Inductive link design with optimal transfer efficiency and a high CMRR

In this paper, we present two key design approaches to optimize an inductive link for contactless energy transfer. Applications of the inductive link include 1.) a wireless technique to energize implanted biomedical devices; and 2.) wireless peripheral I/Os between chips. First, a new hybrid (i.e., surface mount components on a PCB) structure, which consists of a symmetrical coils and matching capacitors for improving the power link efficiency and immunity to misalignment was designed. The maximum transfer efficiency with and without impedance matching will be analyzed and shown. Since biomedical implants often relying on inductive links for power and data transfers, the interference between them is a major concern. Therefore, as the second design approach, this study proposes a full differential signaling scheme to eliminate out of band interference and provide a high CMRR in the interested frequencies. Based on EM modeling and analysis, the simulation result yields transfer responses that are in good agreement with experimental results. According to the results, the maximum transfer efficiency is 87% at 3mm vertical distance and the CMRR is higher than 50dB. At z=12mm, or a lateral misalignment of 9 mm, it is still able to achieve an optimal energy transfer (at 48%), after impedance re-matching.