LED pixel driving circuit and driving method

Abstract

The application discloses an LED pixel driving circuit and a driving method, and relates to the technical field of LED driving.The LED pixel driving circuit adopts seven NMOS tubes and two capacitors to drive a light-emitting diode; the driving method based on the LED pixel driving circuit comprises the following steps: resetting the light-emitting diode, so that the light-emitting diode is in an extinguished state; extracting a threshold voltage value of a second NMOS tube and compensating for the offset of the threshold voltage value, so as to form a compensated LED pixel driving circuit; based on the compensated LED pixel driving circuit, outputting a light-emitting diode emission current to drive the light-emitting diode to emit light.The LED pixel driving circuit and the driving method can effectively improve the uniformity of the screen display brightness, expand the input range of the voltage data, and thus more finely regulate and control the gray scale of the screen.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of LED driving, in particular to an LED pixel driving circuit and a driving method. BACKGROUND

[0002] In order to realize high-quality AR and VR applications, micro-displays need to have high resolution and high brightness uniformity. In order to obtain high resolution, the pixel driving circuit should have a simple structure that can be integrated into a unit sub-pixel area of several tens of μm 2 . However, as the size of the driving transistor in the pixel driving circuit decreases with the decrease of the sub-pixel area, the threshold voltage V th of the driving transistor will change due to the change of the manufacturing process. As the amount of change of the threshold voltage V th increases, the emission current deviation of the Light-Emitting Diode (LED) will increase, resulting in brightness imbalance of the micro-display. Therefore, it is necessary for the pixel driving circuit to compensate for the threshold voltage change of the driving transistor to realize high brightness uniformity. However, the traditional 2T1C driving circuit does not have a threshold voltage compensation mechanism, so the LED emission current deviation is too large, resulting in the situation that the screen display brightness is not uniform. SUMMARY

[0003] The purpose of the present application is to provide an LED pixel driving circuit and a driving method, which can effectively improve the uniformity of screen display brightness, expand the input range of voltage data, and thus more finely control the gray scale of the screen.

[0004] In order to achieve the above purpose, the present application provides the following solutions:

[0005] An LED pixel driving circuit, comprising: a first NMOS tube, a second NMOS tube, a third NMOS tube, a fourth NMOS tube, a fifth NMOS tube, a sixth NMOS tube, a seventh NMOS tube, a first capacitor, a second capacitor, and a Light-Emitting Diode (LED).

[0006] The drain of the first NMOS tube is connected with a power supply VDD; the source of the first NMOS tube is connected with the drain of the second NMOS tube and the source of the third NMOS tube respectively; the gate of the second NMOS tube and the drain of the third NMOS tube are connected with one end of the first capacitor; the other end of the first capacitor is connected with the source of the fifth NMOS tube, one end of the second capacitor and the drain of the fourth NMOS tube respectively; the source of the fourth NMOS tube is connected with the source of the second NMOS tube, the other end of the second capacitor, the anode of the light emitting diode, the drain of the seventh NMOS tube and the source of the sixth NMOS tube respectively; the drain of the fifth NMOS tube and the drain of the sixth NMOS tube are connected with a data signal line DATA; the source of the seventh NMOS tube is grounded; the cathode of the light emitting diode is connected with a reverse bias signal VCOM.

[0007] Optionally, the first NMOS tube is an enable tube, the gate of the first NMOS tube is connected with an enable signal EM; the second NMOS tube is a drive tube; the third NMOS tube, the fourth NMOS tube, the fifth NMOS tube, the sixth NMOS tube and the seventh NMOS tube are all switch tubes; the gates of the third NMOS tube and the sixth NMOS tube are connected with a third scan signal SCAN3; the gates of the fourth NMOS tube and the fifth NMOS tube are connected with a second scan signal SCNA2; the gate of the seventh NMOS tube is connected with a first scan signal SCAN1.

[0008] A driving method of an LED pixel driving circuit, applied to the LED pixel driving circuit, comprising:

[0009] resetting the light emitting diode so that the light emitting diode is in an off state;

[0010] extracting a threshold voltage value of the second NMOS tube;

[0011] compensating for the offset of the threshold voltage value to form a compensated LED pixel driving circuit;

[0012] based on the compensated LED pixel driving circuit, outputting a light emitting diode emission current to drive the light emitting diode to emit light.

[0013] Optionally, the resetting the light emitting diode so that the light emitting diode is in an off state specifically comprises:

[0014] by setting the first scan signal SCAN1 to a high potential, the second scan signal SCAN2 to a low potential, the third scan signal SCAN3 to a low potential, the enable signal EM to a high potential and the reverse bias signal VCOM to a high potential, the light emitting diode is in an off state.

[0015] Optionally, the extracting the threshold voltage value of the second NMOS tube specifically comprises:

[0016] After the first scan signal SCAN1 is set to low potential, the second scan signal SCAN2 is set to high potential, the third scan signal SCAN3 is set to high potential, the enable signal EM is set to low potential, and the reverse bias signal VCOM is set to high potential, the threshold voltage value of the second NMOS tube is extracted.

[0017] Optionally, the offset of the threshold voltage value is compensated to form a compensated LED pixel driving circuit, specifically comprising:

[0018] The offset of the threshold voltage value is compensated by setting the first scan signal SCAN1 to low potential, the second scan signal SCAN2 to low potential, the third scan signal SCAN3 to high potential, the enable signal EM to low potential, and the reverse bias signal VCOM to high potential, to form a compensated LED pixel driving circuit.

[0019] Optionally, the compensated LED pixel driving circuit is used to output the emission current of the light emitting diode to drive the light emitting diode to emit light, specifically comprising:

[0020] The emission current of the light emitting diode is outputted by setting the first scan signal SCAN1, the second scan signal SCAN2 and the third scan signal SCAN3 to low potential, setting the enable signal EM to high potential, and setting the reverse bias signal VCOM to low potential based on the compensated LED pixel driving circuit, to drive the light emitting diode to emit light.

[0021] Optionally, the emission current I of the light emitting diode LED is calculated according to the following formula:

[0022] wherein, is the width-length ratio of the second NMOS tube; n is the sub-threshold slope factor; V T is the thermal voltage; I0 is the residual leakage current; V DATA is the data voltage provided by the data signal line DATA; C1 is the capacitance value of the first capacitor; C2 is the capacitance value of the second capacitor; C PG,N2 is the capacitance value of the parasitic capacitance between the gate of the second NMOS tube and the ground.

[0023] According to the embodiments of the present application, the following technical effects are provided:

[0024] This invention provides an LED pixel driving circuit and driving method. The LED pixel driving circuit structure includes seven N-type MOSFETs, two capacitors, and a light-emitting diode (LED). A voltage-programmed analog driving method is used to drive the LED pixel driving circuit. The driving method mainly consists of four stages: LED reset stage, threshold voltage extraction stage, threshold voltage offset compensation stage, and emission current emission stage. Based on the LED pixel driving circuit provided by this invention, the driving method enables the circuit structure to effectively compensate for the deviation in LED emission current caused by transistor threshold voltage offset, thereby effectively improving the uniformity of screen display brightness, expanding the input range of voltage data, and thus allowing for more precise control of screen grayscale. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 A schematic diagram showing the connection relationship of the LED pixel driving circuit provided by the present invention;

[0027] Figure 2 The timing diagrams for each signal provided by this invention. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] The purpose of this invention is to provide an LED pixel driving circuit and driving method that can effectively improve the uniformity of screen display brightness, expand the input range of voltage data, and thus more precisely control the grayscale of the screen.

[0030] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] Figure 1 This is a schematic diagram showing the connection relationship of the LED pixel driving circuit provided by the present invention. Figure 1As shown, the LED pixel driving circuit disclosed by the present application comprises seven N-type MOS tubes, two capacitors and a light emitting diode, which are first NMOS tube N1, second NMOS tube N2, third NMOS tube N3, fourth NMOS tube N4, fifth NMOS tube N5, sixth NMOS tube N6, seventh NMOS tube N7, first capacitor C1, second capacitor C2 and light emitting diode D1.

[0032] Specifically, the drain of the first NMOS tube N1 is connected with the power supply VDD, and the source of the first NMOS tube N1 is connected with the drain of the second NMOS tube N2 and the source of the third NMOS tube N3 respectively. The gate of the second NMOS tube N2 and the drain of the third NMOS tube N3 are both connected with one end of the first capacitor C1, and the connection point is A. The other end of the first capacitor C1 is connected with the source of the fifth NMOS tube N5, one end of the second capacitor C2 and the drain of the fourth NMOS tube N4 respectively, and the connection point is B. The source of the fourth NMOS tube N4 is connected with the source of the second NMOS tube N2, the other end of the second capacitor C2, the anode of the light emitting diode D1, the drain of the seventh NMOS tube N7 and the source of the sixth NMOS tube N6 respectively, and the connection point is C. The drain of the fifth NMOS tube N5 and the drain of the sixth NMOS tube N6 are both connected with the data signal line DATA. The source of the seventh NMOS tube N7 is grounded GND. The cathode of the light emitting diode D1 is connected with the reverse bias signal VCOM.

[0033] The first NMOS tube N1 is an enable tube, the second NMOS tube N2 is a driving tube, and the third to seventh NMOS tubes N3-N7 are all switch tubes. For the input signals of each NMOS tube, the gate of the first NMOS tube N1 is connected with the enable signal EM. The gates of the third NMOS tube N3 and the sixth NMOS tube N6 are connected with the third scan signal SCAN3. The gates of the fourth NMOS tube N4 and the fifth NMOS tube N5 are connected with the second scan signal SCNA2. The gate of the seventh NMOS tube N7 is connected with the first scan signal SCAN1. In addition, the first capacitor C1 and the second capacitor C2 serve as storage capacitors, which can store the changes of the node voltage in the programming stage, so as to complete the sampling extraction of the threshold voltage value.

[0034] Figure 2 The timing diagram of each signal provided by the present application is shown as follows. Figure 2 As shown, the timing diagram of the scan signals SCAN1, SCAN2, SCAN3, the enable signal EM, the data signal DATA and the control signal COM within one light emitting diode light emitting period (1 frame time) is shown. The control signal COM is opposite to the high and low levels of each stage of the reverse bias signal VCOM, so as to obtain the state of each stage of the reverse bias signal VCOM. Figure 2The illustrated timing diagram is mainly divided into four stages: (1) a reset light emitting diode stage, (2) a threshold voltage value extraction stage, (3) a threshold voltage value offset compensation stage, and (4) an emission current emission stage.

[0035] As shown in Figure 1 and Figure 2 , based on the LED pixel driving circuit, the application further provides a driving method of the LED pixel driving circuit, comprising:

[0036] The reset light emitting diode stage S1: reset the light emitting diode, so that the light emitting diode is in an extinguished state.

[0037] Specifically, by setting the first scan signal SCAN1 to a high potential, N7 is turned on; the second scan signal SCAN2 is set to a low potential, N4 and N5 are turned off; the third scan signal SCAN3 is set to a low potential, N3 and N6 are turned off; the enable signal EM is set to a high potential, N1 is turned on, and the reverse bias signal VCOM is set to a high potential, at this time N2 is turned off, the anode of the LED is directly connected to the ground, the LED cross voltage reaches its opening voltage, and the LED is in an extinguished state. The reset light emitting diode stage is a zero operation on the voltage of the LED anode, so that the LED is extinguished in the reset stage.

[0038] The threshold voltage value extraction stage S2: extracts the threshold voltage value of the second NMOS tube N2.

[0039] Specifically, the first scan signal SCAN1 is set to a low potential, N7 is turned off; the second scan signal SCAN2 is set to a high potential, N4 and N5 are turned on; the third scan signal SCAN3 is set to a high potential, N3 and N6 are turned on; the enable signal EM is set to a low potential, N1 is turned off, and the reverse bias signal VCOM is set to a high potential. At this time, the gate and drain nodes of N2 are connected to form a diode connection. The voltage at point C is V C = V DATA , V DATA is the data voltage provided by the data signal line DATA. The voltage at point A is discharged to V DATA+ V th，N2 . Wherein, V th，N2 is the threshold voltage of N2. Thus, the threshold voltage value V th，N2 of the second NMOS tube N2 is extracted. In the threshold voltage value extraction stage, the extraction of the threshold voltage value V th , N2 of the driving tube N2 is completed, so as to compensate for the offset of the threshold voltage value in the subsequent stage.

[0040] The threshold voltage value offset compensation stage S3: compensates for the offset of the threshold voltage value, and constitutes the compensated LED pixel driving circuit.

[0041] Specifically, by setting the first scan signal SCAN1 to low potential, N7 is turned off; the second scan signal SCAN2 is set to low potential, N4 and N5 are turned off; the third scan signal SCAN3 is set to high potential, N3 and N6 are turned on; the enable signal EM is set to low potential, N1 is turned off; and the inverse bias signal VCOM is set to high potential, thereby compensating for the shift of the threshold voltage value V th，N2 of the second NMOS transistor N2, and forming a compensated LED pixel driving circuit. At this stage, the influence of the threshold voltage value on the emission current is eliminated, so that the emission current is irrelevant to the threshold voltage value, and thus the shift of the threshold voltage value has no effect on the emission current. In the process of compensating for the shift of the threshold voltage value, the data voltage V DATA is added to one side plate of C2 through N6. V DATA Nodes A and B are charged through coupling capacitors C1 and C2, respectively. At this time, the voltage V A at node A is represented as:

[0042]

[0043] where ΔV is the voltage change of node B from the threshold voltage value extraction stage S2 to the threshold voltage value shift compensation stage S3; C PG，N2 is the capacitance value of the parasitic capacitance between the gate of the driving transistor N2 and the ground.

[0044]

[0045] where C1 is the capacitance value of the first capacitor; C2 is the capacitance value of the second capacitor. At this time, the gate-source voltage V GS，N2 of the driving transistor N2 stored in the coupling capacitors C1 and C2 is represented as:

[0046]

[0047] In the threshold voltage value shift compensation stage, the gate-source voltage V GS，N2 is written into the two ends of the coupling capacitors C1 and C2, so that the voltage difference between the two ends of the coupling capacitors C1 and C2 is the gate-source voltage V GS，N2 .

[0048] Emission current emission stage S4: based on the compensated LED pixel driving circuit, outputting a light-emitting diode emission current to drive the light-emitting diode to emit light.

[0049] Specifically, based on the compensated LED pixel driving circuit, the first scan signal SCAN1, the second scan signal SCAN2 and the third scan signal SCAN3 are set to low potential, so that N3, N4, N5, N6 and N7 are all in the off state; the enable signal EM is set to high potential, so that N1 is turned on; the reverse bias signal VCOM is set to low potential, so as to provide negative voltage for the LED emission current. At this time, the output emission current I of the light emitting diode is LED For:

[0050]

[0051] wherein, is the width-length ratio of the second NMOS tube; n is the sub-threshold slope factor; V T is the thermal voltage; I0 is the residual leakage current. Through the output emission current I LED drive the light emitting diode to emit light. In the emission current emission stage, the drive tube N2 passes through the sub-threshold current, that is, the emission current I LED drive the LED to emit light.

[0052] Compared with the existing technology for driving the LED to emit light, the LED pixel driving circuit and the driving method provided by the present application have the following advantages:

[0053] 1) During the operation of the pixel driving circuit, due to the influence of temperature, process, etc., the threshold voltage of the drive tube will be offset, thereby affecting the accuracy of the emission current. The pixel driving circuit provided by the present application extracts the threshold voltage value of the drive tube, and eliminates the influence of the threshold voltage value on the emission current in the subsequent programming stage, thereby realizing the offset compensation of the threshold voltage value.

[0054] 2) Through the coupling effect of the storage capacitor, the pixel driving circuit provided by the present application expands the range of data voltage, so that it can more finely regulate the LED emission current, and also can obtain sufficient voltage across the LED to drive the LED to emit light under a lower power supply voltage, thereby reducing the overall power consumption.

[0055] 3) The application of the COM signal at the cathode of the LED can make the LED in the reverse bias state before the emission current is emitted at the anode. This AC driving scheme can slow down the aging speed of the LED and prolong the service life of the LED.

[0056] In summary, the present application provides an LED pixel driving circuit and a driving method, which can sample and compensate the offset of the threshold voltage value, reduce the deviation of the emission current, and improve the uniformity of the screen display brightness. At the same time, by utilizing the coupling effect of the storage capacitor, the input range of the voltage data is expanded, so as to more finely regulate the gray scale of the screen.

[0057] The various embodiments described in this specification are presented for the purpose of illustrating the principles of the present application and its best mode of operation. Each of the embodiments described in this specification has been provided for the purpose of illustration and is not intended to limit the application.

[0058] The principles and implementations of the present application have been described in the specification with specific examples. The above description of the embodiments is only for the purpose of helping to understand the method of the present application and its core idea. Meanwhile, for those skilled in the art, the specific implementation and application range of the present application can be changed according to the idea of the present application. In summary, the content of the specification should not be understood as a limitation of the present application.

Claims

1. An LED pixel driving circuit, characterized in that, The LED pixel driving circuit comprises: a first NMOS transistor, a second NMOS transistor, a third NMOS transistor, a fourth NMOS transistor, a fifth NMOS transistor, a sixth NMOS transistor, a seventh NMOS transistor, a first capacitor, a second capacitor and a light emitting diode; the drain of the first NMOS transistor is connected to a power supply VDD; the source of the first NMOS transistor is connected to the drain of the second NMOS transistor and the source of the third NMOS transistor; the gate of the second NMOS transistor and the drain of the third NMOS transistor are both connected to one end of the first capacitor; the other end of the first capacitor is connected to the source of the fifth NMOS transistor, one end of the second capacitor and the drain of the fourth NMOS transistor; the source of the fourth NMOS transistor is connected to the source of the second NMOS transistor, the other end of the second capacitor, the anode of the light emitting diode, the drain of the seventh NMOS transistor and the source of the sixth NMOS transistor; the drain of the fifth NMOS transistor and the drain of the sixth NMOS transistor are both connected to a data signal line DATA; the source of the seventh NMOS transistor is grounded; and the cathode of the light emitting diode is connected to a reverse bias signal VCOM.

2. The LED pixel driving circuit of claim 1, wherein, The first NMOS transistor is an enable transistor, the gate of the first NMOS transistor is connected to an enable signal EM; the second NMOS transistor is a drive transistor; the third NMOS transistor, the fourth NMOS transistor, the fifth NMOS transistor, the sixth NMOS transistor and the seventh NMOS transistor are all switch transistors; the gates of the third NMOS transistor and the sixth NMOS transistor are connected to a third scan signal SCAN3; the gates of the fourth NMOS transistor and the fifth NMOS transistor are connected to a second scan signal SCNA2; and the gate of the seventh NMOS transistor is connected to a first scan signal SCAN1.

3. A driving method of an LED pixel driving circuit, characterized by, The LED pixel driving circuit is applied to the LED pixel driving circuit of claim 1, and comprises: resetting the light emitting diode to make the light emitting diode in an off state; extracting a threshold voltage value of the second NMOS transistor; compensating for a shift of the threshold voltage value to form a compensated LED pixel driving circuit; outputting an emitting current of the light emitting diode based on the compensated LED pixel driving circuit to drive the light emitting diode to emit light.

4. The driving method of the LED pixel driving circuit according to claim 3, wherein The resetting the light emitting diode to make the light emitting diode in an off state specifically comprises: making the light emitting diode in an off state by setting the first scan signal SCAN1 to a high potential, setting the second scan signal SCAN2 to a low potential, setting the third scan signal SCAN3 to a low potential, setting the enable signal EM to a high potential and setting the reverse bias signal VCOM to a high potential.

5. The driving method of the LED pixel driving circuit according to claim 3, wherein The extracting the threshold voltage value of the second NMOS transistor specifically comprises: extracting the threshold voltage value of the second NMOS transistor after setting the first scan signal SCAN1 to a low potential, setting the second scan signal SCAN2 to a high potential, setting the third scan signal SCAN3 to a high potential, setting the enable signal EM to a low potential and setting the reverse bias signal VCOM to a high potential.

6. The driving method of the LED pixel driving circuit according to claim 5, wherein The compensating for the shift of the threshold voltage value to form the compensated LED pixel driving circuit specifically comprises: The threshold voltage value is compensated by setting the first scanning signal SCAN1 to a low level, the second scanning signal SCAN2 to a low level, the third scanning signal SCAN3 to a high level, the enable signal EM to a low level, and the reverse bias signal VCOM to a high level, to form a compensated LED pixel driving circuit.

7. The driving method of the LED pixel driving circuit according to claim 3, wherein The compensated LED pixel driving circuit outputs a light emitting diode emission current to drive the light emitting diode to emit light, and specifically includes: The compensated LED pixel driving circuit sets the first scanning signal SCAN1, the second scanning signal SCAN2, and the third scanning signal SCAN3 to a low level, sets the enable signal EM to a high level, and sets the reverse bias signal VCOM to a low level, to output a light emitting diode emission current to drive the light emitting diode to emit light.

8. The driving method of the LED pixel driving circuit according to claim 3, wherein The emission current I of the light emitting diode LED The calculation formula is as follows: wherein, W / L is the width-length ratio of the second NMOS transistor; n is a subthreshold slope factor; V T Vth is the thermal voltage; I0 is the residual leakage current; V DATA Vdata is the data voltage provided to the data signal line DATA; C1 is the capacitance of the first capacitor; C2 is the capacitance of the second capacitor; C PG,N2 Cgd is the capacitance of the parasitic capacitance between the gate and the ground of the second NMOS transistor.

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