Pixel driving circuit, pixel structure, display device and method

Abstract

A pixel driving circuit, pixel structure, display device, and method are disclosed. The pixel driving circuit includes: a capacitor, a driving transistor, a driving type switching unit, a write control unit, and a light-emitting control unit; wherein: the driving type switching unit is adapted to acquire the brightness information of the light-emitting diode and control the driving type of the light-emitting diode based on the brightness information; the write control unit is adapted to write data to the capacitor based on the image signal output by the image signal output by the image signal output by the image signal output terminal under the control of the scan signal output terminal. Specifically, when the driving type of the light-emitting diode is voltage-driven, the image signal output by the image signal output terminal is a voltage signal; when the driving type of the light-emitting diode is current-driven, the image signal output by the image signal output terminal is a current signal. Using the above scheme, the pixel driving circuit can achieve both high linearity and high frame rate.

Description

Technical Field

[0001] This invention relates to the field of OLED technology, and more specifically to a pixel driving circuit, pixel structure, display device, and method. Background Technology

[0002] Compared with the current mainstream Liquid Crystal Display (LCD) technology, Organic-Light-Emitting Diode (OLED) technology has advantages such as active light emission, high luminous efficiency, high contrast, fast response speed, high resolution, low power consumption, and flexible display.

[0003] With the continuous development of technology, OLED display technology is gradually replacing traditional LCD display technology, especially in the field of micro-displays, where OLED is showing vigorous vitality. Each pixel of an OLED display is a light-emitting diode. When current passes through it, these diodes, made of organic materials, emit light. The greater the current, the higher the light intensity. Therefore, OLED displays do not require backlighting and can be made very thin and light with high resolution.

[0004] OLED driving methods are mainly divided into two types: passive matrix OLED (PM-OLED) driving and active matrix OLED (AM-OLED) driving. PM-OLED driving simply uses an array of diode cathodes and anodes to light up pixels in the array in a scanning manner. Each pixel operates in a short pulse mode, so it emits light at high brightness momentarily. The advantages of PM-OLED are its simple structure and low cost, while its disadvantages are high driving voltage, high power consumption, short lifespan, and unsuitability for large-size and high-resolution applications.

[0005] AM-OLED driving uses additional transistors to control the light emission of each pixel. Each pixel can emit light independently and continuously, so it has advantages such as low driving voltage, low power consumption, and long lifespan. AM-OLED driving is gradually becoming the mainstream driving method.

[0006] However, existing AM-OLED pixel driving circuits are either current-driven or voltage-driven. Current-driven circuits are not suitable for high frame rate applications at low brightness, while voltage-driven circuits have a non-linear relationship between the driving voltage and the luminous intensity of the LED. Summary of the Invention

[0007] The problem this invention aims to solve is: how to balance high linearity and high frame rate.

[0008] To address the above problems, embodiments of the present invention provide a pixel driving circuit, which includes: a capacitor, a driving transistor, a driving type switching unit, a write control unit, and a light-emitting control unit; wherein:

[0009] The drive type switching unit is connected to the power supply voltage output terminal and the drive transistor, and is adapted to acquire the brightness information of the light-emitting diode, and control the drive type of the light-emitting diode based on the brightness information of the light-emitting diode;

[0010] The writing control unit has an input terminal connected to the image signal output terminal and the scan signal output terminal, and an output terminal connected to the driving transistor. It is adapted to write data to the capacitor based on the image signal output by the image signal output terminal under the control of the scan signal output by the scan signal output by the scan signal output terminal.

[0011] The light-emitting control unit is connected to the power supply voltage output terminal, the driving transistor, and the light-emitting control signal output terminal. After data is written, it controls the light-emitting diode to emit light based on the light-emitting control signal output by the light-emitting control signal output terminal.

[0012] Specifically, when the driving type of the light-emitting diode is voltage-driven, the image signal output by the image signal output terminal is a voltage signal; when the driving type of the light-emitting diode is current-driven, the image signal output by the image signal output terminal is a current signal.

[0013] Optionally, the drive type switching unit is adapted to control the drive type of the light-emitting diode to be voltage drive when the brightness value of the light-emitting diode is less than the brightness threshold; and to control the drive type of the light-emitting diode to be current drive when the brightness value of the light-emitting diode is greater than or equal to the brightness threshold.

[0014] Optionally, the drive type switching unit includes: a determination subunit, and a first transistor and a second transistor connected to the determination subunit; wherein:

[0015] The judgment subunit is adapted to acquire the brightness information of the light-emitting diode, compare the acquired brightness information with the brightness threshold, and output a first driving type switching signal and a second driving type switching signal based on the comparison result. The first driving type switching signal and the second driving type switching signal are logic inverse signals.

[0016] The control terminal of the first transistor is connected to the first drive type switching signal, the first terminal of the first transistor is connected to the power supply voltage output terminal, and the second terminal of the first transistor is connected to the capacitor.

[0017] The control terminal of the second transistor is connected to the second drive type switching unit, the first terminal of the second transistor is connected to the second terminal of the first transistor, and the second terminal of the second transistor is connected to the first terminal of the drive transistor.

[0018] Optionally, the write control unit includes: a third transistor and a fourth transistor; wherein:

[0019] The control terminals of the third transistor and the fourth transistor are both connected to the scan signal output terminal;

[0020] The first terminal of the third transistor is connected to the image signal output terminal; the second terminal of the third transistor is connected to the first terminal of the driving transistor.

[0021] The first terminal of the fourth transistor is connected to the first terminal of the driving transistor; the second terminal of the fourth transistor is connected to the second terminal of the driving transistor.

[0022] Optionally, the light-emitting control unit includes: a fifth transistor; the control terminal of the fifth transistor is connected to the light-emitting control signal output terminal, the first terminal of the fifth transistor is connected to the power supply voltage output terminal, and the second terminal of the fifth transistor is connected to the first terminal of the driving transistor.

[0023] Optionally, the light-emitting control unit further includes: a sixth transistor; the control terminal of the sixth transistor is connected to the light-emitting control signal output terminal, the first terminal of the sixth transistor is connected to the second terminal of the driving transistor, and the second terminal of the sixth transistor is connected to the light-emitting diode.

[0024] Optionally, the pixel driving circuit further includes: a calibration control unit, connected to the calibration control signal output terminal and the driving transistor, adapted to calibrate the threshold voltage of the driving transistor under the control of the calibration control signal output from the calibration control signal output terminal.

[0025] Optionally, the calibration control unit further includes: a seventh transistor; the gate of the seventh transistor is connected to the calibration control signal output terminal, the first terminal of the seventh transistor is connected to the second terminal of the driving transistor, and the second terminal of the seventh transistor is connected to the preset voltage output terminal.

[0026] This invention also provides a pixel driving method for the above-described pixel driving circuit, the method comprising:

[0027] The brightness information of the light-emitting diode is detected, and the driving type of the light-emitting diode is controlled based on the brightness information of the light-emitting diode;

[0028] Based on the driving type of the light-emitting diode, the corresponding image signal is acquired and data is written.

[0029] After the data is written, the LED is driven to emit light based on the acquired image signal.

[0030] This invention also provides a pixel circuit, which includes the pixel driving circuit described above and a light-emitting diode connected to the pixel driving circuit.

[0031] The present invention also provides a display device, including a pixel array, wherein the pixel array is formed by an array distribution of a plurality of the above-described pixel circuits.

[0032] Compared with the prior art, the technical solution of the embodiments of the present invention has the following advantages:

[0033] The present invention acquires the brightness information of a light-emitting diode (LED) and controls its driving type based on this information. When the LED's driving type is voltage-driven, a voltage signal is input to the pixel driving circuit; when the LED's driving type is current-driven, a current signal is input to the pixel driving circuit. This allows the LED to emit light in a controlled manner based on different input signals. Compared to existing pixel driving circuits, the pixel driving circuit in this invention can adjust the driving type according to the LED's brightness, rather than being limited to a single driving type, thus achieving both high linearity and high frame rate.

[0034] Furthermore, under the control of the calibration control signal, the threshold voltage of the driving transistor can be calibrated through the calibration control unit, thereby avoiding the brightness difference of the light-emitting diode caused by the threshold voltage deviation of the driving transistor and improving the uniformity of the brightness of the light-emitting diode.

[0035] Furthermore, by connecting the first terminal of the seventh transistor to the second terminal of the driving transistor, and then connecting the second terminal of the seventh transistor to the preset voltage output terminal, on the one hand, during the writing phase, the current of the driving transistor during the writing process can be controlled by adjusting the output voltage of the preset voltage output terminal, thus avoiding damage to the driving transistor due to excessive current and improving the lifespan of the driving transistor; on the other hand, when the seventh transistor is disconnected, the voltage stored on the capacitor can be made closer to the threshold voltage of the driving transistor, thus improving the calibration effect. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of an AM-OLED driving circuit.

[0037] Figure 2 This is a schematic diagram of the structure of a pixel driving circuit in an embodiment of the present invention;

[0038] Figure 3This is a schematic diagram of another pixel driving circuit in an embodiment of the present invention;

[0039] Figure 4 This is a schematic diagram of another pixel driving circuit in an embodiment of the present invention;

[0040] Figure 5 This is a schematic diagram of the structure of another pixel driving circuit in an embodiment of the present invention;

[0041] Figure 6 This is a timing diagram of each signal in a pixel driving circuit according to an embodiment of the present invention;

[0042] Figure 7 This is a timing diagram of each signal in another pixel driving circuit according to an embodiment of the present invention. Detailed Implementation

[0043] Figure 1 This is a schematic diagram of a conventional AM-OLED driving circuit. The AM-OLED driving circuit includes a switching transistor M1, a driving transistor Md, and a capacitor C. The control terminal of the switching transistor M1 is connected to the scan signal SCAN, and the first terminal of the switching transistor M1 is connected to the image signal DATA (the voltage of the image signal DATA is VDATA). The second terminal of the first transistor M1 is connected to the control terminal of the second transistor Md. The first terminal of the second transistor Md is connected to the power supply voltage VDD, and the second terminal of the second transistor Md is connected to the light-emitting diode D. The other terminal of the light-emitting diode D1 is grounded. One terminal of the capacitor C is connected to the control terminal of the second transistor Md, and the other terminal is grounded.

[0044] When the scan signal SCAN is low, LED D1 is selected. The image signal DATA writes its voltage VDATA to the upper plate of capacitor C and the gate of driver transistor Md through switching transistor M1. Assuming the anode voltage of LED D1 is VANODE, when VDATA - VANODE is greater than the threshold voltage Vth of driver transistor Md, current begins to flow through LED D1, and LED D1 begins to emit light. The luminous intensity of the LED is proportional to the current flowing through it. Assuming driver transistor Md operates in the saturation region, the current Id flowing through it can be expressed as:

[0045]

[0046] Where μ represents the mobility of the driving transistor Md, Cox represents the gate oxide capacitance per unit area of ​​the driving transistor Md, W is the gate width of the driving transistor Md, and L is the gate length of the driving transistor Md.

[0047] When the scan signal SCAN is high, the switching transistor M1 is turned off, the voltage VDATA of the switching transistor M1 is stored in the capacitor C, and the light-emitting diode D1 continues to light up until the switching transistor M1 is turned on again to refresh the value of VDATA.

[0048] The AM-OLED driving circuit described above is a voltage-driven circuit, meaning that the LED emits light by driving the driving voltage. As can be seen from formula (1), the current Id flowing through the driving transistor Md has a non-linear relationship with the driving voltage VDATA, which affects the linearity of the LED D1.

[0049] If a current-driven circuit is used to drive the LED D1 to emit light, the current in the current-driven circuit (i.e., driving the LED to emit light by driving current) is very small when the driving transistor Md is at low brightness, and the LED settling time is very long, which is not conducive to high frame rate applications.

[0050] To address this problem, the present invention provides a pixel driving circuit, which includes a driving type switching unit. This unit acquires the brightness information of the light-emitting diode (LED) and, based on this information, controls the driving type of the LED, thereby enabling the LED to be driven according to its driving type. Compared to existing pixel driving circuits, the pixel driving circuit of the present invention can adjust the driving type according to the LED brightness, rather than being limited to a single driving type, thus achieving both high linearity and high frame rate.

[0051] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0052] Reference Figure 2 This invention provides a pixel driving circuit, which may include: a capacitor C, a driving transistor Md, a driving type switching unit 21, a write control unit 22, and a light-emitting control unit 23; wherein:

[0053] The drive type switching unit 21 is connected to the power supply voltage output terminal and the drive transistor Md, and is adapted to acquire the brightness information of the light-emitting diode, and control the drive type of the light-emitting diode D based on the brightness information of the light-emitting diode.

[0054] The write control unit 22 has its input end connected to the image signal output end and the scan signal output end, and its output end connected to the driving transistor Md. It is adapted to write data to the capacitor C based on the image signal Data output by the image signal output end under the control of the scan signal Scan output by the scan signal output end.

[0055] The light-emitting control unit 22 is connected to the power supply voltage output terminal, the driving transistor Md, and the light-emitting control signal output terminal. After the data is written, the light-emitting diode D is controlled to emit light based on the light-emitting control signal EM output by the light-emitting control signal output terminal.

[0056] Specifically, when the driving type of the light-emitting diode D is voltage-driven, the image signal Data output by the image signal output terminal is a voltage signal; when the driving type of the light-emitting diode D is current-driven, the image signal Data output by the image signal output terminal is a current signal.

[0057] The drive type switching unit 21 detects the brightness information of the light-emitting diode (LED) and controls its drive type based on this information. Furthermore, different image signals can be selected as inputs based on the drive type of LED D to drive it to emit light according to the controlled drive type. Therefore, when LED D is at low brightness, its drive type can be controlled to voltage drive, avoiding the long settling time that is detrimental to high frame rate applications when LED D is driven by current. When LED D is at high brightness, its drive type can be controlled to current drive, avoiding the non-linear relationship between the drive voltage and the driving transistor Md that affects the linearity of LED D when it is driven by voltage.

[0058] In practical implementation, before driving the LED to emit light using the pixel driving circuit, the brightness information of the LED D can be obtained in advance. The driving type switching unit 21 can obtain the brightness information of the LED D to determine the current emitting state of the LED D.

[0059] In a specific implementation, the drive type switching unit 21 can compare the brightness value of the light-emitting diode D with a preset brightness threshold. When the brightness value of the light-emitting diode D is less than or equal to the brightness threshold, the brightness value of the light-emitting diode D is considered to be a low brightness value. When the brightness value of the light-emitting diode D is greater than the brightness threshold, the brightness value of the light-emitting diode D is considered to be a high brightness value. The brightness threshold can be set according to actual needs.

[0060] In a specific implementation, the drive type switching unit 21 can control the drive type of the light-emitting diode D to be voltage-driven when the brightness value of the light-emitting diode D is less than or equal to a brightness threshold; and control the drive type of the light-emitting diode D to be current-driven when the brightness value of the light-emitting diode D is greater than or equal to the brightness threshold. Thus, the light-emitting diode D can be driven by voltage when its brightness value is low, and by current when its brightness value is high.

[0061] In specific implementations, the drive type switching unit 21 can have various structures, which are not limited here.

[0062] In one embodiment of the present invention, reference is made to... Figure 3 The drive type switching unit 21 may include: a judgment subunit 211, a first transistor P1 and a second transistor P2 connected to the judgment subunit 211.

[0063] The judgment subunit 211 is adapted to acquire the brightness information of the light-emitting diode D, compare the acquired brightness information with a brightness threshold, and output a first drive type switching signal mod_sel and a second drive type switching signal mod_selb based on the comparison result. The first drive type switching signal mod_sel and the second drive type switching signal mod_selb are inverted logic signals. Specifically, when the first drive type switching signal mod_sel is logic "1", the second drive type switching signal mod_selb is logic "0". When the first drive type switching signal mod_sel is logic "0", the second drive type switching signal mod_selb is logic "1".

[0064] In a specific implementation, the control terminal of the first transistor P1 is connected to the first drive type switching signal mod_sel, the first terminal of the first transistor P1 is connected to the power supply voltage output terminal, and the second terminal of the first transistor P1 is connected to the capacitor C.

[0065] The control terminal of the second transistor P2 is connected to the second drive type switching signal mod_selb. The first terminal of the second transistor P2 is connected to the second terminal of the first transistor P1, and the second terminal of the second transistor P2 is connected to the first terminal of the drive transistor Md.

[0066] In a specific implementation, both the first transistor P1 and the second transistor P2 can be PMOS transistors. The gates of the first transistor P1 and the second transistor P2 are connected to corresponding drive type switching signals. The source of the first transistor P1 is connected to the power supply voltage VDD, and its drain is connected to capacitor C. The source of the second transistor P2 is connected to capacitor C, and its drain is connected to the source of the driving transistor Md.

[0067] At this time, when the first drive type switching signal mod_sel is high, the second drive type switching signal mod_selb is low, thus the first transistor P1 is turned off and the second transistor P2 is turned on, and the LED D is driven by current. When the first drive type switching signal mod_sel is low, the second drive type switching signal mod_selb is high, thus the first transistor P1 is turned on and the second transistor P2 is turned off, and the LED D is driven by voltage.

[0068] In some embodiments, the drive type switching unit 21 may not have a judgment subunit 211, but only a first transistor P1 and a second transistor P2. In this case, the brightness of the light-emitting diode D can be manually determined, and the corresponding drive type switching signal can be directly input to the first transistor P1 and the second transistor P2.

[0069] In specific implementations, the write control unit 22 can have various structures, which are not limited here.

[0070] In one embodiment of the present invention, the write control unit 22 may include: a third transistor P3 and a fourth transistor P4. Wherein:

[0071] The control terminals of both the third transistor P3 and the fourth transistor P4 are connected to the scan signal output terminal. The first terminal of the third transistor P3 is connected to the image signal output terminal; the second terminal of the third transistor P3 is connected to the first terminal of the driving transistor Md. The first terminal of the fourth transistor P4 is connected to the control terminal of the driving transistor Md; the second terminal of the fourth transistor P4 is connected to the second terminal of the driving transistor Md.

[0072] In a specific implementation, both the third transistor P3 and the fourth transistor P4 can be PMOS transistors. The gates of both transistors P3 and P4 are connected to the scan signal Scan, and are thus turned on or off under the control of Scan. The source of the third transistor P3 is connected to the image signal Data, and its drain is connected to the source of the driving transistor Md. The source of the fourth transistor P4 is connected to the gate of the driving transistor Md, and its drain is connected to the drain of the driving transistor Md.

[0073] At this time, the fourth transistor P4 is connected across the driving transistor Md. When the scan signal Scan is high, the fourth transistor P4 is turned on, and the driving transistor Md is in a diode-connected state. When the scan signal Scan is low, the fourth transistor P4 is turned off, and the driving transistor Md is in a normal connected state. During the writing phase, the fourth transistor P4 keeps the driving transistor Md in a diode-connected state, allowing the voltage of the image signal Data to be stored on the capacitor, forming a path from the source of the third transistor P3 to the drain of the driving transistor Md.

[0074] In specific implementations, the light-emitting control unit 23 can have various structures to achieve light-emitting control, that is, to control the light-emitting diode D to emit light or not emit light.

[0075] In one embodiment of the present invention, the light-emitting control unit 23 may include a fifth transistor P5. The control terminal of the fifth transistor P5 is connected to the light-emitting control signal output terminal, the first terminal of the fifth transistor P5 is connected to the power supply voltage output terminal, and the second terminal of the fifth transistor P5 is connected to the first terminal of the driving transistor.

[0076] In a specific implementation, the fifth transistor P5 can be a PMOS transistor. In this case, the gate of the fifth transistor P5 is connected to the light-emitting control signal EM, the source is connected to the power supply voltage VDD, and the drain is connected to the source of the driving transistor Md.

[0077] When the fifth transistor P5 is turned on, a circuit is formed between the fifth transistor P5, the driving transistor Md, and the light-emitting diode D. The light-emitting diode D emits light, and the pixel driving circuit is in the light-emitting stage. When the fifth transistor P5 is turned off, the pixel driving circuit is in the non-light-emitting stage.

[0078] In another embodiment of the invention, reference is made to Figure 4 The light-emitting control unit further includes: a sixth transistor P6; the control terminal of the sixth transistor P6 is connected to the light-emitting control signal output terminal, the first terminal of the sixth transistor P6 is connected to the second terminal of the driving transistor, and the second terminal of the sixth transistor P6 is connected to the light-emitting diode.

[0079] In a specific implementation, the sixth transistor P6 can be a PMOS transistor. In this case, the gate of the sixth transistor P6 is connected to the light-emitting control signal EM, the source is connected to the drain of the driving transistor Md, and the drain is connected to the light-emitting diode D. Thus, a switch is formed between the driving transistor Md and the light-emitting diode D, which facilitates further control over whether the light-emitting diode D emits light.

[0080] In the prior art, referring to Figure 1 For voltage-driven circuits, as shown in formula (1), the current flowing through the light-emitting diode D1 is not only related to the driving voltage VDATA, but also to the threshold voltage of the driving transistor Md. Therefore, the deviation of the threshold voltage of the driving transistor Md will cause the difference in the brightness D1 of the light-emitting diode.

[0081] Therefore, in one embodiment of the present invention, referring to Figure 2The pixel driving circuit may further include a calibration control unit 24. The calibration control unit 24 is connected to the calibration control signal output terminal and the driving transistor Md, and is adapted to calibrate the threshold voltage of the driving transistor Md under the control of the calibration control signal cal output from the calibration control signal output terminal.

[0082] The threshold voltage of the driving transistor Md can be calibrated by the calibration control unit 24, thereby avoiding the brightness difference of the light-emitting diode D caused by the threshold voltage deviation of the driving transistor Md and improving the uniformity of the brightness of the light-emitting diode D.

[0083] In practice, the calibration control unit 24 can have various circuit structures, which are not limited here.

[0084] In one embodiment of the present invention, reference is made to... Figure 5 The calibration control unit 24 may include: a seventh transistor P7; the gate of the seventh transistor P7 is connected to the calibration control signal output terminal, the first terminal of the seventh transistor P7 is connected to the second terminal of the driving transistor Md, and the second terminal of the seventh transistor Md is connected to the preset voltage output terminal.

[0085] By connecting the first terminal of the seventh transistor P7 to the second terminal of the driving transistor Md, and then connecting the second terminal of the seventh transistor P7 to the preset voltage output terminal, on the one hand, during the writing phase, the current of the driving transistor Md can be controlled by adjusting the output voltage of the preset voltage output terminal, thus avoiding damage to the driving transistor Md due to excessive current and improving the lifespan of the driving transistor Md; on the other hand, when the seventh transistor P7 is disconnected, the voltage stored on the capacitor can be made closer to the threshold voltage of the driving transistor Md, improving the calibration effect.

[0086] In a specific implementation, the seventh transistor P7 can be a PMOS transistor. In this case, the gate of the seventh transistor P7 is connected to the calibration control signal cal, and its source is connected to the drain of the driving transistor Md, with a preset voltage Vcal applied to the drain. When calibration of the threshold voltage of the driving transistor Md is required, the calibration control signal cal can be controlled to a low level, causing the seventh transistor P7 to conduct. When calibration of the threshold voltage of the driving transistor Md is not required, the calibration control signal cal can be controlled to a high level, causing the seventh transistor P7 to turn off.

[0087] The following is based on Figure 5 Taking an example, the working process of the pixel driving circuit in the embodiment of the present invention will be described in detail:

[0088] First, refer to Figure 5The judgment subunit 211 judges the brightness value of the light-emitting diode D. If the brightness value of the light-emitting diode D is low, the first drive type switching signal mod_sel is low, the second drive type switching signal mod_selb is high, the first transistor P1 is turned on, the second transistor P2 is turned off, the image signal data is a voltage signal with a voltage value of Vdata, and the light-emitting diode D is driven by voltage. If the brightness value of the light-emitting diode D is high, the first drive type switching signal mod_sel is high, the second drive type switching signal mod_selb is low, the first transistor P1 is turned off, the second transistor P2 is turned on, the image signal data is a current signal with a current value of Idata, and the light-emitting diode D is driven by current.

[0089] When a light-emitting diode (LED) D is driven by voltage, the operation of the pixel driving circuit can be roughly divided into three stages: calibration stage, writing stage, and light emission stage. Figure 6 This is a possible timing diagram of the signals in the pixel driving circuit. Tem(n-1) represents the (n-1)th emission process of LED D. Tem(n) represents the nth emission process of LED D. After the (n-1)th emission of LED D, the pixel driving circuit sequentially goes through the write phase and the calibration phase before driving LED D to emit light for the nth time. Twrite represents the duration of the write phase, and Tcal represents the duration of the calibration phase.

[0090] The following combination Figure 5 and Figure 6 The operation of the pixel driving circuit when the light-emitting diode D is driven by voltage is described in detail below:

[0091] 1) Writing stage

[0092] During this stage, the scan signal Scan and the calibration control signal cal are both low, while the light emission control signal EM is high. At this time, the third transistor P3, the fourth transistor P4, the first transistor P1, and the seventh transistor P7 are all closed, while the fifth transistor P5, the second transistor P2, and the sixth transistor P6 are open. The driving transistor Md is in a diode-connected state, and the voltage Vdata of the image signal is written to the capacitor C through the third transistor P3, thereby driving the light emission diode D.

[0093] 2) Calibration phase

[0094] During this stage, the scan signal Scan remains low, the light emission control signal EM is high, the calibration control signal cal changes from low to high, the seventh transistor P7 is turned off, and the current path from the image signal to the preset voltage output terminal is broken. At this time, the voltage Vgs between the gate and source of the driving transistor Md is approximately the threshold voltage Vth. When the fourth transistor P4 is turned off, the voltage at point a is VDD, the voltage at point b is (Vdata-Vth), and the threshold voltage Vth is stored on capacitor C.

[0095] 3) Luminescence stage

[0096] During this stage, the scan signal Scan changes from low to high, the light emission control signal EM changes from high to low, and the calibration control signal cal remains high. The third transistor P3, the fourth transistor P4, and the seventh transistor P7 are all off, while the fifth transistor P5 and the sixth transistor P6 are all closed. At this time, the voltage at point a is VDD, the charge stored in capacitor C remains unchanged, and Vb = Vdata - Vth. The current Id flowing through the driving transistor Md at this time can be expressed as:

[0097] Id = K*(VDD - Vb - Vth) 2 =K*(VDD-Vdata) 2 (2)

[0098] in, μ represents the mobility of the driving transistor Md, Cox represents the gate oxide capacitance per unit area of ​​the driving transistor Md, W is the gate width of the driving transistor Md, and L is the gate length of the driving transistor Md.

[0099] Since the light emission control signal EM is at a low level at this time, the light emission diode D starts to emit light after the current flows through it.

[0100] As can be seen from formula (2), the current Id flowing through the light-emitting diode D is independent of the threshold voltage Vth of the driving transistor Md. The shift in the threshold voltage will not cause a difference in the brightness of the light-emitting diode, thereby improving the uniformity of the brightness of the light-emitting diode D.

[0101] When a light-emitting diode (LED) D is driven by current, the operation of the pixel driving circuit can be roughly divided into two stages: the writing stage and the light-emitting stage. Figure 7 This is one possible timing diagram for the signals of the pixel driving circuit. Tem(n-1) represents the (n-1)th emission process of LED D. Tem(n) represents the nth emission process of LED D. After the (n-1)th emission of LED D, the pixel driving circuit goes through the writing phase, and then drives LED D to enter the nth emission phase. Twrite represents the duration of the writing phase.

[0102] The following combination Figure 5 and Figure 7 The operation of the pixel driving circuit when the light-emitting diode D is driven by current is described in detail below:

[0103] 1) Writing stage

[0104] During this stage, the scan signal Scan and the calibration control signal cal are both low, while the emission control signal EM is high. At this time, transistors P3, P4, and P7 are all closed, while transistors P5 and P6 are open. The driving transistor Md is in a diode-connected state. The image signal current Idata flows through transistor P3, then through driving transistor Md and P7 to the preset voltage output terminal. The current flowing through driving transistor Md at this time is Id = K*(Vgs - Vth). 2 =Idata.

[0105] 2) Luminescence stage

[0106] During this stage, the scan signal Scan changes from low to high, the third transistor P3 and the fourth transistor P4 are both turned off, and capacitor C stores the Vgs of the driving transistor Md. The light emission control signal EM changes from high to low, the calibration control signal cal changes from low to high, the seventh transistor P7 is turned off, and the fifth transistor P5 and the sixth transistor P6 are both turned on. At this time, the voltage at point a is VDD, and the Vgs of the driving transistor Md remains unchanged. Since the light emission control signal EM is low at this time, current flows through the light-emitting diode D, and it begins to emit light. The emitting current is Idata.

[0107] As can be seen from the above, the pixel driving circuit in the embodiments of the present invention combines the advantages of both voltage-driven and current-driven pixel driving circuits.

[0108] Furthermore, in this embodiment of the invention, the pixel driving circuit can compensate for the threshold voltage offset of the driving transistor by setting a calibration control unit, thereby effectively improving the uniformity of the light emission intensity of the light-emitting diode.

[0109] The present invention also provides a pixel circuit, which includes any of the above-described pixel driving circuits and a light-emitting diode connected to the pixel driving circuit.

[0110] This invention also provides a display device, which includes a pixel array formed by an array distribution of a plurality of the aforementioned pixel circuits.

[0111] To enable those skilled in the art to better understand and implement the present invention, the pixel driving method corresponding to the above-described pixel driving circuit is described in detail below.

[0112] The pixel driving method may include:

[0113] Step 81: Detect the brightness information of the light-emitting diode, and control the driving type of the light-emitting diode based on the brightness information of the light-emitting diode.

[0114] In a specific implementation, when the brightness value of the LED is less than or equal to a brightness threshold, the LED is controlled to be driven by voltage. When the brightness value of the LED is greater than or equal to the brightness threshold, the LED is controlled to be driven by current. Thus, the LED can be driven by voltage when its brightness value is low, and driven by current when its brightness value is high.

[0115] Step 82: Based on the driving type of the light-emitting diode, acquire the corresponding image signal and write the data.

[0116] In specific implementation, when the LED is driven by voltage, the image signal output from the image signal output terminal is a voltage signal; when the LED is driven by current, the image signal output from the image signal output terminal is a current signal. Subsequent data writing is performed based on the acquired image signal; the specific writing process can be referred to the above regarding... Figure 6 and Figure 7 The implementation will be carried out as described above, and will not be repeated here.

[0117] Step 83: After the data is written, drive the light-emitting diode to emit light based on the acquired image signal.

[0118] It should be noted that when the LED is driven by voltage, after the data is written, the threshold voltage of the driving transistor can be calibrated first before driving the LED to emit light, or the threshold voltage of the driving transistor can be left uncalibrated and the LED can be driven to emit light directly.

[0119] When the LED is driven by current, after the data is written, the LED can be directly driven to emit light by the current of the image signal.

[0120] The pixel driving method described above can be implemented by referring to the above description of the pixel driving circuit, and will not be repeated here.

[0121] The pixel driving method in this embodiment of the invention can drive the light-emitting diode with an appropriate driving type based on the brightness information of the light-emitting diode, thereby achieving both high linearity and high frame rate.

[0122] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A pixel driving circuit, characterized in that, include: Capacitors, driver transistors, driver type switching unit, write control unit, and light-emitting control unit; among which: The drive type switching unit is connected to the power supply voltage output terminal and the drive transistor, and is adapted to acquire the brightness information of the light-emitting diode, and control the drive type of the light-emitting diode based on the brightness information of the light-emitting diode; The writing control unit has an input terminal connected to the image signal output terminal and the scan signal output terminal, and an output terminal connected to the driving transistor. It is adapted to write data to the capacitor based on the image signal output by the image signal output terminal under the control of the scan signal output by the scan signal output by the scan signal output terminal. The light-emitting control unit is connected to the power supply voltage output terminal, the driving transistor, and the light-emitting control signal output terminal. After data is written, it controls the light-emitting diode to emit light based on the light-emitting control signal output by the light-emitting control signal output terminal. Specifically, when the driving type of the light-emitting diode is voltage-driven, the image signal output by the image signal output terminal is a voltage signal; when the driving type of the light-emitting diode is current-driven, the image signal output by the image signal output terminal is a current signal. The drive type switching unit is adapted to control the drive type of the light-emitting diode to voltage drive when the brightness value of the light-emitting diode is less than the brightness threshold; and to control the drive type of the light-emitting diode to current drive when the brightness value of the light-emitting diode is greater than or equal to the brightness threshold. The drive type switching unit includes: a judgment subunit, and a first transistor and a second transistor connected to the judgment subunit; wherein: The judgment subunit is adapted to acquire the brightness information of the light-emitting diode, compare the acquired brightness information with the brightness threshold, and output a first driving type switching signal and a second driving type switching signal based on the comparison result. The first driving type switching signal and the second driving type switching signal are logic inverse signals. The control terminal of the first transistor is connected to the first drive type switching signal, the first terminal of the first transistor is connected to the power supply voltage output terminal, and the second terminal of the first transistor is connected to the capacitor. The control terminal of the second transistor is connected to the second drive type switching unit, the first terminal of the second transistor is connected to the second terminal of the first transistor, and the second terminal of the second transistor is connected to the first terminal of the drive transistor. The write control unit includes: a third transistor and a fourth transistor; wherein: The control terminals of the third transistor and the fourth transistor are both connected to the scan signal output terminal; The first terminal of the third transistor is connected to the image signal output terminal; the second terminal of the third transistor is connected to the first terminal of the driving transistor. The first terminal of the fourth transistor is connected to the first terminal of the driving transistor; the second terminal of the fourth transistor is connected to the second terminal of the driving transistor.

2. The pixel driving circuit as described in claim 1, characterized in that, The light-emitting control unit includes: a fifth transistor; the control terminal of the fifth transistor is connected to the light-emitting control signal output terminal, the first terminal of the fifth transistor is connected to the power supply voltage output terminal, and the second terminal of the fifth transistor is connected to the first terminal of the driving transistor.

3. The pixel driving circuit as described in claim 2, characterized in that, The light-emitting control unit further includes: a sixth transistor; the control terminal of the sixth transistor is connected to the light-emitting control signal output terminal, the first terminal of the sixth transistor is connected to the second terminal of the driving transistor, and the second terminal of the sixth transistor is connected to the light-emitting diode.

4. The pixel driving circuit as described in claim 1, characterized in that, Also includes: The calibration control unit is connected to the calibration control signal output terminal and the drive transistor, and is adapted to calibrate the threshold voltage of the drive transistor under the control of the calibration control signal output from the calibration control signal output terminal.

5. The pixel driving circuit as described in claim 4, characterized in that, The calibration control unit further includes: a seventh transistor; the gate of the seventh transistor is connected to the calibration control signal output terminal, the first terminal of the seventh transistor is connected to the second terminal of the driving transistor, and the second terminal of the seventh transistor is connected to the preset voltage output terminal.

6. A pixel driving method for the pixel driving circuit according to any one of claims 1 to 5, characterized in that, include: The brightness information of the light-emitting diode is detected, and the driving type of the light-emitting diode is controlled based on the brightness information of the light-emitting diode; Based on the driving type of the light-emitting diode, the corresponding image signal is acquired and data is written. After the data is written, the LED is driven to emit light based on the acquired image signal.

7. A pixel circuit, characterized in that, It includes the pixel driving circuit as described in any one of claims 1 to 5 and the light-emitting diode connected to the pixel driving circuit.

8. A display device comprising a pixel array, characterized in that, The pixel array is formed by an array distribution of the pixel circuits described in claim 7.

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