| |  | Author | Message | | | yangandjiao | | Posted: Tue Jul 01, 2008 2:46 am Post subject: EMI/EMC Suppression in Audio/Video Interfaces | | | | Joined: 23 Apr 2008 Posts: 65 | All electronic products marketed worldwide undergo EMI/EMC (electromagnetic interference/electromagnetic compatibility) testing before they are offered for sale to prove that they will not create interference, or be interfered with by other devices. For testing purposes, products are grouped into two classes: intentional radiators and unintentional radiators. For example, cell phones and walkie-talkies intentionally radiate energy while TVs, PCs, or laptops should not.
Depending on the class of the product and the agencies involved, the EMI/EMC requirements vary. Regardless, EMI/EMC testing is partitioned into two general categories:
Emissions This limits what amplitude and frequency a product can radiate or conduct so that the device does not interfere with others.
Susceptibility (also called Immunity) This testing category compliments the Emissions requirement by limiting the amplitude and frequency of the radiated and conducted signals that can interfere with a product.
As noted above, the two ways EMI can be emitted by a device are conduction and radiation. These are related because all radiated EMI is due to current flow. However, not all current flow causes radiation. Consequently, radiated interference problems are investigated and suppressed before conducted interference issues. Of the two, radiation is more difficult to predict and suppress. Therefore, it causes most unanticipated EMI testing failures in the unintentional radiator product class. We will concentrate on solving the radiation problem in the audio/video interface found in many products.
You can use several methods to meet the limits specified in EMI/EMC regulations. However, these methods tend to fall into the general categories of shielding and filtering. In actual practice, these are combined with application-specific methods to achieve an overall EMI solution. For example, in most products, a metal chassis acts as a shield to radiation and L-C or R-C filters reduce conducted interference on the input/output wires. In addition, we might dither a clock to spread its spectrum and reduce the amount of filtering or shielding required in a specific application.
When the performance appears adequate, a product is formally tested in an approved laboratory. If it passes, it may be marketed; however, failing is a problem. Even a small change to correct a problem can take time to implement. This may delay introduction because passing EMI/EMC-compliance testing is mandatory in all international and domestic markets.¹ Consequently, the EMI design often degrades video performance to ensure that a product passes these tests. This video degradation is exacerbated in modern designs by the size and cost of the parts required to pass EMI testing.
This design challenge is particularly true for the contemporary audio/video analog interface with its reduced product size and high performance expectations. The first step in solving this problem is to find where most EMI/EMC failures occur and then investigate potential solutions. | |
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| sophia86 | | Posted: Wed Jul 02, 2008 2:41 am Post subject: electronic market | | | | Joined: 02 Jul 2008 Posts: 4 | | who can introduce electronic products market for me,please | |
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| yangandjiao | | Posted: Thu Jul 03, 2008 1:40 am Post subject: good place for ic market | | | | Joined: 23 Apr 2008 Posts: 65 | |
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