Symmetry within the sequence-pair representation in the context of placement for analog design

Abstract

This paper addresses the problem of device-level placement for analog layout, focusing mainly on symmetry-related aspects. Different from most of the existent analog placement approaches, employing basically simulated annealing optimization algorithms operating on flat (absolute) spatial representations, our model uses a more recent topological representation called sequence-pair, which has the advantage of not being restricted to slicing floorplan topologies. In this paper, we explain how specific features essential to analog placement, such as the ability to deal with complex symmetry constraints (for instance, an arbitrary number of symmetry groups of cells), can be easily handled by employing the sequence-pair representation. Several analog examples substantiate the effectiveness of our placement tool, which is already in use in an industrial environment.