JPH0831345A - Image display device - Google Patents

Abstract

PURPOSE:To maintain the electron emitting ability of a wire cathode for a long period of time by sensing the absorptive electron current at a beam drawout electrode, and raising the wire cathode heating power in accordance with the wire cathode. CONSTITUTION:An image display device has a wire cathode 2, and when its electron emitting ability sinks, the degree of the secular deterioration is sensed by an absorptive electron current sensing device 110 in the form of a drop of the absorptive electron current of a beam drawout electrode 3. The sensing device 110 converts the drop of the current into a voltage value and sends the result to a wire cathode heating power control device 400, which makes control so that the heating power is raised in accordance with deterioration of the electron emission of the wire cathode 2. This enables the wire cathode 2 to maintain tone electron emitting ability for a long period of time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image display device in video equipment.

[0002]

2. Description of the Related Art Heretofore, a cathode ray tube has been mainly used as a color television image display element. However, a cathode ray tube has a very long depth compared to a screen, and it is not possible to manufacture a thin television receiver. It was possible.
Therefore, EL display elements, plasma display elements, liquid crystal display elements and the like have been developed as flat plate display elements, but they are all insufficient in terms of performance such as brightness, contrast and color reproducibility.

Therefore, for the purpose of displaying a high-quality image similar to that of a cathode-ray tube by a flat-plate device using an electron beam, the screen on the screen is divided into matrix-shaped sections without any gaps, and each section is divided. 2. Description of the Related Art There is an image display device that deflects and scans an electron beam to cause a fluorescent substance to emit light, thereby forming a color television image as a whole.

An example of the above-mentioned conventional image display device will be described below with reference to the drawings. FIG. 7 is an exploded perspective view of a conventional image display device.

In FIG. 7, 1 is a back electrode, 2 is a line cathode as a beam source, 3 is a beam extraction electrode, 4 is a signal electrode, 5 and 6 are focusing electrodes, 7 is a horizontal deflection electrode, and 8 is a vertical deflection electrode. And these components are placed in the glass container 9,
It is housed in the back plate 10 and the inside of the container is evacuated.

The line cathodes 2 are stretched in the horizontal direction so as to generate an electron flow that is uniformly distributed in the horizontal direction, and a plurality of such line cathodes 2 are provided in the vertical direction at appropriate intervals. There is. These wire cathodes 2 are formed, for example, by coating an oxide cathode material on the surface of a tungsten wire.

The back electrode 1 is made of a flat plate-shaped conductive material and is provided in parallel with the line cathode 2. The beam extraction electrode 3 is formed of a conductive plate that faces the back electrode 1 through the line cathode 2 and has rows of through holes 11 that are provided at appropriate intervals in the horizontal direction on a horizontal line that faces each line cathode. Through hole 1
Although 1 is circular in the embodiment, it may be oval or rectangular, or may be slit-shaped.

The signal electrode 4 is composed of a plurality of vertically elongated conductive plates 12 arranged in a position facing each of the through-holes 11 in the beam extraction electrode 3 with a predetermined interval, and in each conductive plate. Has a similar through hole 13 at a position facing the through hole 11 of the beam extraction electrode 3. The shape of the through hole 13 may be an ellipse or a rectangle, or may be an elongated slit shape in the vertical direction.

The focusing electrode 5 is composed of a conductive plate having through holes 14 at positions facing the through holes 13 of the signal electrode 4, respectively. The shape of the through hole 14 may be a circle, an ellipse, or a slit shape. The focusing electrode 6 has a slit hole 15 which is vertically connected at a position facing the through hole 14 of the focusing electrode 5. The shape of the slit hole 15 may be a round hole, an ellipse, or a rectangular shape.

As shown in FIG. 7, the horizontal deflection electrode 8 has conductive plates 16 and 17 connected to each other at its ends, that is, two comb-shaped conductive plates 16 and 17, which are in the same plane and mesh with each other at appropriate intervals. It has a combined structure. The space 18 formed between the conductive plates 16 and 17 faces the through slit hole 15 of the focusing electrode 6.

As shown in FIG. 7, the vertical deflection electrode 8 has conductive plates 19 and 20 connected to each other at its ends, that is, two comb-shaped conductive plates 19 and 20, which are in the same plane and mesh with each other at appropriate intervals. It has a combined structure.

The screen 21 is constructed by applying a phosphor 22 which emits light by irradiation of an electron beam to the inner surface of the glass container 9 and adding a metal back layer (not shown) thereon.

Further, the beam extraction electrode 3, the signal electrode 4, the focusing electrodes 5 and 6, the horizontal deflection electrode 7, and the vertical deflection electrode 8 described above are joined by an insulating adhesive (not shown here). And forms an integral electrode block 24.

The operation of the image display device configured as described above will be briefly described. First, the wire cathode 2 is heated by flowing a heater current in order to facilitate electron emission (emission).

A control circuit for the line cathode 2 is constructed, for example, as shown in FIG. FIG. 8 is a circuit diagram of a line cathode control circuit of a conventional image display device.

In FIG. 8, reference numeral 2 denotes a line cathode, which is formed by coating an oxide cathode material on the surface of the tungsten wire except both ends. Reference numeral 300 is a control pulse input terminal to which a line cathode control pulse is input.

Reference numeral 310 denotes a changeover switch at both ends of the line cathode 2 as shown in the figure. When the line cathode is in an emission state by a line cathode control pulse, the position is indicated by a dotted line in the figure, and in a non-emission (cut-off) state, a solid line in the figure is used. Controlled to be in position. Reference numeral 320 denotes a power supply for setting an electron emission (emission) state, and an additional power supply outputs a voltage Ke at the time of electron emission (emission). Reference numeral 330 denotes a power supply for putting the line cathode 2 into a non-emission (cut-off) state during heating, and outputs a voltage Kc in the non-emission (cut-off) state.
340 is a power supply for heating the line cathode 2 and a heating voltage Kh
Is output.

With the control circuit configured as described above,
The heating and electron emission (emission) of the linear cathode 2 are alternately controlled, and the back electrode 1 and the beam extraction electrode 3 shown in FIG.
A sheet-like electron beam can be emitted from the surface of the line cathode 2 by applying an appropriate voltage to the.

As shown in FIG. 7, this sheet-shaped electron beam is divided into a plurality of electron beam streams 23 by the through holes 11 of the beam extraction electrode 3. The passing amount of the electron beam flow 23 is individually adjusted by the signal electrode 4 in accordance with the image signal applied to the signal electrode 4. Next, the electron beam that has passed through the signal electrode 4 is focused and shaped by the electrostatic lens effect of the through holes 14 and 15 of the focusing electrodes 5 and 6, and then the adjacent conductive plate 16 of the horizontal deflection electrode 7,
17 and the vertical deflection electrode 8 are horizontally and vertically deflected by the potential difference applied to the adjacent conductive plates 19 and 20.

Further, a high voltage (for example, 10 KV) is applied to the metal back layer of the screen 21, and the electron beam is accelerated to high energy and collides with the metal back, causing the phosphor to emit light.

When the television screen is vertically and horizontally divided into a matrix to form a group of subsections 25 in FIG. 7, each subsection is associated with one electron beam separated as described above. By deflecting and scanning the electron beam only within each subsection, the entire screen can be displayed on the screen. Further, by controlling the RGB video signal corresponding to each pixel by the signal electrode 4, a television moving image can be reproduced.

[0022]

However, according to the above configuration, the electron emission (emission) capability of the line cathode 2 decreases as the operating time elapses, which causes a problem of deterioration of image quality. Was.

In view of the above problems, it is an object of the present invention to provide an image display device which maintains the electron emission capability of the line cathode for a long period of time.

[0024]

To achieve the above object, a first means of the present invention is an absorption electron current detecting means for detecting a current due to electron absorption in a beam extraction electrode, and the absorption electron current detecting device. It is equipped with a wire cathode heating power control device which is operated by a signal from.

The second means is one or a plurality of resistors in which the line cathode heating power control device is connected in series to the line cathode and one or a plurality of short circuits capable of individually shorting the resistors. By the switch and the output of the absorption electron current detector,
The control means which controls the said short circuit switch is provided.

[0026]

The decrease in the electron emission (emission) capability of the wire cathode can be detected as a change in current due to absorbed electrons at the beam extraction electrode.

On the other hand, the electron emission capability can be enhanced by raising the temperature of the deteriorated line cathode, that is, raising the heating power. Therefore, by detecting the absorbed electron current and increasing the power for heating the cathode in accordance with the deterioration of the cathode, the electron emission capability of the cathode can be maintained for a long period of time.

[0028]

【Example】

(Embodiment 1) An image display apparatus according to a first embodiment of the present invention will be described below with reference to the drawings. In the following drawings, the same parts as those in FIGS. 7 and 8 described above are designated by the same reference numerals and detailed description thereof will be omitted. FIG. 1 is a block diagram of a main part of an image display device according to a first embodiment of the present invention.

In FIG. 1, 2 is a line cathode, 3 is a beam extraction electrode, 21 is a screen, 23 is an electron beam flow, and 24
Is an electrode block.

Electron beam stream 23 emitted from the line cathode 2
Passes through the electrode block 24 and causes the screen 21 to emit light. At that time, most of the electron beam flow 23 is absorbed as an absorbed electron current by the beam extraction electrode 3.

Reference numeral 140 denotes a power source for the beam extraction electrode 3, which applies an appropriate voltage to the beam extraction electrode 3. Reference numeral 110 is an absorption electron current detection device including a resistor 130 and a differential amplifier 120. A line cathode heating power control unit 400 controls heating power for the line cathode 2. The line cathode heating power control device 400 is configured, for example, as shown in FIG.

FIG. 2 is a circuit diagram of a line cathode heating power control device according to the first embodiment of the present invention, which mainly shows a portion related to the heating power control for the line cathode 2, and therefore the peripheral portion of the line cathode 2 will be described. The current emission (emission) control part is omitted.

In FIG. 2, 401 is an input terminal to which a detection signal from the absorption electron current detection device 110 is input. Four
Power control terminals 02 and 403 are connected in series to the line cathode 2 as shown in FIG.

Resistors 404 and 405 and operational amplifier 408
Are connected as shown in FIG. 2 to form an inverting amplifier. By connecting the resistors 406 and 407 and the operational amplifier 409 as shown in FIG. 2 and feeding back the output voltage of the output terminal 402, a voltage control circuit is configured. A power transistor 410 amplifies the power of the output of the operational amplifier 409.

The operation of the wire cathode heating power control device according to the first embodiment of the present invention constructed as described above will be briefly described below.

Now, assuming that the input signal level from the absorbed electron current detection device 110 decreases, the operational amplifier 408
The output level of the inverting amplifier is increased. Further, since this signal is connected to the reference voltage input to the voltage control circuit by the operational amplifier 409, the output of the operational amplifier 409 rises and the power transistor 410 causes the output terminal 4 to output.
02 increases the output voltage to 02 and increases the heating power to the cathode 2.

The manner in which the heating power control for the line cathode 2 is performed in this apparatus will be described below with reference to FIG.

Although the electron emission (emission) capability of the line cathode 2 decreases as the operating time elapses, the degree of deterioration over time can be detected as a decrease in the absorbed electron current in the beam extraction electrode 3.

In the absorbed electron current detection device 110, the above-mentioned current drop is converted into a voltage to convert the line cathode heating power control device 400.
Output to.

In the line cathode heating power controller 400, the heating power to the line cathode 2 is supplied to the absorption electron current detector 110.
The output is controlled so as to increase the heating power as the linear cathode 2 deteriorates with time.

As a result, the heating power can be increased, that is, the temperature can be increased for the line cathode that has deteriorated with time, and the electron emission capability of the line cathode can be maintained for a long period of time.

Since the temperature of the wire cathode is not increased before deterioration with time, the high temperature does not accelerate the deterioration of the wire cathode more than necessary.

(Second Embodiment) A second embodiment of the present invention will be described below with reference to the drawings. FIG. 3 is a circuit diagram of a wire cathode heating power control device according to the second embodiment of the present invention.

In FIG. 3, 401 is an input terminal to which a detection signal from the absorption electron current detection device 110 is input. Further, reference numerals 402 and 403 are power control terminals, and the above is the same as the configuration of FIG. The difference from the configuration of FIG. 2 is that the power control is realized at a very low cost by a simple configuration here.

In FIG. 3, 501 and 502 are resistors,
A capacitor 504 smoothes the input signal of the input terminal 401 by resistance division. Reference numeral 505 denotes a Schmitt input type inverting circuit, which has a threshold level hysteresis when the input signal changes from H to L or from L to H, as is well known.

A switch 506 and a resistor 503 are connected in series with the line cathode 2, and when the switch 506 is OFF, a voltage drop occurs in the resistor 503.

The line cathode heating power control device configured as described above will be described below with reference to FIG. FIG. 4 is an operation state diagram for explaining the operation of the line cathode heating power control device according to the second embodiment of the present invention. The heating voltage to the line cathode is used as a parameter, and the horizontal axis shows the operation time of the image display device. The vertical axis represents the output of the absorption current detection device 110.

Now, assuming that the voltage drop across the resistor 503 is α and the heating voltage applied to both ends of the line cathode is "A-α", the output of the absorption current detection device 110, that is, the electron of the line cathode will be described. The emission (emission) capability gradually decreases as shown by the curve "A-α" in FIG. 4 due to the deterioration of the wire cathode over time. Usually, this deterioration phenomenon occurs in a period of about several thousand hours.

As described above, when the output of the absorption current detector 110 decreases and the input of the Schmitt input type inversion circuit 505 in FIG. 3 becomes lower than the threshold level from H to L, the output of the Schmitt input type inversion circuit 505 becomes H. The switch 506 is turned on.

As a result, the voltage drop "α" that has been caused by the resistor 503 is eliminated, the heating voltage to the line cathode 2 is increased, and the electron emission (emission) capability of the line cathode is increased again. It behaves like the curve indicated by "A".

At this time, the output of the absorption current detector 110 rises again as shown in FIG. 4, but the Schmitt input type inverting circuit 5
Since the input of 05 is below the threshold level from L → H, the output of the Schmitt input type inverting circuit 505 is again L
It never changes to.

It should be noted here that FIG.
If the heating voltage is set to a high value like the heating voltage "B" shown in Fig. 4, a higher temperature than necessary is given to the line cathode before deterioration, and therefore the deterioration of the line cathode as shown by the curve shown in Fig. 4B. Is to accelerate.

As described above, when a resistor is connected in series to the line cathode and the electron emission (emission) capability is deteriorated due to deterioration of the line cathode over time, a switch connected in parallel with the resistor is turned on, By short-circuiting the resistor, the heating power control for the wire cathode can be easily performed.

(Third Embodiment) A third embodiment of the present invention will be described below with reference to the drawings. FIG. 5 is a circuit diagram of a wire cathode heating power control device according to a third embodiment of the present invention. Here, the description of the same parts as those in FIG. 3 is omitted.

The heating power source 34 is different from the circuit diagram of FIG.
Insert two resistors 503a and 503b in series with 0,
In addition, two short-circuit switches 506a and 506b connected in parallel with these resistors and two Schmitt input inverting circuits 505a and 505b for controlling them are used.

FIG. 6 is an operation state diagram for explaining the operation of the wire cathode heating power control device shown in FIG. 5, in which the abscissa represents the operation time of this image device and the ordinate represents the output of the absorption current detection device 110. Shows. Here, first, the absorption electron current detection device 1
When the output of 10 decreases and the input of the Schmitt input type inversion circuit 503a in FIG. 5 becomes lower than the threshold level from H to L, the output of the Schmitt input type inversion circuit 505a becomes H and the switch 506a is turned on.

As a result, the voltage drop which has been caused by the resistor 503a is eliminated, the heating voltage to the line cathode 2 is increased, the electron emission (emission) capability of the line cathode is increased again, and the curve shown in FIG. Works like.

Further, the output of the absorbed electron current detecting device 110 is lowered, and the Schmitt input type inverting circuit 503b shown in FIG.
When the input of is below the threshold level from H to L, the output of the Schmitt input type inversion circuit 505b becomes H, and the switch 506b is turned on. At this time, the output of the absorption current detection device 110 rises again as shown in FIG.
Since the input of the Schmitt input type inversion circuit 505a is below the threshold level from L → H, the output of the Schmitt input type inversion circuit 505a does not switch to L again.

As described above, by using the two short-circuiting switches, the emission capability of the twisted cathode can be kept more constant. This means that as the number of short-circuit switches increases, the emission performance of the wire cathode can be kept constant, and the life of the wire cathode can be extended accordingly.

[0060]

As described above, according to the invention of claim 1,
By providing an absorption electron current detection device that detects a current due to electron absorption of the beam extraction electrode, and a line cathode heating power control device that operates according to a signal from the absorption electron current detection device, depending on deterioration of the line cathode over time, It is possible to realize a high-quality image display device capable of increasing the electric power for heating the cathode and maintaining the electron emission capability of the cathode for a long period of time.

According to the second aspect of the invention, since the circuit according to the first aspect can be composed of simpler parts, the electron emission capability of the line cathode can be maintained at a lower cost. An image display device with high image quality can be realized.

Further, according to the invention of claim 3, the number of circuit components is slightly larger than that of claim 2, but the image display device of high image quality capable of maintaining the electron emission capability of the line cathode for a longer period of time. Can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram of a main part of an image display device according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a wire cathode heating power control device according to a first embodiment of the present invention.

FIG. 3 is a circuit diagram of a wire cathode heating power control device according to a second embodiment of the present invention.

FIG. 4 is an operation state diagram for explaining the operation of the device.

FIG. 5 is a circuit diagram of a wire cathode heating power control device according to a third embodiment of the present invention.

FIG. 6 is an operation state diagram for explaining the operation of the device.

FIG. 7 is an exploded perspective view showing a configuration of a conventional image display device.

FIG. 8 is a circuit diagram of a line cathode control circuit of a conventional image display device.

[Explanation of symbols]

 2 line cathode 3 beam extraction electrode 21 screen 23 electron beam flow 24 electrode block 110 absorption electron current detector 120 operational amplifier 130 resistor 140 beam extraction electrode bias power supply 300 control pulse input terminal 310 changeover switch 320 line cathode emission bias Power supply 330 Cut-off bias power supply for line cathode 340 Power supply for heating line cathode 400 Line cathode heating power control device 401 Control input terminals 402, 403 Power control terminals 404, 405, 406, 407 Resistors 408, 409 Operational amplifiers 501, 502 , 503, 503a, 503b Resistor 504 Capacitor 505, 505a, 505b Schmitt type inverting circuit 506, 506a, 506b Switch

Claims (3)

[Claims] 1. A conductor coated on the inner surface of the back plate in a space sandwiched between a front glass container having a phosphor coated on the inner surface thereof and a back plate closing a rear opening of the front glass container. Alternatively, a back electrode made of a metal conductive plate, a plurality of line cathodes, a beam extraction electrode made of a metal conductive plate, a signal electrode,
In an image display device comprising an electrode block in which a focusing electrode, a horizontal deflection electrode and a vertical deflection electrode are superposed one on the other, an absorption electron current detection device for detecting a current due to electron absorption of the beam extraction electrode, and the absorption electron current An image display device comprising a line cathode heating power control device that operates according to a signal from a detection device. 2. A line cathode heating power control device comprising a resistor connected in series to the line cathode, a short-circuit switch capable of short-circuiting the single resistor, and an output of an absorption electron current detection device. The image display device according to claim 1, further comprising: a control unit that controls the one short-circuit switch. 3. A line cathode heating power control device comprising a plurality of resistors connected in series to the line cathode, a plurality of short-circuit switches capable of individually short-circuiting the resistors, and an output of an absorption electron current detection device, The image display device according to claim 1, further comprising a control unit that controls a plurality of short-circuit switches.