JP4033034B2 - Pre-pit detection device and optical disk device provided with the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a prepit detection apparatus and an optical disc apparatus including the same, and more particularly to binarization threshold adjustment for extracting a prepit signal from a reproduction signal.
[0002]
[Prior art]
In an optical disk device such as a DVD-R drive, address information previously formed on an optical disk is demodulated to determine an address, and data is recorded / reproduced. As a method of forming address information, there is a method of forming a prepit in a land area adjacent to a groove which is an information recording track, in addition to embedding a track by wobbling. In the DVD-RAM, information recording tracks are lands and grooves, and address information is embedded in an embossed portion of a rewritable area composed of an embossed portion and a data portion. In the present application, a land pre-pit LPP formed in a pre-pit on a land is targeted.
[0003]
Hereinafter, the land prepit LPP will be described.
[0004]
FIG. 10 shows the relationship between an ECC (Error Check and Correct) frame, 16 sectors constituting the ECC frame, a frame constituting each sector, and a land prepit LPP. One ECC frame is composed of a total of 16 sectors from 0 to 15, and each sector is composed of a total of 26 frames from 0 to 25. The 26 frames can be divided into even frames (even frames) and odd frames (odd frames). The LPP is normally recorded at the beginning of an even frame. However, depending on the state of the adjacent track, it may be recorded in an odd frame instead of an even frame. Each LPP is composed of 3-bit data and is recorded at the head of a total of 13 sectors in one block. LPP recorded in the first frame (0th frame) of each sector is SYNC information. The LPP is composed of 3 bits × 13 pieces of information in one sector.
[0005]
FIG. 11 shows the relationship between the LPP and the wobble signal. The wobble signal is formed by meandering of a predetermined frequency (140 kHz) of the information recording track (groove), and each bit of the LPP is formed in synchronization with the peak of the wobble signal.
[0006]
FIG. 12 exemplifies LPP information of each frame from the 0th sector to the 4th sector in the ECC frame. All LPPs are recorded in even frames of sectors. In the figure, for example, “111” is recorded in the 0th frame of the 0th sector, “100” is recorded in the second frame, and “10X” is recorded in the 10th frame. Here, “111” indicates synchronization (SYNC) information in an even frame, “100” indicates data 0, and “101” indicates data 1. The 0th to 8th frames are areas for defining addresses, and the 10th to 25th frames are used as user data. The user data is determined when the optical disc is shipped from the factory. “110” indicates synchronization information in odd frames.
[0007]
In the above format, the LPP is formed in synchronization with the wobble signal. When detecting this LPP from the optical disk, the LPP is obtained by converting the reflected light from the optical disk into an electric signal by the photodetector of the optical pickup. A reproduction signal (reproduction signal in which a wobble signal and an LPP signal overlap) is extracted by binarizing using a threshold value. By the way, the LPP signal overlaps the wobble signal whose amplitude varies, and the LPP signal level also varies due to the fluctuation of the wobble signal amplitude. Therefore, if the binarization is performed with the fixed threshold value, the LPP signal can be accurately extracted. It is difficult.
[0008]
Therefore, in the prior art shown below, the gate is periodically opened only during a predetermined period in which the wobble signal has the maximum amplitude, and only when the gate is opened, the LPP signal is passed and the LPP signal is counted. A technique for adjusting a threshold value for binarization according to the magnitude relationship with the reference number is disclosed.
[0009]
[Patent Document 1]
JP 2002-279642 A
[0010]
[Problems to be solved by the invention]
In this way, the reproduced signal is binarized with the threshold value, the LPP signal is extracted, and the threshold value is adaptively adjusted so that the number of LPP signals matches a predetermined reference number, so that the binary value is finally obtained. Can be adjusted to an appropriate value.
[0011]
However, as shown in FIG. 12, LPP has a total of 13 pieces of 3-bit data in one sector, and differs between even frames and odd frames, so how to set the reference number is a problem. . If the accuracy of the reference number is low, the accuracy of the threshold value for binarization also decreases, and it becomes difficult to extract LPP reliably.
[0012]
An object of the present invention is to set a reference value for adaptively adjusting a binarization threshold value when extracting an LPP signal from a reproduction signal with high accuracy, and thereby an apparatus capable of reliably detecting an LPP signal. An optical disc apparatus provided with the above is provided.
[0013]
[Means for Solving the Problems]
The present invention relates to a prepit detection device that extracts a prepit signal from an optical disc in which prepits are formed in advance on a track adjacent to an information recording track meandering at a wobble frequency, and is obtained by converting reflected light from the optical disc into an electrical signal. An extraction means for extracting the pre-pit signal included in the reproduction signal by binarizing the reproduced signal with a threshold value, a means for determining whether or not the address is fixed, and the address is fixed If there is not, the threshold value is increased or decreased according to the size of the lower limit and upper limit of the number of possible pre-existing numbers in the next address of the pre-pit signal and the number of pre-pit signals extracted by the extracting means, and the address is determined. The threshold value is adjusted to increase or decrease to match the predicted number at the next address of the pre-pit signal. And a threshold adjustment means, and extracting the pre-pit signal from the reproduced signal by adjusting the threshold to an appropriate value. The reference number for adjusting the threshold value is not set to a fixed value, but is adaptively set according to whether the address is determined or not determined. In an undefined state, the land pre-pits (LPP) can exist as a certain range of numbers. For example, if there are 13 even frames in one sector and LPPs are recorded in all even frames, the first sync frame is always “111” and 3 and the rest are “100” or Since it is “101”, the minimum value is 15 and the maximum value is 27. In the address unconfirmed state, the threshold value is increased or decreased so that the number of LPPs is within this range. Further, after the address is determined, the address to be recorded or reproduced next is known, and the number of LPPs at the next address can be uniquely predicted. Therefore, the threshold value is increased or decreased so that the actually obtained number of LPPs matches the predicted number of LPPs at the next address.
[0014]
In the present invention, the threshold value adjusting means sets 14 or 15 as the lower limit of the number that can exist in the next address of the prepit signal and 26 or 27 as the upper limit when the address is not fixed. When the number of pre-pit signals extracted by the extracting means is less than the lower limit, the threshold value is adjusted to decrease, and when the number of pre-pit signals extracted by the extracting means exceeds the upper limit, the threshold is adjusted. It is preferable to increase the value. When all LPPs are recorded in even frames, the minimum value is 15 and the maximum value is 27. When all LPPs are recorded in odd frames, the data in the first synchronization frame is “110”. The number is one less than the even number frame, the minimum value is 14, and the maximum value is 26. Therefore, if it is unclear whether it is recorded in even frames or odd frames, it can be handled by setting 14 or 15 as the lower limit and 26 or 27 as upper and lower. As an example, the lower limit may be 14 and the upper limit may be 27.
[0015]
Also, in the present invention, the threshold adjustment means is configured such that when the address is fixed, the number of prepit signals extracted by the extraction means is N or the predicted number N at the next address of the prepit signal. Preferably, the threshold value is adjusted to decrease when it is less than N-1, and the threshold value is adjusted to increase when the prepit signal extracted by the extracting means exceeds N or N + 1. The expected number N can be calculated assuming that all LPPs are recorded in even frames. Actually, since it may be recorded in an odd frame, it is determined that the value is appropriate not only when it matches N but also when it matches N-1, and in other cases, the threshold value is increased or decreased. To do.
[0016]
In the present invention, it further comprises means for extracting a wobble signal included in the reproduction signal, and means for counting the wave number of the wobble signal, wherein the threshold adjustment means has a predetermined value of the wobble signal. The threshold value may be adjusted up or down when the value is reached.
[0017]
The present invention also relates to a prepit detection device for extracting a prepit signal from an optical disc in which prepits are formed in advance on a track adjacent to an information recording track meandering at a wobble frequency, and an address detection means for detecting a sector address of an ECC frame; A means for setting a predicted number of prepit signals predicted at the next sector address after the sector address is detected by the address detecting means, and a reproduction signal obtained by converting the reflected light of the optical disk into an electrical signal. Signal processing means for binarizing with a threshold value and extracting the pre-pit signal, wherein the number of pre-pit signals extracted in the next sector after detecting the sector address by the address detecting means is the number of predicted pre-pit signals. Feedback the threshold to match And having Gosuru and signal processing means.
[0018]
An optical disk apparatus according to the present invention performs recording or reproduction on an optical disk based on the prepit detection apparatus described above, a decoder that demodulates a prepit signal detected by the prepit detection apparatus, and an address obtained by the decoder. And an optical pickup.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0020]
FIG. 1 shows an overall configuration diagram of an optical disc apparatus according to the present embodiment. An optical disk 10 such as a DVD-R or DVD-RW is rotationally driven by a spindle motor (SPM) 12. The spindle motor SPM 12 is driven by a driver 14, and the driver 14 is servo-controlled by a servo processor 30 so as to have a desired rotation speed.
[0021]
The optical pickup 16 includes a laser diode (LD) for irradiating the optical disk 10 with laser light and a photodetector (PD) that receives reflected light from the optical disk 10 and converts it into an electrical signal, and is disposed opposite to the optical disk 10. . The optical pickup 16 is driven in the radial direction of the optical disk 10 by a thread motor 18, and the thread motor 18 is driven by a driver 20. The driver 20 is servo-controlled by the servo processor 30 similarly to the driver 14. The LD of the optical pickup 16 is driven by a driver 22, and the driver 22 is controlled by an auto power control circuit (APC) 24 so that the drive current becomes a desired value. The APC 24 controls the drive current of the driver 22 so that the optimum recording power selected by OPC (Optimum Power Control) executed in the test area (PCA) of the optical disc 10 is obtained. The OPC is a process of recording test data on the PCA of the optical disc 10 by changing the recording power in a plurality of stages, reproducing the test data, evaluating the signal quality, and selecting a recording power that can obtain a desired signal quality. It is. For the signal quality, β value, γ value, modulation factor, jitter, etc. are used.
[0022]
When data recorded on the optical disk 10 is reproduced, a laser beam of reproduction power is irradiated from the LD of the optical pickup 16, and the reflected light is converted into an electric signal by the PD and output. A reproduction signal from the optical pickup 16 is supplied to the RF circuit 26. The RF circuit 26 generates a focus error signal and a tracking error signal from the reproduction signal and supplies them to the servo processor 30. The servo processor 30 servo-controls the optical pickup 16 based on these error signals, and maintains the optical pickup 16 in an on-focus state and an on-track state. Further, the RF circuit 26 supplies the reproduction signal to the address decoding circuit 28.
[0023]
The address decoding circuit 28 includes an LPP extraction unit and a decoding unit, binarizes the reproduction signal to extract the LPP signal, then decodes the extracted LPP to demodulate the address data, and the servo processor 30 and the system controller 32. To supply.
[0024]
Further, the RF circuit 26 supplies the reproduction RF signal to the binarization circuit 34. The binarization circuit 34 binarizes the reproduction signal and supplies the obtained 8-16 modulation signal to the encoding / decoding circuit 36. In the encode / decode circuit 36, the binarized signal is demodulated and error-corrected by 8-16 to obtain reproduction data, and the reproduction data is output to a host device such as a personal computer via the interface I / F 40. When the reproduction data is output to the host device, the encoding / decoding circuit 36 temporarily stores the reproduction data in the buffer memory 38 and outputs it.
[0025]
When recording data on the optical disk 10, data to be recorded from the host device is supplied to the encode / decode circuit 36 via the interface I / F 40. The encode / decode circuit 36 stores data to be recorded in the buffer memory 38, encodes the data to be recorded, and supplies the data to the write strategy circuit 42 as 8-16 modulation data. The write strategy circuit 42 converts the modulation data into a multi-pulse (pulse train) according to a predetermined recording strategy, and supplies it to the driver 22 as recording data. The recording strategy is composed of, for example, the pulse width of the first pulse, the pulse width of the subsequent pulse, and the pulse duty in the multi-pulse. Since the recording strategy affects the recording quality, it is usually fixed to a certain optimum strategy. A recording strategy may be set at the time of OPC. The laser light whose power is modulated by the recording data is irradiated from the LD of the optical pickup 16 and the data is recorded on the optical disk 10. Data recording is in units of packets. After recording the data in packet units, the optical pickup 16 reproduces the recorded data by irradiating the laser beam with the reproduction power, and supplies it to the RF circuit 26. The RF circuit 26 supplies the reproduction signal to the binarization circuit 34, and the binarized 8-16 modulated data is supplied to the encode / decode circuit 36. The encode / decode circuit 36 decodes the 8-16 modulation data and collates it with the recording data stored in the buffer memory 38. The result of the verification is supplied to the system controller 32.
[0026]
FIG. 2 schematically shows a four-divided photodetector 17 in the optical pickup 16. The quadrant photodetector 17 is composed of A, B, C, and D photodetectors, A and B, C and D are arranged in the radial direction (track width direction) of the optical disc 10, and A and D, and B and C are the optical disc 10. Are arranged in the circumferential direction (track direction). A and C, B and D are arranged diagonally. Since the LPP is formed on a land adjacent to the information recording track (groove), the LPP signal is included in the signals of the A and D photodetectors among the four photodetectors A to D. Therefore, the LPP signal can be extracted by subtracting the B and C photodetector signals from the A and D photodetector signals.
[0027]
FIG. 3 shows a circuit configuration of the LPP extraction unit included in the address decoding circuit 28. The LPP extraction unit includes an operational amplifier 58 that binarizes the LPP signal using a threshold value, a counter 60 that counts the number of LPPs, a counter 78 that counts the wobble signal, and a timing at which the count value of the wobble signal reaches a predetermined value. The microcomputer 62 includes a microcomputer 62 that determines whether or not the count value of the LPP has reached a reference value and adjusts the threshold value supplied to the operational amplifier 58.
[0028]
The signals of the A photo detector and the D photo detector are added by an adder 50 and supplied to an auto gain control circuit (AGC) 52. The signals of the B photo detector and the C photo detector are added by an adder 66 and supplied to the AGC 54. The two signals whose gains are adjusted by the AGC 52 and the AGC 54 so as to have the same amplitude are subjected to a difference calculation by the subtractor 56 and supplied to the non-inverting input terminal (+) of the operational amplifier 58. The operational amplifier 58 compares the reproduction signal including the differential signal, that is, the LPP signal, with the threshold value supplied to the inverting input terminal (−), extracts the LPP signal component, and outputs the LPP signal component to the decoding unit of the address decoding circuit 28. A part of the output from the operational amplifier 58 is supplied to the counter 60, and the number of LPPs is counted by the counter 60 and supplied to the microcomputer 62.
[0029]
On the other hand, the signals from the adder 50 and the adder 66 are also supplied to the AGC 68 and AGC 70, and after the gain is adjusted so that the amplitudes thereof coincide with each other, the difference is calculated by the subtractor 72 and the band pass filter (BPF) 74 is obtained. To be supplied. The BPF 74 is a filter that selectively extracts a difference signal, that is, a signal having a predetermined wobble frequency (140 KHz) from the reproduction signal including the LPP, whereby only the wobble signal is extracted and supplied to the binarization circuit 76. The binarization circuit binarizes the wobble signal and supplies it to the counter 78. The counter 78 counts the wave number of the wobble signal and supplies it to the microcomputer 62.
[0030]
The microcomputer 62 detects the end of one sector in one ECC frame based on the count value from the counter 78. Since one sector includes a total of 208 wobble signals, the sector at the time when the count value of the wobble signal reaches 208 is completed. The microcomputer 62 compares the LPP count value from the counter 60 with a predetermined reference number at the sector end timing. As the predetermined reference number, different values are set depending on whether the sector address has already been determined or not yet determined. Specifically, it is set as follows.
[0031]
(1) When the address is not confirmed
In this case, the number of LPPs is an even number of frames per sector.
Minimum: 3 (SYNC) x 1 + 1 x 12 = 15
Maximum: 3 (SYNC) x 1 + 2 x 12 = 27
In the odd frame, the synchronization information is “110”, which is one less than the even frame.
Minimum: 2 (SYNC) x 1 + 1 x 12 = 14
Maximum: 2 (SYNC) x 1 + 2 x 12 = 26
In consideration of this, a range of 14 or 15 lower limits and 26 or 27 upper limits is set, and the threshold level is adjusted to increase or decrease so as to be within this range. If it is known that recording is performed only in even frames, the lower limit may be set to 15 and the upper limit may be set to 27. Further, the lower limit may be uniformly set to 14 and the upper limit may be set to 27 uniformly. When the range of the reference value is presented, 14 ≦ LPP ≦ 27. The microcomputer 62 adjusts the threshold value so as to be within this reference range.
[0032]
(2) After address confirmation
Since the next address can be predicted after the address is determined, the number of LPPs of the next sector can be predicted. For example, if the current address is the address of the 0th sector and it is predicted that the current sector will be shifted to the 1st sector next, it is the same as the 0th sector until the 0th to 7th frames. The user data of 25 frames is the same as that of the 0th sector, and since the LPP in the 8th frame changes to “101”, it can be predicted that the number of LPPs is one more than the current. Therefore, the microcomputer 62 calculates the predicted number of LPPs in the next sector and sets it as a reference number, and adjusts the threshold value so that the count value from the counter 60 matches this predicted number.
[0033]
As described above, the microcomputer 62 adjusts the threshold value by changing the reference number according to whether the address is confirmed / unconfirmed. The threshold value from the microcomputer 62 is converted into an analog signal by the digital / analog converter D / A 64 and supplied to the operational amplifier 58.
[0034]
FIG. 4 shows a flowchart of LPP detection processing in the present embodiment. The microcomputer 62 in the LPP extraction unit in the address decoding circuit 28 determines whether or not the address has already been determined in the immediately preceding 1 ECC frame (16 sectors) (S101). This determination is made based on a signal from the system controller 32. If the address is not yet determined, for example, immediately after seeking the optical pickup 16, the threshold value for binarization is adjusted in accordance with mode I (S102). In mode I, the threshold value is adjusted by the method (1) described above.
[0035]
On the other hand, if the address has already been determined in the immediately preceding 1 ECC frame, the binarization threshold value is adjusted to increase or decrease in mode II different from mode I (S103). In mode II, the threshold value is adjusted by the method (2) described above. In addition, even if the address is confirmed once, if the address becomes uncertain after that, the mode II is shifted to the mode I.
[0036]
FIG. 5 shows a detailed flowchart of mode 1 in S102 of FIG. First, the microcomputer 62 sets a threshold value for binarization to a certain value (S201). This initial value may be recorded on the optical disc as a default value for each manufacturer of the optical disc 10, and read out and set to that value.
[0037]
Next, the microcomputer 62 determines whether or not the count value from the counter 78, that is, the wobble wave number has reached a predetermined number, specifically 208, which is a specified number included in one sector (S202). When the wobble wave number reaches 208, it is next determined whether or not the number of LPPs from the counter 60 is less than 14 (S203). If the number of LPPs is less than 14, it means that the detected number of LPPs is less than the lower limit number that can exist, and the current threshold value is determined to be too higher than the appropriate threshold value, and the threshold value is set. The decrease is adjusted (S204). The threshold reduction amount may be a predetermined value. On the other hand, when the detected number of LPPs is 14 or more, the microcomputer 62 determines whether or not the detected number of LPPs exceeds 27 (S205). When the number of LPPs exceeds 27, it means that the upper limit value that can exist is exceeded, which means that the binarization threshold is too lower than the appropriate threshold and unnecessary noise is detected as LPP. From this, the threshold value is increased (S206). The increase amount may be a predetermined value. When the number of LPPs is 14 or more and 27 or less, the current threshold is an appropriate threshold and no increase / decrease adjustment is performed. As described above, the threshold is adjusted so that the number of LPPs is 14 or more and 27 or less until the address is determined.
[0038]
FIG. 6 shows a detailed flowchart of mode II in S103 of FIG. First, since the current address is fixed, the microcomputer 62 predicts the number N of LPP addresses of the next address (S301). At this time, the number of LPPs in the user data area is fixed. When the number of LPPs in the 0th sector is m, the number of LPPs in the first sector is m + 1, the number of LPPs in the second sector is m + 1, the number of LPPs in the third sector is m + 2, the number of LPPs in the fourth sector is m + 1,.・ And so on. After calculating the predicted number of LPPs for the next sector, the microcomputer 62 sets the threshold value to a certain initial value (S302). Then, it is determined whether or not the count value from the counter 78 has reached 208 (S303), and the count value from the counter 60 at the time of reaching 208, that is, the number of LPPs coincides with the number N of LPPs predicted in S301. It is determined whether or not (S304). Note that since the LPP value differs by 1 depending on whether the LPP exists in an even frame or an odd frame, in S301, when it is basically predicted that an LPP exists only in an even frame, in S304 When the predicted number of LPPs differs by 1 (when it is less by 1), it may be determined that the numbers match. When the number of LPPs exceeds the predicted number of LPPs N (or N-1), it is determined that the threshold value is too lower than the appropriate value and the threshold value is increased (S305). Is less than the predicted number of LPPs N (or N-1), it is determined that the threshold value is too higher than the appropriate value, and the threshold value is decreased (S306). If it matches the predicted number N of LPPs (including the case where it differs by 1), the current threshold value is not adjusted as an appropriate value. After the address is determined, the threshold value can be adjusted with higher accuracy by narrowing the reference number for adjusting the threshold value to a specific value.
[0039]
7 to 9 show how the threshold is adjusted. FIG. 7 shows an example where the threshold is too low, and binarization picks up not only the original LPP but also noise, and the number of LPPs is larger than the reference number. FIG. 8 shows an example in which the threshold is too high. Although noise is suppressed, the original LPP cannot be binarized, and the number of LPPs is smaller than the reference number. FIG. 9 is an example after the threshold value is adjusted to increase or decrease. Since the threshold value is adjusted to an appropriate value, only LPP can be extracted while suppressing noise.
[0040]
As described above, in this embodiment, the reference number (or reference range) is adaptively set according to the determined / unconfirmed state of the sector address, and matches (or falls within) this reference number (or reference range). Thus, the threshold value is adjusted to increase or decrease as described above, so that the threshold value can be set with high accuracy even when the address is not yet determined. In particular, in this embodiment, the number of LPPs is predicted after address determination, and the threshold value is adjusted so as to match the predicted number of LPPs. Therefore, the threshold value can be adjusted with extremely high accuracy, and the address continues to be determined. As long as it is possible, the threshold adjustment thereafter can be simplified or made unnecessary.
[0041]
In the present embodiment, after the address is determined, the number of LPPs of the next sector address is predicted. If the table data necessary for this prediction is stored in the memory of the microcomputer 62 or the system controller 32 in advance, Good. Since the user data is fixed on the optical disk 10 and the address data changes according to a predetermined rule, the user data may be predicted by simple calculation without using table data.
[0042]
【The invention's effect】
As described above, according to the present invention, the threshold value for extracting the land pre-pit (LPP) can be adjusted to an appropriate value.
[Brief description of the drawings]
FIG. 1 is a configuration block diagram of an optical disc apparatus.
FIG. 2 is a diagram illustrating the arrangement of a four-divided photo detector.
FIG. 3 is a configuration diagram of an LPP extraction unit in an address decoding circuit.
FIG. 4 is an overall process flowchart of the embodiment.
FIG. 5 is a processing flowchart of mode I in FIG. 4;
6 is a process flowchart of mode II in FIG. 4;
FIG. 7 is an explanatory diagram of LPP when a threshold value is inappropriate (over).
FIG. 8 is an explanatory diagram of LPP when the threshold value is inappropriate (under).
FIG. 9 is an explanatory diagram of LPP after threshold adjustment.
FIG. 10 is a diagram illustrating a relationship between an ECC frame, a sector, an even / odd frame, and an LPP.
FIG. 11 is a diagram illustrating a relationship between an LPP and a wobble signal.
FIG. 12 is an explanatory diagram of LPP in an even frame of each sector.
[Explanation of symbols]
10 optical disk, 16 optical pickup, 28 address decoding circuit, 32 system controller.

Claims (6)

A prepit detection device for extracting a prepit signal from an optical disc in which prepits are formed in advance on a track adjacent to an information recording track meandering at a wobble frequency,
Extraction means for extracting the pre-pit signal included in the reproduction signal by binarizing a reproduction signal obtained by converting the reflected light from the optical disc into an electric signal with a threshold value;
Means for determining whether the address is fixed;
When the address is not fixed, the threshold value is increased or decreased according to the size of the lower limit and the upper limit of the number that can exist at the next address of the prepit signal and the number of prepit signals extracted by the extraction unit, Threshold adjustment means for adjusting the threshold to increase or decrease to match the predicted number at the next address of the pre-pit signal when the address is fixed;
And the pre-pit signal is extracted from the reproduction signal by adjusting the threshold value to an appropriate value. The apparatus of claim 1.
The threshold value adjusting means sets 14 or 15 as the lower limit of the number that can exist in the next address of the prepit signal and 26 or 27 as the upper limit when the address is not fixed, and the extracting means If the number of prepit signals extracted in step (b) is less than the lower limit, the threshold value is adjusted to decrease, and if the number of prepit signals extracted by the extraction means exceeds the upper limit, the threshold value is increased. A pre-pit detection device characterized by: The apparatus of claim 1.
The threshold adjustment means is configured such that the number of prepit signals extracted by the extraction means is less than N or N−1 with respect to the predicted number N at the next address of the prepit signal when the address is fixed. In this case, the threshold value is adjusted to decrease, and when the prepit signal extracted by the extracting means exceeds N or N-1, the threshold value is increased and adjusted. The apparatus of claim 1, further comprising:
Means for extracting a wobble signal included in the reproduction signal;
Means for counting the wave number of the wobble signal;
The threshold adjustment means adjusts the threshold to increase or decrease when the count value of the wobble signal reaches a predetermined value. A prepit detection device for extracting a prepit signal from an optical disc in which prepits are formed in advance on a track adjacent to an information recording track meandering at a wobble frequency,
Address detecting means for detecting a sector address of the ECC frame;
Means for setting the number of predicted prepit signals predicted in the next sector address after the sector address is detected by the address detecting means;
Signal processing means for extracting a pre-pit signal by binarizing a reproduction signal obtained by converting reflected light of the optical disc into an electric signal with a threshold value, after detecting the sector address by the address detection means Signal processing means for feedback-controlling the threshold value so that the number of pre-pit signals extracted in the next sector matches the predicted number of pre-pit signals,
A pre-pit detection apparatus comprising: The prepit detection device according to any one of claims 1 to 5,
A decoder that demodulates the prepit signal detected by the prepit detector;
An optical pickup for recording or reproducing an optical disc based on the address obtained by the decoder;
An optical disc apparatus having

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