JPS62298972A - Digital signal reproducing device - Google Patents

Abstract

PURPOSE:To obtain a digital signal reproducing device which can reproduce a satisfactory digital signal even when the recorded digital signal is reproduced and 2n d distortion exists by correcting the inverting interval of the digital signal and executing the synchronizing detecting of two digital signals before and after the correction. CONSTITUTION:At the time of 2n d distortion, a digital signal shown in a waveform 75 is outputted from a waveform shaping circuit 8. In the same way, at an inverting interval correcting circuit 10, the time delay equivalent to one clock is executed, the signal shown in a waveform 76 is obtained and further, an inverting interval correcting signal shown in a waveform 77 is outputted. At a synchronizing signal detecting circuit 11, demodulation is executed by NRZ, a synchronizing signal pattern is collated, at this time, the same signal as the synchronizing signal pattern is reproduced, and therefore, an ON signal is outputted to a selecting circuit 12. On the other hand, the digital signal shown in the waveform 75 is inputted to a synchronizing signal detecting circuit 9, the synchronizing signal pattern cannot be detected and on the contrary, an OFF signal is outputted to a selecting circuit 12.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention Industrial Field of Application The present invention is a method for digitizing signals such as audio and video and for reproducing digital signals on high-density recorded media. Nozufuiri - Prior Art In recent years, devices have been proposed that use a laser beam to reproduce digital signals from a disc medium, such as a compact disc (CD), on which digital signals are recorded at high density. FIG. 5 shows an example of this, and reference numeral 1 denotes an optical disc on which digital signals such as audio are modulated and recorded as pits. 2 is a pickup for reproducing signals recorded on the optical disc 1, and is a semiconductor laser.

It consists of a PIN diode, optical components, etc. 3
is a high frequency amplification circuit that amplifies the reproduced signal and compensates for high frequency characteristics (waveform equalization). 4 binarizes the reproduced signal,
This is a waveform shaping circuit that converts into digital signals. 5 is a demodulation circuit that demodulates the reproduced digital signal.

The operation of the conventional example configured as above will be explained using FIG. 6.

It is assumed that, for example, an audio signal is digitized and recorded on the optical disc 1 in advance using a predetermined modulation method. A few meters from pickup 2
By applying a W laser beam, the reproduced signal 61 in FIG.
is obtained and supplied to the waveform shaping circuit 4 via the high frequency amplifier circuit 3. Reference level v set by waveform shaping circuit 4
The signal is binarized by th, and a digital signal 62 is obtained. Furthermore, the digital signal 52 is supplied to the demodulation circuit 6, and an output signal 53 is obtained.

Now, the reproduction signal input to the waveform shaping circuit 4 rises,
If the reference level vth is kept constant due to waveform distortion such as sluggish falling or 2nd distortion, the correct inversion interval of the sixth digital signal 53 may be output with a shift like the 520 waveform. be. Conventionally, when the recorded digital signal is DC-free, this property is utilized to feed back the DC component of the digital signal after waveform shaping, and to convert it to the binary standard level 7th.
A method has been proposed in which the following settings are made.

FIG. 5 shows this, where 8 is a comparator and 7 is a low-pass filter. A reproduced signal is input to the ten terminal of the comparator 6, and a digital signal is obtained from its output terminal. Further, the DC component is inputted to one terminal of the comparator 6 via the low-pass filter 7, and this is the reference level v for binarization.
It becomes th.

Problems to be Solved by the Invention However, according to this method, the recorded digital signal is required to be DC-free. Also, 2
When there is waveform distortion such as ND distortion, even in the DC-free modulation method, the setting of the reference level vth has a problem that it largely depends on the pattern of the reproduced signal. In the case of optical discs, a means for correcting 2nd distortion caused by the characteristics of the medium during recording is disclosed in, for example, Japanese Patent Laid-Open No. 60-8323.
This method has been proposed in Publication No. 4, etc., but since it depends on the initial characteristics of the medium and the recording location, it is necessary to make corrections each time recording is performed, and it is not a very effective means.

SUMMARY OF THE INVENTION In view of the above, an object of the present invention is to provide a digital signal reproducing apparatus that can reproduce a recorded digital signal with good quality even when there is second distortion.

Means for Solving the Problems The present invention provides means for binarizing a reproduced signal at a predetermined level and outputting a first digital signal, and a first synchronization device for detecting a synchronization signal of the first digital signal. a detection means, a means for correcting an inversion interval of the first digital signal and outputting a second digital signal, a second synchronization signal detection means for detecting a synchronization signal of the second digital signal;
From the information on the first and second synchronization signal detections, the first and second synchronization signals are detected.
A digital signal recording and reproducing apparatus comprising means for selecting which of the second digital signals is output to a subsequent stage.

According to the above-described configuration, the present invention corrects the inversion interval of the digital signal even if the reference level for binarizing the reproduced signal is not set accurately due to DC fluctuations or 2nd distortion, and the two values before and after this correction are By performing synchronous detection of the two digital signals, it is possible to determine which digital data is correct based on the detection result, so that correct digital data can be reproduced.

Embodiment FIG. 1 shows a block diagram of a reproducing circuit of a digital signal reproducing apparatus of the present invention. In FIG. 1, 8 is a waveform shaping circuit that converts the reproduced signal into full binary values. Reference numeral 9 denotes a synchronization signal detection circuit for detecting a predetermined synchronization signal recorded in advance. 1° is an inversion interval correction circuit that corrects the inversion interval of the binary-coded reproduced signal. Reference numeral 11 denotes a synchronization signal detection circuit for detecting a synchronization signal of the corrected digital signal. 12 is a selection circuit that selects which of the two input signals should be output based on information from the synchronization signal detection circuit 9.11. Further, FIG. 2 is a block diagram showing the configuration of the waveform shaping circuit in more detail. In FIG. 2, numeral 13 represents a level comparator that binarizes the reproduced signal using the base level vth. 14 is level comparator 1
P L L (P
haseLocked Loop) circuit. Reference numeral 15 denotes a phase comparison circuit that compares the phases of the two locks and generates a reference level vth. 16 is a level comparator 13
is a D-flip-flop whose output signal is triggered by the edge of the clock.

The operation of the digital signal reproducing apparatus of the present invention constructed as described above will be explained using the waveforms shown in FIGS. 3 and 4. Further, in the following description, an example in which the present invention is applied to an optical disc reproducing device will be shown.

In FIG. 1, a reproduced signal from a pickup is high-frequency amplified and input to a waveform shaping circuit 8. The waveform shaping circuit 8 has a configuration as shown in FIG. 2, and the reproduced signal is input to the + terminal of the level comparator 13. A reference level vth created by means described later is input to one terminal of the level comparator 13. As shown in FIG. 3, information is recorded on the optical disc as pits with a waveform 54 in shading or uneven pits. Now, if the pattern of the recording signal is, for example, '10100101o...2', the reproduced signal will have a waveform 55. There is no 2nd distortion in the waveform,
If the reference level vth applied to one terminal of the level comparator 13 is accurate, its output will be as shown in waveform 55. The output signal of the level comparator 13 is input to a PLL circuit 14 and a D-flip-flop circuit 16. PLL
The circuit 14 generates two clocks (CK1 and CK2) synchronized with each edge of the output signal of the level comparator 13. Figure 3. Waveform 57 of clock CK1 synchronized with the rising edge.
, a clock CK2i waveform 68 synchronized with the falling edge. Furthermore, the clocks CK1 and CK2 are input to a phase comparator circuit 15. Here, the phase difference between the two clocks is determined, and the reference level 7th is output accordingly. As mentioned above, when there is no 2nd distortion, the reference level vth is stable.

On the other hand, as described above, the output signal of the level comparator 13 and one of the two clock outputs of the PLL circuit (C1l in this case) are input to the D-flip-flop 16, and a reproduced signal synchronized with the clock is output. .

Next, the operation when the reproduced signal has 2nd distortion will be explained. In recent years, optical discs on which a metal oxide film (for example, a Te-based oxide film) is deposited have attracted attention as recordable and reproducible optical discs using a semiconductor laser, but 2nd distortion due to insufficient laser power has become a major problem. If the laser power is insufficient, pits are recorded with a shorter pulse width than the pulse width during recording, and the appearance is, for example, as shown in waveform 69 in FIG. 3.

The reproduced signal has a waveform 6Q, and when the reference level vth added to one terminal of the level comparator 13 is at the above-mentioned level, a digital signal of a waveform 61 is obtained, and the two output clocks of the PLL circuit 14 have the waveform It becomes like 62.63. Since a phase difference occurs between the two clock signals, the phase comparator circuit 16 changes the reference level vth, unlike the case where there is no second distortion described above. As shown in waveform 64,
When the reference level vthO value increases, the level comparator 13
The output signal is as shown in waveform 65, and the two clocks CK1. CK2 has a waveform of 66°6, respectively, and the clock input of the phase comparator circuit 1-6 is stable at the reference level vth where the phase difference disappears. A stable reference level is set in the wave-fitting circuit 8 regardless of the presence or absence of 2nd distortion, and the reproduced signal is converted into a digital signal. However, the waveform 56.65
As you can see, there is a difference in the inversion interval of one clock.

Generally, the reciprocal (1/Tw) of the detection window width (Tw) of the modulation method or an integral multiple thereof is used as the frequency of the recovered clock (CK1.CK2). A case can be considered where the value changes by an integer multiple.

Next, the output signal of the waveform shaping circuit 8 described above is input to a synchronization signal detection circuit 9 and an inversion interval correction circuit 10. In the synchronization signal detection circuit 9, a synchronization signal pattern (for example, '101001
0”) is detected.

In the case where there is no 2nd distortion, the waveform shaping circuit 8 also outputs, for example, a digital signal shown as a waveform 8 in FIG. 4 and a clock signal shown as a waveform 69. As a result, the synchronization signal detection circuit 9 demodulates the signal using NRZ, and obtains a demodulated digital signal shown in waveform 7o, which is compared with a preset synchronization signal pattern. In this case, a synchronizing signal pattern is detected (ON), and its output signal (ON signal) is applied to the selection circuit 12. On the other hand, although the same waveform as waveform 68 is shown at 71, the output signal of the waveform shaping circuit 8 is delayed by one clock as shown in waveform 72 in the inversion interval correction circuit 10, and the output signal of the waveform 73 is delayed by one clock as shown in waveform 73. The signal is corrected and input to the synchronization signal detection circuit 11. The synchronizing signal detection circuit 11 detects a synchronizing signal pattern in the same way as the synchronizing signal detecting circuit 9. However, in the case of waveform 74,
No synchronization signal pattern is detected (OFF). The selection circuit 12 detects a synchronization signal from the input data (corresponding to waveform 70.74) demodulated by NRZ according to the ON or OFF output signals from the synchronization signal detection circuits 9 and 11, that is, outputs an ON signal. The data from the synchronizing signal detection circuit 9 is output to the next stage.

Next, a case where there is 2nd distortion will be explained. In FIG. 4, a digital signal having a waveform 75 is outputted from the waveform shaping circuit 8 as described in FIG. Similarly to the above, the inversion interval correction circuit 1o performs a time delay corresponding to one clock, obtains a signal shown in waveform 7e, and further outputs an inversion interval correction signal shown in waveform 77. The synchronization signal detection circuit 11 performs demodulation using NRZ and checks the synchronization signal pattern, but this time, since the same signal as the synchronization signal pattern is being reproduced, an ON signal is output to the selection circuit 12. The digital signal shown in the one-sided type 76 is also input to the synchronization signal detection circuit 9, but the synchronization signal pattern cannot be detected, and on the contrary, the OFF signal is input to the selection circuit 12.
Output to. With the above operation, if there is 2nd distortion, the data from the synchronization signal detection circuit 11 will be output to the next stage.

In this way, correct data is output to the next stage circuit regardless of the presence or absence of 2nd distortion.

As described in detail, according to the present invention, even in a reproduction system where waveform distortion such as 2nd distortion occurs, it is possible to correctly reproduce a digital signal by correcting the inversion interval of the digital signal and detecting synchronization. Its practical effects are great.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a digital signal reproducing device that is an embodiment of the present invention, Fig. 2 is a block diagram of a waveform shaping circuit that constitutes a part of the present invention, and Fig. 3 explains the operation of the waveform shaping circuit. FIG. 4 is a waveform diagram for explaining the present invention in detail, FIG. 5 is a configuration diagram of an example of a conventional optical disc playback device, and FIG. 6 is a waveform diagram for explaining FIG. 6. , 7th
The figure is a configuration diagram of a conventional digital signal reproducing circuit. 8...Waveform shaping circuit, 9...Synchronization signal detection circuit, 10...Inversion interval correction circuit, 11.
...Synchronization signal detection circuit, 12...Selection circuit. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 3 Figure 4 / θ100/θ/θ

Claims (1)

[Claims] means for binarizing a reproduced signal at a predetermined level and outputting a first digital signal; first detecting means for detecting a synchronization signal of the first digital signal; and an inversion interval of the first digital signal. means for correcting and outputting a second digital signal, second detection means for detecting a synchronization signal of the second digital signal, and output signals from the first and second detection means for the synchronization signal. A digital signal reproducing apparatus comprising means for outputting either the first or second digital signal to the next stage according to the output of the digital signal.