In Inphi Corp. v. Netlist, the Court of Appeals for the Federal Circuit reviewed the standard for determining whether a claim can be amended to add a negative limitation.
The case involved an appeal from Inter Partes Review, where the Patentee amended the claims to add the negative limitation. The claim related to a plurality of memory devices comprising double data rate (DDR) dynamic random-access memory (DRAM) devices, wherein chip selects ... are DDR chip selects that are not CAS, RAS, or bank address signals. At issue here was the fact that the specification did not have literal support for this amendment.
The CAFC confirmed the rule to evaluate whether a negative claim limitation is supported under Section 112 involves determining whether the specification describes "a reason to exclude the relevant limitation." Further, the CAFC went on to explain a previous decision (Santarus), noting that while express disclosure of disadvantages of a certain feature is sufficient to provide a reason to exclude, such disclosure is not necessary to satisfy the requirements of the written description requirement.
This decision may be helpful during prosecution where an Examiner objects to negative claim limitations as not being explicitly supported by the original specification.