Optimization of Combinational Logic Circuits Based on Compatible Gates

This paper presents a set of new techniques for the optimization of multiple-level combinational Boolean networks. Such techniques are based on a temporary transformation of the network into an internally unate one. We describe first a technique based upon the selection of appropriate multiple-output subnetworks (consisting of so-called compatible gates) whose local functions can be optimized simultaneously. We then generalize the method to larger subsets of unate gates. Because simultaneous optimization of local functions can take place, our methods are more powerful and general than Boolean optimization methods using don't cares, where only single-gate optimization can be performed. In addition, our methods represent a more efficient alternative to Boolean relations-based optimization procedures because the problem can be modeled by a unate covering problem instead of the more difficult binate covering problem. The method is implemented in program achilles and compares favorably to SIS.