Section 112(a) Requirements for Drafting Negative Claim Limitations

In a recent decision, the Federal Circuit held that for purposes of drafting a negative claim limitation, a patentee is merely required to describe adequate alternative features in order to satisfy the written description requirement of 35 U.S.C. § 112(a). See Inphi Corp. v. Netlist, Inc., No. 15-1179.

Prior to this case reaching the Federal Circuit, Inphi Corp. ("Inphi") had filed a request for inter partes reexamination ("IPR") for U.S. Patent No. 7,532, 537 ("the ‘537 patent") owned by Netlist, Inc. ("Netlist"). During the IPR, the examiner rejected a number of claims as obvious in view of the prior art. To overcome the rejection, Netlist narrowed the claims using a negative claim limitation. The examiner then withdrew the obviousness rejection.

In response, Inphi filed an appeal in the Patent Trial and Appeal Board (the "PTAB"), arguing that the negative claim limitation introduced by Netlist was not supported by the specification and violated the written description requirement of 35 U.S.C. § 112(a). The PTAB disagreed and affirmed the examiner’s decision upholding the amended claims. Inphi then appealed to the Federal Circuit emphasizing the Federal Circuit’s decision in Santarus, Inc. v. Par Pharm., 694 F.3d 1344, 1351 (Fed. Cir. 2012), which stated that "[n]egative claim limitations are adequately supported when the specification describes a reason to exclude the relevant limitation."

In the case of the ‘537 patent, the negative claim limitation at issue excluded RAS and CAS signals that occur in Random Access Memory (RAM), which allow a computer to multi-task and run faster. Inphi argued that Netlist’s patent did not expressly articulate a reason to exclude RAD and CAS signals, and therefore does not pass muster under Santarus.

The Federal Circuit, however, held that the "reason to exclude" requirement of Santarus may simply be satisfied by "properly describing alternative features of the patented invention," without having to describe advantages and disadvantages of each alternative feature and without having to expressly state the negative limitation in the specification. The Federal Circuit stated that Santarus did not create "a heightened written description standard for negative claim limitations" and "simply reflect[ed] the fact that the specification need only satisfy the requirements of § 112(a)."

In view of the above, the Federal Circuit found that, in the case of the ‘537 patent, substantial evidence supported the PTAB’s finding that the specification described adequate alternative features by distinguishing the relevant signal types such as CS, CAS, RAS, and bank address, and reaffirmed the PTAB’s decision.

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