JPS6256622B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electron gun used in an image pickup tube, etc., and aims to provide an optimal structure for a two-pole electron gun. Generally, so-called triode electron guns, which are composed of a cathode electrode, a control electrode, and an anode electrode, are the mainstream electron guns used in picture tubes, image pickup tubes, and the like.
FIG. 1 shows an example of a triode electron gun equipped with an aperture electrode for an image pickup tube. The cathode electrode A consists of a cathode sleeve 2 and an electron emitting material 3 coated on the upper surface of the cathode sleeve, and the electron emitting material 3 is heated by the heater 1 to emit electrons. This cathode electrode A and the cathode electrode A are several tens to hundreds of μm apart.
A triode electron gun is constituted by a control electrode 4 for controlling the amount of cathode current and an anode electrode 5 having an aperture electrode 6 having a micropore of several tens of micrometers, which are arranged at a distance of . Here cathode electrode A
If V G1 is set as a zero potential reference, a negative potential is applied to the control electrode 4 and a positive potential is applied to the anode electrode 5, and the cathode current can be adjusted by the control electrode voltage V _G1 . Figure 2 shows the general characteristics of a triode electron gun. The X-axis is γ (γ = Vgd/Vgc: drive rate, Vgd...
γ=0 indicates a cut-off state, and γ=1 indicates that the potential difference between the cathode electrode and the control electrode is zero. I in the graph
_K is the cathode current, _IS is the aperture transmission current, and α is the divergence angle of the aperture transmission current. In an image pickup tube or the like, the divergence angle α of the beam greatly affects the resolution, so it is desirable that it be as small as possible. However, as shown in the figure, the divergence angle α tends to increase as the cathode current increases. Aperture transmission current I
Assuming that _S is constant, the divergence angle α is better as the cut-off voltage becomes deeper. Generally, the cut-off voltage Vgc has the following relationship for each electrode size. Vgc∝D ³ /t・b・f(
(D: Control electrode hole diameter, t: Control electrode thickness, b: Distance between cathode and control electrode, f: Distance between control and anode electrodes) b is the most problematic during assembly. There are difficulties in setting on the order of tens to hundreds of micrometers, and variations in the setting distance due to thermal expansion of the cathode sleeve 2, and in reality, the cut-off voltage varies considerably, resulting in problems with the uniformity of characteristics. Easy to come out. The present invention provides an optimal range of electrode dimensions in a bipolar electron gun as a method of improving uniformity of electron gun characteristics and reducing assembly accuracy. A dipole electron gun is a triode electron gun without the control electrode, but has a simple configuration and does not require as much assembly precision. Other features include a small beam energy distribution. An embodiment of the present invention will be described below. In a two-pole electron gun with only an anode and a cathode facing each other, electrons are emitted from the entire surface coated with the electron emitting material, and since there is no convergence effect, they spread out on the anode, resulting in poor current transmission efficiency from the aperture hole. I get used to it. The embodiment shown in FIG. 3 solves this problem. In this embodiment, the cathode electrode B is connected to a radiation seal 9 provided on a cathode stand 10, and a cathode sleeve 2 is held by hanging wires 8 made of nickel, tantalum, etc., and a flat plate compensation is attached to the end of the radiation seal 9. It has a structure consisting of an electrode 4'. With such a configuration, electrons are subjected to a weak focusing effect and the current transmission efficiency is improved. Note that the potential of the flat correction electrode 4' is the same as that of the cathode sleeve. The upper surface of the cathode sleeve has a cap with a diameter r smaller than the diameter R of the cathode sleeve to limit the radiation area in order to reduce anode losses. An aperture electrode 6 faces this cathode electrode B.
An anode electrode 5 is located. FIG. 4 shows general characteristics of the dipole electron gun having the configuration shown in FIG. As the anode voltage Va increases, the cathode current I _K and the aperture transmission current I _S increase at the anode voltage.
It increases in proportion to the 1.5 to 2.0 power of Va, but the divergence angle α
is in the direction of decrease. The phenomenon that occurs in conventional triode electron guns, where increasing the current causes the divergence angle to increase, does not occur.
In a dipole electron gun with such a configuration, the size of the divergence angle α is a function of the hole diameter D of the flat correction electrode 4', the distance l of the cathode end from the flat correction electrode 4', and the anode-cathode distance L. . Changes in the divergence angle α were determined with respect to the following parameters: the hole diameter D of the flat correction electrode 4', the distance l of the cathode end from the flat correction electrode 4', and the distance L between the anode electrode 5 and the cathode end. In Figure 5, the distance between the anode and cathode electrodes L=
2mm, flat plate correction electrode hole diameter D = 1.5mm (plate thickness 0.2
mm) These are the experimental results when the distance l between the flat plate correction electrode 4' and the cathode end was changed. Each data uses an aperture hole of 25 μm, and the aperture transmission current I _S =3 μ.
This is the value at time A. However, the effective radiation diameter of the cathode is r
≒0.5mm. In this graph, the value of l is based on the height of the flat correction electrode 4', and is taken as positive when the cathode end face position is closer to the anode electrode, and negative when the opposite is the case. J _K is the aperture current density, Va is the anode voltage, and η is the ratio of the aperture passing current density to the average cathode current density, and the higher this value is, the higher the current utilization efficiency is. Although the values of L and D differ somewhat depending on changes in the dimensions of each electrode, the trends are similar to those shown in FIG. 5. That is, with respect to the positive movement of l, (1) the anode voltage Va increases monotonically and gradually, (2) the cathode current density J _K increases, and (3) the divergence angle α and the current utilization rate η gradually decrease. In particular, regarding the divergence angle α, which tends to affect the resolution, l
There will not be much change unless it becomes significantly negative. In FIG. 5, if it is used in the range l>-0.45 mm, the change in the divergence angle α is minute, so it can be considered that there is almost no effect on the resolution. From the viewpoint of electrode assembly accuracy, this means that some variation in l can be tolerated, making assembly easier. When the anode-cathode distance L and the plate correction electrode hole diameter D are changed, the divergence angle α reaches an inflection point. The distance l _nax takes values as shown in the following table.

[Table] From this, the value of l for arbitrary D and L is l _nax
It is given by ^{the relationship ≒0.25DL 0.6 ,} and there is relatively little variation if the distance l from the flat correction electrode 4' to the cathode end is at least l _nax (where l is in the negative direction) A dipole electron gun with a divergence angle α can be constructed. Taking FIG. 5 as an example, it is sufficient to arrange the cathode end within a depth of 0.45 mm. Therefore, give yourself a little leeway.
If the cathode end is brought to a depth of <l _nax , the divergence angle α will hardly change even if the cathode sleeve moves somewhat due to thermal expansion. Although Fig. 3 shows an example in which a flat plate correction electrode is attached to a radiation seal, 11 in Fig. 6
The flat correction electrode and the radiation seal may be integrally constructed as shown in FIG. As described above, in the present invention, the depth l from the flat plate correction electrode 4' to the cathode end is determined by the relationship between the anode-cathode distance L and the flat plate correction electrode hole diameter D in a two-pole electron gun equipped with a flat plate correction electrode. By selecting the value l≦0.25DL ^{0.6 ,} an electron gun with less variation in the divergence angle α can be obtained.
Moreover, electrode assembly accuracy can be relaxed. Therefore, by using the two-pole electron gun configuration according to the present invention, it is possible to provide a constant current cathode ray tube electron gun with stable resolution characteristics.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a conventional electron gun, FIG. 2 is a diagram showing its characteristics, FIG. 3 is a sectional view of an electron gun in an embodiment of the present invention, and FIGS. 4 and 5 are its characteristic diagrams. , FIG. 6 is a sectional view showing another embodiment of the present invention. 2... Cathode sleeve, 4'... Flat correction electrode, 9... Radiation seal, 10... Cathode stand, B... Cathode electrode, 5... Anode electrode, 6... Aperture electrode.

Claims (1)

[Claims] 1 Consisting of three electrodes: a cathode electrode, an anode electrode equipped with an aperture electrode, and a flat correction electrode provided between the anode electrode and the cathode electrode, the bipolar electron In the gun, where L is the distance between the anode electrode and the cathode electrode, D is the hole diameter of the flat correction electrode, and l is the distance between the flat correction electrode and the cathode electrode, the relationship is l≦ ^{0.25DL 0.6 .} An electron gun characterized by satisfying the following.