On passivity of the super node algorithm for EM modeling of interconnect systems

The super node algorithm performs model order reduction based on physical principles. Although the algorithm provides us with compact models, its passivity has not thoroughly been studied yet. The loss of passivity is a serious problem because simulations of the reduced network may encounter artificial behavior which render the simulations useless. In this paper we find the reason of delivering non-passive models and propose a modified version of the algorithm which guarantees passivity. This is done by applying a passivity enforcement procedure after frequency fitting step within the algorithm. This allows to preserve passivity while keeping the main advantages of the algorithm. Finally numerical examples validate the proposed approach.