JPH07107503A - Method and circuit for correcting earth magnetism influence in cathode-ray tube and television receiver - Google Patents

Abstract

PURPOSE:To provide a method for correcting the inclination of vertical lines in a raster by inputting a sawtooth correct signal, which is provided with the almost same cycle as a vertical synchronizing signal and changes positive and negative polarities at the upper part and a lower part of a picture, while superimposing it together with an AFC signal to the horizontal deflection circuit of a cathode-ray tube. CONSTITUTION:A correct signal 9 with a sawtooth waveform at the frequency of about 60Hz almost equal to the vertical synchronizing signal is outputted by a correcting circuit 10, and this correct signal 9 is superimposed to the output signal of an AFC circuit 8. Such a superimposed control signal is applied to a horizontal oscillation circuit 5 similarly to the conventional AFC output, and a horizontal scanning signal is controlled. By inputting the control signal, to which the AFC output and the sawtooth wave correct signal are superimposed, to the horizontal deflection circuit when the raster is rotationally displaced by the influence of earth magnetism, horizontal scanning is controlled so as to change the phase of the horizontal scanning of an electronic beam at the upper part and lower part of the picture, to advance the phase at one part and to delay the phase at the other part. Therefore, inclined straight lines are recovered to vertical positions, and vertical images at both sides of the picture are properly corrected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a television receiver,
In a cathode ray tube used for a video display, a computer display, etc., a method and a correction circuit for correcting a displacement of a screen raster due to scanning of an electron beam under the influence of geomagnetism to display a normal image And the television receiver.

[0002]

It is known that geomagnetism affects the electron beam of a cathode ray tube and deforms the raster on the screen. The direction of the magnetic field and the strength of the earth's magnetism differ depending on the latitude on the earth. Only vertical component Hz is present at both poles, and horizontal component Hx only at the equatorial region. Hx = in Japan
The strength is 0.3 Gauss and Hz = 0.3 Gauss.

As shown in FIG. 5A, when a cathode ray tube is installed in a magnetic field having a horizontal strength of Hx so that the electron gun of the cathode ray tube is orthogonal to the magnetic field lines, the Fleming's left-hand rule causes the The images of points A to E are biased as shown by the arrows.
The entire raster shifts downward. If the direction of the magnetic field Hx goes from right to left, the raster will shift entirely upwards. In the vertical magnetic field Hz, the raster shifts to the left as shown in FIG.

When the cathode ray tube is installed in the direction of the magnetic field as shown in FIG. 7C and the horizontal direction of the magnetic field and the direction of the electron gun coincide with each other, the direction of the magnetic field and the current overlap at the point E at the center of the screen. Therefore, the force that biases the electron beam does not act. However, when the electron beam sways to both sides of the screen, the horizontal component in the current direction crosses the magnetic field, so that the effect of magnetic lines of force appears on the electron beam. When the screen of the cathode ray tube is installed so as to face south, the electron beam is biased downward on the right side of the screen and upward on the left side. Further, when the electron beam scans the upper and lower parts of the screen, the vertical component in the current direction crosses the magnetic field, so that the electron beam is biased to the right at the upper part of the screen and to the left at the lower part of the screen. After all, the raster rotates slightly clockwise. An image of a vertical line, which was originally a vertical direction on the screen, is tilted to the right or left due to the effect of geomagnetism.

In the case of FIGS. 5 (a) and 5 (b) in which the geomagnetism affects the electron beam in the horizontal or vertical direction, it can be easily corrected by the adjusting knob operation. However, when the raster rotates as shown in FIG. 5C, it is not easy to correct this effect. Even if it is a cathode ray tube, the geomagnetism is shown in Fig. 3 (a).
, Even when acting horizontally, when the electron beam scans the upper and lower parts and both lateral parts of the screen,
Since the current contains vertical and horizontal components, the raster is necessarily prone to rotational displacement. Even if the image is affected by the earth's magnetism, there is almost no obstacle to view the movement of the image on the television receiver. However, when a VHF broadcast image is displayed on a horizontally long screen of a high-definition television receiver, a black non-image area is formed on both sides of the image in vertical strips, and the inclination on both sides of this image is noticeable and unsightly. . In addition, when the cathode ray tube is used for CAD, there is a problem that the inclination of the straight line lowers the drawing accuracy.

Regarding the problem that the geomagnetism affects the electron beam, JP-A-58-123288, 61-23628.
No. 8,61-255193, 63-250988, a method of arranging a magnetic shield plate on the outer surface or inner surface of the funnel of the cathode ray tube to block the intrusion of magnetic field lines, or the outside of the cathode ray tube. Place the electromagnetic coil in
There was a method of canceling the lines of magnetic force by generating a magnetic field in the direction opposite to the earth's magnetism. However, when the shielding plate is attached to the cathode ray tube, the outer shape is not allowed to be large, and the geomagnetism in the direction corresponding to the direction of the electron beam cannot be shielded. A method of arranging a correction coil around the cathode ray tube and generating a correction magnetic field in a direction that cancels the earth's magnetism is effective, but the cathode ray tube becomes large and heavy, and the manufacturing cost becomes expensive. There was a problem.

[0007]

The present invention focuses on the point that the horizontal deflection circuit of the cathode ray tube is phase-controlled by the AFC circuit, and does not use a shielding plate or a magnetic coil for correction, and the vertical direction of the raster. A method and circuit for correcting line inclination and a television receiver are disclosed.

[0008]

According to the present invention, a horizontal deflection circuit for a cathode ray tube is provided with a sawtooth correction in which the positive and negative polarities are changed in the upper and lower portions of the screen with the AFC signal and the vertical synchronizing signal. It is a method of correcting the geomagnetic effect in a cathode ray tube, which is characterized in that signals are superimposed and input to correct the inclination of a vertical raster. Further, according to the present invention, in a cathode ray tube in which an AFC circuit is connected to a horizontal deflection circuit to synchronize a horizontal scanning signal, the output of the AFC circuit has substantially the same period as the vertical synchronizing signal and has an upper portion and a lower portion of the screen. A cathode ray tube characterized in that a correction circuit for generating a sawtooth signal whose positive and negative polarities are changed is connected, and the output of the correction circuit is superimposed on the output of the AFC circuit to correct the inclination of the raster in the vertical direction. The present invention relates to a correction circuit for a geomagnetic effect and a television receiver including the correction circuit.

[0009]

When the raster is rotationally displaced due to the influence of the earth's magnetism, the control signal in which the AFC output and the sawtooth correction signal are superimposed is input to the horizontal deflection circuit, so that the horizontal direction of the electron beam is displayed in the upper and lower portions of the screen. Horizontal scanning is controlled so that the phase of scanning is changed and the phase is advanced on the one hand and delayed on the other. Therefore, the slanted vertical lines are returned to vertical, and the vertical images on both sides of the screen are corrected correctly.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram for explaining the principle of correcting the influence of the earth's magnetism. The cathode ray tube (1) comprises a vertical deflection coil (2) and a horizontal deflection coil (3), as is well known. The electron gun is controlled by a video signal. Horizontal deflection circuit
(4) is connected to the horizontal deflection coil (3), about 15750Hz
The horizontal scanning signal of is output to the horizontal deflection coil (3) to drive the horizontal scanning by the electron beam. Horizontal deflection circuit
(4) is equipped with a horizontal oscillator circuit (5), a horizontal drive circuit (6), and a horizontal output circuit (7), which are separated from the flyback pulse from the horizontal output circuit (7) and the video detection output waveform. The horizontal synchronization signal is input to the AFC circuit (8) and compared, and the control signal corresponding to the phase shift of both signals is output to output the horizontal oscillation circuit.
Input to (5) to control the phase and frequency of the horizontal scanning signal.

Although the above is a known horizontal deflection circuit, the present invention causes the correction circuit (10) to output a correction signal (9) having a sawtooth waveform having a frequency of about 60 Hz which is substantially equal to the vertical synchronization signal.
This correction signal (9) is superimposed on the output signal of the AFC circuit (8). The superposed control signal is added to the horizontal oscillation circuit (5) in the same manner as the conventional AFC output to control the horizontal scanning signal.

FIG. 2 shows an example of implementation of the correction circuit (10). The vertical deflection circuit (4) including the vertical oscillation circuit (11), the vertical drive circuit (12), and the vertical output circuit (13) outputs the vertical scanning signal to the vertical deflection coil (2). About 60Hz sawtooth waveform output for vertical scanning from circuit (14)
(15) is branched and taken out and input to the correction circuit (10). The correction circuit (10) includes two OP amplifiers (16) (1
7), the output signal of either one of the output signals of the AFC circuit (8) is superimposed by the changeover switch (18).
The OP amplifiers (16) and (17) have a variable resistor (19) in the return path, and the adjustment of the variable resistor (19) limits the amplitude of the sawtooth waveform. The sawtooth output waveform continuously changes over both positive and negative polarities, and changes the phase of the horizontal scanning signal symmetrically in the upper half and the lower half of the screen.

FIGS. 3 and 4 show a situation in which the correction signal (9) is superimposed on the known AFC circuit (8) to control the phase of the horizontal scanning signal. The horizontal synchronizing signal pulse (Fig. A) is input to the c terminal connected to the base of the transistor Q ₁ , and the flyback pulse is filtered through a low-pass filter to the d terminal connected to the base of the transistor Q ₅ , and a comparison waveform (23 ) (Figure b) is added. As shown in the example in the figure, when the phase of the video signal lags behind the comparison waveform, the charging and discharging of the capacitor (21) at point a (Figure c) becomes asymmetric, and point b at which the signal passes through the low-pass filter (24). The AFC signal (22) has a positive potential (Fig. D). The image can be moved to the left side of the screen by adding the waveform shown in FIG. Therefore, in FIG. F, the image p of the vertical line moves horizontally to become the vertical line at the q position.

When the sawtooth correction signal (9) from the correction circuit (10) is superimposed at point e in FIG. 3, the positive potential is high and the negative potential is low, as shown in FIG. 4e. Control signal (20) is applied to the horizontal deflection circuit. As a result, the vertical line at the q position on the screen shown in FIG. 4f has a phase that advances at the top of the screen and delays at the bottom of the screen due to the sawtooth control signal (20), and a straight line R inclined to the left. Will be displayed on the screen. Using this principle, when the image rotates clockwise due to the influence of the earth's magnetism and is in the state of FIG. 5 (c), the sawtooth correction signal (19) is superimposed on the output (22) of the AFC circuit. The straight line that was tilted clockwise can be corrected to the correct vertical line.

The above-mentioned correction operation is performed as one of the adjusting works when the television receiver is installed in the room.
By adjusting the variable resistor (19), the tilted image can be returned to the vertical position. When the image rotates counterclockwise and is tilted, the selector switch (18) of the correction circuit (10)
By switching to the other OP amplifier (17), the sawtooth correction signal (9) 'inclined in the opposite direction may be superimposed on the AFC signal (22).

[0016]

According to the present invention, more effective correction can be obtained by combining the present invention with a shield plate and a correction magnetic coil as in the conventional case.
However, without using a shield plate and a magnetic coil for correction, simply connecting the correction circuit (10) to the output side of the AFC circuit (8) corrects the inclination of the vertical line of the rotationally displaced image to a correct vertical posture. Therefore, the weight and size of the television receiver can be avoided.

The above description of the embodiments is for explaining the present invention, and should not be construed as limiting the invention described in the claims or reducing the scope. The configuration of each part of the present invention is not limited to the above-mentioned embodiment, and it goes without saying that various modifications can be made within the technical scope described in the claims.

[Brief description of drawings]

FIG. 1 is a configuration diagram illustrating the principle of the present invention.

FIG. 2 is a configuration diagram showing an embodiment of a correction circuit.

FIG. 3 is a circuit diagram showing superimposition of an AFC circuit and a correction signal.

FIG. 4 is an explanatory diagram showing signal waveforms of respective parts of FIG.

FIG. 5 is an explanatory diagram showing the influence of geomagnetism.

[Explanation of symbols]

 (1) Cathode ray tube (3) Horizontal deflection coil (4) Horizontal deflection circuit (8) AFC circuit (10) Correction circuit

Claims (3)

[Claims] 1. A horizontal deflection circuit of a cathode ray tube is superposed with an AFC signal and a sawtooth correction signal having substantially the same period as a vertical synchronizing signal and having positive and negative polarities changed at an upper portion and a lower portion of a screen. A method for correcting the geomagnetic effect in a cathode ray tube, characterized by correcting the inclination of a vertical raster. 2. In a cathode ray tube in which an AFC circuit is connected to a horizontal deflection circuit to synchronize a horizontal scanning signal, the output of the AFC circuit has substantially the same period as the vertical synchronizing signal and has an upper portion and a lower portion of the screen. A cathode ray tube characterized in that a correction circuit for generating a sawtooth signal whose positive and negative polarities are changed is connected, and the output of the correction circuit is superimposed on the output of the AFC circuit to correct the inclination of the raster in the vertical direction. A correction circuit for geomagnetic effects. 3. The horizontal deflection circuit of the cathode ray tube includes an AFC circuit for synchronizing the horizontal scanning signal, and the output of the AFC circuit has substantially the same period as the vertical synchronization signal and has a top and bottom portion of the screen. A television receiver characterized in that a correction circuit for generating a sawtooth signal with a different positive / negative polarity is connected and the output of the correction circuit is superimposed on the output of the AFC circuit to correct the inclination of the raster in the vertical direction.