A (Nonprecedential) Lesson on the Pitfalls of Means-Plus-Function Claiming
Professor Wegner calls the decision "an important case to teach patent draftspersons the importance of avoiding 'means' claiming." But perhaps a different lesson could be learned on the importance of tightly drafting such means limitaions, and/or on whether the law should require such a high level of specificity in linking disclosed structure to these limitations. Should a sloppy means-plus-function limitation should invalidate an entire claim where a simple "black box" disclosure and switch ("structure-is-function") limitation would have probably saved the day? Regardless of the scope of disclosure, shouldn't means-plus-function language actually be broader, and more functional, than the "structure-is-function" category of devices with implied structure that is loosely understood by those of ordinary skill. Cf "Structure, Function and the Spectrum of Patent Claiming," page 7, columns 3 and 4 (showing the current perverse state of the law).
The case involved Claim 1 of U.S. Patent No. 4,875,154 (above, issued in 1989, ten years before Amtel v. Info Storage Devices cited below):
According to the opinion by Circuit Judge Rader:
A microcomputer data processing apparatus, comprising:
 a Central Processing Unit (CPU) . . .
 first switch means comprised of at least three distinct parts of connecting said dedicated memory address, data, and control circuits of said path configuring means to each of said first three sets of contacts, and
 second switch means for connecting said dedicated memory address, data, and control lines of said path configuring means to said dedicated memory address, data, and control lines of said CPU respectively . . .
 means for causing said first and second switch means to remain in said non signal-conducting state upon application of power to said CPU power circuit and to assume a signal-conductive state upon receipt of an appropriate signal from said CPU, and to
 assume a non signal-conducting state upon receipt of an appropriate signal from said CPU.
Mitchell appears to be arguing that a person of ordinary skill in the art would be able to ascertain the corresponding structure by combining a variety of passages in the specification with their knowledge of the art. However, "in order for a claim to meet the particularity requirement of ¶ 2, the corresponding structure(s) of a means-plus-function limitation must be disclosed in the written description in such a manner that one skilled in the art will know and understand what structure corresponds to the means limitation." Atmel Corp. v. Info. Storage Devices, Inc., 198 F.3d 1374, 1382 (Fed. Cir. 1999). Thus, the statute requires more than just the possibility that an artisan of ordinary skill may be able to figure out the corresponding structure. The quid pro quo for using a meansplus-function limitation requires specificity in reciting structure and linking that structure to the limitation. Id. Mitchell does not carry out its part of the quid pro quo bargain. This court sustains the finding that claim 1 is indefinite under U.S.C. § 112, ¶ 2.
This court need not reach the "switch means" and "path configuring means" limitations because the district court's decision can be affirmed solely on the "means for causing" limitation.