JPH0721615A - Optical disk device - Google Patents

Abstract

PURPOSE:To sufficiently and surely suppress the fluctuation of reproducing signals by correcting a level with the reproducing signal level of a reference area detected from a disk-like recording medium as a reference or performing pre-holding with a correction value. CONSTITUTION:Data for phase matching and level detection are preformated in the servo areas of the optical heads of respective segments for a disk 2. The phase shift of clocks is corrected with the phase matching information of logic '1' and '0' as the reference. Also, a reference level for demodulation is set with the difference RVL of the maximum and minimum of the similar information for the level detection as the reference. A timing generator 9 issues clamp pulses CL1 and CL2 with the output of a PLL circuit 8 as the reference. A sum signal SW is processed with a data clock DCK as the reference, a clamping circuit 14 is operated with a servo clock SCK as the reference and DC fluctuation is reduced. An A/D converter 13 converts the reproducing signal RF of the output of a selector 12 with a signal DCK as the reference and the clamping circuit 14 detects the reproducing signal level in a clamp area and sends it through a detection circuit 15 to a control circuit 16.

Description

Detailed Description of the Invention

[0001]

[Table of Contents] The present invention will be described in the following order. Field of Industrial Application Conventional Techniques Problems to be Solved by the Invention Means for Solving the Problems (FIGS. 1, 3 to 6) Action (FIGS. 1, 3 to 6) Example (1) Example (FIGS. 1 to 3) (2) Clamp circuit (FIGS. 3 to 5) (3) Effects of the embodiment (4) Other embodiments (FIGS. 6 and 7) Effects of the invention

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk device,
For example, it is suitable for application to a magneto-optical disk device or the like that reproduces data recorded on a disk-shaped recording medium by applying the Viterbi decoding method.

[0003]

2. Description of the Related Art Conventionally, in this type of optical disk device, a thermomagnetic recording method is applied to record data, and the Kerr effect is used to reproduce thermomagnetically recorded data. There is something. That is, in this optical disk device, the optical disk is intermittently irradiated with a light beam while a predetermined modulation magnetic field is applied, and thereby the thermomagnetic recording method is sequentially applied to the irradiation position of the light beam to apply the perpendicular magnetization region. Is formed and desired data can be recorded.

On the other hand, at the time of reproduction, this optical disk device irradiates the optical disk with a light beam having a predetermined polarization plane, and decomposes the reflected light into P-wave components and S-wave components. As a result, the optical disc device decomposes the reflected light into P-wave components and S-wave components whose light intensities complementarily change according to the magnetization polarity of the light beam irradiation position, and these P-wave components and S-wave components are decomposed. Light is received by each light receiving element. As a result, the optical disk device subtracts the light reception results of the P-wave component and the S-wave component, and obtains a reproduction signal whose signal level changes according to the magnetization polarity of the light beam irradiation position. The desired data can be reproduced by processing with the signal processing circuit.

When processing the reproduced signal, the optical disk device clamps the signal level of the reproduced signal by using a clamp circuit and then converts the reproduced signal into binary data.

That is, in this type of disk-shaped recording medium, a substrate is formed by molding polycarbonate or the like,
A perpendicular magnetization film is formed on this substrate, and therefore, there is a feature that the magnitude of birefringence changes in each part of the substrate. Therefore, this type of optical disc is characterized in that the light intensity of the P-wave component and the S-wave component changes at each portion of the optical disc even when the light beam is applied to the portion where no information is recorded.

Therefore, in the conventional optical disk device, the reproduction signal is clamped and processed to reduce the DC fluctuation of the reproduction signal which changes in response to the change of the birefringence. The playback data can be detected.

[0008]

By the way, by applying the class 1 of the partial response, the optical disk device of this kind can positively utilize the intersymbol interference between the data and perform the high density recording. Further, when class 1 of the partial response is applied, it is considered that the optical disk device can reduce the bit error rate by applying the Viterbi decoding method at the time of decoding.

However, if the signal level of the reproduced signal input to the decoding circuit fluctuates due to the birefringence of the optical disk,
Even if the Viterbi decoding circuit is applied, it becomes difficult to detect correct reproduction data. In particular, when high density recording is performed by applying the class 1 of the partial response, in the optical disc device, it is necessary to suppress this DC fluctuation more sufficiently and surely than ever before.

That is, this DC fluctuation has a relatively high frequency due to the change in birefringence in each part of the optical disk, whereas the reproduced signal has a frequency band of DC when Class 1 of the partial response is applied. When the class 1 of the partial response is applied to the optical disk device, the frequency band of the DC signal and the frequency band of the reproduction signal overlap each other in the optical disk device. For this reason, when high density recording is performed by applying the class 1 of the partial response, the optical disk device has a clamp circuit so as to sufficiently suppress a relatively high frequency DC fluctuation in which the frequency band overlaps with the reproduction signal. Need to work.

However, if the clamp circuit is operated so as to sufficiently suppress the DC fluctuations having a relatively high frequency as described above, when the signal level of the reproduced signal changes abruptly due to scratches, dust, defects, etc. In the apparatus, the DC fluctuation may be erroneously corrected to cause a bit error rate of the reproduced data to increase.
In particular, since the Viterbi decoding circuit has a characteristic of error propagation, it is necessary to effectively avoid such erroneous correction of DC fluctuation in the optical disk device.

The present invention has been made in consideration of the above points, and it is an object of the present invention to propose an optical disk device capable of suppressing DC fluctuation more sufficiently and reliably than ever before.

[0013]

In order to solve such a problem, according to the present invention, in the optical disk device 1 for reproducing the recording data thermomagnetically recorded on the disk recording medium 2, a light beam is applied to the disk recording medium 2. Reproduced signal detecting means 5 and 6 for irradiating and receiving the reflected light obtained from the disk-shaped recording medium 2 and outputting the reproduced signal RF whose signal level changes in accordance with the change of the polarization plane of the reflected light. R
And analog-to-digital converting circuit 13 for converting the F into digital signals D _RF, a signal level correction circuit 14 and outputting the corrected signal level of the digital signal D _RF, based on the digital signal D _RF corrected in the signal level correction circuit 14 The signal level correction circuit 14 detects a reference area inserted in the disk-shaped recording medium 2 at a predetermined cycle, and a signal of a reproduction signal RF obtained from the reference area. Level is detected and correction level D
By obtaining F and correcting the signal level of the reproduction signal RF with the correction level DF, the DC fluctuation of the reproduction signal RF is reduced.

Further, in the second invention, the disk-shaped recording medium 2 divides the recording area into sectors, divides the sectors into segments, and reproduces the reproduction signal RF in a predetermined area of the segment.
Of the reproduction signal RF obtained from the clamp area by detecting the signal level of the reproduction signal RF formed in the clamp area in which a desired data can be recorded in the subsequent area. Set the correction level DF.

Further, in the third invention, the signal level correction circuit 14 includes a reproduction signal R obtained from the clamp area.
When the signal level of F changes above a predetermined reference level RLVL / N, the correction level DF is pre-held to correct the signal level of the reproduction signal RF.

Further, in the fourth aspect of the present invention, the disk-shaped recording medium 2 assigns one of the segments in the sector to the reference area, and sets the reference pattern in which the reproduction signal RF changes to the maximum value and the minimum value to the reference area. And the signal level correction circuit 14 detects a signal level difference RLVL between the maximum value and the minimum value of the reproduction signal RF,
Reference level RLV based on the signal level difference RLVL
Set L / N.

Further, in the fifth invention, the signal level correction circuit 14 performs a moving average of the signal level of the reproduction signal RF obtained from the reference area a predetermined number of times to obtain a correction level DF.
To set.

Further, in the sixth invention, the optical disk device 1 has predetermined driving circuits 3, 8, 9, and 11, and the driving circuits 3, 8, 9, and 11 drive the disk-shaped recording medium 2. At the same time, the tracking control of the light beam is performed, and the reference signal of the analog digital conversion circuit 13 is generated. If any operation cannot be executed correctly, the error signal SV
LOCK is output, and when the error signal SVLOCK is output, the signal level correction circuit 14 cancels the prehold operation.

Further, in the sixth invention, the signal level correction circuit 14 is provided with a reproduction signal R obtained from the clamp area.
The signal level of F is the reference level RL continuously for a predetermined number of times or more.
When it changes to VL / N or more, the pre-hold is released.

[0020]

If the reference area inserted in the disk-shaped recording medium 2 at a predetermined cycle is detected, the signal level of the reproduction signal RF obtained from the reference area is detected, and the signal level of the reproduction signal RF is corrected, Playback signal R by selecting the reference area
The DC fluctuation of F can be reduced.

That is, a clamp area for holding the signal level of the reproduction signal RF at the saturation level is formed in a predetermined area of the segment, and DC fluctuation of the reproduction signal RF can be reduced with reference to this clamp area.

At this time, the signal level of the reproduction signal RF obtained from the clamp area is a predetermined reference level RLVL / N.
In the case of the above change, the correction level DF is pre-held to correct the signal level of the reproduction signal RF, and erroneous correction of the signal level can be effectively avoided.

Further, the reference level RLVL / N is a signal level difference RLV between the maximum value and the minimum value of the reproduction signal RF.
L can be detected and set based on the signal level difference RLVL.

At this time, the signal level of the reproduction signal RF obtained from the reference area is moved and averaged a predetermined number of times to set the correction level DF to improve the SN ratio.

When the error signal SVLOCK is output, the pre-hold is released, and the signal level of the reproduction signal RF obtained from the clamp area continuously changes to the reference level RLVL / N or more for a predetermined number of times or more. The signal level can be surely corrected by canceling the pre-hold.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings.

(1) Configuration of Embodiment In FIG. 1, reference numeral 1 denotes an optical disk device as a whole,
The desired data is thermomagnetically recorded on the magneto-optical disk 2 by applying the class 1 of the partial response, and the recorded data is reproduced.

That is, the magneto-optical disk 2 is formed by forming a magnetic film on a predetermined disk-shaped substrate, so that the desired data can be thermomagnetically recorded by applying the thermomagnetic recording method. . Further magneto-optical disk 2
As shown in FIG. 2, the information recording surface is divided into sectors, and each sector is further divided into a plurality of segments (FIG. 3 (A)).

Further, the magneto-optical disk 2 is formed such that a servo area SB is formed at the head of each segment and the servo area SB is reproduced to perform tracking control. Further, the magneto-optical disk 2 allocates the head segment of this sector to the address area and pre-formats and records the address data of each sector.
The following segments are assigned to the reference area and the remaining segments are assigned to the data area.

That is, the magneto-optical disk 2 preformats and records the phase matching data and the level detecting data in this reference area. Here, the phase matching data is formed by data in which the data of logic 0 and 1 are continuous every two bits (FIGS. 3B and 3C), and in the optical disc device 1, this phase matching data is formed. Is used as a reference so that the phase shift of the clock can be corrected (FIG. 3 (D)).

On the other hand, the level detection data is formed of data in which logic 0s and 1s are consecutive for a predetermined number of bits, so that in the optical disk device, the saturation level of the reproduction signal is determined by the level detection data. It is designed to be detectable. As a result, the optical disk device 1 can reproduce the data for level detection and detect the maximum value and the minimum value that the reproduction signal can take. Based on the level difference RLVL between the maximum value and the minimum value. A reference level for data demodulation can be set.

On the other hand, as shown in FIG. 3, in the servo area SB, a clock pit is formed on the track center TC, and before and after this clock pit, from the track center TC to the inner and outer peripheral sides of the magneto-optical disc 2. Are offset by a predetermined distance to form a pair of wobble pits (FIG. 3 (A)), whereby the optical disc device 1 detects the reproduction result of the wobble pits with reference to the clock pits. The tracking control is performed so that the reflected light amounts obtained from the pair of wobble pits become equal.

Further, the magneto-optical disc 2 is formed so as to form a clamp area which does not form any pit between the servo area SB and the data area, reference area and address area, respectively. The DC fluctuation is reduced on the basis of the reproduction signal obtained from the clamp area. That is, in the optical disc device 1, based on the reproduction signal obtained from the clamp area that does not form any pit,
The saturation level of the reproduction signal can be detected, and thus the DC fluctuation can be detected based on the signal level of the reproduction signal. As a result, the magneto-optical disk 2 can detect and correct the DC fluctuation of the reproduction signal at the head of each segment and the area following the servo area, thereby sufficiently reducing the DC fluctuation. There is.

In this embodiment, the magneto-optical disk 2 is formed with a groove in the clamp area and the data area so as to sandwich the track center TC from both sides. That is, when the groove is formed in the magneto-optical disk 2 in this way, the reproduction signal of the optical disk device 1 is characterized in that the reproduced signal fluctuates by that amount.
As a result, in this embodiment, the magneto-optical disk 2 is formed with grooves not only in the data area but also on both sides of the clamp area, so that the DC fluctuation caused by forming the groove can be effectively avoided.

With respect to the magneto-optical disk 2, the optical disk device 1 drives the spindle motor by the spindle control circuit 3 to rotate the magneto-optical disk 2 at a predetermined rotational speed. In this state, the optical disc device 1 controls the operation of the laser diode built in the optical pickup 5 by the laser control circuit 4 to drive the optical pickup 5 to irradiate the magneto-optical disc 2 with a light beam to record data. At this time, a reference area is formed, desired data is thermomagnetically recorded in the subsequent data area, and reflected light obtained by irradiating a light beam during reproduction is received by a predetermined light receiving element incorporated in the optical pickup 5.

At this time, the optical pickup 5 is adapted to decompose the P-wave component and the S-wave component and receive the reflected light.
The IV conversion matrix circuit 6 performs a predetermined addition / subtraction process after current-voltage conversion of the output current of the light receiving element. As a result, the IV conversion matrix circuit 6 generates a difference signal SD which is a reproduced signal of thermomagnetically recorded data, a sum signal SW which is a reproduced signal of data recorded by forming a pit, and a focus error signal FE. Output.

As a result, the optical disc device 1 can select the sum signal SW to obtain the reproduction signals of the address area, the servo area SB and the reference area, and select the difference signal SD to select the clamp area and the data area. It is designed to obtain the reproduction signal of. The analog digital conversion circuit (A / D) 7 converts the sum signal SW into a digital signal based on the servo clock SCK and outputs the digital signal. The PLL circuit 8 uses the digital signal as a reference to output the servo clock SCK and the data clock. Tsuku DCK
Is generated and the servo clock SCK is output to the analog digital conversion circuit 7.

As a result, the optical disc device 1 is adapted to generate various reference signals with reference to the servo pattern formed on the magneto-optical disc 2 and the data in the reference area. It is designed to control the behavior of. That is, the timing generator (TG) 9 generates the clamp pulses CL1 and CL2 with reference to the output signal of the PLL circuit 8.

Here, the optical disk device 1 processes the reproduction signals of the data area and the clamp area with reference to the data clock DCK, whereas it processes the reproduction signals of the servo area and tracks them. When the error signal TE or the like is generated, the sum signal SW is processed with the servo clock SCK as a reference, and the clamp circuit 14 is operated with the clamp pulses CL1, CL2 as a reference to reduce the DC fluctuation. ing.

That is, the tracking error generation circuit 10
Input the output signal of the analog digital conversion circuit 7 at the timing of reproducing the servo pattern, and thereby generate the tracking error signal TE based on the reproduction result of the servo pattern. This enables the optical disc device 1
Is a servo control circuit 11 which drives a focusing coil and a tracking coil built in the optical pickup 5 on the basis of the tracking error signal TE and the focusing error signal FE, thereby moving the objective lens vertically and horizontally. Focus control and tracking control.

The selector (SEL) 12 selectively outputs the sum signal SW while the light beam scans the address area and the servo area SB by switching the contact at a predetermined timing, whereas The difference signal SD is selectively output during the period in which the reference area, the clamp area, and the data area are scanned.

The analog digital conversion circuit 13 converts the reproduction signal RF, which is the output signal of the selector 12, into a digital value based on the data clock, and outputs the digital value. The clamp circuit 14 converts the reproduction signal RF into the digital value. The signal level of the signal is detected in the clamp area, and the signal level of the reproduction signal RF is corrected and output based on the detection result.

The data detecting circuit 15 demodulates the digital signal by applying the Viterbi decoding method after equalizing the waveform of the digital signal by the built-in digital equalizer and reproducing signal R obtained from the reference area.
The maximum value and the minimum value of F are detected, and the signal level difference RLVL (FIG. 2) between the maximum value and the minimum value is output to the system control circuit 16.

As a result, the optical disk device 1 can output reproduced data via the data detection circuit 15, and the system control circuit 16 can control the entire operation.

On the other hand, at the time of recording, the optical disc device 1
Is switched to the reproduction mode in the address area and the servo area, and based on the reproduction result obtained by irradiating the servo area or the like with a light beam, the timing generator 9 uses the data clock DCK and the servo clock SC.
The tracking error signal TE is generated by the tracking error generation circuit 10 based on the reproduction result obtained by generating K and reproducing the servo area. As a result, the optical disc device 1 performs tracking control based on the servo clock SCK and the tracking error signal TE, and drives a predetermined recording system based on the data clock DCK.

As a result, the optical disk device switches the light amount of the light beam to the light amount at the time of recording at the timing when the light beam scans the predetermined data area based on the reproduction result of the desired address area, and intermittently irradiates. In this state, a predetermined magnetic field is applied to the irradiation position of the light beam so that desired data can be thermomagnetically recorded in a data area designated by a computer or the like.

Further, the optical disk device 1 records the input data sequentially input by applying the class 1 of the partial response by executing a predetermined encoding process in the recording system during the data recording. Has been done.

(2) Clamp Circuit As shown in FIG. 4, the clamp circuit 14 includes five registers (REG) which operate on the basis of the data clock DCK.
By connecting 21 to 25 in series, the signal level of the reproduced signal obtained from four continuous clamp areas is subjected to moving average, and the signal level of the reproduced signal is corrected based on the average value detection result to reproduce. Reduce DC fluctuations in the signal.

That is, the timing generator 9 generates the data clock DCK (FIG. 3 (B)) whose signal level is switched in the pitch forming cycle based on the reproduction result of the reference area and the servo area, and further, the clamp area. The first clamp pulse CL1 (FIG. 3 (C)) in which the signal level rises in synchronization with the data clock DCK at the timing when the light beam scans the light beam, and delays from this first clamp by one clock cycle of the data clock DCK. Then, the second clamp pulse CL2 at which the signal level rises
(FIG. 3 (D)) is output.

The clamp circuit 14 takes in the output data D _RF of the analog digital conversion circuit 13 into the first register 21 with reference to the first clamp pulse CL1, and the timing at which the second clamp pulse CL2 rises. Then, the data taken in the first register 21 is sequentially transferred to the subsequent registers 22 to 25. As a result, the clamp circuit 14 holds the signal level of the reproduction signal obtained from the clamp area of each of the four continuous segments in the continuous registers 22 to 25.

An adder circuit (ADD) 26 adds and outputs the digital values held in the registers 22 to 25, and a divider circuit (1/4) 27 divides the output data of the adder circuit 26 into 1/4. Divide into and output. The subtraction circuit (SUB) 28 outputs the output data D of the division circuit 27.
F is subtracted from the input data D _RF of the register 21, whereby the value of the input data D _RF is corrected and the DC fluctuation of the reproduction signal RF is reduced.

That is, in the optical disc device 1, the clamp area can be formed to detect the saturation level of the reproduction signal, so that the DC level of the reproduction signal can be detected based on the reproduction result of the clamp area.

Accordingly, in the optical disc device 1,
By detecting the signal level of the reproduction signal in the clamp area of each segment and subtracting the signal level detection result from the reproduction signal of the subsequent data area, the DC fluctuation of the reproduction signal can be reduced. Therefore, in the magneto-optical disk 2, the standard for birefringence can be relaxed accordingly, and the productivity can be improved.

At this time, in the optical disc device 1, a reproduction signal RF converted into a digital value for Viterbi decoding.
The DC level can be reduced with a simple structure by detecting the signal level of the above and the DC level can be reduced, and the signal level can be corrected with higher accuracy compared to the case where the clamp circuit is simply formed by the analog circuit. be able to.

Further, at this time, in the optical disc device 1, the moving average is detected for the four continuous clamp areas to obtain the correction value DF, and the correction value DF is subtracted from the reproduced signal to thereby obtain the frequency of the data clock. With respect to the sampling frequency of the analog digital conversion circuit 13 consisting of, the DC fluctuation is reduced by limiting the band to a frequency of 1/4, and thus the DC fluctuation is practically sufficient for this type of magneto-optical disk. And the SN ratio of the correction value DF is further improved so that DC fluctuations are not erroneously corrected.

By the way, in the case of preventing the DC fluctuation as described above, there are cases where a defect, a scratch, a dust and the like exist in the clamp area, and in this case, the correct saturation level cannot be detected in the clamp area. Therefore, in this embodiment, the data detection circuit 15 detects the signal level difference RLVL (FIG. 2) between the maximum value and the minimum value of the reproduction signal based on the reproduction result of the reference area, and this signal level difference R
Viterbi decoding is performed on the basis of LVL to decode reproduced data, and the detected signal level difference RLVL is separately output to the system control circuit 16.

The system control circuit 16 divides this signal level difference RLVL by a predetermined value N to obtain a reference level RLVL.
/ N is generated, and the clamp circuit 14 generates the reference level R
Based on LVL / N, it is judged whether or not the reproduction signal can be correctly detected. That is, the clamp circuit 14 reproduces between two consecutive clamp areas by subtracting the output data of the registers 21 and 22 by the subtraction circuit (SUB) 30 and converting it to an absolute value by the absolute value conversion circuit (ABS) 31. The signal level difference of the signal RF is detected.

Further, the clamp circuit 14 inputs the output data of the absolute value conversion circuit 31 and the reference level RLVL / N to the comparison circuit 32 and outputs the comparison result, so that the reproduction signal exceeds the reference level RLVL / N. When the RF signal level greatly changes, it is determined that the reproduction signal cannot be correctly detected, and the comparison output DEF is raised. As a result, the clamp circuit 14 outputs the comparison output DEF to the AND circuit 34 via the NAND circuit 33, and controls the output of the second clamp pulse CL2 to the register 22 to stop the output of the register 22. Retain the captured data as it is.

As a result, the clamp circuit 14 pre-holds the reproduction result when the reproduction signal cannot be correctly detected due to a defect, a scratch, etc., so that the DC fluctuation is not erroneously corrected. .

In the clamp circuit 14, the comparison output of the comparison circuit 32 continuously rises at the start of operation, seek, off-track, and data recording, whereby the erroneous digital value D _RF is registered in the register 22.
Therefore, there is a possibility that it may not be possible to rise to the correct operating state after all. Therefore, in this embodiment, the pre-hold is released in such a case.

That is, in this embodiment, the PLL circuit 8
Is the lock signal S when the data clock DCK and the servo clock SCK are generated by locking at the pitch formation cycle formed in the reference area and the servo area.
While outputting VLOCK, the servo control circuit 11
Outputs the servo lock signal SVLOCK when the tracking control can be correctly performed.

The clamp circuit 14 outputs the lock signal SV.
The logical sum of LOCK and the servo lock signal SVLOCK is obtained, and this logical sum SVLOCK is input to the NAND circuit 33. As a result, the clamp circuit 14 operates the register 22 with the second clamp pulse CL2 even when the seek output, the off-track, the operation start, and the comparison output DEF of the comparison circuit 32 rises. The pre-hold operation is released by.

Further, the clamp circuit 14 is the comparison output D of the comparison circuit 32 in the defect mask circuit 40 shown in FIG.
By masking EF, the pre-hold operation is canceled when the comparison output DEF rises four times in succession. That is, in this type of magneto-optical disk, the probability of continuous scratches, dust, and defects occurring in the four clamp areas is extremely low. In this case, the optical disk device 1
Since the recording operation is performed, it can be determined that the signal level of the reproduction signal cannot be correctly detected.

Further, in this case, it can be considered that the optical disk device 1 rises to the state where the tracking control can be correctly performed after the seek and the off-track, and the reproduction signal level can be correctly detected, and further the operation is started. After or after switching from recording mode to playback mode,
It can be considered that the reproduction signal level can be correctly detected.

Therefore, in the clamp circuit 14, the defect mask circuit 40 outputs the second clamp pulse CL.
The registers (REG) 41 to 44 which operate at 2 are connected in series, and the comparison output DEF of the comparison circuit 32 is set to this register (R
EG) 41 to 44 are sequentially transferred. Further, the defect mask circuit 40 outputs the outputs of the registers 41 to 44 to the NAND circuit 45 and outputs the output signal of the NAND circuit 45 to the NAND circuit 33.

As a result, in the clamp circuit 14,
When the servo system etc. rises to the locked state correctly and the correct reproduction signal can be detected, the register 2
Correct the correction value D by capturing the output data D _{RF in} 2 to 25
The F value can be detected, so that the DC value can be corrected with this correction value to sufficiently and surely reduce the DC value.

(3) Effects of the Embodiments According to the above configuration, based on the reproduction result of the clamp area formed after the servo area, the reproduction results of the clamp area are moving averaged to detect the DC fluctuation of the reproduction signal. Then
By correcting the signal level of the reproduction signal based on this detection result, the DC level of the reproduction signal can be markedly reduced as compared with the conventional case. At this time, the DC level can be surely corrected by detecting a defect or the like and pre-holding it, and further canceling the pre-holding with reference to the servo lock signal and the result of continuous defect detection.

(4) Other Embodiments In the above-described embodiment, the clamp circuit 14 detects the correction value DF by adding successive averaging results and averaging them. The present invention is not limited to this, and as shown in FIG. 6, the correction value DF may be detected by correcting only the change in the subsequently input digital value D _RF . That is, the continuous reproduction signal levels Y _{n-3 to} Y _n and the average value ADD are given by

[Equation 1]

[Equation 2] The average value ADD obtained last time by this
_It can be seen that _n can be corrected with signal levels Y _{n + 1} and Y _n-3 to detect the subsequent average value ADD _{n + 1} . As a result, the clamp circuit 54 connects the register 55 to the subsequent stage of the register 25 and holds the digital value corresponding to Y _n-3 in the equation (2), and the subtraction circuit 56 holds (Y _{n + in the} equation (2)). _1-
Y _n-3 ) is executed.

Further, the clamp circuit 54 includes the adder circuit 26.
The addition result of is added to the register 57, the addition result and the output data of the subtraction circuit 56 are added by the addition circuit 26, and the addition value 4ADD _n obtained last time by this is added to the signal level Y.
_The subsequent addition value 4ADD _{n + 1} is detected after correction with _{n + 1} and Y _n-3 , and this is divided by the division circuit 27 to detect the correction value DF.

Further, in the clamp circuit 54, as shown in FIG.
As shown in, when the operation starts, the second clamp pulse CL
2 (FIG. 7 (A)), the clear pulse CLR1 (FIG. 7 (B)) is lowered, and the contents of the register 57 are cleared. At the same time, in the clamp circuit 54, after clearing the clear pulse CLR2 (FIG. 7B), the clear pulse CLR which is the fifth pulse of the clamp pulse CL2.
2, the adder circuit 26 simply adds the input data D _RF for the first four times so that the correct correction value DF can be detected at the time of rising.

Further, in the above-described first embodiment, the case where the subtraction circuit 30 detects a change between the input and output data of the register 22 to detect an abnormality such as a defect has been described, but the present invention is not limited to this. First, subtract the output data of the division circuit 27 from the input data of the register 22,
An abnormality such as a defect may be detected based on the result of the subtraction.

Further, in the above-mentioned embodiment, the case where the pre-groove is formed on both sides of the clamp area and the data area has been described, but the present invention is not limited to this, and the optical disk device of the sample format in which the pre-groove is omitted. Further, it can be widely applied to optical disc devices other than the sample format.

Further, in the above-mentioned embodiment, the case where the class 1 of the partial response is applied to perform the high density recording and the Viterbi decoding is further described. However, the present invention is not limited to this, and the thermomagnetically recorded data is used. It can be widely applied to various optical disk devices for reproduction.

[0074]

As described above, according to the present invention, the reference area inserted in the disk-shaped recording medium at a predetermined cycle is detected, and the reproduction signal is obtained with the signal level of the reproduction signal obtained from the reference area as a reference. By correcting this signal level, it is possible to select this reference area and reduce the DC fluctuation of the playback signal sufficiently. Furthermore, by pre-holding the correction value as necessary, the DC fluctuation can be reliably suppressed. An optical disk device that can be reduced can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing an optical disk device according to an embodiment of the present invention.

FIG. 2 is a schematic diagram for explaining the magneto-optical disk.

FIG. 3 is a schematic diagram used for explaining a clamp area.

FIG. 4 is a block diagram showing a clamp circuit.

FIG. 5 is a block diagram showing a defect mask circuit.

FIG. 6 is a block diagram showing a clamp circuit according to another embodiment.

FIG. 7 is a signal waveform diagram for explaining the operation.

[Explanation of symbols]

1 ... Optical disk device, 2 ... Magneto-optical disk, 3 ...
Spindle control circuit, 7, 13 ... Analog digital conversion circuit, 8 ... PLL circuit, 9 ... Timing generator, 14, 54 ... Clamp circuit, 15 ... Data detection circuit, 16 ... System control circuit.

Claims (7)

[Claims] 1. An optical disk device for reproducing recorded data thermomagnetically recorded on a disk-shaped recording medium, irradiating the disk-shaped recording medium with a light beam, and receiving reflected light obtained from the disk-shaped recording medium, A reproduction signal detecting unit that outputs a reproduction signal whose signal level changes in accordance with the change of the polarization plane of the reflected light, an analog digital conversion circuit that converts the reproduction signal into a digital signal, and a signal level of the digital signal A signal level correction circuit for correcting and outputting, and a decoding circuit for decoding the recording data on the basis of the digital signal corrected by the signal level correction circuit, the signal level correction circuit is provided on the disk-shaped recording medium. Corrects by detecting the reference area inserted at a predetermined cycle and detecting the signal level of the reproduction signal obtained from the reference area Give a bell, by correcting the signal level of the reproduction signal in the correction level, the optical disc apparatus characterized by reducing the DC fluctuation of the reproduced signal. 2. A disk-shaped recording medium, wherein a recording area is divided into sectors, the sectors are divided into segments, and a clamp area for holding a signal level of the reproduction signal at a saturation level is formed in a predetermined area of the segment. Then, the desired data can be recorded in the following area, and the signal level correction circuit detects the signal level of the reproduction signal obtained from the clamp area and sets the correction level. The optical disk device according to 1. 3. The signal level correcting circuit pre-holds the correction level to set the signal level of the reproduction signal when the signal level of the reproduction signal obtained from the clamp area changes above a predetermined reference level. The optical disc device according to claim 2, wherein the optical disc device is corrected. 4. The disk-shaped recording medium allocates one of the segments in the sector to a reference area,
A reference pattern in which the reproduction signal changes to a maximum value and a minimum value is recorded in the reference area, and the signal level correction circuit detects a signal level difference between the maximum value and the minimum value of the reproduction signal, The optical disk device according to claim 3, wherein the reference level is set on the basis of a signal level difference. 5. The signal level correction circuit sets the correction level by moving averaging a signal level of a reproduction signal obtained from the reference area a predetermined number of times. The optical disk device according to claim 3 or 4. 6. The optical disk device has a predetermined drive circuit, the drive circuit drives the disk-shaped recording medium, controls tracking of the light beam, and further is a reference of the analog digital conversion circuit. If a signal is generated and one of the above operations cannot be performed correctly, an error signal is output, and the signal level correction circuit cancels the pre-hold operation when the error signal is output. The optical disk device according to claim 3, claim 4 or claim 5. 7. The signal level correction circuit cancels the pre-hold when the signal level of a reproduction signal obtained from the clamp area continuously changes above the reference level a predetermined number of times or more. The optical disk device according to claim 3, claim 4, claim 5, or claim 6.