An appeals court on Tuesday overruled a decision by the Federal Trade Commission that Rambus Inc. violated antitrust law, sending the computer-chip designer's shares up almost 4 percent.The FTC ruled in 2006 that Rambus illegally obtained a monopoly in the 1990s when it secured patents for two popular types of memory chips used in personal computers. Los Altos, Calif.-based Rambus was accused of failing to disclose to an engineering council that its patents had been incorporated into an industry standard for memory technology. In February 2007, the agency set maximum royalty rates that Rambus could charge on the patents and required the company to license the patents.

But the U.S. Court of Appeals for the D.C. Circuit said the FTC failed to prove that Rambus had illegally obtained its monopoly.

The company's shares rose 87 cents, or 3.9 percent, to $23.41 in midday trading Tuesday.

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