Patent Publication Number: US-9842524-B2

Title: Display device

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims the benefit of priority to Chinese Patent Application No. 201410165640.8, filed with the Chinese Patent Office on Apr. 23, 2014 and entitled “DISPLAY DEVICE”, the content of which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The present invention relates to the field of display, and in particularly to a display device. 
     BACKGROUND OF THE INVENTION 
     Recently, Liquid Crystal Display (LCD) products develop very rapidly, and more and more liquid crystal displays with high quality gradually list in the market and are applied in wider fields. 
     The principle for displaying images by a liquid crystal display is that: liquid crystal are deflected by a certain angle to pass light through when a voltage is applied across two plates sandwiching the liquid crystals, and the light transmissivity of the liquid crystal depends on the size of the deflected angle of the liquid crystal, thus different gray scales are displayed. 
     However, the electrical potential at a common electrode is fixed during the displaying period of the liquid crystal display, and the layer of the liquid crystal is equivalent to a capacitor. When a Driver Integrated Circuit (Driver IC) is illuminated by light and then a photovoltaic effect is caused in the Driver IC, carriers such as electrons generated by the photovoltaic effect enter into a data line and change electrical charges in the data line, and hence electrical charges at a pixel electrode and the common electrode are changed, at this time, a voltage across the pixel electrode and the common electrode is changed, so that a second voltage generated by the photovoltaic effect is formed across the pixel electrode and the common electrode to form an electrical field, the electrical field is caused by residual ions and thus also referred to as a residual electrical field. When the LCD emits light again, the original symmetrical voltage applied across the pixel electrode and the common electrode is applied in combination with such residual electrical field in the LCD, resulting in an asymmetrical voltage applied in the LCD, and the asymmetrical voltage will lead to flicker of the LCD. For now, the photovoltaic effect may be prevented by a shading tape (or a black tape); but after attaching of cover lens onto a capacitance touch screen becomes popular, the shading tape is abandoned, instead, an opaque area is designed on the cover lens of the capacitance touch screen to shield light. However, in producing and manufacturing the LCD, the opaque area on the cover lens cannot shield light very well, thus the photovoltaic effect still exists and causes a negative effect to the display quality. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view showing a structure of a display device in the related art; 
         FIG. 2  is a schematic view showing an effect of a residual direct current (DC) voltage due to the presence of the photovoltaic effect in the display device in the related art; 
         FIG. 3  is a schematic view showing a circuit in a display device according to an embodiment of the present invention; 
         FIG. 4  is a schematic view showing a circuit in a display device according to another embodiment of the present invention; 
         FIG. 5  is a schematic view showing a circuit in a display device according to still another embodiment of the present invention; and 
         FIG. 6  is a schematic view showing a circuit in a display device according to a yet still another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will be further described in detail in combination with accompanied drawings and embodiments. It is understood that embodiments described herein are merely used to explain the present invention but not to limit the present invention. It is additionally noted that only a part of not all of the structures relevant to the present invention is illustrated in the drawings. 
     A display device disclosed by embodiments of the present invention includes an LCD device, an Organic Light Emitting Diode (OLED) display device, etc., and description here is made with a liquid crystal display device as an example. The liquid crystal display device includes a liquid crystal display panel and a flexible printed circuit board bounded with the liquid crystal display panel, wherein the liquid crystal display panel includes a Thin Film Transistor (TFT) array substrate and a color filter substrate disposed opposite to the TFT array substrate and liquid crystal encapsulated between the TFT array substrate and the color filter substrate. The TFT array substrate includes a plurality of data lines and a plurality of gate lines perpendicular to and electrically insulated from the data lines, both of data lines and the gate lines are configured to control TFT switches of all sub-pixels in combination with control signals, where a source of the TFT switch is connected to the data line, a gate of the TFT switch is connected to the gate line, and a drain of the TFT switch is connected to a pixel electrode in the TFT array substrate; additionally, the TFT array substrate also includes a common electrode (the common electrode may be located in a different position depending on the different type of the display panel, for example, the common electrode is disposed at the side of the color filter substrate in a Twisted Nematic display panel, and is disposed at the side of the TFT array substrate in an In-Plane Switching display panel or a Fringe Field Switching display panel), and a driver integrated circuit configured to provide a data signal to each one of the sub-pixels of the TFT array substrate. 
       FIG. 1  is a schematic view showing a structure of a display device in the related art. As illustrated in  FIG. 1 , when a driver integrated circuit  15  is illuminated by light, carries such as electrons generated in the driver integrated circuit  15  by the photovoltaic effect enter into a data line  11  and change electrical charges in the data line  11 ; further, if a TFT switch  12  is controlled to be turned on, electrical charges at a pixel electrode  14  and a common electrode  13  are changed, leading to the change of a voltage across the pixel electrode  14  and the common electrode  13 , so that a second voltage generated by the photovoltaic effect is formed across the pixel electrode  14  and the common electrode  13 . The liquid crystal actually contains various electrical charges, the electrical charges are directionally moved under the effect of the second voltage, thus residual charges are attached finally at the side of the pixel electrode  14  and the side of the common electrode  13  over time, respectively, and the residual charges attached at the side of the pixel electrode  14  and those attached at the common electrode  13  are electrically inversed. Therefore, an electrical field is formed between the pixel electrode  14  and the common electrode  13 , and this electrical field, which is formed by the residual charges, is also referred to as a residual electrical field.  FIG. 2  is a schematic view showing an effect of the residual DC voltage of the residual electrical field caused by the photovoltaic effect of the display device in the related art. As illustrated in  FIG. 2 , when the LCD emits light again, the original voltage of 5V or −5V (which is an example, not necessarily the real value of the second voltage) to be applied to the pixel electrode and the common electrode is applied in the LCD in combination with the residual voltage of the residual electrical field, for example, if the residual DC voltage is 0.2V, the resultant positive voltage of 5.2V and the resultant negative voltage of −4.8V, such asymmetric voltages will cause the flicker of the LCD. 
       FIG. 3  is a schematic view showing a circuit in a display device according to an embodiment of the present invention, and the display device further includes a display panel including: a first display test signal inputting part  26 , a first display test signal controlling part  25 , a second display test signal inputting part  27 , a first test bus  28 , and a second test bus  29 . 
     The first display test signal inputting part  26  is configured to input a first display test signal. 
     In the present embodiment, the first display test signal inputting part  26  can be a pixel test bonding pad  26  configured to input a sub-pixel test signal. 
     The first display test signal controlling part  25  is configured to control the input of the first display test signal. 
     In the present embodiment, the first display test signal inputting part  26  is controlled by the first display test signal controlling part  25 . The first display test signal controlling part  25  may be an N-channel metal oxide semiconductor (NMOS) transistor, which may be controlled to be turned on or off such that different first display test signals respectively corresponding to sub-pixels of different colors may be inputted by the first display test signal inputting part  26 . Here, the first display test signal controlling part  25  is configured to switch among the first display test signals S 1  corresponding to the sub-pixels of different colors. The first display test signals S 1  contain a group of signals which are connected together via NMOS transistors for the purpose of testing. For example, as per colors of the sub-pixels, one test bonding pad is provided for each of red (R), green (G) and blue (B) sub-pixels, and all of the first display test signals S 1  may be controlled by controlling the signals received by the gates of the NMOS transistors, without adding many signal lines. 
     The second display test signal inputting part  27  is configured to input a second display test signal S 2 . 
     In the present embodiment, the second display test signal inputting part  27  (such as a common electrode test bonding pad  27  illustrated in  FIG. 3 ) is connected to a common electrode  22  of the display panel and configured to input a common electrode test signal. 
     The first test bus  28  is connected to the first display test signal inputting part  26 . 
     The second test bus  29  is connected to the second display test signal inputting part  27 . 
     The first test bus  28  and the second test bus  29  both included in the display panel are connected with each other by a short-circuit connection  30 . 
     In the present embodiment, the first display test signal inputting part  26  is connected to the second display test signal inputting part  27  by a short-circuit connection  30  in the display panel via the first test bus  28  and the second test bus  29 . As illustrated in  FIG. 3 , the pixel test bonding pad  26  is connected to the common electrode test bonding pad  27  by a short-circuit connection  30  in the display panel. 
     It is noted that, as illustrated in  FIG. 3 , the first display test signal controlling part  25  and the first display test signal inputting part  26  are connected to the common electrode  22  via an electrostatic protection circuit  24 , for an electrostatic protection effect on the first display test signal controlling part  25  and the first display test signal inputting part  26 . 
     As illustrated in  FIG. 3 , when a driver integrated circuit  23  is illuminated by light so that the photovoltaic effect is caused and hence a DC voltage is produced across the common electrode  22  and a data line  21 , the DC voltage is directly applied to a pixel and thus generates photovoltaic current due to weak ON status of the amorphous-silicon thin-film transistor (A-Si TFT) (i.e. the TFT switch  12  as shown in  FIG. 1 ). However, electrical charges generated by the photovoltaic effect may be conducted to a grounding terminal (GND) (e.g. the common electrode  22 ) through the connection between the pixel test bonding pad and the common electrode test bonding pad, due to weak ON status of the first display test signal controlling part  25  (such as an NMOS transistor). 
     In the present embodiment, the first display test signal inputting part  26  and the second display test signal inputting part  27  are connected with each other to release the photovoltaic current, so that the influence caused on the display effect by the residual direct current generated by the photovoltaic effect of the driver integrated circuit or the amorphous-silicon thin-film transistor is reduced. 
     In the present embodiment, there may be a plurality of the first display test signal inputting parts  26 , the number of which corresponds to the number of base colors of the display device; further, there may be a plurality of the first test buses  28 , including test buses for sub-pixels of the respective base colors, and the plurality of the first display test signal inputting parts are respectively connected to the test buses for sub-pixels of the respective base colors. 
     In the present embodiment, the base colors of the display device included (R), green (G) and blue (B) colors. Most colors can be formed by a red color, a green color and a blue color synthesized in various proportions. These three base colors are independent of each other, and any one of the base colors cannot be formed by other two base colors. Therefore, the plurality of the first display test signal inputting parts  26  may include three test signal inputting parts respectively for these three different colors, likewise, the plurality of the first test buses  28  may include three test buses respectively for pixels of these three different colors, and each one of the three test signal inputting parts from the plurality of the first display test signal inputting parts  26  is connected to one of the test buses for a pixel (which is of the same color as the one of the three test signal inputting parts) from the first test buses  28 . 
     In the present embodiment, the plurality of the first display test signal inputting parts  26  may include a red sub-pixel test signal inputting part, a green sub-pixel test signal inputting part and a blue sub-pixel test signal inputting part, the plurality of the first test buses  28  may include a red sub-pixel signal test bus, a green sub-pixel signal test bus and a blue sub-pixel signal test bus, which are respectively connected to the red sub-pixel test signal inputting part, the green sub-pixel test signal inputting part and the blue sub-pixel test signal inputting part. 
     In the present embodiment, the second display test signal inputting part  27  may include a common electrode test signal inputting part. 
     In the present embodiment, the first display test signal controlling part  25  can be an NMOS transistor, a source of which is connected to the first display test signal inputting part  26 , and a gate of which is configured to receive a first control signal to turn on or off the NMOS transistor; and the first display test signal inputting part  26  is connected to the common electrode test signal inputting part. When the display device is in displaying, the first control signal is at a low level, such that the NMOS transistor is turned off; and when the display device stops displaying, the first control signal is at a high level, such that the NMOS transistor is turned on. 
     In the present embodiment, the NOMS transistor (as illustrated in  FIG. 3 ) is used as a switch to control the input of the first display test signal. The source of the NMOS transistor is connected to the pixel test bonding pad, the drain of the NMOS transistor is connected to the data line  21 , and the gate of the NMOS transistor is configured to receive the first control signal, so that the influence caused on the display device in an inactive state by the photovoltaic effect is reduced. When the display device is in displaying, a negative voltage is applied to the gate of the NMOS transistor to turn off the NMOS transistor, i.e. the source of the NMOS transistor is disconnected from the drain of the NMOS transistor. At this time, the data line  21  can still be normally driven without impact from the NMOS transistor. When the display device stops displaying, a potential at the gate of the NMOS transistor is maintained to be zero, and the NMOS transistor is still turned on when the voltage VGS across the gate and the source of the NMOS transistor is 0, such that electrical charges generated by the photovoltaic effected may be conducted to the GND terminal via the path of the NMOS transistor. 
       FIG. 4  is a schematic view showing a circuit of a display device according to another embodiment of the present invention, and the display device includes: a first display test signal inputting part  36 , a first display test signal controlling part  35 , a second display test signal inputting part  37 , a first test bus  38 , and a second test bus  39 . 
     The first display test signal inputting part  36  is configured to input a first display test signal. 
     In the present embodiment, the first display test signal inputting part  36  may be a pixel test bonding pad which is configured to input a sub-pixel test signal. 
     The first display test signal controlling part  35  is configured to control the input of the first display test signals. 
     In the present embodiment, the first display test signal inputting part  36  is controlled by the first display test signal controlling part  35 , the first display test signal controlling part  35  can be an NMOS transistor. By controlling the NMOS transistor to be turned on or off, different first display test signals are input by the first display test signal inputting part  36 . 
     The second display test signal inputting part  37  is configured to input a second display test signal. 
     In the present embodiment, the second display test signal inputting part  37  (such as a common electrode test bonding pad illustrated in  FIG. 4 ) is connected to a common electrode  32  of the display panel and configured to input a common electrode test signal. 
     The first test bus  38  is connected to the first display test signal inputting part. 
     The second test bus  39  is connected to the second display test signal inputting part. 
     The display device further includes a flexible printed circuit board  310 , the flexible printed circuit board  310  includes the first test bus  38  and the second test bus  39  connected with each other by a short-circuit connection. In the present embodiment, the first display test signal inputting part  36  (such as a pixel test bonding pad as illustrated in  FIG. 4 ) and the second display test signal inputting part  37  (such as the common electrode test bonding pad as illustrated in  FIG. 4 ) are connected to the flexible printed circuit board  310  in the display device, and are connected with each other by a short-circuit connection via a conductive line on the flexible printed circuit board  310 . 
     It is noted that, as illustrated in  FIG. 4 , the first display test signal controlling part  35  and the first display test signal inputting part  36  are connected to the common electrode  32  via an electrostatic protection circuit  34 , to achieve an electrostatic protection effect on the first display test signal controlling part  35  and the first display test signal inputting part  36 . 
     In the present embodiment, there may be a plurality of the first display test signal inputting parts  36 , the number of the first display test signal inputting parts  36  corresponds to the number of base colors of the display device; there may be a plurality of the first test buses  38 , including test buses for sub-pixels of the respective base colors, and the plurality of the first display test signal inputting parts are respectively connected to the test buses for sub-pixels of the respective base colors. 
     In the present embodiment, the plurality of the first display test signal inputting parts  36  may include a red sub-pixel test signal inputting part, a green sub-pixel test signal inputting part and a blue sub-pixel test signal inputting part, and the plurality of the first test buses  38  may include a red sub-pixel signal test bus, a green sub-pixel signal test bus and a blue sub-pixel signal test bus, which are respectively connected to the red sub-pixel test signal inputting part, the green sub-pixel test signal inputting part and the blue sub-pixel test signal inputting part. 
     In the present embodiment, the second display test signal inputting part  37  may include a common electrode test signal inputting part. 
     In the present embodiment, the first display test signal controlling part  35  can be an NMOS transistor, a source of which is connected to the first display test signal inputting part  36 , and a gate of which is configured to receive a first control signal to turn on or off the NMOS transistor; and the first display test signal inputting part  36  is connected to the common electrode test signal inputting part. When the display device is in displaying, the first control signal is at a low level, such that the NMOS transistor is turned off; and when the display device stops displaying, the first control signal is at a high level, such that the NMOS transistor is turned on. 
     As illustrated in  FIG. 4 , when a driver integrated circuit  33  is illuminated by light so that the photovoltaic effect is caused and hence a DC voltage is produced across the common electrode  32  and a data line  31 , the DC voltage is directly applied to a pixel and thus generates photovoltaic current due to weak ON status of the amorphous-silicon thin-film transistor. However, the first display test signal inputting part  36  and the second display test signal inputting part  37  are connected to the flexible printed circuit board  310  and connected with each other by a short-circuit connection, and the NMOS transistor becomes weak ON status in the inactive state of the display device, so that the electrical charges generated by the photovoltaic effect are guided to the GND terminal via the path through the first display test signal inputting part  36  and the second display test signal inputting part  37 , thus reducing the influence caused on the display effect by the residual direct current generated by the photovoltaic effect of the driver integrated circuit  33  or the amorphous-silicon thin-film transistor. 
     In an optional embodiment, as illustrated in  FIG. 4 , there may be a plurality of the pixel test bonding pads, including a red sub-pixel test bonding pad, a green sub-pixel test bonding pad and a blue sub-pixel test bonding pad. The red sub-pixel test bonding pad, the green sub-pixel test bonding pad and the blue sub-pixel test bonding pad are individually connected to the flexible printed circuit board  310  and connected with the common electrode test bonding pad by short-circuit connections on the flexible printed circuit board  310 , such that the NMOS transistor becomes weak ON status in the inactive state of the display device, and the electrical charges generated by the photovoltaic effect may be guided to the GND terminal via the path through the pixel test bonding pads and the short connections, thus reducing the influence caused on the display effect by the residual direct current generated by the photovoltaic effect of a driver integrated circuit  33  or the amorphous-silicon thin-film transistor. 
     In the present embodiment, the first display test signal inputting part and the second display test signal inputting part are connected to the flexible printed circuit board and connected with each other by short-circuit connections, and the NMOS transistor becomes weak ON status in the inactive state of the display device, so that the electrical charges generated by photovoltaic effect may be inducted to the GND via the path through the first display test signal inputting part and the second display test signal inputting part, thus the influence caused on the display effect by the residual direct current generated by the photovoltaic effect of the driver integrated circuit  33  or the amorphous-silicon thin-film transistor is reduced. 
       FIG. 5  is a schematic view showing a circuit in a display device according to another embodiment of the present invention, and the display device includes a display panel including a first display test signal inputting part  46 , a first display test signal controlling part  45 , a second display test signal inputting part  37 , a first test bus  48 , and a second test bus  49 . 
     The first display test signal inputting part  46  is configured to input a first display test signal. 
     In the present embodiment, the first display test signal inputting part  36  may be a pixel test bonding pad which is configured to input a sub-pixel test signal. 
     The first display test signal controlling part  45  is configured to control the input of the first display test signal. 
     In the present embodiment, the first display test signal inputting part  46  is controlled by the first display test signal controlling part  45 , the first display test signal controlling part  45  can be an NMOS transistor. The NMOS transistor may be controlled to be turned on or off such that different first display test signals are input by the first display test signal inputting part  46 . 
     The second display test signal inputting part  37  is configured to input a second display test signal. 
     In the present embodiment, the second display test signal inputting part  47  (such as a common electrode test bonding pad illustrated in  FIG. 5 ) is connected to a common electrode  42  of the display panel and configured to input a common electrode test signal. 
     The first test bus  48  is connected to the first display test signal inputting part. 
     The second test bus  49  is connected to the second display test signal inputting part. 
     The first test bus  48  and the second test bus  49  both included in the display panel are connected with each other via a depletion MOS transistor  410  or a resistor. 
     It is noted that, as illustrated in  FIG. 5 , the first display test signal controlling part  45  and the first display test signal inputting part  46  are connected to a common electrode  42  via an electrostatic protection circuit  44 , to achieve an electrostatic protection effect on the first display test signal controlling part  45  and the first display test signal inputting part  46 . 
     In the present embodiment, the first display test signal inputting part  46  (such as a pixel test bonding pad illustrated in  FIG. 5 ) is connected to the second display test signal inputting part  47  (such as a common electrode bonding pad illustrated in  FIG. 5 ) via the depletion NMOS transistor  410  or the resistor. 
     In the present embodiment, there may be a plurality of the first display test signal inputting parts  46 , the number of the first display test signal inputting parts  46  corresponds to the number of the base colors of the display device; there may be a plurality of the first test buses  48 , including test buses for sub-pixels of the respective base colors, and the plurality of the first display test signal inputting parts are respectively connected to the test buses for sub-pixels of the respective base colors. 
     In the present embodiment, the plurality of the first display test signal inputting parts  46  may include a red sub-pixel test signal inputting part, a green sub-pixel test signal inputting part and a blue sub-pixel test signal inputting part, and the plurality of the first test buses  48  may include a red sub-pixel signal test bus, a green sub-pixel signal test bus and a blue sub-pixel signal test bus, which are respectively connected to the red sub-pixel test signal inputting part, the green sub-pixel test signal inputting part and the blue sub-pixel test signal inputting part. 
     In the present embodiment, the second display test signal inputting part  47  may include a common electrode test signal inputting part. 
     In the present embodiment, the first display test signal controlling part  45  can be an NMOS transistor, a source of which is connected to the first display test signal inputting part  46 , and a gate of which is configured to receive the first control signal to turn on or off the NMOS transistor; and the first display test signal inputting part  46  is connected to the common electrode test signal inputting part. When the display device is in displaying, the first control signal is at a low level, such that the NMOS transistor is turned off; and when the display device stops displaying, the first control signal is at a high level, such that the NMOS transistor is turned on. 
     As illustrated in  FIG. 5 , when a driver integrated circuit  43  is illuminated by light so that the photovoltaic effect is caused and hence a DC voltage is produced across the common electrode  42  and a data line  41 , the DC voltage is directly applied to a pixel and thus generates photovoltaic current due to weak ON status of the amorphous-silicon thin-film transistors. However, the first display test signal inputting part  46  and the second display test signal inputting part  47  are connected with each other via a depletion MOS transistor in the display panel, and the NMOS transistor and the depletion MOS transistor  410  become weak ON status in the inactive state of the display device, so that the electrical charges generated by the photovoltaic effect are inducted to the GND via the path through the first display test signal inputting part  46  and the second display test signal inputting part  47 , thus the influence caused on the display effect by the residual direct current generated by the photovoltaic effect of the driver integrated circuit  43  or the amorphous-silicon thin-film transistor is reduced. 
     In the present embodiment, the first test bus  48  is connected to a first terminal of the depletion MOS transistor  410 , the second test bus  49  is connected to a second terminal of the depletion MOS transistor  410 , and a gate of the depletion MOS transistor  410  is configured to receive a second control signal to control the depletion MOS transistor  410  to be turned on or off. 
     In the present embodiment, when the display device is in displaying, the second control signal is at a low level, such that the depletion MOS transistor  410  is turned off; and when the display device stops displaying, the second control signal is at a high level, such that the depletion MOS transistor  410  is turned on. 
     In the present embodiment, the first terminal of the depletion MOS transistor  410  is a source, and the second terminal of the depletion MOS transistor  410  is a drain; alternatively, the first terminal of the depletion MOS transistor  410  is a drain, and the second terminal of the depletion MOS transistor  410  is a source. 
     In an optional embodiment, there are a plurality of the pixel test bonding pads, including a red sub-pixel test bonding pad, a green sub-pixel test bonding pad and a blue sub-pixel test bonding pad, each of the pixel test bonding pads is connected to the common electrode test bonding pad via the depletion MOS transistor  410 . The source and drain of the depletion MOS transistor  410  are respectively connected to the pixel test bonding pad and the common electrode test bonding pad, and the gate of the depletion MOS transistor  410  is configured to receive the second control signal so that the depletion MOS transistor  410  is turned on in the inactive state of the display device, i.e., in the inactive state of the display device, the gate of the depletion MOS transistor  410  receives a high level, and the gate of the NMOS transistor receives a high level signal to turn on the NMOS transistor, such that the electrical charges generated by the photovoltaic effect are conducted to the GND terminal via the path through the pixel test bonding pad and the common electrode test bonding pad. 
     In the present embodiment, the first display test signal inputting part and the second display test signal inputting part are connected with each other in the display panel via the depletion MOS transistor, and the NMOS transistor and the depletion MOS transistor become weak ON status in the inactive state of the display device, so that the electrical charges generated by the photovoltaic effect are guided to the GND terminal via such path through the first display test signal inputting part and the second display test signal inputting part, thus the influence caused on the display quality by the residual direct current generated by the photovoltaic effect of a driver integrated circuit or anamorphous-silicon thin-film transistor is reduced. 
       FIG. 6  is a schematic view showing a circuit in a display device according to a still another embodiment of the present invention, and the display device includes: a first display test signal inputting part  56 , a first display test signal controlling part  55 , a second display test signal inputting part  57 , a first test bus  58 , and a second test bus  59 . 
     The first display test signal inputting part  56  is configured to input a first display test signal. 
     In the present embodiment, the first display test signal inputting part  56  may be a pixel test bonding pad which is configured to input a sub-pixel test signal. 
     The first display test signal controlling part  55  is configured to control the input of the first display test signal. 
     In the present embodiment, the first display test signal inputting part  56  is controlled by the first display test signal controlling part  55 , the first display test signal controlling part  55  can be an NMOS transistor. The NMOS transistor may be controlled to be turned on or off such that different first display test signals are input by the first display test signal inputting part  56 . 
     The second display test signal inputting part  57  is configured to input a second display test signal. 
     In the present embodiment, the second display test signal inputting part  57  (such as a common electrode test bonding pad illustrated in  FIG. 6 ) is connected to a common electrode  52  of the display panel and configured to input a common electrode test signal. 
     The first test bus  58  is connected to the first display test signal inputting part. 
     The second test bus  59  is connected to the second display test signal inputting part. 
     The display device further includes a flexible printed circuit board  510  which includes the first test bus  58  and the second test bus  59  connected with each other via a depletion MOS transistor  511  or a resistor. 
     It is noted that, as illustrated in  FIG. 6 , the first display test signal controlling part  55  and the first display test signal inputting part  56  are connected to a common electrode  52  via an electrostatic protection circuit  54 , to achieve the electrostatic protection effect on the first display test signal controlling part  55  and the first display test signal inputting part  56 . 
     In the present embodiment, the first display test signal inputting part  56  (such as a pixel test bonding pad illustrated in  FIG. 6 ) is connected to the second display test signal inputting part  57  (such as a common electrode bonding pad illustrated in  FIG. 6 ) via the depletion MOS transistor  510  or the resistor on the flexible printed circuit board of the display device. 
     In the present embodiment, there may be a plurality of the first display test signal inputting parts  56 , the number of the first display test signal inputting parts  56  corresponds to the number of the base colors of the display device; there may be a plurality of the first test buses  58  including test buses for sub-pixels of the respective base colors, and the plurality of the first display test signal inputting parts are respectively connected to the test buses for sub-pixels of the respective base colors. 
     In the present embodiment, the plurality of the first display test signal inputting parts  56  may include a red sub-pixel test signal inputting part, a green sub-pixel test signal inputting part and a blue sub-pixel test signal inputting part, and the plurality of the first test bus  58  may include a red sub-pixel signal test bus, a green sub-pixel signal test bus and a blue sub-pixel signal test bus, which are respectively connected to the red sub-pixel test signal inputting part, the green sub-pixel test signal inputting part and the blue sub-pixel test signal inputting part. 
     In the present embodiment, the second display test signal inputting part  57  may include a common electrode test signal inputting part. 
     In the present embodiment, the first display test signal controlling part  55  can be an NMOS transistor, a source of which is connected to the first display test signal inputting part  56 , and a gate of which is configured to receive the first control signal to turn on or off the NMOS transistor; and the first display test signal inputting part  56  is connected to the common electrode test signal inputting part. When the display device is in displaying, the first control signal is at a low level, such that the NMOS transistor is turned off; and when the display device stops displaying, the first control signal is at a high level, such that the NMOS transistor is turned on. 
     As illustrated in  FIG. 6 , when a driver integrated circuit  53  is illuminated by light so that the photovoltaic effect is caused and hence a DC voltage is produced across the common electrode  52  and a data line  51 , the DC voltage is directly applied to a pixel and thus generates photovoltaic current due to weak ON status of the amorphous-silicon thin-film transistors. However, the first display test signal inputting part  56  and the second display test signal inputting part  57  are connected with each other via the depletion MOS transistor in the display panel, and the NMOS transistor and the depletion MOS transistor  511  become weak ON status in the inactive state of the display device, so that the electrical charges generated by the photovoltaic effect are guided to the GND terminal via such path through the first display test signal inputting part  56  and the second display test signal inputting part  57 , thus the influence caused on the display effect by the residual direct current generated by the photovoltaic effect of the driver integrated circuit  53  or the amorphous-silicon thin-film transistor is reduced. 
     In the present embodiment, the first test bus  58  is connected to a first terminal of the depletion MOS transistor  511 , the second test bus  59  is connected to a second terminal of the depletion MOS transistor  511 , and a gate of the depletion MOS transistor  511  is configured to receive a second control signal to control the depletion MOS transistor  511  to be turned on or off. 
     In the present embodiment, when the display device is in displaying, the second control signal is at a low level, such that the depletion MOS transistor  511  is turned off; and when the display device stops displaying, the second control signal is at a high level, such that the depletion MOS transistor  511  is turned on. 
     In the present embodiment, the first terminal of the depletion MOS transistor  511  is a source, and the second terminal of the depletion MOS transistor  511  is a drain; alternatively, the first terminal of the depletion MOS transistor  511  is a drain, and the second terminal of the depletion MOS transistor  511  is a source. 
     In an optional embodiment, the pixel test bonding pad includes a red sub-pixel test bonding pad, a green sub-pixel test bonding pad and a blue sub-pixel test bonding pad, which are respectively connected to the common electrode test bonding pad via the depletion MOS transistor  511  on the flexible printed circuit board  510 . The source and drain of the depletion MOS transistor  511  are respectively connected to the pixel test bonding pad and the common electrode test bonding pad, and a gate of the depletion MOS transistor  511  is configured to receive the second control signal, so that the depletion MOS transistor  511  is turned on in the inactive state of the display device, i.e., the gate of the depletion MOS transistor  511  receives a high level when the display device is in the inactive state, at the same time, the gate of the NMOS transistor receives a high level to turn on the NMOS transistor, such that the electrical charges generated by the photovoltaic effect is guided to the GND terminal via such path through the pixel test bonding pad and the common electrode test bonding pad. 
     In the present embodiment, the first display test signal inputting part and the second display test signal inputting part are connected with each other on the flexible printed circuit board via the depletion MOS transistor, and the NMOS transistor and the depletion MOS transistor become weak ON status in the inactive state of the display device, so that the electrical charges generated by the photovoltaic effect are guided to the GND terminal, thus the influence caused on the display effect by the residual direct current generated by the photovoltaic effect of a driver integrated circuit or anamorphous-silicon thin-film transistor is reduced. 
     Although the embodiments and technical principles adopted therein have been described as above, it is understood by the skilled person in the art that the present invention is not limited to the particular embodiments. The present invention can be changed, modified and replaced by the skilled person in the art without departing from the scope and principle of the present invention. Therefore, though the present invention has been specifically described through the previous embodiments, the present invention is not merely limited to the previous embodiments; more other equivalent embodiments may be made with the concept of the present invention, and the scope of the present invention is defined by the appended claims.