CN106935201B - Pixel circuit and its driving method and active matrix/organic light emitting display - Google Patents
Pixel circuit and its driving method and active matrix/organic light emitting display Download PDFInfo
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- CN106935201B CN106935201B CN201511029763.XA CN201511029763A CN106935201B CN 106935201 B CN106935201 B CN 106935201B CN 201511029763 A CN201511029763 A CN 201511029763A CN 106935201 B CN106935201 B CN 106935201B
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
- G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
- G09G3/22—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources
- G09G3/30—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels
- G09G3/32—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED]
- G09G3/3208—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED] organic, e.g. using organic light-emitting diodes [OLED]
- G09G3/3225—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED] organic, e.g. using organic light-emitting diodes [OLED] using an active matrix
- G09G3/3233—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED] organic, e.g. using organic light-emitting diodes [OLED] using an active matrix with pixel circuitry controlling the current through the light-emitting element
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- H—ELECTRICITY
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- H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
- H10K59/00—Integrated devices, or assemblies of multiple devices, comprising at least one organic light-emitting element covered by group H10K50/00
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Abstract
In pixel circuit provided by the invention and its driving method and active matrix/organic light emitting display, the data voltage that the electric current that driving transistor is exported is provided by data line, the second source voltage that the threshold voltage and second source of Organic Light Emitting Diode provide determines, and it is unrelated with the first supply voltage that the threshold voltage of driving transistor and the first power supply provide, therefore it can be avoided the brightness disproportionation as caused by drive transistor threshold voltage deviation and IR pressure drop, simultaneously, the electric current that driving transistor is flowed through when the luminous efficiency of the Organic Light Emitting Diode reduces can increase automatically, so that the light emission luminance of the Organic Light Emitting Diode is basically unchanged, and then extend the service life of the active matrix/organic light emitting display.
Description
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 Transistor liquid crystal display (TFT-LCD), does not need a backlight, and has 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 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.
The active matrix organic light emitting display comprises scanning lines, data lines and a pixel array defined by the scanning lines and the data lines, wherein each pixel of the pixel array is connected with the corresponding scanning line and the corresponding data line. For example, the pixel in the nth row and the mth column is connected to the nth scan line Sn and the mth Data line Data. 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 includes a switching transistor T1, a driving transistor T2, a storage capacitor Cs, and an organic light emitting diode OLED, a gate of the switching transistor T1 is connected to a scan line Sn, a source of the switching transistor T1 is connected to a Data line Data, a first substrate of the gate of the driving transistor T2, a drain of the switching transistor T1, and the storage capacitor Cs is connected to a node N1, a second substrate of the source of the driving transistor T2 and the storage capacitor Cs are connected to a first power source ELVDD, a drain of the driving 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 source ELVSS.
When the switching transistor T1 is turned on by the scan line Sn, the Data voltage Vdata provided by the Data line Data is stored in the storage capacitor Cs via the switching transistor T1, so as to control the driving transistor T2 to generate current, and the driving current output by the driving transistor T2 drives 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 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 source voltage Vs of the driving transistor T2 is equal to the power voltage VDD supplied from the first power source ELVDD, the gate voltage Vg of the driving transistor T2 is equal to the Data voltage Vdata supplied from the Data line Data, and thus the gate-source voltage Vgs of the driving transistor T2 is equal to VDD-Vdata. The current Ion flowing between the source and the drain of the driving transistor T2 can be calculated according to the following equation:
Ion＝K×(VDD-Vdata-|Vth|)2
it can be seen that the current flowing through the organic light emitting diode OLED is affected by the threshold voltage Vth of the driving transistor T2 and the power voltage VDD applied to the pixel circuit, and when the threshold voltage Vth and the power voltage VDD of the driving transistor T2 are changed, the current flowing through the organic light emitting diode OLED is greatly changed, resulting in that the organic light emitting diode OLED still emits light of different brightness for the data signal of the same brightness.
However, at present, due to the limitation of the manufacturing process, the threshold voltages of the transistors of the pixels in the active matrix organic light emitting display inevitably have differences, which causes the display to have uneven brightness. Moreover, the power traces connecting the pixel circuits 10 have a certain impedance, and when a current passes through the power traces, an IR drop problem occurs, that is, the impedance of the power traces may affect the power voltage VDD actually reaching the pixel circuits 10, which may cause the power voltage VDD received by each pixel circuit 10 to be inconsistent, thereby aggravating the phenomenon of uneven brightness. Therefore, it is difficult for the existing organic light emitting display to display an image having uniform brightness.
In particular, since the length of the power traces increases as the size of the display panel increases, the brightness deviation between pixels increases as the length of the power traces differs. For a large-sized active matrix organic light emitting display, the IR drop problem caused by the power line impedance becomes more serious, and the display non-uniformity phenomenon becomes more obvious.
Therefore, how to solve the display problem of the conventional active matrix organic light emitting display caused by the threshold voltage deviation and the IR drop of the driving transistor becomes a technical problem to be solved by those skilled in the art.
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 display problem of the conventional active matrix organic light emitting display caused by threshold voltage deviation and IR voltage drop of a driving transistor.
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 transistor connected between a first power source and a second node, a gate of which is connected to a second control line;
a second transistor connected between the first node and the third node, a gate of which is connected to a second control line;
a third transistor connected between the second node and the fourth node, and having a gate connected to the third node;
a fourth transistor connected between the third node and the fourth node, a gate of which is connected to the scan line;
a fifth transistor connected between the data line and the first node, a gate of which is connected to the scan line;
a sixth transistor connected between the fourth node and an anode of the organic light emitting diode, a gate of which is connected to the first control line;
and a storage capacitor connected between the first node and the second node.
Optionally, in the pixel circuit, the first power supply and the second power supply are used as driving power supplies for the organic light emitting diode.
Optionally, in the pixel circuit, the first transistor to the sixth transistor are all P-type thin film transistors.
Alternatively, in the pixel circuit, the first transistor and the second transistor are controlled to be turned on and off by a second control signal supplied from the second control line, the third transistor is controlled to be turned on and off by a potential of the third node, the fourth transistor and the fifth transistor are controlled to be turned on and off by a scan signal supplied from the scan line, and the sixth transistor is controlled to be turned on and off by a first control signal supplied from the first control line.
Optionally, in the pixel circuit, the third transistor is used as a driving transistor, and a current supplied to the organic light emitting diode by the third transistor is determined by a data voltage supplied by the data line, a threshold voltage of the organic light emitting diode, and a second power voltage supplied by the second power source, regardless of the first power voltage supplied by the first power source and the threshold voltage of the third transistor.
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, and a third time period, wherein,
in a first time period, a scanning signal provided by a scanning line is changed from a high level to a low level, a first control signal provided by a first control line is at the high level, a second control signal provided by a second control line is at the low level, a first transistor, a second transistor, a fourth transistor and a fifth transistor are turned on, and a data signal is written;
in a second time period, a scanning signal provided by the scanning line and a first control signal provided by the first control line are both in a low level, a second control signal provided by the second control line is changed from the low level to a high level, the fourth transistor, the fifth transistor and the sixth transistor are turned on, and the first transistor and the second transistor are turned off at the same time, so that the storage capacitor is discharged through the third transistor, the sixth transistor and the organic light emitting diode;
in a third time period, the scanning signal provided by the scanning line is at a high level, the first control signal provided by the first control line and the second control signal provided by the second control line are both at a low level, and the first transistor, the second transistor and the sixth transistor are turned on, so that the third 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 fourth time period, and the fourth time period is set between the first time period and the second time period;
in a fourth time period, the scanning signal provided by the scanning line and the second control signal provided by the second control line are both low level, the first control signal provided by the first control line is changed from high level to low level, and the sixth transistor is turned on.
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 second period and the third period;
in a fifth period, the scanning signal provided by the scanning line is changed from low level to high level, the first control signal provided by the first control line is changed from high level to low level, the second control signal provided by the second control line is high level, the fourth transistor and the fifth transistor are closed, and the writing of the data signal is stopped.
Optionally, in the driving method of the pixel circuit, the scan cycle further includes a sixth time period, and the sixth time period is set between the third time period and the first time period;
in a sixth time period, the scanning signal provided by the scanning line is in a high level, the first control signal provided by the first control line is changed from a low level to a high level, the second control signal provided by the second control line is in a low level, the sixth transistor is turned off, and the organic light emitting diode stops emitting light.
Correspondingly, the invention also provides an active matrix organic light-emitting display which comprises the pixel circuit.
In the pixel circuit, the driving method thereof and the active matrix organic light emitting display provided by the invention, the current output by the driving transistor is determined by the data voltage provided by the data line, the threshold voltage of the organic light emitting diode and the second power voltage provided by the second power supply, and is irrelevant to the threshold voltage of the driving transistor and the first power voltage provided by the first power supply, so that the brightness unevenness caused by the threshold voltage deviation of the driving transistor and the IR voltage drop can be avoided, and simultaneously, the current flowing through the driving transistor can be automatically increased when the luminous efficiency of the organic light emitting diode is reduced, so that the luminous brightness of the organic light emitting diode is basically unchanged, and the service life of the active matrix organic light emitting display is further prolonged.
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 schematic diagram of a pixel circuit according to an embodiment of the present invention;
fig. 3 is a timing diagram of a driving method of a pixel circuit according to an embodiment of the 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. 2, which is a schematic structural diagram of a pixel circuit according to an embodiment of the invention. As shown in fig. 2, the pixel circuit 20 includes:
an organic light emitting diode OLED connected between the first power source ELVDD and the second power source ELVSS;
a first transistor T1 connected between the first power source ELVDD and the second node N2, and having a gate connected to the second control line Em;
a second transistor T2 connected between the first node N1 and the third node N3, and having a gate connected to the second control line Em;
a third transistor T3 connected between the second node N2 and the fourth node N4, and having a gate connected to the third node N3;
a fourth transistor T4 connected between the third node N3 and the fourth node N4, and having a gate connected to the scan line Sn;
a fifth transistor T5 connected between the Data line Data and the first node N1, and having a gate connected to the scan line Sn;
a sixth transistor T6 connected between the fourth node N4 and the anode of the organic light emitting diode OLED, and having a gate connected to the first control line Em-1;
the storage capacitor C is connected between the first node N1 and the second node N2.
Specifically, the pixel circuit 20 is connected to an external power source including a first power source ELVDD and a second power source ELVSS. The first power source ELVDD and the second power source ELVSS serve as a driving power source for the organic light emitting diode OLED. The first power source ELVDD is a high potential pixel power source for supplying a first power source voltage Vdd. The second power source ELVSS is a low potential pixel power source for supplying a second power source voltage Vss.
With continued reference to fig. 2, the pixel circuit 20 is a 6T1C type circuit structure, which includes 6 transistors and 1 capacitor. Preferably, the first to sixth transistors T1 to T6 are all thin film transistors. The first to sixth transistors T1 to T6 may be P-type thin film transistors or N-type thin film transistors. As is known, the P-type tft is turned on when the gate signal is at a low level, and the N-type tft is turned on when the gate signal is at a high level. Therefore, it is sufficient to match the selected transistor type with the on potential.
The on and off of the first transistor T1 and the second transistor T2 are controlled by a second control signal provided by a second control line Em, the on and off of the third transistor T3 are controlled by the potential of the third node N3, the on and off of the fourth transistor T4 and the fifth transistor T5 are controlled by a scan signal provided by a scan line Sn, and the on and off of the sixth transistor T6 are controlled by a first control signal provided by a first control line Em-1.
In this embodiment, the first to sixth transistors T1 to T6 are all P-type thin film transistors. When the scan signal supplied from the scan line Sn transitions to a low level, both the fourth transistor T4 and the fifth transistor T5 are turned on, and the Data signal supplied from the Data line Data is written into the first node N1 via the fifth transistor T5. When the second control signal supplied from the second control line Em is at a low level, both the first transistor T1 and the second transistor T2 are turned on, and the first power voltage Vdd supplied from the first power source ELVDD is applied to the second node N2 via the first transistor T1. When the first control signal provided by the first control line Em-1 is at a low level, the sixth transistor T6 is turned on, and the driving current output from the third transistor T3 flows to the second power source ELVSS along the path of the first power source ELVDD through the first transistor T1, the third transistor T3, the sixth transistor T6, 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 transistor T3 serves as a driving transistor of the pixel, and controls a driving current supplied to the organic light emitting diode OLED corresponding to the potential of the third node N3, 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 transistor T3 is determined by the Data voltage Vdata supplied from the Data line Data, the threshold voltage of the organic light emitting diode OLED, and the second power voltage Vss supplied from the second power source ELVSS, regardless of the first power voltage Vdd supplied from the first power source ELVDD and the threshold voltage of the third transistor T3. Therefore, the pixel circuit 20 can avoid the brightness unevenness caused by the threshold voltage deviation of the transistor and the IR drop, thereby improving the display quality of the display.
Correspondingly, the invention also provides a driving method of the pixel circuit. Referring to fig. 2 and fig. 3 in combination, the driving method of the pixel circuit includes:
the scan cycle includes a first period t1, a second period t2, and a third period t 3; wherein,
in the first period T1, the scan signal provided by the scan line Sn changes from high level to low level, the first control signal provided by the first control line Em-1 is high level, the second control signal provided by the second control line Em is low level, the first transistor T1, the second transistor T2, the fourth transistor T4 and the fifth transistor T5 are turned on, and the data signal is written;
in the second time period T2, the scan signal provided by the scan line Sn and the first control signal provided by the first control line Em-1 are both at a low level, the second control signal provided by the second control line Em changes from the low level to a high level, the fourth transistor T4, the fifth transistor T5 and the sixth transistor T6 are turned on, and the first transistor T1 and the second transistor T2 are turned off at the same time, so that the storage capacitor C is discharged through the third transistor T3, the sixth transistor T6 and the organic light emitting diode OLED;
in the third time period T3, the scan signal provided by the scan line Sn is at a high level, the first control signal provided by the first control line Em-1 and the second control signal provided by the second control line Em are both at a low level, and the first transistor T1, the second transistor T2 and the sixth transistor T6 are turned on, so that the third transistor T3 outputs a current and drives the organic light emitting diode OLED to emit light.
Specifically, the first time period t1 is a data writing phase. In the first period T1, since the scan signal supplied from the scan line Sn is changed from a high level to a low level, the fourth transistor T4 and the fifth transistor T5 controlled by the scan signal are changed from an off state to an on state, the Data signal supplied from the Data line Data is written into the first node N1 via the fifth transistor T5, and simultaneously since the second control signal supplied from the second control line Em is a low level, the first transistor T1 and the second transistor T2 controlled by the second control signal are in an on state, the Data signal supplied from the Data line Data is written into the third node N3 via the fifth transistor T5 and the second transistor T2, and the first power supply voltage Vdd supplied from the first power supply ELVDD is applied to the second node N2 via the first transistor T1.
At this time, the potential of the first node N1 (i.e., the upper substrate potential of the storage capacitor C) is Vdata, and the potential of the second node N2 (i.e., the lower substrate potential of the storage capacitor C) is Vdd.
The second time period t2 is a threshold voltage compensation phase. In the second time period T2, since the scan signal provided by the scan line Sn and the first control signal provided by the first control line Em-1 are both at a low level, the fourth transistor T4 and the fifth transistor T5 controlled by the scan signal are in a conducting state, the sixth transistor T6 controlled by the first control signal is also in a conducting state, and the lower substrate of the storage capacitor C is discharged through the third transistor T3, the sixth transistor T6 and the organic light emitting diode OLED until the conducting current of the organic light emitting diode OLED is almost zero;
when the discharging is finished, the anode voltage of the organic light emitting diode OLED is Voled (i.e. the sum of the threshold voltage of the organic light emitting diode OLED and the second power voltage Vss), and the potential of the second node N2 is Voled + | Vth |. Where Vth is the threshold voltage of the driving transistor T3. Thereby, the threshold voltage of the driving transistor T3 is stored in the storage capacitor C.
Meanwhile, since the fifth transistor T5 is turned on, the data voltage Vdata provided by the data line data is continuously provided to the first node N1 through the fifth transistor T5, and the potential of the first node N1 is still Vdata. Therefore, the voltage difference across the storage capacitor C is equal to Vdata-Voled-Vth.
The third time period t3 is a lighting phase. In the third period T3, since the first control signal provided by the first control line Em-1 and the second control signal provided by the second control line Em are both low level, the first transistor T1, the second transistor T2 and the sixth transistor T6 controlled by the second control signal are all in a turned-on state, and the third transistor T3 outputs current and drives the organic light emitting diode OLED to emit light.
At this time, since the first transistor T1 is turned on, the potential of the second node N2 (i.e., the lower substrate potential of the storage capacitor C) jumps from Voled + | Vth | to Vdd. Due to the coupling effect of the capacitor, the voltage difference between the upper substrate and the lower substrate of the storage capacitor C remains unchanged, so the potential of the first node N1 (i.e., the upper substrate potential of the storage capacitor C) is Vdata + Vdd-Voled-Vth |.
It can be seen that the source voltage of the third transistor T3 is equal to Vdd, and the gate voltage of the third transistor T3 is equal to the voltage of the first node N1, i.e., Vdata + Vdd-Voled-Vth |. Therefore, the gate-source voltage Vgs of the third transistor T3 (i.e., the voltage difference between the gate and the source of the third transistor T3) is calculated by the formula:
vgs ═ Vdd- (Vdata + Vdd-Voled- | Vth |) equation 1;
the calculation formula of the current Ioled flowing through the organic light emitting diode OLED is as follows:
Ioled＝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:
Ioled＝K×(Voled-Vdata)2formula 3;
as can be seen from the expression of formula 3, the current Ioled flowing through the organic light emitting diode OLED is related only to the data voltage Vdata, the threshold voltage of the organic light emitting diode OLED, the second power voltage Vss, and the constant K, and has no relation to the first power voltage Vdd and the threshold voltage Vth of the third transistor T3. Even if the first power voltage Vdd varies or the threshold voltage Vth of the third transistor T3 varies due to the power line impedance, the current Ioled flowing through the organic light emitting diode OLED is not affected. Therefore, the pixel circuit 20 and the driving method thereof can compensate for the threshold voltage and the IR drop, and avoid the uneven brightness caused by the deviation of the threshold voltage and the power trace impedance.
Moreover, when the light emitting efficiency of the organic light emitting diode OLED is reduced, that is, the anode voltage Voled of the organic light emitting diode OLED is higher and higher as the operation time is prolonged, the current Ioled flowing through the organic light emitting diode OLED can be automatically increased to compensate, so that the light emitting brightness of the organic light emitting diode OLED is ensured to be basically unchanged.
The pixel circuit 20 mainly achieves compensation of the threshold voltage and the IR drop through the above three periods of operation, thereby improving the brightness uniformity.
With continued reference to fig. 3, the scan cycle further includes a fourth time period t4, a fifth time period t5, and a sixth time period t 6. The fourth time period t4 is set between the first time period t1 and the second time period t2, the fifth time period t5 is set between the second time period t2 and the third time period t3, and the sixth time period t6 is set between the third time period t3 and the first time period t 1.
In the fourth period T4, the scan signal provided by the scan line Sn and the second control signal provided by the second control line Em are both at a low level, the first control signal provided by the first control line Em-1 changes from a high level to a low level, and the sixth transistor T6 controlled by the first control signal changes from off to on.
In the fifth period T5, the scan signal supplied from the scan line Sn changes from low level to high level, the first control signal supplied from the first control line Em-1 changes from high level to low level, the second control signal supplied from the second control line Em is high level, both the fourth transistor T4 and the fifth transistor T5 controlled by the scan signal are turned on to off, and since the fifth transistor T5 is turned off, the Data signal supplied from the Data line Data cannot be written into the first node N1 via the fifth transistor T5, thereby stopping writing of the Data signal.
In the sixth period T6, the scan signal supplied from the scan line Sn is at a high level, the first control signal supplied from the first control line Em-1 is changed from a low level to a high level, the second control signal supplied from the second control line Em is at a low level, and the sixth transistor T6 controlled by the first control signal is changed from on to off, so that the organic light emitting diode OLED stops emitting light.
The working processes of the first time period t1, the fourth time period t4, the second time period t2, the fifth time period t5, the third time period t3 and the sixth time period t6 are repeated, and the image display function is completed.
Accordingly, the present invention also provides an active matrix organic light emitting display comprising a pixel circuit 20 as described above. Please refer to the above, which is not described herein.
The active matrix organic light emitting display adopting the pixel circuit and the driving method thereof can simultaneously avoid various display problems caused by threshold voltage deviation and IR voltage drop of the driving transistor, and can compensate the luminous efficiency of the organic light emitting diode OLED, so that the active matrix organic light emitting display has higher brightness uniformity and longer service life.
In summary, in the pixel circuit, the driving method thereof and the active matrix organic light emitting display provided by the present invention, the current output by the driving transistor is determined by the data voltage provided by the data line, the threshold voltage of the organic light emitting diode and the second power voltage provided by the second power supply, and is independent of the threshold voltage of the driving transistor and the first power voltage provided by the first power supply, so that the brightness unevenness caused by the threshold voltage deviation of the driving transistor and the IR drop can be avoided, and the current flowing through the driving transistor can be automatically increased when the light emitting efficiency of the organic light emitting diode is reduced, so that the light emitting brightness of the organic light emitting diode is basically unchanged, thereby prolonging the service life of the active matrix organic light emitting display.
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 (10)
1. A pixel circuit, comprising:
an organic light emitting diode connected between a first power source and a second power source;
a first transistor connected between a first power source and a second node, a gate of which is connected to a second control line;
a third transistor connected between the second node and the fourth node;
a sixth transistor connected between the fourth node and an anode of the organic light emitting diode, a gate of which is connected to the first control line;
it is characterized by also comprising:
a second transistor connected between the first node and the third node, a gate of which is connected to a second control line;
a fourth transistor connected between the third node and the fourth node, a gate of which is connected to the scan line;
a fifth transistor connected between the data line and the first node, a gate of which is connected to the scan line;
a storage capacitor connected between the first node and the second node;
wherein a gate of the third transistor is coupled to the third node.
2. The pixel circuit according to claim 1, wherein the first power source and the second power source serve as a driving power source of the organic light emitting diode.
3. The pixel circuit according to claim 1, wherein the first to sixth transistors are P-type thin film transistors.
4. The pixel circuit according to claim 1, wherein on and off of the first transistor and the second transistor are controlled by a second control signal supplied from the second control line, on and off of the third transistor are controlled by a potential of the third node, on and off of the fourth transistor and the fifth transistor are controlled by a scan signal supplied from the scan line, and on and off of the sixth transistor are controlled by a first control signal supplied from the first control line.
5. The pixel circuit according to claim 1, wherein the third transistor functions as a driving transistor, and wherein a current supplied to the organic light emitting diode by the third transistor is determined by a data voltage supplied from the data line, a threshold voltage of the organic light emitting diode, and a second power voltage supplied from a second power source, regardless of the first power voltage supplied from the first power source and the threshold voltage of the third transistor.
6. A driving method of a pixel circuit according to any one of claims 1 to 5, wherein the scanning period includes a first period, a second period, and a third period, wherein,
in a first time period, a scanning signal provided by a scanning line is changed from a high level to a low level, a first control signal provided by a first control line is at the high level, a second control signal provided by a second control line is at the low level, a first transistor, a second transistor, a fourth transistor and a fifth transistor are turned on, and a data signal is written;
in a second time period, a scanning signal provided by the scanning line and a first control signal provided by the first control line are both in a low level, a second control signal provided by the second control line is changed from the low level to a high level, the fourth transistor, the fifth transistor and the sixth transistor are turned on, and the first transistor and the second transistor are turned off at the same time, so that the storage capacitor is discharged through the third transistor, the sixth transistor and the organic light emitting diode;
in a third time period, the scanning signal provided by the scanning line is at a high level, the first control signal provided by the first control line and the second control signal provided by the second control line are both at a low level, and the first transistor, the second transistor and the sixth transistor are turned on, so that the third 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 fourth period of time, the fourth period of time being set between the first period of time and the second period of time;
in a fourth time period, the scanning signal provided by the scanning line and the second control signal provided by the second control line are both low level, the first control signal provided by the first control line is changed from high level to low level, and the sixth transistor is turned on.
8. 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 second period of time and a third period of time;
in a fifth period, the scanning signal provided by the scanning line is changed from low level to high level, the first control signal provided by the first control line is changed from high level to low level, the second control signal provided by the second control line is high level, the fourth transistor and the fifth transistor are closed, and the writing of the data signal is stopped.
9. The method for driving the pixel circuit according to claim 6, wherein the scan cycle further includes a sixth period, the sixth period being provided between the third period and the first period;
in a sixth time period, the scanning signal provided by the scanning line is in a high level, the first control signal provided by the first control line is changed from a low level to a high level, the second control signal provided by the second control line is in a low level, the sixth transistor is turned off, and the organic light emitting diode stops emitting light.
10. An active matrix organic light emitting display comprising the pixel circuit according to any one of claims 1 to 5.
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| US10490126B2 (en) | 2017-07-25 | 2019-11-26 | Wuhan China Star Optoelectronics Semiconductor Display Technology Co., Ltd. | Pixel compensation circuit |
| CN109427287B (en) * | 2017-08-29 | 2020-12-22 | 昆山国显光电有限公司 | Pixel driving circuit suitable for high pixel density, pixel structure and manufacturing method |
| CN107731166B (en) * | 2017-11-23 | 2020-11-27 | 武汉华星光电半导体显示技术有限公司 | Pixel driving circuit, display device and terminal |
| CN107731169A (en) | 2017-11-29 | 2018-02-23 | 京东方科技集团股份有限公司 | A kind of OLED pixel circuit and its driving method, display device |
| CN108053792B (en) * | 2018-01-19 | 2019-09-20 | 昆山国显光电有限公司 | A kind of pixel circuit and its driving method, display device |
| CN108766355B (en) * | 2018-06-01 | 2020-02-14 | 昆山国显光电有限公司 | Pixel driving circuit, driving method, OLED display panel and device |
| CN110047440B (en) * | 2019-05-23 | 2020-07-10 | 京东方科技集团股份有限公司 | Pixel circuit, driving method, display panel and display device |
| CN112365837A (en) | 2020-11-24 | 2021-02-12 | 北京京东方技术开发有限公司 | Pixel circuit, driving method thereof and display device |
| CN115985239B (en) * | 2021-10-14 | 2024-10-22 | 上海和辉光电股份有限公司 | Pixel circuit, driving method thereof and organic light emitting display device |
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