JPH0573317B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a so-called dropout compensation device that compensates for a signal dropout portion of a reproduced signal obtained in a magnetic recording/reproducing device, a video disk device, or the like.

[Conventional technology]

In the conventional dropout compensator, the dropout is reduced, for example, as discussed in Image Electronics Course 4, Image Recording and Reproduction, published by Corona Publishing, 1978, by Minoru Inazu, Masatsugu Yasu, and Kotaro Yokokawa, pages 223 to 225. As a compensation method, the first method detects a signal missing part (dropout part) of the reproduced signal using a dropout detector and compensates by replacing this part with the reproduced RF signal 1H before. There is a second method in which compensation is performed by replacing the demodulated video signal with the demodulated video signal.

Regarding these first and second conventional methods,
This will be explained using FIGS. 3 and 4.

FIG. 3 is a block diagram showing a conventional example of a dropout compensator, which uses the first method described above as a compensation method.

In Figure 3, 1 is a 1H delay circuit that delays the input signal by 1H, 2 is the first switch that switches between the delayed signal and the undelayed signal, and 3 is the demodulator of the video signal from the input reproduced RF signal. Demodulator 4 is a dropout detector.

The reproduced RF signal is supplied to one input terminal of the first switch 2, passes through the 1H delay circuit 1, becomes an RF signal delayed by 1H, and is supplied to the other input terminal of the first switch 2. be done.

Further, the reproduced RF signal is supplied to the 1H delay circuit 1 and the first switch 2, and at the same time, it is also sent to the dropout detector 4. The dropout detector 4 detects the dropout portion of the input reproduced RF signal and outputs a pulse that is at a high or low level during the dropout period.

The first switch 2 is switched by the pulse signal, and normally the first switch 2 is switched to the one that is not delayed.
The RF signal is sent to the demodulator 3, and at the time of dropout, the reproduced RF signal delayed by 1H is sent to the demodulator 3.

As a result, the missing portion (dropout portion) of the input reproduced RF signal is replaced with the reproduced RF signal delayed by 1H, and the demodulator 3 demodulates the video signal with the dropout compensated.

FIG. 4 is a block diagram showing another conventional example of a dropout compensator, which uses the second method described above as a compensation method.

In Figure 4, 1 to 4 are respectively 1 in Figure 3.
~4.

The reproduced RF signal is demodulated into a video signal by the demodulator 3,
It is supplied to one input terminal of the first switch 2. At the same time, the demodulated video signal is
The video signal is delayed by 1H through the delay circuit 1, and is supplied to the other input terminal of the first switch 2. The first switch 2 is switched by a switching signal from the dropout detector 4, and detects the missing part of the reproduced video signal at the time of dropout.
By replacing the reproduced video signal with a 1H delayed reproduced video signal, a reproduced video signal with dropout compensated is output.

Note that the detection method used in the dropout detector 4 described above includes an amplitude detection method that detects a dropout portion from amplitude changes in the reproduced RF signal using envelope clean detection or soft limiting (limiting with a high limiting level); Detects the dropout portion from the change in pulse width (frequency) of a signal that has been hard limited (the limiting level is low, and the resulting waveform is close to a square wave) on the reproduced RF signal using a monomulti. Frequency detection methods are generally known.

In other words, in the dropout part, the input playback
The amplitude of the RF signal naturally decreases, so in the former amplitude detection method, the amplitude of the reproduced RF signal is monitored, and when the amplitude drops below a certain specified value,
That part is detected as a dropout part.

In addition, since the frequency range of the input reproduced RF signal is predefined, the frequency range of the input reproduced RF signal is determined in advance.
When looking at the frequency of the RF signal (i.e., the pulse width of the hard-limited signal), the frequency (pulse width) at which that frequency (pulse width) is specified
It checks whether the frequency is within the specified frequency range, and if it is outside the specified frequency range, that part is detected as a dropout part.

[Problem that the invention seeks to solve]

In the conventional example shown in Figure 3, when the reproduced RF signal uses a modulation method such as frequency or phase modulation in which signal information is determined by the zero passage of the carrier wave, the carrier wave is modulated with the video signal. If the signal delayed by the 1H delay circuit 1 and the signal not delayed are switched by the first switch 2, there is a phase difference between the two signals, so the moment of switching , a sudden phase shift occurs, and in the reproduced video signal obtained by demodulating this, a bright or dark spot-like disturbance appears depending on the phase difference.
In other words, in the case of the configuration shown in Fig. 3, the problem is that spot-like interference appears at the moment when dropout is detected and switch 2 is turned on, and at the moment when switch 2 is returned to its original state after dropout detection is completed. There is.

However, in the conventional example shown in FIG. 4, the replacement is performed in the demodulated video signal, so the problem as in the conventional example shown in FIG. 3 does not occur.

By the way, in general, in magnetic recording/playback devices, video disk devices, etc., fluctuations in the time axis occur due to uneven rotation of the disk motor and head motor, eccentricity of the disk, expansion and contraction of the tape, etc., which causes shaking and hue shifts on the monitor screen. , it is necessary to suppress time axis fluctuations using a time axis compensation circuit (hereinafter referred to as TBC).

Therefore, next, using the conventional example shown in Fig. 4,
Let's consider providing a time axis compensation circuit to the dropout compensation device.

In FIG. 4, the reproduction input to the demodulator 3
The RF signal includes an audio signal in addition to the video signal, but since the audio signal is separated in the demodulator 3, only the video signal is transmitted to the stage subsequent to the demodulator 3. Therefore, when the TBC is provided in FIG. 4, it is convenient to place the TBC at a stage before the demodulator 3, since it is possible to perform time axis compensation for the video signal and the audio signal at once. .

Therefore, as shown in Fig. 5, the
Consider a dropout compensator equipped with a TBC.

In Figure 5, 5 is the time base compensation circuit (TBC)
It is.

The TBC5 first hard limits the input reproduced RF signal and converts it into a pulsed (i.e. square wave) signal.
The time axis correction is performed by shaping the waveform of the signal and controlling the rise and fall times of the signal using a time axis error signal.
Therefore, the signal output from the TBC 5 is output as a hard limited signal, that is, a pulsed signal.

On the other hand, in the example shown in FIG. 5, a frequency-based dropout detection circuit 4b is used as the dropout detector 4. As described above, in the frequency detection method, dropout is detected from changes in the pulse width of a hard-limited signal. Therefore, the output from the TBC 5 may be used as the input to the dropout detection circuit 4b. In other words, the dropout detection circuit 4b
is connected to the output of TBC5, as shown in FIG.

However, the conventional example shown in FIG. 5 has the following problems.

FIG. 6 is a waveform diagram showing signal waveforms of the reproduced RF signal and TBC output in FIG. 5.

That is, as shown in Figure 6a, if noise is superimposed on the dropout part of the reproduced RF signal,
When that portion is hard limited in the TBC 5, the noise portion also becomes a pulse-like signal, as shown in FIG. 6b. Moreover, when the pulse width W ₂ of the noise portion is very close to the pulse width W ₁ of the reproduced RF signal, the dropout detection circuit 4b sets the pulse width W ₂ within the above-mentioned specified pulse width range. There was a risk that the noise portion would be erroneously detected as not being a dropout portion even though it was a dropout portion.

Therefore, in order to prevent such erroneous detection, it is conceivable to use an amplitude detection method as well as a frequency detection method as the dropout detector 4, and to use both in combination.

FIG. 7 shows a conventional dropout compensation device that uses a dropout detection circuit 4a (hereinafter referred to as A.DET) using an amplitude detection method and a dropout detection circuit 4b (hereinafter referred to as F.DET) using a frequency detection method. FIG. 2 is a block diagram showing an example.

The conventional example shown in Fig. 7 is A.DET4a and F.DET
4b, input each dropout detection pulse to the OR circuit 6, and take the logical sum of the two. If either one is considered to be a dropout part, that part is compensated as a dropout. It is.

By the way, the dropout detection circuit using the amplitude detection method, that is, A.DET4a, detects dropout by looking at the amplitude change of the input signal, so the output of TBC5 shown in FIG. 6b,
Dropouts cannot be detected from hard limited signals. Therefore,
A.The signal input to DET4a is a signal that is not hard limited, that is, TBC
The signal before 5 inputs will be used, so A.DET4
a is connected to the input of TBC 5 as shown in FIG.

With this configuration, in this conventional example, as shown in FIG. 6a, even if noise is added to the dropout portion of the reproduced RF signal, the amplitude remains small in the dropout portion, so that A.
DET4a can correctly detect that it is a dropout part, so F.DET4
Erroneous detection due to noise in b can be compensated for.

However, in A.DET4a, as mentioned above, TBC is used as a dropout detection signal.
5. In the conventional example shown in FIG.
Even though the RF signal contains time-axis fluctuations, the playback video signal to which switching is performed contains almost no time-axis fluctuations.
A.The dropout part detected by DET4a,
There is a time lag between the first switch 2 and the dropout portion of the reproduced video signal, and as a result, the timing at which dropout compensation is performed is shifted, making it impossible to completely compensate for the dropout portion. The problem is that it can't be done.

The present invention has been made in view of the problems of the prior art described above, and therefore, an object of the present invention is to perform dropout detection with higher precision by using both a frequency detection method and an amplitude detection method, and to Even in a configuration in which a TBC is placed before the demodulator, the dropout portion detected by the amplitude detection method and the dropout portion of the reproduced video signal that should be compensated can be matched in time to achieve complete dropout compensation. The object of the present invention is to provide a dropout compensating device that can perform the following steps.

[Means for solving problems]

In order to achieve the above-mentioned object, in the present invention,
A first detecting means (i.e., A. DET) and
a first replacing means for replacing a portion considered to be a dropout portion of the reproduced RF signal with a certain predetermined amplitude level according to the detection signal; and inputting the replaced reproduced RF signal to check the frequency;
If the frequency is outside the specified range, the second detection means (i.e., F.
DET) and a second replacement means for replacing a portion deemed to be a dropout portion of the reproduced RF signal by the second detection means with a dropout compensation signal using a detection signal from the second detection means. It was made to consist of . Further, when a time base compensating means (ie, TBC) is provided, it is provided between the first replacing means and the second detecting means.

[Effect]

Since the TBC is arranged after the first replacement means, the reproduction RF input to the A.DET
a signal and a reproduction input to the first replacement means;
The RF signal includes the same time axis fluctuation, so the dropout portion detected in A.DET and the reproduced RF input to the first replacement means
It coincides in time with the dropout portion of the signal. As a result, in the first replacement means, the dropout portion of the input reproduced RF signal is replaced with a certain predetermined amplitude level. The replaced reproduced RF signal is then compensated for time axis fluctuations in the TBC and input to the F.DET.
The portion of the input reproduced RF signal that has been replaced with a certain predetermined amplitude level is a frequency component lower than the frequency of the reproduced RF signal, so it is detected as a dropout portion by F.DET. Thereafter, the dropout portion is replaced by a dropout compensation signal by the second replacement means, thereby performing dropout compensation.

As mentioned above, since A.DET and F.DET are used together, even if there is noise in the dropout part of the reproduced RF signal, there will be no false detection and more accurate dropout detection can be performed. can.
Further, since the dropout portion detected by A.DET and the dropout portion of the reproduced signal to be compensated can be matched in time, the dropout portion can be completely compensated for.

Embodiment An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

FIG. 1 is a block diagram showing one embodiment of the present invention.

In FIG. 1, the aforementioned FIGS. 3 to 5,
And those with the same symbols as those in Figure 7 are:
Assume that the circuits are the same. In addition, 7 is a waveform shaping circuit, 8 is a second switch, and 9 is a power supply.

Further, FIG. 2 is a waveform diagram showing the waveforms of the main signals in FIG. 1.

In FIG. 2, a is the reproduced RF signal, b is the output of the waveform shaping circuit 7, c is the detection pulse of the A.DET 4a, and d is the output of the second switch 2.

The reproduced RF signal shown in FIG. 2a is supplied to the waveform shaping circuit 7 as shown in FIG.
As shown in FIG. b, the signal is hard limited and input to one input terminal of the second switch 8. A voltage V _D approximately equal to the high or low level of hard limiting in the waveform shaping circuit 7 is input from the power supply 9 to the other input terminal of the second switch 8 .

The reproduced RF signal is supplied to the waveform shaping circuit 7, and at the same time, is also supplied to the A.DET 4a, where
Dropout detection is performed as described above. Applicable
A.DET 4a is constructed using a known technique such as envelope detection, and outputs a detection pulse that coincides in time with the dropout portion of the input reproduced RF signal, and at the time of dropout, the second switch 8 is turned off. Switch to the 9 side.

That is, the detection pulse from A.DET4a is the second
As shown in Figure c, the dropout part is at a high level (it does not matter if the dropout part is at a low level and the normal time is at a high level), and by switching the second switch 8 in response to this detection pulse, the dropout is at a high level. part is replaced with a high-level (or low-level) voltage V _D , and the second switch 8 outputs a hard-limited reproduced RF signal with a waveform as shown in FIG. 2d. Ru.

Therefore, noise exists in the dropout portion of the original reproduced RF signal as shown in FIG. 2a, and is hard limited in the waveform shaping circuit 7.
Even if the noise part becomes a _pulse -like signal as shown in FIG. It has a pulse-like waveform with a lower frequency than the reproduced RF signal.

In addition, the detection pulse from A.DET4a is the reproduction RF
Considering that the signal is slightly disturbed immediately after the dropout ends, in order to compensate for this, the trailing edge may be delayed in the sense of making the period longer than the actual dropout occurrence period.

Next, TBC5 is a regenerated RF after hard limiting in which the dropout part is replaced with high level voltage _VD at second switch 8.
The signal is subjected to time axis compensation according to the time axis error signal, and then supplied to the demodulator 3 and the F.DET 4b.

Time axis compensated reproduced RF input to demodulator 3
The signal is demodulated into a video signal, and then connected to one input terminal of the first switch 2 and the 1H delay circuit 1.
supplied to Then, in the 1H delay circuit 1,
The video signal delayed by 1H is supplied to the other input terminal of the first switch 2 as a dropout compensation signal.

In addition, the above F.DET4b is a playback with time axis compensation.
As described above, the dropout portion is detected based on the frequency of the RF signal and a detection pulse is output.

At this time, the part replaced by the high-level voltage V _D by the detection pulse of A.DET4a is a frequency component lower than that of the reproduced RF signal, so F.
It is detected as a dropout part by DET4b. In other words, as shown in FIG. 2d, the pulse width W ₃ of the portion replaced by the high-level voltage V _D is equal to the pulse width W ₁ of the reproduced RF signal.
Since the width is very wide compared to F.DET4b,
The pulse width _W3 is determined to be outside the range of the specified pulse width mentioned above, and that portion is detected as a dropout portion.

Thereafter, the detected pulse from the F.DET 4b is sent to the first switch 2, and compensation is performed by replacing the dropout portion of the demodulated video signal with a demodulated video signal delayed by 1H. Note that the demodulated output is actually band-limited by a low-pass filter, and therefore a time difference occurs between the input and output of the demodulator 3 due to the time constant of the filter. Therefore, F.
It is preferable to delay the detection pulse of DET4b and widen the pulse width by taking into account variations in time constants between components.

As explained above, in this embodiment, A.DET4
A and F.DET4b are used together to perform dropout compensation on the video signal, and at the front stage of the demodulator 3.
In a configuration with TBC5, A.DET4a
The dropout part of the reproduced RF signal detected by F.DET4b is replaced with a high or low level by the second switch 8, and the signal is time-base compensated because the dropout part has a lower frequency than the reproduced RF signal. Dropout compensation is performed by replacing the dropout portion of the video signal detected as a dropout and time-base compensated using the detected pulse with a video signal delayed by 1H. As a result, in effect, A.
The dropout portion detected by the DET 4a and the dropout portion of the reproduced video signal to be compensated can be made to coincide in time, and complete dropout compensation can be performed.

〔Effect of the invention〕

According to the present invention, since A.DET and F.DET are used together, even if there is noise in the dropout part of the reproduced RF signal, there will be no false detection, and dropout detection can be performed with higher accuracy. I can do it. Furthermore, since the dropout portion detected by A.DET and the dropout portion of the reproduced video signal to be compensated can be matched in time, the dropout portion can be completely compensated for.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention.
FIG. 2 is a waveform diagram showing the waveforms of the main signals in FIG. 1, FIGS. 3 to 5 are block diagrams showing conventional dropout compensation devices, and FIG. 6 is the waveform of the main signals in FIG. 5. Waveform diagram showing 7th
The figure is a block diagram showing another conventional example of a dropout compensator. Description of symbols: 1...1H delay circuit, 2...first switch, 3...demodulator, 4...dropout detector,
4a…A.DET, 4b…F.DET, 5…TBC, 7…
Waveform shaping circuit, 8...second switch, 9...power supply.

Claims (1)

[Claims] 1. A first device that checks the amplitude of the input reproduced RF signal and, if the amplitude is outside the specified range, regards that portion as a dropout portion and outputs a detection signal corresponding to that portion. a detecting means; a first replacing means for replacing a portion deemed to be a dropout portion of the reproduced RF signal with a certain predetermined amplitude level according to the detection signal;
a second detection means that inputs an RF signal and checks the frequency, and if the frequency is outside a specified range, considers that part as a dropout part and outputs a detection signal corresponding to that part; and second replacement means for replacing the portion deemed to be a dropout portion of the reproduced RF signal by the second detection means with a dropout compensation signal based on the detection signal from the detection means. dropout compensator. 2. In the dropout compensation device according to claim 1, the signal replaced by the second replacing means is a reproduced video signal obtained by demodulating the reproduced RF signal, and the dropout compensation signal to be replaced is delayed. A dropout compensation device characterized in that the reproduced video signal is the above-mentioned reproduced video signal. 3. The dropout compensating device according to claim 1, further comprising a time axis compensating means after the first replacing means, and the reproduced RF signal input to the second detecting means is The signal is a signal whose time axis fluctuation has been compensated by the axis compensation means, and the signal replaced by the second replacing means and the dropout compensation signal to be replaced are also signals whose time axis fluctuation has been compensated by the time axis compensation means. A dropout compensator characterized by: