JP2001320602A - Image distortion correction device and cathode ray tube with it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device that corrects distortion in a video image caused by the lightness of a screen of a CRT with higher accuracy than that of a conventional correction circuit without making the circuit complicated even when the device utilizes a voltage proportional to a beam current. SOLUTION: The image distortion correction device is provided with a conversion means 24 that receives a 1st voltage ABL in response to a beam current of the cathode ray tube and converts a change in the 1st voltage into a change in an anode voltage depending on the lightness of the screen and with a horizontal correction means and a vertical correction means that correct distortion in the raster caused by the fluctuation in the anode voltage depending on the lightness of the screen on the basis of the conversion value of the 1st voltage converted by the conversion means 24 in horizontal and vertical directions respectively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image distortion correcting apparatus for correcting image distortion caused when an anode voltage changes due to the brightness of a screen, and a cathode ray tube having the same, wherein a voltage proportional to a beam current is provided. Is converted into a change in anode voltage due to the brightness of the screen, and based on this conversion value, the distortion of the raster caused by the change in anode voltage due to the brightness of the screen is corrected, thereby complicating the circuit. In addition, the present invention relates to an image distortion correction device capable of performing correction with higher accuracy than in the past, and a cathode ray tube having the same.

[0002]

2. Description of the Related Art In deflection in a cathode ray tube (hereinafter, referred to as CRT), the amplitude of both horizontal deflection and vertical deflection varies due to the variation of the anode voltage of the CRT.
The raster width d, which is the amount of deflection displayed on the CRT, is generally represented by the following equation. d = A · H / √Ea (Equation 1)

In equation (1), H is the intensity of the magnetic field in the deflection yoke (hereinafter referred to as the intensity of the magnetic field), Ea is the anode voltage of the CRT, A is the length of the deflection yoke, and the distance from the tube surface of the CRT to the electron gun. Is a constant determined by the distance and the like. From Equation 1, it can be seen that the raster width is inversely proportional to the square root of the anode voltage and proportional to the strength of the magnetic field in the deflection yoke. The strength H of the magnetic field generated in the coil of the deflection yoke (hereinafter, referred to as a deflection coil) is proportional to the product NI of the number of turns N of the deflection coil and the current I (hereinafter, referred to as a deflection current) flowing through the coil.
The raster width will be proportional to the deflection current.

On the other hand, there are two types of circuits for generating an anode voltage, one configured to keep the anode voltage value constant even when the load (beam current) fluctuates, and the other type not configured to maintain the anode voltage value. For those with high cost requirements, the latter is mainly adopted. If the anode voltage value is not kept constant, the screen becomes brighter (the beam current increases).
Then, the anode voltage decreases, and from Equation 1, the raster width increases.

[0005]

Therefore, conventionally, a voltage drop caused by the flow of a beam current (hereinafter referred to as AB) is assumed to follow a change in the anode voltage to some extent.
(L terminal voltage) and the raster width is changed accordingly to suppress the fluctuation. However, the amount of change in the ABL terminal voltage does not always match the amount of change in the actual anode voltage. FIG. 7 is a characteristic diagram of the anode voltage and the ABL terminal voltage with respect to the beam current. While the ABL terminal voltage changes linearly with respect to the beam current,
The anode voltage rises sharply in a region where the beam current is small (the screen is dark). This is due to the characteristics of the flyback transformer itself that generates the anode voltage, and is difficult to improve.

To avoid using a region where the anode voltage fluctuates greatly, for example, it is conceivable to connect a high-voltage resistor to flow a bypass current. However, the power consumption increases, the cost increases, and a flyback transformer is not used. This will increase the load. It is also conceivable to connect a high-voltage resistor and take out a high voltage divided therefrom and use it for a correction waveform, but this also results in an increase in power consumption and an increase in cost.

Therefore, the present invention is an apparatus for correcting an image distortion caused by the brightness of a screen of a CRT, and does not make the circuit complicated even if a voltage proportional to the beam current is used. It is an object of the present invention to provide an inexpensive image distortion correcting device capable of accurately correcting image distortion and a cathode ray tube having the same.

[0008]

An image distortion correcting apparatus according to the present invention is an image distortion correcting apparatus for correcting distortion of a screen of a cathode ray tube, wherein a first voltage corresponding to a beam current of the cathode ray tube is adjusted. Conversion means for converting the change in the first voltage, which is input, to correspond to a change in the anode voltage due to the brightness of the screen; and a conversion value of the first voltage converted by the conversion means, Horizontal correction means for correcting in a horizontal direction a raster distortion caused by a change in the anode voltage due to the brightness of the screen; and brightness of the screen based on the converted value of the first voltage converted by the conversion means. Vertical correction means for correcting in a vertical direction the raster distortion caused by the fluctuation of the anode voltage.

A cathode ray tube according to the present invention is a cathode ray tube having an image distortion correcting device for correcting a screen distortion, wherein the image distortion correcting device has a first voltage corresponding to a beam current of the cathode ray tube. Converting means for converting a change in the first voltage which is input and corresponding to a change in the anode voltage due to the brightness of the screen; and converting the first voltage converted by the converting means.
Horizontal correction means for correcting, in the horizontal direction, a raster distortion caused by a change in anode voltage due to the brightness of the screen, based on the converted value of the voltage, and conversion of the first voltage converted by the conversion means. Vertical correction means for correcting, in the vertical direction, raster distortion caused by a change in anode voltage depending on the brightness of the screen based on the value.

In the image distortion correcting apparatus and the cathode ray tube having the same according to the present invention, the conversion means converts the change in the first voltage so as to correspond to the change in the anode voltage due to the brightness of the screen, and the conversion means. Based on the converted value of the first voltage, the horizontal correction means corrects the raster distortion caused by the fluctuation of the anode voltage due to the brightness of the screen in the horizontal direction, and the vertical correction means corrects the raster distortion in the vertical direction. to correct. As a result, even if a voltage proportional to the beam current is used, it is possible to correct the image distortion more accurately than in the past without complicating the circuit, and to provide an inexpensive image distortion correction device and a cathode ray tube having the same. Can be provided.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an image distortion correcting apparatus according to the present invention will be described below with reference to the drawings. The present invention
A change in the ABL terminal voltage, which is a first voltage proportional to the beam current of the cathode ray tube (CRT), is converted by a gain / linearity control circuit 24 and a gain control unit 36, which will be described later, as conversion means into an anode voltage based on the brightness of the screen. The horizontal correction means and the vertical correction means correct the raster distortion caused by the fluctuation of the anode voltage due to the brightness of the screen based on the conversion value, and thereby convert the anode voltage. Raster distortion can be corrected with characteristics close to fluctuation, and correction can be performed with higher accuracy than before without complicating the circuit.

FIG. 1 schematically shows a configuration of a video display device to which the image distortion correcting device of the present invention is applied. The composite video signal is input to the sync separation circuit 2 and separated by the sync separation circuit 2 into a video signal, a vertical sync signal, and a horizontal sync signal. The video signal separated by the sync separation circuit 2 is input to the video processing circuit 3, where the video signal is converted into a color signal composed of, for example, three primary colors of R (red), G (green), and B (blue). , Cathode 10 of CRT 9
Supplied to The horizontal synchronizing signal and the vertical synchronizing signal are input to the synchronous oscillation circuit 5.

In the synchronous oscillation circuit 5, when there is an input synchronization signal, a horizontal drive signal HD and a vertical drive signal VD are generated in synchronization with the input synchronization signal. If there is no input sync signal,
The synchronous oscillation circuit 5 oscillates at a preset cycle. The vertical drive signal VD is supplied to the vertical deflection circuit 6. The vertical deflection circuit 6 and the vertical deflection coil 13 generate a vertical deflection current based on the supplied vertical drive signal VD. The horizontal drive signal HD is supplied to the horizontal deflection circuit 7. The horizontal deflection circuit 7 and the horizontal deflection coil 14 generate a horizontal deflection current based on the supplied horizontal drive signal HD. The pulse voltage generated by the horizontal deflection circuit 7 is boosted to obtain a high voltage of about 30 KV, and this anode voltage is applied to the anode 11 of the CRT 9. in this way,
The scanning of the electron beam of the CRT 9 is controlled by the deflection magnetic field generated by the horizontal deflection coil 14 and the vertical deflection coil 13.

FIG. 2 is a block diagram when the present invention is applied to a vertical deflection circuit. Deflection control IC (Inte
A grated circuit (integrated circuit) 21 also controls a horizontal deflection circuit. The deflection control IC 21 is a vertical counter 2
2. It includes a vertical oscillator 23 and a gain / linearity control circuit 24 as a conversion means. The vertical counter 22 is supplied with the vertical synchronizing signal Vs and the horizontal synchronizing signal 2fH having a frequency twice the horizontal oscillation frequency. The horizontal synchronization signal 2fH is an internal clock of the deflection control IC 21.

In the vertical counter 22, the horizontal synchronizing signal 2fH
Are counted, and the counter is reset by the vertical synchronization signal Vs. This reset pulse is supplied to the vertical oscillator 23, and as shown in FIG. 3, sawtooth waves VD ⁺ ,
VD ^- is generated. The vertical oscillator 23 outputs a vertical synchronizing signal V
If s is not given from the outside, it keeps oscillating at a preset cycle. The pp value (peak value) and the time change (linearity) of the sawtooth waves VD ⁺ and VD ⁻ of the vertical cycle obtained in this way are controlled by the gain / linearity control circuit 24.

Gain / linearity control circuit 2
Reference numeral 4 denotes a configuration in which the amplitudes of the sawtooth waves VD ⁺ and VD ⁻ can be changed by a correction voltage from the outside, here, a correction voltage from the ABL terminal voltage. That is, sawtooth waves VD ⁺ , V
D ^- the amplitude is set by the output of the operational amplifier 26.
As shown in FIG. 7, when the beam current increases and the anode voltage decreases, the pp values of VD ⁺ and VD ⁻ are reduced in order to prevent the raster width from increasing and the image to appear to be elongated. (Dotted lines VD ⁺ and VD ^{− in} FIG. 3). At this time, the amplitude is not changed linearly with respect to the input correction voltage, but as shown in FIG. 4, the characteristic is such that the gain (here, the amplitude) changes at a voltage value X which is a predetermined voltage value. . By making this characteristic close to the relationship between the ABL terminal voltage and the anode voltage shown in FIG.

The point at which the gain changes can be set arbitrarily, and it is possible to cope with a large change in the characteristics of the flyback transformer. Further, this correction curve is not limited to a combination of linear functions, and for example, a quadratic function may be used as the correction curve depending on the characteristics of the flyback transformer.

FIG. 5 is a block diagram showing the case where the present invention is applied to a horizontal deflection circuit. Deflection control IC 31
Includes a vertical counter 32, a vertical oscillator 33, a vertical parabola generation circuit 35, and a gain control unit 36 as a conversion unit. Vertical counter 32, vertical oscillator 33
Have the same functions as the vertical counter 22 and the vertical oscillator 23, respectively.

A vertical parabolic wave generator 35 generates a vertical parabolic wave from the sawtooth wave obtained by the vertical oscillator 33, and the vertical parabolic wave is input to a horizontal amplitude controller 37. The amplitude and DC level of the vertical parabolic wave can be varied by the gain control unit 36 according to data and clock from a microcomputer (not shown). Horizontal output unit 38
The horizontal amplitude controller 37 controls the peak value of the current flowing through the deflection coil 39 to vary the horizontal amplitude. An S-shaped correction capacitor 40 for performing S-shaped correction is connected in series to the deflection coil 39. The ABL terminal voltage is input from the outside to the gain control unit 36, and the level controls the DC level of the vertical parabolic wave. That is, as shown in FIG. 6, when the screen is bright, the DC level of the vertical parabola wave is lowered to reduce the horizontal amplitude, and when the screen is dark, the DC level of the vertical parabola wave is raised to increase the horizontal amplitude and increase the vertical amplitude. As with the deflection circuit, it is possible to suppress a change in the image size due to a change in the anode voltage.

Therefore, since the amplitude can be corrected with characteristics close to the fluctuation of the anode voltage, the image does not expand at an intermediate luminance or the image does not expand rapidly on a dark screen, and the image distortion caused by the brightness of the screen does not occur. Can be satisfactorily corrected.

A as a first voltage corresponding to the beam current
Since the configuration is such that the BL terminal voltage is input to the gain / linearity control circuit 24 and the gain control unit 36, there is no need to add a new means for detecting the anode voltage, and the circuit is simple and inexpensive. Can be realized.

Since the point at which the gain changes can be set arbitrarily, it is possible to cope with a large change in the characteristics of the flyback transformer, and there is no need to change the specifications of the flyback transformer. , And the cost can be reduced, and the operation is extremely simple.

In the above-described embodiment, the first voltage according to the beam current is set as the ABL terminal voltage. However, the present invention is not limited to this, and another voltage according to the beam current may be used. .

[0024]

As described above, according to the present invention,
The conversion means converts a change in the first voltage proportional to the beam current into a change in the anode voltage due to the brightness of the screen, and based on the converted value, the horizontal correction means corrects the raster distortion in the horizontal direction, and Since the correcting means corrects the distortion of the raster in the vertical direction, the amplitude can be corrected with characteristics close to the fluctuation of the anode voltage, so that the image can be extended at intermediate luminance,
The image does not suddenly expand on a dark screen, and the distortion of the image caused by the brightness of the screen can be corrected well.

It is sufficient that the first voltage corresponding to the beam current is input to the conversion means, and there is no need to newly add means for detecting the anode voltage. Can be realized.

If the conversion means can arbitrarily set the point at which the characteristic is changed, it can cope with a large change in the characteristics of the flyback transformer, and there is no need to change the specifications of the flyback transformer. Can be applied to the flyback transformer having the above-mentioned structure, and the cost can be reduced and the operation is extremely simple.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a video display device to which an image distortion correction device of the present invention is applied.

FIG. 2 is a block diagram of the present invention corresponding to a vertical deflection circuit.

FIG. 3 is a diagram showing a vertical synchronizing signal and a sawtooth wave for vertical deflection.

FIG. 4 is a characteristic diagram of amplitude with respect to a correction voltage input to a gain / linearity control circuit.

FIG. 5 is a block diagram of the present invention corresponding to a horizontal deflection circuit.

FIG. 6 is an explanatory diagram of a vertical parabola wave and a horizontal amplitude.

FIG. 7 is a characteristic diagram of an anode voltage and an ABL terminal voltage with respect to a beam current.

[Explanation of symbols]

2 ... Synchronous separation circuit, 5 ... Synchronous oscillation circuit, 6 ...
・ Vertical deflection circuit, 7 ・ ・ ・ Horizontal deflection circuit, 9 ・ ・ ・ CR
T (cathode ray tube), 10: cathode, 11: anode, 13: vertical deflection coil, 14: horizontal deflection coil, 21: deflection control IC, 22: vertical counter, 23 ... vertical oscillator, 24 ... gain / linearity control circuit (conversion means), 26 ...
Operational amplifier, 31: deflection control IC, 35: vertical parabola generation circuit, 36: gain control unit (conversion means)

Claims (5)

[Claims] 1. An image distortion correcting apparatus for correcting a distortion of a screen of a cathode ray tube, wherein a first voltage corresponding to a beam current of the cathode ray tube is inputted, and a change of the first voltage is displayed on the screen. Converting means for converting the anode voltage to correspond to a change in anode voltage due to brightness; and a raster generated due to a change in the anode voltage depending on the brightness of the screen based on the converted value of the first voltage converted by the converting means. Horizontal correction means for correcting horizontal distortion in the horizontal direction, and a vertical distortion caused by a change in anode voltage depending on the brightness of the screen, based on the converted value of the first voltage converted by the conversion means. An image distortion correction apparatus, comprising: a vertical correction unit that corrects in a direction. 2. The image distortion correction device according to claim 1, wherein the first voltage is an ABL terminal voltage. 3. The image distortion correction apparatus according to claim 1, wherein said conversion means changes characteristics at a predetermined voltage value of said first voltage. 4. The image distortion correction apparatus according to claim 3, wherein a predetermined voltage value of the first voltage can be set arbitrarily. 5. A cathode ray tube having an image distortion correcting device for correcting a screen distortion, wherein the image distortion correcting device receives a first voltage corresponding to a beam current of the cathode ray tube, and receives the first voltage. Conversion means for converting the change in the voltage of the first voltage to correspond to the change in the anode voltage due to the brightness of the screen; and, based on the conversion value of the first voltage converted by the conversion means, the anode according to the brightness of the screen. Horizontal correction means for correcting in a horizontal direction the raster distortion caused by the voltage fluctuation, and the anode voltage fluctuates according to the brightness of the screen based on the converted value of the first voltage converted by the conversion means. And a vertical correction means for correcting the distortion of the raster generated in the vertical direction.