JPS5875743A - Pickup tube electron gun - Google Patents

Abstract

PURPOSE:To improve durability and reliability of cathode as well as resolution of a pickup tube by forming a crossover point in a position of high potential on an axis. CONSTITUTION:A plate electrode 31 making the first grid is thickened while the depth l1 of a recess to be formed in the center of said plate electrode 31 is made not less than d1/2 to the inside diameter d1 of said recess. The deepened recess produces and effect of shielding an electric field caused by the second grid 4, a divergent lens is formed near the first grid opening 13, an electron beam 12 passing through the opening 13 once diverges then forms a crossover point 15 at a point away from the first grid opening 13. The rising of the potential V(2) (full line) on the axis near the electrode is gentle and the peak value (crossover point) of the current intensity J(2) (dotted line) on the axis is formed in a position more distant from cathode, wherein the potential on the axis is high, causing stronger control of the expansion of width of speed distribution of an electron group.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image pickup tube electron gun, and more particularly to an electrode structure for an electron gun that suppresses expansion of the layered distribution of electron groups forming an electron beam.

In a vidicon type image pickup tube, a charge pattern corresponding to 4tL object illuminance is generated on a photoconductive film, and the charge pattern is sequentially discharged by scanning the photoconductive film with an electron beam generated by an electron gun. The charging current corresponding to this discharge is taken out as a signal. The electric charge once generated by the object is not normally discharged in its entirety in one beam scan, so even if the object disappears, the electric charge will remain at 1.
In subsequent scans, a false signal corresponding to the residual charge is generated as an afterimage, deteriorating the image quality of a moving subject.

In particular, in an image pickup tube using a blocking photoconductive film, the main component is an afterimage with a time constant determined by the product of the photoconductive film's electromagnetic resistance and the beam resistance of the scanning electron beam. This is called capacitive afterimage. The beam resistance is equivalent to the velocity distribution of the electron group forming the electron beam, and for an electron beam to achieve a low residual one-dimensional state, it is necessary that the velocity distribution of the electron group be narrow.

Electrons emitted from the cathode have a Maxwellian velocity distribution, but in the process of forming a narrow beam, the current density of the beam increases.

It is known that the velocity distribution is expanded due to the energy relaxation phenomenon that electrons give to each other's coulombas.

This phenomenon is called the beige effect, and the expansion rate of the velocity distribution is approximately proportional to J (z) 3/ V (z) VC for the upper current density J (z) and the axial potential V (z). This is known.

In an electron gun that aims to achieve such a low residual output, it is necessary to suppress the increase in beam current density as much as possible.

A bipolar electron gun has been proposed in which the first grid facing the anode is operated at a positive potential with respect to the cathode.

An ideal low-afterimage electron gun would have a so-called no-flow beam, in which electrons are emitted from the cathode parallel to the axis and no crossovers of high current density are formed. However, the conventional 2& type electronic beam has a crossover type configuration due to the need to widen the die size and cleanliness of the beam current line so as not to cause insufficient beam even for subjects with high illuminance.

Furthermore, since the crossover point is formed at a position near the first grid where the axial potential is low, the expansion of the velocity distribution width is not sufficiently suppressed.

The present invention aims to improve the conventional 200 million-type electron gun and provide an electron gun that can generate a larger beam current with less afterimage and a lower cathode load (cathode emission current density L). purpose.

In the dipole electron g according to the present invention, the cathode has l.
1. A diverging electron lens is formed in the vicinity of the small aperture O of the first grating, which is placed facing each other and a positive voltage is applied to the cathode. By forming cross oats (points) at high axial potential positions 1I11 from the first grid aperture, the velocity distribution width of the electron group can be further suppressed, and at the same time, the microscopic Basics II: Increasing the beam current passing through the aperture
The present invention will be described in detail with reference to embodiments below. Figure 1 shows the schematic structure of a vidicon type camera 1.

l is a cathode, 2 is a heater, 3 is a first grating, 4 is a second grating,
5 is a third lattice, 6 is a fourth lattice having mesh-like electrodes,
7 is a light guide IIE experimental target, 8 is a focusing coil, 9 is a deflection coil, and the electron beam 10 emitted from @ pole l
is jR1 lattice 3. It is composed of a second lattice 4. The electron beam is formed into a thin shape using an electron gun, is focused on the target by a magnetic field lens generated by a focusing coil 8, and is scanned by a magnetic field generated by a deflection coil 9. Here, the electromagnetic focusing/electrical deflection type laser tube is shown as upside down, but the first light is the second one from the gap and the other.
This relates to the electron section up to grating 4, and can be applied to any type of imaging tube, regardless of the subsequent beam focusing and deflection methods.

Figure 2 shows 1 of the conventional 200 million-type electron gun! 3 is an enlarged cross-sectional view showing the section III'i cathode surface, 3 is the first grating, and 13 is M
1 is a small aperture provided in the lattice; 4 is the second lattice;

Reference numeral 14 indicates a minute opening provided in the second lattice 4, and lO indicates an electron trajectory emitted from the center of the cathode surface 1.

The electron beam passing through the first grating aperture 13 is focused immediately after passing through the aperture, and forms a crossover 15 at a position close to the first grating 3.

FIGS. 3 and 4 are enlarged sectional views showing essential parts of the bipolar electron gun according to the invention, respectively. In the mesh arrangement shown in FIG. 3, the thickness of the flat plate electrode 31 constituting the l-th lattice 3 is increased, and the depth tl of the concave portion formed at the center of the flat plate electrode 31 is set to 6172 or more with respect to the inner diameter d. Make it. By deepening the illusion.

The effect of confining the electric field generated by the first second grating 4 is generated, and a diverging lens is formed near the first grating aperture 1.3, so that the electron beam 12 passing through the aperture 13 diverges once, and A crossover 15 is formed at a point away from 13.

In the embodiment shown in FIG. 4, an intermediate grating 20 having an opening is provided between the first grating 3 and the second grating 4, and
A voltage equal to or lower than that of the first grating 3 is applied to the first grating 3 to form a diverging lens in the vicinity of the first grating aperture 13 . It is preferable to set the potential of the intermediate grid 20 to the same potential as the ls pole 1 without increasing the stem lead width.

Figures 5 and 6 show that the axial potential vtz) (indicated by the solid line) rises slowly near the cathode, and the axial current density J ( The peak value (corresponding to the crossover point) of Z) (indicated by the dotted line) is formed at a position farther from the cathode where the axial potential is higher1, and the velocity distribution width of the electron group is expanded)□. 0 Figure 7 shows the voltage of the l-th grid 3 becoming stronger! For Jc1, the second
The beam current iB passing through the grating aperture 14 and the current density at the center point of the pole (cathode load >J'c) are shown for the conventional example shown in FIG. 2 and the embodiment shown in FIG. 4, respectively. It is.

Here, two specific examples will be shown regarding the electrode dimensions of the embodiment shown in FIG. The diameter of the second grating opening 14 in the specific example IFi is 30 μm, and in the specific example 2, it is 20 μm, and the other dimensions are completely the same. The plate thickness of the l-th grating 3, the diameter of the l-th grating opening 13, and the gap between the cathode l and the first grating 3 are the same as in the conventional example shown in FIG. 2, and are respectively 0.18 mm, 200 tJm, and 0.1
It is 5mm. Contents: 0.25mm, 1.0mm, 0.2
mm, 0.2 mm. The diameter of the opening of the intermediate grating 20 and the inner diameter of the recess of the first and second gratings 3.4 are all 0.
It is 65mm.

The voltage applied to each #L and others is Ov for the cathode l, 300V for the second grid 4, the same OV as the cathode for the intermediate grid 20, and several volts to several tens of volts for the first grid 3 as shown in FIG. It is.

In FIG. 7, curves 71, 72 and 7 are shown as solid lines.
3 indicates beam current i of specific example 1 specific example 2 according to the present invention and conventional example, respectively; music 4I74 indicated by a one-dot line;
and 75 are the cathode loads ρ of the electron guns of the present invention (concrete examples 1 and 2) and the conventional example, respectively. Regarding Figure 7, which shows the characteristics of the electron gun according to the present invention and the conventional example, 1
As is clear from the curved edges 71 and 72 and the curve 4173, the electron gun of the present invention has the same E. 1, the beam current i is larger than the conventional example, and the rise of is for Ec11c is steeper than the conventional example. On the other hand, if we compare the cathode load ρ (see songs @74 and 75).

The electron gun of the present invention has a lower value for the same Eco, which almost matches the theoretical value given by the ohth d-Langmuir equation, and the relationship is ρC@cBC10 This is 1 In the electron gun of the present invention, potential changes are gradual near the Fi first lattice opening.

This is because the effect of the electric field formed by the potential of the second lattice is ignored. In contrast, in the conventional example.

41 The potential change near the lattice opening is large, and due to the effect of the electric field formed by the second lattice potential, a stronger electric field acts on the center of the cathode, increasing the load. This effect becomes noticeable when 1 is playing small guard, and it deviates greatly from the theory.

In a bipolar electron gun that applies a positive potential to the first grid, the life and reliability of the cathode are the most important points.

According to the present invention, a larger beam current can be generated with a lower cathode load than the conventional example.

It is extremely advantageous from the point of view of the above-mentioned life reliability. Also, the above-mentioned specific example 1. As is clear from 1 and 2, in the electron gun of the present invention, even if the diameter of the second grating aperture 14 is made small, the decrease in beam current iB is small.

It is now possible to use a smaller aperture than in conventional cases,
! It is also advantageous for improving the solution of j & me tube by 1 degree.

As explained above, according to the present invention, it is possible to form the crossover point at a position where the axial potential is high, thereby further suppressing the expansion of the continuous distribution of electron groups, and furthermore, it is possible to generate a large beam current with a lower 11j single pole load. This makes it possible to realize an extremely advantageous electron gun in terms of cathode life reliability, improvement in image pickup tube resolution, and reduction in afterimages.

[Brief explanation of the drawing]

Figure 1 is a diagram showing a schematic configuration of an image pickup tube, Figure 2' is an enlarged sectional view showing the main parts of a conventional two-pole electron gun, Figures 43 and 4.
The figures are an enlarged sectional view, FIG. 5, and FIG. 46, respectively, showing the main parts of the bipolar electron gun according to the present invention. and FIG. 7 are diagrams showing a comparison of beam characteristics of the present invention and a conventional example. l...Cathode, 2...Heater 3...
...III lattice, 4... Second lattice 5...
...Third lattice, 6...Fourth lattice 7...-
Photoconductive film, 8--Focusing coil 9--Deflection coil, 10, 11. ．． 12...electron beam 13.
...First grid micro-aperture 14...Second grid micro-aperture 15...Crossover 20...Intermediate grid agent Patent attorney Sui 1) Licensing ro===yo===ko No. 2 Yasubu 4 Figure 83 Figure lln5m2ftl ZCmm)

Claims (1)

[Claims] 1. At least a cathode that emits electrons, a fit grating disposed at its rear stage and having a first minute opening to which a positive voltage is applied to the cathode, and a first grating disposed at its rear stage. A diverging electron lens was formed between the #11 grating and the second grating in the vicinity of the 1-J) micro aperture. An image tube electron gun that uses % mold. 2. The above first lattice is the above #! The depth of the recess is at least 1/2 of the inner diameter of the plate electrode, and the electric field generated by the second lattice is passed through the recess. The image pickup tube electron gun according to claim 1, characterized in that it forms a diverging electron lens. Arrangement 3, the first grid above and #! It was left between the two grids. Imaging according to claim 1, further comprising an intermediate grating having an aperture to which a voltage equal to or lower than the voltage applied to the l-th grating is applied, and the diverging electron lens is formed by the intermediate grating. 4. The imaging tube electron gun according to claim 3, wherein the voltage applied to the intermediate grid is equal to the voltage applied to the cathode.