Synthesis of nonzero clock skew circuits

It is well known that the clock skew can be exploited as a manageable resource to improve circuit performance. However, due to the limitation of race conditions, the optimal clock skew scheduling often does not achieve the lower bound of sequential timing optimization. This paper proposes a polynomial time complexity algorithm, called delay insertion and nonzero skew algorithm (DIANA), which considers delay insertion to determine the clock skew schedule. The objective here is not only to optimize the clock period but also to heuristically minimize the required inserted delay for resolving the race conditions. Experiments with benchmark circuits consistently demonstrate that the proposed approach achieves the lower bound of sequential timing optimization. Moreover, since the DIANA algorithm attempts to minimize the required inserted delay between two registers, the feasible value for delay insertion is within a very large range. Therefore, even though only the buffers in a standard cell library are used to implement the delay insertion, a feasible solution is easily found.