JP2008135122A - Asymmetry detecting device and optical disk recording device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To detect asymmetry at high speed without enlarging circuit scale uselessly even when interference between codes is caused in a reproduced signal. <P>SOLUTION: Amplitude value data of a reproduced signal in the prescribed sampling timing is obtained by an A/D conversion part 8. A zero cross detecting part 13 detects a point at which the amplitude data of the reproduced signal coincides to a zero level. A zero cross period measuring part 14 counts a zero cross point period being an output of the zero cross detecting part 13. The extreme value detecting part 15 detects the maximum value or the minimum value of the amplitude value data in a zero cross point period. An asymmetry detecting part 1601 performs grouping of the zero cross point period for each separation period nT based on the count value of the zero cross point period and detects asymmetry for each separation period nT from the maximum value or the minimum value of the amplitude value data in the zero cross point period. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a technique for detecting asymmetry of a reproduction signal obtained from an optical disc.

  2. Description of the Related Art Conventionally, in an optical disk apparatus that performs recording and reproduction of a rewritable optical disk, such as a DVD-R (Digital Versatile Disk Recordable), a predetermined area (PCA: Power Perform trial writing while changing the recording laser power in the calibration area), refer to the asymmetry of the playback signal as an index to evaluate the quality of the playback signal, and find the laser power with the best playback signal quality in that area. Yes.

As a method for detecting the asymmetry of the reproduction signal, a method realized by obtaining a peak value envelope voltage and a bottom value envelope voltage of the reproduction signal by an analog circuit and performing a predetermined calculation on these is known. (For example, Patent Document 1)
JP-A-10-55621

  In recent years, high density and high speed recording of optical discs have been achieved, and PRML (Partial) that actively uses intersymbol interference generated by adjacent marks in recording and playback of high density optical discs such as HD DVD and Blu-ray. Response and Maximum Likelihood) is used. When recording and reproducing information using PRML, intersymbol interference occurs in the reproduced signal, and the amplitude level is multivalued. The asymmetry of the playback signal often depends on the amplitude level of the playback signal, and in the conventional method of acquiring the peak value envelope voltage and the bottom value envelope voltage of the playback signal with an analog circuit, the envelope voltage is calculated for each amplitude level. Since an analog circuit to be acquired is required, the circuit scale is unnecessarily large, and it is difficult to increase the speed.

  The present invention has been made in view of such a situation, and even when intersymbol interference occurs in a reproduction signal as in a high-density optical disc such as an HD DVD, the circuit scale is unnecessarily increased. An object of the present invention is to provide an apparatus capable of detecting asymmetry at high speed.

  The present invention provides an apparatus for detecting asymmetry of a reproduction signal obtained from an optical disc, reproduction amplitude value data acquisition means for acquiring amplitude value data of the reproduction signal at a predetermined sampling timing, and the amplitude value data equal to or larger than a predetermined value and a predetermined value. The amplitude value data is determined in units of a discrete period nT (where n is an integer of 1 or more and T is a channel clock of a recording modulation system) based on the measured period and a measuring means for measuring a period that is less than or equal to the value. An extreme value acquisition unit that acquires a maximum value of amplitude value data in a period equal to or greater than a value and a minimum value of amplitude value data in a period equal to or less than a predetermined value; and an asymmetry detection unit that detects asymmetry based on the maximum value and the minimum value The gist is to provide it.

  In addition, the extreme value acquisition unit is configured to use the maximum value and the minimum value based on a measurement result of a period in which the amplitude value data in the period before and after the period is not less than the predetermined value and not more than the predetermined value. It is desirable to determine whether to obtain a value.

  Further, the present invention is an optical disc apparatus having the gist thereof, comprising: laser power setting means for setting a recording laser power based on the asymmetry detected by the asymmetry detection means.

  According to the present invention, even when intersymbol interference occurs in a reproduction signal as in a high-density optical disc such as an HD DVD, an analog circuit that acquires an envelope voltage for each multi-level amplitude level is not required. Therefore, asymmetry can be detected at high speed without unnecessarily increasing the circuit scale.

(First embodiment)
FIG. 1 is a conceptual diagram showing the overall configuration of the optical disc apparatus according to the first embodiment of the present invention. In FIG. 1, an optical disc 1 includes a PCA for performing trial writing. The encoding unit 2 performs processing such as error correction code on the input information. The modulator 3 performs processing such as ETM (Eight Twelve Modulation) on the output from the encoder 2. The laser drive unit 4 outputs a semiconductor laser drive signal corresponding to the output from the modulation unit 3 to the optical pickup 5 at the time of recording, and outputs a semiconductor laser drive signal for emitting a laser having a constant intensity to the optical pickup at the time of reproduction. .

  The optical pickup 5 writes and reads information to and from the optical disc 1 by converging the laser light emitted from the semiconductor laser onto the optical disc 1 with an objective lens. In addition, an objective lens actuator that adjusts the convergence state of the laser beam with respect to the optical disc 1, a photodetector that receives the reflected light from the optical disc, and a laser beam emitted from the semiconductor laser is guided to the objective lens, and the reflected light from the optical disc 1 is reflected. An optical system that guides the light to the photodetector.

  The light reception signal processing unit 6 amplifies the light reception signal photoelectrically converted by the photodetector of the optical pickup 5 to generate a reproduction signal, and generates a wobble signal, a focus error signal, a tracking error signal, and the like.

  The servo unit 7 generates a focus servo signal and a tracking servo signal from the focus error signal and tracking signal output from the light reception signal processing unit 6, and outputs them to the optical pickup 5. Further, a motor servo signal is generated from the wobble signal output from the received light signal processing unit 6 and output to the drive motor of the optical disc 1.

  The A / D conversion unit 8 performs A / D conversion on the reproduction signal output from the received light signal processing unit 6 at a predetermined sampling timing, and outputs amplitude value data of the reproduction signal. Note that the predetermined sampling timing may not be synchronized with the recording modulation channel clock T, but may be asynchronous as long as it is faster than T.

  The EQ 9 is composed of an FIR filter, adjusts the filter coefficient, and performs equalization processing so that the reproduction signal conforms to the PR (1, 2, 2, 2, 1) characteristics.

  In order to perform ML decoding of a reproduction signal having PR characteristics, PRML 10 performs soft decision Viterbi decoding on the amplitude value data of the reproduction signal that is the output of EQ9, compares it with a predetermined expected value, and outputs binary data of the reproduction signal. Decrypt.

  The demodulation unit 11 performs processing such as ETM demodulation on the binary data of the reproduction signal that is the output of the PRML 10. The decoding unit 12 performs processing such as error correction on the output of the demodulation unit 11.

  The zero cross detector 13 detects a point where the amplitude value data of the reproduction signal matches the zero level. The zero cross period measurement unit 14 counts the zero cross point period that is the output of the zero cross detection unit 13.

  The extreme value detection unit 15 detects the maximum value or the minimum value of the amplitude value data within the zero cross point period. Here, when the amplitude value data zero-crosses from negative to positive at the start zero point in the zero cross point period, since the zero cross point period is a mark, the maximum value of the amplitude value data is detected. On the other hand, when the amplitude value data zero crosses from positive to negative at the start zero cross point in the zero cross point period, the minimum value of the amplitude value data is detected because the zero cross point period is a space.

  The control unit 16 includes an asymmetry detection unit 1601 and a laser power control unit 1602. In addition, firmware that controls the entire optical disc apparatus is included, and each unit is controlled according to this firmware.

  The asymmetry detection unit 1601 detects asymmetry from the maximum value or the minimum value of the amplitude value data within the zero cross point period. FIG. 2 is a flowchart (1) of the asymmetry detection procedure. Hereinafter, the operation of the asymmetry detection unit 1601 will be described with reference to the drawings.

  The asymmetry detection unit 1601 acquires the count value of the zero cross point period from the zero cross period measurement unit 14 (S10). Since the data length of the mark or space formed on the optical disc 1 is nT (n is an integer of 1 or more), the count value of the zero cross point period takes a value in the vicinity of the discrete period nT. Therefore, it is determined which discrete period the count value of the zero cross point period is closest to, and grouping is performed for each discrete period (S11). Then, the maximum value or the minimum value of the amplitude value data within the zero cross point period is integrated every discrete period nT to which the zero cross point period belongs (S12). When integration is performed for a predetermined number of samples (Y in S13), the maximum value or the minimum value of the amplitude value data is divided by the number of samples N and averaged for each discrete period nT (S14).

Next, for each discrete period nT, the asymmetry value (A) is calculated from the maximum value (ArgMax) and minimum value (ArgMin) of the averaged amplitude value data.
A = ABS (ArgMax) -ABS (ArgMin)
(S15). Here, ABS (X) means taking the absolute value of X.

For example, when ArgMax is 4.1 and ArgMin is -5.4, the asymmetry value A1 is
A1 = ABS (4.1) -ABS (-5.4) = 4.1-5.4 = -1.3
It becomes.

  The laser power control unit 1602 performs test writing with the PCA of the optical disc 1 with a predetermined recording laser power, reproduces the portion where the test writing has been performed, and receives an asymmetry value for each discrete period nT from the asymmetry detection unit 1601. An approximate straight line is calculated from the received asymmetry value, and the laser power at which the asymmetry value becomes a predetermined value is set as the recording laser power.

FIG. 3 shows a laser power setting method according to FIG. Here, the linear approximation formula of the laser power P and the asymmetry value A is assumed that the slope is a and the intercept is Pb.
P = aA + Pb
Holds. In FIG. 3, when the asymmetry value in the case of the recording laser power Pw1 is A1 and the asymmetry value in the case of the recording laser power Pw2 is A2, the slope a and the intercept Pb of the approximate line are
a = (Pw2-Pw1) / (A2-A1)
Pb = Pw2-A2 * a
It is obtained.

  The laser power control unit 1602 assigns a predetermined asymmetry value to A in the calculated linear approximation formula, and sets the laser power P at that time as the recording laser power.

  For example, when the predetermined value is 0, if the asymmetry value A = 0 is substituted in the linear approximation formula, the laser power P = Pb, so Pb is set as the recording laser power.

  When calculating an approximate straight line, it is preferable to calculate using an asymmetry value of a discrete period nT (n is the number of samples required for PR equalization + 1, that is, an integer of 6 or more). The approximate straight line may be calculated using the asymmetry value for each discrete period nT, and the obtained laser power may be averaged and set as the recording laser power. The approximate straight line may be calculated using only the asymmetry value of the period nT, and the obtained single laser power may be set as the recording laser power.

According to such a 1st embodiment of the present invention, the following operation effects can be enjoyed.
(1) The amplitude value data of the reproduction signal at a predetermined sampling timing is acquired by the A / D conversion unit 8, and the zero cross detection unit 13 detects a point where the amplitude value data of the reproduction signal matches the zero level, and the zero cross period The measurement unit 14 counts the zero cross point period that is the output of the zero cross detection unit 13, the extreme value detection unit 15 detects the maximum value or the minimum value of the amplitude value data within the zero cross point period, and the asymmetry detection unit 1601 In order to detect the asymmetry for each discrete period nT from the maximum value or the minimum value of the amplitude value data in the zero cross point period by grouping the zero cross point period for each discrete period nT based on the count value of the zero cross point period, Requires an analog circuit that acquires the envelope voltage for each multilevel amplitude level Instead, it is possible to detect asymmetry at high speed.
(2) The laser power control unit 1602 receives the asymmetry value for each discrete period nT from the asymmetry detection unit 1601, calculates an approximate straight line, and sets the laser power at which the asymmetry value becomes a predetermined value as the recording laser power. Even when intersymbol interference occurs in the signal, the asymmetry value can be used as an index for optimizing the recording laser pulse, and information can be recorded on the optical disk with high reliability.
(Second Embodiment)
In the first embodiment, the asymmetry detection unit 1601 groups the zero cross point periods into discrete periods nT, and the zero cross point period belongs to the maximum value or the minimum value of the amplitude value data in the zero cross point period. It was averaged over a predetermined number of samples every discrete period nT.

  By the way, if grouping is performed for each discrete period nT using only the count value of the zero cross point period, depending on the pattern before and after the zero cross point period, the grouping is performed in different discrete periods even though the pattern in the zero cross point period is the same. There is a possibility that.

  FIG. 4 is a diagram showing a partial response equalization waveform of a 3T mark (front and rear is 3T space), and FIG. 5 is a diagram showing a partial response equalization waveform of the 3T mark (front and rear is 2T space). Hereinafter, with reference to FIG. 4 and FIG. 5, a case where groups are divided into different discrete periods regardless of the same pattern will be described.

  In FIG. 4, a binary ideal pattern is (1, 1, 1, 0, 0, 0, 1, 1, 1), that is, a pattern having a mark length of 3T and a front and rear space length of 3T. As a normalized amplitude value data, -1 is assigned when the pattern is 1, +1 is assigned when the pattern is 0, and partial response equalization of PR (1, 2, 2, 2, 1) is performed as a solid line in FIG. It becomes a waveform shown by. At this time, since the zero cross point period is 3T, the zero cross point period is grouped into discrete periods 3T.

  On the other hand, in FIG. 5, the binary ideal pattern is (0, 1, 1, 0, 0, 0, 1, 1, 0), that is, a pattern having a mark length of 3T and a preceding and following space length of 2T. As a normalized amplitude value data, -1 is assigned when the pattern is 1, and +1 is assigned when the pattern is 0. When partial response equalization of PR (1, 2, 2, 2, 1) is performed, a solid line in FIG. It becomes a waveform shown by. At this time, since the zero cross point period is 4T, the zero cross point period is grouped into discrete periods 4T.

  When the mark length is 3T and the same pattern is grouped into different discrete periods, the maximum or minimum amplitude value data within the zero cross point period is averaged for each discrete period nT to which the zero cross point period belongs. There is a risk that the accuracy may deteriorate when the process is changed.

  FIG. 6 is a diagram showing a partial response equalization waveform of a 3T mark (front and rear is a 4T space). In FIG. 6, a binary ideal pattern is (1, 1, 1, 0, 0, 0, 0, 1, 1, 1, 1), that is, a pattern having a mark length of 4T and a front and rear space length of 3T. As the normalized amplitude value data, -1 is assigned when the pattern is 1, and +1 is assigned when the pattern is 0. When partial response equalization of PR (1, 2, 2, 2, 1) is performed, a solid line in FIG. It becomes a waveform shown by. At this time, since the zero cross point period is 4T, the zero cross point period is grouped into discrete periods 4T.

  Although the maximum value of the partial response equalization waveform of FIG. 6 is 6, the maximum value of the partial response equalization waveform of FIG. 5 that is grouped into the same discrete period 4T is 4, so these can be mixed to form a discrete period. It is not preferable to average the maximum value in 4T.

  Therefore, in the second embodiment, as shown in the partial response equalization waveform of FIG. 5, in the zero cross point period belonging to the discrete period nT different from the discrete period nT to be grouped due to the influence of the preceding and following patterns. Do not acquire the maximum value or minimum value of the amplitude value data, perform averaging, and avoid deterioration of accuracy.

  FIG. 7 is a flowchart (2) of the asymmetry detection procedure.

  The zero cross detection unit 13 detects a point where the amplitude value data of the reproduction signal matches the zero level, and the zero cross period measurement unit 14 counts the zero cross point period that is the output of the zero cross detection unit 13 (S10).

  The extreme value detection unit 15 detects the maximum value or the minimum value of the amplitude value data within the zero cross point period (S11).

  The asymmetry detection unit 1601 determines whether the count value of the zero cross point period is 6T or more (S12). Here, the judgment based on 6T is that the partial response equalization of PR (1, 2, 2, 2, 1) is performed from the amplitude value data of 5 samples, so the count value of the zero cross point period is PR This is because the maximum value or the minimum value of the amplitude value data within the zero cross point period is saturated when the number of samples required for equalization + 1, that is, 6T or more.

  When the count value of the zero cross point period is 6T or more (Y of S12), the maximum value or minimum value of the amplitude value data in the target zero cross point period is integrated for each discrete period nT to which the zero cross point period belongs. (S14).

  On the other hand, when the count value of the zero cross point period is smaller than 6T (N of S12), it is determined whether the count value of the zero cross point period before and after the target zero cross point period is 3T or more (S13). Here, since the partial response equalization of PR (1, 2, 2, 2, 1) is performed from amplitude data of 5 samples, the count value of the preceding and following zero cross point periods is determined based on 3T. This is because, when (number of samples required for PR equalization + 1) / 2, that is, 3T or more, the count value of the target zero cross point period is not affected by the pattern of the preceding and following zero cross point periods.

  When the count value of the zero cross point period before and after the target zero cross point period is smaller than 3T (N in S13), the maximum value or the minimum value of the amplitude value data in the zero cross point period is not acquired.

  On the other hand, when the count value of the zero cross point period before and after the target zero cross point period is 3T or more (Y of S13), the maximum or minimum value of the amplitude value data in the zero cross point period is indicated by the zero cross point period. Integrate every discrete period nT to which it belongs (S14).

  When integration is performed for a predetermined number of samples (Y in S15), the maximum value or minimum value of the amplitude value data is divided by the number of samples N and averaged for each discrete period nT. Thereafter, asymmetry is detected every discrete period nT in the same manner as in the first embodiment.

According to such a 2nd embodiment of the present invention, in addition to a 1st embodiment, the following operation effects can be enjoyed.
(3) When the target zero cross point period is smaller than 6T and the zero cross point period before and after the zero cross point period is smaller than 3T, the asymmetry detection unit 1601 determines the maximum value or the minimum amplitude value data within the zero cross point period. The value is not acquired and the amplitude value data is averaged at the maximum or minimum value every discrete period nT to detect asymmetry. However, asymmetry can be detected with high reliability.

  Although the best mode for carrying out the present invention has been described above, the present invention is not limited to the configuration of this embodiment, and the scope of application of the present invention defined in the claims. As long as the functions of the configuration of the above-described embodiment can be achieved, various modifications are possible.

  For example, in the embodiment of the present invention, the case of (1, 2, 2, 2, 1) has been described, but in the case of PR (1, 2, 2, 1), PR (1, 2, 1) Even so, it is possible to enjoy the same operational effects.

  In the embodiment of the present invention, the zero value of the amplitude value data of the reproduction signal that is the output of the A / D converter 8 is detected and the maximum value or the minimum value of the amplitude value data within the zero cross point period is detected. However, even if the zero-cross point is detected for the amplitude value data of the reproduction signal that is the output of EQ9 and the maximum value or the minimum value of the amplitude value data within the zero-cross point period is detected, the same effect is obtained. be able to.

  In the embodiment of the present invention, the zero cross detection unit 13 detects a point where the amplitude value data of the reproduction signal matches the zero level, and the zero cross period measurement unit 14 detects the zero cross point that is an output of the zero cross detection unit 13. Although the period is counted, the zero cross detection unit 13 detects a point where the amplitude value data of the reproduction signal matches the predetermined value, and the zero cross period measurement unit 14 detects the predetermined value cross point that is an output of the zero cross detection unit 13. The period may be counted. As the predetermined value, it is preferable to use a value obtained by averaging patterns in which 2T marks and 2T spaces are alternately continued. According to this modification, asymmetry can be detected with high accuracy even if the offset of the entire reproduction signal is not completely eliminated by the signal processing in the previous stage.

  According to the present invention, even when intersymbol interference occurs in a reproduction signal as in a high-density optical disc such as an HD DVD, an analog circuit that acquires an envelope voltage for each multi-level amplitude level is not required. Therefore, the circuit scale is not increased unnecessarily, and asymmetry can be detected at high speed, which is useful as an asymmetry detector.

1 is a conceptual diagram showing the overall configuration of an optical disc apparatus according to an embodiment of the present invention. Diagram showing laser power setting method Flow chart of asymmetry detection procedure (1) Diagram showing partial response equalization waveform of 3T mark (3T space before and after) Diagram showing partial response equalization waveform of 3T mark (2T space before and after) Diagram showing partial response equalization waveform of 3T mark (4T space before and after) Flow chart of asymmetry detection procedure (2)

Explanation of symbols

8 A / D converter 9 EQ
10 PRML
13 Zero Cross Detection Unit 15 Zero Cross Period Measurement Unit 15 Extreme Value Detection Unit 1601 Asymmetry Detection Unit 1602 Laser Power Control Unit

Claims (3)

In an apparatus for detecting asymmetry of a reproduction signal obtained from an optical disc,
Based on the measured period, reproduction amplitude value data acquisition means for acquiring amplitude value data of a reproduction signal at a predetermined sampling timing, measurement means for measuring a period during which the amplitude value data is greater than or equal to a predetermined value and less than or equal to a predetermined value , With a discrete period nT (n is an integer greater than or equal to 1 and T is a channel clock of a recording modulation system) as a unit, the amplitude value data has a maximum value in a period in which the amplitude value data is a predetermined value or more and an amplitude in a period in which the amplitude value data is a predetermined value or less An asymmetry detection device comprising: an extreme value acquisition unit that acquires a minimum value of value data; and an asymmetry detection unit that detects asymmetry based on the maximum value and the minimum value.   The extreme value acquisition means determines whether to acquire the maximum value and the minimum value based on a measurement result of a period in which the amplitude value data in the period before and after the period is equal to or greater than the predetermined value and equal to or less than the predetermined value. The asymmetry detection device according to claim 1, wherein: An optical disc apparatus comprising: laser power setting means for setting a recording laser power based on the asymmetry detected by the asymmetry detection means according to claim 1.

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