A Stacked Capacitor Multi-Microwatts Source Energy Harvesting Scheme With 86 mV Minimum Input Voltage and ${\pm}3$ V Bipolar Output Voltage

A multi-source energy harvesting scheme that emulates the principle of a water bucket fountain using series-stacked storage capacitors to power a multi-V DD mixed-signal wireless sensor node is presented. Feasible miniaturized microwatts energy sources include photovoltaic cell, piezoelectric harvester and thermoelectric generator. A digital logic based shunt regulator with 1 V clamping output is first designed using multi-threshold transistors to minimize static leakage current. Three shunt regulator blocks on separate dies are subsequently paired up with the series-stacked storage capacitors to increase the system output voltage to 3 V. The stacked shunt regulators not only provide voltage regulation and over-voltage protection, but also balance each individual storage capacitor to improve system reliability. By using the mirroring property of pulse transformer-based boost converter and one additional storage capacitor, the system is capable of generating bipolar ± 3 V output voltage at minimum input voltage of 86 mV (boost conversion ratio up to 70) and input power of 26 μW only. The increased supply voltage headroom is desirable for sensitive and high power blocks i.e., sensors, analog and radio-frequency circuits in terms of achieving better analog-to-digital-converter resolution, amplifier gain and linearity. The remaining branches of the stacked capacitors simultaneously provide 2 V and 1 V outputs which can be used by ultra-low power digital blocks of less supply voltage sensitive. The circuit prototypes are implemented on a standard 0.13- μm complementary metal-oxide-semiconductor process.