JPS6053988B2 - Image tube actuator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an imaging system configured to flow a beam current large enough to neutralize the charge image even if the amount of light incident on the image pickup tube becomes excessive due to a change in the subject. It relates to a tube actuator.

Generally, in image pickup tube operating devices using photoconductive type image pickup tubes such as vidicon, if the amount of electron beam that scans the photoelectric conversion surface of the image pickup tube becomes excessive, the resolution will decrease, so the beam amount should be adjusted appropriately. is being restricted to.

However, if the beam amount is uniformly limited, when a bright part of the subject is imaged, the charges accumulated on the photoelectric conversion surface cannot be completely neutralized with one electron beam scan, resulting in so-called whiteout. When this phenomenon occurs and the bright object part moves, a comet tail phenomenon similar to the tail of a common star appears on the monitor screen. As a solution to this problem, an automatic beam optimization circuit has been proposed that changes the beam control electrode voltage of the image pickup tube according to the magnitude of the signal current and increases the beam current only when a bright object part is imaged.

This circuit, which is described in detail in Japanese Patent Publication No. 52-36648, consists of a negative feedback circuit as shown in FIG. Here, set the mutual conductance of the image pickup tube 1, set the cathode current, set the beam current as I5, set the signal current, return beam current 1R1, set the beam current control electrode voltage as ECl, set the amplification factor of the comparator amplifier 2 as A, and set the reference power supply. The reference current from 3 is I
. , the resistance value of the resistor 4 is R, and the constant is α, the beam current 1 and the return beam current 1R can be respectively expressed as follows.

Also Therefore, from these expressions holds true.

As is clear from equation (5), the signal current L and the return beam current h have a relationship as shown by the straight line a in FIG.

On the other hand, since the signal current L has a finite value M determined by the characteristics of the image pickup tube 1, α of A and R to become smaller
To determine the +A-R-Grn value, return beam current 1
R is a constant value 1 regardless of the value of signal current L.

In other words, even if a bright portion is imaged and the signal current L increases, the return beam current 1R does not decrease much, so the beam current h can be increased. Straight line b in FIG. 2 shows its limit value. By the way, the above-mentioned stabilizing operation by the negative feedback circuit can only be achieved in the operation of an imaging device with a conventional triode structure electron gun, and when the circuit is applied to an image pickup tube with a diode gun, an oscillation phenomenon occurs, making it impractical for practical use. It becomes impossible to provide.

This is because in a conventional triode structure electron gun, the cathode current 10 is proportional to the beam current h, as shown in equation (1), whereas in a diode gun, this relationship does not hold, and equation (3) This is because it becomes .

Then, the return beam current IR is calculated from equations (2), (4), (6), and (7), where G=]K. Kmu4 (~4 (β+G.

・R-A) becomes 2.

If this is represented graphically, it becomes a quadratic curve as shown in FIG. 3, and it is difficult to keep the IR constant regardless of the value of .

The diode gun is constructed as shown in FIG.
In addition to the slightly different electrode structure, the difference is that a positive potential is applied to the beam control electrode G1, and the electron beam does not form a crossover (laminar flow type).

The image pickup tube in the image pickup tube operating device of the present invention has a diode gun and receives beam control by, for example, a feedback circuit as shown in FIG.

The circuit configuration shown in FIG. 5 differs from the circuit configuration shown in FIG. and the output signal of the comparator amplifier 8 is connected to the square root circuit 9.
and output the output signal of the square root circuit 9 to the photoconductive image pickup tube 10.
There are two points given to the beam control electrode G1 of
The image pickup tube 10 has a diode gun. In such a configuration, the relational expressions from equations (2), (4), (6), and (9) hold true.

Also, here β<A(G...R)2 holds true, and the signal current L has a certain finite value M determined by the characteristics of the image pickup tube 10, so... - - β of A-R so that the power juice is smaller
+A (?・R) If you define the binary value, return beam current 1R
is a constant value of 1.

can be approached. Note that the square circuit 6 and the square root circuit 9 can be constructed using a wideband multiplier integrated circuit MCl595L (manufactured by Motorola, USA) 11, as shown in FIGS. 6 and 7, respectively, for example.
12 indicates a differential amplifier.

A second embodiment of the invention is shown in FIG. In the circuit configuration shown in the figure, a photoconductive image pickup tube 10 having a diode gun is used.
A signal correction circuit 11 is provided between the target electrode and the operational amplifier 7, and the other circuit configuration is the same as that shown in FIG. The signal correction circuit 11 has an input signal and an output signal characteristic as shown in FIG.
11S@ υ1X'U'IV) Consists of a two-fold line represented by VV--ρ.

However, here γ. , γ, is the V in each region
And ΔI,ru.

This case holds, and if O~, then Equations (2) and (4)
, (6), (11), and (13), the return beam current 1R becomes.

In addition, in h > Isl, formulas (2), (4),
By (6), (12), and (13), the return beam current h
The characteristics of equations (14) and (15) are expressed as two parabolas as shown by solid curves A and b in FIG.

The broken line curve c in the figure shows the characteristic when the signal correction circuit 11 is not provided, and such a characteristic causes an oscillation phenomenon. In the device of the present invention, the return beam characteristics shown by the solid curves A and b can be obtained by selecting appropriate values for γ1 and γ1, so it is extremely stable even when a very large signal current flows. The desired beam control effect can be obtained.

[Brief explanation of drawings]

Figure 1 is a block diagram of a conventional automatic beam optimization circuit, and Figure 2 shows the relationship between the image pickup tube signal current and the return beam current when the circuit uses an image pickup tube with a triode structure electron gun. -1R characteristic diagram, Figure 3 is a -1R characteristic diagram when an image pickup tube with a diode gun is used in the same circuit, Figure 4.
Figure a is a diagram of the electrode configuration of a diode gun, b of the figure is a diagram of the electrode configuration of a triode structure electron gun, Figure 5 is a block diagram showing the circuit configuration of an embodiment of the present invention, and Figure 6 is a square circuit diagram. Figure 7 is a block diagram of the square root circuit; Figure 8 is a block diagram showing the circuit configuration of another embodiment of the present invention;
The figure shows the relationship between the input signal and the output signal of the signal correction circuit in the circuit configuration of FIG. 8, and FIG. 10 is an L-h characteristic diagram in the same circuit configuration. ...Shunt, 6... Square circuit, 7
...Operation amplifier, 8...Comparison amplifier,
9...Square root circuit, 10...Image tube,
11... Signal correction circuit, 12... Clamp circuit, 13... Conversion coefficient correction circuit, 15...
addition circuit.

Claims (1)

[Scope of Claims] 1. Image pickup tube operation in which the output signal of the photoconductive type image pickup tube is guided to a feedback signal processing circuit system, and the output signal of the circuit system is applied to the beam control electrode of the image pickup tube to control the beam current. In the apparatus, the signal processing circuit system includes a first circuit system extending from a target electrode of the image pickup tube through an operational amplifier and a comparison amplifier to the beam control electrode, and a shunt of a cathode circuit of the image pickup tube to the operational amplifier. the image pickup tube has a diode gun, and the signal processing circuit system converts the non-linear beam current versus cathode current characteristic of the image pickup tube having the diode gun into 1. An image pickup tube operating device comprising a correction circuit for approximating linear characteristics of an image pickup tube having a structure. 2. The image pickup tube operation according to claim 1, wherein the correction circuit comprises a square root circuit included in the first circuit system and a square root circuit included in the second circuit system. Device. 3. The image pickup tube operating device according to claim 1, wherein the correction circuit is included in the first circuit system and has a signal conversion characteristic consisting of a broken line.