JPS6294082A - Method and device for controlling electronic beam quantity of image pickup tube - Google Patents

Abstract

PURPOSE:To execute a stable ABO control by operating the 1st lattice electrode at a positive voltage with respect to a cathode and applying a voltage signal corresponding to a return beam from a photoconductive target to the 2nd lattice electrode of an image pickup tube. CONSTITUTION:A beam current out of the cathode 1 of the image pickup tube 10 is absorbed by the 1st and 2nd lattice electrodes 2 and 3, and some of said current turns out to be a scan beam current IB. Some part of the scan beam current becomes a return beam current IR on a photoelectric conversion surface 11, and is absorbed by the 2nd lattice electrode 3. A resistance 20 inserted between the cathode 1 and an earth detects the voltage signal corresponding to the scan beam current, and simultaneously a resistance 12 converts a signal current taken out of the photoelectric conversion surface 11 into a voltage so as to detect. The signals detected by the resistances 12 and 20 are added by an adder circuit 21 to obtain a signal voltage VR corresponding to the return beam current. After a signal showing the difference between the signal voltage and a reference voltage 22 is amplified by an amplifier 23, it is applied to the 2nd lattice electrode 3, thereby executing the stable ABO control.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a scanning electron beam amount control method and apparatus for a low-retention image pickup tube equipped with a dipole electron gun.

[Background of the invention]

In a light guide fixed image pickup tube, a charge pattern corresponding to object illumination is generated on a photoconductive film, and an electron beam generated by an electron gun is scanned over the photoconductive film to sequentially discharge the charge pattern. The charging current corresponding to discharging is taken out as a signal. In the above-mentioned light guide fixed image pickup tube,
Conventionally, there has been a demand for reducing afterimages and expanding the light amount range.

Afterimage is a phenomenon that occurs because the charge generated by the object cannot be completely discharged in one beam scan, and it occurs because the charges left unread from the previous scan are read out together with the next scan. .

In particular, in an image pickup tube using a blocking photoconductive film, capacitive afterimages occur mainly with a time constant determined by the product of the capacitance of the photoconductive film and the beam resistance of the scanning electron beam.

A necessary condition for the beam resistance is that the velocity distribution of the electron group forming the electron beam is narrow. The electron group emitted from the cathode has a Maxwellian velocity distribution, but in the process of forming a narrow beam, the current density of the beam increases and the velocity distribution expands due to the energy relaxation phenomenon due to the Coulomb force between the electrons. It is known that This phenomenon is called the beige effect, and the expansion rate of the velocity distribution is approximately 1 (Z) for the axial current density J (Z) of the beam.
' is known to be proportional to '. Therefore, in an image pickup tube aiming at low image noise, it is necessary to suppress the increase in beam current density as much as possible. Therefore, the first
A bipolar electron gun has been proposed in which the grid electrode is operated at a positive voltage with respect to the cathode, and electrons are emitted from the cathode parallel to the tube axis to generate a laminar beam with high current density and no crossover. (For example, JP-A-50-39869, JP-A-54-129871).

FIG. 6 shows an example of a two-pole electron gun that satisfies the above-mentioned principle, in which 1 is a cathode, 2 is a first grid electrode, and a positive voltage E is applied to the cathode 1. Reference numeral 3 indicates a second grid electrode, which is provided with a minute opening 33 and to which a positive voltage E2 is applied. 4 indicates a generated electron beam, and when the applied voltage E4 is made variable, the electron beam 4 changes from a laminar beam shown by a broken line to a concentrated beam (a beam forming a crossover) shown by a solid line. FIG. 7 is a diagram showing the relationship between the first lattice voltage E and the beam current reaching the photoelectric conversion surface.

Point A is a normal operating point, which is a laminar beam state in which afterimage reduction is possible, and point B is a state where a crossover is formed. This is because the image pickup tube equipped with the electron gun shown in FIG. 6 can obtain a large beam current by making the first grid voltage E1 variable.

A: Control the beam amount according to the subject illuminance
BO operation (Automatic Beam Optim
izer) can be performed.

A conventional ABO circuit is shown in FIG. In the figure, 10 is an image pickup tube equipped with a dipole electron gun as shown in FIG. In the above conventional method, a signal current taken out from a photoelectric conversion surface 11 by electron beam scanning is converted into a voltage by a resistor 12, amplified by an amplifier 13, and then superimposed on a reference bias voltage 15 by an adder circuit 14 to be applied to a beam current control electrode. (
1st. (grid electrode) 2. The following equations hold true for the L circuit.

y5::-l5-R...== (1-)v, = B
−v s −−(2) Era1= v, +
V,, -...-(3) However, ■s: input signal voltage of amplifier 13, Is: signal current, R: resistance, vo
: Output signal voltage of amplifier 13, B: Amplification factor -E of amplifier
GI: Beam current control electrode voltage, Vl, l: Reference bias voltage.

Here, if the ratio between the beam current control electrode voltage and the beam 11 current is g□1, the following equations hold true.

■e = -g□1・EGI...(4)■. x
” gmx・V O1・・・・・・(5) However, 1
B: Scanning beam current, ■. 1: Bias value of scanning beam current.

When In is determined from the above five equations, the following equation [6] is obtained.

From=A-Is+1o1 (6) However, A=gffl-R-B. The above equation (6) shows the control characteristics of the scanning beam current of the circuit shown in FIG.
When A=1, ideal ABO operation is possible. However, the above circuit has two problems.

The first problem is that if capacitive coupling as shown in 17 exists between the first lattice pole 2 of the image pickup tube IO and the photoelectric conversion surface 11, a positive feedback circuit as shown in FIG. 9 will be formed. It is to oscillate. In the above case, since the polarity (negative polarity) of the signal voltage applied to the first grid electrode 2 is the same as the polarity (negative polarity) of the signal charge generated on the photoelectric conversion surface 11, the signal mixed by capacitive coupling is transferred to the photoelectric conversion surface 11. The second problem is that if the beam control circuit shown in FIG. 8 enters a beam shortage state during operation, oscillation may occur depending on the circuit conditions. When the beam becomes insufficient,
The signal current becomes independent of optical information and increases in proportion to the beam current, making the circuit of FIG. 8 a city return circuit. When the proportionality constant between the signal current and the beam current is F, l5=F·IQ...-(7), and equation (8) is established from equations (6) and (7).

The oscillation condition of the feedback circuit is determined by the denominator of equation (8), and if AF<1, no oscillation occurs. F changes depending on the characteristics and condition of the photoelectric conversion film 11, but is mostly a value close to 1,
In order to suppress oscillation, either satisfy the condition of A<1 or
It is necessary to devise measures to prevent the situation from entering into a beam shortage state.

The condition of A<1 can be achieved by lowering the amplification factor B of the amplifier 13, but since the value of gllll generally changes depending on the voltage of the first grid electrode 2, the value of B must not be determined with respect to the maximum value of gllll. It will no longer be possible. As a result, at the operating point where gllll is the minimum value, the amplification factor is insufficient and the control range becomes small.

[Purpose of the invention]

The present invention provides a beam amount control method for an image pickup tube that does not cause oscillation and operates stably even when capacitive coupling exists between the first grid electrode and the photoelectric conversion surface and a beam shortage state occurs during ABO operation. and a control device.

[Summary of the invention]

A method and device for controlling the electron beam amount of an image pickup tube according to the present invention includes: a cathode that emits electrons; and a first grid electrode having an aperture disposed downstream of the cathode.

A second grid electrode having a minute opening arranged after the first grid electrode.
In the electron beam amount control method and device for an image pickup tube having a grid electrode and a photoconductive target, the first grid electrode is operated at a positive voltage with respect to the cathode, and the first grid electrode is operated at a positive voltage with respect to the cathode to correspond to the return beam from the photoconductive target. By applying a voltage signal to the second grid electrode of the image pickup tube, stable ABO operation is performed and the amount of scanning electron beam of the image pickup tube is controlled.

[Embodiments of the invention]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing a first embodiment of an electron beam amount control device for an image pickup tube according to the present invention, FIG. 2 is a circuit diagram showing a second embodiment of the present invention, and FIG. 3 is a second grid electrode voltage FIG. 4 is a circuit diagram showing a third embodiment of the present invention, and FIG. 5 is a circuit diagram showing a fourth embodiment of the present invention. In FIG. 1, most of the beam current extracted from the cathode 1 of the image pickup tube 10 is distributed between the first grid electrode 2 and the second grid electrode 3.
A part of it becomes the scanning beam current IB. A part of the scanning beam current IQ becomes a signal current on the photoelectric conversion surface 11, but the remaining electrons become a return beam current IR and are absorbed by the second grid electrode 3.

Therefore, the return beam current IR is expressed by equation (9).

IR=IB-Is-.= (9) Since the actual circuit processes voltage signals, the voltage signal VQ corresponding to the return beam current IQ is as shown in equation (10).

vR= VB-VS ・--(10) However, vB is a voltage signal corresponding to the scanning beam current,
Detection is performed by a resistor 20 inserted between the cathode 1 and ground. Since the cathode current IC flows through the resistor 20 and the equation (11) holds between IC and IB, vB can be expressed by the equation (12).

■. = cz, ■e ・・・・・・(11)
ve= Rc・a・Is ・= ・= (1
2) However, α is a proportionality constant, and RC is the value of the resistor 20 inserted into the cathode 1.

On the other hand, since the signal current Is flows through the resistor 12, the above (1
) is generated. Therefore (1)
, (10), (12) to find VR.

A signal expressed by the following equation (13) is given.

vR=α-RC・IB-R-Is・・・・・・-(1
3) The signal of the above equation (13) can be easily obtained by adding the voltage signals generated in the resistors 12 and 20 using the adding circuit 21.

The second grid electrode 3 has vR shown in (13) and a reference voltage 22.
Since the difference signal is amplified by the differential amplifier 23 and added,
The following equation (14) holds true.

EG2=B(V.Z VR) ・・・・・・(14
) Here, B is the amplification factor of the differential amplifier, and VO2 is the value of the reference voltage 22.

Also, the ratio of the cathode current IC to the second grid electrode voltage is g, ll
If c, then equation (15) holds true.

C EG2=□...(15)me Here, the base rt pressure ■. 2 for convenience, J: Consider as a current source.

If we set Vnz = I oz' Ra, (13), (
Equation (16) shown below can be found from Equations 14) and (15).

g□.・B Ta = (IoRo + Rs-b a・R
c・IB)−...(16)α Then, by selecting R that satisfies R=RQ=Rs=a ·Re, the above equation (16) can be rewritten as equation (17).

A′ Ie = (I.+(s)・・・・−(
17) 1+A' However, A'=gfflc-B-R·α-1. (
17) In the first embodiment shown in FIG. 1 of the present invention, the larger A' is, the more ideal ABO becomes.
can be made to perform an action.

Also, a beam shortage condition occurs during ABO operation.

Even if the relationship in equation (7) is established between Is and IB and a feedback circuit is configured, the oscillation condition is not established as shown in equation (18) below.

Therefore, even if you enter a beam starvation condition.

Stable beam control can be performed.

Furthermore, even if capacitive coupling exists between the second grid electrode 3 and the photoelectric conversion surface 11, the polarity of the control signal voltage applied to the second grid electrode 3 becomes positive, and a negative polarity is generated on the photoelectric conversion surface 11. Since the polarity is opposite to that of the normal signal charge, a positive feedback circuit is not formed and oscillation does not occur.

The second embodiment shown in FIG. 2 has the same features as the first embodiment described above.
A voltage signal corresponding to the return beam current is applied to the second grid electrode 3, and a control signal is applied to the second grid electrode 3.
1 is characterized in that a voltage signal of /n is generated by a differential amplifier 25 and applied to the first grid electrode 2, and 24 is a reference voltage.

As described above, the ABO circuit of FIG. 1 increases the beam current by changing the laminar beam state shown by the broken line in FIG. 6 to the concentrated beam state shown by the solid line. On the other hand, in the second embodiment shown in FIG. 2, a positive control voltage is applied to the second grid electrode 3, and a positive polarity of about 1/10 of the second grid electrode voltage is applied to the first grid @ pole 2. By applying a positive voltage, the change to a concentrated beam state is suppressed,
ABO operation is always performed in a laminar flow beam state.

This two-electrode control force formula controls the voltage of the first grid electrode 2 by making it dependent on the voltage of the second grid electrode.
and the second grid electrode 3 can be considered as one electrode, and the relationship between the second grid electrode voltage and the beam current is a straight line shown in FIG. the result.

The ratio gmc between the cathode current and the second grid electrode voltage can be treated as an almost perfect constant, and more stable beam operation can be achieved.

The third embodiment shown in FIG. 4 is a modification of the circuit of the first embodiment, in which the signal corresponding to the return beam current is amplified by the amplifier 26, and then the voltage of the bias power supply 27 is adjusted using the DC clamp circuit z8. The ABO operation is the same as in the first embodiment.

The fourth embodiment shown in FIG. 5 is a modification of the second embodiment, in which the first grid electrode 2 and the second grid electrode 3 are controlled simultaneously. A signal corresponding to the return beam current is amplified by an amplifier 26 and applied to the second grid electrode 3 in a superimposed manner to a bias power supply 27 by a DC clamp circuit 28 .

Furthermore, a signal of 1/n of the control signal to be applied to the second grid electrode 3 is generated to the first grid electrode 2 by an amplifier 29, and is applied to the bias power supply 31 for the first grid electrode in a DC clamp circuit 30 in a superimposed manner. The ABO operation of the circuit of the fourth embodiment is similar to that of the second embodiment shown in FIG.

〔Effect of the invention〕

As described above, the method and device for controlling the electron beam amount of an image pickup tube according to the present invention includes a cathode that emits electrons, a first grid electrode having an opening disposed downstream of the cathode, and a stage subsequent to the first grid electrode. A second grating with micro apertures arranged in Ci'
In a method and apparatus for controlling an electron beam area of an image pickup tube having a city pole and a photoconductive target, -)-, the first grid electrode cathode is operated with a positive voltage, and the photoconductive target 71'' is By controlling the amount of the scanning electron beam using a signal corresponding to the return beam χ4, it is possible to ensure that there is a coupling between the first grating electrode and the photoelectric conversion surface, and that there is a beam shortage state during the ABO operation. The camera tube's faF remains stable without causing oscillation even when
・Beam amount control can be performed.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing a first embodiment of an electron beam amount control device for an image pickup tube according to the present invention, FIG. 2 is a circuit diagram showing a second embodiment of the present invention, and FIG. A diagram showing the relationship between voltage and beam current, FIG. 4 is a circuit diagram showing a third embodiment of the present invention, FIG. 5 is a circuit diagram showing a fourth embodiment of the present invention, and FIG. 6 is a two-pole electron A diagram explaining the operation of the gun, Figure 7 is a diagram showing the relationship between the first grid electrode voltage and beam current, Figure 8 is a conventional electron beam amount control circuit diagram, and Figure 9 is a diagram showing the case where capacitive coupling occurs. FIG. 1... Cathode 2... First grid electrode 3.
...Second grid electrode 11...Photoconductive target (photoelectric conversion surface) 21...Addition circuit 23.25...Differential amplifier 26.2
9... Amplifier 28.31... DC clamp circuit attorney Junnosuke Nakamura 1 Figure 2 1 C, ・'/1 28.31 DC back circuit 26 Between 27 Figure 8 Sakae

Claims (5)

[Claims] (1) A cathode that emits electrons, a first grid electrode having an aperture arranged after the cathode, a second grid electrode having a minute opening arranged after the first grid electrode, and a photoconductive target. In the electron beam amount control method for an image pickup tube, the first grid electrode is operated at a positive voltage with respect to the cathode, and the scanning electron beam amount is controlled by a signal corresponding to the return beam from the photoconductive target. Characteristic method for controlling the amount of electron beam in an image pickup tube. (2) The signal corresponding to the return beam is transmitted to the second
2. A method for controlling an electron beam amount of an image pickup tube according to claim 1, wherein the method is applied to a grid electrode. (3) The signal corresponding to the above return beam is transmitted to the first
Claim 1, characterized in that the signal applied to the grid electrode and the second grid electrode is applied simultaneously, and the amplitude of the signal applied to the first grid electrode is smaller than the amplitude of the signal applied to the second grid electrode. A method for controlling the electron beam amount of an image pickup tube. (4) The signal corresponding to the return beam is obtained from the cathode current of the image pickup tube and the signal current corresponding to the subject light. A method for controlling an electron beam amount of an image pickup tube according to any one of the above. (5) a cathode that emits electrons, a first grid electrode having an opening arranged after the cathode, a second grid electrode having a minute opening arranged after the first grid electrode, and a photoconductive target; In an electron beam amount control device for an image pickup tube, the scanning electron beam amount is controlled by obtaining a voltage signal corresponding to a first grid electrode to which a positive voltage is applied to the cathode and a return beam from the photoconductive target. What is claimed is: 1. An electron beam amount control device for an image pickup tube, comprising: means.