JP2000235713A - Pit signal detecting circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent noise appeared by the synchronization with a pulse from being erroneously detected by a comparator binarizing a land prepit signal, by removing the unrequired pulses included in the land prepit signal. SOLUTION: This circuit is provided with a level shift circuit 21 for shifting a DC level of the signal taken out from an optical disk to Vref2 from Vref1, a level shift circuit 22 for shifting a DC level of the output signal of the level shift circuit 2 to Vref1 from Vref2, a high-pass filter 23 for suppressing signals having the frequency <=260 kHz from the output signal of the level shift circuit 22, and the comparator 24 for binarizing the output signal of the high-pass filter 23 by comparing it with a reference voltage Vref3. Since the clamping is effected when a voltage of the Vref2 is close to the negative power supply voltage of an operational amplifier 31, the negative pulse of the land prepit signal is cut in the output signal of the level shift circuit 21.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is mounted on an optical disk drive for recording and reproducing data by causing a light beam to follow a target track on an optical recording medium, and is prerecorded on a land on the optical recording medium. The present invention relates to a pit signal detection circuit for detecting a pit signal generated by a pit.

[0002]

2. Description of the Related Art As disclosed in Japanese Patent Application Laid-Open No. Hei 9-326138, a conventional write-once optical recording medium has wobbled grooves and pits (land pre-recording) at predetermined intervals in land areas between the grooves. Pits) are formed. For recording and reproduction, the rotation of the optical recording medium is controlled by the wobble signal detected from the wobbled groove, and the position on the optical recording medium where data should be recorded is determined by the land pre-pit signal detected from the land pre-pit. This is performed by detecting

A land pre-pit signal is extracted as follows. That is, a light beam is made to follow a target track on an optical recording medium, the return light of this light beam is divided into a plurality of areas by a plurality of photoelectric conversion elements, each of which is received and photoelectrically converted, and an output signal of each photoelectric conversion element is output. Is performed by a predetermined arithmetic unit. Then, a land pre-pit signal is extracted from the output of the arithmetic unit as a predetermined high-frequency component by a high-pass filter. The extracted land pre-pit signal is binarized by comparing it with a predetermined reference value by a comparator.

[0004]

An AC-coupling type filter is used as the high-pass filter, and the gain characteristic is shown in FIG. In FIG. 1, the cutoff frequency fc is increased if the low frequency component is to be completely cut. Note that the horizontal axis of the gain characteristic in FIG.
The frequency f is normalized by the cutoff frequency fc.

However, in this case, the cutoff frequency f
Since the CR time constant becomes smaller when c is increased, as shown in FIG.
In synchronization with the rise of the negative pulse b, the noise c,
d occurs. The positive pulse a of the land pre-pit signal is a signal detected from the land pre-pit located outside the groove on the circumference of the optical recording medium, and the negative pulse b is also detected inside the groove. This is a signal detected from the located land prepit.
The plus pulse a is used as the land pre-pit signal, and the minus pulse b is not used.

In this case, there is a problem that the comparator erroneously detects the noise d rising in synchronization with the negative pulse b as the positive pulse a.

An object of the present invention is to eliminate unnecessary pulses included in a pit signal and prevent a noise appearing in synchronization with the pulse from being erroneously detected by a comparator for binarizing the pit signal. It is to provide a detection circuit.

[0008]

According to a first aspect of the present invention, there is provided an optical disk drive for recording and reproducing data by causing a light beam to follow a target track on an optical recording medium. In a pit signal detection circuit for detecting a pit signal generated by a pit recorded in advance on a land portion, a plurality of photoelectric conversion elements for receiving and photoelectrically converting the return light of the light beam in each of the divided regions, An arithmetic unit that performs addition and subtraction using the output signal of each photoelectric conversion element; and a positive side of the pit signal included in the output signal of the arithmetic unit by shifting the DC level of the output signal of the arithmetic unit by a predetermined amount and clamping the operational amplifier. Alternatively, a first level shift circuit for cutting a pulse on the minus side, and the DC level of the output signal of the first level shift circuit is calculated by A second level shift circuit that shifts the output signal to a DC level, a first high-pass filter that extracts the pit signal as a predetermined high-frequency component from an output signal of the second level shift circuit, and the extracted pit signal And a first comparator that binarizes the pit signal by comparing the pit signal with a predetermined reference value.

Therefore, an unnecessary pulse on the plus side or the minus side of the pit signal can be cut, so that noise generated in synchronization with the pulse is not erroneously detected as a pit signal by the first comparator.

According to a second aspect of the present invention, in the pit signal detecting circuit according to the first aspect, a predetermined high-frequency component is extracted from an output signal of an arithmetic unit provided at a stage preceding the first level shift circuit. And a second high-pass filter for outputting to the first level shift circuit.

Therefore, the low frequency component can be removed to some extent in advance by the second high-pass filter. Therefore, even if the DC level of the wobble signal fluctuates, the plus or minus side of the pit signal is clamped by the operational amplifier. Can be sufficiently cut.

According to a third aspect of the present invention, in the pit signal detecting circuit according to the first or second aspect, a band-pass filter for extracting a wobble signal by extracting a predetermined frequency component from an output signal of the arithmetic unit, A second comparator for binarizing the wobble signal by comparing it with a predetermined reference value; and an AND circuit for ANDing the output signal of the first comparator and the output signal of the second comparator. It is characterized by the following.

Therefore, only the plus pulse of the pit signal at the peak of the wobble signal, which is required as a signal, is taken out, and the noise on the valley of the wobble signal is removed, thereby improving the reliability of the detection of the pit signal. be able to.

[0014] The invention according to claim 4 is the invention according to claims 1, 2, and 3.
3. The pit signal detection circuit according to any one of 3), wherein an error detection and correction circuit that detects and corrects an error of the pit signal detection by using a redundant code included in the pit signal, When the error detection and correction circuit detects an error, the reference value of the first comparator is increased or decreased by a predetermined amount according to a result of the comparison by the counter. And a control unit for maintaining the reference value of the first comparator at a current value when the correction circuit does not detect an error.

Therefore, the reference value of the first comparator which does not cause an error in the detection of the pit signal can be searched for, and the first comparator can be set to the reference value, thereby further reducing erroneous detection of the pit signal. can do.

The invention according to claim 5 is the invention according to claims 1, 2, and
3. In the pit signal detection circuit according to any one of (3), while detecting and correcting an error in the pit signal detection using a redundant code included in the pit signal, and when there is an error, the error data and the corrected data An error detection / correction circuit that compares the data with the data and outputs a signal indicating the type of the error; and, when the error detection / correction circuit detects an error, a first signal corresponding to the signal indicating the type of the error. Increase or decrease the reference value of the comparator of the predetermined amount,
A control unit for maintaining the reference value of the first comparator at a current value when the error detection and correction circuit does not detect an error.

Therefore, the reference value of the first comparator that does not cause an error in the detection of the pit signal can be found, and the first comparator can be set to the reference value, thereby further reducing erroneous detection of the pit signal. can do.

[0018]

[First Embodiment of the Invention] The first embodiment of the present invention will be described below.

An optical disk as an optical recording medium according to the first embodiment of the present invention is a write-once optical disk that can be written once only, has wobbled grooves, and has a predetermined interval in a land area between the grooves. Pits (land pre-pits) are formed. In addition, the recording and reproduction control the rotation of the optical disc by a wobble signal detected from the wobbled groove,
A position on the optical disc where data is to be recorded is detected based on a land pre-pit signal detected from the land pre-pit.

The groove interval (track pitch) is about 0.74 μm and is formed as a continuous spiral from the inner circumference to the outer circumference. A single frequency wobble signal is recorded in the groove as information for controlling the rotation speed of the optical disk and the clock frequency of the recording signal. Note that wobble means that the groove slightly meanders in the radial direction of the optical disk. In this example, the meandering width is about 20 nm, and the meandering cycle is about 25 μm. Therefore, this optical disk is rotated at a linear velocity of 3.5 m / sec.
When the wobble signal is reproduced, its frequency is about 140 kHz.
z.

In a land portion between the grooves,
A groove having a width of about 0.3 μm and a depth equal to that of the groove is formed as a land prepit for recording address information indicating a position on the optical disk.

FIG. 3 is a plan view schematically showing grooves and land prepits. In this example, land prepits 2 are arranged at predetermined intervals in a region between grooves 1 to be wobbled.
Are formed. Each land prepit 2 continues between adjacent grooves and is formed as a groove in the radial direction of the optical disk.

The land pre-pits 2 are formed corresponding to 1/0 of information. That is, the land prepit 2 is formed at the position corresponding to the information 1 and the land prepit 2 is not formed at the position corresponding to the information 0. Therefore, the presence or absence of the land pre-pit 2 corresponds to 1/0 of the information.

Next, the tracking control of the optical disk and the wobble signal of the groove and the land pre-pit signal are
A method of simultaneously reading out a single beam spot using the push-pull method will be described.

FIG. 4 is a block diagram of a tracking control circuit mounted on an optical disk drive for recording and reproducing data by making a light beam follow a target track on the optical disk. 4 is a beam spot B focused on the groove 1 in FIG.
e is photoelectrically converted using the pin diodes 3A, 3B, 3C, and 3D, which are four-divisions as photoelectric conversion elements, as detectors, and IV-converted, and signals corresponding to the four-division diodes are obtained. A, B, C, and D are obtained.

Using these signals A, B, C, and D, "A + B
When the operation of -CD "is performed by the arithmetic unit 4, a so-called push-pull tracking error signal is obtained. This signal is a signal corresponding to the relative position of the groove 1 and the beam spot Be in the radial direction. The wobble signal of the groove 1 is also reproduced at the same time, and even at the position where the land pre-pit 2 is recorded, the formation position of the land pre-pit 2 is on the inner side or the outer side of the optical disk with respect to the groove 1. Depending on the type, a plus or minus pulse signal is detected, which is also included in the signal "A + B-CD".

Therefore, only the tracking error signal is taken out of the signal of "A + BCD" through a low-pass filter (LPF) 5 and is fed to a tracking drive circuit 6
To output a tracking drive signal.

To detect a land pre-pit signal, a land pre-pit signal detection circuit 7 (described later) is used.

Since the wobble signal is a signal of a narrow band, a band-pass filter (BP) that passes the band is used.
By using F) 8, a wobble signal with a good S / N ratio can be obtained. The obtained wobble signal is
The binary data is binarized by the binarization circuit 9, and the binarized data is compared with a predetermined reference frequency in the frequency comparison circuit 10 to obtain a spindle motor control signal. The spindle motor control signal is a signal for controlling a spindle motor (not shown in FIG. 4) for rotating the optical disk.

FIG. 5 shows a waveform of a signal obtained when the beam spot Be is scanned along the groove 1 on which data is not recorded. Specifically, a pulse signal by the land pre-pits 2 on the outer periphery of the optical disc and a pulse signal by the land pre-pits 2 on the inner periphery having a polarity opposite to that of the pulse signal are superposed on the low frequency wobble signal. can get. The land pre-pit signal from the land pre-pits 2 on the outer side contains the address information necessary for each track, and the land pre-pit signal from the land pre-pits 2 on the inner side is not necessary.

Next, tracking using the push-pull method will be described with reference to FIG. In FIG.
Reference numeral 11 indicates an optical disk, reference numeral 12 indicates an objective lens, and reference numeral 1
Reference numeral 3 denotes a tracking actuator that drives the objective lens 12 in the tracking direction, and reference numeral 14 denotes a spindle motor that rotates the optical disk 11. The dotted line indicates the optical axis of the objective lens 12.

First, the reflected light from the optical disk 11 is applied to the photodetector 3 through the objective lens 12. The output of the photodetector 3 is subjected to analog calculation by the tracking drive circuit 6, and a drive signal proportional to the deviation of the beam spot Be from the target track is output. Since the tracks on the optical disk 11 are formed in a counterclockwise spiral shape, the beam spot Be is displaced from the track if the objective lens 12 remains stationary when the optical disk 11 rotates. The tracking actuator 13 is driven by the output tracking drive signal, and the objective lens 12 is moved so that the beam spot Be is moved.
Follows the target track.

Next, the features of the land pre-pit signal will be described. The peak value of the land pre-pit signal fluctuates due to the optical axis shift of the objective lens 12, the tilt of the optical disk 11, and the like. Regarding the optical axis shift of the objective lens 12, FIG.
This will be described with reference to FIG. 7 shows a case where the optical disk 11 is perpendicular to the optical axis of the objective lens 12 and the optical axis of the objective lens 12 is at the center of the photodetector 3. FIG. 8 shows a case where the optical disk 11 is perpendicular to the optical axis of the objective lens 12. However, this shows a case where the optical axis of the objective lens 12 is shifted toward the pin diodes 3A and 3B with respect to the center of the photodetector 3. 7 and 8, (b) is a perspective view of the photodetector 3 when (a) is viewed from the arrow. The peak value of the land pre-pit signal in the case of FIG. 8 is larger than that in the case of FIG. When the optical axis of the objective lens 12 is shifted in a direction opposite to the case of FIG. 8, the peak value of the land pre-pit signal becomes small. During tracking, the amount of deviation between the optical axis of the objective lens 12 and the center position of the photodetector 3 varies, and the peak value of the land prepit signal also varies.

The period of the fluctuation due to the optical axis deviation of the peak value of the land pre-pit signal, the inclination of the optical disk, etc. is 50 KH.
z or less. The addition of the fluctuation of the amplitude of the wobble signal having a period of 140 KHz to this results in the fluctuation of the land prepit signal at the peak value low frequency. The conventional land pre-pit signal detection circuit 7 includes a high-pass filter and a comparator. The low-pass frequency component of the land pre-pit signal is removed by the high-pass filter, and the land pre-pit signal is binarized by the comparator circuit. An AC-coupling type is used as the high-pass filter, and the gain characteristic is shown in FIG. In FIG. 1, the cut-off frequency fc is increased to completely cut low-frequency components. The horizontal axis of the gain characteristic in FIG. 1 is obtained by normalizing the frequency f with the cutoff frequency fc.

However, in this case, the cutoff frequency f
Since the CR time constant becomes smaller when c is increased, as shown in FIG.
In synchronization with the rise of the negative pulse b, the noise c,
d occurs. The positive pulse a of the land pre-pit signal is applied to the groove 1 on the circumference of the optical disk.
, And the negative pulse b is a signal detected from the land pre-pit 2 also located inside the groove 1. The plus pulse a is used as the land pre-pit signal, and the minus pulse b is not used.

In this case, there is a problem that the comparator erroneously detects the noise d rising in synchronization with the negative pulse b as the positive pulse a.

The contents of the land pre-pit signal detection circuit 7 that can prevent such a problem will be described below with reference to FIG.

The land pre-pit signal detection circuit 7
The DC level of the output signal of the arithmetic unit 4 is changed from Vref1 to Vr
level shift circuit 21 that is a first level shift circuit that shifts to ef2, and level shift circuit 22 that is a second level shift circuit that shifts the DC level of the output signal of the level shift circuit 21 from Vref2 to Vref1.
From the output signal of the level shift circuit 22, an AC-coupling type high-pass filter (HP) that suppresses a signal of 260 kHz or less in order to avoid the influence of a wobble signal and the influence of noise in a low frequency band due to wobble meandering.
F) 23, and a comparator 24, which is a first comparator that binarizes the output signal of the high-pass filter 23 by comparing it with a reference voltage Vref3.

The level shift circuit 21 includes an operational amplifier 31
The output of the arithmetic unit 4 is input to the non-inverting input terminal of the operational amplifier 31 via the resistor 32, and the reference voltage Vre
f1 and Vref2 are input to the non-inverting input terminal via the resistors 33 and 34, respectively. Also, the reference voltage Vref1 is
The signal is input to an inverting input terminal via resistors 35 and 36 connected in parallel, and a resistor 37 for negative feedback is also connected.
The level shift circuit 22 includes an operational amplifier 41, inputs an output of the arithmetic unit 4 to a non-inverting input terminal of the operational amplifier 41 via a resistor 42, and outputs reference voltages Vref2, Vre
f1 is input to the non-inverting input terminal via the resistors 33 and 34, respectively. Further, the reference voltage Vref2 is input to the inverting input terminal via the resistors 45 and 46 connected in parallel, and a resistor 47 for negative feedback is also connected. Note that the resistors 32 to 37 and 42 to 47 all have the same resistance value.

In the level shift circuit 21, the input signal Vi
1 and the reference voltage Vref2, the DC level of the input signal Vi1 is changed from Vref1 to Vr1.
ef2 and “output Vo1 = Vi1 + Vref
2 ". The level shift circuit 22 performs an analog subtraction between the input signal Vi2 and the reference voltage Vref2, so that the DC level of the input signal Vi2 becomes Vref2.
From Vref1 to “Vref1” and “output Vo2 = Vi2-
Vref2 ″ holds.

FIG. 10 shows the input signal (a), output signal (b) and level shift circuit 22 of the level shift circuit 21.
The output signal (c) of FIG. The reason why the negative pulse of the land pre-pit signal is cut in the output signal of the level shift circuit 21 shown in FIG. 10B is that the voltage Vref2 is clamped when it is close to the negative power supply voltage of the operational amplifier 31. is there. This clamp will be described with reference to FIG. That is, when the amplitude of the input signal is small, the operational amplifier outputs an output signal obtained by amplifying the input signal, but when the amplitude of the input signal exceeds a certain value, the excess portion is not output. For example, when the input signal is a sine wave (FIG. 11)
(A)), a waveform with the upper and lower clamped is output (FIG. 11 (b)). The level shift circuit 22 is for returning the output of the level shift circuit 21 to the Vref1 level again.

The output of the level shift circuit 22 has its low-frequency removed by the high-pass filter 23. However, since the negative pulse of the land pre-pit signal has been cut, it is generated in synchronization with this negative pulse. And the cutoff frequency fc can be sufficiently increased, thereby completely removing the low frequency. Then, the output of the high-pass filter 23 is binarized by the comparator 24.

[Second Embodiment] FIG. 12 is a circuit diagram of a land pre-pit signal detection circuit 7 used in a tracking control circuit according to a second embodiment of the present invention. In the description of the second embodiment of the present invention, the same reference numerals as in FIG.
And a detailed description is omitted.

The second embodiment of the present invention is different from the first embodiment in that a high-pass filter 51 as a second high-pass filter is provided in a stage preceding the level shift circuit 21. The high-pass filter 51 includes a low-pass filter 52 and an analog subtraction circuit 53.
The analog subtraction circuit 53 includes an operational amplifier 54 and resistors 55 to 58.

Next, the operation will be described.

In the case of the first embodiment of the present invention,
Is directly input to the level shift circuit 21 and the DC level of the wobble signal varies (FIG. 13A).
In some cases, the negative pulse of the land pre-pit signal cannot be completely clamped in the level shift circuit 21 (see FIG. 13).
(Refer to the output signal of the level shift circuit 21 in (b)).

However, according to the second embodiment of the present invention, the low-pass frequency component is removed to some extent by the high-pass filter 51 and then input to the level shift circuit 21. It can be completely clamped and removed.

The high-pass filter 51 extracts low-frequency components using the low-pass filter 52. However, since the output signal of the low-pass filter 52 has a phase difference from the original low-frequency components, The analog subtraction circuit 53 cannot completely remove low frequency components. Therefore, although the performance of the high-pass filter 51 alone is not sufficient, the combination with the high-pass filter 23 has a complementary effect, and the low-frequency components can be more completely removed.

[Third Embodiment] FIG. 14 is a circuit diagram of a land prepit signal detection circuit 7 used in a tracking control circuit according to a third embodiment of the present invention. In the description of the third embodiment of the present invention, the points common to the first and second embodiments of the present invention will be denoted by the same reference numerals in FIG. 14 and detailed description thereof will be omitted.

The third embodiment of the present invention is different from the first and second embodiments of the present invention in that a band-pass filter 61 and a second A comparator 62, which is a comparator of
An AND circuit 63 is provided. The band-pass filter 61 is a circuit similar to the band-pass filter 8, and extracts a wobble signal from the output signal of the arithmetic unit 4.
The comparator 62 binarizes the extracted wobble signal by comparing it with a reference value Vref4. The AND circuit 63 ANDs the output signal of the land pre-pit signal 7 and the output signal of the comparator 62.

Next, the operation will be described.

FIG. 15 shows a wobble signal (FIG. 15).
15A shows a timing chart with the binarized signal (FIG. 15B). The positive pulse of the land pre-pit signal required as a signal is located at the peak of the wobble signal and not at the valley. Therefore, the AND circuit 6
In step 3, by taking the AND of the binarized land pre-pit signal and the binarized wobble signal, noise on the valley position of the wobble signal is removed, and the reliability of the detection of the land pre-pit signal is reduced. Performance can be improved.

[Fourth Embodiment] FIG. 16 is a diagram showing an arrangement of land pre-pit signals in a sector which is one unit of data on an optical disc. The data amount recorded in one sector and one frame is about 2,366 bytes and 91 bytes, respectively, and one sector is composed of 26 frames as shown in FIG. The land pre-pit signal is synchronized with the wobble signal.
6 are output as shown in FIG. In other frames, a land pre-pit signal is recorded in an odd-numbered frame. When 1 is recorded as address information by the land pre-pit signal, a land pre-pit signal indicated by a dotted line in FIG. Is done. When 0 is recorded as the address information, the land pre-pit signal in the dotted line portion is not output. The land pre-pit signal is not normally recorded in the even-numbered frames. Therefore, one sector contains 12-bit address information, of which 4 bits are 16 bits.
The remaining 8 bits are the address of the sector in one ECC block composed of the sector, and the remaining 8 bits are part of 24-bit address information or 1-bit Reed-Solomon code on the optical disk of 1 ECC block. This Reed-Solomon code is a type of redundant code, which is added to the land pre-pit signal sequence in order to improve the reliability of the information. This code is used to check and correct errors when playing back the optical disk. Will be It should be noted that FIG.
It shows the location of address information and the like in the ECCblock.

FIG. 17 is a circuit diagram of the land pre-pit signal detection circuit 7 and the like used in the tracking control circuit according to the fourth embodiment of the present invention. In the description of the fourth embodiment of the present invention, the same points as in the third embodiment of the present invention are denoted by the same reference numerals in FIG. 17 and detailed description thereof will be omitted.

The fourth embodiment of the present invention is different from the third embodiment of the present invention in that an error detection and correction circuit 64 for detecting and correcting an error using Reed-Solomon code is further provided.
And a counter 65 for counting the number of land pre-pit signals after binarization in units of two frames. The output signal Err of the error detection and correction circuit 64 is a signal indicating the presence or absence of an error, and the output signal Ov of the counter 65
Is a signal that outputs 1 when the total of the pulses of the land pre-pit signal of the 25th and 26th frames of one sector is 2 or more, and outputs 0 when it is 1 or less.

Next, the operation will be described.

If the Err signal updated at the time of reading 16 sectors is 1 and there is an error, and the signal Ov is 0, the peak value of the land pre-pit signal may be low. The reference voltage Vref3 of the comparator 24 is reduced by a certain value by a circuit or the like,
When the signal Ov is 1, the reference voltage Vref3 is low, and it is considered that noise is erroneously detected as a land pre-pit signal.
f3 is increased by a certain value. Thereafter, the land prepit signal is read, and the reference voltage Vref3 is not changed until the Err signal is updated again. When the Err signal is updated and an error is detected, the reference voltage Vref3 is changed again according to the signal Ov as described above, and the land pre-pit signal is read. When the error disappears, such an operation is stopped and the reference voltage V at that time is stopped.
ref23 is held. The control unit of the present invention is implemented as described above.

Therefore, the reference voltage V of the comparator 24 which does not cause an error in the detection of the land pre-pit signal.
Since ref3 can be searched for, erroneous detection of the land pre-pit signal can be reduced.

[Fifth Embodiment] FIG. 18 is a circuit diagram of a land prepit signal detection circuit 7 and the like used in a tracking control circuit according to a fifth embodiment of the present invention. In the description of the fifth embodiment of the present invention, the same reference numerals in FIG.
And a detailed description is omitted.

The fifth embodiment of the present invention is different from the fourth embodiment in that an error check of a land prepit signal output from an AND circuit 63 instead of the error detection and correction circuit 64 and the counter 65 is performed. And an error detection and correction circuit 66 for performing correction. The error detection and correction circuit 66 outputs a signal Err indicating the presence or absence of an error to, for example, a microcomputer circuit (not shown). Further, the land pre-pit signal including the error and the corrected land pre-pit signal are compared, and in the case of an error in which one of the bits 1 is 0, 0 is output as a signal Dir, and 0 is output.
In the case of an error in which is set to 1, 1 is output as a signal Dir.

When the Err signal updated when 16 sectors are read is 1 and there is an error, the signal D
When ir is 0, it is considered that the peak value of the land pre-pit signal is low. Therefore, the reference voltage Vref3 of the comparator 24 is lowered by a certain value by control of a microcomputer circuit or the like (not shown). When the signal Dir is 1, , Reference voltage V
ref3 is low and noise may be erroneously detected as a land pre-pit signal.
The reference voltage Vref3 of No. 4 is increased by a constant value. After this,
The reference voltage Vref3 is not changed until the land pre-pit signal is read and the Err signal is updated again. Er
When the r signal is updated and an error is detected, the land prepit signal is read by changing the reference voltage Vref3 again according to the signal Dir as described above. And when the error disappears, stop such operation,
The reference voltage Vref3 at that time is held. The control unit of the present invention is implemented as described above.

Therefore, the reference voltage V of the comparator 24 is set such that no error occurs in the detection of the land pre-pit signal.
Since ref3 can be found and set to the reference voltage Vref3, erroneous detection of the land pre-pit signal can be reduced.

[0063]

According to the first aspect of the present invention, an unnecessary pulse on the plus side or the minus side of the pit signal can be cut, so that noise generated in synchronization with the pulse is removed by the first comparator. There is no false detection as a signal.

According to the second aspect of the present invention, in the pit signal detecting circuit according to the first aspect, the low frequency component can be removed to some extent in advance by the second high-pass filter. Changes,
Unnecessary pulses on the plus side or minus side of the pit signal can be sufficiently cut by the clamp of the operational amplifier.

According to a third aspect of the present invention, in the pit signal detecting circuit according to the first or second aspect, only the plus pulse of the pit signal at the peak of the wobble signal, which is required as a signal, is extracted. The noise on the valley can be removed, and the reliability of the detection of the pit signal can be improved.

The invention according to claim 4 is the invention according to claims 1, 2,
3. In the pit signal detection circuit according to any one of (3), a reference value of the first comparator that does not cause an error in pit signal detection can be found, and the first comparator can be set to the reference value. Therefore, erroneous detection of a pit signal can be further reduced.

The fifth aspect of the present invention provides the first, second, and third aspects.
3. In the pit signal detection circuit according to any one of (3), a reference value of the first comparator that does not cause an error in pit signal detection can be found, and the first comparator can be set to the reference value. Therefore, erroneous detection of a pit signal can be further reduced.

[Brief description of the drawings]

FIG. 1 is a graph showing a gain characteristic of an AC coupling type high-pass filter.

FIG. 2 is a diagram showing a waveform of a land pre-pit signal.

FIG. 3 is a plan view schematically showing grooves and land prepits of the optical disc according to the first embodiment of the present invention.

FIG. 4 is a block diagram of a tracking control circuit according to the first embodiment of the present invention;

FIG. 5 is a diagram showing a waveform of a signal obtained when a beam spot is scanned along a groove on which data is not recorded on the optical disc.

FIG. 6 is a block diagram for explaining a tracking control method.

FIG. 7 is a diagram illustrating an optical axis shift in the tracking control method.

FIG. 8 is a diagram illustrating an optical axis shift in the tracking control method.

FIG. 9 is a circuit diagram of a land pre-pit signal detection circuit of the tracking control circuit.

FIG. 10 is a diagram showing waveforms of an input signal and an output signal of a level shift circuit of the land pre-pit signal detection circuit.

FIG. 11 is a diagram illustrating a clamp of an operational amplifier.

FIG. 12 is a circuit diagram of a land pre-pit signal detection circuit of the tracking control circuit according to the second embodiment of the present invention;

FIG. 13 is a diagram for explaining a problem of the second embodiment of the present invention.

FIG. 14 is a circuit diagram of a land pre-pit signal detection circuit of the tracking control circuit according to the third embodiment of the present invention;

FIG. 15 is a timing chart of a wobble signal and a signal after binarization thereof.

FIG. 16 is a diagram showing an arrangement of a land pre-pit signal in a sector which is one unit of data of the optical disc according to the fourth embodiment of the present invention.

FIG. 17 is a circuit diagram of a land pre-pit signal detection circuit of the tracking control circuit according to the fourth embodiment of the present invention;

FIG. 18 is a circuit diagram of a land pre-pit signal detection circuit of the tracking control circuit according to the fifth embodiment of the present invention.

[Explanation of symbols]

 3A photoelectric conversion element 3B photoelectric conversion element 3C photoelectric conversion element 3D photoelectric conversion element 4 arithmetic unit 11 optical recording medium 21 first level shift circuit 22 second level shift circuit 23 first high-pass filter 24 first comparator 51 first 2 high-pass filter 61 band-pass filter 62 second comparator 63 AND circuit 64 error correction detection circuit 65 counter 66 error correction detection circuit Be light beam

Claims (5)

[Claims] 1. An optical disk drive device which records and reproduces data by causing a light beam to follow a target track on an optical recording medium, and is generated by pits recorded in advance on lands on the optical recording medium. In a pit signal detection circuit for detecting a pit signal, a plurality of photoelectric conversion elements for receiving and photoelectrically converting return light of the light beam by dividing a region, and performing addition and subtraction using output signals of the respective photoelectric conversion elements An arithmetic unit, and a first level shifter for shifting a DC level of an output signal of the arithmetic unit by a predetermined amount and cutting a plus or minus pulse of a pit signal included in the output signal of the arithmetic unit by clamping an operational amplifier. And a circuit for shifting a DC level of an output signal of the first level shift circuit to a DC level of an output signal of the arithmetic unit. A second level shift circuit, a first high-pass filter for extracting the pit signal as a predetermined high-frequency component from an output signal of the second level shift circuit, and comparing the extracted pit signal with a predetermined reference value. A pit signal detection circuit, comprising: a first comparator for binarization. A second high-pass filter provided before the first level shift circuit for extracting a predetermined high-frequency component from an output signal of an arithmetic unit and outputting the extracted high-frequency component to the first level shift circuit; The pit signal detection circuit according to claim 1, wherein: 3. A band-pass filter for extracting a wobble signal by extracting a predetermined frequency component from an output signal of an arithmetic unit; a second comparator for binarizing the wobble signal by comparing the wobble signal with a predetermined reference value; 3. The pit signal detection circuit according to claim 1, further comprising: an AND circuit that ANDs an output signal of the first comparator and an output signal of the second comparator. 4. An error detection and correction circuit for detecting and correcting an error in the detection of the pit signal using a redundant code included in the pit signal, and a counter for counting the pit signal and comparing it with a preset value. When the error detection and correction circuit detects an error, the reference value of the first comparator is increased or decreased by a predetermined amount according to the result of the comparison of the counter, and when the error detection and correction circuit does not detect the error, 4. The pit signal detection circuit according to claim 1, further comprising: a control unit configured to maintain a current reference value of the first comparator. 5. A method for detecting and correcting an error in the pit signal detection by using a redundant code included in the pit signal, and comparing the error data with the corrected data when an error is detected. An error detection / correction circuit that outputs a signal indicating the difference between the two, and when the error detection / correction circuit detects an error, the reference value of the first comparator is increased by a predetermined amount in accordance with the signal indicating the difference in the mode of the error or And a controller for maintaining the reference value of the first comparator at a current value when the error detection and correction circuit does not detect an error. The pit signal detection circuit according to any one of the above.