LITTELFUSE, INC. v. MERSEN USA EP CORP.

Before Prost, Bryson, and Stoll.  Appeal from the U.S. District Court for the District of Massachusetts.

Summary: The Federal Circuit vacated a claim construction that violated the doctrine of claim differentiation by eliminating the scope of several dependent claims.

Littelfuse sued Mersen for patent infringement.  At Mersen’s behest, the district court construed two independent claims to require a multi-piece apparatus.  Littlefuse stipulated to noninfringement under this claim construction and appealed. 

The Federal Circuit held that the district court’s multi-piece construction of the independent claims was erroneous because four dependent claims required a single-piece apparatus.  Under the district court’s construction, these dependent claims were improperly rendered meaningless because they were left with no scope.  Thus, the Federal Circuit vacated the district court’s claim construction and judgment of noninfringement.