JP2005158108A - Wobble detector circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the variations between the circuits making variable control independently in an automatic variable gain control section in a wobble detector circuit which makes feedback control to reduce the amplitude difference between the two optical disk reproducing signals detected by the optical detector. <P>SOLUTION: A control signal is generated in a wobble detector circuit to control the gain of the variable gain amplifiers 3 and 4 by using a comparator 10, a low-pass filter, and a control buffer 17 based on each of the rectified signal of the reproduced optical disk signals 1 and 2 which are the output data of the variable gain amplifiers 3 and 4. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an information recording / reproducing technique for optically readable / writable optical disks, and in particular, wobbles a track in which land portions and groove portions are alternately formed on an information recording surface of an optical disk. The present invention relates to a circuit for detecting a wobble signal from an optical disk reproduction signal in an optical disk and a recording or reproducing apparatus for obtaining the position information of a track.

  Conventionally, Patent Document 1 discloses a wobble detection circuit that detects a wobble signal from an optical disc reproduction signal.

  FIG. 4 is an example of a conventional general wobble detection circuit diagram. In FIG. 4, 3 and 4 are variable gain devices that can change and output the amplitudes of the two optical disc reproduction signals 1 and 2 obtained from the photodetector based on the reflected light of the light applied to the optical disc. And 14 are rectifiers for rectifying the optical disk reproduction signal variably output by the variable gain units 3 and 4, 10 and 11 are comparators for comparing the outputs of the rectifiers 13 and 14 with the reference voltage 12, and 7 and 8 are comparators. LPFs 5 and 6 that integrate the AC components calculated and compared by 10 and 11 into DC components are compared with the reference voltage 9 for the DC components output from the LPFs 7 and 8, respectively. The control buffer 15 controls the output amplitude of the optical disk to be equal to each other. The optical disk reproduction signal variably output by one variable gain device 3 and the light variably output by the other variable gain device 4 Disc is a reproduction signal and a subtractor for subtracting the. The variable gain device 3, the rectifier 13, the comparator 10, the LPF 7, and the control buffer 5 constitute an automatic gain controller 23 that controls the amplitude of the optical disc playback signal 1 to be equal to the amplitude of the optical disc playback signal 2. The variable gain unit 4, the rectifier 14, the comparator 11, the LPF 8, and the control buffer 6 constitute an automatic gain controller 24 that controls the amplitude of the optical disc playback signal 2 to be equal to the amplitude of the optical disc playback signal 1. Yes.

When there is a deviation in the optical system of the optical pickup or when the optical disc is decentered, there is a difference in amplitude between the optical disc reproduction signals 1 and 2 output from the photodetector. In order to eliminate this amplitude difference, the automatic gain controllers 23 and 24 perform automatic gain control with reference to the reference voltages 9 and 12, and the optical disk reproduction signals 1 and 2 are adjusted to arbitrary equal amplitudes by the variable gain units 3 and 4, respectively. Thus, the wobble signal 16 is detected by canceling the RF component by subtraction in the subtractor 15.
Japanese Patent Laid-Open No. 9-73636

  Conventionally, in an information recording / reproducing technique used for an optical disc that obtains track position information by meandering tracks in which land portions and groove portions are alternately formed, there is a shift in the optical system of the optical pickup. When the optical disk is eccentric, even if an amplitude difference occurs in the optical disk reproduction signal of each system output from the photodetector, the automatic gain controllers 23 and 24 function to eliminate the amplitude difference, and the optical disk reproduction signal Was detecting a wobble signal.

  However, a problem arises when it is desired to detect the wobble signal with higher accuracy. The variable gain device 3, the rectifier 13, the comparator 10, the LPF 7, the control buffer 5, and the variable gain device 4, the rectifier 14, and the comparator 11 that configure the automatic gain controller 23. The LPF 8 and the control buffer 6 have the same automatic gain control with reference voltages 9 and 12, respectively. However, the common circuits constituting the automatic gain controllers 23 and 24 have individual variations. Exists. That is, since the automatic gain controllers 23 and 24 independently control the amplitude, the amplitude difference between the variable gain devices 3 and 4 cannot be ignored due to the variation between the constituent circuits. When the wobble signal is detected from the optical disk reproduction signal, the difference in the amplitude of the optical disk reproduction signal subtracted by the subtractor 15 appears as an RF signal remaining in the wobble signal after output from the subtractor 15. The remaining RF signal becomes noise and deteriorates the C / N of the detected wobble signal, resulting in a problem that accurate track position information cannot be obtained.

  The present invention solves the above-described conventional problems, and its object is to reduce the influence of variations between circuits resulting from the individual circuits constituting the automatic gain controllers 23 and 24 acting independently. Another object of the present invention is to provide a wobble detection circuit capable of improving C / N by detecting a wobble signal with higher accuracy.

  In order to solve the above problem, in the present invention, in an automatic variable gain controller for equalizing the amplitudes of the two optical disk reproduction signals output from the photodetector, the amplitude for comparing the amplitudes of the signals of the respective systems A comparator, a low-pass filter that integrates the output signal of the amplitude comparator, and a control buffer that outputs a control signal for controlling the variable gain device based on the output signal of the low-pass filter are each processed by one circuit. .

  That is, the wobble detection circuit according to the first aspect of the present invention is a wobble detection circuit that detects a wobble signal from first and second signals obtained from an optical disc, and is capable of changing an amplitude of the first signal. A variable gain device; a second variable gain device capable of changing an amplitude of the second signal; a first rectifier that rectifies an output signal of the first variable gain device; and the second variable gain device. A second rectifier that rectifies the output signal, a comparator that calculates and compares signals rectified by the first and second rectifiers, and a DC component obtained by integrating the AC component that is compared and calculated by the comparator. A low-pass filter that controls the direct-current component output from the low-pass filter to a reference voltage to control the output signals of the first and second variable gain devices to be equal in amplitude. It is characterized by having .

  According to a second aspect of the present invention, in the wobble detection circuit according to the first aspect, the amplitude of the output signal of the first variable gain device is corrected to be equal to the output signal of the second variable gain device. A first amplitude corrector; a second amplitude corrector for correcting the amplitude of the output signal of the second variable gain device to be equal to the output signal of the first variable gain device; A subtractor for subtracting the signal whose amplitude is corrected by the second amplitude corrector is provided.

  Further, the wobble detection circuit according to the present invention is a wobble detection circuit for detecting a wobble signal from first and second signals obtained from an optical disc, wherein the amplitude of the first signal can be changed. A variable gain device, a second variable gain device capable of changing the amplitude of the second signal, and a subtraction for subtracting the output signal of the first variable gain device and the output signal of the second variable gain device. A comparator, a jitter detector for detecting a jitter amount from the output signal of the subtractor, a comparator for comparing and calculating an output signal of the jitter detector and a reference voltage, and an alternating current that is compared and calculated by the comparator A low-pass filter that integrates the component into a DC component and a DC component output from the low-pass filter are compared with a reference voltage so that the amplitudes of the output signals of the first and second variable gain devices are equal. System to control Characterized by comprising a buffer.

  As described above, according to the first and second aspects of the present invention, in the automatic variable gain controller that automatically equalizes the magnitudes of the amplitudes of the two optical disc reproduction signals detected from the photodetector, Two variables based on the subsequent processing, that is, a comparator for comparing and calculating the rectified signals of each system, a low-pass filter that integrates the results of the comparison and converting to DC, and an output signal of the low-pass filter Since each control buffer that generates a control signal for controlling the gain device is processed by one circuit, an error component due to variation between circuits can be reduced compared to the case of individually processing. Thus, the outputs of the two variable gain devices can be obtained with high accuracy.

  According to a third aspect of the present invention, a comparator which obtains information of an output difference between two variable gain devices through a subtraction circuit and a jitter detector and compares the obtained information with a predetermined reference voltage. A low-pass filter that integrates the results of the comparison operation into a direct current, and a control buffer that generates a control signal for controlling the two variable gain devices based on the output signal of the low-pass filter. Since the processing is performed by one circuit, the error component due to the variation between the circuits can be reduced as compared with the case where the processing is performed individually, thereby making it possible to obtain the outputs of the two variable gain devices with high accuracy. Become.

  As described above, according to the first and second aspects of the invention, the comparator, the low-pass filter, and the automatic variable gain controller that control the amplitudes of the two signals to be equal to each other. In addition, since each control buffer is configured to perform processing with a single circuit, the influence of variation between circuits is reduced compared to the conventional configuration of individual processing for each system signal, and wobble signals are detected with high accuracy. And C / N improvement can be realized.

In particular, according to the second aspect of the present invention, the amplitude of the optical disk reproduction signal output from one variable gain device, which is generated because the automatic gain controller does not share the rectifier, and the other variable gain device By correcting a minute difference from the amplitude of the output optical disk reproduction signal with an amplitude corrector, it is possible to detect a wobble signal with higher accuracy and to improve C / N.
According to a third aspect of the present invention, a jitter detector is provided, and the RF signal remaining in the wobble signal obtained from the output of the subtractor is fed back to the comparator so that the gain of the variable gain device is increased. By performing the control, it is possible to detect a wobble signal with higher accuracy and realize improvement in C / N.

  Embodiments of the present invention will be described below with reference to the drawings.

(First embodiment)
FIG. 1 shows a configuration of a wobble detection circuit in the first embodiment. In FIG. 1, reference numerals 3 and 4 denote variable gain devices (first and second variable outputs) that variably output the amplitudes of two optical disc reproduction signals 1 and 2 obtained from the photodetector based on the reflected light of the light applied to the optical disc. (Variable gain devices), 13 and 14 are rectifiers (first and second rectifiers) for rectifying the optical disk reproduction signals 1 and 2 variably output by the variable gain devices 3 and 4, respectively, and 10 is an output of one rectifier 13; A comparator that compares and calculates the output of the other rectifier 14, an LPF (low-pass filter) that integrates the AC component that is compared and calculated by the comparator 10 into a DC component, and a DC that is output from the LPF 7. A control buffer that controls the variable gain devices 3 and 4 by comparing the component with the reference voltage (first reference voltage) 9, and 15 is an optical disk reproduction signal variably output by one variable gain device 3 and the other variable. Obtained in vessel 4 by subtracting a variable output optical disc reproduced signal is a subtracter for outputting a wobble signal 16. The variable gain devices 3 and 4, the rectifiers 13 and 14, the comparator 10, the LPF 7, and the control buffer 17 constitute an automatic gain controller, which compares the output of one rectifier 13 with the output of the other rectifier 14. The control buffer 17 has an operation to reversely control one variable gain device 3 and the other variable gain device 4, that is, to increase one gain, lower the other gain. By this action, control is performed so that the amplitude of the optical disk reproduction signal 1 variably output by one variable gain device 3 is equal to the amplitude of the optical disk reproduction signal 2 variable by the other variable gain device 4.

  With respect to the wobble detection circuit according to the present embodiment configured as described above, signal processing of the optical disk reproduction signal until the wobble signal 16 is detected from the optical disk reproduction signals 1 and 2 output from the photodetector will be described below. This will be described with reference to the waveform diagram shown in FIG. In this embodiment, it is assumed that the optical system of the optical pickup is deviated or the optical disk is decentered, and there is an amplitude difference between the optical disk reproduction signals 1 and 2 output from the photodetector. The state which has arisen is demonstrated.

  In FIG. 5, (a) shows the optical disc reproduction signal 1 output from the photodetector, and (b) shows the optical disc reproduction signal 2 outputted from the photodetector, where A and C are those in (a) and (b). The wobble signals included in the optical disk reproduction signals 1 and 2, B and D are the RF signals included in the optical disk reproduction signals 1 and 2 of (a) and (b), and (c) is a variable gain device in which gain control is performed. 3 is output from the optical disc reproduction signal 1, and (d) is gain-controlled, and the optical disc reproduction signal 2 is output from the variable gain device 4, and (e) is the RF signal canceled by subtraction. This is the wobble signal 16 obtained as described above. The phase relationship between the wobble signals A and C and the RF signals B and D included in the optical disc playback signal 1 in (a) and the optical disc playback signal 2 in (b) is as follows. That is, the phase difference between the wobble signals A and C included in the optical disc playback signal 1 in (a) and the optical disc playback signal 2 in (b) is 180 °, and the optical disc playback signal 1 in (a) and (b The phase difference between each of the RF signals B and D included in the optical disc reproduction signal 2 is 0 °.

  The automatic gain controller in the present embodiment reversely controls the optical disk reproduction signal 1 in (a) and the optical disk reproduction signal 2 in (b) by one variable gain device 3 and the other variable gain device 4. . That is, when one gain is increased, gain control is performed to decrease the other gain, and control is performed until the optical disk reproduction signals 1 and 2 of (c) and (d) output from the variable gain devices 3 and 4 have the same amplitude. Repeated. Note that the phase relationship between the wobble signal and the RF signal included in the optical disk reproduction signals 1 and 2 of (c) and (d) output from the variable gain devices 3 and 4 is the optical disk of (a) and (b), respectively. It is not different from the playback signals 1 and 2. Therefore, the optical disk reproduction signals 1 and 2 (c) and (d) whose gains are controlled can be removed by subtracting the RF signal having the same amplitude and a phase difference of 0 ° by the subtractor 15. On the other hand, the wobble signal included in the optical disc reproduction signals (c) and (d) whose gains are controlled has a phase difference of 180 °, and is detected without being removed even when subtracting by the subtractor 15.

  As described above, according to the first embodiment, it is possible to obtain a wobble signal having a good C / N with no RF signal remaining, as shown in FIG.

  In this embodiment, in the automatic gain controller, a charge pump provided with a detection capacitor that outputs automatic gain control information instead of LPF 7 that integrates the AC component compared and calculated by comparator 10 into a DC component. It is good.

(Second Embodiment)
Next, a second embodiment of the present invention will be described.

  FIG. 2 shows the configuration of the wobble detection circuit in this embodiment. In the following embodiments, the description of the same configuration as that shown in FIG. 1 in the first embodiment is omitted, and the same reference numerals are used in the drawings.

  In the present embodiment, amplitude correctors 19 and 20 (first and second amplitude correctors) are provided immediately before the subtractor 15 so that the optical disc reproduction signals 1 and 2 that are the outputs of the variable gain units 3 and 4 are output. The configuration in which the amplitude is finely adjusted (corrected) is different from that of the first embodiment.

  Regarding the wobble detection circuit in the second embodiment configured as described above, the signal processing of the optical disk reproduction signal until the wobble signal 16 is detected from the optical disk reproduction signals 1 and 2 output from the photodetector will be described below. This will be described with reference to the waveform diagram shown in FIG. Assuming that there is a deviation in the optical system of the optical pickup or that the optical disk is decentered, if there is an amplitude difference between the optical disk reproduction signals 1 and 2 output from the photodetector, explain.

  In FIG. 6, (a) shows an optical disk reproduction signal 1 output from the photodetector, (b) shows an optical disk reproduction signal 2 output from the photodetector, and A and C in (a) and (b) denote optical disk reproduction. The wobble signals included in the signals 1 and 2, B and D in (a) and (b) are the RF signals included in the optical disc reproduction signals 1 and 2, and (f) is the gain control performed from the variable gain device 3. The output optical disc playback signal 1, (g) is an optical disc playback signal 2 output from the variable gain device 4 after gain control, and (h) is the amplitude of the optical disc playback signal 1 output from the variable gain device 3. The optical disc playback signal 1 after fine adjustment by the corrector 19, (i) is the optical disc playback signal 2 after fine adjustment of the amplitude of the optical disc playback signal 2 output from the variable gain device 4 by the amplitude corrector 20, (e ) Is a subtractor RF signal A wobble signal 16 obtained by subtraction. The phase relationship between the wobble signals A and C and the RF signals B and D included in the optical disc playback signal 1 in (a) and the optical disc playback signal 2 in (b) is as follows. That is, the phase difference between the wobble signals A and C included in the optical disc playback signal 1 in (a) and the optical disc playback signal 2 in (b) is 180 °, and the optical disc playback signal 1 in (a) and the optical disc playback signal 1 in (b) The phase difference between the RF signals B and D included in the optical disc reproduction signal 2 is 0 °.

  The automatic gain controller in the present embodiment reversely controls the optical disk reproduction signal 1 in (a) and the optical disk reproduction signal 2 in (b) by one variable gain device 3 and the other variable gain device 4. That is, when one gain is increased, gain control is performed to decrease the other gain. However, since the rectifiers 13 and 14 are individually processed without sharing the rectifiers 13 and 14, there are inherent variations in the rectifiers 13 and 14. There is a slight difference between the amplitudes of the optical disk reproduction signals 1 and 2 in f) and (g).

  Therefore, in the present embodiment, the amplitude of the optical disk reproduction signal 1 (f) output from one variable gain device 3 and the amplitude of the optical disk reproduction signal 2 (g) output from the other variable gain device 4. Are corrected by the amplitude correctors 19 and 20 to remove a minute difference and output optical disc reproduction signals 1 and 2 having the same amplitude (h) and (i). The phase relationship between the wobble signal and the RF signal included in the optical disk reproduction signals 1 and 2 of (h) and (i) is the same as that of the optical disk reproduction signals 1 and 2 of (a) and (b). Therefore, the optical disk reproduction signals 1 and 2 of (h) and (i) whose amplitudes are finely adjusted by the amplitude correctors 19 and 20 are subtracted by the subtractor 15 from the RF signals having the same amplitude and a phase difference of 0 °. This can be removed. On the other hand, the wobble signals included in the optical disk reproduction signals 1 and 2 (h) and (i) whose amplitudes are finely adjusted by the amplitude correctors 19 and 20 are subtracted by the subtractor 15 because the phase difference is 180 °. Even if it is not removed, it is detected.

  As described above, according to the second embodiment, the amplitude correctors 19 and 20 can be removed with higher accuracy than the wobble detection circuit according to the first embodiment, and as shown in FIG. A wobble signal having a good C / N with no signal remaining is obtained.

  In this embodiment, in the automatic gain controller, a charge pump provided with a detection capacitor that outputs automatic gain control information instead of LPF 7 that integrates the AC component compared and calculated by comparator 10 into a DC component. It is good.

(Third embodiment)
Next, a third embodiment of the present invention will be described.

  FIG. 3 shows a configuration of a wobble detection circuit according to the third embodiment.

  In the first embodiment, information on the amplitude difference between the two optical disc reproduction signals 1 and 2 is obtained from the rectifiers 13 and 14, respectively, and the result of comparison operation by the comparator 10 is used. In the present embodiment, the jitter amount of the wobble signal 16 output from the subtractor 15 is detected by the jitter detector 22 so that the two optical disc reproduction signals 1 and 2 are generated. A control signal for controlling the variable gain devices 3 and 4 is obtained by using the result obtained by obtaining the information of the amplitude difference and comparing the detection result and the predetermined reference voltage 21 (second reference voltage) in the comparator 10. Different in the configuration to be generated.

  Regarding the wobble detection circuit in the third embodiment configured as described above, the signal processing of the optical disk reproduction signal until the wobble signal 16 is detected from the optical disk reproduction signals 1 and 2 output from the photodetector will be described below. This will be described with reference to the waveform diagram shown in FIG. It is assumed that there is a deviation in the optical system of the optical pickup or that the optical disk is decentered, and that the amplitude difference is generated between the optical disk reproduction signals 1 and 2 output from the photodetector. To do.

  In FIG. 7, (a) shows the optical disk reproduction signal 1 output from the photodetector, (b) shows the optical disk reproduction signal 2 output from the photodetector, and A and C in (a) and (b) are the optical disk reproduction signals. Wobble signals included in the signals 1 and 2, B and D in (a) and (b) are RF signals included in the optical disc reproduction signals 1 and 2, and (j) indicates detection information of the jitter detector 22. This shows the wobble signal 16 in the initial state before the variable gain devices 3 and 4 are feedback-controlled, and includes the residual RF signal output from the subtractor 15. (K) is a binarized signal in which jitter is detected by the jitter detector 22 including the residual RF signal (j), and (e) is a binary signal in which jitter is detected by the jitter detector 22 ( This is a wobble signal 16 after the remaining RF signals are removed by controlling the variable gain devices 3 and 4 based on k). The phase relationship between the wobble signals A and C and the RF signals B and D included in the optical disc playback signal 1 in (a) and the optical disc playback signal 2 in (b) is as follows. That is, the phase difference between the wobble signals A and C included in the optical disc playback signal 1 in (a) and the optical disc playback signal 2 in (b) is 180 °, and the optical disc playback signal 1 in (a) and (b). The phase difference between the RF signals B and D included in the optical disc reproduction signal 2 is 0 °. In the initial state where the variable gain units 3 and 4 are not feedback-controlled based on the detection information of the jitter detector 22, the phase difference between the RF signals included in the optical disc reproduction signals 1 and 2 output from the variable gain units 3 and 4 Is the same phase difference 0 ° as the RF signals B and D of the optical disc reproduction signals 1 and 2 output from the photodetector (a) and (b). However, since the amplitudes of the optical disk reproduction signals 1 and 2 output from the variable gain units 3 and 4 in the initial state are different, the wobble signal 16 in which the RF signal remains is obtained at the output of the subtractor 15 (j). . Therefore, in the present embodiment, jitter detection is performed by the jitter detector 22 on the basis of the remaining (j) wobble signal 16 of the RF signal obtained by subtraction in the subtractor 15, and (k) 2 The value signal is detected, and the RF signal is removed from the wobble signal 16 in (j), that is, the subsequent comparator 10, low-pass signal, based on the output of the jitter detector 22 so as not to generate jitter. The gain of the variable gain devices 3 and 4 is controlled by the filter 7 and the control buffer 17 to obtain the wobble signal 16 (e) in which no RF signal remains. However, if the RF signal does not remain in the wobble signal 16, no jitter occurs in the binarized signal.

  As described above, according to the third embodiment, jitter detection is performed based on the wobble signal output from the subtractor 15, and the remaining RF signal is fed back to the comparator 10. The wobble detection circuit according to the second embodiment can be removed, and the (e) wobble signal 16 having a good C / N with no RF signal remaining can be obtained.

  In this embodiment, in the configuration in which the jitter detector 22 detects jitter and feeds back to the comparator 10, control information is used instead of the LPF 7 which integrates the AC component compared and calculated by the comparator 10 into a DC component. A charge pump including a detection capacitor for output may be used.

  The wobble detection circuit according to the present invention has an effect of improving the C / N by detecting a wobble signal with high accuracy, and is an information recording / reproducing technology field for an optical disc on which information can be optically read / written. In an optical disc and its recording or reproducing apparatus for obtaining track position information by wobbling a track in which land portions and groove portions are alternately formed on an information recording surface, in a circuit for detecting a wobble signal from an optical disc reproduction signal, etc. Useful.

It is a block diagram of the wobble detection circuit in the 1st Embodiment of this invention. It is a block diagram of the wobble detection circuit in the 2nd Embodiment of this invention. It is a block diagram of the wobble detection circuit in the 3rd Embodiment of this invention. It is a block diagram of the conventional wobble detection circuit. FIG. 3 is a waveform diagram of an optical disc reproduction signal until a wobble signal is detected from the optical disc reproduction signal in the first embodiment. It is a wave form diagram of an optical disk reproduction signal until it detects a wobble signal from an optical disk reproduction signal in the second embodiment. It is a wave form diagram of the optical disk reproduction signal until it detects a wobble signal from the optical disk reproduction signal in the third embodiment.

Explanation of symbols

3, 4 Variable gain unit 5, 6, 17 Control buffer 7, 8 LPF (low pass filter)
9 First reference voltage 21 Second reference voltage 10, 11 Comparator 13, 14 Rectifier 15 Subtractor 19, 20 Amplitude corrector 23, 24 Automatic gain controller

Claims (3)

In a wobble detection circuit for detecting a wobble signal from first and second signals obtained from an optical disc,
A first variable gain device capable of changing an amplitude of the first signal;
A second variable gain device capable of changing an amplitude of the second signal;
A first rectifier for rectifying the output signal of the first variable gain device;
A second rectifier for rectifying the output signal of the second variable gain device;
A comparator for arithmetically comparing the signals rectified by the first and second rectifiers;
A low-pass filter that integrates the alternating current component calculated by the comparator into a direct current component;
A control buffer for controlling the DC component output from the low-pass filter to be equal to the amplitude of the output signal of the first and second variable gain devices by comparing with a first reference voltage. A wobble detection circuit. The wobble detection circuit according to claim 1.
A first amplitude corrector that corrects the amplitude of the output signal of the first variable gain device to be equal to the output signal of the second variable gain device;
A second amplitude corrector for correcting the amplitude of the output signal of the second variable gain device to be equal to the output signal of the first variable gain device;
A wobble detection circuit comprising: a subtractor that subtracts the signal whose amplitude is corrected by the first and second amplitude correctors. In a wobble detection circuit for detecting a wobble signal from first and second signals obtained from an optical disc,
A first variable gain device capable of changing an amplitude of the first signal;
A second variable gain device capable of changing an amplitude of the second signal;
A subtractor for subtracting the output signal of the first variable gain device and the output signal of the second variable gain device;
A jitter detector for detecting a jitter amount from an output signal of the subtractor;
A comparator for comparing and calculating the output signal of the jitter detector and a reference voltage;
A low-pass filter that integrates the alternating current component calculated by the comparator into a direct current component;
A control buffer for controlling the DC component output from the low-pass filter to be equal to the amplitude of the output signals of the first and second variable gain devices by comparing with a second reference voltage. A wobble detection circuit.

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