JP2000196913A - Velocity modulation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a velocity modulation circuit which can improve the picture quality of videos in a high chroma saturation section by changing the correcting amount of velocity modulation depending upon the level of a color difference signal. SOLUTION: A color difference signal level detecting circuit 6 detects the level of an inputted color difference signal. When the level of the signal is high, a variable amplifier circuit 7 discriminates that the deterioration of a high-frequency component is large and operates an auxiliary deflecting coil 5 to increase its velocity modulating effect when the level of the color difference signal is high by changing a superimposed deflecting magnetic field by increasing the current flowing to the coil 5 so that the scanning speed of a beam current may be changed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a speed modulation circuit in a television receiver or the like, and more particularly to a speed modulation circuit having a color resolution correction effect.

[0002]

2. Description of the Related Art In a television image, a beam current of a cathode ray tube increases in a portion having a high luminance, so that a beam spot size increases and sharpness decreases. Therefore, as a method for correcting the decrease in sharpness, there is a method using a speed modulation circuit. FIG. 4 is a block diagram showing a conventional speed modulation circuit, and FIG. 5 is a waveform diagram for explaining a basic operation of speed modulation, which will be described together.

In FIG. 4, a luminance signal having a waveform shown in FIG. 5A is input and supplied to a video signal processing circuit 3 and a differentiation circuit 1. The video signal processing circuit 3 performs various kinds of signal processing on the luminance signal, synthesizes the luminance signal with a separately input color difference signal, obtains primary color signals R, G, and B, and supplies these to a cathode ray tube (CRT). Is displayed. The differentiating circuit 1 differentiates the luminance signal to obtain a differentiated signal having a waveform shown in FIG. The amplifying circuit 2 amplifies the differential signal and supplies it to the auxiliary deflection coil 5 to supply a current corresponding to the differential signal, thereby generating a superimposed deflection magnetic field having a waveform shown in FIG.

[0004] A horizontal deflection coil 4 and an auxiliary deflection coil 5 are mounted on a cathode ray tube (CRT), whereby a deflection magnetic field of the cathode ray tube is changed by a magnetic field generated by the horizontal deflection coil 4 which changes linearly with time and an auxiliary deflection coil. The magnetic field generated by the deflection coil 5 becomes a superposed magnetic field. Therefore, a slight stagnation occurs in the deflection sweep at the time of the rise and fall of the luminance signal.

As shown in FIG. 5D, the scanning speed of the beam current becomes a differential waveform of the superimposed deflection magnetic field shown in FIG.
The scanning speed is high in the portion and the speed is low in the portion B. Therefore, as shown in FIG. 5 (e), the brightness signal after velocity modulation displayed on the CRT has sharpness improved with preshoot and overshoot in the contour portion, and the area of the white portion is small. In addition, the area of the black portion is increased, and the increase in the beam spot size is suppressed.

[0006]

As is well known in the NTSC system, a luminance signal has a wide band, but a chrominance signal has a narrow band since it is transmitted with its band limited. As is well known, the primary color signal reproduced on the receiving side is an R signal, a G signal, and a B signal. Therefore, the color difference signals (RY) and (BY) will be described as color difference signals (CY) below.

The luminance signal Y has a low-frequency component YL and a high-frequency component YH
However, only the low-frequency component (C−Y) L of the color difference signal is transmitted, and there is no high-frequency component (C−Y) H. Thus, the obtained primary color signal C is given by the following equation. C = YL + (C−Y) L + YH (1) The high-frequency component of the reproduced primary color signal C is only the high-frequency component YH of the luminance signal, and information about the color is lost. Color resolution is degraded.

In the conventional velocity modulation circuit, the amount of correction depends on the amount of change in the luminance signal, that is, the differential signal. Therefore, an increase in the beam spot size due to an increase in the beam current is suppressed, and as a contour correction for improving sharpness. Has the effect of improving the color resolution lost on the transmitting side by the NTSC system. The present invention has been made in order to solve the above-described problem, and a speed modulation circuit capable of improving the image quality of a high-saturation portion image by changing the correction amount of the speed modulation depending on the level of the color difference signal. The purpose is to provide.

[0009]

To achieve the above object, the present invention provides (1) a color difference signal level detection circuit for detecting the level of at least one or more color difference signals, a differentiation circuit for differentiating a luminance signal, An amplification variable circuit that receives the output signal of the differentiating circuit and amplifies the amplification level according to the level of the color difference signal if the level is high, and amplifies the amplification level if the level is low. A speed modulation circuit comprising: an auxiliary deflection coil that receives an output signal of the variable amplification circuit and generates an auxiliary deflection magnetic field to perform speed modulation of a cathode ray tube electron beam. A) a color difference signal level detection circuit for detecting the level of at least one or more color difference signals; and a luminance signal, and if the level is higher, the amplification degree of the luminance signal is increased according to the level of the color difference signal. When the level is small, a luminance signal amplitude variable circuit for amplifying the amplification degree to a small level and outputting the amplified signal, a differentiation circuit for differentiating the output signal of the luminance signal amplitude variable circuit, and an output signal of the differentiation circuit are input and amplified. And an auxiliary deflection coil attached to the cathode ray tube, receiving an output signal of the amplifier circuit, and generating an auxiliary deflection magnetic field to perform velocity modulation of the electron beam of the cathode ray tube. To provide a speed modulation circuit.

[0010]

FIG. 1 is a block diagram showing a first embodiment of the present invention. The same parts as those of the conventional example shown in FIG. 4 are denoted by the same reference numerals, and description thereof will be omitted. In FIG.
The color difference signal level detection circuit 6 clamps the input color difference signal with a separately input clamp pulse, detects the color difference signal level, and supplies the signal to the variable amplification circuit 7. The amplification variable circuit 7 amplifies and outputs the amplification degree according to the level of the color difference signal if the level is high and the amplification degree is low if the level is low. When the level of the color difference signal is high, it is determined that the high-frequency component is largely degraded, and the current flowing through the auxiliary deflection coil 5 is increased to change the superimposed deflection magnetic field, thereby changing the scanning speed of the beam current. In a place where the color difference signal level is large, the operation is performed so as to enhance the speed modulation effect.

FIG. 3 is a circuit diagram showing a specific example of a color difference signal level detection circuit. In FIG. 3, a color difference signal is input from an input terminal IN, and a DC component is cut by a capacitor C1. Then, a clamp pulse using a flyback pulse or the like input from the input terminal IN causes a color difference signal level during a horizontal blanking period. = 0 is clamped so as to be the voltage source E1. The potential at which the level of the color difference signal input to the transistor T1 becomes 0 is equal to the base potential of the transistor T2.

In a portion where the color difference signal becomes negative, the transistor T2 cannot be turned on, and a constant voltage determined by the resistors R3 and R4 is output to the output terminal OUT. On the other hand, in a portion where the color difference signal is positive, the transistor T2 is turned on and the resistance R
2, a voltage determined by R3, R4 and the color difference signal level is output. Therefore, a voltage corresponding to the color difference signal level is output from the output terminal OUT. The gain of the output signal can be arbitrarily selected according to the constant of R2. or,
The variable amplification circuit 7 in FIG. 1 can be realized not only by simple amplitude control but also by a method of controlling the maximum amplitude such as a limiter.

FIG. 2 is a block diagram showing a second embodiment of the present invention. 4 and 1 are denoted by the same reference numerals, and description thereof will be omitted. In FIG. 2, a color difference signal level detection circuit 6 clamps an input color difference signal with a separately input clamp pulse, detects a color difference signal level, and supplies it to a luminance signal amplitude variable circuit 8. The luminance signal amplitude variable circuit 8 has, in principle, an amplification degree of 1 or more. In accordance with the level of the color difference signal, the amplification degree of the luminance signal is increased if the level is large, and the amplification degree of the luminance signal is decreased if the level is small. Amplify and output small. When the level of the color difference signal is high, the amplification degree of the input luminance signal is increased and supplied to the differentiating circuit 1. The differential waveform, which is the output of the differentiating circuit 1, changes, and as a result, the scanning speed of the beam current is changed so that the speed modulation effect is enhanced where the color difference signal level is large.

1 and 2, the color resolution is improved by changing the speed modulation effect in accordance with the color difference signal level. Each of the variable amplification circuit 7 in FIG. 1 and the variable luminance signal amplitude circuit 8 in FIG. 2 is realized by an existing circuit for controlling the output amplitude of an AC signal by an external control signal, such as an electronic volume. Therefore, detailed description will be omitted. In the embodiment, a method of detecting any one level of an arbitrary color difference signal has been described. For example, speed modulation control adapted to the levels of a plurality of color difference signals using a plurality of similar circuits may be performed. Of course, it is also possible.

[0015]

The speed modulation circuit of the present invention has an extremely excellent effect that the image quality of a high chroma portion can be improved by changing the correction amount of the speed modulation according to the level of the color difference signal.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of the present invention.

FIG. 2 is a block diagram showing a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing a specific example of a color difference signal level detection circuit.

FIG. 4 is a block diagram showing a conventional example.

FIG. 5 is a waveform chart for explaining a basic operation of velocity modulation.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 differentiation circuit 2 amplification circuit 3 video signal processing circuit 4 horizontal deflection coil 5 auxiliary deflection coil 6 color difference signal level detection circuit 7 amplification variable circuit 8 luminance signal amplitude variable circuit

Claims (2)

[Claims] 1. A color difference signal level detection circuit for detecting a level of at least one or more color difference signals; a differentiation circuit for differentiating a luminance signal; A variable amplification circuit that amplifies the amplification level to a large value if the level is large, and amplifies the amplification level to a small value if the level is small; and an output signal of the amplification variable circuit, which is attached to a cathode ray tube and receives an auxiliary deflection magnetic field. And an auxiliary deflection coil for performing velocity modulation of the electron beam of the cathode ray tube by generating the velocity modulation circuit. 2. A color difference signal level detection circuit for detecting a level of at least one or more color difference signals, and a luminance signal is input. According to the level of the color difference signal, if the level is large, the amplification degree of the luminance signal is increased. A brightness signal amplitude variable circuit for amplifying the amplification degree to a small value if the level is small, and outputting the amplified signal; a differentiation circuit for differentiating an output signal of the brightness signal amplitude variable circuit; and an output signal of the differentiation circuit. And an auxiliary deflection coil attached to a cathode ray tube, receiving an output signal of the amplifier circuit, and generating an auxiliary deflection magnetic field to modulate the speed of the electron beam of the cathode ray tube. Speed modulation circuit.