Siri personal assistant technology. Photo: Rick Kopstein/ALM

Microsoft Corp. is asking a Delaware federal judge to dismiss an infringement suit targeting the Redmond, Washington-based tech giant's Cortana digital assistant products, seizing on an earlier ruling that invalidated three patents at the heart of the case.

On Thursday, Microsoft said the March 31 ruling from U.S. District Judge Richard G. Andrews of the District of Delaware had doomed the case from IPA Technologies Inc., as the American subsidiary of WiLAN takes aim at the use of personal digital assistant technology underpinning Apple Inc.'s Siri.

Microsoft argued in court papers that Andrews' opinion had wiped out all of IPA's claims on the same three patents that it had accused Microsoft of infringing. A second set of patents, the company said, were also invalid in light of the decision.

The dispute comes amid IPA's broader push to protect technology that it had acquired from SRI International Inc., which had been developing personal digital assistants with a grant from the Defense Advanced Research Projects Agency. SRI spun off Siri Inc. in 2007 and granted the new IPA a nonexclusive license to the patent portfolio, the company has said.

The technology was later released as an iPhone 3GS app in February 2010. That April, Apple acquired Siri Inc. and released the Siri personal digital assistant as an integrated feature of the iPhone 4s the following year. IPA claims to own the patents by assignment.

IPA has sued a contingent of tech heavyweights over the past year, accusing the major American firms of improperly incorporating the patented technology into a variety of mobile devices and tablets.

Last month, however, Andrews found the so-called '021, '061 and '718 patents were “replete” with references to already-existing technology and outlined no inventive concepts to support a finding of validity under U.S. patent law. Though the ruling only applied to the first claim asserted in each patent, IPA has said those were representative of all the remaining claims.

Microsoft said in its brief that the rest of the patents' claims were directed at the same abstract idea and used similar “generic, functional language” to reference well-known and conventional technology.

But Microsoft also asked Andrews to nix a second set of patents, which IPA added to the suit last month. Those too described a way of implementing the same idea, only with a “higher level of abstraction,” the company said, and contained no inventive concept to transform it into patent-eligible subject matter.

What's more, Microsoft said IPA's complaint lacked any specific allegations of infringement and failed to plead a cause of action.

“The [three patents] contain a total of 186 unasserted claims, and the complaint provides no allegations suggesting that even IPA believes that any Microsoft product infringes any of them.”

Attorneys for both sides were not immediately available to comment on Friday.

IPA is represented by Stephen B. Brauerman and Sara E. Bussiere of Bayard P.A. and Alexander E. Gasser, Christopher Hodge, Mieke Malmberg, Sadaf R. Abdullah, Sarah E. Spires and Steven W. Hartsell of Skiermont Derby.

Microsoft is represented by Rodger D. Smith II of Morris, Nichols, Arsht & Tunnell and Nathaniel C. Love, Richard A. Cederoth and Scott M. Border of Sidley Austin.

The case is captioned IPA Technologies v. Microsoft.