Patent Publication Number: US-9852683-B2

Title: Display and sub-pixel driving method therein

Description:
RELATED APPLICATIONS 
     This application claims priority to Taiwan Application Serial Number 103118124 filed May 23, 2014 which is herein incorporated by reference. 
     BACKGROUND 
     Technical Field 
     The present disclosure relates to a display. More particularly, the present disclosure relates to a light-emitting diode display. 
     Description of Related Art 
     Since micrometer scale-light-emitting diode (μ-LED) display uses μ-LED components as pixels for display, it is unnecessary to additionally set a backlight module in the μ-LED display. Therefore, the μ-LED display has advantages such as simple architecture, thin thickness, high contrast, wide viewing angle, fast response, etc. However, since technique for bonding LED components on the glass substrate is immature, LED components have worse contact with transistors of the glass substrate. When the display is turned on in a long period, inner resistance of a LED component is increased. Therefore, when the LED component receives the same driving current, operating voltage of the LED component is increased such that illumination efficiency of the LED component is reduced. Since illumination efficiency of the LED component is reduced, luminance of pixels of a display image is decreased, resulting in that luminance of displayed image becomes non-uniform. In some cases, dark spots even exist in the image displayed on the display. When aforementioned conditions are occurred, abnormal pixels of the image displayed on the μ-LED display fail to be fixed. 
     SUMMARY 
     In order to solve aforementioned problems, the present disclosure is to provide a display and a sub-pixel driving method. When an original light-emitting component of the sub-pixel is abnormal, another light-emitting component is substituted for the original light-emitting component to emit light. 
     One aspect of the present disclosure is to provide a display. The display includes a data line and a sub-pixel. The data line is configured to provide a data voltage signal. The sub-pixel includes a driving unit, a first light-emitting unit and a second light-emitting unit. The driving unit is configured to generate a driving current according to the data voltage signal. The first light-emitting unit is configured to emit light by the driving current and generates an operating voltage according to the driving current. The second light-emitting unit is selectively substituted for the first light-emitting unit to emit light according to a variation of the operating voltage. 
     Another aspect of the present disclosure is to provide a sub-pixel driving method for a sub-pixel. The sub-pixel includes a first light-emitting component and a second light-emitting component. The sub-pixel driving method includes: generating a driving current according to a data voltage signal; driving the first light-emitting component to emit light by the driving current and generating an operating voltage by the first light-emitting component according to the driving current; and selectively substituting the second light-emitting component for the first light-emitting component to emit light according to a variation of the operating voltage. 
     Further one aspect of the present disclosure is to provide a display. The display includes a data line and a sub-pixel. The data line is configured to provide a data voltage signal. The sub-pixel includes a first light-emitting component, a second light-emitting component, a first transistor, a second transistor and a comparator. The first light-emitting component includes a first terminal and a second terminal. The first terminal of the first light-emitting component is configured to receive a first voltage. The second light-emitting component includes a first terminal and a second terminal. The first terminal of the second light-emitting component is configured to receive the first voltage. The first transistor includes a first terminal, a second terminal and a control terminal. The first terminal of the first transistor is configured to receive a driving current corresponding to the data voltage signal, and the second terminal of the first transistor is electrically coupled to the second terminal of the first light-emitting component. The second transistor includes a first terminal, a second terminal and a control terminal. The first terminal of the second transistor is configured to receive the driving current, and the second terminal of the second transistor is electrically coupled to the second terminal of the second light-emitting component. The comparator includes a first input terminal, a second input terminal and an output terminal. The first input terminal is electrically coupled to the second terminal of the first light-emitting component and the second terminal of the first transistor, the second input terminal is configured to receive a reference voltage, and the output terminal is electrically coupled to the control terminal of the first transistor and the control terminal of the second transistor. 
     It is to be understood that both the foregoing general description and the following detailed description are by examples, and are intended to provide further explanation of the disclosure as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure can be more fully understood by reading the following detailed description of the embodiment, with reference made to the accompanying drawings as follows: 
         FIG. 1  is a schematic diagram illustrating a display according to one embodiment of the present disclosure; 
         FIG. 2  is a block diagram illustrating a sub-pixel according to one embodiment of the present disclosure; 
         FIG. 3  is a circuit diagram illustrating a sub-pixel according to one embodiment of the present disclosure; 
         FIG. 4  is a flowchart illustrating a sub-pixel driving method according to one embodiment of the present disclosure; and 
         FIG. 5  is a flowchart illustrating one step of  FIG. 4  according to one embodiment of the present disclosure; 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the present embodiments of the disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. 
     It will be understood that, although the terms first, second, third etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present invention. 
     It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. 
       FIG. 1  is a schematic diagram illustrating a display  100  according to one embodiment of the present disclosure. The display  100  includes several pixels  110 , several scan lines SCL, several data lines DAL, a reference voltage line VRL, a supply voltage line OVD and a supply voltage line OVS. Each pixel includes sub-pixels  111 ,  112  and  113  configured to display red, green and blue, respectively. The scan line SCL is configured to provide a selection signal. The data line DAL is configured to provide a data voltage signal. The reference data line is configured to provide a reference voltage. When the selection signal conducts transistors of the sub-pixels  111 ,  112  and  113  (not shown in the figure), light emitting components of the sub-pixels  111 ,  112  and  113  (not shown in the figure) are driven by the data voltage to display luminance. In one embodiment, light emitting components includes micrometer scale-inorganic light emitting diode (μ-LED) or organic light-emitting Diode (OLED). In other words, the display  100  includes an μ-LED display or an OLED display. 
     Reference is made to  FIG. 1  and  FIG. 2 .  FIG. 2  is a block diagram illustrating a sub-pixel  200  according to one embodiment of the present disclosure. The sub-pixel  200  can apply in the display  100  of  FIG. 1 , but the present disclosure is not limited thereto. The sub-pixel  200  includes a driving unit  210 , a first light-emitting unit  220  and a second light-emitting unit  230 . The driving unit  210  is configured to generate a driving current IDS according to a data voltage signal VDS. The first light-emitting unit  220  is configured to emit light by the driving current IDS, and configured to generate an operating voltage VOP according to the driving current IDS. The second light-emitting unit  220  is configured to be selectively substituted for the first light-emitting unit  210  to emit light according to a variation of the operating voltage VOP. In other words, when the driving unit  210  receives the data voltage signal VDS, the sub-pixel  200  display luminance by one of the first light-emitting unit  220  and the second light-emitting unit  230 . In one embodiment, the first light-emitting unit  220  and the second light-emitting unit  230  includes μ-LED or OLED. 
     In one embodiment, the sub-pixel  200  further includes a comparison unit  240  configured to compare the operating voltage VOP with a reference voltage VREF so as to determine to drive the first light-emitting unit  220  or the second light-emitting unit  230  to emit light. Specifically, if the first light-emitting unit  220  is normal (e.g., contact of the light-emitting component is normal and not decay yet), the operating voltage VOP of the first light-emitting unit  220  formed by the received driving current IDS should be within in an operation range. If the first light-emitting unit  220  is abnormal (e.g., contact of the light-emitting component is abnormal or the light-emitting component is aged such that the inner resistance of the light-emitting component is increased), the operating voltage VOP of the first light-emitting unit  220  formed by the received driving current IDS would beyond the operation range. Accordingly, in one embodiment, a value of the reference voltage VREF is substantially larger than a value of the operation range. When the operating voltage VOP is substantially smaller than the reference voltage VREF, the first light-emitting unit  220  is normal. At this time, the sub-pixel  200  selects the first light-emitting unit  220  to emit light. When the operating voltage VOP is substantially larger than or equal to the reference voltage VREF, the first light-emitting unit  220  is abnormal. At this time, the sub-pixel  200  selects the second light-emitting unit  220  to emit light. In other words, the sub-pixel  200  selects the second light-emitting unit  220  substituted for to first light-emitting unit  230  to emit light. 
     Moreover, the user can adjust value of the reference voltage VREF externally so as to adjust criterion of illumination efficiency of the first light-emitting unit  220 . Accordingly, the sub-pixel  200  can be operated more flexibly, and usage period of light-emitting component is increased. 
     In one embodiment, the sub-pixel  200  further includes a first switch unit  250  and a second switch unit  260 . The first switch unit  250  is electrically coupled to the driving unit  210 , the first light-emitting unit  220  and the comparison unit  240 . The second switch unit  260  is electrically coupled to the driving unit  210 , the second light-emitting unit  230  and the comparison unit  240 . The comparison unit  240  compares the operating voltage VOP with the reference voltage so as to generate a control signal ICS. The control signal ICS is configured to conduct one of the first switch unit  250  and the second switch unit  260  such that one of the first light-emitting unit  220  and the second light-emitting unit  230  corresponding to the conducted one of the first switch unit and the second switch unit to emit light receives the driving current IDS and emits light. In one embodiment, when the operating voltage VOP is substantially smaller than the reference voltage VREF, the control signal ICS conducts the first switch units  250  and cuts off the second switch unit  260 . Therefore, only the first light-emitting unit  220  can receive the driving current IDS and emit light at this time. When the operating voltage VOP is substantially larger than or equal to the reference voltage VREF, the control signal ICS cuts off the first switch units  250  and conducts the second switch unit  260 . Therefore, only the second light-emitting unit  230  can receive the driving current IDS and emit light at this time. 
     The aforementioned operations can be implemented during a transient period before the display is turned on or before the display is turned off. Although reduction of illumination efficiency of light-emitting component is not improved yet, usage period of the display still can be increased and non-uniform luminance on the displayed image of the display still can be improved by aforementioned embodiments. Moreover, by adjusting the reference voltage VREF externally, the display can be operated more flexibly. 
       FIG. 3  is a circuit diagram illustrating a sub-pixel  300  according to one embodiment of the present disclosure. The sub-pixel  300  can apply in the display  100  of  FIG. 1 , but the present disclosure is not limited thereto. The sub-pixel  300  includes a first transistor TN 1 , a second transistor TN 2 , a first light-emitting component  310 , a second light-emitting component  320  and a comparator  330 . A first terminal of the first transistor TN 1  and a first terminal of the second transistor TN 2  are configured to receive the driving current IDS corresponding to the data voltage signal. A second terminal of the first transistor TN 1  is electrically coupled to an anode terminal of the first light-emitting component  310 . A second terminal of the second transistor TN 2  is electrically coupled to an anode terminal of the second light-emitting component  320 . A cathode terminal of the first light-emitting component  310  and a cathode terminal of the second light-emitting component  320  are electrically coupled to the supply voltage line OVS and configured to receive a first voltage. A first input terminal of the comparator  330  is electrically coupled to the anode terminal of the first light-emitting component  310  and the second terminal of the first transistor TN 1 . A second input terminal of the comparator  330  is configured to receive the reference voltage VREF. An output terminal of the comparator  330  is electrically coupled to a control terminal of the first transistor TN 1  and a control terminal of the second transistor TN 2 . 
     In one embodiment, characteristic of the first transistor TN 1  and characteristic of the second transistor TN 2  are complementary, i.e., the first transistor TN 1  and the second transistor TN 2  are unable to be conducted simultaneously. In other words, if the first transistor TN 1  is a P-type MOSFET or a PNP transistor, the second transistor TN 2  is a N-type MOSFET or an NPN transistor. If the first transistor TN 1  is a N-type MOSFET or an NPN transistor, the second transistor TN 2  is a P-type MOSFET or a PNP transistor. 
     In the present embodiment, t the first transistor TN 1  is a N-type TFT (Thin Film Transistor), and the second transistor TN 2  is a N-type TFT, but the present embodiment is not limited thereto. 
     In one embodiment, the sub-pixel further includes a third transistor TN 3  and a capacitor  340 . A first terminal of the third transistor TN 3  is electrically coupled to the supply voltage line OVS, and is configured to receive a second voltage. A second terminal of the third transistor TN 3  is electrically coupled to the first terminal of the first transistor TN 1  and the first terminal of the second transistor TN 2 . A control terminal of the third transistor TN 3  is electrically coupled to the data line DAL, and is configured to receive the data voltage signal VDS. A first terminal of the capacitor  340  is electrically coupled to the first terminal of the third transistor TN 3 . A second terminal of the capacitor  340  is electrically coupled the control terminal of the third transistor TN 3 . 
     In one operation, when the third transistor TN 3  receives the data voltage signal through the data line DAL, the third transistor TN 3  is conducted. Through capacitive coupling effect of the capacitor  340 , the third transistor TN 3  generates the driving current IDS according to the data voltage signal. The first light-emitting component  310  emits light by the driving current IDS, and generates the operating voltage VOP at the anode terminal of the first light-emitting component  310  according to the driving current IDS. The comparator  330  compares the operating voltage VOP with the reference voltage VREF so as to generate the control signal ICS to the first transistor TN 1  and the second transistor TN 2 . 
     When the operating voltage VOP is substantially smaller than the reference voltage VREF, the control signal ICS is at high logic level. Since the first transistor TN 1  is a N-type transistor and the second transistor TN 2  is a P-type transistor, the first transistor TN 1  is conducted and the second transistor TN 2  is cut off. At this time, the first light-emitting component  310  keeps receiving the driving current IDS through the first transistor TN 1  to emit light. When the operating voltage VOP is substantially larger than or equal to the reference voltage VREF, the control signal ICS is at low logic level. Therefore, the first transistor TN 1  is cut off, and the second transistor TN 2  is conducted. At this time, the second light-emitting component  320  is substituted for the first light-emitting component  310  to receive the driving current IDS to emit light through the second transistor TN 2 . 
     Similarly, the user can adjust value of the reference voltage VREF externally so as to adjust criterion of illumination efficiency of the first light-emitting component  310 . Accordingly, the sub-pixel  300  can be operated more flexibly, and usage period of light-emitting component is increased. 
     In one embodiment, the sub-pixel  300  further includes a fourth transistor TN 4 . A first terminal of the fourth transistor TN 4  is electrically coupled to the control terminal of the third transistor TN 3  and the second terminal of the capacitor  340 . A second terminal of the fourth transistor is electrically coupled to the data line DAL. A control terminal of the fourth transistor TN 4  is electrically coupled to the scan line SCL, and is configured to receive a selection signal. When the selection signal conducts the transistor TN 4 , the third transistor TN 3  receives the data voltage signal through the fourth transistor TN 4 , and generates the driving current IDS. 
     In the present embodiment, the third transistor TN 3  and the fourth transistor TN 4  are P-type TFTs, but the present embodiment is not limited thereto. In other embodiments, the third transistor TN 3  and the fourth transistor TN 4  can be N-type TFTs. 
       FIG. 4  is a flowchart illustrating a sub-pixel driving method  400  according to one embodiment of the present disclosure. In order to clearly describe the present embodiment, the sub-pixel driving method  400  is described with the sub-pixel  200  of  FIG. 2 , but the present disclosure is not limited thereto. First, in operation S 410 , the driving current IDS is generated by the driving unit  210  according to the data voltage signal. The data voltage signal can be received through the data line DAL. Next, in operation S 430 , the first unit  220  is driven to emit light by the driving current IDS, and the operating voltage VOP is generated by the first light-emitting unit  220  according to the operating voltage. Next, in operation S 450 , the second light-emitting unit  230  is selectively substituted for the first light-emitting unit  220  to emit light according to a variation of the operating voltage VOP. 
     In one embodiment, operation S 450  further includes operations S 451 -S 455 .  FIG. 5  is a flowchart illustrating one step of  FIG. 4  according to one embodiment of the present disclosure. As shown in  FIG. 5 , in operation S 451 , the operating voltage VOP is compared with the reference voltage VREF by the comparison unit  240 , and a determination is made as to whether the operating voltage VOP is substantially smaller than the reference voltage VREF. When the operating voltage VOP is substantially smaller than the reference voltage VREF, operation S 453  is executed. In operation S 453 , the driving current IDS is provided to the first light-emitting unit  220  by the driving unit  210  such that the first light-emitting unit  220  is driven to emit light. When the operating voltage VOP is substantially larger than or equal to the reference voltage VREF, operation S 4555  is executed. In operation S 455 , the driving current IDS is provided to the second light-emitting unit  230  by the driving unit  210  such that the second light-emitting unit  230  is driven to emit light. 
     When the display is turned on in a long period, inner resistance of a LED component is increased. Therefore, when the LED component receives the same driving current, operating voltage of the LED component is increased such that illumination efficiency of the LED component is reduced. Since illumination efficiency of the LED component is reduced, luminance of a pixel of a display image is decreased, resulting in that luminance of displayed image becomes non-uniform. In some cases, dark spots even exist in the image displayed on the display. When aforementioned conditions are occurred, abnormal pixels of the image displayed on the display fail to be fixed. 
     As illustrated from the aforementioned embodiments of the present disclosure, by comparing an operating voltage of an original light-emitting component of a sub-pixel with a reference voltage, a determination is made as to whether the original light-emitting component is abnormal. When the original light-emitting component of the sub-pixel is abnormal, another light-emitting component is substituted for the original light-emitting component to emit light. Therefore, non-uniform luminance of the displayed image on the display is improved, and usage period of the display is increased. Moreover, by adjusting the reference voltage externally, the display can be operated more flexibly. 
     Although the present disclosure has been described in considerable detail with reference to certain embodiments thereof, other embodiments are possible. Therefore, the spirit and scope of the appended claims should not be limited to the description of the embodiments contained herein. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present disclosure without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the present disclosure cover modifications and variations of this disclosure provided they fall within the scope of the following claims.