JPH0364077B2 - - Google Patents

Description

[Detailed Description of the Invention] This invention displays a graphic image, etc., by disposing a band-shaped (thin line-shaped) anode coated with a phosphor and a thin line-shaped control electrode facing each other in a crossing direction. The present invention relates to a drive circuit for a graphic fluorescent display tube.

Fluorescent display tubes display images by causing electrons emitted from a heated thin wire cathode to collide with a phosphor on an anode, and they can provide sufficient brightness for display with relatively low voltage and consume little power. It has many features such as being able to be directly driven by a driver IC, etc., and being able to emit light in a variety of colors using phosphors. A flat fluorescent display tube for graphic displays (hereinafter referred to as a graphic fluorescent display tube) has been developed to replace the cathode ray tube for graphics.

By the way, conventional graphic fluorescent display tubes are
A large number of band-shaped (thin line-shaped) anodes with phosphor deposited in dots or stripes are arranged side by side on a substrate.
A basic structure having a large number of thin wire-like, net-like, or ladder-like control electrodes facing these anodes and arranged in parallel in a direction crossing the anodes, and a thin wire-like cathode facing the control electrodes and emitting thermoelectrons upward. It has a structure. In order to drive this type of graphic fluorescent display tube, the cathode is heated with electricity to keep it in a thermionic emission state, and a scanning drive pulse voltage is sequentially and repeatedly applied to each control electrode, and the display is displayed. By applying a display signal to a portion of the anode corresponding to the image to be displayed, the phosphor on the anode is bombarded with electrons to cause it to emit light, thereby displaying the desired image.

However, the conventional graphic fluorescent display tube drive circuit has the following problems.

(1) When the phosphor of an arbitrary pixel is caused to emit light locally or partially, the duty ratio differs depending on the way the light is emitted, making so-called random scanning, in which voltage is selectively applied to the control electrode, difficult.

(2) When the IC, etc. in the control electrode driver section is destroyed by heat etc. and becomes no longer conductive,
Alternatively, when the scanning of the applied voltage applied to the control electrodes stops, such as when the scanning clock signal stops, the high DC voltage remains applied only to the specific control electrodes, and therefore the specific control The electrodes become overheated, causing deformation, sagging contact, melting, and other burnout accidents, rendering the expensive graphic fluorescent display tube unusable. This problem is more likely to occur in a graphic fluorescent display tube that has a large number of control electrodes, in other words, a graphic fluorescent display tube that is capable of high-density display. That is, as the number of control electrodes increases, the duty ratio of the applied voltage decreases, so the applied voltage must be set higher to obtain the necessary brightness.

For example, if we consider a graphic fluorescent display tube with 320 anodes and 240 control electrodes, we can reduce the duty ratio to 1/300.
When the applied voltage of the control electrode is set to 90V _pp and the current of each control electrode is set to 5mA _pp , normally 4550mW _pp is applied to the control electrode, but 450mW _pp /300 = 1.5mW _pp is applied to each control electrode. It's just adding to it. However, if the control electrode driver section is damaged and becomes conductive, or if the scanning clock signal stops and scanning stops even if the driver section is healthy, 1.
~450mW was applied to the two control electrodes, destroying the IC and continuing to apply high voltage DC, resulting in burnout of the control electrodes and rendering the expensive graphic fluorescent display tube unusable. .

The present invention has been made in view of the above points. In other words, the present invention facilitates random scanning and allows any pixel to locally or partially emit light for display. If the control electrode driver section is damaged and the control electrode becomes conductive, prevent burnout of the control electrode and damage to the expensive graphic fluorescent display tube, and ensure that the control electrode driver section is healthy and the scanning clock signal It is an object of the present invention to provide a drive circuit for a graphic fluorescent display tube that can similarly prevent damage to the graphic fluorescent display tube and destruction of the control electrode driver section even if the graphic fluorescent display tube stops.

Therefore, in order to achieve this object, a driving circuit for a graphic fluorescent display tube of the present invention includes a plurality of strip-shaped anodes arranged in parallel on a substrate and having a phosphor coated on the upper surface thereof, and a plurality of band-shaped anodes arranged in parallel on a substrate and facing the anodes. A fluorescent display tube for graphic display has at least a plurality of control electrodes arranged in parallel in a direction crossing the anode, and a plurality of cathodes stretched upward facing the anode and the control electrode. In a drive circuit that applies a display voltage and a scanning drive voltage to the control electrode, a capacitor is connected in series to the input circuit to the control electrode, and a ground voltage is connected to the control electrode side through a resistor in parallel. It is characterized by a configuration in which it is connected to the

The present invention will be explained below with reference to an illustrated embodiment.

FIG. 1 is a partially cutaway perspective view showing a graphic fluorescent display tube provided with the drive circuit of the present invention, and FIG. 2 is a sectional view of the same graphic fluorescent display tube.

Reference numeral 1 denotes a substrate made of an insulating material, and in the case of a front-emission type graphic fluorescent display tube in which light emission from a phosphor layer is observed through the substrate 1, the substrate 1 is made of an insulating material having translucency; For example, it is made of glass or the like.

Reference numeral 2 denotes a plurality of band-shaped anodes arranged in parallel in one direction on one surface of the substrate 1 and having a phosphor layer 3 deposited on the upper surface. This anode 2 is, for example, Ag,
A metal film such as Al is used, and conversely, the phosphor layer 3
A front-emission type graphic fluorescent display tube in which light emission is observed from the substrate 1 side is formed of a light-transmitting conductive film.

Further, it is conceivable that the phosphor layer 3 is deposited in the form of dots or stripes only in areas where pixels are to be formed, but the phosphor layer 3 in FIG. 2 is deposited in the form of stripes.

Reference numeral 4 designates thin wire-shaped control electrodes, and a plurality of control electrodes 4 are stretched and arranged in parallel in an intersecting direction at an upper position facing the anode 2 via spacers 5, 5. The area on the anode 2 controlled by each adjacent control electrode 4 constitutes each pixel P constituting the graphic as shown in FIG. Further, reference numeral 6 denotes a plurality of thin wire-shaped (filament-shaped) cathodes stretched upward facing the anode 2 and the control electrode 4.

Furthermore, as shown in FIGS. 1 and 2, 7 is a container part that constitutes an envelope with the substrate 1, and both are sealed in a high vacuum state via a sealing material 7a. The anode 2, control electrode 4 and cathode 6 are in a high vacuum atmosphere. In addition, this container part 7
In a graphic fluorescent display tube in which the light emitted from the phosphor layer 3 is observed from the side of the container 7, at least the display portion 7 facing the phosphor layer 3 is
b needs to be made of a transparent material.

Incidentally, the external terminal 8 of each control electrode 4 hermetically penetrates the sealed part of the substrate 1 and the container part 7 and is led out, and similarly, the external terminal 9 of each anode 2 and the cathode 6 are connected to each other. External terminal 10 is also led out.

Next, a driving circuit for the graphic fluorescent display tube having the above structure will be explained with reference to FIG. This third figure is
This is a diagram showing the driving principle of a graphic fluorescent display tube. For simplicity, five anodes 2 (2 ₁ , 2 2 , 2 ₃ , _{2 4 ,} 2 ₅ ) having a phosphor layer 3 on the upper surface are arranged in the column direction. An example is shown in which eight control electrodes 4 (4 ₁ to 4 ₈ ) are arranged in the row direction intersecting the control electrodes 4 . Then, each portion of the anode 2 controlled by the adjacent control electrodes 4 and 4 corresponds to one pixel P (P ₁₁ to _{P 75} ).
becomes.

In FIG. 3, reference numeral 11 denotes an IC that repeatedly scans and applies control voltages E ₁ to E ₈ to two adjacent control electrodes 4 ₁ to 4 ₈ in sequence based on a clock signal CP ₁ . The control electrode driver section consists of the following components. Further, 12 is an anode driver section that selectively applies anode voltages E2 ₁ to E2 ₅ to the anodes 2 ₁ to _{2 5} .

Further, 13 (13 ₁ to 13 ₈ ) are capacitors each having the same capacitance C and are interposed in series between the control electrode driver section 11 and each control electrode 4 ₁ to 4 ₈ , and 14 (14 ₁ to 14 ₈ ) is the ground G
, the capacitors 13 ₁ to 13 ₈ and the control electrode 4 ₁
These are resistors having the same resistance value Rg and connected in parallel with each of the connection points of _.about.48 .

The capacitance C of the capacitor 13 and the resistance value Rg of the resistor 14 forming the respective pairs are, for example, preferably as shown in FIG _.
~4 ₈ ) and the internal resistance Ri between the cathode 6 (see Figure 2)
The time constant value T=(Rg・Ri/Rg+Ri×C) is the control voltage _E1 to _E8 applied to the control electrode 4.
The pulse voltage time t _p is set to a value that satisfies the condition T≧t _p . The values of the control electrode voltages E4 ₁ to E4 ₈ applied to the control electrodes 4 ₁ to 4 ₈ at this time constant value T correspond to the emission start voltage E _3S of the phosphor layer 3.

Next, the operation of the above configuration will be explained.

First, the operation in a normal state will be explained. Third
In the figure, the cathode 6 is energized and heated by a power source (not shown). Square wave positive control voltages E ₁ to E ₈ are simultaneously applied to two adjacent capacitors 13 ₁ to 13 ₈ of the control electrodes 4 (4 ₁ to 4 ₈ ) at the timing shown in FIG. 6, and Clock signal for scanning
When scanning is sequentially shifted one by one from the top to the bottom using CP ₁ , each control voltage
E ₁ to _{E 8} are capacitors 13 ₁ to 13 ₈ and resistors 14 ₁
Control electrode voltage E4 ₁ of sawtooth waveform by ~14 _8
-E48 , and are sequentially applied to each of the control electrodes ₄₁ to ₄₈ . And this control voltage E ₁ ~ _{E 8}
In synchronization with the scanning, positive anode voltages E2 ₁ to E2 ₅ are selectively applied to the anodes 2 ₁ to 2 ₅ corresponding to the desired display pattern.

For example, to explain with reference to FIGS. 4 and 6, control electrode voltages E4 1 _and E4 ₂ are simultaneously applied to the control electrodes 4 ₁ and 4 ₂ during the period t ₁ , and the anode 2 ₁
Considering the case where the anode voltage E2 ₁ is selectively applied to the pixel P ₁₁ , electrons emitted from the cathode 6 impinge on the pixel P 11 and the phosphor layer 3 of this pixel P ₁₁ emits light.
Similarly, the control electrode voltage E is applied to the control electrodes 4 ₂ and 4 ₃ .
4 ₂ , E4 ₃ and an anode voltage E2 ₂ is applied to the anode 2 ₂ , the pixel P ₂₂ emits light, and further,
When the control electrode voltages E4 ₇ and E4 ₈ are applied to the control electrodes 4 ₇ and 4 ₈ and the anode voltage E2 ₅ is applied to the anode 2 ₅ , the pixel P ₇₅ emits light.

By the way, if the above is working normally,
The time constant value T is set such that T≧ _tp with respect to the pulse voltage time _tp of the control voltages _E1 to _E8 ,
In addition, the control electrode voltages E4 ₁ to E4 ₈ at the time constant value T are the emission start voltages of the phosphor layer 3.
E _3s , so at least the control voltage E ₁ ~
While applying _E8 , each corresponding pixel P (in the above example
P ₁₁ , P ₂₂ , P ₇₅ ) are reliably emitted.

Next, the operation in the case of random scanning performed when selecting a pixel P and emitting light locally or partially to obtain a desired display pattern will be described.

For example, as shown in FIG. 7, the control voltage is selectively applied to the control electrodes 4 ₁ and 4 ₂ for the sake of simplicity.
Consider a case where E ₁ and E ₂ are applied simultaneously and anode voltage E2 ₁ is applied to the anode 2 ₁ . That is, control electrode voltages E4 ₁ and E4 2 of time constant T are applied to the control electrodes 4 ₁ and 4 ₂ , and these control electrode voltages E4 _{1 and E4 2 exponentially} change to each resistor 14 .
₁ , 14 ₂ to the ground G side, and during the discharge, the pixel is discharged for a period of time constant T equal to or greater than the pulse voltage period t _p .
The phosphor layer 3 of _P11 can reliably emit light. Therefore, unlike the conventional case, the control voltages E ₁ and E ₂ are not continuously applied to the control electrodes 4 ₁ and 4 ₂ , preventing burnout of the control electrodes 4 ₁ and 4 ₂ , and reducing the cost of expensive graphic fluorescent display tubes. Not only can breakage be prevented, but also breakage of the control electrode driver section 11 can be eliminated.

In this way, the control electrode 4 ₁
Control electrode voltages E4 ₁ to E4 ₈ that decrease exponentially are selectively applied to two adjacent electrodes of 4 ₈ , and anode voltages E2 ₁ to E2 ₅ are selectively applied to anodes 2 ₁ to 2 ₅ . By doing so, it is possible to perform random scanning in which necessary pixels emit light.

Next, consider a case where the control electrode driver section 11 is destroyed by heat or the like and becomes conductive, or when the clock signal CP ₁ stops and normal scanning of the control voltages E ₁ to _{E 8} is no longer possible. .

In the former case, for example, when the control voltages E ₁ and E ₂ become conductive, a high voltage of, for example, 90V is applied to the capacitors 13 ₁ and 13 ₂ , but the capacitors 13 ₁ and 1
Due to the direct current blocking function of _3.2 , no voltage is applied to the control electrodes _4.sub.1 , _4.sub.2 , and unlike in the past, there is no risk of burnout of the control electrodes, and the expensive graphic fluorescent display tube can be protected.

In the latter case, not only can damage to the graphic fluorescent display tube be prevented for the reasons mentioned above, but also the control electrode driver section 11 can be kept healthy by stopping the rotating operation when the clock signal CP ₁ stops.
It can also prevent the destruction of

Note that the present invention is not limited to the embodiments described above, and can be implemented with various modifications without changing the gist thereof.

As explained above, according to the present invention, a capacitor is connected in series to the input circuit to the control electrode, and the control electrode side is connected to the ground potential side through a resistor in parallel with the control electrode. Although the configuration is relatively simple, it not only facilitates random scanning and enables arbitrary local or partial luminescence display, but also allows for the control electrode to be in a conductive state if the control electrode driver section is destroyed. If the control electrode driver section is healthy and the scanning clock signal has stopped, prevent the control electrode from burning out and damage the expensive graphic fluorescent display tube. This has an excellent effect of preventing damage to the control electrode driver part as well as preventing damage to the control electrode driver part.

In addition, in this invention, the capacitance C and the resistance value Rg of the capacitor are determined by the internal resistance Ri between the control electrode and the cathode of the fluorescent display tube, and the time constant T value (Rg・Ri/Rg+Ri×C). However, if the pulse voltage time t _p applied to the control electrode is set to a value that satisfies the condition T≧t _p , there is an effect that the corresponding pixel can reliably emit light during normal operation.

[Brief explanation of drawings]

FIG. 1 is a partially cutaway perspective view showing a graphic fluorescent display tube equipped with the drive circuit of the present invention, FIG. 2 is a sectional view of the same graphic fluorescent display tube, and FIG. 3 is a drive circuit and driving principle. 4 is an explanatory diagram of the light emission principle of the pixel, FIG. 5 is a diagram showing the waveforms of the control voltage applied to the capacitor and the control electrode voltage applied to the control electrode, and FIG. 6 is a diagram illustrating the drive timing. 7 are diagrams for explaining random scanning. 2... Anode, 3... Phosphor layer, 4... Control electrode, 6...
Cathode, 11... Control electrode driver section, 13... Capacitor, 14... Resistor, P... Pixel.

Claims (1)

[Scope of Claims] 1. A plurality of band-shaped anodes arranged in parallel on a substrate and having a phosphor coated on the upper surface, and a plurality of control electrodes arranged in parallel in an upwardly intersecting direction opposite to the anodes. ,
A drive circuit for applying a display voltage and a scanning drive voltage to the anode and the control electrode of a fluorescent display tube for graphic display, which has at least a plurality of cathodes suspended above and facing the anode and the control electrode, Driving a graphic fluorescent display tube characterized in that each input circuit to the control electrode has a capacitor connected in series, and the control electrode side is connected in parallel to a ground voltage via a resistor. circuit. 2 Values of capacitance C and resistance of the capacitor
Rg is the internal resistance Ri between the control electrode and cathode of the fluorescent display tube, and the value of the time constant T (Rg・Ri/Rg+Ri×C) with respect to the pulse voltage time _tp applied to the control electrode. A drive circuit for a graphic fluorescent display tube according to claim 1, which has a value satisfying the condition ≧t _p .