A sub-threshold demonstrator chip, incorporating innovative features for energy harvesting and power conversion, has been designed and taped-out by Arm R&D engineers and ECS researchers.
Minimum energy systems are important for deployable multi-billion wireless sensor networks (WSNs). This sub-threshold chip, code-name “PIPISTRELLE-1”, was designed in the TSMC 65LP process. It demonstrates power conversion and energy harvesting techniques which are critical features for realising WSN SoCs, and serves as a platform for experimenting with various energy and power management algorithms and techniques.
Back from fabrication in January 2015, the chip and PV energy harvesting circuitry was evaluated using a microscale PV cell. The graph above shows the energy harvested at the PV cell and the utilized energy. Harvested energy is used to charge a NiMH battery and the battery voltage can be seen to increase with time. Changes in incident light levels change the output power and efficiency of the harvesting circuitry but voltage is relatively fixed.