The US Court of Appeals for the Federal Circuit affirmed a district court determination that a patent owner had not provided the “particularized testimony and linking argument” required to demonstrate equivalence under the doctrine of equivalents. NexStep, Inc. v. Comcast Cable Commc’ns, LLC, Case No. 2022-1815 (Fed. Cir. Oct. 24, 2024) (Chen, Taranto, JJ.) (Reyna, J., concurring in part and dissenting in part). In his dissent, Judge Reyna criticized the majority for ignoring the totality of the evidence presented by the patent owner and imposing a new rule requiring patentees to always present expert testimony to prove infringement under the doctrine of equivalents.

NexStep owns a patent directed to a “concierge device” for assisting users with obtaining customer support for smart devices. The claims are directed to a concierge device that initiates a technical support session in response to “a single action” (i.e., a single button press) by a user. After the claimed “single action,” the concierge device conveys consumer device identification information for the product at issue, identifies an appropriate technical support team for the product, and causes the home gateway to initiate a support session for the device and forward the consumer device information during the session.

NexStep sued Comcast for patent infringement, asserting that three tools in Comcast’s mobile smartphone application infringed the concierge device patent: Xfinity Assistant, Troubleshooting Card, and Diagnostic Check. Each of these tools assists users with troubleshooting a given device in response to the user pressing a series of buttons on a smartphone’s display. At trial, NexStep argued that pressing a series of buttons literally met the single action limitation because a single action could comprise a series of steps. By way of illustration, NexStep’s expert explained that throwing a baseball – a single action – required multiple steps: “[W]hen you throw a baseball, you pick it up, you orient it, you get it in your palm, you throw it.”

The jury returned a verdict of no literal infringement but found infringement under the doctrine of equivalents. Comcast moved for judgment as a matter of law, which the district court granted after finding that NexStep had failed to offer the “particularized testimony and linking argument” required to demonstrate equivalence. NexStep appealed.

The Federal Circuit emphasized that the doctrine of equivalents provides a “limited exception” to the principle that the claim defines the scope of the patentee’s exclusivity rights, and that a finding under the doctrine of equivalents is “exceptional.” To guard against overbroad applications of this exception, the Court’s precedent imposes specific evidentiary requirements necessary to prove infringement under the doctrine. The patent owner must provide proof on an element-by-element basis and from the perspective of someone skilled in the art, “for example through testimony of experts or others versed in the technology; by documents . . . and . . . by the disclosures of the prior art.” Finally, the patent owner must provide “particularized testimony and linking argument as to the insubstantiality of the differences between the claimed invention and the accused device.” As the Court explained, generalized testimony concerning the overall similarity of the devices will not suffice. While a finding of equivalence is a determination of fact, the Court noted that a doctrine of equivalents theory can be rejected as a matter of law when it fails to comply with the above requirements.

The Federal Circuit concluded that NexStep failed to meet its evidentiary burden as to the doctrine of equivalents. NexStep’s expert, Ted Selker, PhD, never identified a particular element in Comcast’s app that was equivalent to the claimed “single action.” The Court criticized Selker’s general reference to “several button presses” as insufficient to meet the particularized testimony requirement. Selker also failed to explain why the element in the accused product was equivalent to the claimed limitation for each part of the function-way-result test. The Court was not certain that Selker had even identified a function. With respect to the “way” element, the Court characterized Selker’s testimony as a “word salad” that did not explain why multiple button presses performed the claimed method in the same way as the claimed single action. The Court also found Selker’s testimony regarding the “result” prong insufficient because he merely testified that something would happen to make the device work in response to the multiple button presses, which amounted to “generalized testimony as to the overall similarity between the claims and the accused . . . product.” The Court thus concluded that NexStep’s doctrine of equivalents infringement theory was legally insufficient.

The Federal Circuit also found NexStep’s arguments concerning insubstantial differences, considered alongside Selker’s literal infringement testimony, unpersuasive. The Court explained that NexStep did not present an independent insubstantial differences theory at trial because its expert couched his analysis solely in terms of the function-way-result framework. NexStep pointed to Selker’s literal infringement testimony where he testified that multiple steps can be a single action and argued that NexStep’s literal infringement testimony coupled with its doctrine of equivalents testimony provided an adequate basis for the jury’s finding on equivalence. Forfeiture notwithstanding, the Court disagreed, explaining that “evidence and argument on the doctrine of equivalents cannot merely be subsumed in plaintiff’s case of literal infringement.” In other words, even if a patentee’s literal infringement argument bears on equivalence, the patent owner must still provide particularized testimony and linking argument.

Finally, the Federal Circuit rejected NexStep’s suggestion that the Court should adopt an exception to the particularized testimony and linking argument requirement for cases concerning easily understandable technologies. Pointing to the precedent from which this requirement was derived, the Court noted that such cases dealt with simple technologies such as box springs and handbells. The Court explained, however, that the evidentiary requirement was necessary not because of the complexity or simplicity of the technology but because of the “difficulties and complexities of the doctrine [of equivalents.]”

Judge Reyna’s Concurrence in Part

In his partial dissent, Judge Reyna criticized the majority as ignoring the totality of the evidence presented by NexStep and for imposing a new rule requiring patent owners to always present expert testimony to prove infringement under the doctrine of equivalents. Judge Reyna argued that the majority unduly focused on testimony from NexStep’s expert on the function-way-result test and ignored other evidence the jury received in other contexts. For example, Selker had already identified a specific series of button presses for each accused Comcast tool while testifying about literal infringement. Similarly, the majority faulted Selker for failing to explain why multiple button presses were insubstantially different from a single action, but Selker explained that a “single action” can constitute multiple parts. Accordingly, Judge Reyna concluded that Selker’s testimony as a whole provided substantial evidence on which a reasonable jury could find for NexStep.

Judge Reyna also argued that the majority imposed a rigid new rule requiring expert testimony to prove infringement under the doctrine of equivalents. While under the insubstantial difference test, a patent owner must provide evidence to establish the insubstantial difference between the function, way, and result of the claimed device and the accused device, it can do so without relying on expert testimony, especially where the technology is simple. Judge Reyna also took issue with the majority’s contention that expert testimony was required in view of the “difficulties and complexities of the doctrine,” noting that expert witnesses are specifically not supposed to testify as to the meaning of legal doctrines, no matter how complex.

Practice Note: Even in cases concerning simple technology or where there is significant overlap between literal infringement and doctrine of equivalents arguments, patentees should make sure to clearly articulate the basis for their doctrine of equivalents positions. Patentees should also consider advancing doctrine of equivalents arguments under both the function-way-result and insubstantial differences frameworks to preserve both on appeal.