JPS6329781B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image intensifier device having a microchannel plate voltage control circuit for an image intensifier tube. More specifically, it detects the phosphor current of the image intensifier tube and automatically adjusts the brightness of the phosphor.
An image of an image intensifier tube with a microchannel plate voltage control circuit that alerts the operator by lighting up (flickering) the fluorescent surface when the light incident on the photocathode is excessive. The present invention relates to an intensifier device.

Image intensifier tubes using microchannel plates are widely used for purposes such as observing objects in the dark and monitoring minute luminescence.

The basic structure of an image intensifier tube will be explained with reference to FIG.

A photocathode 3 is provided on the inner surface of the transparent front plate of the glass tube 2. Close to this photocathode 3 a focusing electrode 4 and subsequently a microchannel plate 5 are provided in the glass tube 2 .

The microchannel plate 5 is a well-known microchannel plate having an input electrode 6 and an output electrode 7.

A fluorescent surface 8 is provided inside the metal plate on the transparent rear surface of the glass tube 2. These fluorescent surfaces 8 or electrodes are connected to an external power source and given an appropriate potential. The optical image formed by the optical image forming means on the photocathode 3 is converted into an electronic image by the photocathode 3, and is intensified by the microchannel plate 5 to form an intensified optical image on the fluorescent surface 8. Ru.

In such image intensifier tubes, many proposals have been made to control the brightness of image intensification on the fluorescent surface.

For example, USP, 3,816,774, USP, 4,
195, 222, etc., all control the bias voltage of the microchannel plate in inverse proportion to the screen current in order to adjust the tube gain.

With these configurations, surface brightness is automatically controlled.

Even if such automatic brightness adjustment is performed, there is a problem that a high-quality reproduced image cannot be obtained on the fluorescent surface if there is excessive input light (for example, 1 lux or more). In such a case, the contrast of the reproduced image usually deteriorates rapidly.

Furthermore, if such excessive light incidence continues for a long time, there is a problem that the photocathode itself will be destroyed.

SUMMARY OF THE INVENTION An object of the present invention is to provide an image intensifier device having a microchannel plate bias voltage control circuit which can also solve the above-mentioned problem when the incident light is excessive.

In order to solve the above-mentioned problems, the device according to the present invention divides the operating region of the image intensifier tube into three regions. However, in the first region where the amount of incident light is small, the amplification degree of the microchannel plate is kept as high as possible, and in the second region, the gain of the microchannel plate is adjusted to the phosphor current as the amount of incident light increases. It will be decreased in inverse proportion to the above. However, even in this second region, as the amount of incident light increases,
The brightness of the fluorescent surface is gradually increased.
In this case, the image quality obtained on the fluorescent surface is maintained better.

Next, in the third region where a good reproduced image cannot be obtained even with the above-mentioned automatic brightness adjustment and where excessive light is incident that damages the photocathode, oscillation is caused in the feedback loop. , a warning is generated by flickering the fluorescent surface.

This warning allows the operator to convert to second zone operation by limiting the light incident on the photocathode.

That is, an image intensifier device having a microchannel plate voltage control circuit according to the present invention includes a photocathode, a microchannel plate having input/output electrodes, an automatic brightness adjustment circuit and an alarm circuit for an image intensifier tube having a fluorescent surface. A phosphor current rectifier circuit that rectifies the phosphor current to obtain a signal corresponding to the brightness of the phosphor surface compares the signal of the phosphor current rectifier circuit with a reference signal to detect the phosphor current. a differential amplifier circuit that generates a signal that increases proportionally to the surface current; a gas discharge tube; and a gas discharge tube that is connected in series with the discharge tube to a power source for the discharge tube; a transistor connected to a control input terminal and whose internal resistance is controlled; a DC voltage source for providing a bias voltage to the microchannel plate; and a transistor connected to the DC voltage source in series with the microchannel plate and the gas discharge tube. a photoconductor photoelectrically coupled to a photoconductor; and a delay element provided in a signal path from the phosphor current output terminal to a control input terminal of the transistor; When in the adjustment region, automatic brightness adjustment is performed so that the fluorescent surface current increases slightly, and when the incident light on the photocathode becomes excessive, it is determined by the characteristics of the delay element and the gas discharge tube. The fluorescent surface is configured to flicker due to relaxation vibration.

The circuit according to the invention will now be explained in detail with reference to FIG.

All electric power for this control circuit is supplied from the battery 21 of the power supply section 20. The battery 21 is a mercury battery with an electromotive force of 2.7 volts.

The negative electrode of the mercury cell is connected to the baseline of this control circuit.

A differential amplifier 40, which will be described later, is directly supplied with power by this battery, and other parts and the image intensifier tube are supplied with a boosted voltage from this voltage. The part indicated by 60 and surrounded by a broken line is a well-known voltage stabilizer. This voltage stabilizer 60 was stabilized by a DC-AC converter 70
Supply DC voltage.

The DC-AC converter 70 has a step-up transformer 72 that steps up the output of the transistor oscillator.
This DC-AC converter 70 boosts the output voltage (2.7 volts or less) of the stabilizer 60.

The secondary winding 73 of the step-up transformer 72 has 15K
Hz, a voltage of 700 volts appears. This voltage can be adjusted by adjusting the output voltage of ballast 60.

The part surrounded by the broken line 80 is a well-known voltage doubler rectifier circuit. In this circuit, the point indicated by point 81 has a DC voltage of 3.5KV with respect to the base line, the point indicated by 82 has a DC voltage of 4.5KV, and the point indicated by 83 has a DC voltage of 3.5KV with respect to the base line.
A DC voltage of 7.5KV appears.

Therefore, the image intensifier tube 1
An accelerating voltage of 3 KV is applied between the photocathode 3 and the input electrode 6 of the microchannel plate 5.

Note that the voltages of the focusing electrode 4 and the input electrode 6 of the microchannel plate 5 are at the same potential.

The input electrode 6 and the output electrode 7 of the microchannel plate 5 are connected to a point 81 which is the output terminal of the bias source of the microchannel plate 5 mentioned above.
A voltage of 1KV between and 82 is connected via a photoconductor 99.

The phosphor surface 8 is maintained at a voltage very close to the ground wire of this circuit, as will be explained later.

The photoconductor 99 is inserted into the same shielding box (not shown) as the neon tube 52, which will be described later, and is optically coupled.

The resistance of this photoconductor 99 is the neon tube 5
The bias voltage of the microchannel plate 5 changes inversely to the brightness of the neon tube 52.

To explain in more detail, the resistance value of the photoconductor 99 is determined when the neon tube 52 is at maximum brightness.
2MΩ, 500MΩ at lowest brightness,
When the neon lamp 52 is in the off state,
It becomes 2000MΩ.

Therefore, when the neon tube 52 is at maximum brightness, the microchannel plate 5 has the following values: 1KV x {500/(500+2)} ≒1KV When the neon tube 52 has the lowest brightness, 1KV x {500/(500+500)} ≒0.5KV becomes. The multiplication factor of this microchannel plate 5 is 1 when the voltage between the input and output terminals is 0.5KV.
So, 1KV is 10 ⁴ .

Also, when the neon tube 52 is not lit, 1KV×{500/(500+2000)} ≒0.2KV The amplification factor is approximately 0.

The rectifier circuit block 30 is a circuit for rectifying the fluorescent surface current of the image intensifier tube described above. The fluorescent surface current is representative of the brightness of the fluorescent surface.

This block 30 has a diode 31 and a capacitor 32. The capacitance of capacitor 32 is 0.1 μF in this embodiment.

Charge corresponding to the brightness of the fluorescent surface 3 is accumulated in the capacitor 32.

The differential amplifier 40 has two PNP transistors 42 and 43, and the base electrode of the transistor 42 is connected to the connection point between the capacitor 32 and the diode 31 of the rectifier circuit block described above.

The emitter electrodes of the transistors 42 and 43 are connected to the opposite electrode of the battery 21 via a resistor 41. The collector electrode of transistor 42 is connected to the base line, and the collector of transistor 43 is connected to the base line via capacitor 49. variable resistor 44, and resistors 45, 46, 4
7 constitutes a voltage divider, which supplies a reference voltage to the base electrode of the transistor 43.

This reference voltage is set to a voltage that determines the limits of the second region () and the third region () shown in FIG. A collector current corresponding to the difference between the voltage of the capacitor 32 determined by the fluorescent surface current and the reference voltage is supplied to the base of the next stage transistor 53 via the resistor 48. The values of the elements of this block are shown below.

41 47 KΩ 44 20 KΩ 45 2 KΩ 46 3.9KΩ 47 8.2KΩ The collector current of the transistor 43 is connected to the base electrode of the transistor 53 via the resistor 48.

This resistor 48 and capacitor 49 constitute an output delay circuit of a differential amplifier.

The resistor 48 is 100KΩ, and the capacitor 49 is 2.2μF.

The neon tube brightness control circuit surrounded by the broken line 50 is
This circuit controls the brightness of the neon tube 52 to which the photoconductor 99 described above is connected.

The anode of the diode 51 is the aforementioned DC-AC
It is connected to the secondary winding of the step-up transformer of the converter, and its cathode is connected to one end of the neon tube. The other end of this neon tube 52 is connected to one end of a 5MΩ resistor 54.

The internal resistance of the transistor 53 is adjusted by the output current of the differential amplification cathode, and when the output is large, the internal resistance is decreased, and when the output is small, the internal resistance is increased.

As is well known, gas discharge tubes such as neon tubes have different discharge start voltages and discharge stop voltages.

This neon tube 52 starts discharging when the voltage between the two poles reaches 82 volts, and can maintain discharge light emission up to 80 volts even if the voltage drops thereafter. The minimum current for maintaining discharge is approximately 1 μA.

The present invention utilizes this voltage difference, and the flicker for warning, which will be described later, is created by the voltage difference and the presence of a delay element included in the circuit. There are many delay elements in the circuit. a capacitor 32 included in the circuit;
Reference numeral 49 is a typical delay element, and the response delay of the photoconductor 99 causes a delay, although it is slight.

The operation of the circuit with the above configuration will be explained with reference to FIG. The operating range of all embodiment devices is the first range () where the illuminance of the image incident on the photocathode is 0.01lux or less and the second range () from 0.01lux to 1lux.
It can be considered separately into a third region () exceeding 1 lux.

The first region () is the region where the image intensifier tube exhibits maximum gain, and the second region () is the region where the image intensifier tube exhibits maximum gain.
The area is an area where automatic brightness adjustment is performed. The third region is a region where the fluorescent surface flickers to issue a warning because the incident light is excessive.

Figures A, C, E, G, and I show the neon tube current, neon brightness, photoconductor resistance, microchannel plate amplification factor, and phosphor surface current, respectively, with the incident illuminance as the horizontal axis. This is the graph shown.

It should be noted that the changes in each part are intended to show trends of change for ease of understanding, and do not strictly correspond to actual operations.

In Figure 3 B, D, F, H, and J, the horizontal axis is the time axis, and the time point when entering the third area from the second area is t ₀
This is a graph showing the temporal changes of A, C, E, G, and I.

In the first region ( ), the illuminance of the light incident on the fluorescent surface is 0.01 lux or less, and the brightness of the fluorescent surface 3 is also extremely low.

Therefore, the charge on the capacitor of circuit block 30 is small. Therefore, sufficient current is supplied from transistor 43 of differential amplifier 40 to transistor 53 of the neon tube brightness control circuit.

Therefore, since the resistance of the photoconductor 99 is also sufficiently low (2 MΩ or less), a bias voltage close to 1 KV is applied to the microchannel plate 5.

The microchannel plate 5 exhibits the maximum amplification factor of ¹⁰⁴ .

In this region ( ), no substantial automatic brightness adjustment is performed, and the brightness of the fluorescent surface increases in response to the incident light illuminance, as shown in FIG. 3 ( ).

Next, the second area () will be explained. When the output current of the differential amplifier 40 decreases as the fluorescent surface current increases, the neon tube brightness control circuit 5
Further lower the internal resistance of the zero transistor. The neon tube current gradually decreases until the photoconductor 9
The resistance value of No. 9 also exceeds 2MΩ and gradually increases. As a result, the bias voltage of the microchannel plate 5 also gradually decreases from 1 KV, so that the amplification factor decreases as shown by G in FIG.

In this way, as the incident illuminance increases, the tube gain decreases, but the screen current decreases slightly but surely as the incident illuminance increases.
gradually rises. In the present invention, the purpose is not to keep the screen current constant, but to obtain a high-quality reproduced image by increasing the screen current even slightly as the incident illuminance increases. If feedback is performed to keep the screen current constant, the reproduced image quality will deteriorate in the second region ( ) where the incident illuminance is greater.

Next, the operation in the third region () will be explained with reference to FIG. For example, when the illuminance of the light incident on the photocathode exceeds 1 lux, the phosphor current of the image intensifier tube increases, and the differential amplifier 40
The output current of the neon tube brightness control circuit 50 decreases, and the internal resistance of the transistor 53 of the neon tube brightness control circuit 50 increases.
When the voltage between the terminals of the neon tube 52 becomes 80 volts,
The discharge can no longer be maintained.

When the neon light 52 goes out, the resistance of the photoconductor 99, which had a resistance of about 500MΩ, becomes 2000MΩ.
It rises towards Ω.

As a result, the bias voltage of the microchannel plate 5 drops, and the multiplication factor sharply drops as shown in FIG. 3G. Therefore, even if there is sufficient incident light, the brightness of the phosphor surface 3 rapidly decreases, and the phosphor surface current rapidly decreases as shown in FIG. 3().
As a result, the output of the differential amplifier 40 tends to increase, lowering the internal resistance of the transistor 53 and increasing the neon tube current. However, since the circuit includes delay elements such as capacitors 32 and 49, the neon tube current does not rise rapidly from t ₀ but gradually rises from t ₁ as shown in FIG. 3B. At this point, the voltage across the neon tube terminals reaches 82 volts and lights up.

Since the brightness of the neon tube 52 when it is turned on is greater than the brightness when it is turned off, the resistance of the photoconductor 99 is rapidly reduced. As a result, the amplification factor of the microchannel plate 5 increases rapidly, the brightness of the fluorescent surface increases, and the screen current also increases. However, since there is a delay in the loop, the neon tube current does not decrease rapidly, but decreases with a delay as shown between Bt ₁ and t ₂ in FIG. and,
At time t ₂ , the neon tube goes out. As a result, the resistance of the photoconductor increases and the brightness of the screen decreases. In the same manner as above, the screen brightness continues to flicker.

In this embodiment, the flickering period of the screen is 0.5 seconds.

With this warning, the operator knows that the light incident on the photocathode is excessive, and can limit the incident light with a diaphragm or the like to bring the operating region of the image intensifier tube into the second region (). can.

As explained in detail above, according to the circuit according to the present invention, good automatic brightness adjustment is performed in the second region () without deteriorating image quality, and a warning is provided in the third region (), so that the operator can adjust the incident illumination to bring the operation of the image intensifier tube into the second region ().

This makes it possible to always ensure operation in an optimal state, and also to prevent damage to the image intensifier tube due to excessive incident light illuminance.

[Brief explanation of the drawing]

FIG. 1 is a schematic representation of an image intensifier tube with a microchannel plate, which is the subject of control of a circuit according to the invention. Figure 2 shows
1 is a circuit diagram showing an embodiment of a circuit according to the present invention; FIG.
FIG. 3 is a graph for explaining the operation of the circuit according to the present invention. 1... Image intensifier ear tube, 2...
Glass tube, 3... Photocathode, 4... Focusing electrode, 5
... Microchannel plate, 6 ... Input electrode, 7 ... Output electrode, 8 ... Fluorescent surface, 20 ... Power supply section, 21 ... Battery, 30 ... Rectifier circuit block, 32 ... Capacitor, 40 ... …actuated amplifier,
48...Resistor, 50...Neon tube brightness control circuit,
52... Neon tube, 60... Voltage stabilizer, 70...
...DC-AC converter, 72...Step-up transformer,
80... Voltage doubler rectifier circuit, 99... Photoconductor.

Claims (1)

[Scope of Claims] 1. In an image intensifier device having a photocathode, a microchannel plate having an input/output electrode, and an image intensifier tube having a fluorescent surface, the fluorescent surface current is rectified to form a fluorescent surface. a phosphor current rectifier circuit that obtains a signal corresponding to the luminance of the phosphor current, and a difference that compares the signal of the phosphor current rectifier circuit with a reference signal to generate a signal that increases proportionally to the phosphor current. a dynamic amplifier circuit, a transistor connected in series with the discharge tube to a power source of the gas discharge tube, a signal of the differential amplifier circuit being connected to a control input terminal to control internal resistance, and the microchannel. a DC voltage source providing a bias voltage to the plate; a photoconductor connected to the DC voltage source in series with the microchannel plate and photoelectrically coupled to the gas discharge tube; and a delay element provided in the signal path from the terminal to the control input terminal of the transistor, and when the phosphor surface brightness is in the automatic brightness adjustment region, the phosphor surface current is automatically increased so that the phosphor surface current increases slightly. When the adjustment is made and the incident light on the photocathode becomes excessive, the fluorescent surface is made to flicker by relaxation vibration determined by the characteristics of the delay element and the gas discharge tube. Image intensifier device. 2. The image intensifier according to claim 1, wherein the neon tube and the photoconductor are housed in the same shielding box, and the photoconductor is configured to react only to the luminous flux of the discharge tube. Device. 3 The microchannel plate has a saturation region in which the amplification does not increase even if the bias voltage increases, and when the illuminance of the incident light on the photocathode is low, the amplification remains at the maximum constant level, and the luminance of the fluorescent surface remains the same as the incident light. An image intensifier as claimed in claim 1, which is proportional to light illuminance. 4. The image intensifier device according to claim 1, wherein the photoconductor is a CdS photoconductor. 5. The image intensifier device according to claim 1, wherein the delay element is a capacitor included in the rectifier circuit and a capacitor connected to the output terminal of the differential amplifier circuit.