Today, the Federal Circuit issued a ruling in Lighting Ballast v. Philips on remand from the Supreme Court after the Teva decision changed the standard of review of a district court’s claim construction.  One of the more interesting parts of the case concerns the Federal Circuit’s deference now to the district court’s decision premised on extrinsic expert and inventor testimony that the limitation “voltage source means” connotes sufficiently definite structure to avoid interpreting the limitation as a means-plus-function limitation under 35 U.S.C. § 112 ¶ 6.

This provides good insight into the importance of prevailing on claim construction at the district court level based on extrinsic evidence, to which the Federal Circuit is now more inclined to defer, particularly in light of the Federal Circuit’s recent en banc decision that broadened when functional claim language is subject to § 112 ¶ 6 (see our June 17, 2015 post).


In February 2009, Lighting Ballast sued Philips Electronics for infringing U.S. Pat. No. 5,436,529 directed to electronic ballast circuitry that regulates high current flow in a fluorescent lamp where the electronic ballast can shield itself from destructive levels of current that occur when a lamp is removed or becomes defective.  Asserted Claim 1 includes a “voltage source means” limitation as follows:

voltage source means providing a constant or variable magnitude DC voltage between the DC input terminals.

The district court initially construed this as a means-plus-function limitation subject to interpretation under § 112 ¶ 6.  Because the district court found no corresponding structure in the patent specification, it ruled that the claim was invalid for being indefinite under § 112 ¶ 2.  But the district court changed its ruling in response to a motion for reconsideration, stating that its prior ruling “unduly discounted the unchallenged expert testimony” and “exalted form over substance and disregarded the knowledge of a person of ordinary skill in the art.”  The district court cited testimony from a technical expert and the named inventor that a person skilled in the art would understand the term “voltage source means” to correspond to a rectifier and, thus, the claim limitation had sufficient structure to avoid § 112 ¶ 6.

On appeal to the Federal Circuit, an initial panel decision in Jan. 2013 reversed the district court’s ruling and found the claim subject to § 112 ¶ 6 and  indefinite because the patent specification failed to disclose structure corresponding to the claimed function of that limitation.  The panel relied on the presumption that § 112 ¶ 6 applied because the claim limitation uses the term “means” and found that the expert testimony was not sufficient to overcome this presumption.  The Federal Circuit then took the case on review en banc to determine what deference is owed the district court’s claim construction, and decided to maintain its Cybor standard that affords no deference to the district court’s legal or factual determinations in construing claims. (see our Feb. 21, 2014 post).  The en banc Federal Circuit thus reinstated the original panel decision that had not deferred to the district court’s claim construction ruling.  But, afterwards, the Supreme Court in Teva ruled that the district court’s factual determinations require deference on appellate review, and remanded this case to the Federal Circuit for reconsideration (see our Jan. 23, 2015 post on Teva).


Judge Reyna wrote the decision for the panel, joined by Judges O’Malley and Lourie.  They addressed several claim construction and procedural issues (e.g., waiver of claim construction argument in district court), but this post will focus solely on the means-plus-function aspect.

The Federal Circuit found that the district court properly could consider extrinsic evidence “because the extrinsic evidence was ‘not used to contradict claim meaning that is unambiguous in light of the intrinsic evidence.”  The Federal Circuit “defer[red] to these factual findings, absent a showing that they are clearly erroneous”, the factual findings being described as follows:

For example, the district court determined that “while the ‘voltage source means’ term does not denote a specific structure, it is nevertheless understood by persons of skill in the lighting ballast design art to connote a class of structures, namely a rectifier, or structure to rectify the AC power line into a DC voltage for the DC input terminals.”  The district court went on to note that the language following “voltage source means” in the claim–“providing a constant or variable magnitude DEC voltage between the DC input terminals”–“when read by one familiar with the use and function of a lighting ballast, such as the one disclosed by the 529 Patent, [sic] would understand a rectifier is, at least in common uses, the only structure that would provide ‘a constant or variable magnitude DC voltage'”.  The district court further noted that “[i]t is clear to one skilled in the art that to provide a DC voltage when the source is a power line, which provides an AC voltage, a structure to rectify the line is required and is clear from the language of the ‘voltage source means’ term.”

The Federal Circuit also found that those “factual findings” were supported by the record based on testimony from the patent owner’s expert and the named inventor, stating:

Specifically, these factual findings are supported by the testimony of Dr. Roberts and Mr. Bobel [the named inventor].  Mr. Bobel testified in his deposition that the “voltage source means” limitation connotes a rectifier to one skilled in the art.  Mr. Bobel further explained that a battery could likewise provide the necessary DEC supply voltage described in the patent.  Similarly, Dr. Roberts explained that the “voltage source means” limitation suggests to him a sufficient structure, or class of structures, namely a rectifier if converting AC from a “power line source” to DC for a “DC supply voltage” or a battery if providing the DC supply voltage directly to the DC input terminals.  This expert testimony supports a conclusion that the limitations convey a defined structure to one of ordinary skill in the art.

The Federal Circuit, thus, affirmed the district courts ruling that the claim limitation “voltage source means” conveys sufficient structure to avoid application of § 112 ¶ 6.