Adaptive Buck-Boost Converter for RF Energy Harvesting and Transfer in Biomedical Applications

The continuous improvement in reducing the power consumption of electronic devices, including biomedical ones, makes the use of energy harvesting systems instead of batteries attractive. Conventionally, energy harvesting systems are optimized to operate in a single worst-case scenario. However, it is often the case that the available input power varies in different situations, which creates a need for energy converters that operates efficiently over a broader input power range. In this paper, a versatile buck-boost converter suitable for wireless energy harvesting and transfer is proposed. The converter maximizes the system's efficiency by maintaining its input resistance fixed during harvesting. Harvested energy is stored in a storage capacitor. The converter can be dynamically adjusted for different available input power and voltage levels. This is accomplished by employing pulse frequency modulation and reconfigurable power switches. A novel adaptively biased zero-current-detection comparator is employed to increase the converter's efficiency, its input having an offset that depends on the output voltage. The converter was simulated for input power levels from 1μW to 1 mW and input voltage level from 0.38 to 1.3 V. Its peak efficiency is 76.3% at an input power of 1μW and 86.3% at 1 mW.