Chip technology company Rambus Inc was quizzed in court about destroyed documents and its own use of its patents as graphics chip maker Nvidia Corp sought relief from expensive licensing fees.

The two sides squared off on Thursday before the U.S. Court of Appeals for the Federal Circuit over whether Nvidia infringed Rambus patents for controlling and managing the flow of computer data to and from a chip's memory.

The U.S. International Trade Commission, which hears patent cases involving imports, had previously found Nvidia infringed Rambus chip patents and issued an order barring the importation of any chip made with the infringing technology.

Nvidia licensed the Rambus technology at royalty rates of between 1 percent and 2 percent depending on the type of memory controller involved, to allow its chips to enter the country, but the legal battle has continued.

The ITC had found that Nvidia infringed three patents but did not infringe two others. Both sides appealed to the circuit court and the arguments were consolidated.

Part of the battle has centered on whether Rambus destroyed documents to avoid having them used against it in litigation.

Rambus has acknowledged document destruction but said it was part of ordinary business practices.

Judge Kathleen O'Malley, part of a three-judge panel that heard the case, took issue with an attorney for Rambus who said the company produced the documents that were requested and that all relevant documents were preserved.

You admit you have no idea what was destroyed! You have no record of what was destroyed! she said.

Remember, you saved the ones that helped you and destroyed the ones that hurt you, O'Malley said at another point.

The appeals court previously ruled in cases between Rambus and Micron Technology and Hynix Semiconductor <000660.KS> that Rambus destroyed documents inappropriately. The cases have been remanded back to lower courts for further consideration.

The battle is a key one for Nvidia, whose core business relies on the sale of specialized graphics cards.

Judge Raymond Clevenger on Thursday repeatedly asked whether Rambus had proved that it used the patents that it was seeking to defend.

Companies may not sue at the International Trade Commission unless they show that they are using the patent domestically. Rambus licensed the patents, and used that to proceed with the lawsuit.

Clevenger said district courts cannot order production or importation of infringing products to cease since the Supreme Court said in a 2006 decision that an injunction should not necessarily follow a finding of infringement. It's a factor we should think about, he said.

Rambus and others go to the ITC to file patent complaints because the trade commission, unlike U.S. district courts, can bar the importation of devices made with infringing technology.

The case against Nvidia and others that was before the International Trade Commission is number 337-661. The U.S. Court of Appeals for the Federal Circuit case numbers are 2010-1483 and 2010-1556.

(Reporting by Diane Bartz; Editing by Tim Dobbyn)