| August 27, 2025
Presumption of Validity Does Not Protect a Patent from Invalidity for Lack of Adequate Written Description
Case Name: MONDIS TECHNOLOGY LTD. v. LG ELECTRONICS INC.
Decided: August 8, 2025 (Precedential)
Panel: Taranto, Clevenger, and Hughes, Circuit Judges
Summary
The CAFC held that Mondis’s patent is invalid for lack of adequate written description for a claim limitation introduced by amendment to overcome a prior art rejection during prosecution, where the prosecution history itself clearly suggested a lack of written description so that Mondis could not rely solely on the presumption of validity; expert testimony on infringement issues did not provide substantive evidence of validity; and although the amendment was allowed by the Examiner, allowance alone did not prove written description compliance, where the prosecution history indicated contrary.
Details
Mondis owns U.S. Patent No. 7,475,180. The ’180 patent basically describes a technology using matching of identification information to prevent unauthorized control of a display unit by an external computer sending video signals to the display unit. For example, the patent’s specification describes an embodiment where one or more ID numbers are stored in the display unit’s database and the external computer is assigned a unique ID number. The computer’s ID number is compared against the display unit’s database and the computer is allowed to control the display unit only when there is a match between the ID numbers.
As originally filed, the underlying application recited the following claim language:
…
a memory in which at least display unit information is stored, said display unit information including an identification number for identifying said display unit and characteristic information of said display unit; and … .
During prosecution, the above claim language was amended by the applicant adding a phrase “at least a type of” to overcome an art-based rejection, to read:
…
a memory in which at least display unit information is stored, said display unit information including an identification number for identifying at least a type of said display unit and characteristic information of said display unit; and
… .
The Examiner allowed the application over the prior art in response to the amendment, including the above claim language—referred to as “the type limitation”—which is set forth in claim 14 of the resulting patent. The prosecution record includes the Examiner’s Interview Summary stating that the above amendment was proposed by the applicant during the interview so as “to more clearly specify identification number as a ‘type’ of display unit which examiner agree[d] will read over the previous art applied regarding … the claims.”
Mondis sued LG for infringement of the ’180 patent. In the district court proceeding, LG challenged the patent’s claim 14 and its dependent claim 15 as invalid for lacking written description for the type limitation. The jury determined that the ’180 patent was not proven invalid and was infringed by that LG’s accused products. Both parties appealed—Mondis dissatisfied with the district court vacating an original damages verdict and ordering retrial leading to a reduced damages award, and LG contesting the district court’s denial of its motion for judgment as a matter of law (JMOL) of invalidity and infringement, among other issues.
At issue on appeal is whether the type limitation complies with the written description requirement of 35 U.S.C. § 112, ¶ 1. The CAFC noted that the written description requirement is a question of fact, reviewed for substantial evidence. “Patents are presumed to be valid and overcoming this presumption requires clear and convincing evidence,” and the burden of persuasion was on LG.
Mondis conceded that there is no express support for the type limitation in the patent. Mondis’s main arguments were: (A) the presumption of validity frees it from the requirement to produce evidence of adequate written description support, and (B) substantial evidence of validity is provided by each of (B-1) Mondis’s expert testimony, (B-2) LG’s expert’s admissions, and (B-3) the patent’s prosecution history. The CAFC rejected each argument.
As to (A) the presumption of validity argument, the CAFC noted that some patents are “presumed valid at birth [such that] a patentee need submit no evidencein support of a conclusion of validity,” whereas others are themselves “clear enough that [the patent specification] establishes inadequacy of support in the written description for the full scope of the claimed invention unless there is contrary evidence.” The CAFC found that the ’180 patent falls under the second category, where the prosecution history made clear that the addition of the type limitation to overcome the art rejection changed the nature of the claimed ID number from one identifying a specific display unit to one identifying a type of display unit.
As to (B-1) Mondis’s expert testimony, the expert presented an infringement theory pointing to the patent’s disclosure of an embodiment where an ID number is sent from the display to a computer:
Namely, an ID number is sent to the computer 1 from the display device 6 so that the computer 1 identifies that the display device 6 having a communication function is connected and the computer 1 compares the ID number with the ID number registered in the computer 1.
The Mondis’s expert explained to the jury that the above passage to mean that “the communication function [disclosed in the specification] is an actual video format [such that] the ID number is defining what video format the display is capable of receiving.”
The CAFC noted that the above testimony was “about infringement rather than validity,” and that the plain words of the specification, read in the context of the surrounding disclosure, would convey that the patent discloses a specific display unit, as opposed to a specific type of display unit.
As to (B-2) LG’s expert’s admissions, Mondis asserted that LG’s noninfringement testimony provides substantial evidence that serial numbers could be used to identify a particular display unit, and could hypothetically be a type ID.
The CAFC noted that to meet the written description requirement, “it is the specification itself that must demonstrate possession.” Nothing in the patent specification describes a serial number that identifies any type of display unit, and the expert testimony—which was again about infringement rather than validity—does not address whether a skilled artisan would find support in the specification for the type limitation.
As to (B-3) the patent’s prosecution history, Mondis argued that the fact that the claim amendment was entered without objection led to “an especially weighty presumption of correctness,” citing Commonwealth Sci. & Indus. Rsch. Org. v. Buffalo Tech., Inc. (USA), 542 F.3d 1363, 1380 (Fed. Cir. 2008). That is, Modis argued that “when the examiners allowed the amendment, they agreed to the type limitation because they understood that it was supported by written description.”
The CAFC clarified that Commonwealth Science, while finding a “presumption of validity based on the PTO’s issuance of the patent despite the amendments,” “does not hold that the examiner’s allowance of claims by itself provides substantial evidence that the claims comply with the requirements of § 112.” “If it did, there would rarely be a situation where an issued patent could later be invalidated for lack of written description.”
Further, the CAFC pointed to the Examiner’s interview summary explaining the nature of the claim amendment as overcoming the art rejection, but silent as to whether the Examiner considered compliance with the written description requirement. As such, the prosecution history fell short of substantial evidence.
Takeaways
This case provides a reminder that allowance of claim amendments and presumption of validity of patents alone do not constitute substantial evidence that the claims comply with the written description requirement. Care should be taken when adding a claim limitation that is not expressly supported by the specification, even if the amendment would successfully overcome an art-based rejection.
