JPH0715618A - Speed modulating device - Google Patents

Abstract

PURPOSE:To provide a speed modulating device which can perform the proper modulation of speed over an entire screen. CONSTITUTION:An input video signal Sa inputted from an input terminal 31 is supplied to a differentiating circuit 32 and also to a video signal average level detecting circuit 36. A detection signal Sk showing the average level of the signal Sa is outputted to a correction signal generating circuit 37 from the circuit 36. The circuit 37 outputs a correction signal Sc to perform the variable amplification through a variable amplifier 38 so that the amplitude of the differential signal received from the circuit 32 is limited toward the periphery of a screen in response to the signal Sk (average level of video signal).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used in a television receiver or the like, and supplies a primary differential current generated from a video signal to a velocity modulation coil provided separately from a main deflection yoke to scan in a horizontal direction. The present invention relates to a speed modulation device that modulates.

[0002]

2. Description of the Related Art Conventionally, in a television receiver, in order to improve the sharpness of an image in a high luminance range, a differential modulation generated from a video signal is performed in a velocity modulation coil (auxiliary coil) provided separately from a main deflection yoke. A velocity modulator is used that applies a current to modulate the horizontal scanning velocity.

FIG. 3 is a block diagram showing the structure of a conventional speed modulation circuit. In FIG. 3, the speed modulation circuit includes a differentiating circuit 32 that receives the input video signal Sa from the input terminal 31 and outputs a primary differential signal Sb, an amplifier 33 that amplifies the primary differential signal Sb, and an amplified primary differential signal. An output circuit 34 for generating and transmitting a signal Sb to a drive current,
And a velocity modulation coil 35 to which a drive current is supplied.

Next, the operation of this conventional configuration will be described. FIG. 4 is a waveform diagram showing processing waveforms in the operation of the configuration of this conventional example. 3 and 4, the input video signal S shown in FIG.
a is supplied to the differentiating circuit 32. The differentiating circuit 32 outputs the primary differentiating signal Sb shown in FIG. This primary differential signal Sb is amplified by the amplifier 33, and further, the primary differential signal Sb is sent from the output circuit 34 to the speed modulation coil 35.
Drive current is supplied.

In the velocity modulation coil 35, the magnetic field generated by the drive current and the horizontal deflection magnetic field are added, and the total magnetic field shown in FIG. Figure 4 which differentiated the waveform shown in c)
As shown in (d). Therefore, in the waveform (Aa) in the first half of the rising portion of the video signal in FIG.
Since the scanning speed of the electron beam is high, the brightness is low on the screen of the cathode ray tube, and the scanning speed is low at the timing of the next waveform (Ba), so that the brightness on the screen of the cathode ray tube is rapidly increased.

Further, since the scanning speed of the electron beam is slow in the waveform (Ab) in the first half of the trailing edge of the video signal, the brightness is high on the screen of the cathode ray tube, and the scanning speed is fast in the timing of the next waveform (Bb). Therefore, the brightness on the screen sharply decreases. FIG. 4 (e) shows the luminance change on the screen of the cathode ray tube.
In this way, the sharpness in the horizontal direction is improved.

However, as flattening of the screen surface of a cathode ray tube has progressed in recent years, the difference between the relative speed of the scanning speed by the speed modulation circuit and the relative speed of the scanning by the deflection yoke between the central part and the peripheral part of the screen becomes large, and In the peripheral portion, the phenomenon that the velocity modulation becomes excessive (overmodulation) and has the opposite effect occurs.

FIG. 5 is a diagram showing an overmodulation state in the conventional velocity modulation. When the dot pattern Dp as shown in FIG. 5A is displayed, the dot pattern Dr having a narrow width at the center of the screen as shown in FIG.
However, the sharpness is increased, but the dot pattern Ds having a wider width is formed around the screen as shown in FIG. 5C. That is, the image becomes blurred, and good sharpness cannot be obtained. In order to improve this, the peripheral portion of the screen is corrected so as to reduce the differential signal current of the video signal supplied to the velocity modulation coil as compared with the central portion.

[0009]

However, in the above speed modulator of the prior art, when the average level of the differential signal is high when the correction is performed so as to reduce the differential signal current of the video signal supplied to the speed modulation coil. Since feedback that suppresses the differential signal current flowing through the velocity modulation coil is applied, there is a drawback that optimum correction cannot be performed depending on the average level of the video signal.

The present invention solves the above-mentioned drawbacks of the prior art, and can perform appropriate speed modulation over the entire screen, resulting in improved sharpness of the image in the high luminance range. An object of the present invention is to provide a velocity modulation device that can obtain a good image.

[0011]

In order to achieve the above object, the velocity modulation apparatus of the present invention applies a differential current generated from a video signal to a velocity modulation coil of a cathode ray tube to modulate the scanning velocity to thereby contour the image. In the speed modulator for sharpening the input signal, the value of the differential current from the differentiating means decreases toward the peripheral direction of the screen according to the differentiating means for first-order differentiating the input video signal and the average level detected from the video signal. The average level detection / correction means for performing the above correction is provided.

In this structure, the average level detecting / correcting means includes a detecting means for detecting an average level of the video signal,
A correction control unit that corrects the differential current value from the differentiating unit supplied to the velocity modulation coil to a smaller value in the peripheral direction of the screen corresponding to the average level detected by the detecting unit is provided.

Further, the correction control means for correcting the value of the differential current to a small value uses a variable amplification means for varying the amplification degree of the primary differential signal with the average level signal of the video signal detected by the detection means.

[0014]

With such a structure, in the velocity modulation device of the present invention, the value of the differential current from the differentiating means is corrected so as to decrease toward the peripheral direction of the screen corresponding to the average level detected from the video signal. is doing. Therefore, appropriate speed modulation is performed over the entire screen.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of a velocity modulator of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an embodiment of the velocity modulation device of the present invention. In the following text and drawings, the same constituent elements in the previous FIG. 3 are designated by the same reference numerals. In FIG. 1, the speed modulator includes a differentiating circuit 32 that receives an input video signal Sa from an input terminal 31 and outputs a primary differential signal Sb, and a variable amplifier that amplifies the primary differential signal Sb in accordance with a correction signal Sc. 38 and an output circuit 34 for generating and transmitting the amplified primary differential signal Sb to a drive current. Further, this speed modulation device has a speed modulation coil 35 to which a drive current is supplied, a video signal average level detection circuit 36, and a correction signal generation circuit 37.

Next, the operation of the configuration of this embodiment will be described. FIG. 2 is a waveform diagram showing processing waveforms in the operation of the configuration of this embodiment. 1 and 2, the operation from the differentiating circuit 32 to the output circuit 34 is the same as that in FIG. 3 described above. That is, the primary differentiation signal Sb is output from the differentiation circuit 32 to which the input video signal Sa is supplied from the input terminal 31. The primary differential signal Sb is amplified by the variable amplifier 38 based on the correction signal Sc, and is further generated and output as a drive current to be supplied from the output circuit 34 to the speed modulation coil 35.

In the velocity modulation coil 35, the magnetic field generated by the drive current and the horizontal deflection magnetic field are added, the total magnetic field acts on the electron beam, and the velocity waveform scanned by the electron beam is differentiated. Therefore, in the waveform in the first half of the rising portion of the video signal, the scanning speed of the electron beam is high, and the brightness is low on the screen of the cathode ray tube. further,
At the timing of the next waveform, the scanning speed slows down, and the brightness on the screen of the cathode ray tube rapidly increases.

Further, in the waveform in the first half of the trailing edge of the video signal, the scanning speed of the electron beam becomes slow, so that the brightness becomes high on the screen of the cathode ray tube. Further, at the timing of the next waveform, the scanning speed becomes faster, so that the brightness on the screen sharply decreases. That is, the sharpness in the horizontal direction is improved.

In this case, the input video signal Sa from the input terminal 31 is supplied to the differentiating circuit 32 and the video signal average level detecting circuit 36, and the video signal average level detecting circuit 36 determines the average level of the video signal. The detection signal Sk shown is output to the correction signal generation circuit 37. The correction signal generation circuit 37 performs variable amplification with the variable amplifier 38 so as to limit the amplitude of the detection signal Sk, that is, the amplitude of the differential signal from the differentiating circuit 32 corresponding to the average level of the video signal, toward the periphery of the screen. The correction signal Sc for performing is output.

Here, when a pulse train-shaped signal having a constant amplitude is applied to the input terminal 31, the differentiating circuit 32 in FIG.
A differential signal having a uniform level is obtained over one horizontal period (1H) as shown in (a). Next, in the correction signal generation circuit 37, for example, the parabola wave (1) shown in FIG. 2B obtained by integrating the horizontal synchronization signal twice is generated. Further, the parabolic wave (1) is inverted to generate the parabolic wave (2), and the positive side of the primary differential signal Sb from the variable amplifier 38 shown in FIG. 2C is limited by the parabolic wave (1). Also, the negative side is limited by the parabola wave (2).

The video signal average level detection circuit 36 detects the average level of the video signal. When this average level is high, the average level of the differential signal is also high and the current value of the differential signal flowing through the velocity modulation coil 35 is suppressed, so that the correction amount around the screen (amplitude M in FIG. 2B) becomes small. The signal Sk is output to the correction signal generation circuit 37. On the other hand, when the average level of the video signal is low, the detection signal Sk having a large correction amount around the screen is output to the correction signal generation circuit 37.

In this way, the correction of the periphery of the screen is optimized, and appropriate speed modulation is performed over the entire screen regardless of the video signal. Although the output amplitude of the variable amplifier 38 is limited by the correction signal Sc from the correction signal generating circuit 37 in this embodiment, the same applies to the case where the correction signal Sc is multiplied by the primary differential signal Sb. The effect of is obtained.

[0023]

As is apparent from the above description, in the velocity modulation device of the present invention, the value of the differential current from the differentiating means is changed every time in the peripheral direction of the screen corresponding to the average level detected from the video signal. Since the correction is performed so as to be small, it is possible to perform appropriate velocity modulation over the entire screen, and as a result, it is possible to obtain a good image in which the sharpness of the image in the high luminance region is improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a velocity modulation device of the present invention.

FIG. 2 is a waveform diagram showing processing waveforms in the operation of the configuration of the embodiment.

FIG. 3 is a block diagram showing a configuration of a conventional speed modulation circuit.

FIG. 4 is a waveform diagram showing processing waveforms in the operation of the configuration of the conventional example.

FIG. 5 is a diagram showing an overmodulation state in speed modulation of a conventional example.

[Explanation of symbols]

32 ... Differentiation circuit 34 ... Output circuit 35 ... Velocity modulation coil 36 ... Video signal average level detection circuit 37 ... Correction signal generation circuit 38 ... Variable amplifier Sa ... Input video signal Sb ... Primary differential signal Sc ... Correction signal Sk ... Detection signal

Claims (3)

[Claims] 1. A velocity modulation device for causing a differential current generated from a video signal to flow through a velocity modulation coil of a cathode ray tube to modulate a scanning velocity to sharpen an image contour, and differentiating means for first-order differentiating an input video signal, Average level detection for correcting so that the value of the differential current from the differentiating means becomes smaller toward the peripheral direction of the screen corresponding to the average level detected from the video signal.
A velocity modulation device comprising: a correction unit. 2. The average level detecting / correcting means supplies the detecting means for detecting the average level of the video signal and the velocity modulating coil to the peripheral direction of the screen corresponding to the average level detected by the detecting means. The speed modulation device according to claim 1, further comprising: a correction control unit that corrects a differential current value from the differentiating unit to be small. 3. The correction control means for correcting the value of the differential current to be small uses variable amplification means for varying the amplification degree of the primary differential signal with the average level signal of the video signal detected by the detection means. The speed modulation device according to claim 2.