The U.S. Court of Appeals for the Federal Circuit affirmed a district court’s denial of judgment as a matter of law in connection with its construction of two claims from the two patents at issue and a jury determination that the claims of one of the patents were not infringed and that the claims of the other patent were both not infringed and invalid.  Mettler-Toledo, Inc. v. B-Tek Scales, LLC, Case Nos. 11-1173; -1200 (Fed. Cir., Feb. 8, 2012) (Moore, J.).

Plaintiff Mettler sued defendant B-Tek alleging infringement of two patents relating to technology for weighing objects, such as large commercial trucks.  The patents describe a load cell that measures a force by utilizing a counterforce attached to a circuit board.  The circuit board uses a bridge circuit to create an analog electrical signal corresponding to the object’s weight.  This analog signal is then converted to a digital signal by an analog-to-digital (A/D) converter and then sent to a microprocessor. 

In relevant part, the independent claim at issue required the following means-plus-function limitations: “circuit means associated with said counterforce, said circuit means being responsive to external control,” “means for producing digital representations of loads applied to said counterforce” and “means for transmitting said digital representations.”  For each of these limitations, the associated structure in the specification was limited to a single, preferred embodiment that included a multiple slope integrating A/D converter.  The A/D converter in the accused product was a delta-sigma A/D converter.  After the district court construed the claim element a limited to the disclosed corresponding structure and (structural) equivalents, a jury determined that the accused product did not infringe either literally or under the doctrine of equivalents.

The issue on appeal was whether the district court improperly construed the relevant claim terms to require a multiple slope integrating A/D converter rather than a more generic A/D converter, such as a delta-sigma A/D converter.  Mettler argued that the district court erred by applying only the structure of the preferred embodiment into the claim, reasoning that because A/D converters are well-known in the art, there was no reason to limit the structure to only the multiple slope integrating A/D converter.  Attempting to show that the specification disclosed both generic and multiple slope integrating A/D converters, Mettler also pointed out that figure 5 illustrated an “Analog to Digital Converter 100” and that the Abstract simply mentioned a generic A/D converter.

The Federal Circuit rejected these arguments since the specification only disclosed a single, preferred embodiment that only included the multiple slope integrating A/D converter.  In every instance in which the specification referred to an “A/D converter,” it only referred to the preferred embodiment.  Noting that structure disclosed in the specification is ‘corresponding’ structure only if the specification clearly links or associates that structure to the function recited in the claim, the Federal Circuit affirmed the district court’s holding. 

Practice Note:  If a patentee chooses to disclose a single embodiment, it runs a risk that any means-plus-function claim limitation will be limited to the single disclosed structure and equivalents thereof.  Accordingly, when writing a means-plus-function claim, it is advisable to make certain that more than one structure is described in the written description and, if possible, name as many equivalents as possible.