No Matter How You Festo It, a Non-Switching Multiplier Is Not Equivalent to a Switching Multiplier

In a case decided on remand from the U.S. Supreme Court, the U.S. Court of Appeals for the Federal Circuit has held that incompetence of a patent lawyer is not a defense to prosecution history estoppel and that, if related to patentability, even a voluntarily added limitation may limit, or eliminate, the available range of equivalents. Pioneer Magnetics, Inc. v. Micro Linear Corp., Case No. 00-1012 (Fed. Cir. June 6, 2003).

After a series of procedural motions, the district court construed the claims of the patent in suit to require a "switching analog multiplier circuit." As the accused devices had only "non-switching analog multiplier circuits," the plaintiff attempted to prove that a non-switching analog multiplier circuit is equivalent to a switching analog multiplier circuit.

The switching limitation was found in a dependent claim added after filing. The examiner rejected the original claims as anticipated. The reference applied did not disclose a switching multiplier.

When amending the claims, the Pioneer Magnetics' lawyer imported the switching limitation from the dependent claim into new claim 1. Contrary to the remarks accompanying the amendment, claim 1 now included all the limitations of the original claims, plus the switching limitation. The dependent claim still included the switching limitation as well as a "timer and ramp signal generator" limitation.

The district court ruled that because the switching limitation was added to overcome a cited reference, Pioneer Magnetics was not entitled to a range of equivalence on this element. Because none of the accused devices had a switching multiplier, the parties stipulated to a summary judgment of non-infringement. Pioneer Magnetics appealed.

The Federal Circuit, citing its 2000 en banc Festo decision, affirmed the district court's claim construction and the summary judgment. After Pioneer Magnetics petitioned the Supreme Court for a writ of certiorari, this case, along with a number of other cases, was remanded in light of the Supreme Court's decision in Festo.

Pioneer Magnetics fared no better under the new Festo. The Federal Circuit noted that because the amendment in question narrowed the claim, Pioneer Magnetics has the burden to show that the amendment was not related to patentability.

Relying on a mea culpa declaration from its patent lawyer, Pioneer Magnetics argued that adding the switching limitation was through "inadvertence." The Federal Circuit rejected this evidence because it was not part of the public record of the patent. Pioneer Magnetics also pointed to a discrepancy between only the amendment and the accompanying remarks to the affect that claim 1 was only amended to include the limitations from the original claims. Pioneer Magnetics argued that the remarks were evidence that the amendment was inadvertent. The Court disagreed, pointing out that it is equally likely that the mistake was in the remarks and the amendment was intended.

The Federal Circuit then considered whether Pioneer Magnetics could prove that the particular equivalent in issue, a non-switching multiplier, was unforeseeable at the time of the prosecution of the patent. Since the main cited reference in the case showed a non-switching multiplier, the Federal Circuit concluded that Pioneer Magnetics could not meet its burden that such a structure was not foreseeable at the time of the prosecution of the `366 patent.

Practice Note: Only the public record counts. The file history should clearly explain the reasons for what is going on, if the patent holder wants to rely on the reasons later. The patentee cannot try to explain its reasons for various prosecution activities in after-the-fact testimony from its patent lawyer.