Patent Publication Number: US-2012044271-A1

Title: Active matrix organic light emitting diode display having deterioration detection function in programming period

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the priority of Korean Patent Application No. 10-2010-0080517 filed on Aug. 19, 2010, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an active matrix organic light emitting diode (AMOLED) display which can be applied to a display system, and more particularly, to an AMOLED display which can rapidly detect deterioration by performing deterioration detection in a programming period to thereby perform deterioration compensation rapidly. 
     2. Description of the Related Art 
     In general, in order to manufacture a large-sized display panel by using an organic light emitting diode (OLED), prominent as a next-generation display device, the OLED display is configured to have an active matrix structure, which is referred to as an active matrix OLED display (a so called ‘AMOLED’ display). 
     Since such an AMOLED display does not require an additional light source, the AMOLED display shows outstanding performance in terms of brightness, thickness, definition, speed, and power consumption as compared with an LCD panel using a backlight unit (BLU) as an additional light source. 
     However, the AMOLED display has disadvantages in that uniformity between pixels and uniformity according to time are very low, and a circuit for compensating for uniformity is required. 
     In general, an AMOLED driving method includes a current driving method and a voltage driving method. The voltage driving method of the AMOLED display has a disadvantage in that an output varies due to deterioration of mobility or threshold voltage of a transistor. 
     In order to solve the disadvantages of the AMOLED due to the deterioration of the threshold voltage, a compensation circuit for compensating for the deterioration is required. In addition, in the voltage driving method of the AMOLED display, since a period, in which a deterioration level is detected, is additionally required, excessive time may be required to detect and compensate for deterioration. 
     SUMMARY OF THE INVENTION 
     An aspect of the present invention provides an active matrix organic light emitting diode (AMOLED) display which can rapidly detect deterioration by performing deterioration detection in a programming period to thereby perform deterioration compensation rapidly. 
     According to an aspect of the present invention, there is provided an active matrix organic light emitting diode display including: a data driving unit converting previously prepared correction data into an analog correction signal and generating a driving signal according to the analog correction signal; a pixel unit having an organic light emitting diode connected between first and second power supply terminals receiving first and second powers, respectively, charging a value corresponding to the correction data according to the driving signal in a predetermined programming period, detecting the driving signal in order to detect deterioration, and allowing current to flow through the organic light emitting diode according to the value charged in the predetermined programming period in a predetermined holding period; andan analog-to-digital converter (ADC) detecting the driving signal having deterioration information of the organic light emitting diode of the pixel unit as deterioration voltage in the programming period. 
     The pixel unit may further include first and second MOS transistors connected in series between the first power supply terminal receiving the first power and the organic light emitting diode; a third MOS transistor connected between a first connection node, connected between the first and second MOS transistors, and the data driving unit; a charging capacitor connected between a gate of the second MOS transistor and the first connection node; and a fourth MOS transistor having a drain connected to a drain of the second MOS transistor and a source connected to the gate of the second MOS transistor. 
     The pixel unit may be configured such that the second, third, and fourth MOS transistors are turned on and the first MOS transistor is turned off in the programming period, and the first and second MOS transistors are turned on and the third and fourth MOS transistors are turned off in the holding period. 
     The pixel unit may allow the driving signal of the data driving unit to pass through the second and third MOS transistors and flow through the organic light emitting diode in the programming period and store the value corresponding to the correction data in the charging capacitor. The pixel unit may allow the current to flow from the first power supply terminal to the organic light emitting diode through the first and second MOS transistors according to the value stored in the charging capacitor in the holding period. 
     The ADC may detect the deterioration voltage having the deterioration information of the organic light emitting diode in an input node of the pixel unit, into which the driving signal of the data driving unit is inputted, in the programming period. 
     The active matrix organic light emitting diode display may further include a compensation unit generating a deterioration compensation signal for deterioration compensation by using digital deterioration voltage from the ADC; and a converting unit converting input data into correction data, in which deterioration is compensated for, by using the deterioration compensation signal and providing the converted correction data to the data driving unit. 
     According to another aspect of the present invention, there is provided an active matrix organic light emitting diode display including: a data driving unit converting previously prepared correction data into an analog correction signal and generating a driving signal according to the analog correction signal; a pixel unit having an organic light emitting diode connected between first and second power supply terminals receiving first and second powers, respectively, charging a value corresponding to the correction data according to the driving signal in a predetermined programming period, detecting the driving signal in order to detect deterioration, and allowing current to flow through the organic light emitting diode according to the value charged in the predetermined programming period in a predetermined holding period; an analog-to-digital converter (ADC) detecting deterioration voltage having deterioration information of the organic light emitting diode of the pixel unit and converting the detected deterioration voltage into digital deterioration voltage in the holding period; a compensation unit generating a deterioration compensation signal for deterioration compensation by using the digital deterioration voltage from the ADC; and a converting unit converting input data into correction data, in which deterioration is compensated for, by using the deterioration compensation signal and providing the correction data to the data driving unit. 
     The pixel unit may further include first and second MOS transistors connected in series between the first power supply terminal receiving the first power and the organic light emitting diode; a third MOS transistor connected between a first connection node, connected between the first and second MOS transistors, and the data driving unit; a charging capacitor connected between a gate of the second MOS transistor and the first connection node; and a fourth MOS transistor having a drain connected to a drain of the second MOS transistor and a source connected to the gate of the second MOS transistor. 
     The pixel unit may be configured such that the second, third, and fourth MOS transistors are turned on and the first MOS transistor is turned off in the programming period, and the first and second MOS transistors are turned on and the third and fourth MOS transistors are turned off in the holding period. 
     The pixel unit may allow the driving signal of the data driving unit to pass through the second and third MOS transistors and flow through the organic light emitting diode in the programming period and may store the value corresponding to the correction data in the charging capacitor. The pixel unit may allow the current to flow from the first power supply terminal to the organic light emitting diode through the first and second MOS transistors according to the value stored in the charging capacitor in the holding period. 
     The ADC may detect the deterioration voltage having the deterioration information of the organic light emitting diode in an input node of the pixel unit, into which the driving signal of the data driving unit is inputted, and convert the detected deterioration voltage into the digital deterioration voltage in the programming period. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a block diagram of an active matrix organic light emitting diode (AMOLED) display according to an exemplary embodiment of the present invention; 
         FIG. 2  is a flowchart illustrating the operation of an AMOLED display according to an exemplary embodiment of the present invention; 
         FIG. 3  is a time chart of an AMOLED display according to an exemplary embodiment of the present invention; 
         FIG. 4  is a diagram illustrating the operation of an AMOLED display in a programming period according to an exemplary embodiment of the present invention; and 
         FIG. 5  is a diagram illustrating the operation of an AMOLED display in a holding period according to an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. 
     The present invention is not limited to the exemplary embodiments and the exemplary embodiments are merely used to help in understanding the spirit of the present invention. Like reference numerals refer to like elements in the accompanying drawings. 
       FIG. 1  is a block diagram of an active matrix organic light emitting diode (AMOLED) display according to an exemplary embodiment of the present invention. 
     Referring to  FIG. 1 , an AMOLED display according to an exemplary embodiment of the present invention may include a data driving unit  120  that converts previously prepared correction data into an analog correction signal Scor and generates a driving signal according to the analog correction signal Scor. 
     Further, the AMOLED display according to the embodiment of the present invention may include a pixel unit  150  that has an organic light emitting diode (OLED) connected between first and second power supply terminals EVLDD and ELVSS receiving first and second powers, charges a value corresponding to the correction data according to the driving signal in a programming period (P 1  of  FIG. 3 ), detects the driving signal in order to detect deterioration, and allows current to flow through the OLED according to the value charged in the predetermined programming period in a holding period (P 2  of  FIG. 3 ). 
     The AMOLED display according to the embodiment of the present invention may include an analog-to-digital converter (ADC)  160  that detects deterioration voltage Vd corresponding to a driving signal having deterioration information of the OLED of the pixel unit  150  and converts the detected deterioration voltage into digital deterioration voltage VDd. 
     The pixel unit  150  may further include first and second MOS transistors PM 1  and PM 2  connected in series between the power supply terminal ELVDD receiving the first power and the OLED, a third MOS transistor PM 3  connected between a first connection node NC 1 , connected between the first and second MOS transistors, and the data driving unit  120 , a charging capacitor Ccha connected between a gate of the second MOS transistor PM 2  and the first connection node NC 1 , and a fourth MOS transistor PM 4  having a drain connected to a drain of the second MOS transistor PM 2  and a source connected to the gate of the second MOS transistor PM 2 . 
     The pixel unit  150  may be configured such that the second, third and fourth MOS transistors PM 2 , PM 3  and PM 4  are turned on and the first MOS transistor PM 1  is turned off in the programming period P 1 , and the first and second MOS transistors PM 1  and PM 2  are turned on and the third and fourth MOS transistors PM 3  and PM 4  are turned off in the holding period P 2 . 
     Further, the pixel unit  150  may be configured in the programming period P 1  such that the driving signal passes through the second and third MOS transistors PM 2  and PM 3  and flows through the OLED, and the value corresponding to the correction data is stored in the charging capacitor Ccha . 
     In addition, the pixel unit  150  may be configured in the holding period P 2  such that current from the first power supply terminal ELVDD passes through the first and second MOS transistors PM 1  and PM 2  and the OLED and flows to the second power supply terminal ELVSS according to the value stored in the charging capacitor Ccha. 
     The ADC  160  may be configured to detect the deterioration voltage having the deterioration information of the OLED in an input node Nin of the pixel unit  150 , into which the driving signal of the data driving unit  120  is inputted, in the programming period P 1 . 
     Further, the AMOLED display according to the embodiment of the present invention may further include a compensation unit  170  generating a deterioration compensation signal Scon for deterioration compensation by using digital deterioration voltage VDd from the ADC  160 , and a converting unit  110  converting input data Din into correction data, in which deterioration is compensated for, by using the deterioration compensation signal Scon and providing the converted correction data to the data driving unit  120 . 
       FIG. 2  is a flowchart of an AMOLED display according to an exemplary embodiment of the present invention. In FIG. 
       2 , the programming period P 1  starts in operation S 100 . A deterioration detecting operation is performed in operation S 200 . The programming period P 1  terminates and the holding period P 2  starts in operation S 300 . In addition, deterioration compensation is performed on the basis of the deterioration detection in the holding period P 2  in operation S 400 . 
       FIG. 3  is a time chart of an AMOLED display according to the embodiment of the present invention. In  FIG. 3 , P 1  represents the programming period; P 2  represents the holding period; Sscan represents a gate signal applied to a gate of the third MOS transistor PM 3  of the pixel unit  150 ; and Sscan represents an inversion signal of Sscan supplied to a gate of the first MOS transistor PM 1 . In addition, VDd is the digital deterioration voltage outputted from the ADC  160 . 
       FIG. 4  is a diagram illustrating the operation of an AMOLED display in a programming period according to an exemplary embodiment of the present invention, and  FIG. 5  is a diagram illustrating the operation of an AMOLED display in a holding period according to an exemplary embodiment of the present invention. 
     In  FIG. 4 , PHi represents a current path in the programming period P 1  and PHdet represents a deterioration detection path in the AMOLED display according to the embodiment of the present invention. In  FIG. 5 , PHi represents a current path in the holding period P 2  in the AMOLED display according to the embodiment of the present invention. 
     Hereinafter, operations and effects of the present invention will be described with reference to the accompanying drawings. 
     Referring to  FIGS. 1 to 5 , an AMOLED display according to an exemplary embodiment of the present invention will be described for each of the predetermined programming period P 1  and holding period P 2 . 
     First, the operation of the AMOLED display in the programming period P 1  will be described. 
     Referring to  FIG. 1 , the data driving unit  120  starts the operation corresponding to the programming period P 1 , to convert the previously prepared correction data into the analog correction signal Scor, and generate and supplies the driving signal to the pixel unit  150  according to the analog correction signal Scor as shown in  FIG. 2  (S 100  of  FIG. 2 ). 
     At this time, in the pixel unit  150 , a value corresponding to the correction data may be charged according to the driving signal in the programming period P 1 . 
     That is, in the pixel unit  150 , the second, third and fourth MOS transistors PM 2 , PM 3  and PM 4  are turned on and the first MOS transistor PM 1  is turned off in the programming period P 1 . 
     As a result, the pixel unit  150  may allow the driving signal to pass through the second and third MOS transistors PM 2  and PM 3  and flow through the OLED in the programming period P 1 , and thus the value corresponding to the correction data is stored in the charging capacitor Ccha as shown in  FIG. 4 . 
     Simultaneously, the ADC  160  may detect the deterioration voltage having the deterioration information of the OLED in the input node Nin of the pixel unit  150 , into which the driving signal of the data driving unit  120  is inputted, in the programming period P 1  as shown in  FIGS. 2 and 3 . 
     Subsequently, the compensation unit  170  of the present invention may generate the deterioration compensation signal Scon for deterioration compensation by using the digital deterioration voltage VDd from the ADC  160  and provide the deterioration compensation signal Scon to the converting unit  110 . 
     At this time, the converting unit  110  may convert the input data Din into the correction data, in which deterioration is compensated for, and provide the corresponding correction data to the data driving unit  120 . 
     As a result, as described above, the data driving unit  120  may convert the correction data into the analog correction signal Scor and generate the driving signal according to the analog correction signal Scor. 
     Hereinafter, the operation of the AMOLED display in the holding period P 2  will be described. 
     Referring to  FIG. 1 , in the pixel unit  150  of the present invention, current flows through the OLED according to the value charged in the predetermined programming period in the holding period P 2 . 
     That is, in the pixel unit  150 , the first and second MOS transistors PM 1  and PM 2  are turned on and the third and fourth MOS transistors PM 3  and PM 4  are turned off in the holding period P 2 . 
     As a result, the pixel unit  150  may allow the current to flow from the first power supply terminal to the OLED through the first and second MOS transistors PM 1  and PM 2  according to the value stored in the charging capacitor Ccha in the holding period P 2 . 
     As described above, compensation for deteriorations in terms of aging, temperature, and process can be performed without being affected by deteriorations in terms of mobility and threshold voltage of the transistors. 
     Further, an influence of the deterioration in terms of mobility and threshold voltage of the transistors with respect to the current used to drive the OLED by using the compensation current driving method may be removed. In addition, since deterioration is detected in the programming period, without an additional period to detect the deterioration level of the OLED, deterioration compensation can be performed while displaying. 
     As set forth above, an AMOLED display according to exemplary embodiments of the invention can rapidly detect deterioration by performing deterioration detection in a programming period to thereby perform deterioration compensation rapidly. 
     While the present invention has been shown and described in connection with the exemplary embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the spirit and scope of the invention as defined by the appended claims.