JPH0379768B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention is directed to an information reproducing device that reproduces information recorded from a recording medium such as a video disc or a digital audio disc. The present invention relates to a servo control circuit that performs control to maintain an appropriate focus state in a tracking state or in the case of an optical device.

BACKGROUND ART AND PROBLEMS Information reproduction uses a disk-shaped recording medium provided with an information recording track formed by an arrangement of pits corresponding to information such as a video signal or an audio signal, and reproduces information from the recording medium. Regarding equipment,
Information reproducing systems that reproduce recorded information by scanning an information recording track on a recording medium with a light beam such as a laser beam and detecting changes in the light beam are known as video disk systems and digital audio systems. - Known as disk system, etc. In an information reproducing device of such a system, when scanning an information recording track on a recording medium with a light beam, the light beam is always made to accurately reach the information recording track, and the information recording track is properly placed on the information recording track. Automatic control is required to focus on the state. Automatic control for the purpose of making these light beams reach the information recording track correctly and automatic control for properly focusing the light beam on the information recording track are called tracking control and focus control, respectively. , has become indispensable for this type of optical information reproducing device.

These controls usually involve the output signal obtained by the photosensitive element when the light beam is made incident on the recording medium via the optical head, modulated by the recording medium, and guided back to the photosensitive element via the above-mentioned optical head. An optical means for obtaining tracking error and focus error detection signals according to the arrival state and focusing state of the light beam on the information recording track from the information recording track, and configuring the optical head based on these detection signals, for example, This is achieved by providing respective servo control circuits that drive lenses, mirrors, etc. to control their positions. An example of an optical system provided with such a servo control circuit in an optical information reproducing apparatus is shown in FIG. 1 of the drawings. In the figure, reference numeral 1 denotes a disk as a recording medium, on which an information recording track consisting of an array of pits is formed. 2 is a laser light source, and the laser light from this laser light source 2 enters a polarizing beam splitter 5 via a diffraction grating plate 3 and a collimator lens 4. The laser beam that has passed through the polarizing beam splitter 5 enters an objective lens 7 constituting an optical head via a quarter-wave plate 6, and is focused by the objective lens 7 and made incident on the disk 1. The objective lens 7 can be controlled in position by driving means 8 and 9, for example, in a direction across the information recording track and in a direction toward or away from the recording medium. The laser beam incident on the disk 1 is modulated by the information recording track and reflected, enters the objective lens 7 again, passes through the 1/4 wavelength plate 6, and enters the polarizing beam splitter 5. Then, the reflected laser light that is refracted to the right in the figure by the polarizing beam splitter 5 is transmitted to the lens system 10.
The light reaches the photosensitive section 11 via. And photosensitive part 1
The optical detector 1 detects the reflected laser light modulated by the recording medium from the objective lens 7 forming the optical head, that is, the reading light, and the change thereof is extracted as a signal. This photosensitive section 11
The output signal of A drive signal for driving and controlling the position of the objective lens 7 constituting the head is generated and supplied to drive means 8 and 9 for tracking control and focus control. Furthermore, a reproduction information signal is also obtained from the signal processing section 12.

In the above-mentioned optical system, the laser beam from the laser light source 2 is divided into three laser beams when passing through the diffraction grating plate 3, and in FIG. 1, one line is shown for simplicity. However, in the optical path from the diffraction grating plate 3 onwards, passing through the polarizing beam splitter 5, reflecting on the disk 1, refracting at the polarizing beam splitter 5, and reaching the photosensitive section 11, there is actually There are three laser beams. These three laser beams are, as shown in FIG. Two auxiliary beams 14E and 14F are made incident for detecting a tracking deviation with respect to the track T. In this case, two auxiliary beams 14
E and 14F are positioned symmetrically with respect to the direction along the information recording track T and the direction perpendicular thereto, with the main beam 13 as the center. The main beam 13 and the auxiliary beams 14E and 14F reflected by the disk 1 are sent to separate beams in the photosensitive section 11 via a cylindrical lens for detecting the focus state, which constitutes the common lens system 10. The photodetector is made to reach the photodetector. Therefore, as shown in FIG. 3, the photosensitive section 11 has four photodetectors 15A, 1
5B, 15C and 15D, and two photodetectors 16E and 16F separated from these, a spot is created by the main beam 13 on the four photodetectors 15A to 15D, and a light Auxiliary beams 14E on detectors 16E and 16F, respectively
and 14F spots are created. The main beam 1 for each of the photodetectors 15A to 15D is
Output signals I _A , I _B , _IC and _ID corresponding to the spot portions of 3 are obtained, respectively, and output signals corresponding to the dimensions of the spots of the auxiliary beams 14E and 14F are obtained from the photodetectors 16E and 16F, respectively. Signals I _E and I _F are obtained, respectively.

The signal processing section 12 is conventionally configured as shown in FIG. 4, for example. In addition to a servo control circuit for tracking control and a servo control circuit for focus control, this also includes a circuit for obtaining a reproduction information signal.

The servo control circuit for tracking control uses output signals I _E of photodetectors 16E and 16F.
and _IF are supplied to the subtractor 17 to obtain a detection signal of a tracking error, that is, a tracking error represented by I _{E −IF} , and this detection signal is supplied to the servo amplifier 18 to output the servo amplifier. The configuration is such that a drive current for the tracking control drive means 8 is supplied from the output end of the tracking control drive means 8 .
The driving means 8 is a movable coil for moving the objective lens 7 in a direction across the information recording track.
The objective lens 7 is driven according to the current flowing therein, and the main beam 13 and the auxiliary beams 14E and 14F are
is moved in a direction perpendicular to the direction along the information recording track T. In this case, since the mutual positional relationship between the main beam 13 and the auxiliary beams 14E and 14F is fixed, the main beam 13 and the auxiliary beams 14E and 14F are moved simultaneously in the same direction. The tracking error detection signal represented by I _E - _IF changes in polarity and level depending on the deviation of the tracking of the main beam 13 with respect to the information recording track T toward the center and outer circumference of the disk 1. Although the signal changes, the objective lens 7 is moved so that the tracking error detection signal becomes zero, and tracking control is thereby performed.

A servo control circuit for focus control supplies the output signals I _A and I _B of the photodetectors 15A and 15B to an adder 19 to generate a sum signal I _A +I _B of the two.
In addition, the output signals I _C and I _D of the photodetectors 15C and 15D are supplied to the adder 20 to obtain a sum signal of both.
We get I _C +I _D and both sum signals I _A +I _B and I _C +
Supply I _D to the subtractor 21 and obtain (I _A + I _B ) - (I _C + I _D )
A detection signal of a focus error, that is, a deviation of the focus state from the just focus state expressed by 9, the configuration is such that a drive current is supplied thereto. The driving means 9 is a movable coil for moving the objective lens 7 disposed facing the disk 1 in a direction perpendicular to the surface of the disk 1. lens 7 disk 1
The distance to can be changed. Although not shown, the shape of the spot on the photodetectors 15A to 15D caused by the main beam 13 is controlled by the cylindrical lens constituting the lens system 10, depending on the state of focus of the main beam 13 on the surface of the disk 1. change,
The polarity and level of the focus error detection signal expressed as (I _A + I _B ) - (I _C + I _D ) change. Then, the objective lens 7 becomes a certain distance from the disk 1, and the main beam 13 detects the photodetectors 15A to 15A.
The spot on 15D becomes circular as a whole,
The focus error detection signal expressed as (I _A + I _B ) - (I _C + I _D ) is made to be zero, and thus focus control is performed.

Note that the above-mentioned sum signal from adders 19 and 20
I _A + I _B and I _C + I _D are supplied to the adder 23, and I _A +
A reproduced information signal represented by I _B +I _C +I _D is extracted.

When vibrations due to an external force are applied to an information reproducing apparatus having an optical system equipped with the conventional servo control circuit for tracking control and focus control as described above, the vibrations cause damage to the disk and optical system, especially: A change in the relative positional relationship with the objective lens occurs, and tracking error and focus error easily increase. For example, the tracking error of the light beam that was following a certain information recording track on the disk suddenly increases due to vibration, and the state exceeds the range in which tracking control can be performed.
For example, the light beam moves to an adjacent information recording track and settles down in a tracking state in which it follows this adjacent information recording track, resulting in so-called track skipping. In this case, it is assumed that the focus control continues to be performed properly without becoming uncontrollable even when vibrations are applied. At this time, the tracking error detection signal, as shown by the signal Et in Figure 5A, repeats polarity reversal at a small level before the vibration is applied, but immediately after the time Ts, it suddenly reverses its polarity. The light beam reaches a large level, causing polarity reversal as the light beam moves to the adjacent information recording track. Then, the point at which the tracking control is restored and the light beam starts to follow the adjacent information recording track
After Ts′, the polarity is again repeatedly reversed at a small level. Note that the polarity of the signal Et may be opposite to that shown in the figure.

Furthermore, if the vibrations applied to the information reproducing device are even larger, the focus error will become too large, exceeding the range in which focus control can be performed, and correcting the focus error in the direction perpendicular to the surface of the objective lens disk. This results in a so-called out-of-focus state where no movement occurs. In this case, once the objective lens leaves the position range that can be controlled based on the focus error detection signal, it will not automatically return to its original position even after the vibration has subsided, and tracking control will not be performed. As a result, the reproduction operation of the information reproduction apparatus is essentially stopped. At this time, as shown by the signal Ef in FIG. 5B, the focus error detection signal repeatedly inverts its polarity at a small level before the time point Ts'' when vibration is applied, but immediately after the time point Ts''. When the level suddenly increases and exceeds a predetermined level, focus control is not performed and no focus error is detected, so the level becomes zero. Note that the polarity of the signal Ef may also be reversed from that shown.

When vibrations due to such external forces are applied to the information reproducing device, tracking control and focus control are necessary to maintain the tracking state and focus state appropriately without causing the above-mentioned track skipping or out-of-focus as much as possible. It is advantageous to set the gain of the servo control system in the servo control circuit to a large value. In other words, if the gain of the servo control system is large, it will respond sensitively to even slight changes in the tracking state or focus state.
Since the actual control means is driven, for example, the position of the objective lens is controlled, it is possible to avoid excessive tracking errors and focusing errors when vibrations due to external forces are applied.

However, when the gain of the servo control system is large, even in normal conditions when vibrations due to external forces are not applied, the actual control means driven for tracking control and focus control, such as the objective lens, Since the drive is performed extremely actively, a problem arises in that the control means moves more than necessary under normal conditions, resulting in increased mechanical noise.

Therefore, in order to solve this problem, the present applicant has developed a system that produces changes in response to vibrations caused by external forces applied to an information reproducing device, such as a tracking device.
detecting with a level detection circuit that the level of a specific signal, such as an error or focus error detection signal, is equal to or higher than a first reference level or equal to or lower than a second reference level lower than the first reference level;
The gain of the servo control system is increased only during that period, thereby increasing both the stability of tracking control or focus control in normal times and the vibration resistance when vibrations are applied to the information reproducing device due to external force. We previously proposed a servo control circuit for an information reproducing device that can be used.

However, according to such a servo control circuit, if the disk installed in the information reproducing device has no defects such as scratches on its information recording surface, the vibration resistance can be effectively improved. Although this is convenient, if the disc has defects such as scratches on its information recording surface, it may cause problems. That is, if there is a defect such as a scratch on the information recording surface of the disk, for example, this defect is optically read by the above-mentioned auxiliary beam and appears as pulse-like noise in the tracking error detection signal. When this pulse-like noise is equal to or higher than the first reference level detected by the above-mentioned level detection circuit or equal to or lower than the second reference level that is lower than the first reference level, this pulse-like noise Even if this happens, the gain of the servo control system will be increased. and,
Due to this pulse-like noise, a corresponding drive current for the tracking control drive means is generated in the form of a pulse current, but if the gain of the servo control system is increased at this time, Based on such pulse-like noise, the pulse current flowing through the tracking control driving means becomes extreme, and the tracking control is disturbed, causing the light beam to shift from the information recording track it was following to other information recording tracks. There is a possibility that the so-called track jump may occur.

Similarly, if there is a defect such as a scratch on the information recording surface of the disk, pulse-like noise will also occur in the focus error detection signal. In this case as well, if the gain of the servo control system is set high, the pulsed current flowing through the focus control drive means generated in response to this pulsed noise causes the focus control drive means to be driven. There is a possibility that the objective lens is moved beyond the range in which focus control can be performed, resulting in a so-called out-of-focus state. In this case, once the objective lens leaves the position range where focus control is possible, it does not automatically return to its original position, and tracking control is no longer performed, which effectively causes the information reproducing device to operate. will be stopped.

Purpose of the Invention In view of the above, the present invention provides that even if a recording medium such as a disk installed in an information reproducing device has a defect such as a scratch on the information recording surface, the defective portion cannot be read. When a defective part is detected, tracking control or focus control is performed in a state where it is less affected by the adverse effects of the defect, and tracking control or focus control with excellent vibration resistance is performed except when the defective part is being read. An object of the present invention is to provide a servo control circuit for an information reproducing device that can perform the following functions.

Summary of the Invention A servo control circuit for an information reproducing device according to the present invention includes an error detection signal generating section that obtains a tracking error or focusing error detection signal when information is reproduced from a recording medium installed in the information reproducing device. , a servo control system including a variable gain amplification section that supplies a drive signal based on the detection signal from the error detection signal generation section to a tracking control or focus control drive means, and a tracking/focus control drive means.
a level detection unit that detects that the level of the error or focus error detection signal is equal to or higher than a first reference level or equal to or lower than a second reference level lower than the first reference level; and a defect detection section that detects changes in the reproduced information obtained when the read information is read. The gain of the system is increased. With this configuration, even if the recording medium installed in the information reproducing device has a defect such as a scratch on its information recording surface, the information cannot be read except when the defective part is being read. has excellent vibration resistance, and when a defective portion is read, it is possible to perform tracking control and focus control that are less likely to be affected by the adverse effects of the defect.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 6 shows an example of a servo control circuit of an information reproducing apparatus according to the present invention, for example, a servo control circuit in an optical information reproducing apparatus having an optical system as shown in FIG. It is what was done. Here, the photosensitive section 30 includes photodetectors 15A to 15D, 16E, and 16 shown in FIG.
The output of this photosensitive section 30 is supplied to a reproduction signal generating section 31. The reproduction signal generating section 31 corresponds to, for example, a combination of the subtracter 17 or the adders 19 and 20 and the subtracter 21 in the circuit shown in FIG. an error detection signal generation section that generates an error or focus error detection signal; and an information signal generation section that receives the output of the photosensitive section 30 and generates a reproduced information signal, corresponding to the combination of the adders 19, 20, and 23; It consists of Then, the first one transmits the tracking error or focus error detection signal.
The output end of the variable gain amplification section 32 is connected to the input end of the variable gain amplification section 32, and the output end of the variable gain amplification section 32 is connected to the drive means 3 for tracking control or focus control.
3 to form a servo control system.

Further, the first output terminal of the reproduction signal generating section 31 is
It is also connected to the respective input terminals of a positive level detection section 34 that detects the positive level of the tracking error or focus error detection signal, and a negative level detection section 35 that detects the negative level of the detection signal. As a result, the positive electrode level detection section 34
The tracking error or focus error detection signal is supplied to the negative electrode level detection section 35, and the positive electrode level and negative electrode level of the tracking error or focus error detection signal are selected in both the detection sections 34 and 35, respectively. compared to the positive and negative reference levels +e ₁ and −e ₁ ,
When the positive electrode level is more than the positive reference level + e ₁ or the negative electrode level is less than the negative reference level - e ₁ ,
A detection output is obtained from the positive level detection section 34 or the negative level detection section 35. For example, if the tracking error detection signal is detected by the positive level detector 34,
When the tracking error detection signal is supplied to the negative electrode level detector 35, the level of the tracking error detection signal is compared with the positive reference level + _e1 in the positive electrode level detector 34, and when it is equal to or higher than the positive reference level + _e1 , the positive electrode is detected. A positive voltage is obtained as a detection output at the output end of the level detection section 34. Further, in the negative electrode level detecting section 35, the level of the tracking error detection signal is compared with the negative reference level _-e1 , and when the level is less than the negative reference level _-e1 , the output terminal of the negative electrode level detecting section 35 In addition, a positive voltage is obtained as a detection output.

Similarly, when the focus error detection signal is supplied to the positive level detection section 34 and the negative level detection section 35, the positive level and negative level of the focus error detection signal are set to the selected positive and negative reference levels +e. ₁ and −e ₁ , respectively,
When each becomes greater than or equal to the positive reference level + _e1 or less than or equal to the negative reference level _-e1 , a positive voltage is obtained as a detection output.

Here, the positive reference level +e ₁ in the positive electrode level detector 34 and the negative reference level -e ₁ in the negative electrode level detector 35 are shown in FIG. 5A for the tracking error detection signal. signal E _t
For example, levels +E and -E, and focus error detection signals are shown in Figure 5B.
As shown in the levels +E' and -E' for the signal E _f shown in , the tracking error detection signal or the focusing error detection signal does not reach the small level that is normally taken when no vibration is applied to the information reproducing device; It is selected for the highest level reached when vibration is applied to an information reproducing device.

The output terminals of the positive level detection section 34 and the negative level detection section 35 that generate detection outputs in this manner are connected to an OR gate 36, and the output terminal of the OR gate 36 is connected to one input terminal of an AND gate 37.

On the other hand, the second output terminal of the reproduction signal generation section 31 that sends out the reproduction information signal is connected to the envelope detection section 3.
Connected to 8. An output terminal of the envelope detection section 38 is connected to a comparison input terminal of a level comparison section 39, and a reference voltage source 40 is connected to a reference input terminal of the level comparison section 39. The reference voltage source 40 generates a voltage at a reference level _v1 , and this reference level _v1 is generated when a defect such as a scratch on the disc is read by the optical head of the information reproducing device.
Reproduction from the other output terminal of the reproduction signal generating section 31 obtained when the level of the reproduction information signal from the other output terminal of the reproduction signal generating section 31 is higher than that of the missing section and a normal section that is not defective on the disk is being read. The level of the reproduced information signal is selected to be lower than the level of the information signal, and when vibration from an external force is applied to the information reproducing device when a normal part of the disk with no defects is being read, the level of the reproduced information signal described above decreases. is chosen to be lower than the low level of the information signal that would otherwise occur. The output terminal of this level comparison section 39 is
It is connected to a comparison input terminal of a level comparison section 43 via a diode 41 and a capacitor 42 forming an integrating circuit, and a reference voltage source 44 is connected to a reference input terminal of the level comparison section 43. The output terminal of the level comparison section 43 is connected to the other input terminal of the AND gate 37, and the output terminal of the AND gate 37 is
It is connected to a gain control terminal of the variable gain amplification section 32.

Next, details of the operation of an example of the servo control circuit according to the present invention configured as described above will be described, taking as an example the case where it is used for tracking control.

In a stable operating state in which a defect-free portion of the disk is being read by the optical head, the tracking error detection signal _St obtained from the first output terminal of the reproduction signal generator 31 has a normal level. , no detection output is obtained from the positive level detection section 34 and the negative level detection section 35, and therefore, the AND gate 37 is in the off state and no control signal is supplied to the gain control terminal of the variable gain amplification section 32. . Therefore, the variable gain amplification section 32 amplifies the tracking error detection signal from the first output terminal of the reproduction signal generation section 31 with a predetermined gain,
This is supplied to the tracking control drive means 33. As a result, stable tracking control is performed.

When vibration due to an external force is applied to the information reproducing device in such a state, the tracking error detection signal S _t from the first output terminal of the reproduction signal generating section 31 becomes
For example, it has positive and negative large level parts, such as the large level part in the signal _Et shown in FIG. 5A. The levels of the high level portions of the positive electrode and negative electrode are respectively higher than the positive reference level +e ₁ in the positive electrode level detection section 34 and lower than the negative reference level -e ₁ in the negative electrode level detection section 35, and are at the positive electrode level. A positive voltage V, which is a detection output, is obtained from the detection section 34 and the negative level detection section 35. This positive voltage V is supplied to one input terminal of an AND gate 37 via an OR gate 36.

On the other hand, the reproduced information signal S ₁ obtained from the second output terminal of the reproduced signal generator 31 at this time produces a low level portion based on vibration, but this low level is applied to the reference input terminal of the level comparator 39. The voltage of the connected reference voltage source 40 does not fall below the reference level v ₁ . Therefore, the reproduction information signal S ₁ is supplied to the envelope detection section 38 and the envelope detection output signal S ₂ is supplied from the envelope detection section 38 to the level comparison input terminal. Output S ₃ continues to take a high level. Therefore, diode 41 and capacitor 42
The voltage S ₄ at the connection point with is at a high level, and this is supplied to the comparison input terminal of the level comparison section 43. The reference level v ₂ of the voltage of the reference voltage source 44 connected to the reference input terminal of the level comparison section 43 is the voltage S ₄ when the comparison output S ₃ from the level comparison section 39 is constantly at a high level. is selected to be slightly lower than the high level taken by Therefore, at this time, the comparison output obtained at the output terminal of the level comparison section 43
_S5 assumes a high level, which is supplied to the other input terminal of the AND gate 37. As a result, the AND gate 37 is turned on, and the voltage V from the OR gate 36, which is supplied to one input terminal at this time, is supplied as a control signal to the gain control terminal of the variable gain amplification section 32, and the variable gain amplification The gain of section 32 is increased. Therefore, at this time, tracking control is performed with the gain of the servo control system increased, preventing track jumps caused by vibrations caused by external forces, and maintaining a stable tracking state. is maintained.

By the way, if the disk to be read by the optical head has a defect such as a scratch, the reproduced information signal _S1 obtained from the second output terminal of the reproduced signal generator 31 will be as shown in FIG. 7A. This includes a missing portion d that occurs when a defect in the disk is read. In this case, since the defect on the disk usually extends over a plurality of information recording tracks on the disk, the missing portion d appears every time the disk rotates for a certain period of time corresponding to the scale of the defect. That is, in Figure 7,
t _N indicates the period during which the non-defective portion of the disk is read, and t _L indicates the period during which the defective portion of the disk is read.

Furthermore, when a defect on the disk is read, the tracking error detection signal S _{t obtained from the first output terminal of the reproduction signal generating section 31 includes the tracking error detection signal S t} shown in FIG. 7B.
A large-level pulse-like noise N as shown in FIG. The positive level and the negative level of this pulsed noise N are the positive reference level +e ₁ in the positive level detection unit 34 and the negative level detection unit 3, respectively.
Therefore, the positive level detector ₃₄ outputs a pulse corresponding to the positive level portion of the pulsed noise N as shown in FIG. 7C. A pulsed positive voltage V corresponding to the negative level portion of the pulsed noise N as shown in FIG. 7D is obtained from the negative level detection section 35. It will be done. Therefore, at the output end of the OR gate, a pulsed positive voltage V as shown in _FIG . .

On the other hand, the reproduced information signal _S1 as shown in FIG.
8, and from the envelope detection section 38,
The seventh signal corresponds to the envelope of the reproduction information signal _S1 .
An output signal _S2 as shown in Figure F is obtained. This output signal _S2 has a low level portion d' corresponding to the missing portion d of the reproduced information signal _S1 . Then, in the level comparator 39, the output signal _S2 is compared with the reference level _v1 of the voltage generated by the reference voltage source 40, as shown in FIG. , as shown in FIG. 7G, the comparison output S ₃ takes a low level l corresponding to the low level part d' of the output signal S ₂ that is lower than the reference level v ₁ , and takes a high level h in other cases. is obtained. This comparison output S ₃ is integrated by a diode 41 and a capacitor 42, and a voltage S ₄ as shown in FIG. 7H is obtained at the capacitor 42. In this case, the integral time constant is, during a period t _L during which the comparison output S ₃ changes to a low level l for each revolution of the disk,
The high level that the level of voltage S ₄ takes during period t _N
h It is set so that it does not return to ₀ . The voltage _S4 is determined by the level comparator 43, and the voltage generated by the reference voltage source 44 has the following voltage, as shown in FIG.
The voltage S ₄ is compared with a reference level v ₂ selected to be slightly lower than the high level h ₀ taken during the period t _N , and the level comparison section 43 outputs the voltage S 4 during the period t _N as shown in FIG. 7I. A comparison output _S5 is obtained which takes a high level h at , and takes a low level l from immediately after entering the period t _L until the end of the period t _L. In this way, during the period t _L during which the defective portion of the disk is read, the portion of the comparison output S ₅ that takes the low level l is detected as the detection output, and the level comparison is performed by the envelope detection section 38 described above. The circuit up to section 43 forms a defect detection section.

The comparison output S ₅ from the level comparison section 43 is supplied to the other input terminal of the AND gate 37 . Comparison output
Since S ₅ takes a low level l during the period t _L , the AND gate 37 is in the off state during the period t _L , and the pulse-like positive voltage V obtained from the OR gate 36 during this period t _L has a variable gain. It is not supplied to the gain control terminal of the amplifier section 32. Therefore, the gain of the variable gain amplification section 32 cannot be increased.

In this way, during the period _tL during which the defective portion of the disk is read, the comparison output _S5 takes the low level l, so the AND gate 37 is turned off, and even if the positive level detection unit 34 or the negative level Even if a positive voltage V is obtained from the detection unit 35,
The gain of the variable gain amplifier 32 is not increased, and tracking control is performed without increasing the gain of the servo control system. Therefore, it is possible to prevent the tracking control from being disturbed and track skipping to occur due to the pulse-like noise N generated when a disk defect is read in the tracking error detection signal S _t .

As mentioned above, in the end, when a normal part of the disc with no defects is being read, for example, when vibration is applied to the information reproducing device by an external force, the level of the tracking error detection signal becomes higher than the first reference level or Since the gain of the servo control system is increased only when the value falls below the second reference level, which is lower than the first reference level, the gain of the servo control system is excellent in vibration resistance, and is not susceptible to adverse effects caused by defects such as scratches on the disk. Tracking control, which was supposed to be difficult, will be performed.

Note that the case where the example of FIG. 6 is used for focus control and a focus error detection signal is obtained from the first output terminal of the reproduction signal generator 31 is the same as described above, and the disc is normal and has no defect. When a vibration is applied to the information reproducing device due to an external force while the part is being read, the high level part that occurs in the focus error detection signal is detected due to the vibration, and the gain of the servo control system is adjusted based on the detected output. Also, when a defective part of the disc is read, this is detected from the change in the playback information signal, and its detection output causes a large level in the focus error detection signal as the defective part of the disc is read. Even if noise occurs, the gain of the servo control system is prevented from increasing. Therefore, it is possible to perform focus control that has excellent vibration resistance, minimizes the possibility of defocusing when defects such as scratches on the disk are read, and is less susceptible to the adverse effects of disk defects. Become.

Application Example The servo control circuit of the information reproducing device according to the present invention is not only used as a servo control circuit in the optical information reproducing device as described above, but also in a so-called grooveless capacitance type disc reproducing device. It can also be used as a tracking servo circuit. In the case of a grooveless capacitive disk reproducing device, a tracking error in the reproducing head placed opposite to the recording track formed on the disk is detected, and the reproducing head is driven based on the detection signal to perform tracking. The servo control circuit section for obtaining the tracking error detection signal and supplying the drive signal to the tracking control driving means for the reproduction head is configured with the servo control circuit of the information reproduction apparatus according to the present invention. I can do it.

Effects of the Invention As is clear from the above explanation, according to the servo control circuit of the information reproducing device according to the present invention,
When vibrations are applied to the information reproducing device by an external force while a normal portion of the information recording surface of the recording medium loaded in the information reproducing device is being read, the gain of the servo control system is increased. On the other hand, when a defective part of the information recording surface of the recording medium is being read, the gain of the servo control system is prevented from increasing, so when performing tracking control or focus control, the recording Even if the information recording surface of the medium has defects such as scratches, when the defective portion is read, tracking control or focus control can be performed in a state that is less affected by the adverse effects of the defect, and When a defect-free portion, ie, a normal portion, is read, tracking control or focus control with excellent vibration resistance against vibrations caused by external forces applied to the information reproducing device can be performed.

[Brief explanation of drawings]

FIG. 1 is a schematic configuration diagram showing an example of an optical system in an optical information reproducing device, and FIG. 2 is a diagram for explaining a light beam in the optical system shown in FIG. 1.
3 is a schematic configuration diagram showing an example of the configuration of a photosensitive section used in the optical system shown in FIG. 1, and FIG. 4 is an example of a conventional signal processing section used in conjunction with the optical system shown in FIG. 1. Connection diagram shown in Figure 5 A and B
6 is a waveform diagram for explaining the situation when vibration is applied to the information reproducing device, FIG. 6 is a connection diagram showing an example of the servo control circuit of the information reproducing device according to the present invention, and FIG. FIG. 3 is a waveform diagram used to explain the operation of the example shown in the figure. In the figure, 30 is a photosensitive section, 31 is a reproduction signal generating section,
32 is a variable gain amplification section, 33 is a driving means for tracking control or focus control, 34 is a positive electrode level detection section, 35 is a negative electrode level detection section, 3
6 is an OR gate, 37 is an AND gate, 38 is an envelope detection section, 39 and 43 are level comparison sections, 41 is a diode, and 42 is a capacitor.

Claims (1)

[Scope of Claims] 1. An error detection signal generation unit that obtains a tracking error or focus error detection signal when information is reproduced from a recording medium installed in an information reproduction device; A servo control system is formed that includes a variable gain amplification section that supplies a drive signal based on the detection signal of the above to the tracking control or focus control drive means, and the level of the detection signal of the tracking error or focus error is a level detection unit that generates a first detection output by detecting that the recording medium is equal to or higher than a first reference level or lower than a second reference level that is lower than the first reference level; a defect detection unit that detects a change in reproduction information obtained when the level detection unit detects a change in reproduction information and generates a second detection output, the first detection output from the level detection unit is obtained, and the defect detection unit A servo control circuit of an information reproducing device configured to increase a gain of the servo control system when the second detection output of the above is not obtained.