” again, so that the input terminal a of the switch unit 200 is selected and the switch unit of the LPF 160 167 is turned on (S102, S103), and the process proceeds to the calculation of the index value W of the normal disturbance response.

  As described above, the disturbance response index value W considering the defect of the optical disc 10 is calculated, and the focus bias value FBIAS can be appropriately adjusted based on the calculated index value W.

  As mentioned above, although embodiment of this invention was described, embodiment mentioned above is for making an understanding of this invention easy, and is not for limiting and interpreting this invention. The present invention can be changed / improved without departing from the spirit thereof, and the present invention includes equivalents thereof.

It is a figure which shows the structure of the optical disk apparatus based on one Embodiment of this invention. It is a figure explaining the mechanism in which the dark defect which concerns on one Embodiment of this invention is detected. It is a figure explaining the mechanism by which the bright defect which concerns on one Embodiment of this invention is detected. (A) is a figure explaining the disturbance response with respect to the disturbance signal which concerns on one Embodiment of this invention, (b) is a figure explaining the calculation of the index value of the disturbance response which concerns on one Embodiment of this invention, (C) is a figure explaining the evaluation function which concerns on one Embodiment of this invention. It is a figure explaining adjustment of a focus bias value using the evaluation function concerning one embodiment of the present invention. It is a flowchart explaining the adjustment principle of the focus bias adjustment circuit which concerns on one Embodiment of this invention. It is a figure which shows the structure of the focus servo control circuit which concerns on one Embodiment of this invention, and its peripheral circuit. It is a figure which shows the structure of the disturbance response calculating part which concerns on one Embodiment of this invention. It is a figure explaining the mechanism in which the 2nd defect concerning one embodiment of the present invention is detected. It is a flowchart explaining operation | movement of the disturbance response calculating part which concerns on one Embodiment of this invention. It is a figure explaining the mechanism in which the conventional focus bias value is adjusted.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Optical disk 20 Spindle motor 100 Digital signal processing circuit 110 Spindle servo control circuit 120 Focus servo control circuit 125 Focus bias adjustment circuit 1251 Disturbance generation part 1252 Disturbance response calculation part 130 Tracking servo control circuit 140 Encoder / decoder 150 Amplitude fluctuation measurement part 160 LPF
161, 163, 165 Multiplication unit 162, 164 Delay unit 166 Addition unit 167 Switch unit 170 First defect detection unit 173 OR operation units 171, 172, 174 AND operation unit 180 Second defect detection unit 181 Detection reference level Setting unit 182 Comparison unit 183 Edge detection unit 190 OR operation unit 200 Switch unit 210 Multiplication unit 211 Addition unit 212 Delay unit 1253 Evaluation function setting unit 1254 FBIAS adjustment unit 1255 FBIAS setting unit 1256 Switch unit 1257 FOFF setting unit 1258 Addition unit 200 Analog signal processing circuit 210 RF generation circuit 220 FE generation circuit 230 TE generation circuit 240 Defect determination circuit 400 Optical pickup 410 Objective lens 420 Photo detector 430 Servo mechanism 500 Microcomputer 600 host computer

Claims (8)

In the focus bias adjustment circuit that adjusts the focus bias value for focus servo control of the optical pickup,
An amplitude fluctuation measuring unit that applies a disturbance signal having periodicity to the optical pickup and measures the amplitude fluctuation of the RF signal read from the optical disc;
A disturbance response calculation unit that calculates an index value of a disturbance response to the disturbance signal based on an amplitude variation of the RF signal;
A focus bias adjustment unit for obtaining a focus bias value to be set based on the index value and a predetermined evaluation function,
The disturbance response calculator is
Maintaining the amplitude fluctuation of the RF signal before the defect detection in a period in which the defect of the optical disc is detected;
A focus bias adjustment circuit. The focus bias adjustment circuit according to claim 1,
The frequency of the disturbance signal is set to a frequency that the focus servo control can follow,
A focus bias adjustment circuit. The focus bias adjustment circuit according to claim 1,
The disturbance response calculator is
Multiplying the disturbance signal by the amplitude variation of the RF signal and integrating the result of the multiplication over the computation period;
A focus bias adjustment circuit. The focus bias adjustment circuit according to claim 3.
The disturbance response calculator is
Multiplying the disturbance signal by the amplitude fluctuation of the RF signal before the defect detection, and integrating the result of the multiplication in a period in which the defect is detected;
A focus bias adjustment circuit. The focus bias adjustment circuit according to claim 1,
The disturbance response calculator is
If the upper envelope of the RF signal is below a first detection reference level, detecting a first defect of the optical disc;
A focus bias adjustment circuit. The focus bias adjustment circuit according to claim 1,
The disturbance response calculator is
Detecting a first defect of the optical disc when a lower envelope of the RF signal is equal to or higher than a second detection reference level;
A focus bias adjustment circuit. The focus bias adjustment circuit according to claim 1,
The disturbance response calculator is
Detecting a second defect of the optical disc when a level difference between an upper envelope and a lower envelope of the RF signal is equal to or lower than a third detection reference level;
A focus bias adjustment circuit. The focus bias adjustment circuit according to claim 1,
When the upper envelope of the RF signal is equal to or lower than the first detection reference level, or when the lower envelope of the RF signal is equal to or higher than the second detection reference level, the first defect of the optical disc is detected. A first defect detection unit that
A second defect detection unit that detects a second defect of the optical disc when a level difference between an upper envelope and a lower envelope of the RF signal is equal to or lower than a third detection reference level;
An amplitude fluctuation measuring unit that measures the amplitude fluctuation of the RF signal by obtaining a level difference between the upper envelope and the lower envelope of the RF signal;
A low-pass filter that converts the amplitude fluctuation of the RF signal into a direct current and stops driving during a period in which the first or second defect is detected;
When the first or second defect is not detected, the amplitude variation of the RF signal is selectively output, and when the first or second defect is detected, the DC signal is converted into a direct current. A switch unit that selectively outputs amplitude fluctuations;
A multiplier that multiplies the selection output of the switch unit and the disturbance signal;
A cumulative addition unit that outputs a result of cumulative addition of the multiplication results as the index value;
A focus bias adjustment circuit comprising:

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