Interconnect Bundle Sizing Under Discrete Design Rules

Abstract

The lithography used for 32 nm and smaller very large scale integrated process technologies restricts the admissible interconnect widths and spaces to a small set of discrete values with some interdependencies, so that traditional interconnect sizing by continuous-variable optimization techniques becomes impossible. We present a dynamic programming (DP) algorithm for simultaneous sizing and spacing of all wires in interconnect bundles, yielding the optimal power-delay tradeoff curve. DP algorithm sets the width and spacing of all interconnects simultaneously, thus finding the global optimum. The DP algorithm is generic and can handle a variety of power-delay objectives, such as total power or delay, or weighted sum of both, power-delay product, max delay, and alike. The algorithm consistently yields 6% dynamic power and 5% delay reduction for interconnect channels in industrial microprocessor blocks designed in 32 nm process technology, when applied as a post-layout optimization step to redistribute wires within interconnect channels of fixed width, without changing the area of the original layout.