A Micro-LED display grayscale control method and display device

Abstract

A Micro-LED display grayscale control method and display device, relating to the field of Micro-LED display technology. Aiming at the problem that the existing Micro-LED display technology cannot achieve instant light emission, the present invention proposes a Micro-LED display grayscale control method, wherein the control method is a grayscale hybrid control method combining PAM and PWM proposed based on the display characteristics of Micro-LED. Among them, PAM modulation uses centralized light emission to achieve Micro-LED grayscale control, and PWM modulation uses a sub-field segmentation modulation strategy to achieve an increase in the refresh rate of Micro-LED. The present invention is suitable for display grayscale control of Micro-LED.

Description

Technical Field

[0001] The present invention belongs to the field of Micro-LED display technology, and specifically relates to a Micro-LED display grayscale control method. Background Art

[0002] As a new generation of display technology, Micro-LED (Light Emitting Diode, LED) display combines the advantages of self-luminescence, high contrast, high brightness and high color saturation, high response speed and long life. Compared with Liquid Crystal Display (LCD), Micro-LED has the advantages of fast response speed, high conversion efficiency and high color saturation. Compared with Active Matrix / Organic Light Emitting Diode (AMOLED), AMOLED has low brightness and long-term high brightness use will cause screen burn-in, while Micro-LED display can achieve high brightness display without aging problems. Compared with Mini-LED technology, Micro-LED can achieve higher density and thinner display. Based on the above factors, Micro-LED is regarded as a highly promising next-generation display technology. TFT driving technology based on glass backplane has the advantages of high thermal conductivity, low thermal expansion coefficient, low temperature resistance, impact resistance, high electrical connection density, high flatness, etc., which can meet complex wiring and low cost. This technology is the development trend of realizing Micro-LED display.

[0003] There are currently two control methods for Micro-LED grayscale control in the industry. One is the traditional AMOLED device driving method. Currently, the analog voltage control driving strategy is generally used. The data voltage is written into the gate node of the driving TFT and stored in the storage capacitor to generate driving currents of different amplitudes, thereby achieving control of different grayscale levels. However, Micro-LED display technology is different from the traditional AMOLED driving method. Micro-LED is a current-type driving device with an extremely fast current startup speed. In the process of changing from the lowest brightness to the highest brightness, the required voltage change is very small, about 0.3V, which is significantly different from AMOLED with a data voltage change range of several volts. It is not realistic to use the traditional analog voltage driving architecture to achieve Micro-LED grayscale control. The second is to use the traditional passive driving method, which uses the time slice modulation principle to further subdivide the single subfield time. It cuts the modulation cycle into multiple time segments and adjusts each segment separately to enhance the grayscale level and visual refresh rate of the picture. The TFT-based driving technology requires the subframe data voltage to be stored in the capacitor, and the light is uniformly emitted after all line scans are completed, which cannot achieve timely light emission.

[0004] In summary, a new grayscale control model needs to be developed to achieve high grayscale display based on the display characteristics of Micro-LED. Summary of the invention

[0005] In view of the problem that Micro-LED display technology cannot achieve instant luminescence, the present invention proposes a centralized luminescence driving strategy, namely a Micro-LED display grayscale control method.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides a Micro-LED display grayscale control method, the method comprising:

[0008] The grayscale of Micro-LED is controlled by combining PAM and PWM;

[0009] PAM modulation uses a concentrated light emission method to control the grayscale of Micro-LEDs;

[0010] PWM modulation uses a sub-field segmentation modulation method to control the refresh rate of Micro-LED.

[0011] Furthermore, there is a preferred embodiment, 0~ Gray scale adopts PWM modulation. ~ Gray scale adopts PAM and PWM mixed modulation.

[0012] Furthermore, there is a preferred embodiment: Brightness It is expressed as:

[0013] ;

[0014] ;

[0015] in, is the maximum brightness value of the screen, n is the grayscale level of the display, is the display gamma index, is the proportionality coefficient, is the current flowing through the LED.

[0016] Furthermore, there is a preferred embodiment, the above-mentioned concentrated light emitting method is specifically as follows:

[0017] Each row of the display screen is scanned in sequence. After any row is scanned, it is not immediately stimulated to emit light. The grayscale data voltage corresponding to each row is stored in the storage capacitor in the pixel circuit until all rows of the entire display screen are scanned and uniformly stimulated for display.

[0018] Furthermore, there is a preferred embodiment in which the modulation method for sub-field division is specifically as follows:

[0019] Divide one frame display time into A modulation process;

[0020] PWM and PAM mixed modulation is adopted in each sub-modulation process.

[0021] Furthermore, in a preferred embodiment, the overall grayscale level achieved by the grayscale control method is:

[0022] ;

[0023] ;

[0024] ;

[0025] in, Grayscale level achieved for PAM modulation, Grayscale level achieved by PWM modulation, is one frame time, is the LED response time, and m is the number of different voltage analog values ​​that the data voltage can take within one frame time.

[0026] Furthermore, there is a preferred embodiment in which the modulation data in each sub-modulation process is:

[0027]

[0028] in, As the benchmark data, For superimposed data.

[0029] Furthermore, there is a preferred embodiment: Sub-modulation steps, the total cumulative light emission time of Micro-LED is:

[0030] ;

[0031] in, The pulse width corresponding to the lowest bit.

[0032] Furthermore, there is a preferred embodiment in which the grayscale level is The refresh rate is:

[0033] .

[0034] The present invention also provides a display device implemented based on a Micro-LED display grayscale control method described in any one of the above.

[0035] The beneficial effects of the present invention are:

[0036] 1. Aiming at the problem that existing Micro-LED display technology cannot realize instant luminescence, the present invention proposes a method for controlling grayscale of Micro-LED display, which is a grayscale hybrid control method combining PAM and PWM proposed based on the display characteristics of Micro-LED. Among them, PAM modulation uses concentrated luminescence to realize grayscale control of Micro-LED, and PWM modulation uses a modulation strategy of sub-field division to realize the improvement of Micro-LED refresh rate.

[0037] Furthermore, the present invention is carried out in 0~ Grayscale uses PWM modulation, which divides a frame time into multiple subfields, and controls the grayscale by switching the subfields, thereby achieving low grayscale development, solving the problem that PAM cannot accurately develop grayscale in low grayscale conditions and the color cast caused by chip wavelength drift. ~ The grayscale adopts PAM and PWM mixed modulation to achieve high grayscale display and improve the luminous efficiency of Micro-LED.

[0038] The present invention is applicable to the display grayscale control of Micro-LED. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0040] Figure 1 It is the concentrated light emission timing diagram of the present invention;

[0041] Figure 2 Schematic diagram of the Micro-LED display of the present invention using a PWM+PAM hybrid driving method;

[0042] Figure 3 This is the sub-field modulation strategy diagram described in the present invention. DETAILED DESCRIPTION

[0043] In the following description, specific details such as specific system structures and technologies are provided for the purpose of illustration rather than limitation, so as to provide a thorough understanding of the embodiments of the present application. However, it should be clear to those skilled in the art that the present application may also be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to prevent unnecessary details from obstructing the description of the present application.

[0044] The specific embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings. The following embodiments will help those skilled in the art to further understand the present invention, but are not intended to limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can be made without departing from the concept of the present invention.

[0045] Embodiment 1: This embodiment aims to solve the problem that the existing Micro-LED display technology cannot realize instant light emission, and proposes a Micro-LED display grayscale control method, the control method comprising the following steps:

[0046] The grayscale of Micro-LED is controlled by combining PAM and PWM;

[0047] PAM modulation uses a concentrated light emission method to control the grayscale of Micro-LEDs;

[0048] PWM modulation uses a sub-field segmentation modulation method to control the refresh rate of Micro-LED.

[0049] This embodiment proposes a grayscale hybrid control method combining PAM and PWM based on the display characteristics of Micro-LED. Among them, PAM modulation uses concentrated light emission to achieve grayscale control of Micro-LED. PWM modulation uses a sub-field segmentation modulation strategy to improve the refresh rate of Micro-LED.

[0050] Implementation Method 2: See Figure 2 This embodiment is described. This embodiment is a specific description of the grayscale control of Micro-LEDs by combining PAM and PWM as described in the first embodiment above.

[0051] like Figure 2 As shown, 0~ Gray scale adopts PWM modulation. ~ Gray scale adopts PAM and PWM mixed modulation.

[0052] This implementation method is based on the characteristics of TFT Micro-LED display technology and proposes a hybrid modulation strategy combining PWM (Pulse Width Modulation, PWM) and PAM (Pulse Amplitude Modulation, PAM). According to the photoelectric characteristics of LED, it can be obtained that the luminous intensity of LED and the magnitude of the current passing through it are nearly linearly related:

[0053] ; (1)

[0054] In formula (1), when the LED is on, within a certain current range, the luminous intensity is The current through the LED The magnitudes follow a linear relationship, with a proportionality constant of Therefore, the LED current can be finely adjusted Intensity can achieve precise control of its grayscale display, thereby achieving an ideal brightness adjustment effect. The current flowing through the LED is determined by the following formula:

[0055] ; (2)

[0056] in, is the carrier mobility, is the insulation layer capacitance, is the TFT gate-source voltage, is the TFT threshold voltage, is the aspect ratio of TFT.

[0057] When other parameters remain unchanged, the linear change of current can be achieved by changing the data voltage value, so gray scale modulation can be achieved by adjusting the data voltage value.

[0058] For PAM modulation, the data voltage within one frame The value is not a high or low level, but analog values ​​of different voltages, then you can adjust The grayscale levels that can be achieved by grayscale modulation using an analog voltage are:

[0059] ; (3)

[0060] For PWM modulation, assume that the pulse width corresponding to the lowest bit is , one frame time is Without considering other factors, the achievable grayscale level is:

[0061] ; (4)

[0062] in, is the LED response time.

[0063] Then the overall grayscale level that the system can achieve is:

[0064] ; (5)

[0065] In the PWM and PAM hybrid modulation architecture, PWM modulation is used to achieve low gray fine development in low grayscale conditions, while PAM and PWM hybrid modulation is used to achieve high grayscale modulation in high grayscale conditions. The modulation structure diagram is shown in the figure. Figure 2 As shown in the figure, ~ Gray scale adopts PWM modulation, and ~ Gray scale adopts PAM and PWM mixed modulation.

[0066] From the photoelectric transfer function, we can get Brightness It is expressed as:

[0067] ; (6)

[0068] in, is the maximum brightness value of the screen, n is the grayscale level of the display, Represents the display gamma index.

[0069] set up Point Micro-LED corresponding brightness The current value is , then:

[0070] ; (7)

[0071] in is the proportionality coefficient, The current flowing through the LED is calculated based on the maximum brightness of the project and the LED chip current. .

[0072] The grayscale control method proposed in this embodiment is in the range of 0~ Grayscale uses PWM modulation, which divides a frame time into multiple subfields, and controls the grayscale by switching the subfields, thereby achieving low grayscale development, solving the problem that PAM cannot accurately develop grayscale in low grayscale conditions and the color cast caused by chip wavelength drift. ~ The grayscale adopts PAM and PWM mixed modulation to achieve high grayscale display and improve the luminous efficiency of Micro-LED.

[0073] Implementation method 3: This implementation method specifically describes the grayscale control of Micro-LED using the centralized light emission method described in the above implementation method 1.

[0074] Each row of the display screen is scanned in sequence. After any row is scanned, it is not immediately stimulated to emit light. The grayscale data voltage corresponding to each row is stored in the storage capacitor in the pixel circuit until all rows of the entire display screen are scanned and uniformly stimulated for display.

[0075] like Figure 1 As shown, the centralized light-emitting strategy proposed in this embodiment is different from the existing instant light-emitting drive. After a row of scanning is completed, this strategy does not immediately stimulate light emission, but stores the corresponding grayscale data voltage in the storage capacitor in the pixel circuit until all rows of the entire display screen are scanned, and then uniformly stimulates display.

[0076] The steps for concentrated luminescence are as follows: Site selection stage for progressive scanning; For the light-emitting stage. It is a row scanning signal, which is used to control the on / off state of the switch tube TFT in the pixel circuit and ensure the input of grayscale data voltage. For n-type TFT, When the switch is high, it turns on; for p-type TFT, When the signal is at a low level, the switch tube TFT enters the on state. This embodiment is described by taking the p-type TFT as an example. After the switch tube TFT is turned on, the data voltage is immediately input to the gate of the driving TFT and stored in the storage capacitor. For input data, is the power supply voltage, and its specific operation process is as follows:

[0077] (1) In the scanning and site selection stage, the switch TFTs of each row are activated in sequence, and the duration of each row opening is 3μs. At this time, the data voltage is transmitted to the gate of the driving tube in each pixel circuit. Phase control signal The signal is at a high level, causing the driver tube to remain in the off state, and all pixels do not emit light during this period.

[0078] (2) Entering the light-emitting stage, during a specific period of time All row scan signals are low level. The pixel receiving the high-level data voltage does not emit light at this time; on the contrary, the pixel receiving the low-level data voltage starts to emit light, and the duration of this light-emitting process is the set period. .

[0079] exist Stage and The same as the first stage, each row of switch TFT is activated in sequence, and each row is turned on for 3μs. At this time, the data voltage is transmitted to the gate of the driving tube in each pixel circuit. Phase control signal The signal is at a high level. Since the high level is maintained, the driving tube remains in the off state, and all pixels do not emit light during this period. In this stage, all row scan signals are at low level. At the same time, the control signal The signal also turns to a low potential. The pixels receiving the high-level data voltage do not emit light at this time; on the contrary, the pixels receiving the low-level data voltage begin to emit light, and the duration of this light-emitting process is the set period. The rest Stage and , same, Voltage status and , The same, the luminous duration is In practical applications, the order in which each pixel is lit during the lighting phase can be flexibly adjusted, but it is necessary to ensure that the ratio of the lighting duration of each pixel remains unchanged in the predetermined relationship: .

[0080] Implementation method 4: See Figure 3 This embodiment is described. This embodiment specifically describes the control of the refresh rate of Micro-LED by the modulation method using sub-field division described in the first embodiment above.

[0081] Divide one frame display time into A modulation process;

[0082] PWM and PAM mixed modulation is adopted in each sub-modulation process.

[0083] In order to achieve a higher refresh rate and better viewing effect, this embodiment divides a frame display time into A modulation process such as Figure 3 As shown. In each sub-modulation process, PWM modulation and PAM modulation cooperate with each other to achieve Grayscale level is used as an example. Then a grayscale modulation process is divided into Sub-modulation process, while grayscale data Divided into and The two parts can be called baseline data and overlay data, respectively. and During the modulation process, the reference data is assigned to During the sub-modulation process, the incremental data will be superimposed on In the reference data of the sub-modulation process, the grayscale data of each sub-modulation process is used The relationship among the reference data, superimposed data and modulated data is:

[0084] ; (8)

[0085] exist In the process of processing the modulated signals, these signals are not only superimposed in order on the time axis, but also integrated with each other in the spatial dimension. This model makes full use of the complementary advantages of time and space, and provides a new solution for improving the display effect of Micro-LED.

[0086] According to the theoretical description of the hybrid modulation model, it can be deduced that During each sub-modulation step, the total cumulative light emission time of the LED is:

[0087] ; (9)

[0088] in, It is the pulse width corresponding to the lowest bit.

[0089] Then the refresh rate of the LED display can be obtained as:

[0090] ; (10)

[0091] Among them, grayscale data The binary representation of ,but , , The sizes are:

[0092] ; (11)

[0093] Substituting formula (11) into (9) we can obtain

[0094] ; (12)

[0095] Then for the grayscale level For example, in a complete modulation process, the LED is excited for:

[0096] ; (13)

[0097] From formula (13), we can see that The total time that the LED emits light in each sub-modulation stage is equivalent to the total amount of time that the Micro-LED emits light in a complete grayscale modulation cycle.

[0098] Since Micro-LED display uses TFT technology to drive the display, each sub-modulation process scans all rows during the modulation process, and then emits light for display after the scanning is completed. The grayscale data will only be refreshed once, so the visual refresh rate at this time is not equal to the overall display refresh rate. The visual refresh rate at this time is The refresh rate of the sub-modulation cycle, then we have:

[0099] ; (14)

[0100] From the above formula, we can know that the total sub-modulation time is consistent with the Micro-LED luminescence time of a complete grayscale modulation process. Then we have:

[0101] ; (15)

[0102] Then we have:

[0103] ; (16)

[0104] It can be seen from formula (16) that with the hybrid modulation strategy, the visual refresh rate of the Micro-LED display is not equal to the refresh rate of the display, and the visual refresh rate is increased to the original times.

[0105] Implementation 5: This implementation is to verify and illustrate a method for controlling grayscale of a Micro-LED display as described in any of the above implementations.

[0106] Assuming that the grayscale level required for the Micro-LED system to achieve uniform grayscale display is 12-bit, it can be seen from the above formula (5) that the grayscale level that can be achieved by the hybrid driving model proposed in this embodiment is obtained by superposition of analog voltage PAM and PWM modulation, respectively. -bit and -bit indicates that the superposition scheme is as shown in Table 1. Among the various schemes in the table, it is necessary to select a suitable superposition scheme according to the display characteristics of Micro-LED.

[0107] Table 1

[0108]

[0109] Taking the display screen with a resolution of 1920×1080 as an example, the TFT-based Micro-LED display technology needs to consider the response time of TFT to ensure that the entire pixel circuit can work normally. This time is generally 3μs, so the minimum light-emitting time μs, the scanning time is μs, the total luminous time is:

[0110] (17)

[0111] (18)

[0112] and The value of is limited by the number of subfields The value range of is shown in Table 2.

[0113] Table 2

[0114]

[0115] From Table 2, we can see that The only possible values ​​of are 2 and 4. These two cases are discussed below.

[0116] (1) When When, the luminous time μs, from the above formula (4) and formula (5), we can get the grayscale level achieved by PWM modulation at this time: , then at this time , the refresh rate is 120Hz. From the above formula (3), we can get the analog voltage required at this time Different analog voltage values ​​are used to achieve 2-bit grayscale modulation. At this time, the refresh rate is increased by 2 times to 120Hz.

[0117] (2) When When, the light time μs, from the above formula (4) and formula (5), we can get the grayscale level achieved by PWM modulation at this time: , then at this time , the refresh rate is 240Hz. From formula (3), we can get the analog voltage required at this time Different analog voltage values ​​are used to realize 2-bit grayscale modulation. It can be seen that 8-bit PWM modulation data is superimposed on 4-bit PAM data to realize 12-bit grayscale level. At this time, the refresh rate is increased by times to 240Hz.

[0118] The above description is only an embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may be modified and varied in various ways.

Claims

1. A method for controlling grayscale of a Micro-LED display, characterized in that: The method is: The grayscale of Micro-LED is controlled by combining PAM and PWM; PAM modulation uses a concentrated light emission method to control the grayscale of Micro-LEDs; PWM modulation uses a sub-field segmentation modulation method to control the refresh rate of Micro-LED; The modulation method of sub-field division is specifically as follows: Divide one frame display time into A modulation process; PWM and PAM mixed modulation is used in each sub-modulation process; The modulation data in each sub-modulation process is: ； in, As the benchmark data, For superimposed data; Sub-modulation steps, the total cumulative light emission time of Micro-LED is: ； in, The pulse width corresponding to the lowest bit.

2. A Micro-LED display grayscale control method according to claim 1, characterized in that: 0~ Gray scale adopts PWM modulation. ~ Gray scale adopts PAM and PWM mixed modulation.

3. A Micro-LED display grayscale control method according to claim 2, characterized in that: Brightness It is expressed as: ； ； in, is the maximum brightness value of the screen, n is the grayscale level of the display, is the display gamma index, is the proportionality coefficient, is the current flowing through the LED.

4. The method for controlling grayscale display of Micro-LED according to claim 1, characterized in that: The concentrated luminescence method is as follows: Each row of the display screen is scanned in sequence. After any row is scanned, it is not immediately stimulated to emit light. The grayscale data voltage corresponding to each row is stored in the storage capacitor in the pixel circuit until all rows of the entire display screen are scanned and uniformly stimulated for display.

5. The method for controlling grayscale display of Micro-LED according to claim 1, characterized in that: The overall grayscale level achieved by the grayscale control method is: ； ； ； in, Grayscale levels achieved for PAM modulation, Grayscale level achieved by PWM modulation, is one frame time, is the LED response time, and m is the number of different voltage analog values ​​that the data voltage can take within one frame time.

6. A Micro-LED display grayscale control method according to claim 1, characterized in that: Gray scale level is The refresh rate is: 。 7. A display device, characterized in that The invention is implemented based on a Micro-LED display grayscale control method according to any one of claims 1 to 6.

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