CN108389551B - Pixel circuit, driving method thereof and display device - Google Patents

Pixel circuit, driving method thereof and display device Download PDF

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CN108389551B
CN108389551B CN201810265088.8A CN201810265088A CN108389551B CN 108389551 B CN108389551 B CN 108389551B CN 201810265088 A CN201810265088 A CN 201810265088A CN 108389551 B CN108389551 B CN 108389551B
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CN108389551A (en
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殷新社
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BOE Technology Group Co Ltd
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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
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2320/00—Control of display operating conditions
    • G09G2320/02—Improving the quality of display appearance
    • G09G2320/0233—Improving the luminance or brightness uniformity across the screen

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Abstract

The invention provides a pixel circuit, a driving method thereof and a display device, relates to the technical field of display, and can solve the problem of uneven brightness of a display picture caused by threshold voltage drift and voltage drop on a power line. The pixel circuit comprises a data writing sub-circuit, a first voltage end and a first point, wherein the data writing sub-circuit is connected with the first signal end, the first voltage end and the first point and is used for transmitting a signal of the first voltage end to the first point; the compensation sub-circuit is connected with the second signal end and the driving sub-circuit and is used for compensating the threshold voltage of the driving sub-circuit; the light-emitting control sub-circuit is connected with the enabling signal end, the driving sub-circuit and the light-emitting sub-circuit and is used for connecting the driving sub-circuit and the light-emitting sub-circuit; the driving sub-circuit is also connected with the first point, the second voltage end and the light-emitting control sub-circuit and is used for driving the light-emitting sub-circuit to emit light under the control of the first point and the light-emitting control sub-circuit after the compensation of the threshold voltage is obtained; and the light-emitting sub-circuit is also connected with the third voltage end and is used for emitting light.

Description

Pixel circuit, driving method thereof and display device
Technical Field
The invention relates to the technical field of display, in particular to a pixel circuit, a driving method thereof and a display device.
Background
An Organic Light Emitting Diode (OLED) Display is one of the hot spots in the research field, and compared with a Liquid Crystal Display (LCD), an OLED Display has the advantages of low energy consumption, low production cost, self-luminescence, wide viewing angle, fast response speed, and the like. The pixel circuit design is the core technical content of the OLED display, and has important research significance.
In the prior art OLED driving circuit as shown in fig. 1, since the driving transistor Td is connected in series with the OLED, the driving current I of the driving transistor TdoledThe value of (c) may determine the brightness produced by the OLED device. Drive current IoledI.e., the current flowing through the driving transistor Td, can be expressed as:
Figure BDA0001611169430000011
wherein, COXIs the dielectric constant of the channel insulating layer, μ is the channel carrier mobility, both constants,
Figure BDA0001611169430000012
is the width-to-length ratio, V, of the driving transistor TdGSIs the voltage difference between the gate and the source, VthIs the threshold voltage of the driving transistor Td. Therefore, the OLED current is W, L, Vdata、VDD、VthThe effect of five variables. Since once a product is made, its mu, COXW and L are determined and can be considered as constants, therefore OThe luminous brightness of the LED is VdataVDD and VthAnd (5) controlling.
Due to factors of manufacturing processes, amorphous silicon Thin Film Transistors (TFTs), low temperature polysilicon Thin Film transistors (LTPS TFTs) or Oxide Thin Film transistors (Oxide TFTs) manufactured on a large-area glass substrate often have distribution differences of threshold voltages Vth, even when Vth is close to each other, and in addition, Vth values change under stress, that is, Vth drifts, which causes a problem that display luminance of two adjacent sub-pixels has differences even though input luminance data is the same, that is, an hourglass phenomenon and a luminance non-uniformity phenomenon appear in a picture seen by people.
In addition, the OLED is driven by current drive to emit light, and the drive current IoledThe larger the light emission, the brighter it is. However, when the sub-pixels arranged along the extension direction of the VDD are all bright due to the distributed resistance on the power line VDD, that is, IR drop (voltage drop) is generated when current flows, the VDD line drops a tiny voltage through each sub-pixel when current flows through the VDD line, and the VDD voltage from the VDD line to the sub-pixels has a small voltage drop, so that the VDD voltage of the sub-pixels along the VDD line is gradually reduced, and the formula is generated
Figure BDA0001611169430000021
Drive current I ofoledAnd the brightness of the sub-pixel gradually becomes dark, so that the display brightness has non-uniform brightness along the extending direction of VDD.
Disclosure of Invention
Embodiments of the present invention provide a pixel circuit, a driving method thereof, and a display device, which can solve the problem of uneven brightness of a display screen due to threshold voltage drift and voltage drop on a power line.
In order to achieve the above purpose, the embodiment of the invention adopts the following technical scheme:
in a first aspect, a pixel circuit is provided, which includes a data writing sub-circuit, a compensation sub-circuit, a light emission control sub-circuit, a driving sub-circuit, and a light emission sub-circuit; the data writing sub-circuit is connected with a first signal end, a first voltage end and a first point and is used for transmitting a signal of the first voltage end to the first point under the control of the first signal end; the compensation sub-circuit is connected with a second signal end and the driving sub-circuit and is used for compensating the threshold voltage of the driving sub-circuit under the control of the second signal end; the light-emitting control sub-circuit is connected with an enable signal end, the driving sub-circuit and the light-emitting sub-circuit and is used for connecting the driving sub-circuit with the light-emitting sub-circuit under the control of the enable signal end; the driving sub-circuit is further connected to the first point, the second voltage end and the light-emitting control sub-circuit, and is configured to drive the light-emitting sub-circuit to emit light under the control of the first point and the light-emitting control sub-circuit after compensation of a threshold voltage is obtained; the light-emitting sub-circuit is also connected with a third voltage end and is used for emitting light under the driving of the driving sub-circuit and the third voltage end.
Optionally, the driving sub-circuit includes: the driving circuit comprises a driving transistor, a first capacitor and a second capacitor; one end of the first capacitor is connected with the first point, and the other end of the first capacitor is connected with the grid electrode of the driving transistor; one end of the second capacitor is connected with the first point, and the other end of the second capacitor is connected with the second voltage end; the grid electrode of the driving transistor is also connected with the compensation sub-circuit, the first pole is connected with the second voltage end, and the second pole is connected with the compensation sub-circuit and the light-emitting control sub-circuit.
Optionally, the compensation sub-circuit comprises a first transistor; the grid electrode of the first transistor is connected with the second signal end, the first pole of the first transistor is connected with the driving sub-circuit, and the second pole of the first transistor is connected with the driving sub-circuit.
Optionally, the data writing sub-circuit includes a second transistor; the grid electrode of the second transistor is connected with the first signal end, the first pole of the second transistor is connected with the first voltage end, and the second pole of the second transistor is connected with the first point.
Optionally, the light emission control sub-circuit includes a third transistor; the grid electrode of the third transistor is connected with the enabling signal end, the first pole of the third transistor is connected with the driving sub-circuit, and the second pole of the third transistor is connected with the light-emitting sub-circuit.
Optionally, the light emitting sub-circuit comprises a self-light emitting device; the anode of the self-luminous device is connected with the light-emitting control sub-circuit, and the cathode of the self-luminous device is connected with the third voltage end.
In a second aspect, a display device is provided, which includes the pixel circuit described in the first aspect.
In a third aspect, a driving method of a pixel circuit is provided, the driving method including: in the initialization and compensation stage, the data writing sub-circuit transmits the reference voltage input by the first voltage end to a first point under the control of the first signal end, and initializes the potential of the first point; the compensation sub-circuit compensates the threshold voltage of the driving sub-circuit under the control of the second signal end; in a data writing stage, the data writing sub-circuit transmits the data voltage input by the first voltage end to the first point under the control of the first signal end, and the driving sub-circuit stores the signal of the first point; in the light-emitting stage, the light-emitting control sub-circuit enables the driving sub-circuit to be connected with the light-emitting sub-circuit under the control of an enabling signal end; and the light-emitting sub-circuit is driven by the driving sub-circuit and a third voltage end to emit light.
Optionally, the driving sub-circuit includes a driving transistor, a first capacitor, and a second capacitor, the compensating sub-circuit includes a first transistor, and the data writing sub-circuit includes a second transistor; the initialization and compensation phase specifically comprises: the second transistor is turned on under the control of the first signal terminal, transmits the reference voltage input by the first voltage terminal to the first point, and writes the potential of the first point into one end of the first capacitor and one end of the second capacitor; the first transistor is turned on under the control of the second signal end, so that the grid electrode of the driving transistor is communicated with the second electrode, threshold voltage compensation is carried out on the driving transistor, and the compensated potential is written into the other end of the first capacitor.
Optionally, the data writing stage specifically includes: the second transistor is turned on under the control of the first signal terminal, transmits the data voltage input from the first voltage terminal to the first point, and writes the potential of the first point into one end of the first capacitor and one end of the second capacitor.
Embodiments of the present invention provide a pixel circuit, a driving method thereof, and a display device, in which a compensation sub-circuit is added in the pixel circuit to compensate for a threshold voltage generated by the driving sub-circuit, so as to avoid a display luminance difference caused by different threshold voltage drift amounts of TFTs of each portion of a display panel. In addition, by adding the compensation sub-circuit, the problem of display brightness difference caused by IR drop on the power line can be reduced, and the uniformity of brightness among pixels can be improved.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a schematic structural diagram of a pixel circuit provided in the prior art;
fig. 2 is a schematic structural diagram of a pixel circuit according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of the sub-circuits of FIG. 2;
fig. 4 is a timing chart of respective signals when driving the pixel circuit shown in fig. 3;
FIGS. 5-8 are graphs showing simulation effects of pixel circuits according to embodiments of the present invention;
fig. 9 is a flowchart illustrating a pixel circuit driving method according to an embodiment of the invention.
Reference numerals
10-a data write sub-circuit; 20-a compensation sub-circuit; 30-a light emission control sub-circuit; 40-a drive sub-circuit; 50-a light emitting sub-circuit; s1 — a first signal terminal; s2 — a second signal terminal; an EM-enable signal terminal; v1 — first voltage terminal; v2 — second voltage terminal; v3 — third voltage terminal; c1 — first capacitance; c2 — second capacitance; a-first point; b-second point.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
An embodiment of the invention provides a pixel circuit, as shown in fig. 2, including a data writing sub-circuit 10, a compensation sub-circuit 20, a light-emitting control sub-circuit 30, a driving sub-circuit 40, and a light-emitting sub-circuit 50.
Specifically, the data writing sub-circuit 10 is connected to the first signal terminal S1, the first voltage terminal V1 and the first point a, and is configured to transmit the signal of the first voltage terminal V1 to the first point a under the control of the first signal terminal S1.
The compensation sub-circuit 20 is connected to the second signal terminal S2 and the driving sub-circuit 40, and is used for compensating the threshold voltage of the driving sub-circuit 40 under the control of the second signal terminal S2.
The light-emitting control sub-circuit 30 is connected to the enable signal terminal EM, the driving sub-circuit 40 and the light-emitting sub-circuit 50, and is configured to connect the driving sub-circuit 40 and the light-emitting sub-circuit 50 under the control of the enable signal terminal EM.
The driving sub-circuit 40 is further connected to the first point a, the second voltage terminal V2 and the light emission control sub-circuit 30, and is configured to drive the light emission sub-circuit 50 to emit light under the control of the first point a and the light emission control sub-circuit 30 after the threshold voltage compensation is obtained.
The light emitting sub-circuit 50 is further connected to the third voltage terminal V3 for emitting light driven by the driving sub-circuit 40 and the third voltage terminal V3.
The embodiment of the invention provides a pixel circuit, which compensates the threshold voltage generated by the driving sub-circuit 40 by adding the compensation sub-circuit 20 in the pixel circuit, thereby avoiding the display brightness difference caused by different threshold voltage drift amounts of the TFTs of each part of the display panel. Further, by providing the data writing sub-circuit 10 and the compensation sub-circuit 20, the problem of display luminance difference caused by IR drop on the power supply line can be reduced, and the uniformity of luminance from pixel to pixel can be improved.
Specifically, as shown in fig. 3, the driving sub-circuit 40 includes: a driving transistor Td, a first capacitor C1 and a second capacitor C2.
The first capacitor C1 has one end connected to the first point a and the other end connected to the gate of the driving transistor Td.
The second capacitor C2 has one end connected to the first point a and the other end connected to the second voltage terminal V2.
The gate of the driving transistor Td is further connected to the compensation sub-circuit 20, the first pole is connected to the second voltage terminal V2, and the second pole is connected to the compensation sub-circuit 20 and the light emission control sub-circuit 30.
The driving transistor Td is a transistor for supplying a driving current to a self-light emitting device (e.g., OLED), and has a main function of converting a gate-source voltage into a drain-source current.
The first capacitor C1 and the second capacitor C2 are storage capacitors, the first capacitor C1 is used for storing a threshold voltage of the driving transistor Td to compensate the threshold voltage of the driving transistor Td, and the second capacitor C2 is used for storing a data voltage of the pixel.
It should be noted that the driving sub-circuit 40 may further include a plurality of transistors connected in parallel with the driving transistor Td. The above description is only an example of the driving sub-circuit 40, and other structures having the same functions as the driving sub-circuit 40 are not described in detail here, but all of them should fall into the protection scope of the present invention.
As shown in fig. 3, the compensation sub-circuit 20 includes a first transistor T1.
The gate of the first transistor T1 is connected to the second signal terminal S2, the first pole is connected to the driving sub-circuit 40, and the second pole is connected to the driving sub-circuit 40.
More specifically, the gate of the first transistor T1 is connected to the second signal terminal S2, the first pole is connected to the gate (the second point B) of the driving transistor Td, and the second pole is connected to the second pole of the driving transistor Td.
It should be noted that the compensation sub-circuit 20 may further include a plurality of switching transistors connected in parallel with the first transistor T1. The above description is only an example of the compensation sub-circuit 20, and other structures having the same functions as the compensation sub-circuit 20 are not described in detail here, but all should fall within the protection scope of the present invention.
As shown in fig. 3, the data writing sub-circuit 10 includes a second transistor T2.
The gate of the second transistor T2 is connected to the first signal terminal S1, the first pole is connected to the first voltage terminal V1, and the second pole is connected to the first point a.
The first voltage terminal V1 is used for transmitting a data voltage Vdata and a reference voltage Vref, and is used for compensating IR drop on the power line VDD. The voltage difference TP is generated when the first voltage terminal V1 switches the reference voltage Vref to the data voltage Vdata.
It should be noted that the data writing sub-circuit 10 may further include a plurality of switching transistors connected in parallel to the second transistor T2. The above description is only an example of the data writing sub-circuit 10, and other structures having the same functions as the data writing sub-circuit 10 are not described in detail here, but all of them should fall into the protection scope of the present invention.
As shown in fig. 3, the light emission control sub-circuit 30 includes a third transistor T3.
The gate of the third transistor T3 is connected to the enable signal terminal EM, the first pole is connected to the driving sub-circuit 40, and the second pole is connected to the light emitting sub-circuit 50.
More specifically, the gate of the third transistor T3 is connected to the enable signal terminal EM, the first pole is connected to the second pole of the driving transistor Td, and the second pole is connected to the light emitting sub-circuit 50.
It should be noted that the light emission control sub-circuit 30 may further include a plurality of switching transistors connected in parallel to the third transistor T3. The above is merely an illustration of the light-emitting control sub-circuit 30, and other structures having the same functions as the light-emitting control sub-circuit 30 are not described in detail herein, but all should fall within the scope of the present invention.
As shown in fig. 3, the light emitting sub-circuit 50 includes a self-light emitting device.
The anode of the self-luminous device is connected to the light control sub-circuit 30, and the cathode is connected to the third voltage terminal V3.
More specifically, the anode of the self-light emitting device is connected to the second electrode of the third transistor T3, and the cathode is connected to the third voltage terminal V3.
The pixel circuit provided by the invention comprises 4 transistors and 2 storage capacitors, can solve the problem of nonuniform sub-pixel brightness caused by threshold voltage drift and voltage drop on a power line, and has the advantages of simple structure, low cost and high aperture ratio.
Based on the above description of the specific circuits of the sub-circuits, the following describes the specific driving process of the pixel driving circuit in detail with reference to fig. 3 and 4.
It should be noted that the first and second embodiments of the present invention do not limit the types of transistors in each sub-circuit, that is, the first transistor T1, the second transistor T2, the third transistor T3, and the driving transistor Td may be N-type transistors or P-type transistors. The preferred pixel circuit of the embodiment of the invention comprises P-type transistors. The following embodiments of the present invention are all described by taking the above transistors as P-type transistors as examples.
The first pole of the transistor can be a drain, and the second pole can be a source; alternatively, the first pole may be a source and the second pole may be a drain. The embodiments of the present invention are not limited in this regard.
In addition, the transistors in the pixel circuit can be divided into an enhancement transistor and a depletion transistor according to the conduction manner of the transistors. The embodiments of the present invention are not limited in this regard.
In the second and the third embodiments of the present invention, the second voltage terminal V2 is inputted with the high level VDD, and the third voltage terminal V3 is inputted with the low level VSS, the third voltage terminal V3 may be grounded, and the high and the low merely indicate the relative magnitude relationship between the inputted voltages.
As shown in fig. 4, the driving process of the pixel circuit can be divided into an initialization and compensation phase P1, a data writing phase P2, and a light emitting phase P3. Specifically, the method comprises the following steps:
in the initialization and compensation phase P1, as shown in fig. 4, the first signal terminal S1 and the second signal terminal S2 input the low-level enable signal, and the enable signal terminal EM inputs the high-level disable signal. Based on this, in the equivalent circuit diagram of the pixel circuit shown in fig. 3, as shown in fig. 5 (a), the first transistor T1 and the second transistor T2 are both turned on, the third transistor T3 is turned off, and the transistors in the turned-off state are denoted by "x".
The first signal terminal S1 inputs a low-level turn-on signal to control the second transistor T2 to turn on, and the reference voltage Vref input from the first voltage terminal V1 is output to one end of the first capacitor C1 and one end of the second capacitor C2 through the second transistor T2, that is, a point a in fig. 5, to initialize the first capacitor C1 and the second capacitor C2. The second signal terminal S2 inputs a low level turn-on signal to control the first transistor T1 to turn on, and at this time, as shown in fig. 6, the first transistor T1 connects the gate G and the second pole D of the driving transistor Td such that VGS＝VDS＝VthThe diagram (a) in fig. 5 may be equivalent to the diagram (b) in fig. 5. The second voltage terminal V2 writes a level VDD + Vth (the driving transistor Td is a P-type transistor, and Vth is negative) to the gate (point B in fig. 5) of the driving transistor Td through the driving transistor Td and the first transistor T1, and compensates the threshold voltage of the driving sub-circuit 40. Where VDD is a power voltage of the second voltage terminal V2, and Vth is a threshold voltage of the driving transistor Td.
That is, at the end of the initialization and compensation phase P1, the voltage at the first point a is Vref and the voltage at the second point B is VDD + Vth. The voltage stored on the first capacitor C1 is VDD + Vth-Vref, and the voltage stored on the second capacitor C2 is Vref-VDD.
In the data writing phase P2, as shown in fig. 4, the first signal terminal S1 receives the low-level enable signal, and the second signal terminal S2 and the enable signal terminal EM receive the high-level disable signal. Based on this, the equivalent circuit diagram of the pixel circuit shown in fig. 3 is as shown in (a) of fig. 7, the second transistor T2 is turned on, the first transistor T1 and the third transistor T3 are both turned off, and at this time, the driving transistor Td loses the diode characteristic, and the diagram (a) of fig. 7 can be equivalent to the diagram (b) of fig. 7.
The first signal end S1 inputs a low-level turn-on signal to control the second transistor T2 to turn on, the data voltage Vdata input from the first voltage end V1 is transmitted to one end of the first capacitor C1 and one end of the second capacitor C2 through the second transistor T2, at this time, the voltage at the first point a jumps to Vdata, the jump amount TP equals to Vdata-Vref, and the voltage at the second point B changes to VDD + Vth + Vdata-Vref due to the coupling effect of the first capacitor C1.
That is, at the end of the data writing phase P2, the voltage at the first point a is Vdata, and the voltage at the second point B is VDD + Vth + Vdata-Vref. The voltage held on the first capacitor C1 is VDD + Vth-Vref.
In the light emitting period P3, the enable signal terminal EM inputs a low-level turn-on signal, the first signal terminal S1 inputs a high-level turn-off signal, and the second signal terminal S2 inputs a high-level turn-off signal, based on which the equivalent circuit diagram of the pixel circuit shown in fig. 3 is shown in fig. 8 (a), the first transistor T1 and the second transistor T2 are both turned off, the third transistor T3 is turned on, and the diagram (a) in fig. 8 can be equivalent to the diagram (b) in fig. 8.
The enable signal terminal EM inputs a low level turn-on signal to control the third transistor T3 to turn on, so that the driving transistor Td and the self-luminous device are connected, the power voltage VDD output from the second voltage terminal V2 is transmitted to the driving sub-circuit 40, and the self-luminous device emits light under the driving of the driving signal output from the driving sub-circuit 40 and the power voltage VSS output from the third voltage terminal V3.
That is, in the light emission phase P3, the voltage at the first point a is Vdata, and the voltage at the second point B is VDD + Vth + Vdata-Vref. Vgs-VG-VS-VB-VDD-Vdata-Vref + Vth of the driving transistor Td.
At this time, after the driving transistor Td is turned on, when a value obtained by subtracting the threshold voltage Vth of the driving transistor Td from the gate G-source S voltage Vgs of the driving transistor Td is equal to or less than the drain D-source S voltage Vds of the driving transistor Td, that is, Vgs-Vth ≦ Vds, the driving transistor Td can be in a saturation turn-on state, and at this time, the driving current I flowing through the driving transistor TdoledComprises the following steps:
Figure BDA0001611169430000101
wherein W/L is the width-to-length ratio of the driving transistor Td, COXμ is the channel carrier mobility, which is the dielectric constant of the channel insulating layer.
The above parameters are only related to the structure of the driving transistor Td, the data voltage outputted from the first voltage terminal V1 and the reference voltage Vref outputted from the first voltage terminal V1, and are not related to the threshold voltage Vth of the driving transistor Td, so that the influence of the threshold voltage Vth of the driving transistor Td on the light emitting luminance of the self-light emitting device is eliminated, and the uniformity of the luminance of the self-light emitting device is improved.
In addition, since the driving current of the driving transistor Td does not include the VDD term, the problem of display non-uniformity caused by the influence of the voltage drop on the VDD line can be solved.
In addition, the pixel circuit provided by the invention can further improve the realization of high resolution of the pixel by transmitting Vref and Vdata through one signal line to increase the pixel aperture ratio.
The embodiment of the invention also provides a display device which comprises a plurality of pixel circuits.
The display device can be specifically a product or a component with any display function, such as an OLED display, a digital photo frame, a mobile phone, a tablet computer, a navigator and the like.
An embodiment of the present invention provides a display device, which may include a plurality of pixel unit arrays, each pixel unit including any one of the pixel circuits described above. The display device provided by the embodiment of the invention has the same beneficial effects as the pixel circuit provided by the previous embodiment of the invention, and the pixel circuit has been described in detail in the previous embodiment, so that the description is omitted here.
An embodiment of the present invention further provides a driving method of a pixel circuit, as shown in fig. 9, the driving method includes:
s10, in the initialization and compensation stage, the data writing sub-circuit 10 transmits the reference voltage inputted from the first voltage terminal V1 to the first point a under the control of the first signal terminal S1, and initializes the potential of the first point a; the compensation sub-circuit 20 compensates the threshold voltage of the driving sub-circuit 40 under the control of the second signal terminal S2.
Specifically, the second transistor T2 is turned on under the control of the first signal terminal S1, and transmits the reference voltage inputted from the first voltage terminal V1 to the first point a, and writes the potential of the first point a into one terminal of the first capacitor C1 and the second capacitor C2.
The first transistor T1 is turned on under the control of the second signal terminal S2, connects the gate and the second electrode of the driving transistor Td, compensates the threshold voltage of the driving transistor Td, and writes the compensated potential to the other end of the first capacitor C1.
S20, in the data writing phase, the data writing sub-circuit 10 transmits the data voltage inputted from the first voltage terminal V1 to the first point a under the control of the first signal terminal S1, and the driving sub-circuit 40 stores the signal of the first point a.
Specifically, the second transistor T2 is turned on under the control of the first signal terminal S1, transmits the data voltage inputted from the first voltage terminal V1 to the first point a, and writes the potential of the first point a into one terminal of the first capacitor C1 and the second capacitor C2.
S30, in the light emitting stage, the light emitting control sub-circuit 30 connects the driving sub-circuit 40 and the light emitting sub-circuit 50 under the control of the enable signal terminal EM; the light emitting sub-circuit 50 emits light under the driving of the driving sub-circuit 40 and the third voltage terminal V3.
Specifically, the third transistor T3 is turned on under the control of the enable signal terminal EM to connect the driving sub-circuit 40 and the light-emitting sub-circuit 50, and the light-emitting sub-circuit 50 emits light under the driving of the driving sub-circuit 40 and the third voltage terminal V3.
The embodiment of the invention provides a driving method of a pixel circuit, which is characterized in that a compensation sub-circuit 20 is added in the pixel circuit, and before a driving sub-circuit 40 drives a light-emitting sub-circuit 50 to emit light, the driving compensation sub-circuit 20 compensates for a threshold voltage generated by the driving sub-circuit 40, so that the display brightness difference caused by different threshold voltage drift amounts of TFTs (thin film transistors) of each part of a display panel can be avoided. In addition, by adding the compensation sub-circuit 20, the problem of display brightness difference caused by IR drop on the power supply line can be reduced, and the uniformity of brightness from pixel to pixel can be improved.
The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.

Claims (6)

1. A driving method of a pixel circuit, wherein the pixel circuit includes a data writing sub-circuit, a compensation sub-circuit, a light emission control sub-circuit, a driving sub-circuit, and a light emission sub-circuit;
the data writing sub-circuit is connected with a first signal end, a first voltage end and a first point and is used for transmitting a signal of the first voltage end to the first point under the control of the first signal end;
the compensation sub-circuit is connected with a second signal end and the driving sub-circuit and is used for compensating the threshold voltage of the driving sub-circuit under the control of the second signal end;
the light-emitting control sub-circuit is connected with an enable signal end, the driving sub-circuit and the light-emitting sub-circuit and is used for connecting the driving sub-circuit with the light-emitting sub-circuit under the control of the enable signal end;
the driving sub-circuit is further connected to the first point, the second voltage end and the light-emitting control sub-circuit, and is configured to drive the light-emitting sub-circuit to emit light under the control of the first point and the light-emitting control sub-circuit after compensation of a threshold voltage is obtained;
the light-emitting sub-circuit is also connected with a third voltage end and is used for emitting light under the driving of the driving sub-circuit and the third voltage end;
the driving sub-circuit includes: the driving circuit comprises a driving transistor, a first capacitor and a second capacitor;
one end of the first capacitor is connected with the first point, and the other end of the first capacitor is connected with the grid electrode of the driving transistor;
one end of the second capacitor is connected with the first point, and the other end of the second capacitor is connected with the second voltage end;
the grid electrode of the driving transistor is also connected with the compensation sub-circuit, the first pole is connected with the second voltage end, and the second pole is connected with the compensation sub-circuit and the light-emitting control sub-circuit;
the compensation sub-circuit comprises: a first transistor; the data write sub-circuit includes: a second transistor; the light emission control sub-circuit includes: a third transistor; the driving transistor, the first transistor, the second transistor and the third transistor are P-type transistors;
the potential of the second voltage end is stable;
the driving method includes:
in the initialization and compensation stage, the data writing sub-circuit transmits the reference voltage input by the first voltage end to a first point under the control of the first signal end, and initializes the potential of the first point; the compensation sub-circuit compensates the threshold voltage of the driving sub-circuit under the control of the second signal end;
in a data writing stage, the data writing sub-circuit transmits the data voltage input by the first voltage end to the first point under the control of the first signal end, and the driving sub-circuit stores the signal of the first point;
in the light-emitting stage, the light-emitting control sub-circuit enables the driving sub-circuit to be connected with the light-emitting sub-circuit under the control of an enabling signal end; the light-emitting sub-circuit is driven by the driving sub-circuit and a third voltage end to emit light;
the driving sub-circuit comprises a driving transistor, a first capacitor and a second capacitor, the compensation sub-circuit comprises a first transistor, and the data writing sub-circuit comprises a second transistor; the initialization and compensation phase specifically comprises:
the second transistor is turned on under the control of the first signal terminal, transmits the reference voltage input by the first voltage terminal to the first point, and writes the potential of the first point into one end of the first capacitor and one end of the second capacitor;
the first transistor is started under the control of the second signal end, so that the grid electrode of the driving transistor is communicated with the second electrode, the threshold voltage of the driving transistor is compensated, and the compensated potential is written into the other end of the first capacitor;
wherein, in the light-emitting stage, the drive current is
Figure FDA0002833123150000021
2. The driving method according to claim 1, wherein the data writing phase specifically comprises:
the second transistor is turned on under the control of the first signal terminal, transmits the data voltage input from the first voltage terminal to the first point, and writes the potential of the first point into one end of the first capacitor and one end of the second capacitor.
3. The driving method according to claim 1, wherein the compensation sub-circuit includes a first transistor;
the grid electrode of the first transistor is connected with the second signal end, the first pole of the first transistor is connected with the driving sub-circuit, and the second pole of the first transistor is connected with the driving sub-circuit.
4. The driving method according to claim 1, wherein the data writing sub-circuit includes a second transistor;
the grid electrode of the second transistor is connected with the first signal end, the first pole of the second transistor is connected with the first voltage end, and the second pole of the second transistor is connected with the first point.
5. The driving method according to claim 1, wherein the light emission control sub-circuit includes a third transistor;
the grid electrode of the third transistor is connected with the enabling signal end, the first pole of the third transistor is connected with the driving sub-circuit, and the second pole of the third transistor is connected with the light-emitting sub-circuit.
6. The driving method according to claim 1, wherein the light emitting sub-circuit includes a self-light emitting device;
the anode of the self-luminous device is connected with the light-emitting control sub-circuit, and the cathode of the self-luminous device is connected with the third voltage end.
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