A 50nW Voltage Monitor Scheme for Minimum Energy Sensor Systems

Small, low-cost and energy efficient wireless sensor nodes (WSNs) form a vital part of the Internet of Things (IoT). WSNs spend the majority of their time in low-power sleep mode and wake up for short intervals. To ensure minimum energy (MinE) operation of such sensor nodes, fast wide-range voltage scaling is required. As voltage is aggressively scaled between ultra-low retention levels and sub, near or super-threshold active levels, monitoring circuits become essential to guarantee safe operation of the system. This work demonstrates a 50nW voltage monitor fabricated as part of the power management unit (PMU) of a 65nm MinE WSN. Ultra low power operation is achieved by duty-cycling the comparators. Further, dynamic power-bandwidth balancing results in lower quiescent power without loss of response speed. Measured results show 6μs response time giving a superior power-delay balance compared to prior works. This paper describes the design, implementation and measured results along with system implications of the design choices.