US Patent 7260805 N-level down hierarchical powergrid analysis

Ports at which a cell served by a local powergrid is to be modeled are designated on a selected metal layer N-levels down from the topmost metal layer of the local powergrid. The cell is modeled at the designated ports, excluding any metal layers above the selected metal layer. Any metal layers of the local powergrid above the selected metal layer are included as part of a model of the global powergrid, rather than as part of the local powergrid, and a hierarchical powergrid analysis is performed.