Vibrational energy is an attractive power source for self-powered wireless sensors. A mainstream harvesting technique for vibrational energy is electrostatic MEMS harvesters (e-VEH). Various circuit architectures have already been introduced with many successful implementation, yet a load interface that efficiently manages the harvested energy has rarely been reported.
In this work a load interface is proposed which is suited for any condition circuit (CC) implementing rectangular QV cycles. In general, a rectangular QV conditioning circuit has an optimum interval of which the energy harvested is maximised, thus the harvested energy should be periodically removed to maintain maximising the harvested energy. This is achieved through the load interface (LI). The LI proposed is a switched inductor capacitive architecture with a LI controller allowing the extraction of the energy in a multiple energy shot fashion. The LI controller incorporate an ultra low power clock for switching events, as well as low power comparator for switching decision. Power consumption is reduced by operating at a low supply voltage (1.1V).
The proposed load interface is implemented in AMS0.35HV technology with a mixed high voltage and low power control blocks. It takes into account the harvester operation to maximise the energy extracted from the harvester. It overcomes the constrained limited biasing power, and tackles resistive losses and power handling transis- tor long channels by transferring the energy in a multiple shots fashion. A complete CMOS implementation is proposed along with the simulation results with an average consumed power of the controller less than 100nW allowing the system to operate with input power levels as low as few hundreds of nanowatts.