Modern implantable microelectronic devices (IMDs) require higher performance and power efficiency to enable more efficacious therapies, particularly in neuro-prostheses such as retinal and cochlear implants . Inductive power transmission across the skin is a viable solution for providing sufficient power to such IMDs without imposing size and power constraints of implanted batteries . On the down side, unlike batteries that provide a stable power source, unexpected variations in the coils' mutual coupling from misalignments can lead to wide variations in the received voltage across the secondary coil to the extent that the input voltage may not be sufficient to supply power to the IMD . Hence, there is a need to improve the robustness of inductive power transmission without sacrificing efficiency to allow the IMDs to operate over a wider range of received input voltages. There are also other applications such as wireless sensors and radio-frequency identification (RFID), in which extending the range of loosely coupled inductive links are highly desired.