A Unified Early-Warning AVFS Design With Path Activation-Aware Monitoring Point Optimization

This work proposes a unified early-warning adaptive voltage-frequency scaling (AVFS) system that offers a practical low-power solution for commercial IoT devices. First, a path activation-aware monitoring point optimization strategy is proposed to mitigate the risk of illegal voltage scaling. The strategy combines the path activation evaluation with the required timing guard band, reducing monitoring costs by 18.7%. Second, a delay-compensated dual-shadow monitor is developed and paired with a scalable monitoring window sizing methodology to monitor the timing of paths with memory-type endpoints, overcoming the limitation of monitoring only DFF-type endpoints. Third, a unified architecture that integrates both frequency and voltage scaling is presented to alleviate the problems of the off-chip voltage regulation. Fabricated in 40 nm CMOS, a Cortex M0+ CPU with AVFS achieves voltage reductions between 15.4% and 29.5% and power savings ranging from 32.3% to 49.3% at 50–100 MHz across SS/TT/FF corners.