Initial geometric processing is performed, such as implementing the Conductor Exclude definitions. The extraction system maintains a shadow cell database. The cells in the extraction database may contain modified objects and flattened subcell geometry, different from the cell in the main database. The extraction database is created before grouping. If the Extraction View check box in the Show group in the Views and Operations page of the Extraction Setup panel from the Extract Menu is checked, the physical drawing windows will display the cell content based on this database, and not the main database.
One complexity that arises is that a device such as an inductor or transmission line is often implemented simply as a strip of conducting material. In order to insert the device, the grouping algorithm has to be fooled into thinking that the strip which is the device is actually two disconnected strips, one for each terminal. This can be accomplished with the introduction of special layers used in layout, and the Conductor Exclude directive. The directive will logically remove parts of the conductor that intersect with the special layer. Perhaps a more familiar example is a MOS transistor, whose body is defined by POLY over ACTIVE. Both are required to be conductors, but without ``Conductor Exclude POLY'' in the ACTIVE layer definition block, the source and drain would be shorted together!.
In grouping, conducting nets are identified. Every conducting object is given a group number. The group number is the same for all of the conducting objects in a wire net, and each disjoint wire net has a unique group number.
Grouping is done recursively, starting from the leaf subcells and working up to the current cell. The core of the grouping is an algorithm for determining conductor paths due to touching objects on a layer, and through vias between layers if the Via keyword has been included in the technology file for the via layers, and by contact layers if the Contact keyword was applied in the technology file. Once a cell is processed, it is not regrouped unless the cell is modified. The Groups check box in the Show group in the Views and Operations page of the Extraction Setup panel can be checked to display the group numbers of objects in the layout in the drawing windows. Each group (conductor net) is assigned a number. While the Groups check box is checked, these numbers are printed on-screen near the conducting objects.