Integrated Circuits and Systems for Adaptive Optimization of Energy Storage Efficiency in Resonant Inductive Wireless Power Receivers

Recent developments in highly-miniaturized implantable neuro-stimulators has led to a rapid rise in their required power and data transmission throughput resulting in an increase of instantaneous-to-average ratio in their power consumption. Motivated by crucial role of efficient energy storage in such systems, we introduce energy management strategies in wireless powering links, in which the key performance measure is the energy stored during a limited time interval rather than the average energy delivered to the load.

First, the development of an algorithmic scheme for maximizing energy storage in current-mode (CM) resonant inductive power receivers is presented. The efficacy and precision of the presented analytical model is confirmed with CAD-based simulation results and validated using experimental measurements. Furthermore, a 0.45mm2 integrated circuit (IC) fabricated in 0.18µm CMOS is presented that performs the above-mentioned optimization. By continuous monitoring of incident waveform dynamics, the IC automatically adapts its optimal solution on-the-fly to any change in the inductive link's physical or electrical parameters. The computations are implemented using analog circuits which minimize IC's power consumption while making it needless of high-speed ADC/DAC. Our measurement results show that by using the IC, the energy storage efficiency is improved by 53% and 67% for the two tested links, compared to the conservative schemes, while consuming two orders of magnitude smaller energy than it saves through optimization. To the best of our knowledge, this is the first reported link-adaptive calibration-free IC for optimizing energy storage efficiency in CM receivers.

Second, a 2×2mm2 IC is fabricated in 0.18µm CMOS that maximizes the energy storage efficiency in resonant inductive links with voltage-mode receivers. The IC automatically stores the maximum possible energy while simultaneously providing the required continuous load's power. In the proposed scheme, the optimal operation is maintained by detecting and operating the receiver at a specific optimal voltage, eliminating the need for direct power measurements and adaptive matching circuits. The power reception and delivery phases are isolated which ensures maximum power reception independent of the actual loading at the receiver. The measurement results demonstrate up to 48.44% and 93.97% improvements for the charging time and the stored power, respectively.