Written Description Support for Negative Claim Limitations

By Brian Dawley

In Inphi Corp. v. Netlist, Inc.,[1] the Court of Appeals for the Federal Circuit clarified requirements concerning written description support for negative claim limitations. 

Prior to Inphi, the Federal Circuit established in Santarus, Inc. v. Par Pharmaceutical, Inc., “Negative claim limitations are adequately supported when the specification describes a reason to exclude the relevant limitation.”[2]  The claims at issue in Santarus recited a negative claim limitation that a composition “contains no sucralfate.”[3]  The specification of the patent at issue in Santarus explained that sucralfate is associated with certain disadvantages.[4]  Thus, the Federal Circuit concluded that the claims at issue in Santarus were supported by the patent specification.[5] 


The patent at issue in Inphi[6] concerned random access memory (RAM) memory modules for computers.[7]  The memory modules of the patent include memory chips, also referred to as “memory devices,” which can be selected by “chip selects.”[8]  Inphi filed a request for inter partes reexamination of the ’537 patent. 


During the reexamination proceedings of the patent at issue in Inphi, the patent applicant amended the claims to recite double-data rate (DDR) chip selects “that are not CAS, RAS, or bank address signals.”[9]  The examiner during the reexamination proceedings found that the claims as amended to exclude CAS, RAS, and bank address signals overcame an obviousness rejection, and the Board affirmed.[10]  Inphi requested rehearing of the Board’s decision, asserting that the specification did not provide a reason to exclude the relevant limitation, i.e., CAS, RAS, and bank address signals.  Inphi noted that the patent specification did not expressly articulate a reason to exclude the relevant limitation, and further emphasized that the Board acknowledged this aspect of the specification.[11]


Despite the lack of an express reason for exclusion, the Federal Circuit disagreed with Inphi, and held that the specification of the ’537 patent did indeed support the negative claim limitations.[12]  The Federal Circuit upheld the Board’s conclusion, which relied upon three aspects of the specification in support of this holding. 


First, the Board noted that the patent specification incorporated a Joint Electron Device Engineering Council (JEDEC) standards specification for DDR-1 memory devices.[13]  The JEDEC standard disclosed that DDR signals (such as CS, RAS, CAS, and bank address signals) are distinct from each other.[14]  Second, Table 2 of the patent specification also distinguished among various signals by providing separate columns for CS, RAS, and CAS.[15]  Third, Figure 9A of the patent specification distinguishes chip select signals from command signals (including CAS and RAS) and bank address signals.[16]  The Board concluded from these passages of the specification that the specification disclosed adequate written description support for the exclusion of CAS, RAS, and bank address signals from DDR chip selects.[17] 


Inphi argued that Santarus required that the specification describe “a preference for the included signal(s) over the excluded signals (or alternatively a disadvantage of the excluded signals.)”[18]  However, the Federal Circuit concluded that it is enough that the specification simply describe alternative features without articulating advantages or disadvantages of each feature to support negative claim limitations.[19]


The Federal Circuit also noted that reciting disadvantages, as in Santarus, was sufficient to provide a reason to exclude certain features, but noted that reciting such disadvantages was not necessary to satisfy the written description requirement.[20] 


The Federal Circuit appears to have concluded that the requirements of 35 U.S.C. § 112, first paragraph, are the same for positive claim limitations and negative claim limitations.  That is, the Federal Circuit stated, “[T]he specification need only satisfy the requirements of § 112, paragraph 1 as described in this court’s existing jurisprudence.”[21]  


Thus, the Federal Circuit ultimately held that Santarus “did not create a heightened written description standard for negative claim limitations and that properly described, alternative features are sufficient to satisfy the written description standard of § 112, paragraph 1 for negative claim limitations.”[22]


There are many good reasons for describing alternatives for claimed features, such as to demonstrate broad claim scope.[23]  The ability to ultimately recite negative claim limitations based on such alternatives, as in Inphi, is yet another reason to describe many possible alternatives. 


[1] No. 2015-1179 (Fed. Cir. Nov. 13, 2015). 

[2] 694 F.3d 1344, 1351 (Fed. Cir. 2012). 

[3] Id. at 1350. 

[4] Id. at 1350–51. 

[5] Id. at 1351. 

[6] U.S. Patent No. 7,532,537 (filed Jan. 19, 2006) (hereinafter, the “’537 patent”). 

[7] Inphi, slip op. at 3. 

[8] Id., slip op. at 4. 

[9] Id., slip op. at 5–6. 

[10] Id., slip op. at 6. 

[11] Id. 

[12] Id., slip op. at 14. 

[13] Id., slip op. at 6–7.

[14] Id., slip op. at 7. 

[15] Id. 

[16] Id. 

[17] Id., slip op. at 7–8. 

[18] Id., slip op. at 10. 

[19] Id. 

[20] Id., slip op at 12. 

[21] Id. 

[22] Id., slip op. at 14. 

[23] See, e.g., Telcordia Techs., Inc. v. Cisco Systems, Inc., 612 F.3d 1365 (Fed. Cir. 2010); Nystrom v. TREX Co., Inc., 424 F.3d 1136 (2005).