JP2000196912A - Velocity modulation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a velocity modulation circuit which can well improve the sharpness of videos regardless of the luminance of the videos, whether high or low. SOLUTION: A luminance and amplitude variable circuit 7 detects the luminance level of a luminance signal (a) and generates another luminance signal a' by changing the amplitude of the signal (a) in accordance with the luminance level. A differentiation circuit 2 generates a differentiated signal b' by linearly differentiating the luminance signal a'. The signal b' is inputted to an auxiliary deflecting coil 4 after being amplified by means of an amplifier circuit 3. Thus the deflected velocity of an electron beam is modulated.

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 used for an image display device using a cathode ray tube such as a television receiver.

[0002]

2. Description of the Related Art A cathode ray tube (CR) of a television receiver or the like is used.
In the image display device using T), the beam current of the CRT increases in a portion of the image signal where the brightness is high, so that the beam spot size increases and the sharpness decreases. Therefore, it is well known that a speed modulation circuit is used as a method for compensating for the decrease in sharpness.

FIG. 5 is a block diagram showing a conventional speed modulation circuit, and FIG. 6 is a waveform diagram for explaining its operation. In FIG. 5, a luminance signal a shown in FIG. The video signal processing 1 processes the luminance signal a and inputs the processed signal to the CRT 6. The luminance signal a is
It is also input to the differentiating circuit 2. The differentiating circuit 2 calculates the luminance signal a
Is first-order differentiated to generate a differentiated signal b shown in FIG.

[0004] The differential signal b is input to the amplifier circuit 3. The amplification circuit 3 amplifies the differential signal b and supplies it to the auxiliary deflection coil 4 mounted on the CRT 6. Thereby, as shown in FIG. 6C, an auxiliary deflection current c corresponding to the differential signal b flows through the auxiliary deflection coil 4. A horizontal deflection current d shown in FIG. 6D flows through the horizontal deflection coil 4 mounted on the CRT 6.

The horizontal deflection current d shown in FIG.
The superimposed deflection current c shown in FIG. 6C results in the superimposed deflection current e shown in FIG. CRT6
Is a magnetic field obtained by superposing a magnetic field generated by the horizontal deflection coil 5 and a magnetic field generated by the auxiliary deflection coil 4 that change linearly with time. Therefore, a slight stagnation occurs in the deflection sweep at the rise and fall of the luminance signal a. Since the brightness of the CRT 6 is proportional to the reciprocal of the amplitude of the brightness signal and the horizontal deflection speed, the brightness increases in the white outline portion and decreases in the black outline portion. As a result, after the velocity modulation, the luminance signal f visually appears as shown in FIG. 6 (F), and the luminance difference at the outline increases, thereby improving the contrast.

[0006]

The speed modulation circuit is a CRT.
6 is effective in compensating for the decrease in sharpness. However, the compensation amount is the change amount of the luminance signal, that is,
It depends on the differential signal b shown in FIG. However, the sharpness of the CRT 6 is reduced by the beam amount of the CRT 6,
That is, it depends on the amplitude of the luminance signal. Therefore, the compensation amount of the velocity modulation does not work effectively with respect to the decrease amount of the sharpness, and depending on the video, the compensation amount may be overcompensated or undercompensated.

For example, when the compensation amount is determined for an image having a relatively high luminance such that white includes some black, a compensation amount is determined for an image having a relatively low luminance such as white characters in black. Is too large, the outline of the image shines, and the image quality may be impaired. Furthermore, the character may bend.

On the other hand, if the compensation amount is determined for an image having a relatively low luminance, a sufficient effect cannot be obtained on the spread of the beam spot in an image having a relatively high luminance.
Sharpness does not improve.

The present invention has been made in view of such a problem, and it is possible to satisfactorily improve the sharpness of a high-luminance image and a low-luminance image in any case. It is an object to provide a speed modulation circuit.

[0010]

According to the present invention, in order to solve the above-mentioned problems of the prior art, a differentiation circuit (2) for differentiating a luminance signal to a first order and a deflection magnetic field by a horizontal deflection coil (5) are provided. An auxiliary deflecting coil (4) for superimposing an auxiliary deflecting magnetic field in accordance with an output signal of the differentiating circuit, wherein the velocity modulation circuit modulates the deflection speed of the electron beam; It is an object of the present invention to provide a velocity modulation circuit characterized by comprising a luminance amplitude variable circuit (7) for varying the amplitude of the luminance signal or the amplitude of the output signal of the differentiating circuit according to the luminance level of the signal. .

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A speed modulation circuit according to the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a block diagram showing an embodiment of the speed modulation circuit of the present invention, FIG. 2 is a waveform diagram for explaining the operation of the speed modulation circuit of the present invention, and FIG. FIG. 4 is a circuit diagram showing an example of a specific configuration, and FIG. 4 is a diagram showing characteristics of the brightness amplitude variable circuit 7 in FIG. In FIG. 1, the same portions as those in FIG. 5 are denoted by the same reference numerals.

In FIG. 1, video signal processing 1 includes FIG.
The luminance signal a shown in FIG. Video signal processing 1
Processes the luminance signal a and inputs it to the CRT 6. The luminance signal a is also input to a luminance amplitude variable circuit 7 newly provided according to the present invention, which detects the luminance level of the luminance signal a and varies the amplitude of the luminance signal a according to the detected luminance level. Is done. The brightness amplitude variable circuit 7 increases the amplitude as the brightness level increases, as shown in FIG.
When the luminance level decreases, the amplitude is controlled to be reduced, and the luminance signal is output as a luminance signal a 'shown in FIG.

The brightness signal a 'output from the brightness amplitude variable circuit 7 is input to the differentiating circuit 2. The differentiating circuit 2 first-order differentiates the luminance signal a 'to generate a differentiated signal b' shown in FIG.

This differential signal b 'is input to the amplifier circuit 3. The amplification circuit 3 amplifies the differential signal b 'and supplies it to the auxiliary deflection coil 4 mounted on the CRT 6. This allows
As shown in FIG. 2D, an auxiliary deflection current c 'corresponding to the differential signal b' flows through the auxiliary deflection coil 4. CRT
A horizontal deflection current d shown in FIG. 2 (E) flows through the horizontal deflection coil 4 mounted on 6.

The horizontal deflection current d shown in FIG.
The superposition of the auxiliary deflection current c 'shown in FIG. 2D results in a superposition deflection current e' shown in FIG. CRT
The deflection magnetic field 6 is a magnetic field obtained by superposing a magnetic field from the horizontal deflection coil 5 that changes linearly with time and a magnetic field from the auxiliary deflection coil 4. Therefore, a slight stagnation occurs in the deflection sweep at the rise and fall of the luminance signal a. Since the brightness of the CRT 6 is proportional to the reciprocal of the amplitude of the brightness signal and the horizontal deflection speed, the brightness increases in the white outline portion and decreases in the black outline portion. as a result,
After the velocity modulation, the luminance signal visually becomes the luminance signal f 'shown in FIG. 2 (G), and the luminance difference between the contours increases to improve the contrast.

In the configuration of the present invention, the luminance level of the luminance signal a is detected, the amplitude of the luminance signal a is varied according to the luminance level, and the luminance signal a 'is obtained, and then the velocity modulation is performed.
Therefore, the amount of compensation by the speed modulation circuit changes according to the luminance level of the luminance signal a. By doing so, there is no problem that the image quality is impaired due to too much compensation, or the sharpness is not improved because the compensation amount is too small. Also in the case of, the sharpness can be improved satisfactorily.

In this embodiment, as a preferred embodiment, the brightness amplitude variable circuit 7 is provided in a stage preceding the differentiating circuit 2. A luminance amplitude variable circuit 7 is provided at the subsequent stage of the differentiation circuit 2,
Differentiating circuit 2 according to the luminance level of the inputted luminance signal
A configuration may be adopted in which the amplitude of the differential signal output from the control unit is varied.

The brightness amplitude variable circuit 7 in FIG. 1 can be configured as shown in FIG. 3 as an example. In FIG. 3, the luminance signal a mainly includes the transistors T3, T4, T
5 as well as transistors T1, T2 and resistors R1, R2, R3, R4.
It is input to a luminance level detection circuit composed of R5 and capacitor C1.

The transistor T2 functions as a buffer,
The output of the luminance level detection circuit is input via a resistor R5 to a transistor T3 that determines the amplification amplitude of the differential amplifier circuit. The capacitor C1 is for cutting a DC component. Transistor T1 and resistors R1 to R
Reference numeral 3 denotes a sync tip clamp circuit for clamping the luminance signal a and driving the transistor T2. Here, the clamp is performed by the sync tip clamp circuit. However, when the already-clamped luminance signal is input, a simpler level shift circuit may be used, or a pedestal may be used instead of the sync tip clamp circuit. It is also possible to realize by a clamp circuit. It is within the scope of the present invention to realize the clamp by a method other than the sync tip clamp circuit.

The differential amplifier circuit amplifies the luminance signal a input to the transistor T5 by the transistors T3 and T4. A luminance signal a 'whose amplitude has been changed is output from the collector of the transistor T3. In FIG. 3, R7 is a resistor,
V1 is a power supply, and Vcc is a reference voltage.

In such a configuration, for example, when an image has a high luminance level, the collector current of the transistor T3 increases, so that the output luminance signal a 'increases. Conversely, in an image with a low luminance level, the transistor T
3, the output luminance signal a 'becomes smaller. The specific configuration of the brightness amplitude variable circuit 7 is not limited to that shown in FIG.

[0022]

As described above in detail, the velocity modulation circuit according to the present invention comprises a differentiation circuit for first-order differentiation of a luminance signal, and a deflection magnetic field generated by a horizontal deflection coil. An auxiliary deflection coil for superimposing a magnetic field is provided, and a luminance amplitude variable circuit that varies the amplitude of the luminance signal or the amplitude of the output signal of the differential circuit in accordance with the luminance level of the luminance signal is provided at the preceding or subsequent stage of the differentiating circuit. With this configuration, the sharpness can be improved satisfactorily in both cases, for both high-luminance video and low-luminance video. Therefore, the image quality can be effectively improved.

[Brief description of the drawings]

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

FIG. 2 is a waveform chart for explaining the operation of the present invention.

FIG. 3 is a circuit diagram showing an example of a specific configuration of a brightness amplitude variable circuit 7 in FIG.

FIG. 4 is a diagram showing characteristics of the brightness amplitude variable circuit 7 in FIG.

FIG. 5 is a circuit diagram showing a conventional example.

FIG. 6 is a waveform chart for explaining the operation of the conventional example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 video signal processing 2 differentiating circuit 3 amplifying circuit 4 auxiliary deflection coil 5 horizontal deflection coil 6 cathode ray tube (CRT) 7 brightness amplitude variable circuit

Claims (2)

[Claims] A differential circuit for performing first-order differentiation of a luminance signal; and an auxiliary deflection coil for superimposing an auxiliary deflection magnetic field according to an output signal of the horizontal deflection coil on a deflection magnetic field generated by the horizontal deflection coil. In a speed modulation circuit that modulates a deflection speed, a luminance amplitude variable circuit that detects a luminance level of the luminance signal and varies the amplitude of the luminance signal according to the detected luminance level is provided at a stage preceding the differentiation circuit. A speed modulation circuit characterized by comprising: 2. A differentiation circuit for performing a first-order differentiation of a luminance signal, and an auxiliary deflection coil for superimposing an auxiliary deflection magnetic field according to an output signal of the horizontal deflection coil on a deflection magnetic field by a horizontal deflection coil; In a velocity modulation circuit for modulating a deflection speed, a luminance amplitude variable circuit that varies an amplitude of an output signal of the differentiation circuit in accordance with a luminance level of the luminance signal is provided at a subsequent stage of the differentiation circuit. Speed modulation circuit.