Claim Construction & Doctrine of Equivalents

In the U.S., a prosecution history of a patent (i.e., the proceedings between the patent applicant and the USPTO from application filing to patent issuance) comes into play in the context of claim construction (for example, before a district court, before the PTAB in a post-grant proceeding, or in the eyes of a third party analyzing the patent for freedom to operate reasons), and also in the context of an assessment of infringement under the doctrine of equivalents. The Federal Circuit has recognized distinct roles of the prosecution history in claim construction and infringement under the doctrine of equivalents:

There is a clear line of distinction between using the . . . prosecution history to reach an understanding about disputed claim language and the doctrine of prosecution history estoppel which estops, or limits later expansion of the protection accorded by the claim . . . under the doctrine of equivalents when the claims have been purposefully amended or distinguished over relevant prior art to give up scope.

Biodex Corp. v. Loredan Biomedical, Inc., 946 F.2d 850, 862 (Fed. Cir. 1991) (citations omitted) (emphases added).

Claim interpretation in view of the prosecution history is a preliminary step in determining literal infringement, while prosecution history estoppel applies as a limitation on the range of equivalents if, after the claims have been properly interpreted, no literal infringement has been found. The limit on the range of equivalents that may be accorded a claim due to prosecution history estoppel is simply irrelevant to the interpretation of those claims.

Southwall Techs., Inc. v. Cardinal IG Co., 54 F.3d 1570, 1578 (Fed. Cir. 1995) (citation omitted).  Of course, such claim interpretation can also be significant in terms of patentability and invalidity analysis.

Retractable Techs., Inc. v. Becton, Dickinson and Co., 653 F.3d 1296 (Fed. Cir. 2011), provides an example where the Federal Circuit kept the two uses separate and applied prosecution history in both a claim construction analysis (with respect to the “cutting” limitation) and in a doctrine of equivalents analysis (“statements in the specifications preclude RTI from asserting that a body constructed of two pieces infringes the asserted claims under the doctrine of equivalents.”). Id. at 1307. 

But it is not always so easy to see the supposed “clear line of distinction” between prosecution history used in claim interpretation and prosecution history estoppel used in the doctrine of equivalents that the Biodex court asserted. On the contrary, the line between those two uses tends to be blurry. In Part 1 of this two-part series, we look at the use of prosecution history in claim construction. In Part 2, we discuss its use in a doctrine of equivalents analysis.

Prosecution History in Claim Construction

Prosecution history is used as a tool in claim construction. See Markman v. Westview Instruments, Inc., 52 F.3d 967, 980 (Fed. Cir. 1995). The prosecution history is used to interpret the claims in a manner consistent with the patentee’s representations and/or amendments during prosecution. This prevents claims from being construed one way to obtain their allowance and a different way against accused infringers. See Pall Corp. v. PTI Techs. Inc., 259 F.3d 1383, 1392 (Fed. Cir. 2001); see alsoSalazar v. Procter & Gamble Co., 414 F.3d 1342, 1344 (Fed. Cir. 2005); Schriber-Schroth Co. v. Cleveland Trust Co., 311 U.S. 211, 220-21 (1940). “[T]he prosecution history can often inform the meaning of the claim language by demonstrating how the inventor understood the invention and whether the inventor limited the invention in the course of prosecution, making the claim scope narrower than it would otherwise be.” Phillips v. AWH Corp., 415 F.3d 1303, 1317 (Fed. Cir. 2005) (en banc)see also, MBO Labs., Inc. v. Becton, Dickinson & Co., 474 F.3d 1323 (Fed. Cir. 2007) (“Prosecution arguments like this one which draw distinctions between the patented invention and the prior art are useful for determining whether the patentee intended to surrender territory, since they indicate in the inventor’s own words what the invention is not.”).

Sometimes in claim construction, the prosecution history may result in a narrower claim construction than would be expected from the claim language alone. In UCB, Inc. v. Yeda Rsch. and Dev. Co., 837 F.3d 1256 (Fed. Cir. 2016), UCB’s claims to a monoclonal antibody were construed by the district court to cover only murine monoclonal antibodies, and not also chimeric or humanized antibodies, despite no limitation as such in the claim. The Federal Circuit reasoned that “the content of the specification and actions and arguments during prosecution must also be considered, in defining the scope of a generic term in a claim.” Id. at 1260. “[T]he prosecution history requires this construction, for the scope now sought by Yeda was requested of the Examiner and refused on the ground of new matter. . . . Yeda’s unsuccessful attempt to claim chimeras in the pending application, with acquiescence in the examiner’s rejection on the ground of new matter not supported by the specification, prohibited now obtaining a claim construction that chimeric antibodies, or equivalents thereof, are described in the specification and included in the claims.” Id. at 1259-60.

Hockerson-Halberstadt, Inc. v. Avia Group Int’l, Inc., 222 F.3d 951 (Fed. Cir. 2000), provides another example. HHI’s claims contained the term, “central longitudinal groove.” In distinguishing the prior art, the inventor clearly disavowed footwear having a groove width greater than that disclosed in the prior art.  On appeal, HHI argued that the inventor’s statement was erroneous and not a disavowal of a particular width of the groove. The Federal Circuit made the following colorful comment:

HHI’s argument therefore reduces to a request for a mulligan that would erase from the prosecution history the inventor’s disavowal of a particular aspect of a claim term’s meaning. Such an argument is inimical to the public notice function provided by the prosecution history. The prosecution history constitutes a public record of the patentee’s representations concerning the scope and meaning of the claims, and competitors are entitled to rely on those representations when ascertaining the degree of lawful conduct, such as designing around the claimed invention. Were we to accept HHI’s position, we would undercut the public’s reliance on a statement that was in the public record and upon which reasonable competitors formed their business strategies. 

Id. at 957 (citations omitted).

In Viskase Corp. v. Am. Nat’l Can Co., 261 F.3d 1316 (Fed. Cir. 2001), the limitation at issue read “density below about 0.91 g/cm3.”  The accused product had an ethylene copolymer having a density ranging of 0.912 g/cm3or of 0.908 g/cm3. The district court determined that “about 0.91 g/cm3” meant densities between 0.905 and 0.914, based on the reasoning that numbers in this range would be rounded to 0.91. But once during prosecution, Viskase used 0.91 with a zero in the third decimal place (“0.910”), when distinguishing prior art densities of 0.910 to 0.940 g/cm3. Based on this representation, the Federal Circuit concluded that a person experienced in the field could reasonably be expected to understand “below about 0.91 g/cm3” meant “below about 0.910 g/cm3.” The Federal Circuit reversed the judgment of literal infringement.

In other circumstances, the prosecution history may provide a definition for a claim term when none can be found in the specification. In Biotec Biologische Naturverpackungen GmbH & Co. KG v. Biocorp, Inc., 249 F.3d 1341 (Fed. Cir. 2001), the claim term read, “substantially water free,” but no definition or numerical range was provided in the specification. The court determined that “substantially water free” meant less than 5% water based on arguments to overcome a prior art reference which described a water content ranging from 5% to 30%. See also Day Int’l, Inc. v. Reeves Brothers, Inc., 260 F.3d 1343 (Fed. Cir. 2001); Cordis Corp. v. Medtronic Ave., Inc., 511 F.3d 1157 (Fed. Cir. 2008).

The prosecution history of any parent or grandparent application may also be considered as intrinsic evidence in the claim construction of the child application unless an argument is expressly rescinded. See Hakim v. Cannon Avent Grp., PLC, 479 F.3d 1313 (Fed. Cir. 2007); Ventana Med. Sys., Inc. v. Biogenex Lab’ies, Inc., 473 F.3d 1173 (Fed. Cir. 2006); Biovail Corp. Int’l v. Andrx Pharms., Inc., 239 F.3d 1297 (Fed. Cir. 2001); Elkay Mfg. Co. v. Ebco Mfg. Co., 192 F.3d 973 (Fed. Cir. 1999); Jonsson v. Stanley Works, 903 F.2d 812 (Fed. Cir. 1990).

Representations to foreign patent offices may also impact claim construction, although not always. U.S. courts will sometimes reject such evidence due to varying legal and procedural requirements for obtaining patent protection outside the U.S. See, e.g.AIA Eng’g Ltd. v. Magotteaux Int’l S/A, 657 F.3d 1264 (Fed. Cir. 2011). In Apple Inc. v. Motorola, Inc., 757 F.3d 1286 (Fed. Cir. 2014), Motorola obtained patents on “a system for encrypting data communications” in multiple jurisdictions. During prosecution in Japan, Motorola distinguished its invention from the prior art by representing that its system “never transmitted” certain data. The U.S. court used this statement during claim construction, and because Motorola conceded that “Apple did not infringe under this construction,” the court granted Apple’s motion for summary judgment of non-infringement.  Another example is provided by Gillette Co. v. Energizer Holdings, Inc., 405 F.3d 1367, 1374 (Fed. Cir. 2005). Although Gillette’s patents disclosed a multi-blade razor, Energizer argued that Gillette’s U.S. patent claimed only three-bladed razors. The district court adopted Energizer’s construction and denied the preliminary injunction. On appeal, the Federal Circuit reversed the district court’s construction and injunction denial because during prosecution at the EPO, Gillette represented that a virtually identical claim in Gillette’s European counterpart of its patent-in-suit would not exclude an arrangement with four or more blades. Id.; See also, Iris Connex, LLC v. Acer Am. Corp., 2016 U.S. Dist. LEXIS 118988, at *57-58 n. 9 (E.D. Tex. Sep. 2, 2016).


Consider the following suggestions to avoid a narrow construction based on prosecution history.

  • Be mindful of gratuitous statements or arguments that unnecessarily define or characterize the claimed invention or the prior art during prosecution, which can unintentionally trigger a narrow claim construction.

  • Avoid amending claims more narrowly than necessary to avoid the known prior art.

*Stacy Lewis, a Law Clerk at Finnegan, contributed to this article.

© 2021 Finnegan, Henderson, Farabow, Garrett & Dunner, LLP
National Law Review, Volume XI, Number 130