Phase information is incorporated into a cell-based design methodology. Standard
cells have four edges: top, bottom, left, and right. The top and bottom edges have
fixed phase shifters placed, e.g. 0. A given cell C will have a phase set created
with two versions: 0-180 (left-right) as well as 180-0. Alternatively, the same
phase set: 0—0 and 180—180 could be created for a cell. The phase sets
are selected based on the ability to phase shift the features within the cell C.
By creating a phase set for most of the cells of a cell library, standard cell
placement and routing techniques can be used and phase can then be quickly assigned
using a simple ripple technique. This ensures a phase compliant design upfront
for the standard cell areas. In some instances, phase sets are created for every
cell in a library