A Delaware judge has issued a decision highlighting the sometimes overlooked distinction between issues of law and fact in the patent realm. In a decision released last week, the Court rejected an attempt to revisit an earlier claim construction of the term “MOS transistor” – or metal oxide transistor. The Court held that defendant’s proposed construction was rendered moot because it raised the issue of the doctrine of equivalents, a theory of infringement plaintiff did not choose to pursue.
The decision resolves some uncertainty generated by the Court’s earlier claim construction opinion, in which it declined to address a similar argument by defendant. There, the Court noted that the defendant’s proposed construction involved a related component – a “DMOS transistor” – that the patent-in-suit did not claim and that would be relevant only to a claim under the doctrine of equivalents. Emphasizing that claim construction is a purely legal exercise, the Court refused to inject the factual issue of equivalence into its Markman discussion.
It seems that regardless of the effect an unclaimed term will have on the actual claims, as defendant unsuccessfully argued here, the legal exercise of claim construction will not intrude on the factual turf of the doctrine of equivalents.