CN117612478A

CN117612478A - White balance compensation method and system for LED display screen

Info

Publication number: CN117612478A
Application number: CN202311524859.8A
Authority: CN
Inventors: 欧朋; 杨刚; 陶斯禄; 杜晓扬
Original assignee: Yangtze River Delta Research Institute of UESTC Huzhou
Current assignee: Yangtze River Delta Research Institute of UESTC Huzhou
Priority date: 2023-11-15
Filing date: 2023-11-15
Publication date: 2024-02-27

Abstract

The invention belongs to the technical field of injection type electroluminescent display, and discloses a white balance compensation method and a white balance compensation system for an LED display screen, wherein an FPGA chip is used for driving the LED full-color display screen; the crystal oscillator is divided into 3 synchronous clocks through the FPGA, and red, green and blue LED display driving subsystems are respectively controlled; starting a timer in the driving system, informing the FPGA when the equipment is powered down, writing the current count into the EEPROM by the FPGA, and continuously accumulating the count register on the basis of the EEPROM when the next power-on initialization is performed; before the FPGA leaves the factory, the adjustable resistance value of the primary column gating base electrode is adjusted through the I2C bus for the first time, so that column driving current is adjusted, and the LED display screen achieves white balance; every other column gating base adjustable resistor adjustment period, the FPGA adjusts the column gating base adjustable resistor resistance value once through the I2C bus so as to adjust column driving current, and the LED display screen reaches white balance again. The invention adopts the method of periodically adjusting the resistance value of the column gating base adjustable resistor by the FPGA to enable the LED display screen to automatically achieve white balance.

Description

White balance compensation method and system for LED display screen

Technical Field

The invention belongs to the technical field of injection type electroluminescent display, and particularly relates to a white balance compensation method and system for an LED display screen.

Background

Some substances can generate a luminescence phenomenon under the drive of a certain voltage, and the luminescence phenomenon that the electric energy is directly converted into visible light is 'electroluminescence (Electro Luminescence, EL'). In a broad sense, the EL includes not only light emitting diodes (Light Emitting Diode, LEDs), organic light emitting diodes (OrganicLight Emitting Diode, OLED), electroluminescent displays (Electro Luminescence Display, ELD), but also semiconductor lasers. Wherein the LED belongs to an injection type electroluminescent display device, and the main difference between the LED and the injection type electroluminescent display device is that the LED uses inorganic materials and the OLED uses organic materials.

Along with the development of science and technology and the progress of society, the LED large-screen display is taken as an important branch of novel display, the development is more and more rapid, and the application field is also expanding continuously. The LED full-color display screen has the advantages of large size, high brightness, seamless splicing and the like, and is widely applied to the aspects of service industry, financial industry, traffic and the like. The color of each pixel of the LED full-color display screen is formed by combining LEDs with three colors of red, green and blue according to the gray level of a specified proportion. Therefore, the main characteristic of the white balance of the LED display screen has correlation with the brightness and chromaticity of the red, green and blue LEDs, and the matching proportion parameters of all primary colors are stabilized, so that the white balance of the display can be ensured to be correctly reproduced, and the tone of a display image can be correctly restored. Although there are many advantages of the LED display products, the light emission of the LED is easily affected by various internal and external factors, such as temperature characteristics, attenuation characteristics, and power supply of the driving circuit of the LED, which may change the brightness of each primary color with time, resulting in deviation of brightness of white balance.

The luminous flux of the LED gradually declines with the accumulation of the lighting time, and the current research standard usually indicates the lifetime end corresponding to the LED light source when the luminous flux decays to 70% (or 50%) of the initial value of the factory.

In terms of light attenuation causes, georgy Bobashoev team experiments find that the luminous flux of the LED does not obey exponential decay within the first 1000 hours under the condition of low stress. Researchers such as Rossi and the like show that the main reason for the degradation of the LED is that non-radiative recombination is generated due to the movement defect of carriers, but the influence of parameters such as analysis current, temperature and the like on the light attenuation is not generated. The study of Narendoran indicates that the junction temperature of the chip of the LED has a great influence on the service life of the chip, the higher the junction temperature is, the faster the light attenuation rate of the LED is, but the study does not form a complete mathematical model of the light attenuation rate and the junction temperature, and a certain convincing effect is lacked in the aspect of theory.

In the aspect of light attenuation compensation, guo Jin et al obtain a light attenuation characteristic curve according to a data manual of an LED, design a light attenuation compensation LED driving controller, and the LED controller combines the light attenuation curve, so that the current value maintains the constant output luminous flux of a light source to a certain extent according to preset output, and the light attenuation compensation is realized. However, the light attenuation of the LED is affected by various factors, the junction temperature of the LED is only considered in the light attenuation characteristic curve, the purpose of light attenuation compensation can be achieved in a short time, and the stability of long-term output of the light source is not ideal. In addition, wang Qi and Zhang Bo analyze the light attenuation cause of the LED, and on the basis of researching the light attenuation cause, an LED driving circuit based on the SEPIC is designed, and the circuit can provide proper working voltage and driving current according to the light attenuation phenomenon caused by the change of the working temperature of the lamp, so that the light attenuation self-adaptive compensation effect is achieved. However, the topology circuit design is complex, the number of selected devices is large, and the cost of LED driving design is increased.

Aiming at the problem of light color consistency commonly existing in an LED display screen, chen Yotao analyzes the reasons for causing the problem of light color consistency in aspects of LED characteristics, the principle of full-color display, the characteristics of a constant current driving mode and the like. And further, the feasibility of realizing point-by-point correction by modifying the pixel color gamut space by means of the three-primary-color light mixing principle is analyzed, and a theoretical basis is provided for a control system to realize a light color correction function. Due to the current characteristic of the LED lamp, under the condition of constant current, the LED lamp reaches maximum brightness under the condition of full pulse width modulation (Pulse Width Modulation, PWM), the average current of the LED can not be improved by improving the PWM value, and the whole correction idea is to obtain a new point-by-point PWM value in a color mixing mode, which approximates the average current of the LED; the new PWM value drops to some extent from the original value and thus the brightness in normal operation is reduced. On the other hand, chen Yotao, in combination with the application requirements of the high-density display screen, determines the basic architecture of the control system based on the FPGA.

The LED display technology in the prior art, although widely used in various fields, still has some technical challenges and problems, mainly including:

1) High cost and effort for point-by-point correction:

the large-sized LED display screen is composed of a large number of tiny pixels, each of which needs to be independently corrected to achieve the required brightness.

If each pixel is corrected point by point, a huge amount of data processing will occur, requiring a high performance processor and algorithm.

Furthermore, the cost of point-by-point correction is also very high, involving delicate calibration equipment and time-consuming procedures.

2) Problem of brightness drop:

as the usage time increases, the brightness of the LED display screen gradually decays, a process commonly referred to as "light decay".

Such a reduction in brightness affects the overall visual effect of the display screen, particularly in applications requiring stable display for a long period of time, such as advertising screens, traffic signs, and the like.

3) White balance shift:

on an LED screen, white balance is achieved by adjusting the brightness and chromaticity of the three LED sub-pixels, red, green, and blue.

Over time, the luminous efficiency of the LEDs of each color may change due to various reasons (e.g., temperature change, material aging, etc.), which may cause white balance misalignment, thereby affecting the display effect.

Due to the light decay, white balancing of the screen becomes more difficult after long use, as LEDs of different colors of different materials will decay at different speeds.

Disclosure of Invention

Aiming at the problems existing in the prior art, the invention provides a white balance compensation method and a white balance compensation system for an LED display screen.

The invention is realized in such a way that the white balance compensation method of the LED display screen comprises the following steps:

step one, driving an LED full-color display screen with M rows and N columns by using an FPGA chip, and controlling the crystal oscillator frequency F _co ；

Step two, the crystal oscillator obtains 3 synchronous clocks through W frequency division of an FPGA chipRespectively controlling a red LED display driving subsystem, a green LED display driving subsystem and a blue LED display driving subsystem;

starting a timer in the driving system, informing the FPGA when the equipment is powered down, writing the current count into the EEPROM by the FPGA, and continuously accumulating the count register on the basis of the EEPROM when the next power-on initialization is performed;

step four, the resistance value of the adjustable resistor of the primary column gating base is adjusted through the I2C bus for the first time before the FPGA chip leaves the factory, so that the column driving current I is adjusted _LED The LED display screen achieves white balance;

fifth, every other column gating base adjustable resistance adjustment period T _run The FPGA chip adjusts the resistance value of the adjustable resistor of the primary column gating base through the I2C bus so as to adjust the column driving current I _LED The LED display screen again reaches white balance.

Further, in the first step, each color pixel comprises 1 red, green and blue sub-pixels, and the whole driving system is divided into a general driving subsystem, a red LED display driving subsystem, a green LED display driving subsystem and a blue LED display driving subsystem; each row of scanning time of the red, green and blue driving subsystems is BT _clk The corresponding column on time when any one pixel is lighted is BT _clk 。

Further, the frame period is t=mt _row ,The selected parameters need to satisfy f _r ＝f _g ＝f _b >50Hz。

Further, column driving currentWherein beta is _{Amplification of} For the amplification of the collector of the column-driving transistor, I _{R_col} For column driving triode base current, U _col For column driving triode base voltage, U _be For column driving triode base-emitter voltage, R _col The resistor is adjustable for the base electrode of the column driving triode.

Further, R (j) _{r_col leaves factory} 、R(j) _{g_col leaves factory} And R (j) _{b_col leaving factory} (j=1, 2,3, …, N) respectively represent the resistances of the base adjustable resistors of the j-th columns of the red LED display driving subsystem, the green LED display driving subsystem and the blue LED display driving subsystem at the time of shipment of the product, which satisfy the relative brightness ratio L of the red, green and blue subpixels in each pixel at the time of normal lighting before shipment _{r leaving factory} ：L _{g leaving factory} ：L _{b leaving factory} =1.0000: 4.5907:0.0601, and meets the white balance requirement when the LED display screen leaves the factory.

Further, R (j) _{r_col_min} 、R(j) _{g_col_min} And R (j) _{b_col_min} (j=1, 2,3, …, N) is such that the red LED display driving subsystem, the green LED display driving subsystem, and the blue LED display driving subsystem satisfy a relative luminance ratio of 1.0000 that red, green, and blue sub-pixels within each pixel normally light up: 4.5907: the minimum value of the j-th column base adjustable resistor of 0.0601 is also the minimum value that the j-th column base adjustable resistor of red, green and blue sub-pixels in each pixel and the brightness of the column meet the inverse proportion relation.

Further, when the working time length is nT _run (n＝1,2,3,...n _max )(n _max Depending on the lifetime of the display), the resistance of the base adjustable resistor is R (j) _{r_col outPlant (B)} 、R(j) _{g_col leaves factory} And R (j) _{b_col leaving factory} (j=1, 2,3, …, N), the red, green and blue LED sub-pixels are normally lit with relative brightness L, respectively _{r_nTrun_R leaves factory} ＝α _nTrun L _{r leaving factory} ，L _{g_nTrun_R leaves factory} ＝β _nTrun L _{g leaving factory} ,L _{b_nTrun_R leaves factory} ＝γ _nTrun L _{b leaving factory} ，β _nTrun ﹥α _nTrun ﹥γ _nTrun Wherein alpha is _nTrun 、β _nTrun And gamma _nTrun Is the luminance decay factor corresponding to the on-time.

Further, when the working time length is nT _run (n＝1,2,3,...n _max )(n _max Depending on the lifetime of the display), the FPGA chip adjusts the resistance of the base adjustable resistor and satisfies R (j) _{r_col_nTrun} ＝α _nTrun R(j) _{r_col leaves factory} ≥R(j) _{r_col_min} 、R(j) _{g_col_nTrun} ＝β _nTrun R(j) _{g_col leaves factory} ≥R(j) _{g_col_min} And R (j) _{b_col_nTrun} ＝R(j) _{b_col leaving factory} γ _nTrun ≥R(j) _{b_col_min} (j=1, 2,3, …, N) and the red, green and blue LED sub-pixels are normally lit with relative brightness of respectively Then L is _{r_nTrun} ：L _{g_nTrun} ：L _{b_nTrun} ＝L _{r leaving factory} ：L _{g leaving factory} ：L _{b leaving factory} The LED display screen is automatically adjusted to a white balance state.

Further, when the working time length is nT _run (n＝1,2,3,...n _max )(n _max Depending on the lifetime of the display), alpha _nTrun R(j) _{r_col leaves factory} <R(j) _{r_col_min} 、β _nTrun R(j) _{g_col leaves factory} <R(j) _{g_col_min} And R (j) _{b_col outPlant (B)} γ _nTrun <R(j) _{b_col_min} (j=1, 2,3, …, N), the FPGA chip adjusts the resistance of the base adjustable resistor to satisfy R (j) _{r_col_nTrun} ＝R(j) _{r_col_min} 、R(j) _{g_col_nTrun} ＝R(j) _{g_col_min} And R (j) _{b_col_nTrun} ＝R(j) _{b_col_min} (j=1, 2,3, …, N) and the red, green and blue LED sub-pixels are normally lit with relative brightness of respectively

The LED display automatically approaches the white balance state.

Another object of the present invention is to provide an LED display screen white balance compensation system of the LED display screen white balance compensation method, the system comprising:

the general driving subsystem comprises a crystal oscillator, a frequency dividing module, a timer module and an EEPROM;

the frequency division module is used for obtaining 3 synchronous clocks through frequency division of the FPGA chip, and respectively controlling the red LED display driving subsystem, the green LED display driving subsystem and the blue LED display driving subsystem;

the timer module is used for recording the total working time of the display, recording the current time when the power is off, and continuing to count when the power is on next time;

the red LED display driving subsystem comprises a red LED display hardware module, a red LED display line scanning module and a red LED display column gating module;

the red LED display hardware module comprises a row driving device, a column driving device and other hardware devices suitable for red LED display, wherein an adjustable resistance chip is adopted as a base resistor in the column driving device;

the red LED display line scanning module is used for line-by-line scanning of red LED display;

the red LED display column gating module is used for controlling the gating of each column of red LED display, and when the product leaves the factory, the current of the red LED sub-pixel is controlled by adopting a method of adjusting the resistance value of the base electrode adjustable resistor chip of the column driving triode through an FPGA chip, so that the brightness of the red LED sub-pixel is controlled; and combining the light attenuation rule of the red LED, and adopting an FPGA chip to periodically reduce the resistance value of the base adjustable resistor chip of the column driving triode within a certain range of the resistance value of the base resistor, so as to increase the current of the red LED sub-pixel and further increase the brightness of the red LED sub-pixel.

The green LED display driving subsystem comprises a green LED display hardware module, a green LED display row scanning module and a green LED display column gating module;

the green LED display hardware module comprises hardware devices such as a row driving device, a column driving device and the like which are suitable for green LED display, wherein an adjustable resistance chip is adopted in the column driving device to serve as a base resistance;

the green LED display line scanning module is used for progressive scanning of green LED display;

the green LED display column gating module is used for controlling gating of each column of green LED display, and when a product leaves a factory, the current of the green LED sub-pixel is controlled by adopting a method of adjusting the resistance value of the base electrode adjustable resistor chip of the column driving triode through an FPGA chip, so that the brightness of the green LED sub-pixel is controlled; and combining the light attenuation rule of the green LED, and adopting an FPGA chip to periodically reduce the resistance value of the base adjustable resistor chip of the column driving triode within a certain range of the resistance value of the base resistor to increase the current of the green LED sub-pixel, thereby increasing the brightness of the green LED sub-pixel.

The blue LED display driving subsystem comprises a blue LED display hardware module, a blue LED display line scanning module and a blue LED display column gating module;

the blue LED display hardware module comprises a row driving device, a column driving device and other hardware devices suitable for blue LED display, wherein an adjustable resistance chip is adopted as a base resistor in the column driving device;

the blue LED display line scanning module is used for line-by-line scanning of blue LED display;

the blue LED display column gating module is used for controlling the gating of each column of blue LED display, and the current of the blue LED sub-pixel is controlled by adopting a method of adjusting the resistance value of the base electrode adjustable resistor chip of the column driving triode through an FPGA chip when a product leaves a factory, so that the brightness of the blue LED sub-pixel is controlled; and combining the light attenuation rule of the blue LED, and adopting an FPGA chip to periodically reduce the resistance value of the base adjustable resistor chip of the column driving triode within a certain range of the resistance value of the base resistor, so as to increase the current of the blue LED sub-pixel and further increase the brightness of the blue LED sub-pixel.

In combination with the technical scheme and the technical problems to be solved, the technical scheme to be protected has the following advantages and positive effects:

first, the invention adopts a progressive scanning technology for row driving, and adopts a method of adjusting the resistance value of a base electrode adjustable resistor chip of a column driving triode by adopting an FPGA chip for column driving. According to the scheme, when a product leaves a factory, the current of red, green and blue sub-pixels in each pixel is controlled by adopting a method of adjusting the resistance value of a base electrode adjustable resistor chip of a column driving triode through an FPGA chip, so that the brightness of the sub-pixels is controlled, and the white balance of red, green and blue colors is finally realized by firstly realizing the brightness uniformity of the red, green and blue sub-pixels; and combining red, green and blue light attenuation rules, and in a certain base resistance range, adopting an FPGA chip to periodically reduce the resistance of a base adjustable resistor chip of a column driving triode to increase the current of red, green and blue sub-pixels in each pixel, further increasing the brightness of the sub-pixels, and finally realizing the white balance of red, green and blue colors by firstly realizing the brightness uniformity of the red, green and blue sub-pixels. In summary, the white balance is realized, and meanwhile, the brightness loss caused by light attenuation in the middle and later stages of the work of the LED display screen can be compensated.

Secondly, the invention only needs to correct column by column, the correction times are column numbers, which are far smaller than the line number x column number of the point by point correction, the cost is lower, and the workload is smaller;

according to the invention, according to the difference of the relation between the red, green and blue LED light attenuation and the total working time length of different materials, the working time length of the display screen is recorded by using a timer, and the red, green and blue LED light attenuation is compensated by using a driving system so as to reach the white balance of the display screen again. The invention considers the influence of light attenuation and compensates the light attenuation, and when the screen is lightened for a long accumulated time, the white balance is still good.

Thirdly, the expected benefits and commercial value after the technical scheme of the invention is converted are as follows:

the LED display screen has huge pixel number, is directly corrected point by point based on all pixels of the display screen, and has higher cost and higher workload; the invention corrects by column, the correction times are column numbers, which are far smaller than the line number x column number of the point-by-point correction, the cost is lower, and the workload is smaller.

The invention solves the white balance problem of the LED display screen, ensures that the color is pure when the audience watches the video, improves the perception of the user, and is beneficial to the popularization of products.

The technical scheme of the invention solves the technical problem of white balance of the LED display screen which is always desired to be solved but is not successful.

Fourth, the significant technical improvements achieved by the LED display screen white balance compensation system provided by the present invention include:

1. and (3) accurate control: because each LED display driving subsystem (red, green and blue) in the system comprises a special line scanning and column gating module, the system can accurately control the lighting time and current of each sub-pixel point, thereby providing more accurate color brightness control and white balance adjustment and improving the quality of display effect.

2. High reliability: and the stability and the reliability of the system are improved by realizing each LED display driving subsystem through the FPGA. The parallel processing capability of the FPGA enables the response speed of the system to be faster when the white balance is adjusted, and delay and distortion are reduced.

3. Flexibility and programmability: the FPGA provides high flexibility and programmability, so that the system can dynamically adjust driving parameters according to different LED display screens, light attenuation and other conditions. This flexibility also allows the system to adapt to new display technologies and standards through software updates, protecting investment and extending product life.

4. Maintenance and upgrading are convenient: by using the EEPROM to store operation data and set parameters, the system can store important information after power failure and can be continuously used when power is on, so that the maintenance and upgrading of the system are more convenient.

5. The overall performance is improved: by recording the total duration of operation of the display, the system can monitor and predict the aging of the LED display panel, thereby automatically performing brightness compensation when necessary, ensuring color consistency and display quality over a long period of time.

The design of the system provided by the invention considers various conditions encountered by the LED display screen in the use process, and provides a high-efficiency, reliable and long-term maintainable solution through high customization and flexibility.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings that are needed in the embodiments of the present invention will be briefly described below, and it is obvious that the drawings described below are only some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

FIG. 1 is a flowchart of a method for compensating white balance of an LED display screen according to an embodiment of the present invention;

FIG. 2 is a block diagram of an LED display screen white balance compensation system provided by an embodiment of the invention;

FIG. 3 is a flow chart of a method for compensating white balance of an LED display screen;

FIG. 4 is a diagram of a driving circuit for a single red LED according to an embodiment of the present invention;

FIG. 5 is a schematic diagram of a single green LED drive circuit in accordance with an embodiment of the present invention;

fig. 6 is a driving circuit diagram of a single blue LED according to an embodiment of the present invention.

Detailed Description

The present invention will be described in further detail with reference to the following examples in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.

As shown in fig. 1, an embodiment of the present invention provides a method for compensating white balance of an LED display screen, where the method for compensating white balance of an LED display screen includes the following steps:

step one, driving an LED full-color display screen with M=512 rows and N=1024 columns by using an FPGA chip, and controlling the crystal oscillator frequency F _co ＝20MHz；

Step two, the crystal oscillator obtains 3 synchronous clocks through W=2 frequency division of the FPGA chipRespectively controlling a red LED display driving subsystem, a green LED display driving subsystem and a blue LED display driving subsystem;

fifth, every other column gating base adjustable resistance adjustment period T _run =100h, the fpga chip adjusts the resistance of the primary column strobe base adjustable resistor through the I2C bus to adjust the column driving current I _LED The LED display screen again reaches white balance.

Further, in the first step, each color pixel comprises 1 red, green and blue sub-pixels, and the whole driving system is divided into a general driving subsystem, a red LED display driving subsystem, a green LED display driving subsystem and a blue LED display driving subsystem; each row of scanning time of the red, green and blue driving subsystems is BT _clk The corresponding column on time when any one pixel is lighted is BT _clk Where b=256.

Further, the frame period is t=mt _row ,The selected parameters need to be satisfied

f _r ＝f _g ＝f _b ≈76Hz>50Hz, can meet the visual requirement of human eyes.

Further, R (j) _{r_col leaves factory} 、R(j) _{g_col leaves factory} And R (j) _{b_col leaving factory} (j=1, 2,3, …, N) respectively represent the resistances of the base adjustable resistors of the j-th columns of the red LED display driving subsystem, the green LED display driving subsystem and the blue LED display driving subsystem at the time of shipment of the product, which satisfy the relative brightness ratio L of the red, green and blue subpixels in each pixel at the time of normal lighting before shipment _{r leaving factory} ：L _{g leaving factory} ：L _{b leaving factory} ＝1.0000：

4.5907:0.0601, and meets the white balance requirement when the LED display screen leaves the factory.

Further, whenThe working time length is nT _run For 100n hours (n=1, 2,3, n _max )(n _max Depending on the lifetime of the display), the resistance of the base adjustable resistor is R (j) _{r_col leaves factory} 、R(j) _{g_col leaves factory} And R (j) _{b_col leaving factory} (j=1, 2,3, …, N), the red, green and blue LED sub-pixels are normally lit with relative brightness L, respectively _{r_nTrun_R leaves factory} ＝α _nTrun L _{r leaving factory} ，L _{g_nTrun_R leaves factory} ＝β _nTrun L _{g leaving factory} ,L _{b_nTrun_R leaves factory} ＝γ _nTrun L _{b leaving factory} ，β _nTrun ﹥α _nTrun ﹥γ _nTrun Wherein alpha is _nTrun 、β _nTrun And gamma _nTrun Is the luminance decay factor corresponding to the on-time.

Further, when the working time length is nT _run For 100n hours (n=1, 2,3, n _max )(n _max Depending on the lifetime of the display), the FPGA chip adjusts the resistance of the base adjustable resistor and satisfies R (j) _{r_col_nTrun} ＝α _nTrun R(j) _{r_col leaves factory} ≥R(j) _{r_col_min} 、R(j) _{g_col_nTrun} ＝β _nTrun R(j) _{g_col leaves factory} ≥R(j) _{g_col_min} And R (j) _{b_col_nTrun} ＝R(j) _{b_col leaving factory} γ _nTrun ≥R(j) _{b_col_min} (j=1, 2,3, …, N) and the red, green and blue LED sub-pixels are normally lit with relative brightness of respectively Then L is _{r_nTrun} ：L _{g_nTrun} ：L _{b_nTrun} ＝L _{r leaving factory} ：L _{g leaving factory} ：L _{b leaving factory} The LED display screen is automatically adjusted to a white balance state.

Further, when the working time length is nT _run For 100n hours (n=1, 2,3, n _max )(n _max Depending on the lifetime of the display), alpha _nTrun R(j) _{r_col leaves factory} <R(j) _{r_col_min} 、β _nTrun R(j) _{g_col leaves factory} <R(j) _{g_col_min} And R (j) _{b_col leaving factory} γ _nTrun <R(j) _{b_col_min} (j=1, 2,3, …, N), the FPGA chip adjusts the resistance of the base adjustable resistor to satisfy R (j) _{r_col_nTrun} ＝R(j) _{r_col_min} 、R(j) _{g_col_nTrun} ＝R(j) _{g_col_min} And R (j) _{b_col_nTrun} ＝R(j) _{b_col_min} (j=1, 2,3, …, N) and the red, green and blue LED sub-pixels are normally lit with relative brightness of respectively The LED display automatically approaches the white balance state.

As shown in fig. 2, an embodiment of the present invention provides an LED display screen white balance compensation system of an LED display screen white balance compensation method, the system including:

red LED display hardwareThe module comprises hardware devices such as a row driving device, a column driving device and the like which are suitable for red LED display; as shown in FIG. 4, the red LED sub-pixel row driving adopts a Darlington tube driving mode, and the row driving base resistor is R _{r_row} The column driving selects triode driving mode, and the column driving base resistor R _{r_col} Selecting an adjustable resistance chip, R _{r_row} One of M=512 row driving output pins connected with FPGA chip, R _{r_col} One of N=1024 column driving output pins of the FPGA chip is connected with a red LED driving power supply V _r Providing voltage support for the entire drive circuit;

the green LED display hardware module comprises hardware devices such as a row driving device, a column driving device and the like which are suitable for green LED display; as shown in FIG. 5, the green LED sub-pixel row driving adopts a Darlington tube driving mode, and the row driving base resistor is R _{g_row} The column driving selects triode driving mode, and the column driving base resistor R _{g_col} Selecting an adjustable resistance chip, R _{g_row} One of M=512 row driving output pins connected with FPGA chip, R _{g_col} One of N=1024 column driving output pins of the FPGA chip is connected with a green LED driving power supply V _g Providing voltage support for the entire drive circuit;

the blue LED display hardware module comprises hardware devices such as a row driving device, a column driving device and the like which are suitable for blue LED display; as shown in FIG. 6, the blue LED sub-pixel row driving adopts a Darlington tube driving mode, and the row driving base resistance is R _{b_row} The column driving selects triode driving mode, and the column driving base resistor R _{b_col} Selecting an adjustable resistance chip, R _{b_row} One of M=512 row driving output pins connected with FPGA chip, R _{b_col} One of N=1024 column driving output pins of the FPGA chip is connected with a blue LED driving power supply V _b Providing voltage support for the entire drive circuit;

The technical scheme is that the white balance compensation system of the LED display screen. The detailed working principle is as follows:

1) General drive subsystem: the system firstly generates a reference clock signal through the crystal oscillator, and the clock signal is divided into 3 synchronous clock signals in the FPGA through the frequency division module and is respectively used for controlling the red, green and blue LED display driving subsystems. In addition, the timer module records the total working duration of the display and is used for monitoring the service time of the display so as to perform ageing compensation. The EEPROM is used for storing system parameters and working time length data, and ensures that the data cannot be lost under the condition of power failure.

2) Red, green, blue LED display drive subsystem: the LED display driving subsystem of each color comprises a hardware module, a row scanning module and a column gating module.

The hardware module includes a row driver device and a column driver device, which are hardware that actually drives the LED display element to light up, wherein an adjustable resistance chip is employed in the column driver device to act as a base resistor.

The line scanning module is used for scanning the red, green and blue LEDs line by line.

When the products leave the factory, the column gating module controls the currents of the red, green and blue sub-pixels in each pixel by adopting a method of adjusting the resistance value of the base electrode adjustable resistor chip of the column driving triode through the FPGA chip, so as to control the brightness of the sub-pixels, and finally realize the white balance of the red, green and blue colors by firstly realizing the brightness uniformity of the red, green and blue sub-pixels; and combining red, green and blue light attenuation rules, and in a certain base resistance range, adopting an FPGA chip to periodically reduce the resistance of a base adjustable resistor chip of a column driving triode to increase the current of red, green and blue sub-pixels in each pixel, further increasing the brightness of the sub-pixels, and finally realizing the white balance of red, green and blue colors by firstly realizing the brightness uniformity of the red, green and blue sub-pixels. The white balance is realized, and meanwhile, the brightness loss caused by light attenuation in the middle and later stages of the work of the LED display screen can be compensated.

3) White balance compensation: since the LED luminescent material may have a decrease in brightness and a shift in white balance after a long period of operation, the system needs to adjust the driving current of each subpixel in time to maintain white balance. The FPGA dynamically adjusts the driving current of each sub-pixel point according to the recorded total working time length and a preset aging curve (the row scanning and column selecting time is unchanged, and the size of the driving current is simply changed), and the brightness attenuation and white balance offset caused by aging are compensated so as to maintain the accuracy and consistency of the color of the display panel.

4) Dynamic adjustment: because the FPGA has high flexibility and quick processing capability, the system can monitor the display state in real time and quickly adjust the parameters of each driving module according to the needs so as to respond to different display contents and environmental changes, thereby achieving the aim of maintaining the optimal display effect.

The driving system provided by the embodiment of the invention effectively realizes the timely compensation of the white balance of the LED display screen through the clock management and the method for accurately adjusting the resistance value of the base electrode adjustable resistor chip of the column driving triode, and simultaneously provides a stable solution which can adapt to long-term use change and maintenance and is easy to upgrade.

The foregoing is merely illustrative of specific embodiments of the present invention, and the scope of the invention is not limited thereto, but any modifications, equivalents, improvements and alternatives falling within the spirit and principles of the present invention will be apparent to those skilled in the art within the scope of the present invention.

Claims

1. The white balance compensation method for the LED display screen is characterized by comprising the following steps of:

2. The method of claim 1, wherein in the first step, each color pixel comprises 1 red, green and blue sub-pixels, and the whole driving system is divided into a general driving subsystem, a red LED display driving subsystem, a green LED display driving subsystem and a blue LED display driving subsystem; each row of scanning time of the red, green and blue driving subsystems is BT _clk The corresponding column on time when any one pixel is lighted is BT _clk 。

3. The method of claim 1, wherein the frame period is t=mt _row ,The selected parameters need to satisfy f _r ＝f _g ＝f _b >50Hz。

4. The method of compensating for white balance of an LED display of claim 1, wherein the column drive currentWherein beta is _{Amplification of} For the amplification of the collector of the column-driving transistor, I _{R_col} For column driving triode base current, U _col For column driving triode base voltage, U _be Is in the form of a columnDriving triode base-emission voltage, R _col The resistor is adjustable for the base electrode of the column driving triode.

5. The method for compensating white balance of LED display screen according to claim 1, wherein R (j) _{r_col leaves factory} 、R(j) _{g_col leaves factory} And R (j) _{b_col leaving factory} (j=1, 2,3, …, N) respectively represent the resistances of the base adjustable resistors of the j-th columns of the red LED display driving subsystem, the green LED display driving subsystem and the blue LED display driving subsystem at the time of shipment of the product, which satisfy the relative brightness ratio L of the red, green and blue subpixels in each pixel at the time of normal lighting before shipment _{r leaving factory} ：L _{g leaving factory} ：L _{b leaving factory} =1.0000: 4.5907:0.0601, and meets the white balance requirement when the LED display screen leaves the factory.

6. The method for compensating for white balance of LED display screen of claim 1, wherein R (j) _{r_col_min} 、R(j) _{g_col_min} And R (j) _{b_col_min} (j=1, 2,3, …, N) is such that the red LED display driving subsystem, the green LED display driving subsystem, and the blue LED display driving subsystem satisfy a relative luminance ratio of 1.0000 that red, green, and blue sub-pixels within each pixel normally light up: 4.5907: the minimum value of the j-th column base adjustable resistor of 0.0601 is also the minimum value that the j-th column base adjustable resistor of red, green and blue sub-pixels in each pixel and the brightness of the column meet the inverse proportion relation.

7. The method for compensating white balance of an LED display screen according to claim 1, wherein when the operation time period is nT _run (n＝1,2,3,...n _max )(n _max Depending on the lifetime of the display), the resistance of the base adjustable resistor is R (j) _{r_col leaves factory} 、R(j) _{g_col leaves factory} And R (j) _{b_col leaving factory} (j=1, 2,3, …, N), the red, green and blue LED sub-pixels are normally lit with relative brightness L, respectively _{r_nTrun_R leaves factory} ＝α _nTrun L _{r leaving factory} ，L _{g_nTrun_R leaves factory} ＝β _nTrun L _{g leaving factory} ,L _{b_nTrun_R leaves factory} ＝γ _nTrun L _{b leaving factory} ，β _nTrun ﹥α _nTrun ﹥γ _nTrun Wherein alpha is _nTrun 、β _nTrun And gamma _nTrun Is the luminance decay factor corresponding to the on-time.

8. The method for compensating white balance of an LED display screen according to claim 1, wherein when the operation time period is nT _run (n＝1,2,3,...n _max )(n _max Depending on the lifetime of the display), the FPGA chip adjusts the resistance of the base adjustable resistor and satisfies R (j) _{r_col_nTrun} ＝α _nTrun R(j) _{r_col leaves factory} ≥R(j) _{r_col_min} 、R(j) _{g_col_nTrun} ＝β _nTrun R(j) _{g_col leaves factory} ≥R(j) _{g_col_min} And R (j) _{b_col_nTrun} ＝R(j) _{b_col leaving factory} γ _nTrun ≥R(j) _{b_col_min} (j=1, 2,3, …, N) and the red, green and blue LED sub-pixels are normally lit with relative brightness of respectively

Then L is _{r_nTrun} ：L _{g_nTrun} ：L _{b_nTrun} ＝L _{r leaving factory} ：L _{g leaving factory} ：L _{b leaving factory} The LED display screen is automatically adjusted to a white balance state.

9. The method for compensating white balance of an LED display screen according to claim 1, wherein when the operation time period is nT _run (n＝1,2,3,...n _max )(n _max Depending on the lifetime of the display), alpha _nTrun R(j) _{r_col leaves factory} <R(j) _{r_col_min} 、β _nTrun R(j) _{g_col leaves factory} <R(j) _{g_col_min} And R (j) _{b_col leaving factory} γ _nTrun <R(j) _{b_col_min} (j=1, 2,3, …, N), the FPGA chip adjusts the resistance of the base adjustable resistor to satisfy R (j) _{r_col_nTrun} ＝R(j) _{r_col_min} 、R(j) _{g_col_nTrun} ＝R(j) _{g_col_min} And R (j) _{b_col_nTrun} ＝R(j) _{b_col_min} (j=1, 2,3, …, N) and the red, green and blue LED sub-pixels are normally lit with relative brightness of respectively The LED display automatically approaches the white balance state.

10. An LED display screen white balance compensation system of an LED display screen white balance compensation method according to any one of claims 1 to 9, characterized in that the system comprises: