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Spread spectrum timing for HDD applications

Posted: 01 Mar 2010 ?? ?Print Version ?Bookmark and Share

Keywords:spread spectrum? HDD application? electromagnetic field?

When electrical current flows in a circuit, an electromagnetic field is created. The strength of this field depends on the frequency and magnitude of the current flow. This field radiates outward from the wires and electronic traces in the equipment that it flows in. Any radiation that is an unwanted byproduct of the electrical circuitry's desired function is called EMI. This radiation has the potential for either degrading the performance of the equipment that generates it or other (external) equipment in proximity to it. This occurs through the basic "generator" process that happens when there is relative motion between any conductor and any electro-magnetic field. If the levels of these induced currents are high enough, they can cause malfunctions in equipment, degrade performance, or render it totally useless. Even worse is when they cause other systems to degrade or malfunction. A good example of this is a piece of computing equipment interfering with (and therefore degrading the performance of) a common TV or radio receiver. While some levels of EMI are considered acceptable others are clearly not. Determining whether one device impacts the functionality of another is too complex to include as an element in a user manual/guide. To protect consumers from experiencing these problems, federal regulatory agencies such as the FCC have established measurable limits on the amount of EMI that any piece of electronic equipment may emit at any frequency.

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