| We introduce the concept of utilizing two cell libraries, one for synthesis and another for physical design. We propose a methodology to determine the contents of the most power efficient physical library: function types, drives and beta ratios. This methodology relies on an optimum gate sizing tool. Our results show that the physical library should consist of only 9 functions, each with several drive and beta ratio options, for a total cell count of 186. Since synthesis performs better with the inclusion of more complex cells (but only if they are power efficient), we augment the synthesis library to include numerous combinations of the basic 9 functions. The resulting synthesis library consists of a total of 865 cells. Note that these compound cells require only characterization and no layout. After design synthesis the compound cells are decomposed back to the basic (9) cells in the physical library. Then cell-size selection is performed. Our new dual library approach results in a typical active area reduction of 14% in the most critical portion (knee) of the active area vs. delay (AD) curves, for large current industrial designs, when compared to an industrial library with almost a 50% higher cell count. |
