JPS6235443A - Image pickup tube - Google Patents

Abstract

PURPOSE:To reduce the contrast of a return beam image by either reducing the average atomic number (Z) of the surface substance or increasing the voltage of the electrode plate. CONSTITUTION:When the average atomic number of the surface substance is supposed to be Z and the electric potential of the electrode plate 10 is supposed to be V, the contrast of a return beam image is almost proportional to Z/V. The return beam image including the above contrast can be effectively reduced by adjusting Z/V to be 0.044 or smaller. For example, when the pickup tube of this invention is made of a conductive substance such as a stainless steel, a voltage applied to an auxiliary electrode 1100 is higher than those applied to the electron gun electrode 110 and a deflecting electrode 108. Since the average atomic number (Z) of a stainless steel is 25.8, it is preferable that the voltage applied to the auxiliary electrode 1100 be at least 586V.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to image pickup tubes, and more particularly to electrode configurations and electrical settings suitable for reducing the contrast of returned beam images.

[Background of the invention]

Electromagnetic focusing/electrostatic deflection type image pickup tube (hereinafter referred to as MS type image pickup tube), or electrostatic focusing/electromagnetic deflection type image pickup tube (hereinafter referred to as SM), which combines electrostatic type and magnetic field type for electron beam focusing and deflection. (abbreviated as shape imaging) has excellent uniformity of resolution within the screen, and has been praised for its excellent uniformity within the screen.

However, with MS type image pickup tubes or SM type image pickup tubes,
There is a generation of false signals called return beam images, which is a serious drawback when imaging objects with low illumination.

To explain this return beam image, the structure and operation of the image pickup tube will be explained by taking the MS type image pickup tube as an example.6 FIG. 1 is a schematic diagram of the MS type image pickup tube. Cathode (1
The electron group emitted from the first grid electrode (102),
accelerated and controlled by a second grid electrode (103);
It is restricted by the microhole (104) and becomes an electron beam. This electron beam is focused onto a photoconductive target (107) by the action of a magnetic field created by a solenoid-like focusing coil (106) provided outside the tube (105). Furthermore, this electron beam is deflected by the action of an electric field created by two pairs of horizontal and vertical deflection electrodes (108) formed on the inner wall of the tube body (105), and is scanned over a target (107).

FIG. 2 is a developed view showing an example of the shape of the deflection electrode formed on the inner wall of the tube. 2 is the tube axis direction, and T is the angular direction around the tube axis. The deflection electrodes are horizontal deflection electrodes Hゝ, H'', and text deflection electrode V+.

■It is composed of four electrodes -, each electrode has a bias electrode E, and a voltage of 10 V g /21 is applied on top of 3 (V).
Vll 2 + +MY/ 21-vv/ 2 (
The voltages v) are superimposed to form a deflection electric field. Vll,
Vv are called horizontal deflection voltage and vertical deflection voltage, respectively.

In FIG. 2, F is the electrode plate (110) of the second grid electrode in FIG.
) corresponds to the position.

photoconductive targeter scanned by an electron beam)-(1
07) can be regarded as a collection of capacitors arranged densely in all directions on the surface of the glass substrate (1o9). Each capacitor that has been charged in advance by scanning the electron beam discharges its charge in approximately proportion to the amount of light that has passed through the glass substrate until the next scan, and the target (107)
A corresponding electrical pattern of the optical image is formed thereon.

The current that flows during charging during the next scan becomes a video signal. In addition, the target (107) and the glass substrate (109)
A very thin transparent electrode is placed between them, and the potential of the transparent electrode is approximately 50V, with the cathode potential being Ov. Therefore, the potential of the surface of the target near the electron gun is a low voltage close to the cathode potential in the region scanned by the electron beam, and rises to a value close to the transparent electrode potential in the region not scanned by the electron beam.

In addition, in order to perform low-speed scanning of the electron beam, a mesh-like electrode (111) is placed facing the photoconductive target (lO7).
is installed to generate a deceleration electric field between the mesh-like electrode (111) and the photoconductive target.

The above is the operation of the MS type image pickup tube. Next, the return beam image in the MS type image pickup tube and the principle of its generation will be explained.

FIG. 3 schematically shows the trajectory of an electron beam in an MS type image pickup tube. In the diagrams below, the same parts are given the same symbols to avoid redundant explanations. Electron beam (3
01), a false signal is generated in a region B outside this region A.

The so-called forward beam (301) emitted from the electron gun section is
There is a beam that scans the region A of the target (107), but a part of it is pushed back toward the electron gun section as shown by the tube line, and this becomes a so-called return beam (302). This return beam (302) mainly hits the electrode plate (110) of the second grating electrode (103), and a part of it becomes a so-called reflected beam (303) and heads toward the target again.

The velocity component of this reflected beam (303) in the tube axis (Z) direction is small, and on the other hand, the scanning area A of the beam at the target (107) is maintained near the cathode potential O■ due to the charging of the forward beam (301). Therefore, the reflected beam (303) is difficult to enter this area A, but in area B outside the scanning area Δ, since the beam (301) is not scanned, the number of electricity close to that of the transparent electrode is It is in a potential state of about 10 V, and the reflected beam (30
The charging current caused by 3) becomes a false signal. This false signal.

This causes a so-called return beam image.

The current of the reflected beam heading toward the target is a minute current of several percent of the outgoing beam. Therefore, in imaging under normal illuminance, the false signal read out by the reflected beam is smaller than the video signal read out by the forward beam, and therefore does not pose a major problem. but,
If the sensitivity of the signal amplifier of the imaging device is increased when imaging a subject with low illuminance, a beam image that returns as shown in FIG. 4 will appear on the monitor, resulting in deterioration of image quality. In FIG. 4, (401) is an image frame corresponding to the scanning area, and since the area (402) is read out from the area B outside the scanning area by the reflected beam, the normal area shown with diagonal lines ( 403).

The above is the returned beam image in the MS type image pickup tube and the causes of its generation.

A return beam image is also generated in the SM type image pickup tube due to the same reason. Other types of image pickup tubes, ie.

It is thought that a return beam image is generated for the same reason in an electromagnetic focusing/electromagnetic deflection (MM) type image pickup tube or an electrostatic focusing/electrostatic deflection (SS) type image pickup tube.

Conventionally, in order to avoid this returning beam image, a method described in, for example, Japanese Patent Laid-Open No. 56-38742 is known.

This means that between the amount of deflection of the forward beam (R□), the arrival position R (R2) of the return beam to the electrode plate (110), and the arrival position II (R3) of the reflected beam to the target (107), R222R□, R323R1, therefore Rim
(2/3) Considering the relationship of R,
Electrode plate (110
) is a method of "absorbing the return beam directed to the position above or preventing it from returning to the region B of the target (107)".The concrete method for realizing this is as follows.
Japanese Patent Publication No. 56-38742.

This is proposed in Japanese Patent Laid-Open No. 56-38743.

The first method is to reduce the diameter of the electron gun section and make the electrode plate (110
The second method is to make the diameter of the mesh electrode (1
11) A method of blocking reflected beams directed outside the scanning area by covering the area with a disc electrode (501) having a square window-like opening that matches the shape of the scanning area.The third method is shown in Figure 6. As shown, the electrode plate (110)
This is a method of arranging a cylindrical electrode (601) with a small diameter in close proximity to the target (107) to make the deflection sensitivities of the forward beam and return beam different, and direct the reflected beam to areas other than area B on the target (107). .

The fourth method is to form a material layer or surface treatment layer on the electrode plate (110) that absorbs or scatters the returning beam.The first method is that the mechanical strength deteriorates as the diameter of the electron gun becomes smaller. have shortcomings.

In the second method, the scanning area and the mesh electrode (11
Since it is difficult in manufacturing to perfectly match the shape, size, and arrangement of the corner window in 1), the corner window needs to be larger than the scanning area, and the return beam image cannot be completely erased.

In the third method, when the returning beam image is sufficiently deflected toward the tube (105), it hits the tube and becomes a reflected beam. In this case, although the boundaries of the returned beam image are not sharp as shown in FIG. 4, a returned beam image is still generated.

In the fourth method, there is a possibility that the surface layer of the electrode plate peels off and adheres to the photoconductive target (107), resulting in part of the video signal being lost.

In addition, in order to realize this method, for example,
As described in No. 21.5639, the surface layer has been formed with a substance having a small secondary electron emission ratio δ, or the surface layer has been roughened.

[Purpose of the invention]

An object of the invention is to reduce the contrast of the returned beam image.

[Summary of the invention]

The present invention is based on the following fact, which has been clarified through theoretical and experimental consideration of the mechanism of generation of reflected beams.

That is, among the electrons that form the reflected beam, what causes the returned beam image are reflected electrons generated when the returned beam is elastically scattered by protons in the surface material of the electrode plate 110. Therefore, by decreasing the average atomic number Z of the surface substance or increasing the voltage of the electrode plate,
The contrast of the returned beam image can be reduced.

[Embodiments of the invention]

Below, we will discuss the physical considerations for the generation of a returned beam image, which is the basis of the present invention.

Reflected beams can be considered to be generated mainly due to the following three causes.

(1) The electrons (denoted as eB) in the return beam are transferred to the electrode plate (1
10) are scattered by the Coulomb force with protons in the surface material and become reflected electrons (denoted as ea).

(2) ell is scattered by the Coulomb force with electrons in the surface material (denoted as eII) and becomes e.

(3) During the scattering in (2), ell gives kinetic energy to ell, and the e3 is further scattered in the surface material and flies out of the material to become es.

In the case of (1), the proton is integrated with the atomic nucleus, and the mass of the atomic nucleus is thousands to tens of thousands of times heavier than the mass of the electron, so there is almost no exchange of energy between the atomic nucleus and the electrons. In other words, it is elastic scattering.

In the cases of (2) and (3), since the scattering is between particles of the same mass as electrons, a considerable portion of the kinetic energy of e is transferred to ell. In other words, it becomes inelastic scattering.

Among the reflected electrons generated due to the causes of (1), (2), and (3), those reflected in the returned beam image are mainly the reflected electrons generated by the elastic scattering of (1) for the reasons described below.

The potential at the point (x+ yt z) inside the image pickup tube is Φ(x+ yp z) volts with the cathode as the reference, and the electrode plate (11
0) surface potential is Φ7 volts, reflected electron e.

When the kinetic energy near the electrode plate (110) is v6 electron volts, the velocity V when the reflected electron e6 passes through the point (Xw yp2) is as follows.

v= 2e/m Φ(x, y, z)-(Φ,-V,
)...(1) Here, e is the absolute value of the charge of the electron, and m is the mass of the electron.

Figure 7 shows a typical example of the energy distribution in one reflected electron e (
For example, Sogo Okamura, “Electronic Tube Engineering”, Ohmsha, p.33,
6) The energy of an incident electron is 100 electron volts.

The peak in the distribution at 100 electron volts corresponds to (1) electrons due to elastic scattering. (2) (3)
The electrons generated due to this are distributed below 100 electron volts, with the largest number per 10 electron volts.

By the way, if the surface potential of the target (107) is ΦAvolt, then the inside of the square root in equation (1) cannot physically be negative, so if ΦA (Φ, -V a ) is negative, Electrons cannot reach the target. The surface potential Φ1 of the target is usually 50 volts or less, and for example, if Φ is 100 volts, electrons with ■8 smaller than 50 electron volts cannot reach the target. Therefore, most of the beams generated due to causes (2) and (3) cannot become the cause of the returned beam image.

The above is the reason why we thought that the reflected electrons mainly due to elastic scattering are attributed to the returned beam image.

Next, we will discuss theoretical considerations for reducing elastic scattering.

The probability of elastic scattering between electrons and atoms can be calculated as follows (for example, "Quantum Theory of Scattering" by Shigenobu Sunagawa, Iwanami Zensho, p. 43, 1977).As shown in Figure 8, the probability of elastic scattering per second When one electron is incident at a velocity V through a unit area and is scattered by an atom with an atomic number (number of protons) Z, at a point far enough in front of the atom, it forms a unit solid angle in the direction of the scattering angle θ. The ratio σ(θ) (differential cross section) of the number of scattered electrons is expressed as follows in the cgs unit system.

(2) Here, A(θ) is called an atomic scattering factor, and assuming that the electron density distribution is a function ρ(r) of only the distance r from the atomic nucleus, it is as follows.

Here, if h is Brang's constant, hK/2π represents the change in electron momentum due to scattering, and kW/2π=2mvs
It is expressed as in (θ/2)·(4).

When A(θ) is set to zero in equation (2), it becomes the differential cross section when only the atomic nucleus exists. Therefore, A(O) has the effect that the electrostatic Coulomb field due to the atomic nucleus is suppressed by the presence of electrons around the atomic nucleus.

The electron density distribution ρ can be expressed as the square of the absolute value of the wave function ψ of the electron bound to the atomic nucleus.

ρ=l'FI"...(5)
For example, the wave function of an electron in a hydrogen atom in the ground state is spherically symmetric and is given as follows.

Here a. is the Bohr radius of the hydrogen atom and is given by the following equation. .

ao=h”/ (4z”me”) −(7)
By substituting equations (5) and (6) into equation (3), the atomic scattering factor A(0) can be found as described above.

A(θ)mi□...(8)(1+λ2)2 Here, . ■ is the energy of the incident electron (in electron volts)
Then, πe" 2m = 4.694 J';; 5in (θ/2) - (10)
becomes.

For example, when the energy of the incident electron is 100 electron volts and the scattering angle θ is 180@ (backscattering), A(θ)=2.
06X10-' (11), which is very small, and there is almost no "1-power" effect due to electrons.

This can be considered to hold true for atoms other than hydrogen atoms as well.

Therefore, the following two things can be said from the result that the expression A(θ)=O in Expression (2) is considered to be a good approximation.

(1) If the atomic number 2 is reduced, elastic scattering becomes smaller.

(2) If the velocity V of incident electrons is increased, elastic scattering becomes smaller.

The above discussion is about scattering between one isolated atom and an electron. In reality, there are many atoms in the surface material of the electrode plate (110), which are closely bonded, and electrons are densely distributed near the electrode plate surface, so there are no electrons on the actual electrode plate. It is difficult to calculate the differential cross section of a hit. However, the trends (1) and (2) above can be considered to exist.

The results of (1) and (2) above suggest a method that can reduce the contrast of the returned beam image. Namely.

Possible methods include (a) reducing the atomic number (or average atomic number) of the surface substance on the electrode plate (110), and (b) increasing the potential of the electrode plate.

Next, we will discuss the results of experiments based on the above considerations.

First, in order to confirm the effect of (1) above, the electrode plate (1
The contrast of the returned beam images was measured by changing the surface materials of jO). The surface substances, in descending order of 2, are carbon (2=6.0), crystallized glass (
Sin, 46%, Al220°16%, Mg017%
, 010%, F4%.

B2O37%, z=to, 3), chromic oxide (Cr
Oz ; Z = 14,4), stainless steel (F
e71%.

Ni 10%, Cr 19%; Z=25.8) was used. Immediately after the light is uniformly incident on the photoconductive target and the light is blocked, the abnormal area 402 and the normal area 40 shown in FIG.
The difference in signal output with 3 was measured as contrast.

In Figure 9, the horizontal axis is the average atomic number Z of the surface substance,
This figure shows the results of contrast measurement. From this figure, it can be seen that the contrast increases almost as the atomic number Z increases, confirming the effect of (1) above.

Next, in order to confirm the effect of (2), in the case where the surface substance is carbon, the voltage Ea of the electrode plate (110), and the bias voltage E of the deflection electrode (108) are determined. ,.

The ratio of the voltage EC4 of the mesh electrode (111) is 1:1:
2, all electrode voltages were varied and the contrast of the returned beam image was measured. In addition, when E0□ (f! common with the electron gun acceleration voltage) is changed, the voltage of the grid (E
Adjusted c1.

FIG. 10 shows the measurement results. From the figure, the contrast is
It was found that the voltage decreased approximately in proportion to the reciprocal of the voltage EC2, confirming the effect of (2) above.

From the above two experimental results, it can be seen that the contrast of the returned beam image is approximately proportional to Z/V.

A white object (20001X) is imaged through a lens with an F value of 4.0, the beam current is set to twice the signal saturation, the signal current at that time is set to 100%, and the signal amplifier is amplified immediately after cutting off the light. When the power is further increased four times, the contrast of the returned beam image must be 1% or less, preferably 0.5% or less.

The contrast B measured under the above conditions can be approximately expressed as a function of the average atomic number Z of the surface substance and the voltage V of the electrode plate (110) as follows.

B = 11.3
Must be 44 or less.

Therefore, Z/V can effectively reduce the returned beam image.
The range is Z/V≦0.044 (14).

The above explains the causes of the return beam image and how to reduce it. However, with the electrode configuration simply shown in FIG. 1, increasing the voltage of the electrode plate (110) increases the magnification of the electro-optical lens and reduces the resolution of the image pickup tube.

In addition, if, for example, carbon with a small atomic number is attached to the electrode plate (110), the affinity between the electrode plate (for example, made of stainless steel) and the carbon is small, so the electrode plate (110) may be When heated with a high-frequency magnetic field, carbon often peels off and adheres to the photoconductive target.

Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 11 shows an embodiment of the present invention.

110 is an electron gun electrode, and 108 is a deflection electrode.

An auxiliary electrode 1100 is made of a conductive material such as stainless steel. A voltage higher in potential than that of the electron gun electrode 110 and the deflection electrode 10B is applied to the auxiliary electrode 1100, and since the average atomic number Z of stainless steel is 25.8, from equation (14), the voltage applied to the auxiliary electrode is 586 V or more. is suitable.

FIG. 12 shows another embodiment of the invention. Electron gun electrode 1
10 has a cylindrical part 1140, and an auxiliary electrode 1110
forms a ring. The material of the auxiliary electrode and the applied voltage are the same as in the embodiment shown in FIG.

Furthermore, in the present invention, we devised a method to reduce the return beam image by using an electrode configuration that does not reduce the resolution of the resolution tube of the image pickup tube and also makes it difficult for one surface substance to peel off.

FIG. 13 shows the electrode configuration. In this configuration.

An insulator 1120 facing the electrode plate (110) is provided,
Further, a conductive material 1130 was provided facing the insulator or on the surface of the insulator. When a high voltage is applied to the conductive material, the returned beam image is reduced, but in the meantime, due to the influence of the voltage, an electrostatic lens is formed near the electrode plate 110, the magnification of the electron optical system increases, and the image pickup tube resolution deteriorates. In this embodiment, the influence of high voltage is reduced by adding an elongated cylindrical electrode to the electrode plate (110).

Further, in this embodiment, ceramic is used as the insulator 1120, and aqua adduct (mainly composed of graphite powder and potassium silicate) having a small atomic number is applied as a conductive material thereon.

In this case, there is little chance that the Aquaduck will peel off due to the strong adhesion of potassium silicate to the ceramic.

Further, in this embodiment, the bias voltage Ea3 of the deflection electrode is 180V, which is lower than the voltage of the conductive material 1130 (350V). This is the return beam conductive material 113
The beam is deflected to 0, making it easier to hit the conductive material and reducing the contrast of the returned beam image more effectively.

In addition, by setting the voltage of the conductive material to be equal to the high voltage of the mesh electrode, it is possible to prevent an increase in the number of power supplies that supply different voltages.

In the above example, the insulator 1120 and the conductive material 1130
Although a flat plate-like structure is shown as shown in FIG. 14, any changes such as making it into an arbitrary rotationally symmetrical shape as shown in FIG. 14 are within the scope of the present invention.

Next, another example will be described. FIG. 15 shows a developed view of the deflection electrode used in this example.

An auxiliary electrode (1310) is inserted in a comb-like shape into the four deflection electrodes (H", H-, V", V-) near the electron gun section. This auxiliary electrode voltage is set lower than the bias voltage Ec3 of the deflection electrode, so that the returning beam can be easily deflected to the conductive material (1130). This ensures that the majority of the return beam is a conductive material (113
0), the contrast of the returned beam image can be reduced.

Note that by making this auxiliary electrode voltage equal to the voltage of the cathode (101), it is possible to prevent an increase in the number of power supplies that supply different voltages.

The gist of the invention described above is to arrange a conductive substance facing the electrode plate of an electron gun, and calculate the relationship between the average atomic number Z of the surface substance of the conductive substance and the voltage V' using the equation (14). within a defined range, preferably the voltage of the electrodes around the conductive material is smaller than the voltage of the conductive material to facilitate deflection of the return beam towards the conductive material and reduce the contrast of the return beam image. It is to be.

The above explanation was made using the MS type image pickup tube as an example.
It goes without saying that the present invention can also be applied to other types of SM, MM, and SS type image pickup tubes.

(Effects of the Invention) As described above, according to the present invention, the contrast of the return beam image in the image pickup tube can be reduced, and the image quality of the video camera can be improved.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of the MS type image pickup tube, Fig. 2 is a developed view of the deflection electrode, Fig. 3 is a diagram showing the trajectory of the electron beam in the MS type image pickup tube, and Fig. 4 is a view showing the return beam image. Figure 5 shows a square window mesh electrode, Figure 6 shows the electrode structure around the electron gun, Figure 7 shows the energy distribution of reflected electrons, and Figure 8 shows the reflection of electrons by atoms. Figure 9 is a diagram showing the relationship between the average atomic number of the material on the surface of the electrode plate and the contrast of the returned beam image. Figure 10 is a diagram showing the relationship between the electrode plate voltage and the contrast of the returned beam image. FIG. 11 is a diagram showing an embodiment of the invention, and FIGS. 12 to 15 are diagrams showing other embodiments of the invention. 101... Cathode, 102... First grid electrode, 1
03... Second grid electrode, 104... Microhole, 105
...Tube body. 106... Focusing coil, 107... Photoconductive target, 108... Deflection electrode, 109... Glass substrate,
110... Electrode plate, 111... Mesh-like electrode, H
", H-... Horizontal deflection electrode, v", v-... Vertical deflection electrode, Z... Tube axis direction, F... Electrode plate position, T...
... Angular direction of the tube axis, R1 ... Deflection amount of the forward beam, R7 ... Arrival position of the return beam to the electrode plate, R8
...Position where the reflected beam reaches the target, 301.
...Outbound beam, 302...Return beam 11.303.
... Reflected beam, 401 ... Drawing, 402 ... Return beam image, 403 ... Normal part, 501 ... Disk electrode, 601 ... Cylindrical electrode, e, ... Incident electron, e
a...Scattered electron, C...Atom, ■...Electron incident direction, 0...Scattering angle, Z...Atomic number, M...Inverse proportional curve, 1120...Insulator , 1130... Conductive material, 1140... Cylindrical electrode for "Shiyahei",
1310...Comb tooth-shaped auxiliary electrode, 1100.1110
...Auxiliary electrode. 7・-1

Claims (1)

[Claims] 1. An electron gun unit that has a vacuum vessel and at least a cathode provided inside the vacuum vessel and generates and controls an electron beam;
It has a target part that forms an electrical pattern corresponding to an optical image, and a mesh-like electrode located between the electron gun part and the target part and close to the target part. In an image pickup tube that focuses and deflects a beam onto the target section and extracts an electrical signal corresponding to an optical image from the target section, a portion facing the electron gun or a surface between the electron gun section and the mesh electrode is provided. An auxiliary electrode having a conductive substance on at least its surface is disposed above the conductive substance, and the potential of the conductive substance is set to be higher than the highest potential of the electron gun, and the average atomic number of the conductive substance is set to the potential difference with the cathode. The value divided by (volts) is 0.04
4 or less. 2. The image pickup tube according to claim 1, wherein the auxiliary electrode has a conductive material on the surface of an insulator. 3. In claim 1, a hole is provided in a portion of the auxiliary electrode that includes the tube axis, and the cylindrical electrode concentrically connected to the electron gun portion protrudes through the hole to the mesh electrode side. Characteristic image pickup tube. 4. An image pickup tube according to claims 1, 2, and 3, characterized in that the potential of the conductive material of the auxiliary electrode is equal to the potential of the mesh electrode. 5. In any one of claims 1 to 4, in an electrostatic deflection imaging tube that deflects an electron beam by the action of an electric field of a deflection electrode formed on the inner wall of a vacuum container,
An image pickup tube characterized in that a comb-shaped electrode maintained at the same potential is inserted into a portion of the deflection electrode near the electron gun section, and the potential thereof is lower than the bias voltage of the deflection electrode. 6. The image pickup tube according to claim 5, characterized in that the potential of the comb tooth-shaped electrode is equal to the potential of the cathode.