High-efficiency fully CMOS VCO rectifier for microwatt resonant wireless power transfer

Implantable biomedical devices are expected to be an integral part of future health care. Resonant coupling is a new and efficient method for wireless power transfer (WPT) in the presence of different kinds of body masses and tissues. The coupling also overcomes the problem of exponential decrease in power in inductive coupling with an increase in the distance between a transmitter and a receiver. The main problem with WPT is inefficient rectification at low input power levels. A classical full-wave rectifier has extremely low efficiency at higher frequencies for input voltages less than 2 V. In this letter, we present a solution to the inefficient rectification problem by proposing an integrated voltage-controlled-oscillator-based rectifier. The rectifier operates at 900 MHz and is implemented in the standard 0.13-μm CMOS technology. This design has a measured conversion efficiency of 52.5%, with an output power of 54.76 μW and an output voltage of 0.74 V. The rectifier and the regulator occupy an area of only 0.32 mm², including the resonant inductors and a capacitor.