JPH08304768A - Plasma address display device - Google Patents

Abstract

PURPOSE: To optimize a discharge voltage impressed on discharge channels of plasma cells. CONSTITUTION: A plasma address display device is provided with a panel 1, a plasma driving circuit 2, display driving circuit 3, a constant current circuit 9, a detection circuit 10 and a control circuit 11. The panel 1 has an alternately laminated structure of plasma cells with an array of electric discharge channels 5 for horizontal lines and display cells with an array of the signal electrodes 4 for the vertical lines. The plasma driving circuit 2 sequentially impresses an electric discharge voltage on each discharge channel 5 for driving selectively, and performs line sequential. Scanning of the horizontal lines. Display driving circuit 3 impresses picture signals to the signal electrodes 4 in synchronism with the line sequential scanning and displays a desired picture on the panel 1. The constant current circuit 9, in the case that the discharge current exceeds a certain value at the time at driving, performs a limiting action to keep the current at approximately constant value. The detection circuit 10 detects whether or not there is the limiting action in each discharge channel 5 according to the line sequential Scanning. The control circuit 11 optimally controls the discharge voltage according to the result of the detection.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plasma addressed display device using a panel in which a display cell and a plasma cell are stacked. More specifically, it relates to a driving circuit configuration of a plasma cell. More specifically, it relates to a technique for controlling a discharge voltage supplied to a plasma cell.

[0002]

2. Description of the Related Art A plasma addressed display device is disclosed in, for example, Japanese Patent Application Laid-Open No. 1-217396, and FIG. 4 shows its panel structure. The plasma addressed display panel has a laminated structure in which a display cell 101 and a plasma cell 102 are stacked via an intermediate substrate 103 made of thin glass plate or the like. The plasma cell 102 is formed using the lower substrate 104, and has a plurality of grooves 1 parallel to each other on its surface.
05 is provided. Each groove 105 is hermetically sealed by the intermediate substrate 103. An ionizable gas is enclosed in it, and the discharge channels 1 are individually separated.
06 is formed. The ridge portion 10 interposed between the grooves 105
7 serves as a partition wall for separating the individual discharge channels 106, and also serves as a gap spacer for the lower substrate 104 with respect to the intermediate substrate 103. A pair of discharge electrodes 108 and 109 which are parallel to each other are provided at the bottom of each groove 105. The pair of discharge electrodes function as an anode electrode and a cathode electrode for ionizing the gas in the discharge channel 106 to generate plasma discharge. On the other hand, the display cell 101 includes a liquid crystal 111 sandwiched between an intermediate substrate 103 and an upper substrate 110. A stripe-shaped signal electrode 112 is formed on the inner surface of the upper substrate 110. This signal electrode 112 is orthogonal to the above-mentioned discharge channel 106. The signal electrode 112 becomes a vertical line and the discharge channel 106 becomes a horizontal line, and pixels in a matrix are defined at the intersections of the two.

A plasma driving circuit and a display driving circuit are used to drive the plasma addressed display panel having such a structure. The plasma drive circuit has each discharge channel 10
A sequential discharge voltage is applied to 6 for selective driving, and line sequential scanning of horizontal lines is performed. The display drive circuit applies an image signal to the signal electrode 112 in synchronization with the line-sequential scanning to display a desired image on the panel. When the discharge channel 106 is driven to generate plasma discharge, the inside thereof is maintained at substantially the anode potential. When an image signal is applied to the signal electrode 112 in this state, the liquid crystal 1 of each pixel is passed through the intermediate substrate 103.
The image signal is written in 11. When the plasma discharge ends, the discharge channel 106 becomes a floating potential and the written image signal is held in each pixel. So-called sampling hold is performed, and the discharge channel 106 functions as a sampling switch, while the liquid crystal 111 functions as a sampling capacitor. The transmittance of the liquid crystal changes according to the sampled and held image signal, and the brightness of the display cell can be controlled in pixel units.

[0004]

FIG. 5 is a circuit diagram showing an example of a conventional plasma drive circuit. Where VH
Represents the power supply voltage (discharge voltage) for causing discharge,
Rr is a resistor for limiting the discharge current flowing in the discharge channel. A represents an anode electrode, and K represents a cathode electrode. A pair of the anode electrode A and the cathode electrode K constitutes a discharge channel of one horizontal line. Rp is a pull-up resistor for holding the cathode electrode K at the anode potential when not selected. This plasma drive circuit sequentially turns on switches SW1, SW2, ..., SWn
It is turned off to generate plasma discharge in each discharge channel. In synchronization with this, an image signal is supplied to the signal electrode (not shown), and the image signal is written in each pixel on the horizontal line corresponding to the selected discharge channel.

By the way, it is desirable that the discharge voltage-discharge current (V / I) characteristics of the discharge channels forming the horizontal line are the same for all channels. However, in reality, there is also a problem in the manufacturing process, and it is inevitable that the discharge voltage-discharge current characteristics (discharge characteristics) of the respective discharge channels will vary to some extent. Even if the manufacturing process is improved, it is difficult to completely eliminate the variation in the discharge characteristics. On the other hand, in order to display an accurate image on the plasma addressed display panel, it is necessary that the same amount of discharge current flows through all the discharge channels. Conventionally, in order to drive all discharge channels with the same amount of discharge current, a high discharge voltage is applied to the discharge channels, and a large amount of discharge current is controlled by a constant current circuit (not shown). The discharge current was made constant in all channels by limiting the current in all discharge channels. However, this control method does not cause a problem if the discharge characteristics of the respective discharge channels are constant, but if the discharge characteristics change, the discharge voltage must be adjusted. However, no measures have heretofore been taken regarding this point.

[0006]

Means for Solving the Problems In order to solve the above-mentioned problems of the conventional technique, the following means were taken. That is, the plasma address display device according to the present invention has a panel, a plasma drive circuit, a display drive circuit, a constant current circuit, a detection circuit, and a control circuit as a basic configuration. The panel has a laminated structure in which plasma cells in which discharge channels are arranged as horizontal lines and display cells in which signal electrodes are arranged as vertical lines are overlapped with each other. The plasma drive circuit applies a sequential discharge voltage to each discharge channel to selectively drive the discharge channels to perform line sequential scanning of horizontal lines. The display drive circuit applies an image signal to the signal electrodes in synchronization with the line-sequential scanning to display a desired image on the panel. The constant current circuit performs a limiting operation and suppresses the discharge current to a constant value when the discharge current flowing when driving each discharge channel exceeds a constant value. The detection circuit detects the presence or absence of the limiting operation for each discharge channel along the line-sequential scanning. The control circuit optimally controls the discharge voltage according to the detection result. For example, the control circuit counts the number of times the limiting operation is performed, adjusts the discharge voltage downward when the limiting operation is applied to a certain number or more of discharge channels, and limits the discharge voltage to a certain number or less. If there is no operation, adjust the discharge voltage upward. The constant current circuit has an output terminal of floating potential, and when the limiting operation is started, the floating potential rises and the voltage between the anode electrode and the cathode electrode forming the discharge channel is reduced to cause discharge. Limit the current to a constant value.
In this case, the detection circuit detects the presence or absence of the limiting operation based on the fluctuation of the floating potential.

[0007]

According to the present invention, in the plasma addressed display device, when the discharge channel forming the horizontal line is driven, the floating potential of the constant current circuit for limiting the discharge current is detected, and the discharge voltage is determined based on the result. Optimal control. In other words, when the constant current circuit performs the current limiting operation, the applied voltage between the anode electrode and the cathode electrode forming the discharge channel fluctuates contractively. When this fluctuation is detected and a current limit is applied to a certain number or more of discharge channels by the constant current circuit, the discharge voltage is lowered. On the contrary, when the current limit is applied only to a certain number of channels or less, the discharge voltage is controlled to be increased.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing the basic configuration of a plasma addressed display device according to the present invention. The plasma addressed display device includes a panel 1, a plasma drive circuit 2 and a display drive circuit 3. The panel 1 has a laminated structure in which a display cell and a plasma cell are stacked on each other, and is basically as shown in FIG. The display cell has signal electrodes 4 arranged on vertical lines, while the plasma cell has discharge channels 5 which are horizontal lines. The discharge channel 5 is composed of a pair of an anode electrode A and a cathode electrode K. A pixel 6 is defined at the intersection of the signal electrode 4 and the discharge channel 5. The pixels 6 are arranged in a matrix to form a display screen. The plasma drive circuit 2 applies a sequential discharge voltage to each discharge channel 5 to selectively drive it,
Line-sequential scanning of horizontal lines is performed. On the other hand, the display drive circuit 3 applies an image signal to the signal electrode 4 in synchronization with the line-sequential scanning to display a desired image on the panel 1. A synchronizing circuit 7 is connected to the plasma driving circuit 2 and the display driving circuit 3 and generates a synchronizing signal necessary for synchronizing the two.
An image processing circuit 8 is connected to the display drive circuit 3 and converts a primary image signal such as a composite video signal supplied from the outside into a secondary image signal suitable for AC driving of the panel 1.

A constant current circuit 9, a detection circuit 10 and a control circuit 11 are provided as features of the present invention. When the discharge current flowing when each discharge channel 5 is driven exceeds a constant value, the constant current circuit 9 performs a limiting operation to suppress the discharge current to the constant value. The detection circuit 10 detects the presence or absence of the limiting operation for each discharge channel 5 according to the line-sequential scanning. The control circuit 11 optimally controls the discharge voltage according to the detection result. For example, the control circuit 11 counts the number of times the limiting operation is performed, and when the limiting operation is applied to a certain number or more of the discharge channels 5, the discharge voltage is adjusted downward so that the discharging channel 5 is limited to the certain number or less. If there is no operation, adjust the discharge voltage upward. The constant current circuit 9 has a floating potential output terminal. When the limiting operation is started, the floating potential rises and the voltage between the anode electrode A and the cathode electrode K forming the discharge channel 5 is reduced. The discharge current is limited to a certain value. In this case, the detection circuit 10 detects the presence or absence of the limiting operation based on the fluctuation of the floating potential appearing at the output terminal of the constant current circuit 9.

FIG. 2 is a circuit diagram showing a concrete configuration example of the plasma addressed display device shown in FIG. A in the figure
1 to An are anode electrodes, which are commonly connected to each other. K1 to Kn are cathode electrodes, and the above portions are formed in the panel 1. SW1 to SWn are plasma drivers attached to the outside of the panel 1 and constitute a plasma drive circuit 2. SW1 to SWn are connected to the corresponding cathode electrodes K1 to Kn, respectively. VH
Is a power supply for supplying a predetermined discharge voltage. Normally, the discharge voltage VH is adjusted to around 300V.

Next, the constant current circuit 9 will be described. The constant current circuit 9 is composed of a typical current mirror circuit and includes a pair of output transistor Q1 and input transistor Q2. The collector terminal of the output transistor Q1 has a floating potential that freely changes because a constant current flows through the load resistor R1. D1 is a fast recovery diode added to constantly supply a current between the collector and the emitter of the transistor Q1, and the constant current circuit 9
It is for improving the responsiveness of. VS is a constant current circuit 9
Is a power supply provided to create the reference potential of the transistor Q1 and also serves to constantly supply a current between the collector and the emitter of the transistor Q1. The power supply voltage VS is set to 12V, for example.

The operation of the plasma drive circuit 2 and the constant current circuit 9 will be described. SW1 to SWn are the first SW1
From then on, the on state is selectively turned on, and the horizontal lines on the display screen are line-sequentially scanned. For example, when displaying an NTSC standard image, the on time of SW1 is 10 μs, and the next SW2
The time interval until is selected is 63.4 μs. In the figure, just SW2 is on and the other SWs are off. At this time, the anode electrode A2 / the cathode electrode K
A discharge voltage VH of about 300 V is applied between the two, and a plasma discharge is generated between the anode electrode A2 / the cathode electrode K2. This discharge current flows from the positive side of VH through A2 / K2, after passing through the collector / emitter of the transistor Q1, and then flows from the load resistor R1 to the ground. Approximately 53.4 μs after SW2 returns to the OFF state, SW1 to S
All of Wn are turned off, and at this time, the current flows from the positive electrode side of VS through D1 to the collector / emitter of Q1 and then to the ground. The constant current flowing at this time is determined by the emitter potential V _E1 of the transistor Q1 and the load resistance R1, and V _E1 / R1 = I _C. In this example, this constant current I _C is set to 0.2A.

FIG. 3 shows a typical voltage / current (V / I) characteristic of the discharge channel. As is clear from the graph of the discharge characteristic, once the discharge current is determined to be I _C , the voltage applied between the anode electrode and the cathode electrode is uniquely V _C.
Depends on. At this time, the collector potential V of the transistor Q1
_Focusing on _C1 , V _C1 = 300V−V _C. By the way, since the V / I characteristics vary depending on the individual discharge channels, even if the discharge voltage is constant, the discharge current cannot be made completely the same in all the channels as it is. Therefore, if the discharge voltage is adjusted to be higher and a voltage of I _C = 0.2 A or more is applied to all the horizontal lines, current limitation is applied to all the horizontal lines, and the discharge current can be fixed to 0.2 A. . Here, the optimum discharge voltage is I _C ≧ 0.2 A in all horizontal lines (discharge channels)
It will be the lowest level that satisfies. The reason is that the constant current circuit 9
This is to minimize the current that flows until the response of.

As a feature of the present invention, a detection circuit 10 and a control circuit 11 are incorporated in the concrete configuration shown in FIG. The collector terminal of the output transistor Q1 of the constant current circuit 9 is connected to the base terminal of the transistor Q3 on the detection circuit 10 side via the buffer resistor R4. Therefore, the transistor Q3 is an emitter follower output with respect to the collector potential of the transistor Q1. Resistance R
5 and R6 divide the emitter potential of transistor Q3. The resistor R7 is a resistor that limits the base current of the transistor Q4 in the next stage. The transistor Q4 is a common-emitter switching transistor whose collector terminal becomes 0 V when its base potential becomes higher than V _BE . Note that VD is a power source for adding a potential of about several V to VS, and ensures the operation of the transistor Q3. A control circuit 11 is connected to the detection circuit 10 having such a configuration. The control circuit 11 includes a counter 21 and a power supply voltage controller 22.

Continuing to refer to FIG. 2, the operation of the detection circuit 10 and the control circuit 11 will be described in detail. When the collector potential of the transistor Q1 becomes slightly higher than VS and the limiter (current limiting) of the constant current circuit 9 operates, the base potential of the transistor Q4 becomes _{equal to} or higher than V _BE, and the resistors R5 and R are provided.
A division ratio of 6 is set. For example, when the collector potential of the transistor Q1 is VS + several V, the transistor Q4 is turned on. Then, a high-level pulse is input to the counter 21, and the discharge channel is detected as being current-limited and is counted up. Therefore, when the current limitation is applied to all the discharge channels, the counter 21 issues an instruction to the power supply voltage controller 22 to lower VH a little. When the line-sequential scanning of all the horizontal lines is completed once, the counter 21 is reset in the V cycle (vertical cycle), and similarly in the next V cycle, the presence / absence of current limitation is counted for each horizontal line and a part of If there is no current limit on the line, raise VH a little. Further, when the current limitation is applied again to all the lines in the next V cycle, the operation of slightly lowering VH is repeated. The repetition cycle does not have to be every V cycle in particular, and the discharge voltage may be adjusted in a long cycle as needed. Alternatively, the discharge voltage may be adjusted only once immediately after the power is turned on. Further, in this example, the discharge voltage V is based on the case where the current is limited to all the discharge channels (100%).
Adjusting H up and down. However, the present invention is not limited to this.
The VH may be adjusted up and down with reference to the case where the current is limited to 0% or 80%.

[0016]

As described above, according to the present invention, the constant current circuit performs the limiting operation when the discharge current flowing during the driving of each discharge channel exceeds a constant value, and suppresses the constant value. The detection circuit detects the presence or absence of the limiting operation for each discharge channel according to the line-sequential scanning of the discharge channel. The control circuit optimally controls the discharge voltage according to the detection result. With this configuration, when the discharge characteristic of the discharge channel changes with time, it can be optimized so that the discharge current is constant and the discharge voltage is minimized. Further, the discharge voltage at which the discharge current becomes constant can be automatically set. Thereby, an accurate discharge voltage can be set.

[Brief description of drawings]

FIG. 1 is a block diagram showing a basic configuration of a plasma addressed display device according to the present invention.

FIG. 2 is a circuit diagram showing a specific configuration of a plasma addressed display device according to the present invention.

FIG. 3 is a graph showing typical discharge characteristics of a discharge channel.

FIG. 4 is a perspective view showing an example of a conventional plasma addressed display panel.

FIG. 5 is a circuit diagram showing an example of a conventional plasma drive circuit.

[Explanation of symbols]

 1 panel 2 plasma drive circuit 3 display drive circuit 4 signal electrode 5 discharge channel 6 pixel 7 synchronization circuit 8 image processing circuit 9 constant current circuit 10 detection circuit 11 control circuit 21 counter 22 power supply voltage controller

Claims (3)

[Claims] 1. A panel in which plasma cells in which discharge channels are arranged as horizontal lines and display cells in which signal electrodes are arranged as vertical lines are overlapped with each other, and a discharge voltage is sequentially applied to each discharge channel to selectively A plasma drive circuit that drives and performs line-sequential scanning of horizontal lines, a display drive circuit that applies an image signal to signal electrodes in synchronization with the line-sequential scanning to display a desired image on a panel, and when driving each discharge channel A constant current circuit that performs a limiting operation when the flowing discharge current exceeds a certain value and keeps it at the certain value, a detection circuit that detects the presence or absence of the limiting operation for each discharge channel according to the line-sequential scanning, and the detection result. A plasma address display device comprising a control circuit for optimally controlling the discharge voltage according to the control circuit. 2. The control circuit counts the number of times the limiting operation is performed, adjusts the discharge voltage downward when the limiting operation is applied to a certain number or more of the discharge channels, and adjusts the discharge voltage to a certain number or less. 2. The plasma addressed display device according to claim 1, wherein the discharge voltage is adjusted upward when the limiting operation is applied only. 3. The constant current circuit has an output terminal of a floating potential, and when the limiting operation is started, the floating potential rises to reduce a voltage between an anode electrode and a cathode electrode forming a discharge channel. 2. The plasma address display device according to claim 1, wherein the discharge current is limited to a certain value, and the detection circuit detects the presence or absence of the limiting operation based on the fluctuation of the floating potential.