JP2008047164A - Defect detecting circuit and controller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such a problem that circuit scale is enlarged or a defect is erroneously detected in a conventional defect detecting circuit. <P>SOLUTION: The defect detecting circuit includes a detecting circuit 52 detecting quantity of change in an amplitude level of an input signal and outputting it as a tilt detecting signal, a comparing voltage control circuit 54 changing a level of comparing voltage Vcomp in accordance with an amplitude level of the input signal, and a comparing circuit 53 comparing a level of the tilt detecting signal with a level of the comparing voltage Vcomp and outputting a control signal. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a defect detection circuit and a control device, and more particularly to a defect detection circuit and a control device for detecting a defect in a storage medium.

  In recent years, optical discs and the like are often used as information storage media. The rotation of the optical disc is controlled by servo control. Also, servo control controls the output of the laser beam for reading or recording information on the optical disc and the position control of the pickup for condensing the return beam. The optical disc apparatus reads or records stable information by this servo control. However, the optical disk may have a defective area due to fingerprints on the disk or scratches on the disk surface. In such a defective area, appropriate reflected light cannot be obtained from the optical disc, servo control becomes unstable, and there is a possibility that data reading or recording will be defective.

  Therefore, when the pickup passes over the defective area, the optical disk apparatus fixes the servo control immediately before the defective area and stabilizes the servo control. In such servo control, it is necessary to detect a defective area. Patent Documents 1 and 2 disclose conventional examples of such a defect detection circuit for detecting a defective area.

  FIG. 4 shows a block diagram of the defect detection circuit 100 of Conventional Example 1 disclosed in Patent Document 1. In FIG. As shown in FIG. 4, the defect detection circuit 100 includes an AGC (Automatic Gain Control) circuit 110, a high-speed peak hold detection circuit 111, a low-speed peak hold detection circuit 112, a subtractor 113, and a comparison circuit 114. The amplitude of the input signal X generated according to the amount of reflected light read from the optical disk varies depending on the state of the optical disk. The AGC circuit 110 is an amplifier that keeps the amplitude of the output signal constant by changing the amplification factor. That is, the AGC circuit 110 outputs the AGC output signal Y in which the fluctuation of the amplitude of the input signal X is suppressed to the internal circuit.

  The high-speed peak hold detection circuit 111 and the low-speed peak hold detection circuit 112 output a signal that follows the upper peak level of the input signal X. The high-speed peak hold detection circuit 111 is a detection circuit with higher peak level followability and higher sensitivity than the low-speed peak hold detection circuit 112. The output of the high speed peak hold detection circuit 111 is referred to as a high speed envelope signal, and the output of the low speed peak hold detection circuit 112 is referred to as a low speed envelope signal.

  The subtractor 113 outputs a subtraction signal obtained by subtracting the signal level of the high-speed envelope signal from the signal level of the low-speed envelope signal. The comparison circuit 114 compares the signal level of the subtraction signal with the reference voltage Vref generated by another circuit, and outputs a defect area detection signal Z.

  Here, a timing chart showing the operation of the defect detection circuit 100 is shown in FIG. As shown in FIG. 5, in the defect detection circuit 100, the signal level of the high-speed envelope signal becomes extremely small in the defect region where the amplitude of the input signal X becomes extremely small from timing T3 to T4. On the other hand, the signal level of the low-speed envelope signal does not decrease immediately. Therefore, in this defect area, the signal level of the subtraction signal rises and exceeds the reference voltage Vref. During the period in which the signal level of the subtraction signal is higher than the reference voltage Vref, the defect area detection signal Z becomes high level.

  On the other hand, the signal level of the input signal X also decreases during the periods of timing T1 to T2 and timings T3 to T4. The decrease in the signal level during this period is caused by fluctuations in the laser beam or fluctuations in the disk surface. It is. Therefore, the decrease in the amplitude of the input signal X is small, the change in the signal level of the subtraction signal is small, and the signal level of the subtraction signal is smaller than the reference voltage Vref. Therefore, in such an area, the defect area detection signal Z maintains a low level.

  That is, in Conventional Example 1, the defect area detection signal Z is generated using the difference in sensitivity between the high-speed envelope signal and the low-speed envelope signal. On the other hand, Patent Document 2 discloses a defect detection circuit that is different from that of Conventional Example 1. A block diagram of the defect detection circuit 200 of Conventional Example 2 disclosed in Patent Document 2 is shown in FIG.

  As shown in FIG. 6, the defect detection circuit 200 includes a full addition circuit 210, a differentiation circuit 211, a pulse signal conversion circuit 212, and a defect signal circuit 213. The full addition circuit 210 generates a full addition signal obtained by fully adding the amplitude of the input signal X. The differentiation circuit 211 calculates a differential value of the fully added signal and generates a differential signal. The pulse signal conversion circuit 212 generates a pulse signal having a high level period corresponding to a period in which the signal level of the differential signal exceeds the threshold range (a range indicated between the threshold value Vtha and the threshold value Vthb in FIG. 6). . The defect signal circuit 213 generates a defect signal according to the pulse signal.

  A timing chart showing the operation of the defect detection circuit 200 is shown in FIG. As shown in FIG. 7, the signal level of the full addition signal of the defect detection circuit 200 is greatly lowered at the timing T3. At this time, since the slope of the fully added signal changes greatly, the signal level of the differential signal changes according to the slope of the fully added signal. And a pulse signal is produced | generated in the period when the signal level of a differential signal is below a threshold value. The defect signal rises in response to the rise of this pulse signal.

  On the other hand, the signal level of the fully added signal returns to the normal signal level at timing T4. At this time, since the slope of the fully added signal changes greatly, the signal level of the differential signal changes according to the slope of the fully added signal. And a pulse signal is produced | generated in the period when the signal level of a differential signal becomes more than a threshold value. The defect signal falls in response to the fall of the pulse signal.

That is, the defect detection circuit 200 detects a defect according to the slope of the signal obtained by fully adding the signal levels of the input signal X. In the optical disc apparatus, a DC offset may occur in the input signal X due to, for example, stray light. However, in the DC offset component, the differential value of the fully added signal does not change greatly. Therefore, the defect detection circuit 200 can detect only defects in which the signal level of the input signal X changes greatly even when a DC offset occurs.
JP 2004-273020 A JP 2001-273633 A

  However, the defect detection circuit 100 of the prior art 1 needs to prepare two circuits for generating an envelope signal, and there is a problem that the circuit scale increases. Further, in the defect detection circuit 200 of the conventional example 2, a threshold value is set to detect a defect, and an inclination exceeding the threshold value (the magnitude of the differentiated result) is detected as a defect. Depending on the type of media, for example, CD-ROM, CD-R, CD-RW, and manufacturer-specific variations, characteristics such as reflectivity and disk eccentricity (which may cause fluctuations) differ. For this reason, if the threshold value is fixed, as shown in FIG. 7, there is a small fluctuation of the input signal X caused by the shaking of the laser beam or the shaking of the optical disc, such as the timing T1 to T2 or the timing T5 to T6. As a result, it is detected as a defect, and as a result, there is a problem that sound interruption, video interruption, etc. occur frequently.

  Such a phenomenon occurs particularly when the amplitude level of the input signal X is large, that is, when the reflectance is large. Conversely, when the amplitude level of the input signal X is small, that is, the reflectance is small, even if a defect occurs, the threshold value is not exceeded and detection is not possible. That is, when the input signal X is small, the defect may not be detected even though there is a defect. In such a case, the AGC circuit and the servo control circuit that are controlled so as to maintain stability even if there is a defect are over-controlled because they are controlled even if there is no defect. In particular, when the state where there is a defect shifts to the state where there is no defect, the AGC circuit and the servo control circuit may not be able to follow the change in signal amplitude and the control becomes unstable.

  A defect detection circuit according to the present invention includes a detection circuit that detects a change amount of an amplitude level of an input signal and outputs it as a tilt detection signal, and a comparison voltage control circuit that changes a level of a comparison voltage in accordance with the amplitude level of the input signal And a comparison circuit that compares the level of the inclination detection signal with the level of the comparison voltage and outputs a control signal.

  According to the defect detection circuit of the present invention, the defect area is detected based on the overall amplitude level of the input signal X and the change rate of the amplitude level of the input signal. As a result, it is possible to detect the defect area with high accuracy regardless of the overall amplitude level of the input signal.

  In addition to the above-described defect detection circuit, the control device according to the present invention includes an auto gain control circuit (AGC circuit) that controls gain based on the amplitude level of the input signal, and rotation control of the storage medium. And a servo control circuit that controls the position of the pickup that outputs the input signal according to the amount of reflected light from the storage medium, and whether the AGC circuit changes the gain according to the control signal. The servo control circuit is controlled in operation by the control signal.

  According to the defect detection circuit of the present invention, a defect region is selectively detected without erroneously detecting fluctuations by comparing a threshold corresponding to the amplitude level of the input signal with the signal level of the inclination detection signal. It becomes possible to do.

Embodiment 1
Embodiments of the present invention will be described below with reference to the drawings. The optical disc apparatus 1 according to the first embodiment reproduces and records information from a storage medium (for example, an optical disc such as a CD or a DVD) using a laser beam. The optical disc device 1 reproduces recorded information by irradiating a recording surface with laser light and detecting a change in the amount of reflected light.

  FIG. 1 shows a block diagram of the optical disc apparatus 1 according to the first embodiment. As shown in FIG. 1, the optical disc apparatus 1 according to the first embodiment includes an optical disc rotating motor 10, a pickup 20, a servo control circuit 30, an AGC circuit 40, and a defect detection circuit 50.

  The optical disk rotation motor 10 is a motor that rotates the optical disk, and controls the rotation speed of the optical disk based on a control signal input from the servo control circuit 30. The pickup 20 generates an input signal X having an amplitude corresponding to the output of laser light to the optical disc and the amount of reflected light from the optical disc. The pickup 20 can be moved along the surface of the optical disk by, for example, a servo motor. A servo motor that controls the position of the pickup 20 is controlled by a servo control circuit 30.

  The servo control circuit 30 outputs a control signal for controlling the rotational speed of the optical disc and the position of the pickup in accordance with the state of the input signal X. The servo control circuit 30 fixes the amplification factor based on the hold enable signal output from the defect detection circuit 50. The hold enable signal is a signal having the same logic as the defect area detection signal Z and may be the same as the defect area detection signal Z.

  In an optical disc apparatus, tracking servo control, focus servo control, spindle servo control, and thread servo control are performed when information recording or information reproduction from an optical disc is performed. The tracking servo control detects a positional deviation between the center of the light spot and the center of the groove of the optical disk using the reflected light from the optical disk, and controls the position of the pickup so as to correct this positional deviation. This maintains the center of the light spot at the center of the groove on the optical disc. The focus servo control detects a shift of the focal position of the objective lens that collects the laser light using the reflected light from the optical disc, and controls the position of the pickup so as to correct this focus shift. As a result, the focal position of the objective lens for condensing the laser light is maintained on the surface of the optical disk following the vertical movement of the optical disk. The spindle servo control controls the rotation speed of the optical disk rotation motor so that the data rate and wobble frequency of a reproduction RF (Radio Frequency) signal are constant. The sled servo control enables long-distance seek by controlling the inclination of the pickup so as to follow the DC component of tracking.

  The AGC circuit 40 amplifies the input signal X whose amplitude varies to a signal having a substantially constant amplitude, and outputs the amplified signal as an AGC output signal Y to an internal circuit (not shown). In the internal circuit, signal processing is performed based on the AGC output signal Y. Note that the fluctuation of the amplitude of the input signal X is, for example, a reflection of the laser light when the pickup reads information on a defect area where a defect (defect) such as a fingerprint or a flaw on the surface of the optical disk exists. This occurs because the rate drops. The AGC circuit 40 fixes the amplification factor based on the hold enable signal output from the defect detection circuit 50. The hold enable signal is a signal having the same logic as the defect area detection signal Z and may be the same as the defect area detection signal Z.

  The defect detection circuit 50 detects a defect area based on the amplitude of the input signal X. The defect detection circuit 50 will be described in detail. The defect detection circuit 50 includes a peak hold detection circuit 51, an inclination detection circuit 52, a comparison circuit 53, and a reference voltage control circuit 54.

  The peak hold detection circuit 51 generates an envelope signal whose signal level varies according to the variation of the peak level of the input signal X. In the present embodiment, the envelope signal is a signal that varies according to the upper peak level of the amplitude of the input signal X. The envelope signal may vary according to the lower peak level of the amplitude of the input signal X.

  The inclination detection circuit 52 detects the inclination of the envelope signal based on the rate of change in the signal level of the envelope signal, and outputs an inclination detection signal. For example, when there is no change in the signal level of the envelope signal, the inclination detection signal maintains a predetermined signal level. On the other hand, when the signal level of the envelope signal varies, the signal level of the inclination detection signal is varied according to the rate of change of the envelope signal. The fluctuation in the signal level of the inclination detection signal becomes larger as the change rate of the envelope signal is larger.

  The comparison circuit 53 compares the inclination detection signal with a predetermined range specified by the reference voltage Vref2, and outputs a defect area detection signal Z. For example, when the slope detection circuit 52 detects a drop (negative change rate) in the signal level of the envelope signal and the signal level of the slope detection signal that fluctuates according to the change rate falls outside a predetermined range, The signal level changes from the low level to the high level. On the other hand, when the inclination detection circuit 52 detects an increase (positive change rate) of the signal level of the envelope signal and the signal level of the inclination detection signal that fluctuates according to the change rate falls outside the predetermined range, The signal level changes from high level to low level. For example, the predetermined range is obtained by setting an upper limit value and a lower limit value on the upper and lower sides around the signal level of the inclination detection signal when the envelope signal has no inclination. The upper limit value and the lower limit value are preferably set to such an extent that the change in the amplitude of the input signal X generated by the defect can be detected and does not react to the change in the amplitude of the input signal X generated by the fluctuation of the laser beam. The comparison voltage Vcomp that sets the predetermined range is generated by the comparison voltage control circuit 54.

  The comparison voltage control circuit 54 compares the input signal X with the amplitude reference value, and supplies a comparison voltage Vcomp obtained by multiplying the reference voltage Vref by a coefficient based on the comparison result to the comparison circuit 53. The coefficient may be changed based on a comparison result between the input signal X and the amplitude reference value. The operation of the comparison voltage control circuit 54 will be described in more detail. When the comparison voltage control circuit 54 determines that the overall amplitude level of the input signal X is smaller than the amplitude reference value, the comparison voltage control circuit 54 reduces the coefficient applied to the reference voltage Vref. As a result, the voltage level of the comparison voltage Vcomp is reduced. On the other hand, when it is determined that the overall amplitude level of the input signal X is larger than the amplitude reference value, the coefficient applied to the reference voltage Vref is reduced. As a result, the voltage level of the comparison voltage Vcomp increases.

  In this way, by changing the voltage level of the comparison voltage Vcomp in accordance with the overall amplitude level of the input signal X, a defect whose inclination is reduced by reducing the overall amplitude level of the input signal X is corrected. It becomes possible to detect. On the other hand, when the overall amplitude level of the input signal X is large, it is possible to selectively detect the defect area in accordance with the gradient that has increased as the amplitude level has increased.

  The reference voltage Vref is set in advance as a voltage level at which the defect area can be selectively detected when the amplitude level of the input signal X is an arbitrarily set amplitude level. As the amplitude reference value, a value corresponding to the amplitude level used when setting the reference voltage Vref is set in advance. The reference voltage Vref and the amplitude reference value can be arbitrarily set, and the above setting method shows an example.

  The defect area detection signal Z is input to the servo control circuit 30 and the AGC circuit 40 as a hold enable signal. For example, the servo control circuit 30 and the AGC circuit 40 maintain the control state and the amplification factor before the hold enable signal is at a high level. On the other hand, during the period in which the hold enable signal is at the low level, the servo control circuit 30 performs various controls so that the reproduction of information from the optical disk is stable, and the AGC circuit 40 changes the amplification factor according to the amplitude of the input signal X. To do.

  Here, a timing chart showing an example of the operation of the defect detection circuit 50 is shown in FIG. 2, and the operation of the defect detection circuit 50 will be described with reference to this figure. As shown in FIG. 2, when an input signal X is input, the peak hold detection circuit 51 generates an envelope signal according to the signal level of the input signal X. Subsequently, the inclination detection circuit 52 generates an inclination detection signal according to the inclination of the envelope signal. Then, when the signal level of the tilt detection signal becomes equal to or greater than a predetermined range, the comparison circuit 53 changes the signal level of the defect area detection signal Z. In the example illustrated in FIG. 2, the predetermined range is a range between the upper limit value Vth_H and the lower limit value Vth_L.

  In the example shown in FIG. 2, the amplitude of the input signal X decreases at the timing T3 when the pickup reaches the upper part of the defect area. At this time, the signal level of the envelope signal decreases according to the change in the signal level of the input signal X. Since the rate of change of the envelope signal is negative, the signal level of the inclination detection signal decreases. Further, the signal level of the inclination detection signal at the timing T3 is lower than the lower limit value Vth_L of the predetermined range. As a result, the defect area detection signal Z changes from the low level to the high level.

  Further, when the pickup escapes from the upper part of the defect area at timing T4, the amplitude of the input signal X increases. At this time, the signal level of the envelope signal rises according to the change in the signal level of the input signal X. Since the rate of change of the envelope signal is positive, the signal level of the tilt detection signal increases. Further, the signal level of the inclination detection signal at the timing T4 exceeds the upper limit value Vth_H within a predetermined range. As a result, the defect area detection signal Z changes from a high level to a low level.

  On the other hand, the amplitude of the input signal X also decreases at timings T1 to T2 and timings T5 to T6. The change in the amplitude of the input signal X during this period is due to, for example, fluctuations in the laser beam, and is smaller than the decrease in amplitude at the timings T3 to T4. Therefore, the decrease in the signal level of the envelope signal and the change in the signal level of the inclination detection signal are small compared to the period from timing T3 to T4. At this time, the fluctuation of the signal level of the inclination detection signal is sufficiently within a predetermined range. Therefore, the signal level of the defect area detection signal Z does not change.

  Here, the relationship between the slope of the envelope signal and the detection result of the defect area is shown in FIG. As shown in FIG. 3, for example, when there is a slope A corresponding to the amplitude fluctuation of the input signal X due to the defect and a slope B corresponding to the amplitude fluctuation of the input signal X due to the fluctuation of the laser light, The defect detection circuit 50 does not detect the defect at the inclination B, but detects the defect at the inclination A. On the other hand, in Conventional Example 2, both slope A and slope B are detected as defects. This is because in the conventional example 2, the predetermined range must be set narrow in order to improve the accuracy of the defect detection timing. On the other hand, in the defect detection circuit 50 according to the first embodiment, the predetermined range is set wider than that of the conventional example 2 so that the fluctuation of the amplitude of the input signal X is caused by the gentle fluctuation and the fluctuation of the amplitude of the input signal X. However, it is possible to distinguish between fluctuations due to steep defects.

  From the above description, the defect detection circuit according to the first embodiment generates the defect area detection signal Z based on the slope of the envelope signal that varies according to the amplitude variation of the input signal X. Thus, while the conventional example 1 requires two peak hold detection circuits, the defect detection circuit according to the first embodiment can detect a defect with one peak hole circuit. That is, the defect detection circuit according to the first embodiment can reduce the circuit scale as compared with the first conventional example.

  In addition, it is possible to selectively detect only the defect region by making the predetermined range as the comparison range of the inclination detection signal wider than that of the conventional example 2. Further, the defect detection circuit 100 according to the first embodiment includes a comparison voltage control circuit 54. The comparison voltage control circuit 54 can change the voltage level of the comparison voltage Vcom according to the amplitude level of the input signal X other than the defect area. That is, by adjusting the predetermined range, even if the amplitude level of the input signal X varies as a whole, the voltage level of the comparison voltage Vcomp can be changed accordingly. Therefore, the defect detection circuit according to the first embodiment can generate the defect region detection signal Z with high accuracy even when the amplitude level of the input signal X varies as a whole. As a result, the operations of the servo control circuit and the AGC circuit of the optical disk apparatus can be switched according to the cause of the amplitude fluctuation of the input signal X.

  Furthermore, it is possible to stabilize the control of the optical disc apparatus by setting the control of the servo control circuit and the AGC circuit to the hold state in accordance with the defect area detection signal Z according to the first embodiment. When the control of the servo control circuit and the AGC circuit is caused to follow the fluctuation of the input signal X in the area where the amplitude fluctuation of the input signal X is large, such as the defect area, an overshoot in the control occurs, and the control system There is a confusing problem. However, it is possible to stabilize the overall control of the apparatus by detecting such a defect area and holding the control when passing through this area.

  Note that the present invention is not limited to the above-described embodiment, and can be changed as appropriate without departing from the spirit of the present invention. For example, in the above-described embodiment, the defect detection circuit 50 is used to detect a defect. However, position information embedded in the optical disc in advance may be used as a detection target. For example, position information is detected using a defect detection circuit for an unrecorded disc on which no information is written, and the location of the defect area is specified based on this position information. As a result, for example, it is possible to perform processing such that access is not made to the defect area on the specified unrecorded disc in the subsequent recording / reproducing operation. In the embodiment, the optical disk is used for explanation. However, in addition to the CD and DVD, the present invention can be applied if the input signal (read signal) changes depending on the state of the storage medium.

  In the above embodiment, the comparison voltage control circuit generates the comparison voltage Vcomp from the reference voltage Vref with the input signal X and the amplitude reference value as inputs. On the other hand, an envelope signal from the peak hold detection circuit may be used instead of the input signal X, and the reference value of the envelope signal may be used instead of the amplitude reference value. Then, the voltage level of the comparison voltage Vcomp is set according to the comparison result between the envelope signal and the reference value. In this case, an existing peak hold detection circuit can be used, and a circuit for detecting the amplitude level of the input signal by the comparison voltage control circuit is not required, so that the circuit configuration can be reduced.

1 is a block diagram of an optical disc apparatus according to a first embodiment. 3 is a timing chart showing an operation of the defect detection circuit according to the first exemplary embodiment; It is a figure which shows the relationship between the inclination of the envelope signal of Embodiment 1 and the prior art example 2, and the detection result of a defect. It is a block diagram of a defect detection circuit according to Conventional Example 1. 12 is a timing chart showing the operation of the defect detection circuit according to Conventional Example 1. It is a block diagram of a defect detection circuit according to Conventional Example 2. 12 is a timing chart showing the operation of the defect detection circuit according to Conventional Example 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical disk apparatus 10 Optical disk rotation motor 20 Pickup 30 Servo control circuit 40 AGC circuit 50 Defect detection circuit 51 Peak hold detection circuit 52 Inclination detection circuit 53 Comparison circuit 54 Comparison voltage control circuit Vcomp Comparison voltage Vref Reference voltage X Input signal Y AGC output signal Z defect area detection signal

Claims (10)

A detection circuit that detects the amount of change in the amplitude level of the input signal and outputs it as a tilt detection signal;
A comparison voltage control circuit that changes the level of the comparison voltage according to the amplitude level of the input signal;
A defect detection circuit comprising: a comparison circuit that compares the level of the inclination detection signal with the level of the comparison voltage and outputs a control signal.   2. The defect detection circuit according to claim 1, wherein the comparison voltage control circuit generates the comparison voltage whose level is set by multiplying a reference voltage by a predetermined coefficient.   2. The defect detection circuit according to claim 1, wherein the amplitude level of the input signal is generated by a peak hold detection circuit that generates an envelope signal based on the input signal.   2. The comparison voltage control circuit outputs the comparison voltage obtained by multiplying a reference voltage by a predetermined coefficient based on a result of comparing an amplitude reference value and the input signal. Defect detection circuit.   The detection circuit includes a peak hold detection circuit that generates an envelope signal based on the input signal, and an inclination detection circuit that detects an inclination based on the envelope signal and generates an inclination detection signal. Item 2. The defect detection circuit according to Item 1.   The defect detection circuit according to claim 1, wherein the input signal is generated based on a signal read from a storage medium.   The defect detection circuit according to claim 6, wherein the storage medium is an optical disk. A defect detection circuit according to any one of claims 1 to 7,
An auto gain control circuit (AGC circuit) for controlling the gain based on the amplitude level of the input signal,
The AGC circuit is controlled according to whether the gain is changed by the control signal. A defect detection circuit according to any one of claims 1 to 7,
A servo control circuit that performs rotation control of the storage medium and position control of a pickup that outputs the input signal according to the amount of reflected light from the storage medium;
The servo control circuit is controlled by the control signal. A defect detection circuit according to any one of claims 1 to 7,
An auto gain control circuit (AGC circuit) for controlling a gain based on an amplitude level of the input signal, wherein the AGC circuit controls whether or not the gain is changed by the control signal;
A servo control circuit for controlling the rotation of the storage medium and the position of a pickup that outputs the input signal in accordance with the amount of reflected light from the storage medium, the operation of which is controlled by the control signal A control device comprising:

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