JPH06150549A - Optical information reproducing device - Google Patents

Abstract

PURPOSE:To surely and simply detect information by selecting a most likelihood data group based on information in the state of the transition of an RF signal by a viterbi demodulation method even when the asymmetry amount of the RF signal is fluctuated due to the fluctuation of write power. CONSTITUTION:The asymmetry amount is calculated and a correction table is generated, and the correction table is preserved in a RAM 17 with a digital RF signal in a reference area on an optical disk 3 based on a timing signal from a timing generator 13 by a correction table generation circuit 16. The digital RF signal is corrected by the asymmetry correction data converter circuit 18 based on the correction table preserved in the RAM 17 and demodulated by a detection circuit 19.

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 Recent progress in high-density recording technology in digital recording has been remarkable. This is largely due to the improvement of the recording medium, the recording head, and the improvement of the signal processing method such as the recording code, the signal detection method, and the decoding method. Even in magneto-optical recording, which is attracting attention as a rewritable large-capacity optical memory, signal processing methods have been actively studied in recent years.

The magnetic field modulation method in the magneto-optical disk is
This method is capable of overwriting and is suitable for high density edge recording. It has already been reported that high density can be achieved by combining the laser pulse emission magnetic field modulation method and the sample servo and NRZI code. Furthermore, as a method for achieving high density, partial response,
Also, the Viterbi decoding method is known, and N is used as a recording code.
Using the RZI code, PR (1,
Various studies have been made on the combination of the 1) method and the Viterbi decoding method.

The detection by the Viterbi decoding method is performed by the reproduction signal (R
This is a method for selecting and detecting the most probable data series based on the information on the transition state of the F signal), and is a method for increasing the density by signal processing, unlike physical methods such as shortening the wavelength of a laser. Therefore, it is said that the detection capability is higher than the detection for each bit.

In the optical disc, the RF signal causes inter-code interference due to the recording bit pattern and takes three values, and the detection by the Viterbi decoding method shows the most probable data sequence by the information of the three-valued transition state. It will be selected and detected.

[0006]

However, when the ROM pits of the optical disk are formed or the information pits are formed by the optical modulation recording, the asymmetry amount of the RF signal changes due to the change of the writing power of the laser. Due to this variation in the amount of asymmetry, an error may occur in the detection by the Viterbi decoding method, and the detection capability thereof may decrease.

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

[0008]

An optical information reproducing apparatus of the present invention is an optical information reproducing apparatus for demodulating information recorded on an optical disk as an optical information recording medium by a Viterbi decoding method, and a laser is recorded on an optical disk 3. An optical head 5 as pit information detecting means for irradiating light and detecting pit information based on pits recorded on the optical disc 3;
An asymmetry correction data conversion circuit 18 as a correction means for detecting the asymmetry amount of the pit information and correcting the pit information based on the asymmetry amount to generate corrected pit information, and a demodulation for demodulating the corrected pit information by the Viterbi decoding method. A detection circuit 19 is provided as a means.

The asymmetry correction data conversion circuit 18 is
The asymmetry amount can be detected in the reference area on the optical disc 3 in which a predetermined pit pattern is recorded.

[0010]

In the optical information reproducing apparatus having the above structure, the asymmetry correction data conversion circuit 18 detects the asymmetry amount of the pit information and corrects the pit information based on the asymmetry amount to generate the correction pit information. Then, the detection circuit 19 demodulates the corrected pit information by the Viterbi decoding method. Therefore, even when the asymmetry amount of the pit information changes due to the change of the writing power, the most probable data series is selected based on the transition state of the pit information by the Viterbi decoding method, and the information is detected reliably and easily. be able to.

The asymmetry correction data conversion circuit 18 is
By detecting the asymmetry amount in the reference area in which a predetermined pit pattern is recorded provided on the optical disc 3, the asymmetry amount can be accurately detected, and the variation in the asymmetry amount of the pit information can be reliably and reliably performed. Information can be easily detected.

[0012]

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

The recording data generating circuit 6 generates recording data based on the input data, the recording data is output to the modulating circuit 7, and the modulated recording data modulated by the modulating circuit 7 is output to the laser driving circuit 8. The optical head 5
For example, a laser diode (not shown) incorporated therein is driven.

Further, the optical head 5 includes a detector (not shown) for irradiating the optical disk 3 with a laser having a power lower than that for recording and detecting an RF signal from the return 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 clock pits, which are prepits 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 the 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 the timing generator 13 is adapted to generate various timing signals based on the data clock signal.

Further, the data clock signal is sent to the delay circuit 14
Is input to the A / D conversion circuit 11 via the A / D conversion circuit 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 to generate a digital RF signal. The correction table generation circuit 16 calculates an asymmetry amount by a digital RF signal in a reference area of the optical disc 3 described later based on the timing signal from the timing generator 13 to generate a correction table, and the correction table is stored in the RAM 17. Is designed to be saved.

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

By the way, the optical disk 3 is composed of a plurality of concentric or spiral tracks, and the tracks are composed of a plurality of sectors 3 as shown in FIG.
It is divided into 0, and information is recorded / reproduced in units of 30 sectors. The sector 30 is
Each segment is composed of a plurality of segments, and each segment includes a servo area 31 including prepits such as clock pits and a reference area 32 having a predetermined pit pattern formed therein.
And a data area 33 for recording data.

However, the reference area 32 may not be provided for each segment, but may be provided only once in the sector 30.

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

That is, since there is no pit in the first pattern Pa, the level of the RF signal becomes the maximum value La,
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.
The center value of c should be (= La + Lc) / 2), but the size of the pit formed changes due to the fluctuation of the writing power of the laser, so that the asymmetry amount is generated with respect to the center value of the RF signal. The value becomes Lb. Therefore, the correction table generation circuit 16 calculates the asymmetry amount (Lb- (La + Lc) / 2) and generates the correction table.

Next, the correction table generation in 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 in accordance with the writing power of the laser (the position of the central solid line deviates from the half position 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. In the correction table generation circuit 16, as shown in FIG. 4B, the correction signal Y is corrected (generated) with respect to the digital RF signal X as follows. That is, assuming that 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 in which the digital RF signal is corrected with respect to the asymmetry amount calculated in this way is generated. Figure 4
An example of the generated correction table is shown in (c).

In this way, the correction table generation circuit 16
The asymmetry correction data conversion circuit 18 corrects the digital RF signal based on the correction table generated in.

The detection circuit 19 determines the data string by the Viterbi decoding method by the corrected digital RF signal 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 of 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) if _{or (-1,1), Y k =} 0 ...... (4) (A k, A k-1) = (- 1, -1) if, Y _k = -Β ... (5)

Therefore, it is possible that A _k is +1.
_k (+) (likelihood: 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 selecting the larger one of a and b. For L _k (+), A _k is +1
And that (Y _k − in the equation (6).
Since α) ² is the squared error between the output Y _k and the expected signal level α, L _k (+) becomes larger as the squared error becomes smaller. Therefore, A = L _k−1 (+) + [− (Y _k −α) ² ] ... (7) B = L _k−1 (−) + [− (Y _k −0) ² ]. 8), in the case of a pattern in which A _k-1 = + 1 and A _k = + 1 as shown in FIG. 6B, with respect to the transition of the input bit A _k as shown in FIG. 6A. , L _k (+) = A, and as shown in FIG. 6C, A _k−1 = −1 and A _k =
For a pattern that is +1 then L _k (+) = B.

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

Next, in order to investigate which of L _k (+) and L _k (−) is more likely, ΔL _k = L _k (+) − L _k (−) (12) is calculated. Thus, the transition path of data can be determined. Here, the asymmetry correction data conversion circuit 1
Since the digital RF signal is corrected by 8,
= Β = s, ΔL _k is (i) A> B, C> D, that is, ΔL _k−1 + 2sY _k > s ² (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, that is, , ΔL _k−1 + 2sY _k <−s ² (15), ΔL _k = 2sY _k + s ² .

Therefore, the detection circuit 19 uses the equation (13),
By calculating (14) and (15), equation (13)
7 is satisfied, the pattern transition shown in FIG. 7A is obtained, when the formula (14) is satisfied, the pattern transition shown in FIG. 7B is obtained, and when the formula (15) is satisfied, the pattern transition shown in FIG. The pattern transition shown in c) can be obtained and the data transition path can be determined.

As described above, according to the optical disc recording / reproducing apparatus 1 of the present embodiment, the correction table is generated for the asymmetry amount of the RF signal, and R is calculated based on this 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 with respect to the asymmetry of the RF signal generated by the writing power of the laser.

In the above embodiment, the recording medium is the write-once optical disc, but the present invention is not limited to this, and the optical disc may be a ROM disc in which information is recorded in advance, and an RF signal generated by a change in writing power when the optical disc is produced. 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, 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 correction means detects the asymmetry amount of the pit information and corrects the pit information based on the asymmetry amount to obtain the corrected pit information. Since it is generated and the correction pit information is demodulated by the Viterbi decoding method by the demodulation means,
Even when the asymmetry amount of the RF signal changes due to the change of the writing power, the RF is detected by the Viterbi decoding method.
There is an effect that the most probable data series can be selected based on the information on the transition state of the signal, and the information can be detected reliably and easily.

The correcting means can accurately detect the asymmetry amount by detecting the asymmetry amount in the reference area in which a predetermined pit pattern is recorded provided on the optical information recording medium, and the pit information of the pit information can be detected. Information can be detected more reliably and easily with respect to changes in the amount of asymmetry.

[Brief description of drawings]

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

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

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

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

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

FIG. 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 of FIG.

7 is an explanatory diagram illustrating a data transition path determined by a detection circuit 19 in FIG.

[Explanation of symbols]

 1 Optical Disc Recording / Reproducing Device 3 Optical Disc 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 (2)

[Claims] 1. An optical information reproducing apparatus for demodulating information recorded on an optical information recording medium by a Viterbi decoding method, wherein the optical information recording medium is irradiated with laser light and recorded on the optical information recording medium. Pit information detection means for detecting pit information based on the formed pits, and correction means for detecting the asymmetry amount of the pit information and correcting the pit information based on the asymmetry amount to generate correction pit information. An optical information reproducing apparatus comprising: a demodulation unit that demodulates the corrected pit information by a Viterbi decoding method. 2. The optical apparatus according to claim 1, wherein the correction unit detects the asymmetry amount in a reference area in which a predetermined pit pattern provided in the optical information recording medium is recorded. Expression information reproducing device.