Infinity Computer Products, Inc. (“Infinity”) sued Oki Data Americas, Inc. (“Oki”) for infringement of U.S. Patent 6,894,811 (the “’811 patent”) and three other patents that share a common specification with the ’811 patent (collectively, the “asserted patents”). The asserted patents covered systems and methods for using a fax machine as a printer and scanner for a computer. The asserted claims recited that a “passive link” was used to connect the computer to the fax machine.

While the term “passive link” did not appear in the specification, Infinity used the term to distinguish the ’811 patent from Perkins, a prior art reference that disclosed a conversion box that could connect a computer to a fax machine to use the fax machine as a printer and scanner. Perkins also disclosed that the conversion could be performed by circuitry on a card installed inside a computer. Infinity argued that its invention was distinguishable because the fax machine was connected directly to the main I/O bus of the computer — without the need of any converting circuitry — by a “passive link.” Infinity further argued that even if the Perkins converting circuitry was installed in a card inside the computer, such a card should be considered “peripheral” to the computer. In view of these arguments, the application was allowed.

During a reexamination of the ’811 Patent, Infinity was presented with another reference, Kenmochi, which disclosed a similar system. In an attempt to pre-date the Kenmochi reference, Infinity argued that a figure in an earlier related application supported its claims which showed a computer having an internal fax modem — similar to the card embodiment in Perkins. There, the “passive link” was merely the cable connecting the fax machine to the fax modem of the computer, and the “computer” included the fax modem.

At the Markman hearing, Oki argued that the terms “computer” and “passive link” were indefinite as used in the asserted patents, because a person of ordinary skill could not determine where the passive link ended, and the computer began. Oki argued that the arguments made by Infinity to distinguish the Perkins and Kenmochi references were irreconcilable, leaving a person of ordinary skill without a way to determine what was, or what was not, part of the “computer.” The district court agreed, and ruled that the asserted patents — all of which used the terms “computer” and “passive link” — were invalid and entered a final judgment of invalidity.

The Federal Circuit affirmed, ruling that even ordinary terms like “computer” could be indefinite as a result of inconsistent prosecution history statements by the patentee. The Federal Circuit compared this case to Teva Pharm. USA, Inc. v. Sandoz, Inc., 789 F.3d 1335, 1341 (Fed. Cir. 2015), where the term “molecular weight” was indefinite because there were three separate possible definitions, and neither the specification nor the prosecution history clarified which definition was intended. The term “computer” here was even more clearly indefinite, because the prosecution history supported two conflicting understandings of the term “passive link” and “computer.” Thus, the term “computer” as used in the ’811 patent was indefinite. Further, because statements made during the prosecution of related patents may be considered in construing common terms — like “passive link” and “computer” — the related asserted patents which also used those terms were also invalid.

What This Means For You

This case highlights that statements made during prosecution may not merely limit the scope of claim language, but may render claims invalid. Where applications have long prosecution histories — either through repeated RCEs, continuations, or post-grant proceedings — special care should be taken to ensure that terms are treated consistently when distinguishing prior art. While a shifting-sands approach to claim language may result in issued patents, such inconsistent arguments may not only result in the invalidity of a patent where such an inconsistent statement is made, but can extend to the entire family.