CN115578977B - Pixel driving circuit and display panel - Google Patents
Pixel driving circuit and display panel Download PDFInfo
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- CN115578977B CN115578977B CN202211342995.0A CN202211342995A CN115578977B CN 115578977 B CN115578977 B CN 115578977B CN 202211342995 A CN202211342995 A CN 202211342995A CN 115578977 B CN115578977 B CN 115578977B
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- 238000004146 energy storage Methods 0.000 claims abstract description 69
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- 230000001105 regulatory effect Effects 0.000 abstract description 3
- 208000035405 autosomal recessive with axonal neuropathy spinocerebellar ataxia Diseases 0.000 description 22
- 208000033361 autosomal recessive with axonal neuropathy 2 spinocerebellar ataxia Diseases 0.000 description 6
- 239000010409 thin film Substances 0.000 description 6
- 239000004065 semiconductor Substances 0.000 description 5
- XLOMVQKBTHCTTD-UHFFFAOYSA-N Zinc monoxide Chemical compound [Zn]=O XLOMVQKBTHCTTD-UHFFFAOYSA-N 0.000 description 4
- 238000010586 diagram Methods 0.000 description 3
- 229910021420 polycrystalline silicon Inorganic materials 0.000 description 3
- 229920005591 polysilicon Polymers 0.000 description 3
- GYHNNYVSQQEPJS-UHFFFAOYSA-N Gallium Chemical compound [Ga] GYHNNYVSQQEPJS-UHFFFAOYSA-N 0.000 description 2
- 229910021417 amorphous silicon Inorganic materials 0.000 description 2
- 229910052733 gallium Inorganic materials 0.000 description 2
- 229910052738 indium Inorganic materials 0.000 description 2
- APFVFJFRJDLVQX-UHFFFAOYSA-N indium atom Chemical compound [In] APFVFJFRJDLVQX-UHFFFAOYSA-N 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 239000011787 zinc oxide Substances 0.000 description 2
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- 238000005401 electroluminescence Methods 0.000 description 1
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Classifications
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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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- 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]
-
- 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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- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Computer Hardware Design (AREA)
- General Physics & Mathematics (AREA)
- Theoretical Computer Science (AREA)
- Control Of Indicators Other Than Cathode Ray Tubes (AREA)
Abstract
The application provides a pixel driving circuit and a display panel, wherein a first voltage is input to a first end of an energy storage capacitor through a threshold compensation loop in a threshold compensation stage, the energy storage capacitor is charged, so that the voltage of a second end of the energy storage capacitor reaches a second voltage, a data voltage is connected to the second end of the energy storage capacitor through a data writing loop in a light-emitting stage, the voltage of a control end of a driving transistor is regulated to a third voltage through the energy storage capacitor based on a bootstrap effect, and the driving transistor drives a light-emitting element to emit light based on the driving voltage received by a first connection end and the third voltage received by a control end of the driving transistor through a light-emitting loop, so that the threshold voltage of the driving transistor can be compensated, the light-emitting brightness of the light-emitting element is irrelevant to the threshold voltage, and the problem of uneven display brightness caused by different threshold voltages of the driving transistors among different pixel driving circuits can be solved.
Description
Technical Field
The present application relates to the field of display panels, and in particular, to a pixel driving circuit and a display panel.
Background
An OLED (Organic Light-Emitting Diode), also known as an Organic laser display, an Organic Light-Emitting semiconductor (Organic Electroluminescence Display, OLED). An OLED is a current-type organic light emitting device, which is a phenomenon of emitting light by injection and recombination of carriers, and the intensity of the light emission is proportional to the current injected. The OLED display panel has the advantages of no blue light hazard, soft light, flexible and foldable property, no stroboscopic effect, high color quality, and the like, and has become one of the mainstream display panels in the market.
The light emitting element in each pixel unit in the OLED display panel is driven by a current generated when the driving transistor (Thin Film Transistor ) is in a saturated state. Since the uniformity of the threshold voltages Vth of the driving transistors is poor, that is, the threshold voltages Vth of the driving transistors in different pixel units are not uniform, when the same data voltages are input, the driving currents in the different pixel units are not uniform due to the non-uniformity of the threshold voltages Vth, resulting in poor brightness uniformity of the display panel.
Disclosure of Invention
In view of the above, the main objective of the present application is to provide a pixel driving circuit and a display panel, which are aimed at solving the problem of poor luminance uniformity of the conventional OLED display panel.
The application provides a pixel driving circuit, which is used for driving a light-emitting element to emit light, wherein a first end of the light-emitting element is used for receiving a reference voltage, and the pixel driving circuit sequentially works in a reset phase, a threshold compensation phase and a light-emitting phase in a frame display period. The pixel driving circuit comprises a driving transistor, an energy storage capacitor reset loop, a light-emitting loop, a threshold compensation loop and a data writing loop. The driving transistor comprises a control end, a first connecting end and a second connecting end, wherein the first connecting end is used for receiving reset voltage or driving voltage, and the second connecting end is electrically connected with the second end of the light-emitting element. The first end of the energy storage capacitor is electrically connected with the control end of the driving transistor, and the second end of the energy storage capacitor is electrically connected with the second connecting end of the driving transistor. The driving transistor and the energy storage capacitor are connected in series in the energy storage capacitor reset loop, and the energy storage capacitor reset loop is used for conducting in the reset stage and receiving the reset voltage so as to reset the voltage of the second end of the energy storage capacitor to the reset voltage. The driving transistor and the light emitting element are connected in series in the light emitting loop, and the light emitting loop is used for conducting in the reset stage and receiving the reset voltage so as to reset the voltage of the second end of the light emitting element to the reset voltage. The driving transistor and the energy storage capacitor are connected in series in the threshold compensation loop, the threshold compensation loop is used for being conducted in the threshold compensation stage so as to input a first voltage to a first end of the energy storage capacitor and charge the energy storage capacitor, so that the voltage of a second end of the energy storage capacitor reaches a second voltage, wherein the reset voltage is smaller than the first voltage, and the second voltage is equal to the difference between the first voltage and the threshold voltage of the driving transistor. The energy storage capacitor is further connected in series in the data writing loop, and the data writing loop is used for being conducted in the light-emitting stage to enable the data voltage to be connected to the second end of the energy storage capacitor, so that the energy storage capacitor adjusts the voltage of the control end of the driving transistor to a third voltage based on a bootstrap effect, wherein the third voltage is equal to the sum of the data voltage and the threshold voltage of the driving transistor. The light-emitting circuit is further configured to be turned on in the light-emitting stage, so that the driving transistor drives the light-emitting element to emit light based on the driving voltage received by the first connection terminal and the third voltage received by the control terminal.
According to the pixel driving circuit provided by the application, the first voltage is input to the first end of the energy storage capacitor through the threshold compensation loop in the threshold compensation stage, the energy storage capacitor is charged, so that the voltage of the second end of the energy storage capacitor reaches the second voltage, the data voltage is connected to the second end of the energy storage capacitor through the data writing loop in the light-emitting stage, the voltage of the control end of the driving transistor is regulated to the third voltage through the energy storage capacitor based on the bootstrap effect, and the driving transistor drives the light-emitting element to emit light through the light-emitting loop based on the driving voltage received by the first connection end and the third voltage received by the control end of the driving transistor, so that the threshold voltage of the driving transistor can be compensated, the light-emitting brightness of the light-emitting element is irrelevant to the threshold voltage, and the problem of uneven display brightness caused by different threshold voltages of the driving transistors among different pixel driving circuits can be solved.
Optionally, the pixel driving circuit further includes a first switching tube connected in series to the threshold compensation circuit, a first connection end of the first switching tube is configured to receive the first voltage, and a second connection end of the first switching tube is electrically connected to the first end of the energy storage capacitor. The first switching tube is conducted in the threshold compensation stage based on the scanning signal received by the control end of the first switching tube, so that the first voltage is input to the first end of the energy storage capacitor.
Optionally, the pixel driving circuit further includes a second switching transistor connected in series between the second connection terminal of the driving transistor and the second terminal of the storage capacitor. In the threshold compensation stage, the first switching transistor is turned on based on a scan signal received by a control terminal thereof to transmit the first voltage to the control terminal of the driving transistor, thereby turning on the driving transistor. The second switching tube is conducted based on the scanning signal received by the control end of the second switching tube, so that the threshold compensation loop is conducted.
Optionally, in the reset phase, the first switching transistor is turned on based on a scan signal received by a control terminal thereof to transmit the first voltage to the control terminal of the driving transistor, thereby turning on the driving transistor. The second switching tube is conducted based on the scanning signal received by the control end of the second switching tube, so that the energy storage capacitor reset loop is conducted.
Optionally, the pixel driving circuit further includes a third switching tube connected in series to the data writing circuit, a first connection end of the third switching tube is used for receiving the data voltage, and a second connection end of the third switching tube is electrically connected with the second end of the energy storage capacitor. The third switching tube is conducted based on the scanning signal received by the control end of the third switching tube in the light-emitting stage, so that the data writing loop is conducted.
Optionally, the pixel driving circuit further includes a fourth switching tube connected in series to the light emitting circuit, and the fourth switching tube is electrically connected between the second connection terminal of the driving transistor and the second terminal of the light emitting element. In the reset stage, the first switching tube is turned on based on the scanning signal received by the control end of the first switching tube, so that the first voltage is transmitted to the control end of the driving transistor to enable the driving transistor to be turned on, and the fourth switching tube is turned on based on the scanning signal received by the control end of the fourth switching tube, so that the light-emitting loop is turned on.
Optionally, in the light emitting stage, the third switching tube is turned on based on a scan signal received by a control end of the third switching tube, so as to connect the data voltage to the second end of the energy storage capacitor, so that the energy storage capacitor adjusts the voltage of the control end of the driving transistor to a third voltage based on a bootstrap effect, thereby enabling the driving transistor to be turned on based on the third voltage received by the control end of the driving transistor, and the fourth switching tube is turned on based on a scan signal received by the control end of the fourth switching tube, thereby turning on the light emitting loop.
Optionally, the types of the first switch tube, the second switch tube, the third switch tube, the fourth switch tube and the driving transistor comprise triodes and MOS tubes.
Optionally, the first switch tube, the second switch tube, the third switch tube, the fourth switch tube and the driving transistor are all high-level conducting transistors or all low-level conducting transistors.
The application also provides a display panel which comprises a substrate and the pixel driving circuits, wherein the substrate comprises a display area, and the pixel driving circuits are arranged in the display area of the substrate in an array manner.
Additional aspects and advantages of the application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the application.
Drawings
Fig. 1 is a schematic structural diagram of a display panel according to an embodiment of the present application.
Fig. 2 is a schematic diagram of a conventional pixel driving circuit.
Fig. 3 is a schematic diagram of a pixel driving circuit according to an embodiment of the present application.
Fig. 4 is a timing chart of the operation of the pixel driving circuit shown in fig. 3.
Fig. 5a is a circuit schematic of the pixel driving circuit shown in fig. 3 at a stage a.
Fig. 5B is a circuit schematic of the pixel driving circuit shown in fig. 3 in a B-stage.
Fig. 5C is a circuit schematic of the pixel driving circuit shown in fig. 3 in the C stage.
Description of main reference numerals:
display panel 1
Reference voltage terminal VSS
Substrate 1000
Display area 1001
Non-display area 1002
Pixel driving circuit 100
Scan signal generating circuit 110
Scanning line 111
Data signal generating circuit 120
Data line 121
Light-emitting element OLED
Drive transistor M
Scan transistor T0
First switching tube T1
Second switching tube T2
Third switching tube T3
Fourth switching tube T4
Energy storage capacitor reset loop L1
Light-emitting loop L2
Threshold compensation loop L3
Data write loop L4
Storage capacitor C, C0
The application will be further described in the following detailed description in conjunction with the above-described figures.
Detailed Description
The following description of the embodiments of the present application will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present application, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without any inventive effort, are intended to be within the scope of the application.
In the description of the present application, it should be noted that the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
Referring to fig. 1, the present application provides a display panel 1, the display panel 1 includes a substrate 1000, and the substrate 1000 includes a display area 1001 and a non-display area 1002. A plurality of pixel driving circuits 100 arranged in an array are disposed in the display area 1001, and each pixel driving circuit 100 forms a sub-pixel unit. The scan signal generating circuit 110 (also referred to as a gate driver) is disposed in the non-display region 1002. The scanning signal generating circuit 110 is electrically connected to the pixel driving circuits 100 of each row through a plurality of scanning lines 111, and the scanning signal generating circuit 110 is configured to generate a corresponding plurality of scanning signals for each row of the pixel driving circuits 100.
In the embodiment of the present application, the display panel 1 further includes a data signal generating circuit 120 (also referred to as a source driver), the data signal generating circuit 120 is electrically connected to each column of the pixel driving circuits 100 through a plurality of data lines 121, and the data signal generating circuit 120 is configured to generate a corresponding data signal Vdata for each column of the pixel driving circuits, and output the data signal Vdata to each of the pixel driving circuits 100 in the column of the pixel driving circuits.
Referring to fig. 2, fig. 2 is a conventional pixel driving circuit 100 'with a 2T1C structure, and the pixel driving circuit 100' includes a scan transistor T0, a driving transistor M, a storage capacitor C0, and a light emitting element.
Wherein the pixel driving circuit 100' is used for driving the light emitting element to emit light. In the embodiment of the application, the light-emitting element is an OLED, and the first end and the second end of the light-emitting element are in one-to-one correspondence with the cathode and the anode of the OLED. In other embodiments, the Light Emitting element may be an LED (Light-Emitting Diode), a Micro LED (Micro Light-Emitting Diode), or a Mini LED (sub-millimeter Light-Emitting Diode). The cathode of the light emitting element OLED is electrically connected to the reference voltage terminal VSS to receive the reference voltage signal VSS, the drain of the driving transistor M is configured to receive the driving voltage VDD, the source of the driving transistor M is electrically connected to the anode of the light emitting element OLED, the gate of the driving transistor M is electrically connected to the drain of the scanning transistor T0, the source of the scanning transistor T0 is electrically connected to the data line 121 to receive the data voltage Vdata, and the gate of the scanning transistor T0 is electrically connected to the scanning line 111 to receive the scanning signal. The first end of the energy storage capacitor C0 is electrically connected to the gate of the driving transistor M, and the second end of the energy storage capacitor C0 is electrically connected to the cathode of the light emitting element OLED. Illustratively, when the scan signal is an on signal, the scan transistor T0 is turned on, the data voltage Vdata on the data line 121 charges the storage capacitor C0 through the scan transistor T0 to adjust the voltage of the first end of the storage capacitor C0 to the data voltage Vdata, the driving transistor M drives the light emitting element to emit light based on the data voltage Vdata received by the gate thereof and the driving voltage VDD received by the source thereof, and at this time, the gate-source voltage vgs=vg-vs=vdata-VDD of the driving transistor M, the driving current Ids flowing through the light emitting element OLED has the following relationship with the gate-source voltage Vgs of the driving transistor M:
Ids＝(K/2)(Vgs-Vth) 2 ＝(K/2)(Vdata-VDD-Vth) 2
wherein k=cox×μ×w/L, cox is the gate capacitance per unit area; μ is the mobility of channel electron movement; W/L is the width-to-length ratio of the channel of the driving transistor M; vth is the threshold voltage of the driving transistor M.
Since the luminance of the light emitting element OLED is in direct proportion to the driving current Ids flowing therethrough, that is, is related to the data voltage Vdata, the driving voltage VDD, and the threshold voltage Vth of the driving transistor M. Since the uniformity of the threshold voltage Vth of the driving transistor M is poor, that is, the threshold voltages Vth of the driving transistors M are not uniform in different pixel driving circuits 100, when the same data voltages are input, the driving currents Ids are not uniform in the different pixel driving circuits 100' due to the non-uniformity of the threshold voltages Vth, resulting in poor brightness uniformity of the display panel.
Referring to fig. 3, in order to solve the problem of poor brightness uniformity of the display panel due to poor uniformity of the threshold voltage Vth of the driving transistor M, the present application provides a pixel driving circuit 100. The pixel driving circuit 100 is used for driving the light emitting element OLED to emit light.
The pixel driving circuit 100 includes a storage capacitor C, a driving transistor M, a first switching transistor T1, a second switching transistor T2, a third switching transistor T3, and a fourth switching transistor T4. The control ends of the switching tubes T1 to T4 are electrically connected to the scan signal generating circuit 110, and the switching tubes T1 to T4 may be at least one of transistors or MOS transistors. In this embodiment, the switching transistors T1 to T4 and the driving transistor M are all high-level turned-on transistors, such as NMOS transistors. In another embodiment, the switching transistors T1 to T4 and the driving transistor M are low-level pass transistors, such as PMOS transistors. It can be appreciated that the switch transistors T1 to T4 are all designed into the same type of transistor, which is beneficial to simplifying the manufacturing process of the substrate 1000, reducing the processing difficulty and reducing the production cost. Of course, in other embodiments, the switching transistors T1 to T4 and the driving transistor M may be different types of transistors, which is not limited herein. The switching transistors T1 to T4 and the driving transistor M in the present application may be amorphous silicon thin film transistors (a-Si TFTs), low temperature polysilicon thin film transistors (LTPS TFTs), or Oxide semiconductor thin film transistors (Oxide TFTs). Among them, an active layer of the Oxide semiconductor thin film transistor employs an Oxide semiconductor (Oxide), such as indium gallium zinc Oxide (Indium Gallium Zinc Oxide, IGZO). Illustratively, the switching transistors T1 to T4 are oxide semiconductor thin film transistors, and the driving transistor M is a low-temperature polysilicon transistor, and the mobility of the low-temperature polysilicon transistor is high, so that the turn-on speed of the driving transistor M can be increased, and the reaction speed of the pixel driving circuit 100 can be increased, thereby improving the display effect of the display panel 1.
The circuit structure of the pixel driving circuit 100 and its operation will be described with reference to fig. 4, 5 a-5 c.
As shown in fig. 4, the pixel driving circuit 100 sequentially operates in a reset phase (a phase), a threshold compensation phase (B phase), and a light emitting phase (C phase) in one frame display period.
As shown in fig. 5a, the pixel driving circuit 100 includes a storage capacitor reset loop L1 and a light emitting loop L2. The energy storage capacitor reset circuit L1 includes a driving transistor M, a second switching tube T2, and an energy storage capacitor C, which are sequentially connected in series, wherein a first connection end (i.e., a drain d) of the driving transistor M is configured to receive a reset voltage Vint in the reset stage, a second connection end (i.e., a source s) of the driving transistor M is electrically connected with a first connection end of the second switching tube T2, and a second connection end of the second switching tube T2 is electrically connected with a second end b of the energy storage capacitor C. The energy storage capacitor reset loop L1 is configured to be turned on in the reset phase, and receive the reset voltage Vint to reset the voltage of the second end b of the energy storage capacitor C to the reset voltage Vint. In this way, the influence of the residual charge on the voltage of the energy storage capacitor C in the light-emitting stage of the previous frame display period can be eliminated, so that the initial value of the voltage at the second end b of the energy storage capacitor C is equal in the light-emitting stage of each frame display period, that is, the reset voltage Vint, so as to ensure the uniformity of the display effect of the display panel 1.
The light emitting circuit L2 includes a driving transistor M, the fourth switching tube T4, and the light emitting element OLED sequentially connected in series. The first terminal (i.e., cathode) of the light emitting element OLED is configured to receive the reference voltage VSS, and the fourth switching transistor T4 is connected in series between the second connection terminal of the driving transistor M and the second terminal (i.e., anode) of the light emitting element OLED. The light emitting loop L2 is configured to be turned on during the reset phase and receive the reset voltage Vint to reset the voltage of the second terminal of the light emitting element OLED to the reset voltage Vint. In this way, the influence of the residual charges in the light emitting stage of the previous frame display period on the voltage of the anode of the light emitting element OLED can be eliminated, so that the initial voltage values of the anode of the light emitting element OLED are equal in the light emitting stage of each frame display period, that is, the reset voltage Vint, so as to further improve the uniformity of the display effect of the display panel 1. Optionally, the voltage value of the reset voltage Vint is lower than the voltage value of the reference voltage VSS, so that the reset voltage Vint does not cause the light emitting element OLED to be misfiring to emit light during the reset phase.
It can be appreciated that, in the reset phase, the capacitor reset loop L1 and the light emitting loop L2 multiplex the driving transistor M to be connected to the reset voltage Vint, and in addition, the light emitting loop L2 is used for resetting the voltage of the anode of the light emitting element OLED in the reset phase and driving the light emitting element OLED to emit light in the light emitting phase, so that the number of switching tubes can be reduced, the circuit structure of the pixel driving circuit 100 can be simplified, and the cost can be reduced.
As shown in fig. 5b, the pixel driving circuit 100 further includes a threshold compensation loop L3. The threshold compensation circuit L3 includes the driving transistor M, the second switching transistor T2, the energy storage capacitor C, and the first switching transistor T1 connected in series in sequence. The second switching tube T2 is connected in series between the second connection end of the driving transistor M and the second end b of the energy storage capacitor C, the first connection end of the first switching tube T1 is configured to receive the first voltage V1, and the second connection end of the first switching tube T1 is electrically connected with the first end a of the energy storage capacitor C and the control end of the driving transistor M. The threshold compensation loop L3 is configured to be turned on during the threshold compensation phase, so as to input a first voltage V1 to the first end a of the storage capacitor C, and charge the storage capacitor C, so that a voltage at the second end b of the storage capacitor C reaches a second voltage, where the reset voltage is less than the first voltage, and the second voltage is equal to a difference between the first voltage and the threshold voltage Vth of the driving transistor M, that is, a voltage vb=v1-Vth at the second end b of the storage capacitor C.
Specifically, the driving transistor M is a transistor that is turned on at a high level, that is, the driving transistor M is turned on when its gate-source voltage vgs=vg-vs=v1-Vint > Vth, enters a critical off state when vgs=vth, and is turned off when Vgs < Vth. The first connection of the driving transistor M is further configured to receive a driving voltage VOLED during the threshold compensation phase. In the threshold compensation phase, for the driving transistor M, at the start time of charging the storage capacitor C, the gate voltage vg=v1 and the source voltage vs=vint of the driving transistor M, at which time Vgs > Vth, and therefore, the driving transistor M is turned on. The driving voltage VOLED charges the energy storage capacitor C through the turned-on threshold compensation loop L3, so that the voltage of the second end b of the energy storage capacitor C continuously rises from the reset voltage Vint. When the voltage at the second terminal b of the storage capacitor C increases to the second voltage, that is, vb=v1-Vth, vgs=v1- (V1-Vth) =vth, the driving transistor M is in a critical off state, and the voltage at the second terminal b of the storage capacitor C does not increase any more.
As shown in fig. 5c, the pixel driving circuit 100 further includes a data writing loop L4. The data writing circuit L4 includes a third switching tube T3 and an energy storage capacitor C connected in series in sequence, where a first connection end of the third switching tube T3 is used for receiving the data voltage Vdata, and a second connection end of the third switching tube T3 is electrically connected with a second end b of the energy storage capacitor C. The data writing circuit L4 is configured to be turned on during the light emitting period to connect the data voltage Vdata to the second terminal b of the storage capacitor C, so that the storage capacitor C adjusts the voltage of the control terminal of the driving transistor M to a third voltage based on a bootstrap effect, where the third voltage is equal to a sum of the data voltage and a threshold voltage of the driving transistor M.
Specifically, as described above, in the threshold compensation phase, the voltage vg=va=v1 at the first terminal a of the storage capacitor C, and the voltage vb=v1-Vth at the second terminal b of the storage capacitor C, that is, the voltage difference between the first terminal a and the second terminal b is Vth. When the second terminal b of the storage capacitor C receives the data voltage Vdata, the potential thereof changes from V1-Vth to Vdata, i.e., the potential of the second terminal b of the storage capacitor C changes by (Vdata-v1+vth), and the potential of the first terminal a of the storage capacitor C (i.e., the gate voltage Vg of the driving transistor M) also changes to the third voltage, i.e., vg=va= (vdata+vth) due to the bootstrap effect of the storage capacitor C.
The light emitting circuit L2 is further configured to be turned on during the light emitting period, so that the driving transistor M drives the light emitting element OLED to emit light based on the driving voltage VOLED received by the first connection terminal thereof and the third voltage received by the control terminal thereof, that is, vs=voled, vg= (vdata+vth). At this time, the gate-source voltage vgs=vg-vs=vdata+vth-VOLED of the driving transistor M, and the driving current Ids flowing through the light emitting element OLED has the following relationship with the gate-source voltage Vgs of the driving transistor M:
Ids＝(K/2)(Vgs-Vth) 2 ＝(K/2)(Vdata-VOLED) 2
wherein k=cox×μ×w/L, cox is the gate capacitance per unit area; μ is the mobility of channel electron movement; W/L is the width to length ratio of the channel of the driving transistor M.
As can be seen from the above formula, the threshold compensation circuit L3 can provide the compensation voltage to the driving transistor M, so that the current Ids flowing through the light emitting element OLED is independent of the threshold voltage Vth of the driving transistor M, and is related only to the data voltage Vdata and the driving voltage VOLED. Accordingly, it is possible to eliminate a phenomenon that display luminance is not uniform due to the difference in the threshold voltage Vth of the driving transistor M between different pixel driving circuits 100.
Preferably, the first voltage V1 may be the data voltage Vdata, that is, the first connection terminal of the first switching tube T1 and the first connection terminal of the third switching tube T3 may be simultaneously connected to the data voltage Vdata, so that the number of connected signals of the pixel driving circuit 100 may be reduced, and a circuit structure may be simplified.
As described above, in the present embodiment, the switching transistors T1 to T4 and the driving transistor M are both high-level turned-on transistors. The following describes in detail the working procedure of the pixel driving circuit 100 in one frame scanning period according to the present application with reference to fig. 3 to 5 c:
in the embodiment of the present application, the SCAN signals received by the control ends of the first switch tube T1 and the second switch tube T2 are both the second SCAN signal SCAN2, the SCAN signal received by the control end of the third switch tube T3 is the third SCAN signal SCAN3, and the SCAN signal received by the fourth switch tube T4 is the first SCAN signal SCAN1. The switching transistors having the same turn-on timing can be controlled by the same scan signal, and thus, the wiring structure can be simplified. Of course, in other embodiments, a scan signal may be separately set for each switching tube to control, which is not limited herein. Further, in the display panel 1, the pixel driving circuits 100 located in the same row may share a set of SCAN signals (including the first SCAN signal SCAN1, the second SCAN signal SCAN2, and the third SCAN signal SCAN 3), and the third SCAN signal SCAN3 of the pixel driving circuit 100 in the previous row may be used as the second SCAN signal SCAN2 of the pixel driving circuit 100 in the next row, so that the wiring structure may be further simplified.
In the reset phase (a phase), the first SCAN signal SCAN1 and the second SCAN signal SCAN2 are both at a high level, the third SCAN signal SCAN3 is at a low level, and the voltage connected to the first connection terminal of the driving transistor M is the reset voltage Vint. Therefore, the switching transistors T1, T2, T4 are all turned on, and the switching transistor T3 is turned off, so that the storage capacitor reset circuit L1 is turned on to reset the voltage of the second terminal b of the storage capacitor C to the reset voltage Vint, the light emitting circuit L2 is turned on to reset the voltage of the anode of the light emitting element OLED to the reset voltage Vint, and the data writing circuit L4 is turned off.
In the data writing stage (B stage), the second SCAN signal SCAN2 is at a high level, the first SCAN signal SCAN1 and the third SCAN signal SCAN3 are both at a low level, and the voltage connected to the first connection terminal of the driving transistor M is the driving voltage VOLED. Therefore, the switching transistors T1, T2 and the driving transistor M are all turned on, and the switching transistors T3, T4 are all turned off, so that the threshold compensation circuit L3 is turned on to input the first voltage V1 to the first end a of the storage capacitor C, and the storage capacitor C is charged, so that the voltage at the second end b of the storage capacitor C reaches the second voltage, and the data writing circuit L4 and the light emitting circuit L2 are all turned off.
In the light emitting stage (C stage), the first SCAN signal SCAN1 and the third SCAN signal SCAN3 are both at a high level, the second SCAN signal SCAN2 is at a low level, and the voltage connected to the first connection terminal of the driving transistor M is the driving voltage VOLED. Therefore, the switching transistors T3 and T4 and the driving transistor M are all turned on, and the switching transistors T1 and T2 are all turned off, so that the data writing circuit L4 is turned on, the energy storage capacitor C adjusts the voltage of the control terminal of the driving transistor M to a third voltage based on the bootstrap effect, and the light emitting circuit L2 is turned on to drive the light emitting element OLED to emit light, and the energy storage capacitor reset circuit L1 and the threshold compensation circuit L3 are both turned off.
According to the pixel driving circuit 100 provided by the application, the first voltage is input to the first end a of the energy storage capacitor C through the threshold compensation loop L3 in the threshold compensation stage, and the energy storage capacitor C is charged, so that the voltage of the second end b of the energy storage capacitor C reaches the second voltage, and the data voltage Vdata is connected to the second end b of the energy storage capacitor C through the data writing loop L4 in the light-emitting stage, so that the voltage of the control end of the driving transistor M is regulated to the third voltage based on the bootstrap effect by the energy storage capacitor C, and the driving transistor M drives the light-emitting element to emit light based on the driving voltage VOLED received by the first connection end and the third voltage received by the control end thereof through the light-emitting loop L2, so that the threshold voltage OLED of the driving transistor M can be compensated, the light-emitting brightness of the light-emitting element OLED is irrelevant to the threshold voltage Vth, and the problem of uneven display brightness caused by different threshold voltages Vth of the driving transistor M between different pixel driving circuits 100 can be solved.
Referring to fig. 1 again, based on the same inventive concept, the embodiment of the present application further provides a display panel 1, where the display panel 1 includes a substrate 1000 and the above-mentioned pixel driving circuits 100, the substrate 1000 includes a display area 1001, and the plurality of pixel driving circuits 100 are arranged in an array in the display area 1001 of the substrate 1000.
While embodiments of the present application have been shown and described, it will be understood by those of ordinary skill in the art that: many changes, modifications, substitutions and variations may be made to the embodiments without departing from the spirit and principles of the application, the scope of which is defined by the claims and their equivalents.
Claims (10)
1. A pixel driving circuit for driving a light emitting element to emit light, wherein a first end of the light emitting element is used for receiving a reference voltage, and the pixel driving circuit sequentially works in a reset phase, a threshold compensation phase and a light emitting phase in a frame display period; wherein the pixel driving circuit includes:
the driving transistor comprises a control end, a first connecting end and a second connecting end, wherein the first connecting end is used for receiving reset voltage or driving voltage, and the second connecting end is electrically connected with the second end of the light-emitting element;
the first end of the energy storage capacitor is electrically connected with the control end of the driving transistor, and the second end of the energy storage capacitor is electrically connected with the second connecting end of the driving transistor;
the drive transistor and the energy storage capacitor are connected in series in the energy storage capacitor reset loop, and the energy storage capacitor reset loop is used for conducting in the reset phase and receiving the reset voltage so as to reset the voltage of the second end of the energy storage capacitor to the reset voltage;
the light-emitting circuit is used for conducting in the resetting stage and receiving the resetting voltage so as to reset the voltage of the second end of the light-emitting element to the resetting voltage;
a threshold compensation loop, wherein the driving transistor and the energy storage capacitor are connected in series in the threshold compensation loop, the threshold compensation loop is used for conducting in the threshold compensation stage so as to input a first voltage to a first end of the energy storage capacitor and charge the energy storage capacitor, so that the voltage of a second end of the energy storage capacitor reaches a second voltage, wherein the reset voltage is smaller than the first voltage, and the second voltage is equal to the difference between the first voltage and the threshold voltage of the driving transistor; and
the data writing circuit is used for being conducted in the light-emitting stage to enable a data voltage to be connected to the second end of the energy storage capacitor, so that the energy storage capacitor adjusts the voltage of the control end of the driving transistor to a third voltage based on a bootstrap effect, and the third voltage is equal to the sum of the data voltage and the threshold voltage of the driving transistor;
the light-emitting circuit is further configured to be turned on in the light-emitting stage, so that the driving transistor drives the light-emitting element to emit light based on the driving voltage received by the first connection terminal and the third voltage received by the control terminal.
2. The pixel driving circuit according to claim 1, further comprising a first switching tube connected in series with the threshold compensation loop, a first connection terminal of the first switching tube being configured to receive the first voltage, a second connection terminal of the first switching tube being electrically connected to a first terminal of the energy storage capacitor;
the first switching tube is conducted in the threshold compensation stage based on the scanning signal received by the control end of the first switching tube, so that the first voltage is input to the first end of the energy storage capacitor.
3. The pixel drive circuit of claim 2, further comprising a second switching transistor connected in series between a second connection terminal of the drive transistor and a second terminal of the storage capacitor;
in the threshold compensation stage, the first switching tube is conducted based on a scanning signal received by a control end of the first switching tube so as to transmit the first voltage to the control end of the driving transistor, and thus the driving transistor is conducted; the second switching tube is conducted based on the scanning signal received by the control end of the second switching tube, so that the threshold compensation loop is conducted.
4. A pixel driving circuit according to claim 3, wherein in the reset phase, the first switching transistor is turned on based on a scan signal received by a control terminal thereof to transmit the first voltage to the control terminal of the driving transistor, thereby turning on the driving transistor; the second switching tube is conducted based on the scanning signal received by the control end of the second switching tube, so that the energy storage capacitor reset loop is conducted.
5. The pixel driving circuit according to claim 4, further comprising a third switching tube connected in series with the data writing circuit, a first connection terminal of the third switching tube being configured to receive the data voltage, a second connection terminal of the third switching tube being electrically connected to the second terminal of the storage capacitor;
the third switching tube is conducted based on the scanning signal received by the control end of the third switching tube in the light-emitting stage, so that the data writing loop is conducted.
6. The pixel driving circuit according to claim 5, further comprising a fourth switching tube connected in series with the light emitting circuit, the fourth switching tube being electrically connected between the second connection terminal of the driving transistor and the second terminal of the light emitting element;
in the reset stage, the first switching tube is turned on based on the scanning signal received by the control end of the first switching tube, so that the first voltage is transmitted to the control end of the driving transistor to enable the driving transistor to be turned on, and the fourth switching tube is turned on based on the scanning signal received by the control end of the fourth switching tube, so that the light-emitting loop is turned on.
7. The pixel driving circuit according to claim 6, wherein in the light emitting stage, the third switching tube is turned on based on a scan signal received by a control terminal thereof to switch the data voltage to the second terminal of the storage capacitor, so that the storage capacitor adjusts the voltage of the control terminal of the driving transistor to a third voltage based on a bootstrap effect, so that the driving transistor is turned on based on the third voltage received by the control terminal thereof, and the fourth switching tube is turned on based on a scan signal received by the control terminal thereof, thereby turning on the light emitting circuit.
8. The pixel driving circuit according to claim 7, wherein the types of the first switching transistor, the second switching transistor, the third switching transistor, the fourth switching transistor, and the driving transistor include a transistor and a MOS transistor.
9. The pixel driving circuit according to claim 8, wherein the first switching transistor, the second switching transistor, the third switching transistor, the fourth switching transistor, and the driving transistor are each a high-level on transistor or a low-level on transistor.
10. A display panel comprising a substrate and a plurality of pixel drive circuits according to any one of claims 1 to 9, the substrate comprising a display area, the plurality of pixel drive circuits being arranged in an array within the display area of the substrate.
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