Linear Technology v. Impala Linear (Patent Claim Construction)

Linear Technology Corporation v. Impala Linear Corp., Toyoda Automatic Loom Works, Maxim Integrated Protduct, Unitrode Corp., and Ronald Vinsant (Fed. Cir. June 17, 2004).

After losing a summary judgment in an infringement suit, Linear mounted this appeal based on claim construction and other errors. The technology at suit related to voltage regulators designed to provide constant voltage output from a fluctuating input. (U.S. Patent 5,481,178).

Because the district court erred in construing the “circuit,” “vary the duty cycle,” and “simultaneously off” claim limitations of the ’178 patent, we vacate the judgment of non-infringement and remand for further consideration. We further vacate the district court’s summary judgment of no contributory infringement or inducement of the current reversal method claims of the ’178 patent, because genuine issues of material fact have been raised concerning Maxim’s contributory infringement or inducement. Because the district court did not abuse its discretion on Maxim’s cross-appeal in denying Maxim’s motion for summary judgment that Vinsant was a joint inventor of the ’178 patent, we affirm.

The appellate panel held that the district court had improperly found that the term “circuit” was a means-plus-function limitation and that the district court had failed to apply the “rebuttable presumption that § 112 6 does not apply.”

We hold that because the term “circuit” is used in each of the disputed limitations of claims 1, 44, 55, and 57 of the ’178 patent with a recitation of the respective circuit’s operation in sufficient detail to suggest structure to persons of ordinary skill in the art, the “circuit” and “circuitry” limitations of such claims are not means-plus-function limitations subject to 35 U.S.C. § 112 6. The district court’s holding to the contrary was an error of law.

The appellate panel also found error in the district court’s exclusion of PWM circuits from other means language in the claims.

Linear cites technical textbooks and electronic parts catalogs indicating that PWM circuits are well-known circuit structures to persons of skill in the art. Thus, we conclude that the district court erred in excluding PWM circuits.