JPH0145702B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high resolution electromagnetic focusing picture tube device.

In a picture tube, the diameter of the electron beam spot must be made small in order to obtain a high-resolution reproduced image. In particular, in the case of a beam index type color picture tube (hereinafter referred to as an index tube), unlike the case of a general shadow mask type color picture tube, the diameter of the electron beam spot is much narrower in order to perform color selection using the electron beam itself. It is already a well-known fact that this is necessary.

FIG. 1 shows an example of a conventional optical index tube. In the figure, 1 is a valve, 1' is a face plate,
2 is a fluorescent surface consisting of red, green, and blue phosphor stripes indicated as R, G, and B, respectively; a black material 9 such as graphite is applied between each phosphor stripe, and the fluorescent surface is A metal back 10 is formed inside, and further inside thereof, index stripes 11 for generating index signals are provided at predetermined positions corresponding to the arrangement of the phosphor stripes. 3 is an electron gun, 4 is an index signal detector, 5 is a deflection coil, 6 is a rotator coil which will be explained later, 1
2 is an electron beam, and 13 is an index signal. In the index tube, an index signal 13 generated by scanning an index stripe 11 with an electron beam 12 and excitation to emit light is photoelectrically converted by an index signal detector 4 and detected as an electric signal. Based on this signal, each color is detected. It is well known that a color image is reproduced by switching and selecting a chroma signal to control the cathode potential of a picture tube. Because of this principle, good color purity cannot be obtained unless the diameter of the electron beam spot on the fluorescent surface of the index tube is sufficiently small.

In order to obtain a small electron beam diameter in a picture tube, it is possible to operate it at a high anode voltage, but the picture tube and receiver are required to have high withstand voltage characteristics, and the quality of the X-rays generated on the fluorescent surface becomes hard. Due to this problem, there is a limit to the increase in anode voltage.

It is also known to increase the diameter of the electron gun as a means of reducing the spherical aberration of the electron gun and the diameter of the electron beam spot, but this method involves an increase in the diameter of the electron beam, an increase in deflection power, and an increase in power consumption. Therefore, there is a limit to increasing the diameter of the electron gun.

Furthermore, it is known that a plurality of bipotential focusing (BPF) and unipotential focusing (UPF) lenses of electrostatic electron lenses can be combined to reduce the amount of spherical aberration and reduce the electron beam spot diameter. This method has drawbacks such as an increase in the number of electrodes and applied voltage, complicating the manufacture of the electron gun, and deteriorating withstand voltage characteristics.

Recently, for ease of adjustment in general shadow mask type color picture tubes, three electron guns have been arranged in-line in the same horizontal plane, and phosphor has been applied in stripes. A beam spot is often used. However, with an index tube using a vertically elongated beam, a deflection coil shown as 5 in Fig. 1 can be used to horizontally and vertically electromagnetic deflect
Scanning causes rotation and deflection distortion of the electron beam spot, causing electron beam spot 1 on the fluorescent surface to
2', as shown in Fig. 2, its substantial horizontal diameter becomes larger in areas other than the center of the screen.
Therefore, color fidelity deteriorates in areas other than the central area. As a means for correcting the rotation of the electron beam, a method is also known in which a rotator coil shown as 6 in FIG. 1 is installed and the electron beam itself is rotated by the magnetic field of this coil. However, in a picture tube that uses the rotator coil 6, the magnetic field of the rotator coil enters the main lens of the electron gun, deteriorating the focus characteristics, and the drive circuit that flows current through the rotator coil becomes complicated and expensive. There are drawbacks.

SUMMARY OF THE INVENTION An object of the present invention is to provide a focusing type picture tube device that eliminates the various problems and drawbacks associated with the electron beam focusing of the conventional picture tube and provides high-resolution reproduced images.

In order to achieve the above object, in the present invention,
Electromagnetic focusing, which can reduce spherical aberration, is used as the focusing method. In order to further reduce the aberration without increasing deflection power, a focusing magnetic field generator is installed outside the neck tube of the picture tube, and the inner diameter of this magnetic field generator is 1.1 times or more, preferably 1.5 times or more to about 3 times the outer diameter of the neck pipe, and a non-magnetic heat insulating material layer is installed as a support member to fill the gap between the inner and outer diameters,
The thickness of this nonmagnetic heat insulating material layer was partially adjusted so that the magnetic field generated by the magnetic field generator became a rotationally symmetrical magnetic field with respect to the central axis of the electron gun. If the inner diameter of the magnetic field generator is made larger, the change in the magnetic field due to the position of the electron gun in the network tube will be slow and smooth, and the heat insulating material layer will prevent the heat generated by the electron gun from being transmitted to the magnetic field generator. For example, a ferrite magnet, which has a relatively large magnetic flux change due to temperature rise, can be used as a magnetic field generating device.

FIG. 3 is a sectional view of the vicinity of the electron gun section of the index tube in which the present invention is implemented. 14 is the cathode, 1
5 is a first grid, 16 is a second grid, and 17 is a third grid (anode potential), and their functions are known. 18 is a focusing magnetic field generator; 19 is a non-magnetic heat insulating layer made of plastic, for example;
This is an important member related to the present invention. Hereinafter, the z-axis will be the tube axis of the picture tube, the x-axis will be the horizontal scanning direction, and the y-axis will be the vertical scanning direction, and will be simply abbreviated as x, y, and z axes. Figure 4 is a cross-sectional view taken along the line -' in Figure 3.
As mentioned above, is the picture tube bulb, which is thin because it is the neck tube part. An example of the magnetic field generator 18 is shown in FIG.
Shown in b and c. In the device shown in FIG. 5a, the excitation coil 20 is wrapped in a yoke 21 to induce magnetic flux and generate a strong magnetic field at the end of the pole piece 22. In Fig. 5b, a ring-shaped permanent magnet 23 is used to generate a magnetic field, and the yoke 21 induces magnetic flux, and even when the permanent magnet is in a biased magnetized state, a relatively uniform rotationally symmetrical magnetic field is generated by electrons. Allow it to occur in the gun section. FIG. 5c shows a case where a rod-shaped permanent magnet 24 is used, in which A is a side sectional view and B is a sectional view taken along the line A-A' in A. As for these permanent magnet materials, ferrite magnets are currently relatively inexpensive and can generate a magnetic field of the degree necessary as a focusing magnetic field, but the magnetic field changes relatively large with temperature, changing by about 20% with a change of 100 degrees Celsius. Fluctuations in the intensity of the focusing magnetic field result in fluctuations in focus characteristics, which are accompanied by deterioration of reproduced images. The temperature of the picture tube neck tube section is increased by a cathode heater or the like. However, as shown in FIGS. 3 and 4, in the present invention, a non-magnetic heat insulating layer 19 made of plastic is provided between the magnetic field generator 18 and the neck tube, so that the influence of the increase in temperature of the neck tube can be minimized. Therefore, ferrite magnets can also be put to practical use. Heat insulating materials are generally non-magnetic, so since they are non-magnetic, there is no problem in material selection. The necessity of non-magnetism is self-evident. Rather, the thickness of the heat insulating material layer 19 is partially adjusted to increase or decrease the magnetic field generated by the focusing magnetic field generator 18 to the electron gun 3.
Since it is necessary to adjust the material and structure of the heat insulating material layer 19 so that it is rotationally symmetrical with respect to the central axis of the
This point needs to be taken into consideration. Figure 6 a, b
is the difference in the inner diameter of the magnetic field generator 18 (Da<Db)
Two cases are shown, and a' and b' indicate relative values of the z-axis focused magnetic field Bz generated in each case. By increasing the inner diameter to form a large-diameter electromagnetic lens, the magnetic field acting on the electrons changes smoothly, reducing the amount of spherical aberration of the electromagnetic lens, and making it possible to obtain a small beam spot diameter on the fluorescent surface. .

On the other hand, deflection power P, anode voltage Eb, network tube diameter d,
If the deflection angle is θ, the following equation holds true.

P∝Eb・d・sin ² θ/2 Comparing the two cases shown in Figure 6 a and b, we get
In the case of b, which has a large inner diameter, the lens diameter is larger than in case a, and the amount of spherical aberration is small, so a small beam spot diameter can be obtained, and if the neck tube diameter and other things are the same, there is no increase in deflection power. , high resolution images can be obtained. Increasing the inner diameter of the magnetic field generator in this way makes it possible to obtain high-resolution images without increasing the deflection power, but on the other hand, the magnetic field generator becomes larger and weighs more. Since mutual interference also occurs, the increase in the inner diameter of the magnetic field generator is practically limited to about three times the diameter of the neck pipe.

The index tube according to the present invention shown in FIG. 3 will be explained in more detail. Usually, the cathode 14 has a video signal voltage of about 150V _pp , the first grid 15 has 0V (grounded), the second grid 16 has a voltage of several hundred to 1000V, and the third grid has a voltage of about 10 to 100V.
An anode voltage of about 25 kV is applied. In the case of a small index tube, such as a 5.5 type with 55 degree deflection, the diameter of the bulb's neck tube is usually 20 mm, and the maximum diameter of the main lens of the electrostatic focusing electron gun disposed inside the tube is about 10 mm. On the other hand, when using a normal electromagnetic focusing electron gun, the main lens becomes an electromagnetic lens with a diameter of 20 mm using a magnetic field generator placed outside the net. In contrast, in the embodiment of the present invention, an electromagnetic lens with a larger diameter is used as the main lens. Figure 7 shows the relationship between the main lens inner diameter D (mm) and the measured beam spot diameter in this index tube. However, the beam spot diameter is assumed to be 1.0 when using an electrostatic focusing lens with an aperture of 10 mm. It is shown as a relative value. Below the value of the lens inner diameter D, the multiple to the neck tube outer diameter is shown. The beam spot diameter is 0.72 when the electromagnetic lens inner diameter is 20mm, 0.55 when the inner diameter is 30mm, and 0.50 and 60 when the inner diameter is 36mm.
It is 0.44 in mm. As can be seen from this figure, the change in beam spot diameter is relatively large where the electromagnetic lens inner diameter is small, and the change in beam spot diameter is somewhat saturated where the lens inner diameter is large. Therefore, from the results of this experiment, the inner diameter of the focused magnetic flux generator (or the diameter of the electromagnetic lens) fitted into the neck tube via the heat insulating layer should be determined depending on the effect, size,
Considering the cost, 1.5 to 1.5 of the outside diameter of the neck tube
Practically speaking, it is most advantageous to make it about 2.0 times.

As explained above, according to the present invention, a small beam spot diameter, that is, a high resolution image can be obtained without increasing the diameter of the bulb neck or increasing the deflection power, and it is also relatively inexpensive for generating magnetic fields. Effects such as the ability to use ferrite magnets can be obtained.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of a conventional index tube.
Figure 2 is a diagram of the shape of the beam spot on the fluorescent surface, Figure 3
The figure is a close-up view of the electron gun according to the embodiment of the present invention, and FIG.
-' line sectional view in the figure, a, b, c in Fig. 5,
B is an example of a magnetic field generator according to the present invention, FIG. 6a,
b shows the installed state of magnetic field generators each having a different inner diameter, a' and b' are magnetic field distribution diagrams generated by each device, and Figure 7 is a diagram showing the relationship between the inner diameter of the magnetic field generator and the beam spot diameter. . 1... Bulb (neck tube), 2... Fluorescent surface, 3
...Electron gun, 12'...Electron beam spot, 1
8...Magnetic field generator, 19...Nonmagnetic heat insulating material layer.

Claims (1)

[Claims] 1. In an electromagnetic focusing picture tube device consisting of a picture tube with an electron gun built into the network tube and a magnetic field generator for electron beam focusing mounted on the outside of the network tube of the picture tube, the magnetic field generator for electron beam focusing is , consisting of a ring-shaped permanent magnet, the inner diameter of which is 1.1 to 3 times the outer diameter of the neck tube,
Between the network tube and the magnetic field generator for electron beam focusing, the network tube and the magnetic field generator for electron beam focusing are in contact with each other, and the magnetic field generated by the magnetic field generator for electron beam focusing is directed toward the central axis of the electron gun. An electromagnetic focusing picture tube device characterized in that a non-magnetic heat insulating material formed in a rotationally symmetrical shape is arranged.