Low-Power Circuit Techniques for Efficient Energy Harvesting

This chapter presents the analysis and designs of efficient energy harvesting circuits interfacing two example energy generators: thermoelectric generator and piezoelectric generator. First, the key characteristics of these energy generators are described and the design criteria for the optimal performance of the basic energy harvester circuits are derived. For instance, the condition to minimize the start-up voltage of a blocking oscillator-based thermoelectric energy harvester and the condition to maximize the energy transfer efficiency of a full-bridge rectifier-based piezoelectric energy harvester are derived. Second, new circuit techniques that can overcome the limitations of the basic energy harvester circuits are introduced: the dual-path rectifier, bias-flip rectifier, and switched capacitor array. These circuit techniques either reduce energy losses, converting the voltage into a suitable range, or maintain impedance matching for the highest energy transfer.