JP2931427B2 - Focus voltage generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focus voltage generator for an apparatus having a cathode ray tube, such as an image display device,
In particular, the present invention relates to an improvement for obtaining an optimal dynamic focus level regardless of an image size.

[0002]

2. Description of the Related Art In a cathode ray tube, an optimum value of a focus voltage is generally different between a central portion and a peripheral portion of a tube surface. Therefore, only a static focus voltage having a predetermined ratio of a voltage value to an anode voltage of a cathode ray tube is used. Instead, as shown in FIG. 6, with respect to the horizontal direction and the vertical direction of the tube surface 1,
A focus voltage in which the horizontal correction voltage 2 and the vertical correction voltage 3 of the parabolic waveform are superimposed on the above-mentioned static focus voltage is used, so that a highly accurate image display can be performed.

[0003]

According to the above configuration,
An optimum dynamic focus voltage is determined for each point on the surface of the cathode ray tube.

However, in general, the parabolic waveform used for the dynamic focus voltage is formed by integrating the horizontal retrace pulse, so that when the image size on the screen is changed, the optimal value of the dynamic focus voltage and the parabolic waveform are changed. It is not easy to match the amplitude. This will be described more specifically with reference to FIG. 7 in a case where the horizontal size of the image 4 on the tube surface 1 is changed.

As shown in FIG. 7, when the image 4 is enlarged from the size indicated by the solid line to the size indicated by the dashed line, the image 4 is extended to the peripheral portion of the tube 1 where a higher focus voltage is required. Therefore, as shown in FIG. 8, the parabola amplitude of the horizontal correction voltage 2 must be increased as shown by the broken line. However, when the parabola amplitude is increased in this way, the value of the lowest point 5 of the parabola amplitude decreases. Therefore, the focus voltage at the center of the tube face 1 deviates from the optimum value. If an adjustment is made to obtain the optimum focus at the center of the screen 1, the focus at the periphery of the screen 1 will be inappropriate. As described above, since the focus adjustment in the center portion and the focus adjustment in the peripheral portion cause the other focuses to be deviated from each other, the operation for obtaining an ideal focus state is extremely complicated.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a focus voltage generator which can make focus adjustment according to a change in image size easier.

[0007]

[0008]

SUMMARY OF THE INVENTION The present invention is first directed to a device for generating a focus voltage applied to a focus electrode of a cathode ray tube. , A means for generating a parabolic waveform voltage, and a means for adjusting the amplitude of the parabolic waveform voltage.

According to the present invention, in order to solve the above-mentioned technical problem, a DC bias for compensating for a change in the value of the lowest point of the parabola amplitude caused by a change in the parabola amplitude is generated.
To comprise a DC bias generator, the DC bias is added to the static focus voltage, to the static focus voltage direct current bias is added, by superimposing the adjusted parabolic waveform voltage parabola amplitude when changing the screen size Thus, it is characterized in that it is output as a focus voltage.

The static focus voltage generating means preferably includes a voltage dividing circuit for dividing the high voltage by resistance.

The DC bias generating means is preferably connected to a ground potential side of the voltage dividing circuit.

The DC bias generating means preferably comprises a bias circuit having a transistor.

When the high voltage is generated from a flyback transformer, the voltage dividing circuit is provided in the flyback transformer. Conventionally, the ground side terminal of such a voltage dividing circuit is connected to another ground terminal of the flyback transformer. However, in embodying the present invention, the ground side terminal of the voltage dividing circuit is connected to the flyback transformer. It is preferable not to connect to another ground terminal of the transformer but to connect to DC bias generating means.

[0014]

[0015]

According to the present invention, as the amplitude of the parabola changes ,
Generated a DC bias to compensate for the change in the lowest point of the parabola amplitude, and added to the focus voltage to compensate for the change in the value of the lowest point of the parabola amplitude.
Even if the parabola amplitude changes, the focus voltage at the center of the screen can be kept constant.

[0016]

Therefore, according to the present invention, even if the image size is changed after the focus adjustment of the central portion of the display is once performed, the optimum adjustment over the entire image can be achieved by performing only the focus adjustment at the peripheral portion of the display. The focus state can be obtained. Therefore, the focus adjustment operation for obtaining a high-accuracy image is facilitated.

Further, because of the above-mentioned advantages, the operation for changing the image size can be performed on the user side without any problem. Therefore, the versatility of the image display device including the cathode ray tube is increased.

[0018]

[0019]

FIG. 1 is a schematic diagram showing a focus voltage generator according to an embodiment of the present invention. The embodiment described below is applied to the case where the horizontal size is changed among the image sizes. However, the same configuration can be applied to the case where the vertical size is changed.

Referring to FIG. 1, a device for generating a focus voltage applied to a focus electrode 7 of a cathode ray tube 6 comprises a voltage of a predetermined ratio with respect to an anode voltage applied to an anode 8 of the cathode ray tube 6. Means for generating a static focus voltage having a value. In this embodiment, the static focus voltage generating means 9 is provided by a variable resistor connected to a line 10 for applying an anode voltage. The variable resistor applies a voltage obtained by dividing the anode voltage to the focus electrode 7 via the line 11 as a static focus voltage. The static focus voltage may be obtained, for example, by dividing a voltage extracted from a tap different from a tap for extracting an anode voltage in the secondary coil of the flyback transformer.

On the other hand, the parabolic waveform voltage generating means 12 generates a parabolic waveform voltage obtained by integrating the horizontal retrace pulse. The parabola waveform voltage is adjusted by the parabola amplitude adjustment means 13, and the parabola waveform voltage whose parabola amplitude is adjusted is superimposed on the above-described static focus voltage via the capacitor 14.

In accordance with the operation for changing the horizontal size of the image, the parabolic amplitude adjusting means 13 is driven by a signal provided from the horizontal size control means 15.
Thereby, in the parabola amplitude adjusting means 13,
As shown in FIG. 2, it is adjusted so as to output a parabolic waveform voltage having a parabola amplitude according to the horizontal size.

If the parabola amplitude is simply adjusted, the lowest point 5 of the parabola waveform fluctuates as shown in FIG. That is, as shown by the solid line in FIG. 3, as the parabola amplitude increases, the lowest point undesirably decreases. Ideally, as shown in FIG. 4, it is desirable that the lowest point 17 be kept constant even if the parabolic amplitude of the parabolic waveform 16 changes.

In this embodiment, in order to satisfy the above-mentioned demand, as shown in FIG. 4, a DC bias 18 is used to keep the lowest point 17 constant despite the change in the parabolic amplitude of the parabolic waveform 16. Can be This DC bias 18 is provided from the DC bias generating means 19 shown in FIG. The DC bias is, as shown by the broken line in FIG.
The magnitude is selected to compensate for the change in the value of the lowest point caused by the change in the parabola amplitude. That is, in FIG.
The DC bias generator 19 is driven by a signal corresponding to the horizontal size given from the horizontal size controller 15 so that the DC bias obtained from the DC bias generator 19 is added to the above-described static focus voltage. The DC bias generator 19 is connected to the ground potential side of the static focus voltage generator 9.
Is connected.

As described above, the static focus voltage to which a desired DC bias has been added and the parabolic waveform voltage are superimposed and output as the focus voltage to the focus electrode 7 via the line 11. Therefore, even if the horizontal size of the image is changed, it is possible to apply the optimal dynamic focus voltage to the focus electrode 7 over the entire tube surface.

FIG. 5 is a more specific view of the focus voltage generator according to the present invention.

In FIG. 5, elements corresponding to the elements shown in FIG. 1 are denoted by the same reference numerals, and redundant description will be omitted.

FIG. 5 shows a part of the flyback transformer 20 for generating the anode voltage. As is well known, the flyback transformer 20 incorporates a static focus voltage generating means 9 composed of a variable resistor and a capacitor 14 for superimposing a parabolic waveform voltage on the static focus voltage. However, in this flyback transformer 20,
It should be noted that the ground side terminal 21 of the voltage dividing circuit constituting the static focus voltage generating means 9 is not connected to another ground terminal. That is, in the conventional typical flyback transformer, the ground side terminal of the voltage divider for applying the static focus voltage is connected to another ground terminal such as the ground terminal of the voltage divider for extracting the screen voltage. Connected in the back transformer. On the other hand, in this embodiment, the flyback transformer 20 is modified so that the ground terminal 21 is connected to the DC bias generating means 19.

More specifically, the DC bias generator 19 is constituted by a bias circuit including a transistor 22.

On the other hand, the parabola amplitude adjusting means 13 includes a voltage controlled amplifier (VCA) 23 and a transistor 24.

In such a configuration, the horizontal size control signal input to the horizontal size control means 15 is converted by the horizontal size control means 15 into respective signals for driving the DC bias generation means 19 and the parabola amplitude adjustment means 13, respectively. Is done. The former signal is a transistor 22
And adjusts the DC potential at the ground terminal 21. On the other hand, the latter signal becomes a control signal of the voltage control amplifier 23, controls the base current flowing into the base of the transistor 24, and adjusts the amplitude of the parabolic waveform applied to the focus electrode 7 through the capacitor 14.

Therefore, for example, when the image size is increased, the potential at the ground terminal 21 is increased and the amplitude of the parabolic waveform applied to the capacitor 14 is increased by the size control signal corresponding to the size control signal. The dynamic focus voltage applied to the focus electrode 7 is optimized, and a good focus level can be obtained over the entire surface of the cathode ray tube 6.

In the above-described embodiment, the parabola amplitude adjusting means 13 is transmitted through the horizontal size control means 15 by the horizontal size control signal generated according to the change of the horizontal size.
Although both the DC bias generating means 19 and the DC bias generating means 19 are configured to work together to obtain the optimum focus, the parabolic amplitude adjusting means 13 and the DC bias generating means 19 may be driven by separate operations. Good.

In the above embodiment, the case where the horizontal size of the image is changed has been described. However, as described above, the present invention can be applied to the case where the vertical size is changed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a focus voltage generator according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a magnitude of a parabola amplitude required for a horizontal size of an image to be changed.

FIG. 3 is a diagram showing the relationship between the parabola amplitude and the lowest point of the parabola waveform, and the relationship between the parabola amplitude and the DC bias provided by the present invention.

FIG. 4 is a diagram showing a change in a parabola waveform obtained with a change in the horizontal size of an image, obtained according to the present invention.

FIG. 5 is a more specific circuit diagram of the focus voltage generator according to the present invention.

FIG. 6 is a diagram showing a horizontal correction voltage and a vertical correction voltage for correcting a focus voltage applied in a horizontal direction and a vertical direction on a surface of a cathode ray tube, respectively.

FIG. 7 is a diagram showing a mode in which the horizontal size of an image is changed on the surface of a cathode ray tube.

FIG. 8 is a diagram showing an aspect of a change in the amplitude of a parabolic waveform that is conventionally changed with a change in the horizontal size of an image.

[Explanation of symbols]

 5, 17 lowest point 6 cathode ray tube 7 focus electrode 8 anode 9 static focus voltage generating means 12 parabolic waveform voltage generating means 13 parabolic amplitude adjusting means 14 capacitor 15 horizontal size control means 16 parabolic waveform 18 DC bias 19 DC bias generating means 20 Flyback transformer 21 Ground terminal 22 Transistor

Claims (5)

(57) [Claims] 1. A focus voltage generator for generating a focus voltage applied to a focus electrode of a cathode ray tube, comprising: a means for generating a static focus voltage in a flyback transformer; a means for generating a parabolic waveform voltage; Means for adjusting the parabolic amplitude of the parabolic waveform voltage when the parabolic waveform voltage is changed; and generating a DC bias for compensating for a change in the value of the lowest point of the parabolic amplitude caused by the change in the parabolic amplitude. Bias generating means, means for adding the DC bias to the static focus voltage, and means for superimposing the parabolic waveform voltage and the static focus voltage to which the DC bias has been added, and outputting as a focus voltage. Focus voltage generator. 2. The focus voltage generating apparatus according to claim 1, wherein said static focus voltage generating means includes a voltage dividing circuit for dividing a high voltage by resistance. 3. The focus voltage generating device according to claim 2, wherein said DC bias generating means is connected to a ground potential side of said voltage dividing circuit. 4. The focus voltage generator according to claim 3, wherein said DC bias generator includes a bias circuit including a transistor. 5. The flyback transformer includes the voltage dividing circuit, and a ground terminal of the voltage dividing circuit is connected to the DC bias generating unit without being connected to another ground terminal of the flyback transformer. Claims 2 to 4
The focus voltage generator according to any one of the above.