Multi-Threshold Asynchronous Circuit Design for Ultra-Low Power

This paper presents an ultra-low power circuit design methodology which combines the Multi-Threshold CMOS (MTCMOS) technique with quasi delay-insensitive (QDI) asynchronous logic, in order to solve the three major problems of synchronous MTCMOS circuits: (1) Sleep signal generation, (2) storage element data loss during sleep mode, and (3) sleep transistor sizing. In contrast to most power reduction methods that result in area overhead, the QDI asynchronous MTCMOS circuits are usually smaller than their original versions. Moreover, QDI circuits utilize handshaking protocols instead of clocks for circuit control, resulting in flexible timing requirements, which yields increased circuit robustness and allows for extreme supply voltage scaling to subthreshold region for further power reduction, without requiring any circuit modifications. This QDI asynchronous MTCMOS methodology is used to design a 4-stage pipelined 8-bit × 8-bit unsigned multiplier, which is then compared against the original QDI design (i.e., without incorporating MTCMOS) and its synchronous version. All designs use the IBM 8RF-DM 0.13 m process. Results show 150× and 1.8× leakage power and active energy reductions on average in the QDI asynchronous MTCMOS design compared to the original QDI version, respectively.