Don't-Care-Based Logic Optimization for Threshold Logic

In this paper, we present a don't-care-based threshold logic gate (TLG) minimization method for threshold logic network (TLN) optimization. We first introduce a sufficient condition for the don't cares of a TLG to exist in a TLN and propose a logic-implication-based method to identify the don't cares. Then, we present two different methods for minimizing the TLG with the don't cares. The first one is an integer linear programming (ILP)-based method. We model the minimization problem as an ILP problem, and propose an approach to compute the necessary constraints of the ILP formulation. The second one is a heuristic method adapted from a threshold function identification approach. In the experiments, we applied the proposed methods to two sets of TLNs generated by the up-to-date synthesis technique. The results show that, for the two sets of TLNs, the ILP-based method achieves an average of 12% and 23% area reduction without any overhead on the TLG count and logic depth. Furthermore, the heuristic method is more efficient than the ILP-based method with only a little quality loss.