A dual mode thermoelectric energy harvesting circuit using transformer-based boost converter, charge pump and time-domain digital control

Boost converter designed using miniaturized high turn-ratios transformer is an excellent circuit to achieve fully electrical autonomous start up at low input voltage. Nevertheless, at regulated output voltage, its power conversion loss at high input voltage is significant. A 2× cross-coupled charge pump is added to assist energy harvesting at high input voltage. The charge pump is turned on whenever the input voltage exceeds programmed threshold. Digital-only technique which guarantees minimal quiescent current is used to realize the shunt regulator implementation and power monitoring circuit, where the input voltage (power) is determined by measuring the transformer self-oscillation period. Time-based digital control eliminates the need of conventionally power hungry components i.e. amplifiers and voltage domain ADC. Simulation results using a standard CMOS 0.13-µm technology and thermoelectric generator equivalent circuit model validated the proposed architecture, which can generate output voltage levels at 1 V and 2 V, respectively. Additional voltage headroom provided by the charge pump is instrumental for sensor, analog and RF circuits. The system requires a minimum input voltage of 34 mV and input power of 110 µW to start up.