JPH04232659A - Recorded information reproducing device - Google Patents

Abstract

PURPOSE:To infallibly detect information signals from low-S/N readout signals when the signals are recorded on an optical disk at a high density. CONSTITUTION:This recorded information reproducing device is provided with an amplitude limit circuit 3 which inputs read-out signals of recorded bit rows and limits the amplitude of the signals near the central value only, differentiation circuit 4 which obtains first-order differentiated signals by differentiating the output signal of the circuit 3, another differentiation circuit 6 which obtains second-order differentiated signals by differentiating the first-order differentiated signals, level detection circuit 9 which obtains the changing direction signals of the first-order differentiated signals by performing level comparison on the first-order differentiated signals, zero-cross comparison circuit 7 which obtains edge information signals from the second-order differentiated signals, and gate circuit 12 which incorporates a timing control means for the changing direction and edge information signals and obtains read-out data signals. In addition, a waveform equalization circuit 5 is inserted into the prestage of the amplitude limit circuit 4.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recorded information reproducing apparatus, and more particularly to a recorded information reproducing circuit suitable for a high recording density reproducing system such as an optical disk device.

0002

2. Description of the Related Art A recorded information reproducing apparatus will be described below using a magneto-optical disk, which is a typical erasable optical disk among optical recording, as an example. In general, in magneto-optical disk drives, thermomagnetic recording is performed in which a laser beam is focused and irradiated onto a recording medium made of a magnetic thin film along guide grooves that have been cut in advance on a substrate, and information is recorded as a magnetization pattern on the medium. . This guide groove is carved in a spiral shape and serves as an information track. At this time, a sector format area indicating sector information is previously engraved on the information track as a sector head area. A magneto-optical disk device recognizes the format and records and plays information.

Various methods have been used to record and reproduce information in the sector-divided data area. For example, in a 5-inch magneto-optical disk, a mark interval recording method is used for recording. In this method, information is recorded at the center of a recording pit according to binary information. To identify the reproduction of the reproduced data, the readout signal is differentiated to detect the zero crossing point, and at the same time, the reproduction clock determined by the modulation method is extracted, and the pattern of "0" and "1" is determined from the timing relationship with the data detection window. Data information is being played back.

In optical recording and reproducing apparatuses that record and reproduce large amounts of information, there is a mark length recording method in which information is added to the edges of recording pits in order to further increase the recording capacity. It is well known that, ideally, this method can double the recording density compared to mark interval recording. During playback, edge information is usually detected by pulsing at a fixed slice level, and at the same time, a playback clock determined by the modulation method is extracted and the pattern of "0" and "1" is determined from the timing relationship with the data detection window. The information of the source data is being reproduced. In this case, for example, even if modulated data is recorded using a modulation method that does not have a DC component, a DC component will be generated in the read signal due to heat conduction in the medium. Further, during mass production of optical disks, substrates having birefringence such as polycarbonate are often used. Therefore, DC fluctuations occur in the circumferential direction of the disk due to fluctuations in the envelope of the read signal.

[0005] Therefore, when reading data using a DC amplifier, there is a drawback that envelope fluctuations are directly observed, increasing the possibility of erroneous data identification in the entire data area.

On the other hand, when reading is performed using an AC coupled amplifier, envelope fluctuations due to birefringence are suppressed. However, the read signal output by the AC coupled amplifier causes DC fluctuations near the end of the recording/reproducing data area of the sector. Therefore, the method of pulsing using a comparator at a fixed slice level has the disadvantage that the vicinity of the beginning and end of data is misread.

[0007] Therefore, as an example of a means for solving this drawback, Japanese Patent Application No. 80104/1988 ``Optical Information Reading Apparatus'' has been proposed. As shown in FIG. 5, a readout signal (a) read out by the readout optical head 1 and amplified by the amplifier circuit 2 is differentiated by a differentiator 4, and this first-order differential signal (b) is converted to a binarization circuit, for example. The binarized signal (e) is obtained in step 10, and at the same time, the second-order differential signal (c) obtained by differentiation in the differentiating circuit 6 is used to convert the inflection point signal (both edge signals) of the read signal to the zero cross pulse oscillation circuit 8. This pulse (d) is used to latch the binarized signal in the latch circuit 11, thereby binarizing the read data signal. According to this, the binary signal (f) of the read data information can be stably obtained without being affected by the above-mentioned fluctuations in the DC component.

[0008] As another example, Japanese Patent Application No. 02-0226
No. 14 "Stored Information Reading Circuit" has been proposed. Basically, signal processing is performed using two differentiating circuits as in the example of the patent application, but as shown in FIG. , -VT to obtain a change direction signal of the signal, and obtain a read data signal from the timing relationship between the second-order differential signal from the zero-cross comparator circuit 7 and the zero-cross signal.

[0009]

[Problems to be Solved by the Invention] The above method is basically effective for dealing with DC fluctuations in readout signals that are a problem in optical recording in general, such as mark length recording, but it has the following drawbacks. There is.

[0010]In an information storage device such as an optical disk device,
High density, large capacity, and high speed data transfer are important. First, when the disk rotation speed is increased to improve the data transfer speed, the frequency band for recording and playback expands, so various noises (media noise, laser noise, circuit noise, etc.) that cause problems during readout have a large effect. It is well known that this will happen. That is, the reproduction S/N is inversely proportional to the band. Therefore, when the readout signal (a) having noise indicated by the thick line in FIG. 6 is first-order differentiated and second-order differentiated, the noise is directly superimposed on each pulse signal at the edge position as shown by the thick line. . Therefore, the read data signal (f) is also superimposed with noise during readout and noise due to differentiation, resulting in a pulse signal with very large noise jitter, which hinders high density. That is, it has the disadvantage of lowering the bit error rate.

[0011] Furthermore, if the recording pits are packed together for the purpose of increasing the recording density and increasing the capacity, waveform interference increases during readout, resulting in a decrease in resolution. This becomes more noticeable as the reading light beam diameter becomes larger than the recording pit size. Furthermore, if high-density recording is performed with a large reduction in resolution, noise will have a relative influence on the edge position, which is the data identification point of the read signal. Therefore, it is difficult to achieve high density with high reliability using the method described above. That is, first, differentiation emphasizes the high-frequency amplitude and compresses the low-frequency amplitude in the recording frequency region, so it is necessary to emphasize the high frequency even more strongly in a signal with reduced resolution. For this reason, various noises (medium noise, laser noise, circuit noise, etc.) that cause problems during reading are emphasized by performing differentiation, causing playback errors and hindering high-density recording. In addition, the second effect of reduced resolution is that the inflection point of the second-order differential signal does not correspond to the edge position of the recording pit, which is greatly affected by the recording pattern and causes a worsening of the bit error rate. become.

SUMMARY OF THE INVENTION An object of the present invention is to provide a recorded information reproducing apparatus that improves the above-mentioned drawbacks and stably enables high-density recording methods such as mark length recording methods.

[0013]

[Means for Solving the Problems] A first aspect of the invention is a recorded information reproducing apparatus that obtains a read data signal using a read signal of a recorded pit string recorded on an information recording medium.
an amplitude limiting means inputting the readout signal; and a first differential signal for differentiating the output signal of the amplitude limiting means to obtain a first-order differential signal.
a second differentiating means for differentiating the first-order differential signal to obtain a second-order differential signal; a means for comparing levels of the first-order differential signal to obtain a change direction signal of the differential signal; The present invention is characterized in that it comprises means for obtaining an edge information signal from a signal, and means for obtaining a read data signal including means for controlling the timing of the change direction signal and the edge information signal.

A second invention is characterized in that, in the first invention, a linear phase type equalizing means is inserted before the amplitude limiting means.

[0015]

[Function] According to the present invention, information can be accurately reproduced from a recorded pit string recorded at high density by a mark length recording method on an information recording medium such as an optical disk even under a low S/N reproduction environment with DC fluctuations and amplitude fluctuations. become.

[0016]

Embodiment Next, an embodiment of the present invention will be described with reference to FIGS. 1 to 5. The present invention will be explained using a magneto-optical disk device using a mark length recording method as an example.

FIG. 1 is a block diagram showing an embodiment of a recorded information reproducing apparatus according to the first invention. Further, FIG. 2 is a diagram for explaining the operation according to the present invention.

The magneto-optical disk device of this embodiment includes a read optical head 1 for detecting recording pits recorded on an information recording medium, an amplifier circuit 2 for amplifying a read signal, and an amplitude limiting circuit for inputting the read signal. 3, and a first differentiating circuit 4 which differentiates the output signal of the amplitude limiting circuit 3 and obtains a first-order differential signal.
, a second differentiation circuit 6 that differentiates the first-order differential signal to obtain a second-order differential signal, a level detection circuit 9 that compares the levels of the first-order differential signal and obtains a change direction signal of the differential signal, and a second differentiation circuit 6 that differentiates the first-order differential signal to obtain a second-order differential signal; It consists of a zero-cross comparator circuit 7 that obtains an edge information signal, and a gate circuit 12 that includes timing control means for a change direction signal and an edge information signal and obtains a read data signal.

In this magneto-optical disk device, signals of recording pits detected by the optical head 1 are amplified by, for example, an AC-coupled amplifier 2. This read signal (a) containing a lot of noise is input to the amplitude limiting circuit 3, sufficiently limited, and output. Here, the amplitude limiting circuit 3 uses, for example, a series type diode limiter with very little distortion and a large dynamic range, and clips and amplifies the positive and negative sides of the input signal and outputs the amplified signals. Note that if the vicinity of the average position (center position) of the input signal is not clipped and amplified at this time, edge shifts will occur at the beginning and end of the sector data. For this reason, for example, a configuration in which a peak detection signal of the input signal amplitude is inputted to the bias of the amplifier limits the amplitude only in the vicinity of the center position. Since this series type diode limiter is a well-known technology, a specific circuit example will be omitted.

[0020] Also, at this time, this limiter output waveform (b
) rises and falls very steeply,
At the edge position, a waveform with relatively reduced noise components compared to a normal readout signal waveform is output. This is important in the mark length recording method in which edge positions contain information, and reduces discrimination point noise. At the same time, the upper and lower limit portions of the limiter waveform amplitude become clean, flat waveforms with almost no superimposed noise.

The read data detection operation after the differentiating circuit is described, for example, in the prior art described above (Japanese Patent Application No. 02-022614).
The operation of the present invention is based on a steep waveform that reduces the noise superimposed on the output signal from the amplitude limiting circuit according to the present invention described above. Explain briefly.

The differentiating circuit 4 differentiates the amplitude-limited signal to obtain a waveform (c). At this time, since the signal (b) having amplitude-limited steep rise and fall characteristics is differentiated, the pulse width of the differentiated signal becomes narrower than when the read signal (a) is differentiated. This corresponds to pulse slimming in terms of transmission paths and is important for increasing density. Further, the differential signal itself has a waveform with noise removed. At the same time, waveform (d) shows a signal obtained by differentiating the differential waveform (c), that is, a second-order differential signal. At this time, waveform (e) shows a signal pulsed by the zero cross comparator circuit 7. Further, pulse waveforms (f) and (g) are obtained using a level detection circuit 9 having slice levels for level comparison on the positive side and negative side of the differential waveform (c), respectively.

These pulse waveforms (f) and (g) are subjected to timing control by the gate circuit 12 using the pulse waveform (e) in consideration of circuit delay, and then pulse signals (h) and (i) are obtained. At this time, although there is a noise pulse shown by a dotted line in the pulse waveform (e), it is clear that it does not contribute to the pulse formation of the pulse waveforms (f) and (g). The obtained pulse signals (h) and (i) are passed through an RS flip-flop in the gate circuit 12 to obtain a signal (j) in which the mark length is recorded. The obtained read data signal (j) is sampled based on a reproduced clock extracted by a clock extraction circuit (not shown) to obtain a reproduced data signal. Further, a reproduced data signal is obtained as a source data signal according to a modulation method by a demodulation circuit (not shown).

Next, an embodiment according to the second invention is shown in FIG. The difference from the first invention is that a linear phase type equalization circuit 5 is inserted before the amplitude limiting circuit 3. The linear phase type waveform equalization circuit 5 is configured using, for example, a transversal filter as shown in FIG. Here, for example, semi-fixed tap coefficients (C0, C1,..., C6
) A 7-tap transversal filter is used. Further, Z-1 indicates a time delay element. By optimally setting each tap coefficient of this transversal filter, the resolution of a read signal whose resolution has been degraded due to intersymbol interference is improved.

Waveform equalized signal (a) with improved resolution
is input to the circuit 3 which limits the amplitude only in the vicinity of the center value in the same way as in the first example of the invention, and is sufficiently limited and output. At this time, a differential waveform (c) with noise components sufficiently removed is output at the edge position of the output waveform, compared to a waveform obtained only by normal waveform equalization. especially,
If binarized reproduction is performed after waveform equalization, high frequency enhancement will be performed as a result, which will also increase noise at data discrimination points. Here, the discrimination point noise can be reduced by applying a limiter. Furthermore, if the amplitude is limited without improving the resolution and using a waveform with greatly reduced resolution, fluctuations in the edge position will be directly reflected on the output waveform, causing information errors.

Read data signal detection after this circuit is performed in the same manner as in the first embodiment of the invention.

If a clock extraction circuit (not shown) extracts a reproduced clock based on a signal after waveform equalization, for example, stable clock extraction becomes possible even at high density.

In the above embodiments, a transversal filter with semi-fixed tap coefficients was used as an example of the waveform equalizer, but a transversal filter having an automatic equalizer configuration that can adaptively change the tap coefficients may also be used. .

In this case, it becomes possible to adaptively compensate for deterioration in reproduction characteristics due to variations in the characteristics of the optical disk medium and optical head system, changes over time, etc., so that stable and high-quality recording and reproduction is always possible. Become.

Furthermore, similar effects can be expected even if a configuration using a cosine equalizer is used to reduce costs.

[0031] Here, to describe the relationship between the embodiment of the first invention and the embodiment of the second invention, in order to secure a recording/reproduction margin in a relatively low-density recording/reproduction system with superimposed noise, Center value tracking type amplitude limiting alone is sufficient, and during high-density recording, a recording/reproducing margin can be secured by combining waveform equalization and this amplitude limiting. Therefore, depending on the application of the recording/reproducing system, the selection should be made in relation to cost.

In the above explanation, magneto-optical recording has been described as an example, but it can of course be similarly applied to optical disk systems using write-once type or other reflectance change type media or read-only disks, and the size of various optical disks can be improved. It can contribute to increasing capacity.

[0033]

As described above, the recorded information reproducing apparatus of the present invention is capable of stably detecting the read data signal without error even in the face of DC fluctuations and amplitude fluctuations of the read signal. In addition, since the noise component of the read signal can be reduced and detected, the information recording density can be more than doubled compared to conventional methods using mark length recording, and the information transfer rate can be improved, expanding the range of applications of optical discs. It is something that can be expanded.

[Brief explanation of the drawing]

FIG. 1 is a system diagram showing an embodiment of a signal reproducing device according to a first invention.

FIG. 2 is a diagram for explaining the operation according to the present invention.

FIG. 3 is a system diagram showing an embodiment of a signal reproducing device according to a second invention.

FIG. 4 is a system diagram of a transversal filter according to a second invention.

FIG. 5 is a system diagram showing an example of a conventional signal reproducing device.

FIG. 6 is a diagram for explaining the operation of a conventional signal reproducing device.

FIG. 7 is a system diagram showing another example of a conventional signal reproducing device.

[Explanation of symbols]

1 Readout optical head 2 Amplifier circuit 3 Amplitude limiting circuit 4,6 Differential circuit 5 Waveform equalization circuit 7 Zero cross comparison circuit 8 Zero cross pulse oscillation circuit 9 Level detection circuit 10 Binarization circuit 11 Latch circuit 12 Gate circuit

Claims (3)

[Claims] 1. A recorded information reproducing apparatus that obtains a read data signal using a read signal of a recorded pit string recorded on an information recording medium, comprising an amplitude limiting means receiving the read signal as an input, and an output of the amplitude limiting means. Differentiate the signal 1
a first differentiating means for obtaining a second order differential signal; a second differentiating means for differentiating the first order differential signal and obtaining a second order differential signal;
readout comprising means for comparing the levels of the differential signal to obtain a change direction signal of the differential signal; means for obtaining an edge information signal from the second order differential signal; and timing control means for controlling the timing of the change direction signal and the edge information signal. 1. A recorded information reproducing apparatus comprising: means for obtaining a data signal. 2. The recorded information reproducing apparatus according to claim 1, wherein the amplitude limiting means limits the amplitude by following the vicinity of a center value of the read signal. 3. The recorded information reproducing apparatus according to claim 1, further comprising a linear phase type equalizing means inserted before said amplitude limiting means.