JPH0798461A - Display device - Google Patents

Abstract

PURPOSE:To provide the display device of an active matrix type capable of easily dealing with a trend toward higher densities and higher fineness by making it possible to surely charge pixels and increasing an opening rate even if selection time is shortened according to a trend toward higher frequencies. CONSTITUTION:This display device of an active matrix type is constituted by arranging plural pixels consisting of liquid crystals in a matrix form. A first TFT 11 and second TFT 12 varying in sizes and characteristics are arranged on each pixel. The gate of the first TFT 11 is connected to a scanning line Gn-1 of the stage former than the prescribed scanning line Gn and the drain is connected to a data line Dn-1, different from the prescribed data line Dn. The gate and drain of the second TFT 12 are connected, respectively, to the prescribed scanning line Gn and data line Dn. The prescribed pixel is first charged by the first TFT 11 and the prescribed pixel is charged to a desired voltage by the second TFT 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix type display device in which pixels arranged in a matrix type are driven by using thin film transistors (hereinafter referred to as TFTs) provided for each pixel, and in particular, each pixel The present invention relates to a display device having an improved connection structure of TFTs arranged with respect to each other.

[0002]

2. Description of the Related Art In an active matrix type liquid crystal display device, a plurality of liquid crystal pixels are arranged in a matrix on an insulating substrate, and a TFT for charging each pixel is arranged for each pixel. Is connected to the scanning line and the data line and is driven by a driver.

By the way, in an active matrix type display device, the above-mentioned TFTs are formed in a matrix on an insulating substrate, and if a defect occurs in this TFT, it causes a defect in the pixel in which the TFT is arranged. In order to remedy such a defect, two TFs are provided for one pixel.
A structure in which Ts are connected has been proposed. Referring to FIG.
An example of such a conventional active matrix type display device will be described.

FIG. 3 shows a TFT of a conventional display device.
It is a circuit diagram for explaining a connection structure. Multiple scan lines
G_n-1, G_n, G_{n + 1}Are arranged in parallel and
Scan line G_n-1, G_n, G_{n + 1}Multiple, orthogonal to
Data line D_n-1, D_n, D _{n + 1}Are arranged. This
These scan lines G_n-1~ G_{n + 1}And data line D_n-1~ D
_{n + 1}A plurality of cells formed by intersecting
It is arranged like a ricks, but each cell is
One pixel is arranged and multiple pixels are matrix
It is arranged like a stripe.

In this display device, one pixel has two pixels.
The TFTs 1 and 2 are connected. For example, scan line G
At the (G _n , D _n ) th pixel scanned by _n , T
FT1 and FT2 are connected. The gate and drain of one TFT ₁ are connected to the scanning line G _n-1 and the data line D _n-1 in the preceding stage, respectively. Also, the other TFT2
Has a gate and a drain respectively connected to a predetermined scanning line G _n.
And the data line D _n . In addition, 3 shows an additional capacity.

In the display device shown in FIG. 3, the two TFTs 1 and 2 are arranged for one pixel as described above, but the two TFTs 1 and 2 are arranged in the TFT 1 or the TFT 2. This is because even if a defect occurs in any one of the above, the pixel of the other TFT is surely charged. That is, the TFT for the defect relief
1 and 2 are connected. Therefore, the TFTs 1 and 2 are configured to have the same size and the same charging characteristic, and each of them is configured to independently charge the pixel to the target voltage.

At the time of actual charging, as shown in FIG. 4A, during the selection time in which the scanning line G _n-1 is in the ON state, (G _n-1 , D _n-1 ) Not only to charge the pixels
The (G _n , D _n ) pixel is also charged by the TFT 1.
Therefore, even if the TFT 2 is out of order,
The charging by 1 ensures that the (G _n , D _n ) pixel is charged.

When the TFT1 has a defect, the (G _n , D _n ) pixel is charged by the TFT 2 on the contrary.

[0009]

As described above, in the display device shown in FIG. 3, in view of the insufficient yield of TFTs, in order to enable each pixel to operate reliably, Two TFTs 1 and 2 were connected to one pixel. Therefore, since the TFTs 1 and 2 individually charge the pixel to the target voltage, it is necessary to form two TFTs having a relatively large size for one pixel. In addition, since the pixel is charged to the target voltage by either one of the TFTs 1 and 2, the charging is completed within one selection time.

By the way, in recent years, the yield of TFT has been improved. Therefore, it is not always necessary to connect two TFTs 1 and 2 having the same size and the same characteristics to one pixel as described above.

In recent years, high-definition televisions and the like have been required to drive at higher frequencies, and therefore the selection time has been shortened. However, in the conventional active matrix type display device, charging of the pixels is completed within one selection time, and thus shortage of charging may occur due to shortening of the selection time.

Further, in the above-mentioned conventional display device, since two TFTs having the same size and characteristics which are configured to charge the liquid crystal to the target voltage independently are used, the yield is improved, but the TFT is improved. The area to be formed is 2
Since it doubled, the aperture ratio had to be reduced. When the aperture ratio decreases, it becomes difficult to deal with high density and high definition.

The object of the present invention is to make it possible to prevent insufficient charging even when driven at a high frequency and to increase the aperture ratio, and thus to easily cope with high density and high definition. It is to provide a display device.

[0014]

SUMMARY OF THE INVENTION The present invention is an active device including a plurality of pixels made of liquid crystal arranged in a matrix, a thin film transistor connected to each pixel, and a scanning line and a data line connected to the thin film transistor. In a matrix type display device, a first TF having different dimensions and characteristics is used as the thin film transistor for one pixel.
T and a second TFT are arranged, the gate of the first TFT is connected to a scanning line in a stage preceding a predetermined scanning line, and the drain is connected to a data line different from the predetermined data line, and the second T
The gate and drain of the FT are connected to a predetermined scanning line and data line, respectively, and the first TFT precharges the pixel and the second TFT charges the pixel to a target voltage. And a display device.

Also, preferably, the first TFT is
The liquid crystal is configured to have a size capable of passing a current that enables charging up to near the threshold voltage of the liquid crystal.

[0016]

In the present invention, since the first TFT is connected to the scanning line preceding the predetermined scanning line, the scanning line preceding the predetermined scanning line is in the ON state during the selection time. Then, the first TFT precharges a predetermined pixel, and further, the second TFT charges the pixel to the target voltage during the selected time when the predetermined scanning line is in the ON state. That is, the pixel is charged to the target voltage by using both the first and second TFTs.

That is, according to the present invention, the operation of charging a predetermined pixel to the target voltage is performed by dividing the operation into the first TFT and the second TFT, so that the pixel is charged in two selection times. Done. Further, the first and second TFTs are configured so that their dimensions and characteristics are different as described above, and charge the pixel to the target voltage by the sum of the charging actions of the two TFTs. Therefore, the size of each TFT can be made considerably smaller than that in the case where a pixel is charged to a target voltage with a single TFT.

Therefore, since the pixel is charged to the target voltage by using the two selection times, the pixel can be surely charged even when the selection time becomes shorter due to the higher frequency. Moreover, since the dimensions of the first and second TFTs can be made smaller than the conventional TFT which charges the pixel to the target voltage alone, even when two TFTs are arranged for one pixel. The aperture ratio can be increased as compared to the conventional display device shown in FIG.

Further, as described in claim 2, it is preferable that the first TFT has a size capable of flowing a current that enables charging up to near the threshold voltage of the liquid crystal, whereby the first TFT is provided. Preliminary charging is performed by the TFT and the second TF
Since T only needs to further charge the liquid crystal charged to a voltage close to the threshold voltage to the target voltage, it is possible to display reliably and quickly even when the selection time is shortened.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be clarified by describing embodiments with reference to the drawings.

FIG. 1 is a diagram for explaining an active matrix type display device according to an embodiment of the present invention.
It is a figure equivalent to FIG. 3 shown about the prior art example. With reference to FIG. 1, in this embodiment, a plurality of data lines G _n-1 , D are provided.
_n and G _{n + 1} are arranged in parallel, and a plurality of data lines D _n-1 and D _n are arranged substantially parallel to the scanning lines G _{n-1 to} G _{n + 1} and parallel to each other. , D _{n + 1} are arranged. These scanning lines G _{n-1 to} G _{n + 1} and data lines D _n-1 to
One pixel made of liquid crystal is arranged in each cell formed by intersecting with D _{n + 1} . Therefore, a plurality of pixels are arranged in a matrix. Further, two TFTs, a first TFT and a second TFT, are connected to one pixel.

The source electrode of the first TFT 11 is connected to the (G _n , D _n ) th pixel, but its gate is connected to the preceding stage, that is, the G _n- 1th scanning line. , And the drain is connected to the preceding stage, that is, the D _n− 1th data line. The gate of the second TFT 12 is connected to a predetermined scanning line G _n , and the drain is connected to a predetermined data line D _n .

Further, pixels are connected to the source electrodes of the first and second TFTs 11 and 12. In addition, 13 shows an additional capacity. Up to this point, the process is similar to that of the conventional display device shown in FIG. The feature of this embodiment is that the first TFT 11 is
The second TFT 12 is configured so that the actual dimensions and characteristics are different as shown in the figure with different dimensions, and charging of both the first and second TFTs 11 and 12 is performed. By the action, the (G _n , D _n ) th pixel is charged to the target voltage. That is, the first and second TFT1
1 and 12 are TFTs of the other party when one side has a defect
It is not a substitute for.

Further, in the present embodiment, the charging characteristic of the first TFT 11 is such that a current capable of charging the (G _n , D _n ) th pixel can be charged up to near the threshold voltage. Is configured. In addition, the second TFT 12 is
The pixel is preliminarily charged by the first TFT 11 and has a size capable of flowing a current that allows the pixel to be charged to a target voltage.

Therefore, the first TFT 11 and the second TF
T12 is the conventional TF whose dimensions are shown in FIG.
It can be made smaller than T1 and T2, and in particular, the first TFT can be configured to be smaller because it only needs to be charged up to the vicinity of the threshold voltage of the liquid crystal. Therefore, although the two TFTs 11 and 12 are arranged for one pixel, it is possible to considerably increase the aperture ratio as compared with the conventional display device shown in FIG.

Next, the charging operation of the display device of this embodiment will be described with reference to FIG. As shown in FIG. 2A, consider the selection time when the scanning line G _n-1 is in the ON state.
In this case, not only is the (G _n-1 , D _n-1 ) -th pixel fully charged, but the first TFT 11 causes (G _n-1 ,
The D _n ) th pixel is precharged. This preliminary charge is
The charging is performed so that the liquid crystal forming the (G _n , D _n ) th pixel can be charged to a value near the threshold voltage.

After that, as shown in FIG. 2B, at the selection time when the _nth scanning line G _n is in the ON state, the second T
The FT 12 fully charges the (G _n , D _n ) th pixel. In this book charging, (G _n, D _n) for th pixels are pre-charged by the first TFT 11, thus, it is possible to rapidly charge the liquid crystal to the desired voltage.

Therefore, even when the selection time is shortened by advancing the high frequency, the first and second TFTs as described above are provided.
Since 11 and 12 are used to charge one pixel over two selection times, the pixel can be surely charged.

In this embodiment, the first TFT 11
However, the first TFT 11 and the second TFT 12 cooperate with each other so that the first TFT 11 cooperates with the second TFT 12 to charge the liquid crystal forming the pixel to the vicinity of the threshold voltage. As long as the pixel can be charged to the target voltage by the above, the size is not limited to this. That is, the first and second TFTs 11 and 12 should be smaller than the TFTs 1 and 2 in the conventional display device shown in FIG. 3 as long as the liquid crystal can be charged by being divided into the two TFTs 11 and 12. Therefore, the aperture ratio can be increased.

Further, in the above embodiment, the first TFT 11
The gate and drain of the first scan line were connected to the (n-1) th scan line _Gn-1 and the data line Dn _-1 , respectively.
The gate and the drain of the TFT 11 may be connected to the scanning line and the data line of the stage further than the (n−1) th scanning line as long as they are in the preceding stages of the nth scanning line G _n and the data line D _n . However, in order to simplify the connection structure of the TFT 11, it is preferable to connect to the scanning line and the data line one stage before the predetermined scanning line and the data line as in this embodiment.

Further, the present invention can be applied to the interlace system and the non-interlace system.

[0032]

As described above, according to the present invention, the predetermined pixel is precharged by the first TFT and the predetermined pixel is scanned at the selection time before the selection time for charging the predetermined pixel. At the selected time, the predetermined pixel is charged to the target voltage by the second TFT. That is, a predetermined pixel is charged to the target voltage over the two selection times.

Therefore, in order to achieve high density and high definition, even when the display device is driven at a higher frequency, that is, even when the selection time becomes shorter, a predetermined pixel is selected for two selection times. It is possible to charge the pixel without fail since it is charged. Therefore, driving at a higher frequency in an active matrix display device can be easily accommodated.

Furthermore, the first and second TFTs are for charging the pixel to the target voltage in cooperation with each other, and the size thereof can be made smaller than that of the TFT for independently charging the pixel to the target voltage. it can. Therefore, although the two TFTs are arranged for one pixel, the aperture ratio can be increased as compared with the conventional display device in which two equivalent TFTs are arranged for defect relief. Therefore, since it is possible to prevent the aperture ratio from decreasing, it is easy to cope with high density and high definition.

Further, as described in claim 2, the first T
If the FT is configured to have a size that allows a current to flow near the threshold voltage of the liquid crystal to flow, the liquid crystal can be charged near the threshold voltage by the first TFT and the second TFT can be charged. With this TFT, the liquid crystal can be surely and quickly charged to the target voltage.

[Brief description of drawings]

FIG. 1 is a diagram showing a circuit configuration of a display device of an example.

FIG. 2A and FIG. 2B are timing charts for explaining a charging operation at n−1th and nth selection times in the embodiment, respectively.

FIG. 3 is a diagram showing a circuit configuration of a conventional active matrix type display device.

4A and 4B are timing charts for explaining the charging operation at the (n-1) th and nth selection times in the display device shown in FIG. 3, respectively.

[Explanation of Codes] 11 ... First TFT 12 ... Second TFT 13 ... Additional capacitances G _n-1 , G _n , G _{n + 1} ... Scan lines D _n-1 , D _n , D _{n + 1} ... Data line

Claims (2)

[Claims] 1. An active matrix display device comprising a plurality of pixels made of liquid crystal arranged in a matrix, a thin film transistor connected to each pixel, and a scanning line and a data line connected to the thin film transistor. For the pixel, a first thin film transistor and a second thin film transistor having different dimensions and characteristics are arranged as the thin film transistor, and a gate of the first thin film transistor is provided on a scanning line in a stage preceding a predetermined scanning line and a drain thereof is provided with a predetermined drain. Connected to a data line different from the data line, the gate and drain of the second thin film transistor,
A display device, which is connected to a predetermined scanning line and a data line, precharges a pixel with the first thin film transistor, and then charges a target voltage with a second thin film transistor. 2. The display device according to claim 1, wherein the first thin film transistor is sized so that a current that allows charging to near the threshold voltage of the liquid crystal can flow.