32.2 Self-Tunable Phase-Shifted SECE Piezoelectric Energy-Harvesting IC with a 30nW MPPT Achieving 446% Energy-Bandwidth Improvement and 94% Efficiency

To enhance the power extraction capability of piezoelectric energy harvesters (PEHs), the quality factor of mechanical resonators should be maximized over the extraction-energy frequency bandwidth (EFB). As a result, the EFB is often limited to a few percent around the resonance frequency, which could dynamically shift with temperature variations and aging. Furthermore, the environment vibration frequencies may shift outside the EFB. Currently, the EFB of the PEHs is still too narrow to make them robust to process, temperature, and excitation frequency variations, so their use in real industrial applications is limited.