Patent Publication Number: US-9886906-B2

Title: Pixel circuit, pixel circuit driving method and display device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the U.S. national phase of PCT Application No. PCT/CN2014/087933 filed on Sep. 30, 2014, which claims a priority of the Chinese Patent Application No. 201410226754.9 filed on May 26, 2014, the disclosures of which are incorporated in their entirety by reference herein. 
     The present application claims a priority of the Chinese patent application No. 201410226754.9 filed on May 26, 2014, which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     The present disclosure relates to the field of display technology, in particular to a pixel circuit, a pixel circuit driving method and a display device. 
     BACKGROUND 
     A basic Active Matrix/Organic Light Emitting Diode (AMOLED) pixel driving circuit is a 2T1C pixel driving circuit which has a simple structure. In an AMOLED pixel driving circuit based on low temperature poly-silicon (LTPS), due to problems of LTPS such as non-uniform threshold voltages, a circuit for compensating for threshold voltages of driving thin film transistors (TFTs) is required to be added in pixel design for AMOLED. A typical AMOLED pixel driving circuit with compensation for threshold voltages requires a 6T1C pixel driving circuit or a 5T2C pixel driving circuit, or even more TFTs and/or capacitors. With increasing of the amount of the TFTs and/or capacitors, a larger layout space will be occupied, which makes it difficult to reduce size of AMOLED pixels, i.e., limiting development of the AMOLED pixel driving circuit with high pixel per inch (PPI). 
     SUMMARY 
     A main object of the present disclosure is to provide a pixel circuit, a pixel circuit driving method and a display device, which can improve an aperture ratio of pixels and reduce a current density in an organic light-emitting layer in addition to obtaining uniform display. 
     In order to achieve the above object, the present disclosure provides a pixel circuit including a plurality of row pixel units; each row pixel unit including a plurality of subpixel units; wherein each of the subpixel units includes a subpixel driving circuit and a light-emitting component; the subpixel driving circuit includes a driving transistor coupled with the light-emitting component, and a driving control module which is coupled with a data line and the driving transistor, respectively; each row pixel unit further includes a row sharing unit; 
     each of the subpixel units is coupled with a first signal line and a second signal line; and 
     the row sharing unit is coupled with each subpixel unit included in the row pixel unit through the first signal line and the second signal line, to have a threshold compensation function. 
     Alternatively, the subpixel units are arranged in an effective display area; and the row sharing unit is arranged outside the effective display area. 
     Alternatively, the driving transistor has a first electrode coupled with a first terminal of the light-emitting component, and a second electrode coupled with the first signal line; a second terminal of the light-emitting component is coupled with the second signal line; 
     the driving control module is coupled with a gate electrode, the first electrode and the second electrode of the driving transistor, respectively; 
     the driving control module is further coupled with a scanning line; 
     the row sharing unit includes an initialization module for receiving an initial control signal, and a light-emitting control module for receiving a light-emitting control signal; 
     the initialization module is coupled with the first signal line, and is configured to, when the initial control signal and a scanning signal in the scanning line are valid at the same time, set a gate potential of the driving transistor to be equal to an initial level through the driving control module; 
     the light-emitting control module is configured to, when the light-emitting control signal is valid, control the first signal to receive a first level and enable the second signal line to receive a second level; 
     the driving control module is configured to, when the scanning signal is valid, control to write a data voltage from the data line into the driving transistor; when the light-emitting control signal is valid, control the driving transistor to drive the light-emitting component to emit light and compensate for a threshold of the driving transistor. 
     Alternatively, the driving control module includes a data writing transistor, a driving control transistor and a storage capacitor; 
     the data writing transistor has a gate electrode coupled with the scanning line, a first electrode coupled with the data line, and a second electrode coupled with the first electrode of the driving transistor; 
     the driving control transistor has a gate electrode coupled with the scanning line, a first electrode coupled with the gate electrode of the driving transistor, and a second electrode coupled with the second electrode of the driving transistor; 
     the storage capacitor has a first terminal coupled with the first electrode of the driving transistor, and a second terminal coupled with the gate electrode of the driving transistor. 
     Alternatively, the initialization module includes an initialization transistor; the initialization transistor has a gate electrode for receiving the initial control signal, a first electrode coupled with the first signal line, and a second electrode for receiving the initial level. 
     Alternatively, the light-emitting control module includes: 
     a first light-emitting control transistor having a gate electrode for receiving the light-emitting control signal, a first electrode for receiving the first level, and a second electrode coupled with the first signal line; 
     a second light-emitting control transistor having a gate electrode for receiving the light-emitting control signal, a first electrode coupled with the second signal line, and a second electrode for receiving the second level. 
     The present disclosure further provides a pixel circuit driving method, which is applied to the above pixel circuit, the pixel circuit driving method including: 
     a initialization step: turning on a driving control transistor, writing a data voltage into a first electrode of a driving transistor, and setting, by an initialization module, a gate potential of the driving transistor to be equal to an initial level through the driving control transistor, in an initialization stage, wherein an initial control signal and a scanning signal in a scanning line are valid at the same time; 
     a compensation step: turning on a data writing transistor and the driving control transistor, writing data voltage into the first electrode of the driving transistor, and discharging the gate potential of the driving transistor through a storage capacitor so as to compensate for a threshold voltage of the driving transistor, in a compensation stage, wherein the scanning signal is valid; and 
     a light-emitting step: receiving, by a first signal line, a first level, receiving, by a second signal line, a second level, turning off the driving control transistor to control a second terminal of the storage capacitor to be floated so as to maintain the gate potential of the driving transistor unchanged, and turning on the driving transistor to drive a light-emitting component to emit light, in a light-emitting stage, wherein a light-emitting control signal is valid. 
     The present disclosure further provides a display device including the above pixel circuit. 
     Comparing with the related art, the pixel circuit according to one embodiment of the present disclosure adopts the row sharing units, so that thresholds of the driving transistors may be compensated and at the same time an amount of TFTs in an effective display area may be reduced so as to improve an aperture ratio of pixels. As a result, the display is uniform, and a current density in an organic light-emitting layer is reduced, thereby extending the service life of an AMOLED panel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram of a pixel circuit according to one embodiment of the present disclosure; 
         FIG. 2  is a block diagram of a subpixel unit and a row sharing unit included in the pixel circuit according to one embodiment of the present disclosure; 
         FIG. 3  is a circuit diagram of a subpixel unit and a row sharing unit included in the pixel circuit according to one embodiment of the present disclosure; 
         FIG. 4  is a working timing sequence diagram of the pixel circuit including the subpixel unit and the row sharing unit as shown in  FIG. 3 ; and 
         FIG. 5  is a circuit diagram of the pixel circuit according to one embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The technical solutions of embodiments of the present disclosure will be described hereinafter in a clear and complete manner in conjunction with drawings of the embodiments of the present disclosure. Obviously, the described embodiments are merely some rather than all of, the embodiments of the present disclosure. Based on these embodiments of the present disclosure, a person skilled in the art may obtain other embodiments without creative work, which also fall within the scope of the present disclosure. 
     Transistors adopted in all embodiments of the present disclosure may be thin film transistors, field effect transistors, or other devices having same characteristics. In embodiments of the present disclosure, in order to distinguish two electrodes of a transistor in addition to a gate electrode, a first electrode of the two may be referred to as “source electrode” or “drain electrode”, and a second electrode of the two may be referred to as “drain electrode” or “source electrode”. In addition, transistors may be divided into n-type transistors and p-type transistors according to characteristics of the transistors. In a driving circuit provided in one embodiment of the present disclosure, all transistors being n-type transistors is taken as an example for illustration, it can be conceivable that a person skilled in the art easily thinks of using p-type transistors without creative work, which also fall within the scope of the present disclosure. 
     A pixel circuit according to one embodiment of the present disclosure includes a plurality of row pixel units. Each row pixel unit includes a plurality of subpixel units. Each of the subpixel units includes a subpixel driving circuit and a light-emitting component. The subpixel driving circuit includes a driving transistor coupled with the light-emitting component, and a driving control module which is coupled with a data line and the driving transistor, respectively. Each row pixel unit further includes a row sharing unit. Each of the subpixel units is coupled with a first signal line and a second signal line. The row sharing unit is coupled with each subpixel unit included in the row pixel unit through the first signal line and the second signal line, thereby having a threshold compensation function. 
     In the pixel circuit according to one embodiment of the present disclosure, in addition to the subpixel driving circuit, the subpixel unit further includes the light-emitting component. The subpixel driving circuit and the light-emitting component together form the subpixel unit. The light-emitting component, for example, may be an organic light-emitting diode (OLED). 
     The pixel circuit according to one embodiment of the present disclosure adopts the row sharing units, so that thresholds of driving transistors may be compensated while an amount of TFTs in an effective display area may be reduced so as to improve an aperture ratio of pixels. As a result, the display is uniform, and a current density in an organic light-emitting layer is reduced, thereby extending the service life of an AMOLED panel. 
     Alternatively, the subpixel units are arranged in the effective display area, and the row sharing units are arranged outside the effective display area. By arranging a circuit having general character in each row pixel unit outside the effective display area, the amount of TFTs in the effective display area may be further reduced so as to improve the aperture ratio of pixels. 
     Specifically, the pixel circuit of one embodiment of the present disclosure includes m row pixel units; each row pixel unit includes n subpixel units; all of the n subpixel units included in a j-th row pixel unit are coupled with a j-th scanning line (not shown in  FIG. 1 ); a k-th subpixel unit included in each row pixel unit is coupled with a k-th data line; where either of m and n is an integer greater than 1; j is a positive integer which is less than or equal to m; k is a positive integer which is less than or equal to n. 
     As shown in  FIG. 1 , Vdata_ 1  is a data voltage output from a first data line; Vdata_k−1 is a data voltage output from a (k−1)-th data line; Vdata_k is a data voltage output from a k-th data line; Vdata_k+1 is a data voltage output from a (K+1)-th data line; Vdata_n is a data voltage output from an n-th data line. 
     Each of the subpixel units includes a subpixel driving circuit and a light-emitting component. The subpixel driving circuit includes a driving transistor coupled with the light-emitting component, and a driving control module which is coupled with a data line and the driving transistor, respectively. 
     Each row pixel unit further includes a row sharing unit; m row sharing units form a row sharing circuit. 
     Each of the subpixel units included in each row pixel circuit is coupled with a first signal line and a second signal line. 
     The row sharing unit is coupled with each subpixel unit included in each row pixel unit through the first signal line and the second signal line, thereby having a threshold compensation function. 
     The subpixel units are arranged in an effective display area, and the row sharing unit is arranged outside the effective display area. 
     In  FIG. 1 , V 1 _ 1  is a first signal line for a first row pixel circuit, V 2 _ 1  is a second signal line for the first row pixel circuit; V 1 _ j −1 is a first signal line for a (j−1)-th row pixel circuit, V 2 _ j −1 is a second signal line for the (j−1)-th row pixel circuit; V 1 _ j  is a first signal line for a j-th row pixel circuit, V 2 _ j  is a second signal line for the j-th row pixel circuit; V 1 _ j +1 is a first signal line for a (j+1)-th row pixel circuit, V 2 _ j +1 is a second signal line for the (j+1)-th row pixel circuit; V 1 _ m  is a first signal line for an m-th row pixel circuit, V 2 _ m  is a second signal line for the m-th row pixel circuit. 
     Optionally, the driving transistor has a first electrode coupled with a first terminal of the light-emitting component, and a second electrode coupled with the first signal line. A second terminal of the light-emitting component is coupled with the second signal line. 
     The driving control module is coupled with a gate electrode, the first electrode and the second electrode of the driving transistor, respectively. 
     The driving control module is further coupled with a scanning line. 
     The row sharing unit includes an initialization module for receiving an initial control signal, and a light-emitting control module for receiving a light-emitting control signal. 
     The initialization module is coupled with the first signal line, and is configured to, when the initial control signal and a scanning signal in the scanning line are valid at the same time, set a gate potential of the driving transistor to be equal to an initial level through the driving control module. 
     The light-emitting control module is configured to, when the light-emitting control signal is valid, control the first signal line to receive a first level and enable the second signal line to receive a second level. 
     The driving control module is configured to, when the scanning signal is valid, control to write a data voltage from the data line into the driving transistor; when the light-emitting control signal is valid, control the driving transistor to drive the light-emitting component to emit light and compensate for a threshold of the driving transistor. 
     Optionally, the driving control module includes a data writing transistor, a driving control transistor and a storage capacitor. 
     The data writing transistor has a gate electrode coupled with the scanning line, a first electrode coupled with the data line, and a second electrode coupled with the first electrode of the driving transistor. 
     The driving control transistor has a gate electrode coupled with the scanning line, a first electrode coupled with the gate electrode of the driving transistor, and a second electrode coupled with the second electrode of the driving transistor. 
     The storage capacitor has a first terminal coupled with the first electrode of the driving transistor, and a second terminal coupled with the gate electrode of the driving transistor. 
     Optionally, the initialization module includes an initialization transistor. The initialization transistor has a gate electrode for receiving the initial control signal, a first electrode coupled with the first signal line, and a second electrode for receiving the initial level. 
     Optionally, the light-emitting control module includes: 
     a first light-emitting control transistor having a gate electrode for receiving the light-emitting control signal, a first electrode for receiving the first level, and a second electrode coupled with the first signal line; 
     a second light-emitting control transistor having a gate electrode for receiving the light-emitting control signal, a first electrode coupled with the second signal line, and a second electrode for receiving the second level. 
     Specifically, connections between one subpixel unit and one row sharing unit are taken as an example for illustration in the following. 
     As shown in  FIG. 2 , the subpixel unit includes a subpixel driving circuit and an organic light-emitting diode (OLED). The subpixel driving circuit includes a driving transistor DTFT coupled with the OLED, and a driving control module  21  which is coupled with a data line Data, a gate electrode of the driving transistor DTFT, a first electrode of the driving transistor DTFT and a second electrode of the driving transistor DTFT, respectively. 
     The first electrode of the driving transistor DTFT is coupled with an anode electrode of the OLED; the second electrode of the driving transistor DTFT is coupled with a first signal line V 1 . 
     A cathode electrode of the OLED is coupled with a second signal line V 2 . 
     The driving control module  21  further receives a scanning signal Vscan from a scanning line. 
     The row sharing unit includes an initialization module  22  for receiving an initial control signal CN, and a light-emitting control module  23  for receiving a light-emitting control signal EM. 
     The initialization module  22  is coupled with the first signal line V 1 , and is configured to, when the initial control signal CN and the scanning signal Vscan in the scanning line are valid at the same time, set a gate potential of the driving transistor DTFT to be equal to an initial level VINI through the driving control module  21 . 
     The light-emitting control module  23  is configured to, when the light-emitting control signal EM is valid, control the first signal V 1  to receive a high level VDD and enable the second signal line V 2  to receive a low level VSS. That is, the first level is the high level VDD, and the second level is the low level VSS. 
     The driving control module  21  is configured to, when the scanning signal Vscan is valid, control to write a data voltage Vdata from the data line into the driving transistor DTFT; and when the light-emitting control signal EM is valid, control the driving transistor DTFT to drive the OLED to emit light and compensate for the threshold of the driving transistor DTFT. 
     Specifically, as shown in  FIG. 3 , the driving control module may include a data writing transistor TI, a driving control transistor TC and a storage capacitor Cs. 
     The data writing transistor TI has a gate electrode for receiving the scanning signal Vscan, a first electrode for receiving the data voltage Vdata from the data line, and a second electrode coupled with the first electrode of the driving transistor DTFT. 
     The driving control transistor TC has a gate electrode for receiving the scanning signal Vscan, a first electrode coupled with the gate electrode of the driving transistor DTFT, and a second electrode coupled with the second electrode of the driving transistor DTFT. 
     The storage capacitor Cs has a first terminal coupled with the first electrode of the driving transistor DTFT, and a second terminal coupled with the gate electrode of the driving transistor DTFT. 
     The initialization module includes an initialization transistor TINI. The initialization transistor TINI has a gate electrode for receiving the initial control signal CN, a first electrode coupled with the first signal line V 1 , and a second electrode for receiving the initial level  VINI.    
     The light-emitting control module includes: 
     a first light-emitting control transistor TEC 1  having a gate electrode for receiving the light-emitting control signal EM, a first electrode for receiving the high level VDD, and a second electrode coupled with the first signal line V 1 ; 
     a second light-emitting control transistor TEC 2  having a gate electrode for receiving the light-emitting control signal EM, a first electrode coupled with the second signal line V 2 , and a second electrode for receiving the low level VSS. 
     Each of DTFT, TI, TC, TINT, TEC 1  and TEC 2  is an n-type TFT. 
     In the embodiment shown in  FIG. 3 , the subpixel unit including DTFT, TI, TC, Cs and OLED is arranged in an effective display area; the row sharing unit including TEC 1 , TEC 2  and TINT is arranged outside the effective display area. In each identical row pixel unit, the plurality of subpixel units are coupled with the row sharing unit, thereby having a threshold compensation function. 
     In actual implementation, it is not limited to the above embodiments, it is merely required to adopt the row sharing units to achieve the purpose of reducing the TFTs in the effective display area, thereby reducing size of pixels. 
     An operation timing sequence of the embodiment shown in  FIG. 3  is shown in  FIG. 4  (in which, Vdata is a data voltage, and represents information of images, and is relative to an image to be displayed; when the image is uncertain, data is then uncertain; thus, an output level of Vdata is illustrated by grip-like fill), and may be divided into three stages. 
     Stage A (initialization stage): Vscan and CN are at high levels, EM is at a low level, TI, TC and TIN 1  are turned on, TEC 1  and TEC 2  are turned off, Vdata is written in through TI, a voltage at V 1  is VINI, a voltage at V 2  is a floating voltage, a drain electrode (second electrode) of DTFT is coupled with the gate electrode of DTFT, a gate potential of DTFT is equal to an initial level VINI, and a potential of a source electrode (first electrode) of DTFT is Vdata. 
     Stage B (compensation stage): Vscan is at a high level, CN and EM are at low levels, TI and TC are turned on, TINI, TEC 1  and TEC 2  are turned off, the drain electrode (second electrode) of DTFT is coupled with the gate electrode of DTFT, the source electrode (first electrode) of DTFT receives Vdata, a diode connection is formed on DTFT, the gate potential of DTFT is discharged from the initial level VINI to Vdata+Vth (Vth is the threshold of DTFT), i.e., a potential of a second terminal of Cs is Vdata+Vth; at this time, the voltage at V 1  is Vdata+Vth, the voltage at V 2  is a floating voltage. 
     Stage C (light-emitting stage): Vscan and CN are at low levels, EM is at a high level, i.e., TI, TC and TINI are turned off, TEC 1  and TEC 2  are turned on, the voltage at V 1  is changed to be at a high level VDD, the voltage at V 2  is changed from the floating voltage to be at a low level VSS, the gate potential of DTFT is maintained by the storage capacitor Cs to be Vdata+Vth (at this time, since the second terminal of Cs is floated, thus a discharge path of Cs is shut off; therefore, the potential at the second terminal of Cs, i.e., the gate potential of DTFT is maintained by Cs); at this time, the potential at the source electrode (first electrode) of DTFT is VSS, thus a drain current flowing though DTFT I DS =K×(Vdata+Vth−VSS−Vth) 2 =K×(Vdata−VSS) 2 , where K is a constant related to process and design, then, finally, a current for driving OLED is unrelated to the threshold voltage of DTFT, and only related to Vdata. 
       FIG. 5  is a circuit diagram of the pixel circuit which adopts the subpixel unit and the row sharing unit shown in  FIG. 3 . As can be seen from  FIG. 5 , each row pixel unit shares the row sharing unit on the left side. M row sharing units form a row sharing circuit. For the row sharing unit for a first row pixel circuit, an initial control signal is CN_ 1 , a scanning signal is Vscan_ 1 , and a light-emitting control signal is EM_ 1 ; for the row sharing unit for a j-th row pixel circuit, an initial control signal is CN_j, a scanning signal is Vscan_j, and a light-emitting control signal is EM_j; for the row sharing unit for a (j+1)-th row pixel circuit, an initial control signal is CN_j+1, a scanning signal is Vscan_j+1, and a light-emitting control signal is EM_j+1; for the row sharing unit for an m-th row pixel circuit, an initial control signal is CN_m, a scanning signal is Vscan_m, and a light-emitting control signal is EM_m; j is a positive integer which is less than or equal to m. 
     The present disclosure further provides a pixel circuit driving method, applied to the above pixel circuit, the pixel circuit driving method includes: 
     a initialization step: in the initialization stage, an initial control signal and a scanning signal in a scanning line are valid at the same time, a driving control transistor is turned on, a data voltage Vdata is written into a first electrode of a driving transistor, an initialization module sets a gate potential of the driving transistor to be equal to an initial level VINI through the driving control transistor; 
     a compensation step: in the compensation stage, the scanning signal is valid, a data writing transistor and the driving control transistor are turned on, data voltage is written into the first electrode of the driving transistor, the gate potential of the driving transistor is discharged through a storage capacitor to Vdata+Vth, so as to compensate for a threshold voltage of the driving transistor, where Vth represents the threshold voltage of the driving transistor; and 
     a light-emitting step: in the light-emitting stage, a light-emitting control signal is valid, a first signal line receives a first level, a second signal line receives a second level, the driving control transistor is turned off to control a second terminal of the storage capacitor to be floated, so as to maintain the gate potential of the driving transistor unchanged, the driving transistor is turned on to drive the light-emitting component to emit light. 
     A display device according to one embodiment of the present disclosure includes the above pixel circuit. The display device may include a liquid crystal display device, such as a liquid crystal panel, a liquid crystal TV, a mobile phone, a liquid crystal monitor. In addition to the liquid crystal display device, the display device may also include an organic light-emitting display or other kinds of display devices, such as e-readers. 
     The above descriptions are merely intended to illustrate but not limit the present disclosure. It should be appreciated that, a person skilled in the art may make further modifications, variations or equivalent arrangements without departing from the spirit and scope defined by appended claims. Therefore, all the modifications, variations or equivalent arrangements may fall within the scope of the present disclosure.