JPH0719544B2 - Electrostatic focusing type camera tube device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic focusing type image pickup tube having a laminar flow type electron gun, and a focusing point added to the image pickup tube to give an auxiliary focusing action to an electron beam. The present invention relates to an electrostatic focusing type image pickup tube device including a magnetic field generating means.

2. Description of the Related Art Conventionally, an image pickup tube equipped with a laminar flow type electron gun has been used in a television camera for broadcasting. The laminar flow type electron gun is usually called a diode gun because it consists of a cathode and an accelerating electrode (anode) to which a positive voltage of 5 to 10 V is applied.
An electrostatic focusing type image pickup tube equipped with such an electron gun is, for example,
National Technical Report No.2, February 1985
It is introduced in Vol. 31, No. 1, No. 54-60.

The thermoelectrons emitted from the cathode of the laminar flow type electron gun do not form a crossover point, pass through the focused electric field or focused magnetic field and the pores of the diaphragm, and become a beam. Then, the electron beam enters the deflection magnetic field or the deflection electric field to be deflected, and then passes through the mesh electrode to reach the target electrode or scans the photoconductive film surface of the electrode. Since such an electron gun does not generate a crossover point as described above,
It is possible to obtain an image pickup tube with high resolution characteristics in which the density distribution of the electron beam is not widened and the beam temperature is not increased, and the capacitive afterimage is small.

Problems to be Solved by the Invention By the way, thermoelectrons that could not reach the target electrode return to the electron gun side as a so-called return beam, and when this return beam strikes the electron gun electrode and its peripheral members, so-called reflection Beam is generated. Then, since a part of this reflected beam is incident on the target electrode, noise is mixed in the output signal. In particular, such a noise component in the high-sensitivity electrostatic focusing type image pickup tube device incorporating the laminar flow type electron gun is It reaches 3nA, which cannot be ignored. The noise as a pseudo signal appears as a blurred white spot in the center of the screen of the monitor picture tube. Therefore, it is an object of the present invention to provide an electrostatic focusing type image pickup tube device having a high S / N characteristic which hardly causes the above-mentioned noise.

Means for Solving the Problems An electrostatic focusing type image pickup tube device of the present invention includes a laminar flow type electron gun,
A focusing electrode for applying an electron beam focusing electric field emitted from the electron gun, and a diaphragm having pores for trimming the electron beam focused by the focusing electrode,
Beam deflecting means for deflecting the electron beam trimmed by the diaphragm and irradiating the electron beam to a predetermined position of the target electrode, and the electron at a position between the electron gun and the diaphragm and isolated from the beam deflecting means. Focusing magnetic field generating means for providing an auxiliary focusing action to the beam is provided.

Operation As a result of experiments, it has been found out that the above-mentioned device can almost eliminate the above-mentioned noise. Although the reason is not always clear, it is presumed that the trajectory of the return beam or the reflected beam is bent by the magnetic field generated by the focusing magnetic field generating means. Further, since the electron beam is focused in two stages by the electrostatic focusing electric field and the focusing magnetic field, there is a secondary effect that so-called ion burning of the photoconductive film can be prevented.

EXAMPLE The present invention will be described in more detail with reference to the example shown in the drawings. Thermoelectrons 4 emitted from a laminar flow type electron gun 3 including an impregnated cathode 1 and an acceleration electrode 2 are generated by a focusing magnetic field by a focusing coil 5. After undergoing the preliminary focusing action, the electron lens 8 generated by the first focusing electrode 6 and the second focusing electrode 7 receives the focusing action. Then, it is trimmed into a beam shape by passing through the pores 10 of the diaphragm 9 of the focusing electrode 7, and passes through the deflection magnetic field by the deflection yoke 11 and the electric field by the mesh electrode 12 to pass through the target electrode 13
In the meantime, the photoconductive film surface 14 of the target electrode 13 is scanned. However, the first and second focusing electrodes 6 and 7 are made of a conductive film such as nickel or chromium deposited on the inner peripheral surface of the glass bulb 15, 16 is a cathode terminal, 17 is an accelerating electrode terminal, 1
Reference numerals 8 and 19 denote first and second focusing electrode terminals, 20 denotes a mesh electrode terminal, and 21 denotes a target electrode.

The focusing coil 5 is provided between the electron gun 3 and the diaphragm 9 and at a position separated from the deflection yoke 11. However, the magnetic field generated by the focusing coil 5 should not interfere with the magnetic field generated by the deflection yoke 11, and the yoke 11 should not interfere. It is provided in a position separated from. Further, the thermoelectrons emitted from the laminar flow type electron gun 3 are
Since the focusing magnetic field by the focusing coil 5 and the electron lens 8 focus the light in two stages, the lens magnification of the electron lens 8 is set lower than that of the conventional one. Typical applied voltage to each electrode is a target electrode voltage ...... 45V, mesh electrode voltage ...... 1100V, second focusing electrode voltage ...... 400V, first focusing electrode voltage ・ ・ ・ 45V in 2/3 inch type image pickup tube. … 5-15V
Is.

In the image pickup tube device configured as described above, the noise component is reduced to 2 nA and
A good S / N ratio can be achieved by reducing the current to 1 nA with 5 Gauss and 0.5 nA with 20 Gauss.
The characteristics could be obtained. The reason for this is not clear as described above, but the electron gun 3 is made through the pores 10 of the diaphragm 9.
The return beam returning to the side and the reflected beam generated by this return beam are used not only by the electron lens 8 but also by the focusing coil 5
In order to pass the focusing magnetic field by the target electrode 13
It is speculated that the result is that the reflected beam that can reach the center of the tube is limited to a very small number that travels straight on the tube axis. The degree of this effect can be adjusted by moving the mounting position of the focusing coil 5 in the tube axis direction or changing the axial length of the coil. Further, since the ions emitted from the electron gun 3 are not focused in the magnetic field, that is, they are focused only by the relatively weak electron lens 8, the ion burning of the photoconductive film of the target electrode 13 is reduced. You can

Although the focusing coil is used as the focusing magnetic field generating means in the above-described embodiment, a cylindrical permanent magnet (having N and S magnetic poles at both ends in the axial direction) may be used instead of the focusing coil. This permanent magnet may be provided outside the tube or inside the tube. An electrostatic deflection electrode may be used instead of the deflection yoke.

Effect of the Invention As described above, the present invention can drastically reduce the noise generated by the reflection of the return beam, and can obtain an image pickup tube device having a high S / N characteristic.

[Brief description of drawings]

The drawing is a side sectional view of an image pickup tube device embodying the present invention. 3 ... Electron gun, 5 ... Focusing coil, 6,7 ... Focusing electrode, 1
1 ... Deflection yoke.

Claims (1)

[Claims] 1. A laminar flow type electron gun, and a focusing electrode for applying a focusing electric field to an electron beam emitted from the electron gun.
The electron gun includes a diaphragm having a fine hole for trimming the electron beam focused by the focusing electrode, and a beam deflecting unit for deflecting the electron beam trimmed by the diaphragm and irradiating the electron beam at a predetermined position of the target electrode. An electrostatic focusing type image pickup tube device comprising a focusing magnetic field generating means for giving an auxiliary focusing action to the electron beam, at a position separated from the beam deflecting means with respect to the diaphragm.