CN109036288B - Pixel circuit and control method thereof - Google Patents
Pixel circuit and control method thereof Download PDFInfo
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- CN109036288B CN109036288B CN201811139900.9A CN201811139900A CN109036288B CN 109036288 B CN109036288 B CN 109036288B CN 201811139900 A CN201811139900 A CN 201811139900A CN 109036288 B CN109036288 B CN 109036288B
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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)
- Control Of El Displays (AREA)
Abstract
The invention relates to a pixel circuit and a control method thereof, and the pixel circuit comprises a transistor T1, a transistor T2, a transistor T3, a transistor T4, a transistor T5, a transistor T6, a transistor T7, a capacitor C1 and a light-emitting diode D1. In the pixel circuit, the transistor T1 is a driving transistor, the pixel circuit performs voltage compensation on the control terminal of the transistor T1 through the capacitor C1 by using the second reference voltage Vref2, so that the driving current flowing through the transistor T1 is independent of the voltage value of the first power supply VDD, and the driving current flowing through the transistor T1 is the light emitting current of the light emitting diode D1, thereby eliminating the influence of the on-line current-resistance voltage drop of the first power supply VD on the light emitting current. The driving current flowing through the transistor T1 is related to the second reference voltage Vref2, and the driving current does not flow through the signal line providing the second reference voltage Vref2, so the light emitting uniformity of the panel can be improved due to the influence of the current-resistance voltage drop in wireless.
Description
Technical Field
The present invention relates to the field of display, and in particular, to a pixel circuit and a control method thereof.
Background
Organic light emitting display panels are increasingly used in the display field because of their advantages of high contrast, low power consumption, wide viewing angle, fast response speed, etc. Generally, an organic light emitting display panel includes pixel circuits arranged in an array, the pixel circuits generally include light emitting diodes and a power supply, and a current flowing through the light emitting diodes is related to a power supply voltage. In the display panel, the distances from each light emitting diode to the power supply are different, so that the voltage drop on the line generated in the voltage transmission process is also different, and therefore, the power supply voltage actually obtained by each light emitting diode is different, so that the current flowing through the light emitting diode is different, the brightness of the light emitting diode is also different, and the brightness of the light emitting diode is uneven.
Disclosure of Invention
In view of the above, it is necessary to provide a pixel circuit and a control method thereof for solving the problem of non-uniform brightness of a display panel caused by voltage drop on a line.
The pixel circuit is characterized by comprising a transistor T1, a transistor T2, a transistor T3, a transistor T4, a transistor T5, a transistor T6, a transistor T7, a capacitor C1 and a light-emitting diode D1;
the control terminal of the transistor T4 is used for inputting a first scan signal, the first pole of the transistor T4 is connected to the second pole of the transistor T3, the control terminal of the transistor T1 and the first plate of the capacitor C1, respectively, the second pole of the transistor T4 is connected to the second pole of the transistor T7, and is used for inputting a first reference voltage Vref 1;
a control terminal of the transistor T3 is used for inputting a second scan signal, a first pole of the transistor T3 is connected to the second pole of the transistor T1 and the first pole of the transistor T6, respectively, and the first pole of the transistor T1 is used for inputting a first power VDD;
a control terminal of the transistor T6 is used for inputting a light emitting control signal, a second terminal of the transistor T6 is respectively connected to an anode of the light emitting diode D1 and a first terminal of the transistor T7, a control terminal of the transistor T7 is used for inputting the first scan signal, and a cathode of the light emitting diode D1 is used for inputting a second power source VSS;
a control terminal of the transistor T2 is used for inputting the second scan signal, a first pole of the transistor T2 is used for inputting the data signal, and a second pole of the transistor T2 is connected to the second plate of the capacitor C1 and the second pole of the transistor T5, respectively;
the control terminal of the transistor T5 is used for inputting the light emitting control signal, and the first electrode of the transistor T5 is used for inputting a second reference voltage Vref 2.
In one embodiment, the voltage value of the first reference voltage Vref1 is smaller than the voltage value of the second power source VSS.
In one embodiment, the transistor T1, the transistor T2, the transistor T3, the transistor T4, the transistor T5, the transistor T6, and the transistor T7 are any one of a low temperature polysilicon thin film transistor, an oxide semiconductor thin film transistor, and an amorphous silicon thin film transistor.
In the pixel circuit, the transistor T1 is a driving transistor, the pixel circuit performs voltage compensation on the control terminal of the transistor T1 through the capacitor C1 by using the second reference voltage Vref2, so that the driving current flowing through the transistor T1 is independent of the voltage value of the first power supply VDD, and the driving current flowing through the transistor T1 is the light emitting current of the light emitting diode D1, thereby eliminating the influence of the on-line current-resistance voltage drop of the first power supply VD on the light emitting current. The driving current flowing through the transistor T1 is related to the second reference voltage Vref2, and the driving current does not flow through the signal line providing the second reference voltage Vref2, so the light emitting uniformity of the panel can be improved due to the influence of the current-resistance voltage drop in wireless.
A driving method of a pixel circuit is based on the pixel circuit and comprises the following steps:
an initialization stage, in which the first scan signal is a low level signal and the second scan signal is a high level signal, so that the first reference voltage Vref1 initializes the pixel circuit;
a data writing stage in which the second scanning signal is a low level signal and the first scanning signal and the light emission control signal are high level signals, so that the data signal is written into the pixel circuit;
in the light emitting period, the light emitting control signal is a low level signal, and the first scan signal and the second scan signal are high level signals, so that a current flows through the light emitting diode D1.
In one embodiment, in the initialization phase, the light emitting control signal is a high level signal.
In one embodiment, in the initialization phase, the light emitting control signal is a low level signal.
In one embodiment, the initialization phase includes a first phase and a second phase;
the first phase, in which the first scan signal and the light emission control signal are low level signals, the light emission control signal controls the transistor T5 to be turned on, and the second reference voltage Vref2 initializes the second plate of the capacitor C1 through the transistor T5;
in the second stage, the first scanning signal is a low level signal, and the light-emitting control signal is a high level signal.
In one embodiment, in the initialization phase, the first scan signal controls the transistor T4 and the transistor T7 to be turned on;
the first reference voltage Vref1 initializes the control terminal of the transistor T1 and the first plate of the capacitor C1 through the transistor T4, and the transistor T1 is turned on; the first reference voltage Vref1 initializes the anode of the led D1 through the transistor T7, so that the control terminal of the transistor T1 and the first plate of the capacitor C1 have a potential of Vref 1.
In one embodiment, in the data writing phase, the second scan signal controls the transistor T2 to be turned on, and the data signal is written into the second plate of the capacitor C1 through the transistor T2, so that the potential of the second plate of the capacitor C1 is Vdata;
the first power supply VDD writes a power supply voltage into the transistor T1, so that the potential of the first electrode of the transistor T1 is VDD, and the potential of the control terminal of the transistor T1 is VDD- | Vth |.
In one embodiment, during the light emitting phase, the light emitting control signal controls the transistor T5 to be turned on, and the second reference voltage Vref2 performs voltage compensation on the gate of the transistor T1 through the transistor T5 and the capacitor C1, so that the current flowing through the transistor T1 is independent of the power voltage provided by the first power line.
According to the driving method of the pixel circuit, the second reference voltage is added to compensate the current-resistance voltage drop on the first power line, and meanwhile, the circuit structure and the control method thereof compensate the influence of the threshold voltage on the luminous current, and the uniformity of screen body luminescence is improved.
Drawings
Fig. 1 is a circuit diagram of a pixel circuit provided in an embodiment of the present application;
fig. 2 is a timing diagram of a pixel circuit driving method according to an embodiment of the present application;
fig. 3 is a timing diagram of a pixel circuit driving method according to another embodiment of the present application;
fig. 4 is a timing diagram of a pixel circuit driving method according to another embodiment of the present application.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.
It will be understood that when an element is referred to as being "disposed on" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. The terms "vertical," "horizontal," "left," "right," and the like as used herein are for illustrative purposes only and do not represent the only embodiments.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.
Referring to fig. 1, an embodiment of the present application provides a pixel circuit including a transistor T1, a transistor T2, a transistor T3, a transistor T4, a transistor T5, a transistor T6, a transistor T7, a capacitor C1, and a light emitting diode D1.
The control terminal of the transistor T4 is used for inputting a first scan signal, the first electrode of the transistor T4 is connected to the second electrode of the transistor T3, the control terminal of the transistor T1 and the first plate of the capacitor C1, respectively, and the second electrode of the transistor T4 is connected to the second electrode of the transistor T7 for inputting a first reference voltage Vref 1. The control terminal of the transistor T3 is used for inputting the second scan signal, and the first pole of the transistor T3 is connected to the second pole of the transistor T1 and the first pole of the transistor T6, respectively. A first pole of the transistor T1 is used for inputting the first power supply VDD. The control terminal of the transistor T6 is used for inputting a light emitting control signal, and the second pole of the transistor T6 is connected to the anode of the light emitting diode D1 and the first pole of the transistor T7, respectively. The control terminal of the transistor T7 is used for inputting a first scan signal. The cathode of the light emitting diode D1 is used for inputting the second power supply VSS. The control terminal of the transistor T2 is for inputting the second scan signal, the first pole of the transistor T2 is for inputting the data signal, and the second pole of the transistor T2 is connected to the second plate of the capacitor C1 and the second pole of the transistor T5, respectively. The control terminal of the transistor T5 is used for inputting a light emission control signal, and the first pole of the transistor T5 is used for inputting a second reference voltage Vref 2.
In this embodiment, the transistor T2, the transistor T3, the transistor T4, the transistor T5, the transistor T6, and the transistor T7 are all switching transistors, and the transistor T1 is a driving transistor. The capacitor C1 is an energy storage capacitor, and the light Emitting Diode D1 is an OLED (organic light-Emitting Diode). The transistors in this embodiment are all P-type transistors, and it can be understood that the control terminal is a gate of the transistor, the first electrode is a source of the transistor, the second electrode is a drain of the transistor, and a low level is applied to the control terminal of the transistor to turn on the transistor. Of course, in other embodiments, the transistor may be an N-type transistor, and when the N-type transistor is used as a transistor in the pixel circuit, a high-level signal is input to a control terminal of the transistor to turn on the transistor.
The first scan signal connects the control terminals of the transistor T4 and the transistor T7, and controls the transistor T4 and the transistor T7 to be turned on, so that the first reference voltage Vref1 initializes the gate of the transistor T1 through the transistor T4, and initializes the anode of the light emitting diode D1 through the transistor T7. The second SCAN signal SCAN2 controls the transistor T2 to be turned on, so that the data signal is written into the first plate of the capacitor C1 through the transistor T2. The light emission control signal may control the transistor T5 to be turned on, so that the second reference voltage Vref2 compensates the control terminal of the transistor T1 through the capacitor C1, so that the driving current flowing through the transistor T1 is independent of the voltage of the first power source VDD.
In this embodiment, the first power source VDD may be a positive voltage, and the second power source VSS may be a negative voltage. The driving transistor T1 may generate a current by the first power source VDD, the current flows through the light emitting diode D1 to make the light emitting diode D1 emit light, and the current flows from the light emitting diode D1 to the second power source VSS when the light emitting diode D1 emits light.
In the pixel circuit provided in the above embodiment, the transistor T1 is a driving transistor, the pixel circuit performs voltage compensation on the control terminal of the transistor T1 through the capacitor C1 by using the second reference voltage Vref2, so that the driving current flowing through the transistor T1 is independent of the voltage value of the first power supply VDD, the driving current flowing through the transistor T1 is the light emitting current of the light emitting diode D1, and further the influence of the on-line current-resistance voltage drop of the first power supply VD on the light emitting current can be eliminated. The driving current flowing through the transistor T1 is related to the second reference voltage Vref2, and the driving current does not flow through the signal line providing the second reference voltage Vref2, so the light emitting uniformity of the panel can be improved due to the influence of the current-resistance voltage drop in wireless.
In one embodiment, the transistor T2, the transistor T3, the transistor T4, the transistor T5, the transistor T6, and the transistor T7 may be any one of a low temperature polysilicon thin film transistor, an oxide semiconductor thin film transistor, and an amorphous silicon thin film transistor.
One embodiment of the present application provides a display panel, which includes the aforementioned pixel circuits arranged in an array. The display panel further includes a data driver, a scan driver, and a light emission controller. One end of each of the first scanning signal line and the second scanning signal line is connected with each row of pixel circuits, the other end of each of the first scanning signal line and the second scanning signal line is connected with a scanning driver, and the scanning driver provides scanning signals and transmits the scanning signals to the pixel circuits through the scanning signal lines. One end of each data signal line is connected with each column of pixel circuits, the other end of each data signal line is connected with a data driver, and the data driver provides data signals and transmits the data signals to the pixel circuits through the data signal lines. One end of each light-emitting control signal line is connected with each row of pixel circuits, the other end of each light-emitting control signal line is connected with a light-emitting controller, and the light-emitting controller provides light-emitting control signals and transmits the light-emitting control signals to the pixel circuits through the light-emitting control signal lines.
An embodiment of the present application provides a display device including the above display panel.
Referring to fig. 1 and fig. 2, an embodiment of the present disclosure provides a driving method of a pixel circuit, which is based on the pixel circuit shown in fig. 1. The driving method comprises the following three stages:
in the initialization stage t1, the first scan signal is a low level signal, and the second scan signal is a high level signal, so that the pixel circuit is initialized by the first reference voltage Vref 1.
In the data writing period t2, the second scan signal is a low level signal, and the first scan signal and the light-emitting control signal are high level signals, so that the data signal is written into the pixel circuit.
In the light-emitting period t3, the light-emitting control signal is a low level signal, and the first scan signal and the second scan signal are high level signals, so that a current flows through the light-emitting diode D1.
Specifically, referring to fig. 2, in an embodiment, in the initialization stage T1, the first scan signal is a low level signal, and the first scan signal controls the transistor T4 to be turned on, so that the first reference voltage Vref1 initializes the control terminal of the transistor T1 and the first plate of the capacitor C1 through the transistor T4, so that the transistor T1 is turned on. Meanwhile, the first reference voltage Vref1 initializes the anode of the light emitting diode D1 through the transistor T7. The second scan signal is a high level signal, and the transistor T2 and the transistor T3 are turned off. The light emission control signal is also a high level signal, and the transistor T5 and the transistor T6 are turned off. It is understood that the voltage value of the first reference voltage Vref1 is less than the voltage value of the second power source VSS to ensure that the light emitting diode D1 does not emit light at the time of initialization. The initialization can eliminate the influence of the residual current of the last lighting stage on the lighting stage, ensure that all pixel circuits are in the same initial state, and improve the lighting uniformity of the screen body.
In the data writing phase T2, the second scan signal is a low signal, and the transistor T2 is turned on. The data signal is written into the second plate of the capacitor C1 through the transistor T2, so that the potential of the second plate of the capacitor C1 is Vdata. Since the transistor T1 is turned on in the initialization phase T1, after the circuit state is stabilized in the data writing phase T2, the potential of the first electrode of the transistor T1 is VDD, and the potential of the control terminal of the transistor T1 is VDD- | Vth |, so that the threshold voltage can be compensated.
In the luminescenceAt the period T3, the light emission control signal is at low level, and the transistor T5 and the transistor T6 are turned on. The second reference voltage Vref2 is written to the second plate of the capacitor C1 through the transistor T5. The potential of the second plate of the capacitor C1 is changed from Vdata to Vref 2. Since the transistors T3 and T4 are turned off and the capacitance of the capacitor C1 is much larger than the parasitic capacitance of the other transistors, the voltage difference of the capacitor C1 is not changed, the voltage of the first plate of the capacitor C1 is changed with the second plate, and the change amount is Vref 2-Vdata. Since the control terminal of the transistor T1 is connected to the first plate of the capacitor C1, the variation of the voltage at the control terminal of the transistor T1 is Vref2-Vdata, the voltage at the control terminal of the transistor T1 is VDD- | Vth | + Vref2-Vdata, and further Vgs of the transistor T1 is Vref2-Vdata- | Vth |. According to the leakage current formula I ═ K (Vgs + | Vth |) of the transistor T12It can be seen that the second reference voltage Vref2 compensates the control terminal of the transistor T1 such that the leakage current flowing through the transistor T1 is independent of the first power supply VDD. The leakage current flowing through the transistor T1 is the light emitting current flowing through the light emitting diode D1, so that the light emitting current is independent of the first power supply VDD, thereby eliminating the influence of the current-resistance voltage drop on the first power line on the current and improving the light emitting uniformity of the panel.
In one embodiment, the pixel circuit shown in FIG. 1 can be driven by other methods, and the timing control diagram is shown in FIG. 3. In this embodiment, in the initialization stage t1, both the first scan signal and the light emission control signal are low level signals. The first scan signal controls the transistor T4 and the transistor T7 to be turned on, so that the first reference voltage Vref1 initializes the first plate of the capacitor C1 and the control terminal of the transistor T1 through the transistor T4, and initializes the anode of the light emitting diode D1 through the transistor T7. The transistor T5 and the transistor T6 are controlled to be turned on by the light emission control signal, and the second reference voltage Vref2 initializes the first plate of the capacitor C1 through the transistor T5, so that in the initialization stage, the first plate and the second plate of the capacitor C1 are initialized, the initialization state of each pixel circuit is the same, and the light emission uniformity of the screen body can be better ensured.
The timing signal control method of the data writing period t2 and the light emitting period t3 is the same as the control method shown in fig. 2, and is not repeated here.
In one embodiment, the pixel circuit shown in FIG. 1 can be driven by other methods, and the timing control diagram is shown in FIG. 4. In this embodiment, the initialization phase includes a first phase t1 and a second phase t 2. In the first period t1, both the first scan signal and the light emission control signal are at a low level. The first scan signal controls the transistor T4 and the transistor T7 to be turned on, so that the first reference voltage Vref1 initializes the first plate of the capacitor C1 and the control terminal of the transistor T1 through the transistor T4, and initializes the anode of the light emitting diode D1 through the transistor T7. The light emission control signal controls the transistors T5 and T6 to be turned on, and the second reference voltage Vref2 initializes the first plate of the capacitor C1 through the transistor T5, so that the first plate and the second plate of the capacitor C1 are initialized. In the second phase T2, the first scan signal remains low, and the first reference voltage Vref1 continuously initializes the control terminal of the transistor T1, the first plate of the capacitor C1, and the anode of the light emitting diode D1. The light emission control signal transits from the low level to the high level, and the transistor T5 and the transistor T6 are turned off. Since the transistor T1, the transistor T6 and the transistor T7 are all turned on at the stage T1, a loop current is generated under the action of the first power VDD, and the first power VDD flows to the first reference voltage Vref1 through the transistor T1, the transistor T6 and the transistor T7, so that power consumption is generated in the circuit. In the second stage T2, the light-emitting control signal is changed to high level, the transistor T6 is turned off, the loop is cut off, no current is generated continuously, and the power consumption of the pixel circuit can be reduced.
The timing signal control method of the data writing period t2 and the light emitting period t3 is the same as the control method shown in fig. 2, and is not repeated here.
The operating principle of the control method of the pixel circuit shown in fig. 2, 3 and 4 is similar, and the following mainly describes the operating principle of the pixel circuit based on fig. 1 and 2:
in the initialization period t1, the first scan signal is a low level signal, and the second scan signal and the light emission control signal are high level signals. The transistor T4 and the transistor T7 are turned on, and the transistor T2, the transistor T3, the transistor T5, and the transistor T6 are turned off.
Since the transistor T4 is turned on, the first reference voltage Vref1 initializes the control terminal of the transistor T1 and the first plate of the capacitor C1 through the transistor T4. The first reference voltage Vref1 may be a negative voltage, and the application of the first reference voltage Vref1 to the control terminal of the transistor T1 may turn on the transistor T1. Since the transistor T7 is turned on, the first reference voltage Vref1 initializes the anode of the light emitting diode D1.
It is understood that the voltage value of the first reference voltage Vref1 is less than the voltage value of the second power source VSS to ensure that the light emitting diode D1 does not emit light at the time of initialization. The initialization can eliminate the influence of the residual current of the last lighting stage on the lighting stage, ensure that all pixel circuits are in the same initial state, and improve the lighting uniformity of the screen body.
In the data writing period t2, the second scan signal is a low level signal, and the first scan signal and the light emission control signal are high level signals. The transistor T2 and the transistor T3 are turned on, and in the initialization phase, the transistor T1 is already turned on. The transistor T4, the transistor T7, and the transistor T5 are turned off.
Since the transistor T2 is turned on, the data signal writes the data voltage into the second plate of the capacitor C1 through the transistor T2, so that the potential of the second plate of the capacitor C1 is Vdata. Since the transistor T1 is turned on, the first power supply VDD charges the first electrode of the transistor T1, and when the circuit state is stable, the first electrode of the transistor T1 has a voltage VDD, and the control terminal of the transistor T1 has a voltage VDD- | Vth |, thereby implementing the compensation of the threshold voltage of the transistor T1.
In the light-emitting period t3, the light-emitting control signal is a low level signal, and the first scan signal and the second scan signal are both high level signals. The transistor T5 and the transistor T6 are turned on, and the transistor T1 maintains the on state. The transistor T2, the transistor T3, the transistor T4, and the transistor T7 are turned off.
Since the transistor T5 is turned on, the second reference voltage Vref2 is written into the second plate of the capacitor C1 through the transistor T5, so that the potential of the second plate of the capacitor C1 is changed from Vdata to Vref 2. Since the transistor T3 and the transistor T4 are turned off, and the capacitance of the capacitor C1 is much larger than the capacitance of the parasitic capacitance of the other transistors, the voltage difference of the capacitor C1 is not changed, and according to the capacitive coupling principle, the potential of the first plate of the capacitor C1 changes with the change of the second plate while the voltage difference of the capacitor C1 is not changed. The potential of the second plate of the capacitor C1 is changed from Vdata in the data writing stage T2 to Vref2 in the light emitting stage T3, and the change amount is Vref2-Vdata, so the change amount of the potential of the first plate of the capacitor C1 is the same as the change amount of the potential of the second plate, that is, the change amount of the potential of the control terminal of the transistor T1 is the same as the change amount of the potential of the second plate, and then in the data writing stage T2, the potential of the control terminal of the transistor T1 is VDD- | Vth | + Vref 2-Vdata. Therefore, Vgs of the transistor T1 is VDD- | Vth | + Vref2-Vdata-VDD | -Vref 2-Vdata |. The driving current flowing through the transistor T1 is:
I＝K*(Vgs-Vth)2＝K*(Vref2-Vdata-|Vth|+|Vth|)2＝K*(Vref2-Vdata)2
wherein K1/2 μ Cox W/L. μ is the electron mobility of the transistor T1, Cox is the gate oxide capacitance per unit area of the transistor T1, W is the channel width of the transistor T1, and L is the channel length of the transistor T1. The driving current flowing through the transistor T1 is the light emitting current flowing through the light emitting diode D1. As can be seen from the above formula, the light emitting current flowing through the light emitting diode D1 is independent of the voltage of the first power supply VDD and the threshold voltage of the transistor, and at the same time, the light emitting current does not flow through the second reference voltage line. Therefore, the circuit structure and the driving method thereof provided by the embodiment of the application compensate the current-resistance voltage drop on the first power line by adding the second reference voltage, and simultaneously, the circuit structure and the control method thereof also compensate the influence of the threshold voltage on the light-emitting current, thereby improving the uniformity of the screen body light emission.
The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (10)
1. The pixel circuit is characterized by comprising a transistor T1, a transistor T2, a transistor T3, a transistor T4, a transistor T5, a transistor T6, a transistor T7, a capacitor C1 and a light-emitting diode D1;
a control terminal of the transistor T4 is configured to input a first scan signal, a first pole of the transistor T4 is respectively connected to a second pole of the transistor T3, a control terminal of the transistor T1 and a first pole plate of the capacitor C1, a second pole of the transistor T4 is connected to a second pole of the transistor T7 and is configured to input a first reference voltage Vref1, and when the transistor T4 is turned on, the first reference voltage Vref1 initializes a gate of the transistor T1 through the transistor T4;
a control terminal of the transistor T3 is used for inputting a second scan signal, a first pole of the transistor T3 is connected to the second pole of the transistor T1 and the first pole of the transistor T6, respectively, and the first pole of the transistor T1 is used for inputting a first power VDD;
a control terminal of the transistor T6 is used for inputting a light emitting control signal, a second terminal of the transistor T6 is respectively connected to an anode of the light emitting diode D1 and a first terminal of the transistor T7, a control terminal of the transistor T7 is used for inputting the first scan signal, and a cathode of the light emitting diode D1 is used for inputting a second power source VSS;
a control terminal of the transistor T2 is used for inputting the second scan signal, a first pole of the transistor T2 is used for inputting the data signal, and a second pole of the transistor T2 is connected to the second plate of the capacitor C1 and the second pole of the transistor T5, respectively;
the control terminal of the transistor T5 is used for inputting the light emitting control signal, and the first electrode of the transistor T5 is used for inputting a second reference voltage Vref 2.
2. The pixel circuit according to claim 1, wherein a voltage value of the first reference voltage Vref1 is smaller than a voltage value of the second power supply VSS.
3. The pixel circuit according to claim 1, wherein the transistor T1, the transistor T2, the transistor T3, the transistor T4, the transistor T5, the transistor T6, and the transistor T7 are any one of a low-temperature polysilicon thin film transistor, an oxide semiconductor thin film transistor, and an amorphous silicon thin film transistor.
4. A driving method of a pixel circuit, the pixel circuit according to any one of claims 1 to 3, comprising:
an initialization stage, in which the first scan signal is a low level signal and the second scan signal is a high level signal, so that the first reference voltage Vref1 initializes the pixel circuit;
a data writing stage in which the second scanning signal is a low level signal and the first scanning signal and the light emission control signal are high level signals, so that the data signal is written into the pixel circuit;
in the light emitting period, the light emitting control signal is a low level signal, and the first scan signal and the second scan signal are high level signals, so that a current flows through the light emitting diode D1.
5. The method for driving the pixel circuit according to claim 4, wherein the emission control signal is a high level signal in the initialization stage.
6. The method for driving the pixel circuit according to claim 4, wherein the emission control signal is a low level signal in the initialization stage.
7. The driving method of the pixel circuit according to claim 6, wherein the initialization phase includes a first phase and a second phase;
the first phase, in which the first scan signal and the light emission control signal are low level signals, the light emission control signal controls the transistor T5 to be turned on, and the second reference voltage Vref2 initializes the second plate of the capacitor C1 through the transistor T5;
in the second stage, the first scanning signal is a low level signal, and the light-emitting control signal is a high level signal.
8. The driving method of the pixel circuit according to any one of claims 5 to 7, wherein in the initialization phase, the first scan signal controls the transistor T4 and the transistor T7 to be turned on;
the first reference voltage Vref1 initializes the control terminal of the transistor T1 and the first plate of the capacitor C1 through the transistor T4, and the transistor T1 is turned on; the first reference voltage Vref1 initializes the anode of the led D1 through the transistor T7, so that the control terminal of the transistor T1 and the first plate of the capacitor C1 have a potential of Vref 1.
9. The pixel circuit driving method according to claim 8, wherein in the data writing phase, the second scan signal controls the transistor T2 to be turned on, and the data signal is written into the second plate of the capacitor C1 through the transistor T2, so that the potential of the second plate of the capacitor C1 is Vdata;
the first power supply VDD writes a power supply voltage into the transistor T1, so that the potential of the first electrode of the transistor T1 is VDD, and the potential of the control terminal of the transistor T1 is VDD- | Vth |.
10. The driving method of the pixel circuit according to claim 9, wherein during the light emitting period, the light emitting control signal controls the transistor T5 to turn on, and the second reference voltage Vref2 performs voltage compensation on the gate of the transistor T1 through the transistor T5 and the capacitor C1, so that the current flowing through the transistor T1 is independent of the power voltage provided by the first power line.
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| CN104050916B (en) * | 2014-06-04 | 2016-08-31 | 上海天马有机发光显示技术有限公司 | The pixel compensation circuit of a kind of OLED and method |
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