JPH0527208B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an electromagnetic focusing electrostatic deflection type image pickup tube equipped with a deflectron type deflection electrode.

Conventional configuration and its problems In general, an electromagnetic focusing electrostatic deflection type image pickup tube equipped with a deflectron type deflection electrode has an electrode configuration as shown in Fig. 1, and the thermoelectrons emitted from the cathode 1 are transferred to the control electrode. 2 and the electron beam diameter limiting hole 4 of the accelerating electrode 3, and proceed along the path shown by the solid line arrow under the focusing action of a focusing coil (not shown) and the deflection action of a deflectron-type deflection electrode 5. do. The electron beam passes through the mesh electrode 6 and scans the photoconductive film 8 of the target electrode 7, but the electron beam that could not enter the target electrode 7 returns to the accelerating electrode 3 side as a so-called return beam.

By the way, the return beam in such an electromagnetic focusing electrostatic deflection type image pickup tube differs from the return beam in an electrostatic focusing electromagnetic deflection type image pickup tube or an electromagnetic focusing electromagnetic deflection type image pickup tube, in that the return beam is directed away from the tube axis as shown by the dashed arrow. It is deflected and returns to the accelerating electrode side. When this return beam impinges on the electron gun electrode such as the accelerating electrode and the electrode support structure 9 surrounding it, a so-called reflected beam is generated, which heads toward the target electrode 7 along a path as shown by the dashed line.

Since the reflected beam has low energy and is somewhat scattered, even if it is incident on the scanning area of the photoconductive film 8, it will not adversely affect the output signal current as long as the incident light is not a highlight.
However, when this reflected beam enters the non-scanning area, which is the peripheral area of the photoconductive film 8, a pseudo signal due to this is mixed into the output signal current. The reason for this is that while the back surface potential in the central rectangular scanning region of the photoconductive film 8 is lower than the target voltage (usually 20 to 50 V) applied to the transparent conductive film 10, the back surface potential in the non-scanning region is is close to the target voltage, and therefore even a low-energy reflected beam can be easily landed.

In order to prevent the generation of spurious signals as described above, conventionally, the transparent conductive film 10 or the mesh electrode 6 is trimmed to provide these electrodes only within the scanning area, or almost all of the reflected beam returns within the scanning area. Methods such as reducing the diameter of the electron gun electrode have been adopted. However, trimming requires extremely high precision in the electrode and its assembly, making it unsuitable for mass production. Furthermore, reducing the diameter of the electron gun electrode not only reduces the mechanical strength of the electron gun, but also causes the control electrode to reach a high temperature during operation, making it more likely to be deformed due to thermal expansion. Furthermore, the miniaturization of the cathode makes it difficult to obtain a sufficiently large beam current.

A false signal may also be generated when the accelerating electrode potential is high. This is because the returning beam is drawn toward the accelerating electrode, increasing the amount of reflected beam toward the target electrode from the vicinity of the side wall of the accelerating electrode. In this case, it is sufficient to raise the deflection electrode potential or lower the acceleration electrode potential, but the former increases the power required for focusing and deflection, and the latter decreases the beam current.

Purpose of the Invention It is an object of the present invention to prevent the generation of false signals due to reflected beams without reducing the diameter of the electron gun electrode or requiring strict trimming, and to set the acceleration electrode potential higher than the deflection electrode potential. The purpose of the present invention is to provide an image pickup tube that can be used.

Structure of the Invention In the image pickup tube of the present invention, the cylindrical part of the accelerating electrode has an annular flange on the tip edge, and the flange surrounds the cylindrical part and faces the deflectron-type deflection electrode, which has a potential lower than that of the accelerating electrode. A cylindrical shield electrode held at a potential is provided such that its tip edge is covered by the flange, and this will be described in detail below along with embodiments shown in the drawings.

DESCRIPTION OF EMBODIMENTS In FIG. 2 showing the main parts of an image pickup tube embodying the present invention, an electron gun enclosed in a glass bulb 11 has an electrode configuration consisting of a cathode 1, a control electrode 2, and an accelerating electrode 3. It has a cylindrical shield electrode 12. A film-like deflectron type deflection electrode 5 is attached to the inner peripheral surface of the glass bulb 11, and a mesh electrode and a target electrode similar to the conventional one are arranged in front of the acceleration electrode 3, although not shown. There is.

Like the accelerating electrode 3, the cylindrical shield electrode 12 is made of non-magnetic stainless steel or a nickel-copper alloy, and is insulated and supported by the electrode support structure 9 at the flange 12a. However, the accelerating electrode 3 has an annular non-magnetic metal plate 13 on the tip edge of the cylindrical part 3a.
As a result, the cylindrical portion 3a has a flange at its tip edge. Further, the cylindrical shield electrode 12 coaxially surrounds most of the cylindrical portion 3a of the accelerating electrode 3, faces a part of the deflection electrode 5, and has its tip edge covered with the flange formed by the metal plate 13. There is.

The terminal of the shield electrode 12 is drawn out of the tube independently of the terminal of the accelerating electrode 3, or is connected to the control electrode 2 or the cathode 1 inside the tube.

In operation of such an image pickup tube, for example, a potential of about 200 V is applied to the accelerating electrode 3, a potential of about 150 V (average value) is applied to the deflection electrode 5, and a potential of about 10 V is applied to the shield electrode 12. Higher than average potential.

In the mutually opposing portion of the shield electrode 12 and the deflection electrode 5, an electric field with a higher potential distribution is generated on the outside than on the inside, so the return beam 14a that has entered the mutually opposing portion is bent outward. The reflected beam will no longer be directed toward the target electrode. In addition, although the reflected beam 15b caused by the return beam 14b that has entered the annular non-magnetic metal plate 13 heads toward the target electrode, it is incident on the scanning area of the photoconductive film, so there is almost no problem in practical use. . Furthermore, since the return beam 14c that has entered the metal plate 13 so close to its side circumferential surface goes around to the back side of the metal plate 13, the reflected beam does not go toward the target electrode side.

Note that if the metal plate 13 does not exist, the third
As shown in the figure, a part of the return beam 14d that has entered near the tip edge of the cylindrical shield electrode 12 returns to the target electrode without hitting the electrode, which reduces the effect of suppressing spurious signals. It becomes incomplete. Further, in this case, there is a disadvantage that the electric field 16 generated near the tip edge of the accelerating electrode 3 gives an unwanted lens effect to the electron beam.

The outer diameter of the metal plate 13 must be selected so that the electron beam reflected from the inner part can return to the scanning area of the target electrode. Any material may be used as long as it can provide an annular flange on the edge, and it may be formed as a pair with the accelerating electrode when it is formed.

The shield electrode potential is sufficiently lower than the accelerating electrode potential, and can be selected from a range of 0 to about 120 V, preferably about 30 V or less, but may be a negative potential. Further, the shield electrode 12 may have a funnel shape or a horn shape, or may have a cylindrical shape without a flange. Additionally, the mesh electrode may be trimmed, as long as it has a frame-like border that can prevent the reflected beam that is largely deflected outward or the reflected beam from the electrode support structure from re-entering the target electrode, as described above. In general, it is not necessary to leave a portion of a size that exactly corresponds to the scanning area and to frame and mask the periphery as in the conventional method. In other words, all you have to do is leave a part that is somewhat larger than the area corresponding to the scanning area and mask the surrounding area, so this does not mean that particularly high precision is required for mesh electrodes and electrode assembly. normal precision is sufficient for practical purposes.

Effects of the Invention Since the image pickup tube of the present invention is configured as described above, generation of false signals due to reflected beams can be prevented without reducing the diameter of the electron gun electrode.
Further, there is an advantage that not only can a sufficiently large beam current be passed by setting the accelerating electrode potential to a relatively high value, but also that an unwanted lens electric field is not generated near the tip edge of the accelerating electrode. Furthermore, there is an advantage that no trimming is required for the mesh electrode, and even when trimming is performed, no particularly high precision is required for the electrode and its assembly.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the relationship between the electrode configuration of a conventional image pickup tube and the electron beam path, FIG. 2 is a sectional view of the main part of an image pickup tube in which the present invention is implemented, and FIG. 3 is an accelerating electrode in the present invention. FIG. 6 is an explanatory diagram of the operation when a flange is not provided on the tip edge of the cylindrical portion. 3... Acceleration electrode, 5... Deflection electrode, 11... Glass bulb, 12... Shield electrode, 13... Metal plate.

Claims (1)

[Claims] 1. The accelerating electrode of the electron gun is enclosed in a glass bulb with a deflectron-type deflection electrode attached to the inner circumferential surface. a cylindrical shield electrode which surrounds the cylindrical part and faces the deflection electrode and is held at a potential lower than the potential of the acceleration electrode; An imaging tube characterized by being attached to an electron gun.