JPS6360959B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for detecting a missing section (dropout) of a reproduced signal that occurs when an information signal is time-axis modulated and recorded and reproduced on a recording medium, and is capable of detecting even relatively small dropouts. This made it possible.

Conventionally, as seen in the example of video disks, a light beam such as a laser beam is used on a disk, or an information signal such as a video signal is recorded on a concentric or spiral recording trajectory by using a concave or convex or a mechanical recording path.
There is a device that records and reproduces high-density binary signals of shading. Laser beams are used to reproduce the signals recorded on these disks.
A means for reproducing the unevenness signal by concentrating it into a minute light beam of about 1 μmφ and irradiating it onto the unevenness signal on the disk and detecting changes in the reflected light or transmitted light, and a piezoelectric element attached to the pickup. There are means for converting physical vibration into an electric signal and reproducing a concavo-convex signal, or means for detecting a concavo-convex signal as a change in capacitance.

In addition, in order to record signals on such a disk, a carrier signal of an appropriate frequency is FM modulated with an information signal such as a video signal or an audio signal, and this is converted into a binary signal using a limiter etc. and then recorded. It is common to record and reproduce pit lengths as long and short pit lengths. In such an apparatus, recording can be performed at a high density with a recording track of about 1 .mu.m.phi. and a track pitch of about 1 to 3 .mu.m.phi., thereby making it possible to obtain a recording/reproducing apparatus for a large capacity of information signals.

The signals played from these discs are FM
The signal is demodulated by a demodulator to obtain a video signal or an audio signal. In the demodulated signal obtained in this way, interference signals having a large level different from the signal may occur irregularly and significantly degrade the quality of the demodulated signal. This is mainly due to the dropout of the reproduced FM signal reproduced from the disk. Possible causes of such drop-outs in the reproduced FM signal include dust adhering to the disk, scratches on the disk base material, and the like.

By the way, it is known that if the occurrence of such a dropout can be detected by some method, the demodulated signal in which the dropout has occurred can be compensated for by utilizing the properties of the demodulated signal.
For example, in the case of video signals, one horizontal scanning period (1H) is
Replace the dropout section with the previous signal,
In the case of audio signals, the dropout section is compensated for by replacing the signal with the average level of the signal immediately before and after the dropout section. Therefore, devices that perform FM modulation and record and reproduce data on a disk generally include means for detecting dropouts in the modulated FM signal and compensating for dropouts in the demodulated signal.

In conventional devices such as VTRs, the dropout of the reproduced FM signal occurs during the dropout section.
The FM signal either disappears or its level drops significantly. Therefore, the dropout section is detected by detecting fluctuations in the amplitude of the reproduced FM signal.

FIG. 1 is a block diagram of an example of a dropout detection device used in a VTR or the like. Further, FIG. 2 is a waveform diagram showing waveforms at various parts in FIG. 1. 1 is a limiter circuit, which functions to eliminate small level fluctuations in the reproduced FM signal input from terminal A as shown in Figure 2a. FIG. 2b shows the output waveform of the limiter circuit 1. 2 is a half-wave rectifier circuit that allows only a half-wave of the input signal to pass through. Figure 2c shows the output waveform. 3 is a low-pass filter that extracts the low-frequency components shown in FIG. 2c. Figure 2 d
shows the output waveform of the low-pass filter 3. 4
is a comparator circuit, and the output of low-pass filter 3 is
It detects that the detection level input from terminal C is exceeded and outputs it. The dotted line A in FIG. 2d is the detection level input from terminal C. FIG. 2e shows the output waveform of the comparator circuit 4. At this time, the trailing edge of the output waveform is stretched somewhat to generate a pulse with a width somewhat longer than the dropout section in the reproduced FM signal. This output is output from terminal B to operate the dropout compensation circuit configured as described above.

The methods described above are based on the premise that the FM signal is lost in the dropout section. By the way, when we investigated the dropout in detail in the device that records and plays back on a disk as mentioned above, we found that in the dropout section, not only is the FM signal missing, but there are special cases as shown in Figure 3a. I found out that there is.

FIG. 3a shows the output waveform when the signal on the disk is optically reproduced as a means for reading the signal on the disk. In FIG. 3a, the dropout sections are indicated by D, E, F, G, and H. F is
This is a dropout section where only the FM signal, which is seen on conventional VTRs, is missing. D,
E, G, and H are dropout sections that are different from conventional ones. An irregular waveform dropout with a much larger amplitude than the reproduced FM signal occurs, and the FM signal is missing in that section. In addition, the frequency components of these dropouts are lower than the frequency band of the FM signal, as shown in D, E, and F in Figure 3a, and
The frequency components in the dropout section, such as those included in the modulation frequency band of the FM signal, are also irregular, as shown in G and H (Figure 3b shows an enlarged view of G and H in Figure 3a). .

A case where the dropout section as described above is detected by a conventional dropout detection device as shown in FIG. 1 will be described.

Generally, in the above-mentioned apparatus, a selective amplifier is used to amplify high-frequency components in order to correct the recording/reproducing characteristics of the disk and to remove low-frequency noise. The output is shown in Figure 3c. At this time,
Dropout section of relatively low frequency components, D,
Although the amplitudes of E and F are attenuated, high frequency components such as dropout sections G and H cannot be attenuated and remain as shown in FIG. 3c. Therefore, when added to the dropout detection device shown in FIG. 1, the result will be as shown in FIG. 3 d, e, f, and g. d is the output waveform of limiter 1. e is half wave rectifier circuit 2
This is the output waveform of f is the output of the low-pass filter 3. g is the output waveform of the comparison circuit 4. In this way, in the conventional method as shown in Fig. 1, the third
As shown in Figure a, it was found that the dropout peculiar to a disk, which occurs when recording and reproducing data on a disk, cannot be detected. Furthermore, in the case of disks, it has been found that there are many dropouts with relatively narrow widths such as dropouts G and H.

The present invention provides a dropout detection circuit that can also detect dropouts of such relatively high frequency components. An embodiment of the present invention is shown in FIG. In the configuration diagram of FIG. 4, the same parts as in FIG. 1 are given the same numbers. Input terminal A
The reproduced FM signal from the disc is input. This reproduced FM signal has passed through the aforementioned selective amplifier etc. in order to FM demodulate an information signal such as a video signal, and an example of its waveform is shown in FIG. 3b. The reproduced FM signal input from terminal A is input to bandpass amplifier 5. The bandpass amplifier 5 amplifies high frequency components including the FM modulation frequency band, and eliminates frequency components below that. An example of the frequency characteristics of the bandpass amplifier 5 is shown in the seventh section.
As shown in the figure. The dotted line "" indicates an example of the FM modulation frequency band, and the "" indicates an example of the frequency characteristics of the bandpass amplifier 5.

The output signal of bandpass amplifier 5 is output from limiter 1.
After aligning the amplitude, enter the half-wave rectifier circuit 2,
The output is applied to a low-pass filter 3 to output the amplitude variation, and a comparison circuit 4 compares it with a detection level input from a terminal C to detect a dropout section. On the other hand, the output of the bandpass amplifier 5 is sent to a comparison circuit 8 via a comparison circuit 7 and an inversion circuit 6.
is input to. Comparing circuits 7 and 8 mainly detect dropouts included in the FM modulation frequency band, and compare them with the detection level input from terminal I to detect dropouts.

The output signals of the respective comparison circuits 4, 7, and 8 are added by an adder circuit 9, and output from terminal B as a dropout detection signal.

The operating waveforms of each of these parts are shown in FIGS. 5 and 6. Figure 5a shows the waveform of the reproduced FM signal from the disk, and the dropout waveforms are D, E,
Shown in F, G, and H. Dropouts D, E, and F indicate dropouts of relatively low frequency components,
G and H indicate dropouts of high frequency components included in the FM modulation frequency band, as shown in FIG. 3b. FIG. 5b shows the output waveform of the bandpass amplifier 5. Since the bandpass amplifier 5 has frequency characteristics as shown in FIG. average level. But F.M.
Dropouts G and H that are included in the modulation frequency band are passed through as they are. 5c shows the output waveform of the limiter 1, FIG. 5d shows the output waveform of the half-wave rectifier circuit 2, and FIG. 5e shows the output waveform of the low-pass filter 3. In FIG. 5e, dotted line A indicates the detection level input from terminal C. FIG. 5f shows the output waveform of the comparison circuit 4. Here, dropouts of frequency components lower than the FM modulation frequency can be detected. Next, Figure 6 a is played in the same way as Figure 5 a.
Shows FM signal. FIG. 6b shows the output waveform of the bandpass amplifier 5, and in the comparator circuit 7, the output waveform is
Detection level to be input (shown in Figure 6 b)
, the dropout G appearing above the FM signal is detected. FIG. 6g shows an output waveform obtained by inverting the output signal of the bandpass amplifier 5 by the inverting circuit 6, and the FM signal is Dropout H that appears higher is detected. The output waveforms of the respective comparison circuits 7 and 8 are shown in FIGS. 6h and 6i. Here, it is also possible to detect dropouts of high frequency components such as those included in the FM modulation frequency band. Furthermore, the signals in which dropout was detected are shown in Fig. 6 h, Fig. 6 i, and Fig. 5 f.
are added by the adder circuit 9, resulting in the output waveform shown in FIG. 6j.

As described above, according to the present invention, it is possible to detect dropouts having various frequency components and dropouts having various levels contained in the reproduced signal of the signal recorded on the aforementioned disk. In particular, it is particularly effective for detecting dropouts and the like that have relatively high frequency components that occur during optical reproduction.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of a conventional dropout detection device, FIG. 2 is a waveform diagram showing the operation of the dropout detection device shown in FIG. 1, and FIG.
FIG. 4 is a block diagram showing an embodiment of the present invention, FIG. 5 is a waveform diagram of each part of FIG. 4, and FIG. FIG. 7, which is a waveform diagram of each part in another state of the block diagram of the present invention shown in the figure, is a diagram showing an example of the frequency characteristics of the bandpass amplifier shown in FIG. 4. 1... Limiter, 2... Half wave rectifier circuit, 3...
Low pass filter, 4, 7, 8... Comparison circuit, 5
...Band pass filter, 6...Inversion circuit, 9...
...addition circuit.

Claims (1)

[Claims] 1 Separation means for separating a frequency modulated signal whose dropout is to be detected into a high frequency component including a frequency modulation frequency band and a lower frequency component, and a section where the amplitude of the lower frequency component is below a predetermined level is detected as a dropout. a first detecting means for detecting a section, a second detecting means for detecting a section in which the amplitude of the high frequency component is equal to or higher than a predetermined level as a dropout section, and the first detecting means and the second detecting means. 1. A dropout detection device comprising: addition means for adding outputs, and the output of the addition means is used as a dropout detection signal of a frequency modulated signal.