JPH0128457B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to cathode ray tubes, and more particularly to improving the focus characteristics thereof.

Generally, as shown in FIG. 1, an electron gun assembly for a color cathode ray tube includes a cathode 1, a first grid electrode 3, and a second grid electrode arranged in order along the path of an electron beam 2 emitted from the cathode 1. 4 and a triode electrode consisting of a third grid electrode 5.

In the electron gun assembly having the above configuration, each grid electrode 3, 4, 5 has a voltage of 0V, for example.
Voltages of 700 V and 7 KV are applied to form an electric field distribution as shown by equipotential lines in FIG. 1, thereby forming a crossover point (object point) 6 and accelerating the electron beam 2. Here, if the focus characteristic on the fluorescent surface becomes blooming, the thickness of the second grid electrode 4 is made thinner, thereby moving the crossover point 6 toward the cathode surface and increasing the object point distance ( Optimum focus characteristics can be obtained by shortening the image point distance. On the other hand, if a halo appears on the fluorescent surface, the focus characteristics can be optimized by making the second grid electrode 4 thicker and moving the crossover point 6 toward the third grid electrode 5. Can be done. In this case, equivalently the second
As a method of increasing the thickness of the grid electrode 4, as shown in FIG.
There is also a method of providing a correction electrode 7 for adjusting the beam divergence angle between the two grid electrodes and applying the same potential as the second grid electrode 4. Note that the method described above can also be used to correct deflection aberration.

However, since the fluorescent surface is generally a curved surface, the image point distance is different between the center and the periphery.For this reason, if the focus characteristics are optimal at the center, there will be a halo at the periphery, and conversely, if the focus characteristics are optimal at the periphery, then the center will be the same. Blooming occurs, and it is difficult to obtain an optimal focus state over the entire fluorescent surface.

One way to improve this drawback of focus characteristics is to use a prefocus lens with astigmatism to make the crossover point 6 longer in the tube axis direction and change the object point distance. No effect was obtained.

The present invention has been made in view of the above circumstances, and its purpose is to improve the focus characteristics over the entire fluorescent surface.

In order to achieve such an object, the cathode ray tube according to the present invention includes a correction electrode between the second grid electrode and the third grid electrode, and the correction electrode includes:
V _G2 ≦V≦V _G3 (However, V _G2 and V _G3 are the second,
An unsteady voltage that changes in synchronization with the vertical deflection magnetic field is applied within the range of the voltage applied to the third grid electrode. In this case, the unsteady voltage is small when the beam is at the periphery of the phosphor surface, and large when the beam is at the center. Hereinafter, the cathode ray tube according to the present invention will be explained in detail using Examples.

3 and 4 are diagrams showing an electron gun portion in an embodiment of the cathode ray tube according to the present invention.
In the figure, an electron beam 2 is emitted from the cathode 1 side.
A first grid electrode 3, a second grid electrode 4, and a third grid electrode 5 are arranged along the path toward a fluorescent light surface (not shown), and V _G1 =0V, V _G2 respectively.
= 700V, V _G3 = 7KV voltage is applied. Further, a correction electrode 8 is provided between the second grid electrode 4 and the third grid electrode 5, and an unsteady voltage V having characteristics as shown in FIG. 5, for example, is applied. That is, this unsteady voltage V varies linearly in synchronization with the period T of the vertical deflection magnetic field of the electron beam, and when the electron beam is at both ends of the phosphor plane, the voltage V applied to the second grid electrode 4 changes. It has a value of 700V, the same as _G2 , and a value of 1KV when the electron beam is at the center of the fluorescent surface.

In a cathode ray tube having such a configuration, when the electron beam is located at the end of the phosphor surface, the correction electrode 8 has the same potential as the second grid electrode 4, so that the electron beam is equivalent to that shown in FIG. In other words, an electric field distribution similar to that obtained when the second grid electrode 4 becomes thicker can be obtained. Therefore, the crossover point 6 approaches the third grid electrode side, and the image point distance becomes longer. On the other hand, when the electron beam is located at the center of the fluorescent surface, the correction electrode 8 has a higher potential than the second grid electrode 4, so the electric field distribution changes as shown in FIG. approaches the cathode surface and the image point distance becomes shorter. Therefore, it is possible to simultaneously improve the focus characteristics in the peripheral portion and the focus characteristics in the central portion of the fluorescent surface.

Note that the unsteady voltage V applied to the correction electrode 8 is
It is necessary to make it lower at the periphery and higher at the center in synchronization with changes in the vertical deflection magnetic field, but it is desirable to change it within the range of V _G2 ≦V≦V _G3 .

As explained above, according to the cathode ray tube according to the present invention, the correction electrode provided between the second grid electrode and the third grid electrode is applied to the vertical deflection magnetic field within the range of V _G2 ≦V≦V _G3 . By synchronously applying an unsteady voltage V that varies low at the periphery and high at the center, the image point distance can be made longer at the periphery and shorter at the center. Therefore, it has the excellent effect of making it possible to improve the focus characteristics over the entire fluorescent surface.

[Brief explanation of drawings]

FIGS. 1 and 2 each show an example of an electron gun of a conventional cathode ray tube, FIGS. 3 and 4 show an electron gun of an embodiment of a cathode ray tube according to the present invention, and FIG. FIG. 7 is a waveform diagram showing an unsteady voltage applied to the correction electrode. DESCRIPTION OF SYMBOLS 1...Cathode, 2...Electron beam, 3...First grid electrode, 4...Second grid electrode, 5...
...Third grid electrode, 8...Correction electrode.

Claims (1)

[Claims] 1 comprises a cathode, and a first grid electrode, a second grid electrode, and a third grid electrode arranged sequentially from the cathode side toward the phosphor surface side, and the second grid electrode and the third grid electrode each have a V _G2 In the cathode ray tube to which a voltage of _{V G2} and
A cathode ray tube characterized in that, within the range of V≦V _G3 , an unsteady voltage is applied that changes in synchronization with the vertical deflection magnetic field of an electron beam, being low at the periphery and high at the center.