JP3154215B2 - Optical information reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information reproducing apparatus for demodulating information recorded on an optical disk by a Viterbi decoding method.

[0002]

2. Description of the Related Art There has been a remarkable progress in high-density recording technology in recent digital recording. This largely depends on the improvement of the signal processing system such as the recording code, the signal detection system, and the decoding method, as well as the improvement of the performance of the recording medium and the recording head. In magneto-optical recording, which has attracted attention as a rewritable large-capacity optical memory, a signal processing method has been actively studied in recent years.

[0003] The magnetic field modulation method in the magneto-optical disk is as follows.
This method is suitable for overwrite and high-density edge recording. It has already been reported that a combination of a sample servo and an NRZI code, together with a laser pulse emission magnetic field modulation method, enables higher density. Furthermore, partial response,
And the Viterbi decoding method is known, and N is used as a recording code.
Using the RZI code, PR (1,
1) Various studies have been made on combinations of the method and the Viterbi decoding method.

[0004] Detection by the Viterbi decoding method detects a reproduced signal (R
This is a method of selecting and detecting the most probable data series based on the transition state information of the (F signal). Unlike a physical method such as shortening the wavelength of a laser, this is a method of increasing the density by signal processing. Therefore, it is said that the detection capability is higher than the detection for each bit.

In an optical disk, the RF signal causes intersymbol interference due to a recording bit pattern and takes three values, and the detection by the Viterbi decoding method detects the most probable data sequence based on the information of the three-value transition state. It will be selected and detected.

[0006]

However, when forming ROM pits on an optical disk or forming information pits by optical modulation recording, the amount of asymmetry of the RF signal fluctuates due to fluctuations in the writing power of the laser. Due to the fluctuation of the asymmetry amount, an error occurs in the detection by the Viterbi decoding method, and the detection capability may be reduced.

The present invention has been made in view of the above circumstances, and even when the amount of asymmetry of an RF signal fluctuates due to a change in write power, a Viterbi decoding method is used based on information on a transition state of the RF signal. It is an object of the present invention to provide an optical information reproducing apparatus capable of selecting the most probable data series and detecting information reliably and easily.

[0008]

According to the present invention, there is provided an optical information reproducing apparatus comprising a predetermined reference provided on an optical information recording medium.
Based on the RF signal obtained from the reference area,
The amount of measurement is calculated, and based on the amount of asymmetry, R
It is characterized by comprising a correction means for correcting the F signal .

[0009]

[0010]

[Action] In the optical information reproducing apparatus having the above structure, the light
A predetermined reference area provided on the science information recording medium
Based on the RF signal obtained from
Calculated and based on the amount of asymmetry, the RF signal is
Will be corrected.

[0011]

[0012]

Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG. 1, an optical disk recording / reproducing apparatus 1 according to the present embodiment includes an optical head 5 for optically modulating and recording information by irradiating a recording surface of a write-once optical disk 3 rotated by a spindle motor 2 with laser light. Have.

The recording data generation circuit 6 generates recording data based on the input data, and the recording data is output to a modulation circuit 7, and the modulated recording data modulated by the modulation circuit 7 is output to a laser driving circuit 8. And the optical head 5
Drives a built-in laser diode (not shown), for example.

The optical head 5 is provided with a detector (not shown) for irradiating the optical disk 3 with a laser having a lower power than at the time of recording, and detecting an RF signal from the returned light. The RF signal detected by the optical head 5 is input to the PLL circuit 10 and the A / D conversion circuit 11 via the amplifier 9. The PLL circuit 10 generates a clock synchronized with a clock pit, which is a pre-pit recorded in advance on the optical disc 3, and outputs this clock to the data PLL circuit 12. The data PLL circuit 12 generates a data clock signal based on the clock, and the recording data generation circuit 6 generates recording data based on the input data in synchronization with the data clock signal. The data clock signal is also input to the timing generator 13, and this timing generator 13 generates various timing signals based on the data clock signal.

The data clock signal is supplied to the delay circuit 14
Is input to the A / D conversion circuit 11 through the A / D converter 11, and the A / D conversion circuit 11 A / D converts the RF signal in synchronization with the delayed data clock signal. Further, the A / D-converted signal is shaped by the digital equalizer 15, and a digital RF signal is generated. The correction table generation circuit 16 generates an asymmetry amount based on a digital RF signal in a reference area of the optical disc 3 to be described later based on the timing signal from the timing generator 13, generates a correction table, and stores the correction table in the RAM 17. Is to be saved.

The digital RF signal is D / D converted (corrected) by an asymmetry correction data conversion circuit 18 based on a correction table stored in the RAM 17 and demodulated by a detection circuit 19. .

The optical disk 3 is composed of a plurality of concentric or spiral tracks, and this track is composed of a plurality of sectors 3 as shown in FIG.
The information is divided into 0 and information is recorded and reproduced in units of 30 sectors. The sector 30 comprises:
Each segment is composed of a plurality of segments. Each segment is composed of a servo area 31 composed of pre-pits such as clock pits, and a reference area 32 having a predetermined pit pattern.
And a data area 33 for recording data.

However, instead of providing the reference area 32 for each segment, only one reference area 32 may be provided in the sector 30.

As shown in FIG. 3A, the predetermined pit pattern formed in the reference area 32 is a first pattern Pa in which pits are composed of "0, 0, 0, 0...".
, The second pattern Pb having pits of “1, 0, 1, 0...” And the third pattern Pb having pits of “1, 1, 1, 1,.
The RF signal in this predetermined pit pattern is as shown in FIG. 3B.

That is, since there is no pit in the first pattern Pa, the level of the RF signal becomes the largest value La, and
The third pattern Pc has the smallest value Lc. on the other hand,
The RF signal in the second pattern Pb is ideally La and L
Although it should be the center value of c (= La + Lc) / 2, the size of the formed pit changes due to the fluctuation of the writing power of the laser, and therefore, the asymmetry amount is generated with respect to the center value of the RF signal. It becomes the value Lb. Therefore, the correction table generation circuit 16 calculates the asymmetry amount (Lb- (La + Lc) / 2) to generate a correction table.

Next, generation of a correction table by the correction table generation circuit 16 will be described.

The level of the RF signal corresponding to the recording pit is:
As shown in FIG. 4A, the amount of asymmetry occurs as described above according to the writing power of the laser (the position of the central solid line deviates from the half of the upper and lower ends). . Input to the correction table generation circuit 16,
The digital RF signal based on the RF signal is, for example, 8-bit data, and represents one of 256 levels. The correction table generation circuit 16 corrects (generates) the correction signal Y with respect to the digital RF signal X as shown in FIG. That is, when the digital RF signal corresponding to Lb in FIG. 3B is X0 and the center value of the correction signal is Y0, Y is calculated from the following equation. When X ≦ X0 Y = (Y0 / X0) · X (1) When X> X0 Y = {(Y0−255) / (X0−255)} · (X−X0) + Y0 (2) A correction table is generated by correcting the digital RF signal with respect to the asymmetry amount thus calculated. FIG.
(C) shows one example of the generated correction table.

As described above, the correction table generation circuit 16
The asymmetry correction data conversion circuit 18 corrects the digital RF signal using the correction table generated in step (1).

Based on the corrected digital RF signal, the detection circuit 19 determines a data string by the Viterbi decoding method and demodulates the data. That is, according to the PR (1,1) method,
Since the RF signal causes intersymbol interference due to the pit pattern, it takes three values, α, 0, and −β, as shown in FIG. The Viterbi decoding method, the output Y _k for the input bits A _{k is, (A k, A k-} 1) = (1,1) _{if, Y k = α ...... (3} ) (A k, A k-1 ) = (1, −1) or (−1,1), Y _k = 0 (4) If (A _k , A _k−1 ) = (− 1, −1), Y _k = −β (5)

Therefore, there is a possibility that A _k is +1.
_k (+) (likelihood) is L _k (+) = max ｛L _k−1 (+) + [− (Y _k −α) ² ], L _k−1 (−) + [− ( Y _k −0) ² ]｝ (6) Here, max {a, b} means that the larger one of a and b is selected. L _k (+) indicates that A _k is +1
And (Y _k −
α) ² is the square error between the output Y _k and the expected signal level α. Therefore, L _k (+) increases as the square error decreases. Therefore, A = L _k−1 (+) + [− (Y _k− α) ² ] (7) B = L _k−1 (−) + [− (Y _k− 0) ² ] (7) when 8), the transition of the input bits a _k, as shown in FIG. 6 (a), as shown in FIG. 6 (b), in the case of the pattern is a _k = + 1 at a _k-1 = + 1 , L _k (+) = A, and as shown in FIG. 6C, A _k−1 = −1 and A _k =
In the case of a pattern of +1, L _k (+) = B.

Similarly, the possibility that A _k is -1 L _k (−)
Is L _k (−) = max {L _k−1 (+) + [− (Y _k− 0) ² ], L _k−1 (−) + [− (Y _k + β) ² ]} (9 ). Here, C = L _k−1 (+) + [− (Y _k− 0) ² ] (10) D = L _k−1 (−) + [− (Y _k + β) ² ] (11) ).

Next, in order to check which of L _k (+) and L _k (−) is more likely, ΔL _k = L _k (+) − L _k (−) (12) is obtained. As a result, a data transition path can be determined. Here, the asymmetry correction data conversion circuit 1
8, since the digital RF signal has been corrected, α
= When β = s, ΔL _k is, (i) A> B, C> D _{That, ΔL k-1 + 2sY k} > s 2 ...... when the _{(13), ΔL k = 2sY} k -s 2 (ii ) A <B, C> D That is, when −s ² <ΔL _k−1 + 2sY _k <s ² ... (14), ΔL _k = −ΔL _k−1 (iii) A <B, C <D , ΔL _k−1 + 2sY _k <−s ² (15), ΔL _k = 2sY _k + s ² .

Therefore, the detection circuit 19 is given by the following equation (13).
By calculating (14) and (15), the expression (13) is obtained.
Is satisfied, the pattern transition shown in FIG. 7A is obtained. When Expression (14) is established, the pattern transition shown in FIG. 7B is obtained. Further, when Expression (15) is established, FIG. The transition path of data can be determined as the pattern transition shown in c).

As described above, according to the optical disk recording / reproducing apparatus 1 of the present embodiment, a correction table is generated for the asymmetry amount of the RF signal, and R is calculated based on the correction table.
Since the F signal is corrected and the data is demodulated by the Viterbi decoding method, the data can be demodulated with a simple circuit configuration even for the asymmetry of the RF signal generated by the writing power of the laser.

In the above embodiment, the recording medium is a write-once optical disk. However, the present invention is not limited to this. The optical disk may be a ROM disk on which information is recorded in advance, and an RF signal generated due to a change in writing power when the optical disk is created. It is needless to say that the present invention can be applied to a ROM disk reproducing apparatus that generates a correction table for the asymmetry amount of the above, corrects the RF signal based on the correction table, and demodulates data by the Viterbi decoding method.

[0031]

As described above, according to the optical information reproducing apparatus of the present invention , the portion provided on the optical information recording medium is provided.
Based on the RF signal obtained from a fixed reference area
To calculate the amount of asymmetry, and
Since the RF signal is corrected , the amount of asymmetry can be accurately detected even when the amount of asymmetry of the RF signal fluctuates due to the fluctuation of the write power.
For example, the most probable data sequence is selected based on the information of the transition state of the RF signal by the Viterbi decoding method, and the information can be detected reliably and easily.

[0032]

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of an optical disc reproducing apparatus according to the present invention.

FIG. 2 is a configuration diagram showing a configuration of a sector of the optical disc of FIG. 1;

FIG. 3 is an explanatory diagram illustrating an RF signal reproduced by the optical disc recording / reproducing apparatus of FIG. 1;

FIG. 4 is an explanatory diagram illustrating a method of calculating an asymmetry amount of an RF signal by a correction table generation circuit 16 in FIG. 1;

FIG. 5 is a waveform diagram of an RF signal for explaining a Viterbi decoding method by the detection circuit 19 in FIG. 1;

6 is an explanatory diagram illustrating an output state with respect to a transition of an input bit in the Viterbi decoding method by the detection circuit 19 in FIG.

FIG. 7 is an explanatory diagram illustrating a transition path of data determined by the detection circuit 19 of FIG. 1;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 optical disk recording / reproducing device 3 optical disk 5 optical head 10 PLL circuit 12 data PLL circuit 13 timing generator 16 correction table generation circuit 16 18 asymmetry correction data conversion circuit 19 detection circuit

Claims (1)

(57) [Claims] 1. Optical information having a reference area
Irradiating the recording medium with a laser beam, the optical information recording medium
An optical head for reading pits recorded on the optical head; and a digital RF based on an output signal from the optical head.
A signal generation unit for generating a signal, and a reference area of the optical information recording medium,
From the signal generator obtained as a result of scanning the
Calculate asymmetry amount based on digital RF signal
Generating the signal based on the calculated asymmetry amount.
Correcting means for correcting the digital RF signal from the section, and demodulating the output signal from the correcting means by the Viterbi decoding method
Optical recording medium reproducing device having
Place.