JPH01183287A - Noise suppression circuit - Google Patents

Abstract

PURPOSE:To suppress a noise component contained in a reproduced chrominance signal without using vertical correlativity by balanced-modulating the output signal of a limiter circuit by the output signal of an envelope detection circuit, and summing it with the output signal of the limiter circuit. CONSTITUTION:As for the reproduced chrominance signal to be inputted, the amplitude-modulated component of a large amplitude part is suppressed by amplitude-limiting it by the limiter circuit 2, and simultaneously, an envelope is detected by the envelope detection circuit 3, and the output signal of the limiter circuit 2 is balanced-modulated by the output signal of the envelope detection circuit 3, and the output signal of the limiter circuit 2 and the output signal of a balanced-modulation circuit 5 are summed by an addition circuit 6. Thus, because the output signal of the limiter circuit is made to be the output chrominance signal after returning its linearity to a former state, the output chrominance signal of high quality in which an amplitude-modulated noise component is compressed can be obtained without changing the linearity of the input reproduced chrominance signal.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Industrial Field of Application The present invention suppresses noise components contained in color signals reproduced by a video tape recorder (VTR), etc. to obtain high-quality reproduced color signals. It relates to a noise suppression circuit.

B. Summary of the Invention The present invention relates to a reproduced color signal reproduced by a VTR or the like, in which a reproduced color signal whose amplitude is limited is balanced modulated by an envelope detection output signal of the reproduced color signal, and the balanced modulation output signal is modulated with the amplitude described above. By adding this to the limited reproduced color signal, noise components included in the reproduced color signal can be suppressed to obtain a high-quality reproduced color signal.

C. Conventional technology Conventionally, as a home VTR, a video signal to be recorded is separated into a luminance signal component and a color signal component, the color signal signal component is converted to a low frequency, and this low frequency converted color signal is converted to an FM signal. A so-called chroma low-frequency conversion type VTR is known in which the signal is mixed with a modulated luminance signal component and recorded on a videotape.

The regenerated thread of a VTR that uses the above chroma low-frequency conversion method is
For example, the configuration is as shown in the block diagram of FIG.

In this reproduction system, a reproduction signal reproduced from a video tape 40 by a video rad 41 is supplied to a Y/C separation circuit 43 via a reproduction amplifier 42, and this Y/C separation circuit 43 outputs an FM luminance signal. The (YFM) component and the low frequency converted color signal (C4) component are extracted separately.

FM luminance signal (Y
FM) component is supplied to the FM demodulation circuit 44, and the FM
The signal is demodulated by a demodulation circuit 44 and supplied to a signal mixing circuit 46 via a low-pass filter 45. In addition, the above Y/C
The low frequency conversion color signal (CL) component obtained in the separation circuit 43 is subjected to amplitude correction processing in the ACC circuit 47 and then supplied to the frequency conversion circuit 48.
Normal color carrier frequency (f, = 3.58MHz)
A frequency conversion process is performed to return the signal to .

Then, the regular color carrier frequency (f
, c) color signals (C) are sent to the signal mixing circuit via the noise cancellation circuit 50 for canceling and removing noise components such as cross color interference components caused by luminance signal components leaking into the Y/C separation circuit 43. 46.

This signal mixing circuit 46 combines the luminance signal (you) demodulated by the FM demodulation circuit 44 and the reproduced color signal (you) whose noise component has been canceled and removed by the noise canceling circuit 50.
The signal mixed with the reproduced video signal (Sour
) from the signal output terminal 51.

The noise canceling circuit 50 generally extracts a noise component from the reproduced color signal using a so-called comb filter using the vertical correlation of an image, and cancels and removes this noise component by subtracting and synthesizing the noise component with the reproduced color signal. For example, a configuration as shown in FIG. 8 is used.

The noise canceling circuit 50 shown in FIG.
The first and second signal synthesis circuits 53 and 54 to which a reproduced color signal (CIN) is supplied from 2 and a delay circuit 55 are provided.

The delay circuit 55 forms an IH delayed color signal (CDL) by adding a delay amount corresponding to one horizontal period (IH) to the reproduced color signal (C+s). The IH delayed color signal (C!IL) obtained by the delay circuit 55 is supplied to the first signal synthesis circuit 53 via a level adjustment circuit 56.

Further, the first signal synthesis circuit 53 is configured to perform the first signal synthesis circuit 53 as described above.
By adding and synthesizing the raw color signal (CIN) with the IH delayed color signal (C6L) whose level has been adjusted by the level adjustment circuit 56, color signal components whose phases are inverted every horizontal period (IH) are obtained. By canceling, only the noise signal component (N) included in the reproduced color signal (CIM) is extracted. The noise signal component (N) extracted by the first signal synthesis circuit 53 is subjected to amplitude limiting processing in a limiter circuit 57, and then sent to the second signal synthesis circuit via the level adjustment circuit 56. is supplied to circuit 54.

The second signal synthesis circuit 54 then outputs the noise signal component (
N) to the above reproduced color signal (CIN) with opposite polarity,
That is, by subtracting the noise signal component (N) from the reproduced color signal (C), the reproduced color signal (C) is obtained.
An output color signal (C0UT) is formed by canceling and removing the noise signal component (N) contained in the signal (IN), and is output from the output terminal 59.

D. Problems to be Solved by the Invention Conventionally, the noise canceling circuit 50 provided in the chroma reproduction system of a VTR extracts noise components from reproduced color signals using a so-called comb filter by utilizing the vertical correlation of images. This noise component is subtracted and synthesized with the reproduced color signal to cancel it out and remove it.
In order to eliminate the offset, complicated adjustment is required, and furthermore, there is a problem that the characteristics are unstable. Also, the lH required for extracting the noise component from the reproduced color signal is
The delay circuit 55 is a glass delay line or a charge-coupled device (CCD).
:Charge Coupled Device) etc. are generally used, but there are problems such as the need for a clock and the large circuit scale.Especially when handling PAL video signals, noise components are removed from the reproduced color signal. A 2H delay circuit is required to extract the 2H delay circuit, which has the problem of insufficient bandwidth and an increase in circuit scale.Furthermore, the reproduced color signal also includes color signal components that are uncorrelated in the vertical direction. Therefore, if the signal processing for these uncorrelated color signal components were to be completely performed, the circuit size would be enormous.

Therefore, in view of the above-mentioned conventional problems, the present invention provides V
Regarding the reproduced color signal reproduced by TR etc., the noise component contained in the reproduced color signal is suppressed without using the vertical correlation of the image, and stable operation is achieved with a simple circuit configuration. It is an object of the present invention to provide a noise suppression circuit with a novel configuration that allows no adjustment.

E. Means for Solving the Problems In order to achieve the above-mentioned object, the noise suppression circuit according to the present invention includes a limiter circuit that limits the amplitude of the input reproduced color signal and detects the envelope of the reproduced color signal. An envelope detection circuit, a balanced modulation circuit that balance-modulates the output signal of the limiter circuit with the output signal of the envelope detection circuit, and an addition circuit that adds the output signal of the limiter circuit and the output signal of the balanced modulation circuit. It is characterized by consisting of

F Function In the noise suppression circuit according to the present invention, the amplitude of the input reproduced color signal is limited by the limiter circuit to suppress the amplitude modulation component of the large amplitude portion, and the envelope detection circuit suppresses the amplitude modulation component of the input reproduced color signal. detecting the envelope, and using a balanced modulation circuit to balance-modulate the output signal of the limiter circuit with the output signal of the envelope detection circuit;
By adding the output signal of the limiter circuit and the output signal of the balanced modulation circuit in an adder circuit, the linearity of the output signal of the limiter circuit is restored to the original state and an output color signal is obtained.

G. Example Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

The block diagram of FIG. 1 shows a noise suppression circuit 1 according to the present invention.
0 basic configuration is shown.

In the noise suppression circuit 10 shown in FIG. 1, a reproduced color signal (CIN) is supplied from an input terminal 1 to a limiter circuit 2 and an envelope detection circuit 3.

The limiter circuit 2 has a nonlinear amplitude limiting characteristic as shown by the broken line in FIG. 2, and the reproduced color signal (CIN)
An amplitude limited color signal (CLM) is formed by compressing the large amplitude part of the amplitude modulation component of the amplitude modulation component.
M) is supplied to the balanced modulation circuit 5 and the signal addition circuit 6. The envelope detection circuit 3 also detects the reproduced color signal (
CIN) and supplies this envelope detection output signal to the balanced modulation circuit 5 via the clamp circuit 4.

The balanced modulation circuit 5 balance-modulates the amplitude-limited color signal (CLM) obtained by the limiter circuit 2 with the envelope detection output signal obtained by the envelope detection circuit 3. A modulated output signal (ΔC) of a signal level corresponding to the nonlinearity given to the reproduced color signal (CIN) is formed, and this modulated output signal (ΔC) is supplied to the signal addition circuit 6.

The signal addition circuit 6, as shown in FIG.
The modulation output No. 13 (
By adding ΔC), the output color signal (C
OLI? ) and output from the output terminal 7.

The envelope detection output signal of the reproduced color signal (C process) obtained by the envelope detection circuit 3 contains a random noise component, but the amplitude is limited by the envelope detection output signal in the balanced modulation circuit 5. By performing balanced modulation on the color signal (CLM), the random noise component is compressed.

Therefore, in the noise compression circuit 10 configured as described above, with respect to the reproduced color signal (CIN) supplied to the input terminal 1,
A high-quality output color signal (Cour) with compressed amplitude modulation noise components can be obtained at the output terminal 7 without changing linearity.

Here, the envelope detection circuit 3 and the balanced modulation circuit 5
For example, a commonly available analog IC may be used, and as shown in FIG. 4, a specific circuit configuration example of the noise compression circuit 10 is used as the envelope detection circuit 3. Further, as the balanced modulation circuit 5, for example, 5N16913P can be used.

In the specific example of the circuit configuration shown in FIG. 4, the limiter circuit 3 includes two diodes D1. Furthermore, the clamp circuit 4 is constructed from a capacitor C and a diode D, and the signal addition circuit 6 is constructed from a resistance addition circuit using a potentiometer PT. The amplitude-limited color signal (CLM) obtained by the limiter circuit 3 is supplied to the signal addition circuit 6 via an emitter follower circuit formed by an NPN transistor Q, and is also supplied to the signal addition circuit 6 using a 5N16913P transistor used as the balanced modulation circuit 5. A signal is input from the emitter follower circuit to one signal input terminal via a capacitor C. Further, the envelope detection output signal obtained by the envelope detection circuit 3 is the other signal of the 5N16913P used as the balanced modulation circuit 5 from the series circuit of the low-pass filter 7 and the buffer 1 circuit 8 via the clamp circuit 4. It is input to the input terminal.

In the specific circuit configuration example shown in FIG. 4 above, the signal waveform of the reproduced color signal (CIM) supplied to the input terminal l,
The amplitude limited color signal (CL) obtained by the limiter circuit 2
A signal waveform (SA) obtained by subtracting and synthesizing M) and the reproduced color signal (CIJl), and a signal waveform (SA) obtained by subtracting and synthesizing the output color signal (Coat) obtained at the output terminal 51 and the reproduced color signal (CIN). Figure 5 shows the waveform observation results of S, ), and Figure 6 shows the actual measurement results of its frequency characteristics. , a high-quality output color signal (CII) that compresses amplitude modulation noise components without changing linearity.
II? ) could be obtained at the output terminal 7.

Effects of the Invention In the noise suppression circuit according to the present invention, the limiter circuit limits the amplitude of the manually input reproduced color signal to suppress the amplitude modulation component of the large amplitude portion, and the envelope detection circuit suppresses the amplitude modulation component of the input reproduced color signal. detecting the envelope of the signal, and balanced modulating the output signal of the limiter circuit with the output signal of the envelope detection circuit in a balanced modulation circuit;
By adding the output signal of the limiter circuit and the output signal of the balanced modulation circuit in the adder circuit, the linearity of the output signal of the limiter circuit is restored to the original output color signal. On the other hand, it is possible to obtain a high-quality output color signal in which the amplitude modulation noise component is compressed without changing the linearity.

This noise suppression circuit suppresses the noise component included in the reproduced color signal without using the vertical correlation of the image, so it does not require an IH delay circuit or a 2H delay circuit, and is a simple circuit. The configuration allows stable operation, and almost no adjustment of operating characteristics is required.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of the basic configuration of a noise suppression circuit according to the present invention, FIG. 2 is a characteristic diagram showing the characteristics of a limiter circuit constituting the noise suppression circuit, and FIG.
The figure is a characteristic diagram for explaining the operation of the adder circuit constituting the noise suppression circuit, FIG. 4 is a circuit diagram showing a specific example of the circuit configuration of the noise suppression circuit, and FIG. FIG. 6 is a waveform diagram showing the results of waveform observation of the operating characteristics of the specific circuit configuration example described above, and FIG. 6 is a characteristic line diagram showing the results of actual measurement of the frequency characteristics of the specific circuit configuration example described above. FIG. 7 is a block diagram showing the configuration of a reproduction system of a general home VTR. FIG. 8 is a block diagram showing the configuration of a noise canceling circuit used in the reproduction system of the VTR. 1...Input terminal 2...Limiter circuit 3...Envelope detection circuit 5...Balanced modulation circuit 6...Signal addition circuit 7...Output terminal

Claims (1)

[Claims] A limiter circuit that limits the amplitude of an input reproduced color signal, an envelope detection circuit that detects an envelope of the reproduced color signal, and an output signal of the limiter circuit that is an output signal of the envelope detection circuit. A noise suppression circuit comprising: a balanced modulation circuit that performs balanced modulation; and an addition circuit that adds the output signal of the limiter circuit and the output signal of the balanced modulation circuit.