LED display has gained more and more popularity in the market due to its advantages such as bright colors and clear picture quality, and is gradually entering the mass indoor field from the professional indoor field. Therefore, EMC design and certification standards related to health and safety are more stringent. At present, the need for LED display to pass EMC certification is urgent.
EMC testing is one of the most important indicators of product quality and an important part of 3C certification.
EMC test is also called electromagnetic compatibility. It is a comprehensive assessment of the interference size (EMI) and anti-interference ability (EMS) of electronic products in terms of electromagnetic fields.
LED display working principle is to adjust the flow pulse parameters on the light emitting tube to achieve high grayscale and high refresh. Therefore, its power supply, control card, and internal signal transmission will generate electromagnetic radiation to varying degrees . The higher the refresh rate of the display screen, the higher the signal frequency on the system card, and the stronger the radiation interference. This is an inevitable result of high-quality applications and one of the most important electromagnetic disturbance sources of the display screen.
In order to effectively improve the interference size of the electromagnetic field of the LED display product system, itc uses PWM enhancement technology, frequency spreading technology, hardware adjustment, etc. to improve in order to pursue the highest standard of quality.
01PWM enhancement technology
The visual refresh rate of the display screen reaches 3840Hz. With the application of small pitch 4K/8K high resolution, the number of channels, number of connections, and number of lines of the chip have increased significantly. The changes in the above applications have all greatly increased the display time (GCLK) of grayscale data and the frequency of data transmission writing time (DCLK) and data transmission writing time (DCLK) . GCLK and DCLK frequencies are one of the important sources of interference in electromagnetic fields. The display time received by the driver chip of the LED display is, through PWM enhancement technology, the required data transmission and writing time of (Figure
Figure 1 With/No PWM Enhancement Technology Driver Chip Difference Schematic diagram
Figure 2 With/No PWM Enhancement Technology EMI Schematic diagram
02 Active EMI suppression technology one-to-one spreading technology
spreading technology is used to process semiconductor chip technology, and is known as one of the most advanced and effective active EMI suppression methods today , on the basis of ensuring the integrity of the clock signal, suppresses the EMI peak through the integrated circuit modulation frequency in the clock. By modulating the spike clock, it changes from a narrow band clock to multiple spectrums with sideband harmonics , dispersing the spike energy to multiple frequency segments in the spreading area, thereby achieving the effect of reducing the spike energy and suppressing the interference in the electromagnetic field, and reducing the peak value in the fundamental and harmonic frequency of . The clock and timing signals obtained from the spreading clock will be modulated the spreading effect of the corresponding multiple , the N harmonic of the clock signal, and the spreading width obtained is N times the fundamental wave, so it has a significant effect on suppressing the higher harmonic of , and the overall EMI peak is therefore reduced.
Figure 3 Turn on/off spread technology EMI schematic diagram
03 Hardware adjustment
Module terminal uses resistor, capacitor , inductance , magnetic bead and other components to form RC filter circuit to suppress interference in electromagnetic field , filter out high-frequency harmonics with higher stages to reduce the rise and fall time of the clock signal. In addition, the PCB uses a 4-layer board with a separate GND shielding layer. Through the PCB LAYOUT technique, the 3W principle is followed. The center spacing between the two traces is at least greater than 3 times the line width, and 70% of the electric field between the lines does not interfere with each other. The high-frequency signal line is ground-covered, with less holes, fewer twists and fewer layers changed. In addition, the PCB board is metalized and edge-covered, and the entire board edge-covered edge-covered edge-covered, so that the microwave signal cannot be radiated from the PCB board edge to achieve the effect of reducing radiation.
Figure 4 3W principle differential routing
For many years, the itc team has been devoted to research and development, fine production, constantly innovating reform technical means, and working hard to create high-standard and high-quality LED display screens. Currently, the itcLED display not only passes the national 3C compulsory certification, but also obtains CE, CAQI, CQCh and other series of certificates and international mutual recognition ISO quality management system certificate . Successful cases cover finance, cultural and tourism, theaters, theaters, campuses, enterprises, hotels, governments, cultural and sports venues and other places.
In the future, itc will continue to seek more technological breakthroughs and innovations, continue to deepen industry application and development, break through bottlenecks, create new standards, continue to become bigger, better and stronger, and contribute the strength of national enterprises to a manufacturing power. (Pictures: Allen)
For more industry information, please follow the official account of "itc Sound and Light TV News"
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