JPH0213416B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is a device provided in an image pickup tube having an electron system that generates an electron beam, the electron gun having a cathode, a cathode, a a first anode having an aperture, a second anode having a beam-limiting aperture, and a focusing lens for focusing the electron beam onto a photosensitive layer deposited on the signal plate, the apparatus applying a positive voltage to the cathode to the first anode; The present invention relates to an apparatus comprising an image pickup tube comprising means for supplying a second anode with a positive voltage that is at least ten times as positive as the positive voltage supplied to the first anode.

[Conventional technology]

An overview of conventionally known image pickup tubes includes the Vidicon (trade name) type image pickup tube developed by the American company RCA. This name is often used interchangeably, but officially it should be defined as a photoconductive image pickup tube.

Further, Plumbicon (trade name) developed by Philips Corporation, the applicant of the present invention, is known, and Sachicon (trade name) developed by NHK Giken of Japan and others is also known. All of these are classified as photoconductive image pickup tubes.

One of the factors that determines the characteristics of an image pickup tube is the response speed.
That is, the speed with which the device responds to changes in light intensity. The response speed is determined by the fact that the charge supplied to a pixel by the electron beam during a short period of time when the electron beam passes through a certain pixel is determined by the velocity distribution of the electrons in the electron beam. The actual effect of response speed in the image pickup tube is expressed as beam current inertia.

This will be explained in more detail as follows. When light enters the photosensitive layer, the potential of this layer increases to a certain level, V _Light . When the light incident on the photosensitive layer is blocked, the photosensitive layer tends to return to its initial stable state. This return to a stable state is effected by the action of an electron beam scanning the photosensitive layer.

In steady state, the mesh electrode (typically 900V)
and the photosensitive layer (from 900−V _Light)
900 V), and since the electrons have to pass through such a retarding electric field, only electrons with a velocity above a certain minimum velocity can reach the photosensitive layer. Electrons formed by the cathode have a Maxwellian velocity distribution. Therefore, a certain amount of time is required for the above-mentioned stabilization, and this is called beam current inertia.

To measure the effect of Maxwellian distribution on beam current inertia, we replace the photosensitive layer with a conductive layer.
Add an adjustable potential to this. An electron beam having a constant beam current intensity corresponding to the potential on the conductive layer is made incident on this layer, and the current intensity accepted by the conductive layer is measured. The resulting curve is called an acceptance curve, and it shows the relationship between the voltage of the photosensitive layer with respect to the cathode and the current in the photosensitive layer.

This acceptance curve is closely related to the velocity distribution of the electrons in the beam, since only electrons with a velocity above a certain level can reach this layer (depending on the potential of the layer).

(1) Triode electron gun Considering the electron beam formation structure of the electron gun of this type of image pickup tube, the cathode at zero potential and the + (plus)
A three-pole structure (triode structure) was first developed in which a negative potential grid was placed between a high potential anode.

This structure is also called a crossover type, and the electron beam extracted from the cathode is quickly focused by the convex lens effect of three electrodes including the cathode to form a crossover, and a beam with a diameter of several tens of micrometers is produced on the rear side. A restriction hole is arranged to block beams with a large divergence angle, reduce deflection aberrations, and utilize only high-quality beams.

For example, Philips Technical Review
Vol.29, 1968, No.11 PP325-335 paper “A light weight experimental color
television camera” has a cathode, a grid, and an anode.
A device is described in which an electron beam generated by an electron gun is crossed over by an electric field between these electrodes. This crossover is formed approximately in the anode region. The openings in the grid and the anode both have a cylindrical shape. The anode forms an assembly with the first electrode of the focusing lens, and a positive voltage of 300 volts is applied. The crossover is imaged onto the photoconductive layer by a focusing lens.

FIG. 1 schematically shows the flow of an electron beam in such a known triode electron gun. According to this diagram, the cathode K is set to the ground potential of OV, and the first grid G1 is _set to - With a negative potential of 40V and a positive potential of +300V on the second grid _G2 ,
Due to the length effect between them, a beam crossover was formed just beyond the first grid _G1 at a negative potential as shown in the figure, and a beam limiting hole several tens of μm in diameter was placed beyond the second grid _G2 at a positive potential. It is something. The solid line in the figure shows the flow of the beam, and the dotted line shows its envelope.

Considering the electron emission characteristics of the known triode electron gun of the image pickup tube, the following can be said.

The velocity distribution of the electron beam emitted from the cathode originally exhibits a Maxwell distribution determined by the temperature of the cathode. However, the three-electrode electron gun structure had the drawback of generating excessive high-speed electrons, as will be described later. In other words, there was a characteristic in which more high-speed electrons were generated in the beam than the amount corresponding to the Maxwellian distribution. Such excessive high-speed electrons adversely affect beam current inertia and thus response speed.

In a triode electron gun, the most important factor in generating high-speed electrons is the interaction between the electrons in the electron beam. It has been confirmed that this interaction is an important cause of excessive high-speed electron generation. The interaction occurs, for example, between electrons moving back and forth along a certain path. In this case, the electrons repel each other, causing the front electrons to move more quickly and the rear electrons to move more slowly, so that an excess of high-speed electrons is formed.

As mentioned above, the three-pole electron gun causes crossover of the electron flow, and therefore has the drawback of large beam current inertia. Therefore, in use, if there is a high brightness point on the screen, the afterimage time at that point becomes longer.

(2) Two-pole electron gun
No. 912893, corresponding to U.S. Patent No. 3831058), by making the laminar flow constant without forming a crossover, the beam current inertia was significantly reduced compared to the triple-electron gun structure. We proposed a two-pole electron gun type image pickup tube.

The two-pole (diode) electron gun method mentioned here does not mean that there are two electrodes, but rather it is a method in which electrons are attracted at a positive anode potential relative to the cathode potential, and the operation of a diode tube (diode) is It is defined in the sense that it is the same as the principle. This electron gun is also called a laminar flow type.

FIG. 2 is a schematic diagram showing the electron beam flow and equipotential lines in the first embodiment of the known laminar flow type (dipolar) electron gun type image pickup tube published in Japanese Patent Publication No. 51-32443.

In the example of FIG. 2, the cathode K is at 0V, the grid G is at -6.5V during scanning, and the anode A is at +50V. The beam becomes a laminar flow as shown, and no crossover occurs. In addition, grid G applies a large negative voltage such as -175V during flyback.
The beam current is set to 0. Note that the diameter of the apertures in the grid is much larger than the diameter of the beam-limiting apertures in the anode.

FIG. 3 is a diagram showing the flow of the electron beam and the equipotential lines of the second embodiment, also disclosed in Japanese Patent Publication No. 51-32443.

In a laminar (dipolar) electron gun, the current density of the electron beam in the direction from the cathode to the anode does not increase or increases very little, preferably decreases (i.e. no crossover is formed). This significantly reduces beam current inertia.

In this two-pole structure, the electron flow does not create a crossover, and the electron flow is made to flow as parallel as possible, that is, to form a laminar flow, which eliminates the disadvantage of the large beam current inertia as in the three-pole structure mentioned above. .

In addition, in an image pickup tube with a two-pole electron gun structure that does not cause beam current crossover, an intermediate electrode having an aperture larger than the aperture diameter of the anode is provided between the cathode electrode and the anode electrode, and the intermediate electrode has a potential between the cathode and the anode. In addition, an image pickup tube with a structure that reduces power loss at the anode electrode was developed in U.S. Pat. No. 53-94554.
(published on August 1, 1978).

In this prior art, the total power consumption is said to be approximately 1/9 of that of the previous technology.

[Problem to be solved by the invention]

As mentioned above, the dipole electron gun improves the drawbacks of the triode electron gun, but if there is a strong light part within the image pickup tube screen, if this strong light part moves, the target plate will become unstable. As a result, there is a phenomenon called a comet tail, in which a tail of white light follows a strong light, and this causes discomfort to viewers.
To prevent this, after amplifying the target signal,
returns to the first anode and increases its positive potential;
Dynamic beam control is used to increase the beam current so that more electrons are extracted from the cathode.

If dynamic beam current control is to be applied to a known two-pole electron gun, it is necessary to be able to temporarily increase the beam current by a factor of 5 to 10.

In a conventional two-pole electron gun in which no crossover is formed, the beam current is directly proportional to the cathode current, so if you want to increase the beam current, you must also increase the cathode current by the same factor.
This places the cathode under a heavy load, resulting in a significant reduction in the life span of the cathode.

(Objective of the Invention) The present invention does not have a large beam current inertia like the known triode electron gun, and has the drawbacks of the above-mentioned dynamic beam current control of the dipole electron gun structure and the short life of the cathode at that time. The purpose is to further improve the

In other words, it is an object of the present invention to perform dynamic beam current control that allows the increase in beam current with a much smaller cathode load using a control signal with a smaller amplitude than in known two-pole electron guns; An object of the present invention is to provide an apparatus equipped with an image pickup tube having a small beam current inertia.

[Means to solve the problem]

The present invention is an image pickup tube with a semi-dipolar electron gun structure that is a further improvement on the above-mentioned two-pole electron gun structure, and solves this problem by reversely using the beam crossover that was conventionally prevented from occurring. It is something.

An apparatus equipped with an image pickup tube of the present invention focuses an electron beam at a position between a first and second anode to form a crossover, and changes the electric field of the lens to form a crossover in the beam-limiting aperture. The invention is characterized in that means are provided for bringing the beam closer to or away from the beam limiting aperture.

[Effect]

In the present invention, by controlling the position of the electron beam crossover, it is possible to increase the electron beam incident on the target without substantially increasing the cathode load compared to a conventional two-pole electron gun.

That is, in the semi-dipolar electron gun of the present invention,
The voltage at the first anode is
When increasing with the beam current control voltage, the higher current density portion of the electron beam, or crossover, moves towards the second anode, so that a larger proportion of the total cathode current is transferred to the second anode. It will pass through the constriction section. As a result, the beam current increases at a rate greater than the value proportional to the cathode current, so the known 2
There is no need to amplify the target signal returned to the first anode as in the case of a polar electron gun.

〔Example〕

The present invention will be explained in more detail below with reference to the drawings.

FIG. 4 shows an embodiment of an image pickup tube according to the present invention. This image pickup tube is a so-called plumbicon type image pickup tube as a whole, and is equipped with a glass outer case 1, which is covered with a front glass plate 2 on one side of the glass outer case. An adhesion layer 3 is provided, the adhesion layer 3 comprising a photosensitive layer such as a photoconductive layer;
It is composed of this photosensitive layer and a conductive transparent signal plate between the front glass plate 2. The photoconductive layer consists primarily of specially activated lead monoxide, and the signal plate consists of conductive tin dioxide.
The connection pin 4 of the imaging tube is arranged on the side of the glass outer case 1 opposite to the adhesion layer 3. Along the central axis 5, the imaging tube is equipped with an electron gun 6 and a focusing lens 7. Furthermore, the image pickup tube is equipped with a mesh electrode 8 for making an electron beam perpendicularly incident on the adhesion layer 3, and a set of deflection coils 9 shown diagrammatically in the figure. These deflection coils 9 operate to deflect the electron beam generated by the electron gun 6 in two mutually perpendicular directions, and are arranged around the glass outer casing 1.

The electron gun 6, which is the main part of the present invention, has a cathode 10,
A first anode 11 and a second anode 12 are provided. The adjustment means of these elements and their connections to the connecting pins 4 are not shown in order to simplify the drawing. Next, the electron beam forming structure will be explained. As shown in detail in the enlarged view of FIG. 5, the first anode 11 has a small opening 13. The opening in the second anode 12 is partially closed by a plate member 14 having a small opening 15, the diameter of which is the same as that of the first anode.
The diameter is approximately 1/4 of the diameter of the opening 13 in the anode 11.

In this way, a lens electric field is formed between the first anode 11 and the second anode 12, thereby forming an electron beam crossover between both anodes as described later. Note that this lens electric field is selected so as not to actually have an adverse effect on the electron emission itself of the cathode 10.

The electron beam is focused onto the adherend layer 3 by a focusing coil 16 .

FIG. 5 is an enlarged sectional view of the main parts of the electron gun shown in FIG. 4. The electrode is mounted on a metal support 17 in a known manner.
and are arranged and connected to each other via a glass rod 18. The electron gun includes a cathode 10 and a first anode 11 having an aperture 13 with a diameter of 0.2 mm in a preferred example.
Equipped with. The distance between the cathode 10 and the first anode 11 in the direction of the central axis 5 is 0.3 mm in a preferred example.
shall be. Plate member 14 facing second anode 12
The diameter of the opening 15 is preferably 0.05 mm. Furthermore, the first and second anodes 11 and 1
The distance between 2 is 0.7mm. When the potentials of the cathode 10, the first anode 11 and the second anode 12 are set to the values shown, ie +10V and +300V, the electron gun can operate the crossover formed between the two anodes in an optimal state.

FIG. 6 is a diagram of the operating principle of the electron gun shown in FIGS. 4 and 5. For convenience of explanation, the spacing between the electrodes and the dimensions of the opening in the anode are not exactly the same as those in the preferred example in this description. is not supported.

Furthermore, in FIG. 6, the potentials of the first anode 11 and the second anode 12 are shown by variable voltage sources 24 and 25 solely for the purpose of explaining dynamic beam control, and this does not necessarily mean manual control. It's not a thing.

The first anode 11 is connected to a variable voltage source 24 and is operated at a small positive potential of 5 to 30 volts with respect to the cathode 10. The cathode 10 and the first anode 11 constitute an electron beam source, and the cathode current is determined by the potential of the first anode 11. Under typical operating conditions, first anode 11 will be approximately +10 volts relative to the cathode. First anode 11
and the spacing between the second anode 12 and the potential of the second anode 12 such that a lens electric field is generated forming a crossover 22 that focuses the electrons emitted from the cathode onto the beam axis 5 in the region 23 between the two anodes. It is selected as follows.

The second anode 12 is connected to a power source 25 and operated at a potential between +100 and +400 volts, typically about +300 volts, relative to the cathode 10.
The aperture 13 of the first anode 11 is made small enough so that the lens electric field in the region 23 does not affect the electron emission of the cathode. The diameter of the opening 15 of the second anode 12 is approximately one quarter of the diameter of the opening 13 of the first anode. Proper selection of the diameter thus limits the cross section of the beam to a diameter compatible with the focusing coil 16. The second anode 12 acts as an accelerating electrode in addition to also acting as a beam-limiting element and generating a lens electric field.

According to this configuration, the beam current can be greatly changed by a relatively small change in the potential of the first anode. That is, when the voltage of the first anode is increased, the number of electrons extracted from the cathode increases, and the lens electric field in the region 23 changes so that the crossover 22 approaches the opening 15 of the second anode 12. Since, relative to the current, a larger portion of the emitted electron beam current passes through the aperture 15, the increase in beam current will be greater than proportional to the increase in cathode current. Therefore, with this electron gun configuration, the beam current can be significantly increased with a relatively small increase in the amount of electrons extracted from the cathode.
Similarly, by reducing the voltage on the first anode, the beam current is reduced by moving the crossover 22 away from the second anode 12 to reduce the number of electrons passing through the aperture 15. Can be done. Therefore, according to the present invention, the beam current can be controlled with a signal having a relatively small amplitude change, with almost no load change applied to the cathode.

〔Effect of the invention〕

FIG. 7 shows three acceptance curves for explaining the effects of the present invention.

In the figure, the vertical axis shows the current intensity (A) accepted by the photosensitive layer, and the horizontal axis shows the voltage (V) of the photosensitive layer.

The photosensitive layer voltage is plotted on a linear scale on the horizontal axis in units of 0.2 volts, and the accepted current is plotted on a logarithmic scale on the vertical axis in units of nanoamperes.

For comparison purposes, FIG. 7 also shows acceptance curves for known dipole and triode electron guns.

In FIG. 7, the values of the total beam current of each electron gun were made equal to about 700 nA so that the influence of each electron gun on the response speed of the photosensitive layer could be compared.

In Figure 7, the central curve 40 (T=1300
〓) is an acceptance curve of an embodiment of the device of the present invention.

In Figure 7, the left curve 50 (T = 1900〓)
is the acceptance curve of the three-pole electron gun, and the curve 60 on the right (T=1200〓) is the acceptance curve of the two-pole electron gun.

The acceptance curve is closely related to the velocity distribution of the electrons in the electron beam and is therefore a measure of the performance of the electron gun.

In fact, if the photosensitive layer is at a sufficiently high positive voltage, all of the beam current will be received by the photosensitive layer. As the voltage across the photosensitive layer decreases (in the negative direction), the current intensity that can reach the photosensitive layer decreases.

When an acceptance curve is obtained by plotting the logarithm of the acceptance current against the voltage of the photosensitive layer, the ideal acceptance curve for a true Maxwellian distribution has a first linear portion ( For example, indicated by dotted line 30)
and a second horizontal straight line (eg, shown by dotted line 32) indicating that full beam current is accepted.

Characteristics corresponding to Maxwellian distribution are shown by dotted lines for the curves of the electron gun of the present invention, the triode electron gun on the left, and the dipole electron gun on the right.

The higher the voltage of the photosensitive layer and therefore the lower the corresponding cathode temperature, the steeper the first linear section becomes.

Furthermore, at low voltages that can even negatively charge the photosensitive layer, excessive high-speed electrons cause a so-called tail (shaded area in the figure) in the acceptance curve.
occurs, which means that the further left the acceptance curve in Figure 7, the more high-speed electrons that deviate from the Maxwellian distribution are present in the beam.
The larger the tail, the more high-speed electrons are generated.

In the acceptance curve of the triode electron gun on the left,
It exhibits an acceptance current of about 0.1 nA at a photosensitive layer potential of 0 V (ie, a deceleration potential where the mesh electrode potential is 900 V).
This means that some electrons still overcome the deceleration potential, and in the figure, the area where such high-speed electrons exist is shown as region A.

Compare the regions between each acceptance curve and the first straight line portion (shaded areas A, B, and C in Fig. 7) indicating the presence of excessive high-speed electrons that deviate from the Maxwellian distribution for each acceptance curve. By doing so, the technical effects of the electron gun of the present invention can be understood.

Region B affected by excess electrons of the electron gun of the present invention
The area A affected by excess electrons in the acceptance curve of the triode electron gun is much smaller,
This is comparable to that of a conventional two-pole electron gun.

In the conventional triode electron gun having a crossover point, compared to the electron gun of the present invention and the conventional two-pole electron gun, an extremely large number of excessive high-speed electrons are generated, and therefore the beam current inertia is large. Response speed is poor.

On the other hand, even though the electron gun of the present invention has a crossover point, as can be seen from the comparison of corresponding regions B and C, the degree of generation of excessive high-speed electrons is almost the same as that of the conventional two-pole electron gun. Nothing has changed. In other words, the electron gun of the present invention has a response speed comparable to that of the conventional one.
It has characteristics comparable to a polar electron gun. Moreover, while maintaining its characteristics, the electron gun of the present invention has two conventional
Dynamic beam current control, which is difficult with polar electron guns, can be performed extremely efficiently.

In other words, the image pickup tube of the present invention uses a dynamic current control signal that increases the beam current with a much smaller cathode load and control signal than the dynamic current control signal in a two-pole electron gun with a known configuration.
This has the great effect of enabling beam current control.

[Brief explanation of drawings]

Figure 1 is a schematic diagram showing the operation of a conventional crossover type (tripole) electron gun, and Figures 2 and 3 are diagrams showing the electron beam flow and equipotential lines of a conventional laminar flow type (dipole) electron gun. FIG. 4 is a vertical sectional view of an embodiment of the image pickup tube of the present invention, FIG. 5 is an enlarged view of the main parts of the image pickup tube shown in the circle in FIG. 4, and FIG. 6 is the image pickup tube of the present invention. FIG. 2 is a diagram showing the operating principle of the system, and the variable supply voltage symbol is used merely to explain the dynamic beam current control. FIG. 7 is a diagram showing the acceptance curves of the electron guns of the known image pickup tube and the image pickup tube of the present invention, in order to show the characteristics of the image pickup tube of the present invention. 1... Outer box, 2... Glass plate, 3... Adhesive layer,
4... Connection pin, 5... Center shaft, 6... Electron gun,
7...Focusing lens, 8...Mesh electrode, 9...Deflection coil, 10...Cathode, 11...First anode, 12...Second anode, 13...Aperture, 14
... Plate member, 15 ... Opening, 16 ... Focusing coil, 22 ... Crossover, 23 ... Area, 2
4, 25...variable voltage source.

Claims (1)

[Scope of Claims] 1. An apparatus comprising an image pickup tube having an electron gun that generates an electron beam, wherein the electron gun has a cathode, a first anode having an aperture, and a beam limiting aperture sequentially along a central axis. a second anode having a second anode, a focusing lens for focusing the electron beam on a photosensitive layer deposited on the signal plate, the device providing a positive voltage to the first anode with respect to the cathode; In an apparatus comprising an imaging tube comprising means for supplying a second anode with a positive voltage of at least 10 times the voltage, a lens electric field for focusing the electron beam to form a crossover at a location between the first and second anodes; between first and second anodes; and varying the lens electric field to move the crossover closer to or farther away from the beam-limiting aperture to increase or decrease current in the electron beam. means are provided such that the diameter of the aperture of the first anode is at least twice the diameter of the aperture of the second anode, and the dimensions of the aperture of the first anode are such that the lens electric field formed between the first anode and the second anode An apparatus equipped with an image pickup tube, characterized in that the dimensions are such that it hardly affects emission. 2. A device equipped with an image pickup tube according to claim 1, wherein the diameter of the opening in the first anode is approximately 0.2 mm, the diameter of the opening in the second anode is approximately 0.05 mm, and the distance between the cathode and the first anode. about 0.3mm
An apparatus comprising an image pickup tube, characterized in that the distance between the first and second anodes is approximately 0.7 mm.