The European Patent Office (EPO) has revoked one of Rambus European patents on computer memory chip technology, in response to opposition from rival chip makers.

The EPO's Technical Board of Appeal revoked patent 0525068, which refers to "an access time register", but has yet to explain exactly why. A written decision will explain its reasoning when it is published in four to ten weeks.

In a statement, Rambus said that although the ruling was a disappointment it was "a small part of a larger picture" and it looked forward to reading the EPO's written decision.

Rambus filed for the European patent in 1991 and opposition was filed against it in 2000 by Micron Europe, Micron Technology Italia, Infineon. Hynix and Micron Semiconductor. In response, the EPO amended the patent in November of 2002, but that decision was appealed, leading to Thursday's decision to revoke it in its entirety.

As well as the EPO's decision, Rambus faces a ruling on Tuesday by the US Federal Trade Commission (FTC) on whether it practiced unfair competition by allegedly deceiving a standards-setting body into adopting the memory technology in order to profit from licensing fees.

On top of that, it is also involved in a patent suit over memory chip technologies with Infineon which is expected to go to trial May 10, according to an Infineon spokesman. He added that the company was pleased with the EPO's decision, asserting that Rambus has "no basis for all related claims to its patent infringement suit against Infineon".