JPH08248439A - Display panel - Google Patents

Abstract

PURPOSE: To decrease the fluctuations (noises) in the potential of pixel electrodes generated when scanning lines for auxiliary capacitor lines turn on and off with a liquid crystal display device of an active matrix type in which the scanning lines are commonly used as the auxiliary capacitor lines. CONSTITUTION: As an example, the scanning line 2B of a fore stage connected via a thin-film transistor(TFT) 4B of the fore stage to a pixel electrode 5B of the fore stage of a pixel electrode 5C and the scanning line 2A of the stage before the previous stage connected via the TFT 4A of the stage before the previous stage to the pixel electrode 5a of the stage before the previous stage of the pixel electrode 5C are commonly used for the auxiliary capacitor line for the pixel electrode 5C. Then, the auxiliary capacitor part for the one pixel electrode is eventually divided to two, by which the noises are decreased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display panel in an active matrix type liquid crystal display device or the like.

[0002]

2. Description of the Related Art For example, some active matrix type liquid crystal display devices have an auxiliary capacitance portion in addition to a pixel capacitance portion. In this case, there are a type called an additional capacitance system in which the scanning line also serves as an auxiliary capacitance line, and a type called a storage capacitance system in which a dedicated auxiliary capacitance line is provided in addition to the scanning line. Comparing the two,
The additional capacitance method is said to be advantageous over the storage capacitance method in terms of aperture ratio and yield because it does not have a dedicated auxiliary capacitance line.

4 and 5 show a part of a display panel in a conventional active matrix type liquid crystal display device of the additional capacitance type. This display panel includes a glass substrate 1. On the upper surface side of the glass substrate 1, scanning lines (gate lines) 2A, 2 which also serve as auxiliary capacitance lines
B and 2C and signal lines (drain lines) 3 are provided in a matrix, and thin film transistors 4A, 4B and 4C as switching elements and pixel electrodes 5A, 5B, 5C and 5D are provided in the vicinity of respective intersections thereof.

That is, the scanning lines 2A, 2B, 2C including the gate electrode 6 are provided at predetermined positions on the upper surface of the glass substrate 1.
(A portion which also serves as an auxiliary capacitance line will be described later.) Is formed, and a gate insulating film 7 is formed on the entire upper surface thereof. A semiconductor thin film 8 made of amorphous silicon is formed at a predetermined position on the upper surface of the gate insulating film 7, and a channel protective film 9 is formed at the center of the upper surface of the semiconductor thin film 8. On both sides of the upper surfaces of the semiconductor thin film 8 and the channel protection film 9, contact layers 10 and 1 made of n ⁺ silicon are provided.
1 is formed, the drain electrode 12 and the source electrode 13 are formed on the upper surfaces of the contact layers 10 and 11, and the signal line 3 is formed at the same time when these electrodes 12 and 13 are formed. I is formed at a predetermined position on the upper surface of the gate insulating film 7.
Pixel electrodes 5A, 5B, 5C, and 5D made of TO are formed so as to be connected to the source electrode 13.

Next, a portion of the scanning lines 2A, 2B and 2C which also serves as an auxiliary capacitance line will be described. As an example, the scanning line 2B connected to the pixel electrode 5B via the thin film transistor 4B is provided on the lower side of the pixel electrode 5B, but is provided on the preceding scanning line 2A, that is, on the upper side of the pixel electrode 5B. The scanning line 2A also serves as an auxiliary capacitance line for the pixel electrode 5B. The scanning line 2A in the previous stage is drawn out along the common straight line portion 2a provided at a position corresponding to the upper side portion of the pixel electrode 5B, and from the common straight line portion 2a along the left side portion and the right side portion of the pixel electrode 5B. It consists of drawer parts 2b and 2c. And
The respective predetermined portions of the common linear portion 2a and the lead portions 2b, 2c are overlapped with the upper side portion, the left side portion and the right side portion of the pixel electrode 5B, and the overlapped portion forms an auxiliary capacitance portion. On the other hand, although not shown, the pixel capacitance portion is formed by the pixel electrode 5B, a common electrode arranged to face the pixel electrode 5B, and liquid crystal arranged between them. FIG. 6 shows an equivalent circuit in this case, in which reference numeral 21 indicates a pixel capacitance portion and 22 indicates an auxiliary capacitance portion.

[0006]

However, in such a conventional active matrix type liquid crystal display device, one electrode of the auxiliary capacitance section 22 has the scanning line 2 in the preceding stage.
Since it is connected to A, the potential of the pixel electrode 5B changes when the scanning line 2A in the preceding stage is turned on / off. This fluctuation (noise) occurs in a short time of about several tens of microseconds, but since the fluctuation range reaches as much as tens of volts, the effective voltage applied to the liquid crystal is changed to some extent. By the way, when the capacitance of the auxiliary capacitance section 22 was made equal in the case of the additional capacitance system and the case of the storage capacitance system, the relationship between the luminance and the signal voltage was examined, and the result shown in FIG. 7 was obtained. As is clear from this figure, in the case of the additional capacitance method indicated by the solid curve, the effective voltage applied to the liquid crystal is not small due to the influence of the noise as compared with the case of the storage capacitance method indicated by the dotted curve. Is changing. As a result, there is a problem that it is not possible to obtain a better image quality. An object of the present invention is to provide a display panel capable of reducing noise.

[0007]

According to the first aspect of the present invention,
In a display panel in which a pixel electrode is connected to a scan line and a signal line provided in a matrix via a switching element, each one of two scan lines different from the pixel electrode scan line is connected to the pixel electrode. It is a stack of parts. According to a fourth aspect of the invention, the capacitance of the overlapping portion of one of the other two scanning lines and the pixel electrode is made equal to the capacitance of the overlapping portion of the other one scanning line and the pixel electrode. It is a thing.

[0008]

According to the first aspect of the invention, since a part of each of the two scanning lines different from the scanning line for the pixel electrode is overlapped with the pixel electrode, the auxiliary for one pixel electrode is provided. Since the capacitance section is divided into two, noise can be reduced. In this case, as in the invention described in claim 4, of the capacitance of the overlapping portion of one of the other two scanning lines and the pixel electrode, and the capacitance of the overlapping portion of the other one of the scanning lines and the pixel electrode. When the capacitances are made equal to each other, it is possible to maintain the charge retention capability as it is and reduce the noise to about half as compared with the conventional case.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a main part of a display panel to which an embodiment of the present invention is applied. In this figure, the same reference numerals are given to the same names as those in FIG. 4, and the description thereof will be omitted as appropriate. In this embodiment, as an example, the scanning line 2B in the preceding stage connected to the pixel electrode 5B in the preceding stage of the pixel electrode 5C via the thin film transistor 4B in the preceding stage and the pixel electrode 5A in the preceding stage before the pixel electrode 5C in question are preceded by one. The scanning line 2A on the preceding stage connected via the thin film transistor 4A on the preceding stage also serves as the auxiliary capacitance line for the pixel electrode 5C.

The scanning line 2B in the preceding stage is connected to the pixel electrode 5 concerned.
A common straight line portion 2d arranged between the substantially central portion of C in the vertical direction and the lower side, and the pixel electrode 5 from the common straight line portion 2d.
A pull-out portion 2e that is pulled upward along the left side portion of C is provided. In this case, a predetermined part of the common straight line portion 2d is a substantially U-shaped protruding portion that protrudes downward, that is, a left extending portion 2f that extends downward from a substantially central portion in the left-right direction of the pixel electrode 5C. A right extending portion 2g extending downward along the right side portion of the pixel electrode 5C, and the pixel electrode 5C.
It is a substantially U-shaped projecting portion including a lower portion 2h provided between both extending portions 2f and 2g along the lower side portion. Almost all of the common straight line portion 2d and the left extending portion 2f are overlapped with the pixel electrode 5C, and the predetermined portions of the extending portion 2e, the right extending portion 2g, and the lower portion 2h are the pixel electrode 5 concerned.
The left side portion, the right side portion, and the lower side portion of C are overlapped with each other, and the overlapped portion forms a first auxiliary capacitance portion. The leading end of the lead-out portion 2e serves as the gate electrode 6 of the thin film transistor 4B in the front stage connected to the pixel electrode 5B in the front stage.

By the way, the lower part 2 of the preceding scanning line 2B
The lower side of h is also overlapped with the upper side of the pixel electrode 5D in the subsequent stage. As for this, regarding the scanning line 2A in the previous stage, the lower side of the lower portion 2h of the scanning line 2A in the previous stage is overlapped with the upper side of the pixel electrode 5C. And the 2nd auxiliary | assistant capacitor part is formed of this overlapped part. FIG. 2 shows an equivalent circuit in this case. Reference numeral 21 is a pixel capacitance portion, 22a is a first auxiliary capacitance portion, and 22b is a second auxiliary capacitance portion.

Next, FIG. 3A shows the waveform of the voltage applied to the liquid crystal corresponding to the pixel electrode 5C, and FIG.
(D) shows the gate signals applied to the scanning line 2A in the front stage, the scanning line 2B in the front stage, and the scanning line 2C in the front stage, respectively. In this case, noise is generated when a gate signal is applied to each of the scanning line 2A in the front stage and the scanning line 2B in the front stage.
The pulse widths of the respective noise pulses are V _N2 and V _N1 . These noises change the effective voltage applied to the liquid crystal corresponding to the pixel electrode 5C, and the ratio of this change to the signal voltage is approximately given by the following equation (1). [√ {(T _F V _SIG ² + T _G V _N1 ² + T _G V _N2 ² ) / T _F } -V _SIG ] / V _SIG ≈ (1/2) (T _G / T _F ) {(V _N1 ² + V _N2 ² ) / V _SIG ² } (1) However, T _F is usually about ten and several msec in the field period. T _G is a gate selection time, which is usually about several tens of μsec. V _SIG is the signal voltage.

Further, the capacitance of the liquid crystal capacitance section 21 is C _LC ,
Let C _S1 and C _S2 be the capacitances of the first and second auxiliary capacitance portions 22a and 22b, respectively, and let the sum of these two auxiliary capacitances (C _S1 + C
_S2 ) is C _S and the difference between the maximum value and the minimum value of the gate voltage is V _GHL , the pulse widths V _N1 and V _{N2 of} each noise pulse.
Are given by the following equations (2) and (3), respectively. V _N1 ≈ {C _S1 / (C _S + C _LC )} V _GHL …… (2) V _N2 ≈ {C _S2 / (C _S + C _LC )} V _GHL …… (3)

As is clear from the above three equations, the ratio of the change due to noise to the signal voltage is (C _S1 ² +
Since it is proportional to C _S2 ² ), it is the minimum when C _S1 = C _S2 under the condition that (C _S1 + C _S2 ) is constant. Here, FIG.
As shown in FIG.
Even if it is divided into two parts 2a and 22b, its charge holding capacity is exactly the same as in the case of the conventional one auxiliary capacity portion 22 shown in FIG. 6, and the total capacity (C _S1 + C _S2 ) is shown in FIG. It is assumed that it is equal to the capacity of one conventional auxiliary capacity section 22 shown in FIG. Then, in the conventional case shown in FIG. 6, this corresponds to the case of C _S2 = 0 of (C _S1 + C _S2 ), and the ratio of the change due to noise at this time to the signal voltage becomes maximum. On the other hand, in the case of the present embodiment, if C _S1 = C _S2 , the ratio of the change due to noise to the signal voltage is minimized, and can be half that of the conventional case shown in FIG.
Therefore, in the case of the present embodiment, compared with the conventional case shown in FIG. 6, it is possible to maintain the charge retention capability as it is and reduce the noise to about half, and to obtain a better image quality. it can.

As shown in FIG. 1, since the common straight line portion 2d of the preceding scanning line 2B is disposed between the vertical center of the pixel electrode 5C and the lower side, the transmissive active matrix is used. In the case of applying to a liquid crystal display device of the type, if the scanning line is formed of, for example, ITO which is the same material as the pixel electrode, the aperture ratio can be prevented from lowering. When applied to a reflective active matrix type liquid crystal display device, even if the scanning line is formed of an opaque material such as aluminum or chrome,
It is possible to prevent the aperture ratio from decreasing.

In the above embodiment, the pixel electrode 5C is
Although a case has been described in which the preceding auxiliary scanning line 2B also serves as the preceding scanning line 2A and the preceding preceding scanning line 2A, the present invention is not limited to this, and the succeeding scanning line 2C and the succeeding scanning line may also serve as the auxiliary capacitance line. May be.

[0017]

As described above, according to the first aspect of the present invention, a part of two scanning lines different from the scanning line for the pixel electrode is overlapped with the pixel electrode. Therefore, the auxiliary capacitance portion for one pixel electrode is divided into two, which can reduce noise. In this case, as in the invention described in claim 4, of the capacitance of the overlapping portion of one of the other two scanning lines and the pixel electrode, and the capacitance of the overlapping portion of the other one of the scanning lines and the pixel electrode. When the capacitances are made equal to each other, it is possible to maintain the charge retention capability as it is and reduce noise to about half as compared with the conventional case, and it is possible to obtain a further excellent image quality.

[Brief description of drawings]

FIG. 1 is a plan view of a main part of a display panel to which an embodiment of the present invention is applied.

FIG. 2 is a diagram showing an equivalent circuit of this embodiment.

FIG. 3 is a diagram showing a waveform of a voltage applied to liquid crystal.

FIG. 4 is a plan view of part of a conventional display panel.

5 is a cross-sectional view taken along line XX of FIG.

FIG. 6 is a diagram showing a conventional equivalent circuit.

FIG. 7 is a luminance-signal voltage characteristic diagram shown to explain conventional problems.

[Explanation of symbols]

2A, 2B, 2C Scan line 3 Signal line 4A, 4B, 4C Thin film transistor (switching element) 5A, 5B, 5C, 5D Pixel electrode

Claims (4)

[Claims] 1. In a display panel in which a pixel electrode is connected to a scan line and a signal line provided in a matrix through a switching element, the pixel electrode is provided with a pixel line different from the scan line for the pixel electrode.
A display panel, characterized in that scanning lines of a book are partially overlapped. 2. The display according to claim 1, wherein the other two scan lines are scan lines for the other two pixel electrodes that are continuously arranged in a front stage or a rear stage of the pixel electrode. panel. 3. One of the other two scanning lines is overlapped with one side of the pixel electrode, and the other one is from the substantially central portion to the other side of the one side and the other side of the pixel electrode. The display panel according to claim 2, wherein the display panels are overlapped. 4. The capacitance of the overlapping portion of one of the other two scanning lines and the pixel electrode is equal to the capacitance of the overlapping portion of the other one scanning line and the pixel electrode. The display panel according to any one of claims 1 to 3.