In modern system integrated control, large-scale signal switching systems are indispensable in various places. The current mainstream signal switching systems include CREATOR and other large-scale switching system products, including AV signal switching system, RGB signal switching system, DVI Signal switching system and HDMI signal switching system, etc. But for now, the differences in various environments, especially the impact of peripheral electromagnetic interference, will have a certain degree of impact on various signal switching systems. Therefore, various manufacturers have adopted EMI / EMC in their signal switching systems. Suppression and other technologies. Below, I briefly introduce some related issues:
Different types of products and test institutions, EMI / EMC test requirements are also different. However, EMI / EMC testing can be roughly divided into two categories:
Radiation: This test limits the amplitude and frequency of the signal radiated or conducted by a product so that it will not interfere with other products.
Sensitivity (also called immunity): This test shows the product's ability to suppress radiation by limiting the amplitude and frequency of radiated and conducted signals that interfere with the normal operation of the device.
EMI / EMC test failure usually occurs in the weakest link (signal and interference) in product design from this link to enter or leave the device after screening and filtering. Among the audio / video interfaces, the weakest point is the cable connecting the devices. They are equivalent to antennas. For computers, the cable connecting the monitor and speakers to the computer is the weakest link, and it often causes EMI / EMC problems. We may think that only high-bandwidth video interfaces will cause this problem, while low-frequency audio interfaces will not have this problem. This is true when all amplifiers use Class A audio amplifiers. However, the currently used high-efficiency class D amplifiers have high-frequency switching signals, and if there is no proper filtering and shielding, there will also be EMI problems.
The video format commonly used by computers, which we call "graphics", is different from the video format of television. Computer video includes red, green, and blue (R, G, B) analog video signals, as well as logic signals composed of line, field sync, and DDC5, all of which have fast rise / fall times. Video connectors usually use high-density ultra-micro D-type connectors for connecting monitors and computers. Although this solution combines measures such as video signal shielding (coaxial) and common-mode choke (CMC) to reduce radiated and conducted EMI, it still needs to increase filtering to ensure that EMI requirements are met. In broadcast video applications, similar filtering measures are used to eliminate aliasing defects in TV images. However, this cannot be done in graphic video because the purpose of graphic video is to reproduce a checkerboard pattern of "on" and "off" pixels at the highest possible resolution. Therefore, in order to achieve the best display performance, we hope that the larger the bandwidth, the better. However, in practical applications, EMI and video performance must be weighed, so video bandwidth has to be sacrificed. For multi-signal video interfaces, multiple factors need to be weighed.
To achieve efficiency and performance without generating EMI, the audio interface must solve a series of different problems. In portable applications, we want to maximize battery life without expecting inefficient designs to generate heat, so Class D amplifiers are widely used. The problem is that Class D amplifiers use PWM to achieve high efficiency, which is very similar to switching power supplies. When an unshielded speaker cable is connected to the output, the cable will radiate EMI like an antenna. Although the clock frequency (typically 300kHz to 1MHz) is higher than the audio spectrum, it is a square wave with a lot of harmonic components. The size of the filter used to filter out the harmonic component is relatively large, and the cost is high. In portable applications such as laptops, this is not a viable solution due to size.
Among many EMI / EMC suppression technologies, the MAX9511 and MAX9705 represent advanced technologies for EMI / EMC control, so they are gradually applied to specific products. Applying these devices to products can effectively reduce EMI. There is no need to rely on large-scale external filters and shielding methods that will increase cost and size as before. These devices use the most advanced technology today, effectively ensuring electromagnetic compatibility and performance.
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