“Circuit For” Interpreted as Means-Plus-Function

Even without the word “means,” claims can be interpreted as means-plus-function, as demonstrated by the Central District of California in a decision in Limestone Memory Systems v. Micron Technologies. The court interpreted the phrase “an activation control circuit for…” in one of Limestone’s asserted claims as means-plus-function and found that the description contained insufficient corresponding structure. The claim, therefore, is invalid.

Limestone is a nonpracticing entity that acquires, asserts, and licenses patents. In this case, Limestone’s asserted patents come from a variety of sources: U.S. Patent Nos. 6,697,296 originally assigned to Renesas, 5,805,504 originally assigned to NEC, and 6,233,181 originally assigned to Mitsubishi. All three patents relate to semiconductor memory. Micron, as one might expect, is a memory and storage maker.

This decision from the court is a claim-construction order covering numerous claim terms. The claim term of interest in this post is from claim 13 from the ’296 patent:

an activation control circuit for selectively activating said signal input circuitry according to said operation activation signal and the signal stored in said register circuitry, said activation control circuit selectively activating said signal input circuitry according to said operation activation signal when the stored signal in said register circuitry indicates that control of activation and deactivation on said signal input circuitry by said operation activation signal is valid, and holding said signal input circuitry in an active state all the times when said stored signal in said register circuitry indicates that the control on said signal input circuitry by said operation activation signal is invalid.

Micron argued that “activation control circuit” should be interpreted as a means-plus-function term under 35 U.S.C. § 112 ¶ 6 (now § 112(f)), which states, “An element in a claim for a combination may be expressed as a means or step for performing a specified function without the recital of structure, material, or acts in support thereof, and such claim shall be construed to cover the corresponding structure, material, or acts described in the specification and equivalents thereof.” If a claim uses the term “means for” or “step for” (as two other asserted claims did), the term is presumed to be means-plus-function; other terms are judged on whether they or the rest of the claim provide “a sufficiently definite meaning as the name for structure.”

But, according to the Federal Circuit in Apex v. Raritan Computer, the term “circuit” does not necessarily provide sufficient structure. The court concluded here that “activation control circuit” does not recite sufficient structure.

The question before the court then turned to whether the rest of the claim element—what followed the word “for”—provided sufficient structural limitation. “These components perform logical operations—but the reference to logical operations in the disputed term does not limit the selection of components that may perform such logical operations.” “The claim language reciting the functions of the ‘activation control circuit,’ which Limestone characterizes as ‘logical relationships’ between claim elements, says nothing about the structure of the circuit.” So the rest of the claim element failed to escape the means-plus-function interpretation.

As its backup argument, Limestone tried to point to a section of the specification, but the court does not even get to the substance of its argument. In its briefing, Limestone incorporated a declaration from its expert, which included explanation of the specification and an annotated figure. But in the court’s opinion, the lack of substantive argument in the briefing amounted to an attempt to evade the page limits. “Hence that extrinsic evidence is entitled to no weight.” Without corresponding structure in the specification, the means-plus-function limitation rendered the claim invalid.

Lessons for Practice

For the other claims that actually used the word “means,” the parties agreed that a means-plus-function interpretation was appropriate and only disagreed over the scope of the specification providing the corresponding structure. But claim 13 of the ’296 patent did not use the word “means.” Instead, the word that got Limestone into trouble was “for.” When drafting claims, be cautious about the word “for” followed by some action or function or result. Ask whether the claim has sufficient structure, and ask whether the specification has sufficient structure. The lack of structure in the claim is what sunk Limestone at the first step of inquiry, and the lack of a circuit diagram performing the recited function is what sunk Limestone at the second step of inquiry.

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Preparing and Prosecuting Functional Claims
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