JP2006059447A - Optical disk playback device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical disk playback device having high wobble detection accuracy. <P>SOLUTION: This optical disk playback device is provided with an amplification section, an extraction section, and a control signal generation section to highly accurately generate a wobble signal. The amplification section amplifies a signal outputted from an optical pickup to predetermined amplitude. The extraction section generates a wobble signal on the basis of the signal outputted from the amplification section. The control signal generation section generates a control signal to control the amplification section on the basis of an RF signal component left in the wobble signal outputted from the extraction section. By feeding back the control signal generated by the control signal generation section to the amplification section, control is made to set the RF signal component contained in the wobble signal to a predetermined threshold signal or lower, and a wobble signal is highly accurately generated. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an optical disk reproducing apparatus that reproduces information contained in an optical disk medium, particularly a wobble signal used to determine the type of the optical disk medium.

  In the standard of recordable optical disc media, a wobble signal (WOBBLE signal) is defined in addition to a data signal (RF signal). The wobble signal is used for controlling the rotational speed of the optical disk medium. Therefore, in order to reproduce a data signal from a recordable optical disc medium, it is necessary to accurately extract the wobble signal.

  The following techniques are known for extracting a wobble signal. According to Japanese Patent Laid-Open No. 2002-367180, a rotation driving mechanism that mounts and rotates an optical disk, an optical head that includes a light projecting unit that emits laser light, and a plurality of light receiving units are provided. A technique relating to generation of a WOBBLE signal in an optical disc apparatus for recording and / or reproducing an optical disc is disclosed. The optical disc apparatus has a WOBBLE signal detection circuit that generates a WOBBLE signal from a pregroove formed on the optical disc via an optical head. The WOBBLE signal detection circuit includes a first normalization circuit, a second normalization circuit, and correction means. The first normalization circuit irradiates the optical disk with laser light from the optical head, and receives the reflected light from the optical disk by at least one light receiving section on one end side of the plurality of light receiving sections. Is normalized. The second normalization circuit normalizes the second signal obtained by receiving the reflected light with at least one light receiving unit on the other end side of the plurality of light receiving units. The correcting means corrects the first signal and / or the second signal based on the output signal of the first normalization circuit and the output signal of the second normalization circuit. The WOBBLE signal detection circuit generates a WOBBLE signal based on the normalized first signal and the normalized second signal.

  Japanese Patent Laid-Open No. 2003-338041 discloses a technique for extracting a wobble signal or an LPP signal in an optical disc reproducing apparatus. The optical disc reproducing apparatus has an AGC circuit that controls the amplitude of the read signal to be constant in order to extract a wobble signal or an LPP signal included in the read signal read from the optical disc. The AGC circuit includes a variable gain amplifier, a high pass filter, and a gain control signal generation unit. The variable gain amplifier can amplify the read signal and change the gain according to the gain control signal. The high-pass filter passes a frequency component of a predetermined frequency or higher in the output signal of the variable gain amplifier. The gain control signal generation unit generates a gain control signal based on the output signal of the high pass filter.

  The extraction of the wobble signal is generally performed as follows. The optical pickup irradiates the reflection surface of the optical disk medium with laser light. The reflected light is received by a photodetector divided into four. A photodiode is usually used for the photodetector. Photovoltage conversion is performed to a voltage level corresponding to the amount of light received, and four signals (signal A, signal B, signal C, and signal D) are output from the optical pickup. These four signals are expressed as follows.

A = R1 + W1 (1)
B = R2-W2 (2)
C = R3-W3 (3)
D = R4 + W4 (4)
Here, the signal Rn (n = 1... 4) is a data signal (RF signal). The signals Rn are all in phase and are generally signals of the same amplitude. Therefore, signal Rn = signal R can be established. The signal Wn (n = 1... 4) is a wobble signal. The wobble signal is in phase with signal A and signal D, signal B and signal C, but is out of phase with signal A and signal B, and signal C and signal D. Further, the amplitude of each wobble signal Wn is substantially the same. Therefore, signal Wn = signal W can be obtained. In general, the RF signal is a signal in a higher frequency band than the wobble signal.

  From formulas (1) to (4), (A + D) − (B + C) = 4 × W. That is, only the wobble signal W can be extracted by performing addition and subtraction of each signal as in this arithmetic expression.

  Conventionally, the wobble signal is extracted by a circuit shown in FIG. The wobble signal extraction circuit includes an optical pickup 60, variable gain amplifier circuits (GCAs) 51 and 52, automatic gain control circuits (AGC) 53 and 54, a subtractor circuit 61, an adder circuit 62, and a peak hold circuit ( P / H) 55, 56, subtracting circuits 57, 58, and a band pass filter (BPF) 59.

  The signals A and D output from the optical pickup 60 are input to the variable gain amplifier circuit 51. The signals B and C are input to the variable gain amplifier circuit 52.

  The signal AD output from the variable gain amplifier circuit 51 is branched into two, one being input to the automatic gain control circuit 53 and the other being input to the subtraction circuit 61. The output of the subtraction circuit 61 is input to the automatic gain control circuit 53 as an amplitude reference level signal. A signal ADN output from the automatic gain control circuit 53 is input to the subtraction circuit 57 and the peak hold circuit 55.

  The signal BC output from the variable gain amplifier circuit 52 branches into two, one being input to the automatic gain control circuit 54 and the other being input to the adder circuit 62. The output of the adder circuit 62 is input to the automatic gain control circuit 54 as an amplitude reference level signal. The signal BCN output from the automatic gain control circuit 54 is input to the subtraction circuit 57 and the peak hold circuit 56.

  The output of the subtraction circuit 57 becomes a wobble signal W through the band pass filter 59. The output signal of the peak hold circuit 55 is applied to the plus side input terminal of the subtraction circuit 58, and the output signal of the peak hold circuit 56 is applied to the minus side input terminal. The output signal ΔREF of the subtraction circuit 58 is input to the subtraction circuit 61 and the addition circuit 62.

  The optical pickup 60 irradiates the reflection surface of the optical disc medium with laser light. The reflected light is received by a photodetector divided into four. Photovoltage conversion for converting the voltage level to the amount of light is performed, and the received reflected light is converted into four signals (signal A, signal B, signal C, and signal D) and output from the optical pickup 60.

  The signals A and D output from the optical pickup 60 are input to the variable gain amplifier circuit 51. The variable gain amplifier circuit 51 adds the signal A and the signal D and amplifies the signal with a predetermined gain. Therefore, the output of the variable gain amplifier circuit 51 is a signal AD indicating the result of the operation (A + D). Further, the signals B and C output from the optical pickup 60 are input to the variable gain amplifier circuit 52. The variable gain amplifier circuit 52 adds the signal B and the signal C and amplifies the signal with a predetermined gain. The output of the variable gain amplifier circuit 52 is a signal BC indicating the result of the calculation (B + C).

  The predetermined gain is set so that the output signal has an appropriate amplitude level according to the type of the optical disk medium (for example, CD-R or DVD + RW). That is, when the optical disk medium to be reproduced changes, a gain corresponding to the medium is selected. This gain adjustment is not for correcting variations in the optical pickup 60 itself and variations in the disk medium. Therefore, it is not possible to adjust the gain with respect to variations in output amplitude due to these effects. Further, the variable gain amplifier circuit 51 and the variable gain amplifier circuit 52 generally do not change the output frequency characteristics even when gain adjustment is performed.

  The signal AD output from the variable gain amplifier circuit 51 is connected to the input terminal I of the automatic gain control circuit 53 and also connected to the amplitude reference level input terminal R of the automatic gain control circuit 53 via the subtraction circuit 61. . The signal input to the amplitude reference level input terminal R determines the amplitude reference level of the amplitude of the output signal of the automatic gain control circuit 53. Therefore, the signal obtained by subtracting the offset ΔREF from the signal AD by the subtraction circuit 61 is used as a reference, and the automatic gain control circuit 53 performs gain control. That is, the signal AD is output from the automatic gain control circuit 53 with the amplitude adjusted by an offset amount ΔREF.

  Similarly, the signal BC output from the variable gain amplifier circuit 52 is input to the automatic gain control circuit 54, and the amplitude is adjusted. In this case, since the signal BC is input to the amplitude reference level input terminal R of the automatic gain control circuit 54 via the addition circuit 62, the output of the automatic gain control circuit 54 is different from the case of the automatic gain control circuit 53. It is adjusted in the opposite direction. That is, if the signal ΔREF is a positive signal, the automatic gain control circuit 53 is controlled to the suppression side, and the automatic gain control circuit 54 is controlled to the amplification side. When the signal ΔREF is negative, the automatic gain control circuit 53 is controlled to the amplification side, and the automatic gain control circuit 54 is controlled to the suppression side.

  An example of the configuration of the automatic gain control circuits 53 and 54 is shown in FIG. The automatic gain control circuit includes a variable gain amplifier circuit (GCA) 71, a high pass filter (HPF) 72, a peak detection circuit (DET) 73, and a comparison circuit (CMP) 74. The variable gain amplifier circuit 71 amplifies the input signal I and outputs an output signal OUT. The gain at this time is controlled by a control signal output from the comparison circuit 74. The output signal OUT becomes an output of the automatic gain control circuit and is input to the high-pass filter 72. The high-pass filter 72 extracts the RF signal component of the input signal OUT. The extracted RF signal component is output to the peak detection circuit 73. The peak detection circuit 73 detects the peak value of the input RF signal component. The detected peak value is output to the comparison circuit 74. The comparison circuit 74 receives the detected peak value and the amplitude reference level signal R. The comparison circuit 74 compares the input peak value with the amplitude reference level signal R and outputs the comparison result to the variable gain amplification circuit 71. If the peak value is larger as a result of the comparison, the variable gain amplifier circuit 71 decreases the gain. As a result of the comparison, if the amplitude reference level signal is larger, the variable gain amplifier circuit 71 increases the gain. In this way, the amplitude of the output of the variable gain amplifier circuit 71 is matched with the amplitude reference level signal.

  The output signal ADN of the automatic gain control circuit 53 that operates in this way is input to the subtraction circuit 57 and the peak hold circuit 55. The output signal BCN of the automatic gain control circuit 54 is input to the peak hold circuit 56 and the subtraction circuit 57. The peak hold circuit 55 holds the peak value of the signal ADN, and the peak hold circuit 56 holds the peak value of the signal BCN. Each of the peak values is input to the subtraction circuit 58.

  The subtraction circuit 58 subtracts the peak value of the signal BCN from the peak value of the signal ADN, and outputs a signal ΔREF indicating the subtraction result. The signal ΔREF is supplied to the subtraction circuit 61 and the addition circuit 62.

  If the level of the signal ΔREF is a positive value, the gain of the automatic gain control circuit 53 is lowered and the gain of the automatic gain control circuit 54 is raised. Therefore, the output signal ADN of the automatic gain control circuit 53 is small, the output signal BCN of the automatic gain control circuit 54 is large, and the signal ΔREF is controlled to approach zero. When the signal ΔREF has a negative polarity, the gain of the automatic gain control circuit 53 is increased and the gain of the automatic gain control circuit 54 is decreased. Therefore, the output signal ADN of the automatic gain control circuit 53 is large, the output signal BCN of the automatic gain control circuit 54 is small, and the signal ΔREF is controlled to approach zero. That is, the automatic gain control circuit 53 and the automatic gain control circuit 54 are controlled so that the level of the signal ΔREF is 0 or significantly reduced, and the respective output signals become substantially the same level.

  Thus, the automatic gain control circuits 53 and 54 are controlled by the signal ΔREF, while the subtraction circuit 57 subtracts the signal BCN from the input signal ADN. That is, (A + D) − (B + C) is calculated. Since the RF signal component is controlled to have the same amplitude by the automatic gain control circuits 53 and 54, only the wobble signal component from which the RF signal component disappears is extracted by this calculation. In theory, the RF signal component disappears completely by this calculation. However, for example, the RF signal component does not disappear completely due to the influence of variations in the characteristics of the amplifier circuit, variations in the characteristics of the optical pickup itself, gain variations in the subtraction circuit 57, and the like. Therefore, a wobble signal W is generated by extracting a signal in the frequency band of the wobble signal component by using a band pass filter (BPF: Band Pass Filter) 59.

  The band-pass filter 59 needs a band that attenuates the RF signal component and passes only the wobble signal component. Since the signal band of the RF signal component is about 10 times the frequency of the wobble signal component, a steep cutoff characteristic is required. In order to obtain a steep cut-off characteristic, the filter is higher order. Since a high-order filter has a large circuit area, the cost of the IC chip increases when mounted on an IC (Integrated Circuit).

  Further, as shown in FIG. 7, the frequency characteristics may be a problem. The RF signal component includes signals of a slow frequency band (11T) and a fast frequency band (3T). When the automatic gain control circuit is to be operated with the gain G1, the gain G1 is obtained for the 11T signal (frequency f11T) and 3T signal (frequency f3T), which are signals in the band of the frequency fc1 or lower. For a signal of frequency fc1 or higher, gain G1 is not obtained and the amplitude does not match the reference level.

  Normally, the automatic gain control circuit adjusts the output amplitude to be constant with respect to the 11T signal in the slow frequency band. When the amplitudes of the signals A, B, C, and D vary due to variations in the optical pickup itself and variations in the optical disk medium, the amplitudes of the output signals AD and BC of the variable gain amplification circuits 51 and 52 also vary. For example, it is assumed that the AGC 53 that amplifies the signal AD operates with a gain G1 and the amplitude matches the reference level. When the signal BC is very small with respect to the signal AD, the gain of the automatic gain control circuit 54 that amplifies the signal BC is increased to G2, and the amplitude of the output signal BCN is adjusted to the reference level. At this time, when the RF signal component included in the signal BCN and the RF signal component included in the signal ADN are balanced, the signal ΔREF should be “0”. However, when the automatic gain control circuit 54 is operated at the gain G2, a flat amplification characteristic can be obtained only up to the frequency fc2.

  As described above, when the amplification circuit of the automatic gain control circuit does not have a sufficiently wide frequency characteristic, a sufficient gain cannot be obtained with the 3T signal (frequency f3T) on the B + C side, and the amplitude becomes small. That is, in the output of the subtraction circuit 57 that subtracts the outputs of the automatic gain control circuits 53 and 54, as shown in FIG. 8, the 11T signal component disappears as a result of the subtraction, but the 3T signal component does not disappear even if the subtraction is performed. Remain in. The state is shown in FIG. FIG. 8 (1) shows the waveform of the signal AD, FIG. 8 (2) shows the waveform of the signal BC, and FIG. 8 (3) shows the difference between the signal AD and the signal BC. The left side shows an 11T signal in a low frequency band, and the right side shows a 3T signal in a high frequency band. As shown in FIG. 8 (3), the RF signal component is removed from the 11T signal, and the TF signal component remains from the 3T signal. As described above, the wobble signal component cannot be extracted well, and malfunction may occur during reproduction and recording of the disc.

  Further, even when (A + D) − (B + C) cannot be calculated accurately due to variations in characteristics of the subtracting circuit 57 itself, it is not possible to extract a signal that does not include an RF signal component, that is, a signal that includes only a wobble signal component. Therefore, since an RF signal component remains in the output of the subtracting circuit 57, a band pass filter 59 is required after the subtracting circuit 57.

JP 2002-367180 A JP 2003-338041 A

  An object of the present invention is to provide an optical disk reproducing apparatus with high wobble detection accuracy.

  Another object of the present invention is to provide an optical disk reproducing apparatus with few malfunctions.

  Another object of the present invention is to provide a low-cost optical disk reproducing apparatus.

  Hereinafter, means for solving the problem will be described using the numbers and symbols used in [Best Mode for Carrying Out the Invention]. These numbers and symbols are added to clarify the correspondence between the description of [Claims] and [Best Mode for Carrying Out the Invention]. However, these numbers and symbols should not be used for the interpretation of the technical scope of the invention described in [Claims].

  In an aspect of the present invention, the optical disc reproducing apparatus includes an amplifying unit (1/2/3/4), an extracting unit (5), and a control signal generating unit (6/7/8) with high accuracy. The wobble signal (W) is generated. The amplifying unit (1/2/3/4) amplifies the signal output from the optical pickup (9) so as to have a predetermined amplitude. The extraction unit (5) generates a wobble signal (W) based on the signal output from the amplification unit (1/2/3/4). The control signal generation unit (6/7/8) is configured to generate the amplification unit (1/2/3/4) based on the RF signal component remaining in the wobble signal (W) output from the extraction unit (5). A control signal for controlling is generated.

  In the optical disk reproducing apparatus of the present invention, the amplification unit (1/2/3/4) includes a first amplification unit (1/3 or 2/4) and a second amplification unit (2/4 or 1/3). Is provided. The first amplifying unit (1/3 or 2/4) calculates and amplifies two of the signals output from the optical pickup (9), and outputs a first signal (ADN or BCN). The second amplifying unit (2/4 or 1/3) calculates and amplifies the other two signals out of the signals output from the optical pickup (9), and outputs the second signal (BCN or ADN). To do. The extraction unit (5) includes a subtracter (5) that calculates a difference between the first signal (ADN or BCN) and the second signal (BCN or ADN). The subtracter (5) outputs the wobble signal (W) based on the difference.

  In the optical disk reproducing apparatus of the present invention, the control signal generator (6/7/8) includes a high-pass filter (6). The high-pass filter (6) extracts the remaining RF signal component (ΔR) included in the wobble signal. The control signal generator (6/7/8) generates the control signal based on the amplitude of the remaining RF signal component (ΔR).

  In the optical disk reproducing apparatus of the present invention, the control signal generation unit (6/7/8) includes a level detection circuit (7) and a control unit (8). The level detection circuit (7) detects the amplitude level of the remaining RF signal component. The control unit (8) generates the control signal based on the amplitude level (ΔRpp) detected by the level detection circuit (7). The control unit (8) generates the control signal so that the amplitude level (ΔRpp) is equal to or less than a predetermined threshold value.

  The first amplifying unit (1/3 or 2/4) includes a first automatic gain control amplifier (3 or 4). The first automatic gain control amplifier (3 or 4) automatically controls the gain so that the amplitude of the RF signal component of the output signal (ADN or BCN) becomes the first amplitude reference level. The first amplitude reference level is specified by a first amplitude control signal (REFa or REFb) included in the control signal. The second amplifying unit (2/4 or 1/3) includes a second automatic gain control amplifier (4 or 3). The second automatic gain control amplifier (4 or 3) automatically controls the gain so that the amplitude of the RF signal component of the output signal (BCN or ADN) becomes the second amplitude reference level. The second amplitude reference level is specified by a second amplitude control signal (REFb or REFa) included in the control signal. The control unit (8) generates the first amplitude control signal (REFa or REFb) and the second amplitude control signal (REFb or REFa) so that the amplitude level (ΔRpp) is less than or equal to a predetermined threshold. .

  In the optical disk reproducing apparatus of the present invention, the first amplifying unit (1/3 or 2/4) includes a first gain control amplifier (1 or 2). The gain of the first gain control amplifier (1 or 2) is controlled by a first gain control signal (Ga or Gb) included in the control signal. The second amplification unit (2/4 or 1/3) includes a second gain control amplifier (2 or 1). The gain of the second gain control amplifier (2 or 1) is controlled by a second gain control signal (Gb or Ga) included in the control signal. The control unit (8) generates the first gain control signal (Ga or Gb) and the second gain control signal (Gb or Ga) so that the amplitude level (ΔRpp) is a predetermined threshold value or less. .

  In the optical disk reproducing apparatus of the present invention, the control signal includes an automatic gain control function of the first automatic gain control amplifier (3 or 4) and an automatic gain control function of the second automatic gain control amplifier (4 or 3). An automatic gain control stop signal (GCa, GCb) to be stopped is included. The control unit (8) includes an automatic gain control function of the first automatic gain control amplifier (3 or 4) and the second automatic gain control amplifier (4 or 3) according to the automatic gain control stop signal (GCa, GCb). Stop automatic gain control function. The control unit (8) is configured to gain the first gain control amplifier (1 or 2) so that an output signal (AD or BC) of the first gain control amplifier (1 or 2) is within a predetermined level range. Adjust. Next, the control unit (8) increases the gain of the second gain control amplifier (2 or 1) so that the amplitude level (ΔRpp) detected by the level detection circuit (7) is equal to or lower than a predetermined threshold. adjust.

  In the optical disk reproducing apparatus of the present invention, the predetermined level range in which the output signal (AD or BC) of the first gain control amplifier (1 or 2) is controlled is the first automatic gain control amplifier (3 or 4). The frequency characteristic of the automatic gain control function of the second automatic gain control amplifier (4 or 3) is set to be flat in the frequency band of the wobble signal.

  In the optical disk reproducing apparatus of the present invention, the high-pass filter (6) switches a cutoff frequency according to the frequency of the wobble signal (W).

  In the optical disk reproducing apparatus of the present invention, the amplitude level detector (7) includes a peak hold circuit (11), a bottom hold circuit (12), and a subtractor (13), and the high-pass filter (6). The amplitude level (ΔRpp) of the output (ΔR) is detected. The peak hold circuit (11) detects a positive peak value. The bottom hold circuit (12) detects a negative peak value. The subtracter (13) subtracts the bottom value output from the bottom hold circuit (12) from the peak value output from the peak hold circuit (11).

  In another aspect of the present invention, the wobble signal detection method includes a first amplification step, a second amplification step, an extraction step, a high frequency extraction step, and an amplification control step. In the first amplification step, two signals (A / D or B / C) out of signals output from the optical pickup (9) are calculated and amplified. In the second amplification step, the other two signals (B / C or A / D) out of the signals output from the optical pickup (9) are calculated and amplified. The extraction step obtains a difference between the first signal (ADN or BCN) generated in the first amplification step and the second signal (BCN or ADN) generated in the second amplification step, and based on the difference To output a wobble signal (W). In the high frequency extraction step, an RF signal component (ΔR) included in the wobble signal (W) is extracted. In the amplification control step, the first amplification step and the second step are controlled so that the RF signal component (ΔR) extracted in the high frequency extraction step is equal to or less than a predetermined threshold.

  In the wobble signal detection method of the present invention, the first amplification step includes a first gain control amplification step and a first automatic gain control step. In the first gain control amplification step, the gain is specified by the amplification control step and the signal is amplified. In the first automatic gain control step, the output amplitude is designated by the amplification control step and the signal is amplified. The second amplification step includes a second gain control amplification step and a second automatic gain control step. In the second gain control amplification step, the gain is specified by the amplification control step and the signal is amplified. In the second automatic gain control step, the output amplitude is designated by the amplification control step and the signal is amplified. The amplification control step sets gains of the first gain control amplification step and the second gain control amplification step, and then sets output amplitudes of the first automatic gain control step and the second automatic gain control step. To do.

  In the wobble signal detection method of the present invention, the amplification control step includes an automatic gain control function stop step. The automatic gain control function stop step stops the automatic gain control function of the first automatic gain control step and the automatic gain control function of the second automatic gain control step. The amplification control step adjusts the gains of the first gain control amplification step and the second gain control amplification step by stopping the automatic gain control function by the automatic gain control function stop step.

  In the wobble signal detection method of the present invention, the amplification control step includes an automatic gain control function of the first automatic gain control step and an automatic gain control function of the second automatic gain control step by the automatic gain control function stop step. Stop. With the automatic gain control function stopped, the gain of the first gain control amplification step is adjusted so that the output signal of the first gain control amplification step falls within a predetermined level range. After the gain of the first gain control amplification step can be adjusted, the gain of the second gain control amplification step is adjusted so that the RF signal component extracted in the high frequency extraction step is less than or equal to a predetermined threshold value.

  In the wobble signal detection method of the present invention, the predetermined level range in which the output signal of the first gain control amplification step is controlled is an automatic gain control function of the first automatic gain control step and the second automatic gain control step. Are set to be flat in the frequency band of the wobble signal.

  According to the present invention, a wobble signal can be extracted with high accuracy from a signal output from an optical pickup, and an optical disc reproducing apparatus with high wobble detection accuracy can be provided.

  In addition, according to the present invention, since the wobble signal can be extracted with high accuracy, it is possible to provide an optical disk reproducing apparatus with few malfunctions during disk reproduction and recording.

  Furthermore, according to the present invention, a bandpass filter that has been conventionally required can be eliminated or a low-order bandpass filter can be obtained, and the circuit area can be reduced. be able to.

  The best mode for carrying out the present invention will be described with reference to the drawings. First, extraction of a wobble signal recorded on an optical disk medium will be described again. The optical pickup irradiates the reflection surface of the optical disk medium with laser light. The reflected light is received by a photodetector divided into four. A photodiode is usually used for the photodetector. Photovoltage conversion is performed to a voltage level corresponding to the amount of light received, and four signals (signal A, signal B, signal C, and signal D) are output from the optical pickup. The four signals include an RF signal component (signal R) and a wobble signal component (signal W), which are data signals. The RF signals all have the same amplitude and the same phase, but the wobble signal is a signal having the same amplitude and opposite phase in the signals A and D and the signals B and C. Therefore, it is expressed as the following formula.

A = R + W (5)
B = R−W (6)
C = R−W (7)
D = R + W (8)
Ideally, it can be seen that only the wobble signal W can be extracted by calculating (A + D) − (B + C) = 4W as obtained from these four equations. However, the RF signal component remains in the wobble signal W due to variations in the characteristics of each circuit. A circuit for reducing the residual RF signal component and extracting only the wobble signal with high accuracy will be described below.

  FIG. 1 is a block diagram showing a configuration of a circuit for extracting a wobble signal of an optical disk reproducing apparatus according to an embodiment of the present invention. The circuit for extracting the wobble signal of the optical disk reproducing apparatus includes an optical pickup 9, variable gain amplifier circuits (GCAs) 1 and 2, automatic gain control circuits (AGC) 3 and 4, a subtracting circuit 5, and a high-pass filter. (HPF: High Pass Filter) 6, a level detection circuit 7, and a system controller 8 are provided.

  Of the signals output from the optical pickup 9, the signal A and the signal D are input to the variable gain amplifier circuit 1, and the signal B and the signal C are input to the variable gain amplifier circuit 2. The output signal AD of the variable gain amplifier circuit 1 is input to the automatic gain control circuit 3, and the output signal BC of the variable gain amplifier circuit 2 is input to the automatic gain control circuit 4. The output signal ADN of the automatic gain control circuit 3 and the output signal BCN of the automatic gain control circuit 4 are input to the subtraction circuit 5. The output of the subtracting circuit 5 is output as a wobble signal W to other circuits of the optical disk reproducing apparatus and also input to the high-pass filter 6. The output signal ΔR of the high-pass filter 6 is input to the level detection circuit 7. The output signal ΔRpp of the level detection circuit 7 is input to the system controller 8. The system controller 8 outputs a control signal Ga to the variable gain amplifier circuit 1 and a control signal Gb to the variable gain amplifier circuit 2. Further, the amplitude reference level signal REFa and the control signal GCa are output from the system controller 8 to the automatic gain control circuit 3, and the amplitude reference level signal REFb and the control signal GCb are output to the control signal automatic gain control circuit 4.

  The optical pickup 9 irradiates the reflection surface of the optical disk medium with laser light. The reflected light is received by a photodetector divided into four. Photovoltage conversion is performed to a voltage level corresponding to the received light quantity, and four signals (signal A, signal B, signal C, and signal D) are output from the optical pickup 9.

  The variable gain amplifying circuits (GCAs) 1 and 2 add the input signals A and D and the signals B and C, respectively, and amplify them with a predetermined gain. The predetermined gain is set so that the output signal has an appropriate amplitude level according to the type of the optical disk medium (for example, CD-R or DVD + RW). That is, when the optical disk medium to be reproduced changes, a gain corresponding to the medium is selected. In addition, gain control for correcting variations in circuit characteristics (gain) between the variable gain amplifier circuit 1 and the variable gain amplifier circuit 2 is also possible. These gains are set based on control signals Ga and Gb from the system controller 8. The output of the variable gain amplifier circuit 1 is a signal AD indicating the result of the operation (A + D), and the output of the variable gain amplifier circuit 2 is a signal BC indicating the result of the operation (B + C). The signal AD is input to the automatic gain control circuit 3, and the signal BC is input to the automatic gain control circuit 4.

  The automatic gain control circuits 3 and 4 amplify (or attenuate) the signal applied to the input terminal I so that the amplitude level is applied to the amplitude reference level input terminal R. The amplitude reference level is given from the system controller 8 as signals REFa and REFb. The automatic gain control circuits 3 and 4 have a function of temporarily stopping the operation of automatically controlling the gain and setting the amplitude of the output signal to the reference level. In other words, the automatic gain control circuits 3 and 4 operate as a variable gain amplifier circuit having a constant gain when operating in the fixed gain mode. The fixed gain mode is set based on control signals GCa and GCb sent from the system controller 8. That is, the circuit can finely adjust the output amplitude. The gain of the circuit in the fixed gain mode is preferably instructed from the system controller 8. The signal ADN output from the automatic gain control circuit 3 and the signal BCN output from the automatic gain control circuit 4 are input to the subtraction circuit 5.

  The subtraction circuit 5 subtracts the signal BCN from the signal ADN and outputs it as a wobble signal W. Since the signal ADN is a signal indicating the result of the operation (A + D) and the signal BCN is a signal indicating the result of the operation (B + C), the signal W is a signal indicating the result of the operation (A + D) − (B + C). Become. The signal AD and the signal BC include RF signal components in the same phase and the same level, and the RF signal components are removed by calculating the difference between them. The signal W is supplied as a wobble signal to each part of the optical disk reproducing apparatus. Ideally, the RF signal component is not included in the signal W, but the RF signal component may remain in the signal W due to variations in circuit characteristics. When the RF signal component remains in the signal W, the signal W is input to the high-pass filter 6 and the residual RF signal component is extracted. Feedback control is performed so that the extracted residual RF signal component is minimized.

  The high-pass filter 6 extracts an RF signal component included in the signal W. Therefore, the cut-off frequency of the high-pass filter 6 is set so that the wobble signal component can be cut off. The frequency band of the wobble signal component varies greatly depending on the type of optical disk medium to be recorded and the rotational speed of the optical disk medium. Therefore, the cut-off frequency of the high-pass filter 6 is configured to be changeable according to the rotational speed and the type of medium. The cut-off frequency is preferably switched based on a control signal from the system controller 8 or a control circuit other than the system controller. The residual component signal ΔR of the RF signal extracted by the high-pass filter 6 is input to the level detection circuit 7.

  The level detection circuit 7 measures the amplitude of the signal ΔR input from the high-pass filter 6. For example, as shown in FIG. 2, the signal level is detected by a P-P value (Peak-to-Peak Value). The level detection circuit 7 includes a peak hold circuit (P / H) 11, a bottom hold circuit (B / H) 12, and a subtraction circuit 13. The peak value of the signal ΔR input to the level detection circuit 7 is held by the peak hold circuit 11, and the bottom value is held by the bottom hold circuit 12. The subtraction circuit 13 subtracts the bottom value output from the bottom hold circuit from the peak value output from the peak hold circuit 11 to obtain the amplitude level ΔRpp of the signal ΔR. The amplitude level ΔRpp is sent to the system controller 8.

  The system controller 8 generates amplitude reference level signals REFa and REFb based on the input amplitude level ΔRpp, and controls the automatic gain control circuits 3 and 4 so that the amplitude level ΔRpp is not more than a predetermined threshold value. Further, the operation mode (fixed gain mode) is designated for the automatic gain control circuits 3 and 4 by the control signals GCa and GCb. In the case of the fixed gain mode, the system controller 8 instructs the gains of the automatic gain control circuits 3 and 4 by the control signals GCa and GCb. Further, the system controller 8 instructs the variable gain amplifying circuits 1 and 2 with an appropriate gain according to the type of the optical disk medium by the control signals Ga and Gb. Further, the system controller 8 adjusts and corrects variations in gain characteristics between the variable gain amplifier circuit 1 and the variable gain amplifier circuit 2 by using the control signals Ga and Gb.

  Next, the operation of the present embodiment will be described. The automatic gain control circuits 3 and 4 are set to the fixed gain mode, the subtraction circuit 5 calculates (A + D) − (B + C), and the output is input to the high-pass filter 6. This high-pass filter 6 can remove the wobble signal component and finally extract only the RF signal component to be erased.

  The RF signal component is input to the level detection circuit 7 and the amplitude level of the RF signal component that has passed through the high-pass filter 6 is measured. If this value is minimum (approximately 0 level), the amplitude levels of the RF signal components of the output signals of the automatic gain control circuits 3 and 4 are the same. Here, since the automatic gain control circuits 3 and 4 are set to the fixed gain mode, the amplitude levels of the RF signal components of the output signals of the variable gain amplifier circuits 1 and 2 are substantially the same. That is, when the output value of the level detection circuit 7 is minimized, the amplitude levels of the RF signal components of the output signals of the variable gain amplifier circuits 1 and 2 are substantially the same, and the input of the automatic gain control circuits 3 and 4 The amplitude values (A + D and B + C) are approximately the same RF signal amplitude level. Therefore, the automatic gain control circuits 3 and 4 at the time of AGC operation operate with substantially the same gain, and the frequency characteristics of the mutual automatic gain control circuits are also the same, so that the RF signal component has the same amplitude level from 11T to 3T. It becomes possible to do. That is, the automatic gain control circuits 3 and 4 both operate with the gain G1 in FIG. 7 and have the same frequency characteristics, so that they operate stably.

  The automatic gain control circuits 3 and 4 are circuits in which the gain is controlled so that the output amplitude becomes a specified amplitude level. However, even if the same amplitude level is designated due to variations in circuit elements, a difference may occur in the output amplitude levels of the automatic gain control circuits 3 and 4. In this case, the RF signal component remains in the output of the subtracting circuit 5. Therefore, the output of the level detection circuit 7 is also measured when the automatic gain control circuits 3 and 4 are AGC-operated, and this value is automatically set so as to be below a predetermined threshold such as a minimum (approximately zero level) or an allowable maximum value. The output amplitude level of the gain control circuits 3 and 4 is adjusted. As the automatic gain control circuit capable of changing the output amplitude level, for example, a circuit in which a threshold voltage for determining the output amplitude level is variable can be considered. As a result, the RF signal component is completely removed from the output of the subtraction circuit 5, and only the wobble signal component can be extracted.

  Next, the adjustment operation by the system controller 8 will be described with reference to FIGS. First, the system controller 8 sets the automatic gain control circuits 3 and 4 to the fixed gain mode. When the automatic gain control circuits 3 and 4 are in a normal amplifier state, the outputs of the variable gain amplifier circuits 1 and 2 are reflected in the amplitude level ΔRpp. In this state, as shown in FIG. 3, the gains of the variable gain amplifier circuits 1 and 2 are set, and the gain difference between the variable gain amplifier circuits 1 and 2 is corrected. When the gains of the variable gain amplifying circuits 1 and 2 are set, the system controller 8 returns the automatic gain control circuits 3 and 4 to the automatic gain control mode, and as shown in FIG. Adjust the amplitude.

  First, the gain setting of the variable gain amplifier circuits 1 and 2 will be described in detail. FIG. 3 is a flowchart showing the flow of the gain setting operation of the variable gain amplifier circuits 1 and 2. Here, the system controller 8 adjusts the gain of the variable gain amplifying circuits 1 and 2 so that the balance of the RF signal components included in the outputs of the variable gain amplifying circuits 1 and 2, that is, the amplitude level ΔRpp is equal to or less than the threshold Rth1.

  At the beginning of the setting operation, the system controller 8 performs initial setting. The system controller 8 sets the automatic gain control circuits 3 and 4 to a fixed gain mode with a predetermined gain. Further, the system controller 8 sets the gains of the variable gain amplifier circuits 1 and 2 to a value determined in advance according to the type of the optical disk medium. The threshold value Rth1 is set to a predetermined initial setting threshold value (step S200). At this time, the threshold value Rth1 is desirably about 50 mV.

  First, the system controller 8 takes in the amplitude level, which is the output of the level detection circuit 7, and sets the taken value as ΔRpp1. It is determined whether or not the amplitude level ΔRpp1 is equal to or less than a threshold value Rth1 (step S201). If the amplitude level ΔRpp1 is equal to or less than the threshold value Rth1, it is determined that the outputs of the variable gain amplifier circuits 1 and 2 are balanced, and the setting of the gains of the variable gain amplifier circuits 1 and 2 ends (step S201— NO).

  When the amplitude level ΔRpp1 exceeds the threshold value Rth1 (step S201—YES), the system controller 8 instructs the variable gain amplifier circuit 1 to increase the gain by a predetermined value by the control signal Ga (step S202).

  After the variable gain amplifier circuit 1 increases the gain, the system controller 8 captures the amplitude level, and sets the value of the captured amplitude level as ΔRpp2. It is determined whether or not the amplitude level ΔRpp2 is equal to or less than a threshold value Rth1 (step S203). If the amplitude level ΔRpp2 is equal to or less than the threshold value Rth1, it is determined that the RF signal components of the outputs of the variable gain amplifier circuits 1 and 2 are balanced, and the setting of the gains of the variable gain amplifier circuits 1 and 2 ends. (Step S203-NO).

  When the amplitude level ΔRpp2 exceeds the threshold value Rth1 (step S203—YES), the system controller 8 compares the previously acquired amplitude level ΔRpp1 with the amplitude level ΔRpp2 acquired after increasing the gain of the variable gain amplifier circuit 1. (Step S204). That is, the influence of the gain change of the variable gain amplifier circuit 1 on the amplitude level ΔRpp is examined. When the amplitude level ΔRpp1 is larger than the amplitude level ΔRpp2 (step S204—NO), the amplitude level ΔRpp is lowered by increasing the gain of the variable gain amplifier circuit 1. This means that there is a possibility that the amplitude level ΔRpp can be further reduced by further increasing the gain of the variable gain amplifier circuit 1. Therefore, returning to step S202, the gain of the variable gain amplifier circuit 1 is increased. If the amplitude level ΔRpp2 to be captured while this loop is repeated becomes smaller than the threshold value Rth1, the gain setting is terminated assuming that the outputs of the variable gain amplifying circuits 1 and 2 are balanced only by the gain setting of the variable gain amplifying circuit 1.

  If the amplitude level ΔRpp2 is greater than the amplitude level ΔRpp1 (step S204—YES), it can be seen that the amplitude level ΔRpp2 that is captured as the gain of the variable gain amplifier circuit 1 increases is increased. Therefore, the gain of the variable gain amplifier circuit 2 is adjusted without increasing the gain of the variable gain amplifier circuit 1 any more. The system controller 8 instructs the variable gain amplifier circuit 2 to increase the gain by a predetermined value by the control signal Gb (step S205).

  After the variable gain amplifier circuit 2 increases the gain, the system controller 8 captures the amplitude level and sets the value of the captured amplitude level as ΔRpp3. It is determined whether or not the amplitude level ΔRpp3 is equal to or less than a threshold value Rth1 (step S206). If the amplitude level ΔRpp3 is equal to or less than the threshold value Rth1, it is determined that the outputs of the variable gain amplifier circuits 1 and 2 are balanced, and the setting of the gains of the variable gain amplifier circuits 1 and 2 ends (step S206- NO).

  When the amplitude level ΔRpp3 exceeds the threshold value Rth1 (step S206—YES), the system controller 8 compares the previously acquired amplitude level ΔRpp1 with the amplitude level ΔRpp3 acquired after increasing the gain of the variable gain amplifier circuit 2. (Step S207). That is, the influence of the gain change of the variable gain amplifier circuit 2 on the amplitude level ΔRpp is examined. When the amplitude level ΔRpp1 is larger than the amplitude level ΔRpp3 (step S207—NO), the amplitude level ΔRpp is lowered by increasing the gain of the variable gain amplifier circuit 2. This means that there is a possibility that the amplitude level ΔRpp can be further reduced by further increasing the gain. Therefore, returning to step S205, the gain of the variable gain amplifier circuit 2 is increased. If the amplitude level ΔRpp3 to be captured while this loop is repeated becomes smaller than the threshold value Rth1, the outputs of the variable gain amplifier circuits 1 and 2 are balanced with the gain setting of the variable gain amplifier circuit 2, and the gain setting ends.

  If the amplitude level ΔRpp3 is greater than the amplitude level ΔRpp1 (step S207—YES), it can be seen that the amplitude level ΔRpp3 captured as the gain of the variable gain amplifier circuit 2 increases. That is, even if the gain of the variable gain amplifier circuit 1 is changed or the gain of the variable gain amplifier circuit 2 is changed, the amplitude level ΔRpp does not fall below a certain value. In order to adjust the gains of the variable gain amplifier circuits 1 and 2 so as to be the minimum value of the amplitude level ΔRpp, the gains of the variable gain amplifier circuits 1 and 2 are returned to the initial values, and the amplitude level threshold Rth1 is set to a predetermined value. (Step S208), the process returns to step S201 to repeat a series of operations. In this way, the balance of the outputs of the variable gain amplifier circuit 1 and the variable gain amplifier circuit 2 is adjusted.

  When the gain setting of the variable gain amplifier circuit 1 and the variable gain amplifier circuit 2 is completed, the system controller 8 returns the automatic gain control circuits 3 and 4 to the automatic gain control mode, that is, the operation of setting the output amplitude to a constant level. As shown in FIG. 4, the system controller 8 adjusts the amplitude reference level signals REFa and REFb in order to control the amplitude level. With reference to FIG. 4, the amplitude reference level setting of the automatic gain control circuits 3 and 4 will be described in detail.

  FIG. 4 is a flowchart showing the flow of the setting operation of the amplitude reference level of the automatic gain control circuits 3 and 4. The gains of the variable gain amplifier circuits 1 and 2 are set so that the output difference is minimized. Here, the system controller 8 controls the amplitude reference level of the automatic gain control circuits 3 and 4 so that the RF signal components of the outputs of the automatic gain control circuits 3 and 4 are balanced, that is, the amplitude level ΔRpp is equal to or less than the threshold value Rth2. Adjust.

  At the beginning of the setting operation, the system controller 8 performs initial setting. First, the system controller 8 sets the automatic gain control circuits 3 and 4 to the automatic gain control mode. The automatic gain control circuits 3 and 4 operate in the automatic gain control mode, and the gain is controlled such that the output amplitude becomes the amplitude reference level to which the output amplitude is given. The threshold value Rth2 is set to a predetermined initial setting threshold value (step S210).

  Next, the system controller 8 takes in the amplitude level, which is the output of the level detection circuit 7, and sets the taken value as ΔRpp1. It is determined whether or not the amplitude level ΔRpp1 is equal to or less than a threshold value Rth2 (step S211). If the amplitude level ΔRpp1 is equal to or less than the threshold value Rth2, it is determined that the RF signal components included in the outputs of the automatic gain control circuits 3 and 4 are balanced, and the amplitude reference level of the automatic gain control circuits 3 and 4 is set. Ends (step S211 -NO).

  When the amplitude level ΔRpp1 exceeds the threshold value Rth2 (step S211—YES), the system controller 8 increases the amplitude reference level signal REFa by a predetermined value in order to increase the output amplitude of the automatic gain control circuit 3 (step S212). .

  After the automatic gain control circuit 1 adjusts the output amplitude to the amplitude reference level, the system controller 8 captures the amplitude level ΔRpp and sets the captured value as ΔRpp2. It is determined whether or not the amplitude level ΔRpp2 is equal to or less than a threshold value Rth2 (step S213). If the amplitude level ΔRpp2 is equal to or less than the threshold value Rth2, it is determined that the RF signal components included in the outputs of the automatic gain control circuits 3 and 4 are balanced, and the amplitude reference level of the automatic gain control circuits 3 and 4 is set. Ends (step S213-NO).

  When the amplitude level ΔRpp2 exceeds the threshold value Rth2 (step S213—YES), the system controller 8 determines that the amplitude level ΔRpp1 previously acquired, the amplitude level ΔRpp2 acquired after increasing the amplitude reference level of the automatic gain control circuit 3, and Are compared (step S214). That is, the influence on the amplitude level ΔRpp given by the amplitude reference level change of the automatic gain control circuit 3 is examined. When the amplitude level ΔRpp1 is larger than the amplitude level ΔRpp2 (step S214—NO), the amplitude level ΔRpp is lowered by raising the amplitude reference level of the automatic gain control circuit 3. This means that there is a possibility that the amplitude level ΔRpp can be further reduced by further increasing the amplitude reference level of the automatic gain control circuit 3. Therefore, returning to step S212, the gain of the automatic gain control circuit 3 is increased. If the amplitude level ΔRpp2 to be captured while repeating this loop becomes smaller than the threshold value Rth2, the RF signal components included in the outputs of the automatic gain control circuits 3 and 4 are balanced only by setting the amplitude reference level of the automatic gain control circuit 3. As a result, the amplitude reference level setting is terminated.

  If the amplitude level ΔRpp2 is greater than the amplitude level ΔRpp1 (step S214—YES), it can be seen that the amplitude level ΔRpp2 captured as the amplitude reference level of the automatic gain control circuit 3 increases is increased. Accordingly, the amplitude reference level of the automatic gain control circuit 4 is adjusted without increasing the amplitude reference level of the automatic gain control circuit 3 any more. The system controller 8 increases the amplitude reference level signal REFb by a predetermined value (step S215).

  After raising the amplitude reference level of the automatic gain control circuit 4, the system controller 8 takes in the amplitude level ΔRpp and sets the value of the taken in amplitude level as ΔRpp3. It is determined whether the amplitude level ΔRpp3 is equal to or less than a threshold value Rth2 (step S216). If the amplitude level ΔRpp3 is less than or equal to the threshold value Rth2, it is determined that the RF signal components included in the outputs of the automatic gain control circuits 3 and 4 are balanced, and the amplitude reference level of the automatic gain control circuits 3 and 4 is set. Ends (step S216-NO).

  When the amplitude level ΔRpp3 exceeds the threshold value Rth2 (step S216-YES), the system controller 8 increases the amplitude level ΔRpp1 previously acquired and the amplitude level ΔRpp3 acquired after increasing the amplitude reference level of the automatic gain control circuit 4. Are compared (step S217). That is, the influence on the amplitude level ΔRpp given by the amplitude reference level change of the automatic gain control circuit 4 is examined. When the amplitude level ΔRpp1 is larger than the amplitude level ΔRpp3 (step S217—NO), the amplitude level ΔRpp is lowered by raising the amplitude reference level of the automatic gain control circuit 4. This means that there is a possibility that the amplitude level ΔRpp can be further reduced by further increasing the amplitude reference level. Therefore, returning to step S215, the amplitude reference level of the automatic gain control circuit 4 is increased. If the amplitude level ΔRpp3 to be captured while this loop is repeated becomes smaller than the threshold value Rth2, the RF signal components included in the outputs of the automatic gain control circuits 3 and 4 in the setting of the amplitude reference level of the AGC path 4 are assumed to be balanced. Finish setting the reference level.

  If the amplitude level ΔRpp3 is greater than the amplitude level ΔRpp1 (step S217—YES), it can be seen that the amplitude level ΔRpp3 captured as the amplitude reference level of the automatic gain control circuit 4 increases is increased. That is, even if the amplitude reference level of the automatic gain control circuit 3 is changed or the amplitude reference level of the automatic gain control circuit 4 is changed, the amplitude level ΔRpp does not fall below a certain value. In order to adjust the amplitude reference level of the automatic gain control circuits 3 and 4 so as to be the minimum value of the amplitude level ΔRpp, the amplitude reference level of the automatic gain control circuits 3 and 4 is returned to the initial value, and the amplitude level threshold Rth2 is further set. The value is raised by a predetermined value (step S218), and the process returns to step S211 to repeat a series of operations. In this way, the balance of the RF signal components included in the outputs of the automatic gain control circuit 3 and the automatic gain control circuit 4 is adjusted.

  In this way, by setting the gain of the variable gain amplifier circuits 1 and 2 and setting the amplitude reference level of the automatic gain control circuits 3 and 4, the RF signal component contained in the wobble signal W is minimized. Can do. Further, the gains of the variable gain amplifier circuits 1 and 2 are set so that the amplitudes of the input signals of the automatic gain control circuits 3 and 4 are substantially the same level. Therefore, since the frequency characteristics of the automatic gain control circuits 3 and 4 are almost the same, a phenomenon in which the gain differs depending on the frequency component of the input signal as shown in FIG. 8 does not occur.

  The gain setting of the variable gain amplifier circuit as shown in FIG. 3 and the amplitude reference level setting of the automatic gain control circuit as shown in FIG. 4 may be repeated, or the variable gain amplification shown in FIG. The variable gain amplifier circuit may be adjusted according to the gain setting of the circuit, and then only the amplitude reference level setting of the automatic gain control circuit shown in FIG. 4 may be repeated.

  Further, the threshold value Rth1 and the threshold value Rth2 may be the same or different values. Further, in the flowcharts shown in FIGS. 3 and 4, the gain and the amplitude reference level have been described only in one direction, but a method in which one is increased and the other is decreased may be used.

  Furthermore, in the present embodiment, it has been described that the threshold value Rth1 and the threshold value Rth2 are gradually increased from the minimum value in order to increase the accuracy of the wobble signal. It is also possible to control so that the threshold value Rth1 and the threshold value Rth2 are gradually reduced from the maximum allowable value. This makes it possible to speed up convergence when the variation of each circuit is large. Note that if the gain setting of the variable gain amplifier circuit and the amplitude reference level setting of the automatic gain control circuit do not converge even if the threshold value Rth1 and the threshold value Rth2 are the maximum allowable values, the exception processing may be performed. Needless to say.

  As described above, the high-pass filter 6 that extracts the RF signal component is added to the subsequent stage of the subtraction circuit 5 that performs the operation (A + D) − (B + C). A feedback loop is formed to adjust the gain of the variable gain amplifier circuit and the amplitude of the automatic gain control circuit so that the amplitude value of the extracted RF signal component is minimized (approximately 0 level). By adding such a feedback loop, it is possible to extract a wobble signal component having no RF signal component, and it is possible to perform stable reproduction and recording of the optical disc. In the case of the conventional circuit configuration shown in FIG. 5, the subtraction circuit 57 is arranged outside the feedback loop that controls the amplitude, and thus the characteristics of the subtraction circuit 57 cannot be corrected. As shown in FIG. 1, in the present invention, feedback control is performed so as to remove the RF signal component included in the target wobble signal W, so that the wobble signal component can be extracted with high accuracy.

  That is, since a feedback loop is formed including the subtracting circuit 5, it is possible to extract the wobble signal component with high accuracy even if the subtracting circuit 5 has variations in characteristics.

  Further, the frequency characteristics of the automatic gain control circuits 3 and 4 can be matched by matching the amplitude levels of the RF signal components of the outputs of the variable gain amplifier circuits 1 and 2. Therefore, the dependence of the frequency characteristics of the automatic gain control circuit can be reduced, and the wobble signal component from which the RF signal component is removed can be extracted.

  Furthermore, since it becomes possible to extract the wobble signal component with high accuracy, it is possible to remove the band-pass filter 59 that has been necessary in the past, and the chip area can be reduced. Therefore, the cost can be reduced.

It is a block diagram which shows the structure of the circuit which extracts the wobble signal of the optical disk reproducing | regenerating apparatus concerning embodiment of this invention. It is a block diagram which shows the structure of the level detection circuit which concerns on embodiment of this invention. It is a flowchart which shows the flow of the gain setting operation | movement of the variable gain amplifier circuit which concerns on embodiment of this invention. It is a flowchart which shows the flow of the amplitude reference level setting operation | movement of the automatic gain control circuit which concerns on embodiment of this invention. It is a block diagram which shows the structure of the circuit which extracts the wobble signal of the conventional optical disk reproducing | regenerating apparatus. It is a block diagram which shows the structure of an automatic gain control circuit. It is a figure explaining the frequency characteristic of an automatic gain control circuit. It is a figure which shows the example of a waveform.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2 Variable gain amplifier circuit 3, 4 Automatic gain control circuit 5 Subtraction circuit 6 High pass filter 7 Amplitude level detection circuit 8 System controller 9 Optical pick-up 11 Peak hold circuit 12 Bottom hold circuit 13 Subtraction circuit 51, 52 Variable gain amplification Circuits 53 and 54 Automatic gain control circuits 55 and 56 Peak hold circuits 57 and 58 Subtraction circuit 59 Band pass filter 60 Optical pickup 71 Variable gain amplifier 74 Comparison circuit 73 Peak detection circuit 72 High pass filter

Claims (15)

An amplifying unit for amplifying a signal output from the optical pickup so as to have a predetermined amplitude;
An extraction unit that generates a wobble signal based on a signal output from the amplification unit;
A control signal generation unit that generates a control signal for controlling the amplification unit based on an RF signal component remaining in the wobble signal output from the extraction unit;
An optical disk reproducing apparatus that generates the wobble signal with high accuracy. The amplification unit is
A first amplifying unit that computes and amplifies two of the signals output from the optical pickup and outputs a first signal;
A second amplifying unit that computes and amplifies the other two signals of the signal output from the optical pickup and outputs a second signal;
The extraction unit includes a subtractor for obtaining a difference between the first signal and the second signal,
The optical disc reproducing apparatus according to claim 1, wherein the subtractor outputs the wobble signal based on the difference. The control signal generation unit includes a high-pass filter that extracts the remaining RF signal component included in the wobble signal,
The optical disk reproducing apparatus according to claim 1, wherein the control signal is generated based on an amplitude of the remaining RF signal component. The control signal generator is
A level detection circuit for detecting the amplitude level of the remaining RF signal component;
A control unit that generates the control signal based on the amplitude level detected by the level detection circuit,
The optical disc reproducing apparatus according to any one of claims 1 to 3, wherein the control unit generates the control signal so that the amplitude level is equal to or less than a predetermined threshold value. The first amplifying unit automatically controls the gain so that the amplitude of the RF signal component of the output signal becomes a first amplitude reference level specified by the first amplitude control signal included in the control signal. With one automatic gain control amplifier,
The second amplifying unit automatically controls the gain so that the amplitude of the RF signal component of the output signal becomes a second amplitude reference level specified by the second amplitude control signal included in the control signal. With two automatic gain control amplifiers,
The optical disk reproducing apparatus according to claim 4, wherein the control unit generates the first amplitude control signal and the second amplitude control signal so that the amplitude level is equal to or less than a predetermined threshold value. The first amplifying unit includes a first gain control amplifier whose gain is controlled by a first gain control signal included in the control signal,
The second amplifying unit includes a second gain control amplifier whose gain is controlled by a second gain control signal included in the control signal,
The optical disc reproducing apparatus according to claim 4 or 5, wherein the control unit generates the first gain control signal and the second gain control signal so that the amplitude level is equal to or less than a predetermined threshold value. The control signal includes an automatic gain control stop signal for stopping an automatic gain control function of the first automatic gain control amplifier and an automatic gain control function of the second automatic gain control amplifier,
The controller is
Stopping the automatic gain control function of the first automatic gain control amplifier and the automatic gain control function of the second automatic gain control amplifier by the automatic gain control stop signal;
Adjusting the gain of the first gain control amplifier so that the output signal of the first gain control amplifier is within a predetermined level range;
The optical disk reproducing apparatus according to claim 6, wherein the gain of the second gain control amplifier is adjusted so that the amplitude level detected by the level detection circuit is equal to or lower than a predetermined threshold value. The predetermined level range in which the output signal of the first gain control amplifier is controlled is that the frequency characteristic of the automatic gain control function of the first automatic gain control amplifier and the second automatic gain control amplifier is the frequency band of the wobble signal. The optical disk reproducing apparatus according to claim 7, wherein the optical disk reproducing apparatus is set so as to be flat. The optical disk reproducing apparatus according to any one of claims 3 to 8, wherein the high-pass filter switches a cutoff frequency according to a frequency of the wobble signal. The amplitude level detector
A peak hold circuit for detecting a positive peak value;
A bottom hold circuit that detects negative peak values;
A subtractor that subtracts a bottom value output from the bottom hold circuit from a peak value output from the peak hold circuit;
The optical disk reproducing apparatus according to any one of claims 4 to 9, wherein an amplitude level of an output of the high-pass filter is detected. A first amplification step of calculating and amplifying two signals out of signals output from the optical pickup;
A second amplification step of computing and amplifying the other two signals out of the signals output from the optical pickup;
An extraction step of obtaining a difference between the first signal generated in the first amplification step and the second signal generated in the second amplification step, and outputting a wobble signal based on the difference;
A high-frequency extraction step of extracting an RF signal component included in the wobble signal;
A wobble signal detection method comprising: the first amplification step and an amplification control step for controlling the second step so that the RF signal component extracted in the high-frequency extraction step is less than or equal to a predetermined threshold value. The first amplification step includes
A first gain control amplification step for amplifying a signal with a gain designated by the amplification control step;
A first automatic gain control step for amplifying a signal with an output amplitude specified by the amplification control step,
The second amplification step includes
A second gain control amplification step in which a gain is specified by the amplification control step and a signal is amplified;
A second automatic gain control step for amplifying a signal with an output amplitude specified by the amplification control step,
The amplification control step sets gains of the first gain control amplification step and the second gain control amplification step, and then sets output amplitudes of the first automatic gain control step and the second automatic gain control step. The wobble signal detection method according to claim 11. The amplification control step includes an automatic gain control function stop step,
The automatic gain control function stop step stops the automatic gain control function of the first automatic gain control step and the automatic gain control function of the second automatic gain control step,
The wobble according to claim 12, wherein the amplification control step adjusts the gain of the first gain control amplification step and the second gain control amplification step by stopping the automatic gain control function by the automatic gain control function stop step. Signal detection method. The amplification control step includes
Stopping the automatic gain control function of the first automatic gain control step and the automatic gain control function of the second automatic gain control step by the automatic gain control function stopping step;
Adjusting the gain of the first gain control amplification step so that the output signal of the first gain control amplification step is within a predetermined level range;
The wobble signal detection method according to claim 13, wherein the gain of the second gain control amplification step is adjusted so that the RF signal component extracted in the high frequency extraction step is equal to or less than a predetermined threshold. The predetermined level range in which the output signal of the first gain control amplification step is controlled is that the frequency characteristic of the automatic gain control function of the first automatic gain control step and the second automatic gain control step is the frequency of the wobble signal. The wobble signal detection method according to claim 14, wherein the wobble signal detection method is set to be flat in a band.

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