A Method of Analog IC Placement with Common Centroid Constraints

Abstract

To improve the immunity against process gradients, a common centroid constraint, in which every pair of capacitors which has been derived by dividing some original capacitors into two halves should be placed symmetrically with respect to a common centroid, is widely used. Xiao et al. proposed a method to obtain a placement satisfying the common centroid constraints, but this method has a defect. In this paper, we propose a decoding algorithm to obtain a placement which satisfies common centroid constraints.

Adjacent common centroid placement for analog IC layout design

“…placements whose seq-pair is (a 2 b 1 csb 2 a 1 ; b 1 a 1 csa 2 b 2 ) and whose common centroid group is G{ (a 1 , a 2 ), (b 1 , b 2 ), cs}. step1.2: Determine relative coordinates of all cells in G i from S i by the method described in one of the following: [8], [9], IV-B. And regard the cells as a convex super-block.…”

“…This method can handle all cells together by using seq-pair. But their method has a defect that some cells may be overlapped [8].…”

“…Ue et al proposed another method which uses seq-pair to obtain placement satisfying common centroid constraint [8]. Their algorithm determines relative coordinates of all cells in each common centroid group individually, and determines the whole placement by using convex rectilinear block packing algorithm [12].…”

“…So Fujiyoshi et al improved Ue's method by applying average placement [9]. The only difference with the method of [8] is how to determine relative coordinates of all cells in each common centroid group. In most cases, this method can place cells in each common centroid group closer to the common center point than the method of [8].…”

“…The only difference with the method of [8] is how to determine relative coordinates of all cells in each common centroid group. In most cases, this method can place cells in each common centroid group closer to the common center point than the method of [8]. However, the distance between cells in a common centroid group may be redundantly big as shown in Fig.2(a).…”