Adjacent common centroid placement for analog IC layout design

To improve immunity against process gradients, common centroid constraint, in which every pair of elements should be placed symmetrically with respect to a common center point, is widely used. Several methods to obtain a good placement satisfying the constraint by using sequence-pair and Simulated Annealing were proposed. However, cells in a common centroid group should be placed close to the common center point of the group. In this paper, we propose methods which use mathematical-programming and can place cells in each group close to the common center point, and check the effectiveness of the methods by experimental comparisons.