JPH0589476A - Information reproducing device - Google Patents

Abstract

PURPOSE:To execute highly reliable information reproduction by controlling favorably a threshold at the time of shaping the waveform of a magneto-optical disk reproduced signal even in the case that the amplitude of the reproduced signal varies and in the case that there is a defect on a recording medium. CONSTITUTION:The positive and negative direction peak values of the reproduced signal of specified data recorded before a data area are made initial values, and the maximum value and the minimum value of the amplitude of the reproduced signal are held by a peak detection circuit 4. A threshold to be the center of the amplitude of the reproduced signal is generated by a threshold generation circuit 5, and the waveform is shaped by a waveform shaper 6. Besides, since a defect detection circuit 1 observes a pit signal, and in the case that there is the defect in the recording medium, it outputs a control signal to cut out the input of the peak detection circuit 4 to a switch 3, the peak detection circuit 4 never holds erroneous peak value due to the defect of the recording medium, and the threshold generation circuit 5 does not receive the influence of the defect of the recording medium.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention, when reproducing recorded information from a magneto-optical disk device, changes the reproduction signal amplitude depending on the characteristics of the recording medium and the recording / reproducing conditions of the magneto-optical disk device, and the optical recording medium. The present invention relates to an information reproducing apparatus for appropriately controlling a threshold value for waveform shaping of a reproduction signal even when there is a local defect on a magnetic disk and reproducing information with high reliability.

[0002]

2. Description of the Related Art First, a magneto-optical disk device will be described. The magneto-optical disk device is an optical memory device in which a magnetic film having an easy axis of magnetization in a direction perpendicular to the film surface is used as a recording medium and a laser beam is applied to the magnetic film for recording / reproducing or erasing. The following method is known for recording / reproducing in this magneto-optical disk device. At the time of recording, first, the intensity of the focused laser beam is modulated according to the recording signal. The temperature of the magnetic film locally rises due to the laser beam applied to the magnetic film surface of the magneto-optical disk. At the portion where the temperature rises, the coercive force decreases, so that if an auxiliary magnetic field is applied from the outside at the same time, the direction of magnetization becomes the direction of the auxiliary magnetic field and information is recorded.

During reproduction, the surface of the recorded magnetic film is irradiated with linearly polarized laser light having a weaker light intensity than during recording. Then, the reflected light causes an inclination of the plane of polarization due to the magneto-optical effect (Kerr effect) of the magnetic film. This inclination is detected by an analyzer and converted into light intensity, which is detected by a detector to reproduce information.

Conventionally, when reproducing digital information in a magneto-optical disk apparatus, the reproduced signal in which the tilt of the polarization plane is detected is compared with a certain threshold value and waveform shaping is performed to reproduce the digital information. It was However, when the threshold value is fixed, when the reproduction signal amplitude fluctuates depending on the characteristics of the recording medium and the recording / reproducing conditions of the magneto-optical disk device, the reproduction signal amplitude becomes the optimum threshold value. There is a possibility that the digital information will be wrongly reproduced due to a large deviation from the center. In the information reproducing apparatus using the threshold value detection, in order to reproduce the information with high reliability regardless of which modulation code is used, the threshold value is always set optimally for the fluctuation of the reproduced signal amplitude. There is a need.

Therefore, in the information reproducing apparatus as disclosed in JP-A-1-201832, the peak value of the reproduced signal amplitude is sampled by using the sample hold circuit as shown in FIG. A method of dividing the peak voltage Vp from the peak voltage Vp by a predetermined division ratio of the resistors R1 and R2 to obtain a threshold value Vs used for waveform shaping, shaping the analog reproduction signal S1 and reproducing the digital signal S2 is proposed. Has been done. In this known example, only when the reproduction signal amplitude is Vs or more and the tracking error signal is within a predetermined level region, the switch is opened / closed by the control signal to control so as to sample and hold the peak value of the reproduction signal amplitude. A threshold value Vs for performing waveform shaping that follows the fluctuation of the level
Is getting

[0006]

In the known example, the threshold value Vs is obtained by dividing the reproduction signal amplitude peak value Vp by a constant voltage division ratio. The reproduction signal is a characteristic of the recording medium, the magneto-optical disk. It varies depending on the recording and reproducing conditions of the device. Therefore, the reproduction signal amplitude 4 as shown in FIG.
When the voltage division ratio is set so that the threshold value Vs becomes the reproduction signal amplitude center at 1 and the reproduction signal amplitude 41 changes as shown in FIG. There is a problem that the value Vs cannot be set at the center of the reproduced signal amplitude.

2A, the recording film on the track 21 for reproducing data is defective, or the reflectance on the reproducing track 21 as 24 in FIG. 2B. When there is a congenital or acquired local defect such as a decrease in the total reflection signal level, the total reflection signal levels 23 and 25 from the magneto-optical disk are the total reflection signal level Vp when there is no defect.
It decreases as compared with l. As shown in FIG. 3, the total reflection signal 32 is lowered by the disk defect 31, and the magneto-optical signal 33 which is a reproduction signal is also affected. In this case, a peak value due to a disk defect is generated on the reproduction signal, and the threshold value 34 holds an irregular peak value due to the disk defect, not the divided peak value of the normal reproduction signal amplitude. Since the voltage is the divided voltage value, there is a possibility that the threshold value at the center of the normal reproduction signal amplitude that follows will not be obtained, and erroneous waveform shaping such as 35 may be performed. If the magneto-optical disk has a local defect, there is a problem that it is impossible to reproduce information with high reliability.

[0008]

The information reproducing apparatus of the present invention includes a specific data area detecting means for detecting an area in which predetermined pattern data is written under the same condition as the data at the time of data recording, and a specific pattern data reproduction signal amplitude. A peak detection holding means for detecting the peak value of the reproduction signal amplitude and holding the maximum value and the minimum value of the reproduction signal amplitude, and a waveform from the maximum value and the minimum value of the detected peak value. Threshold generating means for generating a threshold for shaping, waveform shaping means for performing waveform shaping from an analog reproduction signal to a binarized digital signal by the threshold, and a magneto-optical disk as a recording medium. If the total reflection signal exceeds a certain range, it is regarded as a disk defect, and a defect detection means for outputting a control signal, and a peak detection holding means by the control signal. To resolve this problem by an information reproducing apparatus having a switch for interrupting the reproduction signal is power.

[0009]

The peak detection holding means for holding the maximum value and the minimum value of the reproduction signal amplitude clears the maximum value and the minimum value held so far by the detection signal of the specific data area detecting means preceding the data recording area. The peak value in the positive / negative direction of the reproduction signal of the specific data recording area is held as an initial value. The playback signal positive / negative peak value in the specific data area is
Since the data area reproduction signal and the recording / reproduction condition are the same, it can be regarded as the maximum value and the minimum value of the data area reproduction signal amplitude. The threshold value generation means generates a threshold value from the maximum value and the minimum value of the reproduction signal amplitude held in the peak detection holding means,
The waveform shaping means performs waveform shaping. Therefore, even if the reproduction signal amplitude varies depending on the characteristics of the recording medium and the recording / reproduction conditions of the magneto-optical disk device, the threshold value can be set to the central value of the reproduction signal amplitude of the data area.

The defect detecting means always observes the total reflection signal, and if the total reflection signal exceeds a certain range, it is considered that there is a defect on the disk and outputs a control signal. Since the switch is opened by the control signal and the reproduction signal is not supplied to the peak detection holding means, the peak detection holding means does not hold the peak value due to the influence of the disc defect as the maximum value or the minimum value, and It is possible to set a threshold value that makes it possible to reproduce information with high reliability.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings by taking as an example the case where an information reproducing apparatus is adopted in a sample servo type magneto-optical disk apparatus.

FIG. 1 is a circuit block diagram of an information reproducing apparatus of the present invention. In FIG. 1, reference numeral 1 denotes a defect detection circuit which monitors a total reflection signal (hereinafter referred to as a pit signal) from a magneto-optical disk and outputs a control signal by considering a disk defect when a variation exceeding a predetermined range exists in the pit signal. Reference numeral 3 is a switch which is turned on and off by a control signal, and 4 is a peak detector circuit, which detects a positive peak value of a magneto-optical signal (hereinafter, MO signal) which is a reproduction signal and holds the maximum value in the positive direction. It comprises a peak detector 7 and a negative peak detector 8 that detects the negative peak value of the MO signal and holds the minimum value. Reference numeral 5 denotes a threshold value generation circuit for generating a threshold value from the maximum value and the minimum value of the MO signal amplitude output from 7 and 8, and an adder 9 for adding the maximum value and the minimum value of the MO signal and its addition. It consists of a divider 10 that divides the result by half. 6 is a waveform shaper for comparing the MO signal with a threshold value and shaping the MO signal into an H, L, or binary digital signal, 11 is a clock pit detector for detecting clock pits from the pit signal, and 12 is a clock pit. A PLL circuit for generating a reproduction clock from the pit signal detected by the detector,
Reference numeral 2 is a specific data area detector which detects a specific data recording area and outputs a detection signal.

In this embodiment, the sector format is shown in FIG.
The sector format of a 5.25-inch sample servo type optical disc as shown in FIG. The servo bytes shown in FIG. 6B are pre-formatted in each segment. The latter half of this servo byte (N
o. In 2), there is a clock pit for extracting a clock, which is detected by the pit signal and used for clock reproduction. The PLL circuit 12 in FIG. 1 multiplies the clock pit cycle detected by the clock pit detector 11 to generate a reproduction clock.

When data recording is performed, the specific pattern data is recorded in the specific data recording area prior to the data recording. The specific data recording area may be arranged at the head of the data area regardless of the location before the data reproduction and does not depend on the sector format. In this embodiment, after the address area, the 3-byte laser control area is used as the specific data recording area. Also, the size of the specific data recording area is not limited to three bytes as long as the peak value of the reproduction signal amplitude can be sufficiently sampled even when the reproduction signal is deteriorated by the band limitation due to the recording / reproduction characteristics. It may be above or below.

As the specific pattern to be written in advance, in this embodiment, the code "1" is continuously written in half of the specific data recording area, and the code "0" is continuously written in the other half as shown in FIG. Was used. Since the reproduction signal of this specific pattern is written at the time of data recording, the reproduction signal of the data area following the specific data recording area has the same recording / reproduction condition, and the data of the pattern formed by the continuous code "1" and code "0" It is possible to sample the peak value which can be regarded as the maximum value and the minimum value of the reproduced signal amplitude in the area. Of course, various kinds of specific patterns are conceivable other than the pattern used in the embodiment, and a pattern different from the embodiment may be used as long as the maximum value and the minimum value of the reproduction signal amplitude in the data area can be sampled.

When data is reproduced, the specific data recording area is always reproduced before reproducing the data area. At the time of reproducing the specific data recording area, the specific data area detector 2 detects the head of the specific data recording area in which the specific pattern data is written by counting the number of reproduction clocks from the clock pits, and the positive / negative peak detectors 7 and 8 are detected. The detection signal that clears the hold value of is output. The peak detection circuit 4 clears the maximum value and the minimum value of the MO signal amplitude held by the positive and negative direction peak detectors 7 and 8 by the detection signal, and the positive direction peak value and the negative value of the reproduction signal of the specific data recording area are negative. The maximum value Vp + and minimum value Vp- of the reproduced signal amplitude are held with the direction peak value as the initial value. The threshold value generation circuit 5 adds the maximum value Vp + and the minimum value Vp- of the reproduced signal amplitude by the adder 9 and halves the value by the divider 10.
A threshold value Vs that is the center value of the signal amplitude is generated. Therefore, even when the MO signal amplitude 91 fluctuates as shown in FIG. 9A, the threshold value Vs is obtained from the maximum value Vp + and the minimum value Vp− of the MO signal amplitude, instead of the constant voltage division ratio. Therefore, the threshold Vs at the center of the MO signal amplitude can be set. Further, since the threshold value Vs is set before the data reproduction, even when reproducing the data having the inter-code interference due to the deterioration of the reproduction signal due to the band limitation of the recording / reproducing characteristics as shown in FIG. 9B. Reliable information reproduction can be performed with the threshold value Vs at the center of the signal amplitude from the beginning.

The above is the operation when there is no defect on the disk. Next, the operation when there is a defect on the disk will be described.

When there is a defect on the disk, the reflectance is lowered, so that the pit signal is lower than the reference level Vpl when there is no disk defect as shown by 23 and 25 in FIG. The drop in the pit signal also leads to the drop in the MO signal, and as shown in FIG. 3, the peak hold value of the MO signal amplitude changes due to the disk defect, and the threshold value changes, so that the reliability of the reproduction signal detection decreases. Therefore, the defect detection circuit 1
With the configuration shown in FIG. 5, when the pit signal 51 exceeds a range EL of a predetermined value ΔV from the reference level Vpl of the pit signal, it is considered that there is a defect on the disk, and the L level control signal 52 is set. Output to the switch 3. The switch 3 is closed when the control signal 52 is H, and the control signal 52
Open if L is. Due to this action, when there is a disk defect, the MO signal is not sent to the peak detectors 7 and 8, so the peak detectors 7 and 8 can hold the peak value of the irregular MO signal due to the disk defect. In addition, the threshold used by the threshold generation circuit 5 for waveform shaping does not change. In this way, peak detection is not performed when an abnormal waveform appears in the reproduced MO signal amplitude due to a local disk defect, so the threshold value is always reproduced M
It is possible to set the center of the O signal amplitude.

Further, the present invention can be configured by a digital circuit as shown in FIG. The positive direction peak detector 7 and the negative direction peak detector 8 of the peak detection circuit 4 are composed of the comparator 13 and the register 14 by converting the MO signal into a digital signal by the A / D converter 15 which operates with the reproduction clock. can do. Further, by using the adder and the divider of the digital circuit as the threshold value generation circuit 5, it becomes possible to easily change the threshold value calculation condition, and it is also possible to realize with a single calculation circuit. Further, the size of the device can be reduced by forming an IC together with the modulation circuit and the like.

According to this embodiment, since the threshold value for waveform shaping can be always set to the center value of the MO signal amplitude, the reliability of the reproduced signal in the information reproduction can be improved.

Further, in the present embodiment, ΔV for setting the defect detection range EL of the defect detection circuit 1 is set to a predetermined value, but it may be variably set by the reference level Vpl of the pit signal, and the defect detection range EL is Vpl ±. The setting may include Vpl as ΔV.

In the embodiment, the magneto-optical disk device of the sample servo system has been described, but the magneto-optical disk device of the continuous servo system can be similarly adopted. In addition, in each method, in order to eliminate the influence of prepits, a preformatted area may be detected and a gate signal for prohibiting peak value sampling may be output.

[0023]

According to the present invention, in reproducing information from a magneto-optical disk, the threshold value for waveform shaping of the reproduced signal is determined by the characteristics of the recording medium and the reproduced signal due to variations in recording / reproducing conditions of the magneto-optical disk device. It is possible to control the amplitude of the reproduced signal to the center of the amplitude of the reproduced signal, and it is possible to reproduce the information with high reliability.

Further, it is possible to control the amplitude of the reproduced signal due to a defect on the recording medium to the center of the reproduced signal amplitude without erroneously setting the threshold value due to the peak value due to the defect. It is possible to reproduce highly accurate information.

[Brief description of drawings]

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

FIG. 2 is a Pit signal waveform diagram due to a disk defect,

FIG. 3 is an MO signal waveform diagram due to a disk defect,

FIG. 4 is a signal waveform diagram showing a fluctuation of a reproduced signal,

FIG. 5 is a defect detection circuit example and a signal waveform diagram,

FIG. 6 is a sector format diagram of a 5.25-inch sample servo system,

FIG. 7 is a conventional circuit diagram and signal waveform diagram,

FIG. 8 is a specific pattern data diagram,

FIG. 9 is a signal waveform diagram showing the operation of the present invention,

FIG. 10 is a block diagram of a digital circuit according to an embodiment of the present invention.

[Explanation of symbols]

 1 ... Defect detection circuit, 2 ... Specific data area detector, 3 ... Switch, 4 ... Peak detection circuit, 5 ... Threshold value generation circuit, 6 ... Waveform shaper, 7 ... Positive peak detection circuit, 8 ... Negative Directional peak detection circuit, 9 ... Adder, 10 ... Divider, 11 ... Clock pit detector, 12 ... PLL circuit.

Claims (4)

[Claims] 1. In a magneto-optical disk device, a peak detection holding means for detecting a peak value of a reproduction signal amplitude and holding a maximum value and a minimum value of the reproduction signal amplitude, and a reproduction signal held by the peak detection holding means. Threshold value generating means for generating a threshold value when performing waveform shaping from the maximum value and the minimum value; and waveform shaping means for shaping the waveform of the reproduced signal by the threshold value generated by the threshold value generating means,
When the total reflection signal from the recording medium exceeds a certain range, defect detection means for outputting a control signal and circuit opening / closing means for interrupting the input signal of the peak detection means by the control signal are provided. Information reproduction device. 2. The peak detecting and holding means according to claim 1, further comprising a specific data area detecting means for detecting a specific pattern writing area existing prior to the information recording area and outputting a detection signal. The information reproducing apparatus which clears the hold value of the above and holds the maximum value and the minimum value of the reproduction signal amplitude of the specific pattern. 3. The information reproducing apparatus according to claim 2, wherein the specific pattern is a pattern in which the maximum value and the minimum value of the reproduction signal amplitude are reproduced. 4. An optical disc having a recording layer capable of recording and reproducing information by light, comprising a specific pattern recording area for recording specific pattern data for setting a threshold value used when performing waveform shaping during reproduction. An optical disc characterized by having before the data recording area.