JP2000311350A - Automatic gain controller, automatic gain control method and optical disk device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform a correct amplitude correction by suppressing the effect of a noise component to be included in a reproduced signal and correctly detecting the amplitude of the reproduced signal and thereby to perform a correct MTF evaluation. SOLUTION: In this automatic gain controller, the peak level of the reproduced signal is recorded by a peak hold 3 and the bottom level of the reproduced signal is recorded by a bottom hole 5. The reproduced signal whose signal level is within a range from (the peak level-a constant A) to the peak level is extracted by an upper side envelope extracting means 4 and the reproduced signal whose signal level is within a range from the bottom level to (the bottom level + a constant A) is extracted by a lower envelope extracting means 6 and the subtraction between these signals is performed in a subtracting circuit 7. Thereafter, the output signal of the subtracting circuit 7 is substrated from a reference amplitude signal which is to be transmitted from a reference amplitude generating means 9 by a subtracting circuit 8 and then the amplitude of the reproduced signal is corrected by controlling the gain of a variable amplifier 2 while using the output of the circuit 8 as a gain control signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic gain control device, an automatic gain control method for maintaining the amplitude of a reproduced signal at a constant value, and an optical disk apparatus using the same, and more particularly to suppressing the influence of noise components contained in the reproduced signal. The present invention relates to an automatic gain control device and an automatic gain control method capable of performing accurate amplitude correction by accurately detecting the amplitude of a reproduced signal, and an optical disc device capable of performing accurate MTF evaluation by using the automatic gain control method.

[0002]

2. Description of the Related Art The applicant of the present invention has previously disclosed a reproduction signal in which the signal level changes in response to a change in the return light from the optical disk due to the irradiation of the laser beam in an optical disk apparatus for irradiating the optical disk with the laser beam. When the signal level crosses a predetermined reference level, the signal levels of the reproduced signal before and after the reference level are detected at predetermined time intervals, and the level difference between the signal levels is determined by MT.
An application has been filed for an invention of an optical disk device and an optical disk access method that is used as an evaluation value of a high-frequency characteristic of F (Modulation Transfer Function).

A signal waveform of a transient response in which a reproduced signal crosses a predetermined level indicates frequency characteristics in a reproducing system, and a signal level detected at a predetermined time interval when the signal level of the reproduced signal crosses the reference level. Is the MTF
Will correspond. That is, in the case of a transient response in a sufficient MTF, the signal level difference appears large, and conversely, when the frequency characteristic is deteriorated, the signal level difference appears small.

[0004] When the signal level of the reproduced signal crosses the reference level, the MTF evaluation performed by detecting the signal levels before and after the reference level is performed based on the sampled value of the reproduced signal at fixed time intervals. Therefore, the MTF can be evaluated even when the sampling clock is not synchronized with the reproduction signal.

In this MTM evaluation method, it is necessary that the amplitude of the reproduced signal is controlled to a constant value.
In the earlier application, the AGC (Automatic Gain Control) shown in FIG.
ol) Using the circuit 100, the amplitude of the reproduced signal is corrected to be a constant value.

The AGC circuit 100 detects the peak level and the bottom level of the output signal of the variable gain amplifier, adjusts the output of the variable gain amplifier using the difference as an index of the amplitude of the reproduced signal, and keeps the amplitude of the reproduced signal constant. I keep it.

[0007]

However, the AGC circuit 1
In the detection of the amplitude of the reproduced signal by 00, 1/2 of the amplitude of the noise component included in the reproduced signal is added to the true peak level of the reproduced signal and subtracted from the true bottom level. The amplitude detected by the detection method is obtained by adding the amplitude of the noise component to the actual amplitude of the reproduced signal. In particular, when the S / N ratio of the reproduced signal is small, the effect is noticeable. is there.

Further, as a result, there is a problem that an error occurs in the evaluation value of the high-frequency characteristic of the finally obtained MTF. The present invention has been made in view of such a point, and detects an amplitude of a reproduced signal itself without being substantially affected by a noise component included in the reproduced signal, and performs automatic gain correction capable of performing accurate amplitude correction. It is an object to provide a control device.

Another object of the present invention is to provide an automatic gain control method capable of detecting the amplitude of a reproduced signal itself without being substantially affected by a noise component included in the reproduced signal and performing accurate amplitude correction. It is to provide.

Another object of the present invention is to detect an amplitude of a reproduced signal itself without being substantially affected by a noise component included in the reproduced signal and perform an accurate amplitude correction to thereby perform an accurate MTF evaluation. It is an object of the present invention to provide an optical disk device capable of performing such operations.

[0011]

In order to solve the above-mentioned problems, the present invention detects the amplitude of a reproduction signal of an optical disk,
In an automatic gain control device for keeping the amplitude of a reproduction signal constant, a peak level recording means for recording a peak level of the reproduction signal, a bottom level recording means for recording a bottom level of the reproduction signal, and a peak level of the reproduction signal Upper envelope extracting means for extracting an upper envelope signal within a certain range from the lower level, lower envelope extracting means for extracting a lower envelope signal within a certain range from the bottom level of the reproduction signal, and the upper envelope signal And a subtraction means for subtracting the lower envelope signal from the control signal.

Here, the peak level recording means records the peak level of the reproduced signal, the bottom level recording means records the bottom level of the reproduced signal, and the upper envelope extracting means records the peak level within a certain range from the peak level of the reproduced signal. A certain upper envelope signal is extracted, a lower envelope extracting means extracts a lower envelope signal within a certain range from a bottom level of the reproduction signal, and a subtracting means subtracts the lower envelope signal from the upper envelope signal.

In an automatic gain control method for detecting the amplitude of a reproduction signal of an optical disk and keeping the amplitude of the reproduction signal constant, an upper envelope signal within a certain range from a peak level of the reproduction signal; An automatic gain control method characterized by detecting a difference between a lower envelope signal within a certain range from a bottom level of the reproduced signal and performing amplitude correction of the reproduced signal based on a result of the detection. .

Here, the reproduction signal within a certain range from the bottom level of the recorded reproduction signal is subtracted from the reproduction signal within a certain range from the peak level of the recorded reproduction signal. By performing the amplitude correction of the reproduced signal at this time, the influence of noise components included in the reproduced signal in amplitude detection can be suppressed, and accurate amplitude correction can be performed.

Further, in an optical disk device for accessing an optical disk, a light source for irradiating the optical disk with a laser beam, and a reproduction for outputting a reproduction signal whose signal level changes in accordance with return light of the laser beam reflected by the optical disk. Means, peak level recording means for recording a peak level of the reproduction signal, bottom level recording means for recording a bottom level of the reproduction signal, and an upper envelope signal within a certain range from the peak level of the reproduction signal. Upper envelope extracting means for extracting, lower envelope extracting means for extracting a lower envelope signal within a certain range from the bottom level of the reproduced signal, and subtracting means for subtracting the lower envelope signal from the upper envelope signal. An automatic gain control device having: An optical disc device comprising: signal level detecting means for detecting a signal level of the reproduction signal at predetermined time intervals before and after crossing a predetermined reference level; and arithmetic means for detecting a level difference between the signal levels. Is provided.

Here, the light source emits a laser beam, the reproducing means reproduces the reproduced signal, the peak level recording means records the peak level of the reproduced signal, and the bottom level recording means records the bottom level of the reproduced signal. The upper envelope extracting means extracts an upper envelope signal within a certain range from the peak level of the reproduction signal, and the lower envelope extracting means extracts a lower envelope signal within a certain range from the bottom level of the reproduction signal. The subtraction means subtracts the lower envelope signal from the upper envelope signal, the automatic gain control device corrects the amplitude of the reproduction signal based on the result of the subtraction, and the signal level detection means determines that the reproduction signal has a predetermined reference level. Before and after crossing, the signal level of the reproduced signal is detected at predetermined time intervals, and the arithmetic means detects the signal level of the reproduced signal at predetermined time intervals. To detect the issue level.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an AGC circuit 1 according to the present invention.

The AGC circuit 1 has a gain variable amplifier 2 for correcting the amplitude of a reproduced signal by adjusting a gain, a peak hold 3 for recording a peak level of an output signal of the variable gain amplifier 2, and a peak hold 3 for recording. Upper envelope extraction means 4 for extracting only the reproduction signal within a certain range from the peak level, bottom hold 5 for recording the bottom level of the output signal of the variable gain amplifier 2, and a certain level from the bottom level recorded in the bottom hold 5. A lower envelope extraction means 6 for extracting only the reproduction signal within the range, a subtraction circuit 7 for subtracting the reproduction signal extracted by the lower envelope extraction means 6 from the reproduction signal extracted by the upper envelope extraction means 4, A reference amplitude generating means for transmitting a reference amplitude signal of the signal; It is constituted by a low-pass filter 10 performs band limitation of the output signal from the calculation subtracting circuit 8 and the subtracting circuit 8.

The variable gain amplifier 2 has a peak hold 3,
Electrically connected to the bottom hold 5, the upper envelope extracting means 4 and the lower envelope extracting means 6,
The peak hold 3 is electrically connected to the upper envelope extracting means 4, and the bottom hold 5 is electrically connected to the lower envelope extracting means 6. Further, the upper envelope extracting means 4 and the lower envelope extracting means 6 are electrically connected to the subtracting means 7, respectively, and the subtracting means 7 is electrically connected to the subtracting means 8. The subtraction means 8 is electrically connected to the reference amplitude generation means 9 and the low-pass filter 10, and the low-pass filter 10 is electrically connected to the variable gain amplifier 2.

Next, the operation of the AGC circuit 1 will be described. The reproduced signal input to the variable gain amplifier 2 is branched after passing through the variable gain amplifier 2, and a part thereof reaches the peak hold 3. The peak hold 3 to which the reproduction signal has been input compares the peak level of the reproduction signal recorded therein with the signal level of the input reproduction signal. Here, if the peak level recorded in the peak hold 3 is lower than the signal level of the input reproduction signal, the peak hold 3 outputs the signal of the reproduction signal to which the peak level recorded is input. Update to level.
On the other hand, if the peak level recorded in the peak hold 3 is higher than the signal level of the input reproduction signal, the peak level is not updated and the peak hold 3 is not updated.
Holds the peak level recorded there.

A part of the reproduced signal output from the variable gain amplifier 2 also reaches the bottom hold 5. The bottom hold 5 to which the reproduction signal is input compares the bottom level of the reproduction signal recorded therein with the signal level of the input reproduction signal. Here, when the bottom level recorded in the bottom hold 5 is higher than the signal level of the input reproduction signal, the bottom hold 5 outputs the signal of the reproduction signal input with the bottom level recorded therein. Update to level. On the other hand, if the bottom level recorded in the bottom hold 5 is lower than the signal level of the input reproduction signal, the bottom level is not updated, and the bottom hold 5 is replaced with the bottom level recorded there. Hold.

Further, a part of the reproduced signal output from the variable gain amplifier 2 also reaches the upper envelope extracting means 4 and the lower envelope extracting means 6. The upper envelope extracting means 4 reads the peak level recorded in the peak hold 3, and extracts only a reproduced signal having a signal level within a certain range from the read peak level. Specifically, a constant A is given to the upper envelope extracting means 4 in advance, and the upper envelope extracting means 4
Only the reproduced signal whose signal level is equal to or higher than (peak level-constant A) and equal to or lower than the peak level is extracted. Here, if the constant A is set to 0, the same processing as that of the conventional AGC circuit 100 is performed. On the contrary, the value of the constant A is set too large.
When the upper envelope and the lower envelope reach the vicinity of a reference level that greatly affects the MTF evaluation, there is a problem that the amplitude detection accuracy is reduced. Ideally, it is desirable to set the maximum amplitude width of the noise component as the constant A.

On the other hand, the lower envelope extracting means 6 reads the bottom level recorded in the bottom hold 5, and extracts only a reproduced signal having a signal level within a certain range from the read bottom level. Here, as in the case of the upper envelope extracting means 4, a constant A is also given to the lower envelope extracting means 6, and the lower envelope extracting means 6 outputs the signal when the signal level is equal to or more than the bottom level (bottom level + constant A). Only the following reproduced signals are extracted.

The upper envelope signal extracted by the upper envelope extracting means 4 and the lower envelope signal extracted by the lower envelope extracting means 6 are input to a subtracting means 7, which subtracts the upper envelope signal from the upper envelope signal. Subtract the lower envelope signal. The result of the subtraction by the subtracting means 7 is treated as an index for detecting the amplitude of the reproduced signal output from the variable gain amplifier 2, and is compared with a preset reference amplitude. The reference amplitude generating means 9 transmits a reference signal having a reference amplitude set in advance as a condition,
The subtraction means 8 subtracts the output signal of the subtraction means 7 from the reference signal. The result of the subtraction by the subtraction means 8 indicates the difference between the reference amplitude and the amplitude of the reproduced signal. The result of the subtraction is input to the low-pass filter 10 to eliminate the high-frequency components and perform an integration process. The signal is used as a gain control signal. The signal is input to the variable gain amplifier 2 to control the gain of the variable gain amplifier 2.

As described above, the AGC circuit 1 corrects and outputs the signal level of the reproduction signal so that the amplitude of the reproduction signal becomes the reference amplitude value, and the signal level of the input reproduction signal varies. However, a reproduced signal having a stable signal level can be output.

Next, an optical disk device 20 using the AGC circuit 1 of the present invention will be described. FIG. 2 shows A of the present invention.
FIG. 2 is a block diagram showing a configuration of an optical disk device 20 using the GC circuit 1. In the optical disk device 20, data recorded on the optical disk 23 by thermomagnetic recording is reproduced by a magnetic super-resolution method.

In this optical disk device 20, the optical disk 23 has an information recording surface formed by laminating a plurality of magnetic films so as to be applicable to data reproduction by the magnetic super-resolution method. The optical disk device 20 irradiates the information recording surface with a laser beam in a state where a predetermined bias magnetic field is applied, and receives return light of the laser beam to reproduce data thermo-magnetically recorded on the optical disk 23. I do.

The spindle motor 26 drives the optical disk 23 to rotate under the control of the spindle control circuit 29. The spindle control circuit 29 is controlled by the system controller 22 and drives the optical disk 23 to rotate under a certain condition.

The optical pickup 24 moves in the radial direction of the optical disk 23 by driving a sled motor 25 controlled by a servo 27. Here, the servo 27 is controlled by the system controller 22. Also,
The optical pickup 24 emits a laser beam under the control of the laser power control circuit 28 controlled by the system controller 22, and focuses this laser beam on the information recording surface of the optical disk 23 by the objective lens. At this time, the optical pickup 24 outputs a light detection signal of the laser beam to the laser power control circuit 28, and the laser power control circuit 28 controls the laser power.

Further, the optical pickup 24 receives the return light of the laser beam, generates a tracking error signal and a focus error signal from the returned light, and outputs these to the servo 27. The servo 27 is controlled by the system controller 22, controls the objective lens based on the input tracking error signal and focus error signal, and outputs a drive signal to the optical pickup 24 to move the objective lens in the focusing direction. And drive in the tracking direction.

The optical pickup 24 generates a reproduction signal RF whose signal level changes in accordance with the polarization plane of the return light by the return light, and outputs the reproduction signal RF to the reproduction signal processing circuit 30.

The reproduction signal processing circuit 30 includes an AD conversion circuit 3
In step 2, the reproduction signal RF is subjected to analog-to-digital conversion with reference to the reproduction clock, thereby generating a digital reproduction signal DRF. The equalizing circuit 33 is, for example, FI
An adaptive filter constituted by an R filter,
Under the control of the system controller 22, the digital reproduction signal DRF is equalized in waveform and output. AGC circuit 1
Corrects the amplitude of the digital reproduction signal DRF so that the amplitude of the input digital reproduction signal DRF becomes the reference amplitude value, and outputs the corrected digital reproduction signal DRF. The demodulation circuit 34 binarizes the output signal of the equalization circuit 33 and reproduces a clock. Further, the demodulation circuit 34 sequentially latches the binarized signal based on the clock to obtain reproduced data, and demodulates and outputs the reproduced data. The error correction circuit 35 reproduces and outputs the output data of the demodulation circuit 34.

The MTF evaluation circuit 31 detects an MTF evaluation value from the digital reproduction DRF output from the AGC circuit 1 and outputs it. As shown in FIG. 3, the MTF evaluation circuit 31 inputs the digital reproduction signal DRF to the one-clock delay circuit 31b and delays it by one clock period. The MTF evaluation circuit 31 includes an inverted amplitude circuit 31a.
, A digital reproduction signal DRF is input to the terminal, where the polarity of the digital reproduction signal DRF is inverted. The zero-cross detection circuit 31f receives the digital reproduction signal DRF output from the one-clock delay circuit 31b,
Is changed, it is determined that the reproduction signal RF has zero-crossed, and a zero-crossing determination signal is output. The addition circuit 31c adds the digital reproduction signal DRF output from the one-clock delay circuit 31b to the inverted amplitude circuit 31a to determine the level difference between successive sampling values for each sampling value of the digital reproduction signal DRF. Detect and output. The absolute value converting circuit 31d converts the level difference output from the adding circuit 31c into an absolute value and outputs the absolute value.

With such a configuration, the MTF
When the signal level of the reproduction signal RF crosses the zero level, the evaluation circuit 31 converts the level difference of the reproduction signal RF at predetermined time intervals before and after the signal level into an absolute value and detects the absolute value. The level difference of the reproduced signal RF detected in this way is
This indicates the degree of change in the signal level when the reproduction signal RF crosses the 0 level. If the difference between the signal levels is large, the signal level of the reproduction signal RF is rapidly changing, and conversely, the signal level is changed. When the difference is small, the signal level of the reproduction signal RF changes gently.

Here, the change in the signal level of the reproduction signal RF is such that the more rapid the change, the more the MTF has a sufficient value on the high frequency side. The average value is output as the evaluation value.

That is, in the MTF evaluation circuit 31,
The operational amplifier circuit 31e is configured by a register having a bit shift circuit configuration. The data of the level difference output from the absolute value conversion circuit 31d is bit-shifted by a predetermined bit and is output, so that the level difference data is 1 / N
Double and output. The operational amplifier circuit 31g includes the register 3
The output data is multiplied by (1-1 / n) times the output data of 1i. The adder circuit 31h adds the output data of the operational amplifier circuit 31e and the output data of the operational amplifier circuit 31g and outputs the result. The register 31i outputs the adder circuit only when receiving the zero-cross determination signal sent from the zero-cross detector circuit 31f. 3
The data of the added value output from 1h is fetched and held. Thereby, the MTF evaluation circuit 31 outputs the MTF evaluation value data to the system controller 22 while removing the influence of noise.

The system controller 22, which has received the MTF evaluation value data, optimizes the focus control target and the laser beam light amount control target based on the MTF evaluation value data.

FIG. 4 shows the relationship between M and the focus offset.
FIG. 3 is a diagram showing a relationship between a TF evaluation value 41 and a jitter 40.
As shown in the figure, the jitter 40 is most reduced at the peak of the MTF evaluation value 41 at which the response of the high frequency in the reproduction system is most improved. Based on the MTF evaluation value 41 detected by the MTF evaluation circuit 31, the system controller 22
The focus offset is set so that the TF evaluation value 41 is maximized, thereby minimizing jitter.

FIG. 5 shows the MTF with respect to the reproducing laser power.
FIG. 4 is a diagram showing a relationship between an evaluation value 41 and a jitter 42. As shown in this figure, when the MTF evaluation value 41 is within a predetermined range, the jitter 42 is reduced most. The MTF evaluation value 41 corresponding to the range in which the jitter 42 is minimized is experimentally determined in advance, and the system controller 22 determines that the MTF evaluation value 4 in which the jitter 42 determined in advance is minimum.
Jitter can be minimized by controlling the reproduction laser power with 1 as the set target.

As described above, in this embodiment, the peak level of the reproduced signal is recorded by the peak hold 3, the bottom level of the reproduced signal is recorded by the bottom hold 5, and the signal level is set to (peak level) by the upper envelope extracting means 4. A reproduction signal having a peak level within a range from the constant A) is extracted, and a reproduction signal having a signal level within a range from the bottom level to (bottom level + constant A) is extracted by the lower envelope extracting means 6; Since the subtraction is performed by the subtraction circuit 7, the influence of noise components added to the reproduced signal can be suppressed, and accurate amplitude correction can be performed.

In the present embodiment, the upper envelope signal within a certain range from the peak level of the reproduced signal is
Since the lower envelope signal within a certain range is subtracted from the bottom level of the reproduction signal, the influence of the noise component added to the reproduction signal can be suppressed, and accurate amplitude correction can be performed.

Further, in this embodiment, the optical pickup 24 outputs a reproduction signal corresponding to the return light of the laser beam,
The AGC circuit 1 subtracts the lower envelope signal within a certain range from the bottom level of the reproduction signal from the upper envelope signal within a certain range from the peak level of the reproduction signal. After performing the correction, the MTF evaluation circuit 31 detects the signal level of the reproduction signal at predetermined time intervals before and after the reproduction signal crosses the predetermined reference level, and detects the signal level difference. Detecting the amplitude of the reproduced signal itself without being affected by the noise component to be performed, and performing accurate amplitude correction, it is possible to perform accurate MTF evaluation.

[0043]

As described above, according to the present invention, the peak level of the reproduction signal is recorded, the bottom level of the reproduction signal is recorded, and the reproduction signal within a certain range from the peak level is extracted. Since the reproduction signals within a certain range are extracted and their subtraction is performed, the influence of noise components added to the reproduction signals can be suppressed, and accurate amplitude correction can be performed.

In the present embodiment, the upper envelope signal within a certain range from the peak level of the reproduced signal is
Since the lower envelope signal within a certain range is subtracted from the bottom level of the reproduction signal, the influence of the noise component added to the reproduction signal can be suppressed, and accurate amplitude correction can be performed.

Further, in this embodiment, a reproduction signal corresponding to the return light of the laser beam is output, and from the upper envelope signal within a certain range from the peak level of the reproduction signal to a certain range from the bottom level of the reproduction signal. A certain lower envelope signal is subtracted, the amplitude of the reproduction signal is corrected based on the lower envelope signal, and the signal level of the reproduction signal is detected at predetermined time intervals before and after the reproduction signal crosses a predetermined reference level. Because the level difference is detected, the MTF evaluation can be performed accurately by detecting the amplitude of the reproduced signal itself without being substantially affected by noise components included in the reproduced signal and performing accurate amplitude correction. Becomes

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an AGC circuit according to the present invention.

FIG. 2 is a block diagram showing a configuration of an optical disk device using an AGC circuit according to the present invention.

FIG. 3 is a block diagram showing a configuration of an MTF evaluation circuit.

FIG. 4 is a diagram illustrating a relationship between an MTF evaluation value and a jitter with respect to a focus offset.

FIG. 5 is a diagram showing a relationship between an MTF evaluation value and a jitter with respect to a reproduction laser power.

FIG. 6 is a block diagram showing a configuration of a conventional AGC circuit.

[Description of Signs] 1 ... AGC circuit, 2 ... Gain variable amplifier, 3 ... Peak hold, 4 ... Upper envelope extraction means, 5 ... Bottom hold, 6 ... Lower envelope Extraction means, 7 ...
Subtraction circuit, 20 optical disc device, 24 optical pickup, 31 MTF evaluation circuit

Claims (4)

[Claims] 1. An apparatus for detecting an amplitude of a reproduction signal of an optical disk,
An automatic gain control device that keeps the amplitude of the reproduction signal constant; a peak level recording unit that records a peak level of the reproduction signal; a bottom level recording unit that records a bottom level of the reproduction signal; and a peak level of the reproduction signal. An upper envelope extracting means for extracting an upper envelope signal within a certain range from; a lower envelope extracting means for extracting a lower envelope signal within a certain range from a bottom level of the reproduction signal; and the upper envelope signal. And a subtracting means for subtracting the lower envelope signal from the control signal. 2. Detecting the amplitude of a reproduction signal of an optical disk,
In the automatic gain control method for keeping the amplitude of the reproduction signal constant, an upper envelope signal within a certain range from the peak level of the reproduction signal, and a lower envelope signal within a certain range from the bottom level of the reproduction signal. The automatic gain control method comprises: detecting a difference between the signals; and performing amplitude correction of the reproduction signal based on a result of the detection. 3. Recording a peak level of the reproduction signal, recording a bottom level of the reproduction signal, extracting the reproduction signal within a certain range from the peak level, and extracting a reproduction signal within a certain range from the bottom level. 3. The method according to claim 2, further comprising: extracting the reproduction signal in a range from the peak level to subtracting the reproduction signal in a range from the bottom level to the reproduction signal within a range from the peak level. Automatic gain control method. 4. An optical disk apparatus for accessing an optical disk, wherein: a light source for irradiating the optical disk with a laser beam; and a reproduction for outputting a reproduction signal whose signal level changes in accordance with return light of the laser beam reflected by the optical disk. Means, peak level recording means for recording a peak level of the reproduction signal, bottom level recording means for recording a bottom level of the reproduction signal, and an upper envelope signal within a certain range from the peak level of the reproduction signal. Upper envelope extracting means for extracting, lower envelope extracting means for extracting a lower envelope signal within a certain range from the bottom level of the reproduced signal, and subtracting means for subtracting the lower envelope signal from the upper envelope signal. An automatic gain control device having: An optical disk device, comprising: signal level detecting means for detecting a signal level of the reproduction signal at predetermined time intervals before and after crossing the reference level of (i), and arithmetic means for detecting a level difference between the signal levels. .