Organic light emitting diode pixel compensation circuit, and display panel and display device containing the same

This application claims the benefit of priority to Chinese Patent Application No. 201410283835.2, filed with the Chinese Patent Office on Jun. 23, 2014 and entitled “ORGANIC LIGHT EMITTING DIODE PIXEL COMPENSATION CIRCUIT, AND DISPLAY PANEL DEVICE CONTAINING THE SAME”, the content of which is incorporated herein by reference in its entirety.

At present, as shown in FIG. 1 , an organic light emitting diode (OLED) pixel driving circuit generally contains a transistor T 11 , a transistor T 12 , a storage capacitor C 11 and various drive signals for driving the OLED. A specific circuit connection is shown in FIG. 1 . A working process of the pixel driving circuit comprises stages as follows.

In the signal write-in stage, in the case that a scan signal Scan is at high-level, the transistor T 12 is switched on, a data signal Data is input to a gate electrode of the transistor T 11 through the transistor T 12 , hence the transistor T 11 is switched on and a capacitor C 11 is charged.

In the light emitting stage, the scan signal Scan is made to be at low-level, the transistor T 12 is switched off, the capacitor C 11 is discharged to enable the transistor T 11 to be still on. A power supply voltage PVDD keep providing the OLED with a voltage until a next stage arrives. The above cycle is then repeated.

However, due to a limitation of a process level, during a process of manufacturing a transistor circuit of an OLED display, a drive current of the OLED display often deviates and a panel often displays abnormally due to a threshold voltage existed in a driving transistor.

In view of the above, the present disclosure provides an organic light emitting diode (OLED) pixel compensation circuit, and a display panel and a display device which contain the circuit.

An OLED pixel compensation circuit according to an embodiment of the present disclosure is for driving the OLED to emit light. The OLED pixel compensation circuit comprises a first transistor, a second transistor, a third transistor, a fourth transistor, a fifth transistor, a sixth transistor, a seventh transistor and a storage capacitor. Specifically, a gate electrode of the first transistor is coupled to a scan signal, a first electrode of the first transistor is coupled to a data signal, and a second electrode of the first transistor is coupled to a gate electrode of the fifth transistor. A gate electrode of the second transistor is coupled to the scan signal, a first electrode of the second transistor is coupled to a power supply voltage, and a second electrode of the second transistor is coupled to a second electrode of the storage capacitor. A gate electrode of the third transistor is coupled to a first light emitting signal, a first electrode of the third transistor is coupled to the power supply voltage, and a second electrode of the third transistor is coupled to a first electrode of the fifth transistor. A gate electrode of the fourth transistor is coupled to the scan signal, a first electrode of the fourth transistor is coupled to the gate electrode of the fifth transistor, and a second electrode of the fourth transistor is coupled to the first electrode of the fifth transistor. A second electrode of the fifth transistor is coupled to a first electrode of the seventh transistor. A gate electrode of the sixth transistor is coupled to the first light emitting signal, a first electrode of the sixth transistor is coupled to the gate electrode of the fifth transistor, and a second electrode of the sixth transistor is coupled to the second electrode of the storage capacitor. A gate electrode of the seventh transistor is coupled to a second light emitting signal, and a second electrode of the seventh transistor is coupled to a first electrode of the OLED. A first electrode of the storage capacitor is coupled to the first electrode of the seventh transistor. And a second electrode of the OLED is coupled to a low-level signal, and the OLED emits light in response to a drive current generated by the fifth transistor.

A display panel according to an embodiment of the present disclosure contains the above OLED pixel compensation circuit.

A display device according to an embodiment of the present disclosure contains the above OLED pixel compensation circuit or the above display panel.

FIG. 1 is an OLED pixel driving circuit in the prior art;

FIG. 2 a is an OLED pixel compensation circuit according to an embodiment of the present disclosure;

FIG. 2 b is a timing diagram of an operation of the circuit shown in FIG. 2 a;

FIG. 3 a is an OLED pixel compensation circuit according to an embodiment of the present disclosure;

FIG. 3 b is a timing diagram of an operation of the circuit shown in FIG. 3 a;

FIG. 4 a is an OLED pixel compensation circuit according to an embodiment of the present disclosure;

FIG. 4 b is a timing diagram of an operation of the circuit shown in FIG. 4 a;

FIG. 5 a is an OLED pixel compensation circuit according to an embodiment of the present disclosure; and

FIG. 5 b is a timing diagram of an operation of the circuit shown in FIG. 5 a.

To make the above object, features and advantages of the present disclosure more obvious and easy to be understood, in the following, particular embodiments of the present disclosure will be illustrated in detail in conjunction with the drawings.

More specific details will be set forth in the following descriptions for sufficient understanding of the disclosure, however the disclosure can also be implemented by other ways different from the way described herein, and therefore the disclosure is not limited to particular embodiments disclosed hereinafter.

Reference is made to FIGS. 2 a and 2 b . FIG. 2 a is an OLED pixel compensation circuit according to an embodiment of the present disclosure, which is for driving the OLED to emit light. The OLED pixel compensation circuit comprises a first transistor T 1 , a second transistor T 2 , a third transistor T 3 , a fourth transistor T 4 , a fifth transistor T 5 , a sixth transistor T 6 , a seventh transistor T 7 and a storage capacitor Cst. A gate electrode of the first transistor T 1 is coupled to a scan signal Scan, a first electrode of the first transistor T 1 is coupled to a data signal Data, and a second electrode of the first transistor T 1 is coupled to a gate electrode of the fifth transistor T 5 at a node N 1 . A gate electrode of the second transistor T 2 is coupled to the scan signal Scan, a first electrode of the second transistor T 2 is coupled to a power supply voltage PVDD, and a second electrode of the second transistor T 2 is coupled to a second electrode of the storage capacitor Cst at a node N 2 . A gate electrode of the third transistor T 3 is coupled to a first light emitting signal Emit 1 , a first electrode of the third transistor T 3 is coupled to the power supply voltage PVDD and a second electrode of the third transistor T 3 is coupled to a first electrode of the fifth transistor T 5 . A gate electrode of the fourth transistor T 4 is coupled to the scan signal Scan, a first electrode of the fourth transistor T 4 is coupled to the gate electrode of the fifth transistor T 5 at node N 1 , and a second electrode of the fourth transistor T 4 is coupled to the first electrode of the fifth transistor T 5 . A second electrode of the fifth transistor T 5 is coupled to a first electrode of the seventh transistor T 7 . A gate electrode of the sixth transistor T 6 is coupled to the first light emitting signal Emit 1 , a first electrode of the sixth transistor T 6 is coupled to the gate electrode of the fifth transistor T 5 and a second electrode of the sixth transistor T 6 is coupled to the second electrode of the storage capacitor Cst at node N 2 . A gate electrode of the seventh transistor T 7 is coupled to a second light emitting signal Emit 2 and a second electrode of the seventh transistor T 7 is coupled to a first electrode of the OLED. A first electrode of the storage capacitor Cst is coupled to the first electrode of the seventh electrode T 7 at a node N 3 . And a second electrode of the OLED is coupled to a low-level signal VSS and the OLED emits light in response to a drive current generated by the fifth transistor T 5 .

Optionally, the first electrode of the OLED may be an anode of the OLED. The second electrode of the OLED may be a cathode of the OLED. And the “coupling” herein may be a direct connection or an indirect connection.

Specifically, the first transistor T 1 is for transferring the data signal Data to the gate electrode of the fifth transistor T 5 under the control of the scan signal Scan. The second transistor T 2 is for transferring the power supply voltage PVDD to the second electrode of the storage capacitor Cst under the control of the scan signal Scan. The third transistor T 3 is for transferring the power supply voltage PVDD received by the first electrode of the third transistor T 3 to the second electrode of the third transistor T 3 , under the control of the first light emitting signal Emit 1 . The fourth transistor T 4 is for transferring the data signal Data received by the first electrode of the fourth transistor T 4 to the first electrode of the fifth transistor T 5 , under the control of the scan signal Scan. The fifth transistor T 5 is for generating the drive current for driving the OLED to emit light. The sixth transistor T 6 is for switching on the first and second electrodes of the sixth transistor T 6 under the control of the first light emitting signal Emit 1 . The seventh transistor T 7 is for making the drive current generated by the fifth transistor T 5 drive the OLED to emit light. And the storage capacitor Cst is for storing a received voltage (a voltage received by the first electrode of the storage capacitor or a voltage received by the second electrode of the storage capacitor), and couple a change value of voltage on the second electrode of the storage capacitor to the first electrode of the storage capacitor or couple a change value of voltage on the first electrode of the storage capacitor to the second electrode of the storage capacitor.

In the following, a specific working process and a working principle are described. Referring to FIGS. 2 a and 2 b , all transistors in the OLED pixel compensation circuit are N-type Metal Oxide Semiconductor (NMOS) transistors. Therefore, the first electrode of the transistors may be a drain electrode and the second electrode of the transistors may be a source electrode. Driving the OLED pixel compensation circuit may comprise a first stage, a second stage and a third stage. And the first stage is a reset stage of the circuit, for initializing the circuit.

Specifically, in the first stage (denoted “I” in FIG. 2 b ), since Emit 1 is output (also referred to as “supplied” or “provided”) as a low-level signal, the third transistor T 3 and sixth transistor T 6 are switched off. Since the scan signal Scan is output as a high-level signal, the first transistor T 1 , the second transistor T 2 and the fourth transistor T 4 are switched on, and the data signal Data may be written into node N 1 (the node N 1 is an intersection node of the second electrode of the first transistor T 1 , the first electrode of the fourth transistor T 4 , the gate electrode of the fifth transistor T 5 and the first electrode of the sixth transistor T 6 ), that is, VN 1 =Vdata (a voltage of the data signal Data). In this case, since the data signal Data is a high-level signal, the fifth transistor T 5 is switched on under the control of a high-potential (high-level) Vdata. Additionally, since the second light emitting signal Emit 2 is also output as a high-level signal, the seventh transistor T 7 is switched on, the OLED is lighted for a while and a potential of node N 3 is VSS+Vo, with Vo being a voltage drop across the OLED.

The second stage (denoted “II” in FIG. 2 b ) is a threshold compensation stage of a driving transistor (the fifth transistor T 5 in the present embodiment) in the circuit, for capturing a threshold voltage Vth of the fifth transistor. Specifically, in the second stage, the first light emitting signal Emit 1 and the second light emitting signal Emit 2 are output as low-level signals, therefore, the third transistor T 3 , the sixth transistor T 6 and the seventh transistor T 7 are switched off. Since the scan signal Scan is output as a high-level signal, the first transistor T 1 , the second transistor T 2 , the fourth transistor T 4 are switched on, the data signal is written into the node N 1 , that is, VN 1 =Vdata, and a voltage of node N 2 (the node N 2 is an intersection node of the second electrode of the second transistor T 2 , the second electrode of the sixth electrode T 6 and the second electrode of the storage capacitor Cst) is the power supply voltage PVDD. In the second stage, the data signal Data is a high-level signal, thus the fifth transistor T 5 is switched on under the control of the high-potential (high-level) Vdata, and the data signal Data charges the storage capacitor Cst through the first electrode of the storage capacitor Cst. The charging process continues until a potential of node N 3 (the node N 3 is an intersection node of the second electrode of the fifth transistor T 5 , the first electrode of the seventh transistor T 7 and the first electrode of the storage capacitor Cst) is Vdata−Vth and thus a condition for switching on the fifth transistor T 5 (Vg−Vs is larger than Vth, with Vg being a gate voltage of the fifth transistor T 5 , Vs being a voltage of the second electrode of the fifth transistor T 5 , and Vth being a threshold voltage of the fifth transistor T 5 ) is no longer met, hence the fifth transistor T 5 is switched off, and the stage II is ended. In this case, a difference between voltages on two ends of the storage capacitor Cst is PVDD−Vdata+Vth.

The third stage (denoted “III” in FIG. 2 b ) is a light emitting stage of the circuit, for driving the OLED to emit light. Specifically, in the third stage, the scan signal Scan is output as a low-level signal, hence the first transistor T 1 , the second transistor T 2 and the fourth transistor T 4 are switched off. Since the first light emitting signal Emit 1 and the second light emitting signal Emit 2 are output as high-level signals, the third transistor T 3 , the sixth transistor T 6 and the seventh transistor T 7 are switched on, the two ends of the storage capacitor Cst are connected between the gate electrode and the second electrode of the fifth transistor T 5 to maintain a sufficient voltage difference for a gate-source voltage Vgs (i.e. a voltage across the gate electrode of the fifth transistor T 5 and the second electrode of the fifth transistor T 5 ) of the fifth transistor T 5 (as a driving transistor), to enable the fifth transistor T 5 to be in a switched-on state. In this case, the fifth transistor T 5 is switched on since charges stored in the storage capacitor Cst are constant due to charge conservation. With the drive current of the OLED becoming stable, a voltage of the node N 3 will become Voled (Voled is a voltage drop across the OLED and here it is assumed that the low-level signal VSS is 0). In this case, since a bootstrap function of the storage capacitor Cst, i.e. there is a constant voltage difference between the two ends of the storage capacitor Cst, the voltages of the node N 1 and N 2 on the other end of the storage capacitor Cst may be changed to PVDD−Vdata+Vth+Voled. Thus, based on a formula for the drive current generated by the OLED, the drive current Ioled, which passes through the fifth transistor T 5 and is for driving the OLEd to emit light, is directly proportional to a square of a difference value between the gate-source voltage (a voltage across the gate electrode and the second electrode) of the fifth transistor T 5 and the threshold voltage of the fifth transistor T 5 , that is, Ioled∝(Vgs−Vth) 2 =(Vg−Vs−Vth) 2 =((PVDD−Vdata+Vth+Voled)−Voled−Vth) 2 =(PVDD−Vdata) 2 . Therefore, the drive current of the OLED, Ioled, is independent of the threshold voltage Vth of the driving transistor T 5 , hence the threshold voltage of the driving transistor (the fifth transistor T 5 herein) is compensated.

It can be seen that, with the OLED pixel compensation circuit according to the present embodiment, an influence of the threshold voltage of the driving transistor (the fifth transistor T 5 ) on the generated driving current may be counteracted and the threshold voltage of the driving transistor is compensated. Thereby the driving current generated by the driving transistor does not deviate, and an OLED panel tends to display normally.

Referring to FIGS. 3 a and 3 b , an embodiment is obtained based on the embodiment described above, as shown in FIG. 2 a and FIG. 2 b . A difference between the present embodiment and the above-described embodiment is that: in the present embodiment, a first transistor T 1 , a second transistor T 2 and a fourth transistor T 4 are P-type Metal Oxide Semiconductor (PMOS) transistors, and first electrodes of the PMOS transistors are source electrodes and second electrodes of the PMOS transistors are drain electrodes. Correspondingly, levels in the three stages in driving the OLED pixel, accordingly to vary as follows.

In the first stage I (reset stage), the scan signal Scan is a low-level signal, the first light emitting signal Emit 1 is a low-level signal, a second light emitting signal Emit 2 is a high-level signal and the data signal Data is a high-level signal.

In the second stage II (threshold compensation stage), the scan signal Scan is a low-level signal, the first light emitting signal Emit 1 is a low-level signal, the second light emitting signal Emit 2 is a low-level signal and the data signal Data is a high-level signal.

In the third stage III (light emitting stage), the scan signal Scan is a high-level signal, the first light emitting signal Emit 1 is a high-level signal, the second light emitting signal Emit 2 is a high-level signal. It should be noted that the data signal Data in this stage may be a high-level signal or a low-level signal.

A specific implementation process and a working principle in the present embodiment are similar to that in the embodiment as shown in FIGS. 2 a and 2 b , only because transistor types of the first transistor T 1 , the second transistor T 2 and the fourth transistor T 4 are changed from NMOS transistors into PMOS transistors, hence a level of a corresponding drive signal (the scan signal Scan) is also reversed. Since changes or effects of other signals or circuit structures are not involved, specific details of the working modes of the three stages may be understood by referring to the embodiment as shown in FIGS. 2 a and 2 b , and will not be described herein.

Referring to FIGS. 4 a and 4 b , an embodiment is obtained based on the embodiment described above, as shown in FIG. 2 a and FIG. 2 b . A difference between the present embodiment and the above-described embodiment is that: in the present embodiment, a third transistor T 3 , a sixth transistor T 6 are P-type Metal Oxide Semiconductor (PMOS) transistors, and first electrodes of these transistors are source electrodes and second electrodes of these transistors are drain electrodes. Correspondingly, levels in the three stages in driving the OLED pixel, accordingly to vary as follows.

In the first stage I (reset stage), the scan signal Scan is a high-level signal, the first light emitting signal Emit 1 is a high-level signal, the second light emitting signal Emit 2 is a high-level signal and the data signal Data is a high-level signal.

In the second stage II (threshold compensation stage), the scan signal Scan comprises a high-level signal, the first light emitting signal Emit 1 is a high-level signal, the second light emitting signal Emit 2 is a low-level signal and the data signal Data comprises a high-level signal.

In the third stage III (light emitting stage), the scan signal Scan is a low-level signal, the first light emitting signal Emit 1 is a low-level signal and the second light emitting signal Emit 2 is a high-level signal. It should be noted that, the data signal Data in this stage may be a high-level signal or a low-level signal.

A specific implementation process and a working principle in the present embodiment are similar to that in the embodiment as shown in FIGS. 2 a and 2 b , only because transistor types of the third transistor T 3 and the sixth transistor T 6 are changed from NMOS transistors into PMOS transistors, hence a level of a corresponding drive signal (the first light emitting signal Emit 1 ) is also reversed. Since changes or influences of other signals or circuit structures are not involved, specific details of the working modes of the three stages may be understood by referring to the embodiment as shown in FIGS. 2 a and 2 b , and will not be described herein for the sake of brevity.

Referring to FIGS. 5 a and 5 b , an embodiment is obtained based on the embodiment described above, as shown in FIG. 2 a and FIG. 2 b . A difference between the present embodiment and the above-described embodiment is that: in the present embodiment, a first transistor T 1 , a second transistor T 2 , a third transistor T 3 , a fourth transistor T 4 and a sixth transistor T 6 are PMOS transistors, and only a fifth transistor T 5 and a seventh transistor T 7 are NMOS transistors, and first electrodes of these PMOS transistors are source electrodes and second electrodes of these PMOS transistors are drain electrodes. Correspondingly, levels in the three stages in the driving the OLED pixel, accordingly to vary as follows.

In the first stage (reset stage), the scan signal Scan is a low-level signal, a first light emitting signal Emit 1 is a high-level signal, the second light emitting signal Emit 2 is a high-level signal and the data signal Data is a high-level signal.

In the second stage (threshold compensation stage), the scan signal Scan comprises a low-level signal, the first light emitting signal Emit 1 is a high-level signal, the second light emitting signal Emit 2 is a low-level signal and the data signal Data comprises a high-level signal.

In the third stage (light emitting stage), the scan signal is a high-level signal, the first light emitting signal Emit 1 is a low-level signal and the second light emitting signal Emit 2 is a high-level signal. It should be noted that, the data signal Data in this stage may be a high-level signal or a low-level signal.

A specific implementation process and a working principle in the present embodiment are similar to that in the embodiment as shown in FIGS. 2 a and 2 b , only because all transistor types of the first transistor T 1 , the second transistor T 2 , the third transistor T 3 , the fourth transistor T 4 and the sixth transistor T 6 are changed from NMOS transistors into PMOS transistors, hence a level of a corresponding drive signal (the scan signal Scan and the first light emitting signal Emit 1 ) is also reversed. Since changes or influences of other signals or circuit structures are not involved, specific details of the working modes of the three stages may be understood by referring to the embodiment as shown in FIGS. 2 a and 2 b , and will not be described herein.

The OLED pixel compensation circuit according to any one of the embodiments as shown in FIGS. 3 a and 3 b to the embodiment as shown in FIGS. 5 a and 5 b may counteract an influence of the threshold voltage of the driving transistor (the fifth transistor T 5 ) on the generated drive current and compensates the threshold voltage of the driving transistor. Thereby the drive current generated by the driving transistor does not deviate, and an OLED panel tends to display normally.

Furthermore, in all the above embodiments, the seventh transistor T 7 is described by taking a NMOS transistor as example. However, in the case that the level of the second light emitting signal Emit 2 is reversed, the seventh transistor T 7 may be also replaced with a PMOS transistor.

The present disclosure further provides a display panel including the OLED pixel compensation circuit according to any one of the above embodiments.

The present disclosure further provides a display device including the OLED pixel compensation circuit according to any one of the above embodiments, or including the above display panel.

The display panel or display device is capable of counteracting the influence of the threshold voltage of the driving transistor (the fifth transistor T 5 ) on the generated drive current and compensates the threshold voltage of the driving transistor, since it comprises the OLED pixel compensation circuit according to the above embodiments. So that the drive current generated by the driving transistor does not deviate and the OLED panel tends to display normally.

It should be noted that, the above embodiments may make reference to each other, and may be used in combination. Though the present disclosure is disclosed by way of preferred embodiments as described above, those embodiments are not intended to limit the present disclosure. By using the methods and the technical aspects disclosed above, possible variations and changes may be made to the technical scheme of the present disclosure by those skilled in the art without departing from the essential scope of the present disclosure. Therefore, any simple change, equivalent alternation and modification made to the above embodiments according to the technical principle of the present disclosure, which do not depart from the matters of the technical scheme of the present disclosure, all fall within the scope of protection of the technical scheme of the present disclosure.