JPH0668505A - Tracking error signal generator - Google Patents

Abstract

PURPOSE:To generate a correct tracking error signal without effect of a deviation of a recording position of a tracking bit or the like by generating the tracking error signal based on a peak hold signal. CONSTITUTION:A peak hold circuit 14 samples a reproduction signal SPB for a sampling (SP) time with a prescribed time width to detect and hold a peak level corresponding to a wobble pit PW1 thereby generating a tracking error signal TE based thereon. That is, when a reset signal RST rises at a time t1, the circuit 14 samples a peak level of the PW1, a corresponding peak hold signal pH is outputted and its maximum value is latched. When an SP tiing signal SMP1 rises at a time t2, a 1st sample-and-hold circuit 15 samples the signal pH and outputs a peak level of the signal SPB corresponding to the PW1 as a signal A and a 2nd sample-and-hold circuit 16 outputs a peak level of the signal PB corresponding to the PW2 similarly at the rising of the signal SMP2 as a signal B. Then the signal TE (TE=TE'=A-B) is outputted via a subtractor 17 and a polarity changeover device 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tracking error signal generator, and more particularly to a sampled servo system (sample
and a tracking error signal generating device for generating a tracking error signal from an optical disc of high density recording using a d servo method).

[0002]

2. Description of the Related Art A sampled servo recording format is known as a conventional optical disk recording format.

FIG. 4 shows the recording format of a sampled servo type optical disc. The sampled servo type optical disc does not have a pre-group (guide groove) on the recording film of the optical disc, and 137 in one track.
Servo areas (fields) are pre-formatted at 6 locations. For sampled servo optical disks, tracking errors and recording / recording
The feature is that a clock for reproduction and the like can be generated by sampling.

In the program area PA of the optical disk DK
As shown in FIG. 4, the optical disc DK is
A spiral signal track that expands to the circumference
Has been formed. One track is divided into 32 sectors
Has been. Each sector consists of 43 segments.
Each one segment consists of 18 bytes. 1 sec
The first segment # 0 of the
Sector synchronization signal S for_sync(2 bits) and its
Sector address S for indicating the address of the sector
_ADR(16 bits) is pre-formatted. The
Reformat is the mastering of the optical disc DK
Is done in the process of. Each of segments # 1 to # 42
Is a 2-byte servo area F_SAnd 16-byte data area
Area F_DAnd 18 bytes in total.

FIG. 5 shows a servo area F_SRecord format
Indicates the 2-byte servo area F _SIs 1 byte at a time
It is divided into two sub-bytes # 1 and # 2. The servo
The first wobble pit P is at the 3rd bit in byte # 1.
_W1, The second wobble pit P at the 8th bit_W2Is that
Pre-formatted. This first wobble
Tut P_W1The position of 16 tracks as shown in FIG.
In the case of (A), it is the third bit like PW1A, but 16
It becomes PW1 when it becomes a rack (B)_BMove to the 4th bit like
It In this way, the first wobble pit every 16 tracks
P_W1By switching the position of,
The number of racks can be detected accurately.

The first wobble pit P _W1 and the second wobble pit P _W2 are arranged to be offset from each other in the trace direction left and right (in the radial direction of the write-once optical disc DK) by 1/4 of the track pitch with the track center TC as a boundary. The tracking error detection is performed based on the difference between the amount of returned light at the first wobble pit P _W1 and the amount of returned light at the second wobble pit P _W2 . A clock pit CP for synchronization is pre-formatted in the 12th bit of the servo byte # 2. Second wobble pit P _W2 and clock pit C
A mirror surface having an interval of 19 channel clocks is formed between P and P, and 19 channel clocks are counted during this period to synchronize each segment, and a focus error occurs during this synchronization detection period. Detection is also done. FIG. 5 shows the tracking signal S _T1 (S _{T1 A} or S _T1B ) obtained by reading the above servo area F _S with laser light and the sector synchronization signal S _sync .

Next, a method of tracking error detection by wobble pits will be described with reference to FIG. A is a case where the read beam passes on the center axis (track center axis) of the pair of wobble pits P _W1 and P _W2, and the RF signal in that case is shown as S _A. When the light passes through the vicinity of the pit, the amount of reflected light becomes small due to the diffraction effect of light, and the light becomes dark, and when it passes directly above the clock pit CP, it becomes the darkest. B is the case where the read beam has passed the inner circumference side of the track center axis, and the RF signal at that time is S _B
Indicated as. In this case, to pass just above the wobble pits P _W1, dark portion due to the wobble pits P _W1 still darker than the dark portion due to the wobble pits P _W2. C
Is the case where the read beam has passed the outer peripheral side of the track center axis, and the RF signal in this case is shown as S _C ,
In this case, a waveform opposite to S _B is shown.

Here, the signal value obtained by performing signal sampling at the time of the wobble pit P _W1 is SAMPLE.
(T ₁ ) and the signal value obtained by signal sampling at the time of the wobble pit P _W2 is SAMPLE (T ₂ ).
As the difference between them, SAMPLE (T ₁ ) -SAMPLE
Taking (T ₂ ), the value of A is zero, the value of B is a negative value, and the value of C is a positive value. Therefore, SAMPLE
If (T ₁ ) -SAMPLE (T ₂ ) = TE, then TE
Can be used as a tracking error signal.

[0009]

According to the above-mentioned conventional sample servo system, wobble pits P _W1 and P _W1 for servo are used.
W2 and clock pits CP are formed in advance on the optical disk (pre-pits), and various information for servo such as tracking error signals is obtained from these pit rows.

When reading information, the laser light reflected at the signal pit PT is diffracted by the pits and the amount of light returning to the optical pickup is reduced, and it can be regarded as a dark portion. On the contrary, since the intermediate portion between the signal pits PT is a mirror surface and all the laser light is reflected, the amount of return light increases and can be regarded as a bright portion. In order to read the servo information accurately, it is necessary to read these contrasts without error,
For that purpose, conventionally, as shown in FIG. 7A, the track pitch T _P needs to be larger than the spot diameter B _L of the laser light (about 1.6 μm).

In this case, in order to improve the recording density of the optical disk DK, FIG. 7B or FIG. 7C is used.
As shown, conventional 1/2 the track pitch T _P
Considering the case of shortening to about (0.8 μm), there are an on-track state where the laser beam center is on the recording track axis center and an off-track state where the laser beam center is off the recording track axis center. There is a problem that the difference in light amount becomes small and accurate servo cannot be performed, and there is a limit in narrowing the track pitch.

In order to solve this, the applicant has proposed a method in which wobble pits are thinned and recorded (Japanese Patent Application No. Hei 0).
3-64978). FIG. 8 shows the structure of tracks and pits of a CAV optical disk used in the double density recording method proposed by the applicant.

As shown in FIG. 8, in the 2k-th recording track, the wobble pits P _W (2k-
1) and a wobble pit P _W (2k) are provided, a synchronous pit P _SYNC and a recording track identification pit P _DET are provided on the recording track axis, and a data area follows. The next (2k + 1) th recording track has a wobble pit P _W (2k) and a wobble pit P _W (2k + 1) in a zigzag pattern opposite to the 2kth recording track.
In this configuration, the synchronous pit P _SYNC is provided on the recording track axis, but the recording track identification pit P _DET is not provided.

In this case, for the 2kth recording track, the wobble pit P _W (2k-1) corresponds to the first wobble pit P _W1 , and the wobble pit P _W (2k) corresponds to the second wobble pit P _W2 . However, the second (2k +
For the 1) th recording track, the wobble pit P _W
(2k + 1) corresponds to the first wobble pit P _W1 , and the wobble pit P _W (2k) corresponds to the second wobble pit.

In this way, the 2kth recording track and the (2k + 1) th recording track share the wobble pit P _W (2k) with each other. Therefore, this is because one of the staggered wobble pits is thinned out for each recording track, and as a result, the recording track pitch width T _P = 2L and T _P = 4L (see FIG. 7 (a)), recording track pitch T
_P is shortened to 1/2. Therefore, since the number of recordable tracks can be doubled, the recording density can be doubled.

FIG. 9 shows the basic structure of a reproducing apparatus for reproducing the recording signal of the optical disk of FIG. The reproducing apparatus 10P has a decoder 11 which decodes the reproduction signal S _PB (= RF signal) of the reading beam LB and outputs reproduction data D _PB , and a PLL circuit (not shown), and a clock signal CLK based on the reproduction signal S _PB. And a polarity for switching (inverting) the polarities of the first sampling signal SMPP1 of the sampling signal A, the second sampling signal SMPP2 of the sampling signal B, and the tracking error signal TE based on the clock signal CLK. a timing control circuit 13 for outputting a switching signal POL, a first sample and hold circuit 31 based on the first sampling signal signal SMPP1 samples and holds the reproduced signal SPB, and outputs the sampling signal a _P, a second sampling signal SMPP
The reproduced signal S _PB is sampled and held based on 2,
The difference between the second sampling and holding circuit 32 that outputs the sampling signal B _P and the sampling signals output from the first and second sampling and holding circuits 31 and 32 is calculated to obtain the original tracking error signal TE ′.
And the tracking error signal TE by switching the polarities of the original tracking error signal TE '.
And a polarity switching circuit 20 for outputting as.

In this case, when the wobble pits are recorded as a pre-format, a rotation jitter or the like occurs in the recording device, and for example, as shown in FIG.
The recording position of the wobble pit of the second recording track and the second (2
When the recording position of the wobble pit of the (k + 2) th recording track is not on the same radial line but is displaced (deviation amount = Δ
x), since the sampling timing is always fixed to the pulse number of the clock signal = 3, 5 (indicated by circled numbers in the figure), when the (2k + 1) th recording track is reproduced due to the deviation of the sampling timing. In some cases, a correct tracking error signal cannot be obtained. That is, even when the (2k + 1) th recording track is the ON recording track, the tracking error signal TE
Therefore, the correct tracking error signal TE cannot be obtained.

Therefore, an object of the present invention is to easily obtain a tracking error signal even if the recording track pitch is made narrower than the reading laser beam spot diameter for high density recording, and at the same time, for tracking error signal generation tracking. It is an object of the present invention to provide a tracking error signal generation device capable of generating a correct tracking error signal even when the recording position of pits is displaced due to the recording device.

[0019]

In order to solve the above problems, the present invention provides a recording track, a data information area for recording data information, and servo control information for recording servo control information in the recording track. A tracking error signal generating device for generating a tracking error signal from a reproduction signal of a sampled servo type optical disc having a region and a tracking pit used for generating a tracking error signal in the servo control information region, A peak hold circuit that detects and holds a peak level corresponding to the tracking pit of the reproduction signal in a detection period having a predetermined time width including the detection timing of the tracking pit and outputs the peak level as a peak hold signal; To generate and output a tracking error signal. A tracking error signal generating means, and constituting provided.

[0020]

According to the present invention, the peak hold circuit detects and holds the peak level corresponding to the tracking pit of the reproduction signal in the detection period having the predetermined time width including the detection timing of the tracking pit and holds the tracking error as the peak hold signal. Output to the signal generation means.

The tracking error signal generating means generates and outputs a tracking error signal based on this peak hold signal. Therefore, even if the recording position of the tracking pit is deviated, the peak level corresponding to the tracking pit can be easily detected from the reproduction signal, and the correct tracking error signal can be reliably obtained.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will now be described with reference to the drawings. FIG. 1 shows a block diagram of the main part of the optical disk reproducing apparatus of the embodiment.

The optical disc reproducing apparatus 10 uses the reproduction signal S _PB.
Decoder 11 which decodes and outputs as reproduction data D _PB , PLL circuit 12 which extracts and outputs clock signal CLK from reproduction signal S _PB , and reset signal RST and first sampling timing signal SMP1 based on clock signal CLK. , A timing control circuit 13 for outputting the second sampling timing signal SMP2 and the polarity switching signal POL
A peak hold circuit 14 that detects and holds a peak level corresponding to a wobble pit that is a tracking pit based on the reset signal RST and outputs a peak hold signal PH; and a first sampling timing signal SMP1.
Based on the first sampling and holding circuit 15 for sampling the peak holding signal PH and outputting it as the first sampling signal A, and for sampling the peak holding signal PH based on the second sampling timing signal SMP2 and as the second sampling signal B. Second to output
A sampling hold circuit 16, a subtracter 17 that outputs an original tracking error signal TE ′ based on the first sampling signal A and the second sampling signal B, and a polarity inversion of the original tracking error signal based on the polarity switching signal POL. / Non-inverted and tracking error signal T
And a polarity switching circuit 18 for outputting as E.

Next, the tracking error signal generating operation will be described with reference to FIG. First, a case where the reading beam traces on the recording track TR _{2n + 1} as shown in FIG. 2A will be described. In this case, it is assumed that a positional deviation (deviation amount: Δx) of each servo pit occurs due to the rotation jitter of the recording device during wobble pit recording.

First, sampling timing signals SMPP1 and SMPP2 corresponding to the CLK signal obtained when the recording track TR _2n is reproduced by the read beam LB (FIG. 2C).
Considering the case where the reproduction signal S _PB is sampled on the basis of the above), the wobble pit PW ₁ 'is as shown by the "x" mark on the curve of the reproduction signal S _PB in FIG. 2B. Since the sampling timing is shifted, the correct tracking error signal TE cannot be obtained.

Therefore, in the present embodiment, the peak hold circuit 14 samples the reproduction signal S _PB at a sampling time of a predetermined time width including the peak detection timing corresponding to the wobble pits, and the peak value corresponding to the wobble pits is obtained. It is detected and held, and the tracking error signal TE is generated based on this. Therefore, it is possible to obtain the tracking error signal without strictly considering the peak position corresponding to the wobble pit.

Specifically, at time t ₁ , the reset signal RS
When T rises, the peak hold circuit 14 starts sampling the peak level of the wobble pit PW ₁ ′, and the peak hold signal PH corresponding to the sampled value.
Is output. The peak hold signal PH has a maximum value at time t ₂ and holds that value.

After that, when the first sampling timing signal SMP1 rises at time t ₃ , the first sampling and holding circuit 15 samples the peak holding signal PH and reproduces the reproduction signal S _PB corresponding to the wobble pit PW ₁ ′.
The peak value of is output as the sampling signal A.

Next, at time t ₄ , the reset signal R is returned again.
When ST rises and the peak hold signal PH is reset to 0, sampling of the peak level of the wobble pit PW ₂ is started this time, and the peak hold signal PH corresponding to the sampled value is output. The peak hold signal PH has a maximum value at time t ₅ , and holds that value.

After that, when the second sampling timing signal SMP2 rises at time t ₆ , the second sampling and holding circuit 16 samples the peak holding signal PH and the peak value of the reproduction signal S _PB corresponding to the wobble pit PW _2. Is output as a sampling signal B.

As a result, the subtractor 17 obtains and outputs the original tracking error signal TE 'by the following equation. TE '= A-B This original tracking error signal TE' is an even number (2n, 2n) of the recording track number of the recording track traced by the light beam LB when the optical disc has the structure shown in FIG. 2A. In the case of +2, ...) And the case where the recording track number is an odd number (2n + 1, 2n + 3 ,. That is, for even-numbered recording tracks,
In the drawing, when the reading beam LB is shifted to the upper side, the original tracking error signal TE ′> 0, and conversely, when the reading beam LB is shifted to the lower side, the original tracking error signal <0 is obtained. In the case of odd-numbered recording tracks, the original tracking error signal TE ′ <0 when the read beam LB shifts to the upper side in the drawing, and the original tracking error signal TE ′ <0 when the read beam LB shifts to the lower side in the drawing. Signal> 0.

Therefore, the timing control circuit 13 controls the polarity switching circuit 18 by the polarity switching signal POL based on whether the currently traced recording track is an even numbered recording track or an odd numbered recording track. Then, TE = TE 'is set for a recording track having an even number, and TE = -TE' is set for a recording track having an odd number, and a tracking error signal TE having a polarity always corresponding to the deviation direction of the read beam LB is output. Can be made.

After that, at time t ₇ , the reset signal R is restarted.
ST rises, and the peak hold signal PH is reset to 0. As described above, according to the present embodiment, even if the recording position of the tracking pit such as the wobble pit is displaced, the reproduction signal corresponding to the tracking pit during the sampling time of the peak hold circuit 14 is generated. If the peak detection timing of S _PB is included, the tracking error signal TE can be easily obtained.

In the above embodiments, the wobble pits are provided on the even-numbered recording tracks, but it is possible to provide the wobble pits on the odd-numbered recording tracks. In this case, it is necessary to reverse the polarity switching of the polarity switching circuit 18 to the case described above.

In the above description, the case where the wobble pit is used as the tracking pit has been described, but as shown in FIG. 3A, the recording track is formed in one spiral curve shape. The present invention can also be applied to the case where tracking pits TP are formed on different recording lines and on different recording lines between a plurality of adjacent (4 in FIG. 3A) recording tracks. In this case, it is necessary to change the generation timing of the reset signal for each traced recording track.

Further, in the above description, the case where the recording tracks are formed in the shape of one spiral curve has been described, but for example, as shown in FIG. 3B, three parallel recording tracks are formed. Is formed in a spiral curve shape (so-called three spiral structure), and the central recording track TRm
_The present invention can also be applied to the case where the tracking pit TP is formed only in the area ₂ .

[0037]

According to the present invention, since the tracking error signal is generated and output based on the peak level corresponding to the tracking pit detected by the peak hold circuit, even if the recording position of the tracking pit is deviated. The peak level corresponding to the tracking pit can be easily detected from the reproduction signal, and the correct tracking error signal can be reliably obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an optical disc reproducing apparatus.

FIG. 2 is a diagram illustrating generation of a tracking error signal.

FIG. 3 is a diagram illustrating another embodiment of the present invention.

FIG. 4 is a diagram illustrating a recording format of a sampled servo system.

FIG. 5 is a diagram illustrating a recording format of a conventional servo area.

FIG. 6 is a diagram illustrating conventional tracking error detection by wobble pits.

FIG. 7 is a diagram illustrating a conventional problem.

FIG. 8 is a diagram illustrating a proposal for solving a conventional problem.

FIG. 9 is a block diagram showing a schematic configuration of a playback device corresponding to the proposal of FIG.

FIG. 10 is a diagram for explaining points to be improved in the proposal of FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Reproducing device 11 ... Decoder 12 ... PLL circuit 13 ... Timing control circuit 14 ... Peak hold circuit 15 ... First sampling hold circuit 16 ... Second sampling hold circuit 17 ... Subtractor 18 ... Polarity switching circuit A ... Sampling signal B ... Sampling signal CLK ... Clock signal D _PB ... Reproduction data PH ... Peak hold signal POL ... Polarity switching signal RST ... Reset signal S _PB ... Reproduction signal SMP1 ... First sampling timing signal SMP2 ... Second sampling timing signal TE ... Tracking error signal TE '... Original tracking error signal

Claims (1)

[Claims] 1. A recording track is formed, and a data information area for recording data information and a servo control information area for servo control information recording are provided in the recording track, and a tracking error is present in the servo control information area. A tracking error signal generating device for generating a tracking error signal from a reproduction signal of a sampled servo type optical disc provided with a tracking pit used for signal generation, the detection period having a predetermined time width including the detection timing of the tracking pit. A peak hold circuit for detecting and holding a peak level corresponding to the tracking pit of the reproduction signal and outputting it as a peak hold signal; and a tracking error signal generating means for generating and outputting a tracking error signal based on the peak hold signal. , With Tracking error signal generating apparatus according to claim.