## Facts

- O2 Micro owned U.S. Patent No. 6,259,615, covering DC/AC converter circuits used to drive cold cathode fluorescent lamps in computer displays.
- The asserted claims included an “only if” limitation requiring a control pulse for a set of switches to be generated only if a feedback signal exceeded a threshold.
- O2 Micro sued Monolithic Power Systems (MPS) for infringement in the Northern District of California.
- O2’s preliminary and final infringement contentions identified a single infringement theory for the “only if” limitation.
- After deposing an MPS engineer, O2 served “supplemental” infringement contentions about three months later asserting a new infringement theory, without explaining the delay.
- O2 later moved for leave to amend its infringement contentions; the district court denied the motion.
- In opposing MPS’s summary-judgment motion, O2 advanced a third infringement theory not disclosed in the operative contentions.
- The district court limited the case to the operative contentions, declined expert-report supplementation aimed at introducing the new theory, and granted summary judgment of non-infringement for MPS.

## Issues

1. Whether the district court abused its discretion by denying leave to amend infringement contentions to add a new theory after final contentions and an unexplained delay.
2. Whether the district court abused its discretion by refusing supplementation of O2’s expert report to support the excluded theory.
3. Whether summary judgment of non-infringement was proper when O2’s operative infringement theory lacked evidentiary support and later theories were excluded.

## Decision

- The Federal Circuit affirmed the denial of leave to amend infringement contentions.
- The Federal Circuit affirmed the refusal to allow expert-report supplementation tied to the excluded theory.
- The Federal Circuit affirmed summary judgment of non-infringement because, under the only timely disclosed theory, O2 failed to raise a genuine dispute of material fact.

## Legal Principles

- Local patent rules may require early disclosure of infringement theories to prevent late shifts in positions and to provide fair notice.
- A party seeking to amend infringement contentions must show good cause, commonly assessed through diligence and prejudice to the opposing party.
- District courts have broad discretion to enforce local patent rules and scheduling orders, including excluding untimely new infringement theories.
- Expert testimony and reports may be limited to the infringement theories disclosed in operative infringement contentions; expert supplementation cannot be used to circumvent contentions requirements.
- Summary judgment may be evaluated based on the theories properly in the case; excluded theories cannot create a triable issue.

## Conclusion

The Federal Circuit held that the district court acted within its discretion by enforcing local patent rules to exclude O2’s late-added infringement theories and related expert supplementation, and it affirmed summary judgment because O2’s timely disclosed theory did not support a finding of infringement.


O2 Micro Int'l Ltd. v. Monolithic Power Sys., Inc., 467 F.3d 1355 (Fed. Cir. 2006)