IP Law Daily Anticipation findings for interference-reduction technique reversed due to improper claim construction
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Monday, March 19, 2018

Anticipation findings for interference-reduction technique reversed due to improper claim construction

By Thomas Long, J.D.

In a remand decision rejecting, on the ground of anticipation, claims 1, 17, 18, and 19 of a patent describing a technique for reducing electromagnetic interference noise, the Patent Trial and Appeal Board based its rejections on an unreasonably broad claim construction, the U.S. Court of Appeals for the Federal Circuit has held. Weighing in on the issue for the second time, the Federal Circuit determined that the Board’s construction of the claim term "coupled" was unreasonably broad and improperly omitted any consideration of the disclosure in the specification. The court determined—as it had previously—that a district court’s interpretation of the term as requiring two circuits to be connected in a manner "such that voltage, current or control signals pass from one to another" was correct, and under that construction, the anticipation rejections had to be reversed (In re Power Integrations, Inc., March 19, 2018, Mayer, H.).

Patent at issue. Power Integrations, Inc., held the patent at issue, U.S. Patent No. 6,249,876 ("the ’876 patent"), titled "Frequency Jittering Control for Varying the Switching Frequency of a Power Supply." The ’876 patent described a technique for reducing electromagnetic interference (EMI) noise "by jittering the switching frequency of a switched mode power supply." Claim 1 recited a digital frequency jittering circuit comprising (1) an oscillator with a control input for varying the switching frequency; (2) a digital to analog converter coupled to the control input; and (3) a counter coupled to the output of the oscillator and the convertor, which caused the converter to adjust the control input and to vary the switching frequency of the power supply. Claims 17 and 19 related to a method for varying the switching frequency using a varying voltage to control the oscillator. Independent claim 17, as amended, required "cycling a counter" to generate a secondary voltage that varied over time. This claim also contained the dispute claim term "coupled."

Previous litigation. In 2004, Power Integrations sued Fairchild Semiconductor International, Inc. and related parties (collectively "Fairchild") in the District of Delaware. It alleged that Fairchild had willfully infringed the ’876 patent, as well as three other patents. During claim construction proceedings, Power Integrations argued that the term "coupled" in claim 1 of the ’876 patent, when read in light of the specification and surrounding claim language, required two circuits to be connected in a manner "such that voltage, current or control signals pass from one to another." It further contended that the "recited coupling" between the counter and the digital to analog converter must be "present for the purposes of control." The district court adopted Power Integrations’ proposed claim construction, and also emphasized that the term "coupled" did not require a direct connection or preclude the use of intermediate circuit elements. In the wake of the trial court’s claim construction, Fairchild withdrew its anticipation argument and instead argued at trial that U.S. Patent No. 4,638,417 ("Martin") rendered claim 1 of the ’876 patent obvious. A jury returned a verdict of nonobviousness. On appeal, the Federal Circuit affirmed the jury’s finding that claim 1 of the ’876 patent was not invalid for obviousness.

In December 2016, the Federal Circuit affirmed a jury’s determination that claim 1 was not invalid as anticipated by Martin or Andrew C. Wang & Seth R. Sanders, Programmed Pulsewidth Modulated Waveforms for Electromagnetic Interference Mitigation in DC–DC Converters, 8 IEEE Transactions on Power Elecs. 596–605 (1993) ("Wang"). The court explained that while both Martin and Wang "reduce the EMI signature associated with a power supply’s oscillator," they "accomplish this reduction by varying the oscillator frequency through the use of a pseudo-random code stored in read-only memory (ROM)." In addition, in both Martin and Wang "[t]he ROM takes the output of the upstream counter as its input," and "then outputs a different, stored value to the digital-to-analog converter." Because Martin and Wang decoupled the counter and the digital to analog converter, the court concluded that substantial evidence supported the determination that these references did not disclose claim 1’s "coupled" limitation.

Reexamination proceedings. In December 2006, the USPTO granted Fairchild’s request for ex parte reexamination of claims 1, 17, 18, and 19 of the ’876 patent. The Board affirmed the USPTO examiner’s rejection of claim 1 as anticipated by Martin and Wang, as well as by Thomas G. Habetler & Deepakraj M. Divan, Acoustic Noise Reduction in Sinusoidal PWM Drives Using a Randomly Modulated Carrier, 6 IEEE Transactions on Power Elecs. 356–63 (1991) ("Habetler"). Relying on a definition in a generalist dictionary, the Board interpreted the term "coupled" as meaning "to join (electric circuits or devices) into a single … circuit." Under this construction, the Board held that Martin, Wang, and Habetler each disclosed a counter "coupled" to a digital to analog converter because the two components were joined in one circuit. The Board did not address the district court’s conclusion that claim 1’s "coupled" limitation required the counter and the digital to analog converter to be connected in a manner "such that voltage, current or control signals pass from one to another." The Board also affirmed the examiner’s rejection of claims 17, 18, and 19 as anticipated by Habetler.

In August 2015, the Federal Circuit vacated the Board’s decision because the Board had "failed to straightforwardly and thoroughly assess the critical issue of whether claim 1, when viewed in light of the specification and the surrounding claim language, requires the counter itself—and not the counter and a memory functioning together—to drive the digital to analog converter to adjust the control input and to vary the switching frequency of the power supply."

On remand, the Board again affirmed the examiner’s anticipation rejections. The Board reasoned that that a comparison of its claim construction with that of the district court was "unwarranted." In the Board’s view, a district court’s claim construction was "typically" narrower than the broadest reasonable construction of a term. In the remand decision, the Board continued to adhere to a generalist dictionary definition of the term "coupled." Power Integrations again appealed to the Federal Circuit.

Claim construction. The Federal Circuit noted that, even under the rubric of the broadest reasonable construction, the Board must "consider the claims in light of the specification and teachings in the underlying patent." In the court’s view, there was no reason that the broadest reasonable construction could not coincide with that of a district court adjudicating a lawsuit. The Federal Circuit agreed with the district court’s conclusion that "in light of the claim language and specification," the "coupled" limitation required a specific control relationship between the counter and the converter. The counter must be connected to the digital converter in a way that allowed the counter to pass "voltage, current or control signals" to it; that is, the counter itself drove the digital to analog converter. The Board’s construction, according to the appellate court, was too expansive because it would mean that every element anywhere in the same circuit was potentially "coupled" to every other element in that circuit, no matter how far apart they were, how many components were between them, or whether they were connected in series or in parallel. This construction did not define what type of functional relationship was required.

The court noted that claim 1 required the counter to "caus[e]" the converter to adjust the control input and to vary the switching frequency. Nothing in the claim language suggested that this requirement will be met if, as in the prior art, the digital to analog converter’s output varied based on data stored in a memory rather than according to signals relayed from the counter itself, the court explained. Moreover, the Board’s construction rendered claim language meaningless, because the phrase "the digital to analog converter [is] coupled to the counter" would be superfluous if, as the Board said, it meant only that the two components were in the same circuit. Most importantly, the Board’s construction was not supported by the specification, which explained that the patent was meant to create a more compact circuit. The court noted that every embodiment disclosed in the ’876 patent showed a counter that passed voltage, current, or control signals to the digital to analog converter. Nothing in the specification suggested that the claims could cover a system in which a memory separated the counter and the digital to analog converter and severed the requisite control relationship between them, as in the prior art.

Anticipation. Because the Board’s decision affirming the examiner’s rejection of claim 1 was based on an erroneous claim construction and the rejection was not supported under the proper construction, the court reversed the rejection of claim 1. In Martin, Wang, and Habetler, no voltage, current, or control signals passed from the counter to the digital to analog converter. In each of these references, the counter was separated from the digital to analog converter by a pre-programmed memory. The switching frequency changed based on data from the memory, rather than the output of the counter, as claim 1 required. The incorrect claim construction also required reversal of the anticipation rejections of claims 17, 18, and 19 because independent claim 17 contained a "coupled" limitation similar to that of claim 1.

The case is No. 2017-1304.

Attorneys: Howard G. Pollack (Fish & Richardson, PC) for Power Integrations, Inc. Nathan K. Kelley, U.S. Patent and Trademark Office, for Andrei Iancu.

Companies: Power Integrations, Inc.

MainStory: TopStory Patent TechnologyInternet FedCirNews

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