Patent Application
20180336819
This application claims the priority of Chinese Patent Application No. 2017102961149, entitled “Pixel Driving Circuit, Display Panel and Pixel Driving Method”, filed on Apr. 28, 2017, the disclosure of which is incorporated herein by reference in its entirety.
The present invention relates to the field of display, and in particular to the field of pixel driving circuit, display panel and pixel driving method.
The current organic light-emitting diode (OLED) display has the advantages of small size, simple structure, active luminescence, high brightness, large viewing angle and short response time, and attracts a wide range of attention.
A conventional OLED display includes a transistor as a driving transistor for controlling the current through the OLED, so that the importance of the threshold voltage of the driving transistor is apparent. Any positive or negative drift of the threshold voltage will cause different currents flowing through the OLED under the same signal. At present, the transistor may experience threshold voltage drift during the use process because of, such as, lighting on oxide semiconductor, the voltage stress on the source and drain and other factors, which results in the current flowing through the OLED unstable, and thus causes the panel luminance not uniform.
The primary object of the present invention is to provide a pixel driving circuit, display panel and pixel driving method, to solve the problem of threshold voltage drift causing unstable current in OLED in the known technology, to achieve uniform luminance for display panel.
To solve the aforementioned issues, the present invention provides a pixel driving circuit, comprising:
a driving switch, connected between a driving power source and an organic light-emitting diode (OLED);
a first switch, connected between a source and a drain of the driving switch, and being a transistor of the same model as the driving switch;
a control circuit, connected between a drain and a source of the first switch, for inputting a first control signal and outputting a compensation current to compensate threshold voltage drift of the first switch;
a storage unit, connected between a source of a second switch and a gate of the first switch, for storing a compensation voltage of the compensation current provided to the first switch;
the second switch having a gate for inputting a second control signal and a drain for inputting a data signal, the storage unit being for storing a data voltage generated by the data signal;
the storage unit being for applying the compensation voltage and the data voltage to the driving switch.
According to an embodiment of the present invention, the control circuit comprises:
a compensation current output end, for outputting the compensation current;
a third switch, connected between the compensation current output end and the drain of the first switch, and having a gate for inputting the first control signal;
a fourth switch, connected between the compensation current output end and the source of the first switch, and having a gate for inputting the first control signal.
According to an embodiment of the present invention, the first switch, the second switch, the third switch, and the fourth switch are N-type thin film transistors (TFT).
According to an embodiment of the present invention, the first switch, the second switch, the third switch, and the fourth switch are P-type thin film transistors (TFT).
The present invention provides a display panel, comprising:
a pixel driving circuit; the pixel driving circuit comprising: a driving switch, connected between a driving power source and an organic light-emitting diode (OLED);
a first switch, connected between a source and a drain of the driving switch, and being a transistor of the same model as the driving switch;
a control circuit, connected between a drain and a source of the first switch, for inputting a first control signal and outputting a compensation current to compensate threshold voltage drift of the first switch;
a storage unit, connected between a source of a second switch and a gate of the first switch, for storing a compensation voltage of the compensation current provided to the first switch;
the second switch having a gate for inputting a second control signal and a drain for inputting a data signal, the storage unit being for storing a data voltage generated by the data signal;
the storage unit being for applying the compensation voltage and the data voltage to the driving switch.
According to an embodiment of the present invention, the control circuit comprises:
a compensation current output end, for outputting the compensation current;
a third switch, connected between the compensation current output end and the drain of the first switch, and having a gate for inputting the first control signal;
a fourth switch, connected between the compensation current output end and the gate of the first switch, and having a gate for inputting the first control signal.
According to an embodiment of the present invention, the first switch, the second switch, the third switch, and the fourth switch are N-type thin film transistors (TFT).
According to an embodiment of the present invention, the first switch, the second switch, the third switch, and the fourth switch are P-type thin film transistors (TFT).
The present invention also provides a pixel driving method, providing a pixel driving circuit, the pixel driving circuit comprising: a driving power source, an organic light-emitting diode (OLED), a driving switch, a first switch, a second switch, a storage unit and a control circuit; the driving switch being connected between the driving power source and the OLED; the first switch being connected between a source and a drain of the driving switch, and being a transistor of the same model as the driving switch; the control circuit being connected between a drain and a source of the first switch; the storage unit being connected between a source of the second switch and a gate of the first switch; the method comprising:
in a first time period, loading in a first control signal and a second control signal, conducting the second switch and the control circuit, the control circuit loading in a compensation current to compensate threshold voltage drift of the first switch, and storing a compensation voltage in the storage unit;
in a second time period, loading in the first control signal and the second control signal, conducting the second switch and cutting off the control circuit, outputting a data signal to the storage unit, and the storage unit storing a data voltage generated by the data signal;
in the third time period, loading in the first control signal and the second control signal, cutting off the second switch and the control circuit, the storage unit applying the compensation voltage and the data voltage to a gate of the driving switch, the driving power source driving the OLED to emit light.
According to an embodiment of the present invention, the control circuit comprises: a compensation current output end, for outputting the compensation current; a third switch, connected between the compensation current output end and the drain of the first switch, and having a gate for inputting the first control signal; a fourth switch, connected between the compensation current output end and the gate of the first switch, and having a gate for inputting the first control signal.
According to an embodiment of the present invention, the first switch, the second switch, the third switch, and the fourth switch are N-type thin film transistors (TFT).
According to an embodiment of the present invention, the first switch, the second switch, the third switch, and the fourth switch are P-type thin film transistors (TFT).
According to an embodiment of the present invention, a transitional time period is provided between the first time period and the second time period, and between the second time period and the third time period, for reserving time to propagate the first control signal, the second control signal, and the data signal.
The advantage of the present invention is as follows: in the first time period, the compensation current compensates the threshold voltage drift of the first switch and stored in the storage unit in a form of compensation voltage; the storage unit stores the data voltage in the second time period and releases the compensation voltage and the data voltage in the third time period to control the driving voltage to drive the OLED to emit light; the source of the first switch is connected to the source of the driving switch, the gate of the first switch is connected to the gate of the driving switch, and the first switch and the driving switch are the same model of transistors, thus having the same threshold voltage drift; i.e., compensating the first switch is to compensate the driving switch. The compensation current and data signal are independently applied to the pixel driving circuit. Without affecting the data signal, the threshold voltage drift of the driving switch is compensated and the current through the OLED is stable, leading to uniform luminance of the display panel.
To make the technical solution of the embodiments according to the present invention, a brief description of the drawings that are necessary for the illustration of the embodiments will be given as follows. Apparently, the drawings described below show only example embodiments of the present invention and for those having ordinary skills in the art, other drawings may be easily obtained from these drawings without paying any creative effort.
To further explain the technical means and effect of the present invention, the following refers to embodiments and drawings for detailed description. Apparently, the described embodiments are merely some embodiments of the present invention, instead of all embodiments. All other embodiments based on embodiments in the present invention and obtained by those skilled in the art without departing from the creative work of the present invention are within the scope of the present invention.
The pixel driving circuit of the present invention is applicable to OLED display, for providing stable current to the OLED to drive the OLED to emit light with uniform luminance. The OLED has the advantages of energy-saving, fast response, light weight, thinness, simple structure, and low cost, and is widely used in display devices.
Refer to
I
ds
=K(Vgs−Vth)2 (1)
Wherein, K=μCoxW/(2L), and μ is the carrier migration rate of the driving switch 40, W and L are the width and length of the driving switch 40 respectively.
The current Ids flowing through the driving switch 40 to drive the OLED 10 depends on the voltage difference Vgs between the gate and the source and the threshold voltage Vth. When the threshold voltage Vth of the driving switch 40 drifts, the compensation to the threshold voltage Vth drift of the driving switch 40 must be performed through the voltage difference Vgs between the gate and the source.
The first switch 502 is connected between a source and a drain of the driving switch 40. Furthermore, the source of the first switch 502 and the source of the driving switch 40 are both connected to the OLED 10. In the present embodiment, the first switch 502 is also a TFT, and the first switch 502 and the driving switch 40 are transistors of the same model. That is, the first switch 502 and the driving switch 40 have the same carrier migration rate μ, channel width W and channel length L, so that the first switch 502 and the driving switch 40 have the same threshold voltage Vth drift. In combination with the connections of the first switch 502 and the driving switch 40 (the gate of the first switch 502 is connected to the gate of the driving switch 40, and the source of the first switch 502 is connected to the source of the driving switch 40), compensating the threshold voltage Vth drift of the first switch 502 is equal to compensating the threshold voltage Vth drift of the driving switch 40.
The control circuit 30 is connected between a drain and a source of the first switch 502h, for inputting a first control signal Vs1 and outputting a compensation current Iref to compensate threshold voltage Vth drift of the first switch 502. Specifically, the first control signal Vs1 controls conduction and cut-off of the control circuit 30, so as to control whether the compensation current Iref can flow to the first switch 502. In the present embodiment, the first control signal Vs1 is provided by a first scan line of the display panel.
The storage unit 20 is connected between a source of the second switch 504 and a gate of the first switch 502, for storing charge and releasing charge. The storage unit 20 stores different voltages at different time periods. Specifically, in the first time period, the storage unit 20 stores a compensation voltage of the compensation current Iref provided to the first switch 502; in the second time period, the storage unit 20 stores a data voltage Vdata; in the third time period, the storage unit 20 releases both the compensation voltage and the data voltage Vdata. In a preferred embodiment, the storage unit 20 is a capacitor; in other embodiments, the storage unit 20 can also be electronic elements with storage function.
The second switch 504 has a source connected to the storage unit 20, a drain connected to a data line, and a gate connected to a second scan line. The second scan line outputs a second control signal Vs2 to the gate, the data line outputs a data signal Vd to the second switch 50, and stores the data signal Vd in a form of data voltage Vdata in the storage unit 20 for subsequent outputting to the driving switch 40 to control the OLED 10 to emit light.
In the first time period, the compensation current Iref compensates the threshold voltage Vth drift of the first switch 502, and is stored in a form of compensation voltage in the storage unit 20. In the second time period, the storage unit 20 stores the data voltage Vdata, and in the third time period, releases both the compensation voltage and the data voltage Vdata to control the driving voltage Vdd to drive the OLED 10 to emit light. The first switch 502 has the gate connected to the gate of the driving switch 40, the source connected to the source of the driving switch 40, and the first switch 502 and the driving switch 40 are transistors of the same model with the same threshold voltage Vth drift. Thus, compensating the first switch 502 is to compensate the driving switch 40. The compensation current Iref and the data signal Vd are independently applied to the pixel driving circuit. Without affecting the data signal, the threshold voltage Vth drift of the driving switch 40 is compensated and the current through the OLED 10 is stable, leading to uniform luminance of the display panel.
In the present embodiment, the control circuit 30 comprises: a compensation current output end, a third switch 506, and a fourth switch 508. The compensation current output end is for outputting the compensation current Iref; the compensation current Iref flows passing the third switch 506 and the fourth switch 508 and to the first switch 502. Moreover, the third switch 506 is connected between the compensation current output end and the drain of the first switch 502, and the fourth switch 508 is connected between the compensation current output end and the gate of the first switch 502. The gate of the third switch 506 and the gate of the fourth switch 508 are for inputting the second control signal Vs2. Under the control of the second control signal Vs2, the third switch 506 and the fourth switch 508 maintain the same conduction/cut-off state simultaneously. When both the third switch 506 and the fourth switch 508 are conductive, the gate and the drain of the first switch 502 are shorted, and the first switch 502 is equivalent to a diode. The compensation current Iref flows through the first switch 502 to compensate the threshold voltage Vth drift of the first switch 502, and is stored in a form of compensation voltage in the storage unit 20, for subsequent (in the third time period) compensation of the threshold voltage Vth drift of the driving switch 40.
In another embodiment, the first switch 502, the second switch 504, the third switch 506, and the fourth switch 508 are N-type thin film transistors (TFT). In other embodiments, the first switch 502, the second switch 504, the third switch 506, and the fourth switch 508 are P-type TFTs.
In the first time period, the compensation current Iref compensates the threshold voltage Vth drift of the first switch 502, and is stored in a form of compensation voltage in the storage unit 20. In the second time period, the storage unit 20 stores the data voltage Vdata, and in the third time period, releases both the compensation voltage and the data voltage Vdata to control the driving voltage Vdd to drive the OLED 10 to emit light. The first switch 502 has the gate connected to the gate of the driving switch 40, the source connected to the source of the driving switch 40, and the first switch 502 and the driving switch 40 are transistors of the same model with the same threshold voltage Vth drift. Thus, compensating the first switch 502 is to compensate the driving switch 40. The compensation current Iref and the data signal Vd are independently applied to the pixel driving circuit. Without affecting the data signal, the threshold voltage Vth drift of the driving switch 40 is compensated and the current through the OLED 10 is stable, leading to uniform luminance of the display panel.
The present invention also provides a display panel comprising the aforementioned pixel driving circuit.
The present invention also provides a pixel driving method, to be realized through the pixel driving circuit provided by the present invention. Specifically, the pixel driving circuit comprises: a driving power source, an OLED 10, a driving switch 40, a first switch 502, a second switch 504, a storage unit 20 and a control circuit 30; the driving switch 40 being connected between the driving power source and the OLED 10; the first switch 502 being connected between a source and a drain of the driving switch 40, and being a transistor of the same model as the driving switch; the control circuit 30 being connected between a drain and a source of the first switch 502; the storage unit 20 being connected between a source of the second switch 504 and a gate of the first switch 502. In the present embodiment, the first switch 502, the second switch 504, the third switch 506, and the fourth switch 508 are N-type TFTs.
In combination of
S101: in a first time period t1, in combination of
In the present embodiment, when the control circuit 30 is conductive, the gate and the drain of the first switch 502 are shorted, and the first switch 502 is equivalent to a diode. The compensation current Iref flows through the first switch 502, i.e., Ids=Iref. According to equation (1), the voltage difference between the gate and the source of the first switch 502 is:
V
gs=(Ids/K)1/2+Vth
Furthermore, because:
V
gs
=V
g
−V
s
V
s
=V
oled
Thus, Vg=(Ids/K)1/2+Vth+Voled
Wherein, Vg is the potential of the gate of the first switch 502, Vs is the potential of the source of the first switch 502, and Voled is the potential of the OLED 10.
Furthermore, assume that the storage unit 20 comprises a first connection end A and a second connection end B. The first connection end A has a potential VA equal to the potential of the gate Vg of the first switch 502. That is,
V
A
=V
g=(Ids/K)1/2+Vth+Voled
The second connection end B has a potential VB being a reference voltage Vref passing through the second switch 504. That is,
V
B
=V
ref
The reference Vref is a reference value, for subsequent comparison with data voltage Vdata.
Therefore, in the first time period t1, the potentials at the two ends of the storage unit 20 are VA=(Ids/K)1/2+Vth+Voled and VB=Vref respectively. The compensation current Iref compensating the threshold voltage Vth drift of the first switch 502 is stored in a compensation voltage in the storage unit 20. Because the first switch 502 and the driving switch 40 are transistors of the same model, in subsequent third time period (light-emitting phase), the compensation to the first switch 502 is equivalent to the compensation to the driving switch 40.
S102: in a second time period t2, in combination with
V
A=(Ids/K)1/2+Vth+Voled+Vdata−Vref
Accordingly, in the second time period t2, the potentials of the two ends of the storage unit 20 are VA=(Ids/K)1/2+Vth+Voled+Vdata−Vref, VB=Vdata respectively; the storage unit 20 stores the data voltage Vdata for subquent third time period (light-emitting phase) to control the driving switch 40 to make OLED 10 emit light.
In the third time period t3, in combination with
In the first time period t1, the compensation current Iref compensates the threshold voltage Vth drift of the first switch 502, and is stored in a form of compensation voltage in the storage unit 20. In the second time period t2, the storage unit 20 stores the data voltage Vdata, and in the third time period t3, releases both the compensation voltage and the data voltage Vdata to control the driving voltage Vdd to drive the OLED 10 to emit light. The first switch 502 has the gate connected to the gate of the driving switch 40, the source connected to the source of the driving switch 40, and the first switch 502 and the driving switch 40 are transistors of the same model with the same threshold voltage Vth drift. Thus, compensating the first switch 502 is to compensate the driving switch 40. The compensation current Iref and the data signal Vd are independently applied to the pixel driving circuit. Without affecting the data signal, the threshold voltage Vth drift of the driving switch 40 is compensated and the current through the OLED 10 is stable, leading to uniform luminance of the display panel.
In the present embodiment, the control circuit 30 comprises: a compensation current output end, a third switch 506, and a fourth switch 508. The compensation current output end is for outputting the compensation current Iref; the compensation current Iref flows passing the third switch 506 and the fourth switch 508 and to the first switch 502. Moreover, the third switch 506 is connected between the compensation current output end and the drain of the first switch 502, and the fourth switch 508 is connected between the compensation current output end and the gate of the first switch 502. The gate of the third switch 506 and the gate of the fourth switch 508 are for inputting the second control signal Vs2. Under the control of the second control signal Vs2, the third switch 506 and the fourth switch 508 maintain the same conduction/cut-off state simultaneously. When both the third switch 506 and the fourth switch 508 are conductive, the gate and the drain of the first switch 502 are shorted, and the first switch 502 is equivalent to a diode. The compensation current Iref flows through the first switch 502 to compensate the threshold voltage Vth drift of the first switch 502, and is stored in a form of compensation voltage in the storage unit 20, for subsequent (in the third time period) compensation of the threshold voltage Vth drift of the driving switch 40.
In another embodiment, the first switch 502, the second switch 504, the third switch 506, and the fourth switch 508 are N-type TFTs. In other embodiments, the first switch 502, the second switch 504, the third switch 506, and the fourth switch 508 are P-type TFTs.
In a preferred embodiment, a transitional time period is provided between the first time period t1 and the second time period t2, and between the second time period t2 and the third time period t3, for reserving time to propagate the first control signal Vs1, the second control signal Vs2, and the data signal Vd.
In the first time period t1, the compensation current Iref compensates the threshold voltage Vth drift of the first switch 502, and is stored in a form of compensation voltage in the storage unit 20. In the second time period t2, the storage unit 20 stores the data voltage Vdata, and in the third time period t3, releases both the compensation voltage and the data voltage Vdata to control the driving voltage Vdd to drive the OLED 10 to emit light. The first switch 502 has the gate connected to the gate of the driving switch 40, the source connected to the source of the driving switch 40, and the first switch 502 and the driving switch 40 are transistors of the same model with the same threshold voltage Vth drift. Thus, compensating the first switch 502 is to compensate the driving switch 40. The compensation current Iref and the data signal Vd are independently applied to the pixel driving circuit. Without affecting the data signal, the threshold voltage Vth drift of the driving switch 40 is compensated and the current through the OLED 10 is stable, leading to uniform luminance of the display panel.
Embodiments of the present invention have been described, but not intending to impose any unduly constraint to the appended claims. Any modification of equivalent structure or equivalent process made according to the disclosure and drawings of the present invention, or any application thereof, directly or indirectly, to other related fields of technique, is considered encompassed in the scope of protection defined by the clams of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201710296114.9 | Apr 2017 | CN | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/CN2017/086738 | 5/31/2017 | WO | 00 |
