In 1998, Nghi Nho Nguyen had an idea for a “voice mouse” for a computer. The mouse would combine the traditional position signals of a pointing device with audio input signals, e.g., from a microphone in the mouse.

Mr. Nguyen’s sought to obtain a patent for his idea and met some resistance at the U.S. Patent and Trademark Office (USPTO). The USPTO Examiner rejected Mr. Nguyen’s claims based on a reference that disclosed a pointing device integrated with physiological sensors. While the reference did not specifically discuss the frequencies of the signals generated by the physiological sensors, it did provide examples, including an electromyograph (EMG) (muscle tension) sensor. Mr. Nguyen argued that the reference only worked for “slow varying signals” and did not anticipate use with signals containing “audio or higher frequencies.” Based on that argument, the USPTO granted Mr. Nguyen a patent for his “voice mouse” idea.

Nintendo introduced its Wii game system in 2012, which uses Nintendo’s Wii Remote and Nunchuk controllers. Later, Nintendo introduced its Switch game systems and controllers. Genuine Enabling Technology LLC accused the Wii and Switch of infringing Mr. Nguyen’s patent.

Nintendo replied that the patent should be limited based on disclaimer. It hired an expert to provide an opinion for an upper limit on the frequencies associated with the physiological sensors of the reference. The expert opined that the upper limit was 500 Hz based on literature in the field relating to EMG sensors. Thus, Nintendo reasoned that Mr. Nguyen’s arguments disclaimed signals below 500 Hz from the scope of the claims, as well as the types of signals in the reference (user selection information, physiological response information, and other slow-varying information). The district court deciding the case agreed with Nintendo.

The Federal Circuit has now reversed, finding Mr. Nguyen’s patent limited to use an “audio or higher frequency” signals. The Federal Circuit noted that, for a statement during prosecution to qualify as a disavowal of claim scope, it must be “so clear as to show reasonable clarity and deliberateness,” and “so unmistakable as to be unambiguous evidence of disclaimer.” If the challenged statements are ambiguous or amenable to multiple reasonable interpretations, prosecution disclaimer is not established.

In this case, although not mentioned in the opinion, voiced speech of a typical adult has a fundamental frequency from 85 to 255 Hz. That fact should have been a clue to Nintendo and its expert that a restriction of a claim in a patent directed to a “voice mouse” to frequencies higher than 500 Hz was erroneous. Indeed, the Federal Circuit noted that the construction advanced was not contemplated by the intrinsic record but, instead, relied on “extrinsic evidence upon extrinsic evidence to draw a bright line in claim scope not suggested anywhere in the intrinsic record.” It also felt that Mr. Nguyen’s focus on “audio or higher frequency” signals did not clearly disavow signals based on their content or nature—namely, “signals generated from positional change information, user selection information, physiological response information, and other slow-varying information.”