JPS62252282A - Noise elimination circuit - Google Patents

Abstract

PURPOSE:To decrease the noise of not only the flat part but the edge part of a signal with a cheap circuit by providing the second HPF to remove the signal of the band higher than a reproducing video signal removed by the first high pass filter (HPF) and a sub-pass to remove the noise component only of the amplitude smaller than the second HPF output and subtracting the output signal and the reproducing signal. CONSTITUTION:The first noise elimination circuit is composed of a subtracter 3, an HPF 4, a limiter circuit 5 and an LPF 6. An HPF 7 is an HPF to remove only the high area component higher than the high area component to remove it with the HPF 4 from a video signal. The second noise elimination circuit is composed of the HPF 7, a limiter circuit 8 and the subtracter 3. A limiter 8 removes the noise component only of a small amplitude from the output of the HPF 7. By such constitution, the first noise elimination circuit inputs the output of the limiter circuit 5 to the subtracter 3 and removes the noise from the video signal. The second noise elimination circuit is provided in parallel with the first noise elimination circuit and both a flat part noise and an edge noise are decreased. In such a case, the LPF 6 is provided at the rear stage of the circuit 5 and the subtracting quantity of the high area is made smaller at the noise elimination circuit as a whole.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a noise removal circuit used in a magnetic recording/reproducing device, etc., and particularly to a noise removal circuit suitable for reducing edge noise in a reproduced video signal. It is.

[Conventional technology]

Traditionally, in magnetic recording and reproducing devices, so-called noise removal circuits [Ho-i Video Technology (edited by Japan Broadcasting Corporation, author Yokoyama), vol. Pages 102 to 103] are provided.

This noise removal circuit extracts only small-amplitude high-frequency components corresponding to noise from the reproduced video signal and subtracts them from the reproduced video signal to cancel the noise.

[Problem that the invention seeks to solve]

Although the above-mentioned conventional noise removal circuit can apparently improve the shank by 5 dB or more, it is configured to extract the noise component by clipping, so it cannot reduce the noise present in the rising parts of the image, etc. There was a problem in that noise in the outline of the image was visually noticeable.

The present invention has been made to eliminate the above-mentioned drawbacks, and its purpose is to provide a noise removal circuit with good cost performance.

[Means for solving problems]

In order to achieve the above object, the present invention provides a second bypass filter that extracts a reproduced video signal in a higher frequency band than a reproduced video signal in a high frequency band extracted by a first high frequency filter (hereinafter abbreviated as HPF). (hereinafter HPF
) and a second limiter circuit that extracts only small-amplitude noise components from the output of this second bypass filter, and subtracts the output signal of this subpath from the reproduced video signal. There are characteristics.

[Effect]

The second HPF extracts a higher frequency band from the reproduced video signal than the high frequency band extracted by the first HPF,
It is also possible to extract noise from the edges.

As a result, it is possible to obtain the same effect as the conventional noise removal channel in the flat parts of the reproduced video signal, and it is possible to remove noise in a relatively high frequency band in the edge parts, so that a good reproduced image can be obtained. can be realized.

〔Example〕

The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing a noise removal circuit according to an embodiment of the present invention. In the figure, 1 is a video signal input terminal, 2 is a noise removal circuit output terminal, 3 is a subtracter that subtracts noise components from the video signal, 4 is a GL (GL) IPF that extracts only high frequency components from the video signal, and 5 is ) IPF4
a first limiter circuit that limits the output amplitude of the limiter 5;
A low-pass filter (hereinafter referred to as L) for band-limiting the output of
(abbreviated as PF).

Then, the above subtractor 3. 17th/)l-IPF4. First limiter circuit5. The low-pass filter 6 constitutes a first noise removal circuit. 7 is the first signal from the video signal.
A second HPF 8 which extracts only high-frequency components higher than those extracted by the HPF 4 is a second limiter circuit which limits the output amplitude of the HPF'7.

The cutoff frequency fc of the 20th HPF7 is the 10th HPF
The cutoff frequency fc of F4 is set higher.

The second HPF 7, the second limiter circuit 8, and the subtracter 3 constitute a second noise removal circuit.

1. Fig. 2 is a diagram showing the frequency characteristics of each part of Fig. 1, and Fig. 3 is a diagram showing waveforms of each part of Fig. 1. Hereinafter, referring to Figs. The operation of the embodiment shown in FIG. 1 will be explained.

First, a video signal as shown in FIG. 3(a) having the frequency characteristics shown in FIG. 2(a) is inputted from the input terminal 1. The input video signal is input to the subtracter 3 at the same time as the 10th H
PF4. It is input to the second HPF 7.

The first HPF 4 outputs the video signal shown in FIG. 3 having the frequency characteristics shown in FIG. 2(b).

That is, this video signal has a differentiated waveform because the 10th HPF 4 constitutes a differentiating circuit.

This video signal is then suppressed within a certain amplitude by the limiter circuit 5.

The first noise removal circuit inputs the output of the limiter circuit 5 to a subtracter 5 to remove noise from the video signal. However, in the limiter circuit 5, noise in periods having an amplitude above a certain level, such as the edge portion, is removed, so edge noise remains in the difference signal between the video signal and the signal that has passed through the circuit. ing.

In order to prevent edge noise from remaining, the first H
What is necessary is to reduce the PF40 time constant. However, the first H
If the time constant of PF'4 is made smaller, the cutoff frequency fc becomes higher and edge noise is reduced.

Although it can be done, the low frequency noise cannot be extracted and noise removal is performed.

The effect will deteriorate.

For this reason, the cutoff frequency fc of the first HPFa is set higher than that of the second (1) HPFa.
A second noise removal circuit including No. 7 is provided in parallel with the first noise removal circuit, and is configured to reduce both flat part noise and edge noise.

However, in a lamp in which a second noise removal circuit is provided in parallel with the first noise removal circuit, the amount of high-frequency subtraction increases, causing deterioration in image quality.

Therefore, a second noise removal circuit is provided in parallel with the first noise removal circuit, and an LP11 is provided after the first limiter circuit of the first noise removal circuit, so that the amount of subtraction in the high frequency range is reduced to noise. The entire removal circuit is designed to have a small amount.

As mentioned above, the signal processed by HPFa of gt in FIG. 1 and the first limiter circuit 5 has a frequency characteristic shown in FIG. Only the amplitude noise component is present.

Next, LP1 provided after the first limiter circuit 5
1, only the band lower than the cutoff frequency fc of the second HPF 7 is extracted from among the small amplitude noise components extracted by the first limiter circuit 5, as shown in FIG. 2(d).

In addition, the output of the 20th HP)'7 is shown in Fig. 2(c).
The video signal shown in FIG. 3(c) having the frequency characteristics shown in ) is taken out, and the second limiter circuit 8 contains only small-amplitude noise components.

The outputs of the limiter circuits 8 of the LP11 and Wf,2 are input to the subtracter 5 and subtracted from the video signal to remove noise from the video signal.

By doing the above, the effect as a noise removal circuit can be achieved by the sum of the path of the first HPFa and the path of the second HPF7, and the edge noise removal can be achieved by the path of the g20HPF7. ◇ Figure 4 shows a specific circuit example of the noise removal circuit of the present invention shown in the block diagram in Figure 1. 8 in Figure 4 with the same reference numerals, ・H, 2
~R+25 is a resistor, Q5 to Q28 are transistors, 02
~C4 is the capacity.

Below are the times lol! Let us briefly explain r. The resistor R,10 and the capacitor C2 constitute a primary LPF, and the transistor Q5
．． Q6 and resistance Rat~R[in combination with M117
) constitutes I-IPF'4.

The next stage transistor Q7. Q8. and resistor R14,
R15 constitutes the first limiter circuit 5.

Also, the resistor 16 and the capacitor tC3 constitute LP11, and the way this LP11 is produced depends on the resistor 17. Suitably attenuated by R18, transistor Q9. Q+o, resistance 19. R
, 3 to remove noise components from the original video signal.

- On the other hand, the video signal input from input terminal 1 is transmitted to transistor Q25. Q26. It is also supplied to the second HPF 7 composed of resistors 20 to R25 and capacitance C4 (capacitance C4,
Only high frequency components with time constant determined by resistance R, 20.

Output.

Next stage transistor Q27. Q28# and resistance) L
24. 25 is the second limiter circuit 8'? : Configured.

The output signal of this second limiter circuit is connected to resistor R+8 and FL
After being attenuated by a ratio of 9, the signal is input to the subtracter 3, and noise components can be removed from the video signal input from the transistor Q9.

FIG. 5 shows another embodiment of the noise removal circuit of the present invention.

In this embodiment, a second HPF 7 and an IJ limiter circuit 8 are connected in series, a reproduced video signal is input to the second HPF 7, and the limiter circuit outputs Y! A first HPFa which inputs the output of the first subtracter 101, a limiter circuit 5 and LP11 are connected in series, and the output of II and PF'6 is It is configured so that the output is input to the second subtractor 102, and the operation and effect are similar to the embodiment shown in FIG.

Figure 9.6 shows another embodiment of the noise removal circuit of the present invention. In Fig. 6, the noise removal circuit in Fig. 1 had a feedforward configuration, whereas it has a feedback configuration. ◎Figure 7 shows a system of a magnetic recording and reproducing device using the noise removal circuit of the present invention. A block diagram is shown.

The % characteristics in FIG. 7 are that the above-described noise removal circuit is provided on the reproduction side, and that a correction circuit 54 for the signal lost by the reproduction noise removal circuit is provided on the recording side.

In FIG. 7, 51 is an input terminal for a video signal, 52 is an AGC amplifier for adjusting the input video signal to a constant value, and 55
54 is an LPF for limiting unnecessary bands, and 54 is a noise removal correction circuit that emphasizes in advance on the recording side the signal that is lost by the reproduction side noise removal circuit. L P F 57 adder 58 to limiter circuit 5. ) JPF59 and a limiter circuit 60.

-61 is a pre-emphasis circuit, and 62 is a clip circuit, which suppresses the video level below a specified level.

Reference numeral 65 is a frequency modulator, 64 is a recording amplifier, 65 is a magnetic head, and 66 is a magnetic tape, and these are the respective constituent members on the recording side.

67 is a magnetic head, 6B is a preamplifier, 69 is an AGC amplifier for making head output signals uniform due to gIL, 70 is an FM modulator, 71 is a de-emphasis circuit,
72 is a mixing circuit for the reproduced luminance signal and the 72 signal, 75 is an output terminal, and 74 is an input terminal for the a-ma signal. Reference numeral 10 denotes a noise removal circuit, which is a component on the reproduction side.

Since the system shown in FIG. 7 is well known, a description of its operation will be omitted.

As described above, the feature of FIG. 7 is that the noise removal circuit 10 shown in FIG. 1 is provided on the reproduction side, and its correction circuit 54 is provided on the recording side. The noise removal circuit 10 considers small-amplitude high-frequency components as noise and subtracts them from the video signal, and is not necessarily limited to noise (it also subtracts signals, which may lead to deterioration of sharpness. It is effective to provide the correction circuit 54 on the recording side.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, both flat part noise and edge noise can be reduced in the noise removal circuit, so that good image quality with good S can be achieved with good cost performance. .

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the noise removal circuit of the present invention. FIG. 2 is an explanatory diagram showing the frequency characteristics of each part in FIG. 1. FIG. 3 is an explanatory diagram showing waveforms at various parts of the ts1 diagram. FIG. 4 is a diagram showing an example of a different circuit according to the present invention. FIG. 5 is a block diagram showing another embodiment of the present invention. FIG. 6 is a diagram 1072 showing still another embodiment of the present invention. FIG. 7 is a 1072 diagram showing a system of a magnetic recording/reproducing apparatus using the noise removal circuit of the present invention. DESCRIPTION OF SYMBOLS 1... Input terminal, 2... Output terminal, 3... Subtractor, 4-- First HPF, 5... First limiter circuit, 6
...LPF%7°°°second apr, a...second limiter circuit. Figure 1 Atsushi Z appearance Figure 4 Figure 5 Figure 6 Figure 6

Claims (3)

[Claims] (1) a first signal extracting means for extracting a reproduced video signal in a high frequency band from a reproduced video signal; a first signal suppressing means for suppressing the signal obtained by the first signal extracting means to a signal having a certain amplitude or less; a first noise removal circuit having a band attenuation means for attenuating only a frequency band higher than a high frequency band extracted by the first signal extraction means among the signals obtained by the first signal suppression means; a second signal extracting means for extracting a reproduced video signal in a higher frequency band than the high frequency band extracted by the signal extracting means; and a second signal suppressing means for suppressing the signal obtained by the second signal extracting means to a signal having a predetermined amplitude or less. and a subtraction circuit that subtracts the output of the first noise removal circuit, the output of the second noise removal circuit, and the reproduced video signal. noise removal circuit. (2) The output of the first noise removal circuit, the output of the second noise removal circuit, and the reproduced video signal are subtracted by a common subtraction circuit.
Noise removal circuit described in section 1). (3) The output of the first noise removal circuit, the output of the second noise removal circuit, and the reproduced video signal are subtracted by separate subtraction circuits.
Noise removal circuit described in section 1).