JP2000358168A - Speed modulation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a speed modulation circuit which can perform proper speed modulation only when thickening of a beam actually occurs regardless of the setting of a contrast and the amplitude of an input signal, and accordingly can prevent deterioration of picture quality that is caused by the thickening of the beam or the excessive speed modulation. SOLUTION: A level detection circuit 11 of this speed modulation circuit detects a part having a level higher than a prescribed DC level of the output of a contrast amplifier 4 and acquires a level detection signal. An area pulse generation circuit 12 adds the prescribed pulse width β to the level detection signal in response to a filter setting signal to generate an area pulse. A primary differentiation circuit 3 applies the primary differentiation to an input video signal to acquire a speed modulation signal. The amplifier 4 amplifies the speed modulation signal. A gate circuit 13 gates the output signals of an amplifier 8 only for a period of the area pulse and acquires a speed modulation output signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a cathode ray tube (CR)
The present invention relates to a speed modulation circuit for modulating the scanning speed of an electron beam used in an image display device such as a television receiver using T).

[0002]

2. Description of the Related Art In an image display apparatus such as a television receiver using a CRT, a beam is concentrated by a deflection correction (velocity modulation) coil against a so-called beam thickening caused by an increase in beam current. A speed modulation circuit for keeping the magnitude of the apparent signal light output constant is provided. The speed modulation signal is generated by first-order differentiating the luminance component of the video signal and amplifying this by an amplifier.
The speed modulation is unnecessary when the beam current is small, and is necessary when the beam current is large. If the velocity modulation is applied excessively, the beam is concentrated on a certain place, and conversely, the gradation characteristic is deteriorated, and the image quality may be degraded. Therefore, conventionally, a configuration in which the contrast setting and the speed modulation gain are linked is generally used. FIG. 3 is a block diagram showing a conventional speed modulation circuit, and FIG. 4 is a waveform diagram for explaining the operation of FIG. 3, which will be described together.

In FIG. 3, an input video signal (luminance signal) is input from an input terminal 1 and supplied to a contour correction circuit 2 and a primary differentiation circuit 3. The contour correction circuit 2 operates as a so-called enhancer for correcting (enhancing) the contour of the video of the input signal, and supplies the output signal to the contrast amplifier 4. The contrast amplifier 4 adjusts the contrast of the video signal in accordance with the contrast setting signal supplied from the input terminal 5 to obtain a video output signal having a waveform shown in FIG. I have. In FIG. 4A, the portions where the beam thickening is likely to occur are particularly at the b, c, e, and f portions.

The primary differentiating circuit 3 converts an input video signal into
A first-order differentiation is performed by a filter corresponding to a filter setting signal supplied from the input terminal 7 to generate a velocity modulation signal, which is supplied to the amplifier 8. The amplifier 8 amplifies the input signal according to the speed modulation gain setting signal supplied from the input terminal 9 and the contrast setting signal supplied from the input terminal 5, and outputs a speed modulation output having a waveform shown in FIG. Get the signal,
The signal is output from the output terminal 10. In FIG. 4B,
The velocity modulation output signal is generated in the portions a, b, c, d, e, and f in FIG. 4A, and appropriate contour correction is performed to eliminate the beam thickening. In this circuit, since the contrast setting signal supplied from the input terminal 5 is input to both the contrast amplifier 4 and the amplifier 8, when the user lowers the contrast, the amplification of the amplifier 8 also decreases. Excessive velocity modulation is suppressed.

[0005]

However, the conventional speed modulation circuit shown in FIG. 3 does not consider the absolute value (DC component) of the signal component affecting the optical output, so that the input signal has a small amplitude.
When the DC component is high (contrast is small), when the contrast is reduced by the contrast setting signal, the gain of the speed modulation is also reduced, and the effect of the speed modulation is reduced. That is, the velocity modulation output signal output from the output terminal 10 has a waveform as shown in FIG. 4C, the signals of the a, b, c, and d portions having low contrast disappear, and the beam thickening occurs. There was. When the contrast is increased by the contrast setting signal, the gain of the speed modulation is increased even if the input signal has a large amplitude, so that the speed modulation is performed even when the DC component is low. As a result, there has been a problem that excessive speed modulation is applied and image quality is deteriorated.

Further, since the gain of the speed modulation is controlled only by the contrast setting by the contrast setting signal,
When the signal amplitude in the middle and high frequency ranges is changed by the contour correction circuit 2, there is also a problem that it is not possible to set an optimum speed modulation gain corresponding to the change. The present invention has been made in order to solve such a problem, and it is possible to apply appropriate velocity modulation only when beam fattening actually occurs, regardless of the contrast setting and the amplitude of an input signal. Therefore, it is an object of the present invention to provide a speed modulation circuit capable of performing optimum speed modulation without causing image quality deterioration due to beam thickening or excessive speed modulation.

[0007]

In order to achieve the above object, a speed modulation circuit for modulating a scanning speed of an electron beam, comprising: a contour correction circuit for correcting an input video signal;
A contrast amplifier that obtains a video output signal by adjusting a contrast of the output signal of the contour correction circuit according to a contrast setting signal, and a level detection signal that detects a portion of the video output signal that is equal to or higher than a predetermined DC level. A level detection circuit for obtaining the level detection signal, an area pulse generation circuit for generating an area pulse in which a predetermined pulse width is added to the level detection signal in accordance with a filter setting signal, and a first derivative of the input video signal with a filter corresponding to the filter setting signal A first-order differentiating circuit for obtaining a speed-modulated signal, an amplifier for amplifying the speed-modulated signal, and a gate circuit for gating and outputting the output signal of the amplifier only during the area pulse. Is provided.

[0008]

FIG. 1 is a block diagram showing an embodiment of a speed modulation circuit according to the present invention, and FIG. 2 is a waveform diagram for explaining the operation of FIG. The same parts as those in the conventional example shown in FIG. 3 are denoted by the same reference numerals, and description thereof will be omitted. 1, the main difference from FIG. 3 is that a level detection circuit 11, an area pulse generation circuit 12, and a gate circuit 13 are provided, which will be described in detail below. The contrast amplifier 4 adjusts the contrast of the video signal in accordance with the contrast setting signal supplied from the input terminal 5 to obtain a video output signal having a waveform shown in FIG. , Level detection circuit 11. In FIG. 2A, beam thickening is likely to occur particularly at the b, c, e, and f portions. Level detection circuit 11
Detects a DC level portion of the video signal which is equal to or higher than the level indicated by the broken line shown in FIG. 2A, obtains a level detection signal having a waveform shown in FIG. 2B, and supplies it to the area pulse generation circuit 12. ing.

The area pulse generation circuit 12 adds a pulse width β determined by a filter constant corresponding to a filter setting signal supplied from the input terminal 7 to the front and rear sides of the level detection signal (pulse signal), as shown in FIG. An area pulse having the waveform shown in C) is obtained and supplied to the gate circuit 13.
The primary differentiating circuit 3 performs primary differentiation of the input video signal with a filter corresponding to a filter setting signal supplied from the input terminal 7 to generate a velocity modulation signal, and supplies it to the amplifier 8. The amplifier 8 amplifies the input signal according to the speed modulation gain setting signal supplied from the input terminal 9, and
A velocity modulation signal having the waveform shown in FIG.
To supply. The pulse width α in FIG. 2D is set by the filter setting signal in the primary differentiating circuit 3. The gate circuit 13 gates the velocity modulation signal having the waveform shown in FIG. 2D with an area pulse having the waveform shown in FIG. 2C to obtain a velocity modulation output signal having the waveform shown in FIG. Output from the output terminal 10.

As apparent from FIG. 2E, when an area pulse is input, that is, when the DC level of the output signal of the contrast amplifier 4 is equal to or higher than a predetermined level, the output of the amplifier 8 is gated and output. By doing so, the velocity modulation signal is output only when the beam is actually thickened and velocity modulation is required. The area pulse generation circuit 1
2, as shown in FIG. 2 (C), by adding a pulse width β to both front and rear sides,
Almost all periods of the contour correction signal in the b and c portions of (D) can be gated. However, if the width of the area pulse is too wide, a signal more than necessary is output, and if it is too narrow, a necessary signal is lost. Therefore, the width β is set optimally according to the filter setting signal, similarly to the pulse width α in FIG.

Further, according to the present invention, the contrast amplifier 4 and the amplifier 8
Are not simultaneously controlled, so that speed modulation is not applied even when the DC level component is low. Therefore, excessive speed modulation does not occur and image quality does not deteriorate.
Further, when the signal amplitude in the middle and high frequency ranges is changed by the contour correction circuit 2, the change is detected by the level detection circuit 11, so that the optimum speed modulation gain can be obtained.

[0012]

According to the velocity modulation circuit of the present invention, appropriate velocity modulation can be applied only when beam thickening actually occurs regardless of the contrast setting or the amplitude of the input signal. There is an extremely excellent effect that optimum speed modulation can be performed without image quality degradation due to speed modulation.

[Brief description of the drawings]

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

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

FIG. 3 is a block diagram showing a conventional example.

FIG. 4 is a waveform chart for explaining the operation of FIG. 3;

[Explanation of symbols]

 1, 5, 7, 9 input terminal 2 contour correction circuit 3 primary differentiation circuit 4 contrast amplifier 8 amplifier 6, 10 output terminal 11 level detection circuit 12 area pulse generation circuit 13 gate circuit

Claims (1)

[Claims] 1. A speed modulation circuit for modulating a scanning speed of an electron beam, comprising: a contour correction circuit for correcting a contour of an input video signal; and adjusting an output signal of the contour correction circuit according to a contrast setting signal. A contrast amplifier that obtains a video output signal by performing the above operation; a level detection circuit that detects a portion of the video output signal that is equal to or higher than a predetermined DC level to obtain a level detection signal; An area pulse generation circuit that generates an area pulse to which a pulse width is added; a first differentiation circuit that performs a first differentiation of the input video signal with a filter according to a filter setting signal to obtain a velocity modulation signal; An amplifier for amplifying; and a gate circuit for gating and outputting the output signal of the amplifier only during the area pulse. And a speed modulation circuit characterized by the above.