Patent Abstract:
A scan line is used to control two thin film transistors and a video data line is used to transmit video signal to pixel capacitors and maintenance capacitors. When the thin film transistors are selected by the selection signal, the video signal stored therein charges the pixel capacitors and maintenance capacitors. When the selection signal is removed, the charge in the pixel capacitors is preserved until the next repetition when that scan line is again selected by a selection signal and new voltages are stored therein. Thus a picture is displayed on the matrix display by the charges stored in the pixel capacitors.

Full Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a display circuit structure for a liquid crystal display (LCD), and more particularly to a display circuit structure for a liquid crystal display (LCD) having reflection and transmission regions.  
         BACKGROUND OF THE INVENTION  
         [0002]    Liquid crystal displays (LCD) have been widely applied in electrical products, such as digital watches, calculator, etc. for a long time. Moreover, with the advance of techniques for manufacture and design, thin film transistor-liquid crystal display (TFT-LCD) has been introduced into portable computers, personal digital assistants, and color televisions, as well as gradually replacing the CRT used for conventional display. The demands of TFT-LCD tend to be large scale.  
           [0003]    In general, a typical circuit of a liquid crystal display having both reflection and transmission regions is illustrated in FIG. 1A, in which the LCD matrix display device commonly comprises a LCD display array  200  that further includes a plurality of display elements  50 , whose enlarged diagram is shown in the FIG. 1B, arranged in a matrix of rows and columns. Switching devices (not shown in this figure) are coupled with display elements  50  to control the application of video signals thereto. Each display element  50  acts as a switching device that includes a pixel capacitor  106  and a maintenance capacitor  108  driven by a switching transistor  104 , referring to FIG. 1B.  
           [0004]    [0004]FIG. 1B is an enlarged schematic diagram of a circuit of a liquid crystal display having both reflection and transmission regions according to one preferred embodiment of the present invention. The switching transistor  104  is usually a thin-film transistor (TFT) that is deposited on a transparent substrate such as glass. The switching transistor  104  is deposited on the glass on the same side of the display matrix as the switching transistor and has its source/drain electrode respectively connected to the capacitor electrodes of the pixel capacitor  106  and the maintenance capacitor  108 . The source/drain electrode of the switching transistor  104  is connected to a column data driver (not shown in this figure) through the video data line  100  to which video signals are applied. The gate electrodes of the switching transistor  104  is coupled to a row select driver (not shown in this figure) through a scan line  102 , and a scan signal is applied to turn on the switching transistor  104 .  
           [0005]    By scanning the scan lines  102  and in accordance with the scan signals, all of the switching transistors  104  in a given scan line  102  are turned on. At the same time, video signals are provided in the video data lines synchronously with the selected scan line  102 . When the switching transistors  104  in a given scan line  102  are selected by the scan signals, the video signals supplied to the switching transistors  104  charge the pixel capacitors  106  and the maintenance capacitor  108  to a voltage value corresponding to the video signal on the video data line. Thus each pixel capacitor  106  with its electrodes on opposite sides of the matrix display acts as a capacitor. When a signal for a selected scan line  102  is removed, the charge in the pixel capacitor  106  is preserved until the next repetition when that scan line is again selected by a scan signal and new voltages are stored therein. Thus a picture is displayed on the matrix display by the charges stored in the pixel capacitors  106 .  
           [0006]    However, for a liquid crystal display having both reflection and transmission regions, the pixel capacitor  106  crosses both regions. Once the switching transistor  104  or the pixel capacitor  106  is broken, the display element  50  fails.  
           [0007]    On the other hand, the main function of the maintenance capacitor  108  is to maintain the constancy of the voltage value applied to the pixel capacitor  106 . That is, before the data stored in the pixel capacitor  106  is refreshed, the voltage applied to the pixel capacitor  106  is maintained by the maintenance capacitor  108 . However, with regard to the conventional liquid crystal display having both reflection and transmission regions, the pixel capacitor  106  crosses both regions; therefore, the maintenance capacitor  108  needs to simultaneously maintain the voltage applied to the reflection and transmission regions. The capacitor value of the maintenance capacitor  108  needs to be enlarged to avoid electric charge leakage which would result in a sharp decrease of the voltage applied therein. Accordingly, the enlarged capacitor value of the maintenance capacitor  108  requires a larger current to drive the refresh data process so as to finish this refresh process in the same time. However, this increases the difficulties of circuit design.  
         SUMMARY OF THE INVENTION  
         [0008]    According to the above descriptions, with regard to the conventional liquid crystal display having reflection and transmission regions, each display element  50  comprises a pixel capacitor  106  and a maintenance capacitor  108  both driven by a switching transistor  104 . Therefore, once one of them is broken, the whole display element fails.  
           [0009]    On the other hand, the pixel capacitor  106  crosses both regions. Therefore, the maintenance capacitor  108  needs to simultaneously maintain the voltage applied to the reflection and transmission regions. The capacitor value of the maintenance capacitor needs to be enlarged to avoid electric charge leakage which would result in a sharp decrease of the voltage applied therein. The enlarged capacitor value of the maintenance capacitor  108  requires a larger current to drive the refresh data process so as to finish this refresh process in the same time. This increases the difficulties of circuit design. Therefore, the present invention provides a circuit structure to solve the above problems.  
           [0010]    The primary object of the present invention is to provide a circuit for liquid crystal displays with reduced power consumption.  
           [0011]    Another object of the present invention is to provide a circuit for liquid crystal displays with reduced drive current in the refresh process.  
           [0012]    A further object of the present invention is to provide a circuit for liquid crystal displays in which each display element comprises a plurality of pixel capacitors, a plurality of maintenance capacitors and a plurality of switching transistors and those capacitors and transistors are isolated from each other. Such a structure avoids failure of the entire display element when one capacitor or transistor breaks. The present invention provides a circuit for liquid crystal displays having reflection and transmission regions. In accordance with the present invention, each display element comprises a plurality of pixel capacitors, a plurality of maintenance capacitors and a plurality of switching transistors. The reflection and transmission regions respectively comprise a pixel capacitor, a maintenance capacitor and a switching transistor. Therefore, the two regions are isolated from each other. That is, a breakage in the reflection region does not affect the transmission region work, and vice versa. Furthermore, in accordance with the circuit structure of the present invention, because each maintenance capacitor only needs to maintain the voltage applied the pixel capacitor of the reflection or transmission region, the capacitor value does not require enlargement. Therefore, the charge current may be decreased.  
           [0013]    In accordance with the structure of the present invention, a scan line is used to control two thin film transistors and a video data line is used to transmit a video signal to pixel capacitors and maintenance capacitors. When the thin film transistors are selected by the selection signal, the video signal stored therein charges the pixel capacitors and maintenance capacitors. When selection signal is removed, the charge in the pixel capacitors is preserved until the next repetition when that scan line is again selected by a selection signal and new voltages are stored therein. Thus a picture is displayed on the matrix display by the charges stored in the pixel capacitors. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:  
         [0015]    [0015]FIG. 1A is a schematic diagram of a display circuit structure of the liquid crystal display in accordance with the conventional invention;  
         [0016]    [0016]FIG. 1B is an enlarged schematic diagram of a display circuit structure of the liquid crystal display in accordance with the conventional invention;  
         [0017]    [0017]FIG. 2 is a schematic diagram of a display circuit structure of the liquid crystal display in accordance with the first embodiment of the present invention; and  
         [0018]    [0018]FIG. 3 is a schematic diagram of a display circuit structure of the liquid crystal display in accordance with the second embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0019]    Without limiting the spirit and scope of the present invention, the circuit structure in a liquid crystal display (LCD) proposed in the present invention is illustrated with one preferred embodiment. Skilled artisans, upon acknowledging the embodiments, can apply the circuit design of the present invention to any kind of liquid crystal display to form a display circuit structure. In accordance with the circuit structure of the present invention, the present invention avoids the drawback existing in the conventional liquid crystal display circuit structure having display elements composed only of a pixel capacitor, a maintenance capacitor and a switching transistor. However, this kind of conventional circuit structure may result in total display element failure once one of the three devices breaks. The structure of the present invention uses display elements comprising plurality of pixel capacitors, a plurality of maintenance capacitors and a plurality of switching transistors; therefore, when one , the devices can replace it to make the whole display element keep working.  
         [0020]    On the other hand, the circuit structure of the present invention also avoids the drawback of the conventional circuit design in which only one maintenance capacitor having a larger capacitor value is used to maintain the voltage applied to the reflection and transmission region. In accordance with this conventional structure, the enlarged capacitor value of the maintenance capacitor requires a larger current to drive the refresh data process, which increases the power consumption. The application of the present invention is not limited by the following description.  
         [0021]    The present invention provides a circuit structure for liquid crystal displays having reflection and transmission regions. In accordance with the present invention, each display element comprises a plurality of pixel capacitors, a plurality of maintenance capacitors and a plurality of switching transistors. The reflection and transmission regions respectively comprise a pixel capacitor, a maintenance capacitor and a switching transistor. Therefore, the two regions are isolated from each other. That is, breakage in the reflection region does not affect the transmission region work, and vice versa. Furthermore, in accordance with the circuit structure of the present invention, because each maintenance capacitor only needs to maintain the voltage applied the pixel capacitor of the reflection or transmission region, the capacitor value does not require enlargement. Therefore, the charge current may be decreased. The detailed description of the present invention is as follows.  
         [0022]    [0022]FIG. 2 is a schematic diagram of a display circuit structure  300  of a liquid crystal display in accordance with the first embodiment of the present invention. This circuit structure  300  is used in a thin film transistor liquid crystal display (TFT-LCD) having reflection and transmission regions therein. In this circuit structure, each display element comprises two pixel capacitors  206  and  208 , two maintenance capacitors  210  and  212  and two switching transistors  202  and  204 . The pixel capacitors  206 , maintenance capacitor  210  and switching transistor  202  are used to control the reflection region in the thin film transistor liquid crystal display. The pixel capacitors  208 , maintenance capacitor  212  and switching transistor  204  are used to control the transmission region in the thin film transistor liquid crystal display.  
         [0023]    The gate electrodes of the switching transistors  202  and  204  are both coupled with a scan line  302 . The scan line  302  is used to control the turning on/off of the switching transistors  202  and  204 . The source/drain electrode of the switching transistors  202  is coupled with the video data line that is used to transmit the video signal. The video data line  304  and the scan line  302  work simultaneously to select a display element from a display element array (not shown in this figure). The other source/drain electrode of the switching transistor  202  is respectively coupled with the electrodes of the pixel capacitor  206  and the maintenance capacitor  210 , and is also coupled with the source/drain electrode of the other switching transistor  204 . The other source/drain electrode of the switching transistors  204  is respectively coupled with the electrodes of the pixel capacitor  208  and the maintenance capacitor  212 .  
         [0024]    When operation, a selection signals is transmitted to the scan line  302 ; that is, a high voltage is applied to the scan line  302  to turn on the switching transistors  202  and  204 . At the same time, video signals are transmitted form the video data line  304  to the source/drain electrode of the switching transistor  202 . Then, the video signal transmits to the pixel capacitor  206  and the maintenance capacitor  210  through the channel of the switching transistor  202 , and also transmits to the pixel capacitor  208  and the maintenance capacitor  212  through the channel of the switching transistor  204 . The video signals may respectively charge the pixel capacitor  206  and  208  and the maintenance capacitor  210  and  212  to the corresponding voltage value applied to the video data line to drive the liquid crystal in the reflection and transmission regions.  
         [0025]    When the selection signals in the scan line  302  are removed and another selection signals are not transmitted to the scan line  302  yet, the switching transistors  202  and  204  are turned off. The charge still retained in the pixel capacitor  206  and  208  and the maintenance capacitor  210  and  212 . Therefore, a picture is displayed on the display by the charges stored in the pixel capacitors  206  and  208 .  
         [0026]    In accordance with the structure described in the above, the reflection and transmission regions respectively comprise a pixel capacitor, a maintenance capacitor and a switching transistor. Therefore, the two regions are isolated from each other. That is, the break in the reflection region does not affect the transmission region work, and vice versa. For example, if the pixel capacitor  206  breaks, it only affects the reflection region of the circuit structure  300 . The transmission region of the circuit structure  300  still works well.  
         [0027]    Furthermore, in accordance with the circuit structure of the present invention, the voltage applied to the pixel capacitors  206  and  208  are respectively maintained by the maintenance capacitors  210  and  212 . Therefore, the capacitor value does not require enlargement. The charge current can be decreased. In other words, the circuit structure of the present invention uses two pixel capacitors and maintenance capacitors to control respectively the reflection and transmission regions, which is different from the conventional structure using only one pixel capacitor and maintenance capacitor to control the reflection and transmission regions. Therefore, the electric charge leakage ratio in a constant time of the present invention structure is lower than the conventional structure. In other words, because each maintenance capacitor only needs to maintain the voltage applied the pixel capacitor in the reflection or transmission region, the capacitor value does not require enlargement. Therefore, the charge current is decreased when a refresh process is conducted.  
         [0028]    [0028]FIG. 3 is a schematic diagram of a display circuit structure  400  of the liquid crystal display in accordance with the second embodiment of the present invention. This circuit structure  400  is also used in a thin film transistor liquid crystal display (TFT-LCD) having reflection and transmission regions therein. In this circuit structure, each display element comprises two pixel capacitors  406  and  408 , two maintenance capacitors  410  and  412  and two switching transistors  402  and  404 . The pixel capacitors  406 , maintenance capacitor  410  and switching transistor  402  are used to control the reflection region in the thin film transistor liquid crystal display. The pixel capacitors  408 , maintenance capacitor  412  and switching transistor  404  are used to control the transmission region in the thin film transistor liquid crystal display.  
         [0029]    The gate electrodes of the switching transistors  402  and  404  are both coupled with a scan line  302 . The scan line  302  is used to control the turning on/off of the switching transistors  402  and  404 . The source/drain electrode of the switching transistors  402  is coupled with the video data line that is used to transmit the video signal. The video data line  304  and the scan line  302  can work simultaneously to select a display element from a display element array (not shown in this figure). The other source/drain electrode of the switching transistor  402  is respectively coupled with the electrodes of the pixel capacitor  406  and the maintenance capacitor  410 . The source/drain electrode of the switching transistors  404  is respectively coupled with the electrodes of the pixel capacitor  408  and the maintenance capacitor  412 , and the other source/drain electrode of the switching transistors  404  is also coupled with the video data line  304 .  
         [0030]    During operation, a selection signal is transmitted to the scan line  302 ; that is, a high voltage is applied to the scan line  302  to turn on the switching transistors  402  and  404 . At the same time, video signals are transmitted from the video data line  304  to the source/drain electrode of the switching transistors  402  and  404 . Then, the video signal is transmitted to the pixel capacitor  406  and  408  and the maintenance capacitor  410  and  412  respectively through the channel of the switching transistor  402  and  404 . The video signals respectively charge the pixel capacitors  406  and  408  and the maintenance capacitor  410  and  412  to the corresponding voltage value applied to the video data line so as to drive the liquid crystal in the reflection and transmission regions.  
         [0031]    When the selection signals in the scan line  302  are removed and another selection signal is not transmitted to the scan line  302  yet, the switching transistor  402  and  504  is turned off. The charge is still retained in the pixel capacitor  406  and  408  and the maintenance capacitor  410  and  412 . Therefore, a picture is displayed on the display by the charges stored in the pixel capacitors  406  and  408 .  
         [0032]    In accordance with the structure described in the above, the reflection and transmission regions are respectively composed of a pixel capacitor, a maintenance capacitor and a switching transistor. Therefore, the two regions are isolated from each other. That is, the break in the reflection region does not affect the transmission region work, and vice versa. For example, if the pixel capacitor  406  breaks, it only affects the reflection region of the circuit structure  400 . The transmission region of the circuit structure  400  still works well.  
         [0033]    Furthermore, in accordance with the circuit structure of the present invention, the voltage applied to the pixel capacitors  406  and  408  are respectively maintained by the maintenance capacitors  410  and  412 . Therefore, the capacitor value does not require enlargement. The charge current can be decreased. In other words, the circuit structure of the present invention uses two pixel capacitors and maintenance capacitors to control respectively the reflection and transmission regions, which is different from the conventional structure using only one pixel capacitor and maintenance capacitor to control the reflection and transmission regions. Therefore, the electric charge leakage ratio in a constant time of the present invention structure is lower than the conventional structure. In other words, because each maintenance capacitor only needs to maintain the voltage applied the pixel capacitor in the reflection or transmission region, the capacitor value does not require enlargement. Therefore, the charge current can be decreased when a refresh process is operated.  
         [0034]    As is understood by a person skilled in the art, the foregoing preferred embodiments of the present invention are illustrative of the present invention rather than limiting of the present invention. They are intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims, the scope of which should be accorded the broadest interpretation so as to encompass all such modifications and similar structure.

Technology Classification (CPC): 6