A Delaware federal judge has invalidated three patents at the center of a series of lawsuits accusing major companies of infringing upon the technology that underpins Siri, the digital assistant built into Apple products.

U.S. District Judge Richard G. Andrews of the District of Delaware on March 31 said the patents' ”high level of generality” prevented a subsidiary of the Canadian intellectual property firm WiLAN from claiming infringement by a contingent of tech heavyweights, including Amazon.com Inc. and Sony Electronics Inc.

The asserted patents, he said, drew on existing technology and outlined no inventive concepts to support a finding of validity under U.S. patent law.

The ruling delivers a setback to IPA Technologies Inc. in its campaign targeting the use of personal digital assistant technology featured on Apple Inc. devices.

According to court documents, IPA—a California-based subsidiary of WiLAN—acquired the patents-in-suit from SRI International Inc., which had been working on personal digital assistants with a grant from the Defense Advanced Research Projects Agency. SRI spun off Siri Inc. in 2007 and granted the new company a nonexclusive license to the patent portfolio.

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.

In 2016, IPA filed suit against Amazon, whose personal digital assistant Alexa has become a leading product in the sector, claiming infringement of the so-called '021, '061 and '718 patents. The company has since brought similar cases against Sony, DISH Network Corp., TCL Communication Technology Holdings Ltd., LG Electronics Inc. and Huawei Technologies Co.