Practical methodology of post-layout gate sizing for 15% more power saving

We present a practical methodology of post-layout gate sizing for power reduction. Wire capacitance presumed in logic synthesis typically contains excessive margin for better timing closure in layout design. Power waste due to this can be reduced by post-layout gate sizing based on information obtained by backannotation. Here, we discuss a theory of optimal gate sizing in a signal path with surplus timing. We also, propose a practical design methodology where standard cells are reselected from a cell library by the theory, replaced by engineering change order, and timing constraints are verified by a static timing analyzer. We have applied the methodology to a 700k-gate commercial application processor for 3G cellular phones. Even though the original design was optimized for 133MHz, 170mW operation in a 0.18μm CMOS technology, power dissipation was further squeezed by 15% in combinational logic without compromising the performance.