Integrated Control Audio Video Interface EMI/EMC Suppression Technology

In modern system integration control, large-scale signal switching systems are indispensable in various places. At present, mainstream signal switching systems include CREATOR and other large-scale switching system products, including AV signal switching system, RGB signal switching system, and DVI. Signal switching system and HDMI signal switching system, etc. However, at present, the differences in various environments, especially the influence of peripheral electromagnetic interference, will have a certain degree of influence on various signal switching systems. Therefore, each manufacturer adopts EMI/EMC in its own signal switching system. Suppression and other technologies. Below, I will briefly introduce some related issues:

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The type of product is different from the test organization, and the test requirements for EMI/EMC are also different. However, EMI/EMC testing can be roughly divided into two categories:

Radiation: This test limits the amplitude and frequency of a signal radiated or conducted by a product so that it does not interfere with other products.

Sensitivity (also known as immunity): This test illustrates the product's ability to suppress radiation by limiting the amplitude and frequency of radiated and conducted signals that interfere with proper operation of the device.

EMI/EMC test failures typically occur in the weakest part of the product design (signal and interference) from this link into or out of the shielded and filtered device. In the audio/video interface, the weakest point is the cable that connects the devices, which is equivalent to the antenna. For computers, the cable that connects the display and speakers to the computer is the weakest link, and it often causes EMI/EMC problems. We might think that only high-bandwidth video interfaces will cause this kind of problem, and low-frequency audio interfaces will not have this problem. This is true when all amplifiers use Class A audio amplifiers. However, the high-efficiency Class D amplifiers currently in use have high-frequency switching signals, and EMI problems can occur if proper filtering and shielding are not performed.

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 line, field sync, and logic signals consisting of DDC5, all of which have fast rise/fall times. Video connectors typically use high-density ultra-micro D-type connectors for connecting monitors and computers. Although this solution combines video signal shielding (coaxial) and common mode choke (CMC) to reduce radiated and conducted EMI, it is necessary to add filtering to ensure EMI requirements are met. In broadcast video applications, similar filtering measures are employed to eliminate aliasing artifacts in television images. However, this cannot be done in graphics video because the purpose of graphics video is to reproduce the 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 is sacrificed. For multi-signal video interfaces, multiple factors need to be weighed.

The audio interface needs to solve a series of different problems to achieve efficiency and performance without generating EMI. 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 for high efficiency, which is very similar to switching power supplies. When an unshielded speaker cable is used to connect to the output, the cable radiates 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 large number of harmonic components. The filter used to filter out the harmonic components is relatively large in size and costly. In portable applications such as laptops, this is not a viable solution due to size.

Among the many EMI/EMC suppression technologies, the MAX9511 and MAX9705 represent advanced technologies for EMI/EMC control, and are gradually being applied to specific products. Applying these devices to the product can effectively reduce EMI. There is no need to rely on large external filters and shielding to increase cost and size as before, and these devices use today's most advanced technology to ensure electromagnetic compatibility and performance.

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