Functional Claiming

The term "functional claiming" encompasses two distinct concepts under U.S. patent law. The first is expressly provided for by statute - specifically, 35 U.S.C. § 112(f)1 - which provides that an element in a claim may be expressed as a means or step for performing a specified function without reciting structure in the claim. This so-called "means plus function" claiming has, over the years, lost favor as courts have applied increasingly narrow interpretations to such claims and have imposed increasing burdens on the use of such claims2. But "functional claiming" also refers more generally to claiming parts of an invention by what they do (their functions), rather than reciting their structure. This paper is primarily concerned with the latter method of claiming.

Beyond the requirements for novelty and nonobviousness, the patent statute requires that inventions be claimed in such a way as to be supported and enabled by the written description of the invention3. It also requires that inventions be claimed with particularity4. Nothing in the patent statute prohibits an invention from being claimed using "functional" language. But a review of the case law suggests that the use of so-called "functional" language in a patent claim may increase the likelihood that the claim will be held unpatentable or invalid. Consider the following hypothetical claim:

Claim 1: An apparatus configured to:

receive a satellite signal; process the signal to detect a synchronization indicator; extract the synchronization indicator; and display the synchronization indicator on a display device. Why would anyone want to draft such a patent claim? The natural reason is that it is exceedingly broad in scope5. This claim, if granted, would apparently cover any and every apparatus that is "configured to" perform the functions recited in the body of the claim. It would be exceedingly difficult to design around such a claim unless the functions of the accused device were different from those recited in the claim. Yet the validity or scope of such a claim -- and similarly "functional" claims -- might be subject to attack on a number of grounds, each of which is discussed separately below.

1. Failure of Enablement or Written Description -

   Scope of Claim Exceeds Scope of Disclosure

   A first line of attack would be to challenge the validity of the hypothetical claim on the basis that it is not fully enabled, or that it lacks sufficient written description support in the specification. Because the hypothetical claim purports to include every type of apparatus that performs the recited functions, its breadth is likely not commensurate in scope with the scope of the structures disclosed in the specification for performing such functions. In LizardTech, Inc. v. Earth Resource Mapping, Inc.6, the Federal Circuit held that a patent claim was invalid on the basis that it was broader than was enabled by or described in the patent specification.7

   LizardTech's patent specification repeatedly described a compression process as "seamless," and the prosecution history also emphasized that it was "seamless." According to the Federal Circuit, the specification only described a single way of performing a "seamless" compression, but that single way was not recited in the claim at issue. The court stated that "a person of skill in the art would not understand how to make a seamless DWT generically and would not understand LizardTech to have invented a method for making a seamless DWT, except by 'maintaining updating sums of DWT coefficients,'"8 a feature that was not recited in the claim. Therefore, the claim was held to be invalid because the full breadth of the claim scope was not enabled.

   Judge Bryson, writing for the court, drew an analogy to claiming an automobile engine:

   By analogy, suppose that an inventor created a particular fuel-efficient automobile engine and described the engine in such detail in the specification that a person of ordinary skill in the art would be able to build the engine. Although the specification would meet the requirements of section 112 with respect to a claim directed to that particular engine, it would not necessarily support a broad claim to every possible type of fuel-efficient engine, no matter how different in structure or operation from the inventor's engine. The single embodiment would support such a generic claim only if the specification would "reasonably convey to a person skilled in the art that [the inventor] had possession of the claimed subject matter at the time of filing" . . . and would "enable one of ordinary skill to practice 'the full scope of the claimed invention.'"9 The Federal Circuit invalidated a claim based on a similar rationale in National Recovery Technologies, Inc. v. Magnetic Separation Systems, Inc.10 As explained by the court, "The case before us presents a classic example of a claim that is broader than the enablement as taught in the specification."11

   And in Automotive Technologies International v. BMW of North America12, a means-plus-function claim limitation that was asserted to cover both a mechanical sensor and an electronic sensor was held to be invalid because "the full scope [of the claim] must be enabled, and the district court was correct that the specification did not enable the full scope of the invention because it did not enable electronic side impact sensors."13 Although the patent specification provided a detailed description of a mechanical sensor, it provided only a cursory description of an electronic sensor, thus dooming the claim.

   Given that the patent system was created to promote innovation by encouraging the disclosure of useful inventions to the public and promoting progress in the arts, the policy of invalidating "overly broad" claims would appear to further the goals of the patent system. If an inventor is able to develop a drug that cures cancer, for example, it seems unthinkable that he or she should be able to claim the drug by merely reciting "A drug having a composition that cures cancer." 14 Such a broad claim, if upheld, would clearly stifle further innovation in the field of cancer research. Patent applicants therefore should be mindful of overreaching by claiming an invention using nothing more than functional language.15

2. Indefiniteness: Improper Mixing of Statutory Invention Categories

   A second possible attack on the hypothetical claim would be to allege that it is indefinite because it improperly mixes two statutory categories of invention - a machine (apparatus) and a method (process steps). More specifically, the preamble purports to define the statutory category of the invention as an apparatus, but the body of the claim recites only functions or steps.

   The Federal Circuit invalidated a claim on that basis in IPXL Holdings, L.L.C. v. Amazon.com, Inc.16 A dependent claim that recited "the system of claim 2 wherein . . . the user uses the input means to either change the predicted transaction information or accept the displayed transaction type and transaction parameters" was held to be indefinite and thus invalid. Noting that "[w]hether a single claim covering both an apparatus and a method of use of that apparatus is invalid is an issue of first impression in this court," the Federal Circuit held that the claim was indefinite because it was unclear whether infringement of the claim occurred upon creation of a system that allowed the user to perform the recited step, or whether infringement occurred only when the user actually used the claimed apparatus in the recited manner.17

   A district court invalidated two patent claims because they improperly mixed apparatus and method categories of invention. In HTC Corp. v. IPCom GMBH & Co., KG18, the invention related to a synchronization technique for mobile telephones. Claim 1 of the patent recited the following:

   1. A mobile station for use with a network including a first base station and a second base station that achieves a handover from the first base station to the second base station by:

   storing link data for a link in a first base station,

   holding in reserve for the link resources of the first base station, and

   when the link is to be handed over to the second base station:

   initially maintaining a storage of the link data in the first base station,

   initially causing the resources of the first base station to remain held in reserve, and

   at a later timepoint determined by a fixed period of time predefined at a beginning of the hand-over, deleting the link data from the first base station and freeing up the resources of the first base station, the mobile station comprising:

   an arrangement for reactivating the link with the first base station if the handover is unsuccessful. [emphasis added]19

   As can be seen in the italicized text above, the claim preamble begins by defining the invention in terms of an apparatus (a mobile station), but the body of the claim contains several functions or steps that appear to define a method. The court concluded that although this claim and another similar claim recited an apparatus, they also recited six method steps in a way that described the apparatus as actually performing the method. According to the court, "Claims One and Eighteen improperly claim both an apparatus and method steps and thus are indefinite and invalid."20 So the lesson from this case is that failure to recite sufficient structure in an apparatus claim, while reciting primarily functions or steps in the claim, may lead to invalidity. For a contrary result, see Toshiba Corp. v. Juniper Networks, Inc21. Although the Federal Circuit ultimately reversed the district court's decision in the HTC case,22 the risk of an adverse judgment can be avoided by taking care during the claim drafting process.

   The Federal Circuit revisited the mixed-category claim issue in Microprocessor Enhancement Corp. v. Texas Instruments Inc.23 In that case, a method claim that recited many structural details of the...