Practical Mixed-Cell-Height Legalization Considering Vertical Cell Abutment Constraint

Propelled by aggressive technology scaling, adopting mixed-cell-height design in VLSI circuits has made conventional single row-based cell legalization techniques obsolete. Furthermore, the vertical abutment constraint (VAC) among cells on consecutive rows emerges as an advanced design requirement, which has rarely been considered because the power/ground rails were sufficiently tall in conventional process nodes to isolate cells on different rows. Although there have been a number of studies on mixed-cell-height legalization, most of them cannot be trivially extended to well-tackle the general VAC due to the analytical optimization scheme. To address these issues, this work proposes the first mixed-cell-height legalization algorithm that addresses the general inter-row cell abutment constraint (i.e., VAC). The experimental results show that the proposed algorithm outperforms previous mixed-cell-height legalization works, even in the absence of the VAC. Upon applying the VAC, our algorithm offers superior performance and delivers promising results.