A motion asking Judge Payne to make such a ruling had been expected since a jury in the Richmond, Va., federal district court last month found Rambus had committed fraud. Based on the fraud verdict, Infineon told Judge Payne it would seek to have the SDRAM patents declared unenforceable.

Legal briefs on post-trial motions were due yesterday, but Infineon decided not to present arguments on the patent unenforceability issue, according to the firm's attorneys.

Infineon officials could not be reached immediately for comment on why the firm backed away from seeking estoppel relief muting the Rambus patents because of fraud. Some industry sources believed that Judge Payne, having already dismissed all Rambus infringement claims against Infineon, felt any further motions to throw out the patents were moot.

Also, the sources said Infineon can still file a motion later to have the patents ruled unenforceable, should an appellate court overturn Judge Payne's dismissal of Rambus's patent claims.

The judge earlier had dismissed all Rambus patent infringement claims against Infineon, so the German chip maker was absolved of all charges against it. However, at the time the attorneys said they would seek the additional ruling as a safeguard in case the appellate court reversed Judge Payne's dismissal of all infringement claims. Now apparently Infineon has decided to wait to see the appellate court does.

The Infineon withdrawal seems sure to disappoint two other Rambus synchronous patent litigants, Micron Technology and Hynix Semiconductor Co. They were probably hoping the Richmond court would find the patents unenforceable because of fraud, in order to cite the ruling as a precedent in their own cases against Rambus.

The Richmond jury decided that Rambus had committed fraud by failing to disclose its synchronous patent applications in the 1992-96 period when the firm participated in the industry JEDEC panel drafting an open SDRAM standard.

Patents awarded under fraudulent conditions can be challenged as unenforceable. Rambus filed a post-trial brief seeking to have Judge Payne throw out the jury verdict of fraud.

Rambus also filed another brief seeking a new trial. Infineon filed a brief asking that Rambus be enjoined from filing any further infringement claims against the German firm on any of the dozens of synchronous patents that weren't involved inthe Richmond case. Infineon argued that the jury verdict of fraud for its silence in the JEDEC standard deliberations would negate all of the Rambus synchronous patents, even those not part of the Richmond trial.

The two sides will present rebuttal briefs and second reply briefs over the next several weeks. A hearing on all motions will be held at 9:30 a.m. July 6 before Judge Payne. The judge could rule on the flurry of motions sometime after that.