JP2008158239A - Active matrix type display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an active matrix type display device which is improved in yield and aperture ratio by decreasing the number of wirings. <P>SOLUTION: In the active matrix type display device having display elements 33 and storage capacitors 32 by pixels defined by crossing data lines 12 and gate lines 11, one-end sides of the display element 33 and the storage capacitor 32 of each pixel are connected to a data line 12a of a right adjacent pixel. Consequently, the need for a cathode line is eliminated and the number of wirings can be decreased. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an active matrix display device, and more particularly to an active matrix display device that realizes an improvement in yield and an aperture ratio.

  FIG. 13 is a typical circuit configuration diagram of one pixel of a conventional organic EL display device. This organic EL display device includes a gate line 11, a previous gate line 11a, a data line 12, a data line 12a on the right side, a power supply line 13, a cathode line 14, a first TFT 21, a second TFT 22, and a storage capacitor 23. , And OLED (Organic Light Emitting Display) element 24.

  Here, the first TFT 21 constituting the first stage is for selecting and holding a data signal through the data line 12. The second TFT 22 constituting the second stage is for driving the OLED element 24. In addition, in order to compensate for the Vth fluctuation of the second TFT 22 for driving with respect to such a basic two-stage TFT configuration, a circuit in which a TFT is further added has been invented.

  Such an organic EL display device is a kind of active matrix display device in which the gate lines 11 and 11a and the data lines 12 and 12a cross each other, and a cathode line in which one end of the storage capacitor 23 and the cathode of the OLED element 24 are connected. 14 is wired separately from the gate lines 11 and 11a, the data lines 12 and 12a, and the power supply line 13 (see, for example, Patent Document 1).

  FIG. 14 is a typical circuit configuration diagram of one pixel in a conventional liquid crystal display device. The liquid crystal display device includes a gate line 11, a previous gate line 11 a, a data line 12, a data line 12 a on the right side, a cathode line 14, a selection TFT 31, a storage capacitor 32, and a liquid crystal element 33.

  Such a liquid crystal display device is also a kind of active matrix display device in which the gate lines 11 and 11a and the data lines 12 and 12a are crossed, and is one end of the storage capacitor 32 and a liquid crystal element that is equivalently expressed as a capacitance component. The cathode line 14 to which one end of 33 is connected is wired separately from the gate lines 11 and 11a and the data lines 12 and 12a.

International Publication W2004 / 049286 Pamphlet

However, the prior art has the following problems.
In the conventional active matrix display device, as shown in FIGS. 13 and 14, it is necessary to provide the cathode line 14 separately from the gate lines 11 and 11a and the data lines 12 and 12a. As a result, the number of wirings is increased, which is a cause of a decrease in panel yield due to disconnection due to defects. In addition, there is a demerit that the aperture ratio decreases as the number of wires increases.

  In particular, in an IPS (In Plane Switching) liquid crystal, since the common line needs to be on the TFT substrate side, such a decrease in yield and a reduction in aperture ratio due to the large number of wirings are problematic.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain an active matrix display device that realizes yield improvement and aperture ratio improvement by reducing the number of wirings.

  An active matrix display device according to the present invention is an active matrix display device having a display element and a storage capacitor for each pixel defined by intersecting a data line and a gate line. One end of the storage capacitor is connected to the data line of the pixel on the right.

  According to the present invention, one end of the display element and the storage capacitor is connected to the data line of the adjacent pixel on the right side, and the cathode line is not necessary, thereby improving the yield and the aperture ratio by reducing the number of wirings. A mold display device can be obtained.

  Hereinafter, preferred embodiments of an active matrix display device of the present invention will be described with reference to the drawings.

Embodiment 1 FIG.
FIG. 1 is a circuit configuration diagram of one pixel of the organic EL display device according to Embodiment 1 of the present invention. This organic EL display device includes a gate line 11, a previous gate line 11a, a data line 12, a data line 12a on the right side, a power supply line 13, a first TFT 21, a second TFT 22, a storage capacitor 23, and an OLED element. 24 and an auxiliary capacitor 25.

  Compared with the component of FIG. 13 showing the conventional configuration, the component of FIG. 1 is different in that an auxiliary capacitor 25 is newly provided instead of making the cathode line 14 unnecessary. That is, in the organic EL display device according to the first embodiment shown in FIG. 1, one end of the storage capacitor 23 and the cathode of the OLED element 24 are connected to the data line 12a of the adjacent pixel on the right instead of being connected to the cathode line 14. By doing so, the cathode line 14 is unnecessary.

  The newly added auxiliary capacitor 25 will be described in detail later in Embodiment 2 with reference to FIG.

  Next, FIG. 2 is a circuit configuration diagram of one pixel of the liquid crystal display device according to Embodiment 1 of the present invention. This liquid crystal display device includes a gate line 11, a previous gate line 11 a, a data line 12, a data line 12 a on the right side, a power supply line 13, a selection TFT 31, a storage capacitor 32, a liquid crystal element 33, and an auxiliary capacitor 34. It is configured.

  Compared with the components shown in FIG. 14 showing the conventional configuration, the components shown in FIG. 2 are different in that an auxiliary capacitor 34 is newly provided instead of making the cathode line 14 unnecessary. That is, in the liquid crystal display device according to the first embodiment shown in FIG. 2, one end of the storage capacitor 32 and one end of the liquid crystal element 33 are connected to the data line 12a of the pixel on the right instead of being connected to the cathode line. As a result, the cathode line 14 is unnecessary.

  Next, by using FIG. 3 and FIG. 4, one end of the storage capacitor 32 and one end of the liquid crystal element 33 are connected to the data line 12 a of the pixel on the right instead of being connected to the cathode line 14. The operation for realizing the display will be described. In the following description, the description is based on the liquid crystal display device of FIG. 2, but the operation principle is the same for the organic EL display device of FIG.

FIG. 3 is an explanatory diagram of a display operation by connection using the data line 12a of the pixel on the right in the first embodiment of the present invention. As shown in FIG. 3, when one end of the storage capacitor 32 is connected to the data line 12a adjacent to the right instead of the cathode line 14, the voltage applied to Cs corresponding to the storage capacitor 32 is Vp1, and the data lines 12, 12a. Assume that the voltages are V1 and V2, respectively. At this time, if the selection TFT 31 is turned on, Vp1, V1, and V2 have the relationship of the following expression (1).
Vp1 = V1-V2 (1)

Next, in the pixel on the right side of this pixel, it is assumed that the voltage applied to Cs is Vp2, and the data line voltage is V2 and V3, respectively. At this time, if the selection TFT 31 is turned on, Vp2, V2, and V3 have the relationship of the following expression (2).
Vp2 = V2-V3 (2)

Similarly, if the pixel on the right side is further continued, Vpk, Vk, and Vk + 1 have the relationship of the following expression (3) in the kth pixel.
Vpk = Vk−Vk + 1 (3)

  When these equations are added from V = 1 to V−1 for Vpk, the relationship of the following equation (4) is obtained.

  When the above equation (4) is solved for Vn, the following equation (5) is obtained.

  Accordingly, the input voltage signal Vn of the nth pixel can be expressed by subtracting V1 from the sum of the original signals from 1 to the nth. That is, as shown in FIG. 3, when one end of the storage capacitor 32 is connected to the right data line 12a, each of the input voltage signals V1 to Vn is connected to the cathode line 14 at one end of the storage capacitor 32 as in the prior art. Using the input voltage signal (corresponding to Vp1 to Vpn in the above formulas (1) to (4)) when connected to, it can be obtained from the relationship of the above formula (5).

  In the configuration as shown in FIG. 3 in which one end of the storage capacitor 32 is connected to the right adjacent data line 12a, the input voltage signals V1 to Vn satisfying the relationship of the above equation (5) are actually applied to each data line. There are the following two methods. In the first method, Vp1 to Vpn corresponding to conventional input voltage signals are added one after another digitally.

  The second method uses an adder to sequentially add previous outputs. FIG. 4 is a circuit diagram for realizing the second method using the adder according to the first embodiment of the present invention. By using such a circuit, input voltage signals V1 to Vn corresponding to the display device of the present invention can be obtained from conventional input voltage signals Vp1 to Vpn.

  However, the problem here is that the output increases as n increases as positive numbers are added. Therefore, in order to prevent an increase in the addition result, the voltage level is inverted between adjacent data lines. Then, on a smooth screen, the average value is almost 0, and the output obtained from the above equation (5) changes around V1, and an increase in output can be prevented.

  Next, FIG. 5 is a diagram showing a specific example when the display device according to the first embodiment of the present invention is applied to a pixel of an IPS liquid crystal. FIG. 5A shows a conventional configuration (corresponding to the circuit of FIG. 14), and FIG. 5B shows a configuration of the present invention (corresponding to the configuration of FIG. 2). Since a part of the data line can be used for the display electrode, there is an advantage that the aperture ratio is improved. Further, since the common electrode of the display portion is formed by the data line, the common and the wiring can be made completely common.

  As described above, according to the first embodiment, the number of wirings can be reduced by connecting one end of the display element and the storage capacitor to the data line of the pixel on the right and eliminating the need for the cathode line. As a result, it is possible to obtain an active matrix display device that realizes an improvement in yield and an improvement in aperture ratio.

  Further, the voltage applied through the data line can be prevented from increasing with increasing n by inverting the positive / negative voltage level between the data lines.

Embodiment 2. FIG.
In the first embodiment, the basic configuration in which the cathode line 14 is unnecessary is adopted, and the problem that the output increases as n increases by reversing the positive / negative of the voltage level between adjacent data lines. The illustrated active matrix display device has been described. Next, in the second embodiment, a further improvement measure for the problem that the output increases will be described.

  In the circuit as shown in FIG. 3 showing the basic configuration in the first embodiment, a further problem is an increase in the output signal with respect to the flicker pattern conventionally found in liquid crystals. That is, for a pattern that repeats 1, 0, 1, 0 every other data line, or a pattern close thereto, even if the voltage level is inverted between adjacent data lines, n is increased as a result. As the output increases with time, such a problem needs to be improved.

  This also has the same problem with repeated patterns such as 1, -0.5, 1, and -0.5, and is weak to such a pattern that fluctuates in synchronization with the inversion period. If the number of outputs increases to 100 or more, the output theoretically increases to several hundred volts.

  As a countermeasure against this, it is conceivable to perform pre-processing that leaves the signal level at its original level. Such pre-processing may be added from the stage of the digital signal, but in order not to impair the dynamic range of the driver IC, it is effective to add an offset near the output of the driver.

  Therefore, the display device according to the second embodiment includes the auxiliary capacitor 25 shown in FIG. 1 or the auxiliary capacitor 34 shown in FIG. 2 so that an offset can be set for each pixel. The function of the auxiliary capacitor 34 in the liquid crystal display device of FIG. 2 is the same as the function of the auxiliary capacitor 25 in the organic EL display device of FIG. Therefore, the function of the auxiliary capacitor 25 or the auxiliary capacitor 34 will be described using a liquid crystal display device as an example with reference to FIG.

  FIG. 6 is an explanatory diagram showing the function of the auxiliary capacitor according to the second embodiment of the present invention. Compared to the previous configuration of FIG. 3, the configuration of FIG. 6 has an auxiliary capacitor 34 connected between the Cs connection line corresponding to the selection TFT 31 and the storage capacitor 32 and the previous gate line 11a. Is provided. As a result, an offset voltage is applied to Cs by the action of Cc connected to the previous gate line 11a, so that it is possible to obtain the same effect as applying the getter to the original signal level. it can.

  There are several methods for giving an offset to the entire data for an active matrix type display device composed of pixels having the basic configuration as shown in FIG. FIG. 7 is a circuit diagram showing offset processing by the first method according to Embodiment 2 of the present invention. As shown in FIG. 7, in the first method, the digital adder 43 gives the digitally offset data to the data driver 41, and the digital subtracter 44 performs the subtraction according to the offset. On the other hand, the analog signal converted by the D / A converter 45 is given to the gate driver 42.

  As shown in FIG. 7, by having a configuration in which subtraction by the digital subtracter 44 can be performed according to the offset amount by the digital adder 43, it is possible to cope with a case where no offset is added. In addition, such a configuration can be used not only for switching by a simple offset but also for performing an offset with a certain relational expression according to a display pattern, for example.

  The above-described circuit of FIG. 7 can sequentially vary the offset according to data. On the other hand, when it is not necessary to vary the offset sequentially and the offset amount is handled as being fixed in hardware, the second method shown below is realistic and will be described with reference to FIGS.

  FIG. 8 is a circuit diagram relating to power supply for performing offset processing by the second method according to Embodiment 2 of the present invention. FIG. 9 is a circuit diagram showing offset processing by the second method in the second embodiment of the present invention.

  FIG. 8A shows the configuration of the data driver VREF circuit. By using a variable power supply and a variable resistance value according to the circuit design, a desired voltage can be generated in V1 to V9. More specifically, an offset amount can be added to the power supply of the VREF circuit by adding an offset voltage V0 to V1 and V9.

  On the other hand, FIG. 8B shows the configuration of the gate driver voltage circuit, and a desired voltage can be generated in VG1 to VG4 by using a variable power supply according to the circuit design. As described above, by using the voltage values of the circuits of FIGS. 8A and 8B in the circuit of FIG. 9, an active matrix display device in which the offset amount is fixed in hardware can be realized.

  FIG. 10 is a diagram showing a specific voltage waveform when the offset process according to the second method in the second embodiment of the present invention is performed, which is a known technique in principle. As the normal output level of the gate voltage, ON / OFF control is normally performed with two values of VG1 and VG2. By using four values including VG3 and VG4, the offset as shown in FIG. It is possible to perform the compensated driving. The present invention is characterized in that such compensation driving on the gate driver side is performed in conjunction with offset processing on the data driver side.

The relationship between VG3 and VG4 and the offset voltage V0 can be expressed by the following equation.
V0 = (VG3-VG4) × Cs / Call (6)
In the above equation (6), Cs corresponds to, for example, the auxiliary capacitor 34 in FIG. 2, and Call corresponds to the total value of the capacitors of the storage capacitor 32, the liquid crystal element 33, and the auxiliary capacitor 34 in FIG. The desired offset control can be performed by adjusting VG3 and VG4 so as to obtain the offset voltage V0 represented by the above equation (6).

  FIG. 11 is a circuit diagram showing offset processing by the third method according to Embodiment 2 of the present invention. As shown in FIG. 11, the third method is to add a constant voltage to the analog part of the data driver 41 and subtract it from the analog part of the gate driver 42. Such an analog circuit can also realize the offset function.

  As described above, according to the second embodiment, the storage capacitor can be offset by the function of the auxiliary capacitor connected to the previous gate line. As a result, it is possible to obtain an active matrix type display device that can prevent an increase in voltage value accompanying an increase in n even for a pattern that varies spatially in synchronization with the inversion period.

  Note that the connection of the OLED elements 24 in the circuit configuration diagram of the organic EL display device in FIG. 1 is an example, and other connection methods may be used. FIG. 12 is another circuit configuration diagram of one pixel of the organic EL display device according to the present invention. Even if the OLED elements 24 are connected as shown in FIGS. 12A and 12B, the same effects as those of the first and second embodiments described based on the configuration of FIG. 1 can be obtained.

It is a circuit block diagram in one pixel with the organic electroluminescence display in Embodiment 1 of this invention. It is a circuit block diagram in one pixel with the liquid crystal display device in Embodiment 1 of this invention. It is explanatory drawing of the display operation by the connection using the data line 12a of the pixel on the right side in Embodiment 1 of this invention. It is a circuit diagram for implement | achieving the 2nd method using the adder in Embodiment 1 of this invention. It is a figure which shows the specific example at the time of applying the display apparatus in Embodiment 1 of this invention to the pixel of the IPS liquid crystal. It is explanatory drawing which shows the function of the auxiliary | assistant capacity | capacitance in Embodiment 2 of this invention. It is the circuit diagram which showed the offset process by the 1st method in Embodiment 2 of this invention. It is a circuit diagram regarding the power supply for performing the offset process by the 2nd method in Embodiment 2 of this invention. It is the circuit diagram which showed the offset process by the 2nd method in Embodiment 2 of this invention. It is the figure which showed the specific voltage waveform at the time of performing the offset process by the 2nd method in Embodiment 2 of this invention. It is the circuit diagram which showed the offset process by the 3rd method in Embodiment 2 of this invention. It is another circuit block diagram in one pixel with the organic electroluminescence display in this invention. It is a typical circuit block diagram in one pixel with the conventional organic electroluminescence display. It is a typical circuit block diagram in one pixel with the conventional liquid crystal display device.

Explanation of symbols

  11 gate line, 11a previous gate line, 12 data line, 12a right next data line, 13 power line, 14 cathode line, 21 first TFT, 22 second TFT, 23 storage capacitor, 24 OLED element, 25 Auxiliary capacity, 31 selection TFT, 32 storage capacity, 33 liquid crystal element (display element), 34 auxiliary capacity, 41 data driver, 42 gate driver, 43 digital adder, 44 digital subtractor, 45 D / A converter.

Claims (7)

In an active matrix display device having a display element and a storage capacitor for each pixel defined by intersecting a data line and a gate line,
An active matrix display device, wherein one end of the display element and the storage capacitor in each pixel is connected to a data line of a right adjacent pixel. The active matrix display device according to claim 1,
The active matrix display device, wherein the display element is an IPS liquid crystal or an organic EL display. The active matrix display device according to claim 1 or 2,
An active matrix display device, wherein the data line is applied with a voltage whose polarity is inverted between adjacent data lines. The active matrix display device according to claim 3,
An active matrix display device, wherein a voltage obtained by adding an offset to a voltage whose polarity is inverted between adjacent data lines is applied to the data line. The active matrix type display device according to any one of claims 1 to 4,
An active matrix display device, further comprising an auxiliary capacitor connected between the other end of the storage capacitor and the previous gate line, and applying an offset voltage to the storage capacitor. The active matrix display device according to claim 5,
The active matrix display device, wherein the gate line applies an average value of a voltage to be applied to all pixels in the gate line direction through the data line as the offset voltage through the auxiliary capacitance of each pixel. The active matrix display device according to claim 5,
A voltage value obtained by adding a DC voltage larger than the fluctuation range of the input signal as an offset amount is applied to the data line,
An active matrix display device, wherein a voltage value by which the DC voltage is subtracted through the auxiliary capacitor is applied to the gate line.

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