Abstract:
A pixel driving circuit array is disclosed, comprising a first capacitor and a second capacitor. The first capacitor comprises a first electrode, an insulator layer and a common electrode. The second capacitor comprises a second electrode, the insulator layer and the common electrode. The first capacitor and the second capacitor share the same common electrode. The first electrode and the second electrode are on the same plane.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to a pixel driving circuit array, and in particular relates to a plurality of capacitors sharing one pixel driving circuit array. 
         [0003]    2. Description of the Related Art 
         [0004]    Organic light emitting diode (OLED) displays that use organic compounds as a lighting material for illumination are flat displays. The advantages of the OLED displays are that they have smaller sizes, lighter weights, wider viewing angles, higher contrast ratios and faster speeds. 
         [0005]    Recently, higher display resolution has been one technological area, which has seen developmental improvement. Specifically, given a fixed display panel size, a display panel requires a greater amount of pixels for higher resolutions. Thus, continued miniaturization of a pixel circuits is required for higher resolution applications. Namely, it has become more of a priority to develop a system for reduced sized pixel circuits. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    A detailed description is given in the following embodiments with reference to the accompanying drawings. 
         [0007]    An embodiment of a pixel driving circuit array is provided. The pixel driving circuit array comprises a plurality of pixel driving circuits. Each pixel driving circuit comprises a first capacitor and a second capacitor. The first capacitor comprises a first electrode and a common electrode. The second capacitor comprises a second electrode and the common electrode. The common electrode extends along a horizontal direction. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
           [0009]      FIG. 1  shows 2T1C pixel driving circuits according to an embodiment of the invention; and 
           [0010]      FIG. 2  shows a conventional cross diagram of two capacitors on a substrate; 
           [0011]      FIG. 3  shows a cross diagram of two capacitors on a substrate according to an embodiment of the invention; 
           [0012]      FIG. 4  shows a layout diagram of a Poly-Si layer of the pixel driving circuit, wherein the poly-Si layer is a first layer on the substrate; 
           [0013]      FIG. 5  shows a layout diagram of a first metal layer (Metal — 1 layer) of the pixel driving circuit; 
           [0014]      FIG. 6  shows a layout diagram of a second metal layer (Metal — 2 layer) of the pixel driving circuit; 
           [0015]      FIG. 7  shows a layout diagram of a Poly-Si layer of the pixel driving circuit according to an embodiment of the invention; 
           [0016]      FIG. 8  shows a layout diagram of a first metal layer (Metal — 1 layer) of the pixel driving circuit according to an embodiment of the invention; 
           [0017]      FIG. 9  shows a layout diagram of a second metal layer (Metal — 2 layer) of the pixel driving circuit according to an embodiment of the invention; 
           [0018]      FIG. 10  schematically shows another embodiment of a system for displaying images according to the invention; 
           [0019]      FIG. 11  shows a completed layout diagram of the pixel driving circuit; and 
           [0020]      FIG. 12  shows a completed layout diagram of the pixel driving circuit according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
         [0022]      FIG. 1  shows 2T1C pixel driving circuits  10  and  20  according to an embodiment of the invention. Each 2T1C pixel driving circuit has two thin film transistors and one capacitor. The pixel driving circuits  10  and  20  can be one part of a pixel driving circuit array  100 . The pixel driving circuit  10  comprises transistors TFT 1  and TFT 2 , light emitting unit OLED 1 , and capacitor C 1 . The pixel driving circuit  20  comprises transistors TFT 3  and TFT 4 , light emitting unit OLED 2 , and capacitor C 2 . When a scanning signal SCAN_X turns on the transistors TFT 1  and TFT 3 , data signals DATA_Y and DATA_Y+1 are respectively loaded to the gates of the transistors TFT 2  and TFT 4  and stored into the capacitors C 1  and C 2 . The transistors TFT 2  and TFT 4  are turned on according to the data signals DATA_Y and DATA_Y+1. The current will flow from the voltage source PVdd through the transistors TFT 2  and TFT 4  and light emitting units OLED 1  to the voltage source Vdd. When the current flows through the light emitting units OLED 1  and OLED 2 , light is emitted, and vice versa. 
         [0023]      FIG. 2  shows a conventional cross diagram of two capacitors on a substrate. The capacitors  210  and  220  are respectively corresponding to the capacitors C 1  and C 2  of  FIG. 1 . The capacitor  210  comprises an upper electrode  211 , an insulator  230  and a lower electrode  213  and the capacitor  220  comprises an upper electrode  221 , an insulator  230  and a lower electrode  223 . The capacitors  210  and  220  are disposed on the substrate  250 . The substrate  250  can be a glass substrate. Based on the layout rule limit, the upper electrode is usually smaller than the lower electrode. Thus, the upper electrode  211  is smaller than the lower electrode  213  and the upper electrode  221  is smaller than the lower electrode  223 . As shown in  FIG. 2 , there is a minimum length d 1  between one side of the upper electrode  211  and that of the lower electrode  213  in a projection direction according to the layout rule. Similarly, the minimum length d 1  exists between one side of the upper electrode  221  and that of the lower electrode  223  in the projection direction according to the layout rule. In addition, there is a minimum length d 2  between the lower electrodes  213  and  223  according to the layout rule. Thus, the minimum distance between the upper electrode  211  of the capacitor  210  and the upper electrode  221  of the capacitor  220  is (2*d 1 )+d 2 . 
         [0024]      FIG. 3  shows a cross diagram of two capacitors on a substrate according to an embodiment of the invention. The capacitors  310  and  320  are respectively corresponding to capacitors C 1  and C 2  of  FIG. 1 . The capacitor  310  comprises an upper electrode  311 , an insulator  330  and a lower electrode  323  and the capacitor  320  comprises an upper electrode  321 , the insulator  330  and the lower electrode  323 . The capacitors  310  and  320  are disposed on the substrate  350 . As shown in  FIG. 3 , capacitors  310  and  320  share the lower electrode  323  (common electrode) so the minimum distance between the upper electrodes  311  and  321  is d 2 . Thus, the minimum distance between the capacitors  310  and  320  of  FIG. 3  is less than that between the capacitors  210  and  220  of  FIG. 2  by 2*d 1 . Referring to  FIG. 3  with  FIG. 1 , the lower electrode  323  is coupled to the voltage source PVdd which is a fixed voltage. The upper electrode  311  is coupled to the transistor TFT 1  to receive the data signal DATA_Y and the upper electrode  321  is coupled to the transistor TFT 3  to receive the data signal DATA_Y+1. Note that while two capacitors share one lower electrode, it is not limited thereto. Three capacitors can also share one lower electrode. 
         [0025]    When the storage size of the capacitors C 1  and C 2  of the pixel driving circuits  10  and  20  are fixed (the overlap area of the upper electrode and the lower electrode are fixed), the sum of the area of the capacitors  310  and  320  of  FIG. 3  is less than the sum of the area of the capacitors  210  and  220  of  FIG. 2 . Using the above layout method, the advantages are as follows: (1) the size of the pixel driving circuit is reduced, (2) the display panel achieves higher resolution, (3) the aperture ration is increased for bottom emission, and (4) more pixels are disposed in a fixed display area. In addition, by decreasing the size of the pixel driving circuits, the total display area for the light emitting unit OLED 1  and OLED 2  can be increased for brightness. 
         [0026]      FIG. 4  shows a layout diagram of a Poly-Si layer of the pixel driving circuit. The poly-Si layer is a first layer on the substrate. Referring to  FIG. 1 , the lower electrode  402  of the capacitor C 1  and the lower electrode  404  of the capacitor C 2  are separated. The areas  406  and  408  are respectively a source area and a drain area of the transistor TFT 1 . The areas  416  and  420  are respectively a source area and a drain area of the transistor TFT 2 . The areas  410  and  412  are respectively a source area and a drain area of the transistor TFT 3 . The areas  414  and  418  are respectively a source area and a drain area of the transistor TFT 4 . 
         [0027]      FIG. 5  shows a layout diagram of a first metal layer (Metal — 1 layer) of pixel driving circuit. The first metal layer is a second layer on the substrate. The upper electrode  502  of the capacitor C 1  and the upper electrode  504  of the capacitor C 2  are separated. The areas  506  and  508  are respectively gate areas of the transistors TFT 1  and TFT 3 . The areas  510  and  512  are respectively gate areas of the transistors TFT 2  and TFT 4 . As shown in  FIG. 5 , the gate of the transistor TFT 2  is coupled to the upper electrode  502  of the capacitor C 1 , and the gate of the transistor TFT 4  is coupled to the upper electrode  504  of the capacitor C 2 . The area  514  is an electrical contact area of the transistor TFT 1  and the capacitor C 1 . The area  516  is an electrical contact area of the transistor TFT 3  and the capacitor C 2 . A scanning line SCAN_X_L is electrically coupled to the gate area  506  of the transistor TFT 1  and the gate area  508  of the transistor TFT 3 . 
         [0028]      FIG. 6  shows a layout diagram of a second metal layer (Metal — 2 layer) of the pixel driving circuit. The second metal layer is a third layer on the substrate. A data line DATA_Y_L is electrically coupled to the source area  406  of the transistor TFT 1  through a metal area  614 . A data line DATA_Y+1_L is electrically coupled to the source area  410  of the transistor TFT 3  through a metal area  616 . The voltage line PVdd_L is coupled to the source area  416  of the transistor TFT 2  and the source area  414  of the transistor TFT 4  respectively through metal areas  618  and  620 . The metal areas  602  and  604  are respectively electrically coupled to the drain areas  408  and  412 . The metal areas  606  and  608  are respectively electrically coupled to the areas  514  and  516 . Thus, the drain of the transistors TFT 1  is electrically coupled to the upper electrode  502  of the capacitor C 1 , and the drain of the transistor TFT 3  is electrically coupled to the upper electrode  504  of the capacitor C 2 . The metal areas  610  and  612  are respectively electrically coupled to the drain area  418  of the transistors TFT 2  and the drain area  420  of the transistors TFT 4 . 
         [0029]      FIG. 7  shows a layout diagram of a Poly-Si layer of the pixel driving circuit according to an embodiment of the invention. The poly-Si layer is a first layer on the substrate. The lower electrodes  702  and  704  of the capacitor C 1  are connected. Thus, the lower electrodes  702  and  704  comprise a common electrode of the capacitors C 1  and C 2 . The areas  706  and  708  are respectively a source area and a drain area of the transistor TFT 1 . The areas  716  and  718  are respectively a source area and a drain area of the transistor TFT 2 . The areas  710  and  712  are respectively a source area and a drain area of the transistor TFT 3 . The areas  716  and  720  are respectively a source area and a drain area of the transistor TFT 4 . 
         [0030]      FIG. 8  shows a layout diagram of a first metal layer (Metal_ 1  layer) of the pixel driving circuit according to an embodiment of the invention. The first metal layer is the second layer on the substrate. The upper electrode  802  of the capacitor C 1  and the upper electrode  804  of the capacitor C 2  are separated. The areas  806  and  808  are respectively gate areas of the transistors TFT 1  and TFT 3 . The areas  810  and  812  are respectively gate areas of the transistors TFT 2  and TFT 4 . As shown in  FIG. 8 , the gate area  810  of the transistor TFT 2  is coupled to the upper electrode  802  of the capacitor C 1  and the gate area  812  of the transistor TFT 4  is coupled to the upper electrode  804  of the capacitor C 2 . The area  814  is an electrical contact area of the transistor TFT 1  and the capacitor C 1 . The area  816  is an electrical contact area of the transistor TFT 3  and the capacitor C 2 . A scanning line SCAN_X_L is electrically coupled to the gate area  806  of the transistor TFT 1  and the gate area  808  of the transistor TFT 3 . 
         [0031]      FIG. 9  shows a layout diagram of a second metal layer (Metal — 2 layer) of the pixel driving circuit according to an embodiment of the invention. The second metal layer is the third layer on the substrate. A data line DATA_Y_L is electrically coupled to the source area  706  of the transistor TFT 1  through a metal area  914 . A data line DATA_Y+1_L is electrically coupled to the source area  710  of the transistor TFT 3  through a metal area  916 . The voltage line PVdd_L are respectively coupled to the source area  716  of the transistor TFT 2  and the source area  716  of the transistor TFT 4  through metal areas  918 . The capacitor  310  of the pixel driving circuit  10  and the capacitor  320  of the pixel driving circuit  20  share one voltage line PVdd_L to couple to the lower electrodes  702  and  704 . The metal areas  902  and  904  are respectively electrically coupled to the drain areas  708  and  712  and the metal areas  906  and  908  are respectively electrically coupled to the areas  814  and  816 . Thus, the drain of the transistors TFT 1  is electrically coupled to the upper electrode  802  of the capacitor C 1  and the drain of the transistor TFT 3  is electrically coupled to the upper electrode  804  of the capacitor C 2 . The metal areas  910  and  912  are respectively electrically coupled to the drain area  718  of the transistors TFT 2  and the drain area  720  of the transistors TFT 4 . 
         [0032]    According to the above layout method, the first pixel driving circuit  10  and the second pixel driving circuit  20  are symmetrical in layout. The plurality of capacitors of the pixel driving circuits can share one electrode to reduce layout size. Following are four advantages of the layout method. The first advantage is that display resolution can be increased. The second advantage is that the aperture ration can be increased. The third advantage is that the capacitor can be enlarged given a fixed layout size. And the last advantage is that the original manufacturing process can be utilized. 
         [0033]      FIG. 10  schematically shows another embodiment of a system for displaying images according to the invention that, in this case, is implemented as a display panel  1400  or an electronic device  1600 . As shown in  FIG. 10 , the display panel  1400  comprises the pixel driving circuit  100  of  FIG. 1 . The display panel  1400  can be a part of a variety of electronic devices (in this case, the electronic device  1600 ). Generally, the electronic device  1600  can comprise the display panel  1400  and a power supply  1500 . Further, the power supply  1500  can be operatively coupled to the display panel  1400  and provide power to the display panel  1400 . The electronic device  1600  can be a mobile phone, a digital camera, a PDA (personal data assistant), a notebook computer, a desktop computer, a television, or a portable DVD player, for example. 
         [0034]      FIG. 11  shows the completed layout diagram of a pixel driving circuit.  FIG. 1I  is an overlap layout diagram of the Poly-Si layer of  FIG. 4 , the first metal layer of  FIG. 5  and the second metal layer of  FIG. 6 . 
         [0035]      FIG. 12  shows the completed layout diagram of the pixel driving circuit according to an embodiment of the invention.  FIG. 12  is also an overlap layout diagram of the Poly-Si layer of  FIG. 7 , the first metal layer of  FIG. 8  and the second metal layer of  FIG. 9 . 
         [0036]    While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited to thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.