JP2002123945A - Signal processing circuit and optical disk drive using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem of the conventional disk drive that cannot have optimally compensated a deteriorated signal level due to missing of a signal caused by a defect such as a flaw or due to dirt such as a fingerprint in accordance with a reproduction speed of an optical disk when a time constant of an AGC circuit and a cut-off frequency of an HPF(High Pass Filter) are fixed. SOLUTION: When an operation section 17 selects a reproduction mode in the optical disk drive of this invention provided with an RF amplifier section 14 having an AGC circuit 21 and an HPF 22 and reproduction speed information corresponding to the selected reproduction mode is given to the RF amplifier section 14, a control section 24 sets a time constant corresponding to the reproduction speed to the AGC circuit 21 and a cut-off frequency corresponding to the reproduction speed to the HPF 22.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal processing circuit and an optical disk apparatus using the same, and more particularly to a signal processing circuit for processing a signal reproduced by reading recorded information from an optical disk and an analog signal processing system. And an optical disk device used as an RF amplifier unit.

[0002]

2. Description of the Related Art There is an optical disk device having a function of recording and / or reproducing information on a plurality of types of optical disks having different recording formats and the like. Optical discs include CDs (Compact Discs) and DVDs (Digits).
al Versatile Disc) is known.

In these optical disks, there are various clock pulses having a frequency n times the reference clock. For example, in a DVD, there are clock pulses of 3T to 11T (T is a reference clock frequency of a signal inscribed in a pit of the disk). Then, at the time of reproduction, by judging which of these clock pulses it is, it is possible to recognize whether the recording information of the disc is music, video or other data.

In an optical disk apparatus, information recorded on an optical disk is read by an optical pickup using laser light, and is photoelectrically converted by a photodetector to obtain an electric signal. Then, the signal is demodulated, and the only signal component actually desired in the demodulation processing is the AC component of 3T to 11T described above. Therefore, various signal processing is performed on the signal output from the optical pickup prior to the demodulation processing.

The signal processing system for that purpose is provided with various circuits such as an AGC (automatic gain control) circuit and an HPF (high-pass filter). The AGC circuit automatically controls the signal level, so that the signal level can be stabilized even if the signal level fluctuates due to media or mechanism, or if the level decreases due to aging such as temperature or contamination of the optical pickup lens. It has a function to enable demodulation. In addition, the HPF removes unnecessary DC components on signals with an optical pickup and uses AC of 3T to 11T.
It has the function of separating components.

[0006] Incidentally, the optical disc may have manufacturing variations, may be scratched by mishandling by the user, or may be stained by fingerprints when the user directly grasps it with bare hands. For example,
When an optical disk having a defect such as a scratch is reproduced, information cannot be read at the defective portion, and a signal loss occurs in that section.
Also, when an optical disk to which dirt such as fingerprints is adhered is reproduced, the top light quantity of the reflected light from the disk is reduced in the dirt portion, so that the signal level is reduced in that section.

If such a signal is demodulated as it is, the jitter (fluctuation of the digital signal in the time axis direction) is deteriorated, and the playability of the optical disk device is reduced.
For this reason, in the optical disk device, a signal loss due to a defect such as a scratch or a decrease in a signal level due to a stain such as a fingerprint is reduced by a time constant or an HP of the AGC circuit.
The compensation (absorption) is performed at the cutoff frequency of F. In particular, the time constant of the AGC circuit is set so as to follow a slower one, such as a level decrease due to a temporal change such as contamination of a medium, a mechanism, or a temperature or a pickup lens.

[0008]

However, in the conventional optical disk apparatus, since the time constant of the AGC circuit and the cutoff frequency of the HPF are fixed, signal loss due to defects such as scratches and contamination such as fingerprints are caused. Thus, an optimum compensation process corresponding to the reproduction speed of the optical disk could not be performed with respect to the decrease in the signal level caused by the above.

That is, in the optical disk device, for example,
CD1x CLV (Constant Linear Velocity), CD2
Double-speed CLV, CD48-times CAV (Constant Angular Ve
locity), DVD 1x CLV, DVD 12x CAV
And a number of playback modes are realized on the set. On the other hand, defects such as scratches on the optical disc and stains such as fingerprints change the reproduction time of the optical disc, and the time of the missing portion of the signal or the reduced portion of the signal level changes in inverse proportion to the reproduction speed.

On the other hand, the time constant of the AGC circuit and the HP
Since the cut-off frequency of F is fixed, the time constant and the cut-off frequency must be set to values that are intermediately satisfied with respect to the reproduction speed of the optical disk from low speed to high speed. However, an optimum compensation process cannot be performed for each reproduction speed from a low speed to a high speed of the optical disc, and the playability of the optical disc apparatus is reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has as its object to reduce a signal level caused by a loss of a signal caused by a defect such as a scratch or a stain caused by a fingerprint or the like. Another object of the present invention is to provide a signal processing circuit capable of improving playability by performing an optimal compensation process according to a reproduction speed of an optical disk, and an optical disk device using the same.

[0012]

A signal processing circuit according to the present invention comprises an AGC circuit for controlling the level of a signal corresponding to light reflected from an optical disk, and a high-frequency component of a signal corresponding to light reflected from an optical disk. At least one of the HPFs to be extracted is provided, and when switching the reproduction speed of the optical disk, at least one of the time constant of the AGC circuit and the cutoff frequency of the HPF is controlled in conjunction with the switching operation. This signal processing circuit is used as an RF amplifier section in an analog signal processing system of an optical disk device.

The signal processing circuit having the above-described structure and the RF
In an optical disk device used as an amplifier, by switching the time constant of the AGC circuit in conjunction with the switching operation of the optical disk reproduction speed, an optimal time constant corresponding to the reproduction speed can be set. This makes it possible to compensate (absorb) a drop in signal level due to stains such as fingerprints regardless of the reproduction speed. Further, by switching the cutoff frequency of the HPF in conjunction with the switching operation of the reproduction speed of the optical disk, it is possible to set an optimal cutoff frequency corresponding to the reproduction speed. This allows you to play
Loss of a signal due to a defect such as a scratch can be compensated (absorbed).

[0014]

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

FIG. 1 is a block diagram showing an example of the configuration of a signal processing system in an optical disk device according to the present invention.
In FIG. 1, an optical disk 11 such as a CD or a DVD
It is rotationally driven by a spindle motor 12. Information recorded on the optical disk 11 is read by the optical pickup 13. The optical pickup 13 is mounted on a carriage (not shown) and is configured to be movable in the disk radial direction.

The optical pickup 13 has a semiconductor laser as a light source, an objective lens for converging a light beam emitted from the semiconductor laser on a signal surface of the optical disk 11, and a focus for moving the objective lens in the optical axis direction. An actuator, a tracking actuator for displacing a beam spot converged on the signal surface of the optical disk 11 in the radial direction of the disk, and a photodetector such as a photodiode for receiving reflected light from the optical disk 11 and performing photoelectric conversion are incorporated therein.

An output signal of the optical pickup 13, that is, a signal obtained by reading recorded information of the optical disk 11 and performing photoelectric conversion is supplied to an RF amplifier section 14 in an analog signal processing system. The RF amplifier unit 14 has an AGC circuit 21, an HPF 22, an equalizer (EQ) 23, and the like.

In the RF amplifier section 14, the AGC circuit 2
1 is a signal level variation due to media, mechanism, etc.,
Alternatively, a process for automatically controlling the signal level to a constant level is performed in order to stably demodulate the level even due to a temporal change such as temperature or contamination of the lens of the optical pickup. The HPF 22 performs a process of removing unnecessary DC components on signals in the optical pickup 11 and separating AC components of 3T to 11T. The equalizer 23 performs equalizing processing of high-speed clock pulses such as 3T and 4T having a low aperture ratio.

The specific configuration of the RF amplifier section 14 is a feature of the present invention, and details thereof will be described later. The RF signal that has been subjected to the signal processing as described above in the RF amplifier unit 14 is converted into a digital signal processing circuit (DSP) 1
5 is supplied. The digital signal processing circuit 15 has a demodulation circuit (not shown), and performs signal processing such as demodulation.

In the optical disk device having the above configuration, the control of the entire system is performed by the system controller 16. For this system controller 16,
Various modes are set by the user from the operation unit 17. The modes include, for example, CD 1 × CLV, CD 2 × CLV, CD 48 × CAV, DV
Playback modes such as D1 × CLV and DVD 12 × CAV are exemplified. When a reproduction mode is designated from the operation unit 17, the system controller 16 supplies reproduction speed information corresponding to the reproduction mode to the RF amplifier unit 14.

FIG. 2 is a block diagram showing an example of the configuration of an RF amplifier section (signal processing circuit) 14 according to one embodiment of the present invention. In FIG. Is shown.

The RF amplifier section 14 includes an AGC circuit 21, an HPF 22, and an equalizer 23.
The control unit 24 controls the time constant of the C circuit 21 and the cutoff frequency of the HPF 22. This control unit 24
Is supplied with reproduction speed information of the optical disk 11 from the system controller 16 described above. When the playback speed information is given, the control unit 24 sets a time constant corresponding to the playback speed in the AGC circuit 21 and sets a cutoff frequency corresponding to the playback speed in the HPF 22.

FIG. 3 shows an example of the configuration of the AGC circuit 21 having a variable time constant. As is clear from the figure, the AGC circuit 21 includes a VCA (Voltage Controlled Amplifier) 3
1, a configuration including a detector 32 and a comparator 33. The VCA 31 has an input terminal connected to the circuit input terminal 34 and an output terminal connected to the circuit output terminal 35.

The detector 32 has an emitter follower 321 having a base connected to the output terminal of the VCA 31 and a collector connected to the power supply Vcc, and a current source 322 connected between the emitter of the transistor 321 and the ground. And a capacitor 323 connected in parallel to the current source 322. The comparator 33 has a detection output of the detector 32 as an inverted (-) input and a target voltage Vt as a non-inverted (+) input.

In the AGC circuit 21 having the above configuration, the VCA 3
1 is detected by a detector 32, and the detected output is compared with a target voltage Vt by a comparator 33.
The comparison output is fed back to the VCA 31 as a voltage for controlling the gain. Accordingly, a loop is performed so as to be the same as the target voltage Vt, and the level of the signal AGCout output from the circuit output terminal 35 becomes constant.

Here, in the detector 32, the power supply Vcc
Is the voltage of V, the current of the current source 322 is I,
Assuming that the capacity of C is 3, the time constant t of the AGC circuit 31 is t = CV / I (1). Then, as is apparent from the equation (1), by changing the current I of the current source 322, the time constant t of the AGC circuit 31 can be controlled.

As a method for changing the current I of the current source 322, for example, a plurality of current sources having different currents I are prepared as the current source 322, and a current corresponding to the reproduction speed of the optical disk 11 is selected from the plurality of current sources. A method of selecting one source or a combination of a plurality of sources can be considered. In the case of the present example, the control unit 24 controls the current I of the current source 322 according to the reproduction speed information.

The circuit shown in FIG. 3 as a specific example of the AGC circuit 31 is merely an example.
Is not limited to this circuit example, but may be any circuit configuration that can control the time constant t from outside.

FIG. 4 shows an HPF with a variable cutoff frequency.
22 shows an example of the configuration of FIG. As is apparent from FIG.
The PF 22 includes a capacitor 41, a gm amplifier 42, a current source 43, and a buffer 44. One end of the capacitor 41 is connected to the circuit input terminal 45. The other end of the capacitor 41 is connected to the output terminal of the gm amplifier 42 and the input terminal of the buffer 44. The output terminal of the buffer 44 is connected to the circuit output terminal 46 and to the inverting (-) input terminal of the gm amplifier 42. A reference voltage Vr is applied to a non-inverting (+) input terminal of the gm amplifier 42.

In the HPF 22 having the above configuration, if the capacitance of the capacitor 41 is C and the transconductance of the gm amplifier 42 is 1 / r, the transfer function HPFout is HPFout = SCr / (1 + SCr) (2) The frequency fc is as follows: fc = 1 / 2πCr (3)

Here, the transconductance 1 / r of the gm amplifier 42 is given by K, where I is the current of the current source 43.
It is determined by I (K is a constant). Therefore, the current source 4
3, the cutoff frequency fc of the HPF 22 can be controlled.

As a method of changing the current I of the current source 43, for example, a plurality of current sources having different currents I are prepared as the current source 43, and a current corresponding to the reproduction speed of the optical disk 11 is selected from the plurality of current sources. A method of selecting one source or a combination of a plurality of sources can be considered. In the case of the present example, the control unit 24 controls the current I of the current source 43 according to the reproduction speed information.

The circuit shown in FIG. 4 as a specific circuit example of the HPF 22 is merely an example, and the HPF 22 is not limited to this circuit example, and has a circuit configuration capable of controlling the cutoff frequency fc from outside. Anything is fine.

Next, the operation of the RF amplifier unit 14 when the reproduction mode is switched to, for example, two stages of low-speed reproduction and high-speed reproduction in the optical disk device according to the present embodiment having the above configuration will be described.

First, during low-speed reproduction, the optical disk 1
When dirt such as fingerprints is present on the optical pickup 1,
When the recorded information is read, the top light quantity of the reflected light from the optical disk 11 drops at the stained portion, and therefore, as shown in FIG. 5A, the signal level of the RF signal drops in that section. If this RF signal is demodulated as it is, it causes aggravation of jitter. However, by passing through the AGC circuit 21 having a certain time constant, a drop in signal level can be compensated (absorbed) as shown in FIG.

Next, consider the case where the reproduction mode is switched to increase the reproduction speed. At the time of high-speed reproduction, even with the same dirt, the rotation speed of the optical disk 11 is high, so that the portion where the signal level falls is relatively shorter than that at the time of low-speed reproduction, as shown in FIG. At this time, when the signal passes through the AGC circuit 21 having the same time constant as that at the time of low-speed reproduction,
The waveform shown in FIG. That is, the absolute time of the reaction of the AGC circuit 21 does not change despite the same dirt pattern, so that the waveform becomes relatively more unstable, which leads to the deterioration of jitter.

Therefore, the time constant of the AGC circuit 21 is also switched in conjunction with the switching of the playback mode, that is, the switching of the playback speed. Specifically, the time constant of the AGC circuit 21 is set to be smaller during high-speed playback than during low-speed playback. As described above, the AG having a smaller time constant than that during the low-speed reproduction is
By performing the level control on the RF signal by the C circuit 21, the absolute time of the reaction of the AGC circuit 21 becomes shorter than that at the time of low-speed reproduction, so that the level absorption becomes faster as shown in FIG. 6C. As a result, deterioration of jitter can be prevented.

The signal reproduced from the optical disk 11 has clock pulses of 3T to 11T as described above.
Since each level is different, the AGC circuit 2
If the time constant is set small in order not to cause 1 to react, on the contrary, jitter will be worsened. That is, the optimum time constant differs depending on the reproduction speed.

Therefore, as described above, by setting the optimal time constant corresponding to the reproduction speed in conjunction with the switching operation of the reproduction speed, the signal level caused by the stains such as fingerprints can be obtained regardless of the reproduction speed. Can be compensated for, jitter characteristics can be improved, and playability can be improved.

Next, the operation of the HPF 22 will be described. In the HPF 22, in the characteristic diagram of FIG.
If the cutoff frequency fc is too high, as in case 2,
A delay difference occurs between 3T and 11T, causing jitter deterioration. However, as in the case of fc = f1, the cutoff frequency fc
You can prevent that by setting. That is, normally, the cutoff frequency fc is set sufficiently low to make the delay time in the band flat.

However, some optical discs that are actually reproduced have defects such as scratches. Then, when an optical disk having a defect such as a scratch is reproduced, information cannot be read at the defect portion. Therefore, as shown in FIG. . When the missing signal is filtered by the HPF 22, a differential waveform is obtained, and it takes a time corresponding to the time constant until the signal becomes stable.

When a certain cutoff frequency fc is set for the HPF 22 at the time of low-speed reproduction, and the signal missing by the HPF 22 is filtered, the defect waveform becomes a differential waveform as shown in FIG. 8B. On the other hand, at the time of high-speed reproduction, the rotation speed of the optical disk 11 increases, so that the defect waveform becomes short as shown in FIG. On the other hand, if filtering is performed by the HPF 22 having the same cutoff frequency fc as that at the time of low-speed reproduction, as shown in FIG. 9B, the stabilization time for the defect becomes relatively long, and the jitter deteriorates.

Even at the same defect pattern, the defect waveform looks short at the time of high-speed reproduction in which the rotation speed of the optical disk 11 is high, and 3T to 11T corresponding to data.
Since T is also shifted higher, the cutoff frequency fc of the HPF 22 may be higher. Therefore, at the time of high-speed reproduction, the cutoff frequency fc of the HPF 22 is set higher than at the time of low-speed reproduction.
As a result, as shown in FIG. 9C, the stabilization time of the defect waveform due to the time constant becomes relatively smaller than that of the defect pattern, and the deterioration of jitter can be prevented.

As described above, by setting the optimal cutoff frequency fc corresponding to the reproduction speed for the HPF 22 in conjunction with the switching operation of the reproduction speed, the cutoff frequency fc caused by defects such as scratches can be obtained regardless of the reproduction speed. Therefore, it is possible to improve jitter characteristics and playability.

In the above description of the operation, the case where the reproduction mode (reproduction speed) is switched between low-speed reproduction and high-speed reproduction is described as an example. However, this is only an example for easy understanding. However, the present invention is not limited to this. That is, the reproduction mode is set to, for example, CD 1 × speed CL
V, CD 2x CLV, CD 48x CAV, DVD1
The switching can be performed in multiple stages such as double speed CLV and DVD 12 × speed CAV, and the time constant of the AGC circuit 21 and the cutoff frequency of the HPF 22 are set to values corresponding to the playback speed in conjunction with the switching operation of the playback mode. Good.

In the above embodiment, the AGC circuit 21
And the cutoff frequency of the HPF 22 is simultaneously controlled. However, the present invention is not limited to this. That is, AG
It is also possible to adopt a configuration in which only one of the time constant of the C circuit 21 and the cutoff frequency of the HPF 22 is controlled in accordance with the switching of the reproduction mode.

When the configuration for controlling only the time constant of the AGC circuit 21 is employed, a drop in signal level due to stains such as fingerprints can be compensated, and the playability of the optical disk device can be improved. HPF22
When only the cut-off frequency is controlled, the loss of a signal due to a defect such as a flaw can be compensated, so that the playability of the optical disc device can be improved. However, adopting a configuration in which both the time constant of the AGC circuit 21 and the cutoff frequency of the HPF 22 are simultaneously controlled is more advantageous in improving playability.

[0048]

As described above, according to the present invention,
AGC by switching the playback speed of the optical disk in conjunction with the switching operation
By switching the time constant of the circuit and the cut-off frequency of the HPF, the optimal time constant and cut-off frequency corresponding to the playback speed are set, so that the signal level drops due to fingerprints Signal loss due to such defects can be compensated, so that playability can be improved by improving jitter characteristics.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating an example of a configuration of a signal processing system in an optical disc device according to the present invention.

FIG. 2 is a block diagram illustrating a configuration example of an RF amplifier unit (signal processing circuit) according to an embodiment of the present invention.

FIG. 3 is a circuit diagram showing an example of a specific circuit configuration of an AGC circuit having a variable time constant.

FIG. 4 is a circuit diagram illustrating an example of a specific circuit configuration of an HPF having a variable cutoff frequency.

FIG. 5 is a waveform diagram at the time of low-speed reproduction, showing a signal waveform including a decrease in signal level due to a stain such as a fingerprint.

FIG. 6 is a waveform diagram at the time of high-speed reproduction showing a signal waveform including a decrease in signal level due to a stain such as a fingerprint.

FIG. 7 is a characteristic diagram of the frequency-delay time of the HPF.

FIG. 8 is a waveform diagram at the time of low-speed reproduction showing a signal waveform including a loss of a signal due to a defect such as a scratch.

FIG. 9 is a waveform diagram at the time of high-speed reproduction showing a signal waveform including a loss of a signal due to a defect such as a scratch.

[Explanation of symbols]

11 optical disk, 13 optical pickup, 14 RF
Amplifier section, 15 ... Digital signal processing circuit (DSP),
21: AGC circuit, 22: HPF (high-pass filter)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5C052 AA02 AC01 CC01 5C053 FA23 HA21 KA08 KA13 KA16 5D080 AA07 DA08 FA07 FA42 5D090 AA01 CC04 DD03 DD05 EE16 EE17 HH03 LL05

Claims (33)

[Claims] An automatic gain control circuit for controlling a level of a signal corresponding to light reflected from an optical disk; and an automatic gain control circuit for switching the reproduction speed of the optical disk in conjunction with the switching operation. A signal processing circuit comprising: a control unit that controls a constant. 2. The signal processing circuit according to claim 1, wherein the control unit changes the time constant of the automatic gain control circuit by controlling current. 3. The control unit according to claim 1, wherein when the reproduction speed of the optical disc is switched from a first speed to a second speed higher than the first speed, the time constant of the automatic gain control circuit is set to a first time. 2. The signal processing circuit according to claim 1, wherein the switching is performed from a constant to a second time constant smaller than the first time constant. 4. The signal processing circuit according to claim 3, wherein the control unit switches the time constant of the automatic gain control circuit from small to large when switching the reproduction speed of the optical disk from high to low. . 5. The signal processing circuit according to claim 3, wherein the control unit changes the time constant of the automatic gain control circuit by switching a current. 6. A high-pass filter for extracting a high-frequency component of a signal corresponding to light reflected from an optical disk, and the high-pass filter interlocking with the switching operation when switching the reproduction speed of the optical disk. And a control unit for controlling a cutoff frequency of the signal processing circuit. 7. The signal processing circuit according to claim 6, wherein the control unit changes the cutoff frequency of the high-pass filter by controlling a current. 8. The control unit, when switching the reproduction speed of the optical disk from a first speed to a second speed higher than the first speed, sets a cutoff frequency of the high-pass filter to a first speed. 7. The signal processing circuit according to claim 6, wherein the cutoff frequency is switched to a second cutoff frequency higher than the first cutoff frequency. 9. The signal processing according to claim 8, wherein the control unit switches the cutoff frequency of the high-pass filter from high to low when switching the reproduction speed of the optical disk from high to low. circuit. 10. The signal processing circuit according to claim 8, wherein the control unit changes the cutoff frequency of the high-pass filter by switching a current. 11. An automatic gain control circuit for controlling a level of a signal corresponding to light reflected from an optical disk, a high-pass filter for extracting a high-frequency component of a signal corresponding to light reflected from the optical disk, A signal processing unit for controlling a time constant of the automatic gain control circuit and a cutoff frequency of the high-pass filter in conjunction with the switching operation when switching the reproduction speed of the optical disc. circuit. 12. The signal processing device according to claim 11, wherein the control unit changes a time constant of the automatic gain control circuit and a cutoff frequency of the high-pass filter by controlling current. circuit. 13. The control unit, when switching the reproduction speed of the optical disk from a first speed to a second speed higher than the first speed, sets a time constant of the automatic gain control circuit to a first time. Changing the cutoff frequency of the high-pass filter from a first cutoff frequency to a second cutoff frequency higher than the first cutoff frequency from a constant to a second time constant smaller than the first time constant; The signal processing circuit according to claim 11, wherein the frequency is switched to each of the frequencies. 14. The control unit, when switching the reproduction speed of the optical disk from high speed to low speed, changes the time constant of the automatic gain control circuit from low to high, and changes the cutoff frequency of the high-pass filter from high to low. 14. The signal processing circuit according to claim 13, wherein the signal processing circuit is switched to each of the following. 15. The signal processing according to claim 13, wherein the control unit changes the time constant of the automatic gain control circuit and the cutoff frequency of the high-pass filter by switching a current. circuit. 16. A spindle motor for rotating an optical disk, a pickup for reading recorded information on an optical disk rotationally driven by the spindle motor, and controlling a level of a signal output from the pickup when reading recorded information on the optical disk. An automatic gain control circuit; a control unit that controls a time constant of the automatic gain control circuit in conjunction with the switching operation when switching the reproduction speed of the optical disc; and a demodulation that demodulates a signal that has passed through the automatic gain control circuit. An optical disk device comprising a circuit. 17. The optical disk device according to claim 16, wherein the control unit changes the time constant of the automatic gain control circuit by controlling a current. 18. The control unit, when switching the reproduction speed of the optical disk from a first speed to a second speed higher than the first speed, sets a time constant of the automatic gain control circuit to a first time. 17. The optical disk device according to claim 16, wherein the constant is switched to a second time constant smaller than the first time constant. 19. The optical disk device according to claim 18, wherein the control unit switches the time constant of the automatic gain control circuit from small to large when switching the reproduction speed of the optical disk from high to low. 20. The optical disk device according to claim 18, wherein the control unit changes the time constant of the automatic gain control circuit by switching a current. 21. A pickup comprising: a laser light source for emitting laser light to an optical disk; and a photodetector for receiving reflected light from the optical disk based on the laser light emitted from the laser light source and performing photoelectric conversion. 17. The optical disk device according to claim 16, comprising: 22. A spindle motor for rotationally driving an optical disk, a pickup for reading recorded information on an optical disk rotationally driven by the spindle motor, and a high-frequency component of a signal output from the pickup when reading recorded information on the optical disk. A high-pass filter to be extracted; a control unit for controlling a cut-off frequency of the high-pass filter in conjunction with the switching operation when switching a reproduction speed of the optical disc; and demodulating a signal passed through the AGC circuit. An optical disc device comprising a demodulation circuit. 23. The optical disk device according to claim 22, wherein the control unit changes the cutoff frequency of the high-pass filter by controlling a current. 24. The control unit, when switching the reproduction speed of the optical disc from a first speed to a second speed higher than the first speed, sets a cutoff frequency of the high-pass filter to a first speed. 23. The optical disc device according to claim 22, wherein the cut-off frequency is switched to a second cut-off frequency higher than the first cut-off frequency. 25. The optical disk device according to claim 24, wherein the control unit switches the cutoff frequency of the high-pass filter from high to low when switching the reproduction speed of the optical disk from high speed to low speed. . 26. The optical disk device according to claim 24, wherein the control unit changes the cutoff frequency of the high-pass filter by switching a current. 27. A pickup comprising: a laser light source for emitting laser light to an optical disk; and a photodetector for receiving reflected light from the optical disk based on the laser light emitted from the laser light source and performing photoelectric conversion. 23. The optical disk device according to claim 22, comprising: 28. A spindle motor for rotating an optical disk, a pickup for reading recorded information on an optical disk rotationally driven by the spindle motor, and controlling a level of a signal output from the pickup when reading recorded information on the optical disk. An automatic gain control circuit; a high-pass filter for extracting a high-frequency component of a signal output from the pickup when reading recorded information on the optical disc; and, when switching a reproduction speed of the optical disc, interlocking with the switching operation. A control unit that controls a time constant of the automatic gain control circuit and a cutoff frequency of the high-pass filter; anda demodulation circuit that demodulates a signal that has passed through the gain control circuit circuit and the high-pass filter. Characteristic optical disk device. 29. The optical disk device according to claim 28, wherein the control unit changes the time constant of the automatic gain control circuit and the cutoff frequency of the high-pass filter by controlling current. . 30. The control unit, when switching a reproduction speed of the optical disc from a first speed to a second speed higher than the first speed, sets a time constant of the automatic gain control circuit to a first time. Changing the cutoff frequency of the high-pass filter from a first cutoff frequency to a second cutoff frequency higher than the first cutoff frequency from a constant to a second time constant smaller than the first time constant; 29. The optical disk device according to claim 28, wherein the frequency is switched to each of the frequencies. 31. When switching the reproduction speed of the optical disk from high speed to low speed, the control unit changes the time constant of the automatic gain control circuit from low to high, and changes the cutoff frequency of the high-pass filter from high to low. 31. The optical disk device according to claim 30, wherein each of the optical disk devices is switched. 32. The optical disk apparatus according to claim 30, wherein the control unit changes the time constant of the automatic gain control circuit and the cutoff frequency of the high-pass filter by switching a current. . 33. A pickup comprising: a laser light source for emitting laser light to an optical disk; and a photodetector for receiving reflected light from the optical disk based on the laser light emitted from the laser light source and performing photoelectric conversion. 29. The optical disk device according to claim 28, comprising: