A Hybrid Inductive and Resonant Transmitter for Dual-mode Wireless Charging

As wireless charging becomes popular, a transmitter that can support multi-mode operation seems to be essential for broad and rapid deployment. In this paper, a dual-mode transmitter is proposed to accommodate the tightly inductive coupled and loosely magnetic resonant coupled charging technologies. The challenge is to meet charging distance requirements, as they have opposite characteristic with respect to coupling coefficients. When two different coils are stacked on top of each other, proximity effect due to the nearby two sets of coils should also be mitigated. The coexistence issue is resolved by stacking and separating the different types of coils on top of each other and by making use of the tightly inductive charging coils to extend the charging distance of the magnetic resonant charging, allowing a further physical separation between the two sets of coils. The details of design stackup, prototype, and measurement result are presented.