The European Commission said Thursday it had filed antitrust charges against U.S. memory chip designer Rambus for claiming unreasonable royalties for its patents.

The commission said it sent a statement of objections, a formal step in the European Union (EU)'s antitrust investigations, to Rambus on July 30. The document alleged that the company set too high a price for licensing the use of some of its patents for Dynamic Random Access Memory (DRAM) chips.

DRAM is a type of electronic memory primarily used in computer systems. It is also used in a wide range of other products which need to temporarily store data, like servers, workstations, printers, PDAs and digital cameras.

The California-based Rambus, founded in 1990, specializes in the design and patenting of DRAM chips. It has licensed its patents to companies including Nintendo and Sony, but does not manufacture any of the products itself.

DRAM has been standardized by the Joint Electron Device Engineering Council (JEDEC), an industry-wide U.S. based organization. Rambus owns and is asserting patents which it claims cover the technology included in these JEDEC standards.

Therefore, every manufacturer wishing to produce synchronous DRAM chips or chipsets consequently must either acquire a license from Rambus or litigate its asserted patent rights.

The U.S. regulator ruled several weeks ago that Rambus engaged in intentional deceptive conduct in the context of the standard-setting process by not disclosing the existence of the patents which it later claimed were relevant to the adopted standard.

Without the so-called "patent ambush," Rambus would not have been able to charge the royalty rates it currently does, the commission said in a statement.

Rambus was consequently deprived of its right to collect royalties on U.S. patents and foreign ones relating to goods imported into or from the United States.

But the European Commission said it had to act because European companies may not seek relief on the basis of the U.S. decision and they are still exposed to litigation over the relevant patents Rambus obtained in Europe.

This is the first time that the commission has dealt with a "patent ambush" under its antitrust competence.

Rambus has nine weeks to reply in writing or request an oral hearing to present its comments on the case. If the charges are confirmed, the commission may require Rambus to cease the abuse and may impose a fine.