The hottest LED display design and technology deve

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LED display design and technology development trend

the large screen has always been an important part of the hot development in the LED field and an important part of the theme display of large-scale entertainment, sports events and square decoration. Since the birth of blue LED, it has maintained a high-speed development trend. In the decorative display market, LED will play a positive role, with obvious market expansion. China is a major producer of LED display screens in the world, and it plays a leading role in LED chip, driver IC, controller and screen manufacturing

led screen status quo

the origin of 16 bit shift constant current IC: the dual color screen is mainly used to display text, and it is convenient for single chip microcomputer to scan. Due to the increase in the number of LEDs, 74HC595 shift scanning is used to save o/i resources. In order to be more suitable for the application of LED, the constant current setting function is integrated on this basis, which increases the current driving ability, more meets the needs and cost needs, and the 16 bit device is encapsulated, which is widely used in the current full-color screen

the current drive capability has been continuously reduced. Earlier, the tlc5940 had a single drive current capability of 120mA. Later, the current drive capability of TB62726, st2221 and mbi5026 was reduced to ma. At present, 45mA current drive capability is basically adopted, such as mbi5024 and cyt62726. The main reason for the reduction of current driving capability is that the LED devices have higher and higher luminous intensity. In order to improve the image quality, more and more static screen designs are adopted, and the demand for driving current capability is reduced. From the perspective of IC cost, the chip size can be reduced to reduce the cost. Therefore, a 25mA static screen driver chip cyt62727 is designed

at present, 80% of the world's large LED screens are produced in Chinese Mainland. The 16 channel constant current device design is widely used. It will continue in the short term and will not disappear in at least the next five years. The main reason is that the supporting control technology is mature and the products have been serialized. Unless there is a huge leap in system control technology and chip design and the cost is further reduced, the current situation will not change. In recent years, many companies have continuously launched new structures, which will be recognized by the market in the future. The biggest problem with LED screen is to change the color consistency of led through control technology. Before there is no major breakthrough in new technology, it is not very attractive to users and does not have a strong willingness to buy

in recent years, chip design companies in mainland China will occupy the LED display market instead. For example, smart core is a mainstream LED display chip supplier. Besides excellent quality assurance, a good direct sales model is the magic weapon to win the market. In the future, the direct selling mode is also required for drive IC, and of course, quality is also very important. Most of the display screen enterprises are local enterprises in the mainland, and the trust with Taiwan IC in the distribution account date and delivery date needs to be further improved

in terms of driving application technology, the bottleneck of color correction technology needs to be solved urgently. The problem of attenuation consistency of display screen is prominent. Wavelength correction and brightness correction are the next key breakthrough goals. The first is to solve the problem of brightness consistency, and then wavelength consistency correction. This is not only a worldwide problem, but also a technical problem that needs to be solved urgently at present

the development of control technology has been in the forefront in China. The existing problem is that the new control concept is stagnant. The reason is that the controller manufacturers and IC design manufacturers do not cooperate well, each does its own thing, the driving technology and control technology can not be well connected, the 16 channel compatibility design has a high maturity of development, and there are few new control technologies, let alone technological innovation. For example, mbi5026 has designed LED screen for more than ten years. Up to now, mbi5024 is only to reduce current and deal with the competitive price. There is no technical breakthrough. Taiwan Jiji has also launched a number of upgraded ICs, but the reason for this phenomenon has not been well applied, which is caused by the lack of control technology. Today, with the rapid development of computer technology, it can replace and simplify the scale of the controller, but the transplantation of technology also needs the support of IC design manufacturers. The market lacks a solution provider of control technology and chip driven integration

in 2009, the domestic market scale of the LED display industry exceeded 30 billion yuan. There were more than 30 enterprises with an annual output value of more than 100 million yuan, and there were thousands of large and small enterprises engaged in the display manufacturing industry. The LED display continues to maintain a growth rate of 15% and the technology is becoming more and more mature. China's large-scale event projects continue to drive strong led growth. For example: Olympic Games, WorldExpo, Asian Games, Shanghai Disney, subway, high-speed rail and other engineering events

basic design principle

text display screen, as long as the content is displayed clearly and has sufficient brightness, it will basically meet the needs of customers. But it is much more complicated to evaluate the display quality of image display screen. Generally, the display quality of the display screen is evaluated in a subjective way. The so-called subjective evaluation is the artificial evaluation, which is made by observing the image display quality. So. The evaluation result is not only related to the display quality of the image itself, but also to the subjective factors of the observer. It is difficult to say that it is a fair and accurate standard. However, there is still no good method at present. Before there is no objective measurement method, the subjective method is still the most effective and practical method

maximum number of display colors

the color of each pixel of the display is composed of RGB (red, green and blue). For low-end LCD panels, each primary color can only represent 6-bit color, i.e. 26=64 colors. Through simple calculation, we can know that the maximum number of colors that each independent pixel can represent is 64 × sixty-four × 64=262144 colors; The high-end LCD panel uses FRC technology so that each primary color can represent 8-bit color, that is, 28=256 colors, and the maximum number of colors that a pixel can represent is 256 × two hundred and fifty-six × 256=16777216 colors. This kind of display panel displays a richer picture color and a better sense of hierarchy. At present, the LCD and these two kinds of display panels on the market are used. You can pay attention to them

in practical use, the data units that are easy to measure or change direction are often used for light intensity calculation. For the LED display screen, the active illuminant generally uses cd/square meter as the luminous intensity unit, and the observation angle as the auxiliary parameter, which is equivalent to the illuminance unit of the screen surface lux; Multiply this value by the effective display area of the screen to obtain the luminous intensity of the whole screen at the best viewing angle. Assuming that the luminous intensity of each pixel in the screen is constant in the corresponding space, this value can be considered as the luminous flux of the whole screen. Generally, the outdoor LED display screen must have a brightness of more than 4000 cd/M2 before it can have an ideal display effect in sunlight. The maximum brightness of ordinary indoor LED is about 700 ~ 2000 cd/m2

the luminous intensity of a single LED is in CD and equipped with viewing angle parameters. The luminous intensity has nothing to do with the color of the LED. The luminous intensity of a single tube ranges from a few MCDs to fivethousand MCDs. The luminous intensity given by the LED manufacturer refers to the point with the highest luminous intensity at the best viewing angle and the central position when the LED is lit under 20mA current. When packaging LED, the shape of the top lens and the position of the LED chip from the top lens determine the LED viewing angle and light intensity distribution. Generally speaking, the larger the viewing angle of the same led, the smaller the maximum luminous intensity, but the accumulated luminous flux on the whole three-dimensional hemisphere remains unchanged

when multiple LEDs are closely and regularly discharged, their light-emitting spheres overlap each other, resulting in a relatively uniform distribution of light-emitting intensity in the whole light-emitting plane. When calculating the luminous intensity of the display screen, it is necessary to multiply the maximum point luminous intensity provided by the manufacturer by 30% ~ 90% according to the LED viewing angle and led emission density as the average luminous intensity of a single tube

generally, LED has a long luminous life, and the manufacturer usually indicates that it is more than 100000 hours, which is under the best set conditions. In fact, attention should also be paid to the brightness attenuation cycle of LED. The brightness attenuation cycle has a great relationship with the material process and manufacturer of LED production. Generally, brands with slow brightness attenuation should be selected when economic conditions permit

most screens use in-line Oval LEDs, and most domestic packaging technologies can meet the needs of screen design. LEDs with good reputation are Cree or packaged with domestic LED light-emitting chips such as shimingxin and Xiamen San'an


cyt62726 is internally a 16 bit shift register, multiple cyt62726 serial data shifts, each clock cycle CLK transfers 1 bit of data SDI, and the serial data input driver is controlled on/off. Schmidt buffered input. The rising edge of CLK when the switch in which the data "1" is written to the SDI controls the shift register/

clk serial data shift clock. Schmidt buffered input. All data/off controlled transition shifts are synchronized by the highest bit of 1 bit on the rising edge of CLK, and single channel data is shifted to SD at the same time. After the rising edge input of CLK is approved, it will last for 100ns

le edge triggers latch. Schmidt buffered input. The data in the current corresponding shift register is latched at this rising edge

oe all outputs are blank. Schmidt buffered input. When OE is at low level, all constant current outputs (out0 ~ 15) are executed. When oe=1, all switches of constant current output control are in data control data/latch status. OE determines the execution data length time

block diagram of driving constant current chip

selection of peripheral devices

set 1000 when the screen design is about within the PCB distributed by cyt62726 μ F. when selecting filter capacitor, low ESR (equivalent series resistance) capacitor shall be used to minimize output ripple. Compared with other dielectrics, these materials can maintain their capacity in a wide range of voltage and temperature

a decoupling capacitor is connected between the power supply and the ground, which has three functions: one is as the energy storage capacitor of the integrated circuit; The second is to filter out the high-frequency noise generated by the device and cut off its transmission path through the power supply circuit; The third is to prevent the noise carried by the power supply from interfering with the circuit

for the design of LED lighting products, it is very important to add filter capacitors inside the lighting points, mainly because the more color changes, the more power supply fluctuations will increase. Filter capacitors are more important here than in any product design. For most high current designs, a 470 to 1000 is recommended μ F capacity. The design here cannot be without this capacitor

see the figure below. Usually, when we design the circuit, we will design decoupling capacitors at the IC input: on the one hand, it is the energy storage capacitor of the integrated circuit, on the other hand, it bypasses the high-frequency noise of the device. The typical decoupling capacitance value in a digital circuit is 0.1 μ F。 The typical value of the distributed inductance of this capacitor is 5 μ H,0.1 μ The decoupling capacitance of F is 5 μ The parallel resonance frequency of H distributed inductor is about 7MHz, which has a good decoupling effect for noise below 10MHz. The selection of decoupling capacitor is not strict. It can be taken as 0.1 according to c=1/f, i.e. 10MHz μ F。

for most high circuit designs, a range of 0.01 to 0.1 is used at the input μ F capacitance is enough. The design here cannot be without this capacitor

it is recommended to connect a 10 Ω resistor in series in the VCC power supply. The content of the LED screen fluctuates greatly when it works, which will exceed 10V. It is suggested that VCC still needs resistance to reduce impact, mainly to reduce the wave crest caused by voltage fluctuation, especially for LED display, Vp-p will be several times higher. The IC power input is also the most vulnerable place to impact, and the existence of resistance will also increase

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