JP3731966B2 - Luminescent display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a display device having a plurality of light emitting elements, and more particularly to a display device having a circuit for inspecting light emission of individual light emitting elements.
[0002]
[Prior art]
There is known a display device that forms a desired display image by regularly arranging a plurality of light emitting elements in a matrix and individually controlling light emission and non-light emission of each light emitting element. A light emitting element which is a minimum unit for forming an image is called a pixel. In such a display device, a light emitting diode (LED) or a phosphor is generally used as a light emitting element. In general, an LED display device includes a drive circuit for each LED, and controls light emission by the operation of each drive circuit.
[0003]
A fluorescent display tube emits light by applying thermoelectrons to a phosphor. Conventionally, a pixel that emits light is selected by time-division driving that includes one drive circuit and uses a strip electrode. In recent years, in order to avoid inconveniences inherent to time-division driving, a fluorescent display tube is also provided with a driving circuit for each pixel to individually control light emission. When a driving circuit is provided for each pixel, the driving voltage can be lowered, and there are many advantages such as reduction of power consumption, reduction of heat generation, simplification of the driving circuit, and longer life of the phosphor.
[0004]
In the above LED display device and fluorescent display tube, the light emitted from the light emitting element is observed with the naked eye, or measured with an optical device, to check the quality of the light emitting operation.
[0005]
[Problems to be solved by the invention]
However, observation of light emission with the naked eye is relatively easy with a display device in which a small number of pixels are arranged at wide intervals, and it is possible to make all pixels emit light at the same time. However, generally, labor and time are required. It is a difficult task. In particular, in a display tube in which a large number of pixels are arranged close to each other, if all the pixels emit light at the same time, the pixels that do not emit light may be overlooked. For this reason, it is necessary to individually emit light from the pixels, and the inspection requires a lot of labor and a long time.
[0006]
When light is detected using an optical device, the inspection efficiency is improved. However, in a fluorescent display tube in which a large number of pixels are arranged close to each other, it is necessary to individually emit light, and the inspection time becomes long. Moreover, a special and expensive optical device is required for inspection.
[0007]
An object of the present invention is to provide a light emitting display device that does not require a special device for inspection and can easily perform a light emission inspection.
[0008]
[Means for Solving the Problems]
To achieve the above object, the display in the present invention, comprising with a plurality have a light emitting portion composed of the light-emitting element and its driving circuit, a light receiving element for converting into an electric signal by receiving light the light emitting element emits per light emitting portion In the apparatus, a plurality of driving circuits are formed on a semiconductor chip, a light emitting element is formed on each driving circuit to form the light emitting unit, and the light receiving element is formed on the surface of the semiconductor chip in the vicinity of the driving circuit. A reflecting plate that reflects the light emitted from the light and guides it to the light receiving element is provided above the semiconductor chip between the drive circuit and the light receiving element. In this way , each light emitting unit has a light emitting element and its drive circuit, and emits light individually according to the operation of the drive circuit. When the light emitting element emits light , part of the light is reflected by the reflecting plate, and the light receiving element that receives the reflected light outputs an electrical signal. By detecting this electric signal, it can be individually determined for each light emitting unit whether or not the light emitting element emits light.
[0009]
Further, it is preferable that a logic circuit for performing a logical operation of a control signal for controlling the driving circuit and an electric signal output from the light receiving element is provided for each light emitting unit. The time when the light emitting element emits light and the time when the light emitting element stops emitting light can be determined from a control signal for controlling the drive circuit. On the other hand, whether or not the light emitting element actually emits light can be determined from an electric signal output from the light receiving element. By performing a logical operation of these signals, it is possible to know whether or not the light emitting element emits light when emitting light and when the light emitting element prohibits light emission.
[0010]
You may make it provide the output terminal which connected the output of the logic circuit of all the light emission parts. The operation results of all the logic circuits appear at this output terminal. One output terminal can be obtained by measuring the signal appearing at this terminal while operating each light-emitting unit individually by the control signal given to the drive circuit. The light emission of all the light emitting parts can be examined with.
[0012]
In the display device having the above structure, each light-emitting element is formed of a phosphor, and a semiconductor chip is accommodated in a vacuum tube to form a fluorescent display tube.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a fluorescent display tube according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a plan view schematically showing the configuration of the fluorescent display tube. The fluorescent display tube 1 includes 16 semiconductor chips 2 arranged in two rows in a transparent glass tube 3 and is evacuated. Each chip 2 has a size of 5.4 × 5.6 mm, and has a square display portion 2a and an input / output portion 2b along one edge.
[0014]
A plan view of the semiconductor chip 2 is shown in FIG. On the upper surface of the chip 2, 256 pixels 11 forming the display unit 2a and 11 input / output terminals 12 forming the input / output unit 2b are formed. Each pixel 11 has a size of approximately 0.2 × 0.2 mm, and is arranged in a 16 × 16 matrix at equal intervals. The distance from the outermost pixel to the edge of the chip is set to approximately ½ of the pixel interval. For this reason, when the chips 2 are brought into contact with each other and arranged as shown in FIG. 1, all the pixel intervals are equal, and a continuous image can be displayed as a whole.
[0015]
On the upper surface of the semiconductor chip 2, 256 light receiving portions 17 are also formed. The light receiving unit 17 is provided to inspect the light emission of each pixel 11, and is regularly arranged in the vicinity of the pixel 11. The configuration and operation of the light receiving unit 17 will be described in detail later.
[0016]
The input / output terminal 12 includes a ground terminal and an output terminal 12a in addition to the input terminals of the power supply terminal and the signal supply terminal. The output terminal 12 a is an inspection terminal used for light emission inspection, and is connected to each light receiving unit 17.
[0017]
FIG. 2 shows a part of the cross section of the fluorescent display tube 1. The semiconductor chip 2 is fixedly installed on the glass substrate 3a, and a plurality of hot cathodes 4 are arranged in parallel above it. Between the chip 2 and the hot cathode 4, a single grid 5 is provided to cover the entire display unit 2a. In addition, a light shielding plate 6 is provided near the top surface of the chip 2 in order to prevent the chip 2 from being irradiated with light from the outside. An opening is formed in the light shielding plate 6 at a position facing each pixel 11. The chip 2, the hot cathode 4, the grid 5, and the light shielding plate 6 are surrounded by glass plates 3b and 3c forming the glass tube 3 together with the glass substrate 3a, and the environment is evacuated.
[0018]
Inside the semiconductor chip 2, 256 drive circuits 13 are formed at positions to be the pixels 11. An electrode 14 is formed on the top of each drive circuit 13, and the output voltage of the drive circuit 13 is applied to the electrode 14. A phosphor 15 is attached to the upper surface of each electrode 14, and one set of the drive circuit 13, the electrode 14, and the phosphor 15 constitutes one light emitting unit 16.
[0019]
The thermoelectrons emitted from the hot cathode 4 pass through the openings of the grid 5 and the light shielding plate 6 and collide with the phosphor 15 to cause the phosphor 15 to emit light. Whether or not the thermoelectrons collide with the phosphor 15 varies depending on the voltage of the electrode 14, and the light emission of the phosphor 15 can be controlled for each light emitting unit, that is, for each pixel, by the drive voltage. The phosphor 15 continuously emits light while the drive circuit 13 outputs the drive voltage, and stops emitting when the drive circuit 13 stops outputting the drive voltage.
[0020]
A control circuit is provided at a portion (not shown) of the semiconductor chip 2. All the drive circuits 13 are connected to the control circuit and the power supply terminal, and the output operation is controlled by a control signal supplied from the control circuit. The control circuit is connected to the signal supply terminal and controls each drive circuit 13 in accordance with a signal supplied from the outside through the signal supply terminal. As a result, an appropriate pixel 11 is selected to emit light, and an image is displayed.
[0021]
FIG. 4 shows an enlarged view of the vicinity of the light emitting unit 16. This figure is a cross-sectional view perpendicular to the cross section of FIG. 2 (up and down direction of FIG. 3). The semiconductor chip 2 is formed with a light receiving portion 17 at a position close to the light emitting portion 16, and aluminum is vapor-deposited on the lower surface of the light shielding plate 6 at a portion from the edge of the phosphor 15 to the light receiving portion 17. The reflective surface 6a formed in this way is provided. Part of the light emitted from the phosphor 15 is reflected by the reflecting surface 6 a and guided to the light receiving unit 17.
[0022]
The lower surface of the light shielding plate 6 excluding the reflecting surface 6a absorbs light without reflecting it. The size of the reflecting surface 6 a is set so that the light from the light emitting unit 16 is guided to only one light receiving unit 17. Therefore, the light receiving unit 17 receives only light from the nearest light emitting unit 16, and does not receive light from other light emitting units 16.
[0023]
A schematic configuration of the light emitting unit 16 and the light receiving unit 17 is shown in FIG. The drive circuit 13 that constitutes the light emitting unit 16 together with the electrode 14 and the phosphor 15 has an amplifier 21, a p-channel transistor 22 and an n-channel transistor 23 connected in series between a 15 V power supply line 18 and a ground line. ing. The amplifier 21 amplifies the control voltage of 0 / 5V supplied from the control circuit via the input terminal 13a and supplies the amplified voltage to the gates of the transistors 22 and 23. Thereby, the operation of the transistors 22 and 23 is controlled, and a voltage of 0 V or 15 V is output from the connection point between the two to the electrode 14, and the light emission of the light emitter 15 is controlled.
[0024]
The light receiving unit 17 includes a photodiode 31 and a resistor 34 connected in series between a 5V power line 19 and a ground line, and a p-channel transistor 32 and an n channel connected in series between the 5V power line 19 and the ground line. A transistor 33, an inverter 35, and an AND circuit 36 are included. The photodiode 31 is formed exposed on the surface of the semiconductor chip 2 and receives the light L from the light emitting unit 16 reflected by the reflecting surface 6a. By this light reception, a current flows from the photodiode 31 toward the resistor 34.
[0025]
The p-channel transistor 32 has a gate grounded and is always operable. The n-channel transistor 33 has a gate connected to a connection point between the photodiode 31 and the resistor 34, and operates in response to light reception by the photodiode 31. The connection point of the transistors 32 and 33 is connected to the input of the inverter 35, and the input voltage to the inverter 35 is 0V when the photodiode 31 is receiving light and 5V when not receiving light. The inverter 35 inverts and outputs the input voltage, and the output voltage becomes 5 V when the photodiode 31 receives light and becomes 0 V when not receiving light.
[0026]
The AND circuit 36 receives the output voltage of the inverter 35 and the control voltage supplied to the amplifier 21. The light emitting unit 16 emits light when the control voltage is 5V and does not emit light when the control voltage is 0V. Therefore, the result of the logical operation becomes true only when the control circuit instructs the light emitting unit 16 to emit light and the photodiode 31 receives light. In spite of the control circuit instructing to emit light, the light emitting unit 16 does not emit light for some reason such as a failure of the drive circuit 13, and therefore the operation result is false when the photodiode 31 does not receive light. Thereby, it can be investigated whether the light emission part 16 operate | moves correctly according to the light emission instruction | indication.
[0027]
The AND circuit 36 outputs 5V or 0V depending on whether the operation result is true or false. The output of the logical product circuit 36 is connected to the inspection terminal 12a of the semiconductor chip 2 through the logical sum circuit 37, and the light emission operation of the light emitting unit 16 is inspected by the voltage of the inspection terminal 12a. The output terminals of the logical product circuits 36 of all the light emitting units 16 are connected to the input terminals of the logical sum circuit 37. By giving a light emission instruction to each light emitting unit in order, only one inspection terminal 12a is used. All the light emitting units 16 can be inspected.
[0028]
In the present embodiment, the light is detected by the photodiode 31, but the light may be detected using another light receiving element such as a phototransistor. Further, the light emission test can be performed by omitting the AND circuit 36 and directly connecting the output of the inverter 35 to the test terminal 12a. However, in that case, it becomes difficult to understand the correspondence between which light emitting unit is given a light emission instruction and which light receiving unit output is detected, and the inspection process becomes complicated. It is desirable to provide.
[0029]
Furthermore, the relationship between the control voltage and the light emission and the relationship between the light reception and the detection voltage are not limited to those illustrated, but can be arbitrarily set. At this time, the logic circuit is appropriately selected from a logical product circuit, a logical sum circuit, and an exclusive logical sum circuit in consideration of these relationships.
[0030]
【The invention's effect】
When the display device according to claim 1 is used, the light emission of the light emitting element can be detected as an electric signal by the light receiving element, so that the light emission is observed with the naked eye, or an optical device for measuring the light emission is used. It is possible to inspect whether or not the display device emits light properly. Therefore, the inspection becomes easy and the time required for the inspection is shortened. Moreover, since a plurality of light emitting units are provided, the light emission of each light emitting unit can be individually examined, and all the light emitting units can be reliably inspected. Note that each light-emitting element can be formed in a very small size and a large number of light-emitting portions can be formed, so that a small-sized and high-resolution display device can be obtained. Moreover, even a device having a large number of light emitting units can easily inspect all the light emitting units in a short time. Further, since the drive circuit and the light receiving element are formed on the same semiconductor chip, it is not necessary to form the drive circuit and the light receiving element in separate steps, and the number of manufacturing steps is shortened.
[0031]
In the display device according to claim 2, each light emitting element emits light when commanding light emission, and whether light emission is stopped when light emission is prohibited can be examined without being affected by outside light. The result is highly reliable.
[0032]
In the display device according to the third aspect, it is possible to inspect all the light emitting units with the same output terminal, and there is no need to change the terminal to be measured depending on which light emitting unit emits light. Therefore, the inspection efficiency is improved. Further, it is not necessary to form a large number of inspection output terminals, and the configuration on the outer surface of the display device is simple.
[0034]
The display device of claim 4 is a bright display device because the luminance of the light emitting element is high.
[Brief description of the drawings]
FIG. 1 is a plan view showing a configuration of a fluorescent display tube according to an embodiment of the present invention.
FIG. 2 is a partial cross-sectional view of the fluorescent display tube.
FIG. 3 is a plan view of a semiconductor chip used in the fluorescent display tube.
FIG. 4 is an enlarged cross-sectional view showing the vicinity of a light emitting portion of the fluorescent display tube.
FIG. 5 is a diagram showing a configuration of a light emitting unit and a light receiving unit formed on the semiconductor chip.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Fluorescent display tube 2 Semiconductor chip 2a Display part 2b Input / output part 3 Glass tube 4 Hot cathode 5 Grid 6 Shading plate 6a Reflecting surface 11 Pixel 12 Input / output terminal 12a Inspection terminal 13 Drive circuit 14 Electrode 15 Phosphor 16 Light emitting part 17 Light reception Part 31 photodiode 36 AND circuit

Claims (4)

A light emitting portion composed of the light-emitting element and its drive circuit with a plurality Yes, in a display device comprising a light receiving element for converting into an electric signal by receiving light the light emitting element emits per light emitting portion,
A plurality of driving circuits are formed on a semiconductor chip, a light emitting element is formed on each driving circuit to form the light emitting portion, the light receiving element is formed on the surface of the semiconductor chip near the driving circuit, and light emitted from the light emitting element A display device characterized in that a reflection plate that reflects light and guides it to the light receiving element is provided above the semiconductor chip between the drive circuit and the light receiving element . The display device according to claim 1, further comprising a logic circuit that performs a logical operation of a control signal for controlling the driving circuit and an electric signal of the light receiving element for each light emitting unit. The display device according to claim 2, further comprising an output terminal to which outputs of the logic circuits of all the light emitting units are connected. The display device according to claim 1, wherein each light emitting element is made of a phosphor, and the semiconductor chip is housed in a vacuum tube to form a fluorescent display tube .

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