JPH0540978A - Optical information recording / reproducing device - Google Patents

Abstract

(57) [Summary] [Purpose] To enable accurate reproduction even if the level of the reproduced signal fluctuates due to various causes. Constitution: Two sensors for detecting the reflected light of the reproducing light flux irradiated on the magneto-optical recording medium, means for binarizing the difference signal of the outputs of the sensors at a predetermined slice level, and the binarized signal. In a device having means for extracting a clock signal of a magneto-optical information signal from the optical disc and means for synchronizing the binarized signal with the clock signal, an output signal of the binarizing means and an output signal of the synchronizing means are provided. The slice level of the binarizing means is controlled so that the average value or the pulse width becomes substantially equal, and the slice level is always maintained at an appropriate level.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording / reproducing apparatus for recording or reproducing information on an optical information recording medium such as a magneto-optical disk.

[0002]

2. Description of the Related Art In recent years, optical recording media such as optical disks have been
From a read-only type CD to a write-once type, to a rewritable type magneto-optical disk, rapid progress has been made as a high-density and large-capacity memory. In particular, the magneto-optical disk is expected as a high-density and large-capacity external memory for computers. Since information is recorded at high density in such a magneto-optical disk, it is required to accurately read the recorded information during reproduction. Therefore, conventionally, after amplifying the magneto-optical signal read from the two optical sensors by the preamplifier,
A magneto-optical signal is reproduced by generating a difference signal between two sensor outputs, detecting a peak value and a bottom value of the difference signal, slicing the difference signal at the center value, and binarizing the difference signal.

[0003]

However, in the prior art, the slice level is set to the center value of the peak value and the bottom value of the difference signal and binarized with the magneto-optical signal. When the recording condition is changed or when there is an influence from the outside, the level of the reproduction signal fluctuates, so that the magneto-optical signal may not be reproduced accurately. (1) In the magneto-optical disk device, the writing level of the magneto-optical signal differs depending on the device. (2) In the magneto-optical disk device, the writing level of the magneto-optical signal differs for each disk, and the writing level also differs depending on the position of the disk. (3) When dust or dirt is attached to the magneto-optical disk, the reproduction signal level fluctuates in a complicated manner. (4) Waveform interference occurs due to high density recording. (5) Depending on the modulation method (for example, 2-7 modulation), it is affected by the DC component.

FIG. 8 is a waveform diagram showing changes in the reproduced signal when the write level of the magneto-optical signal is changed. FIG. 8A is an excessive level, FIG. 8B is an appropriate level, and FIG. ) Is a reproduction signal when written at an underlevel. As is clear from this figure, when written at an excessive or underlevel, the slice level, which is the center value of the peak value and the bottom value, is not correct and the pulse width that should be reproduced cannot be reproduced. I understand. Further, FIG. 9 shows a problem caused by the influence of a direct current component, and in 2-7 modulation or the like, a reproduced waveform as shown in the figure may occur depending on the modulation pattern. In such a case, there is no problem in the section B, but in the section A, if the center value of the peak value and the bottom value is the slice level, the correct pulse width could not be reproduced.

The present invention has been made in view of the above problems, and an object of the present invention is to accurately reproduce a magneto-optical signal irrespective of a complicated fluctuation of a reproduction signal level due to a change of a writing level of the magneto-optical signal. Another object of the present invention is to provide an optical information recording / reproducing device.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to detect the reflected light of a reproducing light beam applied to a magneto-optical recording medium.
One sensor, means for binarizing a difference signal of the outputs of the sensors at a predetermined slice level, means for extracting a clock signal of a magneto-optical information signal from the binarized signal, and the binarized signal In a device having means for synchronizing with a clock signal, an average value or pulse width of the output signal of the binarizing means and the output signal of the synchronizing means is substantially equal to each other,
This is achieved by an optical information recording / reproducing device characterized by controlling the slice level of the binarizing means.

[0007]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of an optical information recording / reproducing apparatus of the present invention. In FIG. 1, reference numerals 1 and 2 are optical sensors provided in an optical head (not shown), and detect reflected light of a reproducing light beam applied to a magneto-optical disk (not shown). The detection signals of the optical sensors 1 and 2 are amplified by the preamplifiers 3 and 4, respectively, and then output to the differential amplifier 5 to generate a difference signal. This difference signal is output to the binarization circuit 7 via the AGC circuit (automatic gain control circuit) 6 and binarized by comparing with the slice level of the other terminal. As will be described later in detail, reference numeral 8 is a starting slice level generating circuit for giving a predetermined slice level to the binarizing circuit 7 when the slice level is not fixed at the time of starting, for example. Reference numeral 9 is a switching circuit for switching the slice level of the binarization circuit 7, which is normally connected to the b side, but is switched to the a side when the VFO pattern of the magneto-optical disk is reproduced. The output of the activation slice level generation circuit 8 is the binarization circuit 7.
Given to. Reference numeral 10 is a clock extraction circuit for extracting the clock signal of the magneto-optical signal from the binary signal, and 11 is a synchronization circuit for synchronizing the binary output with this clock signal.
Further, 12 is a low-pass filter for converting the output of the binarization circuit 7 into a direct current, and 13 is a low-pass filter for converting the output of the synchronization circuit 11 into a direct current. Reference numeral 14 is a comparison operation circuit that compares the two input signals of these low-pass filters 12 and 13 and controls the slice level of the binarization circuit 7 so that these signal levels match.

Next, the operation of this embodiment will be described. First,
FIG. 2A is a diagram showing the relationship between the magneto-optical signal and FIG. 2B, which shows the relationship between the magneto-optical signal and the slice level. Here, the slice level is the peak value and the bottom of the average amplitude of the magneto-optical signal as in the conventional case. It is set to the center value of the values, and thus is not the optimum slice level. Further, FIG. 2C is a diagram showing a binarized signal when the magneto-optical signal is binarized at the slice level in FIG. 2B. If the slice level is inappropriate, it is shown in the center and the right of FIG. The pulse width becomes abnormal as shown by the waveform. In such a case, an erroneous operation will occur in the demodulation processing in the subsequent stage, and this problem is particularly remarkable in pit edge recording. 2 (d) shows the synchronization clock extracted by the clock extraction circuit 10, and FIG. 2 (e) shows the output of the synchronization circuit 11. The binarized output of FIG. 2 (c) is the synchronization clock. It is a synchronized output signal synchronized with. in this case,
It can be seen that the pulse width is constant due to the synchronization. Here, the slice level is proper when the pulse widths of FIGS.
By controlling the slice level so that the digitized output and the synchronized output are equal to each other, the slice level is always maintained at an optimum value and the magneto-optical signal is reproduced accurately.

Therefore, the detailed operation of this embodiment will be described based on the above concept. First, a magneto-optical disk is irradiated with a reproducing light beam of a semiconductor laser (not shown), and the reflected light is incident on the optical sensors 1 and 2 and photoelectrically converted. The detection signals of the optical sensors 1 and 2 are amplified by the preamplifiers 3 and 4, respectively, and then output to the differential amplifier 5. Differential amplifier 5
Is used as a signal of a pre-pit portion (not shown), and the differential output is converted into a signal having a constant amplitude by the AGC circuit 6 and then input to the non-inverting terminal of the binarization circuit 7. The output of the comparison operation circuit 14 is input to the inverting terminal of the binarization circuit 7 as a slice level, and the binarization circuit 7 binarizes the differential output at this slice level. The binarized signal is input to the clock extraction circuit 10, and a clock signal synchronized with the VFO pattern is generated by the PLL operation from the VFO pattern of the magneto-optical signal. The binarized signal is input to the synchronization circuit 11 and converted into a binarized signal synchronized with the clock signal. This synchronized signal is sent to a signal processing circuit (not shown) and reproduced as the original information. The binarized signal of the binarization circuit 7 is converted into a direct current by the low pass filter 12 and input to the-terminal of the comparison operation circuit 14. In addition, the synchronization circuit 11
Is also converted into a direct current by the low pass filter 13 and input to the + terminal of the comparison operation circuit 14. The comparison operation circuit 14 compares the two signals and controls the slice level so that the levels of both signals match. As a result, the slice level changes accordingly, for example, when the write signal level changes, so that the slice level of the binarization circuit 7 can always be maintained at the optimum value, and the magneto-optical signal can be accurately reproduced. can do.

On the other hand, when the slice level is not fixed, for example, at the time of start-up, the binarizing circuit 7 is not operating at an appropriate slice level, so that the switching circuit 9 stabilizes the magneto-optical signal in terms of direct current. It is switched to the side a when the VFO pattern is reproduced. As a result, the output of the activation slice level generation circuit 8 is input to the inverting terminal of the binarization circuit 7 as a slice level. A concrete example of the startup slice level generating circuit 8 is shown in FIG. 3, in which the VFO pattern signal is input to the non-inverting terminal of the comparator 15, and the binarized output thereof is converted into a direct current by the low pass filter 16. The DC signal and the output of the reference voltage source 18 are compared in the arithmetic circuit 17,
A signal corresponding to the comparison result is fed back to the inverting terminal of the comparator 15. As described above, in the startup slice level generation circuit 8, the VFO pattern has a duty of 50%.
Generates a slice level for binarization, and outputs it to the inverting terminal of the binarization circuit 7 as a slice level. Therefore, even when the slice level is not fixed at the time of start-up, the slice level is automatically set to a predetermined level, so that the reproducing operation can be normally performed without malfunction.

FIG. 4 is a block diagram showing another embodiment of the present invention. In this embodiment, the reference voltage source 19 is connected to the side b of the switching circuit 9, and the switching circuit 9 is connected to the side b when the slice level is not fixed. The rest of the configuration is exactly the same as that of the embodiment shown in FIG. In the present embodiment, the switching circuit 9 is normally connected to the side a, and the slice level is controlled by the comparison operation circuit 14 so that the binarized output and the synchronized output coincide with each other, as in the above embodiment. On the other hand, when the slice level is not fixed at the time of start-up, the binarization circuit 7 does not operate at an appropriate slice level. Therefore, when reproducing the VFO pattern of the magneto-optical disk,
The switching circuit 9 is connected to the b side. As a result, the comparison operation output of the voltage of the reference voltage source 19 and the binarized output is given to the inverting terminal of the binarization circuit 7 as a slice level. Therefore, even in this embodiment, reproduction can always be performed accurately as in the embodiment of FIG.

FIG. 5 is a diagram showing still another embodiment of the present invention, in which a gate circuit 20 and a gate circuit are provided between the binarizing circuit 7 and the low pass filter 12 and between the synchronizing circuit 11 and the low pass filter 13. This is an example in which 21 is provided. FIG. 6 shows the waveforms of the respective parts of the above-described embodiment. FIG. 6A shows the output signal of the binarization circuit 7, FIG. 6B shows the synchronization clock generated by the clock extraction circuit 10, and FIG. (C) is a synchronization circuit 1
1 output signal. When the pulse width of the output signal of the binarization circuit 7 is wider than the pulse width of the output signal of the synchronization circuit 11, the pulse width of the output of the gate circuit 20 becomes narrower as shown in FIG. In this case, the pulse width of the output of the gate circuit 20 becomes wider. In addition, the pulse width of the output of the gate circuit 21 is, as shown in FIG.
Has the opposite relationship to the output of. From the above relationship, when the output pulse widths of the gate circuits 20 and 21 are equal, the output pulse width of the binarization circuit 7 and the output pulse width of the synchronization circuit 11 are equal, and at this time, the binarization circuit 7 The slice level becomes the optimum value. Therefore, in the present embodiment, the outputs of the gate circuits 20 and 21 are converted into direct current by a low-pass filter and then input to the comparison operation circuit 14, and the slice level is set so that the pulse widths of the binarized output and the synchronized output become equal. To control. As shown in FIG. 7, the binarized output and the synchronized output are directly input to the comparison operation circuit 14,
The slice level may be controlled by the comparison operation circuit 14 so that the pulse widths of the binarized output and the synchronized output become equal.
In this case, the output signal of the comparison operation circuit 14 is DC-converted by the low-pass filter 22 and then applied to the inverting terminal of the binarization circuit 7.

[0013]

As described above, according to the present invention, in order to automatically adjust the slice level to the optimum value, the difference in the write level of the magneto-optical signal, the fluctuation of the reproduction signal level due to dust, the direct current component, etc. Even if the reproduction signal level fluctuates due to waveform interference or waveform interference, the magneto-optical signal can be reproduced accurately regardless of the fluctuations. Therefore, it is possible to reproduce the magneto-optical signal sufficiently accurately even in the high density and large capacity pit edge recording system.
Processing can also be performed with a C-coupled signal transmission system.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an optical information recording / reproducing apparatus of the present invention.

FIG. 2 is a time chart showing signal waveforms of various parts of the embodiment of FIG.

FIG. 3 is a circuit diagram showing a specific example of a startup slice level generation circuit.

FIG. 4 is a block diagram showing another embodiment of the present invention.

FIG. 5 is a circuit diagram showing still another embodiment of the present invention.

FIG. 6 is a time chart showing signal waveforms of various parts of the embodiment of FIG.

FIG. 7 is a circuit diagram showing a further improvement of the embodiment of FIG.

FIG. 8 is a waveform diagram showing how the reproduction signal changes depending on the difference in write level of the magneto-optical signal.

FIG. 9 is a waveform diagram showing an example of a reproduced waveform based on a modulation pattern such as 2-7 modulation.

[Explanation of symbols]

 1, 2 optical sensor 5 differential amplifier 7 binarization circuit 8 startup slice level generation circuit 9 switching circuit 10 clock extraction circuit 11 synchronization circuit 12, 13 low-pass filter 14 comparison operation circuit 20, 21 gate circuit

Claims (5)

[Claims] 1. A sensor for detecting reflected light of a reproducing light beam applied to a magneto-optical recording medium, means for binarizing a difference signal of outputs of the sensor at a predetermined slice level, and the binary value. In a device having means for extracting a clock signal of a magneto-optical information signal from a binarized signal and means for synchronizing the binarized signal with the clock signal, an output signal of the binarized means and an output of the synchronizer An optical information recording / reproducing apparatus, characterized in that the slice level of the binarizing means is controlled so that the average value or pulse width of signals becomes substantially equal. 2. A first and a second low-pass filters for converting the output signals of the binarizing means and the synchronizing means into a direct current, respectively, and slicing so that the output signal levels of the two low-pass filters become substantially equal. The optical information recording / reproducing apparatus according to claim 1, wherein the level is controlled. 3. A switching unit for switching the slice level, and when the slice level is not fixed at the time of starting, a predetermined slice level is given to the binarizing unit by the switching operation of the switching unit. The optical information recording / reproducing apparatus according to claim 1, wherein 4. The optical information recording / reproducing apparatus according to claim 3, wherein the switching means performs switching so as to give a predetermined slice level to the binarizing means at the time of reproducing the VFO pattern. 5. The optical information recording / reproducing apparatus according to claim 3, wherein the predetermined slice level is a level at which the VFO pattern is binarized to a duty of about 50%.