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CN104575377A - Pixel circuit and driving method thereof as well as active matrix organic light emitting display - Google Patents

Pixel circuit and driving method thereof as well as active matrix organic light emitting display Download PDF

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Publication number
CN104575377A
CN104575377A CN201410809255.2A CN201410809255A CN104575377A CN 104575377 A CN104575377 A CN 104575377A CN 201410809255 A CN201410809255 A CN 201410809255A CN 104575377 A CN104575377 A CN 104575377A
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thin film
film transistor
line
scanning
node
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张九占
川岛进吾
朱修剑
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Kunshan Guoxian Photoelectric Co Ltd
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Kunshan Guoxian Photoelectric Co Ltd
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Abstract

The invention provides a pixel circuit and a driving method thereof as well as an active matrix organic light emitting display. By eliminating the current flowing through a third thin film transistor before threshold voltage compensation to prevent the lag effect of the third thin film transistor, and thus a response speed is increased; meanwhile, the current output by the third thin film transistor is determined by data voltage provided by a data wire and a first supply voltage provided by a first power supply, and is unrelated to the threshold voltage of the third thin film transistor, so that uneven brightness caused by threshold voltage deviation can be avoided. Accordingly, display problems caused by threshold voltage deviation and the lag effect of the driving transistor can be avoided by adopting the pixel circuit and the driving method thereof as well as the active matrix organic light emitting display and higher uniformity of luminance and the higher response speed are achieved.

Description

Pixel circuit, driving method thereof and active matrix organic light emitting display
Technical Field
The invention relates to the technical field of flat panel display, in particular to a pixel circuit, a driving method thereof and an active matrix organic light emitting display.
Background
The Organic light Emitting display displays images by using Organic Light Emitting Diodes (OLEDs), is an active light Emitting display, has a display mode different from that of a conventional Thin Film Transistor liquid crystal display (TFT-LCD), does not need a backlight, and has many advantages of high contrast, fast response speed, light weight, and the like. Therefore, the organic light emitting display is known as a new generation display that can replace the thin film transistor liquid crystal display.
Depending on the driving method, the Organic light Emitting Display is classified into a Passive Matrix Organic Light Emitting Display (PMOLED) and an Active Matrix Organic Light Emitting Display (AMOLED), which are also called Active Matrix Organic light Emitting displays.
An active matrix organic light emitting display includes scan lines, data lines, and a pixel array defined by the scan lines and the data lines, each pixel of the pixel array typically including an organic light emitting diode and a pixel circuit for driving the organic light emitting diode. Please refer to fig. 1, which is a schematic structural diagram of a pixel circuit of an active matrix organic light emitting display in the prior art. As shown in fig. 1, the conventional pixel circuit 10 generally includes a switching thin film transistor T1, a driving thin film transistor T2, and a storage capacitor Cs, wherein a gate of the switching thin film transistor T1 is connected to a scan line Sn, a source of the switching thin film transistor T1 is connected to a data line, a gate of the driving thin film transistor T2 is connected to a drain of the switching thin film transistor T1, a source of the driving thin film transistor T2 is connected to a first power ELVDD through a first power trace (not shown), a drain of the driving thin film transistor T2 is connected to an anode of the organic light emitting diode OLED, and a cathode of the organic light emitting diode OLED is connected to a second power ELVSS through a second power trace (not shown).
When the switching transistor T1 is turned on by the scan line s (n), the data voltage Vdata provided by the data line is stored in the storage capacitor Cs via the switching transistor T1, thereby controlling the driving transistor T2 to generate current to drive the organic light emitting diode OLED to emit light. At this time, the calculation formula of the current Ion flowing between the source and the drain of the driving transistor T2 is:
Ion=K×(Vgs-|Vth|)2
where K is the product of the electron mobility, the width-to-length ratio, and the unit area capacitance of the thin film transistor, Vgs is the gate-source voltage of the driving transistor T2, i.e., the voltage difference between the gate and the source, and Vth is the threshold voltage of the driving transistor T2.
Since the gate-source voltage Vgs2 of the driving transistor T2 is equal to ELVDD-Vdata, the current Ion flowing between the source and drain of the driving transistor T2 may be calculated according to the following formula:
Ion=K×(ELVDD-Vdata-|Vth|)2
however, when the pixel circuit 10 drives a pixel, since the driving current Ion continuously flows through the driving transistor T2 to the organic light emitting diode OLED, the driving transistor T2 generates a hysteresis effect (hysteresis) due to continuous voltage stress (voltage stress), that is, the characteristic curve of the driving transistor T2 is lagged.
Please refer to fig. 2, which is a graph illustrating a characteristic curve from on to off of a driving transistor in a pixel circuit according to the prior art. As shown in fig. 2, a characteristic curve a of the driving transistor from on to off and a characteristic curve B from off to on are different, i.e., the transistor characteristic curve is changed. In other words, when a pixel displays white after displaying black for many frames, a transistor characteristic curve may be changed due to a continuous off-voltage of a driving transistor during a period of displaying black, and then a target luminance value is not sufficiently reached at an initial period of displaying white, and thus a response speed becomes slow. The slow response speed of the pixels causes display problems such as poor definition of the display screen and image sticking.
Therefore, how to solve the problem that the response speed of the pixel of the existing active matrix organic light emitting display is slow due to the lag of the driving transistor becomes a technical problem to be solved by the technical personnel in the field.
Disclosure of Invention
The invention aims to provide a pixel circuit, a driving method thereof and an active matrix organic light-emitting display, which aim to solve the problem that the response speed of pixels is reduced due to the hysteresis of driving transistors of the conventional active matrix organic light-emitting display.
To solve the above problem, the present invention provides a pixel circuit, including:
an organic light emitting diode connected between a first power source and a second power source;
a first thin film transistor connected between a first power source and a second node, a gate of which is connected to an emission control line;
a second thin film transistor connected between the third node and an anode of the organic light emitting diode, a gate of which is connected to the emission control line;
a third thin film transistor connected between the second node and the third node, and having a gate connected to the first node;
a fourth thin film transistor connected between the first node and the third node, a gate of which is connected to the third scan line;
a fifth thin film transistor connected between the first node and a third power supply, a gate of which is connected to the second scan line;
a sixth thin film transistor connected between the data line and the second node, and having a gate connected to the third scan line;
a seventh thin film transistor connected between the first power source and the first node, and having a gate connected to the first scan line;
and a storage capacitor connected between the first power source and the first node.
Optionally, in the pixel circuit, the first power supply and the second power supply are used as driving power supplies of the organic light emitting diode, and the third power supply is used for providing a reference voltage.
Optionally, in the pixel circuit, the first to seventh thin film transistors are all P-type thin film transistors.
Optionally, in the pixel circuit, the third thin film transistor serves as a driving transistor, and a current supplied to the organic light emitting diode by the third thin film transistor is determined by a data voltage supplied by the data line and a first power voltage supplied by the first power source, and is independent of a second power voltage supplied by the second power source, a reference voltage supplied by the third power source, and a threshold voltage of the third thin film transistor.
Optionally, the seventh thin film transistor is controlled by a first scan line, the fourth thin film transistor and the sixth thin film transistor are controlled by a third scan line, and the first thin film transistor and the second thin film transistor are controlled by an emission control line.
Correspondingly, the invention also provides a driving method of the pixel circuit, which comprises the following steps: the scan cycle includes a first time period, a second time period, a third time period, and a fourth time period, wherein,
in a first time period, a scanning signal provided by a first scanning line is changed from a high level to a low level, the scanning signals provided by a second scanning line and a third scanning line are both high levels, a control signal provided by an emission control line is low level, a first thin film transistor, a second thin film transistor and a seventh thin film transistor are turned on, and current flowing through the third thin film transistor is eliminated;
in a second time period, the scanning signals provided by the first scanning line and the third scanning line and the control signal provided by the emission control line are all at high level, the scanning signal provided by the second scanning line is changed from high level to low level, the fifth thin film transistor is turned on, and the first node is initialized through the third power supply.
In a third time period, the scanning signals provided by the first scanning line and the second scanning line and the control signals provided by the emission control line are both high level, the scanning signal provided by the third scanning line is changed from high level to low level, the fourth thin film transistor and the sixth thin film transistor are turned on, and the threshold voltage of the third thin film transistor is compensated;
in a fourth time period, the scanning signals provided by the first scanning line and the second scanning line are both high level, the scanning signal provided by the third scanning line is changed from low level to high level, the control signal provided by the emission control line is changed from high level to low level, the first thin film transistor and the second thin film transistor are opened after the fourth thin film transistor and the sixth thin film transistor are closed, and the third thin film transistor outputs current and drives the organic light emitting diode to emit light.
Optionally, in the driving method of the pixel circuit, the scan cycle further includes a fifth period, and the fifth period is set between the first period and the second period;
in a fifth time period, the scanning signal provided by the first scanning line keeps low level, the scanning signals provided by the second scanning line and the third scanning line keep high level, the control signal provided by the emission control line changes from low level to high level, and the organic light emitting diode stops emitting light.
Optionally, in the driving method of the pixel circuit, the scan cycle further includes a sixth time period; the sixth time period is set between the second time period and the third time period;
in a sixth period, the scanning signals provided by the first scanning line and the third scanning line and the control signal provided by the emission control line are all kept at a high level, the scanning signal provided by the second scanning line is changed from a low level to a high level, the fifth thin film transistor is turned off, and initialization of the first node is stopped.
Accordingly, the present invention also provides an active matrix organic light emitting display comprising: a display unit, a scan driver and a data driver; the display unit includes a plurality of pixels arranged in a matrix form at intersection regions of scanning lines and data lines, each pixel being connected to the scanning lines and the data lines, the pixels including the pixel circuits as described above.
In the pixel circuit, the driving method thereof and the active matrix organic light emitting display provided by the invention, the current flowing through the third thin film transistor is eliminated before threshold voltage compensation, so that the hysteresis effect of the third thin film transistor is prevented, and the response speed is improved.
Drawings
FIG. 1 is a schematic diagram of a prior art pixel circuit of an active matrix organic light emitting display;
FIG. 2 is a graph of a characteristic of a drive transistor from on to off versus off to on for a prior art pixel circuit;
FIG. 3 is a schematic diagram of a pixel circuit according to an embodiment of the present invention;
fig. 4 is a timing chart of a driving method of a pixel circuit according to an embodiment of the present invention;
fig. 5 is a schematic structural diagram of an active matrix organic light emitting display device according to an embodiment of the present invention.
Detailed Description
A pixel circuit, a driving method thereof, and an active matrix organic light emitting display according to the present invention will be described in detail with reference to the accompanying drawings and specific embodiments. Advantages and features of the present invention will become apparent from the following description and from the claims. It is to be noted that the drawings are in a very simplified form and are not to precise scale, which is merely for the purpose of facilitating and distinctly claiming the embodiments of the present invention.
Please refer to fig. 3, which is a schematic structural diagram of a pixel circuit according to an embodiment of the invention. As shown in fig. 3, the pixel circuit 20 includes: an Organic Light Emitting Diode (OLED) connected between the first power supply and the second power supply; a first thin film transistor M1 connected between the first power supply and the second node N2, and having a gate connected to the emission control line EMn; a second thin film transistor M2 connected between the third node N3 and the anode of the organic light emitting diode OLED, and having a gate connected to the emission control line EMn; a third thin film transistor M3 connected between the second node N2 and the third node N3, and having a gate connected to the first node N1; a fourth thin film transistor M4 connected between the first node N1 and the third node N3, and having a gate connected to the third scan line Sn + 1; a fifth thin film transistor M5 connected between the first node N1 and the third power supply, and having a gate connected to the second scan line Sn; a sixth thin film transistor M6 connected between the data line and the second node N2, and having a gate connected to the third scan line Sn + 1; a seventh thin film transistor M7 connected between the first power source and the first node N1, and having a gate connected to the first scan line Sn-1; the storage capacitor Cst is connected between the first power source and the first node N1.
Specifically, the pixel circuit 20 is connected to an external power source including a first power source, a second power source, and a third power source. Wherein the first power supply and the second power supply serve as a driving power supply of the organic light emitting diode OLED. The first power supply is a high potential pixel power supply for supplying a first power supply voltage VDD. The second power supply is a low potential pixel power supply for supplying a second power supply voltage VSS. The third power supply is typically a low level voltage source for providing a reference voltage Vref.
In this embodiment, the voltage value of the reference voltage Vref is close to the voltage value of the second power voltage VSS.
With continued reference to fig. 3, the pixel circuit 20 is a 7T1C type circuit structure, which includes 7 thin film transistors and 1 capacitor, where the 7 thin film transistors are all P-type thin film transistors, the gate of the third thin film transistor M3, the drain of the fourth thin film transistor M4, the drain of the fifth thin film transistor M5, the source of the seventh thin film transistor M7 and the lower substrate of the storage capacitor Cst are all connected to the first node N1, the drain of the third thin film transistor M3, the drain of the first thin film transistor M1 and the source of the sixth thin film transistor M6 are all connected to the second node N2, the sources of the second thin film transistor M2, the third thin film transistor M3 and the fourth thin film transistor M4 are all connected to the third node N3, the gate of the seventh thin film transistor M7 is connected to the first scan line Sn-1, and the gate of the fifth thin film transistor M5 is connected to the second scan line Sn-1, the fourth thin film transistor M4 and the sixth thin film transistor M6 are connected to a third scan line Sn +1, and the first thin film transistor M1 and the second thin film transistor M2 are connected to an emission control line EMn.
As shown in fig. 3, the pixel circuit 20 controls the seventh thin film transistor M7 through the first scan line Sn-1, the fifth thin film transistor M5 through the second scan line Sn, the fourth thin film transistor M4 and the sixth thin film transistor M6 through the third scan line Sn +1, and the first thin film transistor M1 and the second thin film transistor M2 through the emission control line EMn.
When the scan signal supplied from the first scan line Sn-1 transitions to a low level, the seventh thin film transistor M7 is turned on. When the scan signal supplied from the second scan line Sn transitions to a low level, the fifth thin film transistor M5 is turned on, and the reference voltage Vref supplied from the third power source is applied to the first node N1 through the fifth thin film transistor M5. When the scan signal supplied from the third scan line Sn +1 transitions to a low level, the fourth thin film transistor M4 and the sixth thin film transistor M6 are both turned on, the gate and the drain of the third thin film transistor M3 are shorted by the fourth thin film transistor M4, and the data voltage Vdata supplied from the data line is written into the second node N2 via the sixth thin film transistor M6. When the control signal provided by the emission control line EMn transitions to a low level, the first thin film transistor M1 and the second thin film transistor M2 are both turned on, and the driving current flows to the second power source along the path of the first power source through the first thin film transistor M1, the third thin film transistor M3, the second thin film transistor M2 and the organic light emitting diode OLED, so that the organic light emitting diode OLED lights up to emit light.
In this embodiment, the third thin film transistor M3 serves as a driving transistor of a pixel, and controls a driving current supplied to the organic light emitting diode OLED corresponding to the voltage of the first node N1, the organic light emitting diode OLED emitting light of a corresponding luminance according to the driving current, thereby displaying an image. The driving current supplied to the organic light emitting diode OLED by the third thin film transistor M3 is determined by the data voltage Vdata supplied by the data line and the first power voltage VDD supplied by the first power source, and is independent of the second power voltage VSS supplied by the second power source, the reference voltage Vref supplied by the third power source, and the threshold voltage of the third thin film transistor M3. Therefore, the pixel circuit 20 can prevent the brightness unevenness caused by the threshold voltage deviation of the thin film transistor, thereby improving the display quality of the display.
The pixel circuit 20 not only has the threshold voltage compensation function, but also can eliminate the current flowing through the third thin film transistor M3 before the threshold voltage compensation, so as to prevent the third thin film transistor M3 from generating the hysteresis effect, and avoid the slow response speed caused by the hysteresis effect.
Correspondingly, the invention also provides a driving method of the pixel circuit. Referring to fig. 3 and fig. 4 in combination, the driving method of the pixel circuit includes:
the scan cycle includes a first period t1, a second period t2, a third period t3, and a fourth period t 4; wherein,
in a first period t1, the scan signal provided by the first scan line Sn-1 changes from high to low, the scan signals provided by the second scan line Sn and the third scan line Sn +1 are both high, the control signal provided by the emission control line EMn is low, and the first thin film transistor M1, the second thin film transistor M2 and the seventh thin film transistor M7 are turned on to eliminate the current flowing through the third thin film transistor M3;
in the second period t2, the scan signal provided by the first scan line Sn-1 and the third scan line Sn +1 and the control signal provided by the emission control line EMn are both at a high level, the scan signal provided by the second scan line Sn changes from the high level to a low level, the fifth thin film transistor M5 is turned on, and the first node N1 is initialized by the third power supply.
In the third period t3, the scan signals provided by the first and second scan lines Sn-1 and Sn and the control signal provided by the emission control line EMn are both at a high level, the scan signal provided by the third scan line Sn +1 changes from the high level to a low level, the fourth and sixth thin film transistors M4 and M6 are turned on, and the threshold voltage of the third thin film transistor M3 is compensated;
in a fourth time period t4, the scan signals provided by the first scan line Sn-1 and the second scan line Sn are all at a high level, the scan signal provided by the third scan line Sn +1 changes from a low level to a high level, the control signal provided by the emission control line EMn changes from a high level to a low level, the first thin film transistor M1 and the second thin film transistor M2 are turned on after the fourth thin film transistor M4 and the sixth thin film transistor M6 are turned off, and the third thin film transistor M3 outputs current and drives the organic light emitting diode OLED to emit light.
Specifically, in the first period t1, since the scan signal supplied from the first scan line Sn-1 is changed from a high level to a low level, the seventh thin film transistor M7 controlled by the first scan line Sn-1 is changed from off to on, and since the control signal supplied from the emission control line EMn is at a low level, the first thin film transistor M1 and the second thin film transistor M2 are in an on state, and thus no current flows through the third thin film transistor M3. By eliminating the current flowing through the third thin film transistor M3, the hysteresis effect of the third thin film transistor M3 can be prevented, thereby improving the response time and increasing the response speed.
In the second period t2, since the scan signal supplied from the second scan line Sn is changed from a high level to a low level, the fifth thin film transistor M5 controlled by the second scan line Sn is changed from off to on, the reference voltage Vref supplied from the third power source is supplied to the first node N1 via the fifth thin film transistor M5 and initializes the first node N1, and the voltage of the first node N1 after initialization is equal to the reference voltage Vref. Since the reference voltage Vref is close to the second power supply voltage VSS, the next phase data can be written. At this time, the gate voltage of the third thin film transistor M3 is equal to the reference voltage Vref.
In the third period t3, since the scan signal supplied from the third scan line Sn +1 is changed from the high level to the low level, both the fourth thin film transistor M4 and the sixth thin film transistor M6 controlled by the third scan line Sn +1 are turned off to on, the gate and the drain of the third thin film transistor M3 are shorted due to the fourth thin film transistor M4 being turned on, and meanwhile, since the sixth thin film transistor M6 being turned on, the data voltage Vdata supplied from the data line is supplied to the second node N2 via the sixth thin film transistor M6, so that the voltage of the first node N1, i.e., the lower substrate voltage of the storage capacitor Cst is vd- | Vth |. Where Vth is the threshold voltage of the third thin film transistor M3. In other words, the threshold voltage of the third thin film transistor M3 is stored in the storage capacitor Cst during this process, and the threshold voltage of the third thin film transistor M3 is compensated.
In the fourth period t4, since the scan signal supplied from the third scan line Sn +1 changes from low level to high level, the fourth thin film transistor M4 and the sixth thin film transistor M6 controlled by the third scan line Sn +1 both turn on and turn off, and the data voltage Vdata supplied from the data line stops being written. Then, since the control signal provided by the emission control line EMn changes from high level to low level, the first thin film transistor M1 and the second thin film transistor M2 controlled by the emission control line EMn both turn off and turn on, and the driving current output by the third thin film transistor M3 flows to the second power supply along the path of the first power supply through the first thin film transistor M1, the third thin film transistor M3, the second thin film transistor M2 and the organic light emitting diode OLED, so that the organic light emitting diode OLED lights up to emit light.
Since the first thin film transistor M1 is turned on, the first power voltage VDD is supplied to the second node N2 through the first thin film transistor M1. At this time, the voltage of the second node N2 is the first power voltage VDD, and the voltage of the first node N1 is Vdata- | Vth |. Since the gate voltage of the third thin film transistor M3 is equal to the voltage of the first node N1, i.e., Vdata- | Vth |, the source voltage of the third thin film transistor M3 is equal to the voltage of the second node N2, i.e., VDD. Therefore, the gate-source voltage Vgs of the third tft M3 (i.e., the voltage difference between the gate and the source of the third tft M3) is calculated by the formula:
vgs ═ VDD- (Vdata- | Vth |) formula 1;
and the calculation formula of the current Ion flowing through the organic light emitting diode OLED is:
Ion=K×(Vgs-|Vth|)2formula 2;
wherein K is the product of the electron mobility, the width-to-length ratio and the unit area capacitance of the thin film transistor.
From equation 1 and equation 2, we can obtain:
Ion=K×(VDD-Vdata)2formula 3;
as can be seen from the expression of formula 3, the current Ion flowing through the organic light emitting diode OLED is related only to the data voltage Vdata and the first power voltage VDD and the constant K, and has no relation to the second power voltage VSS, the reference voltage Vref, and the threshold voltage Vth of the third thin film transistor M3. Even if the threshold voltage Vth of the third thin film transistor M3 is deviated, the current Ion flowing through the organic light emitting diode OLED is not affected. Therefore, the pixel circuit 20 and the driving method thereof can compensate the threshold voltage, and prevent the uneven brightness caused by the deviation of the threshold voltage.
The pixel circuit 20 mainly works in the above four periods, so that not only can the compensation of the threshold voltage be realized, but also the hysteresis effect of the driving transistor can be prevented, and the display problem caused by the hysteresis effect can be eliminated.
With continued reference to fig. 3, the scan cycle further includes a fifth time period t5 and a sixth time period t 6. Wherein, the fifth time period t5 is set between the first time period t1 and the second time period t2, and the sixth time period t6 is set between the second time period t2 and the third time period t 3.
In the fifth period t5, the scan signal supplied from the first scan line Sn-1 is maintained at a low level, the scan signals supplied from the second scan line Sn and the third scan line Sn +1 are maintained at a high level, the control signal supplied from the emission control line EMn is changed from a low level to a high level, and both the first thin-film transistor M1 and the second thin-film transistor M2 controlled by the emission control line EMn are turned on to be turned off due to the control signal supplied from the emission control line EMn being changed from a low level to a high level, so that the organic light emitting diode OLED stops emitting light.
In the sixth period t6, the scan signals supplied from the first and third scan lines Sn-1 and Sn +1 and the control signal supplied from the emission control line EMn are all maintained at the high level, the scan signal supplied from the second scan line Sn is changed from the low level to the high level, the fifth thin film transistor M5 controlled by the second scan line Sn is changed from on to off due to the scan signal supplied from the second scan line Sn being changed from the low level to the high level, and the third power supply cannot supply the reference voltage Vref to the first node N1 via the fifth thin film transistor M5 due to the fifth thin film transistor M5 being turned off, thereby stopping the initialization of the first node N1.
The working processes of the first time period t1, the fifth time period t5, the second time period t2, the sixth time period t6, the third time period t3 and the fourth time period t4 are repeated, and the image display function is completed.
Correspondingly, the invention also provides an active matrix organic light-emitting display device. Referring to fig. 5, as shown in fig. 5, the active matrix organic light emitting display device includes: a display unit 100, a scan driver 200, and a data driver 300; the display unit 100 includes a plurality of pixels 110, the plurality of pixels 110 being arranged in a matrix form at crossing regions of scan lines S1 to Sn and data lines D1 to Dm, each pixel 110 being connected to the scan lines and the data lines, the pixel 110 including the pixel circuit 20 as described above.
Specifically, the display unit 100 receives a first power supply, a second power supply, and a third power supply provided from the outside. Wherein the first power supply is a high potential pixel power supply for supplying a first power supply voltage VDD. The second power supply is a low potential pixel power supply for supplying a second power supply voltage VSS. The third power supply is typically a low level voltage source for providing a reference voltage Vref.
As shown in FIG. 5, the display unit 100 includes a plurality of pixels 110, and the plurality of pixels 110 are distributed in an m × n array, where m is the number of columns of the pixels 110, n is the number of rows of the pixels 110, m ≧ 1, and n ≧ 1. Each pixel 110 is connected to a scan line, an emission control line EMn, and a data line (the data line is connected to a column of pixels 110 in which the pixel 110 itself is located). For example, the pixels 110 located in the ith row and jth column are connected to the ith scan line Si, the ith emission control line EMi, and the jth data line Dj.
Wherein the scan lines and the emission control lines are connected to a scan driver 200, the scan driver 200 generating scan signals and control signals corresponding to scan control signals externally supplied (e.g., supplied from a timing control unit). The scan signals generated by the scan controller 200 are sequentially supplied to the pixels 110 through the scan lines S1 to Sn, respectively, and the control signals generated by the scan controller 200 are sequentially supplied to the pixels 110 through the emission control lines EM1 to EMn, respectively. The data lines are each connected to a data driver 300, and the data driver 300 generates data signals corresponding to data and data control signals supplied from the outside (e.g., supplied from a timing control unit). The data signals generated by the data driver 300 are supplied to the pixels 110 through the data lines D1 through Dm in synchronization with the scan signals.
Referring to fig. 4 and 5 in combination, during the first time period t1, the response time of the pixel 110 is improved; during a second time period t2, the pixel 110 is initialized; during a third time period t3, the pixel 110 accepts the data signal supplied from the data line while performing compensation of the threshold voltage; during the fourth period t4, the pixel 110 emits light having a brightness corresponding to the data signal to display an image after the data signal stops being written.
In summary, in the pixel circuit, the driving method thereof and the active matrix organic light emitting display provided by the invention, by eliminating the current flowing through the third thin film transistor M3 before the threshold voltage compensation, the hysteresis effect of the third thin film transistor M3 is prevented, thereby improving the response speed, and at the same time, the current outputted by the third thin film transistor M3 is determined by the data voltage provided by the data line and the first power voltage VDD provided by the first power source, regardless of the threshold voltage of the third thin film transistor M3, it is possible to avoid brightness unevenness caused by threshold voltage deviation, thus, the active matrix organic light emitting display adopting the pixel circuit and the driving method thereof can simultaneously avoid the display problems caused by the threshold voltage deviation of the driving transistor and the hysteresis effect, and has higher brightness uniformity and faster response speed.
The above description is only for the purpose of describing the preferred embodiments of the present invention, and is not intended to limit the scope of the present invention, and any variations and modifications made by those skilled in the art based on the above disclosure are within the scope of the appended claims.

Claims (9)

1. A pixel circuit, comprising:
an organic light emitting diode connected between a first power source and a second power source;
a first thin film transistor connected between a first power source and a second node, a gate of which is connected to an emission control line;
a second thin film transistor connected between a third node and an anode of the organic light emitting diode, a gate of which is connected to an emission control line;
a third thin film transistor connected between the second node and the third node, and having a gate connected to the first node;
a fourth thin film transistor connected between the first node and the third node, a gate of which is connected to the third scan line;
a fifth thin film transistor connected between the first node and a third power supply, a gate of which is connected to the second scan line;
a sixth thin film transistor connected between the data line and the second node, and having a gate connected to the third scan line;
a seventh thin film transistor connected between the first power source and the first node, and having a gate connected to the first scan line; and
and a storage capacitor connected between the first power source and the first node.
2. The pixel circuit according to claim 1, wherein the first power supply and the second power supply serve as a driving power supply of the organic light emitting diode, and the third power supply is configured to supply a reference voltage.
3. The pixel circuit according to claim 1, wherein the first to seventh thin film transistors are all P-type thin film transistors.
4. The pixel circuit according to claim 1, wherein the third thin film transistor functions as a driving transistor, and a current supplied to the organic light emitting diode by the third thin film transistor is determined by a data voltage supplied from the data line and a first power voltage supplied from a first power source, regardless of a second power voltage supplied from the second power source, a reference voltage supplied from a third power source, and a threshold voltage of the third thin film transistor.
5. The pixel circuit according to claim 1, wherein the seventh thin film transistor is controlled by a first scan line, wherein the fourth thin film transistor and the sixth thin film transistor are controlled by a third scan line, and wherein the first thin film transistor and the second thin film transistor are controlled by an emission control line.
6. A driving method of the pixel circuit according to any one of claims 1 to 5, wherein the scanning period includes a first period, a second period, a third period, and a fourth period, wherein,
in a first time period, a scanning signal provided by a first scanning line is changed from a high level to a low level, the scanning signals provided by a second scanning line and a third scanning line are both high levels, a control signal provided by an emission control line is low level, a first thin film transistor, a second thin film transistor and a seventh thin film transistor are turned on, and current flowing through the third thin film transistor is eliminated;
in a second time period, the scanning signals provided by the first scanning line and the third scanning line and the control signals provided by the emission control line are all high level, the scanning signal provided by the second scanning line is changed from high level to low level, the fifth thin film transistor is turned on, and the first node is initialized through the third power supply;
in a third time period, the scanning signals provided by the first scanning line and the second scanning line and the control signals provided by the emission control line are both high level, the scanning signal provided by the third scanning line is changed from high level to low level, the fourth thin film transistor and the sixth thin film transistor are turned on, and the threshold voltage of the third thin film transistor is compensated;
in a fourth time period, the scanning signals provided by the first scanning line and the second scanning line are both high level, the scanning signal provided by the third scanning line is changed from low level to high level, the control signal provided by the emission control line is changed from high level to low level, the first thin film transistor and the second thin film transistor are opened after the fourth thin film transistor and the sixth thin film transistor are closed, and the third thin film transistor outputs current and drives the organic light emitting diode to emit light.
7. The method for driving the pixel circuit according to claim 6, wherein the scan cycle further includes a fifth period of time, the fifth period of time being provided between the first period of time and the second period of time;
in a fifth time period, the scanning signal provided by the first scanning line keeps low level, the scanning signals provided by the second scanning line and the third scanning line keep high level, the control signal provided by the emission control line changes from low level to high level, and the organic light emitting diode stops emitting light.
8. The method for driving the pixel circuit according to claim 6, wherein the scan cycle further includes a sixth period; the sixth time period is set between the second time period and the third time period;
in a sixth period, the scanning signals provided by the first scanning line and the third scanning line and the control signal provided by the emission control line are all kept at a high level, the scanning signal provided by the second scanning line is changed from a low level to a high level, the fifth thin film transistor is turned off, and initialization of the first node is stopped.
9. An active matrix organic light emitting display, comprising: a display unit, a scan driver and a data driver; the display unit includes a plurality of pixels arranged in a matrix at crossing regions of scan lines and data lines, each pixel being connected to the scan lines and the data lines, the pixels including the pixel circuit as claimed in any one of claims 1 to 5.
CN201410809255.2A 2014-12-22 2014-12-22 Pixel circuit and driving method thereof as well as active matrix organic light emitting display Pending CN104575377A (en)

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