Characterization of wake-up delay versus sleep mode power consumption and sleep/active mode transition energy overhead tradeoffs in MTCMOS circuits

Multi-threshold voltage CMOS (MTCMOS) is an effective technique for reducing the leakage energy consumption of idle circuits. The MTCMOS circuits, however, suffer from high energy overhead during the transitions between the active and standby modes. The trade-offs between the mode transition energy overhead, the wake-up delay, and the standby mode power consumption of the MTCMOS circuits are evaluated in this paper. The short-circuit power consumed by an MTCMOS circuit during a wake-up event is characterized. Appropriate sleep signal buffer sizing guidelines to achieve sleep-to-active mode transitions with low energy overhead are provided. An optimum range of sleep transistor buffer sizes is identified for a 32-bit Brent-Kung MTCMOS adder in a 65 nm CMOS technology. It is shown that reducing the buffer size below the lower boundary of this optimum region is not effective for lowering the overall energy overhead and standby mode power consumption while causing a significant degradation in the wake-up speed.