JP2009104749A - Optical disk apparatus and tracking control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To generate a high-precision tracking error signal by simply and reliably removing a high frequency component which causes deterioration in signal quality. <P>SOLUTION: A DPD circuit generates a tracking error signal by a phase difference detecting technique (DPD) based on a signal received by an optical pickup. A digital signal processing circuit generates an information signal based on the received signal. When the information signal contains a specific signal component (2T signal), a 2T detecting circuit 36 generates mask pulses. A 2T masking circuit 27 removes the tracking error signal only during a mask pulse period by a masking process. A timing generating circuit 35 synchronizes the mask pulse with the tracking error signal. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical disc apparatus for recording and reproducing information signals on an optical disc and a tracking control method for an optical pickup.

  As a tracking method during reproduction with respect to an optical disk medium, a push-pull method, a phase difference detection method, a three-beam method, and the like are used. Among these methods, the phase difference detection method is called a DPD method (Differential Phase Detection) and is adopted as a tracking method for a high-density disk. In the DPD method, a phase difference between light receiving signals from a plurality of light receiving elements is detected from a pit row formed corresponding to an information signal, and then tracking error signals are generated to perform tracking control.

  As the density of the optical disk increases, the length of the recording pits decreases, and the received light signal obtained from the disk becomes weak, reducing the reliability of the tracking error signal. For example, in Patent Document 1, there is a possibility that a threshold value having a predetermined hysteresis width is set in the binarization circuit for the purpose of ensuring the accuracy of the tracking error signal, and a sufficient amplitude level cannot be obtained and is buried in noise. A configuration is described in which binarization is performed by removing a certain short pit signal component.

JP 2006-53968 A

  The conventional DPD tracking signal generation circuit and its signal transmission system perform digital processing similar to that of the RF signal processing system, and therefore exceed 100 MHz, which is much higher than the originally required servo signal (several kHz) band. It is necessary to handle signals in the high frequency band. In such a high frequency band, the signal quality is significantly degraded. Although a certain level of quality degradation can be compensated for a strong error correction circuit for the RF signal system, it is a good idea to provide a special means for compensating for this because the DPD system causes an increase in cost more than necessary. Not.

  Since the technique described in Patent Document 1 uses the hysteresis phenomenon in an analog circuit, it requires a highly accurate threshold setting, and it is difficult to easily and reliably remove a target signal. It is expected to be.

  An object of the present invention is to generate a highly accurate tracking error signal by simply and reliably removing high-frequency components that cause signal quality degradation.

  An optical disc apparatus according to the present invention includes an optical pickup that records and reproduces an information signal by irradiating an optical disc with an optical beam, and a DPD circuit that generates a tracking error signal by a phase difference detection method (DPD method) based on a light reception signal of the optical pickup. And a servo circuit that controls tracking of the optical pickup based on the tracking error signal and a digital signal processing circuit that generates an information signal based on the light reception signal of the optical pickup, and the DPD circuit is generated by the digital signal processing circuit When a specific signal component is included in the information signal, the tracking error signal in a period in which the specific signal exists is removed and output.

  Furthermore, the information signal generated by the digital signal processing circuit is monitored, and when a specific signal component is detected, a specific signal detection circuit that generates a mask pulse, and a tracking error signal is masked only during the period in which the mask pulse is generated A mask circuit. In addition, a timing generation circuit for synchronizing the timing of the mask pulse generated by the specific signal detection circuit and the timing of the tracking error signal masked by the mask circuit is provided. Here, the specific signal component includes a signal having the shortest pit length constituting the information signal.

  An optical pickup tracking control method according to the present invention includes a step of irradiating an optical disc with a light beam and generating a tracking error signal by a phase difference detection method based on the received light signal, and generating an information signal based on the received light signal. And, when the generated information signal includes a specific signal component, removing a tracking error signal during a period in which the specific signal exists, and controlling tracking of the optical pickup based on the tracking error signal Prepare.

  According to the present invention, high-precision tracking control can be easily realized when reproducing a high-density optical disc.

  FIG. 1 is a block diagram showing an embodiment of an optical disc apparatus according to the present invention. The apparatus of the present embodiment rotates the optical disk 1 with a spindle motor 3, irradiates the recording surface of the optical disk 1 with laser light generated by a semiconductor laser, records an information signal (data), and returns. Regenerate information signal from light. As the optical disc 1, for example, a disc capable of high-density recording such as BD (Blu-ray Disc) is suitable. The stepping motor 4 moves the optical pickup 2 in the radial direction of the disk. The driver 5 drives the pickup 2, the spindle motor 3, and the stepping motor 4.

  The analog signal processing circuit 6 amplifies the plurality of received light signals A, B, C, D and the RF signal from the pickup 2 to generate a focus error signal (FER). The phase difference detection (DPD) circuit 7 generates a tracking error signal (TER) by digitally processing the signals A, B, C, and D as will be described later. The focus error signal and tracking error signal are sent to the servo circuit 9 and used for focus control and tracking control, respectively. The digital signal processing circuit 8 generates an information (data) signal based on the RF signal from the analog signal processing circuit 6 and transfers it to the host device (PC). When the digital signal processing circuit 8 detects a predetermined high-frequency component (for example, the shortest pit length 2T signal, T is a clock cycle) from the information signal, it sends a mask signal to the DPD circuit 7, and the DPD circuit 7 synchronizes with it. The tracking error signal is corrected (mask process). The microcomputer 10 optimally controls the entire apparatus including tracking control according to a program stored in the flash memory 11. The elements from the analog signal processing circuit 6 to the flash memory 11 are housed in the analog / digital integrated LSI 12.

  FIG. 2 is a diagram showing an internal configuration of the DPD circuit 7 and the digital signal processing circuit 8 of FIG. Here, a configuration from generation of a tracking error signal from a light reception signal of a pickup to output to a servo circuit is shown.

  Two OEIC output signals 21 (A, B, C, and D divided main beam signals) from the pickup are respectively equalized in waveform by an equalizer (EQ) circuit 22 and converted into a digital signal by a binarization circuit 23. . The phase comparison circuit 24 calculates the phase difference components DPDP and DPDN with the pair of digitized signals A and B, C and D, and the subtraction circuit 25 subtracts them to generate a tracking error pulse.

  On the other hand, the RF signal 31 (added signals A, B, C, and D) of the OEIC output signal from the pickup is equalized by the equalizer circuit 32 and converted to a digital signal by the AD converter 33. The digitized RF signal is descrambled and error-corrected by the digital signal processing circuit 34 (8) to generate an information (data) signal.

  The 2T detection circuit 36 monitors the generated information signal (data string) and, when detecting a specific signal (here, the 2T signal having the shortest pit length), sends a mask signal (mask pulse) to the 2T mask circuit 27. . The 2T mask circuit 27 masks the tracking error pulse for the period of the mask pulse width at the timing of receiving the mask signal. For example, by inputting an error pulse and a mask signal to the latch circuit, the error pulse is rewritten to zero level. At this time, in consideration of the time required for the 2T detection circuit 36 to identify the 2T signal, a delay pulse for delaying the tracking error pulse is generated from the timing generation circuit 35 and sent to the synchronization circuit 26. The synchronization circuit 26 delays the tracking error pulse by the delay pulse width and supplies it to the 2T mask circuit 27. In this way, the tracking error pulse in the period corresponding to the 2T signal detected from the RF signal (data string) is removed.

  Thereafter, a high-frequency component is removed by the low-pass filter 28 to generate a DPD tracking error signal, which is processed by the AD converter 29 and the servo signal filter 30 and supplied to the servo circuit.

  In the configuration of this embodiment, the digital signal processing circuit 34 and the 2T detection circuit 36 can easily detect at which timing the 2T signal is generated in the data string, so that the detection accuracy is high and the circuit is simple. realizable.

  FIG. 3 is a diagram illustrating operation waveforms of respective units in the tracking error signal generation of FIG. Here, a case will be described in which information having a pit length of 4T, 2T, and 6T is reproduced from an optical disk, and a tracking error signal in a 2T section having the shortest pit length is masked (removed).

  (A) is a waveform of the OEIC output signal 21 (A, B, C, D) and is digitized by the binarization circuit 23. (B) shows the phase difference pulses DPDP and DPDN from the phase comparison circuit 24. (C) shows a tracking error pulse obtained by subtracting these values by the subtracting circuit 25. E4, E2, and E6 are error pulses in the sections where the pit lengths 4T, 2T, and 6T exist, respectively. Here, the error pulse E2 in the 2T section is masked.

  (D) is a delay signal from the timing generation circuit 35, and delays the tracking error pulse of (c) by time Td. (E) shows the delayed tracking error pulses E4 ', E2', E6 'from the synchronizing circuit 26. FIG. (F) is a mask signal (2T mask pulse) from the 2T detection circuit 36. The mask pulse M is generated when the 2T signal is detected, that is, when the pit length 2T is almost finished, and the pulse width is 2T interval. Is the width that covers. Although the timing of the mask pulse M is shifted from the error pulse E2 to be masked, the error pulse E2 ′ can be accommodated within the range of the mask pulse M by giving a delay time Td to the tracking error pulse. . (G) shows a waveform obtained by masking (removing) E2 ′ by the 2T mask circuit 27. (H) is a tracking error signal processed by the LPF 28.

FIG. 4 is a flowchart showing a procedure for generating a tracking error signal according to the present embodiment.
In step 101, the DPD circuit 7 inputs light reception signals (A, B, C, D) from the pickup 2. In step 102, a DPD signal (tracking error pulse in FIG. 2) is generated from the phase difference of each received light signal.

  In step 103, the digital signal processing circuit 8 identifies the data string generated from the RF signal and determines whether or not the signal is a specific signal (2T signal). If it is determined that the signal is other than 2T (No in Step 103), the process proceeds to Step 106, and the DPD signal is output to the servo circuit 9 as it is. If it is a 2T signal (Yes in Step 103), the process proceeds to Step 104, and the timing of the DPD signal is adjusted. Specifically, the DPD signal is delayed by a predetermined time and synchronized with the 2T signal. In step 105, the section corresponding to the 2T signal of the DPD signal is masked and removed. In step 106, the tracking error signal subjected to mask processing is output.

  In the above embodiment, the tracking error signal synchronized with this is masked (removed) in the period when the specific signal (2T) is detected from the RF signal. Therefore, high-frequency components that cause signal quality degradation can be easily and reliably removed, and a highly accurate tracking error signal can be generated.

  In the apparatus of this embodiment, when a special signal, for example, a continuous signal having a pit length of 2T is provided on the optical disc, the DPD circuit 7 does not perform the reproduction of that region. A valid tracking error signal is not output, and as a result, tracking control becomes impossible. On the other hand, in a region where a normal signal including 3T or more is recorded, an effective tracking error signal is output, and normal tracking control becomes possible.

  In the above embodiment, the high-frequency signal to be masked is the 2T signal that is the shortest pit length of the BD. For example, in the case of a DVD, a 3T signal can be targeted, and a plurality of types of signals (2T and 3T) can also be targeted.

1 is a block diagram showing an embodiment of an optical disc apparatus according to the present invention. The figure which shows the internal structure of the DPD circuit 7 and the digital signal processing circuit 8. FIG. The figure which shows the operation | movement waveform of each part in tracking error signal generation. The flowchart which shows the procedure of tracking error signal generation.

Explanation of symbols

1 ... Optical disc,
2 ... Optical pickup,
3 ... Spindle motor,
4 ... Stepping motor,
5 ... Driver,
6 ... Analog signal processing circuit,
7: Phase difference detection (DPD) circuit,
8: Digital signal processing circuit,
9 ... Servo circuit,
10 ... Microcomputer,
11: Flash memory,
12. Analog / digital integrated LSI,
21 ... OEIC output signals (A, B, C, D),
22 ... Equalizer (EQ) circuit,
23... Binarization circuit,
24. Phase comparison circuit,
25: Subtraction circuit,
26: Synchronous circuit,
27 ... 2T mask circuit,
28 ... Low-pass filter,
29 ... AD converter,
30: Servo signal filter,
31 ... RF signal,
32 ... Equalizer circuit,
33 ... AD converter,
34. Digital signal processing circuit,
35 ... Timing generation circuit,
36... 2T detection circuit.

Claims (8)

In an optical disc apparatus for recording and reproducing information signals on an optical disc,
An optical pickup that records and reproduces an information signal by irradiating the optical disk with a light beam;
A DPD circuit that generates a tracking error signal by a phase difference detection method (hereinafter referred to as a DPD method) based on a light reception signal of the optical pickup;
A servo circuit for controlling tracking of the optical pickup based on the tracking error signal;
A digital signal processing circuit that generates an information signal based on a light reception signal of the optical pickup,
The DPD circuit, when a specific signal component is included in the information signal generated by the digital signal processing circuit, removes and outputs a tracking error signal in a period in which the specific signal exists. Optical disk device to perform. The optical disk apparatus according to claim 1, wherein
A specific signal detection circuit that monitors the information signal generated by the digital signal processing circuit and generates a mask pulse when a specific signal component is detected;
An optical disk apparatus comprising: a mask circuit that masks the tracking error signal only during a period in which the mask pulse is generated. The optical disk apparatus according to claim 2, wherein
An optical disc apparatus comprising: a timing generation circuit for synchronizing the timing of a mask pulse generated by the specific signal detection circuit and a timing of a tracking error signal masked by the mask circuit. The optical disk apparatus according to claim 1, wherein
The optical disc apparatus characterized in that the specific signal component includes a signal having the shortest pit length constituting the information signal. The optical disc apparatus according to claim 4, wherein
2. The optical disk apparatus according to claim 1, wherein the shortest pit length is a signal of 2T (T is a clock cycle). In an optical pickup tracking control method for recording and reproducing information signals on an optical disc,
Irradiating the optical disk with a light beam and generating a tracking error signal by a phase difference detection method based on the received light signal;
Generating an information signal based on the received light signal;
If the generated information signal includes a specific signal component, removing a tracking error signal in a period in which the specific signal exists;
Controlling the tracking of the optical pickup based on the tracking error signal;
A tracking control method comprising: The tracking control method according to claim 6, wherein
Monitoring the information signal and generating a mask pulse if a specific signal component is detected;
And a step of masking the tracking error signal only during a period in which the mask pulse is generated. The tracking control method according to claim 7,
A tracking control method comprising: delaying the tracking error signal by a predetermined time in order to synchronize the mask pulse with the timing of the tracking error signal to be masked.

Images