September 28, 2021

Volume XI, Number 271


September 27, 2021

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Double-Check The Prior Art and Validate the Math: Lessons from Apple Inc. v. Corephotonics, Ltd.


In Apple Inc. v. Corephotonics, Ltd., No. 2020-1438 (Fed. Cir. June 23, 2021) (Taranto, Hughes, and Stoll), the Federal Circuit affirmed the PTAB’s finding of no anticipation but vacated its determination of nonobviousness. The Federal Circuit remanded the PTAB’s conclusion that there was no motivation to combine because it held that conclusion was premised on a clear mathematical error.


Apple filed a petition seeking inter partes review of Corephotonics’ patent relating to a miniature telephoto lens assembly that can be used in portable electronic devices, such as cell phones. Cell phone cameras require a compact imaging lens system with a small total track length (“TTL”), which is the distance between the first camera lens to “an electronic sensor, film, or image plane corresponding to either the electronic sensor or a film sensor.” Id. at *2. Whereas prior art lens assemblies contained four or five lenses with long TTLs, Corephotonics’ patent claimed a five lens assembly with a TTL that is smaller than the effective focal length (“EFL”), resulting in a TTL/EFL ratio that is less than one. According to the patent, the lower the TTL/EFL ratio, the better the image quality.

Apple’s petition alleged that (1) a prior art reference, Konno, anticipated the patent’s claims and (2) Konno in view of a second reference, Bareau, would have rendered the claims obvious. Notably, Konno disclosed a lens system with a TTL/EFL ratio that is less than one. However, Konno also contained a mathematical error such that the multiple lenses it described would physically overlap and impossibly occupy the same space.

The PTAB found that Apple failed to establish either of its challenges. Among other things, the PTAB found that Apple’s identification of the error in Konno “overcame the presumption of enablement afforded to patents and printed publications.” Id. at *9. But, the Board found, Apple’s “failure to address the issue of enablement” necessarily meant it failed to establish anticipation. Id. at *9.

On appeal, Apple raised three arguments: that the PTAB applied the wrong legal framework for enablement of an anticipatory prior art reference; that the PTAB erred in finding the claims were not anticipated by Konno; and that the PTAB’s conclusion regarding nonobviousness was improper because it relied on a clear mathematical error.

Federal Circuit

The Federal Circuit first addressed Apple’s argument that the PTAB improperly shifted the burden to prove that Konno was enabling to Apple. Reviewing its precedent, the Federal Circuit explicitly stated that “in the context of both district court litigation and patent prosecution [] the burden of proving that a prior art reference is not enabling is on the patentee/applicant, and that it is error to shift that burden to the patent challenger/examiner.” Id. at *10.

Though the PTAB recognized this precedent, it reasoned that none of the prior cases were AIA proceedings and that AIA trial proceedings were different. The Federal Circuit disagreed. More specifically, the Federal Circuit held that “regardless of the forum, prior art patents and publications enjoy a presumption of enablement, and the patentee/applicant has the burden to prove nonenablement for such prior art.” Id.

Notwithstanding the PTAB’s erroneous burden shifting, the Federal Circuit found that the error was harmless because even if Konno was deemed enabled, the court found that it did not anticipate the challenge claims as a matter of law. Konno claimed a lens assembly in which lenses overlapped, which is physically impossible. To anticipate the disputed claim limitation, Konno would need to be modified such that the lenses no longer overlapped. This modification would be improper for an anticipation analysis. Because “inoperative embodiments cannot be anticipatory,” the Federal Circuit concluded that Konno did not anticipate the challenged claims. Id. at *12.

Lastly, the Federal Circuit addressed the clear mathematical error fundamental to the PTAB’s finding that there was not sufficient motivation to combine Konno and Bareau. Apple presented evidence to the PTAB that a skilled artisan would have reduced the F number of Konno, which refers to the amount of light that enters a lens assembly. Specifically, Apple alleged that the skilled artisan would have reduced Konno’s F number from 4.0 to 2.8 in view of Bareau. The PTAB rejected Apple’s argument, finding that lowering the F number to 2.8 would violate a limitation expressed in Konno.

The Federal Circuit held that the PTAB’s mathematical determination was incorrect. Decreasing the F number to 2.8 would not, per an established mathematical relationship, violate Konno’s conditional expression. Because the Federal Circuit could not conclude that the PTAB would reach the same decision absent its mathematical mistake, the Court vacated the PTAB’s determination and remanded for reconsideration.


It has long been accepted that the burden of proving a prior art reference is not enabling falls on the patentee/applicant in district court litigation and patent prosecution. In Apple v. Corephotonics, the Federal Circuit confirmed that the same is true in AIA trial proceedings. But perhaps the bigger lesson is a warning to patent challengers—choose your prior art references carefully. Inoperable or faulty prior art will not be sufficient to support an allegation of anticipation. Arguing a retroactive modification of that art, such that it is operable and potentially anticipatory, is not likely a viable solution. Lastly, using this case as a cautionary tale, always validate any requisite math. Should the PTAB rely on faulty mathematic calculations, these false calculations are likely grounds for appeal.

Samantha Leff, Summer Associate at Finnegan, also contributed to this article.

© 2021 Finnegan, Henderson, Farabow, Garrett & Dunner, LLPNational Law Review, Volume XI, Number 187

About this Author

Brooke Wilner Patent Attorney Finnegan

Brooke Wilner, a registered patent attorney, enjoys a varied trial and appellate litigation practice. She practices before U.S. district courts, state courts, the Patent Trial and Appeal Board (PTAB), the U.S. Court of Appeals for the Federal Circuit (CAFC), and the U.S. International Trade Commission (ITC).

Brooke represents both patent owners and accused infringers across a broad range of mechanical and electrical technologies, including clients in the aerospace, automotive, consumer products, software, and hardware industries. She has...

Amanda Murphy IP Lawyer Finnegan

Amanda Murphy, Ph.D., focuses her practice on strategic client counseling, portfolio management, and patent prosecution for a range of clients, including small startup companies, research foundations, and large biotechnology and pharmaceutical companies.

Amanda provides patentability opinions, prepares new patent applications, prosecutes U.S. and foreign applications, and represents appellants before the Patent Trial and Appeal Board (PTAB) of the U.S. Patent and Trademark Office (USPTO). She has experience in prosecuting inter partes ...

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