CN106920518A - Image element circuit and its driving method and active matrix/organic light emitting display - Google Patents
Image element circuit and its driving method and active matrix/organic light emitting display Download PDFInfo
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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]
- G09G3/3266—Details of drivers for scan electrodes
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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
- G09G3/3258—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 voltage across the light-emitting element
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- Electroluminescent Light Sources (AREA)
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Abstract
In the image element circuit and its driving method and active matrix/organic light emitting display that the present invention is provided, by third transistor, the compensation circuit of the 4th transistor and the 5th transistor composition is compensated to the threshold voltage of transistor seconds, so that the first supply voltage that the data voltage that is provided by data wire of the electric current that the transistor seconds is exported and the first power supply are provided is determined, and it is unrelated with the threshold voltage of the transistor seconds, therefore, it is possible to the brightness disproportionation for avoiding the threshold voltage deviation from causing, simultaneously, the quantity of the transistor of the image element circuit is reduced, so that the active matrix/organic light emitting display easily realizes high-resolution.
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 Thin Film 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 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.
A pixel of an active matrix organic light emitting display includes an organic light emitting diode and a pixel circuit for supplying a driving current corresponding to a data signal to 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 pixel circuit 10 of the conventional active matrix organic light emitting display generally includes a first transistor T1, a second transistor T2, and a storage capacitor Cs, wherein a gate of the first transistor T1 is connected to a scan line Sn, a source of the first transistor T1 is connected to a data line Dm, a gate of the second transistor T2, a drain of the first transistor T1, and a first substrate of the storage capacitor Cs are all connected to a gate of the second transistor T2, a source of the second transistor T2 and a second substrate of the storage capacitor Cs are all connected to a first power source ELVDD, a drain of the second 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.
The first transistor T1 serves as a switching transistor, and the second transistor T2 serves as a driving transistor. When the first transistor T1 is turned on by the scan line Sn, the data voltage Vdata provided by the data line Dm is stored in the storage capacitor Cs via the first transistor T1, thereby controlling the second transistor T2 to generate a 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.
As can be seen from the above description, the current Ion flowing through the organic light emitting diode OLED is affected by the threshold voltage Vth of the driving transistor T2.
In actual production, it is difficult to ensure that the threshold voltages of the thin film transistors of the respective pixels are the same in the current process level, and the threshold voltage of the driving transistor inevitably varies. The threshold voltage of the driving transistor T2 varies, which causes a large variation in the current flowing through the organic light emitting diode OLED.
And the brightness of the pixel is determined by the current Ion flowing through the organic light emitting diode OLED. Due to the deviation of the threshold voltage Vth of the driving transistor T2, even if each pixel receives a data signal of the same luminance, the current Ion flowing through the organic light emitting diode OLED is different, and the luminance of the pixel is also different, so that the active matrix organic light emitting display has a problem of display non-uniformity.
For this reason, various pixel circuits having threshold voltage compensation functions are proposed to improve the brightness uniformity of the active matrix organic light emitting display. However, in practical use, it is found that although these pixel circuits have a certain threshold voltage compensation capability, the circuit structure is complex, at least 6 transistors and 1 storage capacitor are required, the number of transistors is large, and a large area is required, so that it is not easy to realize high resolution.
Therefore, how to solve the problem that the existing active matrix organic light emitting display cannot realize high resolution on the basis of ensuring the brightness uniformity becomes a technical problem to be solved urgently by 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, and aims to solve the problem that the conventional active matrix organic light emitting display cannot realize high resolution on the basis of ensuring brightness uniformity.
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 the first node and the second node, a gate of which is connected to the scan line;
a second transistor connected between the first power source and an anode of the organic light emitting diode, a gate of which is connected to the first node;
a third transistor connected between the data line and the drain of the fourth transistor, the gate of which is connected to the second control line;
a fourth transistor connected between the second node and the drain of the third transistor, the gate of which is connected to the second node;
a fifth transistor connected between the third power supply and the second node, a gate of which is connected to the first control line; and
and a storage capacitor connected between the first power source and the first node.
Alternatively, in the pixel circuit, the first power supply is a high-potential pixel power supply, the second power supply is a low-potential pixel power supply, and the first power supply and the second power supply serve as a driving power supply for the organic light emitting diode.
Optionally, in the pixel circuit, the third power supply is a low-level voltage source for providing an initialization voltage.
Optionally, in the pixel circuit, the first transistor to the fifth transistor are all thin film transistors.
Optionally, in the pixel circuit, the first transistor to the fifth transistor are all P-type thin film transistors.
Alternatively, in the pixel circuit, on and off of the first transistor is controlled by the scan line, on and off of the fifth transistor is controlled by the first control line, and on and off of the third transistor is controlled by the second control line.
Optionally, in the pixel circuit, the second transistor serves as a driving transistor, and a current supplied to the organic light emitting diode by the second transistor is determined by a data voltage supplied from the data line and a first power voltage supplied from the first power source, regardless of a second power voltage supplied from the second power source and a threshold voltage of the second transistor. Accordingly, the present invention also provides a driving method of a pixel circuit, the driving method of the pixel circuit including 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 at a low level, a control signal provided by a first control line is changed from the high level to the low level, a control signal provided by a second control line is at the high level, a first transistor and a fifth transistor are turned on, and a first node is initialized through a third power supply;
in a second time period, the scanning signal provided by the scanning line keeps low level, the control signal provided by the second control line is changed from high level to low level, the control signal provided by the first control line is high level, the fifth transistor is closed, the third transistor is opened, and the threshold voltage of the fourth transistor is sampled while the data signal is written;
in a third time period, the scanning signal provided by the scanning line is changed from low level to high level, the control signals provided by the first control line and the second control line are kept at high level, the first transistor is closed, and current is output through the second transistor to drive the organic light-emitting diode to emit light.
Optionally, in the driving method of the pixel circuit, in a second period, the data signal provided by the data line is kept at a low level; in the first period and the third period, the data signal supplied from the data line maintains a high level.
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 compensation circuit composed of the third transistor, the fourth transistor and the fifth transistor compensates the threshold voltage of the second transistor, so that the current output by the second transistor is determined by the data voltage provided by the data line and the first power voltage provided by the first power supply, and is irrelevant to the threshold voltage of the second transistor, therefore, the uneven brightness caused by the deviation of the threshold voltage can be avoided, and simultaneously, the number of the transistors of the pixel circuit is reduced, so that the active matrix organic light emitting display is easy to realize high resolution.
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. The pixel circuit 20 includes:
an Organic Light Emitting Diode (OLED) connected between the first power supply and the second power supply;
a first transistor M1 connected between the first node N1 and the second node N2, and having a gate connected to the scan line Sn;
a second transistor M2 connected between the first power source and the anode of the organic light emitting diode OLED, and having a gate connected to the first node N1;
a third transistor M3 connected between the data line and the drain of the fourth transistor M4, and having its gate connected to the second control line Sa 2;
a fourth transistor M4 connected between the second node N2 and the drain of the third transistor M3, and having a gate connected to the second node N2;
a fifth transistor M5 connected between the third power supply and the second node N2, and having a gate connected to the first control line Sa 1; and
the storage capacitor Cs is connected between the first power source and the first node N1.
Specifically, the pixel circuit 20 is connected to an external power source, the external power source includes a first power source, a second power source, and a third power source, and the first power source, the second power source, and the third power source are all dc voltage sources. Wherein the third power supply is generally a low level voltage source for providing an initialization voltage Vref. 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, and the first power supply and the second power supply serve as a driving power supply of the organic light emitting diode OLED. It should be understood that the high potential pixel power supply herein is relative to the low potential pixel power supply herein, i.e., the first power supply is at a higher potential relative to the second power supply, which is at a lower potential relative to the first power supply.
In this embodiment, the voltage value of the initialization voltage Vref is close to the voltage value of the second power supply voltage Vss.
As shown in fig. 2, the pixel circuit 20 is a 5T1C type circuit structure, and includes 5 transistors and 1 capacitor. A first electrode of the first transistor M1 is connected to the data line through the third transistor M3, a second electrode of the first transistor M1 is connected to the first node N1, a gate of the first transistor M1 is connected to the scan line Sn, and the first transistor M1 transmits the data signal Vdata provided by the data line to the first node N1 according to the scan signal provided by the scan line Sn. That is, the first transistor M1 functions as a switching transistor of the pixel.
A first electrode of the second transistor M2 is connected to a first power source, a second electrode of the second transistor M2 is connected to an anode of the organic light emitting diode OLED, a gate electrode of the second transistor M2 is connected to the first node N1, and the second transistor M2 is used to supply a driving current corresponding to a data signal from the first power source to the organic light emitting diode OLED. That is, the second transistor M2 functions as a driving transistor of the pixel.
The storage capacitor Cs is connected between the first node N1 and a first power source for storing the data signal Vdata-Vth. Where Vth is the threshold voltage of the fourth transistor M4.
A first electrode of the third transistor M3 is connected to the data line, a second electrode of the third transistor M3 is connected to a second electrode of the fourth transistor M4, a first electrode of the fourth transistor M4 is shorted with a gate thereof to the second node N2, a first electrode of the fifth transistor is connected to the third power supply, and a second electrode of the fifth transistor is connected to the second node N2. The third transistor M3, the fourth transistor M4, and the fifth transistor M5 constitute a compensation circuit for compensating the threshold voltage of the driving transistor. Here, the first electrode and the second electrode are different electrodes. For example, when the first electrode is set as a source, the second electrode is set as a drain. Here, since the fourth transistor M4 and the driving transistor M2 have the same structure and are located close to each other, the fourth transistor M4 has a uniform threshold voltage as a mirror transistor of the driving transistor M2.
In this embodiment, the first transistor M1 to the fifth transistor M5 are all thin film transistors. Preferably, the first transistor M1 to the fifth transistor M5 are all P-type thin film transistors.
With continued reference to fig. 2, the pixel circuit 20 controls the first transistor M1 to be turned on and off by the scan line Sn, controls the fifth transistor M5 to be turned on and off by the first control line Sa1, and controls the third transistor M3 to be turned on and off by the second control line Sa 2.
When the scan signal provided by the scan line Sn transitions to a low level, the first transistor M1 is turned on. When the scan signal supplied from the scan line Sn transitions to a high level, the first transistor M1 is turned off.
When the control signal supplied from the first control line Sa1 transitions to a low level, the fifth transistor M5 is turned on, and the initialization voltage Vref supplied from the third power source is applied to the second node N2 via the fifth transistor M5. When the control signal supplied from the first control line Sa1 transitions to a high level, the fifth transistor M5 is turned off, and the initialization voltage Vref supplied from the third power supply cannot be applied to the second node N2 via the fifth transistor M5.
When the control signal supplied from the second control line Sa2 transitions to a low level, the third transistor M3 is turned on, and the data signal Vdata supplied from the data line is supplied to the second node N2 via the third transistor M3 and the fourth transistor M4. When the control signal supplied from the second control line Sa2 transitions to a high level, the third transistor M3 is turned off, and the data signal Vdata supplied from the data line cannot be supplied to the second node N2 through the third transistor M3.
In this embodiment, the second transistor M2 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 second transistor M2 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 initialization voltage Vref supplied by the third power source, and the threshold voltage of the second transistor M2. 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.
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 T3; wherein,
in a first period T1, the scan signal provided by the scan line Sn is at a low level, the control signal provided by the first control line Sa1 changes from a high level to a low level, the control signal provided by the second control line Sa2 is at a high level, the first transistor M1 and the fifth transistor M5 are turned on, and the first node N1 is initialized by the third power supply;
in the second period T2, the scan signal supplied from the scan line Sn is kept at a low level, the control signal supplied from the second control line Sa2 is changed from a high level to a low level, the control signal supplied from the first control line Sa1 is at a high level, the fifth transistor M5 is turned off, the third transistor M3 is turned on, and the threshold voltage of the fourth transistor M4 is sampled while the data signal is written;
in the third period T3, the scan signal supplied from the scan line Sn changes from low level to high level, the control signals supplied from the first control line Sa1 and the second control line Sa2 are both kept at high level, the first transistor M1 is turned off, and current is output through the second transistor M2 to drive the organic light emitting diode OLED to emit light.
Specifically, in the first period T1, since the scan signal supplied from the scan line Sn is at a low level, the first transistor M1 controlled by the scan line Sn is in a turned-on state, and since the control signal supplied from the first control line Sa1 is changed from a high level to a low level, the fifth transistor M5 controlled by the first control line Sa1 is changed from a turn-off state to a turn-on state, and thus the initialization voltage Vref supplied from the third power supply is supplied to the first node N1 via the fifth transistor M5 and the first transistor M1.
The first period T1 is an initialization period during which the storage capacitor Cs is initialized with the third power supply. After the initialization, the voltage of the first node N1 is Vref, i.e., the lower substrate voltage of the storage capacitor Cs is Vref.
In the second period T2, since the control signal supplied from the first control line Sa1 maintains the high level, the fifth transistor M5 is in an off state, and the initialization voltage Vref supplied from the third power source cannot be supplied to the first node N1 via the fifth transistor M5 and the first transistor M1. Meanwhile, since the scan signal provided by the scan line Sn is maintained at a low level, the first transistor M1 controlled by the scan line Sn is still in an on state, since the control signal provided by the second control line Sa2 is changed from a high level to a low level, the third transistor M3 controlled by the second control line Sa2 is changed from off to on, the data signal Vdata provided by the data line starts to be written into the pixel via the third transistor M3, since the first transistor M1, the third transistor M3 and the fourth transistor M4 are all turned on at this time, the data signal Vdata provided by the data line is sequentially provided to the first node N1 via the third transistor M3, the fourth transistor M4 and the first transistor M1, the voltage of the first node N1 starts to rise from Vref, and the fourth transistor M4 is changed from on to off when the voltage of the first node N1 rises to Vdata- |.
The second period T2 is a programming period during which the data signal Vdata supplied from the data line and a voltage reflecting the threshold voltage of the fourth transistor M4 are stored in the storage capacitor Cs, thereby enabling sampling of the threshold voltage of the fourth transistor M4. At this time, the voltage of the first node N1, i.e., the lower substrate voltage of the storage capacitor Cs, is equal to Vdata- | Vth |.
In the third period T3, since the scan signal supplied from the scan line Sn is changed from the low level to the high level, the first transistor M1 controlled by the scan line Sn is changed from on to off, and since the control signals supplied from the first control line Sa1 and the second control line Sa2 are both kept at the high level, the fifth transistor M5 controlled by the first control line Sa1 and the third transistor M3 controlled by the second control line Sa2 are both in an off state. At this time, the voltage of the first node N1 is maintained at Vdata | Vth |.
The third period T3 is a light emitting period, and since the second transistor M2 is turned on, the driving current Ion output by the second transistor M2 flows to the second power source along the path of the first power source through the second transistor M2 and the organic light emitting diode OLED, so that the organic light emitting diode OLED is turned on to emit light.
At this time, the source voltage of the second transistor M2 is Vdd, the gate voltage of the second transistor M2 is equal to the voltage of the first node N1, i.e., Vdata- | Vth |, and therefore, the calculation formula of the gate-source voltage Vgs of the second transistor M2 (i.e., the voltage difference between the gate and the source of the second transistor M2) is:
vgs ═ Vdd- (Vdata- | Vth |) equation 1;
and the calculation formula of the current Ion flowing through the organic light emitting diode OLED is:
Ion＝K×(Vgs-|Vth2|)2formula 2;
where K is the product of the electron mobility, the width-to-length ratio, and the capacitance per unit area of the transistor, and Vth2 is the threshold voltage of the second transistor M2. Since the second transistor M2 and the fourth transistor M4 have uniform threshold voltages as mirror transistors, it can be obtained according to equations 1 and 2:
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 first power voltage Vdd supplied from the first power source, the data voltage Vdata, and the constant K, and is not related to the second power voltage Vss supplied from the second power source and the threshold voltage Vth2 of the second transistor M2. Therefore, even if the threshold voltage Vth2 of the second transistor M2 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 data signal Vdata supplied from the data line maintains a high level for the first period T1, maintains a low level for the second period T2, and maintains a high level for the third period T3.
The working processes of the first period T1, the second period T2 and the third period T3 are repeated to complete the image display function.
Accordingly, the present invention also provides an active matrix organic light emitting display including the pixel circuit 20 as described above. Please refer to the above, which is not described herein.
The active matrix organic light emitting display using the pixel circuit 20 and the driving method thereof can not only avoid brightness unevenness caused by threshold voltage deviation of driving transistors, but also easily achieve high resolution because the number of transistors used in the pixel circuit 20 is only 5, which is less than the number (at least 6) of transistors used in a conventional pixel circuit having a threshold voltage compensation function.
In summary, in the pixel circuit, the driving method thereof and the active matrix organic light emitting display provided by the present invention, the compensation circuit composed of the third transistor, the fourth transistor and the fifth transistor compensates the threshold voltage of the second transistor, so that the current output by the second transistor is determined by the data voltage provided by the data line and the first power voltage provided by the first power supply, and is independent of the threshold voltage of the second transistor, thereby preventing the brightness unevenness caused by the threshold voltage deviation, and simultaneously, the number of transistors of the pixel circuit is reduced, so that the active matrix organic light emitting display easily realizes high resolution.
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 the first node and the second node, a gate of which is connected to the scan line;
a second transistor connected between the first power source and an anode of the organic light emitting diode, a gate of which is connected to the first node;
a third transistor connected between the data line and the drain of the fourth transistor, the gate of which is connected to the second control line;
a fourth transistor connected between the second node and the drain of the third transistor, the gate of which is connected to the second node;
a fifth transistor connected between the third power supply and the second node, a gate of which is connected to the first control 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 source is a high-potential pixel power source, wherein the second power source is a low-potential pixel power source, and wherein the first power source and the second power source serve as a driving power source for the organic light emitting diode.
3. The pixel circuit according to claim 1, wherein the third power supply is a low level voltage supply for providing an initialization voltage.
4. The pixel circuit according to claim 1, wherein the first to fifth transistors are thin film transistors.
5. The pixel circuit according to claim 4, wherein the first to fifth transistors are all P-type thin film transistors.
6. The pixel circuit according to claim 1, wherein on and off of the first transistor is controlled by the scan line, on and off of the fifth transistor is controlled by the first control line, and on and off of the third transistor is controlled by the second control line.
7. The pixel circuit according to claim 1, wherein the second transistor functions as a driving transistor, and a current supplied to the organic light emitting diode by the second transistor is determined by a data voltage supplied from the data line and a first power voltage supplied from the first power source, regardless of a second power voltage supplied from the second power source and a threshold voltage of the second transistor.
8. A driving method of a pixel circuit according to any one of claims 1 to 7, 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 at a low level, a control signal provided by a first control line is changed from the high level to the low level, a control signal provided by a second control line is at the high level, a first transistor and a fifth transistor are turned on, and a first node is initialized through a third power supply;
in a second time period, the scanning signal provided by the scanning line keeps low level, the control signal provided by the second control line is changed from high level to low level, the control signal provided by the first control line is high level, the fifth transistor is closed, the third transistor is opened, and the threshold voltage of the fourth transistor is sampled while the data signal is written;
in a third time period, the scanning signal provided by the scanning line is changed from low level to high level, the control signals provided by the first control line and the second control line are kept at high level, the first transistor is closed, and current is output through the second transistor to drive the organic light-emitting diode to emit light.
9. The driving method of a pixel circuit according to claim 8, wherein in the second period, the data signal supplied from the data line is kept at a low level; in the first period and the third period, the data signal supplied from the data line maintains a high level.
10. An active matrix organic light emitting display, comprising: a pixel circuit as claimed in any one of claims 1 to 7.
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| Application Number | Priority Date | Filing Date | Title |
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| CN201510991538.8A CN106920518A (en) | 2015-12-25 | 2015-12-25 | Image element circuit and its driving method and active matrix/organic light emitting display |
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| CN201510991538.8A CN106920518A (en) | 2015-12-25 | 2015-12-25 | Image element circuit and its driving method and active matrix/organic light emitting display |
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| WO2020252913A1 (en) * | 2019-06-20 | 2020-12-24 | 深圳市华星光电半导体显示技术有限公司 | Pixel drive circuit and display panel |
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Application publication date: 20170704 |