JPS6115632B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device that performs signal processing in a color television receiver or the like so that color noise is not noticeable.

In color television receivers, etc., color noise occurs when the input signal contains a lot of noise signals, but this color noise is less noticeable in bright areas of the screen and more noticeable in dark areas, which affects image quality. This has the disadvantage of significantly reducing the

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an apparatus capable of processing a color television signal with the simplest configuration and at a low cost so that the color noise, particularly in dark areas, can be made inconspicuous and the image quality can be improved. For this purpose, the amplification degree of the carrier chrominance signal of the band amplification circuit is controlled to be reduced when the level of the luminance signal becomes closer to the black level than a predetermined level, that is, when the screen becomes dark. , is characterized by suppressing color noise in dark areas.

In particular, in the present invention, in a color television receiver equipped with a video detection circuit, a video amplification circuit, a band amplification circuit, and a variable resistor for color saturation adjustment,
A constant voltage diode is connected in parallel with the variable resistor for color saturation adjustment, one end of the parallel circuit is grounded via a resistor, and the diode is connected to the point where the luminance signal appears in the video amplification circuit. The feature is that the other end of this parallel circuit is connected to a power supply via another resistor. With such a simple circuit configuration, when the luminance signal is closer to the black level than the predetermined level, the color saturation can be lowered in accordance with the level to reduce color noise.

In particular, with this configuration, it can be realized by adding one constant voltage Zener diode, two resistors, and one diode, and if the circuit constants are set, it is the simplest and cost effective method with a small number of additional components. The present invention is made of inexpensive parts, is easy to assemble, requires few man-hours, and can be made at low cost, and has the effect of reducing color noise in dark areas of brightness levels to provide an easy-to-read color image.

EMBODIMENT OF THE INVENTION Hereinafter, the present invention will be described in detail with reference to the drawings showing one embodiment thereof.

First, Figure 1 shows its circuit configuration, where:
1 is a video detection circuit, 2 is a video amplification circuit, and 3 is a band amplification circuit, and these circuits themselves are exactly the same as those in a conventional color television receiver. That is, the video detection circuit 1 is
VIF signal input transformer 4 and detection diode 5
and a low-pass filter circuit 6, the video amplification circuit 2 has transistors 7 and 8 for luminance signal amplification, and a delay line 9, and the band amplification circuit 3 has a composite differential amplification circuit configuration for amplifying carrier color signals. Transistor 10 connected to
It has 15. The composite differential amplifier circuit of the band amplifier circuit 3 amplifies the carrier color signal applied to the base of the transistor 10, and the carrier color signal is applied to the bases of the transistors 12 and 15 from a variable resistor 16 for color saturation adjustment. The degree of amplification is controlled by a control voltage for color saturation control. In the illustrated case, the amplification degree is controlled to increase as the control voltage increases.

In addition to such a general circuit, in this device, a constant voltage diode 17 is connected in parallel with the variable resistor 16, and one end of the parallel circuit is grounded through a resistor 18 and connected through a diode 19. The point at which the luminance signal appears in the video amplifier circuit 2 is connected to the emitter of the transistor 8, and the other end of this parallel circuit is connected to the power supply V _cc via a resistor 20.
I am trying to connect to.

Next, the operation in such a configuration will be explained with reference to the waveform diagram of FIG. 2. First, it is assumed that a luminance signal having a waveform as shown in FIG. 2A appears at the emitter of the transistor 8 in the video amplifier circuit 2.
Assume that color noise is noticeable in a dark part of the screen where the black level is higher than the predetermined level indicated by the broken line in the figure. Therefore, in this circuit, the resistors 16, 18, and 20 are selected so that the diode 19 becomes conductive when the luminance signal becomes closer to the black level than this predetermined level.
Set the voltage at the interconnection point C of 6 and 18. In this way, when the luminance signal is closer to the black level than the predetermined level as shown in FIG. The voltage decreases to approximately the same voltage according to the luminance signal (range a), and when the luminance signal is closer to the white level than the predetermined level, the diode 19 shuts off, resulting in a constant level (range b). At this time,
Due to the presence of the constant voltage diode 17, the voltage waveform at the interconnection point B of the resistors 16 and 20 is always higher than the voltage at point C by the voltage E at the other end of the constant voltage diode 17, as shown in FIG. It will look like B. That is, the voltage difference across the variable resistor 16 is always constant at E, and only the voltage relative to the ground point decreases in range a.

Therefore, when the voltage at the other end is divided by the sliding terminal of the variable resistor 16 to create a control voltage for controlling the amplification degree, a control voltage such as D shown by a chain line in FIG. 2 is obtained. In other words, in bright areas on the screen where the luminance signal is closer to the white level than a predetermined level, the amplification degree of the carrier color signal is kept constant as before, but once the luminance signal is closer to the black level than the predetermined level. When it becomes a dark area on the screen where color noise is noticeable, the amplification degree of the carrier color signal is automatically reduced, suppressing the color signal that causes color noise and preventing the generation of color noise. It will be oppressed. As a result, color noise is not noticeable even in dark areas on the screen, and a color television image with good image quality is displayed.

In this way, by using this circuit, it is possible to suppress the color noise that was conventionally noticeable in dark areas on the screen.

As detailed above, in the present invention, the level of the luminance signal is detected, and when the luminance signal becomes closer to the black level than a predetermined level, the amplification degree of the carrier color signal in the band amplifier circuit is reduced. Therefore, it is possible to obtain an apparatus that can suppress the occurrence of color noise in dark areas on the screen and can display color television images of good quality.

In particular, according to the invention, one constant voltage Zener;
By simply adding two resistors and one diode, it is possible to provide the lowest cost and most rational circuit configuration.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a color noise suppression device according to an embodiment of the present invention, and FIG. 2 is a waveform diagram for explaining the operation of the device. 1...Video detection circuit, 2...Video amplification circuit, 3
...bandwidth amplifier circuit, 16...variable resistor, 17...
... Constant voltage diode, 18 ... Resistor, 19 ... Diode, 20 ... Resistor.

Claims (1)

[Claims] 1 The level of the luminance signal is detected, and when the luminance signal is closer to the black level than a predetermined level, the amplification degree of the carrier color signal in the band amplifier circuit is lowered, and the carrier color signal in the band amplifier circuit is lowered. A constant voltage diode is connected in parallel to a variable resistor that generates a control voltage for controlling the degree of amplification of the signal, and one end of the parallel circuit of the variable resistor and the constant voltage diode is grounded via the resistor. Connect to the point where the luminance signal appears in the video amplifier circuit through a diode that becomes conductive when the luminance signal becomes blacker than a predetermined level, and connect the other end of the parallel circuit to the power supply via another resistor. A color noise suppression device characterized in that: