JP2004361571A - Electrooptic device and electronic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress gray-scale deviation of pixels caused by a leak current of a protective circuit. <P>SOLUTION: This electrooptic device has a plurality of data lines X supplied with a data current regulating the gray scale of the pixel 2, and the protective circuit 6 connected to the data lines X for preventing dielectric breakage of an inner circuit, and discharging static electricity of the data lines X by causing the leak current to flow therethrough. A resistance value of a route through which the leak current flows in the protective circuit is set so that no deviation occurs in the display gray scale of the pixel due to a variation in data current caused by the leak current. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electro-optical device and an electronic apparatus, and more particularly, to a protection circuit connected to a data line to which data is supplied at a current level.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an electro-optical device in which a protection circuit for preventing electrostatic breakdown of an internal circuit is connected to a data line has been proposed (for example, Patent Documents 1 to 6). In particular, Patent Document 4 discloses that a resistance value of a protection circuit is set in consideration of a leak current flowing through the protection circuit in order to ensure inspection accuracy at the time of inspection of pixel characteristics.
[0003]
[Patent Document 1]
Japanese Patent Publication No. 3-54475 [Patent Document 2]
Japanese Patent Application Laid-Open No. 11-231345 [Patent Document 3]
Japanese Utility Model Publication No. 64-3827 [Patent Document 4]
Japanese Patent Application Laid-Open No. Hei 8-22024 [Patent Document 5]
JP-A-10-303431 [Patent Document 6]
JP-A-7-294952.
[0004]
[Problems to be solved by the invention]
By the way, in the current programming method in which data is supplied to the data line on a current basis, there is a problem that if a leak current of a protection circuit connected to the data line becomes large, a display gray level of a pixel deviates from an original gray level. Occurs. Each of the above-mentioned patent documents basically relates to a voltage programming system (the liquid crystal adopts this system) in which data is supplied to data lines on a voltage basis. No consideration is given to the gradation shift due to the leak current.
[0005]
Therefore, an object of the present invention is to suppress a gradation shift caused by a leak current of a protection circuit in a current programming method.
[0006]
[Means for Solving the Problems]
In order to solve such a problem, a first aspect of the present invention is to connect a plurality of data lines to which a data current defining a gray level of a pixel is supplied and a data line connected to the data line to prevent electrostatic breakdown of an internal circuit. And a protection circuit that discharges static electricity of the data line by flowing a leak current. Here, the resistance value in the path through which the leakage current flows in the protection circuit is set to a resistance value that does not cause a shift in the display gradation of the pixel due to the fluctuation of the data current due to the leakage current. This resistance value is preferably set based on the maximum value of the voltage applied to the protection circuit.
[0007]
In the first invention, the protection circuit may be connected to the pair of data lines. In this case, it is preferable that the resistance value of the protection circuit is set to a resistance value such that the leak current is smaller than 最小 of the minimum value of the current change amount between adjacent gray scales.
[0008]
In the first invention, the protection circuit may be connected to the data line and a power supply line supplied with a predetermined voltage. In this case, it is preferable that the resistance value of the protection circuit is set to a resistance value such that the leak current is smaller than the minimum value of the current change amount between the mutually adjacent gradations.
[0009]
According to a second aspect, there is provided an electronic apparatus in which the electro-optical device according to the first aspect is mounted.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
(1st Embodiment)
FIG. 1 is a block diagram of the electro-optical device according to the present embodiment. In the display unit 1, pixels 2 of m dots × n lines are arranged in a matrix (in a two-dimensional plane). Further, the display unit 1 is provided with horizontal lines Y1 to Yn each extending in the horizontal direction and data lines X1 to Xm each extending in the vertical direction. Pixels 2 are arranged corresponding to the intersections. The scanning line driving circuit 3 and the data line driving circuit 4 control the display of the display unit 1 in cooperation with each other. That is, the scanning line driving circuit 3 sequentially selects the scanning lines Y1 to Yn corresponding to the pixel rows (pixel groups existing on one horizontal line) to which data is to be written in a predetermined scanning direction. . The data line driving circuit 4 supplies a data current Idata defining the gradation of the pixel 2 to the pixel row to which data is to be written, via the data lines X1 to Xm. Data writing is performed by a current programming method in which data is supplied to the data line X on a current basis.
[0011]
FIG. 2 is a circuit diagram of the pixel 2 as an example in the current programming method. One pixel 2 includes an organic EL element OLED, four transistors T1 to T4, and a capacitor C that holds data. The gate of the switching transistor T1 is connected to the scanning line Y to which the scanning signal SEL is supplied, and the source is connected to the data line X to which the data current Idata is supplied. The drain of the first switching transistor T1 is commonly connected to the source of the second switching transistor T2, the drain of the driving transistor T3, and the drain of the control transistor T4. The gate of the second switching transistor T2 is connected to the scanning line Y to which the scanning signal SEL is supplied, similarly to the first switching transistor T1. The drain of the second switching transistor T2 is commonly connected to one electrode of the capacitor C and the gate of the driving transistor T3. The power supply voltage Vdd is applied to the other electrode of the capacitor C and the source of the driving transistor T3. The control transistor T4 having the gate supplied with the control signal GP is provided between the drain of the driving transistor T3 and the anode (anode) of the organic EL element OLED. A voltage Vss lower than the power supply voltage Vdd is applied to a cathode (cathode) of the organic EL element OLED.
[0012]
The driving process of the pixel 2 in the current programming method is roughly classified into a data writing process and a subsequent driving process. In the write process, data is written to the capacitor C. Specifically, during a line selection period in which the scanning signal SEL is at a high level (hereinafter, referred to as “H level”), both the transistors T1 and T2 are turned on (conducting). Thus, the data line X is electrically connected to the drain of the transistor T3, and the transistor T3 has a diode connection in which its own gate and its own drain are electrically connected. The transistor T3 allows the data current Idata supplied from the data line X to flow through its own channel, and a gate voltage Vg corresponding to the data current Idata is generated at its own gate. Charges corresponding to the generated gate voltage Vg are accumulated in the capacitor C connected to the gate of the transistor T3, and data corresponding to the accumulated charge is written.
[0013]
In the driving process following the data writing process, the driving current Ioled flows through the organic EL element OLED, and the organic EL element OLED emits light. When the above-described line selection period elapses, the scanning signal SEL becomes L level, and the transistors T1 and T2 are both turned off (non-conductive). As a result, the data line X to which the data current Idata is supplied is electrically separated from the drain of the transistor T3, and the gate and drain of the transistor T3 are also electrically separated. However, even after the separation, the gate voltage Vg according to the charge stored in the capacitor C is continuously applied to the gate of the transistor T3. When the drive signal GP goes high in synchronization with the scan signal going low, the drive current Ioled via the transistors T3 and T4 and the organic EL element OLED from the power supply voltage Vdd toward the reference voltage Vss. Is formed. The drive current Ioled flowing through the organic EL element OLED corresponds to the channel current of the transistor T3, and its current level is controlled by the gate voltage Vg caused by the charge stored in the capacitor C. The organic EL element OLED emits light at a luminance corresponding to the drive current Ioled, whereby the gradation of the pixel 2 is set.
[0014]
The protection circuit 6 is a circuit that prevents electrostatic breakdown of the internal circuit. In the present embodiment, the protection circuit 6 is provided corresponding to the pair of data lines X, and is specifically connected to an external connection terminal connected to an FPC (Flexible Printed Circuit). FIG. 3 is a circuit diagram showing a configuration of a single protection circuit 6. The protection circuit 6 is generally called a diode ring, and has a configuration in which two diode rows 6a and 6b are connected in parallel in opposite directions. Each of the diode rows 6a and 6b is a series connection of a plurality of transistors functioning as nonlinear resistance elements by diode connection. The terminals a of the diode rows 6a and 6b are connected to the left data line X1, and these terminals b are connected to the right data line X2 adjacent to the data line X1.
[0015]
The protection circuit 6 discharges static electricity on the data line X by flowing a leak current Ileak according to the voltage Vab between the two terminals a and b. Specifically, when the voltage of the data line X1 becomes higher than the voltage of the data line X2 by the breakdown voltage of the protection circuit 6 or more, the path of the leak current Ileak from the terminal a to the terminal b via the diode array 6a. Is formed. On the other hand, when the voltage of the data line X2 becomes higher than the voltage of the data line X1 by the breakdown voltage of the protection circuit 6 or more, a path of the leak current Ileak from the terminal b to the terminal a is formed through the diode array 6b. You. Thus, when the applied voltage Vab of the protection circuit 6 exceeds a predetermined withstand voltage due to static electricity, the leak current Ileak flows in any direction, and acts in a direction to decrease the voltage Vab. As a result, the static electricity is discharged, and the internal circuit including the circuit system at the subsequent stage connected to the data lines X1 and X2 is prevented from being destroyed by the static electricity.
[0016]
By the way, in the current programming method, since the display gradation of the pixel 2 is defined by the current value of the data current Idata, when the leak current Ileak flows through the protection circuit 6, the current value of the data current Idata changes. For example, in the configuration of FIG. 3, when a leak current Ileak flows from the data line X1 to the data line X2, the current value I1 ′ of the data line X1 is Ileak smaller than the original value I1 supplied from the data line driving circuit 4. And the current value I2 'of the data line X2 increases by Ileak from the original value I2. The amount of the leak current Ileak depends on the applied voltage Vab of the protection circuit 6, and basically increases in proportion to the applied voltage Vab. Therefore, when the leak current Ileak becomes large, there is a disadvantage that a gradation shift or a gradation inversion of the pixel 2 occurs.
[0017]
In order to solve such inconvenience, in the present embodiment, in the protection circuit 6, the amount of the leak current Ileak is regulated by appropriately setting the resistance value R in the path where the leak current Ileak flows. FIG. 4 is a schematic characteristic diagram showing the relationship between the gradation and the data current Idata. Since the gray scale changes linearly with the current change, the current change amount ΔI (hereinafter referred to as a step value ΔI) between adjacent gray scales is set at equal intervals. In this case, the resistance value R of the protection circuit 6 is set so that the leak current Ileak is smaller than 1/2 of the step value ΔI. This resistance value R can be arbitrarily set by setting the channel length and channel width of each transistor constituting the diode rows 6a and 6b, or the impurity concentration doped into the channel.
[0018]
Specifically, the resistance value R is set according to Equation 1. Here, the maximum value Vmax is the applied voltage Vab of the protection circuit 6 generated when the potential difference between the data lines X1 and X2 is maximized. For example, in the case of the 64 gradation display shown in FIG. 4, a data current I0 corresponding to gradation 0 is supplied to the data line X1 (the voltage of the data line X1 becomes the maximum voltage), and the data line X2 is supplied to the data line X2. When the data current I63 corresponding to the gradation 63 is supplied (the voltage of the data line X2 becomes the minimum voltage), the applied voltage Vab of the protection circuit 6 becomes the maximum.
[Equation 1]
Ileak <ΔI / 2
Vmax / R <ΔI / 2
R> 2 · Vmax / ΔI
[0019]
Thereby, the condition of Ileak <ΔI / 2 is satisfied in the entire voltage region that can occur between data lines X1 and X2. As a result, even if the leak current Ileak flows through the protection circuit 6, the amount of the leak current Ileak is effectively regulated, so that the gradation shift of the pixel 2 can be suppressed and the inversion of the gradation between adjacent pixels is also suppressed. it can.
[0020]
In the characteristics shown in FIG. 4, the relationship between the gradation and the data current Idata is shown linearly. However, this is an example, and in consideration of the characteristics and the like of the organic EL element OLED, the relationship is non-linear. The relationship may be set as follows. In this case, the resistance value R may be set so that the leak current Ileak is smaller than 1/2 of the minimum value of the step value ΔI.
[0021]
Further, in the present embodiment, an example in which a diode ring is used as the protection circuit 6 has been described. However, the present invention is not limited to this, and can be widely applied to various circuit configurations for preventing electrostatic breakdown of an internal circuit, including the modifications of FIGS. 5 and 6.
[0022]
FIG. 5 is a circuit diagram of a protection circuit 6 using a resistance element as a modification. The protection circuit 6 is, for example, a sheet resistance formed by diffusing impurities such as boron or phosphorus into the polycrystalline silicon layer. The resistance element of the protection circuit 6 is set to a resistance value R satisfying the above-described conditions.
[0023]
FIG. 6 is a circuit diagram of a protection circuit 6 using a transistor as another modification. The protection circuit 6 includes three transistors 6a, 6b, 6c. Two transistors 8a and 8b are connected in series between the data lines X1 and X2. The gate of one transistor 8a is connected to the data line X1, and the gate of the other transistor 8b is connected to the data line X2. ing. A transistor 8c is also provided between the data lines X1 and X2, and the gate of the transistor 8c is connected to a connection node between the two transistors 8a and 8b. In the protection circuit 6, the resistance in the path through which the leak current Ileak flows corresponds to the channel resistance of the transistor 8c, which is set to the resistance value R satisfying the above-described conditions.
[0024]
(Second embodiment)
FIG. 7 is a block diagram of the electro-optical device according to the present embodiment. The protection circuit 9 for preventing electrostatic breakdown of the internal circuit is provided for each data line, and is constituted by a resistance element connecting between the data line X and a power supply line Vss supplied with a predetermined voltage. . Elements that are the same as the circuit elements shown in FIG. 1 are given the same reference numerals, and descriptions thereof will be omitted.
[0025]
As in the first embodiment, also in the present embodiment, the protection circuit 9 regulates the amount of the leak current Ileak by appropriately setting the resistance value R in the path where the leak current Ileak flows. In this case, the resistance value R of the protection circuit 9 is set so that the leak current Ileak becomes smaller than the step value ΔI. Specifically, the resistance value R is set according to Equation 2. Here, the maximum value Vmax is the applied voltage Vab of the protection circuit 9 generated when the voltage of the data line X becomes maximum. For example, in the case of the 64 gradation display shown in FIG. 4, when the data current I63 corresponding to the gradation 63 is supplied to the data line X (the voltage of the data line X becomes the maximum voltage), the protection circuit 9 The applied voltage Vab becomes maximum.
[Equation 2]
Ileak <ΔI
Vmax / R <ΔI
R> Vmax / ΔI
[0026]
Accordingly, the condition of Ileak <ΔI is satisfied in the entire voltage region that can be applied to the data line X. As a result, even if the leak current Ileak flows through the protection circuit 9, the gradation shift of the pixel 2 can be suppressed, and the inversion of the gradation between adjacent pixels can be suppressed.
[0027]
In this embodiment, an example in which a resistance element is used as the protection circuit 9 has been described. However, the present invention is not limited to this, and can be widely applied to various circuit configurations for preventing electrostatic breakdown of the internal circuit, including the modifications of FIGS. 8 and 9.
[0028]
FIG. 8 is a circuit diagram of a protection circuit 9 as a modification. The protection circuit 9 includes two diode rows 9a and 9b in which diode-connected n-channel transistors are connected in series. One diode row 9a is connected to a data line X and a power supply line VHH to which a high voltage (a voltage higher than the power supply voltage Vdd) is supplied, and the other diode row 9b is connected to a data line and a low voltage. It is connected to a power supply line Vss to which a voltage is supplied. The resistance in the path through which the leak current Ileak flows corresponds to the resistance of the diode row 6a (or 6b), and is set to the resistance value R satisfying the above-described conditions.
[0029]
FIG. 9 is a circuit diagram of a protection circuit 9 as another modification. In this configuration example, the diode array 9a composed of n-channel transistors in FIG. 8 is changed to a p-channel transistor.
[0030]
In each of the above-described embodiments, an example in which the organic EL element OLED is used as the electro-optical element has been described. However, the present invention is not limited to this, and an electro-optical element (inorganic LED display device, field emission display device, etc.) whose brightness is set according to the drive current, or a transmittance according to the drive current -It can be widely applied to electro-optical devices (electrochromic display devices, electrophoretic display devices, etc.) exhibiting reflectance.
[0031]
Further, the electro-optical device according to each embodiment described above can be mounted on various electronic devices including, for example, a television, a projector, a mobile phone, a mobile terminal, a mobile computer, a personal computer, and the like. If the above-described electro-optical device is mounted on these electronic devices, the commercial value of the electronic devices can be further increased, and the product appeal of the electronic devices in the market can be improved.
[0032]
【The invention's effect】
According to the present invention, the resistance value in the path of the protection circuit through which the leak current flows is set to a resistance value that does not cause a shift in the display gray level of the pixel due to the fluctuation of the data current due to the leak current. Thus, it is possible to suppress a gradation shift caused by a leakage current of the protection circuit.
[Brief description of the drawings]
FIG. 1 is a block diagram of an electro-optical device according to a first embodiment.
FIG. 2 is a circuit diagram of a pixel as an example in a current programming method.
FIG. 3 is a circuit diagram of a protection circuit according to the first embodiment.
FIG. 4 is a schematic characteristic diagram showing a relationship between a gradation and a data current.
FIG. 5 is a circuit diagram of a protection circuit using a resistor as a modification.
FIG. 6 is a circuit diagram of a protection circuit using a transistor as another modification.
FIG. 7 is a block diagram of an electro-optical device according to a second embodiment.
FIG. 8 is a circuit diagram of a protection circuit as a modification.
FIG. 9 is a circuit diagram of a protection circuit as another modification.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Display part 2 Pixel 3 Scanning line drive circuit 4 Data line drive circuit 6, 9 Protection circuits T1-T4 Transistor C Capacitor OLED Organic EL element

Claims (7)

In electro-optical devices,
A plurality of data lines to which a data current defining a pixel gradation is supplied;
A protection circuit that is connected to the data line in order to prevent electrostatic breakdown of the internal circuit and that discharges static electricity of the data line when a leak current flows;
A resistance value in a path of the protection circuit through which the leakage current flows is set to a resistance value that does not cause a shift in display gradation of the pixel due to a change in the data current due to the leakage current. An electro-optical device, comprising: The electro-optical device according to claim 1, wherein the resistance value is set based on a maximum value of a voltage applied to the protection circuit. 3. The electro-optical device according to claim 1, wherein the protection circuit is connected to the pair of data lines. 4. The resistance value according to claim 3, wherein the resistance value is set so that the leak current is smaller than １ ／ of a minimum value of a current change amount between adjacent gray scales. 5. Electro-optical device. The electro-optical device according to claim 1, wherein the protection circuit is connected to the data line and a power supply line to which a predetermined voltage is supplied. 6. The electro-optical device according to claim 5, wherein the resistance value is set to a value such that the leak current is smaller than a minimum value of a current change amount between adjacent gray scales. . An electronic apparatus comprising the electro-optical device according to claim 1.

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