By Ambar Nayate, Shumaker & Sieffert, P.A.

In Williamson v. Citrix,[1] the Federal Circuit changed the analysis for when a claim term is a mean-plus-function limitation in accordance with 35 U.S.C. § 112(f).[2]  The Federal Circuit removed the heightened standard that a term does not invoke § 112(f) if the term “means” is not used and stated, “The standard is whether the words of the claim are understood by persons of ordinary skill in the art to have a sufficiently definite meaning as the name of structure.”[3]  If a term is deemed to invoke §112(f), and there is not sufficient structural support for the term in the patent disclosure, the claim is indefinite under 35 U.S.C. § 112(b).[4]

As a brief review of Williamson, the question was whether “distributed learning control module” in claim 8 of the asserted patent[5] invoked § 112(f).  The Federal Circuit found the term “module” to be a nonce word that can operate as a substitute for “means” in § 112(f)[6] and further determined that “distributed learning control” does not impart structure to the term “module.”[7]  On this basis, the court found that “distributed learning control module” invokes § 112(f).  Turning to § 112(b), the court was unable to identify corresponding structure for “distributed learning control module” in the specification. 

Although the Federal Circuit considered expert testimony that one of ordinary skill in the art would understand the term “distributed learning control module” to connote structure based on knowing how to program a computer to perform the functions after reviewing the specification,[8] the court stated that the mere ability of one of skill in the art to program the computer to perform the functions does not create structure where none is otherwise disclosed.[9]  Ultimately, the court found claim 8 indefinite under § 112(b) because there was no corresponding structure for the term that invoked § 112(f).

For patent practitioners looking to avoid invocation of § 112(f), the natural question presented is: What words have a sufficiently definite meaning as the name of structure?  Fortunately for patent practitioners, MPEP § 2181(I)(A) provides a list of words that the Federal Circuit has found to not invoke § 112(f).

There are two words conspicuously missing from the list: “processor” and “controller.”  Like all terms in a claim limitation (even “means”), there is no bright-line rule for whether a given term invokes § 112(f).  While the Federal Circuit has not opined directly on “processor” and “controller,” there have been decisions by the Board of Patent Appeal and Interferences (BPAI)[10] and district courts addressing these terms.  The appeal board and court decisions are split as to whether “processor” invokes § 112(f), however, and there is insufficient case development for whether “controller” invokes § 112(f).  Patent practitioners should therefore rely on best practices for properly defining terms instead of blindly relying on case law that remains ambiguous.

The U.S. Patent and Trademark Office provides “informative opinions” on functional claiming available at:  In these opinions, the BPAI determined that the term “processor” is a nonce word that merely substitutes for means plus function language, is not the name of structure, and invokes § 112(f).  The four decisions identified as informative are: Ex Parte Lakkala,[11] Ex Parte Erol,[12] Ex Parte Smith,[13] and Ex Parte Cadarso.[14] 

Practitioners should review all four decisions, but this article uses Ex Parte Lakkala as illustrative of the reasoning used by the BPAI.  Claim 27 of the application at issue in Ex Parte Lakkala uses the term “processor” and claims the processor as performing various functions.  The BPAI stated that “[b]ased on our review of dictionary definitions, we conclude that a skilled artisan would not recognize ‘processor’ as the name of a sufficiently definite structure for performing the control functions recited by the ‘processor’ limitation.”[15]  The BPAI goes on to state, “Rather, a person skilled in the art of computer programming would recognize the term ‘processor’ to mean a general purpose computer, a central processing unit (“CPU”), or a program that translates another program into a form acceptable by the computer being used.[16]”  The BPAI noted that “[t]his interpretation is consistent with Appellant’s Specification, which refers only to a CPU, without providing a definition of ‘processor’ or any additional description sufficient to inform a skilled artisan that the term connotes a sufficiently definite structure.”[17]

Next, the BPAI turned its attention to whether a commercially available off-the-shelf processor could perform the claimed functions.  Concluding that there were functions that an off-the-shelf processor could not do, the BPAI determined “the claimed ‘processor’ alone is not sufficient structure to perform the functions in claim 27.”[18]

The BPAI took care to distinguish other cases where terms like processor were found to connote structure.  For instance, the BPAI contrasted the processor of claim 27 with “computing unit” as analyzed in Inventio AG v. ThyssenKrupp Elevator Americas Corp.[19] on the basis that, in Inventio, the computing unit was claimed to be connected to structure which was needed to perform the function.  But, in Ex Parte Lakkala, “claim 27 does not recite any structure connected to the ‘processor’ other than a memory device, which is not sufficient for performing the control recited functions,”[20] and “claim 27 [does not] recite the specific steps that the processor undertakes to perform the recited control functions.”[21]

The BPAI also contrasted the term processor from circuit and circuitry by stating, “The term ‘circuit’ coupled with a description in the claims of the circuit’s operation typically conveys the structural arrangement of the circuit’s components.”[22]  The BPAI noted that “the recited processor and claim language here do not convey to a person skilled in the art anything about the internal components, structure, or specific operation of the processor.”[23]

In summary, the BPAI in Ex Parte Lakkala found that “processor” does not convey enough structure because the description did nothing to define a processor as structure.  The claim did not use terms known to connote structure, such as “circuit.”  Also, the application did not fully develop how the processor could perform the claimed functions.

Patent practitioners should take note of these lessons from Ex Parte Lakkala and the other informative opinions, and ensure that the specification is fully developed with respect to how the actual operations for implementing the function are being performed with examples of what is meant by a processor to provide the needed structure.  Patent practitioners should also review SyncPoint Imaging,[24] a district court opinion that found the term “processor” to not be a nonce term but rather a structural term in a class of structure.

Before reviewing the term “processor,” SyncPoint Imaging provides some guidance on the manner in which the analysis for whether a term invokes § 112(f) should be performed.  In Aristocrat Technologies, the Federal Circuit found that where a general-purpose computer or microprocessor is called out as performing a claimed function, the corresponding structure is not a general-purpose computer but rather the special-purpose computer programmed to perform the disclosed algorithm.[25]  SyncPoint Imaging, quoting Apple Inc. v. Motorola, Inc., 757 F. 3d 1286, 1298 (Fed. Cir. 2014), asserts that the Aristocrat rule applied only after § 112(f) has been invoked.[26]  Although Apple pre-dates Williamson, the court in SyncPoint Imaging found, based on Apple, that if a term does not invoke § 112(f), then an algorithm is not needed to provide the structure.[27] 

SyncPoint Imaging explains that the initial question is whether a term invokes § 112(f).  If the answer is no, then review of the specification for an algorithm is not needed to avoid indefiniteness.  If yes however, an algorithm is needed to provide structure to the term to satisfy § 112(b). 

With respect to the term “processor,” the court in SyncPoint Imaging relied on the ordinary definition of processor to find that processor connotes structure, and specifically noted that the plain definition of processor is the same as that of circuit.[28]  It is noted that the BPAI in Ex Parte Lakkala also relied on the plain meaning of processor and found that processor does not connote structure, which is opposite to conclusion in the SyncPoint Imaging that the plain meaning of processor connotes structure.

Furthermore, the court in SyncPoint Imaging found that “one of ordinary skill in the art would understand the structural arrangements of the processor from the recited objectives and operation of the processor.”[29]  To support this contention, the court cited to expert testimony for how one of skill in the art would know how to cause the processor to perform various functions.

This line of reasoning in the decision seems to be at odds with the reasoning in Williamson.  The Federal Circuit, in Williamson, quoted the declaration of an expert witness as follows: “Dr. Souri also testified that, ‘as one of ordinary skill in the art, reading the specification, I would know exactly how to program’ a computer to perform the recited functions and further testified that structure ‘could be in software or it could be in hardware.’”[30]  The Federal Circuit noted however, “But the fact that one of skill in the art could program a computer to perform the recited function cannot create structure where none is otherwise disclosed.”[31]

The reliance of the court in SyncPoint Imaging to explain that one of skill in the art would know how to perform various functions as providing sufficient structure, and the Federal Circuit in Williamson specifically avoiding reliance on one of skill in the art to provide sufficient structure appears to conflict.  Patent practitioners are better off providing algorithmic support even if using processor or circuit or another arguably-structural component.  In this way, the claim can still be found definite under §112(b) even if a claimed limitation is found to invoke §112(f).

As seen from Ex Parte Lakkala and SyncPoint Imaging, it is possible to start from a plain meaning of the same term—“processor”—and yet arrive at opposite conclusions: structural term according to SyncPoint Imaging and non-structural term according to Ex Parte Lakkala.  Patent practitioners should provide examples in the specification of what is meant by a processor, especially using structural components, so that over-reliance on extrinsic sources for defining the term can be minimized. 

Like “processor,” “controller” is another term where it may be unclear if the term connotes structure or not.  Sound View Innovations[32] analyzes the term “controller,” and based on the specific facts found that the term “controller” is structural and does not invoke § 112(f).

As with SyncPoint Imaging, the court in Sound View Innovations reviewed the plain meaning of controller and concluded that controller is not a nonce term that lacks structure.[33]  The court in Sound View Innovations stated that “‘[c]ontroller’ may be a class of structures, rather than one specific structure, and may be defined with functional terms, but that does not make it means-plus-function.”[34]

The court quoted col. 4, lines 52–57 of U.S. Patent No. 6,125,371 (one of the patents at issue), which states, “Those skilled in the art should be familiar with the use of controllers in processing environments generally and, more specifically, with main memory databases,” and “Controllers may be implemented in software, firmware, hardware or some suitable combination of at least two of the three.”  The court interpreted such language to mean that “‘controller’ connotes, not one particular type of controller, but controllers implemented in any of those mediums.[35]”  The court went on, “Put otherwise, this statement does not define the term ‘controller’ broader than the class of structures ‘controller’ would ordinary connote,” and that “[i]n fact, the patent stresses in that part that ‘controller’ is used in its ordinary sense.[36]

It should be noted that the ‘840 patent (the patent at issue in Williamson) states, “As understood in the art, the functionality of the DLS [distributed learning server] 102, presenter 106, and audience member 108 computer systems described below may be performed by software or hardware modules within the computer systems.[37]”  The ‘840 patent further states, “The modules according to one embodiment are software programs stored on the storage device 208, loaded into the memory 206, and executed by the processor 202.[38]”  DLS 102 includes distributed learning control module (DLCM) 310,[39] and as noted above, “distributed learning control module” was found to be non-structural. 

In Williamson, although the DLS 102, which includes DLCM 310, was described as being software or hardware modules, and when software, loaded into a processor and executed, the Federal Circuit still found that the phrase “distributed learning control module” is non-structural.  However, in Sound View Innovations, the court gave weight to the definition of controller being software or hardware as defining a specific type of controller, rather than a mere functional definition of a controller as being anything that controls.

The above analysis of case law shows that the application of § 112(f) remains in flux.  Further development in case law will be needed to better understand what terms connote structure and what the specification needs to provide to ensure that a term connotes structure. 

Patent practitioners should provide examples of terms such as “processor” and “controller” to root those terms as structural components by providing, for instance, a list of processor and controller types.  Moreover, patent practitioners should see whether it is possible or practical to describe the interconnection of components within the processor or controller to show the structural aspects of the terms.  At times, such description may not be practical or possible, as this will be case-by-case.  In any event, patent practitioners should describe the algorithm implemented by the processor or controller so that the operations of each is clear.  In particular, any operation that an off-the-shelf processor cannot perform should be described in detail with description of interactions between components in performing the operation.


[1] No. 2013-1130 (Fed. Cir. June 16, 2015).

[2] § 112, ¶ 6 (pre-AIA).

[3] Williamson, slip op. at page 16.

[4] In re Donaldson Co., Inc., 16 F. 3d 1189, 1195 (Fed. Cir. 1994).

[5] US 6,155,840.

[6] Williamson, slip op. at page 17.

[7] Williamson, slip op. at page 18.

[8] Williamson, slip op. at page 19.

[9] Id.

[10] The precursor to the Patent Trial and Appeal Board (PTAB).

[11] Appeal 2011-001526 in Application No. 10/949,656 March 13, 2013.

[12] Appeal 2011-01143 in Application No. 11/461,109 March 13, 2013.

[13] Appeal 2012-007631 in Application No. 12/579,383 March 14, 2013.

[14] Appeal 2010-008797 in Application No. 10/911,393 April 26, 2013.

[15] Ex Parte Lakkala page 10.

[16] Id.

[17] Ex Parte Lakkala pages 10 and 11.

[18] Ex Parte Lakkala page 12.

[19] 649 F. 3d 1350, 1359–1360 (Fed. Cir. 2011).

[20] Ex Parte Lakkala at page 12.

[21] Id.

[22] Ex Parte Lakkala at page 13.

[23] Id.

[24] SyncPoint Imaging, LLC v. Ninento of America Inc. et al, No. 2:2015cv00247 – Document 230 (E.D. Tex. 2016)

[25] Aristocrat Techs. Austl. Pty Ltd. v. International Game Tech., 521 F. 3d 1328, 1333 (Fed. Cir. 2008).

[26] SyncPoint Imaging at pages 38 and 39.

[27] SyncPoint Imaging at pages 38 and 39.

[28] SyncPoint Imaging at page 41.

[29] SyncPoint Imaging at page 42.

[30] Willamson at page 19.

[31] Id.

[32] Sound View Innovations, LLC., v. Facebook, Inc. No. 16-cv-116 (RGA) (D. of Del. 2017).

[33] Sound View Innovations at page 11.

[34] Id.

[35] Sound View Innovations at page 12.

[36] Id.

[37] ‘840 patent col. 4, lines 41–44.

[38] ‘840 patent col. 4, lines 44–46.

[39] ‘840 patent FIG. 3.