JPH07320402A - Optical disk reproducing device - Google Patents

Abstract

PURPOSE:To exclude the influence of a defect by sampling-and-holding the level of a reproduced signal at every prescribed cycle and holding the value of the sample-and-hold of a previous period in the case the defect is present in the area for detecting the DC. level of a disk. CONSTITUTION:A sample-and-hold (an SH) circuit 50 holds the signal level of the reproduced signal S10 of the clamp area of each segment to output it as a DC. level signal S30. An SH circuit 51 holds a present DC. level signal S30 when a delay signal 31 is '1' and holds the DC. level signal S30 of a previous period when the delay signal S31 is '0'. A differential amplifier circuit 53 components the DC. level fluctuation of the reproduced signal S10 due to the dispersion of the film thickness of the disk to make it an output signal S16 by the DC. level signal S32. A comparator circuit 64 allows the delay timing signal S31 to be '0' by judging that the defect is present in the clamp area when the difference between DC. level signals S30, S32 is greater than a reference voltage 65.

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 Technology (FIG. 4) Problem to be Solved by the Invention Means for Solving Problem (FIGS. 1 to 3) Action (FIGS. 1 to 3) Example (1) Overall Configuration (FIG. 1) (2) Configuration of gain controller (FIG. 3) (3) Operation and effect of embodiment (FIGS. 1 to 3) (4) Other embodiment Effect of the invention (FIGS. 1 to 3)

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk reproducing apparatus, and is suitable for application to an optical disk reproducing apparatus for reproducing desired recording data recorded by a thermomagnetic recording method.

[0003]

2. Description of the Related Art Conventionally, as an optical disk reproducing apparatus of this type, a thermomagnetic recording method was applied to record data, and the Kerr effect was used to reproduce thermomagnetically recorded data. There is something. That is, this optical disk reproducing apparatus continuously irradiates the optical disk with a light beam in a state in which a predetermined modulation magnetic field is applied, thereby sequentially applying the thermomagnetic recording method to the irradiation position of the light beam to form a perpendicular magnetization region. However, desired data can be recorded.

During reproduction, the reflected light obtained by irradiating the recording surface of the optical disk with a light beam causes the direction of the plane of polarization of the reflected light to slightly rotate in the normal and reverse directions depending on the magnetization polarity of the light beam irradiation position. Therefore, it is decomposed into light components in two directions in which the directions of the polarization planes change complementarily. As a result, the optical disc reproducing device receives the light components in these two directions by the light receiving element, and the reproduction signal whose signal level changes according to the magnetization polarity of the light beam irradiation position based on the light amount difference between the two light receiving elements. The desired signal can be reproduced by processing the reproduced signal with a predetermined signal processing circuit.

In this kind of optical disk recording medium, a substrate is formed by molding polycarbonate or the like, and a perpendicular magnetization film is formed on this substrate. However, there is a characteristic that the optical disk surface changes due to variations in the film thickness during the molding of the optical disk, and thus the magnitude of birefringence changes in each part of the substrate. As a result, the DC level of the reproduction signal that changes following this change in birefringence fluctuates, and the frequency bandwidth of the DC level becomes wider, so that the DC level of the reproduction signal is in the original frequency band of the reproduction signal. There are overlapping features.

Therefore, in the optical disc reproducing apparatus, it is necessary to operate the sample hold circuit so as to sufficiently suppress the fluctuation of the DC level on which the frequency band is superimposed. For this reason, the conventional optical disc reproducing apparatus samples and holds the direct current level of the reproduced signal at a constant cycle when processing the reproduced signal, so that the direct current level of the reproduced signal generated by the change of the birefringence in each part of the optical disc. Fluctuations are canceled by the sampled and held DC level. As a result, the reproduced data can be surely detected.

That is, the conventional optical disk reproducing apparatus has a DC level correcting circuit 1 as shown in FIG.
In the level correction circuit 1, a reproduction signal S1 obtained from an optical pickup (not shown) is output to the non-inverting input terminals of the sample hold circuit 3 and the differential amplifier circuit 4 via the buffer circuit 2. The sample and hold circuit 3 is provided at the beginning of each segment, and is synchronized with the sample signal S2 rising at each start position of the area for DC level detection following the data area (hereinafter referred to as a clamp area). Repeat on or off.

As a result, the sample-hold circuit 3 charges and discharges the hold capacitor 7 provided via the resistor 6 with a voltage equal to the output voltage of the reproduction signal S1, and the voltage charged in the hold capacitor 7 is passed through the operational amplifier 8. And outputs it as a DC level signal S3 to the inverting input terminal of the differential amplifier circuit 4. The differential amplifier circuit 4 is configured to remove the low frequency component of the reproduction signal S1 by subtracting the output voltage of the DC level signal S3 from the output voltage of the reproduction signal S1 and outputting it as the reproduction signal S4. .

[0009]

However, when the sample and hold circuit is operated so as to sufficiently suppress the fluctuation of the direct current level of the reproduced signal, the sampling point provided at a predetermined position on the disk is damaged. If there is a defect (defect) such as dust, the signal level of the reproduction signal at the sampling point may change abruptly. Therefore, if it is attempted to correct the DC level of the reproduction signal based on the value of the sampling point, the reproduction data may not be detected only in the sampling cycle at the sampling point.

The present invention has been made in consideration of the above points, and an optical disk reproducing apparatus capable of surely reproducing data even if a defect exists in the area for detecting the DC level of the disk-shaped recording medium. Is to propose.

[0011]

In order to solve such a problem, according to the present invention, in an optical disk reproducing apparatus 10 for reproducing record data from a disk-shaped recording medium 11 in which record data is thermomagnetically recorded, a disk-shaped recording is performed. Medium 1
1 is irradiated with a light beam to output a first reproduction signal S10 for obtaining a signal level according to the light direction of the reflected light obtained from the disk-shaped recording medium 11, and a first pick-up means 12 for every predetermined period. DC voltage correction circuits 50, 51, 58, 64, 6 which take in the signal level of the reproduced signal S10 of No. 1, sample and hold the DC level, and output the DC level S32 sampled and held at the present or previous period.
6, 59 and DC voltage correction circuits 50, 51, 58, 6
The difference between the output voltages of the first reproduction signal S10 and the DC level S32 sample-held at the present or the previous period of 4, 66, 59 is calculated, and the second reproduction signal S having the difference voltage is obtained.
A differential amplifier circuit 53 for outputting 16 and a DC voltage correction circuit 50 if no defect DF exists in the area CL for detecting the DC level of the disk-shaped recording medium 11.
51, 58, 64, 66, 59 are the first reproduction signals S10
Area for detecting the DC level of the disk-shaped recording medium 11 by sampling and holding the DC level of the disk-shaped recording medium 11 every predetermined period.
When the defect DF exists in L, the DC voltage correction circuit 5
For 0, 51, 58, 64, 66, 59, the voltage value sampled and held in the previous period is held as it is.

[0012]

When the defect DF exists in the area CL for detecting the DC level of the disk-shaped recording medium 11, the output voltage of the first reproduction signal S10 changes abruptly.
The second sample and hold circuit 51 holds the voltage value sampled and held in the previous period as it is, and outputs it as a DC level S32. As a result, the second reproduction signal S16 obtained by detecting and correcting the variation in the DC level of the first reproduction signal S10 based on the difference result between the DC level S32 and the first reproduction signal S10 is obtained. Even if the defect DF exists in the area CL for detecting the DC level of the disk-shaped recording medium 11, the data can be surely reproduced.

[0013]

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

(1) Overall Structure In FIG. 1, reference numeral 10 denotes an optical disk reproducing device as a whole, which is a light-emitting device by applying a magnetic field modulation method, that is, a method of modulating a magnetic field at high speed according to an input signal to determine the direction of magnetization. The desired data is thermomagnetically recorded on the magnetic disk 11, and the recorded data is reproduced. That is, the magneto-optical disk 11
Is designed to form a magnetic film on a predetermined disk-shaped substrate, whereby thermomagnetic recording can be applied to thermomagnetically record desired data.

Here, the magneto-optical disk 11 forms recording tracks concentrically, divides each recording track into sector units, and further divides each sector into a plurality of segments. Further, as shown in FIG. 2, the magneto-optical disk 11 allocates each segment of this sector to a data area (DATA). In this case, the data area contains not only the data but also the address (FIG. 2 (A)).

Further, the magneto-optical disk 11 forms a clamp area (CL) at the beginning of each segment, and the optical disk reproducing apparatus 10 detects the signal level of the clamp area to detect the DC level of the reproduced signal. The change can be detected. That is, the optical disk reproducing apparatus 10 is adapted to detect and correct the DC level fluctuation of the reproduced signal at the head of each segment of the magneto-optical disk 11 and the area following the data area.

In the optical disk reproducing apparatus 10, the optical block 12 drives the magneto-optical disk 11 to rotate at a predetermined rotational speed by the spindle motor 13, and in this state, irradiates the magneto-optical disk 11 with a light beam, and thereby the desired signal is emitted. Is recorded and reproduced, and a tracking error signal, a focus error signal, etc. can be generated.
That is, in the optical block 12, the optical pickup 1
The operation of the laser diode built in 4 is LD (Laser Di
ode) The driver 15 controls the optical pickup 14, and the actuator 16 drives the optical pickup 14 to irradiate the magneto-optical disk 11 with a light beam.

As a result, at the time of data recording, the magnetic field head drive unit 17 drives the magnetic field generating coil 18 based on desired recording data, so that the magneto-optical disk 11 concerned.
A predetermined modulation magnetic field is applied to the irradiation position of the light beam, and a desired data can be recorded by applying the magnetic field modulation method. Further, at the time of reproduction, the optical pickup 14 decomposes the reflected light obtained by irradiating the light beam into light components in two directions in which the directions of the polarization planes are changed complementarily and decomposes them into a predetermined light receiving element incorporated in the optical pickup 14. It is designed to receive light. I-V (current voltage)
The conversion unit 19 converts the output current of the light receiving element into a current voltage, and then performs a predetermined addition process and a subtraction process to obtain 2
It is designed to generate one reproduction signal.

That is, the IV conversion section 19 forms a reproduction signal (hereinafter referred to as MO signal) S10 of the data thermomagnetically recorded based on the light reception result of the optical pickup 14 and the data recorded by forming the pit. A reproduction signal (hereinafter referred to as an RF signal) S11 is generated, and the MO signal S10 and the RF signal S11 are output to the gain controllers 20 and 21, respectively. At that time, the IV converter 19 generates a focus error signal S12, a slide error signal S13, and a tracking error signal S14 based on the light reception result of the optical pickup 14, and outputs them to the servo controller 22. A front auto power control signal S15 for controlling the laser power of the LD driver 15 is generated and output to an ALPC (Auto Laser Power Control) 23.

The gain controller 20 controls the MO signal S1.
The MO signal S16 obtained by clamping 0 is output to the pulse detection unit 24. The pulse detection unit 24 detects the pulse of the MO signal S16, and then the PLL (Phase Locked Loo
p) unit 25 and R / W (Read / Write) unit 26. Further, the gain controller 21 outputs the RF signal S17 obtained by clamping the RF signal S11 to the pulse detection unit 27, and the pulse detection unit 27 outputs the RF signal S1.
After pulse detection of 7, the PLL unit 25 and the R / W unit 26
Output to.

The PLL section 25 has a phase comparison section 28 and a voltage control type transmission section (hereinafter referred to as VCO section) 29. The PLL unit 25 detects the phase difference between the output signals from the pulse detection units 24 and 27 that are input to the phase comparison unit 28 and the transmission output of the VCO unit 29, and thereby the VCO unit 2 concerned.
9 is used to generate the phase synchronization signal S18 which is a data clock synchronized with the output signals from the pulse detectors 24 and 27.

As a result, the PLL section 25 uses the phase synchronization signal S18 as a reference to lock signals S19 and S from the VCO section 29 to the gain controllers 20 and 21, respectively.
The phase synchronization signal S18 is output to the R / W unit 26 while being output as 20. Further R / W
The section 26 is configured to output a signal generated based on the phase synchronization signal S18 and the output signals from the pulse detection sections 24 and 27 to the timing generator (TG) 30.

The timing generator 30 generates a clamp pulse with reference to the signal output from the R / W unit 26 via the bus 31, and uses the clamp pulse as a timing signal S24, respectively, in the gain controller 20.
And 21. Further, the timing generator 30 uses the phase synchronization signal S18 output from the PLL unit 25 via the bus 31 as a reference, and the reference signals obtained with the extracted data clock as a reference, respectively, as the data clock signal S25. It is adapted to be sent to the gain controllers 20 and 21.

Incidentally, the data clock signal S25 divides the recording area of the magneto-optical disk 11 into concentric circles, and switches the data clock in each area, that is, the outer peripheral side and the inner peripheral side (hereinafter, this is zoned. Therefore, it is a signal that is output in order to synchronize with the application period of the modulation magnetic field in each of the outer peripheral side region and the inner peripheral side region.

Further, the R / W unit 26 has a sector mark (S
M) detection, data detection, data modulation / demodulation, and address data (ID) decoding are executed.
Further, the R / W unit 26 uses the bus 31 to control the controller 3
2 and is connected to the controller 32 to input / output data to / from the controller 32. Further, the controller 32 is a SCIS bus 3
It is connected via 4 to the host computer 35.

Here, when a command for writing desired data is sent from the host computer 35 to the controller 32, the controller 32 specifies a sector in the recording system of the optical disk reproducing apparatus 10 and also regarding the desired data. The error correction code (ECC) is encoded and then transferred to the R / W unit 26.

The R / W section 26 sends control signals S21 and S22 to the magnetic field head drive section 17 and the LD driver 15 respectively in synchronization with the data clock from the PLL section 25, and based on the control signals S21 and S22. The desired data is recorded on the magneto-optical disk 11 by controlling the magnetic field head drive section 17 and the LD driver 15 by means of the magnetic field head drive section 17.

At this time, the ALPC 23 is connected to the IV converter 19
The laser power of the LD driver 15 is controlled by sending the control signal S23 obtained based on the front auto power control signal S15 output from the LD driver 15 to the LD driver 15.

Further, the servo control section 22 has an IV conversion section 19
The control signal S26 obtained based on the focus error signal S12, the slide error signal S13, and the tracking error signal S14 output from the actuator 16
To control the actuator 16. As a result, the recording system of the optical disc reproducing apparatus 10 can control and drive the optical pickup 14 to seek the optical pickup 14 to a designated sector.

On the other hand, on the other hand, the host computer 3
When a command for reading desired data is sent from the controller 5 to the controller 32, the controller 32 designates a sector in the reproducing system of the optical disk reproducing device 10. The reproducing system of the optical disc reproducing apparatus 10 controls and drives the optical pickup 14 under the control of the servo control unit 22 to seek the optical pickup 14 to a designated sector.

The R / W unit 26 converts the reproduced signal into binary data and then transfers it to the controller 32. The controller 32 decodes the error correction code for the data and then transfers the data to the host computer 35. As a result, the reproducing system of the optical disc reproducing device 10 can reproduce desired data recorded on the magneto-optical disc 11.

(2) Configuration of Gain Controller As shown in FIG. 3, the gain controller 20 includes a first sample-hold (S / H) circuit 5 for sampling and holding the DC level of the MO signal S10 input every predetermined period.
0 and a second sample hold (S / S) that samples and holds the DC level of the first S / H circuit 50 and outputs the DC level sampled and held at the present or previous period.
H) circuit 51. And gain controller 2
0 is the difference between the output voltage of the MO signal S10 and the DC level of the second S / H circuit 51, and the variation of the DC level of the MO signal S10 is detected and corrected based on the difference result. The signal S16 is output.

First, the gain controller 20 outputs the input MO signal S10 to the first S signal via the buffer circuit 52.
It is sent to the / H circuit 50 and the differential amplifier circuit 53. The first S / H circuit 50 samples and holds the DC level of the MO signal S10 when the timing signal S24 which is output from the R / W unit 26 (FIG. 1) and rises at each start position of each clamp area is given. To the second S / H circuit 51 and the differential amplifier circuit 58.

That is, the first S / H circuit 50 is provided via the resistor 55 to a voltage equal to the output voltage of the MO signal S10 by repeatedly turning on and off the switch 54 in synchronization with the timing signal S24. The hold capacitor 56 is charged and discharged. As a result, the first S / H circuit 5
0 outputs the voltage charged in the hold capacitor 56 to the non-inverting input terminals of the second S / H circuit 51 and the differential amplifier circuit 58 as a DC level signal S30 via the operational amplifier 57.

The second S / H circuit 51 has a delay timing signal S3 output from the D-type flip-flop circuit 59.
When 1 is applied, the DC level signal S30 output from the first S / H circuit 50 is sampled and held and applied to the differential amplifier circuits 53 and 58. That is, the second S / H circuit 51 uses the delay timing signal S31.
By repeatedly turning the switch 60 on and off in synchronization with the hold capacitor 62, a hold capacitor 62 provided via the resistor 61 to a voltage equal to the output voltage of the DC level signal S30.
Charge and discharge. As a result, the second S / H circuit 51 causes the voltage charged in the hold capacitor 62 to change to the operational amplifier 6
The differential amplifier circuit 5 as a DC level signal S32 via
3 and the inverting input terminal of the differential amplifier circuit 58.

Here, the delay timing signal S31 (see FIG.
(G)) is delayed by two clocks from the timing of raising the timing signal S24 (FIG. 2 (D)) on the basis of the trigger of the D-type flip-flop circuit 59 and is output. As a result, the delay timing signal S3
When 1 is given, the voltage value held by the first S / H circuit 50 is stable and the second S / H circuit 50 is stable.
The circuit 51 is adapted to sample and hold the DC level signal S30.

When the delay timing signal S31 is not given, the second S / H circuit 51 is operated by the first S / H circuit.
One voltage clamp period before the DC level signal S30 is output from the circuit 50, the voltage value held by the second S / H circuit 51 is directly output as the DC level signal S32. By the way, the magneto-optical disk 11
Due to variations in film thickness during molding of
The DC level of the MO signal S10 fluctuates, so that the level of the output voltage of the DC level signal S30 is slightly fluctuating in each clamp cycle, and along with this, the level of the output voltage of the DC level signal S32 also fluctuates. is there.

The differential amplifier circuit 58 is the first S / H circuit 5
DC level signal S30 output from 0 and the second S / H
The difference between the output voltage and the DC level signal S32 output from the circuit 51 is calculated, and this difference is output to the comparator circuit 64 as the output signal S33. The comparator circuit 64 compares the output voltage of the output signal S33 with the offset voltage of the offset power supply 65 and outputs the comparison result to the AND circuit 66 as the comparison output signal S34. Here, the offset voltage is set to a predetermined value larger than the output voltage of the output signal S33 in the clamp area CL where the defect DF does not exist.

In the clamp area CL where the defect DF does not exist, the difference between the output voltage of the output signal S33 and the offset voltage has a relatively small value. As a result, the comparator circuit 64 outputs the comparison output signal S34 in the state of rising to the logic "H" to the input terminal of the AND circuit 66.

The other input terminal of the AND circuit 66 is supplied with the timing signal S24. When both the timing signal S24 and the comparison output signal S34 are in the input state, the AND circuit 66 outputs the AND output signal S35. This is applied to the data input terminal of the D-type flip-flop circuit 59. Further, the D-type flip-flop circuit 59 receives the data clock signal S25 output from the timing generator 30 (FIG. 1) at its clock input terminal and also outputs the lock signal S output from the PLL section 25 (FIG. 1).
19 is received at the synchronizing pulse input terminal.

That is, in the D-type flip-flop circuit 59, when the PLL section 25 is locked, the lock signal S19 falls to the logic "L" (FIG. 2 (B)). In this state, the D-type flip-flop circuit 59 triggers the rising edge of the data clock signal S25 to delay the output timing of the AND output signal S35 by two clocks, and outputs the delayed timing signal S31 from the Q output terminal. The output is provided to the switch 60 of the second S / H circuit 51.

(3) Operation and effects of the embodiment With the above configuration, when the defect DF exists in the clamp area CL on the magneto-optical disk 11 as shown in FIG. 2, the time t at the start position of the clamp area CL.
_{At 1} , the output voltage of the MO signal S10 rapidly changes due to damage of the clamp area CL due to the defect DF (FIG. 2 (C)).

The lock signal S output from the PLL unit 25
In the state in which 19 is falling (FIG. 2 (B)), that is, in the state in which the defect DF can be detected, the first S / H
The circuit 50 synchronizes with the timing signal S24 (FIG. 2 (D)) that rises at each start position of each clamp area CL.
The DC level of the O signal S10 is sampled and held, and the result is used as a DC level signal S30 for the second S / H circuit 5
1 and the differential amplifier circuit 58. In this case, the DC level signal S30 has a remarkably high output voltage from the time point t ₁ to the time point t ₂ one clamp cycle after the MO signal S10 (FIG. 2 (E)).

The second S / H circuit 51 samples and holds the DC level signal S30 in synchronization with the delay timing signal S31, and outputs the result as a DC level signal S32 to the differential amplifier circuit 58. At this time, the DC level signal S
32 by being output to the first clamping period before the DC level signal S30, the output voltage of the DC level signal S32 at time point t ₁ is a DC level signal S30 in the first clamping period before time t ₁ the sample and hold the time It has the same value as the output voltage (FIG. 2 (H)).

The differential amplifier circuit 58 takes the difference between the output voltages of the DC level signal S30 and the DC level signal S32 at the time point t ₁ , and outputs it as the output signal S33 to the comparator circuit 64. At this time, the DC level signal S3
The output voltage of 0 has a remarkably high value between the time point t ₁ and one clamp cycle (FIG. 2 (E)), and the DC level signal S
Since the output voltage of 32 becomes the same value as the output voltage one clamp cycle before the time point t ₁ (FIG. 2 (H)), the output voltage of the output signal S33 becomes almost the same value as the output voltage of the DC level signal S30. Become.

The comparator circuit 64 outputs the output signal S33.
When the output voltage of the output signal S33 is compared with the predetermined offset voltage, the difference between the output voltage of the output signal S33 and the predetermined offset voltage is significantly increased, so that the comparison output signal S3
4 is in the state of falling to the logic "L" between the time point t ₁ and one clamp period (FIG. 2 (F)). As a result, the comparator circuit 64 outputs the comparison output signal S34 to the AND circuit 66.
Do not output to. As a result, the AND circuit 66 does not output the AND output signal S35 to the D-type flip-flop circuit 59.

Therefore, the D-type flip-flop circuit 59 is
By not outputting the delay timing signal S31 to the second S / H circuit 51 at the time point t ₁ (FIG. 2 (G)),
The S / H circuit 51 does not sample and hold the DC level signal S30. As a result, the second S / H circuit 51 receives the second S / H circuit 51 one clamp period before the time point t _1.
The voltage value held by is held as it is, and this is output to the differential amplifier circuit 53 as a DC level signal S32.

As a result, the differential amplifier circuit 53 takes the difference between the DC level signal S32 and the MO signal S10, and the gain controller 20 detects and corrects the change in the DC level of the MO signal S10 based on the difference result. Will be M
The O signal S16 is output (FIG. 2 (I)).

According to the above configuration, the gain controller 20 samples and holds the DC level of the input MO signal S10 and outputs the DC level sampled and held at the present time or the previous period. That is, when the defect DF does not exist in the clamp area CL on the magneto-optical disk 11, the gain controller 20 samples and holds the DC level of the MO signal S10 every predetermined period. On the other hand, when the defect DF exists in the clamp area CL on the magneto-optical disk 11, the gain controller 20 holds the voltage value sampled and held in the previous period as it is.

As a result, the gain controller 20 causes the DC level after the sample and hold and the MO signal S1.
By taking the difference between the output voltage and 0, it is possible to output the MO signal S16, which is obtained by detecting and correcting the variation of the DC level of the MO signal S10 based on the difference result, and thus the presence or absence of the defect DF. Therefore, the data can be reproduced without fail.

(4) Other Embodiments In the above embodiment, the relationship between the timing signal S24 output from the timing generator 30 and the delay timing signal S31 output from the D-type flip-flop circuit 59 is delayed. The timing signal S31 is 2 times longer than the timing when the timing signal S24 rises.
The case where the clock is delayed and output is described, but the present invention is not limited to this, and the delay timing signal S31 is a number other than 2 than the timing at which the timing signal S24 rises, for example, a number of 1 or 3 or more. The present invention can be applied to the case where the output is delayed by the clock. In this case, the second S / H circuit 51 can sample and hold the DC level signal S30 while the voltage value held by the first S / H circuit 50 is stable.

[0052]

As described above, according to the present invention, the signal level of the first reproduction signal is fetched at every predetermined period, the DC level is sampled and held, and the DC level sampled and held at the current or previous period is output. A DC voltage correction circuit is provided, and when there is no defect in the area for detecting the DC level of the disk-shaped recording medium, the DC level of the first reproduction signal is sampled and held every predetermined period to If there is a defect in the area for DC level detection, the voltage value sampled and held in the previous period is held as it is, so that the area for DC level detection in the disk-shaped recording medium is defective. It is possible to realize an optical disc reproducing device capable of surely reproducing data even when there is a disc.

[Brief description of drawings]

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

FIG. 2 is a signal waveform diagram for explaining the operation when a defect occurs.

FIG. 3 is a block diagram showing a gain controller.

FIG. 4 is a block diagram showing a DC level correction circuit of a conventional optical disk reproducing device.

[Explanation of symbols]

10 ... Optical disk reproducing device, 11 ... Magneto-optical disk, 12 ... Optical block, 14 ... Optical pick-up,
19 ... I-V conversion section, 20, 21 ... Gain controller, 25 ... PLL section, 26 ... R / W section, 30 ...
Timing generator, 32 ... Controller, 35
...... Host computer, 50 …… First S / H circuit,
51 ... Second S / H circuit, 53, 58 ... Differential amplifier circuit, 59 ... D-type flip-flop circuit, 64 ... Comparator circuit, 66 ... AND circuit.

Claims (3)

[Claims] 1. An optical disk reproducing apparatus for reproducing the recorded data from a disk-shaped recording medium on which the recorded data is thermomagnetically recorded, wherein the disk-shaped recording medium is irradiated with a light beam to obtain from the disk-shaped recording medium. An optical pick-up means for outputting a first reproduction signal for obtaining a signal level according to the light direction of the reflected light, and a signal level of the first reproduction signal is taken in every predetermined period, and a DC level is sampled and held, A DC voltage correction circuit that outputs a DC level sampled and held during the current or previous period, and a difference between the output voltage of the DC level that is sampled and held during the present or previous period of the DC voltage correction circuit and the output voltage of the first reproduction signal is obtained. And a differential amplifier circuit that outputs a second reproduction signal having the differential voltage, and detects the DC level of the disk-shaped recording medium. If there is no defect in the area (1), the DC voltage correction circuit samples and holds the DC level of the first reproduction signal at every predetermined period, and the DC level is detected in the area for detecting the DC level of the disk-shaped recording medium. When there is a defect, the DC voltage correction circuit holds the voltage value sampled and held in the previous period as it is, and the optical disk reproducing device. 2. The DC voltage correction circuit includes a first sample and hold circuit for taking in a signal level of the first reproduction signal at a predetermined cycle and sampling and holding the DC level, and a first sample and hold circuit. A second sample-and-hold circuit for sampling and holding the direct-current level and outputting the sampled and held direct-current level; a direct-current level of the first sample-and-hold circuit and a direct-current level of the second sample-and-hold circuit; Difference of the output voltage of, and compare the difference voltage with a predetermined reference voltage,
The optical disk reproducing device according to claim 1, further comprising a control unit that determines and controls whether or not to sample and hold the second sample and hold circuit based on the comparison result. 3. The timing at which the first sample-and-hold circuit samples and holds the first reproduced signal at predetermined intervals is set by the second sample-and-hold circuit by the first and second signals.
3. The optical disk reproducing apparatus according to claim 2, wherein the DC level of the sample hold circuit is shifted by a predetermined time from the timing of sample hold.