Pixel compensation circuit, scanning driving circuit and display device

The disclosure relates to a display technical field, and more particularly to a pixel compensation circuit, a scanning driving circuit and a display device.

OLED display devices have been developed rapidly in recent years due to superior properties such as wide color gamut, the high contrast ratio and so on, which are more and more competitive in the display realm. The conventional OLED display devices basically adopt the active driving manner. As the organic light-emitting diode is a current device, precise control of the current has been a critical consideration.

The conventional pixel compensation circuit consists of two thin film transistors and a memory capacitor, as shown in FIG. 1 . The pixel compensation circuit includes a controllable switch T 1 , a driving switch T 2 and a memory capacitor C 1 . The driving current of the organic light-emitting diode D 1 is controlled by the driving switch T 2 , the current thereof is I OLED =k(V gs −V th ) 2 , where k is a current amplification coefficient of the driving switch T 2 , which is determined by the inherent property of the driving switch T 2 , Vth is a threshold voltage of the driving switch T 2 . As the threshold voltage Vth of the driving switch T 2 can easily shift, the organic light-emitting diode D 1 drives the current to be changed, which leads to the brightness of the OLED display device to be uneven, further affecting image quality.

An embodiment of the disclosure provides a pixel compensation circuit, a scanning driving circuit and a display device to solve the problem of uneven brightness of the panel caused by the bias of the threshold voltage.

In order to solve the technical problem above, the disclosure provides a pixel compensation circuit, including a first controllable switch, a second controllable switch, a third controllable switch, a driving switch, an organic light-emitting diode, a fourth controllable switch, and a memory capacitor.

The first controllable switch includes a control terminal, a first terminal and a second terminal. The control terminal of the first controllable switch is connected with a scanning line. The first terminal of the first controllable switch is connected with a reference voltage terminal.

The second controllable switch includes a control terminal, a first terminal and a second terminal. The control terminal of the second controllable switch is connected with a light-emitting control terminal. The first terminal of the second controllable switch is connected with the second terminal of the first controllable switch.

The third controllable switch includes a control terminal, a first terminal and a second terminal. The control terminal of the third controllable switch is connected with the scanning line. The first terminal of the third controllable switch is connected with a data cable. The second terminal of the third controllable switch is connected with the second terminal of the second controllable switch.

The driving switch includes a control terminal, a first terminal and a second terminal. The control terminal of the driving switch is connected with the second terminal of the second controllable switch and the second terminal of the third controllable switch.

The organic light-emitting diode includes an anode and a cathode. The anode of the organic light-emitting diode is connected with the second terminal of the driving switch. The cathode of the organic light-emitting diode is connected with a ground.

The fourth controllable switch includes a control terminal, a first terminal and a second terminal. The control terminal of the fourth controllable switch is connected with the light-emitting control terminal. The first terminal of the fourth controllable switch is connected with a first voltage terminal. The second terminal of the fourth controllable switch is connected with the first terminal of the driving switch.

The memory capacitor includes a first terminal and a second terminal. The first terminal of the memory capacitor is connected with the second terminal of the first controllable switch and the first terminal of the second controllable switch. The second terminal of the memory capacitor is connected with the second terminal of the fourth controllable switch and the first terminal of the driving switch.

In order to solve the technical problem above, an embodiment of the disclosure provides a scanning driving circuit. The scanning driving circuit includes a pixel compensation circuit. The pixel compensation circuit includes a first controllable switch, a second controllable switch, a third controllable switch, a driving switch, an organic light-emitting diode, a fourth controllable switch, and a memory capacitor.

The first controllable switch includes a control terminal, a first terminal and a second terminal. The control terminal of the first controllable switch is connected with a scanning line. The first terminal of the first controllable switch is connected with a reference voltage terminal.

The second controllable switch includes a control terminal, a first terminal and a second terminal. The control terminal of the second controllable switch is connected with a light-emitting control terminal. The first terminal of the second controllable switch is connected with the second terminal of the first controllable switch.

The third controllable switch includes a control terminal, a first terminal and a second terminal. The control terminal of the third controllable switch is connected with the scanning line. The first terminal of the third controllable switch is connected with a data cable. The second terminal of the third controllable switch is connected with the second terminal of the second controllable switch.

The driving switch includes a control terminal, a first terminal and a second terminal. The control terminal of the driving switch is connected with the second terminal of the second controllable switch and the second terminal of the third controllable switch.

The organic light-emitting diode includes an anode and a cathode. The anode of the organic light-emitting diode is connected with the second terminal of the driving switch. The cathode of the organic light-emitting diode is connected with a ground.

The fourth controllable switch includes a control terminal, a first terminal and a second terminal. The control terminal of the fourth controllable switch is connected with the light-emitting control terminal. The first terminal of the fourth controllable switch is connected with a first voltage terminal. The second terminal of the fourth controllable switch is connected with the first terminal of the driving switch.

The memory capacitor includes a first terminal and a second terminal. The first terminal of the memory capacitor is connected with the second terminal of the first controllable switch and the first terminal of the second controllable switch. The second terminal of the memory capacitor is connected with the second terminal of the fourth controllable switch and the first terminal of the driving switch.

In order to solve the technical problem above, an embodiment of the disclosure provides a display device. The display device includes a scanning driving circuit. The scanning driving circuit includes a pixel compensation circuit. The pixel compensation circuit includes a first controllable switch, a second controllable switch, a third controllable switch, a driving switch, an organic light-emitting diode, a fourth controllable switch, and a memory capacitor.

The first controllable switch includes a control terminal, a first terminal and a second terminal. The control terminal of the first controllable switch is connected with a scanning line. The first terminal of the first controllable switch is connected with a reference voltage terminal.

The second controllable switch includes a control terminal, a first terminal and a second terminal. The control terminal of the second controllable switch is connected with a light-emitting control terminal. The first terminal of the second controllable switch is connected with the second terminal of the first controllable switch.

The third controllable switch includes a control terminal, a first terminal and a second terminal. The control terminal of the third controllable switch is connected with the scanning line. The first terminal of the third controllable switch is connected with a data cable. The second terminal of the third controllable switch is connected with the second terminal of the second controllable switch.

The driving switch includes a control terminal, a first terminal and a second terminal. The control terminal of the driving switch is connected with the second terminal of the second controllable switch and the second terminal of the third controllable switch.

The organic light-emitting diode includes an anode and a cathode. The anode of the organic light-emitting diode is connected with the second terminal of the driving switch. The cathode of the organic light-emitting diode is connected with a ground.

The fourth controllable switch includes a control terminal, a first terminal and a second terminal. The control terminal of the fourth controllable switch is connected with the light-emitting control terminal. The first terminal of the fourth controllable switch is connected with a first voltage terminal. The second terminal of the fourth controllable switch is connected with the first terminal of the driving switch.

The memory capacitor includes a first terminal and a second terminal. The first terminal of the memory capacitor is connected with the second terminal of the first controllable switch and the first terminal of the second controllable switch. The second terminal of the memory capacitor is connected with the second terminal of the fourth controllable switch and the first terminal of the driving switch.

Beneficial effects of the disclosure are distinguishing from the prior art, the pixel compensation circuit, the scanning driving circuit and the display device of the disclosure prevent the threshold voltage bias of the driving switch and the organic light-emitting diode to achieve the evenly displayed brightness of the panel.

FIG. 1 is a schematic circuit diagram of a conventional pixel compensation circuit.

FIG. 2 is a schematic circuit diagram of a pixel compensation circuit according to a first embodiment of the disclosure.

FIG. 3 is a schematic circuit diagram of a pixel compensation circuit according to a second embodiment of the disclosure.

FIG. 4 is a schematic view of a sequential waveform of FIG. 3 .

FIG. 5 is a schematic view of a simulation wave of FIG. 3 .

FIG. 6 is a structural schematic view of a scanning driving circuit of the disclosure.

FIG. 7 is a structural schematic view of a display device of the disclosure.

Referring to FIG. 2 , FIG. 2 is a schematic circuit diagram of a pixel compensation circuit according to a first embodiment of the disclosure. The pixel compensation circuit includes a first controllable switch T 1 , a second controllable switch T 2 , a third controllable switch T 3 , a driving switch T 0 , an organic light-emitting diode D 1 , a fourth controllable switch T 4 , and a memory capacitor C 1 . The first controllable switch T 1 includes a control terminal, a first terminal and a second terminal. The control terminal of the first controllable switch T 1 is connected with a scanning line Scan. The first terminal of the first controllable switch T 1 is connected with a reference voltage terminal Vref.

The second controllable switch T 2 includes a control terminal, a first terminal and a second terminal. The control terminal of the second controllable switch T 2 is connected with a light-emitting control terminal EM. The first terminal of the second controllable switch T 2 is connected with the second terminal of the first controllable switch T 1 .

The third controllable switch T 3 includes a control terminal, a first terminal and a second terminal. The control terminal of the third controllable switch T 3 is connected with the scanning line Scan. The first terminal of the third controllable switch T 3 is connected with a data cable Data. The second terminal of the third controllable switch T 3 is connected with the second terminal of the second controllable switch T 2 .

The driving switch T 0 includes a control terminal, a first terminal and a second terminal. The control terminal of the driving switch T 0 is connected with the second terminal of the second controllable switch T 2 and the second terminal of the third controllable switch T 3 .

The organic light-emitting diode D 1 includes an anode and a cathode. The anode of the organic light-emitting diode D 1 is connected with the second terminal of the driving switch T 0 . The cathode of the organic light-emitting diode D 1 is connected with a ground.

The fourth controllable switch T 4 includes a control terminal, a first terminal and a second terminal. The control terminal of the fourth controllable switch T 4 is connected with the light-emitting control terminal EM. The first terminal of the fourth controllable switch T 4 is connected with a first voltage terminal VDD. The second terminal of the fourth controllable switch T 4 is connected with the first terminal of the driving switch T 0 .

The memory capacitor C 1 includes a first terminal and a second terminal. The first terminal of the memory capacitor C 1 is connected with the second terminal of the first controllable switch T 1 and the first terminal of the second controllable switch T 2 . The second terminal of the memory capacitor C 1 is connected with the second terminal of the fourth controllable switch T 4 and the first terminal of the driving switch T 0 .

In the embodiment, the driving switch T 0 , the first controllable switch T 1 to the fourth controllable switch T 4 are PMOS thin-film transistors. The control terminals, the first terminals and the second terminals of the driving switch T 0 , the first controllable switch T 1 to the fourth controllable switch T 4 are respectively corresponding to a gate electrode, a drain electrode and a source electrode of the thin-film transistor. In other embodiments, the driving switch, the first controllable switch to the fourth controllable switch can also be other types of switches, which can achieve the objective of the disclosure.

In the embodiment, the operational principle of the pixel compensation circuit is as follows.

In the period t 1 , the light-emitting control terminal EM and the scanning line Scan both output low level signals. The first controllable switch T 1 to the fourth controllable switch T 4 are all turned on. The data cable Data outputs the low level. The point C is the low electric potential at the moment. As the fourth controllable switch T 4 is turned on, the point A is the high electric potential output from the first voltage terminal VDD.

After the period t 1 , the point C is still the low electric potential, and the point A is still the high electric potential. At the moment the driving switch T 0 is turned on. In the period t 2 , the light-emitting control terminal EM outputs the high level signal. The second controllable switch T 2 and the fourth controllable switch T 4 both are turned off. The scanning line Scan outputs the low level signal. The first controllable switch T 1 and the third controllable switch T 3 are both turned on. The point B is the high level output from the reference voltage terminal Vref. The point C is the low level output from the data cable Data. The driving switch T 0 is turned on. The point A discharges through the driving switch T 0 and the organic light-emitting diode D 1 . The electric potential at the point A finally is VData−Vth(Vth<0), where Vth is the threshold voltage.

After the period t 2 , the compensation of the threshold voltage Vth of the driving switch T 0 is completed.

Finally, after the light-emitting control terminal EM outputs the low level signal, the electric potential at the point B and that at the point C are the same. The electric potential at the point A is turned from the original VData−Vth to the output voltage of the first voltage terminal VDD simultaneously. The voltage Vgs between the gate electrode and the source electrode of the driving switch T 0 is (Vref−VData+Vth)+VDD. The current in the saturation region is directly proportional to the square of (Vref−VData), which can eliminate the deviation of the threshold voltage Vth to generate the even current, and the brightness of the panel is evenly displayed.

Referring to FIG. 3 , FIG. 3 is a schematic circuit diagram of a pixel compensation circuit according to a second embodiment of the disclosure. The difference of the second embodiment of the pixel compensation circuit and the first embodiment is the pixel compensation further includes a fifth controllable switch T 5 . The fifth controllable switch T 5 includes a control terminal, a first terminal and a second terminal. The control terminal of the fifth controllable switch T 5 is connected with a reset signal terminal Reset. The first terminal of the fifth controllable switch T 5 is connected with the second terminal of the driving switch T 0 and the anode of the organic light-emitting diode D 1 . The second terminal of the fifth controllable switch T 5 is connected with a second voltage terminal Vi.

In the embodiment, the driving switch T 0 , the first controllable switch T 1 to the fifth controllable switch T 5 are PMOS thin-film transistors. The control terminals, the first terminals and the second terminals of the driving switch T 0 , the first controllable switch T 1 to the fifth controllable switch T 5 are respectively corresponding to a gate electrode, a drain electrode and a source electrode of the thin-film transistor. The driving switch, the first controllable switch to the fifth controllable switch can also be other types of switches, which can achieve the objective of the disclosure.

The operational principle of the pixel compensation circuit can be obtained according to the schematic circuit diagram of the pixel compensation circuit of FIG. 3 and the schematic view of the sequential waveform of the pixel compensation circuit shown in FIG. 4 as follows.

In the period t 1 , the light-emitting control terminal EM and the scanning line Scan both output low level signals. The first controllable switch T 1 to the fourth controllable switch T 4 are all turned on. The data cable Data outputs the low level. The point C is the low electric potential at the moment. As the fourth controllable switch T 4 is turned on, the point A is the high electric potential output from the first voltage terminal VDD.

After the period t 1 , the point C is still the low electric potential, and the point A is still the high electric potential. At the moment the driving switch T 0 is turned on. In the period t 2 , the light-emitting control terminal EM outputs the high level signal. The second controllable switch T 2 and the fourth controllable switch T 4 both are turned off. The scanning line Scan outputs the low level signal. The first controllable switch T 1 and the third controllable switch T 3 are both turned on. The point B is the high level output from the reference voltage terminal Vref. The point C is the low level output from the data cable Data. The driving switch T 0 is turned on. The reset signal terminal Reset outputs the low level signal. The fifth controllable switch T 5 is turned on. The point A leaks electricity to the second voltage terminal Vi through the driving switch T 0 and the fifth controllable switch T 5 . The electric potential at the point A finally is VData−Vth(Vth<0), where Vth is the threshold voltage.

After the period t 2 , the compensation of the threshold voltage Vth of the driving switch T 0 is completed.

Finally, after the light-emitting control terminal EM outputs the low level signal, the electric potential at the point B and that at the point C are the same. The electric potential at the point A is turned from the original VData−Vth to the output voltage of the first voltage terminal VDD simultaneously. The voltage Vgs between the gate electrode and the source electrode of the driving switch T 0 is (Vref−VData+Vth)+VDD. The current in the saturation region is directly proportional to the square of (Vref−VData), which can eliminate the deviation of the threshold voltage Vth to generate the even current, and the brightness of the panel is evenly displayed.

Referring to FIG. 5 , FIG. 5 is a schematic view of a simulation wave of the pixel compensation circuit according to the second embodiment of the disclosure. It can be seen from FIG. 5 that the electric potential of the point A in the pixel compensation circuit shown in FIG. 3 has an obvious process of grabbing the threshold voltage.

Referring to FIG. 6 , FIG. 6 is a structural schematic view of a scanning driving circuit of the disclosure. The scanning driving circuit 2 includes any one of the pixel compensation circuits 1 , configured to reduce the deviation of the threshold voltage in the scanning driving circuit 2 to achieve the brightness evenness of the panel. Other elements and functions of the scanning driving circuit are identical to the elements and functions of the conventional scanning driving circuit, which will not be repeated.

Referring to FIG. 7 , FIG. 7 is a structural schematic view of a display device of the disclosure. The display device 3 can be an OLED, which includes any scanning driving circuit 2 and any pixel compensation circuit 1 described above. The scanning driving circuit 2 with the pixel compensation circuit is disposed adjacently to the display device 3 , such as two ends of the display device 3 . Other devices and functions in the display device are identical to the devices and functions of the conventional display device, which will not be repeated.

The pixel compensation circuit, the scanning driving circuit and the display device of the disclosure prevent the threshold voltage bias of the driving switch and the organic light-emitting diode to achieve the evenly displayed brightness of the panel.

The description above is merely embodiments of the disclosure, which cannot limit the protection scope of the disclosure. Any equivalent structure or process according to contents of the disclosure and the figures, or direct or indirect application in other related fields should be included in the protected scope of the disclosure.