Prior art addressing different problem shows what was “common knowledge,” obviousness affirmedOctober 15, 2007

In a decision Friday, the Federal Circuit affirmed the rejection of all claims subject to reexamination as obvious. The USPTO had rejected the claims based on a combination of three prior art references.

The court provided an expansive discussion of obviousness post-KSR. The court noted that where the Federal circuit had gone wrong in KSR was holding that because a prior art reference did not address the same problem as the invention, it was not relevant, or at least less relevant, to the obviousness analysis. According to the court's opinion today, this "overlooks the fundamental proposition that obvious variants of prior art references are themselves part of the public domain."

As applied to this case, the court held that despite the fact that one prior art reference was directed to a different problem did not make the reference less relevant in the obviousness analysis. As stated by the court:

[The patentee] mistakenly argues that variants of a circuit connecting 2:1 multiplexers in series are not relevant prior art with respect to [the patent-in-suit] because these variants do not address the same problem, namely an improved multiplexer circuit. However, this argument overlooks the fundamental proposition that the series circuits in Gorai are prior art within the public domain and the common knowledge of a person of ordinary skill in the art. Thus, the Gorai reference is a relevant prior art reference with respect to the '666 patent and clearly discloses a series 2:1 multiplexer circuit.

Essentially, the court used the prior art to show what one of ordinary skill in the art would have in his or her base of knowledge. As a result, the USPTO's combination of prior art references, and the concomitant obviousness rejection, were affirmed.

Translogic Technology is the owner of a patent relating to multiplexers. Multiplexers are electrical circuits that have multiple inputs, at least one control line, and a single output. The signals on the control line(s) select the input that should, at a given time, be passed through to the output. In the claimed invention, a series of transmission gate multiplexers, or TGMs (a particular type of multiplexer) are coupled together in series. An example of this schematic is Figure 3 of the patent below:

A, B, and C are the transmission gate multiplexers, I0-I3 are the inputs, S1-S3 are the control lines, and Z is the output. The invention claims either a 4:1 or a 5:1 multiplexer, using three TGMs connected in series.

Translogic sued Hitachi , among others, for infringing its patent. Hitachi filed five requests for ex parte reexamination over the course of several years, and the various reexaminations were consolidated. The USPTO eventually finally rejected the claims based on a combination of three prior art references:

Gorai, R.K., and Pal, A., Automated synthesis of combinational circuits by cascade networks of multiplexers, IEE Proc., Vol. 137, Pt. E, No. 2, March 1990, pages 164-170. Weste, Neil H.E., and Eshraghian, Kamran, Principles of CMOS VLSI Design: A Systems Perspective (Addison-Wesley Publ. Co. 1985), pages 14-17 and 172-175. Tosser, A.J., and Aoulad-Syad, D., Cascade networks of logic functions built in multiplexer units, IEE Proc., Vol. 127, Pt. E, No. 2, March 1980, pages 64-68.

Translogic appealed the final rejection.

The Federal Circuit first addressed the teachings of the three references. Gorai taught three stage multiplexers with four inputs and three control inputs, but did not disclose use of TGMs. Weste disclosed a single TGM circuit, but not TGMs connected in series. Tosser disclosed a 4:1 multiplexer from three 2:1 multiplexers in series, but, like Gorai, did not disclose the use of TGMs.

After resolving a claim construction issue, the court then turned to the obviousness determination. The court addressed KSR, and specifically the error committed by the Federal Circuit that the Supreme Court addressed. As described by the court:

On one level, KSR corrected a rather straightforward error. The error appears right before footnote 3 in this court's opinion:

In this case, the Asano patent does not address the same problem as the '565 patent. The objective of the '565 patent was to design a smaller, less complex, and less expensive electronic pedal assembly. The Asano patent, on the other hand, was directed at solving the "constant ratio problem."

This passage overlooks the fundamental proposition that obvious variants of prior art references are themselves part of the public domain.

. . .

The Supreme Court highlighted that error in its opinion:

The primary purpose of Asano was solving the constant ratio problem; so, the court concluded, an inventor considering how to put a sensor on an adjustable pedal would have no reason to consider putting it on the Asano pedal. Common sense teaches, however, that familiar items may have obvious uses beyond their primary purposes, and in many cases a person of ordinary skill will be able to fit the teachings of multiple patents together like pieces of a puzzle. Regardless of Asano's primary purpose, the design provided an obvious example of an adjustable pedal with a fixed pivot point; and the prior art was replete with patents indicating that a fixed pivot point was an ideal mount for a sensor. The idea that a designer hoping to make an adjustable electronic pedal would ignore Asano because Asano was designed to solve the constant ratio problem makes little sense.

This is relevant because Translogic argued that Gorai was not prior art for obviousness purposes, because it addresses a different problem and also teaches away from using TGMs. In this regard, the court stated that:

In its prior art argument, Translogic is making the same error corrected by the Supreme Court in KSR. Translogic mistakenly argues that variants of a circuit connecting 2:1 multiplexers in series are not relevant prior art with respect to the '666 patent because these variants do not address the same problem, namely an improved multiplexer circuit. However, this argument overlooks the fundamental proposition that the series circuits in Gorai are prior art within the public domain and the common knowledge of a person of ordinary skill in the art. Thus, the Gorai reference is a relevant prior art reference with respect to the '666 patent and clearly discloses a series 2:1 multiplexer circuit.

Having addressed that Gorai was properly considered in the obviousness analysis, the court then had little difficulty affirming the obviousness determination, stating that "[w]hile other circuits could have been used to implement the 2:1 multiplexers, TGMs were a well-known circuit as shown by the explanation of TGM circuits in the 1985 textbook by Weste." As a result, the rejection of the claims as obvious was affirmed.

This case is potentially important, as it addresses the role of what, before KSR, may have been considered "non-analogous art" in the obviousness analysis. Here, the court used prior art addressed to a different problem to show the "common knowledge of a person of ordinary skill in the art." As a result, it appears that the problem addressed by the prior art is at least much less significant in the obviousness analysis, given that references directed toward solving different problems may still be considered to the extent they illustrate "common knowledge." This arguably conflicts with the Federal Circuit's decision in In re Icon Health & Fitness, where the court applied the traditional analogous art test, holding that a prior art reference was reasonably pertinent to the problem addressed by the invention. The decisions may be reconcilable if the three references in this case are considered to be in the same "field of endeavor," but the issue was not mentioned by the court.

To read the full decision in In re Translogic Tech., Inc., click here.