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Allegedly Inadvertent Amendment Bars Any Scope of Equivalence

January 23, 2001

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Last Month at the Federal Circuit - February 2001

Judges: Mayer (author), Newman, and Lourie

In Pioneer Magnetics, Inc. v. Micro Linear Corp., No. 00-1012 (Fed. Cir. Jan. 23, 2001), the Federal Circuit affirmed a judgment of noninfringement based on prosecution history estoppel, relying on its decision in Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 234 F.3d 558 (Fed. Cir. 2000) (en banc).

Pioneer Magnetics, Inc. (“Pioneer”) owns U.S. Patent No. 4,677,366 (“the ’366 patent”) that is directed toward a switched power supply, in particular, electrical circuits for converting alternating current to a constant output voltage. Pioneer sued Micro Linear Corporation (“Micro Linear”) for patent infringement of the ‘366
patent. During a Markman briefing, the parties requested the district court to identify what scope of equivalents of a “switching multiplier” limitation, if any, was barred by prosecution history estoppel. The district court interpreted the claims and ruled that a “non-switching multiplier” is outside the proper scope of equivalents, given the amendments made during prosecution. The parties then stipulated to SJ of noninfringement, and Pioneer appealed.

During prosecution of the ‘366 patent, in response to a prior art rejection, Pioneer added two limitations to the independent claim, namely “switching analog multiplier circuit,” and “pulse-width modulator.” In the Remarks, Pioneer stated that the reference cited by the Examiner did not disclose the combination as set forth in the amended claim, but Pioneer provided no explanation for the addition of the “switching “ limitation.

At the district court level, Keith Beecher, the patent attorney who had prosecuted the ‘366 patent, submitted a Declaration stating that the “switching” limitation was added inadvertently. Specifically, the independent claim was said to have been amended to include the limitations of a dependent claim, and that dependent claim did not include the “switching” limitation. Thus, Pioneer argued that the inclusion of the “switching” limitation was obviously inadvertent.

The Federal Circuit refused to consider the Beecher Declaration, concluding, based on Festo, that only the public record of a patent’s prosecution may be used to establish a reason for an amendment. The Court also concluded that regardless of the Beecher Declaration, inadvertence was not an acceptable reason to overcome the estoppel in this case. According to the Court, although the Remarks section of the Amendment at issue indicates that Pioneer had amended claim 1 to state dependent claim 6 in independent form, it is equally possible that Pioneer had intentionally added the “switching” limitation, but inadvertently failed to update the Remarks. Moreover, according to the Court’s review of the prosecution history, Pioneer had voluntarily amended the claims to avoid prior art, which raises the estoppel issue. Under Festo, the Court concluded, it need not speculate as to the materiality of the amendment. Thus, the Federal Circuit affirmed the judgment of noninfringement.