A Self-Sustaining Micro-Watt Programmable Smart Audio Sensor for Always-On Sensing

Self-sustainable always-on sensors are crucial for the Internet of Things and its emerging applications. However, achieving perpetual work with active sensors poses many challenges, especially in ultra-low power design and micro-power energy harvesting that can supply the sensors. This paper presents a self-sustaining programmable smart microphone, combining energy harvesting and a micro-power event-driven sensor. The proposed solution can achieve programmable pattern recognition with up to 128 simultaneous time-frequency features exploiting mixed-signal low power design. Experimental results show that the designed event-driven circuit consumes only 26.89 μW in always-on mode, during the time-frequency feature-extraction, while the whole system consumes only 63 μW during pattern recognition including the power for a commercial MEMS microphone and the energy harvesting subsystem. We demonstrate that the sensor can operate perpetually powered with a small form factor flexible photovoltaic panel in indoor lighting conditions. Finally, the smart sensors achieved an accuracy of 100% in the detection of two different audio streams.