Functional Claiming in Device Claims

A recent Patent Trial and Appeal Board case, Ex parte Matsushita, Appeal 2023-002685, Application 17/022,815 (PTAB October 23, 2024), brings up the thorny issue of the use of functional language in device claims. Depending on how the claim is phrased, functional language in a device claim can:

1) be treated as not having patentable weight,

2) be treated as means-plus-function limitations under 35 USC 112(f),

3) be treated as a claim limitation outside of 35 USC 112(f), or

4) be judged an impermissible mixing of method claim limitations in a device, rendering the claim indefinite.

The result in Ex parte Matsushita involved the last of these possibilities, so let’s start there, and then discuss the other three outcomes.

The main claim in the case involved a drive device that included “an overcurrent detection circuit detecting overcurrent flowing in a switching element based on voltage occurring in a shunt resistance connected to a source of the switching element,” and “at least one drive circuit applying potential of a connection node of the source of the switching element and the shunt resistance as reference potential and generating a drive signal being input to a gate of the switching element.” This was not to the Board’s liking, and they remanded the case with a new ground of rejection for indefiniteness, replacing the prior art rejection that the Examiner had made. The reasoning of the Board was brief on the issue of indefiniteness:

A single claim covering both an apparatus and a method of using that apparatus is indefinite because it is unclear what acts constitute infringement of the claim. IPXL Holdings, L.L.C. v. Amazon.com, Inc., 430 F.3d 1377, 1384 (Fed. Cir. 2005). In this case, apparatus claim 1 recites a “drive device” with components such as “an overcurrent detection circuit” as well as operational method steps such as “detecting overcurrent flowing in a switching element” and “generating a drive signal.” Additional claim language such as “being input to a gate of the switching element” is ambiguous as to whether the “gate of the switching element” is a required structure and whether the “being input” is a required method step of transmitting an input to the gate.

What could have been done instead to avoid what the Board saw as an impermissible inclusion of method language in a device claim? One obvious solution would be to put the language into means-plus-function form that invokes 35 USC 112(f), for example reciting “an overcurrent detecting circuit that includes means for detecting overcurrent flowing in a switching element.” But that solution has the downside that the claim scope would be limited to the particular means that are described in the specification and that a failure to describe any means could result in the claim being invalid for falling into the “Halliburton dead zone,” which I discussed here.

What then is an acceptable non-means-plus-function way of putting functional language into a device claim? Phrases such as “configured to,” “adapted to,” or “operable to,” have been used. An example would be “an overcurrent detection circuit configured to [or adapted to] detect overcurrent flowing in a switching element.” But an important follow-on question is, will such language be given patentable weight? That is, will a patent examiner give effect to such language when determining patentability, or will it be discarded from consideration?

Thanks for asking, but it’s hard to give a clear answer, so put that question aside for a bit. First, functional language can be indefinite, apart from using method claim language. This is addressed in MPEP 2173.05(g), which states that when “a claim limitation employs functional language, the examiner’s determination of whether the limitation is sufficiently definite will be highly dependent on context (e.g., the disclosure in the specification and the knowledge of a person of ordinary skill in the art)” (citing Halliburton Energy Servs., Inc. v. M-I LLC, 514 F.3d 1244, 1255 (Fed. Cir. 2008)).[1]  MPEP 2173.05(g) sets out a number of factors for the Examiner to consider in determining if functional language is indefinite:

“(1) whether there is a clear cut indication of the scope of the subject matter covered by the claim;

(2) whether the language sets forth well-defined boundaries of the invention or only states a problem solved or a result obtained; and

(3) whether one of ordinary skill in the art would know from the claim terms what structure or steps are encompassed by the claim.”

In an apparent attempt to offer some comfort to applicants, the MPEP then goes on to state, “During prosecution, applicant may resolve the ambiguities of a functional limitation in a number of ways,” followed by some enumerated examples.

Now, to address the deferred question of whether functional language in a device claim has patentable weight, we turn to MPEP 2114. There it states, “Features of an apparatus may be recited either structurally or functionally.” MPEP 2114(I). Yay! But then, “’apparatus claims cover what a device is, not what a device does.’” MPEP 2114(II) (quoting a Federal Circuit case). Okay. “A claim containing a ‘recitation with respect to the manner in which a claimed apparatus is intended to be employed does not differentiate the claimed apparatus from a prior art apparatus’ if the prior art apparatus teaches all the structural limitations of the claim.” Id. Fair enough (though that underlining is concerning). But it’s noteworthy that even “if the prior art device performs all the functions recited in the claim, the prior art cannot anticipate the claim if there is any structural difference.” MPEP 2114(III). Finally with regard to computer-implemented claims, “Functional claim language that is not limited to a specific structure covers all devices that are capable of performing the recited function.” MPEP 2114(IV).

So where does that leave us? If you want to use functional language in a device claim, and you want it to get patentable weight outside of the means-plus-function provision of 35 USC 112(f), here are some recommendations: 1) avoid gerunds, which are associated with method claims and means-plus-function recitations; 2) make sure the functional language provides a clear demarcation of scope, with support in the specification (and preferably with some recitation of structure, either in the claim at issue or a dependent claim), 3) don’t expect patentable weight to be given for mere recitations of a problem to be solved or a result obtained, and 4) don’t rely on a statement of intended use to have a patentable weight.

[1] N.B.: not anywhere near the same case as the one responsible for the aforementioned “Halliburton dead zone.”