The European Patent Office (EPO) has revoked a European Patent owned by memory chipmaker Rambus.

An EPO Technical Board of Appeal decided to revoke Rambus's European patent for a semiconductor memory device following public oral proceedings on February 10 and 11.

The reasoning behind the decision will be delivered in writing in about four to 10 weeks.

Rambus's senior vice-president and general counsel John Danforth said although the ruling was disappointing it represented only "a small part of a larger picture".

"We look forward to seeing the EPO Appeals Board written decision when it is available," he said. "In addition, we look forward to further progress with respect to our unaffected US patents, some of which are set for infringement trials in US courts in May and November of this year."

European patent EP 0525068 covers a technology called an "access time register" which increases the speed of communication between processing and memory devices in computers.

The patent was granted by the EPO in April 2000 for Germany, France, the UK and Italy.

However Infineon Technologies, Hynix Semiconductor Deutschland, and Micron Semiconductor Deutschland each filed separate oppositions. Micron Europe and Micron Technology Italia filed a joint opposition.

In November 2002, the EPO's opposition division ruled that the patent be maintained in amended form. Both Rambus and the opposing companies lodged appeals.

The EPO, in reviewing the case last week, did not consider matters of infringement or any other legal proceedings between the parties involved.

Some revocation and infringement proceedings before national courts in EPO member states were stayed pending the outcome of the appeal hearing.

Reinhardt Schuster, a partner of German firm Bardehle Pagenberg Dost Altenburg Geissler, which represented Micron, said: "The appeal was on classical grounds of opposition – lack of sufficient disclosure and not novel or inventive over prior art."

Schuster added that one of the central questions argued by all the opposition parties concerned the so-called "cut off effect" and its application in EPO law and practice.

The cut-off effect refers to when the claims of a patent are amended during the time between the filing and granting of a patent. According to this principal, followed by the German Patent Office, during an opposition proceeding a patent will be examined in the form it was filed and as it was granted.

The EPO decision is final and will influence whether other proceedings before national courts go ahead.

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