# Patent

## Title
Pixel circuit and driving method thereof

## Abstract

Pixel circuit includes first and second scan lines, data line, three switches, and pixel. Three switches all include first end, second end, and control end. Pixel includes first and second sub-pixels. First end of first switch is coupled to data line. Control end of first switch is coupled to first scan line. First end of second switch is coupled to second end of first switch. Control end of second switch is coupled to second scan line. First end of third switch is coupled to data line. Control end of third switch is coupled to first scan line. First sub-pixel is coupled to second end of second switch for coupling to second end of third switch through second and first switches. Second sub-pixel is coupled to second end of third switch for coupling to data line through third switch.

## Background
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a pixel circuit and driving method thereof, and more particularly, to a pixel circuit and driving method thereof capable of improving the color washout phenomenon.
2. Description of the Prior Art
Since the Liquid Crystal Display (LCD) has the advantage of the smaller size, the lower power consumption and no radiance, the LCD is becoming the main stream of the market gradually. However, the desire of the LCD with the wider viewing angle, the higher resolution and the larger size is the market trend.
However, when watching the LCD from a large viewing angle, the color washout phenomenon is generated so that the color of the image is distorted. The so-called color washout phenomenon means that when watching the LCD from a larger viewing angle, the color of the image is distorted to be whiter than normal. That is, when watching the LCD from a larger viewing angle, the distortion for the pixels with the medium and low gray-level luminance is more serious. As a result, reducing the redundant luminance can effectively improve the color washout phenomenon. Therefore, because of the trend of the image without distortion, the development of the wide viewing angle technology is necessary.
SUMMARY OF THE INVENTION
The present invention provides a pixel circuit. The pixel circuit comprises a first scan line, a second line, a data line, a first pixel switch, a second pixel switch, a third pixel switch, and a pixel. The first pixel switch comprises a first end, coupled to the data line, a second end, and a control end, coupled to the second scan line. The second pixel switch comprises a first end, coupled to the second end of the first pixel switch, a second end, and a control end, coupled to the first scan line. The third pixel switch comprises a first end, coupled to the data line, a second end, and a control end, coupled to the first scan line. The pixel comprises a first sub-pixel and a second sub-pixel. The first sub-pixel is coupled to the second end of the second pixel switch for coupling to the data line through the first pixel switch and the second pixel switch. The second sub-pixel is coupled to the second end of the third pixel switch for coupling to the data line through the third pixel switch.
The present invention further provides a pixel circuit. The pixel circuit comprises a first scan line, a second scan line, a data line, a first pixel switch, a second pixel switch, a third pixel switch, and a pixel. The first pixel switch comprises a first end, a second end, and a control end, coupled to the second scan line. The second pixel switch comprises a first end, coupled to the second end of the first pixel switch, a second end, coupled to the data line, and a control end, coupled to the first scan line. The third pixel switch comprises a first end, coupled to the data line, a second end, and a control end, coupled to the first scan line. The pixel comprises a first sub-pixel and a second sub-pixel. The first sub-pixel is coupled to the first end of the first pixel switch for coupling to the data line through the second pixel switch and the first pixel switch. The second sub-pixel is coupled to the second end of the third pixel switch for coupling to the data line through the third pixel switch.
These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram illustrating the LCD according to a first embodiment of the present invention.
FIG. 2 is a diagram illustrating the equivalent circuit of the LCD according to the first embodiment of the present invention.
FIG. 3 is a diagram illustrating the driving principle of the LCD.
FIG. 4 is a diagram illustrating the LCD according to a second embodiment of the present invention.
FIG. 5 is a diagram illustrating the equivalent circuit of the LCD according to the second embodiment of the present invention.



DETAILED DESCRIPTION
Please refer to FIG. 1. FIG. 1 is a diagram illustrating the LCD 100 according to a first embodiment of the present invention. The LCD 100 comprises a plurality of data lines, for example, D1, and D2, and a plurality of scan lines, for example, G1, G2 and G3. The scan lines G1, G2, G3 and so on are orientated to a first direction (the horizontal direction) and are approximately arranged in parallel with each other. The data lines D1, D2, and so on are orientated to a second direction (vertical direction) and are approximately arranged in parallel with each other.
The LCD 100 is divided into a plurality of display areas by the scan lines G1, G2, G3 and so on, and the data lines D1, D2, D3 and so on. The display areas are arranged in an array. In each display area, a pixel P is disposed, for example, the pixels P11, P12, P21 and P22. In this way, a pixel array (pixel circuit) 110 is formed on the LCD 100. In one preferred embodiment, each pixel is divided into at least a first sub-pixel and a second sub-pixel. For example, the pixel P11 is divided into a first sub-pixel SP11A and a second sub-pixel SP11B. In the present embodiment, the first sub-pixels of the pixels of the Mth row in the horizontal direction are all coupled to the Mth scan line GM and the (M+1)th scan line GM+1, and the second sub-pixels of the Mth row in the horizontal direction are all coupled to the Mth scan line GM. In addition, the first sub-pixel and the second sub-pixel of the pixels of the Nth column in the vertical direction receive the data signal SD transmitted from the data line DN, wherein both M and N are positive integers.
Each pixel comprises a first sub-pixel, a second sub-pixel, a first pixel switch, a second pixel switch and a third pixel switch. The first sub-pixel is coupled through the first and the second pixel switches to the corresponding scan lines and the corresponding data line. The second sub-pixel is coupled through the third pixel switch to the corresponding scan line and the corresponding data line. For instance, the pixel P11 comprises a first sub-pixel SP11A, a second sub-pixel SP11B, a first pixel switch SW11A, a second pixel switch SW11B and a third pixel switch SW11C. Each pixel switch comprises a first end, a second end and a control end. Each pixel switch, according to the voltage level of the control end of the pixel switch, couples the first end of the pixel switch to the second end of the pixel switch. More precisely, when the voltage on the control end of a pixel is at a high voltage level, the pixel switch is turned on. That is, the first end 1 of the pixel switch is coupled to the second end 2 of the pixel switch. In the pixel P11, the control end C of the first pixel switch SW11A is coupled to the scan line G2 for receiving the scan signal SG2, the first end 1 of the first pixel switch SW11A is coupled to the data line D1, and the second end 2 of the first pixel switch SW11A is coupled to the first end 1 of the second pixel switch SW11B; the control end C of the second pixel switch SW11B is coupled to the scan line G1 for receiving the scan signal SG1, the first end 1 of the second pixel switch SW11B is coupled to the second end 2 of the first pixel switch SW11A, and the second end 2 of the second pixel switch SW11B is coupled to the first sub-pixel SP11A; the control end C of the third pixel switch SW11C is coupled to the scan line G1 for receiving the scan signal SG1, the first end 1 of the third pixel switch SW11C is coupled to the data line D1, and the second end 2 of the third pixel switch SW11C is coupled to the second sub-pixel SP11B. By means of this design, when the LCD 100 displays the image, the first sub-pixel SP11A and the second sub-pixel SP11B of the pixel P11 have the luminance with different gray level so as to solve the problem related to the color washout phenomenon. The related operational principle is described in detail hereinafter. The structures of the rest pixels are similar to the pixel P11 and hereinafter will not be repeated again for brevity.
Please refer to FIG. 2. FIG. 2 is a diagram illustrating the equivalent circuit of the LCD according to the first embodiment of the present invention. As shown in FIG. 2, each sub-pixel comprises a liquid crystal capacitor and a storage capacitor. For instance, in the pixel P11, the first sub-pixel SP11A comprises a liquid crystal capacitor CLC and a storage capacitor CST. The capacitors CLC and CST are connected in parallel with each other between the second end 2 of the pixel switch SW11B and a common end VCOM. The common end VCOM is utilized for providing a common voltage VCOM. The second sub-pixel SP11B comprises a liquid crystal capacitor CLC and a storage capacitor CST. The capacitors CLC and CST are connected in parallel with each other between the second end 2 of the pixel switch SW11C and a common end VCOM. The structures of the rest pixels are similar to the pixel P11 and hereinafter will not be repeated again for brevity.
Pleas refer to FIG. 3. FIG. 3 is a timing diagram illustrating the principle for driving the LCD 100. In FIG. 3, only the pixel P11 is illustrated as an example and the driving method of the rest pixels is similar to the pixel P11. In the LCD 100, when a pixel is driven, the corresponding scan signal (means the voltage on the corresponding scan line) is raised up to a high voltage level and keeps for a predetermined period TP1, and then the corresponding scan signal is lowered down to a low voltage level and keeps for a predetermined period TP2. Then the corresponding scan signal is raised up again to the high voltage level and keeps for a predetermined period TP3. The length of the predetermined period TP3 is the sum of the predetermined periods TP1 and TP2. As shown in FIG. 3, at the moment T3, the scan signal SG1 is raised up to the high voltage level and keeps for the predetermined period TP3 (means to keep until the moment T5) and the scan signal SG2 is raised up to the high voltage level and keeps for a predetermined period TP1 (means to keep until the moment T4). In this way, between the moment T3 and the moment T4, The pixel switches SW11A, SW11B, SW11C, SW21A and the SW21B are all turned on so that the data signal SD1 transmits the data +B through the data line D1, the pixel switch SW11A and the pixel switch SW11B to the first sub-pixel SP11A and through the data line D1 and the pixel switch SW11C to the second sub-pixel SP11B. Between the moment T4 and the moment T5, the scan signal SG1 still keeps at a high voltage level, but the scan signal SG2 is lowered down to a low voltage level so that the pixel switch SW11A is turned off and the pixel switches SW11B and SW11C still keep turned on. Since the pixel switch SW11A is turned off, the data signal SD1 can not transmit the data +A to the first sub-pixel SP11A (even though the pixel switch SW11B is still turned on). The data signal SD1 still transmits the data +A through the data line D1 and the pixel switch SW11C to the second sub-pixel SP11B. That is, the data stored in the second sub-pixel SW11B is updated to be the data +A. In other words, both the pixel switches SW11A and SW11B have to be turned on for coupling the first sub-pixel SP11A to the data line D1 so as to receive the data signal SD1, but only the pixel switch SW11C has to be turned on for coupling the second sub-pixel SP11B to the data line D1 so as to receive the data signal SD1. In this way, the second sub-pixel SP11B is charged up to the voltage level of the data +B first and is then further raised up to the voltage level of the data +A so that the second sub-pixel SP11B can be more precisely charged up to the voltage level of the data +A. In this way, after driving by the scan signals SG1 and SG2, the first sub-pixel SP11A and the second sub-pixel SP11B have different data (means to have different gray levels and different luminance) so as to reduce the color washout phenomenon.
Please refer to FIG. 4. FIG. 4 is a diagram illustrating the LCD 400 according to a second embodiment of the present invention. The LCD 400 is similar to the LCD 100. The difference between the LCDs 100 and 400 is that the coupling relation between the pixel switches of the pixels of the pixel array 410 is different from that between the pixel switches of the pixels of the pixel array 110. The detailed coupling relation is described hereinafter.
For instance, in the pixel array 410, the pixel P11 comprises a first sub-pixel SP11A, a second sub-pixel SP11B, a first pixel switch SW11A, a second pixel switch SW11B and a third pixel switch SW11C. In the pixel P11, the control end C of the first pixel switch SW11A is coupled to the scan line G2 for receiving the scan signal SG2; the first end 1 of the first pixel switch SW11A is coupled to the first sub-pixel SP11A; the second end 2 of the first pixel switch SW11A is coupled to the first end 1 of the second pixel switch SW11B. The control end C of the second pixel switch SW11B is coupled to the scan line G1 for receiving the scan signal SG1; the first end 1 of the second pixel switch SW11B is coupled to the second end 2 of the first pixel switch SW11A; the second end 2 of the second pixel switch SW11B is coupled to the data line D1. The control end C of the third pixel switch SW11C is coupled to the scan line G1 for receiving the scan signal SG1; the first end 1 of the third pixel switch SW11C is coupled to the data line D1; the second end 2 is coupled to the second sub-pixel SP11B. By means of such design, when the LCD 400 displays the image, the first sub-pixel SP11A and second sub-pixel SP11B have the luminance with different gray level so as to solve the problem related to the color washout phenomenon. The related operational principle is described in detail hereinbefore. The structures of the rest pixels are similar to the pixel P11 and hereinafter will not be repeated again for brevity.
Please refer to FIG. 5. FIG. 5 is a diagram illustrating the equivalent circuit of the LCD 400 according to the second embodiment of the present invention. As shown in FIG. 5, each sub-pixel comprises a liquid crystal capacitor and a storage capacitor. For instance, in the pixel P11, the first sub-pixel SP11A comprises a liquid crystal capacitor CLC and a storage capacitor CST. The capacitors CLC and CST are connected in parallel with each other between the first end 1 of the pixel switch SW11A and a common end VCOM. The common end VCOM is utilized for providing a common voltage VCOM. The second sub-pixel SP11B comprises a liquid crystal capacitor CLC and a storage capacitor CST. The capacitors CLC and CST are connected in parallel between the second end 2 of the pixel switch SW11C and the common end VCOM. The structures of the rest pixels are similar to the pixel P11 and hereinafter will not be repeated again for brevity.
In conclusion, by means of the pixel array (pixel circuit) provided by the present invention, the different data are effectively transmitted to the different sub-pixels of a pixel so that the different sub-pixels of the pixel have the luminance with different gray level so as to reduce the color washout phenomenon, causing a great convenience.
Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention.

## Claims

1. A pixel circuit, comprising:
a first scan line;
a second scan line,
a data line;
a first pixel switch, comprising:
a first end, coupled to the data line;
a second end; and
a control end, coupled to the second scan line;

a second pixel switch, comprising:
a first end, coupled to the second end of the first pixel switch;
a second end; and
a control end, coupled to the first scan line;

a third pixel switch, comprising:
a first end, coupled to the data line;
a second end; and
a control end, coupled to the first scan line; and

a pixel, comprising:
a first sub-pixel, coupled to the second end of the second pixel switch for coupling to the data line through the first pixel switch and the second pixel switch; and
a second sub-pixel, coupled to the second end of the third pixel switch for coupling to the data line through the third pixel switch;
wherein the first sub-pixel and the second sub-pixel are on a same side of the data line;

wherein a driving method for the pixel circuit comprises:
at a first moment, driving the first scan line for turning on the second pixel switch and the third pixel switch for a first predetermined period;
at the first moment, driving the second scan line for turning on the first pixel switch for a second predetermined period;
wherein the second predetermined period is shorter than the first predetermined period;
wherein the difference between the first predetermined period and the second predetermined period is a third predetermined period;

during the second predetermined period, providing a first data to the first and the second sub-pixels through the first pixel switch and the third pixel switch, respectively; and
during the third predetermined period, providing a second data to the second sub-pixel through the third pixel switch.

2. The pixel circuit of claim 1, wherein:
the first sub-pixel comprises:
a liquid crystal capacitor, coupled between the second end of the second pixel switch and a common end; and
a storage capacitor, coupled between the second end of the second pixel switch and the common end; and

the second sub-pixel comprises:
a liquid crystal capacitor, coupled between the second end of the third pixel switch and the common end; and
a storage capacitor, coupled between the second end of the third pixel switch and the common end.

3. The pixel circuit of claim 1, wherein when a first scan signal of the first scan line controls the second pixel switch to turn on and a second scan signal of the second scan line controls the first pixel switch to turn on, the first sub-pixel receives a signal from the data line.

4. The pixel circuit of claim 1, wherein when a first scan signal of the first scan line controls the third pixel switch to turn on, the second sub-pixel receives a signal from the data line.

5. The pixel circuit of claim 1, wherein:
the first sub-pixel comprises:
a liquid crystal capacitor, coupled between the second end of the second pixel switch and a common end; and
a storage capacitor, coupled between the second end of the second pixel switch and the common end; and

the second sub-pixel comprises:
a liquid crystal capacitor, coupled between the second end of the third pixel switch and the common end; and
a storage capacitor, coupled between the second end of the third pixel switch and the common end.

6. The pixel circuit of claim 1, wherein when a first scan signal of the first scan line controls the second pixel switch to turn on and a second scan signal of the second scan line controls the first pixel switch to turn on, the first sub-pixel receives a signal from the data line.

7. The pixel circuit of claim 1, wherein when a first scan signal of the first scan line controls the third pixel switch to turn on, the second sub-pixel receives a signal from the data line.

8. A pixel circuit, comprising:
a first scan line;
a second scan line,
a data line;
a first pixel switch, comprising:
a first end, coupled to the data line;
a second end; and
a control end, coupled to the second scan line;

a second pixel switch, comprising:
a first end, coupled to the second end of the first pixel switch;
a second end; and
a control end, coupled to the first scan line;

a third pixel switch, comprising:
a first end, coupled to the data line;
a second end; and
a control end, coupled to the first scan line; and

a monochromatic pixel, comprising:
a first sub-pixel, coupled to the second end of the second pixel switch for coupling to the data line through the first pixel switch and the second pixel switch; and
a second sub-pixel, coupled to the second end of the third pixel switch for coupling to the data line through the third pixel switch;
wherein the first sub-pixel and the second sub-pixel are on a same side of the data line;

wherein a driving method for the pixel circuit comprises:
at a first moment, driving the first scan line for turning on the second pixel switch and the third pixel switch for a first predetermined period;
at the first moment, driving the second scan line for turning on the first pixel switch for a second predetermined period;
wherein the second predetermined period is shorter than the first predetermined period;
wherein the difference between the first predetermined period and the second predetermined period is a third predetermined period;

during the second predetermined period, providing a first data to the first and the second sub-pixels through the first pixel switch and the third pixel switch, respectively; and
during the third predetermined period, providing a second data to the second sub-pixel through the third pixel switch.