JPH11298755A - Speed modulation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform appropriate speed modulation, only when beam thickening actually occurs regardless of the contrast setting or the amplitude of input signals. SOLUTION: A contour correction circuit 1 executes contour correction for inputting video signals, a contrast amplifier 2 adjusts contrast corresponding to contrast setting signals, and a level detection circuit 5 detects a part higher than a prescribed DC level in the output of the contrast amplifier 2. A first-order differential circuit 3 performs the first-order differentiation of the video signals and generates speed modulation signals, an amplifier 4 amplifies the speed modulation signals and a gate circuit 6 gates and outputs the speed modulation signals outputted from the amplifier 4, only for the part which is higher than the prescribed DC level detected by the level detection circuit 5.

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 device 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 velocity modulation is unnecessary when the beam current is small, and is necessary when the beam current is large.

When 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 lowered. Therefore, conventionally, a configuration in which the setting of the contrast and the gain of the speed modulation are linked is generally used. FIG. 3 is a block diagram showing such a conventional speed modulation circuit.

In FIG. 3, an input video signal (luminance signal) is input to a contour correction circuit 1 and a primary differentiation circuit 3. The contour correction circuit 1 is a so-called enhancer circuit. The output of the contour correction circuit 1 is input to a contrast amplifier 2 where the contrast is adjusted according to a contrast setting signal and output.

A first-order differentiating circuit 3 performs a first-order differentiation on an input signal to generate a velocity modulation signal. The output of the primary differentiating circuit 3 is input to the amplifier 4 and amplified and output according to the contrast setting signal. Since the contrast setting signal is input to the contrast amplifier 2 and the amplifier 4, when the user lowers the contrast, excessive speed modulation is suppressed.

[0006]

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 large amplitude and a DC voltage. If the contrast is reduced by the contrast setting signal when the component is high, the gain of the speed modulation is forcibly reduced, and the effect of the speed modulation is lost. As a result, the beam became fat.

When the contrast is increased by the contrast setting signal, the speed modulation gain 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, excessive speed modulation is applied, and the image quality is deteriorated. Further, since the speed modulation gain 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 1, the optimum speed modulation gain corresponding to the change is set. Could not.

SUMMARY OF THE INVENTION The present invention has been made in view of such a problem, and a speed modulation circuit capable of applying an appropriate speed modulation only when beam thickening actually occurs regardless of the contrast setting and the amplitude of an input signal. The purpose is to provide.

[0009]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems of the prior art, the present invention provides a velocity modulation circuit for modulating the scanning speed of an electron beam, which performs contour correction on an input video signal. A circuit (1), a contrast setting signal, and a contrast amplifier (2) for adjusting the contrast of the output of the contour correction circuit according to the contrast setting signal; and a predetermined DC level or more at the output of the contrast amplifier. A level detecting circuit (5) for detecting a portion, a first-order differentiating circuit (3) for first-order differentiating the input video signal to generate a velocity modulation signal,
An amplifier (5) for amplifying the speed modulation signal, and a gate circuit (6) for gating and outputting the speed modulation signal output from the amplifier only in a portion equal to or higher than the predetermined DC level detected by the level detection circuit. ) Is provided.

[0010]

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 one embodiment of the speed modulation circuit of the present invention, and FIG. 2 is a waveform diagram for explaining the operation of the speed modulation circuit of the present invention.
In FIG. 1, the same parts as those in FIG. 3 are denoted by the same reference numerals.

In FIG. 1, an input video signal (luminance signal) is input to a contour correction circuit 1 and a primary differentiation circuit 3. The contour correction circuit 1 is a so-called enhancer circuit, and performs contour correction on an input signal. Contour correction circuit 1
Is input to the contrast amplifier 2 where the contrast is adjusted in accordance with the contrast setting signal from the user and output. The output of the contrast amplifier 2 is input to the level detection circuit 5, where the level of the DC component is detected.

A first-order differentiating circuit 3 performs a first-order differentiation on the input signal to generate a velocity modulation signal. The output of the primary differentiating circuit 3 is input to an amplifier 4 and amplified and output according to a fixed or variable setting signal. 1, the contrast setting signal is input only to the contrast amplifier 2, and when the contrast setting signal is changed, both the contrast amplifier 2 and the amplifier 4 are not adjusted at the same time.

The output of the amplifier 4 is input to a gate circuit 6. A detection signal is input to the gate circuit 6 from the level detection circuit 5, and when the detection signal is input,
That is, when the DC component of the output of the contrast amplifier 2 is equal to or higher than a predetermined level, the output of the amplifier 4 is gated and output. As a result, a velocity modulation signal is output only when it is necessary to apply velocity modulation that actually causes beam thickening.

The operation of FIG. 1 will be further described with reference to the waveform diagram of FIG. 2, (A) is an input signal, (B) is an output of the contrast amplifier 2, (C) is an output of the level detection circuit 5, (D) is a velocity modulation signal which is an output of the gate circuit 6, (E). Shows an example of a conventional velocity modulation signal for reference.

The output of the contrast amplifier 2 is shown in FIG.
, The level detection circuit 5 detects a portion indicated by a broken line, which is higher than a predetermined level to be subjected to velocity modulation at which beam thickening actually occurs, and a detection signal (gate signal) as shown in FIG. Is output. The gate circuit 6 is shown in FIG.
Since the signal from the amplifier 4 is output only during the period of the detection signal shown in (C), the velocity modulation signal is as shown in FIG.

As shown in FIG. 2E, conventionally,
2A and 2B, the speed modulation is required even if it is not necessary to apply the speed modulation.
On the other hand, in the present invention, as shown in FIG. 2 (D), the speed modulation is applied only to the portion where the speed modulation that actually causes the beam thickening should be applied.

Further, since the contrast amplifier 2 and the amplifier 4 are not simultaneously adjusted when the contrast setting signal is changed, the speed modulation is not applied when the DC component is low. . Therefore,
Excessive speed modulation does not occur and does not degrade image quality. Further, when the signal amplitude in the middle and high frequency ranges is changed by the contour correction circuit 1, the change is detected by the level detection circuit 5.
Therefore, the speed modulation gain can be optimized.

[0018]

As described above in detail, the speed modulation circuit of the present invention is provided with a contour correction circuit for performing a contour correction on an input video signal, and a contrast setting signal. A contrast amplifier that adjusts the contrast of the output of the contour correction circuit; a level detection circuit that detects a portion of the output of the contrast amplifier that is equal to or higher than a predetermined DC level; A first-order differentiating circuit for generating the signal, an amplifier for amplifying the speed modulation signal, and a gate circuit for gating and outputting the speed modulation signal output from the amplifier only for a portion equal to or higher than a predetermined DC level detected by the level detection circuit. , Regardless of the contrast setting or the amplitude of the input signal, it is appropriate only when beam fattening actually occurs. It is possible to apply a degree modulation. Further, even when the signal is enhanced by the contour correction circuit 1, it is possible to obtain the optimum speed modulation gain.

[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 block diagram showing a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Contour correction circuit 2 Contrast amplifier 3 Primary differentiation circuit 4 Amplifier 5 Level detection circuit 6 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 performing contour correction on an input video signal; and a contrast setting signal, and the contour correction signal is input in accordance with the contrast setting signal. A contrast amplifier that adjusts the contrast of the output of the circuit; a level detection circuit that detects a portion of the output of the contrast amplifier that is equal to or higher than a predetermined DC level; a first-order differentiation of the input video signal to generate a velocity modulation signal A first-order differentiating circuit, an amplifier for amplifying the speed modulation signal, and a gate for outputting the speed modulation signal output from the amplifier only for a portion equal to or higher than the predetermined DC level detected by the level detection circuit. A speed modulation circuit comprising a gate circuit.