Highest Maximum Power Point of Radially Distant Inductively Coupled Power Receivers With Deep Submicron CMOS

Inductively coupled power receivers for embedded microsensors are often tiny and distant from their transmitting sources. To sustain microsensors as long as possible, the power receiver should draw power whenever possible and output the highest power possible. Of reported state-of-the-art technologies, switched resonant half-bridges require fewer components, are less breakdown-limited, and output as much or more power than the others. This paper derives and shows with measurements the highest possible maximum power point (MPP) for switched resonant half-bridges. The theory predicts the optimal time, duration, and frequency of the energy transfers that charge the battery. Measurements of a 0.18-μm CMOS power receiver demonstrate that the receiver outputs more than 98.7% of the actual MPP at the predicted settings when the coupling factor between the transmitting and the receiving coils is 0.15%-1.14%.