Return-to-one protocol for reducing static power in C-elements of QDI circuits employing m-of-n codes

The scaling of microelectronic technologies brings new challenges to the design of complex SoCs. For example, fully synchronous SoCs may soon become unfeasible to build. Asynchronous design techniques increasingly mingle within SoC design procedures to achieve functional and efficient systems, where synchronous modules are independently designed and verified. This is followed by module integration by means of asynchronous interfaces and communication architectures, forming a globally asynchronous, locally synchronous (GALS) system. Among multiple asynchronous design styles, the quasi delay insensitive (QDI) stands out for its robustness to delay variations. When coupled to delay insensitive (DI) codes like m-of-n and to four-phase handshake protocols, the QDI style produces the dominant asynchronous template currently in use. This work presents a technique to reduce the static power consumption of asynchronous QDI circuits using any m-of-n code and a four-phase handshake protocol, by proposing the utilization of a non-classical spacer encoding, namely all-1s. The article shows that the use of the traditional all-0s spacers may lead to static power consumption figures that are in some cases more than twice larger than the static power consumed by all-1s spacers in C-elements, the most common device used in asynchronous templates. Experiments demonstrate the new spacer reduces static power consumption without increase in complexity.