JPH08256287A - Electron beam control method in image pickup tube - Google Patents

Abstract

PURPOSE: To reduce the adjustment time for an automatic beam optimum (ABO) control function and to improve the yield of a low power impregnated cathode image pickup tube by improving reduction in a beam current in the ABO control in a television camera employing the low power impregnated cathode image pickup tube. CONSTITUTION: A DC potential (or amplification factor) of an ABO processing circuit A2 is made proportional to an integrated value of a signal current of the image pickup tube 1 in a television camera employing the low power impregnated cathode image pickup tube. Since a special ABO process circuit to manage a history of an integration value of a signal current of the image pickup tube 1 is not required, a beam current is increased so as to have provision for a screen requiring a high mean beam current by having only to add an integration circuit A5 to a DC recovery circuit of an existing ABO processing circuit A2 to attain a stable ABO characteristic.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improvement of the characteristics of a television camera using an image pickup tube when a large amount of light is incident.

[0002]

2. Description of the Related Art In general, a laminar flow diode gun type image pickup tube using a cathode in which porous tungsten is impregnated with barium oxide (hereinafter referred to as an impregnated cathode) consumes a large amount of power but has a high resolution image. It has the characteristic of being obtained. In recent years, a laminar flow diode gun type imaging tube (hereinafter referred to as a low power impregnation cathode imaging tube) with reduced power consumption by reducing the diameter of the impregnated cathode portion has been put into practical use, and a television camera such as a high-definition camera. Is used for.

The beam characteristics of the low power impregnated cathode image pickup tube will be described with reference to FIG. In FIG.
The horizontal axis E _C1 represents the voltage applied to the first control electrode (hereinafter referred to as the first grid or G1), and the vertical axis Ib represents the beam current.

The voltage E _C1 applied to G1 of this image pickup tube,
Alternatively, even if the current is, for example, substantially constant, if a large amount of beam current continues to flow for a long time, the beam current Ib of the image pickup tube decreases due to thermal deformation of the components of the image pickup tube. Therefore, for example, the characteristic shown by the solid line in FIG. 4 changes to the characteristic shown by the dotted line, and the beam current further decreases. Further, when a small amount of beam current continues to flow, this time the beam current decreases, and the decreasing tendency of the beam current due to factors such as the above thermal deformation disappears, and the beam current gradually recovers and increases, The characteristics are as shown by the solid line in FIG. Therefore, this fluctuation is repeated depending on the degree of the dynamic change of the beam current. It should be noted that this variation in beam characteristics is generally called beam drift.

In general, the low power impregnated cathode image pickup tube has a relationship that the beam diameter is substantially proportional to the beam current value. Therefore, when it is desired to reduce the beam diameter in order to increase the resolution of the image pickup tube, the number of beams should be as small as possible. It is what is desired to be used with electric current.

Based on the characteristics of the low-power-impregnated cathode image pickup tube described above, a conventional technique for improving the drift characteristic when a large amount of light is continuously incident on an image pickup apparatus using an image pickup tube to perform image pickup is described. , The electron beam control method of the image pickup tube described below (the automatic electron beam optimum control method: hereinafter, A
Known as BO (for example, Japanese Patent Publication No. Sho 53-3)
0564). This is because the image pickup device is designed so that an electron beam (hereinafter, referred to as a base beam) having a current amount about twice the signal current corresponding to the rated signal is made to flow through the image pickup tube when light is shielded or when a very low amount of light is incident. Set it. When the amount of light exceeding the rated signal is incident, the voltage of G1 is non-linearly controlled according to the signal current of the image pickup tube. The electron beam amount at this time corresponds to the base beam amount according to the signal current at this time. It will be the sum of the amount of current. As a result, even when the amount of incident light is about 8 to 16 times the amount of light corresponding to the rated signal, the electron beam corresponding to the amount of light can be kept larger than the signal current of the image pickup tube.

In such ABO control, the amplification degree of the amplifier of the ABO circuit which constitutes a negative feedback circuit for nonlinearly controlling the voltage applied to G1 of the image pickup tube according to the signal current of the image pickup tube is set. If it is large, the shortage of the electron beam is hard to occur, but it is a phenomenon (hereinafter referred to as ABO oscillation) in which the signal current of the image pickup tube changes independently of the incident light amount.
Due to the large amplification degree, oscillation (hunting) that occurs when the negative feedback system becomes positive feedback easily occurs, which is a problem. For this reason, the above-mentioned amplification degree cannot be made very large.

[0008]

FIG. 3 is a diagram showing the video signal voltage Vi of the output of the image pickup tube, the voltage E _C1 applied to G1, and the beam current Ib in the above-mentioned conventional technique in association with each other. It is a waveform diagram.

In the above-mentioned prior art, since the amplification degree of the amplifier of the ABO circuit cannot be set so large, when the image is picked up such that a large amount of light is incident on a large area like the waveform shown in FIG. When the light quantity continues, the beam quantity decreases due to the beam drift, and the video signal output is clipped due to the lack of the electron beam when a large quantity of light is incident, for example, the level of the portion indicated by the dotted line of the Vi waveform in FIG. But,
As shown by the solid line, the phenomenon of deterioration occurs.

Further, in a high-definition camera, the amount of base beam must be made small in order to give priority to high resolution, and the beam drift prevents the ABO oscillation even if the beam amount with respect to E _C1 changes.
The amplification degree of the O circuit must be reduced, and the electron beam tends to be insufficient.

That is, in the above-mentioned prior art, in order to make the electron beam larger than the signal current of the image pickup tube even when a large amount of light is incident, if the base beam amount and the amplification degree are set to be large, ABO oscillation easily occurs. , If you set it small, the beam will be insufficient. This makes the adjustment work of the base beam amount and ABO difficult, resulting in a time-consuming adjustment.

Therefore, conventionally, the characteristics of the image pickup tube, for example, the voltage or current of the control electrode (also referred to as a suppression electrode) and the characteristic of the electron beam (hereinafter, referred to as drive characteristic), the photoelectric conversion characteristic when a large amount of light is incident, etc. are allowed. There is a problem that the range that can be formed is narrowed, so that the yield of the image pickup tube is lowered and the cost of the image pickup apparatus is increased.

The present invention eliminates these drawbacks, improves the yield of a laminar flow diode gun type image pickup tube in which the diameter of the impregnated cathode is reduced to reduce the power consumption, and the base beam amount is reduced and the ABO circuit is adjusted. The purpose is to reduce the time.

[0014]

In order to achieve the above-mentioned object, the present invention provides a control electrode (G1) of an image pickup tube in an image pickup apparatus which nonlinearly controls the electron beam amount of the image pickup tube according to a signal current. The direct current is superimposed on the integrated value of the signal current of the image pickup tube, which has been integrated by an integrating circuit having a predetermined discharge characteristic.

The present invention also provides the amplification degree of the ABO circuit,
Integrated by an integrating circuit having a predetermined discharge characteristic,
The control is performed in proportion to the integral value of the signal current of the image pickup tube.

[0016]

As a result, in a high-definition camera using a laminar flow diode gun type image pickup tube in which the diameter of the impregnated cathode is reduced to reduce power consumption, the electron beam amount becomes the integral value of the signal current when a large amount of light is continuously incident. Controlled proportionally,
The base beam when a large amount of light is continuously incident is equivalently increased with respect to the base beam when shielded. Alternatively,
AB when the large amount of light is continuously incident, compared to the ABO amplification when the light is blocked
O amplification degree will increase.

Therefore, if the image pickup device is adjusted so that neither ABO oscillation nor beam shortage occurs when a small amount of light is incident, the beam becomes insufficient even if the beam amount slightly decreases due to beam drift when the large amount of light is incident. Does not arrive. Further, even if there are some individual differences in the characteristics of the image pickup tube (drive characteristics and photoelectric conversion characteristics when a large amount of light is incident), the ABO characteristics are improved, and ABO oscillation and beam shortage hardly occur.

Therefore, the yield of the image pickup tube is improved,
The base beam amount and ABO adjustment time are also shortened.

[0019]

1 is a block diagram showing an example of the overall configuration of the present invention. In FIG. 1, the incident light Lin is imaged on the target of the image pickup tube 1 by the lens 11, and the image signal current I
converted to sj. The video signal current Isj is equal to the preamplifier A1.
And the feedback resistor R2 converts it into a video signal voltage Vi. Here, Vi = Isj × R2.

In general, the video signal voltage Vi becomes the video signal output Vo by adjusting the black level, the white level and the gamma by the signal processing circuit A4. This operation is well known in the prior art, and the present invention is also applicable. Since it is not a directly related part, its explanation is omitted.

Further, the video signal voltage Vi is non-linearly amplified by the non-linear amplification circuit A3 of the ABO processing circuit A2 and becomes the voltage E _C1 of the control electrode G1 of the image pickup tube, which is about 8 to _{1 of} the rated signal.
A known ABO control is performed to keep the electron beam above the signal current of the image pickup tube even when the incident light amount is 6 times. Since this general ABO control is known, the description of the operation of the non-linear amplifier circuit A3 is omitted.

The video signal voltage Vi becomes a signal Vd integrated by the integrating circuit A5, and the above-mentioned AB signal is output by the DC mixing circuit A6.
DC is superimposed on the O signal voltage Va. Alternatively, although not shown, the integrated signal Vd may be input to the amplification degree variable circuit A7 to control the amplification degree of the ABO signal voltage Va. As a result, when a large amount of light is continuously incident, in the G1 voltage E _C1 applied to G1, there is no signal period corresponding to the base beam which is the electron beam at the time of the above-mentioned light blocking or the incidence of a low amount of light. The voltage value of (the period sandwiched between the periods of the signals generated by photoelectric conversion of the incident light) increases, and the base beam amount also increases accordingly.

In the present invention, the non-linear amplifier circuit A3 and the DC mixing circuit A in the ABO processing circuit A2 of FIG. 1 are used.
The order of connecting 6 and the amplification degree variable circuit A7 does not impair the present invention regardless of the order shown in FIG.

An embodiment of the integrating circuit A5, the DC mixing circuit A6 and the amplification variable circuit A7 in the ABO processing circuit A2 of the present invention will be described below with reference to FIGS. 5, 6 and 7. Also,
The video signal voltage Vi of the output of the image pickup tube according to the present invention and G1
The operation will be described with reference to FIG. 2, which is a waveform diagram showing an example of the relationship between the voltage E _C1 applied to the beam and the beam current Ib.

FIG. 5 shows an embodiment of an integrating circuit A5 used in the present invention, FIG. 6 shows an embodiment of a DC mixing circuit A6, and FIG. 7 shows an embodiment of an amplification variable circuit A7. Here, the integrator circuit of FIGS. 5A and 5B is a low-frequency pass amplifier circuit using a well-known technique of diode detection and an operational amplifier, and the circuit of FIG. 6A is a well-known transistor. 6B is a well-known capacitive coupling and transistor clamp circuit.
Since the circuits (a) and (b) are a combination of a well-known transistor amplifier circuit and a variable resistor using an FET, detailed description thereof will be omitted, and the operation of the circuit will be briefly described below.

The DC mixing circuit A6 of FIG. 6A and FIG.
The amplification degree variable circuit A7 in (a) is an ABO output circuit.
6A and 7A, the base beam amount of the image pickup tube is determined by the idling current flowing through the negative power source V _EE and the load resistor R10. Further, the voltage E _C1 0 of the control electrode at the time of emitting the base beam is determined by the base beam amount and the control electrode G1
It is determined by the impedance of.

In FIG. 6A, the transistor Q1 is proportional to the ABO signal voltage Va input to the base and the integrated signal Vd input via the resistor R11, and the emitter resistor R1
9 and a value inversely proportional to the resistance R11 are added to output a collector current I _C1 represented by the following equation (1). I _C1 = (Va + V _BE ) / R9 + (Va + V _BE + Vd) / R11 (1) Further, in FIG. 6B, the integral signal Vd is input to the emitter of the transistor Q5 via the resistor R5, and the ABO signal is input. The integral signal Vd is mixed with the reference potential of the voltage.

As a result, assuming that the waveform of the signal current Isj does not fluctuate when a large amount of light is incident and the same signal waveform is repeated, as shown in FIG.
1 voltage E _C1 has a constant waveform repetition and its peak value does not increase. However, in the present invention, as shown in FIG.
The G1 voltage E _C1 increases.

Therefore, as shown by the solid line in the waveform diagram of the beam current Ib in FIG. 2, the current value of the bottom portion corresponding to the base beam increases based on the value of the integral component of the signal current Isj. Therefore, as shown in FIG. 3, the peak value of the beam current Ib decreasing during the signal period is changed to a predetermined value as shown by a broken line in FIG. Can be held above the level.

As a result, the beam current Ib does not become insufficient even if the amplification degree of the amplifier of the ABO circuit is not increased so much, and the waveform of the video signal voltage Vi is clipped due to the beam shortage in the waveform diagram 3 described above. On the other hand, as shown in FIG.
Then, the video signal voltage Vi is not clipped.

In the above embodiment, the integrated value of the signal current of the image pickup tube is mixed with the emitter of the transistor circuit, but the present invention is not limited to this, and the current may be mixed with an operational amplifier, for example. Needless to say.

In FIGS. 7A and 7B, the Q of the FET is
The drain source resistance Rds of 2 or Q4 is inversely proportional to the integrated signal Vd input to the gate. Therefore, their amplification degree is proportional to the integrated signal Vd.

In FIG. 7A, the collector current I _C2 is I _C2
= (Va + V _BE ) / (R9 × Rds / (R9 + Rds)),
In FIG. 7B, the collector current I _C3 is I _C3 = (Va−
V _BE ) / (R7 × Rds / (R7 + Rds)).

In the above embodiment, the integrated value of the signal current of the input image pickup tube is mixed with the gate of the FET connected to the emitter of the transistor circuit. However, the present invention is not limited to this, and analog processing, for example, may be used. Needless to say, the gain may be changed by a multiplier using the.

[0035]

According to the present invention, there is no need to add a special (for example, digital processing) ABO process circuit that manages the history of the integrated value of the signal current of the image pickup tube, without existing. It is possible to obtain stable ABO characteristics with a small-scale analog system circuit devised from the ABO circuit. Therefore, although it is an ultra-high resolution, the beam amount decreases when a large amount of light enters a large area and the time elapses.
By using a laminar flow diode gun type image pickup tube with reduced power consumption, it is possible to realize a compact high-definition camera capable of taking good images even under the condition that the range of brightness in the same screen is wide.

Further, since the variation in the characteristics of the expensive low power impregnated cathode image pickup tube can be absorbed, the selection standard of the image pickup tube is loosened, and the low cost of the high power impregnated cathode image pickup tube can be achieved without lowering the yield. realizable.

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of the overall configuration of the present invention.

FIG. 2 is a waveform chart showing an example of an operation according to the present invention.

FIG. 3 is a waveform chart showing an example of an operation of a conventional technique.

FIG. 4 is a beam characteristic diagram of a low power impregnated cathode image pickup tube.

FIG. 5 is a circuit diagram showing an embodiment of an integrating circuit used in the present invention.

FIG. 6 is a circuit diagram showing an embodiment of a DC superimposing circuit used in the present invention.

FIG. 7 is a circuit diagram showing an embodiment of an amplification variable circuit used in the present invention.

[Explanation of symbols]

1: image pickup tube, A1: preamplifier, A2: ABO processing circuit, A3: non-linear amplification circuit, A4: video signal processing circuit,
A5: Integration circuit A6: DC mixing circuit, A7: Variable amplification circuit G1: First grid (control) electrode V _CC : Positive power supply, V _EE : Negative power supply, Vref: Reference power supply

Claims (5)

[Claims] 1. In a television camera using an image pickup tube and applying a current corresponding to a signal current value of the image pickup tube to a control electrode of the image pickup tube, a signal current of the image pickup tube is provided by an integrating circuit having a predetermined discharge characteristic. Current obtained by superimposing the current corresponding to the integrated value obtained by superimposing on the current corresponding to the signal current,
Alternatively, the current corresponding to the average value of the signal current of the image pickup tube is also superimposed on the current corresponding to the signal current, and the obtained current is applied to the control electrode of the image pickup tube. Beam control method. 2. The image pickup tube of a television camera having a circuit for controlling a voltage or a current applied to a control electrode of the image pickup tube in a nonlinear manner with respect to a signal current of the image pickup tube by using the image pickup tube. In a circuit for amplifying a signal voltage or a signal current applied to the control electrode of, the signal current or the signal voltage applied to the control electrode of the image pickup tube is integrated by integrating the signal current by an integrating circuit having a predetermined discharge characteristic. An image pickup tube characterized in that a current value corresponding to the value or a voltage value proportional to an integrated value obtained by integrating the signal current is superimposed, and an integral waveform of the signal current of the image pickup tube is applied to a control electrode of the image pickup tube. Electron beam control method. 3. A control electrode for a pickup tube of a television camera having a circuit for controlling the voltage or current of the control electrode of the pickup tube in a non-linear manner with respect to the signal current of the pickup tube. In a circuit that amplifies a signal voltage or a signal current applied to, the reference potential of the direct current reproduction of the amplifier circuit corresponds to an integrated value obtained by integrating the signal current of the image pickup tube with an integrating circuit having a predetermined discharge characteristic. An electron beam control method for an image pickup tube, characterized in that an integral waveform of a signal current of the image pickup tube is applied to the control electrode of the image pickup tube by changing. 4. A control of the image pickup tube of a television camera having a circuit for controlling a voltage or a current of a control electrode of the image pickup tube in a nonlinear manner with respect to a signal current of the image pickup tube using the image pickup tube. In a circuit for amplifying a signal voltage or a signal current applied to an electrode, the amplification degree of the amplifier circuit is changed in accordance with an integrated value obtained by integrating the signal current of the image pickup tube with an integrating circuit having a predetermined discharge characteristic. By so doing, an integral waveform of the signal current of the image pickup tube is applied to the control electrode of the image pickup tube. 5. A control of the image pickup tube of a television camera having a circuit for nonlinearly controlling a voltage or a current of a control electrode of the image pickup tube with respect to a signal current of the image pickup tube using the image pickup tube. In a circuit for amplifying a signal voltage or a signal current applied to an electrode, a multiplier or a variable amplifier inputs the integrated value obtained by integrating the signal current of the image pickup tube with an integrating circuit having a predetermined discharge characteristic. An electron beam control method for an image pickup tube, comprising applying an integral waveform of a signal current of the image pickup tube to a control electrode of the image pickup tube.