In Inphi Corporation v, Netlist, Inc., [2015-1179] (November 13, 3015), the Federal Circuit affirmed the BPAI decision affirming the examiner’s final decision declining to reject claims amended during inter partes reexamination to add a negative limitation. At issue in this appeal is a negative claim limitation Netlist introduced by amendment, limiting the
claimed chip selects to exclude three particular types of signals (CAS, RAS, and bank-address signals):

wherein the system memory domain is compatible with a first number of chip selects, and the physical memory domain is compatible with a second number of chip selects equal to twice the first number of chip selects, wherein the plurality of memory devices comprises double-data rate (DDR) dynamic random-access memory (DRAM) devices and the chip selects of the first and second number of chip selects are DDR chip selects that are not CAS, RAS, or bank address signals.

The Federal Circuit said that “[n]egative claim limitations are adequately
supported when the specification describes a reason to exclude the relevant limitation.” Santarus, 694 F.3d at 1351.  The Federal Circuit characterized the issue as  whether the specification of the ’537 patent provides a “reason to exclude” CAS, RAS, or bank address signals that is sufficient to satisfy the written description requirement.  The Federal Circuit quoted from Santarus that:

Negative claim limitations are adequately supported when the specification describes a reason to exclude the relevant limitation. Such written description support need not rise to the level of disclaimer. In fact, it is possible for the patentee to support both the inclusion and exclusion of the same material.

The Federal Circuit said that the “reason” required by Santarus is provided, for instance,
by properly describing alternative features of the patented invention.

The parties agreed that the disclosure in the ’537 patent distinguishes among the relevant
signal types, but disagreed about whether that distinction creates a “reason to exclude” that satisfies the requirements of § 112, paragraph 1, and the Federal Circuit held that the disclosure as an alternative was a sufficient reason to exclude.

As long as the disclosure makes a distinction, you don’t have to accentuate the positive, or eliminate the negative, the disclosure will support a negative limitation.