The US chip designer Rambus has been sued by a group of its shareholders in a case filed on Friday in the US District Court of California. The lawsuit alleges that during the course of Rambus’ legal dispute with German chip maker Infineon, it became clear that some of Rambus’ patents relating to computer memory had been fraudulently obtained. The investors claim that the were misled about the status of these patents and the royalties that the company would gain form them.

The lawsuit was filed on the same day that a US district court set aside part of the earlier verdict that Rambus had been guilty of fraudulently obtaining certain patents. However, the court allowed other findings of fraud to stand and ordered Rambus to pay Infineon the sum of $7.1 million in legal fees.

The Court found that Rambus did not commit fraud when it allegedly hid its patents for double data rate SDRAM memory technology from the industry body, JEDEC. However, the court also found that Rambus did commit fraud with single data rate SDRAM technology by filing for patents on SDRAM technology without informing JEDEC. The result was a partial victory for Rambus, meaning it can now bring patent infringement proceedings in connection with double data rate SDRAM.

Legal wrangles have contributed to an 82% drop in the value of Rambus shares since February. Its shares now trade below $10, down from a high of $450.

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