When is a limitation that does not use the operative term "means" still a means plus function limitation?

Massachusetts Institute of Technology (MIT) and Electronics for Imaging, Inc. (EFI) are the assignee and exclusive licensee of U.S. Pat. No. 4,500,919 (’919 Patent) which discloses a color processing system for producing copies of originals. The claims of the ’919 Patent contained two different limitations which do not recite the operative “means” term so as to invoke 35 USC 112, 6th paragraph. Nonetheless, the first limitation “colorant selection mechanism” was construed to be a means plus function limitation, whereas, the second limitation “aesthetic correction circuitry” was not construed to be a means plus function limitation. MIT and EFI alleges that Microsoft Windows infringes the claims of the ‘919 Patent.

The Federal Circuit held that the “colorant selection mechanism” limitation is a means plus function limitation because (1) generic terms such as “mechanism,” “means,” “element,” and “device,” typically do not connote sufficiently definite structure, (2) the patentee used “means” and “mechanism” synonymously in the specification, (3) at least one dictionary equates means and mechanism, and (4) the terms “colorant selection” is not defined in the specification and has no dictionary definition.

In relation to the “aesthetic correction circuitry” limitation, the Federal Circuit held that such limitation is not a means plus function limitation because (1) the dictionary definition for “circuit” connotes sufficient structure, (2) two prior cases of the Federal Circuit have determined that “circuit” with a function (or operation of a circuit) denotes sufficient structure, and (3) it is sufficient that the term “circuit” be used in common parlance or by persons of skill in the pertinent art to designate structure even if the term covers a broad class of structures and even if the term identifies the structures by their function.

The Federal Circuit limited the meaning of “circuit” to hardware and did not extend the definition of “circuit” to include software. Massachusetts Institute of Technology v. Abacus Software, 80 USPQ2d 1225 (Fed. Cir. 2006).