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Claim Construction Under 35 U.S.C. § 112, ¶ 6 Found Unduly Restrictive Brett G. Alten

02-1024
March 31, 2003

Decision icon Decision

Last Month at the Federal Circuit - April 2003

Judges: Bryson (author), Mayer, and Friedman

In Northrop Grumman Corp. v. Intel Corp., No. 02-1024 (Fed. Cir. Mar. 31, 2003), the Federal Circuit reversed the district court’s judgment of noninfringement of a patent for a serial bus interface unit and remanded the case on the ground that the district court had erred in its claim construction.

Northrop Grumman Corporation (“Northrop”) is the assignee of U.S. Patent No. 4,453,229 (“the ’229 patent”), entitled “Bus Interface Unit.” In late 2000, Northrop filed suit in the United States District Court for the Eastern District of Texas against several Defendants (collectively “3Com”), alleging that the Defendants had infringed several claims of the ’229 patent.

The district court adopted a SM’s recommendations with regard to three claim construction issues and ruled in the Defendants’ favor on the issue of infringement. The district court subsequently entered a final judgment under Fed. R. Civ. P. 54(b), and Northrop appealed.

Claims 1 and 13 are directed to a bus interface unit that supervises the exchange of data between a host computer and a network serial bus. Both claims included, in essentially identical form, “means for monitoring” and “means for defining.” Northrop argued that the district court had erroneously construed those two limitations, as well as the term “bus interface unit,” by interpreting each of them as limited to devices employing a command/ response protocol.

The Federal Circuit agreed that the district court had properly determined that the “means for monitoring,” recited in claims 1 and 13, performs two functions: “monitoring a plurality of logical signals characterizing the operational status of the bus interface unit” and “generating a plurality of control signals regulating a data transfer process.” The Court also agreed that the written description made clear that certain sequence logic performed the monitoring and generating functions, and that the structures within the sequence logic include, at a minimum, an AND array, an OR array, and a number of flip-flops.

The Federal Circuit disagreed, however, that additional elements were also required as part of the corresponding structure, even though the district court had identified those additional elements as directly tied to the claimed functions. The Federal Circuit acknowledged that under 35 U.S.C. § 112, ¶ 6, structure disclosed in the specification is corresponding structure only if the specification or the prosecution history clearly links or associates that structure to the function recited in the claim. Features that do not perform the recited function do not constitute corresponding structure and, thus, do not serve as claim limitations. Thus, the Federal Circuit concluded that the additional elements identified by the district court could not be part of the structure corresponding to the functions of the “means for monitoring” limitation because they concerned other functions.

Next, the Federal Circuit considered the limitation “means for defining a functional state of the bus interface unit.” The district court had previously held that the function of the “means for defining” is to define the functional state of the bus interface unit, and concluded that such function requires, at a minimum, determining whether the bus interface unit is functioning in the bus controller or remote terminal mode. The district court had also determined that this necessarily involved monitoring an operating mode signal and identified the corresponding structure, including, at a minimum, an AND array, an OR array, the operating mode signal, and flip-flops of the state register necessary to define the bus interface unit as functioning in either a bus controller or remote terminal mode, and any equivalents thereof.

As in the case of the “means for monitoring” limitation, the Federal Circuit ruled that the district court had defined the structure corresponding to the recited function too broadly. According to the Federal Circuit, the ’229 patent describes the structure corresponding to the function of defining a functional state of the bus interface unit as a set of flip-flops. The Federal Circuit therefore reversed the district court’s construction with respect to the “means for defining” and construed the structural component to include only the set of flip-flops.

The third claim construction issue raised on appeal was the district court’s construction of the term “bus interface unit” to mean “a bus interface unit capable of functioning as a bus controller or a remote terminal when connected to a biphase serial bus in a command/response system.” The Federal Circuit looked into whether the specification disavowed any embodiment other than one operating in a bus controller/remote terminal environment and concluded that the specification did not. The Federal Circuit considered the stated objectives of the ‘229 patent and statements made in the Background and Preferred Embodiment Sections of the patent, but did not find any reason to narrowly construe claims 1 and 13 for use only in the bus controller/remote terminal environment. Accordingly, the Federal Circuit declined to read the bus controller/remote terminal limitation into claim 1 or 13. Instead, the Federal Circuit accorded the term “bus interface unit” its ordinary meaning: a unit for interfacing with a serial data bus.

The Federal Circuit also noted that even though the inventors may have believed that the ’229 patent would be used principally in a command/ response environment, and that the patent referred repeatedly to the advantages of the invention in that context, these were not found to constitute a limitation on the scope of the invention. Absent a clear disclaimer of particular subject matter, the Federal Circuit found that even if an inventor anticipated that the invention would be used in a particular way does not mean that the scope of the patent is limited to that context.