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Multiplexer Patent Held Invalid as Obvious over Combination of References

October 12, 2007

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Last Month at the Federal Circuit - November 2007

Judges: Mayer, Rader (author), Prost

[Appealed from: Board]

In In re Translogic Technology, Inc., No. 06-1192 (Fed. Cir. Oct. 12, 2007), the Federal Circuit affirmed the Board’s determination during reexamination that U.S. Patent No. 5,162,666 (“the ’666 patent”) was obvious at the time of the invention over a combination of prior art references.

The ’666 patent discloses and claims a configuration of multiplexers connected in series. Multiplexers are electronic circuits that have a certain number of inputs and an appropriate number of control lines to select one of the inputs to use as the output. A 2:1 multiplexer is a multiplexer with two inputs (not including one control line) and one output. The ’666 patent claims multiplexers created by connecting multiple 2:1 multiplexers in series. Each relevant claim explicitly defines each 2:1 multiplexer to be a transmission gate multiplexer (“TGM”). By stringing together multiple 2:1 TGMs, it becomes possible to build multiplexers with more inputs, such as 4:1 and 5:1 multiplexers. These 4:1 and 5:1 multiplexers are described as having multiple stages, with one stage corresponding to each 2:1 TGM multiplexer.

Translogic Technology, Inc. (“Translogic”) sued Hitachi, Ltd. et al. (“Hitachi”) for infringement of the ’666 patent. Hitachi filed multiple reexamination requests, which were merged by the PTO into a single proceeding. The Board held that numerous claims would have been obvious at the time of the invention. Translogic appealed.

In the meantime, the district court case continued in parallel. A jury upheld the ’666 patent as valid and the district court granted Translogic’s motion for SJ of infringement against Hitachi. The jury awarded over $80 million in damages and the district court entered a permanent injunction. Hitachi appealed the district court result to the Federal Circuit as well. The Federal Circuit stayed the lower court’s injunction and combined Hitachi’s appeal with Translogic’s appeal from the Board.

On appeal, the Federal Circuit first considered the construction of the claimed phrase, “control input terminal coupled to receive a control signal.” (Emphasis added.) The Board construed “coupled to receive” to mean a “[t]erminal capable of receiving a control signal” and not including the control signal itself. Translogic argued that the Board should have followed the claim construction from the district court. Specifically, the district court determined that “signal input terminal ‘coupled to receive’ an input variable” meant “connected to receive an input variable, directly or through one or more intervening inverters or buffers.” The Federal Circuit noted that under the district court’s construction, the claims would require each input and control input terminal to be connected to receive a variable signal from a different source. According to Translogic, the Gorai prior art reference did not disclose that each input and control input terminal must receive a variable signal from a different source. Instead, Translogic argued that Gorai teaches logic circuits with input terminals coupled to share signals and receive constants.

The Federal Circuit concluded that the words of the claim coupled with the specification supported the Board’s construction. The Court first noted that the claim terms did not specify any structural connection for the input terminals. Furthermore, the figures in the ’666 patent showed no structural connection for the input terminals. Moreover, the Court found that, as Translogic admitted, “as is proper for a structural circuit, the input variables (i.e., signals) are not part of the claimed invention.” Slip op. at 13.

The Court also found that the Board’s construction was supported by comparing the phrases “coupled to” and “coupled to receive,” both of which appeared in the claims. Specifically, the Court found that “coupled to” was used in the claims to define a connection between two circuits, whereas “coupled to receive” did not specify a particular connection. The Court concluded that the different usage of the two phrases supported the Board’s construction that “coupled to receive” meant merely “capable of receiving.”

After construing the disputed claim term, the Court turned to the Board’s holding of obviousness. Translogic disputed the relevance of the Gorai reference, arguing that it did not specifically disclose an N:1 series multiplexer but only disclosed an algorithm to realize logic functions by using 2:1 multiplexers connected in series. The Federal Circuit rejected this argument, explaining that “Translogic is making the same error corrected by the Supreme Court in KSR [International Co. v. Teleflex Inc., 127 S. Ct. 1727 (2007)].” Slip op. at 18. Specifically, the Federal Circuit explained that Gorai need not be directed to the same problem as the ’666 patent in order to qualify as relevant prior art. Instead, the Gorai reference was relevant because it was “prior art within the public domain and the common knowledge of a person of ordinary skill in the art.” Id. at 19.

The Court further rejected Translogic’s argument that there was no specific teaching, suggestion, or motivation to combine Gorai—which did not disclose the use of TGMs for each multiplexer stage—with the Weste reference, which disclosed a TGM circuit. The Court explained that “an obviousness analysis ‘need not seek out precise teachings directed to the specific subject matter of the challenged claim, for a court can take account of the inferences and creative steps that a person of ordinary skill in the art would employ.’” Id. at 20 (quoting KSR, 127 S. Ct. at 1741). The Court found that TGMs were well-known multiplexer circuits and, thus, “in looking for a multiplexer circuit for the individual 2:1 multiplexers disclosed in Gorai, a person of ordinary skill in the art would have solved this design need by ‘pursu[ing] known options within his or her technical grasp.’” Id. (quoting KSR, 127 S. Ct. at 1742). The Court thereby affirmed the Board’s holding of obviousness.