Last Week In The Federal Circuit (April 4 - 8): Claim Differentiation Carries The Day

Last week was argument week at the Federal Circuit, and we’ve already begun seeing decisions from the argued cases trickle in. Below we provide our usual weekly statistics and a detailed discussion of our case of the week—our highly subjective selection based on whatever case piqued our interest.

Precedential opinions: 2

Non-precedential opinions: 8

Rule 36: 3

Longest pending case from argument: Roche Diagnostics Corporation v. Meso Scale Diagnostics, LLC, No. 21-1609 (157 days)

Shortest (non-Rule 36) pending case from argument: Littelfuse, Inc. v. Mersen USA EP Corp., No. 21-2013 (26 days)

Case of the week: Littelfuse, Inc. v. Mersen USA EP Corp.

Panel: Judges Prost, Bryson, and Stoll, with Judge Bryson writing the opinion

You should read this case if: you have a matter involving claim construction, and particularly the principle of claim differentiation.

This week’s case of the week looks at the doctrine of claim differentiation. Littelfuse, Inc. owns a patent for fuse end caps to electrically connect a fuse and an electrical conductor. Littelfuse sued Mersen USA EP, Corp. but stipulated to non-infringement after the district court construed the claims to require a multi-piece construction.

The Federal Circuit rejected the district court’s claim construction based on claim differentiation, the specification, and the prosecution history. The Court found the structure of the claims “enlightening.” Independent claim 1 recites a fuse end cap with three elements. Dependent claims 8 and 9 further limit claim 1 by requiring that the end cap be formed “from a single, contiguous piece of conductive material.” The Court explained: “By definition, an independent claim is broader than a claim that depends from it, so if a dependent claim reads on a particular embodiment of the claimed invention, the corresponding independent claim must cover that embodiment as well.” A claim construction that leads to a different result “is generally disfavored.” Therefore, the Court reasoned, claim 1 must cover single-piece embodiments.

The Federal Circuit acknowledged that any presumption created by the doctrine of claim differentiation can be overcome but concluded that nothing in the written description or prosecution history dictated a different conclusion. The Court reviewed the specification’s description of three different embodiments: two where the end cap is machined or stamped from a “single piece of any suitable, electrically conductive material”; and one—an “assembled end cap”—where the terminal and mounting cuff are formed from two separate pieces of electrically conductive material that are joined together by, for example, a fastening stem. The Court noted that the descriptions of the single-piece embodiments do not mention a fastening stem, an element required by claim 1. The Court acknowledged this inconsistency but cautioned that courts should not limit the claimed invention to preferred embodiments or specific examples in the specification. After all, nothing in the specification states that a fastening stem cannot be present in a single-piece apparatus, and the Court concluded that the specification supports the construction of claim 1 to include both single-piece and multi-piece end caps.

Finally, the Federal Circuit turned to the prosecution history. During prosecution, the examiner had noted that the three embodiments described in the specification represented distinct species of claim 1 and issued a restriction requirement. Littelfuse initially elected the species corresponding to the “assembled end cap”, i.e., the multi-piece end cap. The examiner then withdrew dependent claims 8 and 9 since they were directed to the “machined end cap” and the “stamped end cap” embodiments. But Littelfuse later amended its claims to add a “fastening stem” element in response to a different rejection. The examiner then allowed claim 1 and rejoined dependent claims 8 and 9 after concluding that dependent claims 8 and 9 “require all the limitations of the allowable claims.” The Court concluded that this history also supported its construction of claim 1 to cover both multi-piece and single-piece end caps.