The last of three patents that tech licensing patent trolling company Rambus used to win infringement lawsuits against Nvidia Corp, Hewlett-Packard and others has been declared invalid according to legal documents.

The three patents - collectively known as the Barth patents - pertain to memory chips used in personal computers and are considered to be among Rambus' most valuable intellectual property.

An appeals board at the US Patent and Trademark Office declared the patent invalid on January 24, according to a ruling posted on their website. The previous two were declared invalid in September.

The invalidation is more bad news for Rambus, whose stock shed 60 percent of its value in the weeks after a November 16 court decision in which it lost a $4 billion antitrust lawsuit against Micron Technology Inc and Hynix Semiconductor Inc.

The Barth patents had been used to accuse a long list of tech companies of infringement, earning Rambus millions of dollars in licensing fees through settlements.

Source: Reuters