JP3551347B2 - Optical disc apparatus and tracking error signal calculation method - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical disk device and a tracking error signal calculation method, and more particularly, to an optical disk device that detects first and second light reception detection signals by a light receiving element divided at least into two in a direction perpendicular to a track of the optical disk, and The present invention relates to a tracking error signal calculation method.
[0002]
[Prior art]
In the optical disk device, when recording or reproducing information on or from an optical disk as a recording medium, it is necessary to control so that a light beam accurately traces a track.
[0003]
In a conventional optical disk device, for example, a reflected light from an optical disk is converted into an electric signal by a light receiving element or the like divided into two in a direction perpendicular to a track, and a difference between these signals is calculated to calculate a tracking error signal. For example, a so-called push-pull method has been used.
[0004]
However, in the push-pull method, for example, an offset may appear in the tracking error signal due to a deviation of the optical axis of the objective lens, an inclination of the optical disk, or an imbalance in the groove shape of the optical disk. When an offset appears, even if the tracking error signal is actually 0, the irradiation position of the laser beam shifts by an amount corresponding to the offset component, so that tracking cannot be performed accurately. There was a problem.
[0005]
In order to solve such a problem, a signal obtained by subtracting a value obtained by multiplying a peak value of each signal by a predetermined coefficient K from each signal output from the above-described light receiving element is used as a tracking error signal. A so-called top hold push-pull (hereinafter abbreviated as TPP) system has been proposed.
[0006]
Further, a method has been proposed to improve the access performance by setting such a coefficient K of the top hold push-pull method to be large when the frequency is low and small when the frequency is high. ing.
[0007]
[Problems to be solved by the invention]
By the way, in the above-mentioned TPP system, when the coefficient K has a frequency characteristic, the gain of the tracking error servo system may decrease in a low frequency band, for example, as shown in FIG. In such a case, for example, there is a problem that the tracking performance for an eccentric disk or the like is reduced.
[0008]
The present invention has been made in view of the above situation, and a tracking error servo system of a TPP system in which a coefficient K has a frequency characteristic accurately performs tracing even on an eccentric disk or the like. It is possible to do.
[0009]
[Means for Solving the Problems]
The optical disk apparatus according to claim 1 from the value obtained by multiplying the coefficient K ₁ the peak value of the first light-receiving detection signal, a first arithmetic means for subtracting the first light detection signal, the second from a value obtained by multiplying the coefficient K ₂ with respect to the peak value of the photodetection signal, a second calculating means for subtracting the second light detection signal, the difference between the output of the first arithmetic means and second arithmetic means a calculating means for calculating for, at a low frequency band than a predetermined cutoff frequency, so that the gain than higher frequency band than the cut-off frequency is increased by a predetermined value, and a amplifying means for amplifying an output signal of the calculating means , each coefficient K ₁ and K _2, the value at a frequency band lower than the cut-off frequency, characterized in that it is made of a larger than the value in the frequency band higher than the cut-off frequency.
[0010]
Tracking error signal calculating method according to claim 3, the coefficients K ₁ from the value obtained by multiplying the peak value of the first light-receiving detection signal, a first arithmetic step of subtracting the first light detection signal, from a value obtained by multiplying the coefficient K ₂ with respect to the peak value of the second light receiving detection signal, a second arithmetic step of subtracting the second light detection signal, the output of the first operational step and a second calculation step And an amplification step of amplifying an output signal of the calculation step so that the gain is increased by a predetermined value in a frequency band lower than the predetermined cutoff frequency in a frequency band lower than the predetermined cutoff frequency. wherein the respective coefficients K ₁ and K _2, the value at a frequency band lower than the cut-off frequency, characterized in that it is made of a larger than the value in the frequency band higher than the cut-off frequency
[0011]
The optical disc device according to claim 1 from the value obtained by multiplying the coefficient K ₁ the peak value of the first light-receiving detection signal, a first photodetection signal is first arithmetic means subtracts the second from a value obtained by multiplying the coefficient K ₂ with respect to the peak value of the photodetection signal, the second light receiving detection signal by subtracting the second arithmetic means, the difference between the output of the first arithmetic means and second arithmetic means Is calculated by the calculating means, and the amplifying means amplifies the output signal of the calculating means so that the gain is increased by a predetermined value in a frequency band lower than the predetermined cutoff frequency than in a frequency band higher than the cutoff frequency . Here, each of the coefficients K ₁ and K ₂ is such that a value in a frequency band lower than the cutoff frequency is larger than a value in a frequency band higher than the cutoff frequency. For example, the first computing means, the result of multiplying the coefficient K ₁ the peak value of the first light-receiving detection signal, subtracts the first photodetection signal and, second calculating means, first from the result of multiplying the coefficient K ₂ with respect to the peak value of the second light receiving detection signal, the second light receiving detection signal is subtracted to calculate the calculation means the difference output from the first and second arithmetic means , the output signal from the calculating means amplifying means for amplifying only loss by a factor K ₁ and K _2.
[0012]
Tracking error signal calculating method according to claim 3, the value obtained by multiplying the coefficient K ₁ the peak value of the first light-receiving detection signal, a first photodetection signal is the first operational step is subtracted, from a value obtained by multiplying the coefficient K ₂ with respect to the peak value of the second light receiving detection signal, the second light receiving detection signal by subtracting the second calculation step, the first operation step and the second calculating step outputs The calculation step calculates the difference between the two, and the amplification step amplifies the output signal of the calculation step so that the gain increases by a predetermined value in a frequency band lower than the predetermined cutoff frequency and in a frequency band higher than the cutoff frequency. I do. Here, each of the coefficients K ₁ and K ₂ is such that a value in a frequency band lower than the cutoff frequency is larger than a value in a frequency band higher than the cutoff frequency. For example, a first calculation step, the result of multiplying the coefficient K ₁ the peak value of the first light-receiving detection signal, a first photodetection signal by subtracting, also the second calculation step, the from the result of multiplying the coefficient K ₂ with respect to the peak value of the second light receiving detection signal, the second light receiving detection signal is subtracted to calculate the calculation step the difference between the outputs from the first and second calculating step , amplification step the output signal from the calculating step is amplified by loss by the factor K ₁ and K _2.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a block diagram illustrating a configuration example of an optical disc device according to an embodiment of the present invention.
[0014]
In FIG. 1, a DRAM 1 (Dynamic Random Access Memory) temporarily stores input data. An EDC (Error Detection Code) encoding unit 2 is configured to add EDC for error detection to the data supplied from the DRAM 1 and output the data. The scrambler 3 scrambles data output from the EDC encoder 2. The ID encoding unit 4 adds an ID code to the scrambled data.
[0015]
The data output from the ID encoding unit 4 is stored in an SRAM (Static Random Access Memory) 5, and when one block is stored, an ECC (Error Correction Code) encoding unit 6 converts an ECC for error correction. Will be added. The modulator 7 sequentially reads out the data stored in the SRAM 5, performs predetermined modulation, and supplies the data to the optical pickup 11.
[0016]
The optical pickup 11 irradiates the CD-R 10 with a recording laser beam (a beam having a higher intensity than for reproduction) in accordance with the data supplied from the modulation unit 7 to record information, and also reproduces a laser beam for reproduction. Is irradiated on the CD-R 10, the laser beam reflected from the CD-R 10 is photoelectrically converted into an electric signal, and output as a reproduction RF signal.
[0017]
The demodulation unit 12 performs a predetermined demodulation process on the reproduced RF signal output from the optical pickup 11, and stores the obtained data in a predetermined area of the SRAM 13. The ECC decoder 14 executes an error correction process when the data supplied from the demodulator 12 is stored in the SRAM 13 for one block.
[0018]
The ID decoding unit 15 reads data stored in the SRAM 13 and extracts an ID code. The descrambling unit 16 descrambles the data output from the ID decoding unit 15. The EDC decoding unit 17 extracts the EDC from the data output from the descrambling unit 16, and determines whether or not the reproduced data includes an error. The DRAM 18 temporarily stores and outputs data output from the EDC decoding unit 17.
[0019]
The servo unit 20 is configured to perform servo control such as focus, tracking, and sled.
[0020]
FIG. 2 shows an example of the configuration of a TPP tracking error signal detection unit built in the servo unit 20 of FIG.
[0021]
As shown in this figure, the TPP tracking error signal detection unit includes a top hold constant multiplication circuit 40 , a top hold constant multiplication circuit 41 , differential amplifier circuits 42 to 44 , and a low boost filter (hereinafter abbreviated as LBF). It is more configuration 45.
[0022]
The top hold constant multiplying circuits 40 and 41 are provided with light receiving detection signals E and F output from the light receiving units incorporated in the optical pickup 11 shown in FIG. 1 (each of the two light receiving units divided in a direction perpendicular to the track). ), And the peak value is held, and a value obtained by multiplying the held peak value by a constant K is output.
[0023]
Note that the constant K has a frequency characteristic as shown in FIG. 3, where a cutoff frequency is around 410 Hz, K = 0.64 at lower frequencies, and K = 0.64 at higher frequencies. It is set so that K = 0.5.
[0024]
The differential amplifying circuit 42 subtracts the signal E from the output of the top hold constant multiplying circuit 40, amplifies it with a predetermined gain, and outputs the result. Similarly, the differential amplifier circuit 43 subtracts the signal F from the output of the top hold constant multiplication circuit 41, amplifies the signal with a predetermined gain, and outputs the amplified signal.
[0025]
The differential amplifier circuit 44 subtracts the output of the differential amplifier circuit 42 from the output of the differential amplifier circuit 43, amplifies the output with a predetermined gain, and outputs the amplified signal.
[0026]
The LBF 45 amplifies the low frequency band of the output of the differential amplifier circuit 44 with a predetermined gain.
[0027]
FIG. 4 is a circuit diagram showing an example of the configuration of the LBF 45 shown in FIG. As shown in this figure, the LBF 45 includes resistors 60 and 61, a capacitor 62, and an amplifier 63.
[0028]
FIG. 5 is a diagram illustrating a frequency characteristic of the LBF 45 illustrated in FIG. As shown in this figure, the LBF 45 is a filter that uses a cutoff frequency around 410 Hz and boosts (amplifies) a lower frequency band with a gain of +2.1 dB.
[0029]
Next, the operation of this embodiment will be described.
[0030]
The input data is temporarily stored in the DRAM 1 and then output to the EDC encoder 2. The EDC encoder 2 adds an error detection EDC to the data output from the DRAM 1 and supplies the data to the scrambler 3. The scramble unit 3 performs a scramble process on the data (data) in order to prevent the error from being concentrated on a predetermined sector or frame when the CD-R 10 has a flaw or the like so that the data cannot be reproduced. Is performed, and the result is output to the ID encoding unit 4.
[0031]
The ID encoding unit 4 inserts an ID code for detecting the address of the CD-R 10 at the head of each sector, and then sequentially stores the ID code in the SRAM 5. The ECC encoding unit 6 performs processing for adding an ECC when one block of data is stored in the SRAM 5.
[0032]
The data to which the ECC is added by the ECC encoder 6 is sequentially read from the SRAM 5 and supplied to the modulator 7. The modulation unit 7 adds a synchronization pattern to the data, performs predetermined modulation, and outputs the data to the optical pickup 11. The optical pickup 11 irradiates a predetermined area of the CD-R 10 with a recording laser beam.
[0033]
In the CD-R 10 irradiated with the recording laser beam, information is recorded because the heat of the beam causes a physical irreversible change in the recording medium (for example, sublimation of the recording medium). . The operation of the servo unit 20 will be described later.
[0034]
Next, a case where the data recorded on the CD-R 10 as described above is reproduced will be described.
[0035]
The optical pickup 11 irradiates a predetermined area of the CD-R 10 with a reproduction laser beam having a lower intensity than the recording laser beam, and generates a reproduction RF signal by photoelectrically converting the reflected light. . The reproduced RF signal is demodulated by the demodulation unit 12 and then stored in the SRAM 13 in units of one block. The operation of the servo unit 20 in this case is the same as that in the case of recording, and the details will be described later.
[0036]
One block of data stored in the SRAM 13 is subjected to error correction by the ECC decoding unit 14, and is sequentially read by the ID decoding unit 15 to extract an ID code. The descrambler 16 descrambles the data output by the ID decoder 15 with reference to the extracted ID code, and outputs the data to the EDC decoder 17. The EDC decoding unit 17 detects an EDC from the descrambled data, and determines whether or not the reproduced data includes an error. As a result, when it is determined that no error is included, the data is output to the DRAM 18. When it is determined that an error is included, for example, the optical pickup 11 is controlled to read the same data again from the CD-R 10.
[0037]
The DRAM 18 temporarily stores the data output from the EDC decoding unit 17, and then outputs the data in synchronization with the data reading speed of an external device (not shown).
[0038]
Next, the operation of the servo unit 20 will be described with reference to FIG.
[0039]
The light beam emitted from an LD (Laser Diode) not shown is applied to the recording surface of the CD-R 10 via an objective lens (not shown) built in the optical pickup 11. Depending on the state of the recording surface, the diffracted or reflected light beam is again incident on the light receiving element (not shown) which is divided into two parts in a direction perpendicular to the track via the objective lens.
[0040]
The output signals from the light receiving element divided into two are denoted by E and F, respectively. FIG. 6 shows a waveform of the RF envelope signal of the signal E.
[0041]
In this figure, a curve CV1 indicates a change in a peak of the RF envelope of the signal E due to a shift of the objective lens, a skew, or the like. A curve CV2 shows a waveform of a signal obtained by applying a low-pass filter to the tracking error signal TE used when applying tracking servo by the push-pull method. A curve CV3 indicates a change in the offset of the tracking error signal actually used. The signal is denoted by A, and the width is denoted by b. The signal F is the same as the above case.
[0042]
It is assumed that the envelope signal as described above is input to the TPP tracking error signal detector shown in FIG. In this case, a signal obtained by subtracting the signal E from the output of the top hold constant multiplying circuit 40 and amplifying it with a predetermined gain is output from the differential amplifier circuit 42. Now, the gain of the differential amplifier circuit 42 is set to 0 dB, and the peak holding value of the signal E is set to _ETP . At that time, the output TPP (E) of the differential amplifier circuit 42 can be expressed by the following equation.
[0043]
TPP (E) = K × E _TP −E (1)
[0044]
Similarly, the output TPP (F) of the differential amplifier circuit 43 can be expressed as follows.
[0045]
TPP (F) = K × F _TP −F (2)
[0046]
Here, _FTP is the peak holding value of the signal F.
[0047]
Therefore, the output TPP (TE) of the differential amplifier circuit 44 can be expressed as follows.
[0048]
TPP (TE) = (E−F) −K (E _TP −F _TP ) (3)
[0049]
Note that the coefficient K is determined as follows. That is, in FIG. 6, the offset b is set to be a product of the coefficient K and the peak a (b = K × a). Therefore, the signal from which the offset has been canceled can be expressed as (E−K × a).
[0050]
At this time, peak a is _{E TP} obtained by the top holding the curve CV1 (signal E) of FIG. 6. Accordingly, the output TPP (E) of the differential amplifier circuit 42 shown in FIG.
[0051]
Similarly, the output TPP (F) of the differential amplifier circuit 43 is obtained by removing the offset from the signal F.
[0052]
The difference between the thus obtained signals E and F from which the offset has been removed is obtained in the differential amplifier circuit 44, and the top hold push-pull signal TPP (TE) is generated.
[0053]
By the way, as described above, the coefficient K is set so that the value increases in a low frequency band as shown in FIG. 3 in order to improve access performance. When the coefficient K is set in this way, as shown in FIG. 7, the gain of the tracking servo in the low frequency band decreases.
[0054]
That is, since _ETP and _FTP are top hold signals, they include not only offset components but also signal components (components of signal E or signal F). Therefore, as shown in Expression (3), when (E _TP −F _TP ) multiplied by the coefficient K is subtracted from the signal component (E−F), the signal component becomes large when the value of the coefficient K is large. Will decrease. That is, as the value of the coefficient K is larger, the input signal is substantially reduced, and as a result, the gain of the system is reduced. Accordingly, the gain of the tracking servo system decreases in a low frequency region where the value of the coefficient K is large (see FIG. 3).
[0055]
In this embodiment, the decrease in the gain of the tracking servo system in such a low frequency band is 2.1 dB as shown in FIG.
[0056]
Therefore, in the present embodiment, the LBF 45 is added to the subsequent stage of the differential amplifier circuit 44 to compensate for the low-frequency gain. That is, as shown in FIG. 5, the LBF 45 is set so that the cutoff frequency is around 410 Hz and the gain is increased by +2.1 dB in a lower band. This makes it possible to compensate for a decrease in gain in the low frequency band caused by the coefficient K.
[0057]
The circuit constants of the configuration example shown in FIG. 4 are determined as follows.
[0058]
That is, assuming that the gain of the amplifier circuit 63 is g, the transfer function T (jω) of the LBF 45 shown in FIG. 4 can be expressed as follows.
[0059]
T (jω) = g × (jωCR ₂ +1) / (jωC (R ₁ + R ₂ ) +1) (4)
[0060]
In this equation, when ω = 0, that is, when the frequency is 0, the gain T (0) is g.
[0061]
Further, the gain in the case of ω → ∞ is T (∞) = g × R ₂ / (R ₁ + R ₂ ).
[0062]
Therefore, the values of g, R ₁ , and R ₂ are set so that the gain in the low range is increased by +2.1 dB as compared with that in the high range, and the value of C is set so that the cutoff frequency is around 410 Hz. By doing so, it is possible to realize the LBF 45 having the frequency characteristics shown in FIG.
[0063]
According to the above-described embodiment, even when the coefficient K has a frequency characteristic, it is possible to compensate for a decrease in gain in the low frequency band of the tracking servo system. it becomes possible to perform accurate tracking.
[0064]
In the above embodiment, the optical disk device that records or reproduces information on the CD-R 10 has been described as an example. However, the present invention is not limited to only such a case. Of course, the present invention can be applied to (Mini Disk) and the like.
[0065]
【The invention's effect】
According to the present invention, a value obtained by multiplying the coefficient K ₁ the peak value of the first light-receiving detection signal, subtracts the first photodetection signal, coefficients for the peak value of the second light receiving detection signal After subtracting the second light reception detection signal from the value obtained by multiplying K ₂ and calculating the difference between the obtained signals, the calculated output signal is divided by a frequency band lower than the cutoff frequency from the cutoff frequency. Since the gain is amplified so that the gain is increased by a predetermined value compared to the high frequency band, it is possible to accurately apply the tracking servo to the eccentric disk.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating an example of a configuration of an embodiment of an optical disc device according to the present invention.
FIG. 2 is a block diagram showing an example of a configuration of a TPP tracking error signal generation unit built in the servo unit shown in FIG.
3 is a diagram illustrating a frequency characteristic of a coefficient K of the top hold constant multiplication circuit illustrated in FIG. 2;
FIG. 4 is a circuit diagram illustrating an example of a configuration of an LBF illustrated in FIG. 2;
FIG. 5 is a diagram illustrating a frequency characteristic of the LBF illustrated in FIG. 4;
FIG. 6 is a diagram showing an envelope of a signal E output from the optical pickup 11 shown in FIG.
7 is a diagram showing a decrease in the low-frequency gain of the tracking servo system when a frequency characteristic is given to the coefficient K of the top hold constant multiplication circuit shown in FIG. 2;
[Explanation of symbols]
40 top hold constant multiplication circuit (first operation means), 41 top hold constant multiplication circuit (second operation means), 44 differential amplifier circuit (calculation means), 45 LBF (amplification means)

Claims (3)

In an optical disk device for detecting first and second light reception detection signals by a light receiving element divided into at least two in a direction perpendicular to a track of an optical disk,
The coefficients K ₁ from the value obtained by multiplying the peak value of the first light receiving detection signal, first calculating means for subtracting said first light detection signal,
The coefficient K ₂ from the value obtained by multiplying the peak value of the second light detection signal, second calculating means for subtracting said second light detection signal,
Calculating means for calculating a difference between outputs of the first calculating means and the second calculating means;
Amplifying means for amplifying an output signal of the calculating means , so that a gain is increased by a predetermined value in a frequency band lower than the predetermined cutoff frequency and a frequency band higher than the frequency band higher than the cutoff frequency ,
Each of the coefficients K ₁ and K ₂ is such that a value in a frequency band lower than the cutoff frequency is larger than a value in a frequency band higher than the cutoff frequency.
Optical disc apparatus characterized by. It said amplifying means, an optical disk apparatus according to claim 1, characterized in that it has a characteristic that compensates the gain loss due to the coefficient K ₁ or K ₂ are respectively multiplied at said first or second calculation means. In a tracking error signal calculation method for an optical disk device, the first and second light reception detection signals are detected by a light receiving element divided at least into two in a direction perpendicular to a track of the optical disk.
The coefficients K ₁ from the value obtained by multiplying the peak value of the first light receiving detection signal, a first arithmetic step of subtracting the first light receiving detection signals,
The coefficient K ₂ from the value obtained by multiplying the peak value of the second light detection signal, a second arithmetic step of subtracting the second light detection signal,
A calculating step of calculating a difference between outputs of the first calculating step and the second calculating step;
An amplification step of amplifying an output signal of the calculation step , so that a gain is increased by a predetermined value from a frequency band higher than the cutoff frequency in a frequency band lower than the predetermined cutoff frequency ,
Each of the coefficients K ₁ and K ₂ is such that a value in a frequency band lower than the cutoff frequency is larger than a value in a frequency band higher than the cutoff frequency.
Tracking error signal calculation method characterized by.

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