JP3254965B2 - Plasma address display - Google Patents

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 flat panel in which a display cell and a plasma cell are overlapped. Specifically, the present invention relates to a driving circuit configuration of a plasma cell. More specifically, the present invention relates to a technology for protecting a constant current circuit incorporated in a drive circuit.

[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 a panel structure thereof. 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 or the like. The plasma cell 102 is formed using a lower substrate 104, and has a plurality of grooves 1 parallel to each other on the surface thereof.
05 is provided. Each groove 105 is hermetically sealed by the intermediate substrate 103. An ionizable gas is sealed therein, and the discharge channels 1 are individually separated.
06 is formed. Protrusions 10 interposed between grooves 105
Reference numeral 7 serves as a partition for separating the individual discharge channels 106, and also serves as a gap spacer of the lower substrate 104 with respect to the intermediate substrate 103. A pair of discharge electrodes 108 and 109 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 a plasma discharge. On the other hand, the display cell 101 includes an electro-optical material such as a liquid crystal 111 sandwiched between the intermediate substrate 101 and the upper substrate 110. On the inner surface of the upper substrate 110, a stripe-shaped signal electrode 112 is formed. This signal electrode 112 is orthogonal to the discharge channel 106 described above. The signal electrode 112 becomes a column drive unit (vertical line) and the discharge channel 106 becomes a row scan unit (horizontal line), and a matrix of pixels is defined at the intersection of the two.

An external scanning circuit and signal circuit are used to drive the plasma addressed display panel having such a configuration. The scanning circuit selectively scans the discharge channel 106 line-sequentially to generate a plasma discharge, and the signal circuit displays a desired image by applying an image signal to the signal electrode 112 in synchronization with the line-sequential scanning described above. I do. When a plasma discharge occurs in the discharge channel, the inside thereof is maintained at substantially the anode potential. In this state, the signal electrode 1
When an image signal is applied to the pixel 12, the image signal is written to the liquid crystal 111 of each pixel via the intermediate substrate 103. When the plasma discharge ends, the discharge channel 106 becomes a floating potential, and the written image signal is held in each pixel. A so-called sampling hold is performed, and the discharge channel 10
6 functions as a sampling switch, while the liquid crystal 1
11 functions as a sampling capacitor. The transmittance of the liquid crystal changes in accordance with the image signal that is sample-holded, and the brightness of the plasma addressed display panel can be controlled in pixel units.

[0004]

FIG. 5 is a circuit diagram showing an example of a conventional scanning circuit. Here, VH represents a power supply voltage for causing a discharge, and Rr is a resistor for limiting a discharge current flowing through a discharge channel. A represents an anode electrode, and K represents a cathode electrode. One discharge channel is constituted by the pair of anode electrode and cathode electrode. Rp is a pull-up resistor for keeping the cathode electrode K at the anode potential when not selected. This scanning circuit includes switches SW1, SW2,.
n is sequentially turned on / off to supply a discharge current to each discharge channel to generate a plasma discharge. In synchronization with this, an image signal is supplied to a signal electrode (not shown), and the image signal is written to each pixel corresponding to the selected discharge channel (horizontal line). In the plasma addressed display device, line-sequential scanning of a horizontal line during image display is performed by sequentially selecting an anode electrode and a cathode electrode and performing a plasma discharge. At this time, as a means for limiting the discharge current, a constant current circuit (not shown) is provided in a common path of each cathode electrode. Thus, the discharge current flowing through each discharge channel can be accurately controlled. As an operation of the constant current circuit, when the discharge current exceeds a certain value, the voltage between the anode electrode and the cathode electrode is correspondingly reduced to reduce the current. Conversely, when the value is smaller than the predetermined value, the voltage between the anode electrode and the cathode electrode is increased to increase the discharge current. Normally, the electrical resistance between the anode electrode and the cathode electrode during plasma discharge is substantially constant, and the voltage between the anode electrode and the cathode electrode is also substantially constant. However, if the resistance between the anode electrode and the cathode electrode drops for some reason, or if the anode electrode / cathode electrode is short-circuited, the constant current circuit tries to lower the voltage between the anode electrode and the cathode electrode, and the voltage is fixed. It is consumed in the current circuit. At this time, if the voltage between the anode and the cathode is, for example, normally 300 V and the constant current value (current limit value) is 0.2 A, the constant current circuit is 60 W
Will be consumed. In this case, the constant current circuit generates a large amount of heat, which is not always desirable as a product, and some countermeasures are required.

[0005]

In order to solve the above-mentioned problems of the prior art, the following measures have been taken. That is, the plasma addressed display device according to the present invention includes a panel, a scanning circuit, a signal circuit, a constant current circuit, and a protection circuit. The panel has a stacked structure in which plasma cells having discharge channels serving as horizontal lines and display cells having signal electrodes serving as vertical lines are stacked on each other. The scanning circuit sequentially supplies a discharge current to the discharge channel to perform line-sequential scanning of a horizontal line. The signal circuit applies an image signal to a signal electrode in synchronization with line-sequential scanning to display an image. When the discharge current exceeds a predetermined limit value, the constant current circuit performs a limiting operation to stabilize the discharge current. As a characteristic feature, the protection circuit measures the power consumed by the limiting operation as needed, and suppresses the limiting operation itself of the constant current circuit when excessive power is consumed. Specifically, the constant current circuit has a floating potential output terminal for performing a discharge current limiting operation by increasing and decreasing a voltage between a pair of anode electrode and cathode electrode constituting each discharge channel. In this case, the protection circuit measures power consumption based on the integrated value of the floating potential. Further, the protection circuit stops (prohibits) the limiting operation of the constant current circuit when the power consumption measured at any time exceeds a predetermined level.

[0006]

According to the present invention, a constant current circuit is used for limiting a discharge current in a plasma addressed display device. When a constant or more heat loss is applied to the constant current circuit, the operating current is suppressed to protect the constant current circuit and protect the panel.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing a basic configuration of a plasma addressed display device according to the present invention. The present plasma address display device includes a panel 1, a scanning circuit 2, and a signal circuit 3 as a basic configuration. Panel 1
Has a stacked structure in which a display cell and a plasma cell are stacked on top of each other, and is basically as shown in FIG. The display cell has a signal electrode 4 serving as a vertical line, while the plasma cell has a discharge channel 5 serving as a horizontal line. The discharge channel 5 is composed of a pair of an anode electrode A and a cathode electrode K. Pixel 6 is defined at the intersection of signal electrode 4 and discharge channel 5. The pixels 6 are arranged in a matrix to form a display screen. The scanning circuit 2 sequentially supplies a discharge current to the discharge channels to perform line-sequential scanning of horizontal lines. on the other hand,
The signal circuit 3 displays an image by applying an image signal to a signal electrode of a vertical line in synchronization with line-sequential scanning of a horizontal line.
A synchronizing circuit 7 is connected to the scanning circuit 2 and the signal circuit 3 and generates a synchronizing signal necessary for synchronizing the two. An image processing circuit 8 is connected to the signal 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 driving the panel 1.

As features of the present invention, a constant current circuit 9 and a protection circuit 10 are provided. When the discharge current exceeds a predetermined limit value, the constant current circuit 9 performs a limiting operation to stabilize the discharge current. The protection circuit 10 measures the power consumed by the limiting operation as needed, and suppresses the limiting operation itself of the constant current circuit 9 when excessive power is consumed. Specifically, the constant current circuit 9 raises and lowers the voltage between the pair of anode electrodes A and the cathode electrodes K constituting each discharge channel (voltage between the anode electrode and the cathode electrode) to perform a floating current limiting operation. A potential output terminal is provided. In this case, the protection circuit 10 measures the power consumption based on the integrated value of the floating potential. Further, the protection circuit 10 stops (prohibits) the limiting operation of the constant current circuit 9 when the power consumption measured as needed exceeds a predetermined level. This protects the constant current circuit 9 and the panel 1 as well.

FIG. 2 is a circuit diagram showing a specific configuration example of the scanning circuit 2, the constant current circuit 9, and the protection circuit 10 shown in FIG. In the figure, A1 to An are anode electrodes, which are commonly connected. K1 to Kn are cathode electrodes, and the above-mentioned portions are provided in the panel 1. Switch S
W1 to SWn are plasma drivers mounted outside the panel 1 and constitute the scanning circuit 2. Each of the switches SW1 to SWn has a corresponding cathode electrode K1 to Kn.
It is connected to the. The main power supply supplies a discharge voltage VH, which is usually around 300V.

Next, the constant current circuit 9 will be described. This constant current circuit 9 is a typical current mirror circuit, and has an output transistor Q1. Since the collector of Q1 allows a constant current to flow through the load resistor R1, it has a floating potential that fluctuates freely. The diode D1 is a first recovery diode added to constantly supply a current between the collector and the emitter of the output transistor Q1. This is used to speed up the response of the constant current circuit 9. The sub power supply VS is a power supply for generating a reference potential of the constant current circuit 9, and also has a role of constantly supplying a current between the collector and the emitter of the output transistor Q1. For example, the output voltage of the sub power supply VS is set to 12V.

Here, the overall operation will be described. Switch S
W1 to SWn are selectively turned on in order from the first SW1 to scan a horizontal line on the screen. For example, when displaying an image signal according to the NTSC standard, the ON time is 10 μs, and the time for selecting the next SW2 is 63.4 μs.
s. In the figure, SW2 is on, and the other SWs are off. At this time, VH of about 300 V is applied between the anode electrode A and the cathode electrode K, and plasma discharge occurs between the anode electrode and the cathode electrode. At this time, the discharge current flows from the positive terminal of VH through A2 / K2, passes through the collector / emitter of the transistor Q1, and then flows from the load resistor R1 to the ground. During about 53.4 μs immediately after SW2 is turned on, SW1 to SWn are all off. At this time, the current in the constant current circuit 9 flows from the positive side of VS through the diode D1, through the collector / emitter of the transistor Q1, and then to ground. The current flowing at this time is the emitter potential V _E1 of the transistor Q1.
And determined by the load resistor R1, it becomes V _E1 / R1 = I _C. In this example, the constant current I _C generated by the constant current circuit 9 is equal to 0.1.
2A is set.

FIG. 3 shows a typical voltage / voltage of each discharge channel.
It shows current (V / I) characteristics. As is apparent as from the discharge characteristic graph, when determining the discharge current to a constant value I _C, the voltage between the anode / cathode electrode uniquely determined V _C. At this time, focusing on the collector potential V _C1 of the transistor Q1, V _C1 = 300V−V _C. On the other hand, the emitter potential V _E1 of the transistor Q1 is determined from the constant of the current mirror circuit, and {R3 / (R2 + R3)} × (VS
−V _BE ) −V _BE . Accordingly, the collector / emitter potential V _C1 -V _E1 of the transistor Q1 is expressed as follows.

(Equation 1) The power consumed by the transistor Q1 is W _Q1 = (V _C1
-V _E1) because it is × I _C, as V _C decreases W _Q1
Turns out to be larger. By the way, considering the case where the anode electrode A / cathode electrode K is short-circuited for some reason, the potential between the collector and the emitter of the transistor Q1 becomes 3
It is fixed near 00V. Therefore, W _Q1 is 60W
And excessive power is applied to the transistor Q1, which may cause breakdown. At this time, the transistor Q1
If an open fault occurs between the collector and the emitter, there is no current path and only discharge does not occur. Conversely, when a short circuit occurs between the collector and the emitter of the transistor Q1, the limiting operation of the constant current circuit becomes ineffective, and some countermeasures are required.

In view of this point, in the present invention, a protection circuit 10 is added as shown in FIG. In this protection circuit 10, the resistor R4 and the capacitor C2 integrate the collector potential V _C1 of the transistor Q1 with a sufficiently large time constant to give a base potential V _B3 of the transistor Q3. Resistor R connected in series
5, R6 are the emitter potential V _E3 (= V
_C3 -V _BE ). The resistor R7 is a resistor for setting the base current of the transistor Q4.
When the base potential V _B4 of the transistor Q4 becomes _{equal to} or higher than V _BE , the transistor Q4 is turned on, and the base potential V _B1 of the transistor Q1 is reduced to 0V. At this time, I _C = 0, and
Since W _Q1 = 0, the transistor Q1 does not fail. Here, by changing the division ratio of the resistors R5 and R6, can be set W _Q1 which W _Q1 protection circuit operates above a certain level. For example, I _C = 0.2 A, R 5 = 100 k, R 6
= 1k, V _BE = 0.6V, V _C1 is about 60V,
When W _Q1 = V _C1 × I _C = 12 W, the protection circuit 10 operates. In this case, the transistor Q1 on the constant current circuit 9 side
If the power P _{C at} the limit of thermal destruction is larger than 12 W, there is no possibility of failure.

[0014]

As described above, according to the present invention, the power consumed by the limiting operation of the constant current circuit is measured by the protection circuit at any time, and when the excessive power is consumed, the power consumption of the constant current circuit is reduced. The limiting operation itself is suppressed. Thereby, the failure of the constant current circuit can be prevented, and the protection of the panel is ensured. Further, since the heat generation of the constant current circuit can be suppressed to a certain level or less, the heat radiation design becomes easy and the size can be reduced.

[Brief description of the 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 scanning circuit, a constant current circuit, and a protection circuit incorporated in the plasma addressed display device shown in FIG.

FIG. 3 is a graph showing a voltage / current characteristic of a discharge channel.

FIG. 4 is a partially cutaway perspective view showing a general configuration of a plasma addressed display panel.

FIG. 5 is a circuit diagram for explaining the operation of the plasma addressed display panel shown in FIG. 4;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Panel 2 Scanning circuit 3 Signal circuit 4 Signal electrode 5 Discharge channel 6 Pixel 7 Synchronization circuit 8 Image processing circuit 9 Constant current circuit 10 Protection circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02F 1/133 G02F 1/1333 G09G 3/36

Claims (3)

(57) [Claims] 1. A panel in which a plasma cell having a discharge channel serving as a horizontal line and a display cell having a signal electrode serving as a vertical line are overlapped with each other. A scanning circuit for performing an operation, a signal circuit for applying an image signal to a signal electrode in synchronization with the line-sequential scanning to display an image, and performing a limiting operation when the discharge current exceeds a predetermined limit value to reduce the discharge current. A plasma address comprising a constant current circuit for stabilizing, and a protection circuit for measuring the power consumed by the limiting operation as needed and suppressing the limiting operation itself of the constant current circuit when excessive power is consumed. Display device. 2. The constant current circuit according to claim 1, further comprising a floating potential output terminal for performing a discharge current limiting operation by increasing or decreasing a voltage between a pair of anode electrode and cathode electrode constituting each discharge channel. 2. The plasma addressed display device according to claim 1, wherein the protection circuit measures power consumption based on an integrated value of the floating potential. 3. The plasma addressed display device according to claim 1, wherein the protection circuit stops the limiting operation of the constant current circuit when the power consumption measured as needed exceeds a predetermined level.