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.