JPH03253187A - Noise reduction device - Google Patents

Abstract

PURPOSE:To eliminate an edge noise effectively without attenuating a reduction signal by controlling a noise reduction circuit to be operated only for an edge period of a large amplitude of an input signal. CONSTITUTION:The device is provided with noise reduction circuits 2, 4A and a control circuit 6. Then a comparator 60 of the control circuit 6 detects an edge period of a large amplitude causing the edge noise, a low pass filter 61 and a comparator 62 adjust the timing of the detected signal and applies the signal to a switch circuit 47 of the noise reduction circuit 4A to activate the noise reduction circuit 4A for the edge period only and to stop the operation for the other period. Thus, a minute signal component is subject only to the effect of the noise reduction of the noise reduction circuit 2 and not much attenuated. Moreover, the edge noise is sufficiently eliminated by the noise reduction effect of the noise reduction circuit 4A.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a noise reduction device that reduces noise in a reproduced signal in luminance signal processing of a VTR or the like.

[Prior Art] The configuration of a conventional example will be described with reference to FIGS. 4, 5, and 6.

FIG. 4 is a block diagram showing a conventional noise reduction device, and FIGS. 5 and 6 are circuit diagrams showing a noise reduction circuit of the conventional noise reduction device.

In FIG. 4, the conventional noise reduction device has an input terminal (1
) and a noise reduction circuit (
2), an input/output terminal (3) connected to this noise reduction circuit (2), a noise reduction circuit (4) connected to this input/output terminal (3), and this noise reduction circuit N (4). and an output terminal (5) connected to.

In FIG. 5, the noise reduction circuit (2) has an input terminal (1
), a low-pass filter consisting of a resistor (20) and a capacitor (21), a subtracter (22) connected to the input terminal (1) and the low-pass filter, and a limiter connected to this subtracter (22). (23) and the input terminal (
1) and a subtractor (24) connected to the low-pass filter.
, a subtractor 25) connected to the limiter (23) and the subtracter (24), and a low-pass filter and subtractor (25).
) and a booster (26) whose input side is connected to the input/output terminal (3) and whose output side is connected to the input/output terminal (3).

In FIG. 6, the noise reduction circuit (4) has an input/output terminal (
The delay line (40) connected to
), an adder (42) connected to the input/output terminal (3) and the delay line (41), and a coefficient multiplier (43) connected to the adder (42). ) and a subtracter (44) connected to the delay line (40) and the coefficient unit (43).
) and a limiter (45) connected to this subtracter (44).
), and a subtracter (46) whose input side is connected to the delay line (40) and the limiter (45), and whose output side is connected to the output terminal (5>).

Next, the operation of the conventional example described above is shown in FIGS. 7, 8, and 9.
This will be explained with reference to the figures and FIG.

7(a) to 7(f) are waveform diagrams showing signals of each part of the noise reduction circuit (2>) of a conventional noise reduction device, and FIG. 8(a) to
(g) is a waveform diagram showing the signals of each part of the noise reduction circuit (4), Figure 9 is a characteristic diagram showing the frequency characteristics of the noise reduction circuit (2), and Figure 10 is the frequency characteristic of the noise reduction circuit (4). FIG.

As shown in FIG. 7(a), a signal A containing noise is input to the input terminal (1). The high-frequency components and noise are removed by a low-pass filter, and the signal B shown in Figure 7(b)
The waveform becomes A subtracter (22) takes the difference between signals A and B and outputs a signal C as shown in FIG. 7(c). The high-frequency components of this signal C are cut off by a limiter (23), resulting in the signal E shown in FIG. 7(d). 25), the high-frequency component signal F is obtained as shown in FIG. 7(e).
By adding the signals B and F in an adder (26), it is possible to obtain a signal G in which the high-frequency components of the signal B are restored and the noise is reduced.

In the noise reduction circuit (2) shown in Fig. 5, the limiter (23
), as shown in FIG. 7(d), high-frequency signal components below the limit level remain, resulting in edges being shaved off like signal G. Moreover, since the noise in this part is not removed, it becomes edge noise and remains in the output signal. In order to improve the noise, the next stage noise reduction circuit (4) shown in FIG. 6 is used.

As shown in FIGS. 8(b) and (c), the signal G that has passed through the noise reduction circuit (2) is delayed by a certain period of time t in the delay lines (40> and (41), respectively. Become.

The adder (42) adds the signals G and J, and this output becomes a signal of 1/2 level by the coefficient unit <43> as shown in FIG. 8(d).

The subtracter (44) subtracts the signal K from the signal H to obtain the result shown in FIG.
) is obtained. From this signal, a limiter (45
) to remove large-amplitude components, the signal M shown in Fig. 8 (f>
get. Then, when the subtracter (46) subtracts the signal M from the signal H, the 8th Q? As shown in I(g), a signal N with almost no edge noise can be obtained.

However, as shown in Figures 9 and 10, the frequency characteristics of the noise reduction circuits (2) and (4) are greatly attenuated when the input level is below the -20 dB and -30 dB limiter levels, so the noise component However, at the same time, even minute signal components are attenuated.

“Problems to be Solved by the Invention” In the conventional noise reduction device as described above, the noise component as well as the minute signal component are attenuated. There was a problem that it could not be removed sufficiently.

The present invention was made to solve the above-mentioned problems, and an object of the present invention is to obtain a noise reduction device that can effectively remove edge noise without attenuating minute signals.

[Means for Solving the Problems] A noise reduction device according to the present invention includes the following means.

(i) a plurality of noise reduction circuits that reduce noise in the input signal;

(ii) A control circuit that detects edge portions of the input signal and controls the noise reduction circuit to operate only during large amplitude edge periods of the input signal.

[Operation] In the present invention, the noise of the input signal is reduced by a plurality of noise reduction circuits.

Further, the control circuit detects an edge portion of the input signal, and controls the noise reduction circuit to operate only during the large amplitude processing period of the input signal.

[Embodiment] The configuration of an embodiment of the present invention will be described with reference to FIGS. 1 and 2.

FIG. 1 is a block diagram showing an embodiment of the present invention, including input terminals (1) to input/output terminals (3), and output terminals (5).
is exactly the same as that of the conventional device described above.

In FIG. 1, one embodiment of the present invention has a device that is exactly the same as that of the conventional device described above, and a noise filter having an input side connected to the input/output terminal (3) and an output side connected to the output terminal (5). It is connected to a reduction circuit (48) and a control circuit (6) whose input side is connected to the noise reduction circuit (2) and whose output side is connected to the noise reduction circuit (4^).

FIG. 2 is a circuit diagram showing a specific tank bottom of the embodiment shown in FIG. 1.

The noise reduction circuit (4^) is the same as the noise reduction circuit (4^) of the conventional device.
), a switch circuit (47) is inserted between the limiter (45) and the subtracter (46).

The control circuit (6) also includes a comparator (60) connected to the subtracter (22) of the noise reduction circuit (2), and a low-pass filter (60) connected to the comparator (60).
1) and a switch circuit (47>) whose input side is connected to this low-pass filter (61>) and a noise reduction circuit (48).
and a comparator (62) whose output side is connected to. Note that the noise reduction circuit (2>) is exactly the same as that of the conventional device.

Next, the operation of the above embodiment will be explained with reference to FIG.

First? I(a) to (f) are waveform diagrams showing signals of various parts in an embodiment of the present invention.

The signal C, which is the output of the subtracter (22), is a signal obtained by first-order differentiation of the input signal, as shown in FIG. 3(a). This signal C becomes the signal P shown in FIG. 3(b) through a comparator (60), and becomes the signal Q through a low-pass filter (61) with optimally selected constants.
), a signal R in the form of a rectangular wave is obtained by the comparator (62).

This signal R causes the limiter of the noise reduction circuit (4^) to
45> is switched to operate the noise reduction circuit (4^) only during the edge period of the signal H shown in FIG. 3(e). As a result, during the edge period, the noise reduction circuit (2) and (
4^) operates, and the noise reduction circuit (2) operates except during the edge period.
Only the noise reduction circuit (4^>) operates and the signal only passes through, and the minute signal component is not attenuated.

As described above, in one embodiment of the present invention, a comparator (60) detects a large-amplitude edge period in which edge noise occurs, and a low-pass filter (61) and a comparator (62) detect the timing and time width of the detected signal. By adjusting the signal and applying that signal to the switch circuit (47) of the noise reduction circuit (4^), the noise reduction circuit (4^) is operated only during the edge period, and its operation is stopped during other periods. 5 Small signal components are processed by a noise reduction circuit (2)
It receives only the noise reduction effect of , and does not attenuate much.
Further, edge noise can be sufficiently removed by the noise reduction effect of the noise reduction circuit (4^).

Note that in the above embodiment, the noise reduction circuit (
Although the operation of 4^) was stopped, the same operation can be expected even if the noise reduction effect is reduced.

Further, in the above embodiment, the noise reduction circuit (2) generates a signal indicating the edge period, but other means may also be used.
It goes without saying that the intended purpose can be achieved even if the noise reduction effect is reduced without stopping the operation of the noise reduction circuit (4^) outside the edge period.

By the way, in the above explanation, the case was described where two different types of noise reduction circuits are used (2) and (4^), but the same type of noise reduction circuits may be used, and two or more other noise reduction circuits may be used. Needless to say, the present invention can also be used in a noise reduction device that has the present invention.

[Effects of the Invention] As explained above, the present invention includes a plurality of noise reduction circuits that reduce noise in an input signal, detects edge portions of the input signal, and reduces the noise only during large amplitude edge periods of the input signal. Since the present invention includes a control circuit that controls the operation of the circuit, it is possible to effectively remove edge noise without attenuating minute signals.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing a specific configuration of an embodiment of the invention, and FIG.
The figure is a waveform diagram showing the signals of each part of an embodiment of the present invention, FIG. 4 is a block diagram showing a conventional noise reduction device, and FIGS. 5 and 6 show the noise reduction circuit of the conventional noise reduction device. The circuit diagrams, Figures 7 and 8, are shown in Figures 5 and 6 [! 9 and 10 are characteristic diagrams showing the frequency characteristics of the noise reduction circuit shown in FIGS. 5 and 6. FIGS. In the figure, (1) ... Input terminal, (2>(3> (4^) (47) (5) (6) (60) (61> (62)) ... Noise reduction Circuit, ... input/output terminal, ... noise reduction circuit, ... switch circuit, ... output terminal, ... control circuit, ... comparator, ... low-pass filter, ... comparator In each figure, the same symbols are the same.

Claims (1)

[Claims] A plurality of noise reduction circuits that reduce noise in an input signal, and a control circuit that detects an edge portion of the input signal and controls the noise reduction circuit to operate only during a large-amplitude edge period of the input signal. A noise reduction device featuring: