JP2914017B2 - Optical disk drive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reproducing recorded information by an optical disk apparatus, which reduces S / N due to various conditions such as a reduction in noise margin due to waveform equalization, contamination of an objective lens, and aging of the optical disk. If the deterioration to play error tends to increase to compensate for the reduction in the S / N is controlled so as reproducing laser output is increased, the optical disc equipment having a high information reproduction reliability is to allow Related.

[0002]

2. Description of the Related Art An optical disk apparatus performs high-density recording and reproduction of information using a laser beam. The optical disk as a recording medium has a large recording capacity and is hardly affected by scratches and dust. have.

Generally, to reproduce recorded information of an optical disk apparatus, a laser beam is applied to a track of an optical disk rotating at a constant angular velocity (access time to an intermediate portion is short) or at a constant linear velocity (recording capacity can be increased). And pick up the reflected or transmitted light with an optical head,
Then, the reproduced signal detected by the photodetector is binarized to reproduce the recorded digital data.

However, in the case of the constant angular velocity (CAV) system, the amplitude of the reproduced signal at the inner periphery is reduced due to the increase in intersymbol interference as compared with the outer periphery due to the difference in resolution between the inner and outer tracks of the optical disk. Would. This tendency is conspicuous when the recording frequency is increased (the recording bit length is shortened) in order to increase the recording density. Intersymbol interference is a problem to increase the recording density without changing the optical system, and waveform equalization is performed to suppress intersymbol interference. Waveform equalization methods include zero-symbol to minimize intersymbol interference.
A method using a forcing algorithm, a method for making the characteristics of a reproducing system a cosine equalization characteristic so as to satisfy the first Nyquist criterion, and a method in which a specific waveform sampled as described in JP-A-1-229516 is used as a reference signal waveform. Many methods are known, such as a method of equalizing so as to approach each other. The waveform equalization performed by such a method suppresses intersymbol interference by emphasizing the high frequency range of the reproduced signal whose resolution is reduced, and has high reliability and high density information even on the inner circumference of the optical disk. Reproduction can be performed.

[0005]

However, when waveform equalization is performed by the above-described method, not only the reproduced signal but also high-frequency noise is simultaneously emphasized, and low-frequency signal components are attenuated. For this reason, when waveform equalization is performed, an S / N that can obtain a sufficiently good error rate even with an increase in high-frequency noise due to waveform equalization and a decrease in low-frequency reproduced signal amplitude must be secured. There is a problem that the S / N ratio relatively decreases and the error rate in data reproduction may deteriorate.

Further, in an optical disk apparatus in which an optical disk of a recording medium is not easily affected by scratches and dust, when dust adheres to an objective lens of an optical pickup, the amount of laser light decreases and the amplitude of a reproduction signal decreases. Even when the amount of reflected light or the amount of transmitted light decreases due to aging of the optical disk recording medium, the amplitude of the reproduction signal also decreases. In such a state, the S / N ratio is reduced, and the error rate at the time of data reproduction is deteriorated. .

The present invention suppresses an increase in the error rate even when the S / N ratio is deteriorated due to a decrease in noise margin due to the above-described waveform equalization, aging of the recording medium, contamination of the objective lens, etc. It is an object of the present invention to provide an optical disk device capable of reproducing information at high speed and an optical disk for that.

[0008]

In order to achieve the above object, according to the present invention, when an optical disk device is started,
Alternatively, at the time of optical disk exchange, specific data previously recorded on the optical disk is reproduced a predetermined number of times, and an error counting means for measuring the number of reproduction errors, and an S / N for calculating S / N from the number of errors measured by the error counting means. Calculating means;
Based on the S / N obtained by the N calculating means, the S / N in the track of the optical disc for reproducing information is calculated, and the value is used to reduce the error rate of the reproduced information to a desired value or less. If not reached, a laser output control means for increasing the output of the reproducing laser in accordance with the degree is provided in the optical disk device. Also, the innermost one track of the optical disc information recording area used in this apparatus is used as a test track, and specific data (which the optical disc apparatus has adopted for recording information) which is the basis of S / N calculation on the track where information is reproduced. In the code modulation method, a data pattern in which a reproduction error occurs most frequently due to intersymbol interference is repeated).

[0009]

When the optical disk device of the present invention is started,
Alternatively, when the optical disk is replaced, in the CAV method, the test specific data recorded in advance on the innermost test track of the information recording area having the highest recording density and the highest error rate is reproduced. Since the specific data is a data pattern in which reproduction errors occur most frequently due to intersymbol interference by the code modulation method adopted for recording information by the optical disk device, the optical disk is uniformly stained or aging. When performing reproduction on a general track having a larger radius than the test track, the error rate should not be higher than when reproducing the test track. The content of the specific data is known in advance, and errors in reproducing the data are easily found, and are counted and recorded by error counting means. The S / N calculator calculates the S / N in the test track from the counted error number. On the basis of the S / N in the test track, the laser output control means performs the S / N in the track to be actually reproduced.
N is calculated, and the S / N required for the calculated S / N of the reproduction track to be equal to or less than a desired error rate.
If it is lower than that, when actually reproducing the data of the track, the laser output for reproduction is controlled so as to increase, the reflected light amount or transmitted light amount is increased, and the amplitude of the reproduced signal is increased. S / N should be improved. That is,
S / N is compensated by controlling the laser output for reproduction to increase noise due to waveform equalization, decrease in low frequency signal amplitude, aging of recording medium, deterioration of S / N due to contamination of objective lens, etc. The increase in the error rate is also suppressed. In the case of controlling the laser output as described above, the error rate of the actually reproduced data may still be high due to the above-described causes. A warning is issued to the user of the optical disk device. In this way, it is possible to prevent the information reproduction from becoming impossible due to the deterioration of the reproduction condition, and to perform the information reproduction with high reliability.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment applied to a magneto-optical type optical disk apparatus rewritable by the CAV method according to the present invention will be described below with reference to the drawings. FIG. 1 is a circuit block diagram of the optical disk device of the present invention. In the figure, 1 is an optical disk as a recording medium, 2 is a motor for rotating the disk 1, 3
Is a laser light oscillator for recording / reproducing on / from the disk 1,
Reference numeral 4 denotes a beam splitter for separating incident light from the laser light oscillator 3 and reflected light from the disk, 5 an objective lens for converging the laser light, and 6 a converted light reflected from the disk 1 into an electric signal. 7, an equalizer for suppressing intersymbol interference of the reproduced signal, and 8 a waveform shaping of the reproduced signal after the equalization into a binary digital signal of "1" and "0". A waveform shaper 9 for detecting and correcting a reproduction error of the reproduced digital signal by using an error correction code added to the recording information;
Is a counter for counting the number of errors detected when the error correction circuit 9 performs error detection using the error correction code. An S / N calculation circuit 12 for calculating N is a laser light oscillator at the time of data reproduction from a difference between the S / N calculated by the S / N calculation circuit 11 and the S / N required to satisfy a desired error rate. 3, a laser output control circuit for controlling the output of 3, a drive microcomputer 13 for controlling the entire optical disk device, and an interface 14 for transferring data and commands to and from the host computer.

An optical disk 1 used as a recording medium in the optical disk apparatus of the present invention has an information recording area 2 as shown in FIG.
One innermost track is used as the test track 22. In the test track 22, specific data is recorded by the user at the time of initialization (writable because of the magneto-optical method in this embodiment). (If the optical disc is a reproduction-only disc such as a so-called CD, specific data is recorded in the test track 22 in advance.) The specific data to be recorded is the modulation method used in the standard adopted by this optical disc device. Is the worst pattern repetition. Here, the worst pattern is a data pattern in which a code detection error frequently occurs due to intersymbol interference. For example, NRZ (Non Return to Ze
ro) Modulation is a continuous pattern of 1010... The worst pattern on the optical disk device by making the specific data the worst pattern is when the test track 22 is reproduced.

When the optical disk device of the present invention is started,
Or, when the disk 1 is replaced, the drive microcomputer 13
After the state of the optical disk device is stabilized, the innermost test track 22 is reproduced a predetermined number of times by normal reproduction laser output. The number of times the test track 22 is reproduced depends on the data format of the standard adopted by the optical disk device and the target error rate. By reproducing the same track a predetermined number of times, the influence of the number of samples on the reproduction error generated at random is reduced. I can do it.

As shown in FIG. 3A, the reproduced signal of the reproduced test track 22 has a reduced amplitude of the reproduced signal having a high recording frequency due to intersymbol interference, and the aperture ratio of the eye pattern is reduced. In this case, the margin at the time of waveform shaping is small, the probability of occurrence of a detection error of a reproduced signal is high, and reliable information reproduction cannot be performed. Suppress. Although there are many equalization algorithms for performing waveform equalization as described above, the reproduced signal that has been optimally equalized by the equalization algorithm used for the equalizer 7 has reduced resolution due to the equalization processing. High frequencies are emphasized. As a result, as shown in FIG. 3B, the intersymbol interference at the code discrimination point is suppressed, the signal amplitude at a high recording frequency increases, and the aperture ratio of the eye pattern increases. However, high-frequency noise is also emphasized at the same time by the equalization, the low-frequency signal component is attenuated, and the reproduced signal amplitude at the low recording frequency is reduced, so that the noise margin is reduced. Therefore, even if waveform equalization is performed, if the amount of increase in jitter due to noise is larger than the amount of decrease in jitter due to intersymbol interference, the probability of occurrence of a detection error increases and information cannot be reproduced with high reliability. .

The reproduced signal equalized by the equalizer 7 is converted into a binary digital signal of "1" and "0" by the waveform shaper 8, and the error correction circuit 9 corrects the error based on the corresponding format of the optical disk apparatus. An error is detected and corrected by the code. At this time, the counter 10 counts the number of reproduction errors detected by the error correction circuit 9. The unit of the reproduction error depends on the error correction method. When error detection and correction are performed in byte units, when the test track 22 has been reproduced a predetermined number of times, the counter 10 holds the total number of byte errors that occurred when the test track 22 was reproduced. It is needless to say that the counter 10 is reset when the optical disk apparatus is started or when the optical disk 1 is replaced.

In general, when the noise included in the reproduced signal is Gaussian noise and the reproduced data is random binary digital data having the same appearance probability of "1" and "0", S
/ N ratio and the bit error rate (hereinafter b)
ER) can be obtained by the following equation (Equation 1) as shown in FIG.

[0016]

## EQU1 ## bER = (1-erf (M)) / 2
............ (Equation 1)

[0017]

(Equation 2)

Here, M = S _rms / N _rms . The error function erf is obtained from the S / N ratio of the reproduced signal as shown in (Equation 2). From this, conversely, it is also possible to obtain the S / N ratio from the bER, and from the number of reproduction errors counted by the counter 10, the S / N calculation circuit 11 calculates the S / N ratio from the error rate when the test track 22 is reproduced. Error function er
The S / N ratio at the innermost circumference is calculated using f. As described above, when the test track 22 is reproduced, the worst S / N ratio is calculated because of the worst reproduction characteristics.

The S / N calculation circuit 11 is configured, for example, as shown in FIG. In the S / N calculation circuit 11 of FIG. 5, the error rate calculation circuit 51
Then, a byte error rate (hereinafter referred to as BER) is calculated from the total number of reproduced bytes when reproducing No. 2 and the total number of byte errors output from the counter 10. When error detection and correction are performed not in units of bytes but in units of words or blocks, the word error rate and the block error rate are obtained, but the BER can be estimated from the word length and the block length as random errors. The S / N is calculated by the error function calculation circuit 52 from the BER calculated by the error rate calculation circuit 51. Assuming that only random errors occur without burst errors using 1-bit 8-bit NRZ modulation, bER is bE
R = BER / 8. Here, assuming that the reproduced specific data is random data having the same appearance probabilities of “1” and “0”, the bER is expressed by (Equation 1). The S / N can be obtained by the following (Equation 3) using an error function.

[0020]

Equation 3] _{S rms / N rms = erf ~} 1 (BER / 4-1)
(Equation 3) Here, erf- ¹ is an inverse function of the error function erf. An arithmetic circuit is actually constructed, and S / N is calculated using an inverse function of the error function.
Since it is difficult to obtain the error function erf from the problems of the circuit scale and the operation processing speed, the error function erf can be obtained from a function table.

The laser output control circuit 12 controls the laser output at the time of data reproduction based on the S / N at the innermost circumference obtained by the S / N calculation circuit 11 and the track position at which reproduction is performed. The laser output control circuit 12 is configured, for example, as shown in FIG. In FIG. 6, reference numeral 61 denotes a register for holding the S / N calculated by the S / N calculation circuit 11, 62 denotes a gain calculation circuit for calculating an S / N increase in a reproduction target track, 63 denotes a multiplier, and 64 denotes a multiplier. A divider for obtaining a ratio with the S / N required to achieve the target BER, 65 is a register for holding S / N data necessary to achieve the target BER, and 66 is a register for storing the target. A laser output calculating circuit 67 for calculating a laser output required to compensate for the S / N which is insufficient to achieve the BER,
A register for holding a laser output control signal in the case of a normal laser output that does not need to compensate for / N, a multiplexer 68 for selecting a laser output control signal, 6
Reference numeral 9 denotes a D / A converter for converting a laser output control signal into an analog signal.

When reproducing data, a signal from a track from which data is reproduced is input from the drive microcomputer 13 to the gain calculating circuit 62. When the track to be reproduced is not at the innermost circumference, the resolution is improved from the inner circumference to the outer circumference, and therefore, as shown in FIG.
Assuming that the ratio of N improvement is 0, S / N increases toward the outer periphery.
Will be improved. The rate at which this S / N improves is
For example, IEE, Transaction on Consumer Electronics, August 1976
Months 258-268 (IEEE Transaction on consumer)
electronicsAUG 1976, pp258-268), by changing the disk radius value of the frequency characteristic equation e (f) expressed by (Equation 4) and (Equation 5) below, based on the innermost radius of the disk It can be obtained as shown in (Equation 6).

[0023]

[Equation 4] e (f) = [(2cos ~ ¹ (f / fco) -sin (2cos ~ ¹ (f / f
co))) / π] ² ... (Equation 4)

[0024]

Fco = (2NA × 2πr × F) / λ
............ (Equation 5)

[0025]

## EQU6 ## S / N improvement ratio = (e (f) _{r =} reproduced _track ) / (e (f) _{r =} innermost circumference) (Equation 6) where f is the recording frequency In Equation (5), NA is the lens aperture ratio, r is the disc radius,
F is the disk rotation frequency, and λ is the laser wavelength. The gain calculation circuit 62 calculates the rate of improvement of the S / N with respect to the reproduction track on the basis of the innermost circumference using the above (Equation 6). S / S at the innermost circumference held in the register 51
N and the improved S / N calculated by the gain calculation circuit 62
Is multiplied by the multiplier 63 to obtain the S / N of the track to be reproduced. The divider 64 calculates the ratio between the S / N satisfying the target BER held in the register 65 and the S / N in the track to be reproduced.

When the quotient of the divider 64 is 1 or less, that is, when the S / N in the reproduction track is equal to or more than the S / N satisfying the target BER, the divider 64 sets a flag. If the quotient of the divider 64 is 1 or more, the reproduction laser output is increased to compensate for the S / N that is insufficient to satisfy the target BER. Assuming that the S / N of the reproduction signal is determined by the shot noise of the photodetector, the S / N is proportional to the square of the amount of reflected light or the amount of transmitted light. In the case of a magneto-optical disk, there is the following relational expression.

[0027]

(Equation 7)

Where I is the amount of reflected light and θ is the Kerr rotation angle. Therefore, increasing the laser output increases the amount of reflected light,
The S / N is improved because the amplitude of the reproduction signal increases. However, actually, laser noise, disk noise, and the like also increase. Therefore, as shown in (Equation 7), S / N is increased by the amount of reflected light.
Does not improve. Therefore, the ratio of the S / N to the ratio RP '/ RP between the normal laser output RP and the laser output RP' controlled and increased by the characteristics of the laser oscillator, photodetector, and the like used in the optical disc device is improved. Are determined in advance as shown in FIG. FIG. 8 shows RP '/ R
When P = 1, that is, when the controlled laser output is the same as the normal laser output, the ratio at which the S / N is improved is defined as 0 dB, where
It is represented by The laser output calculation circuit 66 calculates the reproduction laser output necessary to improve the S / N which is insufficient to achieve the target error rate, using the characteristics previously obtained as shown in FIG. . However, if the output of the reproduction laser is increased to compensate for the S / N, the deterioration of the recording medium due to heat is accelerated. Therefore, the output of the reproduction laser is increased only when performing data reproduction, and is usually performed during seek and pause. Is controlled so that the laser output becomes. Also, the maximum value of the reproduction laser output needs to be set to a value that does not destroy the recorded data even when the output of the laser oscillator 3 fluctuates.

At the time of data reproduction, the laser output control signal calculated by the laser output calculation circuit 66 is such that the S / N of the track to be reproduced satisfies the target error rate.
Only if it does not reach N is it selected by the multiplexer 68. For other seeks and poses, and enough S
/ N, the flag of the divider 64 and the read signal from the drive microcomputer 13 cause the multiplexer 6
8, the control signal of the register 67 in which the laser output control signal in the normal state is recorded is selected. The selected laser output control signal is converted into an analog signal by the D / A converter 69 and input to the laser oscillator 3 to control the reproduction laser output.

If the normal laser output control signal is not selected at the time of reproducing the information, the drive microcomputer 13 informs the user of the error due to contamination of the lens, aging of the recording medium, etc.
/ N is degraded. As a warning method, a method of installing a warning lamp or the like in the optical disk device and lighting it, a method of sending a message to the host computer via the interface 14, and the like are used.

An operation of reproducing information from a recording medium having a deteriorated S / N in the optical disk apparatus embodying the present invention will be described. The value of S / N required to achieve the target error rate is s. When the reproduction laser output is not controlled based on the innermost S / N obtained from the reproduction error of the test track at the time of start-up or replacement of the recording medium, a track whose S / N becomes s or more due to the improvement in resolution is set to X. Then, when the track on which information is to be reproduced is on the inner side of X, the target error rate cannot be achieved due to the deterioration of S / N. Therefore, when the track on which information is to be reproduced is located on the inner side of X, the reproduction laser output is controlled to increase in accordance with the position of the reproduction track, and the degraded S / N is compensated as shown in FIG. Then, the value of S / N is set to s or more in all tracks. Further, the reproduction laser output at that time is controlled so as to compensate for the shortage S / N in the reproduction track as shown in FIG. Therefore, the reproduction laser output is not increased more than necessary, and the recording medium,
The burden on the laser oscillator can be reduced. When the track on which information is to be reproduced is on the outer peripheral side of X, the normal laser output n, which is the same as during seek and pause, is constant.
Further, in the embodiment, when the reproduction laser output is controlled to be n or more during the information reproduction, the user is notified that the reproduction condition is deteriorating due to the deterioration of the S / N. In consideration of the variation of S / N, when the reproduction laser output is higher than n ′ (n ′> n), the S / N
May be notified.

As described above, by controlling the reproduction laser output and increasing the reproduction signal amplitude, the noise due to waveform equalization increases, the signal amplitude decreases, the lens becomes dirty, and the recording medium changes over time due to aging. / N can be compensated for, and highly reliable information reproduction can be performed. In addition, when the reproduction laser output is controlled, the user is notified that the reproduction condition is deteriorating due to the deterioration of S / N, so that the user can be prevented from being unable to reproduce the recorded information. .

In the above embodiment, the arithmetic processing is performed by the S / N calculating circuit 11, the gain calculating circuit 62 of the laser output control circuit 13, and the laser output calculating circuit 66. The arithmetic processing is collectively performed by the microcomputer. It does not matter. Also, in order to increase the operation processing speed and reduce the circuit scale, the operation results are prepared in advance in the ROM as a table, and the number of reproduction errors of the test track 22 and the input of the reproduction track are referred to the ROM table. The laser output control signal may be obtained.

Further, in the above embodiment, the reproduction error of the test track is detected from the error correction circuit. However, since the specific data to be recorded is known, the output of the reproduction data from the waveform shaper is compared with the comparator and directly. A configuration for detecting a reproduction bit error may be adopted.

In the above embodiment, the optical disk apparatus of the CAV system has been described.
The present invention is also effective in reproducing information in each of the divided zones in an optical disk device employing a fied CAV (fied CAV) system, and can be employed in the MCAV system as well as the CAV system. When the present invention is applied to the MCAV optical disk device, a test track may be provided at the innermost circumference in each of the divided zones, but the recording / reproducing characteristics of the innermost circumference in each zone are the same. If the condition can be considered, the test track may be limited to the innermost track of the information recording area as in the CAV method.

[0036]

As described above, according to the present invention, various factors such as an increase in noise due to waveform equalization at the time of reproducing information, a decrease in signal amplitude for reduction, contamination of a lens, aging of a recording medium, etc. Even if the S / N deteriorates due to the condition and the reproduction error increases, the track whose information is to be reproduced on the basis of the S / N of the innermost test track calculated at the time of starting or when the recording medium is replaced is determined. Can be controlled so as to increase the reproduction laser output to an appropriate output level corresponding to the track without detecting the output. By appropriately controlling the reproduction laser output, the reproduction signal amplitude can be increased, the degraded S / N can be guaranteed, and an increase in the reproduction error can be suppressed to perform highly reliable information reproduction. . Also, by alerting the user that the reproduction signal amplitude may have decreased due to lens contamination and aging of the recording medium, it is possible to prevent the information recorded on the recording medium from being reproduced. Can be prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram of a circuit according to an embodiment of the present invention.

FIG. 2 is a format diagram of an optical disk recording medium.

FIG. 3A is a diagram showing that the aperture ratio of an eye pattern of a reproduced signal is low due to intersymbol interference;
(B) is a diagram showing a state in which the equalization processing is performed on the reproduced signal to suppress intersymbol interference at the code discrimination point.

FIG. 4 is a diagram illustrating a relationship between S / N and a bit error rate bER when noise follows a Gaussian distribution.

FIG. 5 is a block diagram illustrating an example of an S / N calculation circuit.

FIG. 6 is a block diagram illustrating an example of a laser output control circuit.

FIG. 7 is a diagram showing that S / N improves as the position of a track to be reproduced goes from the inner circumference to the outer circumference.

FIG. 8 is a diagram showing a state in which the S / N is improved with an increase in the reproduction laser output.

FIG. 9 shows a position of a reproduction track and S in the embodiment of the present invention.
FIG. 6 is a diagram showing a relationship of / N.

FIG. 10 is a diagram showing a relationship between a position of a reproduction track and a laser output for reproduction in the embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Recording medium, 2 ... Motor, 3 ... Laser oscillator, 4 ...
Beam splitter, 5: Objective lens, 6: Photodetector, 7
... Equalizer, 8 ... Waveform shaper, 9 ... Error correction circuit, 10 ...
Counter: 11: S / N calculation circuit, 12: Laser output control circuit, 13: Drive microcomputer, 14: Interface.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-151040 (JP, A) JP-A-63-25871 (JP, A) JP-A-4-141827 (JP, A) (58) Survey Field (Int.Cl. ⁶ , DB name) G11B 7/00 G11B 7/125

Claims (2)

(57) [Claims] 1. A prerecorded identified data to the optical disc by a predetermined number of times reproduction, an error counting means for measuring the number of reproduction error from the measured error number to the error counting means S /
S / N calculating means for calculating N, and S / N on a track of an optical disc for reproducing information based on the S / N obtained by the S / N calculating means, and the value is used to determine the error of the reproduced information. An optical disk device comprising: laser output control means for increasing the output of a reproducing laser according to the degree of S / N required to reduce the ratio to a desired value or less. . 2. The output control of the reproducing laser is performed only when reproducing the information recorded on the optical disk, and the output of the reproducing laser is fixed at a predetermined value during a seek or pause. 2. The optical disc device according to 1.