JP2008021362A - Optical information reproducing method and apparatus - Google Patents

Abstract

An optical information information reproducing method and apparatus capable of completely removing a wobble frequency component from an RF signal even if the low frequency band and the wobble frequency band of the RF signal overlap.
An amplitude of a wobble component is detected in an area (for example, a sync area) where a repetitive pattern between data areas of an optical disk is recorded based on an RF signal obtained by an addition signal of a two-divided photodetector. On the other hand, the wobble removal signal is generated by adjusting the gain of the signal based on the differential output of the two-divided photodetector 11 based on the amplitude. Then, the RF signal is corrected by removing the wobble removal signal from the RF signal in the data area of the optical disk 4.
[Selection] Figure 7

Description

  The present invention relates to an optical information reproducing method and apparatus for reproducing information from an information recording medium such as an optical disk on which wobbles are formed.

  Conventionally, address information is recorded in advance on an optical disc. When information is recorded or reproduced on an optical disc, the information is recorded or reproduced at a target address position while reading the address information.

  As a method of recording address information on an optical disk, there is a method of recording address information by wobbling both side walls of a guide groove (groove) at a constant period and modulating the meander with the address information.

  In this method, as schematically illustrated in FIG. 8, the wobble is formed in a sinusoidal shape having a certain period and amplitude by meandering the wall portion of the groove. When reproducing information recorded on an information recording medium such as an optical disk on which wobbles are formed, the wobble component affects the reproduction signal as a low-frequency level fluctuation, and deteriorates the error rate of the reproduction information. Is a problem.

  FIG. 9 shows an optical system having a wavelength of 405 nm and an objective lens with a numerical aperture of 0.85, a track pitch of 0.32 μm, and a 0.2 μm repetitive signal on a groove of a substrate on which a wobble is formed, a linear velocity of 4.92 m / s. The reproduction result of the reproduction signal when recorded by is shown. As apparent from FIG. 9, it can be seen that the swell is generated in the reproduction signal. When this is analyzed with a spectrum analyzer, it can be seen that it is a wobble component in the vicinity of 1 MHz.

  Therefore, in order to reproduce information with higher accuracy, it is necessary to remove the wobble component from the reproduced signal. As a method for removing the wobble component, for example, there is a method described in JP-A-10-340537 (Patent Document 1). The method disclosed in this publication uses a wobble signal input to a PLL circuit for generating a synchronous clock to reduce or remove a wobble component from an RF signal.

In this case, the wobble signal is obtained from the differential output of the two-divided photodetector that receives the return light from the optical disk. Then, a wobble removal signal is generated by a band pass filter (BPF) having a characteristic that passes a frequency corresponding to the wobble frequency component, and is subtracted from the RF signal.
JP 10-340537 A

  When information pits are recorded on the optical information recording medium using a predetermined modulation method, a component in a lower frequency range than the signal frequency of the longest pit is included as information in the RF signal. At this time, since the band of the wobble frequency component and the band of the low frequency component of the RF signal overlap, if the band pass filter is used to remove the wobble frequency component from the RF signal, the low frequency component of the RF signal is also removed. There is a fear. Therefore, it has been difficult to completely remove only the wobble frequency component from the RF signal.

  An object of the present invention is to provide an optical information reproducing method and apparatus capable of completely removing a wobble frequency component from an RF signal even if the low frequency band and the wobble frequency band of the RF signal overlap. .

  The present invention detects the amplitude of a wobble component based on an RF signal by an addition signal of a two-divided photodetector that detects reflected light from an information recording medium in an area where a repetitive pattern between data areas of the information recording medium is recorded. . In addition, a wobble removal signal is generated by adjusting the gain of the signal based on the differential output of the two-divided photodetector based on the amplitude. Then, the RF signal is corrected by removing the wobble removal signal from the RF signal in the data area in the data area of the information recording medium.

  According to the present invention, a wobble removal signal is generated in a repetitive pattern-recorded area of an information recording medium between data areas, and the wobble component is subtracted from the RF signal in the data area, thereby generating a wobble component from the RF signal. Can be completely removed. For this reason, it is possible to prevent errors caused by level fluctuations caused by wobble components included in the RF signal, and to reproduce information with high accuracy.

  Next, the best mode for carrying out the invention will be described in detail with reference to the drawings. First, in order to analyze the wobble component, the inventor of the present application compared the differential output of the two-divided photodetector with the wobble component included in the RF signal by calculation by optical simulation. As a result, it was found that the amplitude and phase are not the same.

  2, 3 and 4 show the differential outputs (S1-S2) and RF signals (S1 + S2) of the outputs S1 and S2 of the two-divided photodetector calculated by optical simulation.

  The calculation conditions were an optical system with a wavelength of 405 nm and NA of 0.85. In this optical system, a light spot is scanned in the track direction by one wobble period in the track direction with a track pitch of 320 nm (groove width 100 nm, land width 120 nm, sidewall width 50 nm), depth 24 nm, and wobble amount ± 20 nm. It was supposed to be.

  2 to 4, the change in the signal level in one wobble period (S1-S2) is shown on the left axis, and the change in the signal level in one wobble period (S1 + S2) is shown on the right axis. T / 4 and 3 / 4T on the horizontal axis correspond to the wobble amounts +20 nm and −20 nm, respectively. Here, FIG. 2 shows a case where the light spot scans the center of the wobble groove (track offset is 0).

  FIG. 3 shows a case where a light spot is scanned by generating a +40 nm track offset with respect to the center of the wobble groove. FIG. 4 shows a case where a light spot is scanned by generating a -40 nm track offset with respect to the center of the wobble groove.

  As is apparent from FIG. 2, when no track offset occurs, the wobble component of the RF signal is sufficiently small and can be ignored. On the other hand, when the track offset shown in FIGS. 3 and 4 occurs, it was found that the wobble component of the RF signal is about 60 times larger than the wobble component shown in FIG.

  In an actual drive (information recording / reproducing apparatus), it is difficult to operate without causing a track offset at all. Therefore, it is necessary to assume the cases of FIGS. 3 and 4 in which a track offset occurs.

  Further, it can be seen that the wobble component amplitude of the RF signal in FIGS. 3 and 4 is about 1/30 of the differential output amplitude. Further, it was found that when the track offset was −40 nm, the phase was positive with respect to the differential output, whereas when the track offset was +40 nm, the phase was opposite with respect to the differential output.

  That is, it can be said that the wobble component of the RF signal and the differential output have different amplitudes, and further change in the opposite phase and the normal phase across the track center in the track offset direction.

  Therefore, the present invention accurately removes the wobble component contained in the reproduced signal even when the differential output of the two-divided photodetector and the amplitude of the wobble component of the RF signal are different from each other and are changed in the reverse phase and the normal phase due to the track offset. It provides a possible way.

  Based on the above results, embodiments of the present invention will be described. FIG. 1 is a block diagram showing a configuration of an embodiment of an optical information recording / reproducing apparatus according to the present invention. The optical information recording / reproducing apparatus 1 includes a control circuit 2, a spindle motor 3, an optical disk 4, an optical head 5, an optical head control circuit 6, an information recording circuit 7, an information reproducing circuit 8, a spindle motor controller 9, and an interface controller 10.

  The control circuit 2 controls transmission / reception of information to / from an information processing apparatus such as an external computer, and performs recording / reproduction of information with respect to the optical disc 4 by controlling the information recording circuit 7 and the information reproduction circuit 8. Control the working part. The information recording circuit 7 records information on the optical disk 4, and the information reproducing circuit 8 reproduces information from the optical disk 4. Address information and the like are recorded on the information track of the optical disc 4 by forming wobbles as shown in FIG.

  The spindle motor 3 is controlled by the spindle motor controller 9 and drives the optical disk 4 to rotate. The optical disk 4 is an optical information recording medium that can be inserted into or ejected from the optical information recording / reproducing apparatus 1 by a mechanism (not shown).

  The optical head 5 optically records or reproduces information on the optical disk 4. For example, if the optical head 5 has a wavelength λ of the light source of 405 nm and the numerical aperture NA of the objective lens is 0.85, the size of the light spot, 1.2 (λ / NA) is about 0.57 μm. Become. The track pitch of the optical disk 4 is 0.32 μm. The optical head control circuit 6 controls the position of the light spot by the optical head 5, and performs auto tracking control, seek operation control, and auto focusing control.

  The information reproduction circuit 8 is responsible for the removal of the wobble component in information reproduction, which is the object of the present invention. FIG. 5 is a diagram showing a configuration of an arithmetic circuit for removing a wobble component from an RF signal according to the present invention. The arithmetic circuit of FIG. 8 is provided in the information reproducing circuit 8. The two-divided photodetector 11 is provided in the optical head 5 and detects reflected light from the optical disk 4. The dividing direction of the two-divided photodetector 11 is parallel to the track direction of the optical disc 4.

  The outputs S1 and S2 of the two-divided photodetector 11 are differentiated by the differential amplifier 15, and the differential outputs (S1-S2) are input to the wobble removal signal generation circuit 12. The wobble removal signal generation circuit 12 adjusts the gain of the wobble removal signal as will be described later. On the other hand, the differential output is amplified by the amplifier circuit 13 and used for tracking control as a track error signal.

  Further, the outputs S1 and S2 of the two-divided photodetector 11 are added by an adder 16 to generate an RF signal (S1 + S2). The wobble removal signal generated by the wobble removal signal generation circuit 12 is subtracted from the RF signal (S1 + S2) by the subtractor 17 and input to the amplitude detection circuit 14. The amplitude detection circuit 14 calculates the level fluctuation due to the wobble component of the RF signal, and calculates the amplitude of the wobble component included in the RF signal.

  Here, in order to calculate the level fluctuation due to the wobble component of the RF signal, the amplitude detection circuit 14 operates only when reading the RF signal from the predetermined pattern area of the optical disc 4 shown in FIG. As shown in FIG. 6, the predetermined pattern area of the optical disc 4 is provided at regular intervals between the data areas, and is composed of repetitive marks recorded at a predetermined frequency other than the wobble frequency. For example, a sync area is used as the predetermined pattern area.

  Therefore, the amplitude of the wobble component is calculated by processing the RF signal from the predetermined pattern region with a band pass filter (BPF) having a characteristic of passing the frequency corresponding to the wobble frequency component. The calculated amplitude of the wobble component is fed back to the wobble removal signal generation circuit 12, and the wobble removal signal generation circuit 12 adjusts the gain of the wobble removal signal as follows based on the amplitude.

That is, the amplitude of the wobble signal component obtained from the RF signal from the predetermined pattern of the optical disc 4 is Sa, and the amplitude of the wobble signal that is the differential output of the two-divided photodetector 11 is Sb. And
k = Sa / Sb
The gain adjustment of the wobble removal signal is performed using the positive coefficient k calculated by the calculation consisting of Specifically, the wobble removal signal generation circuit 12 adjusts the gain of the wobble removal signal by multiplying the differential output (S1-S2) from the differential amplifier 15 by a constant k. As will be described later, the wobble removal signal generation circuit 12 also creates a phase inversion signal of the wobble removal signal.

  Next, an example of a procedure for removing the wobble component from the RF signal will be described using the flowchart of FIG. First, the predetermined pattern area of the optical disk 4 is reproduced in step 1, and the level fluctuation amount due to the wobble component is calculated by the amplitude detection circuit 14 as described above in step 2.

  Next, in step 3, the level fluctuation amount is compared with a preset threshold value (performed by the amplitude detection circuit 14). When the level fluctuation amount does not exceed the threshold value, the operation is terminated. When the level fluctuation amount exceeds the threshold value, the process proceeds to step 4.

  In step 4, as described above, the gain of the wobble removal signal is adjusted based on the amplitude of the wobble component calculated from the RF signal having a predetermined pattern.

  Next, in step 5, the wobble removal signal generation circuit 12 generates a phase inversion signal (reverse phase) of the wobble removal signal (also generates a wobble removal signal without phase inversion (normal phase)). Next, in step 6, the subtractor 17 subtracts the wobble removal signal from the RF signal (S1 + S2) of the adder 16. In this case, the wobble removal signal is removed from the RF signal for each of the normal phase signal and the reverse phase signal of the wobble removal signal.

  Next, the processing from step 3 is performed in the same manner, and the same processing is repeated until the wobble fluctuation amount does not exceed the threshold value in step 3. Then, when the reproduction area of the optical disc 4 becomes the data area as shown in FIG. 6, the subtractor 17 subtracts the wobble removal signal generated by the wobble removal signal generation circuit 12 in the predetermined pattern area as described above from the RF signal. Thus, the RF signal is corrected.

  Further, when the next predetermined pattern area of the optical disc 4 is reached, a wobble removal signal is generated in the same manner, and in the next data area, the RF signal is similarly corrected by subtracting the wobble removal signal. Thereafter, similarly, a wobble removal signal is generated in a predetermined pattern area, and an RF signal is corrected in a data area.

It is a block diagram which shows the structure of one Embodiment of the optical information recording / reproducing apparatus based on this invention. It is a figure which shows the differential output (S1-S2) and RF signal (S1 + S2) of each output S1 and S2 of the 2 division | segmentation photodetector computed by the optical simulation in case track offset is 0. FIG. It is a figure which shows the differential output (S1-S2) and RF signal (S1 + S2) of each output S1 and S2 of the 2 division | segmentation photodetector calculated by the optical simulation in case track offset is +40 nm. It is a figure which shows the differential output (S1-S2) and RF signal (S1 + S2) of each output S1 and S2 of the 2 division | segmentation photodetector calculated by the optical simulation in case track offset is -40 nm. It is a figure which shows an example of the arithmetic circuit which removes a wobble component from RF signal which concerns on this invention. It is a figure explaining the predetermined pattern area | region provided in the fixed space | interval between each data area. It is a flowchart which shows an example of the procedure which removes a wobble component from RF signal of this invention. It is a figure which shows typically the wobble formed in the groove. A reproduction result of a reproduction signal in a case where a repetitive signal of 0.2 μm is recorded on a groove of a substrate having a track pitch of 0.32 μm and a wobble formed in an optical system having a wavelength of 405 nm and a numerical aperture of an objective lens of 0.85 is shown. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical information recording / reproducing apparatus 2 Control circuit 3 Spindle motor 4 Optical disk 5 Optical head 6 Optical head control circuit 7 Information recording circuit 8 Information reproducing circuit 9 Spindle motor controller 10 Interface controller 11 2 division | segmentation photo detector 12 Wobble removal signal generation circuit 13 Amplification Circuit 14 Amplitude Detection Circuit 15 Differential Amplifier 16 Adder 17 Subtractor

Claims (7)

In a method for reproducing recorded information from an optical information recording medium in which wobbles are formed in an information track, reflected light from the information recording medium is detected in an area where a repetitive pattern between data areas of the information recording medium is recorded Detecting the amplitude of the wobble component based on the RF signal obtained by the addition signal of the two-divided photodetector, and adjusting the gain of the signal based on the differential of the output of the two-divided photodetector based on the amplitude. An optical information reproducing method comprising: generating and correcting an RF signal by removing the wobble removal signal from an RF signal in the data area in the data area of the information recording medium. 2. The gain adjustment according to claim 1, wherein the gain adjustment is performed until an inverted signal of the wobble removal signal is generated and a normal signal and an inverted signal amplitude of the wobble removal signal are equal to or less than a preset threshold value. Optical information reproduction method. The gain adjustment calculates the amplitude of the RF signal from the area where the repetitive pattern is recorded and the amplitude of the signal by the differential of the output of the two-divided photodetector, and the gain of the wobble removal signal based on both signal amplitudes The optical information reproducing method according to claim 1, wherein adjustment is performed. When the amplitude of the RF signal from the area where the repetitive pattern is recorded is Sa, and the amplitude of the signal that is the differential output of the two-divided photodetector is Sb,
k = Sa / Sb
4. The optical adjustment according to claim 3, wherein gain adjustment of the wobble removal signal is performed by multiplying a signal that is a differential output of the two-divided photodetector by a positive coefficient k calculated by an operation comprising: Information reproduction method. The information recording medium is alternately provided with the data area and the area where the repetitive pattern is recorded, and the wobble removal signal generated in the area where the repetitive pattern is recorded 5. The optical information reproducing method according to claim 1, wherein the RF signal is corrected by being subtracted from the RF signal in the data area. 6. The optical information reproducing method according to claim 1, wherein a dividing direction of the two-divided photodetector is parallel to a track direction of the information recording medium. In an apparatus for reproducing recorded information from an optical information recording medium in which wobbles are formed on an information track, reflected light from the information recording medium is detected in an area where a repetitive pattern between data areas of the information recording medium is recorded Means for detecting the amplitude of the wobble component based on the RF signal obtained by the addition signal of the two-divided photodetector, and adjusting the gain of the signal based on the differential of the output of the two-divided photodetector based on the amplitude, An optical information reproducing apparatus comprising: generating means; and means for correcting the RF signal by removing the wobble removal signal from the RF signal in the data area in the data area of the information recording medium .