Synthesis for mixed CMOS/PTL logic

Abstract

Summary form only given. High noise immunity and level-restoring capabilities of static CMOS gates, combined with small area and low power of PTL cells, make a mixed CMOS/PTL design style an ideal alternative to the all-CMOS technology. However, the synthesis of mixed CMOS/PTL circuits imposes a great challenge to the existing synthesis methodology. Neither traditional techniques based on algebraic factorization nor methods based on direct BDD mapping are applicable to this new circuit style. We have recently proposed a new BDD-based logic optimization method for static CMOS. It is based on iterative BDD decomposition using various dominators which correspond to decomposable BDD structures leading to AND, OR, XOR and MUX decompositions. Synthesis results show that the method is very efficient for both AND/OR- and XOR-intensive functions. Since PTL structures can be easily identified on a BDD, our method can be readily extended to perform logic decomposition leading to mixed CMOS/PTL logic implementation. In contrast to other PTL synthesis techniques, based on direct BDD mapping, our method is not limited to decomposition onto PLTs only; its logic decomposition and optimization is driven by the capabilities of both the static CMOS and PTL logic. Our BDD decomposition method can also account for various parameters associated with circuit performance, thus avoiding drawbacks of direct BDD mapping-based synthesis, such as large fanouts and long transistor chains.