12.7 A power-management ASIC with Q-modulation capability for efficient inductive power transmission

A wide variety of applications can benefit from near-field wireless power transfer using coupled inductive links, such as wireless sensors and implantable microelectronic devices. The use of inductive power transmission is expected to see an explosive growth over the next decade as engineers try to cut the last cord from mobile electronics, small home appliances, and even electric vehicles [1]. The inductive link power transfer efficiency (PTE) is highly dependent of the loading of the receiver (Rx) coil, referred to as R_L. As shown in Fig. 12.7.1a, magnetic resonance-based power transmission in the form of a 3-coil link has been proposed to maximize PTE for any given R_L by transforming it to an optimal load, using k₃₄ variable [2,3]. Alternatively, an off-chip matching circuit has been used to transform R_L [4]. However, these methods need either an additional coil or a network of off-chip capacitors and inductors, which add to the size/cost of Rx. Moreover, in the above applications, R_L can change drastically during operation and there is a need for Rx to dynamically compensate for a wide range of R_L to maintain high PTE.