JPH0634295B2 - Dropout detection device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial Field of the Invention The present invention relates to dropout detection devices, particularly video signals,
The present invention mainly relates to a dropout detection device suitable for detecting dropouts in an FM signal.

(Prior Art) As is well known, in a video signal reproducing apparatus, when a video signal on a recording medium is reproduced, a signal is lost due to various causes.
That is, dropouts often occur, and therefore, in such devices, it is customary to take measures to compensate for signal dropouts.

It is necessary to accurately detect dropouts in order to perform good dropout compensation, and various proposals have been made for this purpose.

FIG. 3 shows an example thereof, in which an FM luminance signal as shown in S-1 of FIG. 4 is inputted to the input terminal 1, which is amplified by the amplifier (hereinafter, AMP) 2. After that, AM detection is performed by the AM detection circuit 3 to obtain a signal as shown in S-3 in FIG. In this case, the time constant is selected so that the carrier component of the FM signal S-1 is removed and the dropout portion is passed. The AM detection signal S-3 is further smoothed at the dropout portion by a low-pass filter (LPF) 4 having a sufficiently large time constant (S-4 in FIG. 4). L
The output S-4 of the PF 4 is applied to one input of the comparator 5, where it is compared with the output S-3 of the AM detection circuit 3 applied to its + input, and its output is shown in FIG. 4 S-5. During the dropout period as shown, a low level signal is obtained and is output from the output terminal 6 as a dropout detection signal.

However, in the apparatus having the configuration shown in FIG. 3, dropout detection is performed based on the level of the envelope detection output by the AM detection circuit 3, so that it is called, for example, 1 to 2 μs. Such a dropout having an extremely short period is difficult to detect satisfactorily.

FIG. 5 shows another conventional example. This conventional example can overcome the above-mentioned difficulties in the conventional example shown in FIG.

In the figure, for example, an FM luminance signal as shown in S-11 in FIG.
After being amplified by the limiter 13 shown in FIG.
The signal has a constant level as shown by -13. The output S-13 of the limiter 13 is set to be high while a signal of a predetermined period T or less (or a predetermined frequency f = 1 / T or more) is being input, and the period becomes longer than T. (Or the frequency becomes lower than f) it is applied to the period detector 14 which makes its output low. Therefore, if the set period T of the period detector 14 is selected to be, for example, about 1 to 2 μs, its output is low when there is a long dropout exceeding T as shown in S-14 of FIG. Next to
Thus, the output S-14 of the same period detector 14 is obtained from the output terminal 15 as a dropout detection signal.

However, even in the configuration shown in FIG. 5, other problems will occur. That is, when the dropout period is relatively long and noise is generated during the dropout period, this noise causes the period detector 1
4 may be triggered, and a detection signal indicating that it is not a dropout may be output despite the dropout.

In consideration of the above, in order to be able to detect a dropout of an extremely short period to a dropout of a relatively long period, for example, the output of the output terminal 6 of FIG. 3 and the output of the output terminal 15 of FIG. Both devices may be combined so that the logical sum of both detection outputs of the devices of FIGS. 3 and 5 can be obtained by inputting.

(Problems to be solved by the invention) However, when the devices of FIGS. 3 and 5 are combined by an OR gate, the response performance of the OR gate, particularly, the mechanism of FIG. 5 can be obtained. There is concern about the response performance to a detection signal for a dropout of an extremely short period of about 1 to 2 μsec, and there is a fear that the detection signal may be blocked by the OR gate.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a dropout detection device that can detect very well from a very short time dropout to a relatively long time dropout by simple means. And

(Means for Solving the Problems) In order to achieve the above object, the present invention is a device for detecting a dropout in an input signal, the dropout in the input signal having a relatively long period. A first dropout detection unit for detecting the first dropout detection unit; and a second dropout detection unit capable of detecting a dropout in a period shorter than the period detectable by the first dropout detection unit. A dropout detection device characterized by performing dropout detection by supplying the output obtained through the first dropout detection means to the second dropout detection means.

(Operation) According to the present invention having the above-described configuration, a wide range of dropouts from a relatively long dropout to a short dropout can be achieved by the cooperation of the first dropout detection means and the second dropout detection means. Can be detected.

(Embodiment) An embodiment of the present invention will be described below with reference to FIG.

The example shown in FIG. 1 is a combination of the conventional examples shown in FIGS. 3 and 5 according to the present invention. In the figure, the same reference numerals as those in FIGS.

In the figure, 16 is an AND gate which is an example of a regulation circuit for regulating the output of AMP2, that is, the input signal based on the output of the comparator 5, that is, the dropout detection output. Output S-5
, And therefore its output S-16 is shown in FIG.
As shown in -16, a signal corresponding to the input signal S-1 having a constant amplitude in which the signal including noise is removed only during the dropout period is obtained. The output of the AND gate 16 is input to the synchronism detector 14, and as a result, from the same period detector 14, the output S-5 of the comparator 5 and the output S- of the synchronism detector 14 described in FIG. A signal S-5 + S-14 obtained by synthesizing 14 and 14 is obtained, and the same signal is output from the output terminal 15 as a dropout detection signal.

Here, in the output S-16 of the AND gate 16, while the output S-5 of the comparator 5 is low, noise is satisfactorily blocked by the action of the AND gate 16, so during this low period. The fear of the period detector 14 being triggered is eliminated, and the configuration shown in FIG. 1 eventually makes it possible to cope well with a very short dropout to a relatively long dropout.

In FIG. 1, elements 3 to 5 form a first dropout detection circuit, and the period detector 14 is a second dropout detection circuit.
In this case, the dropout detectability of the period detector 14 as the second detection circuit is higher than that of the first detection circuit, that is, the dropout detection circuit is detected by the first detection circuit. It goes without saying that the settings are made so that dropouts in a shorter period than possible can be detected.

(Effects of the Invention) As described in detail above, according to the present invention, it is possible to satisfactorily detect from an extremely short-term dropout to a relatively long-term dropout by an extremely simple means. It is extremely useful in a seed dropout detection device.

[Brief description of drawings]

 FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a diagram showing input / output of essential parts in FIG. 1, FIG. 3 is a diagram showing an example of the prior art, and FIG. FIG. 5 is a diagram showing input / output of main parts, FIG. 5 is a diagram showing another conventional example, and FIG. 6 is a diagram showing input / output of main parts in FIG. 3 ... AM detector, 4 ... LPF, 5 ... comparator, 14 ... period detector, 16 ... AND gate.

Claims (1)

[Claims] 1. An apparatus for detecting a dropout in an input signal, comprising: first dropout detection means for detecting a dropout in the input signal for a relatively long period of time; Second dropout detecting means capable of detecting a dropout in a period shorter than the above period detectable by the dropout detecting means of the above, and the output obtained through the first dropout detecting means is described above. A dropout detection device, which performs dropout detection by supplying the dropout detection means to a second dropout detection means.