8.1 An 80nW retention 11.7pJ/cycle active subthreshold ARM Cortex-M0+ subsystem in 65nm CMOS for WSN applications

The Internet of Things is widely expected to comprise billions of connected devices, many of which will be wireless sensor nodes (WSN). One challenge this poses is energy efficiency, as it will prove cost-prohibitive to regularly replace billions of batteries. Node cost is another concern, which will demand ever-greater integration. Ease of SW development must also remain a priority to HW designers. Addressing all of the above, this paper presents an 11.7pJ/cycle subthreshold WSN processing sub-system implemented in low-leakage 65nm CMOS, scalable from 850nW active power at 250mV to 66MHz at 900mV, with a fully integrated 82% peak-efficiency voltage regulator for direct-battery operation, and supporting 80nW CPU and RAM state-retention power gating for SW-transparent leakage reduction.