JP2000251283A - Tracking error signal detecting circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a tracking error signal detecting circuit that can generate an accurate tracking error signal even in the case where the objective lens position is deviated from the center by the lens shift. SOLUTION: The phase comparison circuits 31, 32 calculate phase differences ΔϕA-B, ΔϕC-D of the photo-electric conversion signals of the photo-electric conversion element and also calculates the basic tracking error signal TE0 by adding these phase differences with an adding circuit 34. The DC elements x, y of the phase differences ΔϕA-B, ΔϕC-D are extracted with filters 41, 42, the compensation signal Δz is calculated with the compensation signal generating circuit 44, and the basic tracking error signal TE0 is compensated with the compensation circuit 50 using the compensation signal Δz. The compensation signal generating circuit 44 calculates the differences Δx=VC-x between the DC element x and reference value VC and the difference Δy=VC-y between the DC element y6 and reference value VC, also calculates Δx+Δy, Δx-Δy as the compensation signal Δz and outputs any one of Δx+Δy, Δx-Δy depending on the difference between the DC element (x) and reference value VC and the difference between the DC element (y) and the reference value VC.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tracking error signal detection circuit for calculating a tracking error signal used for tracking control in an optical information reproducing apparatus, and more particularly, to a method for detecting a detection signal from a four-division photoelectric converter. The present invention relates to a technique for improving detection accuracy in a tracking error signal detection circuit that detects a tracking error signal by a phase difference method.

[0002]

2. Description of the Related Art Compact discs (CD, CD-RO)
M) In various optical information reproducing devices that reproduce information optically, such as devices and magneto-optical (MO, MD) recording devices, tracking control is performed to position an optical head at an information recording section of a recording medium. For the tracking control, the optical information reproducing apparatus is provided with a tracking error signal detection circuit for detecting how much the optical head is deviated from the target track of the recording medium. . The tracking control means in the optical information reproducing apparatus controls the positioning of the optical head so that the tracking error detected by the tracking error signal detection circuit becomes zero.

Various tracking error signal detection methods have been proposed (for example, supervised by Morio Onoe,
"Optical disc technology", Radio technology selection book 198, 85-9
9, page 9). Among such tracking error signal detection methods, a conventional technique of a phase difference type tracking error signal detection circuit will be described. The phase difference tracking error signal detection method is to arrange at least two photoelectric conversion elements so as to sandwich a track of a recording medium and detect a phase difference between detection signals of the photoelectric conversion elements to detect a tracking error. It is a method of detecting.

As an example of conventional tracking error detection, a four-division photoelectric converter having four photoelectric conversion elements divided into two in the track direction of a recording medium and divided into two in the radial direction, that is, divided into four in total. There is a method of detecting a tracking error by a phase difference method.
The principle of calculating the tracking error is to calculate the sum of the photoelectric conversion elements at diagonal positions among the four photoelectric conversion elements, and then calculate the difference (phase difference) between the two sum signals as the tracking error. Is assumed.
In addition, even if the far-field image of the photoelectric converter moves in the direction perpendicular to the direction in which the information track is mapped, the phase is located in front of the rotation direction of the recording medium so that an accurate tracking error signal can be calculated. After the detection signal of the photoelectric conversion element that generates the advanced signal is delayed for a predetermined time to adjust the phase, the sum of the detection signals of the two photoelectric conversion elements at the diagonal positions is calculated, and the sum signal is calculated. The phase difference is detected as a tracking error.

[0005] Another conventional tracking error signal detection method is a phase difference method using a four-division type photoelectric converter, in which the position of an objective lens mounted on an optical head is deviated from the center due to a lens shift. Some can calculate an accurate tracking error signal. However, in this phase difference detection method, the detection signals of a pair of photoelectric conversion elements located at the same radial position are not used as a pair of the photoelectric conversion elements located at diagonal positions.

A tracking error signal detection circuit using detection signals of a pair of photoelectric conversion elements located at the same radial position will be described with reference to FIG. The tracking error signal detection circuit illustrated in FIG. 8 is divided into two in the track direction of the recording medium and divided in two in the radial direction, and has a four-division type having photoelectric conversion elements A, B, C, and D divided into four in total. Process the output signal of the photoelectric converter. The first phase comparison circuit 511 calculates a phase difference Δφ1 between the output signals of the photoelectric conversion elements A and B which are in the same phase state with respect to the moving direction of the track of the recording medium. Phase difference Δ between output signals of photoelectric conversion elements C and D in the same phase state
φ2 is calculated by the second phase comparison circuit 512, and these phase differences are added by the adder 510.
06, a tracking error signal TE is output.
In tracking error detection in this circuit,
Since the phase difference between the photoelectric conversion elements at the same radial position is calculated, the first phase comparison circuit 511 and
There is no problem of phase shift in the calculation of the phase difference in the second phase comparison circuit 512, and it is not necessary to adjust the delay as in the circuit system using the photoelectric conversion elements located at diagonal positions as a pair.

[0007]

In the case of a system in which photoelectric conversion elements located at diagonal positions are combined and used as a pair, 1
Timing adjustment due to the positional difference between the front and rear of the pair of photoelectric conversion elements in the information track moving direction is indispensable, and the timing adjustment must be adjusted for each disc of the optical information reproducing apparatus, which is very difficult to adjust. It is. Further, the delay amount must be changed up to about 180 ° with a resolution of several nanoseconds, and at the same time, the increment of the delay amount needs to be changed depending on the rotation speed of the disk.
The adjustment and the circuit configuration are complicated. In addition, since a delay is given using an analog filter, it is difficult to accurately adjust the phase lead, and it is also difficult to always accurately adjust the phase lead due to a characteristic change of the analog filter due to a temperature change or the like.

In the tracking error signal detection circuit shown in FIG. 8, since only the phase difference between the photoelectric conversion elements at different positions is added to the moving direction of the information track, the objective lens mounted on the optical head is used. When the position is shifted from the center due to the lens shift, there is a problem that a sufficiently accurate tracking error signal cannot be calculated.

As described above, the correction method differs depending on the calculation method of the basic tracking error signal. Therefore, a problem that correction depending on the method of calculating the basic tracking error signal must be performed is encountered.

An object of the present invention is to detect an accurate tracking error signal with a simple circuit configuration even when a far-field image of an objective lens mounted on an optical head moves in a direction perpendicular to a direction in which an information track is mapped. It is to provide a possible tracking error signal detection circuit.

Another object of the present invention is to move a far-field image of an objective lens mounted on an optical head in a direction perpendicular to a direction in which an information track is mapped, irrespective of a method of calculating a basic tracking error signal. An object of the present invention is to provide a tracking error signal detection circuit that can detect an accurate tracking error signal even with a simple circuit configuration.

[0012]

According to a first embodiment of the present invention, a first and second quadrant photoelectric converters for converting reflected light from a disc-shaped information recording medium into an electric signal. A tracking error signal detection circuit for detecting a tracking error signal used for tracking control of the optical head with respect to the information recording medium based on an electric signal output from the third and fourth photoelectric conversion elements; A first phase difference calculating circuit for calculating a first phase difference signal which is a phase difference between the electric signals of the first and second photoelectric conversion elements positioned forward in the moving direction with respect to the information track; A second phase difference calculation for calculating a second phase difference signal which is a phase difference between electric signals of the third and fourth photoelectric conversion elements located behind the moving direction of the medium with respect to the information track. Path, a first addition circuit for adding the first phase difference signal and the second phase difference signal to calculate a basic tracking error signal, and a positional relationship of the optical head with respect to the information track. Correction signal generating means for calculating a correction signal from offset components included in the first and second phase difference signals, and a correction circuit for correcting the basic tracking error signal based on the correction signal and outputting a tracking error signal. Is provided.

The correction signal generating means extracts a first DC component which is a DC component of the first phase difference signal.
And a second low-pass filter for extracting a second DC component that is a DC component of the second phase difference signal, and a difference between the first DC component and a reference value. First
A first subtraction circuit that calculates a difference signal between the second DC component and the reference value; a second subtraction circuit that calculates a second difference signal that is a difference between the second DC component and the reference value; A subtraction circuit that calculates a third difference signal that is a difference from the second difference signal; and an addition that calculates a first sum signal that is a sum of the first difference signal and the second difference signal. And a selection circuit that outputs the third difference signal or the first sum signal as the correction signal according to the magnitude relationship between the first DC component, the second DC component, and the reference. Including. The correction circuit is an addition circuit that calculates the tracking error signal by adding the basic tracking error signal and the correction signal. Preferably, a low-pass film having predetermined low-pass characteristics is provided between the first addition circuit and the correction circuit.

According to a second embodiment of the present invention,
Based on the electric signals output from the first, second, third, and fourth photoelectric conversion elements of the four-division photoelectric converter that converts reflected light from the disc-shaped information recording medium into electric signals, In a tracking error signal detecting circuit for detecting a tracking error signal used for tracking control of an optical head with respect to a recording medium, the first and second photoelectric conversion elements located in front of a moving direction of the information recording medium with respect to an information track. A first phase difference signal circuit for calculating a first phase difference signal which is a phase difference between the electric signals, and the third and fourth photoelectric elements located behind the information recording medium with respect to the information track in the moving direction. A second phase difference calculating circuit for calculating a second phase difference signal which is a phase difference between the electric signals of the conversion element, and a diagonal in a moving direction of the information recording medium with respect to the information track. A first phase sum calculation circuit for calculating a first phase sum signal which is a phase sum of the electric signals of the first and third photoelectric conversion elements located at the position, and a moving direction of the information recording medium with respect to the information track. A second phase sum calculation circuit for calculating a second phase sum signal that is a phase sum of the electric signals of the second and fourth photoelectric conversion elements located at diagonal positions of the first and second photoelectric conversion elements, and the first phase sum signal A subtraction circuit for calculating a basic tracking error signal by subtracting the first and second phase sum signals from each other, and being included in the first and second phase difference signals according to a positional relationship of the optical head with respect to the information track. A tracking error generator comprising: a correction signal generating means for calculating a correction signal from an offset component; and a correction circuit for correcting the basic tracking error signal based on the correction signal and outputting a tracking error signal. Signal detection circuit is provided. Preferably, the first, second, third and fourth
A first addition circuit that calculates an RF signal from the sum of the electric signals of the photoelectric conversion elements, and a first difference signal that is a phase difference between the electric signal of the first photoelectric conversion element and the RF signal. A third phase difference calculation circuit, a fourth phase difference calculation circuit that calculates a second difference signal that is a phase difference between the electric signal of the second photoelectric conversion element and the RF signal, and a third phase difference calculation circuit. A fifth phase difference calculating circuit for calculating a third difference signal which is a phase difference between the electric signal of the photoelectric conversion element and the RF signal, and a position of the electric signal of the fourth photoelectric conversion element and the RF signal; A fifth phase difference calculation circuit that calculates a fourth difference signal that is a phase difference, wherein the first phase difference calculation circuit calculates the first difference signal from the first difference signal and the second difference signal. A phase difference signal is calculated, and the second phase difference calculation circuit calculates the phase difference signal from the third difference signal and the fourth difference signal. Calculating a serial second phase difference signal, the first is the phase sum calculating circuit said first difference signal and the third
And the second phase sum calculation circuit calculates the second phase sum signal from the second difference signal and the fourth difference signal. Further, the correction signal generating means includes a first low-pass filter for extracting a first DC component, which is a DC component of the first phase difference signal, and a DC component of the second phase difference signal. A second low-pass filter for extracting a second DC component; a first subtraction circuit for calculating a fifth difference signal that is a difference between the first DC component and a reference value; A second subtraction circuit that calculates a sixth difference signal that is a difference between the DC component and the reference value;
A seventh difference between the fifth difference signal and the sixth difference signal.
A third subtraction circuit for calculating a difference signal of the first and second components, an addition circuit for calculating a first sum signal that is a sum of the fifth difference signal and the sixth difference signal, A selection circuit that outputs the seventh difference signal or the first sum signal as the correction signal in accordance with the magnitude relationship between the second DC component and the reference value. Further, the correction circuit is an addition circuit that calculates the tracking error signal by adding the basic tracking error signal and the correction signal. More preferably, a low-pass filter having a predetermined low-pass characteristic is provided between the first and second phase sum calculation circuits and the correction circuit.

The correction signal generating means according to the first aspect includes a first low-pass filter for extracting a first DC component of a first phase difference calculated by the first phase difference calculating circuit; A second low-pass filter for extracting a second DC component of the second phase difference calculated by the second phase difference calculation circuit, and calculating a first difference between the first DC component and a reference value A first subtraction circuit, a second subtraction circuit for calculating a second difference between the second DC component and a reference value, and a third difference between the first difference and the second difference A third subtraction circuit for calculating the sum of the first difference and the second difference, and a magnitude comparison between the first DC component and the reference value. Outputting a first level logic signal when the DC component of the first DC component is larger than the reference value, wherein the first DC component is smaller than the reference value; A first comparison circuit that outputs a second-level logic signal; and a magnitude comparison between the second DC component and the reference value. When the second DC component is greater than the reference value, a first level A second comparison circuit that outputs a second-level logic signal when the second DC component is smaller than the reference value, and exclusive control of the output signals of the first and second comparison circuits. An exclusive-OR operation circuit for performing an exclusive-OR operation, and selectively outputting an output signal of the third subtraction circuit when an output signal of the exclusive-OR operation circuit is at a high level; And a selection circuit for selecting and outputting the output signal of the adder circuit when the output signal of the adder is at a low level.

The correction circuit is an addition circuit for adding the correction signal calculated by the tracking error correction means to the basic tracking error signal calculated by the addition circuit.

Preferably, a low-pass filter having predetermined low-pass characteristics is provided between the addition circuit and the correction circuit.

According to the second aspect of the present invention, the pit position formed on the information recording medium is optically converted by the photoelectric converter having four photoelectric conversion elements divided into four in the direction of the information track and in the radial direction. A tracking error signal detection circuit for detecting and detecting a tracking error used for tracking control in an optical information reproducing apparatus, wherein a detection signal of a photoelectric conversion element located at a diagonal position among the four photoelectric conversion elements is compared with each other. A first and second phase sum calculating circuit for calculating the first and second phase sums by adding, and two of the four photoelectric conversion elements located in a radial direction of the information track. First and second phase difference calculation circuits for calculating first and second phase differences for each of the detection signals, and the first and second addition circuits A third phase difference calculation circuit for calculating a basic tracking error signal obtained by calculating the phase difference between the first and second phase sums calculated in the above, and the third phase difference calculation circuit is included in the first phase difference and the second phase difference. Correction signal generation means for calculating a correction signal for correcting the basic tracking error signal from an error; and a tracking error signal correction signal obtained by calculating the basic tracking error signal calculated by the third phase difference calculation circuit by the correction signal generation means. A tracking error signal detection circuit comprising: That is, in the second embodiment, the basic tracking error signal is generated from the mutual phase difference of the sum of the detection signals of the photoelectric conversion elements located at the diagonal positions, and the position of the detection signal of the photoelectric conversion element located in the radial direction is generated. A tracking error signal correction signal is calculated from the phase difference signal to correct the basic tracking error signal.

Preferably, an RF signal calculation circuit for calculating a sum of detection signals of the four photoelectric conversion elements to calculate an RF signal, and the first and second circuits for calculating the first and second phase sums. 2 before the phase sum calculation circuit, or before the first and second phase difference calculation circuits for calculating the first and second phase differences, respectively. The apparatus further includes a phase difference calculation circuit for calculating a difference between the RF signal and the RF signal. In this configuration, the first and second phase sum calculation circuits calculate the first and second phase sums for a phase difference signal from the RF signal, and calculate the first and second phase difference. Calculation of the first and second phase differences in the circuit is performed on a phase difference signal from the RF signal. The use of the RF signal improves the reliability of signal processing.

The correction signal generating means in the second embodiment includes a first low-pass filter for extracting a first DC component of the first phase difference calculated by the first phase difference calculating circuit; A second low-pass filter for extracting a second DC component of the second phase difference calculated by the second phase difference calculation circuit, and calculating a first difference between the first DC component and a reference value A first subtraction circuit, a second subtraction circuit for calculating a second difference between the second DC component and a reference value, and a third difference between the first difference and the second difference A third subtraction circuit for calculating the sum of the first difference and the second difference, and a magnitude comparison between the first DC component and the reference value. Outputting a first level logic signal when the DC component of the first DC component is larger than the reference value, wherein the first DC component is smaller than the reference value; A first comparison circuit that outputs a second-level logic signal; and a magnitude comparison between the second DC component and the reference value. When the second DC component is greater than the reference value, a first level A second comparison circuit that outputs a second-level logic signal when the second DC component is smaller than the reference value, and exclusive control of the output signals of the first and second comparison circuits. An exclusive-OR operation circuit for performing an exclusive-OR operation, and selectively outputting an output signal of the third subtraction circuit when an output signal of the exclusive-OR operation circuit is at a high level; And a selection circuit for selecting and outputting the output signal of the adder circuit when the output signal of the adder is at a low level. The correction signal generation means in the second embodiment is substantially the same as the correction signal generation means in the first embodiment described above. Therefore, the tracking error signal can be corrected without depending on the calculation method of the basic tracking error signal.

The correction circuit is a subtraction circuit for subtracting the correction signal calculated by the tracking error correction means from the basic tracking error signal.

Preferably, a waveform shaping circuit for shaping the waveform of the photoelectric conversion signal from the photoelectric conversion element is provided in a stage preceding the first and second phase difference calculating circuits, and the first and second phase difference calculating circuits are provided. The calculation circuit calculates a phase difference for the photoelectrically converted signal whose waveform has been shaped.

More preferably, a coupling capacitor is provided before the waveform shaping circuit.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of a tracking error signal detection circuit according to the present invention will be described with reference to the accompanying drawings.

[0025] Embodiment Figure 1 of the first embodiment the first tracking error signal detection circuit of the present invention
Tracking error signal detection circuit 1 as an embodiment
FIG. The tracking error signal detection circuit 1 illustrated in FIG. 1 includes four current / voltage conversion circuits 11 to 14.
, Four waveform shaping circuits 21 to 24, a phase comparison circuit (phase difference calculation circuit) 31, a phase comparison circuit (phase difference calculation circuit) 32, an addition circuit 34, and a low-pass filter 36
, A low-pass filter 41, a third low-pass filter 42, a correction signal generation circuit 44, and a correction circuit 50. Here, the tracking error correction means 40 is configured by the correction signal generation circuit 44 and the correction circuit 50. An AC coupling capacitor 10 is provided between the current / voltage conversion circuits 11 to 14 and the waveform shaping circuits 21 to 24.
It is desirable to provide 1 to 104.

In the first embodiment, as the photoelectric converter, a first photoelectric conversion element (A) 61, a second photoelectric conversion element (B) 62, divided into four parts in the track direction T and the radial direction R, The third photoelectric conversion element (C) 63 and the fourth
A four-division photoelectric converter 60 having the photoelectric conversion element (D) 64 is used. First to fourth photoelectric conversion elements 61 to 64
Is a photodetector that generates a current corresponding to the amount of received light. In the first embodiment, the first photoelectric conversion element (A) 61 and the second photoelectric conversion element (B) 62 are connected to the third photoelectric conversion element (C) 63 and the third photoelectric conversion element (C) 63 in the moving direction of the information track. It is located forward with respect to the fourth photoelectric conversion element (D) 64. This positional relationship is opposite to the positional relationship in the four-division photoelectric converter described with reference to FIG. That is, the moving direction of the information track illustrated in FIG. 8 is opposite to the moving direction of the information track illustrated in FIG.

The tracking error signal detection circuit 1 and the four-division photoelectric converter 60 described above are mounted on an optical information recording medium, for example, an optical head for reading and reproducing information stored in a CD-ROM. ing. The optical head includes an optical system used for tracking control and focus control, such as an objective lens, in addition to the above-described components.

The current / voltage conversion circuits 11 to 14 respectively convert the currents detected by the four first to fourth photoelectric conversion elements 61 to 64 of the four-division photoelectric converter 60 into voltages of a predetermined level. . The current / voltage conversion circuits 11 to 14 can be configured using resistors.

The waveform shaping circuits 21 to 24 shape the waveforms of the voltages converted by the current / voltage converting circuits 11 to 14. As described later, the detection signals of the first to fourth photoelectric conversion elements 61 to 64 ideally have a sine wave characteristic.
In the state detected by the fourth photoelectric conversion elements 61 to 64, noise and the like may be superimposed. In order to accurately detect a phase difference described later, the waveform shaping circuits 21 to 24
After shaping the waveforms of the voltage signals output from the current / voltage conversion circuits 11 to 14, a voltage comparison operation is performed to perform 2
Outputs the quantified signal.

The phase comparison circuit (phase difference calculation circuit) 31
The waveform shaping circuit 21 and the waveform shaping circuit 22 which binarize the detection signals of the first photoelectric conversion element (A) 61 and the second photoelectric conversion element 62 which are located in the same radial direction and are divided in the track direction. The first phase difference Δφ _AB is calculated by comparing the phase of the output signal (hereinafter, this output signal may be simply referred to as the detection signal of the photoelectric conversion element). As a method of calculating the phase difference, for example, from the rise (or fall) of the detection signal of the first photoelectric conversion element (A) 61 to the rise (or fall) of the second photoelectric conversion element (B) 62 The time difference is the first phase difference Δφ
_AB . Second phase comparison circuit (phase difference calculation circuit) 3
Reference numeral 2 denotes a waveform shaping circuit 23 which binarizes detection signals of the third photoelectric conversion element (C) 63 and the fourth photoelectric conversion element 64 which are located in the same radial direction and are divided in the track direction, and a waveform shaping circuit. The second phase difference Δφ _CD is calculated by comparing the phase of the output signal of the circuit 24 (hereinafter, this output signal may be simply referred to as the detection signal of the photoelectric conversion element). As a method of calculating the phase difference, for example, the rise (or fall) of the detection signal of the third photoelectric conversion element (C) 63 to the rise (or fall) of the detection signal of the fourth photoelectric conversion element (D) 64 ) Is defined as a second phase difference Δφ _CD .

The phase comparison circuit 31 is different from the above-mentioned example in that the first photoelectric conversion element (A) starts from the rising (or falling) of the detection signal of the second photoelectric conversion element (B) 62.
The difference in time 61 the detection signal of the rising (or falling) may be used as the first retardation [Delta] [phi _{A- B.} Similarly,
The phase comparison circuit (phase difference calculation circuit) 32 changes the rising (or falling) of the detection signal of the fourth photoelectric conversion element (D) 64 to the rising (or falling) of the detection signal of the third photoelectric conversion element (C) 63. The time difference until the falling edge may be used as the second phase difference Δφ _CD . The phase comparison circuit 31 and the phase comparison circuit 32 are respectively provided on the same side of the information track,
For example, the time difference between the rise (or fall) of the detection signal of the photoelectric conversion element located inside and the rise (or fall) of the detection signal of the photoelectric conversion element located outside is determined.

The method of calculating the above-described phase difference in the first embodiment is the same as that of the tracking error signal detection circuit shown in FIG. 8, and is not the phase difference between the detection signals of the photoelectric conversion elements at diagonal positions. . Therefore, the first phase difference Δφ _AB calculated by the phase comparison circuit 31 has no problem of delay depending on whether the photoelectric conversion element is ahead or behind the information track. However, there is a difference between the first phase difference Δφ _AB and the second phase difference Δφ _CD between forward and backward.

The calculation of the tracking error signal TE when the optical head is in the on-track state will be described.
FIG. 2 is a diagram illustrating the positional relationship between a pit formed on a recording medium and a beam spot. FIG. 3 (A),
FIG. 3B is a waveform diagram of detection signals of the first to fourth photoelectric conversion elements 61 to 64 in the on-track state.
(A) shows the first to fourth cases when the pit depth is equal to λ / 4.
FIG. 3B is a detection signal waveform diagram of the first to fourth photoelectric conversion elements 61 to 64 when the pit depth is shallower than λ / 4. is there.
λ indicates the wavelength of the light (beam) emitted from the optical head to the pit of the information recording medium.

First, the on-track state will be described.
As illustrated in FIG. 2, when the center axis of the objective lens mounted on the optical head is located in a pit on the information track of the recording medium to be positioned, that is, when the objective lens is in an on-track state, the light is emitted through the objective lens. The center of the beam spot reflected from the pits of the recording medium coincides with the center of the four-division photoelectric converter 60. At this time, the first to fourth photoelectric conversion elements 61 to 64 of the four-division photoelectric converter 60
When the same amount of light enters and the pit depth is equal to λ / 4, as illustrated in FIG.
The amplitudes and phases of the detection signals of the fourth photoelectric conversion elements 61 to 64 match, and become the same sine wave (or cosine wave).

In the on-track state and the pit depth is λ /
4, the detection signal of the first photoelectric conversion element (A) 61 is equal to the detection signal of the second photoelectric conversion element (B) 62, and the first phase difference Δφ calculated by the phase comparison circuit 31
_AB is 0. Similarly, when the pit depth is equal to λ / 4 in the on-track state, the second phase difference Δφ _CD calculated by the phase comparison circuit 32 is also zero.

The adding circuit 34 calculates the phase by the phase comparing circuit 31
First phase difference Δφ_ABCalculated by the phase comparison circuit 32
Second phase difference Δφ_CDAnd the tracking error
-Calculate the signal. Basically this tracking error signal
Tracking error signal TE ₀Call. On track
Basic track when the pit depth is equal to λ / 4
Error signal TE₀Is 0.

The low-pass filter 36 is, for example,
It has a low-pass characteristic on the order of 0KH _Z, passing only a low-frequency component of the tracking error signal TE _0. The low-pass filter 36 can be configured as an RC filter using ordinary resistors and capacitors.

As illustrated in FIG. 3B, in the on-track state and when the pit depth is smaller than λ / 4, the first
The detection signals of the photoelectric conversion element (A) 61 and the second photoelectric conversion element (B) 62 of the third photoelectric conversion element (C) 6
Although the detection signals of the third and fourth photoelectric conversion elements (D) 64 have different phases, the detection signals of the first photoelectric conversion element (A) 61 and the detection signals of the second photoelectric conversion element (B) 62 Is the first phase difference Δφ _AB
Is 0, and the amplitude and phase of the detection signal of the third photoelectric conversion element (C) 63 and the detection signal of the fourth photoelectric conversion element (D) 64 match, so that the second phase difference Δφ _CD 0
It is. That is, in the first embodiment, the difference between the photoelectric conversion elements at diagonal positions, for example, the difference between the detection signals of the first photoelectric conversion element (A) 61 and the third photoelectric conversion element (C) 63 is calculated. Since it is not calculated, the first phase difference Δφ _AB = 0 and the second phase difference Δφ _CD even when the pit depth is shallower than λ / 4 (even when it is deep) and in the on-track state.
= 0.

As described above, in the on-track state, the first phase difference Δφ _AB = 0 and the second phase difference Δφ _CD = 0, regardless of the depth of the pit, which is shallower than λ / 4. Yes, the error in the correction signal generation circuit 44 is 0,
Basic tracking error signal TE in correction circuit 50
The correction of ₀ is not performed substantially. Therefore, the tracking error signal TE output from the correction circuit 50 remains the same as the basic tracking error signal TE ₀ . Regarding the operation of the correction signal generation circuit 44 and the correction circuit 50,
This will be described in the description of the operation in the off-track state.

Next, the tracking error signal TE in the detrack state where the optical head is deviated from the on-track state.
The calculation of is described. FIGS. 4A and 4B are waveform diagrams of the first to fourth photoelectric conversion elements 61 to 64 in a detrack state, and FIG. 4A shows a waveform chart when the pit depth is equal to λ / 4. FIG. 4B is a detection signal waveform diagram of the first to fourth photoelectric conversion elements 61 to 64, and FIG. 4B shows detection of the first to fourth photoelectric conversion elements 61 to 64 when the pit depth is smaller than λ / 4. It is a signal waveform diagram.

As shown in FIG. 4A, when the track is in the detrack state and the pit depth is equal to λ / 4, the track is detracked from the information track to be tracked to the adjacent inner track side. The first photoelectric conversion element (A) 61 inside the information track to be positioned.
Is advanced in phase from the detection signal of the second photoelectric conversion element (B) 62 outside the information track. As a result, the first phase difference Δφ _AB in the phase comparison circuit 31 has a positive value. Similarly, the detection signal of the outer fourth photoelectric conversion element (C) 63 leads the detection signal of the inner fourth photoelectric conversion element (D) 64 in phase. As a result, the second phase difference Δφ _CD in the phase comparison circuit (phase difference calculation circuit) 32 has a positive value. Conversely, when detracking occurs on the outer track side from the information track targeted for tracking control, the first phase difference Δφ _AB and the second phase difference Δ
The sign of φ _CD is reversed.

As illustrated in FIG. 4B, when the pit depth is shallower than λ / 4, when the detrack occurs on the inner track side from the information track to be tracked, the information track is With respect to the moving direction, the detection signals of the preceding (front) first photoelectric conversion element (A) 61 and second photoelectric conversion element (B) 62 and the third photoelectric conversion element (C ) 63 and the detection signal of the fourth photoelectric conversion element (D) 64 are all signals having different phases. However, in this case, the phase differences Δt between the first and second photoelectric conversion elements (A) and (B) and between the third and fourth photoelectric conversion elements (C) and (D) are equal to each other in FIG. As illustrated, when a lens shift occurs, Δt ₁ ≠ Δt ₂ when the pit depth is shallower than λ / 4, so that the first and second photoelectric conversion elements (A) 61 and (B) )
The phase difference 62 is different from the phase difference between the third and fourth rear photoelectric conversion elements (C) 63 and (D) 64. Therefore, the result of the phase comparison circuit 31 (first phase difference Δφ _AB )
And the result of the phase comparison circuit 32 (second phase difference Δφ _CD )
Is simply added in the adder circuit 34, an accurate tracking error signal TE cannot be calculated. Therefore, in the first embodiment of the present invention, the tracking error correction means 40 calculates an accurate tracking error signal TE even in the detrack state, and corrects it in the correction circuit 50.

Referring to FIG. 5, a method of correcting a tracking error signal in tracking error correction means 40 will be described. When the position of the objective lens changes in the radial direction with respect to the pits of the recording medium in a state where detrack has occurred, the signal levels and phases of the first to fourth photoelectric conversion elements 61 to 64 are individually shifted. In a state where such a shift is present, the first value calculated by the phase comparison circuit 31 is calculated.
Of the adding phase difference [Delta] [phi _AB and the second phase difference [Delta] [phi _CD calculated in the phase comparator circuit 32, the tracking error signal including an offset. Therefore, such an offset is detected, and the tracking error signal TE ₀ calculated by the adding circuit 34 is corrected.

The offset value is included in both the first phase difference Δφ _AB and the second phase difference Δφ _CD . Therefore,
For each of the first phase difference Δφ _AB and the second phase difference Δφ _CD , integration processing is performed for a predetermined period (predetermined period). The integrated values are referred to as a first DC component x and a second DC component y, respectively. If there is no offset,
The integrated values x and y are each 0. When the integrated values x and y are subtracted from the reference level VC, an offset value can be calculated. That is, the first offset Δx = VC−x, the second offset Δx = VC−x
Offset Δy = VC−y.

FIG. 5 (A) illustrates a part of the first offset Δx = VC−x and the second offset Δy =
VC-y occurs in various forms. Therefore, methods for determining the value of the tracking error signal correction signal Δz in various embodiments will be described.

[0046]

[Table 1]

The results shown in Table 1 can be simplified as follows when arranged.

[0048]

[Table 2]

The tracking error correction means 40 corrects the tracking error signal TE ₀ calculated by the adding circuit 34 using the tracking error signal correction signal Δz based on the above-described correction method.

The low-pass filter 41 includes a phase comparison circuit 3
A low-frequency component of the first phase difference Δφ _AB calculated in step 1, ie, a DC component is extracted. This DC component is called a first DC component x (or DC _AB ). . Similarly, the low-pass filter 42 extracts a low-frequency component of the second phase difference Δφ _CD calculated by the phase comparison circuit 32, that is, a DC component.
This DC component is called a second DC component y (or DC _CD ).

FIG. 6 shows a circuit configuration example of the correction signal generation circuit 44.
Shown in The correction signal generation circuit 44 includes subtraction circuits 441 and 4
42, a subtraction circuit 443, an addition circuit 444, comparison circuits 446 and 447, an exclusive-OR (EXCLUSIVE-OR) circuit 448, and a selection circuit 445.

The subtraction circuit 441 subtracts the first DC component x from the low-pass filter 41 from the reference level VC to obtain Δx
Is calculated. That is, the first offset Δx = VC−
Calculate x. Similarly, the subtraction circuit 442 calculates Δy by subtracting the second DC component y from the low-pass filter 42 from the reference level VC. That is, the second offset Δ
Calculate y = VC-y. The reference level VC is, for example, 0.

The subtraction circuit 443 calculates a tracking error signal correction signal Δz = Δx−Δy. Adder circuit 444
Calculates the tracking error signal correction signal Δz = Δx + Δy. One of these provisional tracking error signal correction signals Δz is selected from the selection circuit 445 and output.

The comparison circuit 446, the comparison circuit 447, and the exclusive OR circuit 448 perform the logical operation illustrated in Table 2 to calculate the selection control signal output from the selection circuit 445 and determining the tracking error signal correction signal Δz. I do.
The comparison circuit 446 compares the reference level VC with x,
When x> VC, a high-level “H” signal is output, and x <VC
In the case of VC, a low level "L" signal is output. The comparison circuit 447 compares the reference level VC with y, and y> V
In the case of C, a high-level "H" signal is output, and in the case of y <VC, a low-level "L" signal is output. The exclusive OR circuit outputs a selection control signal based on the operation result of Table 3 below to the selection circuit 445 so that the result shown in Table 2 is obtained.

[0055]

[Table 3]

The selection circuit 445 includes the exclusive OR circuit 44
8 is the high level “H”, the addition result Δz = Δ from the addition circuit 444
x + Δy, and when the level of the selection control signal is low level “L”, the subtraction result Δz = Δ from the subtraction circuit 443
x-Δy is output. As a result, the tracking error signal correction signal Δz shown in Table 2 is output from the selection circuit 445 to the correction circuit 50, and the correction circuit 50 outputs the tracking error signal T before correction output from the low-pass filter 36.
The tracking error signal correction signal Δz is added to E ₀ to output a corrected tracking error signal TE. In this example, the correction circuit 50 is an addition circuit.

As described above, according to the first embodiment of the present invention, in the on-track state as well as in the detrack state, regardless of whether the pit depth is smaller or larger than λ / 4, in other words, Even when the far-field image of the objective lens mounted on the optical head moves in a direction perpendicular to the direction in which the information track is mapped, an accurate tracking error signal can be calculated. The circuit configuration illustrated in FIGS. 1 and 6 is simple.

The implementation of the tracking error signal detection circuit 1 described above is not limited to the circuit configuration illustrated in FIGS. 1 and 6, but may be configured in various other forms. For example, the phase comparison circuit 31, the phase comparison circuit 32,
Addition circuit 34, low-pass filter 36, low-pass filter 41, low-pass filter 42, correction signal generation circuit 44
The correction circuit 50 can be integrated with a high-speed operation circuit such as a digital signal processor or a microcomputer instead of the circuit.

In the optical information reproducing apparatus, the RF signal required in the same manner as the tracking error signal TE may be obtained by adding all the output signals of the waveform shaping circuits 21 to 24. Therefore, an RF signal can be obtained by providing an adding circuit for adding the output signals of the waveform shaping circuits 21 to 24.

FIG. 7 shows a second embodiment of the tracking error signal detecting circuit according to the present invention.
Tracking error signal detection circuit 1 as an embodiment
FIG. 2 is a configuration diagram illustrating A. The tracking error signal detection circuit 1A includes four current / voltage conversion circuits 11-14.
And waveform shaping circuits 21 to 24. These circuits correspond to the current / voltage conversion circuit 11 in the tracking error signal detection circuit 1 of the first embodiment described with reference to FIG.
14 and the waveform shaping circuits 21 to 24. That is, the current / voltage conversion circuits 11 to 14
The current detected by the four first to fourth photoelectric conversion elements 61 to 64 of the split photoelectric converter 60 is converted into a voltage of a predetermined level. The current / voltage conversion circuits 11 to 14 can be configured using resistors. Waveform shaping circuits 21 to
24 shapes the waveform of the voltage converted by the current / voltage conversion circuits 11 to 14.

Note that, like the tracking error signal detection circuit 1 illustrated in FIG. 1, in the tracking error signal detection circuit 1A illustrated in FIG. 7, the current / voltage conversion circuits 11 to 14 and the waveform shaping circuits 21 to 24 are connected. It is desirable to provide the AC coupling capacitors 101 to 104 between them.

In the second embodiment, as in the first embodiment described with reference to FIG. 1, as the photoelectric converter, a first photoelectric conversion element (divided into four in the track direction T and the radial direction R) is used. A) 61, second photoelectric conversion element (B) 6
2. A four-division photoelectric converter 60 having a third photoelectric conversion element (C) 63 and a fourth photoelectric conversion element (D) 64 is used. The first to fourth photoelectric conversion elements 61 to 64 are photodetectors that generate a current corresponding to the amount of received light. Similarly to the first embodiment described with reference to FIG. 1, in the second embodiment, the first photoelectric conversion element (A) 61 and the second photoelectric conversion element ( B) 62 is located forward of the third photoelectric conversion element (C) 63 and the fourth photoelectric conversion element (D) 64. Therefore, the positional relationship between the pits formed on the recording medium illustrated in FIG.
FIGS. 4A and 4B show the waveforms of the detection signals of the first to fourth photoelectric conversion elements in the on-track state, and FIGS. 4A and 4B show the waveforms of the detection signals in the detrack state. The waveforms of the detection signals of the first to fourth photoelectric conversion elements are also applied to the second embodiment.

The tracking error signal detection circuit 1A illustrated in FIG. 7 has the following different configuration from the tracking error signal detection circuit 1 illustrated in FIG. The tracking error signal detection circuit 1A includes a waveform shaping circuit 21 to 24.
And an RF signal calculating addition circuit (addition circuit) 71 for calculating an RF signal by fully adding the output signals of the above. Of course, the RF signal is also used in the optical information reproducing apparatus using the tracking error signal detection circuit 1 illustrated in FIG. In this case, an RF signal is generated by a circuit corresponding to the RF signal calculation addition circuit 71. In the second embodiment, the RF signal generated by the RF signal calculation addition circuit 71 is used for detecting the tracking error signal TE. use.

The tracking error signal detection circuit 1A
Phase comparison circuits (phase difference calculation circuits) 81 to 84 are provided.
The phase comparison circuit (phase difference calculation circuit) 81 compares the detection signal of the first photoelectric conversion element (A) 61 with the phase of the RF signal, and detects the first photoelectric conversion element (A) 61 for the RF signal. _A first reference phase difference Δφ _A indicating the phase difference of the signal is output. The phase comparison circuit 82 (phase difference calculation circuit) compares the phase of the detection signal of the second photoelectric conversion element (B) 62 with the phase of the RF signal, and outputs the second photoelectric conversion element (B) for the RF signal.
62, a second reference phase difference Δφ _B indicating the phase difference of the detection signal.
Is output. The phase comparison circuit 83 (phase difference calculation circuit)
A third reference phase difference indicating the phase difference between the detection signal of the third photoelectric conversion element (C) 63 and the RF signal by comparing the phase of the detection signal of the third photoelectric conversion element (C) 63 with the RF signal. Outputs Δφ _C. Phase comparison circuit (phase difference calculation circuit) 8
4 is the detection signal of the fourth photoelectric conversion element (D) 64 and RF
Outputting a fourth reference phase difference [Delta] [phi _D indicating a phase difference detection signal of the fourth photoelectric conversion element (D) 64 compares the phases of the signal to the RF signal.

The tracking error signal detection circuit 1A
An addition circuit (phase sum calculation circuit) 74 and a low-pass filter 75, an addition circuit (phase sum calculation circuit) 76, and a low-pass filter 77 are provided. The tracking error signal detection circuit 1A further has a subtraction circuit (basic tracking error signal calculation circuit) 91. Adder circuit 74, adder circuit 7
6, and the circuit of the subtraction circuit 91 generates the basic tracking error signal TE ₀ . The processing contents are described below.

The tracking error signal detection circuit 1A
It has a subtraction circuit (phase difference calculation circuit) 72 and a low-pass filter 73, a subtraction circuit (phase difference calculation circuit) 78 and a fourth low-pass filter 79. The subtraction circuit 72 and the subtraction circuit 78 generate a signal for the tracking error signal correction signal Δz calculated in the correction signal generation circuit 95 described later.

The phase difference calculation circuit or the subtraction circuit 72 which operates as a phase comparison circuit includes the first reference phase difference Δφ _A calculated by the phase comparison circuit (phase difference calculation circuit) 81 and the phase comparison circuit (phase difference calculation circuit). A first phase difference Δφ _AB is calculated by calculating a difference from the second reference phase difference Δφ _B calculated in 82. The first phase difference Δφ _{A− B} calculated in this manner
Indicates a phase difference Δφ _AB between the first photoelectric conversion element (A) 61 and the second photoelectric conversion element (B) 62 located in the same radial direction. This phase difference Δφ _AB corresponds to the first phase difference Δφ _AB calculated by the phase comparison circuit (phase difference calculation circuit) 31 in FIG. However, in FIG.
The phase difference between the reference RF signal calculated by the RF signal calculation addition circuit (addition circuit) 71 (first reference phase difference Δ
Since a φ phase difference between the _A and the second reference phase difference [Delta] [phi _B), the accuracy of the phase difference (reliability) is high. The low-pass filter 73 has a predetermined low-pass characteristic, and has a first phase difference Δφ
A low frequency component of the _AB signal, that is, a DC component is output. Characteristics of the low-pass filter 73 is similar to the low-pass filter 41 and 42 illustrated in FIG. 1, about several 10H _Z, it can be configured as a normal RC filter.

An addition circuit (phase sum calculation circuit) 74 operating as a phase sum calculation circuit includes a first reference phase difference Δφ _A calculated by a phase comparison circuit (phase difference calculation circuit) 81 and a phase comparison circuit (phase difference calculation circuit). (Circuit) 83 to calculate the first phase sum Δφ _{A + C} by calculating the sum with the third reference phase difference Δφ _C calculated in 83. The first phase sum Δφ _{A +} thus calculated
_C is the RF of the detection signal of the first photoelectric conversion element (A) 61
_A first reference phase difference Δφ _A which is a phase difference with respect to the signal;
This is the sum of the detection signal of the third photoelectric conversion element (C) 63 and a third reference phase difference Δφ _C which is a phase difference with respect to the RF signal. This first phase sum Δφ _{A + C} is the sum of the detection signals of the photoelectric conversion elements located at diagonal positions, and is highly reliable in that the calculation uses an RF signal. Low pass filter 75 has a different low-pass characteristics and the low-pass filter 73, similar to the low-pass filter 36 illustrated in FIG. 1, about several 10KH _Z, the first phase sum [Delta] [phi _A A low frequency component of the _{+ C} signal, that is, a DC component is output. The low-pass filter 75 can also be configured as a normal RC filter.

Addition circuit operating as phase sum calculation circuit
(Phase sum calculation circuit) 76 is a phase comparison circuit (phase difference calculation circuit).
Circuit) The second reference phase difference Δφ calculated in 82_BAnd phase ratio
The fourth reference position calculated by the comparison circuit (phase difference calculation circuit) 84
Phase difference Δφ_DAnd the second phase sum Δφ_{B + D}To
calculate. The second phase sum Δφ calculated in this manner
_{B + D}Is the R of the detection signal of the second photoelectric conversion element (B) 62
A second reference phase difference Δφ which is a phase difference with respect to the F signal
_BAnd the RF of the detection signal of the fourth photoelectric conversion element (D) 64
Fourth reference phase difference Δφ which is a phase difference with respect to the signal_DWith
It is sum. This second phase sum Δφ_{B + D}Also in the diagonal position
The sum of the detection signals of the photoelectric conversion elements
High reliability in using signals. Low pass
The filter 77 has a predetermined low equivalent to the low-pass filter 75.
A second phase sum Δφ_{B + D}Low frequency of signal
And outputs the DC component. Low-pass filter 77
Can also be configured as a normal RC filter.

As a phase difference calculation circuit or a phase comparison circuit
The operating subtraction circuit 78 includes a phase comparison circuit (a phase difference calculation circuit).
Path) Third reference phase difference Δφ calculated in 83_CAnd phase comparison
The fourth reference phase calculated by the circuit (phase difference calculation circuit) 84
Difference Δφ_DTo calculate the second phase difference Δφ_CDIs calculated
Put out. The second phase difference Δφ calculated in this manner
_CDIs the third photoelectric conversion element located in the same radial direction
Phase between child (C) 63 and fourth photoelectric conversion element (D) 64
Difference Δφ_CDIs shown. This phase difference Δφ_CDIn Figure 1
The first phase difference Δφ calculated by the phase comparison circuit 32_CDTo
Equivalent to. However, in FIG.
Phase difference between the output reference RF signal (third reference
Phase difference Δφ_CAnd the fourth reference phase difference Δφ_DPhase difference with
Therefore, the reliability of the phase difference is high. Low-pass filter 7
9 is a predetermined low-pass characteristic equivalent to the low-pass filter 73.
And the second phase difference Δφ_CDLow frequency components of the signal,
That is, a DC component is output. The low-pass filter 79 is also a normal
It can be configured as an RC filter.

The subtraction circuit 91, which operates as a phase difference calculation circuit or a phase comparison circuit, calculates the first phase sum Δφ calculated by the addition circuit 74 that has passed through the low-pass filter 75.
_The total phase difference Δφ _{(A + C) − (D + A)} is the difference between the DC component of _{A + C} and the DC component of the second phase sum Δφ _{B + D} calculated by the addition circuit 76 that has passed through the low-pass filter 77. _{B + D)} . The phase difference detection result is similar to the method of calculating the tracking error signal TE using the phase difference between the photoelectric conversion elements at diagonal positions illustrated as a conventional example. But,
In the second embodiment, since the processing is performed using the RF signal, the reliability of the total phase difference Δφ _{(A + C)-(B + D)} is high. Total phase difference Δφ calculated by subtraction circuit 91
_{(A + C)-(B + D)} is called a basic tracking error signal TE ₀ .

The correction signal generation circuit 95 has a low-pass filter.
Calculated by the subtraction circuit (phase difference calculation circuit) 72 that has passed through the
First phase difference Δφ_ABDC component and low-pass
Subtraction circuit (phase difference calculation circuit) 78 that has passed through filter 79
The second phase difference Δφ calculated by _CDUsing the DC component of
A racking error signal correction signal Δz is calculated. Correction letter
The signal generation circuit 95 has the complement described with reference to FIGS.
By performing substantially the same processing as the positive signal generation circuit 44,
A locking error signal correction signal Δz is generated. Sand
That is, the correction signal generation circuit 95 outputs the correction signal illustrated in FIG.
It has the same circuit configuration as the generation circuit 44 and is illustrated in FIG.
Low-pass filter 73 corresponding to low-pass filter 41
A first DC component x from the subtraction circuit (phase difference calculation
Path) First phase difference Δφ calculated in 72_ABDC component
Input and corresponds to the low-pass filter 42 illustrated in FIG.
From the low-pass filter 79 as the second DC component y.
Second phase difference calculated by the arithmetic circuit (phase difference calculation circuit) 78
Δφ_CDInput to the circuits 441 to 448
Calculate the tracking error signal correction signal Δz with the corresponding circuit
Put out. Calculate tracking error signal correction signal Δz
The operation algorithm and judgment conditions are the same as those described above.
It is like.

The subtraction circuit 92 as a tracking error signal correction circuit corrects the tracking error signal TE obtained by subtracting the tracking error signal correction signal Δz calculated by the correction signal generation circuit 95 from the basic tracking error signal TEφ calculated by the subtraction circuit 91. Generate The subtraction circuit 92, which corresponds to the correction circuit 50 of FIGS. 1 and 6, performs subtraction.

In the second embodiment, as described above, the first phase sum Δφ _{A + C} and the second phase sum Δφ between the photoelectric conversion elements located at diagonal positions are used for calculating the basic tracking error signal TE _{0. From} the difference from _{B + D} , the basic tracking error signal TE
_It differs from the first embodiment in that ₀ is calculated.
In this respect, the phase difference method is similar to that exemplified as the conventional example, but in the second embodiment, the RF difference method is used.
Since the signal is used, the calculation of the basic tracking error signal TE ₀ is highly reliable.

Of course, the subtraction circuit 72, the addition circuit 74, the addition circuit 76, and the subtraction circuit
Although it is not essential to perform the above-described arithmetic processing in 8, reliability is improved by using an RF signal.

In the tracking error signal detection circuit 1 of the first embodiment illustrated in FIG. 1, an RF signal calculation circuit similar to the RF signal calculation addition circuit 71 illustrated in FIG. After calculating the phase difference between the output signals of the waveform shaping circuits 21 to 24 using the RF signal, the phase comparison circuit (phase difference calculation circuit) 31 and the phase comparison circuit (phase difference calculation circuit) 32 calculate the phase difference. Can also be calculated. Thereby, the reliability is also improved in the tracking error signal detection circuit 1 illustrated in FIG.

Further, in the second embodiment, the first embodiment
As in the embodiment, the first phase difference Δφ _ABAnd second place
Phase difference Δφ_CDTracking error signal correction signal using
Calculate Δz and use the correction signal Δz to
Error signal TE₀Has been corrected. Therefore,
As in the first embodiment, a highly accurate tracking error signal
No. TE can be generated. In the second embodiment, the optical
It does not require adjustment for each formula information reproducing device,
The need to use tightly adjustable analog delay circuits, etc.
Because it is not used, it can be used stably without depending on temperature change etc.
You. The circuit configuration of the second embodiment is a relatively simple circuit.
Can be configured.

The tracking error signal detecting circuit 1A and the quadrant photoelectric converter 60 described above are used in an optical information recording medium, for example, an optical head used to read and reproduce information stored in a CD-ROM. It is installed. The optical head includes an optical system used for tracking control and focus control, such as an objective lens, in addition to the above-described components.

As described above, an accurate tracking error signal TE can be calculated by either the first embodiment or the second embodiment of the present invention. Therefore, using this tracking error signal TE improves the accuracy of tracking control.

Further, as is apparent from the description of the first and second embodiments, in the present invention, the basic tracking error signal TE ₀ is calculated based on the same radial position of the four-division photoelectric converter 60. phase difference between those located in (first phase difference [Delta] [phi _{A- B} and a second phase difference Δ
Even when calculated from φ _CD ), the phase sum (first phase sum Δφ) of those located at diagonal positions of the four-division photoelectric converter 60 is calculated.
_{A + C} and the second phase sum Δφ _{B + D} ), the tracking error signal correction signal Δz is finally calculated from the first phase difference Δφ _AB and the second phase difference Δφ _CD. , Can be used to commonly correct the basic tracking error signal TE ₀ . That is, the present invention has an advantage that an accurate tracking error signal TE can be generated without depending on the method of calculating the basic tracking error signal TE ₀ .

[0081]

According to the present invention, there is provided a tracking error signal detection circuit capable of detecting an accurate tracking error signal with a simple circuit configuration even when an objective lens mounted on an optical head is shifted from the center due to a lens shift. it can.

According to the present invention, an accurate tracking error signal can be obtained with a simple circuit configuration even when the objective lens mounted on the optical head is deviated from the center by a lens shift, without depending on the method of calculating the basic tracking error signal. A detectable tracking error signal detection circuit can be provided.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a tracking error signal detection circuit as a first embodiment of the tracking error signal detection circuit of the present invention.

FIG. 2 is a diagram showing positions of pits formed on a recording medium,
FIG. 3 is a diagram illustrating a positional relationship between beam spots.

FIGS. 3A and 3B are waveform diagrams of detection signals of first to fourth photoelectric conversion elements in an on-track state, and FIG. 3A shows a pit depth of λ / FIG. 3 is a detection signal waveform diagram of the first to fourth photoelectric conversion elements in the case of being equal to 4, and FIG.
(B) shows the first to fourth cases when the pit depth is shallower than λ / 4.
3 is a detection signal waveform diagram of the photoelectric conversion element of FIG.

FIGS. 4A and 4B are waveform diagrams of detection signals of first to fourth photoelectric conversion elements in a detrack state,
FIG. 4 (A) shows the first to pit depths equal to λ / 4.
FIG. 4 is a detection signal waveform diagram of the fourth photoelectric conversion element,
(B) shows the first to fourth cases when the pit depth is shallower than λ / 4.
3 is a detection signal waveform diagram of the photoelectric conversion element of FIG.

FIGS. 5A and 5B are waveform diagrams of a tracking error signal and a detection signal of first to fourth photoelectric conversion elements when a pit depth is deviated from λ / 4 in a detrack state. FIG. 5A is a waveform diagram of a tracking error signal by the first and second photoelectric conversion elements and a waveform diagram of a tracking error signal by the third and fourth photoelectric conversion elements.
FIG. 5B is a waveform diagram of each of the detection signals of the first to fourth photoelectric conversion elements.

FIG. 6 is a circuit diagram illustrating a circuit configuration example of the correction signal generation circuit illustrated in FIG. 1;

FIG. 7 is a circuit diagram of a tracking error signal detection circuit as a second embodiment of the tracking error signal detection circuit of the present invention.

FIG. 8 is a diagram illustrating a circuit configuration of a conventional tracking error signal detection circuit.

[Explanation of symbols]

1, 1A tracking error signal detection circuit 11-14 current / voltage conversion circuit 21-24 waveform shaping circuit 31 phase comparison circuit (phase difference calculation circuit) 32 phase comparison circuit (phase difference calculation Circuit) 34 addition circuit 36 low-pass filter 40 tracking error correction means 41, 42 low-pass filter 44 correction signal generation circuits 441 to 443 subtraction circuit 444 addition circuit 445 selection circuit 446-447 comparison circuit 448 exclusive OR circuit 50 correction circuit 60 four-division photoelectric converter 61-64 first to fourth photoelectric conversion element (A) ~
(D) 71... RF signal calculation addition circuit 72, 78... Subtraction circuit 73, 75, 77, 79 low-pass filter 74, 76... Addition circuit 81 to 84 phase comparison circuit 91. Subtraction circuit 92 Subtraction circuit 95 Correction signal generation circuit 101-104 Coupling capacitor

Continued on the front page (72) Inventor Toshio Yamauchi 3-6-12 Kitaaoyama, Minato-ku, Tokyo Fuji Aoyama Building Japan Texas Instruments Co., Ltd. F-term (reference) 5D118 AA13 BA01 CA24 CB03 CD03 CF05

Claims (9)

[Claims] An electric signal output from first, second, third and fourth photoelectric conversion elements of a four-division photoelectric converter for converting light reflected from a disc-shaped information recording medium into an electric signal. A tracking error signal detection circuit for detecting a tracking error signal used for tracking control of the optical head with respect to the information recording medium, wherein the first and second positions are located ahead of the information recording medium in the moving direction with respect to the information tracks. A first phase difference calculating circuit for calculating a first phase difference signal which is a phase difference between electric signals of the photoelectric conversion elements, and the third and the third positions located behind the information recording medium in the moving direction with respect to the information track. A second phase difference signal for calculating a second phase difference signal, which is a phase difference between the electric signals of the photoelectric conversion element of No. 4;
A first phase difference calculation circuit for calculating a basic tracking error signal by adding the first phase difference signal and the second phase difference signal, and a first addition circuit for calculating the information track of the optical head. Correction signal generating means for calculating a correction signal from an offset component included in the first and second phase difference signals according to a positional relationship; and correcting the basic tracking error signal based on the correction signal to generate a tracking error signal. And a correction circuit for outputting a signal. 2. The method according to claim 1, wherein the correction signal generating means extracts a first DC component which is a DC component of the first phase difference signal.
And a second low-pass filter for extracting a second DC component that is a DC component of the second phase difference signal, and a difference between the first DC component and a reference value. First
A first subtraction circuit that calculates a difference signal between the second DC component and the reference value; a second subtraction circuit that calculates a second difference signal that is a difference between the second DC component and the reference value; A third subtraction circuit that calculates a third difference signal that is a difference from the second difference signal; and a first sum signal that is a sum of the first difference signal and the second difference signal. An adding circuit for calculating, and outputting the third difference signal or the first sum signal as the correction signal according to the magnitude relationship between the first DC component, the second DC component, and the reference value. The tracking error signal detection circuit according to claim 1, further comprising a selection circuit. 3. The correction circuit according to claim 1, wherein the correction circuit is an addition circuit that adds the basic tracking error signal and the correction signal to calculate the tracking error signal.
2. A tracking error signal detection circuit according to item 1. 4. The tracking error signal detection circuit according to claim 1, further comprising a low-pass filter having a predetermined low-pass characteristic between said first addition circuit and said correction circuit. 5. A four-divided photoelectric converter for converting light reflected from a disc-shaped information recording medium into an electric signal.
And a tracking error signal detection circuit for detecting a tracking error signal used for tracking control of the optical head with respect to the information recording medium based on an electric signal output from the fourth photoelectric conversion element. A first phase difference calculation circuit for calculating a first phase difference signal which is a phase difference between the electric signals of the first and second photoelectric conversion elements located in the forward direction with respect to the information recording medium; Calculating a second phase difference signal which is a phase difference between electric signals of the third and fourth photoelectric conversion elements located behind the moving direction with respect to the track;
And a first phase sum signal which is a phase sum of electric signals of the first and third photoelectric conversion elements located at diagonal positions in a moving direction of the information recording medium with respect to the information track. First
And a second phase sum signal which is a phase sum of electric signals of the second and fourth photoelectric conversion elements located at diagonal positions in a moving direction of the information recording medium with respect to the information track. Second
A phase sum calculation circuit, a subtraction circuit for calculating a basic tracking error signal by subtracting the first phase sum signal and the second phase sum signal, and a position relationship between the optical head and the information track. Correction signal generation means for calculating a correction signal from offset components included in the first and second phase difference signals, and a correction circuit for correcting the basic tracking error signal based on the correction signal and outputting a tracking error signal And a tracking error signal detection circuit comprising: 6. A first adder circuit for calculating an RF signal from a sum of electric signals of the first, second, third, and fourth photoelectric conversion elements, and an electric signal of the first photoelectric conversion element. A third phase difference calculation circuit that calculates a first difference signal that is a phase difference with the RF signal; and a second difference that is a phase difference between the electrical signal of the second photoelectric conversion element and the RF signal. A fourth phase difference calculation circuit that calculates a signal, a fifth phase difference calculation circuit that calculates a third difference signal that is a phase difference between the electric signal of the third photoelectric conversion element and the RF signal, A fifth phase difference calculation circuit that calculates a fourth difference signal that is a phase difference between the electric signal of the fourth photoelectric conversion element and the RF signal, wherein the first phase difference calculation circuit Calculating the first phase difference signal from the first difference signal and the second difference signal; Circuit calculates the second phase difference signal from the third differential signal and the fourth differential signal, said first is the phase sum calculating circuit said first difference signal and the third
A first phase sum signal from the second difference signal and the second phase sum signal, and the second phase sum calculation circuit calculates a second phase sum signal from the second difference signal and the fourth difference signal. 6. The tracking error signal detection circuit according to 5. 7. The correction signal generating means includes: a first low-pass filter for extracting a first DC component which is a DC component of the first phase signal; and a DC component of the second phase difference signal. A second low-pass filter for extracting a second DC component, a first subtraction circuit for calculating a fifth difference signal that is a difference between the first DC component and a reference value; A second subtraction circuit that calculates a sixth difference signal that is a difference between the DC component of the second and the reference value, and a seventh difference that is a difference between the fifth difference signal and the sixth difference signal. A third subtraction circuit that calculates a signal; an addition circuit that calculates a first sum signal that is a sum of the fifth difference signal and the sixth difference signal; The seventh difference signal or the first sum signal is output as the correction signal in accordance with the magnitude relationship between the DC component 2 and the reference value. Tracking error signal detecting circuit according to claim 5 or 6 and a 択回 path. 8. The tracking error signal detection circuit according to claim 5, wherein the correction circuit is an addition circuit for adding the basic tracking error signal and the correction signal to calculate the tracking error signal. . 9. A low-pass filter having a predetermined low-pass characteristic between said first and second phase sum calculation circuits and said correction signal, respectively. Tracking error signal detection circuit.