JPH03114369A - Noise elimination circuit - Google Patents

Abstract

PURPOSE:To allow waveform distortion to hardly take place by controlling the gain of a 1st amplifier circuit, adjusting the amplitude of a quadratic differ entiating signal to be added to a video signal, controlling the gain of a 2nd amplifier circuit so as to adjust the elimination of noise component included in the video signal. CONSTITUTION:A quadratic differentiating waveform of a video signal is obtained by a quadratic differentiating circuit 3 and the gain of a 1st amplifier circuit 4 is adjusted to control picture quality. Moreover, the gain of a 2nd amplifier circuit 8 is adjusted to control noise elimination quantity. Thus, a disturbing signal is eliminated in an excellent way, the noise elimination effect is unchanged by the picture quality control of a television receiver, the position of pattern is unchanged by noise reduction ON/OFF and waveform distortion hardly takes place.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a noise removal circuit for removing unnecessary interference components such as noise on a video signal in, for example, a color television receiver.

[Conventional technology]

Color television! The video signal of the I/signal contains noise contained in the signal source, noise caused by the electric circuit system,
A bridge in which unnecessary interference components such as a chroma signal (resulting in dot interference) leak into the luminance signal (Y signal) due to insufficient separation of the luminance and color signals. In areas with poor signal conditions, snow noise could be seen on the two screens, which was undesirable.

In particular, when the image quality of the receiver is increased using the 1-image quality control circuit, the high-frequency components of the video signal containing many noise components are amplified, making the screen extremely difficult to view.

In cases where there are many such interference components, lowering the image quality of the receiver (that is, reducing the high-frequency components of the video signal) will make the image easier to see, but it will be undesirably blurry overall.

Therefore, conventionally, a noise removal circuit as shown in FIG. 8 has been used. The explanation will be given with reference to the operation waveforms of each part shown in FIG. In addition, the waveforms from ■ to ■ in Fig. 9 correspond to A in Fig. 8.
The signal waveforms from point to point E are shown.

If a waveform containing noise as shown in Figure 9 ■ is input to the input terminal 21 in Figure 8, the HPF (/・I path
The waveform after passing through the filters 22f and s is as shown in ■. Next, by the coring circuit 23, the minute signal amplitude 7
If you cut the part and extract only the outline component of the video signal, O
The waveform will be like this. Furthermore, the input original signal is subjected to an LPF (low bus filter) 24 to remove high-frequency components, resulting in a waveform of 00. This is added to the aforementioned waveform O in an adder circuit 25, and a waveform (■) is obtained at the output terminal 26. It will be done. In other words, the amount of interference component removal is determined by the high frequency attenuation m: of the LPF 24.

As the coring circuit 23, a circuit as shown in FIG. 10 is used. This is diode D1. A circuit consisting of D2 and bias source v1-Vs, each bias voltage v1+
V2. By choosing V3 to an arbitrary value, the diode D
1+ Depending on whether D2 is conductive or non-conductive, signal waveforms 1 to 1 in FIG. 11 can be obtained. The waveforms from ■ to ■ in FIG. 11 show the waveforms at points A to D in FIG. 10.

A signal from the HPF 22 is input to point A, and an output from point D is supplied to an adder circuit 25. In addition, in Figure 11, V
,, V2. V indicates the level of each bias voltage.

vF indicates the forward voltage drop when each diode D, , D2 is conductive.

In this way, unnecessary signal components are removed by the circuit shown in FIG.

By the way, since the circuit shown in FIG. 8 is inserted before the video signal processing circuit (usually implemented as an IC), the amount of unnecessary interference components removed will ultimately vary.

The overall f, including the video processing circuit and the CFtT drive stage, is particularly variable.

In other words, the amount of noise removed by turning on and off this noise ψ reduction circuit is determined by the characteristics of LPFz+, but the final amount of noise on the screen is.

This will vary depending on the amount of image quality control on the receiver.

Therefore, when the image quality control is set to soft and the noise reducer, y(NR), is turned on, the screen becomes quite blurry. Also, if you increase the image quality to the maximum,
Even when noise reduction was turned on, the noise was not reduced sufficiently, and the noise reduction effect was changed by the two image quality controls.

In addition, the noise reduction circuit converts the original signal to LPF24.
, so this will cause a delay.

The screen position changed depending on whether the noise reduction circuit was turned on or through.

Also, when adding the output signals of LPF24 and HPF'22, if the group delay characteristics of each filter are not flat (it is very difficult to create LPF and HPF' with the same group delay characteristics), , there was a problem that waveform distortion occurred.

[Problem to be solved by the invention]

As described above, the conventional circuits have problems such as the amount of noise removed changes depending on the image quality control of the receiver, the screen position changes depending on whether noise reduction is turned on or off, and waveform distortion occurs.

Therefore, the present invention solves the above problems and further improves the image quality control to change the noise removal amount and change the screen position when the noise reduction circuit is turned on and off. It is an object of the present invention to provide a noise removal circuit that is free from noise and is less likely to cause waveform distortion.

[Means to solve the problem]

The present invention includes a first delay circuit that inputs and delays a video signal from a video signal source, and a second delay circuit that inputs and delays a video signal delayed by the first delay circuit.

and obtaining a difference signal between the video signal from the video signal source and the video signal from the first delay circuit.

a second-order differential circuit that obtains a difference signal between the video signal from the first delay circuit and the video signal from the second delay circuit and adds the two difference signals to generate a second-order differential signal;

a first amplification circuit that amplifies the second-order differential signal from the second-order differential circuit;

a second amplification circuit that performs inversion limiter amplification of the second-order differential signal from the second-order differential circuit;

an addition circuit that adds the video signal from the first delay circuit, the second-order differential signal from the first amplifier circuit, and the inverted second-order differential signal from the second amplifier circuit;

a first control means for controlling the gain of the first amplifier circuit and adjusting the magnitude of the second-order differential signal to be added to the video signal;

The noise removal circuit comprises second control means for controlling the gain of the second amplifier circuit and adjusting the effect of removing noise components contained in the video signal.

[For production]

In the present invention, the second-order differential waveform of the video signal is obtained by the second-order differential circuit, the image quality is controlled by adjusting the gain of the first amplifier circuit, and the gain of the second amplifier circuit is adjusted. You can control the amount of noise removed. Further, by increasing the gain of the second amplifier circuit in the portion where the luminance level of the video signal is low (the dark portion of the iiij plane), the noise removal effect can be enhanced.

〔Example〕

The present invention will be described below based on an embodiment shown in one drawing.

FIG. 1 shows one embodiment of the present invention, and is a block diagram showing a noise removal circuit for a video signal in a color television receiver.

In this figure, reference numeral 11 is an input terminal for a video signal,
Assume that a signal waveform with a constant pedestal voltage is applied.

The input signal is delayed by a first delay circuit 1 and further delayed by a second delay circuit 2.

The input signal and the delayed signals from the first and second delay circuits 1 and 2 are respectively supplied to a second-order differentiator circuit 3.

Further, the input signal is supplied to a level shift circuit 7 via an LPF (low bus filter circuit) 6. The DC level shift by the level shift circuit 7 is controlled by a noise reduction (NR) control circuit 12.

The second-order differential signal obtained by the second-order differential circuit 3 is:

The signal is supplied to the image quality correction amplifier circuit 4 and the noise reduction inverting amplifier IJ transmitter circuit 8.

The gains of the image quality correction amplifier circuit 4 and the inverting amplification limiter circuit 8 are controlled by the image quality control circuit 10. Further, the output voltage of the gain control circuit 9 is changed depending on the luminance signal level from the level shift circuit 7. In other words, the pressure control is performed so that the larger the amount of image quality correction is, and the lower (dark) the luminance signal level is, the higher the gain of the inverting amplification limiter circuit 8 for noise resolution ace. and the first delay circuit 1. The respective outputs of the amplifier circuit 42 and the anti-inversion width limiter 8 are added together in the adder circuit 5, and an output signal is obtained from the output terminal 13.

The operation of the circuit shown in FIG. 1 will be explained with reference to waveform diagrams and the like.

First, the second-order differential circuit 3 will be explained. FIG. 2 shows the second-order differentiator circuit 3, which includes subtraction circuits 31, 32, . Addition circuit 33
The input terminal A has an input signal.

The output signal of the first delay circuit 1 is input to B, and the output signal of the second delay circuit 2 is input to CK. here.

If we consider the delay circuits 1 and 2 as ideal (gain is OdB, frequency 1 group delay characteristic is flat).

The waveforms of each part A to D in FIG. 2 are as shown in FIG. 3, and a clean second-order differential signal is obtained at the output terminal O.

It is a well-known fact that the second-order differential signal (2) obtained here has a flat second group delay characteristic.

This signal ◎ is amplified by the 1 image quality correction amplifier circuit 4, and combined with the output signal ◎ of the first delay circuit 1 in the adder circuit 5, thereby obtaining the contour-corrected output signal ◎. In other words, the contour can be corrected without causing unnecessary ringing or the like.

Further, the second-order differential signal 0 is applied to the adder circuit 5 via an inverting amplification limiter circuit 8. This inversion amplification +7
The Mituta circuit 8 operates linearly only in the minute signal region of the second-order differential signal O. This inverting amplification limiter circuit 8 inverts the second-order differential signal 0, and adds it to the adder circuit 5, thereby increasing the minute signal region of the video signal. It is possible to reduce high frequency components.

In other words, considering a small signal region where unnecessary interference components such as noise exist, the amplifier circuit 4 and the inverting amplification limiter circuit 8 operate linearly only in the small signal region. Noise can be removed by controlling the gain of the inverting amplification limiter circuit 8 according to the control voltage applied to the inverting amplification limiter circuit 8.

Furthermore, when this second-order differential signal is inverted and added to an inverted signal having the same amplitude as the output signal amplitude of the delay circuit 1, the output becomes zero. (Because the group delay characteristic is 7rat). In other words, if you apply pressure to add an inverted signal component of the same amplitude at the peak frequency of one image quality correction (assuming the delay time of the delay circuit, the peak frequency fpg = ■1), the frequency characteristics of the output will become a trap at fPK. have. (4th
(See figure) This means that by adding the inverted component of the second-order differential signal, it is possible to drop the high-frequency component, especially.

When fPK is set to around 3.58 MHz, it is possible to sufficiently reduce the chroma signal component that is mixed with the Y signal, so that dot interference can be sufficiently reduced.

In this way, it becomes possible to control the image quality, and the noise removal effect does not change due to the image quality control trap as in the past, and noise removal can be performed satisfactorily.

A specific example of this amplifier circuit 411 inversion increase limiter circuit 8 is as follows.
It is shown in FIG. In FIG. 5, transistors Ql, Q
The differential amplifier by z constitutes the 1-inversion amplification limiter circuit 8, and the differential amplifier by +Q31 Q4 constitutes the image quality correction amplifier circuit 4.

The common emitters of transistors Qz, Qz are coupled via transistor Q8 to the collector of transistor Q5, which together with transistor Q7 forms a differential amplifier, and the common emitters of r Q71 Qa are connected to current source IIK.

On the other hand, the transistors Qa and Q4 each have a plurality of diode-connected transistors connected in series, and have a dynamic range n times larger than the input dynamic range of the transistors Ql and Qz.

The common emitters of transistors Qs, Q4 are coupled to the collector of transistor Q6, transistors Q5 .
The common emitter of Qa is coupled to a variable current source IoK.

Note that the emitter area of e Qs is n times the emitter area of r Qs.

Furthermore, the base of the transistor Q7 is connected to a switch sw1 that controls on/off of the noise reduction (NR,), and this switch SW1 is connected to the voltage source v
When connected to the l side, transistor Q8 turns off, so N
-R is off, and when connected to the ground side, N-R is on.

The second-order differential signal mentioned above is generated by the transistor Qt.

The base of Qz and the transistor Q3. Q4 is supplied to the base of the first stage of transistor Q2. A trap is arranged so that the collector output of Qs is supplied to the adder circuit 5.

Also, the base of the transistor Q8 is connected to a bias source v2 (V
□〉v2) is connected, and a bias source v3 is connected to the bases of +Qs and Qa. Also, the transistor Ql
.

The collector of Q4 is connected to voltage source VCC.

In this FIG. 5, the two image quality controls are constant current source I
This is done by varying the value of Q, and the current value of this IQ is G5. 'n+
1"' is +Q3# to G4 differential amplifier. +1・Io
+It is supplied to the differential amplifier of Ql and G2.

Here, +Qt* Inverting amplification limiter circuit 8 by Qz
To find the gain (I) of ・T 11=- Also, the gain of the amplifier circuit 4 due to e Qs+ Qa (G1n
2) is calculated as 'Gm2=4h''n (n-)-1
・Io)=-(Io).

4hn+1 Therefore, when the input signal amplitude is within the input dynamic range of the differential amplifier of r ) 呵Gmz Gm1 = 1・工1h, and if there is no influence from IoK, it becomes K.

Therefore, even if one image quality control is performed, the frequency characteristics of the minute signal region are not affected, that is, the noise removal effect remains constant.

Moreover, the second-order differential signal supplied to the adder circuit 5 is as follows.

Because it was created using delay circuits 1 and 2, the group delay characteristic is flat, and there is little waveform distortion due to correction, and there is no screen phase change when noise reduction (NR) is turned on and off. do not have.

FIG. 6 shows an embodiment in which a circuit is added that changes the effect of the amount of noise removed depending on the brightness level of the video signal. This is shown in Figure 1.

The input signal input to the input terminal 11 is supplied to the level shift circuit 7 (with a frequency of 500 KHz) via the LPF 6, and is changed to the voltage of the noise reduction four (NR) control circuit 2. This shows an example in which a video signal whose DC level has been shifted accordingly is obtained and the gain control circuit 9 controls it to have an arbitrary amplitude. The difference from FIG. 5 is that a transistor Qe having a common base and emitter with the transistor Q7 is added, and a level-shifted video signal is applied to the base of Qe.

The higher the voltage of the video signal input to transistor Q9,
Since the current supplied to the transistors Ql and Qz decreases, the amount of noise removed in bright video parts decreases, and the amount of noise removed increases in dark video parts.

Therefore, it is possible to reduce noise in dark areas of the screen that is visually distracting, and reduce the amount of noise removed in relatively bright detail areas, such as a human face, which may impair the texture of the skin. Effective noise removal can be performed without any noise.

Furthermore, since the amount of noise removal can be controlled by controlling the base voltages of the transistors Qy and Q9, the amount of DC level shift of the level shift circuit 7 can be varied, that is, by the control circuit 12, It is clear that the amount of noise removed can be controlled.

FIG. 7 shows the noise removal characteristics of the circuit shown in FIG.

In FIG. 7, the horizontal axis represents the input signal level supplied to the base of transistor QrrQ9.

The vertical axis indicates the amount of noise removed. Note that the one-dot line and the one-dot chain line represent the characteristics when the DC level is shifted by the level shift circuit 7 in FIG.

〔Effect of the invention〕

As described above, according to the present invention, interfering signals can be removed satisfactorily, and the noise removal effect does not change depending on the image quality control of the television receiver. Furthermore, the screen position does not change depending on whether the noise reduction (N-FL) is turned on or off, making it difficult for waveform distortion to occur. moreover.

Increases the amount of noise removed from dark areas of the screen that are visually disturbing.
By reducing the removal amount of bright areas, noise can be removed without comparably degrading the image quality on one screen.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the basic configuration of the noise removal circuit of the present invention, FIG. 2 is a circuit diagram showing an example of a second-order differential signal generation circuit used in the circuit of FIG. 1, and FIG. FIG. 4 is a signal waveform diagram for explaining the operation of FIG. 1, and FIG. 4 is a characteristic diagram showing the frequency characteristics of the inverting amplification limiter circuit used in the circuit of FIG. FIG. 5 is a circuit diagram showing one embodiment of the main part of the circuit of FIG. 1, and FIG. 6 is a circuit diagram showing another embodiment. FIG. 7 is a characteristic diagram showing the operating characteristics of the circuit shown in FIG. 6. FIG. 8 is a block diagram showing a conventional noise removal circuit. FIG. 9 is a signal waveform diagram for explaining the operation of FIG. 8, and FIG. 1O is a circuit diagram showing a conventional coring circuit. FIG. 11 is a signal waveform diagram for explaining the operation of FIG. 10. 1.2...Delay circuit. 3...Second order differential circuit. 4...First amplifier circuit, 5...Addition circuit. 6...Low pass filter. 7...Level shift circuit. 8... Second amplifier circuit, 9... Gain control circuit. 10... Image quality control circuit. Agent Patent Attorney Nori Ken Chika Hiroshi Uji Figure Vl) V2 Figure Input Signal Figure Figure 10

Claims (2)

[Claims] (1) The first input and delay video signal from the video signal source.
a second delay circuit that inputs and delays the video signal delayed by the first delay circuit; and a difference between the video signal from the video signal source and the video signal from the first delay circuit. a second-order differential circuit that obtains a signal, obtains a difference signal between the video signal from the first delay circuit and the video signal from the second delay circuit, and adds both difference signals to generate a second-order differential signal. a first amplifier circuit that amplifies the second-order differential signal from the second-order differential circuit; a second amplifier circuit that inverts and limits the second-order differential signal from the second-order differential circuit; an addition circuit that adds the video signal from the delay circuit, the second-order differential signal from the first amplifier circuit, and the inverted second-order differential signal from the second amplifier circuit; a first control means that controls the gain and adjusts the magnitude of the second-order differential signal added to the video signal; and a first control means that controls the gain of the second amplifier circuit and adjusts the removal effect of noise components included in the video signal. and a second control means for controlling the noise. (2) The second control means includes means for controlling the gain of the second amplifier circuit according to the brightness level of the video signal from the video signal source, and lowers the gain when the brightness level is high; 2. The noise removal circuit according to claim 1, wherein the gain is increased when the brightness level is low.