Improving the Characteristics of Multi-Level LUT-Based Mealy FSMs

Contemporary digital systems include many varying sequential blocks. In the article, we discuss a case when Mealy finite state machines (FSMs) describe the behavior of sequential blocks. In many cases, the performance is the most important characteristic of an FSM circuit. In the article, we propose a method which allows increasing the operating frequency of multi-level look-up table (LUT)-based Mealy FSMs. The main idea of the proposed approach is to use together two methods of structural decomposition. They are: (1) the known method of transformation of codes of collections of outputs into FSM state codes and (2) a new method of extension of state codes. The proposed approach allows producing FPGA-based FSMs having three levels of logic combined through the system of regular interconnections. Each function for every level of logic was implemented using a single LUT. An example of the synthesis of Mealy FSM with the proposed architecture is shown. The effectiveness of the proposed method was confirmed by the results of experimental studies based on standard benchmark FSMs. The research results show that FSM circuits based on the proposed approach have a higher operating frequency than can be obtained using other investigated methods. The maximum operating frequency is improved by an average of 3.18 to 12.57 percent. These improvements are accompanied by a small growth of LUT count.